Crown Glass Breakage

[NeilUher2]

We have a Kirk chem. hardener and our glass lenses keep failing the drop ball test (recent problem). The lenses come out looking hazy and pitted. Temperature looks ok (about 840F) and just replaced the salts which were purchased new from BPI, we ran a couple cycles as suggested. Tried running a test lens and still having the same problems. We're going to try cleaning out the machine this time and we're in the process of it now; but in case this doesn't work, any suggestions?

[Lensman11]

Fogged lenses are a sign of impurities in the salt. I forgot what it is you have to add to fix the problem many years since I been near chem unit. Your machine is likely many years old and might not be reading the temperature correctly. Get an external thermometer and measure the temperature of the salt.

[Lensman11]

There is a trouble shooting guide on line from XCel optical follow the steps to solve your problem.

[NeilUher2]

We're using an external thermometer and already have the Xcel guide you mention. Thanks

[lensmanmd]

Crown glass should be immersed in potassium nitrate @570F . PGX In sodium nitrate @842F.
I’m thinking that the incorrect salts are being used for the material.
When I ran a lab that processed glass, we had two
chem units, loaded with different salts for crown and PGX.

I feel that your situation is due to having incompatible salts/temps for crown.

[NeilUher2]

PGX is recommended 743 to 761F. Crown is 833 to 851F (ref. Xcel). We have separate machines for crown and pgx too, appreciate it.

[ChrisBowers]

Add ¼ teaspoon of sialic acid. You might also want to change the Burlington controller. These thermal couplers can get “sticky” and cause huge fluctuations in temperatures. The best process is to place the stainless-steel bucket on the solid salt the turn on and let the salt melt and the basket will sink. Cycle should be 16 hours post cycle, lift bucket hang over closed doors and turn off. Let the lenses come to room temperature. Use 100% kno3 cycle for a few days after full change. Never use this bath for a two-hour PGX™ run. It is possible that your salt is not 100% kno3 but a 60/40 PGX™ mix. Also, a best practice is to replace 10% of your bath per month.



Best of luck,



Chris