Mermonkey at 01:06, 19 December 2007

2007-12-19T01:06:20Z

Mermonkey at 22:52, 17 December 2007

2007-12-17T22:52:23Z

Mermonkey at 21:27, 17 December 2007

2007-12-17T21:27:51Z

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Northstar® Borocolour®

Annealing Chart

July 2004

Borosilicate Annealing

Anneal Time: 1 hour for every 0.25 inches of piece thickness

Soak Time @ A/T – 125 deg: 50% of the Anneal Time for pieces 0.25 inches thick or
less. 100% of the anneal time for pieces greater the 0.25 inches thick

Soak Time @ A/T – 200 deg: 25% of the Anneal Time

Soak Time @ A/T – 350 deg: 25% of the Anneal Time

Soak Time @ A/T – 550 deg: 25% of the Anneal Time

All temperatures are in degrees F and for 33 expansion borosilicate glass.

A/T = Annealing Temperature.

Critical temperatures for clear:

• Working temperature: 2228 degrees F
• Softening temperature: 1508 degrees F
• Annealing temperature: 1050 degrees F
• Strain temperature: 960 degrees F

For closed forms, assume the wall thickness to be doubled (i.e. 0.125 wall = 0.5 wall for
annealing, 0.5 wall = 1.0 wall, etc.).

A piece may also be brought to temperatures 100 to 150 degrees above the A/T for a few
minutes to improve the vibrancy of certain colors. This does not improve the annealing
process.

As the wall thickness increases, the first soak stage (the soak time at the first temperature
drop equal to the A/T minus 125 degrees), becomes more critical in the overall annealing
process. This temperature is just below the strain point and allows the thicker, more
complex pieces to cool slowly and come to a steady state before continuing with the ramp
down in temperature. Additional soak points allow the piece to cool in a controlled
fashion and to stabilize before continuing the cooling process.

The times listed for each of the soak periods includes the ramp down time as well as the
time at the new temperature. For example, for a one inch thick piece, the time at the A/T
is approximately 4 hrs. After 4 hrs, reduce the temperature by 125 degrees and allow the
piece to soak for another 4 hrs. Then reduce the temperature again for a 1 hour soak, etc.
Effective 01/03

The schedule is based on clear and may need to be adjusted for the different colors being
used. Specifically, metallic based colors may need a slightly higher A/T (maybe 25
degrees). The magnitude of the temperature decrease may need to be adjusted as well.
The soak times can also be a variable that can be adjusted by color in conjunction or
separately with the ramp down temperatures.

For non-metallic colors, the soak duration may be able to be reduced and the last one to
two ramps eliminated altogether. For pieces that are to be re-worked, it may be necessary
to ramp up the temperature of the piece in reverse order to avoid cracking. The thought
being that a piece that can crack during the annealing and cooling process, might also
crack during re-heating.

While having compatible COE’s between the different colors and the clear tubing and rod
is of primary importance, similar annealing characteristics of the different glass
components is also something that needs to be considered. If the annealing temperatures
are different enough, and the cycle is set for a component with a lower annealing
temperature, the higher end component(s) may not be fully annealed and therefore there
may be enough residual stress to cause the piece to check either during cooling or at some
later date.

Colors like Forest Green, Blackberry, Moss, and Blue Spruce all have anneal and strain
temperatures approximately 100 degree lower than either the clear or the other standard
colors. This is by design and is accomplished in the formulation process. The softening
point of these colors is still the same (approximately 1508) so there will not be any piece
deformity even though annealing is occurring 100 degrees above the A/T. These colors
were prone to cracking before the re-formulations about 18 months ago and one of the
objectives was to make them more “annealing friendly”.

In general, the assumption built into the schedule is that even if the COE’s of the clear
and different colors are compatible, the annealing temperatures may not be. If this is the
case, care must be taken to minimize/eliminate the possibility of cracking by increasing
the different soak times and decreasing the temperature drops between each soak. An
additional soak period may also be necessary with some colors.

Other factors that can increase or require changes to the annealing cycle include:

• The piece complexity and amount of sharp angles (design induced stresses)
• Thickness variation within the piece
• Thermal gradients in the annealing kiln itself (more pronounced in larger kilns)
• The absorption characteristics of the colors used (variation in the absorption of
light in the different spectrums and how this affects radiant cooling/heating rates)
• The amount of re-work and extended heating and cooling

←Older revision		Revision as of 01:06, 19 December 2007
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	• The amount of re-work and extended heating and cooling		• The amount of re-work and extended heating and cooling

−	http://www.northstarglass.com/	+	used by permission of abe fleishman/northstar glass http://www.northstarglass.com/

←Older revision		Revision as of 22:52, 17 December 2007
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	light in the different spectrums and how this affects radiant cooling/heating rates)		light in the different spectrums and how this affects radiant cooling/heating rates)
	• The amount of re-work and extended heating and cooling		• The amount of re-work and extended heating and cooling
		+
		+	http://www.northstarglass.com/

Annealing schedule - Revision history

Mermonkey at 01:06, 19 December 2007

Mermonkey at 22:52, 17 December 2007

Mermonkey at 21:27, 17 December 2007