Tricks to Keeping Heat Shrink from Activating While Soldering?

[techie1234]

Obviously, keeping your dwell time short and the heat shrink as far away from the solder joint as practical are key.  But, sometimes, when working on short wires it just doesn’t seem to carry the day and I end up with the heat shrink activating in its “holding” position while I’m soldering.  Any tips or tricks that folks have when soldering in close quarters to un-shrunk heat shrink tubing?

[digsys]

Use a longer piece than you require, then cut off the end. easy

[techie1234]

Use a longer piece than you require, then cut off the end. easy

Thanks!

A bonus question:  is there a technique for slicing heat shrink lengthwise (i.e., making a small “sheet” from a “tube”), wrapping it around the wire, and heating it to “reform”/hold back into a tube– say, when you have an existing cable with a large diameter connector but small diameter wire connected to it (and are too lazy to re-solder the whole thing)?

[tautech]

Few tricks I use:
Hold the wire below the heatshrink with a pair of pliers to suck away some of the heat.
Pre-tin ends to minimize dwell time.
Use a larger heatshrink than you might consider necessary.
Low melting temp solder.

[SeanB]

For when you have forgotten, self amalgamating tape works very well. Otherwise the ultra high shrink ratio types are a very useful thing, there are some that have 6x shrink ratio now.

[tech5940]

To add to tautech's suggestion you can buy small heatsinks to use while soldering which may help.

[techie1234]

To add to tautech's suggestion you can buy small heatsinks to use while soldering which may help.

Thank you for the suggestion.  I've got a few of those and have tried to use them for this exact purpose - but in close quarters, they seem to both get in the way and increase the dwell time. 

[techie1234]

For when you have forgotten, self amalgamating tape works very well. Otherwise the ultra high shrink ratio types are a very useful thing, there are some that have 6x shrink ratio now.

Hadn't seen the 6:1 stuff until I just looked on Newark - going to buy some of the 4:1 to keep around (although at 4 foot minimum orders, I'm going to be well-stocked for the foreseeable future...

Thanks!

[Zero999]

Use a longer piece than you require, then cut off the end. easy

I've encountered situations where that's not possible, such as when I'm putting a connector on the end of some multicore cable and don't have much room between the heat shrink and stripped back outer sheath.

Obviously, keeping your dwell time short and the heat shrink as far away from the solder joint as practical are key.  But, sometimes, when working on short wires it just doesn’t seem to carry the day and I end up with the heat shrink activating in its “holding” position while I’m soldering.  Any tips or tricks that folks have when soldering in close quarters to un-shrunk heat shrink tubing?

I wrap a piece of moistened paper towel around the heat shrink, while I solder the end of the wire. Water has a very high heat capacity, compared to plastic so takes a long time to heat up and if the heat shrink doesn't activate until above boiling, then even better.

[rsjsouza]

Obviously, keeping your dwell time short and the heat shrink as far away from the solder joint as practical are key.  But, sometimes, when working on short wires it just doesn’t seem to carry the day and I end up with the heat shrink activating in its “holding” position while I’m soldering.  Any tips or tricks that folks have when soldering in close quarters to un-shrunk heat shrink tubing?

I wrap a piece of moistened paper towel around the heat shrink, while I solder the end of the wire. Water has a very high heat capacity, compared to plastic so takes a long time to heat up and if the heat shrink doesn't activate until above boiling, then even better.

I do a similar thing, only that I use the wet solder sponge... :/

[CatalinaWOW]

It is probably not acceptable for commercial work, but something I use on my own stuff for situations like this is a product called "Liquid Electrical Tape".  Works great for those times when you forget to slip on a piece of shrink, or don't have room, or just don't want to dis-assemble to the required point.  If you want a neat installation ignore the brush that comes attached to the lid of the bottle and use a small brush suited to the job at hand.

[james_s]

I wrap a strip of wet paper towel around the heatshrink and the wire immediately after it, it draws the heat away while I solder.

