Hi all. I am new to casting parts and new to this forum so please forgive my ignorance. I am currently molding a motor mount for a quadcopter using High Strength 3 molding rubber. There is a narrowing shaft in the center of the part (where the prop shaft goes) that does not seem to want to cure. Still tacky after several days. I noticed that the middle of the mold took much longer tl fully cure than the surface. So my question is: is there a way to save this mold? Or did I get the catalyst mix slightly off and the mold is useless?
I just wanted to clarify that the rubber is still curing, just what I would say is extremely slowly. The rubber inside the prop shaft void is more firm than yesterday, but still slightly tacky. This is now seven days since the mold was poured. Would heating it, or increasing relative humidity help the process?
Not sure why it seems to be curing slowly. It seems weird how much of it seems to have cured but other areas are taking longer to cure?? Typically not the case. Warm, humid environments will help it finish curing faster. The outside edge is curing faster due to the moisture from the air which helps it cure. If you can remove it from your mold box (without damaging), this would allow more surface area for it to accept humidity/moisture from the air and hopefully cure more quickly.
Did you mix the entire kit all at one time? I'm assuming you dumped the entire catalyst into the base and mixed thoroughly. Is that correct?
Thanks for the reply Mike. I did not use the whole bottom. This was a 1lb pack and I only needed about 4fl.oz. for the mold. I used 2 scoops (provided in package)/4fl.oz of silicone, as per the instructions on the insert. My best guess is that because I used volume instead of weight, my measurements may have not been accurate on a small scale. Or possibly I did not mix it well enough. I didn't see any visible streaks in it though. My only other thought is that because I was in a hurry to get it poured, I used foam board to make the box instead of corrugated plastic board so perhaps the paper lining on the foam board absorbed some of the moisture and slowed the curing of the lower half. Again, I am new and don't really know if any of that makes sense. I have taken the mold out of the box and I don't think there is any distortion in it but I suppose I won't know for sure until I try to cast with it. Again, thank you for the advice.
Ive been using Amazing Mold rubber and I found that #1 you Must mix the base before you start, and #2 take a cup of water and four paper towels, fold the towels together in a square... Saturate the towels, and place the cup and towels in the microwave for 2:30 right before you cast. Place your mold in the microwave with the water and towels, and let sit for 10 minutes or longer. The steam generated from boiling the water gives me 102.1% humidity creating a supersaturated environment greatly accelerating the cure. I typically de mold after 10 minutes with full strength. You may want to remove your part and re boil the water since it is a large part.
Same problem with the catalyst not curing with the 1 lb tub. Mixed both together fully but never reached "normal" color and consistency i.e. pink. I work with this product all the time and this is only the second time I have had a problem. Got to light pink, but not more. RTV itself was clumpy and I spent some time before mixing the two parts breaking up the clumps. Ended up with a cottage cheese like consistency. Poured, did not set, but after 2 days it is slowly setting....I hope.
Great customer service/tech support from Carol. She provided exactly the type of help I was looking for. Thanks!
Post by carol - Alumilite Corp on May 11, 2015 10:10:54 GMT -5
Thank you Andrew, glad to help. Mike had some useful tips in a previous post as well. I think that perhaps we are on the right track and it will cure for you over the next few days. Some times the age can be a factor in the curing schedules of silicone, rarely ... but it happens. If we can be of anymore assistance here please let us know. Thanks once more for the kind words!