The extrusion is a manufactoring process Mécanique by which a material pressurized is constrained to cross a Filière which will give him the form of a Profilé big length. One should not confuse this process with the Tréfilage which also consists in making pass a material in a die, but under the effect of a traction. This process is led cold.
This process gives parts to the forms even more precise than those which are carried out with stamping or dieing and have excellent surface qualities, which often makes it possible to use them without complementary machining. The average mass of the extruded parts is about one kilogram.
Extrusion applies to various products like metals (see the article spinning), the plastics, rubbers, the composite materials, but also clay, the pasta products, etc Contrairement to the Laminage and the Profilage of bands which are generally limited to simple forms, it makes it possible to obtain very complex forms and hollow sections.
To extrude a Polymeric Thermoplastic, one feeds in granules a cylindrical sleeve thermobabbited inside whose an endless screw turns. This screw mixes and transports the granules towards a die, making it possible to obtain a homogeneous mixture similar to a paste, by the effect of heat and shearing. The die will confer on the plastic mass the desired form. In the case of the manufacture of shaped the extrusion machine is generally followed of a vat of calibration which adjusts the part with the required tolerances. The setting with dimensions is done at the entry of the vat via a calibrator then lubricated the part is cooled by heat exchange with a circulating water flow. Extrusion is especially useful in the manufacture of the shaped tubes, sheets or plates windows type of PVC or various joints.
Various technologies apply to extrusion:
- extrusion film: who allows to draw from plastic films into weak thickness of 15 Micron S up to 30 microns
- the Extrusion-soufflage: used for the manufacture of the bottles.
- extrusion sheaths (or extrusion inflation): used for the manufacture of bag.
Industry of rubber
To extrude a rubber, one supplies an extrusion machine either by bands or by believed rubber pellets. The rubber extrusion machine consists of an endless screw which turns in a cylinder called body of the extrusion machine, itself constituted of several zones of thermal regulation and of a shirt, part in contact with rubber. The endless screw itself is controlled in temperature in the majority of the cases. Heated rubber softens and is pushed by the rotation of the screw towards the head of extrusion. The head is made up various elements (body, shell) which guide the rubber flow towards the die. It is this tools which give the final section of shaped (without calibration contrary to the extrusion machines figure). The temperatures fixed for the various zones are regulated sufficiently to soften rubber (and thus to be able to extrude with a pressure as low as possible) without vulcanizing it. One speaks about profile of temperature of the extrusion machine.
By analogy one calls extrusion one of the special effects applicable to a vectorial Dessin. It consists in creating a three-dimensional form starting from an object plane, completely comparable with what would be obtained in an ideal way by mechanical extrusion, the die, which one then calls section being defined according to the plane form.
The Hachoir is a kitchen utensil using extrusion to chop the Viande.
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