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SUMMARY

A Guide to Injection Molding of Plastics.

 

There is no mystery in injection moulding of plastics. Each and every phenomenon has its scientific reasons. Since injection moulding involves Polymers, Mould and Machinery, it is necessary to understand all of them; their role and their limitations. We explore in this book –Cavity pressure profile, pvT diagram, Shear thinning of plastics, Flow mechanism- simultaneous flow and freeze of melt with skin formation and fountain flow.

We also appreciated the root cause of most of the quality problems lie with three balancing tricks in the process.

  • Flow balance in part,
  • Heat balance in mould,
  • Uniform freezing in mould.

We should appreciate that major cause for failure of plastic part in service is environmental stress cracking. If we understand this, then we must explore all that is relevant for moulded-in stress. These facts are discussed in this book - A Guide to Injection Moulding of Plastics.

FACTORS INFLUENCING QUALITY OF MOULDING

MATERIAL

MOULD

MACHINE

Characteristics of Polymer

Design factors in Part and; Mould

Specification to meet the requirement of Part and; Mould

  • Molecular weight,
  • MFI,
  • pvT characteristics,
  • Response to shear rate and limitation,
  • Heat and Thermal stability,
  • Shear thinning,
  • Shrinkage behaviour,
  • Maximum flow ratio,
  • Hygroscopic or not.
  • Gate location, size and type,
  • Sprue / runner size balanced type,
  • Air vent,
  • Wall thickness uniform and capable of promoting balancing of melt flow,
  • Balancing of flow in unsymmetric part geometry,
  • Mould release.

 

  • Maximum shot capacity of plasticating unit,
  • Residence time,
  • Maximum injection rate,
  • Number of stroke controlled steps for filling phase,
  • Maximum injection pressure,
  • Number of time- controlled steps for pressure phase,
  • Plasticating rate,
  • Clamp force and; Platen dimensions / Tiebar clearances
  • Uninterrupted trouble free performance of machine

 

Moulding process in this book is not discussed in lay man's point of view but it is discussed in terms of physics of plastic melt, which is best described by pvT characteristic, shear thinning characteristic and orientation characteristic of melt.

This book provides technical perspective to the process that is relevant to understand CAE technologies. You can develop skills to visualise the happenings inside the Screw-Barrel and inside the Mould. This knowledge can help you to understand the root causes of all the quality related problems.

Very vital information are provided with figures and tables about Screw Design, Machines, Support Equipment, Service lines, Injection Moulding Process, Quality related Problems, Mould, Hot Runners, Mechanical failures in Moulds, Energy efficiency, Testing of Machines, Robot, Multi-component Moulding, Gas assisted Moulding, Thermoset Moulding, CAE, CAD, CAM Technology. A chapter on Myths and Truth clarifies the most misunderstood aspects in the industry.

This book is an ideal companion to Practicing Engineers as well as Students- Students of Engineering colleges, Students of Polytechnics, Students of Plastics Course and working technicians.

Prabodh C. Bolur

e-mail: bolurpc@gmail.com

 


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