Shrinkage mould material

Glass-reinforced grades of SAN exhibit a modulus several times that of the unfilled polymer and, as with other glass-filled polymers, a reduced coefficient of thermal expansion and lower moulding shrinkage. The materials are thus of interest on account of their high stiffness and dimensional stability. 

Polystyrene can be polymerised by foam processes, mass polymerisation, solution polymerisation, suspension polymerisation and emulsion polymerisation. Each contributes to the final characteristics of the plastics and the likely residues. A limit for styrene monomer may be imposed. Styrene can be readily analysed down to a 0.01% level. Polystyrene exhibits low shrinkage, hence is an excellent moulding material. 

SO 2577. Plastics Thermosetting moulding materials Determination of shrinkage. 1984. 

DIN 53464, Testing of Plastics Determination of Shrinkage Properties of Moulded Materials from Thermosetting Moulding Materials, 1962. 

DIN 53464, Testing of plastics, determination of shrinkage properties of moulding materials from thermosetting moulding materials, 1962. 

Plastics — Thermosetting moulding materials - Determination of shrinkage, 2008... 

Table 1. Expected shrinkage of various compression moulding materials.

Mould Shrinkage A measurement of the contraction of the moulded material in comparison with the original mould dimensions. Two values may be quoted where material flow induces anisotropy in material microstructure, e.g. preferential alignment of reinforcing phases. Example 2.0/3.0 indicates 2.0 % shrinkage in direction of material flow, with 3.0% shrinkage transverse to mould flow direction. 

This paper presents the results from investigations into the differences in moulding with a novel anodised machined aluminium mould material and a conventional machined aluminium mould material. Significant differences in terms of cycletime were observed between the moulding carried out with the anodised moulding and the conventional aluminium mould surface material with no change in the shrinkage, part appearance or mechanical properties noted between either. 

Following the extensive and detailed investigation into rotomoulding with anodised treated aluminium it was found that typically there is a 20 - 25 % saving on overall cycletime when compared with non-treated Conventional aluminium. There were no differences observed between the two mould materials in terms of impact, shrinkage or surface properties. 

Since the material is amorphous the moulding shrinkage is low and normally less than 0.008 cm/cm. 

Being amorphous, the materials have a low moulding shrinkage (0.044-0.008 cm/cm). 

The manufacturers stress ease of processing as a particular feature of the material. Recommended melt temperatures are in the range 320-340°C and mould temperatures are 135-165°C. Mould shrinkage of glass-filled grades is usually of the order of 0.2-0.4% in the flow direction and up to twice this value in the transverse direction. The materials are notable for their ability to withstand vapour phase and infrared soldering processes. 

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