Soldering sponges: the "thermal shock" myth

[MaximRecoil]

I've seen a lot of people on the internet claim that cleaning your iron on a damp sponge will cause the plating on the tip to crack/degrade/fail due to thermal shock. If that's true, it's funny that most soldering iron manufacturers, including the most reputable names in the industry, include a place on the workstand for a sponge, and some of them even market their own line of sponges.

When I worked at a PCB factory in the late 1990s, we all used damp sponges to clean the tips, Metcal brand sponges. There was no brass wool in the entire factory that I know of.

In any case, if your tip can't handle the thermal shock from a damp sponge, then it definitely can't handle the thermal shock of soldering. Solder is way more thermally conductive than water is:

Water - 0.58 W/mK
Solder (63/37) - 50 W/mK
Solder (SAC) - ~60 W/mK

Here's an example of what happens when you solder:



The temperature of the tip drops almost instantly by about 75° C, and that's with some of the highest-performing irons on the market. The temperature drop with lesser irons is even more. Not only is that a lot more thermal shock than wiping the tip on a damp sponge, but it happens a lot more often, unless you wipe your tip after every joint (and who does that?).

[AlfBaz]

I've seen a lot of people on the internet claim that cleaning your iron on a damp sponge will cause the plating on the tip to crack/degrade/fail due to thermal shock.

First I've heard of it, and my tips last for ages doing just that. It is quite possible that a lot of people on the internet have an opinion about everything but that's just my opinion

[Fgrir]

In any case, if your tip can't handle the thermal shock from a damp sponge, then it definitely can't handle the thermal shock of soldering. Solder is way more thermally conductive than water is:

Water - 0.58 W/mK
Solder (63/37) - 50 W/mK
Solder (SAC) - ~60 W/mK

I don't think the thermal conductivity difference is very important here.  The difference is in the two different material phase changes you are having to dump energy into.  Solder melting at ~180C vs. water vaporizing at ~100C.
I've used wet sponge forever as well so I'm not saying you are wrong about tip reliability, but while you have provided interesting data to show the thermal shock of soldering you have nothing to support your assertions that a wet sponge case would be less stressful.

[Neilm]

I believe that the tips cracking is more prevalent on lead free systems due to the composition of the tip.

[MaximRecoil]

In any case, if your tip can't handle the thermal shock from a damp sponge, then it definitely can't handle the thermal shock of soldering. Solder is way more thermally conductive than water is:

Water - 0.58 W/mK
Solder (63/37) - 50 W/mK
Solder (SAC) - ~60 W/mK

I don't think the thermal conductivity difference is very important here.  The difference is in the two different material phase changes you are having to dump energy into.  Solder melting at ~180C vs. water vaporizing at ~100C.
I've used wet sponge forever as well so I'm not saying you are wrong about tip reliability, but while you have provided interesting data to show the thermal shock of soldering you have nothing to support your assertions that a wet sponge case would be less stressful.

Regardless of phase changes, it boils down to the amount of temperature change in a given amount of time. A tip wiped across a damp sponge isn't even being submerged in water (and a sponge only has to be ever-so-slightly damp in order to work for this), while solder, which is about 100 times more thermally conductive than water, typically flows all around a tip when soldering a joint.

I don't have the equipment to measure temperature changes in real time while soldering or wiping on a damp sponge like the folks a JBC who made that chart do, but I'd be willing to bet that soldering cools the tip more. Neither one cools the tip enough to prevent you from immediately soldering another joint if you have an iron with a fast recovery time. During the time that I had a cheap $7 Radio Shack wall iron, soldering slowed me down more than cleaning the tip on a damp sponge did.

[saturation]

Its not just 'internet' banter but mentioned in professional circles as well as Hakko's  older comments on brass wire.

http://www.eptac.com/ask/wet-sponge-cleaning-vs-dry-brass-sponge-cleaning/

http://www.circuitnet.com/experts/80463.html

I don't know if the issue of thermal shock via wet sponge is worse versus brass wool nor has it been tested to prove its enough to be a concern.

Hakko no longer mentions that and just says this:

http://www.hakko.com/english/products/hakko_599b_feature.html#productNav

[thm_w]

They give some good arguments:

• No water required for cleaning, minimizes the drop in tip temperature at each cleaning to ensure better workability.
• Dome-shaped design reduces solder splash
• Flux contained in cleaning wires prevents oxidation of soldering tips

Brass lasts longer than sponge and is simpler/faster to use.
I hope manufacturers all switch to brass only (I see some models like this but not many).

[stj]

I believe that the tips cracking is more prevalent on lead free systems due to the composition of the tip.

lol - BS
the tips are the same, they never changed.
some people will blame anything on lead-free!!

[saturation]

Also see their maintenance link:

http://www.hakko.com/english/products/hakko_599b_maintenance.html#productNav

I've used the sponge for several decades but I too like the wool more because the tip is always kept fluxed and shiny.  Now the only use for the sponge is to truly clean out the tip to apply fresh flux and solder, which I do far less often.  Excess solder balls up and if you shake the Hakko brass container solder falls to the bottom of the container, makes it easier to clean too and last longer.

They give some good arguments:

• No water required for cleaning, minimizes the drop in tip temperature at each cleaning to ensure better workability.
• Dome-shaped design reduces solder splash
• Flux contained in cleaning wires prevents oxidation of soldering tips

Brass lasts longer than sponge and is simpler/faster to use.
I hope manufacturers all switch to brass only (I see some models like this but not many).

[jonatanrullman]

I believe, although I'm not sure I recall that correctly, that I switched to brass for the simple reason that it seemed to make more sense to me. And my sponge was on its last elbow so I had to buy something anyway.
Brass just had that shine of obvious improvement that sounds logical but perhaps isn't. I also like the added benefit that it lasts longer and doesn't need have water added to work. That alone was worth the small investment.

Cheers

[tautech]

I went away from sponges the very moment alternatives were available to:
Not brass but stainless wool. 

With the hobbyist irons I've always had, thermal shock was never the issue per se but the recovery time of the iron was and right when you're in the middle of solder and the tip needs cleaning. 
When you don't solder for a few days the sponge was always dry......how dry ? Well when it was covered in scorch marks you know it was too dry. 

[MaximRecoil]

Phase changing takes a LOT of energy. Think of this, water or ethanol based heatpipes have much higher thermal conductivity than copper, in the range of 10x to 10kx.

They can have a higher effective thermal conductivity than copper, but it greatly depends on the design/length of the heat pipes. It is a tuned system, optimized for cooling. There is also circulation involved, which, in and of itself, makes a huge difference. Randomly, rapidly evaporating water isn't drastically more effective at cooling than water that is barely evaporating. You can stick the tip of an e.g., Metcal in a small container of water and it will boil it all away, without ever cooling too much to continue boiling it.

Consider how easy it is to boil water on the stove top. Have you ever seen water stop boiling after it started because the rapid vaporization cooled things down too much? Now dump in a box of macaroni (e.g., from a standard size box of Kraft Macaroni & Cheese). It will stop boiling (assuming you're using a typical burner, 2-quart pot, and 6 cups of water as directed), because the macaroni, despite its very low thermal conductivity, has enough mass for the heat to dump into that it pulls the water down significantly below its boiling point.

With a damp sponge, we are only talking about a minuscule amount of water that evaporates when you wipe the tip on it. You would probably need a very precise scale to even measure it. If you want to try, wet a sponge, wring it out as much as you can, weigh it, immediately wipe a hot soldering iron tip on it, then immediately weigh it again.

On the other hand, the amount of solder you are melting onto an iron tip for a typical through-hole joint has enough mass that it can easily be weighed on an inexpensive consumer-grade scale. For example, I weighed 1 inch of 0.025" 63/37 solder wire, 1.1% flux, and it was 0.09 grams.

Keep in mind that flux also vaporizes when soldering, more or less depending on the type of flux.

[jpanhalt]

I see a lot of stuff here about the heat of vaporization of water.  Have you forgotten about the Leidenfrost effect (https://en.wikipedia.org/wiki/Leidenfrost_effect )?  Vaporized water acts as a thermal insulator and inhibits cooling.  That is why oil is much more effective at cooling than water, if that is what you want to do.

[sleemanj]

I can't spill my copper wool like I can a bottle of water which I would inevitably leave on the bench and forgot to cap :-)

[SeanB]

I have both types, and also a block of resinous pine wood to rub the tip on to clean hard deposits off using the rosin in the wood. The sponge is nice, the brass scouring pad ( a lot cheaper at the grocers than at the electronics shop) in a small tin can is also good, plus the brass holds the solder balls nicely.

