• Document: A Guide to Polyolefin Injection Molding A Guide to Polyolefin Injection Molding Table of Contents Introduction... 2 Polyolefins are derived from petrochemicals... 2 Molecular structure and...
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A Guide to Polyolefin Injection Molding A Guide to Polyolefin Injection Molding Table of Contents Introduction ....................................................................................................... 2 Polyolefins are derived from petrochemicals .................................................... 2 Molecular structure and composition affect properties and processability ......... 2 Chain branching .......................................................................................... 3 Density ......................................................................................................... 3 Molecular weight ........................................................................................ 4 Molecular weight distribution ...................................................................... 4 Copolymers ................................................................................................ 5 Modifiers and additives .............................................................................. 5 Working closely with molders ............................................................................ 5 How polyolefins are made .................................................................................. 5 Low density polyethylene (LDPE) ............................................................... 6 High density polyethylene (HDPE) ............................................................. 6 Linear low density polyethylene (LLDPE) .................................................... 7 Polypropylene ............................................................................................. 7 Shipping and handling polyolefin resins ............................................................. 7 Material handling ........................................................................................ 7 How to solve material handling problems ................................................... 9 Other material handling practices ............................................................... 10 The injection molding process ........................................................................... 11 Injection units .............................................................................................. 11 Plasticator specifications ............................................................................ 13 Screw designs ............................................................................................. 13 Nozzles ...................................................................................................... 14 Clamp mechanisms ................................................................................... 15 Clamp specifications ................................................................................... 16 Injection molds ........................................................................................... 17 Types of mold ............................................................................................ 17 Sprues and runners ................................................................................... 17 Mold venting ............................................................................................... 19 Gating ........................................................................................................ 20 Mold cooling .............................................................................................. 20 Ejection devices ........................................................................................ 21 Spiral flow measurement ........................................................................... 21 General injection molding operating procedures .............................................. 22 General safety ........................................................................................... 22 Heat ........................................................................................................... 23 Electricity ................................................................................................... 23 Machinery motion ...................................................................................... 23

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