Injection Molding Guidelines for
PLENCO BMC Polyester Molding Compound
ParameterSuggested Press Settings
Mold Temperatures 143° - 171°C (290° - 340ºF)
Front Barrel Temperature
Rear Barrel Temperature 27° - 44°C (80° - 110°F)
27° - 44°C (80° - 110°F)
Stock Temperature 32° - 71°C (90° - 160°F)
Injection Time 3 - 6 Seconds
Clamp Tonnage27.6 - 41.4 MPa (2 - 3 Tons/in2) Of Projected Part Area
Screw Back Pressure 0.18 MPa (25 psi) or Less
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 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 can be used to process these molding 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. Another method of processing, is to force the material out of the barrel with a plunger, also called a ram.
- 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 ProblemsPotential Solutions
Blistering Increase mold temperature
Increase stock temperature
Increase cure time
Gas BurnsSlow injection time
Check for blocked vent(s)
Lower stock temperature
Short PartsIncrease shot length
Increase back pressure
Lower mold temperature
Sticking PartsIncrease 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
9-28-07