Can using Clay plus pressure cause distorted Silicone Mold?

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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby mangozac » Tue Jul 31, 2012 8:25 am

Hiflt4 has summed it up quite well. While your mould is very impressive, it just doesn't facilitate the air escape so no reasonable amount of pressure is going to be able to remove the air pockets. Trying a different orientation (still in conjunction with pressure) should be able to fix the issue.
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby RobFayette » Tue Jul 31, 2012 1:45 pm

hi guys,
thanks for all of your help. I'm not sure if you guys are aware that there are about 60 vent holes around the perimeter of the steering wheel. After I built the little channels around the vent holes to hold the resin like I mentioned in an earlier post, I did another cast and It got rid of 99 per cent of the bubbles but not all of them. Since the second casting I've tried enlarging the vent holes by removing the slight silicone flashing where each vent enters the cavity at the rim of the steering wheel. I also rigged up a crude vibration table and did another cast today. I will let you know how it turns out.
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby Hiflt4 » Tue Jul 31, 2012 9:35 pm

Im glad you found a solution :)
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby mangozac » Thu Aug 02, 2012 9:31 am

Great stuff! Looking forward to seeing the final results!
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby RobFayette » Fri Aug 03, 2012 8:30 am

Here is a pic of the third wheel I have cast. Each time I get a little better but there is always a few pesky little bubbles at the rim and at the highest part of the hub. I am afraid I may have to gouge a little trough all the way around the high point of the rim and the high point of the hub in the silicone mould to give the little bubbles a high place to be. Then I would sand off the high point ridge that was formed and that would finally get rid of the bubbles. here is a pic of the latest pour after a lot of sanding and polishing. Thanks for your encouragement. Rob
Image
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby mangozac » Fri Aug 03, 2012 12:46 pm

Those last couple of bubbles are always a pain - doubly so when you're using clear resin so that it can't be filled. The physical size of the wheel doesn't help either!

Very cool work though. The the kind of wheel for the cars I'm into though ;). What is it from/for?
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby RobFayette » Fri Aug 03, 2012 2:24 pm

The wheel is for a 1951 Hudson Pacemaker. I did the translucent color just for fun. Since the wheel doesnt have a metal core in it it will never go on a car. I'm glad you mentioned the little bubbles. I have a question about that that has me puzzled. I cast another wheel but in translucent blue . It also has some little bubbles in it. This time I poured off a little of the pigmented part B resin before making the pour. When I found it had bubbles I mixed up a little of the saved resin and put a little drop of it into one of the little holes and let it cure. I then sanded it out and rubbed it shiny with rubbing compound. To my amazement you could literally not see where the hole had been! Cool I thought. So this afternoon I mixed up some more and filled some more holes on the wheel. This time the resin turned real funny and doesnt match at all. The first time I pressurized but this time I didnt. Does this make sense? I'm thinking that somehow the resin had moisture in it the second time but what would have caused it? Rob
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby mangozac » Sat Aug 04, 2012 9:38 pm

I had no idea what a Hudson Pacemaker was so I had to Google it. A real gangster mobile!

As to your question, I'm not really sure. Not pressurising certainly shouldn't have been a problem. Was the amount so small that you screwed up the mixing ratios perhaps? For me moisture has only ever made foaming issues and not effected the curing.
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby Hiflt4 » Sun Aug 05, 2012 2:30 am

Unless you mix the pigment to the bottle ahead of time, Its very very hard to color match it.

Mix up alittle more of the resin *not the catalist* then you need and put it in a sealed container after mixing the dye in it. then mix what you need for the cast and use the extra in the sealed container that *should* be the same color mix to fix any minor defects. Usually moisture will affect it cureing not its color.
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby RobFayette » Sun Aug 05, 2012 7:30 am

I guess the problem I'm having wasn't so much that the color changed but that it got so many minute bubbles in it that it did look like the color had gone from a dark blue to a light blue. When I say that the resin didnt cure I mean that it was still pliable and soft. Not sticky but pliable. When repaired ar I picked at it I was able to pick it off of the repaired area and it hadnt bonded at all to the original defect. I'm thinking it must have been moisture and I'm thinking about getting an humidifier for the room I do the casting in.

I definitely agree that it is very difficult to try to match the color and the only way I could ever do it is to pour off some of the mixed/pigmented part B resin to save for later repairs.

Thanks again for you guys comments and keep them coming please. Rob
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby mangozac » Mon Aug 06, 2012 9:20 am

Ahh I see what you mean about the colour change from the tiny bubbles. They are quite likely to have been caused by the humidity. Perhaps they also caused bad adhesion to the existing resin too?

