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Thread: Casting rubber parts
08-13-2010, 09:23 AM #1
Casting rubber parts
Is there a way to cast rubber parts where you do not need a high temp oven and high pressure injector? I need to make rubber weather stripping parts for a truck I am restoring, the parts go under the cab lights and are no longer available.
08-13-2010, 09:31 AM #2
They make a two part urethane that can be poured into molds and does not require heat. I purchased it here:
Mold Making Videos - Silicone Rubber, Urethane Casting Resin, & more
I also have a silicon that is about like clay until you mold and bake it at 450 for one hour. Any oven works well, however the molds are a little tricky to make. I cannot find the place easily, it will take a little digging, if you are interested shoot me an email.
08-13-2010, 09:46 AM #3
Encapulated foam seals or hard rubber seals? Most likely hard rubber seals.
Unless you have an excellent example of the form you would need to mold I would say you will have a tough time actually sealing the window.
Most people have sticker shock when they see what reproduction seals cost ($50 to $500 depending upon window type and size). It is an expensive process to machine the corners to join the extrusions together.
You will also have troubles if you do not use a Shore hardness close to the original.
08-14-2010, 05:08 PM #4
I have also used 2 part silicone to make flexible molds.
This stuff seems to be pretty tough and might make a good gasket.
I get it from BCC Products. I think it's about $35.00 for a quart kit.
08-14-2010, 05:31 PM #5
I have a carver lab press used for making rubber parts. Hydraulic pump closes the plattens. You put an aluminum mold in between (with a heater in it) and inject rubber.
Manual, Bench Top Heated Lab Presses for Molding, Laminating, Embossing and Bonding
I am not using the press and will sell it.
08-14-2010, 05:56 PM #6
I've cast gears using rubber molds and I don't see why you couldn't do what you want quite easily. I get my materials from Eager Plastics and a phone call should steer you to the right type of materials. You may also want to get some colorant to match the originals (black?).
08-14-2010, 08:18 PM #7
This interesting as I need to make rubbers for quarter vent windows for a old truck that are not avalable. have a patern and can make a die, will be able to sell some extra's.
I know about die-casting and have worked on plastic injection moulding, but how do they do rubber?
Hand made cut rubber is just not good enough, and prefer not to use a casting urethane or silicone. Must be some one here on the PM how knows about real ruber moulding.
Thanks from Jake.
08-14-2010, 09:16 PM #8
It requires heavy machinery: a big powered mangle (really big) with polished steel rollers to mix and heat the raw rubber, and a big press to push it into the mould.
My toolmaker neighbour just made a mold for aluminium wheels (like miniature so-called 'mag' wheels) to be overmoulded with solid rubber tyres. The customer overfilled the mould slightly on the first trial shot (ie charged it with a little too much raw rubber), and the aluminium wheel was crushed and broken by the compressive hoop stress.
So you can probably guess the moulds need to be strong, heavy walled, and designed by folks who know about these things.
Last edited by Troup; 08-14-2010 at 11:57 PM.
08-15-2010, 02:50 AM #9
"How To Cast Small Metal and Rubber Parts" by William Cannon, TAB Books, deals with making molds and casting parts with Devcon flexane polyurethanes. Available in a couple of different hardnesses. Regards, Earl
08-15-2010, 07:50 AM #10
I don't know if recapping rubber is still available. It does not melt to a liquid but to a viscous paste that is easily formed. Many years ago, I built a machine for making rubber polishing cups for cleaning teeth. The rubber used for them is difficult to mold. Just for fun, I ran some recapping rubber through it and found they formed very easily. One of my friends made a lot of replacement motorcycle parts like grips and footboards. He used mostly epoxy molds with heaters. These were compression molds that he laid a strip of rubber in and closed with a press. They did take a fair amount of pressure. Aluminum also works well. Use a silicone release agent.
08-19-2010, 04:02 AM #11
now we are getting somewere, thanks Bill.
what shrinkage % is allowed for?
what temps are the die run at?
I have a 60 ton hyd shop press, think that should do?
Thanks from Jake.
08-19-2010, 06:43 AM #12
I am a practical user, I am in no way a plastics expert but I use quite a lot of the two part plastics which are available in cured durometers from rubber band consistency to as hard as acrylic. For a small part like a seal you can make a pattern from modeling clay, wood or metal, use this to make a mold, then pour as many actual parts as you need. If you do not like the strength or size of the first result it is easy to try again with a different durometer material or a rebuilt pattern and new mold.
All this work is done cold. It helps if you have a small vacuum chamber to de-gas the freshly mixed materials and some sort of pressure pot (40 to 60 psi) for the final molding process so that the project solidifies under pressure which reduces any remaining bubbles in the mix.
I once had a positive shape for a mold made by a local shop. They scanned the shape of the original broken part into a CAD program, repaired the worn sections in CAD and then printed a plastic model of the rebuilt part. I then used this model to make my mold. Magic.
08-19-2010, 09:51 AM #13
Tonnage by itself does nothing unless you are injecting a resin or epoxy type material. You need to have heated plattens for vulcanized material. Uncured EPDM runs around 325F. Every material is different depends upon what you decide to use.