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  #1  
Old 06-17-2021, 01:29 PM
AlpineYoda AlpineYoda is offline
 
Join Date: Nov 2019
Location: Boulder, CO
Posts: 318
Default West 105 got really hot. Normal?

Mixed up a batch of West 105 / 206 (slow) with a very large proportion of cab-o-sil. I've mixed 105/206 several times, but this was a first.

Within about 3 minutes, the mixture got very hot. I was using an old plastic take-out food bowl and it got too hot to hold. I even started to see steam / smoke come out of the bowl. Within 10 minutes, chunks started to form in the mixture. I was using 206 - SLOW hardener - but this hardened up really fast.

I've made 10-12 batches of West before and it has gotten warm, but nothing like this.

I used about 7-8 squirts of both fluids (I use the measured pumps to get my mixture right.)

It is about 95 degrees today. Probably 90+ in the hangar right now.

Is this normal? Or did I make a big mistake somewhere?

The parts I was bonding / filling both appear okay. Warm but not hot. It's a thin layer applied of the mix between fiberglass and aluminum.

I left the bowl outside on a pile of gravel in case it catches fire - still very hot, but no flames.
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Last edited by AlpineYoda : 06-17-2021 at 02:13 PM.
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  #2  
Old 06-17-2021, 01:43 PM
MED MED is offline
 
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Location: Aiken, SC
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Default

Mixing large quantities of epoxy will result in it getting very hot. It can “cook off” and melt your container. It may affect the properties of the epoxy, too. A larger surface area, like in a pan, will not be as deep and won’t get as hot. I usually just mix smaller batches, 2-3 pumps.
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  #3  
Old 06-17-2021, 01:51 PM
AlpineYoda AlpineYoda is offline
 
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I didn't realize 8 pumps was a "large" quantity.

How do the pros do it? When Van's makes a cowling or a cabin top, they must be using a heck of a lot more than 8 pumps worth of epoxy.
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  #4  
Old 06-17-2021, 01:53 PM
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DanH DanH is offline
 
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Default

As a general rule, all epoxies exotherm, more so when using a faster hardener. The trick is allowing the generated heat to escape before it further accelerates the cure, which generates even more heat, which rapidly leads to a runaway cure.

In addition to hardener choice, the other factors are ambient temperature, additives, and container size/shape/material.

High shop temperatures require slower hardener.

Additives, particularly micro balloons, tend to serve as built-in insulation. Heat from the center of the batch has trouble reaching the external surface of the container (where it can escape) because the hollow air spaces limit conduction.

A large bucket shaped container also limits heat transfer from the mix. Foam and plastic materials too.

So, any time you mix a large batch of epoxy/micro, or in this case epoxy/cabo, immediately dump the entire contents of the mixing cup out onto a sheet of 4 mil plastic. Spread it out on the sheet so it can stay cool, and the cure rate will be as appropriate for the hardener choice and ambient temp.

Speaking of which, 90F is mighty warm. Pot life is generally rated near 77F/25C.
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  #5  
Old 06-17-2021, 01:55 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by AlpineYoda View Post
I didn't realize 8 pumps was a "large" quantity.
How do the pros do it? When Van's makes a cowling or a cabin top, they must be using a heck of a lot more than 8 pumps worth of epoxy.
Google the magic word: prepreg.
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  #6  
Old 06-17-2021, 01:55 PM
xavierm xavierm is offline
 
Join Date: Aug 2005
Location: Los Angeles, CA
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Default It's the cab-o-sil

I have experienced the same thing when mixing in a large quantity of cab-o-sil.
I repeated it by mixing the same amount of epoxy with no cab-o-sil and it was fine. Kept adding cab-o-sil and at a certain point it got really hot and started smoking.
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  #7  
Old 06-17-2021, 02:05 PM
AlpineYoda AlpineYoda is offline
 
Join Date: Nov 2019
Location: Boulder, CO
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Default

Quote:
Originally Posted by DanH View Post
As a general rule, all epoxies exotherm, more so when using a faster hardener. The trick is allowing the generated heat to escape before it further accelerates the cure, which generates even more heat, which rapidly leads to a runaway cure.

In addition to hardener choice, the other factors are ambient temperature, additives, and container size/shape/material.

High shop temperatures require slower hardener.

Additives, particularly micro balloons, tend to serve as built-in insulation. Heat from the center of the batch has trouble reaching the external surface of the container (where it can escape) because the hollow air spaces limit conduction.

A large bucket shaped container also limits heat transfer from the mix. Foam and plastic materials too.

So, any time you mix a large batch of epoxy/micro, or in this case epoxy/cabo, immediately dump the entire contents of the mixing cup out onto a sheet of 4 mil plastic. Spread it out on the sheet so it can stay cool, and the cure rate will be as appropriate for the hardener choice and ambient temp.

Speaking of which, 90F is mighty warm. Pot life is generally rated near 77F/25C.

This was very useful. Thank you for so much thought and effort.

And yeah, 90F is pretty hot today. The hangar has heat, but no AC. I can work on these parts now in this heat, or, checking the forecast... October??
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  #8  
Old 06-17-2021, 02:10 PM
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wirejock wirejock is online now
 
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Location: Estes Park, CO
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Default Pumps

Also possible the pumps are not dispensing exact quantites but it sounds like a combination of factors resulted in a runaway exotherm. Generally it's considered unusable. I toss the cup in a bucket of cold water.
Like Dan said. Prep everything and pour it as soon as possible or pour it into something so it's more spread out.
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  #9  
Old 06-17-2021, 02:15 PM
Larry DeCamp Larry DeCamp is offline
 
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Location: Clinton, Indiana
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Default Great comments from Dan

Question- I have experienced random episodes of faster than normal cure rate with reasonably small quantities. I concluded the common thread was mixing new ingredients in a container with “ work in progress “ material and a wet stir tool from the previous batch. Is it possible for material late in the reaction process to act as “ super “ catalyst ?
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  #10  
Old 06-17-2021, 02:32 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by Larry DeCamp View Post
Question- I have experienced random episodes of faster than normal cure rate with reasonably small quantities. I concluded the common thread was mixing new ingredients in a container with “ work in progress “ material and a wet stir tool from the previous batch. Is it possible for material late in the reaction process to act as “ super “ catalyst ?
Don't know! I use a fresh cup for every batch.
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