Do you have any vacuum equipment? You could try vacuum degassing the resin you're using for the repairs before pouring it - that will remove those humidity caused bubbles.
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby RobFayette » Fri Sep 07, 2012 2:52 am

Hi again, Its been a while since I've posted. I had somewhat of a breakthrough on eliminating the bubbles from my steering wheels. I thought maybe it would be of interest to some of you. I was trying to figure out a way to set up a system for vacuuming the resin into the mold like had been mentioned by guys earlier in this thread. I was having a hard time figuring out a way to do it practically ,when I thought of maybe using pressure to inject the resin into the mold.

I thought about it and realized it seemed a lot easier to accomplish than vacuuming so I decided to try it. Here is what I did: The mold has about a 5/16 in. hole for pouring in the resin. I took a piece of 5/16 in O.D. clear pvc hose and plugged it into the pour hole. It fit nice and snug so that was good.I made the hose about 3 ft long. I ran the hose through a fitting I made in the side of my pressure pot that sealed OK, not great ,but ok. I have a pressure regulator and gauge on the inlet air to the pressure pot. I mixed the resin parts A and B together and put it into the pressure pot .I then placed the end of the pvc hose into the cup of resin so that the end was at the bottom of the cup. I then put the lid on the pressure pot and tightened it down. Now by turning the pressure up on the pressure pot I could see the resin start flowing through the tube and into the mold.

I had the pressure at about 6 psi and in about 3 to 4 minutes I saw the resin start coming out of the vents at the perimeter of the steering wheel. I let the troughs, surrounding the vents ,fill up with resin for about another 30 seconds and then stopped the transfer. I then put the resin filled mold into my large pressure pot under 50 psi for 4 hours and to my amazement when i demolded I had no bubbles in the steering wheel, not a single one!

I then did a second wheel and this time I lost control of the transfer; I let the resin cup accidentally empty and it then pressurized air down into the mold. It ended up having bubbles in the finished wheel. The next time instead of using a metal lid on the small pressure pot ,that held the cup of resin, I used the clear lid off of my vacuum chamber. Then I could see the resin going down in the resin cup and I was able to control the transfer and stop it before I forced air into the mold.

Another thing I found is that if I degassed the part A and part B of the resin separately I could get a huge amount of air out of it. I was able to degas the part B for about 5 minutes before I got most of the bubbles out of it. Part A didnt take near as long. ( I read recently that if you degas until about half the surface of the resin is free of bubbles then its time to stop degassing). To get to this stage with the part B it took about 5 minutes. I also degassed briefly after I had mixed the two parts together but it only took about a minute to get the mixture to the point where half the surface of the resin was free of bubbles.

In summary, I think what might have been happening is that when I was just pouring the resin in it was also taking air in along with it; but when I was pressurizing it in there was no way for air to enter along with the resin.
Does that sound plausible?
I was using Smooth On 327 resin that has a 10 to 20 minute pot life. It took be about 8 to 10 minutes from the time I mixed A and B together until I had the mold under the 50 lbs of pressure.

I was going to upload a picture of a finished wheel but it looks like PhotoBucket is experiencing problems right now (9/6/12) so I will try to remember to do it later. Happy Casting :D Rob
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby mangozac » Fri Sep 07, 2012 12:54 pm

Thanks for the update Rob. I hope you don't mind but your post was a bit hard to read so I broke it up into several paragraphs.

Your results and process sound interesting, although it's difficult to understand your process exactly from your description. I'll look forward to when you get the pictures posted... ;)
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby Hiflt4 » Fri Sep 07, 2012 3:33 pm

Its a pos pressure feed mangozac, similir to useing a syringe in a small mold but with more force.

Pressure source *compressor* is the plunger, the tubeing is the resavore *tube* Releasing the higher pressure air behind the resin forces a all resin stream into the mold which can reduce the air thats mixed in with a hand pour.

Its a less equipment driven way of doing a vacuume feed thru, without the negative pressure
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Re: Can using Clay plus pressure cause distorted Silicone Mo

Postby RobFayette » Sat Sep 08, 2012 6:45 am

Hi guys,
Here is a sketch I made of the setup I am trying to describe. I took a jpg picture of it and posted the pic on here. I hope this makes what I was trying to describe a little clearer.

Image

Here is a pic of the completed steering wheel.

Image

Happy Casting :D Rob
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