Requesting Recommendations for High Glass-Transition-Temperature Epoxy (or other two-part pourable plastic) for 5gm Part

[dgfoster]

I am thinking of making a small part from a pourable two-part plastic. To my untrained mind epoxy seems like a good possible choice. Adding a glass or carbon fiber filler might be included. Though I have used quite a bit of common 1:5 epoxies like West System's excellent product, I have not explored epoxies that would tolerate high temperatures. My initial investigation suggests that there may be epoxies that remain stiff into the 500 or 600 F range and maybe higher, I have no experience with them. A product with strength similar to Delrin (acetal) would be adequate. Has anyone here used high temperature pourable epoxies. What brand might you recommend? Are there hidden caveats?

I'd rather not give a full description of the part but what I have in mind would weigh only 5 grams or so and would be 2.5 inches in length, an inch high, and .25" thick with various features molded in. I would be thinking of low volumes---like batches of 20 to 50 and I would like to mold them in silicone or urethane molds. Injection molding parts like this or die casting them in aluminum would be obvious choices for high volumes. But this is a niche product.

Product recommendations and experience-based suggestions would be much appreciated.

Denis

 

[Joe Gwinn]

How strong does this part need to be while at temperature? Is creep an issue? Is the temperature sustained, or occasional events.

I think that sustained 500F to 600F well exceeds any epoxy. I would call such as Henkel and ask an app engineer.

 

[dgfoster]

How strong does this part need to be while at temperature? Is creep an issue? Is the temperature sustained, or occasional events.

I think that sustained 500F to 600F well exceeds any epoxy. I would call such as Henkel and ask an app engineer.

Thanks, Joe.

I also thought those sorts of temps were out of the reach of any epoxy. But then I read a couple of references to epoxy products that can withstand that sort of heat. However, those references did not cite brands or makers. I am a bit skeptical. However, asking a question here can get some surprising results. The actual working environment I am considering would be 150F or below. But I would like to use a product that would be rated significantly higher to provide a nice cushion. Maybe I will not find 500, but even 300 would be good. I am just on a fact finding mission right now.

The plastic (PET) item I am considering replacing has had creep failure at 140.

Once I understand actual parameters and not just my preconceived notions, I'll know better how to proceed.

Denis

 

[Rob F.]

I have some americraft/kitchencfraft pans in the kitchen. The plastic handles on them are rated to be in the oven at something like 375ºF. You may want to ask them what the material is, they are made in USA.

Americraft Cookware

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Here is kitchencraft:

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The 11 Piece Set is the perfect beginning to your Kitchen Craft collection. Whether you are moving into your first apartment or your nest is empty, this set is equipped with all the essential pieces needed for smaller meal preparation using our healthy waterless cooking system. The stacking...

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[Joe Gwinn]

I have some americraft/kitchencfraft pans in the kitchen. The plastic handles on them are rated to be in the oven at something like 375ºF. You may want to ask them what the material is, they are made in USA.

Probably Bakelite.

Bakelite

 

[Conrad Hoffman]

Epo-tek 353ND might do it, though it's quite brittle. Also their H77T. Epoxies are often used well above their glass transition temperatures. Both those have degradation temperatures in excess of 400 C (750 F), though I wouldn't run them near that. JB Weld can supposedly handle 500 F for long periods of time. Hint- the glass transition temperature can't be higher than the maximum temperature reached during cure. Be sure to read the data sheet for how they achieved the glass transition temperature they did, likely something like "Dynamic cure: 20-200C /ISO 25 Min; ramp -10-200C @ 20C/min". Even then, the GTT will be way lower than you'd hope. I've successfully cast gears out of JB Weld, but you have to pull a vacuum on it to fill the mold and get rid of the bubbles!
You might also consider ceramics like those here- https://www.aremco.com/potting-casting-materials/

 

[L Vanice]

When I was still working, I learned that some large semi-low quantity production parts were made of a two-part plastic (epoxy?) in what was known as a "cold mold." I was not involved in dealing directly with the vendor or the material spec, so I know little about the fine details. But I do recall that the mold had metal tubing embedded in a non-metallic substrate. Cold liquid was pumped through the tubing to transfer the heat of the exothermic reaction to enable proper curing of the material and prolong the life of the mold. I think similar parts with high enough production requirements justified machining steel injection molds for thermoplastic.

I found this reference that sounds exactly like the parts I remember.

Cold Molding - Services - McClarin Composites

McClarin Composites is a premier supplier of large Thermoplastic and Fiberglass Reinforced Plastic components providing production throughout the Midwest and East Coast. Our services/products include fiberglass reinforced plastic, vacuum forming, pressure forming, thermoforming, and various...

www.mcclarincomposites.com

Larry

 

[gbent]

Belzona comes to mind when one wants high performance epoxies.

 

[crrmeyer]

JB weld works well for higher temperature applications.

 

[CalG]

"Glass transition" is a function of cure temperature. That can be used to advantage, but I have never read papers on just how.
Single part heat cure systems may be of interest to you.

Lord
Ciba-Giegy
Epo-Tec
3M

 

[Erich]

353ND is amazing stuff, but you need to hit the lottery before you place an order. The prices are eye watering.

A little margin on temps is good but padding your specs by 150 degrees is not getting you margin its just eliminating useful candidate materials. 25 to 50 degrees is plenty of margin.

 

[Conrad Hoffman]

I think Epo-tek has a $250 minimum order, unless they're raised it. Once you decide to use enough to hit the minimum it's not too bad. OTOH, once the goop hits a certain price you might as well machine the thing out of aircraft grade billet.

