Flex 70

[Fomen38]

I think this question is geared more towards Mike than Larry, although Larry, you may know the answer to this. I am making some lures where I'm encapsulating lead with the Flex 70 casting resin. I've used various other Alumilite casting resins without incident, but the Flex 70 seems to be VERY temperamental as far as curing. It doesn't seem to like dyes or powders mixed in with the resin (even in small quantities). I use a digi scale that measures down to hundreds of an ounce, as well as grams- so I know my A and B portions are identical. The resin starts to cure, and even changes from translucent to opaque. But after 24 hours (which is the recommended cure/demold time) it remains tacky, and I can still tear it. It's hit and miss though! That's what I find baffling about it! Sometimes it cures perfectly, and other times it ends up in the aforementioned state. When the product doesn't cure right, it's a TOTAL WASTE, and I have to cut it off of the lead core and re-pour a new batch. When I'm using 30 grams of each A and B on each pour, and I have to toss it out, I get very frustrated. The product isn't exactly cheap. The ONLY THING I can think of that I might be doing wrong is warming up the A and B in a warm water bath prior to mixing (for about 5 minutes). I keep the product stored in my garage (in San Diego, Ca), so it's not freezing cold. It's between 50 and 60 degrees. I thought (and this may be ignorance on my part, and may even be the answer to my question) that the product would cure better if I brought it up to between 85 and 90 degrees, then mixed it. When it's cooler, it's very viscous. When I warm it up a bit, the viscosity changes to a little thinner and makes it easier for me to shake it well (which I always do prior to mixing). So guys, and ideas as to why this is happening? Do you think I got a bad batch of product? I know that no water is getting into the product either, and there's no moisture in my silicone mold. I know this for a FACT. Thanks in advance for your replies.

Scott

[aka anglinarcher]

The only Alumilite product I have tried that I cannot master is the Flex 70. I thought it was just me.

Good luck, and I hope you get more responses that I will learn from as well. Preheating the mold did not work, preheating the parts did not work, ....... I am still learning about the 70.

[Mike - Alumilite]

Very interesting ... warming the mold is good, warming the resin is good, shaking prior to mixing is good in the B side (too much shaking can put a lot of air into the resin which can get trapped in the cast resin piece and actually the air will expand during the exotherm and can create crumbly parts). Adding too much dye or air is also bad and can create crumbly parts. Too much dye ... specifically the BLACK dye can cause curing issues in any of the Flex Systems. We recommend adding less than 1% of the dye to the Flex series right before mixing to eliminate these issues. Typically only .5% is needed to effectively color the Flex but the Black dye is by far the most tempermental to the Flex.

I'm not sure on the tackiness?? Is the tackiness where it came in contact with the mold or where it was exposed to the air or both? Was it a brand new mold? If a part is tacky, I'd probably demold it and then give it a mild post cure with some heat ... 130-140 degrees F for 30-60 minutes in a designated toaster oven.

So my recommended process: Warm mold, warm resin, shake B side to make sure it is homogenous and no separation. Measure B side and allow it to sit for a few minutes if you feel there is significant amount of air in it which simply allows some of the air to come up to the top and pop, pour the equivalent amount of A side by weight into the B side and add .25% of dye of the total weight into the cup. Mix thoroughly but avoid whipping in air if possible. Simply stir slowly and methodically until it is thoroughly mixed and there are no swirls in the cup of resin or dye. Then slowly pour into your warm mold and allow to cure. If possible at the 10 minute point, throw the mold and part in a designated toaster oven for 30 minutes at 130-140 degrees F. After 30-40 minutes, remove from the oven, allow to cool and demold.

Excessive air that is whipped in or incorporated during shaking can cause problems because everything expands during the exotherm of the resin and if you have hundreds of tiny bubbles or even thousands and they expand under the heat and then cure, you will have a lot of porosity throughout your part and it will seem crumbly and/or have very little physical properties because the resin chains are not close enough because they have bubbles throughout the part which weakens the physical properties.

Not sure if that is it or perhaps the dye but hopefully sheds some light on how the resin reacts and cures especially when the material is not being vacuumed.

