Help with material

[skinnyj]

I am in charge of designing a part but I am not familiar with plastics or rubber. I was hoping some of you pros could help. Here is what I need:

This part will be used as an insert compressed between two stationary metal pieces. The part is to prevent scratching or damage to metal pieces, but needs to provide some "grip" as to minimize twisting and slippage.

1. Part needs to be molded (odd in shape)
2. Coefficient of friction needs to be as high as possible
3. UV stable
4. Thickness of part will range from .125"-.375"

I have considered rubber but I'm concerned about the "squish factor." Maybe a very hard rubber??

 

[GrahamBennett]

Skinnyj.

The "squish factor" as you call it really isn't that much of a problem - it's the weight of the top plate that counts. If you are allowed to, send me a .pdf of the application and as much detail as you have available and I'll ask around for you at TARRC.

Regards,
Graham Bennett

 

[skinnyj]

Thanks for the reply Graham. My application doesn't really make too much sense now that I look back at my original post. Let me shed some light on this.

A steel collar fits over a steel shaft. This collar is larger than the shaft, but needs to clamp down on the shaft to provide a slip-free fit. However, the steel shaft varies in size from shaft to shaft. We need a molded rubber part that will fit between the collar and shaft. The rubber parts will range in sizes to accomadate the different size shafts. I hope this makes sense.

The collar is attached to other hardware and is subjected to some torque. This is why we need a product to minimize slippage and movement between the collar and shaft. I was thinking a very hard rubber, but there may be something better for this?

 

[skinnyj]

Oops...I forgot to add that the shafts are about 1.5" in diameter.

BTW, what is TARRC?

 

[GrahamBennett]

Skinnyj - thanks for the clarification. What you are talking about is essentially a rubber bush. As torque is applied it would be best to coat both metal surfaces with something like Chemlock adhesive, apply an uncured rubber to the shaft, then fit the collar. Finally, you need to cure it at elevated temperatures (around 150 or 160°C) in a heated press. Depending on the torque, a compound with Shore A hardness between 40 and 60 should be OK.

 

[GrahamBennett]

TARRC = Tun Abdul Razak Research Centre, Hertford, UK.

http://www.tarrc.co.uk

 

[edrush]

What about casting urethane between the two metal pieces? Does this thing need to be dissasembled? If not, you could bond them together when casting. A primer is likely required to achieve an acceptable bond to metal.

Regardless of the disassembly issue, many urethanes are easy to work with (pourable and therefore castable)and provide very good mechanical properties.

http://www.conap.com/index.cfm?page=ToolingList

Look at the bottom half of the page under "Flexible Urethane Tooling and Mechanical Elastomers"

 

[deleger]

I went through all these exchanges, and will recommend to pay a visit to the 2 below websites:

http://omnexus.com/news/news.aspx?id=13587

http://www.omnexus4adhesives.com/bc/transportation/index.aspx?lr=mas0763&li=58800