[Bud]

Speaking from experience, 15 years of soldering using the same Weller chiesel tip and wet sponge, still good as new and is preferred over a recently bought JBC.

[MaximRecoil]

Speaking from experience, 15 years of soldering using the same Weller chiesel tip and wet sponge, still good as new and is preferred over a recently bought JBC.

I think issues with the plating is a cheap tip problem, not a damp sponge problem. I've never seen the plating on a Metcal tip go bad, for example. Metcal is all I've ever used since I learned to solder at the PCB factory in 1997; not counting the $7 Radio Shack wall iron I had before getting my own Metcal in 2007. The tip on that Radio Shack iron was junk from day one.

I've been using the same STTC-126 tip cartridge since I bought it new in 2007, and it is still like new. I've never even seen a Metcal tip oxidize by any perceptible amount. At the PCB factory, I never even bothered to tin the tips I used there, and I never had any problems with them. I knew of the practice, because I saw other people doing it, or other people's tips in the stand with big blobs of solder on them, but I didn't know why people did it, and I never noticed any benefit to doing it so I didn't bother. When I was done work each morning, I simply wiped my tip on the damp sponge and put it in my locker, and it was always still shiny silver and working perfectly the next night. I tin my tip at home when I'm done with it, just because I've since learned the reasoning behind it and it seems like a good precaution, but I'm not religious about it. Sometimes I've forgotten to do so, and like the identical tips I used at work, I've never had a problem because of it.

[KL27x]

Here's another data point. Flux. Flux has low boiling point solvents. Touching the tip to a load of flux will reduce the temp quite a bit. This busts another myth, IMO, that flux, in and of itself, increases thermal transfer to the joint. Err, no. It can increase thermal transfer via increasing the speed/formation of solder bridge between tip and joint. But flux, itself, can only reduce the temp, at least until the solvent is all boiled away. The main thing is does, IMO, is increase the liquidity and wetting of the solder, once it has reached its melting point.

In practice, I can easily melt a joint with zero flux, as long as there is good solder bead to touch to... BUT the melted solder will look solid because it's chunky and not totally liquid. It won't look like it is melted, and it wouldn't bridge itself to, say, a jumper wire. But pop the button on the solder sucker, and it all gets sucked up... and doesn't clog the device with sticky flux residue.

Anyhoo, I use the brass wool to remove parts from the tip. To clean my tips, I SCRAPE THEM! With a bit of brass tubing. This removes the crusted flux. And to date, this has no ill effect on the iron or chrome plating. There is no wet sponge in my soldering.

[MaximRecoil]

Here's another data point. Flux. Flux has low boiling point solvents. Touching the tip to a load of flux will reduce the temp quite a bit. This busts another myth, IMO, that flux, in and of itself, increases thermal transfer to the joint. Err, no. It can increase thermal transfer via increasing the speed/formation of solder bridge between tip and joint. But flux, itself, can only reduce the temp, at least until the solvent is all boiled away. The main thing is does, IMO, is increase the liquidity and wetting of the solder, once it has reached its melting point.

In practice, I can easily melt a joint with zero flux, as long as there is good solder bead to touch to... BUT the melted solder will look solid because it's chunky and not totally liquid. It won't look like it is melted, and it wouldn't bridge itself to, say, a jumper wire. But pop the button on the solder sucker, and it all gets sucked up... and doesn't clog the device with sticky flux residue.

Anyhoo, I use the brass wool to remove parts from the tip. To clean my tips, I SCRAPE THEM! With a bit of brass tubing. This removes the crusted flux. And to date, this has no ill effect on the iron or chrome plating. There is no wet sponge in my soldering.

I don't use separate flux for anything other than plumbing with 1/8" diameter solid-core lead-free solder wire and a propane torch. At work, drag soldering wasn't allowed; every solder joint had to be done one at a time with fresh solder fed into it, so I never used separate flux for anything there. They probably had some there, but I never saw it. Plus, I can drag solder if I want to with just flux-core wire, though I still don't usually drag solder anything. The only type of electronics soldering I know of that requires separate flux is when you use a large tip and store solder on it for use on multiple joints (the flux already in the solder would soon burn away, so you'd have to put separate flux on each joint). I don't do that either.

I've never put separate flux on a joint before desoldering with a Soldapullt, nor do I know what the point of doing it would be. When people are having trouble desoldering a joint with a solder sucker, it is because of improper technique. When I trained new employees at work to solder/desolder, a common mistake they made was trying to desolder without the iron, i.e., they would put the iron to the joint and then remove the iron and quickly try to get the solder sucker tip onto the joint and pull the trigger. I think they were afraid that the iron would melt the "plastic" tip if they didn't move the iron out of the way, or that the tip of the solder sucker wouldn't be able to fit over the joint if the iron was in the way. Of course, that's an exercise in futility. At best you'll only get partial removal of the solder in the joint. It should be like this when you pull the trigger:

 

The flux in the solder wire I've always used (i.e., the same stuff I used at work: Alpha Metals Cleanline SMT Core Plus) doesn't leave any residue/crust on the tip, at least not any that remains after a quick wipe on a damp sponge.

[nctnico]

I'm not a fan of brass wool because it seems to abbrasive to me. I only use it if a tip is so crusty it cannot be cleanedwith a sponge. IMHO the biggest disadvantage of a sponge is that it needs to be wet (I have a squeeze bottle with water for that purpose) and many people use it upside down so it falls apart quickly.

[Carl_Smith]

I can't spill my copper wool like I can a bottle of water which I would inevitably leave on the bench and forgot to cap :-)

I use an old contact lens solution bottle for wetting the soldering iron sponge.  It won't spill more than a drip or two if tipped over.  It's a bit of a fight to pry off the cap to refill it since they are pressed on, but I don't have to do that very often since a full 12 oz bottle will wet the sponge many times.

[MaximRecoil]

I go to the sink so that I have a place to thoroughly wring it out. At work the closest water source was a water fountain, so I used that. Some other people there used water bottles, but I don't like the sponge to be any wetter than it needs to be.

[tggzzz]

I'm not a fan of brass wool because it seems to abbrasive to me.

Brass: 3 mohs
Steel: 4-4.5 mohs
Harddened steel: 7-8 mohs

http://www.jewelrynotes.com/the-mohs-scale-of-hardness-for-metals-why-it-is-important/

[madires]

I've used the wet sponge for a long time and never had any issues with tips becoming bad early because of this. A few years ago I've moved to brass wool, and I like the convenience of not having to wet the sponge each time. The solder which is removed from the tip while cleaning simply falls down into the wool's container. And no corroded sponge holders anymore.

[KL27x]

I've never put separate flux on a joint before desoldering with a Soldapullt, nor do I know what the point of doing it would be.

We agree on this. I've seen a lot of people recommend adding flux when desoldering, to "increase thermal transfer." In fact adding a little flux can help you to melt the joint a little faster in some cases where you can't get a good contact to the joint. But mostly, it just LOOKS "more melted" and you get to clearly see exactly the point when it melts vs a dried up joint, because it will go shiny and surface tension will make it ball/flow!

As for never using additional flux... Well that's fine if you were born with 3 hands, lol. Holding solderwire with one hand is not always an option. Some people use little octopus helping hands. I use flux.
 
I believe you mentioned, before, that you did thru hole soldering at your work. Extra flux is not needed for thru hole manual soldering. You need to feed so much solder wire into the joint, the flux will be there, anyway.  Fluxing the joint and then adding solder is commonplace in industry. Google "wave soldering." For SMD, drag soldering is used in military/aero, I believe. Seen videos by NASA trainers/workers doing drag soldering, anyhow.

And sometimes you simply need flux. Try installing a BGA without flux.

A common saying you might have heard before: you can't use too much flux. A lot of professionals and hobbyists use flux. It is helpful in a lot of situations.

*Also, as I mentioned before, the Metcal is top notch for not burning up the flux. That's what it is great at. Break out your Rat Shack for a solder session. You will have crusted flux.

[MaximRecoil]

I believe you mentioned, before, that you did thru hole soldering at your work. Extra flux is not needed. You need to feed so much solder wire into the joint, the flux will be there, anyway. With SMD soldering, fluxing the joint and then adding solder is commonplace in industry. Google "wave soldering."

At work I mainly did through-hole soldering (terminal blocks) on PCBs that were already populated with SMDs when I got them (the huge Panasonic SMT PnP machine did that). However, I also did rework on the SMDs that failed in the Hewlett-Packard HP3070 bed-of-nails tester or that were crooked. To solder an SMD in place, I put a small amount of solder on one of the pads, placed the SMD with tweezers and tacked one of its legs to the pad with my iron, soldered the other legs one at a time (feeding solder wire to each one, usually 0.015" diameter), then reflowed the tacked joint.

