SCREW PLASTICISATION

Zitzenbacher, G., Karlbauer, R., and Thiel, H., A New Calculation Model and Optimization Method for Maddock Mixers in Single Screw Plasticising Technology, Int. Polym. Process. 22, 73 (2007)... 

The Remaker, built by Kleindiant in Germany, employs an intrusion moulder. The screw-plasticised mixture is injected at a relatively low pressure through a large diameter gate into aluminium moulds mounted on a conventional press. This machine is very effective for small flexible items but cannot handle mixtures containing PVC because of the relatively long dwell time in the machine. 

You can process LSR with modem injection moulding machines. However, you need special LSR equipment for the machine. Today injection moulding of LSR is solely done with screw injection moulding machines. The screw plasticises the prepared compound. During the plasticising the material is kept at a temperature of 5 to 25 °C. This is followed by material injection by the screw with low pressure into the mould. 

The dry material is readily ignited, bums very rapidly and is moderately sensitive to heat, shock, friction or contact with combustible materials. When heated above its m.p. (103-105°C), instantaneous and explosive decomposition occurs without flame, but the decomposition products are flammable. If under confinement (or in large bulk), decomposition may be violently explosive [1], An explosion which occurred when a screw-capped bottle of the peroxide was opened was attributed to friction initiating a mixture of peroxide and organic dust in the cap threads [2], Waxed paper tubs are recommended to store this and other sensitive solids [3], Crystallisation of the peroxide from hot chloroform solution involves a high risk of explosion. Precipitation from cold chloroform solution by methanol is safer [4], Water- or plasticiser-containing pastes of dibenzoyl peroxide are much safer for industrial use. 

A machine for masticating rubber. The principle is that of an extruder, the rubber being softened by working between the threads of the screw and the surface of the barrel. The best known type is the Gordon Plasticator . Now obsolete. Plasticiser... 

Machines differ in their mode of heating, plasticisation of the mix and delivery of the mix to the mould cavity. This may be by simple ram (plunger or piston) or by screw. 

Simple ram machines are cheaper than screw machines having equivalent shot volumes. Although the simple ram injection moulding machine was once quite widely used it was generally obsolescent by 1977. Plasticisation by screw is quicker and more controllable than by heat conduction in simple ram machines. A higher and more uniform compound temperature and thus a more uniform viscosity is achieved. 

The advantage of screw machines is that work done by the screw heats and plasticises the mix, under conditions which can be carefully regulated by jacket temperature, screw speed and back pressure. A natural rubber mix leaves the extruder section of the machine 20-30 °C higher than the jacket control temperature. 

To a continuing process the pigment dispersions are added directly to the plasticising equipment by volumetric or gravimetric measuring units. Further blending can then be done on a single- or twin-screw extruder. 

To optimize the metallic effect when using an injection-molding machine, a higher screw speed, a longer plasticising period, sufficient backpressure, and a suitable screw design are prerequisites. The pigments are added as ready-to-use compounds, masterbatches, or powders. 

For extrusion blow moulding, the blow moulding machine is based on a standard extruder barrel and screw assembly to plasticise the polymer. The molten polymer is led through a right angle and through a die to emerge as a hollow (usually circular) pipe section called a parison. 

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