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Plastics are defined as polymers which are organic, carbon-based compounds whose molecules are linked together in long chain patterns. Plastics can be basically divided into two types as Thermoplastics and Thermosetting Plastics. Thermoplastics melt when heated so they can be melted and re-formed again and again; hence, the chemical structure remains unchanged during heating and shaping. Thermosets undergo curing process during shaping causing a permanent change (called cross-linking) in molecular structure. They harden when heat is re-applied on the moulded surface and if heated further, they will break down chemically and lose their properties. Here above you will find a wide selection of used plastic processing machinery and other plastic equipment from various sellers and auction houses. Compare prices and specs and find the best deal for your used plastics machine offer.
Plastics Processing Process
Because of the properties of polymers, it is possible to mould them and modify their shape using different manufacturing processes collectively termed as Plastic processing. Plastics processing is a form conversion process. Plastic raw materials in the form of
powder, pellets, beads are heated, melted and then transformed into usable plastic products through plastic processing equipment and tooling. Over the past century, plastic processing has evolved from crude equipment, in which melting and forming of material was a strenuous task to the present microprocessor controlled plastic processing equipment. A well-maintained processing machine can easily last for at least 20 years. This is the reason for the growing trend towards buying used plastic processing equipment.
Types of Plastics Processing
Moulding and extrusion are the two common processing methods for Thermoplastic resins. Moulding involves non-continuous processes such as injection moulding, blow moulding, rotational moulding, and compression moulding, in which parts are made in a closed mould. In extrusion, the plastic pellets are melted by a screw conveying system and forced to flow through a die. Calendering, thermoforming and casting are other operations through which thermoplastics can be processed. Generally used processing methods for thermosetting plastics are compression moulding, transfer moulding, and injection moulding. Fiber-reinforced thermosets are fabricated by specialised techniques namely open-mould processing, protrusion and reaction injection moulding.
Extrusion is a process in which plastic pellets are fed into a heated cylinder where it is driven by rotating screws compacting and squeezing it through a die to give a finished or semi-finished product with the desired profile.
Blow moulding is a simple process where compressed air is introduced underneath a pre-heated sheet of thermoplastic material forcing the material into a mould cavity, or allowing it to expand freely.
It is basically the opposite of Blow moulding. Instead of the plastic sheet being forced into a mould by air pressure, in vacuum forming the air is drawn out from the bottom of the softened plastic sheet, so it is forced over or into a mould by atmospheric pressure.
Extrusion Blow Moulding
It is a combination of extrusion and blow moulding and is often used when there is a sudden change in thickness of the product such as the presence of a narrow neck. The plastic material is first extruded into a tube shape into an open die. The die is then closed to seal the ends of the tube and the air is blown in forcing the plastic tube which then takes up the shape of the die cavity.
Injection moulding is one of the most common of all plastics manufacturing processes in which the polymer in the form of granules is heated and forced into a closed mould. As very high pressure is required to feed the fused polymer into the mould, the machine and the mould should be capable of withstanding the force involved during operation.
Rotational moulding is used for producing hollow thermoplastic products such as drums, storage tanks and litter bins. A pre-determined amount of plastic is placed in a closed mould which is then thoroughly heated in an oven to a set temperature and rotated slowly around both vertical and horizontal axes.
In calendaring, the fused thermoplastic is extruded onto heated rotating rollers that squeeze the material into a continuous sheet or film.
It is one of the oldest techniques of manufacturing which is mostly used for the processing of thermosetting plastics. A pre-heated lower mould cavity which has the thermosetting polymer is subjected to further heat and pressure provided by a press. Polymerization and the flow of the plasticized material within the mould take place due to the excess pressure and heat applied.
Used Plastics Machines for Sale
when looking for a plastics machine you might realise that it can be quite an expensive affair. One of the most popular solution that many plants and businesses do is to buy a used plastics machinery for their plant. These days manufacturers produce machines that are long lasting and require minimum maintenance. Due to the high price of new machines the owners take good care of the machines that why when they are offered for sale the used plastic processing machines can be in top condition.
Manufacturers of Plastic Processing Equipment
A few leading plastic processing equipment manufacturers in the world are Krauss-Maffei, BBM Maschinenbau und Vertriebs GmbH, Davis-Standard Extrusion Systems, ARBURG, BOY, Meccanoplastica S.r.l., Urola s.c, TECHNE, Enpas, KOSME and Windsor.