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Extruder The Solid Material Is Melted And Melted Into A Homogeneous Melt And Continuously Extruded

The role of the extruder is to melt the solid material into a uniform temperature melt and continuous extrusion. Depending on the state of the material in the extruder and the role of the various parts of the extruder, the extruder barrel can be divided into three parts according to the axial direction of the screw, solidification of plastic melt and melt , The three functional segments are not exactly the same as the three geometric segments (feeding section, compression section and metering section) of the standard screw. The boundaries of the functional section vary with the performance and process conditions of the material used, while the geometrical section is fixed: to achieve stable yield and quality of the extruded plastic product, on the one hand, The mass flow rate of the cross section must be kept constant and equal to the yield; on the other hand, the melt delivery rate should be equal to the melting rate of the material.

(1) solid transport solid transport is the basis of all plastic extrusion process, its main role is to solid material after the melt into the melt section. Solid transport is carried out in the barrel feed section, the material from the hopper into the extruder and the barrel of the inner wall of the composition of the space, was compacted to form a solid plug (bed). And moving at a constant rate, the movement of the solid plug is related to the friction between the material and the screw and the barrel. If the friction between the material and the screw is less than the friction between the material and the barrel, Instead, the material rotates together with the screw.

(2) melt plasticization by the feeding section of the solid material transported in the extruder melting section through the barrel outside the heater heating and heating of the material and the role of heat under the joint heat, and gradually melt, and finally completely become melting body. The melt of the material is carried out in such a way that the dense solid bed is in contact with the surface of the heated barrel and forms a melt film on the surface of the barrel which is constantly thickened and when the thickness of the melt film is greater than When the ribs are in the gap with the barrel, the melt is "scraped" by the ribs and sent to the advancing surface of the thread to form the melt pool. Heat through the melt - solid interface continue to pass to the solid bed, so that the solid bed heating up, the width is decreasing, the melt pool width gradually increased, and finally the solid bed completely disappeared, that is, the material completely melted.

(3) melt transfer melt transfer is from the complete melting of the material began, its main function is to further mix the molten material, homogenization, and to overcome the considerable flow resistance to the die delivery. The melt flow in the melt section has four basic forms of positive flow, countercurrent, cross flow and leakage. The true flow of the melt in the extruder is a combination of these four basic flows. The positive flow is the flow of the melt along the groove in the direction of the die, and the countercurrent is caused by a pressure gradient caused by the choke and so on. The flow direction is opposite to the positive flow. The cross flow is due to the relative movement of the screw and the barrel in the direction perpendicular to the direction of the melt caused by the melt flow, due to the constraints of the threaded side wall, this flow is generally circulation. This circulation has a great effect on the mixing and homogenization of the melt, but has little effect on the total flow rate. Leakage is also caused by the pressure gradient, it is the melt from the screw and the barrel of the gap along the screw axial to the hopper in the direction of the flow, because the gap between the screw and the barrel is small, leakage and the positive flow compared to small many.

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