By: Martina Celegato
Submitted: 2009-06-29 03:36:52 | Word Count: 490
All those artificial materials with a macromolecular structure that under certain conditions of temperature and pressure undergo permanent changes in shape are called plastics. Plastics are divided into thermoplastics, thermosets and elastomers. The rubbers, although they chemically and technologically have much in common with plastics, are usually not considered as such.
A lot of plastics (nylon, Teflon, Plexiglas, etc..) apply well to industrial production processes with machine tool quite similar to metallic materials, so they are often produced in semi-finished products (rods, angles, plates, etc.) from which the finished products (such as bushings, rollers, rings, pins, wheels) are obtained by machining.
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The most used process to produce mass series objects is molding. This is done with special presses, presses with thermoplastic injection that melt the plastic pellets and inject plastics at high speed and pressure in the molds.
The plastic molding injection is an industrial production process of the type of merger, in which liquid material is placed in a permanent mold that, aided by a force of "injection". Generally, the injection occurs at very high pressures and temperatures that enable the flow of the "plastic" material in the appropriate section of the press itself. The appropriate molds are kept hydraulically or mechanically closed in special presses for molding. The pressures are around hundreds bar.
The injection molding is considered one of the most economical processes of plastics transformation.
Molds are of course essential for these processes, the mold is a matrix that is specially designed and used to give the final or intermediate form to the piece or material to be processed. Depending on the different type of work, the characteristics and technology of the mold can change.
Another process that has a good application in the production of plastic products is thermoforming, where we start from granules of polystyrene or polypropylene. This is the extrusion of films or sheets which are passed to an appropriate temperature in a mold in which the object is forged with the pressure of compressed air or atmospheric air, with very cheap production equipment.
A common method to obtain polyethylene film is the bubble. This process consists of passing the polymer heated by the extruder through a circular chain in a horizontal position. The film obtained is cooled and passed through a towing grille terminating the system. It is also included some air to increase the volume of the system, inflating what is very similar to a balloon. This will produce the rear retractable film used to produce packaging.
Plastics are widely used worldwide in thousands of products and processes. Without the plastics there would not be a lot of daily use items that we take for granted, often making our life much less comfortable and practical.
