|
Correct processing of Polyphenylene Sulfide (aka
PPS, Ryton®, or FORTRON®) is critical in order to
achieve the stated properties of this material.
At Rebling Plastics, we employ state of the art
equipment in order to mold Polyphenylene Sulfide
components in a fully crystalline state. Mold
temperatures of at least 275°F are required
to achieve crystallinity. Rebling Plastics typically
molds in excess of 300°F using either "hot
oil "units or cartridge heaters for mold
heating.
When polyphenylene sulfide is molded below 275°F,
the moldings are amorphous or semi crystalline
and remain in this state until they are exposed
to higher service temperatures. If the service
temperature exceeds the molding temperature, the
parts will become more crystalline resulting in
dimensional and property changes. For example,
the Heat Deflection Temperature (HDT) of PPS molded
in a non crystalline state is only 350°F but
increases to 500°F in the crystalline state.
Polyphenylene sulfide is a high flow material
and is an excellent choice for thin walled plastic
injection moldings. Insert
molding is routinely performed at Rebling
using PPS as the molding compound.
There are several grades of this material available
for the plastic injection molding process. All
of these material grades contain fairly high concentrations
of glass and/or minerals, in some cases up to
70% by weight. The extremely excellent chemical
resistance of PPS, coupled with its high heat
deflection temperature, makes it an ideal candidate
for replacing metal parts as well as an alternative
to thermosets. PPS is also suitable for cryogenic
applications as it retains its mechanical properties
at low temperatures.
Rebling Plastics molds PPS for a variety of end
uses including electrical connectors, instrumentation
housings, telecommunication devices, and military
applications.
Properties of Polyphenylene
Sulfide plastic
PPS is inherently flame retardant and can achieve
UL 94 V0 ratings in wall thicknesses as low as
.015 inches without the use of flame retardant
additives. The shrinkage of PPS varies depending
on the part wall thickness and the flow direction
of the material during the molding process with
shrinkage in the transverse flow direction two
times greater than that in the flow direction,
typical of crystalline materials. Extremely tight
tolerances therefore may be more difficult to
achieve when selecting a crystalline material
like PPS over an amorphous material which has
uniform shrinkage in all directions.
The two important properties to consider when
selecting PPS are its excellent across the board
chemical resistance and high heat deflection temperature.
The UL temperature index of this material (often
referred to as the continuous use temperature)
can exceed 200°F. This is surpassed only by
thermoset plastics and a few thermoplastic materials
costing 10 to 20 times more in price.
PPS is available in brown, black and blue opaque
colors and there are a limited number of color
concentrates available for PPS.
When designing PPS parts for plastic injection
molding, undercuts should be avoided since the
material has very little elongation.
Secondary Operations for Polyphenylene
Sulfide plastic parts
Rebling Plastics ultrasonically welds PPS materials
and utilizes the ultrasonic process for installing
metal inserts into PPS moldings.
The material can be machined but is very abrasive
to cutting tools due to the high filler concentrations.
|
