What is annealing and what are the procedures for annealing ACRYLITE® acrylic sheet?

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What is annealing and what are the procedures for annealing ACRYLITE® acrylic sheet?

Annealing Procedure

Annealing is the process of relieving stress by heating, followed by slow cooling. Here are the steps:

Anneal sheets and fabricated parts in a forced air circulating oven to insure uniform heating and proper ventilation. Air velocity should be about 1 m/s. Temperature control should be within ± 6°C.

Pre-heat the oven to 80°C. This is just below the deflection temperature of ACRYLITE®. Higher temperatures increase the risk of warpage.

Place the part in the oven. Consider supporting thermoformed parts with jigs in case of relaxation.

Maintain annealing temperature for 2 hours for parts 6.0 mm and thinner. Above 6.0 mm, divide the millimeter thickness by 3. See annealing chart for details.

Turn off the oven or run a ramped cooling cycle down to at least 60°C. Removing too soon can offset annealing's positive effects. Cool at least 2 hours. Above 8.0 mm, divide the millimeter thickness by 4. See annealing chart for details.

NOTES:

  • Be sure parts are clean and dry before annealing.
  • Remove paper masking to avoid baking it onto the material. Most plastic masking may remain in place, but test a small sample prior to annealing an expensive part.
  • Machining forms stresses only at and slightly below the surface. If the only fabrication was surface or edge machining, annealing time can be reduced to 2 hours of heating and 2 hours of cooling.
  • If holes have been drilled through the sheet, position the part so heated air flows through the holes.
  • If annealing following cementing, allow the part to sit at least six hours. This avoids bubble formation resulting from rapid solvent evaporation in the joint.
ACRYLITE® Annealing Times      
Metric Units      
Sheet Thickness Heating Time Cooling Time 80°C to 60°C Cooling Rate 80°C to 60°C
mm hours hours °C/hr
1.5 2.0 2.0 10.0
2.0 2.0 2.0 10.0
2.3 2.0 2.0 10.0
2.5 2.0 2.0 10.0
3.0 2.0 2.0 10.0
4.0 2.0 2.0 10.0
4.5 2.0 2.0 10.0
5.0 2.0 2.0 10.0
5.6 2.0 2.0 10.0
6.0 2.0 2.0 10.0
8.0 2.7 2.0 10.0
9.0 3.0 2.3 8.9
10.0 3.3 2.5 8.0
12.0 4.0 3.0 6.7
18.0 6.0 4.5 4.4
24.0 8.0 6.0 3.3
30.0 10.0 7.5 2.7
40.0 13.3 10.0 2.0
50.0 16.7 12.5 1.6
60.0 20.0 15.0 1.3
63.5 21.2 15.9 1.3
70.0 23.3 17.5 1.1
76.2 25.4 19.1 1.0
80.0 26.7 20.0 1.0
90.0 30.0 22.5 0.9
100.0 33.3 25.0 0.8
101.6 33.9 25.4 0.8
ACRYLITE® Annealing Times      
Imperial Units for Annealing:
Oven Air Velocity: About 200 fpm
Oven Temperature Control: ± 10°F
Annealing Temperature: 176°F
Final Temperature: 140°F
     
Imperial Units      
Sheet Thickness Heating Time Cooling Time 176°F to 140°F Cooling Rate 176°F to 140°F
in hours hours °F/hr
0.060 2.0 2.0 18.0
0.080 2.0 2.0 18.0
0.090 2.0 2.0 18.0
0.098 2.0 2.0 18.0
0.118 2.0 2.0 18.0
0.157 2.0 2.0 18.0
0.177 2.0 2.0 18.0
0.197 2.0 2.0 18.0
0.220 2.0 2.0 18.0
0.236 2.0 2.0 18.0
0.315 2.7 2.0 18.0
0.354 3.0 2.3 16.0
0.394 3.3 2.5 14.4
0.472 4.0 3.0 12.0
0.708 6.0 4.5 8.0
0.944 8.0 6.0 6.0
1.181 10.0 7.5 4.8
1.575 13.3 10.0 3.6
1.969 16.7 12.5 2.9
2.362 20.0 15.0 2.4
2.500 21.2 15.9 2.3
2.756 23.3 17.5 2.1
3.000 25.4 19.1 1.9
3.150 26.7 20.0 1.8
3.543 30.0 22.5 1.6
3.937 33.3 25.0 1.4
4.000 33.9 25.4 1.4

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