Health and Safety Precautions
Annealing Plexiglas® acrylic sheet should not result in the release of harmful concentrations of vapors or gases under the annealing conditions recommended in this manual. However, Plexiglas® acrylic sheet may release high concentrations of vapors and monomers if heated to temperatures in excess of 350°F without adequate ventilation.
The annealing oven should have forced-circulation and should have bleed and makeup vents, so that the air is changed at least twice an hour to remove fumes and cement-solvent vapors. Fumes and cement-solvent vapors should be exhausted to the outdoors. Parts should be heated to and held at the recommended annealing temperatures for the recommended times (see Table 6).
Plexiglas® acrylic sheet is a combustible thermoplastic material. Observe fire precautions appropriate for comparable forms of wood and paper products.
Proper annealing is one of the most effective single measures that can be taken to insure good service from parts made of Plexiglas® acrylic sheet.
necessary to anneal the parts to reduce internal stresses set up in the parts during fabrication or thermoforming operations. Annealing results in greater dimensional stability and greater resistance to crazing. Heat treating also improves the strength of certain cemented joints.
To obtain the benefits of annealing, the Plexiglas® acrylic sheet parts must be annealed after all fabrication steps, including polishing, are completed. In addition to annealing after final finishing, machined parts should be annealed before cementing to reduce stress due to machining in the cement joint area.
Determination of Best Annealing Temperature
The optimum temperature for annealing any specific part can best be determined by experimenting with a few samples to find the maximum temperature at which the part can be heated for the times indicated in Table 6 without objectionable deformation. Parts should be annealed at as high a temperature as possible. Annealing at temperatures lower than those listed in Table 6, below, will not give effective relief and redistribution of stresses. Machined Plexiglas® acrylic sheet parts that have not been heated to forming temperature should be annealed with caution in the higher temperature ranges.
Annealing consists of prolonged heating of the acrylic part at temperatures lower than those used for forming, followed by slow cooling. Internal stresses set up during fabrication of the article are reduced or eliminated by this treatment. All edges should be cut or machined with as little internal stress as possible. If excessive internal stress is present in the parts to be cemented, crazing will occur during the cementing process. It may be
The annealing temperature should be approximately 10°F below the minimum temperature at which the part shows deformation of one percent. A greater change indicates that the part has not been properly formed. The fabrication process should be carefully reviewed and revised until the parts will withstand these annealing temperatures. Particular attention should be given to forming temperatures and conditions because parts
Recommended Annealing Times and Temperatures for Plexiglas® Acrylic Sheet
Maximum Thickness (Inches)
0.944 1.500 to 1.750 2.0
Time* (Hours) to Heat Mid-Plane
1 2 3 6 8
Heating Time (Hours) i Temperature for Parts
n Forced-Circulation Air Made of Plexiglas® G an
11 2 3 4 7 9
31 4 5 6 9 11 ⁄ 2
Ovens Maintained at the Indicated d MC Acrylic Sheet
71 8 9 10 13 15 ⁄ 2
241 25 26 27 30 32
The time required to raise the temperature of the mid-plane to a temperature equal to room temperature plus 99% of the difference between room temperature and annealing temperature.
Notes: (1) Anneal parts at the highest temperature for indicated time. If distortion occurs, try the next lowest temperature.
The cycles given will be satisfactory for most formed parts. For extreme forming, such as 100% biaxial stretching, use lower temperatures.
Air should circulate around each part.