EXPERIMENTAL FLOW-FRONT VISUALISATIONIN COMPRESSION MOULDING OF SMC

摘要

This work is primarily focused on experimental visualisation of the flow during mouldclosure in compression moulding of sheet moulding compound (SMC). Circular platesare manufactured with industry scale equipment at close to production conditions. Specialattention is given to the advancing flow front, for which the full complexity is capturedby means of continuous high resolution close-up monitoring. From the experimentalvisualisation of the flow front, three phases are defined, namely pitch, floating, andboiling. During the initial phase, pitch, outer layers do not remain outer layers, the actualflow is very complex and air is likely to be entrapped. The governing process parametersduring this phase are mould temperature, mould closing speed and amount of preheatingin the mould. During the second phase, floating, the flow is stable and seemingly viscous.During the last phase, boiling, bubbles are observed in the low pressure region at the flowfront, favouring the void content both internally and on the surface. Based on a chemicalanalysis including mass spectrometry and thermogravimetry, the gas is probably styrene.Finally a qualitative investigation of the surface quality of the moulded plates is carriedout. It is observed that the surface void is reduced with an increased mould temperatureand that the mould closing speed does not seem to have any influence on the surfacequality at lower mould temperatures while at higher mould temperatures, an increasedmould closing speed clearly gives a reduction of surface void