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I want to implement a piece of glass to set various pieces of steel on and take picture through it.

The pieces of steel weigh anywhere between 20-150 lbs.

The purpose of the glass is so pictures can be taken of both sides of the piece at the same time to speed up production instead of having to flip it over by hand.

I'm no expert in this, but I am assuming there are many different compositions of glass as there is steel. According to Wikipedia, steel has a hardness of 4-4.5 and glass has a hardness of 5.5. I don't know how true this holds, which is why I'm here.

So what this boils down to is I'm looking for a sheet of glass that will with stand weights over 150 lbs and won't be scratched by constant pieces of steel being laid on it.

This question could be as easy as "All glass will work" but I've seen glass on cars that have been scratched and gouged by other parts, so I wasn't sure how true the Mohs scale I saw was.

Another problem I have thought about is which is better, Anti-Glare or Anti-Reflection. I would like to try and keep a high quality picture through the glass.

EDIT Here is a picture as requested.

enter image description here

Timmy
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  • I'm lost, how does placing steel on a sheet of glass help you avoid flipping it over? A quick sketch might be helpful. – grfrazee Sep 28 '15 at 16:27
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    Pictures have to be taken of both sides. So instead of flipping it over, I want to just have cameras facing up through the glass ontop of the already existing cameras facing down. That way both sides can be taken at the same time. – Timmy Sep 28 '15 at 16:35
  • Ok, that's more clear. Thanks for clarifying. – grfrazee Sep 28 '15 at 17:04
  • To clarify, are you planning to just drop the part on the glass? Or are you going to be setting it down very delicately? Put another way, is this in floor conditions or lab conditions? Is every production part subject to this examination a la Six Sigma, or are parts sampled? Will this be occuring once every few seconds in an automated fashion, once every few minutes by hand, once every hour, once per day? – do-the-thing-please Sep 28 '15 at 21:39
  • This is floor conditions. Parts shouldn't be dropped, but I can't say how hard they will set down. (Even though it should be pretty gently) This would be used on a busy day every 30 minutes or so. – Timmy Sep 29 '15 at 11:49
  • This is two questions. Hardness and strength (ability to hold 150kg) are not the same. i suggest focussing this question on the hardness (maybe edit accordingly) since that is what most answers are about anyway, and ask a separate question on the strength. – mart Oct 16 '15 at 05:16

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Consider using tempered glass. Because it has a compressive residual stress at the surface, it will take greater force to scratch it, all else equal. The downside is that a deep enough scratch will shatter the entire plate. However, producing such a scratch may be quite challenging depending on the exact pressure involved, which would depend specifically on the steel part and its weight, etc.

I personally dislike using the Mohs hardness scale as it is a relative scale, intended only for minerals, which relies on the qualitative measure of "A readily scratches B and B does not readily scratch A, so Mohs( A ) > Mohs( B )", but it is the only data commercial producers supply. They often claim values of 8 or 9, but those values are not likely accurate. A more likely range is 6-7, putting it above most steels in the 4-5 range, and typical window glass in the 5-6 range. Unfortunately, it is challenging to find Vickers or Brinell hardness measurement (or any quantitative values really) for glass. You may have to contact a supplier to get a sample, then do your own testing (or farm it out).

Make sure your steel parts are free of grit, sand, etc. as those are going to cause by far more damage than the steel. And of course, like anything subject to wear conditions, you will have to replace the glass periodically if it experiences frequent, continuous use. It is unclear how long it will take before your ability to image the underside suffers. If you are working with very high-strength steels, wear will occur more rapidly.

do-the-thing-please
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If hard transparent plates like synthetic sapphire glass plates (Mohs 9) are not available or too expensive, I would cover the glass with some type of cheap quickly replaced transparent material like a automated roll of vinyl sheeting.

Netduke
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  • Neat! I've heard of the sapphire glass plates made for electronic devices but I didn't even think it about that on a larger scale! The only thing I can think of is, will the glass be able to support the weight and still be transparent? – Timmy Sep 29 '15 at 12:02
  • You could support it with a thick layer of glass under it, since only the top surface needs to be hard. – Netduke Sep 29 '15 at 13:18
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Tempered glass and clean parts will help as starrise has mentioned. It will scratch over time however, so you may however want to consider a different, more reliable process.

If you increase the amount of light in the photography area and use a quality digital camera, you should be able to take a quality photo of the part even when it is not perfectly still; such as in a persons hands or attached to a gantry. If straps or hands are in the way of the photo, you could use an electromagnetic lift attachment for taking the bottom shot. http://www.zoro.com/mag-mate-lifting-magnet-250-lb-cap-5-in-oal-pnl0250/i/G3212553/

ericnutsch
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