Supplier for standard nitrile washers

[hringm]

Does anyone know of any suppliers who have an inventory of nitrile washers? Seems like every place I've looked at so for either doesn't have the size I need, or would have to custom make the washers which would be too expensive just for testing.

A few days ago I asked here on how to cut nitrile sheets down to make washers that I could test. My boss didn't like that idea though, and wants me to find some standard washers that I could just cut the sides off of. The reason that I would need to cut the sides off is because the flange that the washers are going on has grooves 32 mm wide, which most washers won't fit in. The attached drawing shows the flange setup. I'm having trouble finding nitrile washers that would work.

I'm looking for washers with an inside diameter of little more than 20mm (.7874 in), with a thickness of around 3 mm, and it doesn't matter how big the outside diameter is because I could cut it down just for the testing. Looking at engineeringhandbook.com, I found that there is a standard washer size that would work for me- nominal size .75" regular or wide would work, but so far I haven't found any place that has these in nitrile. Several people have suggested McMaster, but the nitrile washers there jump from an ID of .75" to an ID of 1", neither which will work for me.

I'm not asking anyone to find the exact washer I'm looking for, I'm just wanting to know if anyone knows of any good washer suppliers that might have some nitrile washers in stock.

 

[btrueblood]

The .037 difference in i.d. (from a .75 washer to your .787 desired size) is too great for you? I'd think the rubber would easily stretch over your .75" bolts. I'd also bet the tolerance on McMaster's .75 i.d. washers is more than .015 to .030 to the oversize condition, to ensure the washer slips over bolts of that nominal dimension. Order a couple and see.

 

[hringm]

I hadn't thought about the washers stretching. I guess that makes sense, that there would be a better seal that way. I'll probably get some of those then to test.

My boss was also wanting to get some washers with different levels of hardness. I think Durometer Shore hardness 70A would be sufficient, but he wanted to get some of different hardness to be sure. McMaster doesn't seem to have options to choose different hardness for nitrile washers. I was hoping if I kept looking for washer suppliers there would be one with stock washers of different hardness levels, but maybe I'm just hoping for too much.

 

[btrueblood]

It's not clear to me, but you are expecting this washer to seal against pressure acting outwards relative to the bolt head? If so, and the pressure differential is significant, you may find the washer tends to "blow out" regardless of the rubber durometer or bolt torque, etc. A better method for sealing is to use an O-ring under the bolt head. Google "seal screw" for one commercialized variant of the the idea. It may be necessary to have your bolts custom machined to get the O-ring size/material/durometer and bolt size combination you need.