Monthly archive for December 2019

Details of the Process for Injection Molding Machines The earliest injection moulding machines were of the plunger type and there are still many of these machines in use today. A pre-determined quantity of moulding material drops from the feed hopper into the barrel. The plunger then conveys the material along the barrel where it is heated by the conduction from the external heaters. The material is then plasticised under pressure so that it may be forced through the nozzle into the mould cavity. In order to split up the mass of the material in the barrel and improve the heat transfer, a torpedo is fitted in the barrel . But there are few disadvantages in this type of machine i.e. it is difficult to produce consistent mouldings. The main problems are: 1. There is little mixing or homogenization of the molten plastic. 2. It is difficult to meter accurately the shot size. Since metering is on a volume basis, any variation in the density of the material will alter the shot weight. 3. Since the plunger is compressing material which

Injection molding Processing of Plastic One of the most common processing methods for plastics is injection moulding. Nowadays wide range of articles are made by means of injection molding. These include such things as electric drill casing, television housings, gearwheels etc. The original injection moulding machines are based on the pressure die casting techniques for casting metals. The first machine is reported to have been patented in the United States in 1872, specifically for use with celluloid. this was an important invention but probably before its time because in the following years very few developments in injection moulding processes were reported and it was not until the 1920s, in Germany, that a renewed interest was taken in the process. The first German machines were very simple pieces of equipment and relied totally on manual operation. In the late 1930s the next major development in injection molding , i.e. the introduction of the hydraulically operated machines get available. However, these machines still tended to be hybrids based on the die casting technology and the design of injection moulding machines for plastic

Extrusion Processing of Plastic One of the most common methods of processing plastics is Extrusion using a screw inside the barrel. The plastic, usually in the form of granules or powder, is fed from the hopper on to the screw. It is then conveyed along the barrel where it is heated by conduction from the barrel heaters and shear due to its movement along the length of the screw flights. The depth of the screw channel is reduced along the length of the screw so as to compact the material. At the end of the extruder the melt passes through a die to produce an extrudate of the desired shape.

Processing Introduction of Plastic One of the most outstanding features of the plastics is the ease with which theycan be processed. In some cases semi-finished articles such as sheets or rods are produced and subsequent fabricated into shape using conventional methods such as welding or machining. In the majority of the cases, however, the finished article, which may be quite complex in shape, is produced in a single operation.The processing stages of heating, shaping and cooling may be continuous (e.g. production of pipe by extrusion), or a repeated cycle of events (e.g. production of telephone housing by injection moulding), but in most cases the processes may be automated and so are particularly suitable for mass production. There is wide range of processing methods which may be used for plastics. In most cases the choice of method is based on the shape of the component and whether it is thermoplastic or thermosetting. There are two principal methods for processing plastics. 1. Extrusion Processing of Plastic 2. Injection molding Processing of Plastic