One thing I can see separate flux coming in handy for is soldering a wire to a surface-mount pad. A wire doesn't like to stay in place on its own, and unlike an SMD there's no way to tack one end of it in place to keep the end you're soldering from moving, unless it's a particularly stiff wire. I might buy some flux just for doing stuff like that.

By the way, most through-hole soldering at the place I worked was done in the wave; I have no idea why they had us solder in all those terminal blocks manually (I did thousands of them every night). No one I asked there knew either.

And sometimes you simply need flux. Try installing a BGA without flux.

As far as I know, that's not a hand-soldering procedure. That's an oven procedure.

[MaximRecoil]

And sometimes you simply need flux. Try installing a BGA without flux.

As far as I know, that's not a hand-soldering procedure. That's an oven procedure.

Hot air station. I consider anything soldered with hands, not fully automated, hand soldering, no matter direct or convection heat transfer.

By "hand-soldering" I meant with a soldering iron. Doing it with a heat gun could be considered hand-soldering I suppose, though it's effectively the same thing as doing it in a reflow oven.

[KL27x]

To solder an SMD in place, I put a small amount of solder on one of the pads, placed the SMD with tweezers and tacked one of its legs to the pad with my iron, soldered the other legs one at a time (feeding solder wire to each one, usually 0.015" diameter), then reflowed the tacked joint.

There are a lot of things in industry that are done, simply because they work, so don't F with it. Your terminal block example, for instance. Perhaps there was a good reason (thermal mass of the legs too high?) Or maybe they just need something to keep you guys busy in downtime for when they really need you?

In practice, if you used the same flux that is in the wire. And you preloaded the tip with solder. And you let the flux IN that solder drop off  and/or burn off onto the edge of tip where chrome plating starts. Then you touch the crusty solder to the pads which are fluxed with the appropriate amount of flux and drag solder it.... the end result is same as point to point soldering with solder-wire, alone.

Perhaps due to being high end test equipment, they are concerned with excess flux residue, if too much liquid flux were to be applied. Because in frequency approaching GHz, rosin/resin residue can cause unintended effects. In your home projects, this is probably not a concern. I've watched NASA soldering video where not only tip of the iron must be cleaned before each and every joint, but also the solder wire must be cleaned with a GD Kimwipe before making each joint. Am I going to do that for all my soldering?

[MaximRecoil]

Or maybe they just need something to keep you guys busy in downtime for when they really need you?

Maybe. There were only two to four people there at any one time doing what I did, usually two, and the job was called "inspecting". We got the boards after they came out of the Panasonic PnP machine and had to visually inspect each solder joint. If we saw any problems, such as crooked SMDs, or SMDs with a contact that didn't get soldered, we fixed it. Then we had to place and solder in all of the terminal blocks (like these). That part always seemed like an afterthought, given that the name of the job was "inspecting". Then we trimmed the terminal blocks' legs with flush cutters and sent the board to the HP3070. Depending on the workload, there might be someone assigned to the HP3070 for the night, or I might walk over and do the tests myself. The HP3070 would give a printout of any failures and their locations, and then we'd fix them manually, by replacing the SMD(s) that failed, and run the test again. It had to pass that test 100% before it could leave our area.

In practice, if you used the same flux that is in the wire. And you preloaded the tip with solder. And you let the flux IN that solder drop off  and/or burn off onto the edge of tip where chrome plating starts. Then you touch the crusty solder to the pads which are fluxed with the appropriate amount of flux and drag solder it.... the end result is same as point to point soldering with solder-wire, alone.

Yes, I know that the results of drag soldering can be perfectly fine; they didn't allow it though. They would always point out that we were building "life-saving equipment" to justify their fussiness about how things were done.

I've watched NASA soldering video where not only tip of the iron must be cleaned before each and every joint, but also the solder wire must be cleaned with a GD Kimwipe before making each joint. Am I going to do that for all my soldering?

They didn't take their fussiness that far. They were very concerned about ESD though. Our area, in a small corner of the factory near the tail-end of that Leviathan of a PnP machine, was the only area that worked on those particular "life-saving" boards. The area was enclosed in glass walls and temperature- and humidity-controlled. We wore ESD blue smocks, ESD wrist straps (along with a hand-cream type substance which was conductive, applied to the wrist beneath the conductive part of the strap), and ESD heel straps. When carrying PCBs out of that area, they had to be placed in ESD bags. Our Soldapullts were the ESD-safe variants of the original blue DS017, i.e., the black DS017LS (which is what I bought for use at home) and the chrome (or whatever that plating is) AS196.

They also had us attend ESD training classes every now and then.

[RobertHolcombe]

I prefer a wet sponge with a hole in it, as it provides a convenient location to wipe contaminants off the tip before wiping clean on the top surface of the sponge. In my experience metal wool has always trapped solder, components, component leads, etc, thus requiring more effort to maintain a clean tip - but 99% of the work I do is rework.

Question then for people who prefer wool; do you work on production of new boards/circuits, rework, or a mix of both, and how do you keep the wool from trapping debris?

[tautech]

Question then for people who prefer wool; do you work on production of new boards/circuits, rework, or a mix of both, and how do you keep the wool from trapping debris?

Mix of both but like you but mainly rework.
I never bothered with brass wool and use stainless wool in a short stout ceramic tumbler, easy to clean.
If you've ever tried to solder to stainless you'll know why I use it. 

[KL27x]

Bulk of my soldering is assembly, by volume. Of course if you do any assembly, it often works out that way. I also routinely do fine rework, usually when building prototype from scratch, or "optimizing" less than perfect pcb prototypes. I also simply build one-off stuff for my own use.

Debris goes into the wool, and it usually stays there. Every year, empty out the crud in the bottom of the holder, shake out the wool, and then put it back in. If removing a lot of parts, I'll wipe them off on a paper towel (or tap them off into a dish, if I want to save them), but the occasional 0603 ends up jabbed into the wool and occasionally comes back out on the tip. No big deal. Not building life-saving equipment in my lab. That said, wool does not really clean the tip very well, IMO, for how I solder. It is usually just a stop gap measure or to remove the odd part that gets stuck and is easier to dump in the wool than to re-tweezer. When I need to clean... brass tube and paper towel (dry). This is usually about once per session, often before I start. Works cold or hot. (The part that needs the deep cleaning is the chrome plated part that is not covered with solder.)

I have nothing against a wet sponge. It requires water, and that requires work and/or bench space for the bottle. Brass wool is always on.

[timb]

I've used the wet sponge for a long time and never had any issues with tips becoming bad early because of this. A few years ago I've moved to brass wool, and I like the convenience of not having to wet the sponge each time. The solder which is removed from the tip while cleaning simply falls down into the wool's container. And no corroded sponge holders anymore.

I keep a bottle of distilled water nearby for my sponge. I find that tap water causes the neck of the soldering iron and the base of the top to form white streaks after awhile. This is caused by the minerals in the water I imagine. (I'm on well water here and it's high in fluoride and other minerals. Great for preventing cavities, not so great for ultrasonic humidifiers and soldering iron sponges!)

I also use brass wool (or brass tribbles, as I like to call them). I use the sponge to wipe flux off the tip after a couple of joints; I use the brass a few times per session to keep the tip nicely tinned. If you apply a little solder to the tip then poke it in the brass and rotate it a few times, it comes out perfectly tinned.

The Hakko FX's base has both a sponge holder and a brass wool slot, so it's not a big deal.

[Someone]

I'm not a fan of brass wool because it seems to abbrasive to me.

Brass: 3 mohs
Steel: 4-4.5 mohs
Harddened steel: 7-8 mohs

http://www.jewelrynotes.com/the-mohs-scale-of-hardness-for-metals-why-it-is-important/

Wow, thats a radical oversimplification of abrasion. Just comparing hardness is almost worthless in this application, stainless steel works:

Question then for people who prefer wool; do you work on production of new boards/circuits, rework, or a mix of both, and how do you keep the wool from trapping debris?

Mix of both but like you but mainly rework.
I never bothered with brass wool and use stainless wool in a short stout ceramic tumbler, easy to clean.
If you've ever tried to solder to stainless you'll know why I use it. 

[nanofrog]

I'm not a fan of brass wool because it seems to abbrasive to me. I only use it if a tip is so crusty it cannot be cleaned with a sponge. IMHO the biggest disadvantage of a sponge is that it needs to be wet (I have a squeeze bottle with water for that purpose) and many people use it upside down so it falls apart quickly.

