Design Guide - Solvay Plastics

Figure 59: HDT of 30% - 33% GR Resins
Deflection Temperature, °C
300
280
260
240
220
200
180
160
A-1133 HS PA 6,6 PPS PEI
In summary, deflection temperature does not measure
thermal capability, it simply provides one point on the
modulus versus temperature curve.
In general, HDT can only be used as a general indicator
of short-term thermal capability. It is useful for comparing
similar materials but can be misleading if, for example,
an amorphous material is compared to a semi-crystalline
material. It doesn’t provide any information about longterm
thermal stability. The actual loads and performance
requirements will dictate the suitability of the material.
Many semi-crystalline resins can be used in applications
that experience temperatures higher than their deflection
temperature value.
Deflection Temperature Values for
Amodel Resins
Deflection temperature values by both ASTM D648
and ISO 75Af for 19 representative grades of Amodel ®
PPA are shown in the Tables starting on page 7.
Figure 59 compares the deflection temperature at
1.8 MPa (264 psi) of Amodel AS-1133 HS resin with
a 33% glass fiber reinforced PA 6,6, a 30% glass fiber
reinforced polyphenylene sulfide, and a 30% glass
fiber reinforced polyetherimide. Amodel resin offers
a 75°C HDT advantage relative to PEI, a 42°C advantage
relative to PA 6,6, and a 22°C advantage relative to PPS.
550
500
450
400
350
Deflection Temperature, °F
Coefficient of Linear Thermal Expansion
The dimensions of most materials increase with
increasing temperature. The coefficient of linear thermal
expansion (α) is the ratio of the change in length to the
change in temperature.
If the coefficient α is known, the change in length of an
uniform straight bar raised to a temperature T f can be
calculated from:
where
ΔL = αL (T F
− T O
)
ΔL = change in length
L = original length
α = coefficient of linear thermal expansion
T F
= final temperature
T O
= original temperature
The coefficient of linear thermal expansion (α), as
measured by ASTM E831, of several Amodel grades
and some common metals is given in Table 19. This
method provides an average value for the expansion
coefficient over a temperature range.
The thermal expansion behavior of metals is uniform
over the temperature range of concern. As shown in
Table 19, the thermal expansion coefficients of the
polymer materials are a function of the temperature
range used for the measurement. In general, the
polymer materials expand slightly more above their
glass transition temperature than they do below it and
the behavior in the vicinity of the T g is also somewhat
non-linear. However, over large temperature ranges,
the variations are usually insignificant and excellent
prediction of dimensional properties can be obtained
using the values provided in the table. Also, the addition
of glass fiber and other reinforcing additives results in
the thermal expansion becoming directional. Since fibers
tend to become oriented in the flow direction, and since
glass has a lower thermal expansion coefficient than
the polymers, the coefficient of expansion are generally
lower in the flow direction than the transverse direction.
The values shown in Table 19 should allow the design
engineer to estimate the magnitude of the thermal
stresses in parts molded from Amodel resins due
to thermal expansion.
Property Data
Amodel ® PPA Design Guide
43