Author Topic: Cheap potting compounds?  (Read 22302 times)

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Offline Chris Wilson

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Cheap potting compounds?
« on: February 05, 2015, 03:38:45 pm »
Low voltage none critical application, is there a cheap potting compound available, preferably one that sets hard, but very viscous gel a possibility? The commercial stuff looks very expensive... Could I get away with fibreglass resin? Thanks.
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Offline peter.mcnair

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Re: Cheap potting compounds?
« Reply #1 on: February 05, 2015, 03:45:39 pm »
Candle wax.
 

Offline Chris Wilson

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Best regards,

                 Chris Wilson.
 

Offline SeanB

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Re: Cheap potting compounds?
« Reply #3 on: February 05, 2015, 03:59:59 pm »
Beeswax is better, as it is non crystalline. Otherwise you can just use 2 part epoxy resin for small jobs, or if it is large just encapsulate the major part in acetoxy free silicone ( for compliance) and then fill the rest of the box with fibreglass resin. Choose a gelcoat resin for clear, or add fine silica sand to bulk it up for a harder resin. For a very opaque resin get talcum powder from your resin supplier, it is used as a filler.

For cheap ready mixed resin and powder use auto body filler and catalyst. Cheap, sets hard and is machinable as well as easy to use, though you will need throw away spatulas and a plastic painters sheet to do everything on.
 

Offline PeterFW

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Re: Cheap potting compounds?
« Reply #4 on: February 05, 2015, 04:03:23 pm »
Could I get away with fibreglass resin? Thanks.

Depending on the type, this stuff gets very hot while curing, some parts might not like that.
I used one of these two barrel syringes with a static mixer once to pot a circuit, afaik it is still running.
And it shrinks ever so slightly, some SMD components might not like that.

 

Online wraper

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Re: Cheap potting compounds?
« Reply #5 on: February 05, 2015, 04:08:02 pm »
Should be cautious with hard stuff. If it significantly shrinks while setting or have thermal expansion coefficient significantly different than PCB it can just tear off the parts from the PCB.
 

Offline macboy

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Re: Cheap potting compounds?
« Reply #6 on: February 05, 2015, 06:17:40 pm »
Should be cautious with hard stuff. If it significantly shrinks while setting or have thermal expansion coefficient significantly different than PCB it can just tear off the parts from the PCB.
I think this is why SeanB suggested a layer of compliant silicone first, then a hardening resin to fill the bulk.
 

Offline PeterFW

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Re: Cheap potting compounds?
« Reply #7 on: February 05, 2015, 06:30:23 pm »
I think this is why SeanB suggested a layer of compliant silicone first, then a hardening resin to fill the bulk.

You could use a hardware store non-acidic caulking for that, in the same isle you get the 2 part syringe epoxy.

Greetings,
Peter
 

Offline SeanB

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Re: Cheap potting compounds?
« Reply #8 on: February 05, 2015, 06:46:45 pm »
Caulk tends to shrink, and most of those I have met are water based, not something you want to put next to conductors. No matter how long you let it dry unless you cook it to rock hard it will contain moisture. I have to redo some I used to fill some drywall repair as it has cracked during curing, but it is not serious there. On a PCB it will be bad.
 

Offline marshallh

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Re: Cheap potting compounds?
« Reply #9 on: February 05, 2015, 06:55:26 pm »
Silicone caulk has absolutely no business outside the bathroom, and maybe PCBs... that stuff is the bane of my life
Verilog tips
BGA soldering intro

11:37 <@ktemkin> c4757p: marshall has transcended communications media
11:37 <@ktemkin> He speaks protocols directly.
 

Offline Falcon69

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Re: Cheap potting compounds?
« Reply #10 on: February 05, 2015, 07:10:03 pm »
I've been using this

https://www.creativewholesale.com/ProductDetail/tabid/174/ProductID/255/Default.aspx

it works great, didn't seem to shrink at all, and does not get hot.  Crystal clear when dry. It takes about a day for it to cure.

You don't have to buy a full gallon either, they sell in smaller quantities, really easy to use, a simply equal two part mix.  You just have to be careful of air bubbles.  Don't mix it too fast.

You can see the switches I've done on my Site www.x2df.com

I'll post a pic here too so you can see them.  I'm not sure of your application, but I had to make a mold for the switches using silicon.

 

Offline PeterFW

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Re: Cheap potting compounds?
« Reply #11 on: February 06, 2015, 01:44:14 pm »
Caulk tends to shrink, and most of those I have met are water based, not something you want to put next to conductors.

I thought non acidic silicone should not have anny significant water content, im curious but could not find anny information on that besides a patent with too many fancy words for me to understand. Do you have anny additional information?

Greetings,
Peter
 

Offline SeanB

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Re: Cheap potting compounds?
« Reply #12 on: February 06, 2015, 03:30:13 pm »
Caulks tend to be different here to silicones. The typical caulk is an acrylic based item, which is water cleanable. then you get the silicones with assorted cures and finally the urethanes with a cyanamid cure. The urethanes do shrink very little, and they tend to be compatible with copper surfaces as well, but are expensive  and hard to clean up. They do make an excellent encapsulant though, at about 6 times the cost of silicones. they also take a day per millimeter to cure, so if you want to overcoat them with a hard epoxy you will need to leave the job for a week or two to cure, otherwise it will never cure once oxygen is excluded from it by the outer shell. It is slightly conductive until well cured though, like most single component sealers.
 

