Brief Description of Plastic Extruder Molding Control

A.Heating and cooling system

The heating and cooling system of the extruder mainly refers to the heating and cooling of the barrel (also including the molding die and screw) in the extrusion plasticizing system.The purpose of heating or cooling the barrel (forming mold and screw) is to control the process temperature of the raw materials during extrusion and plasticization and limit it to a certain range to ensure the normal production of plastic products made by the plastic extruder.

Heating of barrel

The heating methods of the barrel (forming mold) in the extruder include resistance heating, electric induction heating and heat carrier heating. At present, the most commonly used heating method is resistance heating.

1) Resistance heating.
The resistance heating method has a relatively simple structure. It mainly allows the current to pass through a wire (resistance wire) with a relatively large resistance to generate heat and conduct it to the barrel that needs to be heated. The cast aluminum sleeve resistance heater installs the resistance wire in a metal tube, fills the tube with insulating materials such as magnesium oxide powder, and then casts the metal tube in aluminum alloy. This kind of resistance wire heating cast aluminum sleeve resistance heater. The resistance wire is insulated with magnesium oxide insulating powder in the tube and is well sealed, which prevents premature oxidation of the resistance wire and has a long life. The contact area between the aluminum alloy sleeve and the outer circle of the barrel is large. , good heat transfer performance.

2) Electric induction heating.
Electric induction heating device. When the barrel adopts electric induction heating, a coil is installed on the outer circumference of the barrel, and a magnetic conductive silicon steel sheet is installed around the coil. When current passes through the coil, the silicon steel sheet and the barrel form a closed magnetic circuit. The alternating magnetic flux induction causes the barrel to generate current, and the barrel generates heat due to its certain resistance value. The barrel adopts the electric induction heating method to heat up quickly, and the materials used to make up the inductor have a long working life, but the components used to make up the inductor are more complicated.

3) Heating by heat carrier.
Heating machines that use water vapor or oil as the heat carrier require pipeline transportation and a heating source (boiler or resistance heat source) for the heat carrier. The equipment is complex, expensive, and temperature control is difficult, so it is very practical. However, this heating method has a gentle and even temperature, which is very suitable for heating heat-sensitive plastics.

Cooling of barrel

The cooling of the screw and barrel of the extruder, the cooling of the plasticizing part of the extruder, the cooling of the hopper seat and the cooling of the screw. Cooling of the extruded plasticized part in the machine. The cooling of the plasticized part is mainly a cooling measure to prevent the temperature of the machine from being too high during operation. There are two cooling methods: water cooling and air cooling. At present, the most widely used method is air cooling. It uses a fan to directly blow the parts of the barrel that need to be cooled, and the cold air takes away the heat of the barrel, thereby achieving the purpose of cooling the barrel. The fan cooling barrel method is simple, the equipment structure is simple, the thermal impact on the barrel is small, the cost is not high, and maintenance and production operations are relatively convenient.

Cooling of the hopper seat

Cooling water is often used for cooling the hopper seat. The purpose of cooling is to prevent excessive heat generated in the hopper due to forced feeding. In addition, it is also to prevent the temperature of the screw feeding section from being too high. If the temperature of these two parts is too high, it will mainly affect the feed of the hopper and the forward transportation of materials entering the screw feeding section.

Cooling of the screw

Heat-conducting medium oil is commonly used for screw cooling. A rotary joint structure is used to connect the center hole of the rotating screw to the oil pipeline. The heat-carrying medium oil passes into the screw body through the rotary joint and takes away the heat of the screw to achieve the purpose of cooling the screw.

B.Control system

The control system of the extruder mainly refers to the control of the working speed of the screw, the heating temperature of each barrel section, the temperature of the molding die, and the pressure required for the molding of molten materials for products. The function of these part control devices is to ensure that the extruder works within the set process conditions, so that the extruder can produce molded plastic products stably and smoothly.