type of glass for deep fryer?

[cdg1]

I am building a deep fryer with one side that is glass. I used a 1/2" piece of tempered borosilicate that is rated at 500 f. The typical operating temp of the fryer is 375f. I have the fryer working and have no leaks with the seal. I did have an issue of the Stainless tank deflecting/warping. I took the glass out and reinforced the tank with a strap. That cured that issue. I did however break the glass as I was putting it back together. I dropped it a distance of about 2-3 inches and hit the bare metal of the tank. I am concerned that the glass broke so easily. I have been told that tempered glass is very susceptible to any strike or force on its edges and am wondering if this is why it broke so easily. The glass had the edges ground before tempering so it wasn't a raw edge.
Now that I need to buy a new piece of glass I am wondering if anyone may have suggestions as to whether I should be looking at a different type of glass. I am not an engineer but I hope someone out there is willing to help an average working guy. Thanks

 

[IRstuff]

Tempered glass, by design, contains a lot of stress.

Are you using Pyrex?

TTFN

 

[cdg1]

Yes, It is Pyrex.

 

[IRstuff]

Ok, there's not much you can do then. You might consider a thicker glass.

TTFN

 

[unclesyd]

Another glass that you may want to look at is Vycor.

http://www.corning.com/specialtymat..._overview/glass-ceramics/substrate-glass.aspx

 

[cdg1]

I was looking at vycor as another possibility. Do you have any experience with this glass?

 

[IRstuff]

I would have thought that Vycor, being a purer silicate glass than the borosilicate Pyrex, would actually be more brittle than Pyrex.

TTFN

 

[unclesyd]

We used Vycor for labware and sight glasses.
One glass was originally Pyrex but failed after a short exposure. A far as I know we never had a failure, 11 years, while the process was operating. There is large thermal shock on this sight port.
We have another process where the sight ports are at a high enough temperature that the Vycor is cooled with a gas stream.

 

[kenvlach]

Vycor & pure fused silica glass are stronger, more thermal shock resistant & have much higher temperature limit than borosilicate glasses (Pyrex, Kimax).

But, this design seems potentially dangerous due to accidental or malicious breakage of the glass. You actually have hot oil contained by a panel of glass?
What about CTE mismatch with the stainless (maybe use an Invar-type alloy)?
What is the seal material?

 

[cdg1]

I'm not sure what the CTE mismatch is. Yes, the oil is contained by the glass. In fact, about 15 gallons in this tank. That is one of my concerns. Is the pane strong enough to withstand the sideload that the volume of oil is causing? So far , it seems fine. I am actually pressing the pane against the outside wall of the tank with basically a wedge. The seal material is a silicone tape material.
It works very well so far but I do not have more than 10 hours on the fryer at operating temp. The glass is completely contained in a channel so none of the edges are exposed once it is in place.
When you speak of thermal shock are you refer to the rapid temp change of the glass? If so, I think this isn't a big issue. The heating of the oil from room temp to 375f takes about 30 minutes. The cooling from 375f back to room temp takes 5 /6 hours.

 

[IRstuff]

But is the increased resistance to thermal shock achieved via a decreased resistance to mechanical shock?

An option would be to apply a laminate on the outside that could constrain the glass or the seals should they fail.

TTFN

 

[cdg1]

I have thought of a dual pane system (both panes being the same material) but what kind of laminate are you suggesting?
Anyone have any ideas how I can determine,other than trial and error, what the proper thickness of the primary pane needs to be? Also, what about the pros/cons of tempered vs. annealed glass?

 

[dvd]

Okay, I'll ask. Why on earth do you want to put glass on this deep-fryer?

 

[kenvlach]

Average coefficients of linear thermal expansion, from

http://www.MatWeb.com:

304 SS: 17.8 [μ]m/m-^oC 9.89 [μ]in/in-^oF from 0-315^oC
430 SS: 11 [μ]m/m-^oC 6.11 [μ]in/in-^oF from 0-315^oC

Mild steel, 1018: 12.2 [μ]m/m-^oC 6.78 [μ]in/in-^oF from 0-300^oC

Invar 36® Alloy: 4.18 [μ]m/m-^oC 2.32 [μ]in/in-^oF (at 260^oC)
Kovar®: 5.13 [μ]m/m-^oC 2.85 [μ]in/in-°F from 25-300^oC
Pyrex® 7740: 3.25 [μ]m/m-^oC 1.81 [μ]in/in-^oF from 0-300^oC
96% Silica Glass: 0.75 [μ]m/m-^oC 0.417 [μ]in/in-^oF from 0-300^oC

The 96 & 100% silica glasses are better than borosilicates in every physical & chemical property of which I am aware, but cost more and have limited availability in shapes and sizes (and much higher working temperature when forming).

I have some doubts about the long-term ability of silicone rubber to withstand 375 ^oF oil and whether any business with liability and OSHA concerns would buy such a fryer. Pyrex glass laminated/reinforced with Invar or Kovar wire mesh should work, but costly.

 

[cdg1]

This fryer is for my own use in my current business. The reason for the glass is for show. It will attract attention.
Attention is GOOD!
There is no doubt that there are safety issues to be concerned with. However, I do think that there is a way of designing it that will work safely and efficiently.
The laminated glass with the wire reinforcement: Who manufactures this product? I would like to see how much it would cost.
I am leaning toward a dual pane system. Sort of the double hull theory.
High temp RTV is said to withstand 500f and is NSF approved. That is why I chose to work with it. Your concern is warranted as to the long term reliability. That is something I will have to watch as I test the tank over the next few months.
I appreciate your input and any suggestions you may have. Keep them coming please!