Do keep in mind, that although brass wool is harder than a damp sponge, it's not as hard, and therefore abrasive, as the steel plating on your soldering iron tip.    So it's not like you're putting your tips to a grinder. FWIW, tips will wear out faster with lead-free alloys IME. Not only due to the higher temps cracking the iron plating when using a sponge vs. brass wool (greater temp differential), but lead-free alloys also have a greater affinity for iron than lead based alloys.

Steel/stainless steel are approximately equal in hardness to the iron plating on your tips (depending on the specific alloy), but will also remove more stubborn deposits than brass wool or a damp sponge.

[nanofrog]

Question then for people who prefer wool; do you work on production of new boards/circuits, rework, or a mix of both, and how do you keep the wool from trapping debris?

Mostly rework (repairs), but some new (my own projects), as my gear is used purely in a hobbyist setting.

I find that the brass wool used makes a difference. For example, I find Hakko's wool to be a lot better than what I get from Weller (my soldering station is Weller), as it's coated with flux. I don't have definitive proof, but I don't think the Weller wool has flux on it. Or if it does, not nearly as much as Hakko's.

At any rate, when it works properly, I find solder balls & other debris falls to the bottom of the well/housing that contains it.  If not, it's an annoyance at best.

[stj]

FWIW, tips will wear out faster with lead-free alloys IME. Not only due to the higher temps cracking the iron plating when using a sponge vs. brass wool (greater temp differential), but lead-free alloys also have a greater affinity for iron than lead based alloys.

but lead free solder usually has less agressive flux in it than older solder formulations.
i have not used a lead-free solder that leaves burned flux residue on my iron yet, but most 60/40 formulations always did that.
IMO the biggest threat to the iron tip is large amounts of rosin in the flux.
before lead-free i used to go through tips every few months (production level use),
now tips last years with lead-free solder with no-clean fluxes.

[tautech]

FWIW, tips will wear out faster with lead-free alloys IME. Not only due to the higher temps cracking the iron plating when using a sponge vs. brass wool (greater temp differential), but lead-free alloys also have a greater affinity for iron than lead based alloys.

but lead free solder usually has less agressive flux in it than older solder formulations.
i have not used a lead-free solder that leaves burned flux residue on my iron yet, but most 60/40 formulations always did that.
IMO the biggest threat to the iron tip is large amounts of rosin in the flux.
before lead-free i used to go through tips every few months (production level use),
now tips last years with lead-free solder with no-clean fluxes.

There's the difference^^^ production where comparatively little flux is required as most everything is clean. Rework is an entirely different proposition where aggressive fluxes are often required.

Horses for courses. 

[MaximRecoil]

There's the difference^^^ production where comparatively little flux is required as most everything is clean. Rework is an entirely different proposition where aggressive fluxes are often required.

Horses for courses. 

I use the same 1.1% (P1) no-clean flux-core solder wire at home for rework (mostly on arcade PCBs from the 1980s, some of which are pretty nasty, especially CRT monitor chassis) that we used at work on brand new boards. I've never run into a situation where I needed a lot of and/or more aggressive flux. To replace a part or resolder a joint, I first desolder it (I don't use any flux to do that) and then the pads are inherently clean and lightly tinned after that, because they've been protected by solder fillets since they were manufactured; they accept new solder just as easily as brand new pads do.

I am curious though, about what sort of situations you encounter that require a lot of and/or aggressive flux.

[tautech]

There's the difference^^^ production where comparatively little flux is required as most everything is clean. Rework is an entirely different proposition where aggressive fluxes are often required.

Horses for courses. 

I use the same 1.1% (P1) no-clean flux-core solder wire at home for rework (mostly on arcade PCBs from the 1980s, some of which are pretty nasty, especially CRT monitor chassis) that we used at work on brand new boards. I've never run into a situation where I needed a lot of and/or more aggressive flux. To replace a part or resolder a joint, I first desolder it (I don't use any flux to do that) and then the pads are inherently clean and lightly tinned after that, because they've been protected by solder fillets since they were manufactured; they accept new solder just as easily as brand new pads do.

I am curious though, about what sort of situations you encounter that require a lot of and/or aggressive flux.

Yeah, I accept that the fillets DO protect pads but often a lead has degraded with age and if one leg of a component has needed to be pulled sometimes a neat fillet can be hard to make when resoldering.

When I've mentioned rework it's probably a little misleading. Electronics and things electrical have been a hobby for decades. From distant Scots heritage I will have a go at most things that many wouldn't give a second look and some are in poor state. Also part of being frugal by nature I have all manner of componentry and cabling tucked away for the day it might come in handy, some 2nd hand, some new, despite some being new it all degrades over time and gets harder to solder.
So there's joints that require solder with active fluxes in order to be properly soldered and they're just part of the arsenal of goodies I keep. The last new 1lb roll of solder I bought was ~20 yrs ago, some fancy RS stuff with 2% silver.......reserved for special occasions. Day to day solder is anything I can get my hands on for bugger all, formulation....well I don't care as long as it's not that lead free muck. 
Of my collection some have more aggressive fluxes than others .........how do I know ? Use one on shitty work......doesn't work.....use another til one cuts through the gunk and wets the joint properly.
Magnification while soldering is my friend. 

There's been times when I've wanted addition flux and to date I have only added fluxed solder to get flux to a joint but I grabbed a flux pen recently from a supplier so we'll see how that goes when I need some flux next. Might be the dawn of a new world. 

[nanofrog]

FWIW, tips will wear out faster with lead-free alloys IME. Not only due to the higher temps cracking the iron plating when using a sponge vs. brass wool (greater temp differential), but lead-free alloys also have a greater affinity for iron than lead based alloys.

but lead free solder usually has less aggressive flux in it than older solder formulations.
i have not used a lead-free solder that leaves burned flux residue on my iron yet, but most 60/40 formulations always did that.
IMO the biggest threat to the iron tip is large amounts of rosin in the flux.
before lead-free i used to go through tips every few months (production level use),
now tips last years with lead-free solder with no-clean fluxes.

Huh?  What does this have to do with a sponge v. brass or even a steel/stainless-steel wool?

As per the burnt/crispered flux, that tends to have to do with the operating temperature IME. FWIW, I've dealt with that as well as a clean tip, depending on operating temp (iron's recovery v. set temp has had a HUGE impact on this IME).

Regarding flux activity, what are you talking about?  I ask, as there's variations in the activity level of no-clean, organic (water-soluble), and of course, rosin-based fluxes. Please understand, I'm not trying to be an ass, but there' multiple variations in all formulations' activity, and they do matter IME. That said, it can be harder to determine what's-what regarding no-clean & water-soluble formulations in particular vs. traditional rosin based formulations.

Specifically, the newer fluxes designed for lead-free alloys have a shorter time to activate before the solder is molten & is looking for clean surfaces to join (higher temp to activate, and therefore a shorter time between cleaning off the oxides and joining the metallic surfaces = more aggressive vs. rosin formulations, even RA).

Granted, the actual cleanliness (oxidation) is both a function of both temp & time, but I've found that I prefer the results of rosin-based, including modified rosin based no-clean formulations, as a general rule.*

*Not only do I like the performance in regard to cleaning the oxides off of both new & older boards, but whether declared as rosin-based or modified-rosin no-clean,  I find they're much easier to clean than their synthetic no-clean counterparts. Water-soluble/organic fluxes are easy to clean of course, but they must be cleaned off, and within a particular amount of time before it causes problems (oxidizes traces & component leads). For a hobbyist, the latter is more trouble than it's worth IMHO.

[KL27x]

As per the burnt/crispered flux, that tends to have to do with the operating temperature IME. FWIW, I've dealt with that as well as a clean tip, depending on operating temp (iron's recovery v. set temp has had a HUGE impact on this IME).

Yup. Pretty much 2 main settings on my iron. Low: I'm either making something up as I go, where iron is on for hours but making joints only once per 20 minutes. High: I'm assembling a batch of PCB's, and the iron is either singing along making a joint every couple seconds or it's frying in the stand. This is perfectly fine. I'm done for the day by the time tip needs cleaning.

Steel wool, brass wool... I am pretty sure steel wool will scratch elemental iron. Who really knows what kind of iron is actually in your soldering iron tip? Cast irons* are harder than many steels and are commonly used in industry for extreme resistance to wear and oxidation in high temp environments. And contrary to "iron plating" which is the common way to refer to it, the iron skin on say Hakko tip is far from a plating. It's quite thick and I doubt it is plated onto the copper core. My guess would have been that pure copper is swaged into the iron jacket, just by looking at the remains of a Dremeled-in-half iron tip. Anyway, if it works, who cares?   

