Plastics Engineering Company



BOX 758

Injection Molding Guidelines

PLENCO Granular Polyester Molding Compound



Suggested Press Settings

Mold Temperatures

163 - 182C (325 - 360F)

Front Barrel Temperature

Rear Barrel Temperature

85 - 93C (185 - 200F)

49 - 71C (120 - 160F)

Stock Temperature

93 - 100C (200 - 212F)

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 RPM

30 - 60 RPM


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



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 Plenco Thermoset materials. These parameters are for your evaluation and may or may not be compatible for all mold designs, runner systems, press configurations, and material rheology. Please feel free to call Plenco and a Plenco Technical Service Representative will be happy to assist you. Revised 4-30-03