 

[Goff]

You might try www.cotronics.com. They make high temp epoxies, etc.

 

[dgfoster]

I think Epo-tek has a $250 minimum order, unless they're raised it. Once you decide to use enough to hit the minimum it's not too bad. OTOH, once the goop hits a certain price you might as well machine the thing out of aircraft grade billet.

Epo-tek 353ND might do it, though it's quite brittle. Also their H77T. Epoxies are often used well above their glass transition temperatures. Both those have degradation temperatures in excess of 400 C (750 F), though I wouldn't run them near that. JB Weld can supposedly handle 500 F for long periods of time. Hint- the glass transition temperature can't be higher than the maximum temperature reached during cure. Be sure to read the data sheet for how they achieved the glass transition temperature they did, likely something like "Dynamic cure: 20-200C /ISO 25 Min; ramp -10-200C @ 20C/min". Even then, the GTT will be way lower than you'd hope. I've successfully cast gears out of JB Weld, but you have to pull a vacuum on it to fill the mold and get rid of the bubbles!
You might also consider ceramics like those here- https://www.aremco.com/potting-casting-materials/

I did look at 353ND's spec sheet and as you indicated it is quite specific about a heat curing regimen with a ramp speed and hold temp. Following those recommendations would be no problem as I have several programmable kiln/heat treat ovens. Without actually purchasing some and trying it out I do not think I can get reliable information about its deflection under load and yield strength. I did find it available in small quantities at least---Cablesplus sells it by the packet.

I think Epo-tek has a $250 minimum order, unless they're raised it. Once you decide to use enough to hit the minimum it's not too bad. OTOH, once the goop hits a certain price you might as well machine the thing out of aircraft grade billet.

So I am learning. When I first posted the question I did not know what to expect. So far it appears that:
353ND is amazing stuff, but you need to hit the lottery before you place an order. The prices are eye watering.

A little margin on temps is good but padding your specs by 150 degrees is not getting you margin its just eliminating useful candidate materials. 25 to 50 degrees is plenty of margin.
1) There seem to be very few people who have day-to-day experience with high temp epoxies.
2) The usual applications rather than stand-alone parts are as potting and encasing agents used in electronics and fiber optics.

And, BTW, Conrad, that is just what I did for the prototype. But rather than use aircraft grade aluminum I upped the ante to "Tactical."

If anyone had some carbon fiber powder and could drop an ounce or two in the mail, I'd love to see what it does to common epoxies. I have finally wrapped my head around the idea that the fiber in embedded in the epoxy to a large extent requires that the epoxy slip to creep---fibers have to slide past each other rather than unfibered epoxy which can creep due to simple stretch of the epoxy macromolecules themselves. The carbon or fiberglass fibers are stable to high heat. The epoxy not so much as the macromolecules are much more subject to stretch than is carbon or glass. (I hope my head is wrapped clockwise on this subject and not counterclockwise! Please straighten me out if this last paragraph is bollocks.)

Denis

 

[mnl]

Stycast 2850GT with catalyst 11 has a quoted working temperature of 155C. Disregard their lower limit. I’ve used it down to ~1.5mK, although with catalyst 9.

 

[Conrad Hoffman]

There are actually many things you can fill epoxy with including carbon fiber, chopped Kevlar, mineral fillers, metallic fillers and ceramics. All are easily available in smallish quantities if you search a bit. https://www.fibreglast.com/category/Fillers

 

[jim rozen]

The 2850 epoxy is loaded with quartz microspheres and is matched to stainless steel for thermal expansion rate. Good stuff for cryogenics.

If there's any chance you could machine the features rather than mold them, suggest SP1 vespel material for high temperature applications.

 

[dgfoster]

There are actually many things you can fill epoxy with including carbon fiber, chopped Kevlar, mineral fillers, metallic fillers and ceramics. All are easily available in smallish quantities if you search a bit. https://www.fibreglast.com/category/Fillers

Yes, I have some West System Microfibers to try. I'm mostly curious about carbon fibers and am not thinking they are magic.

The 2850 epoxy is loaded with quartz microspheres and is matched to stainless steel for thermal expansion rate. Good stuff for cryogenics.

If there's any chance you could machine the features rather than mold them, suggest SP1 vespel material for high temperature applications.

I sure could machine them---I machined the ones I'm using from 6061 and it works great. If I had a CNC mill, I'd just set it up and let it run part after part.

I started down the molding path as I have done a modest amount of molding using silicone, urethan e rubber, and pourable hard urethane and like the low labor intensity of the process. With a decent mold I could pour 10 or twenty and put them in the kiln at whatever specified curing program.

Stycast 2850GT with catalyst 11 has a quoted working temperature of 155C. Disregard their lower limit. I’ve used it down to ~1.5mK, although with catalyst 9.

Sounds like a remarkable product. Henkel says they are having supply issues for raw ingredients. It is also quite pricey----1000+ for a gallon plus 200+ for catalyst if I read things correctly.

Sometimes simple is better. Maybe it's time to break out the epoxy and filler I have and do a little thermal creep testing under load.

Denis

 

[CalG]

I have used diatomaceous earth as "stiffener" along with 3M 2216 for several applications. Much like "glass micro-balloons" only available at the garden store.. ;-) (was with acetone prior to mixing...)

No comparisons. It worked, I was satisfied. Never looked beyond.

 

[mnl]

Sometimes simple is better. Maybe it's time to break out the epoxy and filler I have and do a little thermal creep testing under load.

Denis

Nothing beats test.