Material Selection: Clear polymer for site glass

[jekriez]

I have an application where we have seen failures on a site glass due to external material (dirt/rocks) impacts. The site glass is ~1" in diameter and made of Borosilicate. Apparently this is essentially "Pyrex". I would like to move towards another material that is more impact resistent, transparent, and able to function with oil splash of up to 120 deg C. I would think something like a Polycarbonate might be an option. Given the dirt environment, would that material lose transparency due to scratches/fading? The purpose of this part is to give the operator a go/no go check of oil in the machine during a walk around. If its not already clear, non-metallics have not been my specialty. Any hints on available materials (and other design considerations) would be great. Thanks.

 

[btrueblood]

All of the clear/translucent polymers will be less likely to shatter, but will also be more easily scratched, and few (if any) will stand up well to 120 C oil.

Why not put a clear acrylic or polycarbonate cover around/over the sight glass to keep the rocks/sand from impinging on it directly? Or put a mudflap or similar to block whatever path the dirt/rocks are taking to strike the sightglass.

 

[jekriez]

Yes my first thought was to eliminate the ability of debris to get to it. Also, I confirmed that the customer actually values this feature. I have some ideas for surrounding geometry changes that could shield this part, but an improved site glass would be quickest to implement.

I like your idea of "dual pane" type gage with a clear acrylic being expose to the debris, and the Borosilicate on the oil side.