[ebastler]

Use a longer piece than you require, then cut off the end. easy

How does that help, in a situation where you do not have enough room to push the cut-to-length piece of tubing out of harm's way in the first place? 

I have increasingly used flexible, non-shrinking tubing (silicone-covered cloth) where possible. If it gets pushed over e.g. a switch's contact tabs after soldering, it sits nice and tight, but can still be removed and repositioned for service later on. It is not applicable in all situations, of course; sometimes you need the shrinking to make sure the isolation stays in place.

[timb]

Use a longer piece than you require, then cut off the end. easy

Thanks!

A bonus question:  is there a technique for slicing heat shrink lengthwise (i.e., making a small “sheet” from a “tube”), wrapping it around the wire, and heating it to “reform”/hold back into a tube– say, when you have an existing cable with a large diameter connector but small diameter wire connected to it (and are too lazy to re-solder the whole thing)?

What I do is take a pair of needle nose pliers, get an appropriate sized piece of heatshrink for the wire, slide it over the nose of said pliers, then stretch the heatshrink by opening the jaws of the pliers. (You might have to stretch half the heatshrink open then push it down further on the pliers, stretch more, rinse repeat.)

It also helps if you stretch it halfway open, then rotate the heatshrink 180 and stretch further. For very small sizes you can start with tweezers until you can get the nose of the pliers in.

Using the above process I can normally expand a piece of heatshrink by at least 5 times it's normal size, sometimes more. When you heat it, it will shrink back down to the correct, shrunk size.

[BrianHG]

High activation temperature heat shrink tubing.
You will need a good paint stripper or SMD hot air station without any nozzle on the end for a wide hot blast of air...
This stuff wont shrink unless you directly just about touch it with your Weller, but I guarantee you cant afford it...
https://www.digikey.com/products/en/cables-wires-management/heat-shrink-tubing/483?k=heat+shrink&k=&pkeyword=heat+shrink&FV=fff4001a%2Cfff800b0%2Cffe001e3%2C17a40018%2C17a4001a%2C17a4001c%2C17a4001d&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=500

These guys are a not as difficult to shrink:
https://www.digikey.com/products/en/cables-wires-management/heat-shrink-tubing/483?FV=ffe001e3%2C17a4000a%2C17a4000d%2C17a4000f%2C17a40014%2C17a40015&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=500

Within the list, the 180c shrink tube probably give you the least hassle.
Obviously check the shrink temperature of the product you are currently using.  If it is already over 150c, then the 150c through 180c in the link I sent wont do anything.  If the tubing you are currently using is 100c-125c and you have only a bit of and annoyance problem, the top 180c tubing might work fine.

[digsys]

How does that help, in a situation where you do not have enough room to push the cut-to-length piece of tubing out of harm's way in the first place?   

Having done many 1,000s of DBs, miniature connectors in my lifetime, I've rarely had to re-do. As others say, prepare wire and connector, and if necessary, practice !
Then I scrunch the h/shrink back a little and in very tight places, I use the next size up. Then do it FAST and do it right. Sometimes, I do have to cut the spare end off.
Maybe I've done it wrong the last 10,000+ times :-) And If I'm really lazy, I just cut a slit in the end bit to get it on.

[electrolust]

A bonus question:  is there a technique for slicing heat shrink lengthwise (i.e., making a small “sheet” from a “tube”), wrapping it around the wire, and heating it to “reform”/hold back into a tube– say, when you have an existing cable with a large diameter connector but small diameter wire connected to it (and are too lazy to re-solder the whole thing)?

The problem with that approach is that you have to glue the seams.  The glue (RT125) is pretty rigid so you end up with something fairly ugly and fairly stiff.  There is a commercially sold product that's premade for you but it's damn expensive.

Self-adhering silicone tape is better if you don't care about permanence.

Otherwise the ultra high shrink ratio types are a very useful thing, there are some that have 6x shrink ratio now.