Mike

[Fomen38]

Mike- do these "rules of thumb" apply to all of the Flex products, or just the Flex 70? I'm willing to step up in shore hardness to the Flex 80 if I can avoid these issues. I've stopped adding ANY dyes or powders to the mix. I use straight Flex 70. I use Alumidust dusted onto the inside of the mold for coloration of the lure. Maybe I'm whipping it up too fast. In your explanation of the texture of the end product if too much air is incorporated, you describer EXACTLY what my product looks like. Unfortunately on the bottles of the A and B product it specifically says "Shake well before use". I take this as shake the hell out of the product JUST PRIOR to mixing. I wish it had better instructions as I have wasted 1/2 of my product in failed attempts. I think from now on I will warm the mold, and the lead core that the product will encapsulate. I will shake the product well, then let it sit for about 5 minutes for the trapped air bubbles to escape. Maybe I will continue to warm the resin in a water bath, but after I shake it I will return it to the water bath for several minutes to let the bubbles escape and avoid dissipating any heat. I will be sure to mix it really slowly. I will try to avoid ANY air being incorporated. Thanks for your help.

[Mike - Alumilite]

These rules of thumb are consistent with all of the Flex systems ... not just the 70. As far as incorporating air, it might be a little more sensitive with the higher durometers because they are a little thicker. Yes, shaking does incorporate air and you are correct ... by letting it sit just a couple of minutes will help reduce the amount of air in the finished system however, I've found and what I was trying to convey ... was the mixing process. Even if you do shake the living daylights out of it, if you mix it evenly without whipping it too fast/excessively, you should not see the vast bubbles throughout your part that could cause the crumbly nature of the material because there is porosity throughout the casting. The B side is thinner than the A and the A is the one that I believe holds air in the system more so than the B. The B is "wetter" and that is why we typically don't have issues with shaking the B prior to mixing as the instructions state.

My best suggestion is to be mindful of the amount of air you introduce and I think you will notice a big difference in your parts. And please email me directly and I'd be happy to replace your lost resin and if you'd like to try another durometer, I'll replace it with a different hardness. Just let me know.

Thanks,
Mike
mike(at)alumilite(dot)com

[Fomen38]

Mike- SUCCESS!!!! I followed your advice regarding the propper way to mix the casting resin, and voila- perfect cast! Thinking that was the only issue I was having, I decided to add some dye to my next casting. I added 1 drop of red dye to 58 grams (combined weight) of A & B parts of the Flex70 resin. I know it specifically says to add the dye to the A side of the resin, then combine the resins. Since the A side is already maple syrup colored, I can't really see the dye in it, so I added it to the B side instead, then I mixed. Although my casting didn't come out crumbly, it didn't set quite properly. I was able to tear it off of the lead core I was encapsulating. Does it really make that much of a difference in which side of the casting resin it gets added to (especially in such small quantities)? Also, I noticed the dye I ordered is very thick. I have to really squeeze the bottle to get it to come out. Do I need to warm it up first in a warm water bath, then add it? Should it normally be that thick. It's the consistency of Elmers glue.

Lastly, how much of a role does temperature play in the final cure of the product? It specifically says on the bottle of the Flex product to store it above 70 degrees. I'm thinking that it cures best within a specific temperature range. I have a jointed lamp stand at home that I can twist to accommodate any angle I want. I'm thinking I'll place a 60 watt spotlight in it and turn it on the silicone mold about 30 minutes prior to pouring. I'll also leave it on for a few hours after I pour. That way I can keep the mold at a constant temperature of about 100 degrees. I'm still thinking the warm water bath is a good idea, as well as heating the lead core I'm trying to encapsulate. I'm sure trial and error will eventually guide me to the foolproof recipe for success- but I covet your expertise. I can say this- Flex 70 is a VERY temperamental casting resin! Thanks Mike. You ROCK!!!!

[Mike - Alumilite]

Sorry for the slow response. Glad the tips helped.

Yes, the Flex series works SO much better if you can degas and is more tempermental when it is not but still can give you good parts if you baby it a little more. Temperature plays a huge role especially when pouring small parts! Warm and keep warm temps on the materials as you pour it and as it cures.

If you are adding the dye right before mixing the A and B together, it doesn't matter which side you put it in as it doesn't have time to react before you mix the A & B.

Mike