How to control the setting temperature of extruder molding process

The temperature control of extrusion molding throughout,including feeding section (feeding raw material section), melting section (compression section) and metering section (homogenization section). The heat from the temperature increase has two sources:one external heating, the other internal mechanical friction and shearing. Feeding section and metering section are the key and difficulty of temperature regulate in the whole extrusion process. It should be remembered that the temperature control body is material temperature rather than the temperature of the screw and the mold. The following temperature control machine setting knowledge is for practical reference only. 

1、Feeding section (Feeding Raw Material section)
The barrel temperature of the feeding section should be controlled at 100~140℃ generally. If the feeding temperature is too low, the solid conveying area will be prolonged, while the length of the plasticizing area and melt conveying zone will be reduced, which will cause bad plasticizing and affect the product quality. In practice, it is also recommend that the temperature of the feeding section be set at 185-195℃,because the temperature of the feeding section is transferred to the screw by the electric heater, and the temperature displayed is the temperature of the screw barrel, not the temperature of the material.The material temperature is often far lower than the displayed temperature, the actual material temperature is only 100~130℃.

2、Melting section (compression section)
The temperature of material plasticizing zone is controlled at 170~190℃. Control the vacuum degree in this section is a significant process index, if the vacuum degree is low, it will affect the exhaust influence, resulting in bubbles in the pipe, seriously reduce the mechanical properties of the pipe. In order to make the gas inside the material to escape easily, the plasticization degree of the material in this section should not be too high, and the exhaust pipes are supposed to be cleaned frequently to avoid blocking. The vacuum degree of barrel is generally 0.08~0.09MPa.  

3、Metering section (homogenization section)
The temperature of the measurement section should be slightly lower, generally 160~180℃. It is mainly based on extruder shear performance and extrusion capacity,to make sure displayed temperature is 185℃. For thermal sensitive plastics such as PVC, should not stay too long in this period , screw speed is generally 20~ 30R /min. The head is a vital part of extrusion molding, which is to produce higher melt pressure and shape the melt into the desired form.The melt temperature is too high will accelerate the decomposition of PVC into product yellowing,discoloration line, foaming and so on which will affect products quality. Consequently,if necessary, the screw temperature and feeding speed can be adjusted respectively.

4、The reason why extrusion mould body need control temperature is to prevent the melt from cooling in the mold. It is generally set at about 185℃. In the production process of most products,there is no problem with the temperature setting in this range. Some products (bellows) are higher than this, reaching 190℃.

5、Mouth mould temperature: generally set at 190℃ ~ 210℃, depending on the product extrusion surface brightness and extrusion pressure size. In general, increasing mouth model temperature can reduce the friction shear heat in the extruder, and vice versa.  

Dongguan Songhu Plastic Machinery Corp. adopts advanced temperature control device, temperature control precision reaches ±0.1℃, provides a strong guarantee for the temperature control of extrusion molding.  

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