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pvT DIAGRAM

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

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

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