Stainless steel friction / galling

[pete]

Hi, I’m looking for some advice on materials. In the picture A, B and C are stainless steel. Pressure is applied at B rotating D in the socket and raising A. D needs to be as strong as possible to resist the load but I’m concerned about D rubbing against C as there is no lubrication. I can't change A, B and C and need D to be non corrosive, stainless steel is going to course galling so was considering a plastic like Tufnol, or maybe some kind of ceramic? Any advice?

 

[jrmichler]

Brass does not gall against stainless steel. Nylatron is a good plastic, it is commonly used to make gears.

 

[pete]

Thanks, both look like good suggestions, I'm looking to see if I can sit a strip of PTFE or Nylon between D and C then maybe
D in Brass or Bronze, I think Bronze is also good and makes for a stronger part?

 

[jrmichler]

Brass or bronze will be good where A&B contact D. If you want to reduce friction between C and D, then UHMW tape will work well: https://www.mcmaster.com/#uhmw-polyethylene-tape/=1bq1pkb. It's just as slippery as Teflon, more wear resistant, and a lot cheaper.

 

[pete]

I have to close this up and forget about it and know it’ll do it’s job for as long as possible so tape sounds a bit scary, the force at B is a M12 lever and A is a fixed surface, it’s part of a clamp. I’ll have a look at UHMW though sounds like interesting stuff.

 

[Baluncore]

What is the corrosive fluid? Water? Salt brine? Acid?

There are less corrosion problems with bronze than with brass. Stainless steel is only stainless in an excess oxygen environment.

Lubrication will be difficult or inefficient because the C to D surface cannot be sealed. If D is plastic, grit will become embedded in the surface of D and act as an abrasive against A, B and C.

The total force of A and B on D must be carried on the D-C contact. But the area of the A-D and B-D contacts are significantly smaller with much higher pressures. Any horizontal movement of the A-D or B-D will wear those surfaces. To reduce that horizontal movement, the axis of D should lie on the straight line, or plane, between the axes of rotation of A and B. If that cannot be done, the flat face of D should not be a diameter, but be cut as two planes or a chord.

The A to B lever ratio will be highly dependent on the distances of the A-D and B-D contact lines from the axis of D. That will change as movement occurs because of the shape of the A and B contact bumps will roll along the sloped flat surface of D.

 

[pete]

Thanks for the input Baluncore, I missed you post. That's not really an accurate picture of the part I just wanted to describe the type of surface contact. Never the less some of the points you made are valid to the original component idea and were very helpful. It’s a type of clamp so just corrosive resistant as in left outdoors over night, it’s not a marine or corrosive industrial environment though I suppose it could be used around salt water.