Composition of plastic extruder

I. extrusion system

The extrusion system includes a screw, a barrel, a hopper, a head, and a mold. The plastic is plasticized into a uniform melt through the extrusion system, and is continuously extruded by the screw under the pressure established in the process.

⑴Screw: It is the most important part of the extruder, which is directly related to the application range and productivity of the extruder, and is made of high-strength and corrosion-resistant alloy steel.

⑵Cylinder: It is a metal cylinder, generally made of heat-resistant, high compressive strength, strong wear-resistant, corrosion-resistant alloy steel or composite steel pipe lined with alloy steel. The barrel cooperates with the screw to realize the crushing, softening, melting, plasticizing, exhausting and compacting of the plastic, and continuously and uniformly transport the rubber to the molding system. Generally, the length of the barrel is 15 to 30 times its diameter, so that the plastic can be fully heated and plasticized as a principle.

(3) Hopper: A cut-off device is installed at the bottom of the hopper to adjust and cut off the material flow. The side of the hopper is equipped with a viewing hole and a calibration metering device.

⑷ Machine head and mold: The machine head is composed of an alloy steel inner sleeve and a carbon steel outer sleeve. There is a forming mold inside the machine head. Set, and give the plastic the necessary molding pressure. The plastic is plasticized and compacted in the machine barrel, and flows into the molding mold of the machine head through the porous filter plate along a certain flow channel through the neck of the machine head. A continuous dense tubular covering is formed around the core wire. In order to ensure that the plastic flow path in the machine head is reasonable and eliminate the dead angle of accumulated plastic, a shunt sleeve is often installed. In order to eliminate pressure fluctuations during plastic extrusion, a pressure equalizing ring is also installed. There is also a mold correction and adjustment device on the machine head, which is convenient for adjusting and correcting the concentricity of the mold core and mold sleeve.

According to the angle between the flow direction of the head and the center line of the screw, the extruder divides the head into a beveled head (120o included angle) and a right-angled head. The shell of the machine head is fixed on the machine body with bolts. The mold inside the machine head has a core seat and is fixed on the inlet port of the machine head with a nut. The front of the core seat is equipped with a core, the core and the core seat There is a hole in the center for passing the core wire, and a pressure equalizing ring is installed at the front of the machine head for equalizing the pressure. The extrusion molding part is composed of a die sleeve seat and a die sleeve. The position of the die sleeve can be adjusted by the bolt through the support. , to adjust the relative position of the mold sleeve to the mold core, so as to adjust the uniformity of the thickness of the extruded cladding, and the outside of the head is equipped with a heating device and a temperature measuring device.

II. transmission system

The function of the transmission system is to drive the screw and supply the torque and speed required by the screw during the extrusion process. It is usually composed of a motor, a reducer and a bearing.

On the premise that the structure is basically the same, the manufacturing cost of the reducer is roughly proportional to its overall size and weight. Because the shape and weight of the reducer are large, it means that more materials are consumed during manufacturing, and the bearings used are also relatively large, which increases the manufacturing cost.

For extruders with the same screw diameter, high-speed and high-efficiency extruders consume more energy than conventional extruders, the power of the motor is doubled, and the frame size of the reducer is correspondingly increased. But high screw speed means low reduction ratio. For the reducer of the same size, the gear modulus of the low reduction ratio is larger than that of the large reduction ratio, and the load bearing capacity of the reducer is also increased. Therefore, the increase in volume and weight of the reducer is not linearly proportional to the increase in motor power. If the extrusion volume is used as the denominator and divided by the weight of the reducer, the number of high-speed and high-efficiency extruders is small, and the number of ordinary extruders is large.

In terms of unit output, the motor power of the high-speed and high-efficiency extruder is small and the weight of the reducer is small, which means that the unit production cost of the high-speed and high-efficiency extruder is lower than that of ordinary extruders.

III. heating and cooling device

Heating and cooling are necessary conditions for the plastic extrusion process to work.

⑴The extruder usually uses electric heating, which is divided into resistance heating and induction heating. The heating sheet is installed in each part of the fuselage, machine neck and machine head. The heating device heats the plastic in the cylinder externally to heat up to the temperature required for the process operation.

(2) The cooling device is set up to ensure that the plastic is in the temperature range required by the process. Specifically, it is to eliminate the excess heat generated by the shear friction of the screw rotation, so as to avoid the plastic decomposition, scorch or difficulty in shaping due to excessive temperature. There are two types of barrel cooling: water cooling and air cooling. Generally, air cooling is more suitable for small and medium-sized extruders, and water cooling or a combination of the two types of cooling is often used for large-scale extruders. The screw cooling mainly uses central water cooling to increase the solid delivery rate of materials. , stabilize the glue output, and improve product quality at the same time; but the cooling at the hopper is to strengthen the conveying effect on solid materials and prevent plastic particles from sticking due to temperature rise and block the feed port, and the second is to ensure the normal operation of the transmission par