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1、COMPREHENSIVE Mold Design And Processing Conditions A Guide to Processing Injection Molding Grade Specialty Compounds English/Standard and SI Metric web site: 1 General Molding Guidelines Standard Molding Equipment Machine Type: We recommend using a screw injection machine for molding reinforced th
2、ermoplastics. A screw injection machine improves melt homogeneity, reduces variations in the molded parts, and minimizes degradations and cold spots of the polymer melt. Machine Size: The machine should be sized to use approximately 50-70% of machine barrel capacity per shot. This maintains a short
3、barrel residence time and eliminates material degradation. The machine should have adequate clamp pressure to obtain 4-8 tons per square inch (55-110 N/mm 2) of projected surface area. Generally, a reinforced material requires 50-70% higher clamping pressures than a nonreinforced polymer of the same
4、 type. Molding Conditions Drying: Successful molding of reinforced thermoplastics requires adequate drying. Inadequate drying can cause extremely erratic molding conditions and less than perfect molded parts. Excessively wet materials outgas and can undergo a viscosity change during processing. This
5、 may cause brittleness, blisters, voids, silver streaking and poor surface finish. RTP Company materials are dried prior to packaging in moisture resistant containers. However, we recommend thoroughly drying the materials in a dehumidifying type dryer. This is important with hygroscopic materials bu
6、t can also be essential for non-hygroscopic materials. Condensed surface moisture can dramatically affect high temperature molded parts. The recommended drying times are provided as guidelines; however, an actual moisture check is necessary. Barrel Temperature: Refer to Processing Conditions in this
7、 guide for recommended starting temperatures. Typically the rear zone/zones are set 10-20 degrees F (6-12 degrees C) cooler than the front zone and nozzle. Some modifications may be needed depending on part size and configuration. Melt Temperature: Refer to Processing Conditions in this guide for re
8、commended starting temperatures. General Processing Tips Machine Setting Barrel Temperature Compounds with Fillers Slightly higher than unfilled resin Mold Temperature: Refer to Processing Conditions in this guide for recommended starting temperatures. Normally, reinforced materials require higher m
9、old temperatures than nonreinforced materials. Higher mold temperatures will achieve a smoother, more blemish-free surface by providing a resin rich skin on reinforced materials. Injection Pressure: Injection pressure should be set low initially and increased to the point of filling the part just sh
10、ort of causing flash. Maximum pressure without flash generates optimum physical properties for your RTP Company material. Back Pressure: Low back pressure (approx. 50 psi or 0.34 MPa) minimizes fiber breakage and property deterioration. Injection Speed: Generally, the fastest possible cavity fill ti
11、me is best. This minimizes glass orientation and maximizes weld line integrity. Screw RPM: The lowest possible rpm is recommended to minimize fiber breakage and screw recovery should be set accordingly. Slower rpms result in a more uniform melt by minimizing shear heat buildup. Mold Temperature Inje
12、ction Pressure Back Pressure Injection Speed Screw Speed Mineral slightly higher than unfilled resin; carbon black higher than mineral filled Must be higher than unfilled resin because of higher viscosities 50-100 psi (0.34-0.69 MPa) 1-2“/sec (25-50 mm/sec) 60-90 rpm Compounds with Fibers Glass fibe
13、r slightly higher than particulate; carbon fiber slightly lower than unfilled resin Glass fiber higher than particulate; carbon fiber higher than glass or particulate Must be higher than unfilled resin because of higher viscosities 50-100 psi (0.34-0.69 MPa) Slowest speed without sacrificing appeara
14、nce Minimum speed without causing delays in molding cycles General Molding Guidelines Tips to Improve Mechanical Properties Property Tensile Strength 2 Tensile Elongation Flexural Modulus Flexural Strength Notched Izod Impact Shrinkage Warpage Regrind Usage Process Use hotter mold temperatures Use h
15、igh injection speed Avoid high melt temperature Injection pressure has little effect Use hotter mold temperatures Avoid high melt temperature Use higher melt temperatures Use high injection speed Injection pressure has only moderate effect Use hotter mold temperatures Avoid high melt temperature Inj
16、ection pressure has only moderate effect Use hotter mold temperatures (cold mold can cause 50% loss in impact strength) Avoid high melt temperatures Use cold mold to reduce shrinkage Use high injection pressure Avoid high screw rpm Avoid high melt temperatures Use longer hold time to reduce warpage Reduce stress with high mold and melt temperatures Generally, 20% regrind is
