Image icon  Injection-moulded protractor

 
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Description: The colours in the image are the result of birefringence and relate to the residual strain in the polystyrene. The pattern of strain is indicative of the flow of material during the injection process and it highlights the injection point (at 152 degrees on the outer scale), and two 'weld lines' (at 338 and on the central bar) where two distinct flows of material meet. The weld line is a common point of failure because there is limited intermixing of the two fronts during the time allowed.
Keywords: alignment • birefringence • injection moulding • polymer • polystyrene (PS) • protractor • sprue • weld
Categories: Science approaches > Microstructure
Materials > Polymers & elastomers > Plastics > Thermoplastics > Polystyrene (PS)
Testing, analysis & experimentation > Metallography
Scale > Micro
Created by: J A Curran, Department of Materials Science and Metallurgy, University of Cambridge
DoITPoMS, University of Cambridge
Published by: DoITPoMS, University of Cambridge
License: This resource is released under the Creative Commons Attribution Non-Commercial Share Alike license (2.0 UK: England & Wales).
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Date created: 03 October 2002
Date added: 21 August 2009
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Resource ID: 1609