Rubber vulcanizing and molding?

[DennisCNC]

Any one here been around rubber injection molding and vulcanizing process? I have a few Q's

How is the raw rubber supplied?
Once injected in the mold is it just heated for some time and it's ready? or....?
If you know names for rubber suppliers that would be great.

From the videos online that i have seen looks like a simple process, squirt it in and cook it!

Thanks

[mcphill]

You may find some answers here...

http://science.howstuffworks.com/rubber.htm

[DennisCNC]

Thanks for link, it said that after the rubber is in the mold it is steam vulcanized.

[Geof]

Google 'tire molds' and you should find some pictures.

The mold is the negative shape of your part and a blob of uncured rubber large enough to slightly over fill the mold is put in and the mold closed. You need pinholes to let trapped air escape in the detail of the mold; on tires you see small round bits of rubber sticking up all over the tread, these are where the soft rubber entered the pinholes. Once the mold is locked closed it is heated by steam or electrically for several minutes to cure the rubber and then opened and the part taken out.

It is simple.

For small quantities of raw rubber you should find a company making rubber products and see if they will sell you a few pounds. The uncured rubber has to be kept in a deep freeze or it will slowly cure at room temperature.

[sweckard]

Not trying to hijack. But how are timing belts made? I can't seem to find anything through google. My guestimate is it is a extrusion process or maybe a mold that is wrapped. Been looking for videos and/or diagrams but nothing seems to pop up. Any help is appreciated.

Sweck

[awerby]

to make molds for intricate wax patterns. The rubber traditionally comes in sheet form; it's cut and fit around a metal master, then placed in a heated vulcanizing press. That melts the rubber, which is chemically more stable once it cools. The master is cut out, and wax is injected into the resulting void.

There are now RTV (Room Temperature Vulcanizing) rubber compounds that don't need the heat and pressure; you mix part A and part B, pour the mixture around your master model, and it sets overnight.]

Originally Posted by DennisCNC Any one here been around rubber injection molding and vulcanizing process? I have a few Q's How is the raw rubber supplied? [You can either get natural rubber in sheets, or synthetic rubber as a putty.] Once injected in the mold is it just heated for some time and it's ready? or....? [Basically, but it isn't injected into the mold, it's cut and placed there carefully around the master pattern.] If you know names for rubber suppliers that would be great. [It would help if you told us what size molds you wanted to make. There are different suppliers for the large-scale molds used for direct pewter casting (like Conquest Industries) and the small ones used for jewelry (like Contenti).] From the videos online that i have seen looks like a simple process, squirt it in and cook it! Thanks

[Not exactly - what videos are you referring to?]

Andrew Werby
www.computersculpture.com

[DennisCNC]

Like this video here:

YouTube- TIP-H Horizontal Rubber Injection Molding Machine

YouTube- TIP-H Horizontal Rubber Injection Molding Machine

[ronsii]

I have used natural rubber and a few of the silicone variants of the vulcanizable types and also some of the 'mixit' type, but I have not used an injection machine for any of my molds. So I can tell you about the curing or vulcanization process...and also about how to make hand layup molds.

[mc_n_g]

You normally specify a durometer to the supplier for the compound hardness you want. We use a type called EPDM rubber. The sheets of unvulcanized rubber can vary in size and thickness. We process our 'raw' rubber into a small screw extruder to remove air bubbles from the mixing process. We have various extruder dies sizes to give us slugs of rubber of known size for the capacity of the compression mold.
We use the compression mold technique (this is not the injection technique). The molds are on heated platens with hydraulic pumps providing the pressure. Every once and a while the molds are sprayed with a mold release agent.
The mold is squeezed with the slug, pressure released to get rid of trapped air, squeezed, released then final pressure is applied.
Depending upon the part size the curing with heat (vulcanizing) the process can take any where from 5-15 minutes at roughly 325 degrees.
It is best to apply a small over flow channel around the part for excess rubber to have some where to escape. If you don't you add rubber to the parting line and get flash.

As a side note. Vulcanized rubber once cured cannot be reused. You cannot grind it up and melt it again. You can use it as filler but it will not 'melt' for lack of a better word. There are plactic rubbers which can be reground and used again.

[DennisCNC]

^^ Do you know the rubber supplier info?

[ronsii]

Hey DennisCNC, Lately I have been getting my mold blanks from Tekcast Industries they are in New York (tekcast.com) I have gotten rubber from quite a few suppliers in the past but these guys are very knowledgeable and can supply rubber in just about any form/type known to man (they have a 50 lb. minimum I think). If you mean the mixit type of mold rubber than we have got some from Smooth On (smooth-on.com) they have a good assortment of durometers and tensile strength RTV type mold rubbers and polyurethane types as well I think the Fl. distributor is reynoldsam.com.
Hope this helps, Ron