making metalastik type bushings

[Tmoose]

We are looking to have some large metalastik style bushings made.

Steel inner and out sleeves nominally ~ 0.2" thick.
IDs 5.7" to 7" . ODs 6.75" to 8.0". 8" to 9.5" long.​

So far I'm finding the typical elastomer is some flavor of vulcanized natural rubber.
Often bonded only to the inner sleeve.

Is the rubber bought as vulcanized sheet? Or vulcanized as part of bonding the rubber to the inner shell?

Specifying or even describing Natural Rubber materials seems shrouded in mystery. At least to me.

Swedish specs seem to specify Natural rubber as either -
Type 1 high tensile properties and good compression set properties
Type 2.moderate tensile properties and moderate compression set properties

ASTM D2000 (mirrored by SAE J200) lumps Natural rubber, reclaimed rubber, SBR, butyl, EP polybutadiene, polyisoprene into Classification AA.
Their basic AA requirements (Table 6) are limited to durometer, tensile strength, elongation, before and after heat aged aging.
Oil resistance is not among the requirements.

Any comments are appreciated.

thanks,

Dan T

 

[MintJulep]

Plenty of established manufacturers for this. Don't try to do this from scratch on your own.

Give theme your performance requirements and environment. Don't try to tell them what rubber to use.

 

[btrueblood]

What Mint said - rubber mixing and molding is a mix of art and science, you pay for good artists. Rubber is purchased as raw polymer in crumb or cake form, which you have to break up and add the desired fillers and vulcanizing agents in a mixer/miller. A master chemist at a rubber shop once told me that rubber is a lot like making a cake, you add the specified ingredients in specified ratios, mix/mill for a specified time, dump it in a mold and bake it for a specified time and temperature. What you get is a lot like cake too, in that the properties can vary quite a bit from batch to batch (relative to things we are more accustomed to, like steel and aluminum alloys).

 

[btrueblood]

You mentioned oil resistance - do you need that? Natural rubber will absorb oil and soften, so it's not really "resistant" to oil. If you need the bushing to keep its dry properties when soaked in oil, you need to change to a different base polymer, like Buna-N, HNBR, Viton...

 

[Tmoose]

thanks all.
No oil resistance required. Kind of confirms that some flavor of natural rubber is used in our application, unlike, say, an engine mount.
Nor abrasion resistance.

Just boing-osity stuff.
And maybe able to twist/shear 4° without tearing. Investigation into whether existing designs slip has begun.

 

[GregLocock]

There are advantages and disadvantages to single bonded (inner or outer only) and double bonded. For automotive these days double bonded is de rigeur for durability reasons, as dust and grit will work their way into an unbonded interface.Single bonded means you can assemble the joint in any orientation and after a while it will settle down to a nominal position. Sizing is crucially important, that is the process of compressing the outer sleeve so that the rubber is in compression. That's to make sure cracks can't propagate. Variation of stiffness inside a batch can be small, but batch to batch is 15%.

Cheers

Greg Locock


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