Processing moulding

The use of wooden sticks for ice cream and water ice products dates back to 1921. For many years, most stick products were ice lollies, and most bars were couverture coated ice creams ( choc ices ). Today the variety is much greater and ice cream, water ice and milk ice are sold in a number of different formats. For example, premium chocolate-coated ice creams are now often produced as stick products, and water ices are sold in tubes. Two main processes, moulding and extrude and cut are used to produce stick products. Tubes use the package as the mould and bars are made by extrude and cut. Bars and stick products are often coated with chocolate or couverture, and sometimes also dry pieces such as nuts. 

Full mould process moulding technique using a foam model in chemically bonded sand, in which the model is lost upon pouring, generally used only for large castings... 

Heat is an essential part of any moulding process. Moulding materials have a high heat capacity and in their hot plastic state will stick on contact with the skin and are difficult to remove. Protection can be afforded by the use of suitable industrial gloves. Some of the materials used can cause dermatitis, which can be prevented by the use of gloves. 

Polypropylene (PP) is a high-volume, low-cost plastic first commercialized in 1959 and produced by many companies. It is unusual in that it is processed in large quantities by all four major fabrication processes moulding, extrusion, film, and fibre technology. Major engineering plka-tions include pipe and automobile parts. It does not absorb water. 

Design parts for easy tooling/jigging using standard systems Utilise special characteristics of processes (moulded-inserts, colours)... 

Malic acid crystallizes in colourless needles m.p. lOO C. It o- curs in many acid fruits, such as grapes, apples and gooseberries. It can be prepared by microbiological processes using various moulds or from ( + )-bromosuccinic acid by the action of NaOH. 

Polymers owe much of their attractiveness to their ease of processing. In many important teclmiques, such as injection moulding, fibre spinning and film fonnation, polymers are processed in the melt, so that their flow behaviour is of paramount importance. Because of the viscoelastic properties of polymers, their flow behaviour is much more complex than that of Newtonian liquids for which the viscosity is the only essential parameter. In polymer melts, the recoverable shear compliance, which relates to the elastic forces, is used in addition to the viscosity in the description of flow [48]. 

Hiebcr, C, A. and Shen, S.F., 1980. A finite element/finite difference simulation of the injection-moulding filling process. J. Non-Newtonian Fluid Mech. 7, 1-32. 

M. E. Edwards, Chemical Reaction Engineering of Polymer Processing Reaction Injection Moulding Inst. Chem. Eng. Symp. Ser. 8(87), 783—796 (1984). 

This is also known as Bulk Moulding Compound (BMC). It is blended through a mix of unsaturated polyester resin, crosslinking monomer, catalyst, mineral fillers and short-length fibrous reinforcement materials such as chopped glass fibre, usually in lengths of 6-25 mm. They are all mixed in different proportions to obtain the required electromechanical properties. The mix is processed and cured for a specific time, under a prescribed pressure and temperature, to obtain the DMC. 

It is found that a force F will inject a given weight of a thermosetting polymer into an intricate mould in 30 s at 177°C and in 81.5 s at 157°C. If the viscosity of the polymer follows an Arrhenius Law, with a rate of process proportional to calculate how long the process will take at 227°C. 

Fig 9 3 A simple laboratory set-up for observing the casting process directly. The mould volume measures about 50 X 50 X 6 mm. The walls are cooled by putting the bottom of the block into a dish of liquid nitrogen. The windows are kept free of frost by squirting them with alcohol from a wash bottle every 5 minutes. 

In slip easting a thin slurry, or suspension, of clay in water is poured into a porous mould. Water is absorbed into the mould wall, causing a layer of clay to form and adhere to it. The excess slurry is tipped out of the mould and the slip-cast shell, now dry enough to have strength, is taken out and fired. The process allows intricate shapes (like plates, cups, vases) to be made quickly and accurately. 

Fig. 24.5. Compression moulding the thermoset is squeezed to shape and cured (by heating) at the some time. Once it has cured it con be token from the mould while still hot - so the process is faster than the moulding of thermoplastics.

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