*For some reason, if iron has less than 0.3% carbon alloyed into it, it is called iron, or wrought iron. If it has between 0.3 and 2%, it is steel. And if it has >2% carbon, it is called cast iron. My numbers might be slightly off, but that's the gist.

** Found via google, random forum:

Yes you can soft solder cast iron. The best advise I can give you is keep everyting clean. A fresh ground surface works better than one that has sat for several days. Use a high tin alloy and the best flux you can get. Even heat with a propane torch kept moving works better than anything I have found. Tin the parts well and use a clean, steel bristle brush to rub the solder into the area.

So, regular iron is highly susceptible to oxidation. It is a very reactive metal. And it's not particularly hard. Copper tip plus relatively soft plating = soft tip. Soldering iron tips are not particularly malleable. Unless they're by Radio Shack.
Cast iron is hard and resists oxidation and scratching. But unlike stainless steel, it has a high thermal conductivity.... and it will hold solder. Unless you leave it bare for a few days.... Hmmm..? Maybe at some point pure iron was commonly plated onto a copper tip...

[Someone]

OKi makes no mention of thermal shock in their lengthy document discussing tip life:
http://www.newark.com/pdfs/techarticles/oki-metcal/extendingTipLife.pdf
And suggest the only problem with a sponge is the cleanliness of it!

[tszaboo]

So, I have to replace the tips (if I use it often) every 4-5 months, without sponge, they are like 50% more durable, than I can save enough money in a few years, to eat an ice cream.

[madires]

Question then for people who prefer wool; do you work on production of new boards/circuits, rework, or a mix of both, and how do you keep the wool from trapping debris?

Hobbyist usage, i.e. repairs and projects. Most remains simply fall through the wool down to the bottom of the container. So I empty the container and slap the wool a few times against the inside of my bin.

[TheBay]

I believe that the tips cracking is more prevalent on lead free systems due to the composition of the tip.

lol - BS
the tips are the same, they never changed.
some people will blame anything on lead-free!!

I blame the EU 

[MaximRecoil]

So, regular iron is highly susceptible to oxidation. It is a very reactive metal. And it's not particularly hard. Copper tip plus relatively soft plating = soft tip. Soldering iron tips are not particularly malleable. Unless they're by Radio Shack.
Cast iron is hard and resists oxidation and scratching. But unlike stainless steel, it has a high thermal conductivity.... and it will hold solder. Unless you leave it bare for a few days.... Hmmm..? Maybe at some point pure iron was commonly plated onto a copper tip...

Well, pure iron doesn't exist, for all intents and purposes. There are laboratory examples that are ~99.99% pure, and it is softer than lead; it can be cut with a knife. It doesn't take much carbon to drastically increase its hardness though.

I just skimmed through the Metcal article that Someone linked to above, and it is bizarre. For starters:

A tip typically consists of a solid copper core, a plated layer of iron, a plated layer of nickel behind the
working surface, and a plated chrome layer. Copper is used for the core primarily to ensure good heat
transfer. The nickel layer is a non-wetting layer designed to keep the solder from wicking away from the
tip's working surface. Without this layer, the solder would travel preferentially up the tip toward the heat
source, making it impossible to apply solder to the solder joint. The chrome layer is applied as an
additional protective layer.

We know that can't be technically accurate, because they can't simply be using iron, because it effectively doesn't exist; it has to be an iron alloy (steel) of some sort. Also, the Metcal tips use the Curie point for temperature regulation, which is determined by the type of alloy they use, but it's the heater that's made of that alloy, and I have no idea what that alloy is (I assume it is copper-based though). I wonder if the heater is integral with the tip:



It would make sense for the heater and "copper" core of the tip to be one piece, as that would give the best thermal response and thermal regulation, and Metcals excel in both areas.

I also find it strange that nickel is a non-wetting material while chrome is a wetting material. I would expect both of them to be non-wetting under typical circumstances. The chromium content of stainless steel is the reason it is pretty much a non-wetting material. The chrome very quickly forms a passivation layer of chromium oxide (i.e., oxidation, the enemy of soldering), which is what protects stainless steel from further corrosion (rust in this case). So how does solder wet to a chrome-plated tip, given chrome's rapidly-forming, tough, and tenacious passivation layer?

But the most bizarre part of the article is how they talk about iron's wetting characteristics. For example, in the section called "Why Iron Plating?", it says:

Must Be Wettable
The working surface of the tip must wet to transfer molten solder to the joint and to aid heat transfer. Iron
wets. Molybdenum doesn't.

And in another section:

Dewetting is the most common form of plating failure and is preventable, for the most part, with good
daily tip care. Thermal dewetting is caused by oxidation of the iron plating to iron oxide. Iron oxide is
non-wetting.

But how is that relevant to a tip that's chrome-plated? The solder will never contact the iron plating beneath it, so what do the wetting characteristics of iron have to do with anything? The iron plating can't even oxidize in the first place as long as the chrome plating is intact, because the chrome plating prevents oxygen from contacting the iron plating.

I wonder if the chrome plating is thin "decorative chrome" (thickness measured in the millionths of an inch) or thick "industrial hard chrome" (thickness measured in the thousandths of an inch). Industrial hard chrome is tough as a bag of badgers; it is what they plate e.g., hydraulic cylinders on big earth-moving machinery with, for example. It is also what they commonly plate the barrel bores of military rifles with, such as the M16 and AK-47. In my experience, the Metcal tips never fail, nor do they even need to be tinned when you're done with them. When a Metcal tip cartridge fails, it is always a heater failure, so it wouldn't surprise me if the plating is industrial hard chrome, and it wouldn't surprise me if the iron "plating" is a jacket rather than actual plating, like the copper jacket on a lead bullet.

It's funny that Metcal wrote such a lengthy article called "Extending Soldering Iron Tip Life", when their tip plating never fails to begin with, even if you don't keep it tinned (still speaking in the context of my own experience).

[KL27x]

^If you look at the cross section, the chrome plating is only over the shaft part of the tip. It stops where the solder bead begins. The chrome plating is there to prevent solder from adhering. If you look closely at a tip, you will see where the tip doesn't wet, it's thicker. It's a chrome plating OVER the wettable "iron" plating. This is how is appears on my Hakko tips, anyway. On a cheaper station I used before, the base of the tips were covered with some thicker/crustier stuff that almost looked like ceramic.

We know that can't be technically accurate, because they can't simply be using iron, because it effectively doesn't exist;

I wonder if early irons were plated with pure iron. I am not sure you can electroplate an alloy? So unless case hardened, after, perhaps some tips used to be made with pure iron plating. Radio Shack copper tips actually come with a thin plating that lasts about 3 days... perhaps this might be example of electroplated "pure" iron?

Some gears are coming loose in the attic of my brain. IIRC, what qualifies "steel" is ability to undergo martensic hardening. Probably misspelled it. Whereas cast iron is hard even without a heat treat. Which seems like a good idea for something which operates at over 700F for extended periods of time, which is above tempering level of common carbon steel. So carbon steel sucks for an iron due to corrosion and need for heat treat. Stainless steel sucks because it can't be wetted and lower thermal conductivity. Cast iron would seem to be pretty much ideal. It seems to me, modern iron tips probably have nothing to fear from unhardened steel wool.

[MaximRecoil]

^If you look at the cross section, the chrome plating is only over the shaft part of the tip. It stops where the solder bead begins. The chrome plating is there to prevent solder from adhering. If you look closely at a tip, you will see where the tip doesn't wet, it's thicker. It's a chrome plating OVER the wettable "iron" plating. This is how is appears on my Hakko tips, anyway. On a cheaper station I used before, the base of the tips were covered with some thicker/crustier stuff that almost looked like ceramic.

The way you're interpreting that diagram doesn't match what the text says, and if your interpretation were correct, then the nickel plating would be useless, because it would be completely covered by the chrome plating. The text says that the nickel plating is there specifically because it is non-wetting, thus it prevents the solder from wicking up the tip away from the joint. It couldn't serve that function if it were completely covered by chrome. Also, the implication is that the chrome plating is wettable, else they could just use chrome in place of nickel for the non-wetting barrier.

I wonder if early irons were plated with pure iron. I am not sure you can electroplate an alloy?

Here is a paper called "Electrodeposition of Iron and Iron Alloys":

http://www2.bren.ucsb.edu/~dturney/port/papers/Modern%20Electroplating/11.pdf

So unless case hardened, after, perhaps some tips used to be made with pure iron plating. Radio Shack copper tips actually come with a thin plating that lasts about 3 days... perhaps this might be example of electroplated "pure" iron?

If it were "pure" iron, you couldn't case harden it. Only steel can be case hardened, and even then you need a certain amount of carbon to do so. Some low-carbon steels (and pure iron could be called no-carbon steel) have no hardenability at all.

