How are molded rubber bellows made? 3

[BrianE22]

It's the inside that I'm interested in. I assume the outside is made from a split mold pulled radially. I can't see how you would remove the inside mold.

 

[GrahamBennett]

The bellows are moulded around a metal core.

 

[btrueblood]

The convolutions have to be shallow enough so that the mold core can be stripped (rubber stretched over the bumps). So, a rubber with higher elongation can be made with deeper folds, and vice versa. Some bellows are made by dip molding over the core (no external mold cavity). There are also collapsible core constructions that could be used, with features not unlike expanding mandrels used for part fixturing on lathes and/or tube expanders in muffler shops.

 

[BrianE22]

Ah, I get it. Just stretch the rubber enough to pull out the core. The reason I ask is that I would like to mold something similar. Sounds like if the stretching isn't too severe I can get away with the internal projections I'd like.

Thanks guys -

 

[GrahamBennett]

If you hot mould rubber bellows then what you need is a compound that has a high level of hot tear strength and hot elongation to allow the finished part to be blown over the convolutions using a compressed air gun. This YouTube video

https://www.youtube.com/watch?v=NeUfkGbN1mA

shows how the parts are stripped off the mandrel.

 

[tom1953]

Great find on the video, Graham! I'm guessing the parts in the video were not very hot, as the operator wasn't wearing gloves (and I didn't hear any "ouch"-es).

 

[GrahamBennett]

Thanks for the star Tom. I suspect the company in the video has at least 3 or 4 sets of mandrels in use to allow the cured parts to cool down sufficiently. One company I used to visit in Malaysia used 2 sets - 1 in the press, 1 being stripped and readied for the next cycle. The operators use to wear 2 pairs of cotton gloves.

 

[BrianE22]

Very nice video Graham and thanks for the info on the important rubber properties.