The structure of the nose
from the extrusion of plastic parts, although have established shape, the temperature is higher, but because of the product due to gravity deformation will happen, so you need to use the sizing device will be the shape of the parts for cooling to finalize the design, which can meet the requirements of the correct size, geometric shape and surface quality. Usually adopt the method of cooling, pressure or vacuum, the extrusion of plastic pieces from the nose shape set temperature, and finishing, to get more accurate cross section size, surface more bright plastic parts.
for head does not need to tap device, melt through the nose after intermediate port, its width must be increased, need an extension area, in order to reduce or plastics melt density does not, therefore, in the compression of the nose should be set in a certain area, produces a certain resistance to flow, packaging plastic melt or a compact organization. To consider plastic parts from mould expansion effect and the effect of shrinkage, can ensure the cross section shape of the plastic.
as many specifications of plastic parts, therefore the nose is also used in the production of a variety of. According to the plastic pieces from the nose of the extrusion in a different direction, can be divided into straight through the nose and Angle of the nose, etc. In through the nose, the melt in the nose of the extrusion flow parallel to the axis of the extruder screw. In the Angle of the nose, melt in the nose of the extruder screw axis Angle, when the melt extrusion flow with the screw axis vertical, called a crosshead.
according to the size of the pressure on the plastic melt in the nose, divided into low pressure head and high pressure head. Low pressure head is melt pressure is less than 4 mpa the nose. High pressure head namely melt pressure is greater than 10 mpa. According to the need to molding plastic parts structure characteristics and process requirements, the right to choose the structure of the nose. Melt in the cylinder by the action of the screw rotation, through the nose, the melt spinning movement must be transformed into linear motion for molding flow, at the same time, it must be appropriate on the melt flow resistance, make the screw on the melt pressure appropriately.
head body is equal to the die set, used to assemble and bearing parts of the nose, and connected with extruder cylinder. In order to ensure that the plastic melt in the nose to the normal flow and quality of extrusion molding, general equipped with temperature control system on the nose. Adjustment screw is used to adjust control molding in the mouth and the clearance between the mandrel and alignment, to ensure the extrusion molding processing parts uniform wall thickness, usually the number of the adjusting screw for 4 - Eight.
set filter plate and filter in the nose, can will melt the rotation movement into linear motion, at the same time increase the melt flow resistance. In order to reduce the pressure loss, make the flow of the melt along the flow channel is steady, the nose of the inner surface must be smooth, sleek, cannot have the part of the stop band, the surface roughness should be less than 0. 1. In order to make the molten material into the machine head further plasticizing, inside the nose are generally set up shunt and shunt stent shunt device, make the melt into the mold mouth before must through the shunt device in the nose.
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