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PLASTICS ENGINEERING COMPANY |
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3518 LAKESHORE |
Injection Molding Guidelines
PLENCO Granular Polyester Molding
Compound
|
Parameter |
Suggested
Press Settings |
|
Mold Temperatures |
163° - 182°C (325° - 360ºF) |
|
Front Barrel Temperature Rear Barrel Temperature |
85° - 93°C (185° - 200ºF) 49° - 71°C (120° - 160ºF) |
|
Stock Temperature |
93° - 100°C (200° - 212ºF) |
|
Injection Time |
3 - 6 Seconds |
|
Clamp Tonnage |
27.6 - 41.4 MPa
(2 - 3 Tons/in2) Of Projected Part Area |
|
Screw Back Pressure |
0.21 - 0.41MPa (30 - 60 psi) |
|
Screw |
30 - 60 |
Additional Technical Information
·
A clean, highly polished, chrome plated mold is recommended.
Use a mold release such as Carnauba Wax, being careful to coat the entire
surface including the sprue bushing. After
several shots wipe off the excessive mold release using a clean, soft cloth.
·
The orifice size of the nozzle should be 1 mm (1/32”) less
than the sprue bushing orifice. This
will allow material to be pulled from the nozzle, which helps minimize nozzle
freeze off. The nozzle and sprue orifice
should be of the same radius, to provide a leak free shut off. In some cases, it may be necessary to have a
smaller radius on the nozzle, to reduce the heat transfer from the sprue, which
may be causing nozzle freeze off.
·
A tapered, highly
polished, D2 steel, sprue bushing, will provide easy release of the sprue from
the sprue bushing.
·
The shot weight (part & runner volume) should be between
20% and 80% of the barrel capacity of the injection press. A Thermoset injection
screw and barrel provides optimum performance when molding these
materials. A Thermoset screw is one with
a 12:1 L/D (length/diameter) Ratio, a 1:1 Compression Ratio and a 40° included
angle on the tip.
·
Adding a cushion of 3 mm (1/8”) and switching to secondary
or holding pressure at 6 mm – 10 mm (1/4” - 3/8”) before the screw bottoms out,
will help maintain a part density that maximizes physical and electrical
properties.
|
Common
Molding Problems |
Potential
Solutions |
|
Blistering |
Increase mold temperature Increase
stock temperature Increase
cure time |
|
Gas Burns |
Slow injection time Check for
blocked vent(s) Lower stock
temperature |
|
Short Parts |
Increase
shot length Increase
back pressure Lower mold
temperature |
|
Sticking Parts |
Increase
mold temperature Increase
cure time |
|
Precure ( set marks ) |
Increase
injection speed Lower mold
temperature Lower stock
temperature |
The listed parameters
are suggested for use as a guide when setting up an injection molding machine
for molding