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Referring to the cavity pressure profile and PVT-diagram it is observed that-

  • The polymer melt at A in the diagram is at 230 C and 1 bar pressure. Between A and; B about 90 % of mould filling takes place by injection speed resulting in pressure build up at more or less constant melt temperature.
  • At B injection speed is terminated and switch over to follow-up pressure takes place after a slight delay on account of switching delay and response time of hydraulic valves.
  • At C peak cavity pressure is reached during the pressure control phase of moulding.
  • CD describes the constant follow up pressure applied on melt. The specific volume of melt is decreased between C and; D resulting in void / shrinkage which is filled up by further transfer of melt from nozzle.
  • The melt is cooled between D and; E. Specific volume of melt remains constant and the cavity pressure drops to 1 bar. E is the point on 1 bar curve. At this point the moulded part can be ejected.
  • After demoulding the moulded part is further cooled up to room temperature out side the mould.

Let us understand the factors influencing quality consistency in processing and quality in performance

Let us understand moulding problems.

Let us see the analysis of plastic part failurs carried out by RAPRA.

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pvt diagram

Thermal stability Balancing melt Flow Balancing Heat Freezing Quality Problems
Three Balances

Moulded-in Stress Shrinkage Inconsistent Dimension Sink-mark Weld-lines
Moulding Problems

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