Slush moulding

This is a method for making hollow articles using liquid plastics, particularly PVC plastisols. A shell-like mould is heated to a pre-determined temperature (typically 130°C for plastisols) and the liquid is then poured into the mould to completely fill it. A period of time is flowed to elapse until the required thickness of plastic gels. The excess liquid is then pour out and the plastic skin remaining in the mould is cured in an oven. The moulding is then taken from the mould. 

ComjHession moulding is one of the most common methods used to produce articles from thermosetting plastics. The process can also be used for thermoplastics but this is less common - the most familiar example is the production of LP records. The moulding operation as used for thermosets is illustrated in Fig. 4.62. A pre-weighed charge of partially polymerised thermoset is placed in the low - half of a heated ntould and the upper half is then forced down. This causes the material to be squeezed out to take the shape of the mould. The application of the heat and pressure accelerates the polymerisation of the 

During compression moulding, the charge of material may be put into the mould either as a powder or a preformed cake . In both cases the material is preheated to reduce the temperature difference between it and the mould. If the material is at a uniform temperature in the mould then the process may be analysed as follows. 

Consider a cake of moulding resin between the compression platens as shown in Fig. 4.63. When a constant force, F, is fyrplied to the upper platen the resin flows as a result of a pressure gradient If the flow is assumed Newtonian then the pressure flow equation derived in Section 4.2.3 may be used 

Fot the annular element of radius, r, in Fig. 4.63 it is more convenient to use cylindrical co-ordinates so this equation may be rewritten as 

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In recent years rotational casting methods have made the slush moulding process virtually obsolete. In these processes an amount of material equal to the weight of the finished product is poured into a mould. The mould is then closed and rotated slowly about two axes so that the paste flows easily over the cavity walls in an oven at about 200-250°C. When the compound has gelled, the moulds are cooled and the moulding removed. Compared with the slush moulding process there is no wastage of material, little flash, and more even wall thickness. Completely enclosed hollow articles such as playballs are most conveniently made. 

A development of slush moulding used for the production of hollow articles from plastisols. The moulds are continuously rotated in two directions during the curing cycle. 

Injection is by far the most used moulding process but compression and compression-transfer are used for specific cases. Rotomoulding is specifically used for polyethylene and a few other powdered resins. Slush moulding is broadly used for automotive dashboards. Generally ... 

Slush moulding used with thermoplastics in powder form for the fabrication of automotive dashboards ... 

Slush moulding is broadly used for automotive dashboards. 

Slush moulding is also suitable for other polymer powders such as TPU or for polymer liquids. 

PVC plastisol compounds can be manipulated into shapes, or applied to fabrics in the ungelled state by either simple flow techniques or by very low pressure processes. The main techniques are spreading, dipping, spraying and rotational and slush moulding. 

Slush moulding utilises heated open moulds which are inverted to remove excess plastisol. Layer thickness is controlled by the rheology of the paste, timing and... 

Butyl benzyl phthalate is a plasticizer added to polymers to give flexibility and softness. It is used extensively in polyvinyl chloride and in cellulose plastics, polyvinyl acetate, polysulfides, and polyurethane. Also used in flexographic inks for food packaging applications and acrylic coatings, profile extrusions, slush moulding, film and sheeting, coated fabrics, floor and wall coverings, vinyl foams and plastisols for car sealants. 

Expanding polyacrylonitrile microspheres, filled with pressurized iso-pentane which expand when the shell softens at moulding temperatures, are offered by Akzo Nobel Casco Products Division, under the Expancel name. New applications include shoe soles and slush-moulded PVCs. 

Powder and paste Dip coating, slush moulding, calendering, fluidized bed coating, rotational moulding, sintering Compression moulding... 

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