Stacking Washers 1

[franhd]

Hi everyone,

I have an application for which I'm using plastic washers (delrin or nylon) to prevent dissimilar metals corrosion between an AL plate and SS fasteners in a marine environment.

I'm being asked to stack SS washers on top of plastic ones.

Are there standards or references that describe washer stacking and how acceptable it is?

I think double stacking is pointless because 1) it increases risk of slip especially since fasteners are horizontal and therefore under shear load, and 2) who cares if it mars plastic washers (even if it will considering they're #8 and #10 screws), we can just replace them.

Thanks!

 

[PipeFloyd]

ASME B18.22 governs some types of washers. I would start there maybe.

I would agree with you that one washer is preferable to multiple.

I would say that reason 2) depends on how often these are fastened and released. If you are releasing them multiple times a day it may be impractical to replace the nylon washers often.

Freshly graduated please bear with me

 

[3DDave]

A steel washer will spread the load across the nylon washer better than the nut or screw head alone will. Plastics that aren't uniformly loaded tend to creep out the sides to escape the load and that will relieve the load on the screw allow preload, such as it is, to decrease, potentially allowing the fastener to exit the hole.