Mould sticking

Report 150 Mould Sticking, Fouling and Cleaning, D.E. Packham, Materials Research Centre, University of Bath. 

Moulded stick products may be made from water ice, milk ice, ice cream, or any combination of these. Moulded products are quiescently frozen, often using a rotating table (Figure 5.6). The moulds are made... 

The TMS rheometer has been used to study mould release in rubbers. It contains a biconical rotor (representing the mould surface). The polymer is placed in the transfer chamber, injected around the rotor and cures in situ. Fig. 1. The shear stress required to free the rotor is taken as the mould-sticking index . The rheometer has the advantage that small experimental mixes of rubber can be evaluated. Further, the rotors are easily changed, so as to evaluate changes in mould surface, and the parted surfaces are amenable to examination by XPS and other methods of surface analysis. The obvious disadvantage is that access to special equipment (the TMS rheometer) is required. The same basic concept could be adapted for the study of mould adhesion of non-elastomeric polymers. 

Solid, rubbery silicones likewise retain their plasticity at low temperatures and are resistant to many forms of chemical attack they are now incorporated in paints for resisting damp and for waterproofing. Silicones are also used in moulds to avoid sticking of the casting to the mould. 

Because of their light weight, ability to be moulded into intricate shapes in one piece, low coefficients of friction and absence of slip-stick behaviour, acetal resins find use as bearings. 

Other ingredients may be added to prevent sticking to moulds (lubricants), to promote the curing reaction (accelerators), to improve the flow properties (plasticisers) and to colour the product (pigments). 

Basic materials such as lime or magnesium oxide increase the hardening rate of novolak-hexa compositions and are sometimes referred to as accelerators. They also function as neutralising agents for free phenols and other acidic bodies which cause sticking to, and staining of, moulds and compounding equipment. Such basic substances also act as hardeners for resol-based compositions. 

Expanded polystyrene. The plastic is formed into beads containing an expanding agent. When placed in a mould and heated they swell and stick together. The blocks are then cut into thicknesses as required. 

Ice lollies are made from juice (water, sugar, citric acid, flavour and colour) and are frozen into shape using moulds immersed in a cold brine solution, in a similar manner to can ice making (see Section 12.4). The moulds are made from stainless steel or nickel, and pass in rows through a brine bath at - 45°C. Different layers of confection may be built up by allowing one outside layer to freeze, sucking out the unfrozen centre and refilling with another mix. The sticks are inserted before the centre freezes solid. The moulds finally pass... 

A method of manufacturing footwear by simultaneously forming and vulcanising the rubber sole and heel direct to a leather upper, as compared to moulding the unit separately and sticking it to the upper. 

Any substance used to prevent rubber sticking to itself or to the surface of a mould. The lubricant may be a dry powder such as soapstone or a liquid such as silicone emulsion. See Dusting Agent and Mould Release Agent. 

Any substance used to prevent sticking of rubber to a mould surface, thus facilitating removal of the product without risk of tearing or splitting. The lubricant may be painted or sprayed on the mould surface or applied to the surface of the... 

Many rubber compounds have a tendency to stick in the mould cavity after vulcanisation and require some type of mould release agent. The substances used are surface-active materials such as detergents, soaps, wetting agents, silicone emulsions, aqueous dispersions of talc, mica and fatty acids, applied by spray or brush. Alternatively, dry types based on polytetrafluoroethylene or polyethylene, usually carried in a solvent, can be aerosol applied. An alternative is the addition of an incompatible material to the rubber compound which will bleed to the rubber surface during vulcanisation. 

Sticking to mould. Dirty mould, inadequate lubricant and undercure. Frequent cleaning and proper maintenance of moulds and proper application of mould lubricant. 

Melt the mixture III at 60°C, stir it into the suspension II and finally add I. When a homogeneous suspension has been obtained cast the sticks in preformed moulds. 

Little used today is Dragon s blood, an oleoresin obtained from the fruits of Daemonorops draco, a native palm of southeastern Asia and the Molucca Islands The resins exudes from the surface of the ripening fruits. It is removed from them by boiling in water, The resin is then moulded into balls or long sticks. It is sometimes used in making varnishes and lacquers. 

J. Boeseken, and A. Stock. A. Smits and H. L. de Leeuw purified the element by distillation and fractional crystallization in a highly exhausted atm., and obtained a colourless crystalline product. The phosphorus melted under hot water can be readily moulded into any desired shape, and it is commonly moulded into sticks. 

Hand moulding is the oldest method. Wooden moulds with six or seven compartments of the desired size are used. First these are cleaned and then lubricated with sand to prevent the clay from sticking. A lump of clay is then rolled through sand or sawdust and forcefully thrown into a compartment. With a piece of wire, excess clay is removed from the top of the mould. Next the mould turned upside down and the shaped bricks fall out and are ready for transport. The baked bricks are characterized by an non-uniform texture. Nowadays handmoulding is often done mechanically. 

---