Spray on rubber coating

I need a coating to go on a capstan wheel to increase the friction drive on a 0.004" steel wire being pulled through it. Has anyone any offerings for this and any experience of it in use?.

I think that I want a rubberised/polymer coating that dries to be non tacky and an initial experiment shows that a coefficient of frction similar to an elastic band (as thrown away by posties) would be sufficient. An Aerosol application would be ideal! Do you know of anything like that?

Heres hoping

Bob D

How about a Hellerman sleeve as used to insulate wiring connections. It rather depends on the size of your capstan though.

John

As John says, what size is the capstan in question?

T

In an earlier thread "anti-corrosion coatings", spray on urethane bedliner as used for trucks was mentioned. In North America a good brand is RhinoLiner and in UK several people mentioned POR-15. KWIL sent the following info:

Frost car restorer supplies, FROST.CO.UK sells POR 15.

Bear in mind this is not a process to be done at home, you would need to contact a service doing spray in bedliners and take the part to them to have it coated. The materials are dangerous chemicals and must be handled by professionals with proper protective clothing and respirators.

It is a very tough rubber with excellent adhesion. The finish may be a bit pebbly for ,004" wire to ride on though. Are you sure a piece of cut bicycle inner tube stuck to the capstan with contact cement would not work? I used that on bandsaw wheels and it has been successful in use for over 20 years. Very smooth too.

Good luck, JD

Is a mild form of knurling out of the question?

Regards, Bear..

If the item is small enough, would a layer or two of heat-shrink do the job?

There is a self adhesive foam sheet about 1mm thick available, at the moment the supplier details are not to hand but I can get them later.

We use this to bed prisms in housingg an they never move.

Clive

Thanks to all for your interest

The capstan is approx 80mm dia, the present one is made from Tufnol and to all intents is like an A profile Vee belt pulley

The wire wraps around the root of the groove for approx 300 degrees and as made the wire slips on the tufnol periphery.

The slipping was overcome by introducing said rubber band for the wire to ride on but in practice the 0.004" wire gets into a trap between the side of the rubber band and the 20 degree slope of the flanges. When this nip occurs the wire wraps round the capstan several times before the wire breaks.Hence I'm thinking that a spray on conformal coating is going to avoid this nipping problem.

Bob D

What about a spray on adheasive and allow it to dry completely?

Not sure what you are doing but can you pass the wire round the wheel 360 deg so it cover all of the wheel, some years ago i made a device for mearuing of fishing line from very large bult spools and that slipped on the measureing wheel -- the solution was to go right around the wheel one full turn--result no more slipping !

Good luck John

Edited By JohnF on 16/11/2012 21:55:30

Hi Robert,

I would have thought that such a fine wire would cut through any such coating in a short space of time if it is under aeven a minimum of tension. Would a mechanical solution such as has been suggested not be possible?

Regards

Terry

300 degrees of wrap on a diameter of 80mm, and the wire only 0.004" thick, I would have though friction on slat surface would be more than enough. From your description I doubt any form of coating on Tufnol would help and it would alter the effective diameter (if that matters).

Is the wire under great tension or load?

How does the wire feed on and off the capstan, since you say it can wrap round several times?

Ian

What about increasing the width of the rubber band so when fitted it is still wider than the thickness of the capstan?

Maybe you could make one out of an inner tube from a kiddies bike tube ?

If you wanted you could glue it in place with contact adhesive so it conforms to the profile of the capstan then trim off the excess width with a sharp knife .

Ian

I'm not too sure that any coating is going to help, I see the problem that .004" does not have enough surface area in contact with the capstain to get enogh friction, and a wire that size would soon cut through most resilient coatings if made tight enough to get any grip. If the wire was only moving back and forth a short distance, winding the wire two or three times around the capstain might work. Ian S C

how does the diameter of "pulley" make any difference to friction ? sliding friction is a property of materials and normal force ..

To increase friction either increase normal force ( pinch roller?) or change the materials ( coating?)..

Contact adhesive has been suggested.. ( effectively latex rubber in solvent)..What about belt dressing / rosin?..only down side is horror to remove and might contaminate the wire..

Can you use a coated wire?

It is interesting to note that "wire recorders" which used a steel wire of similar dimensions did not use a capstan because of the problems of having enough friction to drive the wire. These machines merely relied upon pulling the wire through by the take up spool, which was of a "large diameter" with a shallow but wide slot for the wire to reel into.

Edited By KWIL on 20/11/2012 12:04:47

If you increase the diameter of the pully, you increase the amount of wire in contact with the pully, there by increasing the friction. Ian S C

just had a thought...silicon rubber .rtv "snot"..

Jason

As is frequently the case on this forum, several contributors suggest ideas often without many details so often a lot of speculation about the intended purpose leads contributors down blind or irrelevant alleys. Many times a thread meanders on without the OP adding any further details (does not apply to this one) based on what 'picture' is in the head of each contributor.

My take on the original questions was that it was some sort of wire driven encoder drum, or feed mechanism for a (long forgotten) wire recorder.

My reference to pulley diameter was not because it would make a difference to the friction, but that it change the effective diameter or calibration.

Only the OP knows the facts and since we do not know all of them our suggestions can only be regarded as guesswork.

To me there is no point in ideas like suggesting coated wire (yet) as the OP might be trying to make something that has to work with the raw material he already has.

I think of several 'slip free' methods of ensuring the wire stays in contact with the drum but I do not know if they are a solution to the OPs problem. A lot depends on which is driving and which is driven.

Ian

I have just re-read the original question but instead of editing my previous post had added another.

The OP states he want to 'increase friction on the wire that is being pulled through'.

I can deduce several meanings to that but my first suggestion would be to reduce the friction or torque needed to turn the capstan!

If the capstan is driving a measuring device, (or in fact whatever load), it is turning, it seems to me that it must to be too high for a very thin wire.

Basically we need more input from the OP.

Ian

Thanks again for all the interesting comments.

I'm going with a version of Slotdriller's idea.

By remaking the Vee pulley as three separate components (2side cheeks and a spigotted centre root ) I can get a rubber band to fit on the centre root and into the spigot recess and so eliminate the nip trap that the one piece pulley with rubber band fitted suffers from.

A bag of rubbber bands off Fleabay cost like £4 and should last a long time .

With no slip of the wire on the rubber band surface you don't get any cut through from the wire. Its only when it slides that cut thoug occurs and as its a high Ni/Cr wire it will sucessfully cut through most materials given time and the ability to slip!

The wrap round several turns is the fault condition that I must avoid, as also anything more than approx 300 degree wrap. The wire does have occasional knots, which can be toerated except when they cross each other and kiss together, as in a total wrap of the pulley. This is the time that the two strands hook up, back wind the output side onto the capstan with the infeed wire and just wind round the capstan until breakage instead of as intended to feed on at one side and off on the other.

Bob D

Edited By Robert Dodds on 20/11/2012 12:36:15