I wouldn't be surprised if cheap tips such as on a $7 Radio Shack wall iron were just solid mild steel, i.e., the same thing as a nail from the hardware store. In fact, I've heard of some cheap irons that actually did use an ordinary nail for the tip.

Edit: Scratch that. I just checked my 64-2067C Radio Shack iron (with severely deformed tip, despite not having been used much), and a strong magnet has no perceptible attraction to the tip.

[nanofrog]

The chrome plating is there to prevent solder from adhering. If you look closely at a tip, you will see where the tip doesn't wet, it's thicker. It's a chrome plating OVER the wettable "iron" plating.

Chrome won't adhere directly to iron, but it will adhere to nickel, which will adhere to iron. So plate iron with nickel, and the nickel with chromium, and the tip we're all familiar with is formed. 

[KL27x]

^ That. +1 If we could figure out a way to deposit the chrome, directly, we would be doing it like that. Nickel is a more reactive metal and chrome plating often fails via the nickel layer corroding away. This is why you have to avoid certain cleaners on chrome plated guns and whatnot.

If it were "pure" iron, you couldn't case harden it. Only steel can be case hardened,

Steel can be heat-treated to make it hard. Very low carbon iron can't. Case hardening is a way of introducing carbon to the surface of very mild steel (or one would think pure iron), to get the top few microns or whatnot high enough in carbon so that it CAN be heat treated.  Very low carbon steel, wrought iron, there's not much difference. 

From the study you linked:

It [iron] can be deposited as a
hard and brittle metal which, by heat treatment, can be
rendered soft and malleable, or as a soft and ductile metal
to which surface hardness can be imparted by carburizing,
cyaniding, and nitriding. The fatigue strength of surfaces
prepared by case hardening electrodeposited iron has been
reported to be equal to the best commercial rolling-element
bearing materials [26].

So some people think iron can be case hardened. I guess there might be different definitions. Per other parts of the study I skimmed, iron can apparently be plated quite thick and also relatively hard. So I wouldn't worry about steel wool eating away your iron tip based on moh rating of "iron" or "steel." Steel wool is very mild and unhardened. And apparently "iron" means a lot of different things. Iron... steel.. .how bout we call it ferrous metal?

[MaximRecoil]

^ That. +1 If we could figure out a way to deposit the chrome, directly, we would be doing it like that. Nickel is a more reactive metal and chrome plating often fails via the nickel layer corroding away. This is why you have to avoid certain cleaners on chrome plated guns and whatnot.

Nickel is a far more common outer plating for guns than chrome; generally you only see chrome plating on the cheapest guns, such as the "Ring of Fire" guns (Davis, Raven, etc.); the frames and slides are made of Zamak (glorified pot metal) and chrome (decorative) plated. Hard chrome is a different story, though it is rare for a gun to be hard-chromed from the factory (aside from the barrel bores of some military guns). Hard chrome is a popular aftermarket finish for guns that see hard usage, such as "race guns".

In any case, the text of that Metcal article seems to be wrong. It is at odds with what the accompanying diagram appears to show, and it is at odds with what would actually work, which is why I said the article is bizarre.

Steel can be heat-treated to make it hard. Very low carbon iron can't. Case hardening is a way of introducing carbon to the surface of very mild steel (or one would think pure iron), to get the top few microns or whatnot high enough in carbon so that it CAN be heat treated.  Very low carbon steel, wrought iron, there's not much difference.

Case hardening isn't a way of introducing carbon to the surface of very mild steel, though carbon can be introduced to the surface of "iron" to allow it to be case hardened. But in that case, you are creating steel, at the surface at least. Case hardening is normally done to steel which already has enough carbon to be hardenable as-is, including high-carbon steel. A famous example is the frame of the Colt Single Action Army revolver, which isn't made from "iron" or mild steel; it is made from high-carbon steel, just as all quality machined gun parts are.

I would like to know what makes a Metcal tip so maintenance-free. I've never had one show any signs of not wanting to wet, and like I mentioned before, at work, I never even bothered to tin the tip when I was done or before I started soldering. I just wiped it on a damp sponge every now and then to remove excess solder, not giving any thought at all to maintenance.

[KL27x]

Hard chrome is a different story

Far as I know, they both are plated over nickel.

If it were "pure" iron, you couldn't case harden it. Only steel can be case hardened,

+

Case hardening isn't a way of introducing carbon to the surface of very mild steel, though carbon can be introduced to the surface of "iron" to allow it to be case hardened.

= 



 


Steel is iron with 0.003% carbon to 2.1% carbon. Mild steels, with carbon under about 0.3% don't harden. Or not much. So I don't get why you can case harden iron but not mild steel. Oh I see what you're doing, playing semantics.
Wikipedia:

For iron or steel with low carbon content, which has poor to no hardenability of its own, the case-hardening process involves infusing additional carbon into the surface layer.

Case-hardening involves packing the low-carbon iron within a substance high in carbon, then heating this pack to encourage carbon migration into the surface of the iron. This forms a thin surface layer of higher carbon steel, with the carbon content gradually decreasing deeper from the surface. The resulting product combines much of the toughness of a low-carbon steel core, with the hardness and wear resistance of the outer high-carbon steel.

Of course, who cares what Wikipedia says. It's usually wrong. And again, iron vs steel. Seems like these terms are used without much objectivity nor precision everywhere I look. Here they call the material low carbon iron, then in the next sentence low carbon steel. I doubt they are referring to the 0.003% cutoff point. Or w/e it is.

[MaximRecoil]

Far as I know, they both are plated over nickel.

That's not what I meant by hard chrome being a different story. Hard chrome isn't for cheap guns, which makes it a different story than standard chrome, which is mostly only used on cheap guns. Nickel plating (without anything plated on top of the nickel) on the other hand, has been using on many high-end guns, such as from Smith & Wesson and Colt.

If it were "pure" iron, you couldn't case harden it. Only steel can be case hardened,

+

Case hardening isn't a way of introducing carbon to the surface of very mild steel, though carbon can be introduced to the surface of "iron" to allow it to be case hardened.

= 



 

Hmm.. Wikipedia says:

For iron or steel with low carbon content, which has poor to no hardenability of its own, the case-hardening process involves infusing additional carbon into the surface layer.

You said that case hardening is a way of introducing carbon to the surface of very mild steel. It isn't. Case hardening is a surface hardening method, and if you start with steel which already has sufficient carbon content, you don't have to add any carbon at all. If you start with "iron", you have to turn it into steel in order to case harden it, i.e., by introducing carbon (steel is an iron/carbon alloy).

Steel is iron with 0.003% carbon to 2.1% carbon. Mild steels, with carbon under about 0.3% don't harden. Or not much. So I don't get why you can case harden iron but not mild steel.

You can't case harden iron; you can only case harden steel. If you want to case harden iron you have to turn the surface into steel by adding carbon, which can then be hardened. The same applies to "mild steels, with carbon under about 0.3%"; add carbon and you can case harden those too.

[KL27x]

if you start with steel which already has sufficient carbon content, you don't have to add any carbon at all. If you start with "iron", you have to turn it into steel in order to case harden it

I'm curious how one would case-harden high carbon steel? I'm familiar with how katanas were differentially heat treated by covering the entire blade except for the edge in wet clay before firing, so that only the edge of the blade reaches critical temperature. How do you selectively surface harden a Colt SAA which is already high carbon steel all the way through, without adding more carbon to the surface? Expose it to core of nuclear reactor for 1 second before quench?

AFAIK, case hardening has always been applicable to lower carbon steel/iron. Carburizing the surface being part of the process. Semantics and Wikipedia be damned.

Heh, I like you, Maxim. You remind me of me. 10 years ago.

[MaximRecoil]

if you start with steel which already has sufficient carbon content, you don't have to add any carbon at all. If you start with "iron", you have to turn it into steel in order to case harden it

I'm curious how one would case-harden high carbon steel? I'm familiar with how katanas were differentially heat treated by covering the entire blade except for the edge in wet clay before firing, so that only the edge of the blade reaches critical temperature. How do you selectively surface harden a Colt SAA which is already high carbon steel all the way through, without adding more carbon to the surface? Expose it to core of nuclear reactor for 1 second before quench?

AFAIK, case hardening has always been applicable to lower carbon steel/iron. Carburizing the surface being part of the process. Semantics and Wikipedia be damned.

Carburizing only needs to be done to "iron" / very low-carbon steel.

