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ANNEALING PARTS MOLDED OF
PLEXIGLAS® ACRYLIC RESIN
Annealing is recommended to insure optimum quality and maximum
useful service life from parts molded of Plexiglas acrylic resin. The
primary benefits of annealing Plexiglas parts are improved resistance
to external stresses (mechanical or chemical) and greater dimensional
stability at elevated service temperatures.
Annealing is the process of heating a molded part for a period of
time at a temperature near, but below, its softening point. After
heating the part, slow, uniform cooling will cause stress relaxation
without distortion of shape. The ultimate goal of annealing is to
redistribute and reduce the stresses in the part generated by the
injection molding process. Annealing does not completely
eliminate molded-in stresses in a well-molded part, and can only
partly relieve the internal stresses in a poorly-molded part.
SELECTING THE BEST ANNEALING CYCLES FOR YOUR
PLEXIGLAS MOLDED PARTS
(This procedure is only intended to establish a suitable
temperature and time period for annealing your parts. To achieve the
maximum benefits from annealing, also follow the suggestions listed
below the table.)
- Place several carefully measured, as-molded parts in the
annealing oven at the higher temperature from the table below for
the specific grade from which the parts were molded.
- Heat-treat them for the length of time indicated for the
maximum applicable part thickness.
- Remove the parts form the oven and let them stand for several
hours at room temperature before remeasuring their dimensions.
- If the dimensional change following this heat treatment proves
no greater than 1%, or the maximum permissible change for your
specific application, the parts may be properly annealed with
these conditions. In certain cases, even additional heating time
may be required to further relieve internal stresses.
- If the dimensional change exceeds 1% (or maximum permissible),
repeat the test at the lower temperature and time indicated in the
table. If unacceptable dimensional changes continue to occur, this
is positive evidence the part is poorly molded and requires
improvement of molding conditions.
Maximum
Thickness
(inches)
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Plexiglas
V825, V826
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Plexiglas
V052, V045, V044, V920,
DR, MI-7, HFI-10, HFI-7, SG-10, SG-7
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Plexiglas
VM, VS, VH
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Maximum
Cooling Rate
(°C/Hour)
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95°C
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90°C
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85°C
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80°C
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75°C
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70°C
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0.060 to 0.150
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2.5
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7.5
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2.5
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7.5
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1.5
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7.5
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40
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0.151 to 0.375
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3
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8
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3
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8
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2
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8
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20
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0.376 to 0.750
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4
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9
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4
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9
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3
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9
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10
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0.751 to 1.125
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5
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10
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5
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10
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4
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10
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8
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1.126 to 1.500
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8
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13
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8
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13
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7
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13
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5
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SUGGESTIONS FOR MAXIMIZING ANNEALING
EFFECTIVENESS
- Annealing should be performed in forced circulating air ovens
with the parts supported so they are not under stress. Air should
circulate freely around each part.
- Slow-cooling will produce the best annealing after heating.
Strictly observe the maximum recommended cooling rates from the
table. Annealed parts should not be removed from the oven until
the temperature reaches 50°C.
- If practical, parts should be annealed after all fabrication
is complete, including cementing, machining, polishing, and
decorating. If crazing occurs when unannealed parts are cemented
or decorated, this may be remedied by annealing the parts both
before and after these operations.
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