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Rebling Plastics injection molds many grades
of PBT for applications ranging from under the
hood automotive parts to plastic components for
the electrical utility industry. This crystalline
material is commonly referred to by its trade
name, VALOX® or Celanex®.
There are many grades of PBT available depending
upon the application and intended usage.
These include: unfilled and high gloss versions;
grades with various concentrations of glass fiber;
and mineral and glass filled grades. Many
grades of PBT have UL flammability approvals to
UL 94 V 0 in wall thicknesses as low as .015 inches.
This plastic injection molding material
is available in a full range of colors.
This material is an excellent candidate for molding
thin cross sections due to its low melt viscosity.
Properties of PBT Plastic
As with most crystalline plastic injection molding
materials, PBT has a very low coefficient of friction
both against metal and against itself. The
moisture absorption of PBT is also very low, in
the range of .38% for the unfilled grades at equilibrium
and .26% for the highly glass filled grades.
This compares very favorably to other crystalline
materials. For example, nylon
6-6 has 8.5 % moisture absorption at equilibrium
and Acetal absorbs .8%
at equilibrium. PBT also possesses excellent
abrasion and creep resistance. These properties
lend themselves to the use of PBT in gears, bushings
and bearings, particularly when exposed to high
moisture environments.
The Tensile Strength of Polybutylene Teraphthalate ranges from 7000 psi for the unfilled grades to 17,000 psi for the highly glass filled grades. The Flexural Modulus for the unfilled plastic injection molding compound is 350,000 psi increasing to 1,100,000 psi for the 30% glass filled grade. The heat deflection temperatures at 66 psi range from 325°F for the unfilled grade to 420°F for the glass filled grades.
PBT has excellent chemical resistance to both strong and weak acids, but should not be used when exposure to strong bases is a possibility. Due to its low moisture absorption and crystalline nature, PBT can maintain its tensile strength when immersed in water at temperatures up to 150°F.
PBT plastic injection
molding design
Rebling Plastics design
engineers have extensive experience in optimizing
PBT part designs for functionality, cosmetics,
cost and processing. As with other plastics,
maintaining a uniform wall thickness throughout
the part is essential in producing an aesthetically
pleasing part. Ribs, gussets and bosses
incorporated in the design can result in sink
marks if not properly specified. The notch
sensitivity of PBT needs to be addressed through
the use of generous corner radii in order to reduce
stress concentration factors. When specifying
molded threads, coarse threads are preferred over
fine threads and a .005 to .010 inch radius should
be specified at the root of the thread.
Molded-in metal inserts need to be correctly designed
to minimize any sharp corners affecting the notch
sensitivity of this material. Consultation with
Rebling Plastics engineering staff will insure
that the molded part will meet the intent of the
design engineer.
Secondary Operations
for PBT plastic parts
Machining operations such as drilling, turning, milling, grinding and cutting can be performed on PBT using conventional high speed metal working equipment. Polybutylene Teraphthalate can be decorated using the hot stamping and pad printing processes.
Ultrasonic welding of this material through the use of energy directors designed into the part is common. Ultrasonic insertion of metal inserts is also feasible providing the metal insert is properly designed to eliminate any sharp corners.
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