The function of three functional zones of PVC EXTRUDER
The melting temperature and degradation temperature of PVC are close to each other, so it is necessary to prevent the degradation of PVC melt while plasticizing. Therefore, generally according to the work function division, with the extruder screw barrel exhaust hole as the boundary, can be divided into two functional areas: Feeding Section and compression section is called heating zone, melting section and metering section become constant temperature zone. The confluent core and die after the extruder are called the heat preservation zone.
The functions of the three functional zones of the extruder are different.
Generally, under the normal production condition, the material enters the feeding section and the compression section, because the temperature difference between just entering the extruder and the temperature set is too large, and the shearing heat effect is not obvious, mainly relies on the heating ring to provide a large amount of external heat Therefore, the heating ring does not need to stop working, so called these two sections of the heating zone. Mainly by external heating and screw shearing, calendering and friction combined action, provide heat (the so-called shear heat, namely by the screw relative screw motion, material between the screw and the friction heat between the screw tube; one screw edge and the other screw groove bottom of the material caused by calendering heat; between the two screw sheared material generated shear heat. The three sources of heat due to shear heat accounted for the largest proportion, generally referred to as shear heat) .
The melt has been basically plasticized after compression into the melting section and the metering section, and even has a surplus of "shearing heat" . The goal of temperature control at this stage is not to further heat supply, but to timely implement "cooling" when the melt is "over temperature" To get the excess heat out. Only in the case of large heat loss of the screw tube, occasionally to supplement the heat loss, so called the two sections "constant temperature zone. ".
When the melt enters the confluent core and die, it has already changed from the spiral variable velocity to the linear uniform velocity, so the shear heat is no longer existed. A part of the heat is consumed when the melt reaches the die along the flow path specified by the confluent core. In order to ensure that the melt moves uniformly along the swallow tail channel of the die, an appropriate amount of heat needs to be added, and the die is set at a slightly higher temperature Therefore, it is called "thermal insulation area" .