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Rubber coating of a shaft

Rubber coating of a shaft

Rubber coating of a shaft

What is a simple way to apply a uniform coating of rubber (thickness 0.15-0.35 mm) to a mandrel?
The mandrel is essentially a cylindrical shape and made of aluminium.
The coating is a urethane rubber: https://www.smooth-on.com/products/simpact-60a/

RE: Rubber coating of a shaft

Tricky with it being so thin .

Build a cylindrical female mould that splits in 2. Experiment with release agents and surface prep.

Or maybe paint it on and then turn it down to size on a lathe, if it is a one-off.

If the cylinder is short relative to length then maybe cast a urethane sleeve and slide it over.

Given the absence of info in the OP, the answers are many.


Greg Locock

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RE: Rubber coating of a shaft

The pot life is only 4 minutes so you have to work fast but dip coating should work for this. You need a bath that fit close to your cylinder so you do not waste a lot. Lower the cylinder into the bath length-wise until fully immersed without splashing or generating bubbles. Then withdraw from the bath at a constant speed. The faster you withdraw the thicker the coating. After withdrawal you let it hang till the coating cures. If there is a problem with drips or sags, turn the cylinder horizontal and rotate it during cure, or withdraw more slowly so the coating is thinner.

RE: Rubber coating of a shaft

I actually built a mold, with cavity split in half and a core.
Problem is material didn't cure after closing the mold:

I was looking for alternative techniques, and in fact I considered dip molding.
But the pot life is really short and I don't want to waste material for the bath.

Will try spinning the core / mandrel while pouring material over, sort of like spin coating.


RE: Rubber coating of a shaft

Davide Recchia:
Put the cylinder in a lathe and spin it slowly, as you mention above. Add a sharp edged, straight edge (spreader, smoother) bar, .35mm away from the cylinder surface. Might be good if you could rotate the straight edge a bit to become a scrapper/cutter as the rubber starts to set up, to remove excess rubber. The straight edge goes from pointing down 5° to spread the liquid rubber to pointing up 5-6° to kinda shear the firming rubber smooth, and roll excess back onto the straight edge.

RE: Rubber coating of a shaft

What material didn't cure? If it was regular single part silicone, then that's the reason. Two part/catalyzed urethanes cure in molds unless you left out the catalyzer.

RE: Rubber coating of a shaft

Probably wouldn't translate to your application, but this is a common item in the material handling business -

roller sleeve


RE: Rubber coating of a shaft

We do custom extruded rubber gaskets sometimes (i.e. make a thin wall tube). You have to order quite a bit of material (1000ft), but its cheap per foot.

RE: Rubber coating of a shaft

Must it be urethane?
How about a heat shrink tube?

RE: Rubber coating of a shaft

One option is to spin it on an axis that's perpendicular to the longitudinal axis, but I think you'd have to slowly rotate along the longitudinal axis, as well. Spinning on the longitudinal axis is probably not going to work, since there's no way to shed the excess material.

Spin coating of silicon wafers with photoresist could achieve 1 um thicknesses with something like ±2% variation

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Rubber coating of a shaft

Admittedly I like MintJulep's suggestion of heat shrink better than this (no seam), but would a self adhesive tape/film work? Mcmaster has a few options in PTFE, UHMW, polyurethane and a few other materials in the thickness range you want. It would have the advantage of being dead simple to replace the cover if it was damaged.

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