Flame or induction hardening is the usual process for hardening steel that already has enough carbon (and is also often used after carburization in cases where you started with "iron" / very low-carbon steel). This was used on certain areas of the slides of M1911 and M1911A1 pistols, i.e., near the muzzle and around the cutout for the slide stop. Post-war commercial Colt Government Models (civilian versions of the M1911/M1911A1) used better steel and through-hardening rather than selective case hardening.

An area of steel doesn't need to have more carbon than another area in order to be harder; it is the transformation of the structure to martensite that makes it harder.

The process for the Colt SAA and a lot of other firearms of the era was commonly called "color case hardening", because it resulted in mottled colors (http://www.turnbullmfg.com/wp-content/gallery/2341/2341_r.jpg). It's been decades since I read about the process, but from memory, it involved packing it in various organic materials while being heated, e.g., charcoals of bone, leather, wood, and maybe some other stuff.

I agree that some of this boils down to semantics.

[KL27x]

The process for the Colt SAA and a lot of other firearms of the era was commonly called "color case hardening", because it resulted in mottled colors (http://www.turnbullmfg.com/wp-content/gallery/2341/2341_r.jpg). It's been decades since I read about the process, but from memory, it involved packing it in various organic materials while being heated, e.g., charcoals of bone, leather, wood, and maybe some other stuff.

This "stuff" is all packed with carbon. And the flames are for vaporizing it and carburizing the surface. I don't believe it is possible to selectively surface-harden high carbon steel by selectively heat-treating just the surface with flames. The thermal conductivity is too high, in my estimation. At least not without exotic setup that would be prohibitively expensive and probably impossible in the 1800's. If they were doing induction surface hardening in 1800's, that is pretty amazing.

[MaximRecoil]

This "stuff" is all packed with carbon. And the flames are for vaporizing it and carburizing the surface.

Yes, but it wasn't necessary. The carbon content of the steel was already high enough to be hardenable as-is. The addition of the organic materials was primarily for the color effect; different "recipes" yielded different colors/patterns, and they were tightly-guarded secrets. With USGI M1911s and M1911A1s (introduced in 1911), the selective case hardening was purely for functional purposes, so there was no mottled color effect, though if you look closely at the parkerized ones you can see the difference in the color of the finish around the areas that were case hardened, because parkerizing takes on different shades depending on the hardness/structure of the steel. Here's an example:



And the note accompanying that picture:

1943 Ithaca M1911A1 - note heat treatment discoloration around slide stop notch and slide at muzzle end.

And:

Below are a few typical wartime 1911s. Note that some may have what appears to be a blemish around the slide stop, and even the muzzle. This is due to the heat treatment process, and was not considered cause for rejection during the war.

Nothing on a USGI M1911 or M1911A1 is low carbon steel. They were last purchased in 1945 and used until 1985, and to this day some of them are still in use. Mild steel is junk for the purpose of gun parts; it doesn't hold up. No reputable manufacturer would use it, nor would the U.S. military buy mild steel guns.

I don't believe it is possible to selectively surface-harden high carbon steel by selectively heat-treating just the surface.

Yes, it is:

Flame or induction hardening are processes in which the surface of the steel is heated very rapidly to high temperatures (by direct application of an oxy-gas flame, or by induction heating) then cooled rapidly, generally using water; this creates a "case" of martensite on the surface. A carbon content of 0.3–0.6 wt% C is needed for this type of hardening.

"High carbon" technically starts at 0.6%, though I've simply been using the term to distinguish from unhardenable mild / low carbon steel / "iron".

The thermal conductivity is too high, in my estimation. At least not without some exotic setup that would be prohibitively expensive and probably impossible in the 1800's.

I don't know, but keep in mind that Colt still manufactures the SAA, and they certainly don't use mild steel today (nor did they ever, but today they use 4140 chromoly, which is better quality than any steel that existed in the 1800s), and they still color case harden the frames. Whatever carburization that happens during that process definitely isn't necessary, because 4140 is hardenable on its own.

[KL27x]

Well, I accept being wrong, no problem. Google to the resuce and flame-hardening is a thing. Apparently using oxyacetylene flame, and which produces depth of hardening as "thin" as 50 mils. Usually used on larger parts than firing pins and gun hammer. And BTW oxyacetylene torch invented in 1901. 

I think it is a stretch to call flame or induction or nitridization "case-hardening." It seems more logical that case-hardening, nitrides, cynade, induction, and flame hardening are all subtypes of surface hardening. But I accept that by your worldview that case-hardening not only describes induction and flame hardening, but that somehow, illogically, "case-hardening" actually discludes the oldest method of surface hardening, by carborization, even though that's how, perhaps, it got the name.

(I have found many references to case-hardening of wrought iron. Apparently it even has a special name "blister steel." According to Wikipedia (lol) even the term "case-hardening" comes from the box/case/container in which the "ferrous metal" is sealed with various carbon sources to produce oxygen free environment in which the carburization takes place.)

SAA maybe flame or induction hardened in 1800s, sure. Hek, maybe they even nitrocarburized it. And they just used the charcoal to add the colors.

[MaximRecoil]

I think it is a stretch to call flame or induction or nitridization "case-hardening." It seems more logical that case-hardening, nitrides, cynade, induction, and flame hardening are all subtypes of surface hardening. But I accept that by your worldview that case-hardening not only describes induction and flame hardening, but that somehow, illogically, "case-hardening" actually discludes surface carburization subtype of surface hardening, even though that's how it got the name.

"Case hardening" doesn't exclude carburization. This got tangled up in semantics, i.e., if you start with "iron" which can't be hardened as-is, and then you carburize it during heat treatment, you are turning the area that's being hardened into steel, thus you haven't hardened "iron"; you've made a thin layer of steel and hardened that. The transformation to the martensite structure is what makes steel harden, and that transformation is a process involving carbon atoms, which is why you can't harden "iron", because it has little to no carbon atoms. 

[tautech]

We learnt how to set a oxy torch to a reducing flame, that is a flame with an excess of acetylene, in metalwork classes at high school but the result was never as good as the case hardened punches and chisels we made back then.
I can't remember the steels used but they were not just mild for hardening and tempering processes don't well work on mild steels.

[KL27x]

Case hardening seems like a super useful thing, back in the days when belt sanders and angle grinders weren't available from Harbor Freight for $30.00. LOL. Case hardened chisels and punches.... imagine that. Super cool. Now we have tools so hard, I can't even cut them with my Arkansas stones, and grinding them on even a belt sander takes forever.

@Maxim: gotcha. All good.

[eKretz]

Whoa has this gone off topic. Hardening of steel and iron is a very complex subject and there are many facets involved. Iron can be hardened without being transformed into steel - Google "chilled cast iron" - it's some viciously hard stuff. As far as iron vs. steel: at the most basic level, iron is a pure element; steel is iron + carbon.

Regarding the original topic - I use both a damp sponge and wool for tip cleaning. Both seem to work about the same to me, but the sponge seems a bit quicker and is easier to do for me one handed. Probably mainly because my iron stand has a built in sponge holder and my wool is just stuffed into a light little cup.

[MaximRecoil]

Whoa has this gone off topic. Hardening of steel and iron is a very complex subject and there are many facets involved. Iron can be hardened without being transformed into steel - Google "chilled cast iron" - it's some viciously hard stuff. As far as iron vs. steel: at the most basic level, iron is a pure element; steel is iron + carbon.

"Cast iron" already is a form of steel. In fact, it has more carbon in it than what we normally call "steel". Pure iron can't be hardened because it doesn't have any carbon, so there's no way for its structure to transform into martensite.

[eKretz]

Oh yes, cast iron has higher carbon percentage than steel, but the hardening of chilled cast iron is a completely different process than the austenite/martensite transformation that occurs with steel. As I recall, the chilled layer is largely composed of iron carbides (and yes, this of course does require the presence of carbon). And as I recall from turning chilled iron rolls, they are as hard as a coffin nail, to use an old turn of phrase. It could also be said that steel is just another type or alloy of cast iron. All that said however, the context of the post I was referring to with iron being an element was related to the iron plating on the soldering tip - which I assume is just plain iron and not the cast variety with added carbon.

[tautech]

Oh yes, cast iron has higher carbon percentage than steel, but the hardening of chilled cast iron is a completely different process than the austenite/martensite transformation that occurs with steel. As I recall, the chilled layer is largely composed of iron carbides (and yes, this of course does require the presence of carbon). And as I recall from turning chilled iron rolls, they are as hard as a coffin nail, to use an old turn of phrase. It could also be said that steel is just another type or alloy of cast iron. All that said however, the context of the post I was referring to with iron being an element was related to the iron plating on the soldering tip - which I assume is just plain iron and not the cast variety with added carbon.

Yes, that could be said and it would be wrong.

