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Several types of acrylic sheet are
produced at Aristech Acrylics in Florence, Kentucky. The three
most common thermoformable sheets are GPA (General Purpose
Acrylic), Acrysteel l-GP (Impact Resistant Acrylic), and 1-300
(Crosslinked Acrylic). All three products have very good thermoformability,
which is one of many important and useful properties offered
by Aristech Acrylics. With three products available, there
is an Aristech Acrylic Sheet to satisfy most needs and applications
requirements.
GPA is ideally suited for all types of outdoor signs, skylights,
and general fabrication. This weather-resistant acrylic is
solvent cementable and is inventoried in many colors, thicknesses
and sizes.
IGP Impact Resistant Acrylic offers the same high performance
qualities as GPA plus additional impact resistance to reduce
breakage in handling, manufacture, and transportation.
1-300 is a partially cross-linked Aristech Acrylic Sheet with
unparalleled performance for the more demanding thermoforming
application requiring stain and chemical resistance. This
product is most commonly used in the plumbingware and spa
markets.
Good formability is one of the most important and useful properties
of Aristech Acrylic Sheet. When Aristech sheet has been properly
heated, it feels like a sheet of soft rubber. In this state
the material can be formed to almost any desired shape. On
cooling, the acrylic becomes rigid and retains the shape to
which it has been formed. Forming thermoplastic sheet is probably
the simplest type of plastic fabrication. The cost of molds
and equipment is relatively low. Both two and three dimensional
forming of Aristech Acrylic Sheet can be accomplished by a
number of different methods. The selection will depend on
the shape, thickness, tolerance and optical quality required
for the formed part as well as the equipment available and
number of parts to be made.
It is imperative that all of the above Aristech Acrylic products
be heated properly for thermoforming. Too low forming temperatures
on these products will leave stresses in the formed part that
could possibly be relieved by solvents in reinforcing resin,
paint and decorating materials causing cracks or crazing.
Too high forming temperatures can cause sheet blistering.
Thermoforming Temperatures
and Cycles
The following curves (Figures 1 & 2) were derived from
tests performed at Aristech. Due to the large variety of heating
equipment available, heating times may vary. The following
heating cycles should be used as a starting point only in
obtaining optimum forming temperature times and cycles. The
temperature and cycle times depend upon the thickness of acrylic
sheet as well as the type of heating and forming equipment
used.
Surface temperatures should not exceed 380°F. It is common
practice, especially in high production operations, to allow
surface temperatures to exceed 380°F. Higher temperatures
can be tolerated up to 30 seconds depending on sheet thickness
in most cases. But due to blistering potential, it is not
recommended to exceed
380°F.
Figure 2 outlines the heating cycles when using electric infra-red
radiant heaters on one or two sides. Again, heating times
can vary depending on the type of heating equipment used,
percentage times, distance between sheet and heaters, and
heat loss factors.
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