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Heating system of plastic extruder for cable production equipment

Author：hlyb Add Time：2016-04-20 09:18:16

Temperature is the main condition for plastics to change from solid particle state to viscous flow state. The temperature heating control system of extruder is an important facility to realize the transformation of plastic state. Poor temperature control has a great impact on product quality.

1、 Temperature control system

The temperature control system of the extruder is composed of electric heating and cooling to realize the rise and fall and adjustment of the temperature in each area of the extruder. Controlling the appropriate temperature can ensure the extrusion quality.

1. Temperature control mechanism

The electric heater and cooling fan installed on the plastic extruder are the main control mechanisms. Because electric heating has the characteristics of rapid temperature rise and temperature drop, and too high and too low temperature should be avoided in extrusion, electric heating must have a set of temperature regulating device with high sensitivity, Youxi generally includes automatic measuring instruments, control instruments and effective cooling facilities. A measuring element thermocouple is installed at the appropriate position of the extruder (the closer it is to the plastic layer, the better). Thermocouple is an extremely important temperature detection element. In the process of heating and extrusion, the thermoelectric potential signal measured by the thermocouple of the temperature measuring element at any time is sent to the temperature controller. After amplification, it is compared with the temperature setting value. When the temperature instrument indicates that the setting value cannot be reached, it continues to heat. If it approaches or reaches the setting value, the instrument will send different indication signals according to different regulation rules. When the set value is exceeded, start the cooling fan to cool the fuselage, reduce the temperature and return to the preset value. In this way, the temperature can be stabilized near the controlled value by automatic control or manual adjustment.

2. Temperature control part of extruder

According to the extrusion principle, the temperature of each part of the extruder should be different, which can be realized by the capacity difference of the electric heating plate set at each part. Generally, the capacity of feeding section * * * is small, and the capacity of (compression) plasticizing section and homogenizing section is larger, while the head is a thermal insulation area, which is mainly used to overcome heat dissipation, so it is not easy. In the extruder, the temperature control is generally divided into 6 ~ 8 sections according to the number of heating plates. The small plastic extruder is generally divided into six sections, and the large extruder is divided into eight sections. The six heating areas of the extruder are temperature controlled through the display of the temperature instrument on the control screen. Taking the six section heating extruder as an example, the temperatures of the six temperature control parts or heating sections of the extruder can be displayed one by one on the temperature instrument on the control panel, which can be directly observed by the operator for easy adjustment.

3. Functions of temperature control parts

Take the six stage heating extruder as an example. There are six temperature control parts, three at the head of the extruder and three at the fuselage. The temperature can be adjusted automatically as required, but it shall meet the temperature range specified in the process. In the process of use, the temperature in the heating area of the feeding section is low, the temperature in the neck heating area is high, and the temperature in the mold heating area is slightly low, resulting in the change of general temperature control parts from low to high to slightly low, which is determined by the role of each part.

(1) Function of head area 1 and 2: the temperature control of head area plays a decisive role in the surface quality of plastic extrusion. If the temperature is controlled properly and the mold is selected properly, the surface of plastic products will be flat and smooth.

(2) Function of head 3 temperature zone (neck): after the plastic is plasticized, it enters the neck from the barrel under the action of screw rotation. Due to the small volume of the neck compared with the barrel and the role of filter plate, it produces large resistance. The thrust generated by screw rotation makes the plastic dense, plasticized and compacted to ensure the plasticizing effect. At this time, a higher temperature is required, which is conducive to the smooth entry of plastic melt into the head.

(3) Function of temperature zones 4 and 5 of the fuselage: this heating zone is a homogenization section and a plasticization section. Due to the stirring and compression effect of screw rotation, the preheated solid plastic becomes a plastic viscous liquid (molten state). Under the action of temperature, the plastic completes plasticization evenly.

(4) Function of body 6 temperature zone: granular plastic enters the barrel from the feeding hopper. Due to the effect of temperature, the plastic begins to be preheated and the excess gas is discharged from the feeding port. The temperature control of this section should not be too high to avoid affecting the blanking of granular plastics, so it is a heating area with low temperature control area.

2、 Control the influence of temperature on product quality

Temperature is an effective means for plastics to change from solid state to viscous flow state. At the same time, it may also cause scorch or decomposition of plastics. When the temperature is low, it may also cause serious equipment accidents. Due to the difference of plastic varieties, extrusion speed, extrusion outer diameter and extrusion thickness, the temperature control is different in the actual extrusion process. Therefore, the corresponding extrusion temperature is adopted for specific varieties. In addition, in addition to the different temperature control caused by plastic and structural dimensions, the ambient temperature should also be considered. Therefore, it is the responsibility of every operator to strictly control the temperature according to the process requirements, ensure the smooth progress of the extrusion process and ensure good product quality.

(1) Too high temperature: it refers to that the temperature control exceeds the * * * good plasticizing temperature of a certain plastic, which is easy to scorch and age the plastic, and also easy to produce quality problems such as pores, bubbles, air holes, poor setting and so on. If the temperature is too high, the extrusion pressure will fluctuate during the extrusion process, the plastic will "slip" in the barrel, and the extrusion amount will be unstable, resulting in uneven dimensions of the extrusion cladding and the outer diameter of the product.

(2) Low temperature: it refers to that the temperature control is lower than the * * * good plasticizing temperature of plastic, resulting in poor plasticization of plastic, resin bumps or small particles not plasticized on the extruded surface. In particular, poor glue bonding and stitching will not only affect the product quality, but also easily cause disconnection, crack and glue breaking of the plastic layer. Therefore, the temperature should be controlled in strict accordance with the process regulations and should not be too high or too low.

In the actual operation process, the extrusion process and temperature control are different due to the new and old equipment and different outer diameter. The plastics used for Extrusion insulation and sheath are the same, but the temperature control is also different due to different additives in resin. In addition, the ambient temperature will also affect the control of extrusion temperature. The difference between winter and summer is 5 ~ 10oC.

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Heating system of plastic extruder for cable production equipment