Offline rdl

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Re: Cheap potting compounds?
« Reply #13 on: February 06, 2015, 03:34:34 pm »
Yeah, I figured that was in reference to the lower cost, consumer grade caulk that you get at places like Home Depot. Most of those are water based, and some of them may not actually contain much silicone at all.

I was a formulator at one of the big paint companies for a long time. Years ago the guys in their consumer division came up with what they thought was a great formula for a water-base clear wood finish. They sold it in two versions. One used 100% acrylic  for the resin part, the other was 90% (the same) acrylic, with 10% polyurethane. This was so they could print labels with 2 inch tall letters that advertised "Polyurethane" (and charge a considerably higher price). The actual performance of the two versions was nearly identical.



Caulk tends to shrink, and most of those I have met are water based, not something you want to put next to conductors.

I thought non acidic silicone should not have anny significant water content, im curious but could not find anny information on that besides a patent with too many fancy words for me to understand. Do you have anny additional information?

Greetings,
Peter
 

Offline PeterFW

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Re: Cheap potting compounds?
« Reply #14 on: February 06, 2015, 03:49:30 pm »
Caulks tend to be different here to silicones.

Ahhhh... i think i identified the problem. Until today i thought "caulk" was generic english term for anny kind of gap brideing sealant.
I will update my vocabulary accordingly :)

Greetings,
Peter
 

Offline robrenz

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Re: Cheap potting compounds?
« Reply #15 on: February 06, 2015, 04:54:04 pm »
I know you are in England but this stuff is outstanding and is extremely cheap compared to the electronic branded stuff. His site is extremely informative on all epoxies.  :-+ :-+ :-+ 

http://www.ebay.com/itm/EPOXY-RESIN-CIRCUIT-BOARD-POTTING-COMPOUND-WATERPROOF-MASKING-SEALANT-96-OZ-KIT-/310368256789?pt=LH_DefaultDomain_0&hash=item484363c315

Offline Zero999

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Re: Cheap potting compounds?
« Reply #16 on: February 06, 2015, 09:24:38 pm »
I know you are in England but this stuff is outstanding and is extremely cheap compared to the electronic branded stuff. His site is extremely informative on all epoxies.  :-+ :-+ :-+ 

http://www.ebay.com/itm/EPOXY-RESIN-CIRCUIT-BOARD-POTTING-COMPOUND-WATERPROOF-MASKING-SEALANT-96-OZ-KIT-/310368256789?pt=LH_DefaultDomain_0&hash=item484363c315
Price: $43.43
Shipping: $73.39
Lol
 

Offline Kjelt

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Re: Cheap potting compounds?
« Reply #17 on: February 06, 2015, 09:42:48 pm »
Lot of companies use some sort of tar for potting. That is commercially sold products.
If you need a fast non optimal potting for your hobby product that can be easily reversed: silversand.
 

Offline robrenz

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Re: Cheap potting compounds?
« Reply #18 on: February 06, 2015, 10:16:49 pm »
I know you are in England but this stuff is outstanding and is extremely cheap compared to the electronic branded stuff. His site is extremely informative on all epoxies.  :-+ :-+ :-+ 

http://www.ebay.com/itm/EPOXY-RESIN-CIRCUIT-BOARD-POTTING-COMPOUND-WATERPROOF-MASKING-SEALANT-96-OZ-KIT-/310368256789?pt=LH_DefaultDomain_0&hash=item484363c315
Price: $43.43
Shipping: $73.39
Lol

That is 3 quarts for about $39.00 a quart including shipping.

This MG chemicals on Mouser works out to 89.40 per quart before shipping

Offline IanB

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Re: Cheap potting compounds?
« Reply #19 on: February 06, 2015, 11:14:25 pm »
Until today i thought "caulk" was generic english term for anny kind of gap brideing sealant.

Strictly speaking, yes, that is correct. "Caulk" is a generic term for something used to seal gaps and keep water out.

However, in the hardware store and around the home caulk has taken on a more specialized meaning to differentiate it from other items like silicone sealant or pitch. Caulk from the hardware store is what might be used to fill a gap between a window frame and the wall.
 

Offline mzzj

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Re: Cheap potting compounds?
« Reply #20 on: February 07, 2015, 07:37:22 am »
Pot of hot glue  ;D

Sikaflex 221 is my choice of poison, quaranteed mess :-DD

 

Offline ovnr

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Re: Cheap potting compounds?
« Reply #21 on: February 07, 2015, 11:22:35 am »
On silicones: Consider buying a two-part silicone, then just dipping your parts in it to get a compliant coating before immersing in epoxy. They have low enough viscosity that it's not a problem, compares to caulks and shit.
 

Offline ivan747

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Re: Cheap potting compounds?
« Reply #22 on: February 08, 2015, 02:04:08 am »
Heatshrink and silicone to seal the edges.
 

Offline LabSpokane

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Re: Cheap potting compounds?
« Reply #23 on: February 08, 2015, 04:15:42 am »
Until today i thought "caulk" was generic english term for anny kind of gap brideing sealant.
I will update my vocabulary accordingly :)

If you went to any hardware store in the US and asked them to take you to the caulk, you would go to an aisle full of tubes which would have virtually every variety described here: silicone, acrylic, etc.  Your current understanding is correct at least in 'Merica.
 

Offline Chris Wilson

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Re: Cheap potting compounds?
« Reply #24 on: February 11, 2015, 10:52:23 pm »
Some great info and links here, and confirmation we pay too much for stuff in the UK, as if I didn't know :( Thanks, all very informative and useful, much appreciated.
Best regards,

                 Chris Wilson.
 


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