Catching Up

When I began this blog, I admitted that I was NOT a blogger. Well, I proved it! Over the short life of my blog, a couple of readers have submitted questions. Now, I hate to admit it but I could not figure out how to respond and no one left a return email for me. So I’ve decided to dedicate this blog to catching up with the questions. Sorry it took so long but, hey, I didn’t forget. So, here we go.

From my first blog, Mr. George Usinowicz asked: “While at PPG, did you know my uncle Red Rhenholz Mutzberg?

Sorry George, but I didn’t have the pleasure. Of course, keep in mind that over my 40 years with PPG the total number of employees ranged between 30,000 and perhaps 38 0r 39,000 – roughly as many as a fair size city.

From my third blog, Mr. Jeff Nixon asked: “Is there a known value for the amount of stress that will develop with a given thermal gradient? I’ve heard that it can be 50 psi per degree Fahrenheit, but no citation was given. If true, then could not a reasonably conceived thermal gradient in the field cause thermal stress breakage in heat strengthened glass?”

To the first part of your question, 50 psi per degree Fahrenheit is a reasonable value to use when calculating the stress caused by a thermal gradient. The value is a function of the modulus of elasticity and the thermal expansion coefficient of soda lime float glass.

To the second part of your question, it is conceivable that a situation could arise where an extreme thermal gradient, combined with heat strengthened glass at the low end of the specified range could result in breakage. While I personally have never seen such an occurrence, a colleague with impeccable credentials says that he has seen it happen. In fairness, he also believes that there was significant edge damage involved. Also, typical heat strengthened glass almost always runs in the mid to upper range of the specified range.

I would also like to thank the several readers who submitted compliments. It is appreciated.

OK, in my next blog we’ll bet back to business!


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