Page 326 - Engineering Plastics Handbook

284 Engineering Plastics

TABLE 12.6 Recommended
Barrel Temperatures*
Three-zone
control

Zone °F °C
Feed 580 304
Middle 620 327
Front 650 343
Nozzle 700 371
∗
Actual temperature profile
may vary depending on grade.
Compression molding
Polyamide-imide powders may be compression-molded into standard
shapes and geometries. This operation produces parts that may be used
as is or further machined into intricate parts. The mechanical prop-
erties of compression-molded parts are somewhat less than those of the
corresponding injection-molded grades. The typical compression-molding
operation uses a fine particle size of polyamide-imide powder. The powder
material should have particles which are 100% less than 150 µm and 95%
less than 75 µm. Polyamide-imide powders may also be used as an addi-
tive or adhesive binder in the sintering of other shapes based on PTFE
powders, metal powders, or abrasive materials.
One example of the compression-molding process is outlined in
Table 12.7 [28]. Polyamide-imide powder particles with a maximum
particle size of 150 µm and a median particle size in the range of 10 to
50 µm are preheated in an oven for 1 to 24 h at 260 to 316°C. The pur-
pose is to increase molecular weight and complete the imidization
processes, both of which create water and can lead to voids in the com-
pression-molded article. The compression-molding schedule depends on
the size and geometry of the mold. A pressure-molding schedule for a
14.0 cm × 1.6 cm disk mold is shown in Table 12.8, where the mold tem-
perature is set in the range of 315 to 329°C.

TABLE 12.7 Compression Molding Process
Step Machine pressure, kN Time, min Part pressure, MPa
1 11.1 10 1.4
2 44.5 4 5.8
3 111.2 3 14.5
4 222.4 3 29.0
5 111.2 5 14.5
Cool to 260°C at 111.2 kN and then eject immediately.