Sunday, 4 March 2018

CoE Varies with Temperature

Information from Bullseye shows that the Coeficient of Linear Expansion changes rapidly around the annealing range.

The following is from results of a laboratory test of Bullseye clear (1101F)
Temperature range.......................COE
20C-300C (68F -­ 572F).................90.6
300C-400C (572F - ­752F).............102.9
400C-450C (752F - 842F).............107.5
570C-580C (1058F-1076F)............502.0

Bullseye glass is probably typical of soda lime glasses designed for fusing.

The change of CoE by temperature is further illustrated by Kugler (a blowing glass) who state their CoE by temperature range. Remember CoE is an average expansion over a stated range of temperatures)
CoE 93 for the range 0C-300C
CoE 96 for the range 20C - 300C
CoE 100 for the range 20C - 400C

The extension of the range by 100C has a distinct effect on the average expansion over the (larger) range. 

This shows why it is not helpful to refer to CoE without also mentioning the range of temperature.

In addition, here is an illustration of the effect. 




(If the owner of this illustration comes across this, please let me know, as I have lost the source)