The main machine of the plastic extrusion line is the extruder, which consists of an extrusion system, transmission system and heating and cooling system.
The extrusion system includes a screw, barrel, hopper, head, and die, plastic through the extrusion system and plasticized into a uniform melt, and in the process established under pressure, by the screw continuous extrusion head.
(1) screw: is the most important part of the extruder, it is directly related to the scope of application and productivity of the extruder, made of high-strength corrosion-resistant alloy steel.
(2) barrel: is a metal cylinder, generally made of heat-resistant, high-pressure strength, strong wear-resistant, corrosion-resistant alloy steel or alloy steel lined with a composite steel pipe. The barrel cooperates with the screw to realize the crushing, softening, melting, plasticizing, exhausting and compacting of the plastic, and continuously and evenly conveying the rubber to the molding system. The length of the barrel is generally 15-30 times its diameter, so the plastic is fully heated and fully plasticized as a principle.
(3) Hopper: The bottom of the hopper is equipped with a cut-off device for adjusting and cutting off the material flow, and the side of the hopper is equipped with a sight hole and a calibrated measuring device.
(4) Head and mold: The head is composed of alloy steel inner sleeve and carbon steel outer sleeve, and the head is equipped with a molding mold. The role of the head is to transform the rotating plastic melt into a parallel linear motion, which is evenly and smoothly introduced into the mold sleeve and gives the plastic the necessary molding pressure. The plastic is plasticized and compacted in the barrel of the machine and flows through the neck of the head through a certain flow path through the perforated filter plate into the forming mold of the head, and the mold core and mold sleeve are properly matched to form an annular gap with decreasing cross-section so that the plastic melt forms a continuous dense tubular cladding layer around the core line.
In order to ensure that the plastic flow channel in the head is reasonable and to eliminate the dead angle of the accumulated plastic, there is often a diversion sleeve placed, and to eliminate the pressure fluctuation of plastic extrusion, there is also a pressure equalization ring set. The head is also equipped with a die correction and adjustment device to facilitate the adjustment and correction of the concentricity of the die core and die sleeve.
The extruder head is divided into an angled head (120o angle) and a right angle head according to the angle between the head material flow direction and the screw centerline. The shell of the head is bolted to the machine body, the die inside the head has a die core sitting and is fixed to the head inlet port with a nut, the front of the die core seat is equipped with a die core, and the center of the die core and die core seat has a hole for passing the core;
the front of the head is equipped with an even pressure ring for equalizing the pressure; the extrusion package forming part is composed of a die sleeve seat and die sleeve, and the position of the die sleeve can be adjusted by bolts through the support to adjust the die sleeve to the die core The position of die sleeve can be adjusted by bolts through support to adjust the relative position of die sleeve to die core, which is convenient to adjust the uniformity of thickness of the extruded layer. The outside of the head is equipped with a heating device and a temperature measuring device.
The role of the transmission system is to drive the screw, supply the screw in the extrusion process required torque and speed, usually by the motor, reducer and bearings, etc.
Heating and cooling are necessary conditions for the plastic extrusion process to be able to carry out.
(1) Nowadays, the extruder is usually heated by electricity, which is divided into resistance heating and induction heating, and the heating piece is installed in the body, neck and head parts of the machine. The heating device from the outside heats the plastic inside the barrel so that it heats up to reach the temperature required for the process operation.
(2) The cooling device is installed to ensure that the plastic is in the temperature range required for the process. Specifically, it is to exclude the excess heat generated by the shear friction of the rotating screw in order to avoid the high temperature of plastic decomposition, scorching or setting difficulties. Barrel cooling is divided into two kinds of water-cooled and air-cooled, generally small and medium-sized extrusion machine using air-cooled is more appropriate, large is more water-cooled or a combination of two forms of cooling;
screw cooling is mainly used in the center of water-cooled, the purpose is to increase the rate of solid material delivery, and stabilize the amount of rubber while improving product quality; but the cooling at the hopper, Purpose One is to strengthen the role of solid material delivery, to prevent the plastic grain sticky blockage because of the heating, The second purpose is to ensure the normal work of the transmission part.