The problem with those are that the end result is thick and stiff.  It's still better than the method above, so if you can get a 6:1 tube over the connector in most cases it's the better way to go.

[ebastler]

[...]
Maybe I've done it wrong the last 10,000+ times :-)

I'm sure you are doing it right and with great success. It was just the recommendation to use a longer piece of tubing, when the OP had described his problem in situations where he does not have enough room to keep the required length out of harm's way, that threw me.

[Brumby]

A bonus question:  is there a technique for slicing heat shrink lengthwise (i.e., making a small “sheet” from a “tube”), wrapping it around the wire, and heating it to “reform”/hold back into a tube– say, when you have an existing cable with a large diameter connector but small diameter wire connected to it (and are too lazy to re-solder the whole thing)?

Won't work.  The normal direction of shrinkage is radial - when you slit it lengthwise, wrap it around and apply heat, the heatshrink will shrink alright ... it will become narrower - and the length won't change much if at all.

I have had some success by cutting on a spiral.  The shallower the angle of the spiral, the better but you want as wide a piece as you can - so it's better to start with a large diameter.

The only disadvantage is that you need to do a spiral wrap with an overlap.  Getting that overlap right is something you would have to assess for each job.  Securing the tail is not too difficult ... simply thread it under a previous spiral or two and when heat is applied, it will all pull in.

IMO, the result will never be as good as using the appropriate sized heatshrink, but if you can't get a piece in place, then it can be useful.

[MacMeter]

A bonus question:  is there a technique for slicing heat shrink lengthwise (i.e., making a small “sheet” from a “tube”), wrapping it around the wire, and heating it to “reform”/hold back into a tube– say, when you have an existing cable with a large diameter connector but small diameter wire connected to it (and are too lazy to re-solder the whole thing)?

The problem with that approach is that you have to glue the seams.  The glue (RT125) is pretty rigid so you end up with something fairly ugly and fairly stiff.  There is a commercially sold product that's premade for you but it's damn expensive.

Self-adhering silicone tape is better if you don't care about permanence.

Otherwise the ultra high shrink ratio types are a very useful thing, there are some that have 6x shrink ratio now.

The problem with those are that the end result is thick and stiff.  It's still better than the method above, so if you can get a 6:1 tube over the connector in most cases it's the better way to go.

Zippertubing’s Shrink-N-Repair™ (Thin) Wrap-Around Heat Shrink.

$20 for a SINGLE FOOT:
http://tinyurl.com/mxkgekj

Looked at their website, longer rolls are crazy expensive.

[SeanB]

Well, needed some really wide Cryovac sheet 2 weeks ago, so took the regular roll, and used a heat sealer to splice 2 lengths together along the one long edge, then took it and made the parcel, and sealed it like usual, though I did use a heat gun, as it would not fit in the shrink machine at all.  Took 2 tries to not burst the sheet, but could heat seal the film and have it shrink afterwards reasonably well.

[Mechatrommer]

never done it. but if you dont have room to slide the heatshrink away, put sticks into the heatshrink along the wire you want to solder, this will avoid it from shrinking during soldering. remove the sticks when its cooled down. btw dont slice the heatshrink into sheet, it will not form a tube again when heated, it just becomes shrinked sheet moving away from wire it supposed to wrap. and if connector is too big compared to wire connected to it, what i did is i use 2 different heatshrink size one is big for connector one is smaller for the wire, but big enough to slide into the shrinked bigger heatshrink, overlap them and shrink the smaller heatshrink. fwiw.

[electrolust]

Zippertubing’s Shrink-N-Repair™ (Thin) Wrap-Around Heat Shrink.

$20 for a SINGLE FOOT:
http://tinyurl.com/mxkgekj

Looked at their website, longer rolls are crazy expensive.

Haven't seen that kind before.  I wonder how well it works.  Raychem RT-555 () is the type I was thinking of.  Note that it is adhesive lined.