Designing Molds for Styrenic Block Copolymers (SBC) For best results manufacturers should understand the material’s processing benefits and limitations before designing a mold. 

Learn how molded-in color can offer the same eye-popping effects of paint at a greater efficiency and lower cost. Molded-in color hides scratches, withstands tough weather and helps you optimize manufacturing efficiency

Plate-out’ (deposits on the surface of an injection mold) is a common problem when using additives during injection molding of preforms.

When PolyCase Ammunition was getting ready to produce its new line of high performance ammunition, the project team knew they needed a material that would be easily enable them to produce their patent-pending, injection molded projectile designs that function as well or better than conventional lead-core projectiles.  The Avient team used their extensive knowledge and experience working with high-density polymers to develop a specialized Gravi-Tech™ high-density polymer composite that met PolyCase’s needs and fit the profile of their proprietary injection molding process.

These bio-based plastisols can be used in a variety of manufacturing processes, including dip coating, dip molding, rotational molding, and cast or laminate coating.

These materials are commonly used in injection molding, blow molding, film extrusion and other plastics processes.

Mold Flow Analysis Mold Design

In insert molding, a pre-molded rigid plastic substrate or metal part is inserted into the cavity via robotics or an operator. Insert Molding can be done using conventional injection molding equipment. The testing is done on a molded substrate with a TPE skin insert molded on it.

MOLD DESIGN RECOMMENDATIONS Gates • Many different types of gates can be used such as pin, fan, tunnel, tab and edge gates. Hot runner molds are acceptable and should be sized by the manufacturer. PROBLEM CAUSE SOLUTION Incomplete Fill Melt and/or mold temperature too cold Shot Size • Increase nozzle and barrel temperatures • Increase mold temperature • Increase injection speed • Increase pack and hold pressure • Increase nozzle tip diameter • Check thermocouples and heater bands • Enlarge or widen vents and increase number of vents • Check that vents are unplugged • Check that gates are unplugged • Enlarge gates and/or runners • Perform short shots to determine fill pattern and verify proper vent location • Increase wall thickness to move gas trap to parting line • Increase cushion Brittleness Melt temperature too low Degraded/Overheated material Gate location and/or size • Increase melt temperature • Increase injection speed • Measure melt temperature with pyrometer • Decrease melt temperature • Decrease back pressure • Use smaller barrel/excessive residence time • Relocate gate to nonstress area • Increase gate size to allow higher flow speed and lower molded-in stress Fibers on Surface (Splay) Melt temperature too low Insufficient packing • Increase melt temperature • Increase mold temperature • Increase injection speed • Increase pack and hold pressure, and time Sink Marks Part geometry too thick Melt temperature too hot Insufficient material volume • Reduce wall thickness • Reduce rib thickness • Decrease nozzle and barrel temperatures • Increase shot size • Increase injection rate • Increase packing pressure Flash Injection pressure too high Excess material volume Melt and/or mold temperature too hot • Decrease injection pressure • Increase clamp pressure • Decrease injection speed • Increase transfer position • Decrease pack pressure • Decrease shot size • Decrease injection speed • Decrease nozzle and barrel temperatures • Decrease mold temperature • Decrease screw speed TROUBLESHOOTING RECOMMENDATIONS PROBLEM CAUSE SOLUTION Excessive Shrink Too much orientation • Increase packing time and pressure • Increase hold pressure • Decrease melt temperature • Decrease mold temperature • Decrease injection speed • Decrease screw rpm • Increase venting • Increase cooling time Not Enough Shrink Too little orientation • Decrease packing pressure and time • Decrease hold pressure • Increase melt temperature • Increase mold temperature • Increase injection speed • Increase screw rpm • Decrease cooling time Burning Melt and/or mold temperature too hot Mold design Moisture • Decrease nozzle and barrel temperatures • Decrease mold temperature • Clean, widen and increase number of vents • Increase gate size or number of gates • Verify material is dried at proper conditions Nozzle Drool Nozzle temperature too hot • Decrease nozzle temperature • Decrease back pressure • Increase screw decompression • Verify material has been dried at proper conditions Weld Lines Melt front temperatures too low • Increase pack and hold pressure • Increase melt temperature • Increase vent width and locations • Increase injection speed • Decrease injection speed • Increase gate size • Perform short shots to determine fill pattern and verify proper vent location • Add vents and/or false ejector pin • Move gate location Warp Excessive orientation • Increase cooling time • Increase melt temperature • Decrease injection pressure and injection speed • Increase number of gates Sticking in Mold Cavities are overpacked Part is too hot • Decrease injection speed and pressure • Decrease pack and hold pressure • Decrease nozzle and barrel temperatures • Decrease mold temperature • Increase cooling time • Increase draft angle • Decrease nozzle and barrel temperatures • Decrease mold temperature TROUBLESHOOTING RECOMMENDATIONS www.avient.com Copyright © 2020, Avient Corporation.

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