Steel IS an iron alloy. Period

[eKretz]

Lol, that's kind of what I was hinting at - as Maxim has it the other way around.

[KL27x]

All that said however, the context of the post I was referring to with iron being an element was related to the iron plating on the soldering tip - which I assume is just plain iron and not the cast variety with added carbon.

I would have ventured same guess before really thinking about it.

Earlier, Maxim posted link to some paper on iron plating. Per this source, iron can be plated hard or soft. Assuming this to be true, I can't say for sure how or why an iron plating can be hard. To venture a guess, perhaps it is more difficult to get the carbon out of iron than one might assume? Even when plating it, perhaps it will alloy with carbon, if present?

I always thought steel was "invented" by adding carbon to iron. And this true, to be exact. I might get some details wrong, but wrought iron (the carbonless type of iron) was obtained from bogs, or something weird like that. And in very small quantities. Adding carbon to this perhaps man created the first steel. But in industrial age, smelting of iron ore to obtain iron in reasonable quantities that make it the cheap commodity it is, today, the coke used to smelt the ore creates high carbon iron. The trick then is to get the carbon OUT of the iron to make steel.

For this reason, I cannot assume to know what the hell is on an iron tip. But it stands to reason that harder > softer, if all else equal. And earlier I pointed out that iron with high carbon content is not only hard without heat treat, but it is also wettable by solder, and it is highly resistant to rusting. So why wouldn't anyone use it, if it were possible... AND... Cast iron can apparently be plated onto aluminum engine pistons. I think all signs point to ... pure iron is not very much common in industrial use, at all, and there would be no obvious reason to use it for soldering iron tips, unless for some cost reason. Pure iron corrodes very easily, not even taking into account sustained use at high temperature.

Low carbon steel isn't cheap because adding carbon is more expensive. Low carbon steel is cheap because it is easier to shape and machine. But when you go from mild steel, with low carbon content, and further refine to "pure iron," this increases expense. High carbon iron is cheap and abundant. But pure iron not so, methinks.

 

[MaximRecoil]

Lol, that's kind of what I was hinting at - as Maxim has it the other way around.

"Cast iron" is a misnomer that has stuck. It is like calling brass "cast copper". What do you call ~pure iron that has been cast?

In any case, as I said, iron (actual iron, AKA: "Fe", not the misnomer) can't be hardened without turning it into steel by alloying it with carbon.

[tautech]

Lol, that's kind of what I was hinting at - as Maxim has it the other way around.

"Cast iron" is a misnomer that has stuck. It is like calling brass "cast copper". What do you call ~pure iron that has been cast?

Pig iron.

[KL27x]

Wikipedia:

Pig iron has a very high carbon content, typically 3.5–4.5%,[2] along with silica and other constituents of dross, which makes it very brittle and not useful directly as a material except for limited applications.

"Misnomer" is one way to look at it.

Another way to look at it: iron with any degree of carbon content is iron. Steel is a subset of iron which is heat treatable and can include other alloying elements. The martewhatsee crystallization give steel such unique property and toughness, it gets a special name.

[tautech]

Wikipedia:

Pig iron has a very high carbon content, typically 3.5–4.5%,[2] along with silica and other constituents of dross, which makes it very brittle and not useful directly as a material except for limited applications.

"Misnomer" is one way to look at it.

Another way to look at it: iron with any degree of carbon content is iron. Steel is a subset of iron which is heat treatable and can include other alloying elements.

Exactly.

Back to Pig iron, it's the most raw iron product I know of direct from the smelter. That it might have contaminants in it is quite understandable IMO, it's a raw product to which the various additives are blended with to make the range of iron based products we know and use.

[MaximRecoil]

Lol, that's kind of what I was hinting at - as Maxim has it the other way around.

"Cast iron" is a misnomer that has stuck. It is like calling brass "cast copper". What do you call ~pure iron that has been cast?

Pig iron.

Pig iron is far from pure iron (it has a lot of carbon, among other things). It is like what we call "cast iron", but more crude.

Iron (Fe, nothing else) that has been cast would, by definition of the words "cast" and "iron", be "cast iron", but it would be drastically different than the misnomer version of cast iron.

[eKretz]

I think we're basically down to semantics here, but personally I'd have to go with steel is an alloy of iron. Steel is at its most basic composed of iron and carbon. Iron is composed of a pure element. What is in common parlance referred to as "cast iron" is composed of? Steel and more carbon - or one could say [iron + carbon (which is steel)] + more carbon.

[MaximRecoil]

I think we're basically down to semantics here, but personally I'd have to go with steel is an alloy of iron. Steel is at its most basic composed of iron and carbon. Iron is composed of a pure element. What is in common parlance referred to as "cast iron" is composed of? Steel and more carbon - or one could say [iron + carbon (which is steel)] + more carbon.

Which gets a bit ridiculous when an iron alloy with 1.99% carbon content is steel and an iron alloy with 2% carbon content is "cast iron", even though they would be, for all practical purposes, the same thing.

[eKretz]

I will certainly brook no argument there! But there has to be a defined cutoff point somewhere I suppose.

It would be sensible that such a point might have some defining characteristic, such as the percentage of carbon for an alloy defined as steel must not have any or very little "free" carbon - or carbon out of solution, while an alloy deemed cast iron would contain some arbitrary amount of "free" carbon out of solution.

[KL27x]

Which gets a bit ridiculous when iron with 1.99% carbon content is steel and iron with 2% carbon content is "cast iron", even though they would be, for all practical purposes, the same thing.

Very practical difference begins to occur at that point, though.

There's dissolved oxygen, carbon dioxide, and nitrogen in my tap water. And fluoride. And calcium. And who knows what else. I still call it water.

Perhaps if it's predominantly iron with just minor trace contaminants, like say carbon, we are perfectly ok to still call it iron. Except when it is steel. Which has formally been defined by percentage of carbon content. But the important thing about the 0.003% to 2.1% carbon is the ability to make the martinizi crystals.

Gee this is fun, but I gotta stop. I think I might go insane. Peace.

[KL27x]

It would be sensible that such a point might have some defining characteristic, such as the percentage of carbon for an alloy defined as steel must not have any or very little "free" carbon - or carbon out of solution, while an alloy deemed cast iron would contain some arbitrary amount of "free" carbon out of solution.

Damn, one more thing:
Ekratz: it is my understanding that when over 2.1ish% carbon, the alloy can no longer take the physical microstructure of hardened steel. But all that carbon is still alloyed with the iron. Smelted iron, pig iron, cast iron, or as you have put it "steel plus more carbon", is not steel with extra "unused" carbon. This high carbon iron has very different microstructure and physical properties from pure iron and from steel.

[eKretz]

I don't think that is wholly the case - gray iron for instance definitely has free carbon that is not alloyed - in the form of graphite. So does nodular iron.

Edit: just Googled and found this also:

http://www.afsinc.org/content.cfm?ItemNumber=6890

[eKretz]

And here:

http://m.machinedesign.com/metals/cast-iron

After the cutoff of 2.1% apparently there is always a percentage of free carbon, as that's the maximum amount soluble before free carbon starts to form in the alloy. If you've ever machined cast iron it's pretty obvious that there's plenty of free carbon in the form of graphite - the dust produced as chips is pretty much like pencil lead.

[KL27x]

Interesting stuff, indeed. I'm learning a lot more about iron than I ever wanted to.  I thought you were just making an analogy. Yeah, I see, now, what you meant. I think you maybe mixed terminology though, "free carbon" and "carbon out of solution" seem to mean two different things from what I am reading. But I know which you mean, in either case. For instance, by some source, steel would contain considerable iron "out of solution," even if under 2%, particularly when annealed.

I wonder if anyone would assume soldering iron tip is made of elemental iron, anymore, after reading any of this.

[ChunkyPastaSauce]

I think we're basically down to semantics here, but personally I'd have to go with steel is an alloy of iron. Steel is at its most basic composed of iron and carbon. Iron is composed of a pure element. What is in common parlance referred to as "cast iron" is composed of? Steel and more carbon - or one could say [iron + carbon (which is steel)] + more carbon.

Which gets a bit ridiculous when an iron alloy with 1.99% carbon content is steel and an iron alloy with 2% carbon content is "cast iron", even though they would be, for all practical purposes, the same thing.

See phase diagram for iron-carbon:



Note the horizontal 2066F degree line across the entire cast-iron range over a wide range of carbon %... starting at 2%
Line represents the lowest temp where liquid (with precipitates if present) solidifies -> most easily castable.... cast iron
This is for simple iron-carbon. Most have small amounts of si and possibly others added (which will change carbon point / temp), but the idea is generally the same [lowest solidifying temp]