a large manufacturer of plastic extrusion machinery in China

What is a plastic extrusion machine?

In the plastic extrusion molding equipment, the plastic extruder is usually called the main machine, and the supporting equipment plastic extrusion molding machine, is called the auxiliary machine. After more than 100 years of development, the plastic extruder has evolved from the original single screw, such as twin screw, multi-screw, and even no screw. Plastic extruder (main machine) can be used with various plastic molding auxiliary machines, such as pipes, films, holding materials, monofilaments, flat filaments, packing belts, extruded nets, plates (sheets), profiles, granulation, and cable coating. Match and form various plastic extrusion molding production lines to produce various plastic products. Therefore, plastic extrusion molding machinery is one of the widely used machines in the plastic processing industry, now and in the future.

Composition of the plastic extrusion machine

The main machine of a plastic extrusion machine is an extruder, which is composed of an extrusion system, a transmission system and a heating and cooling system.

Extrusion system

The extrusion system includes a screw, a barrel, a hopper, a head, and a die. 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.

1. Screw: It is the most important part of the extruder. It is directly related to the application range and productivity of the extruder. It is made of high-strength and corrosion-resistant alloy steel.
2. Barrel: It is a metal cylinder, which is generally made of alloy steel or composite steel pipe lined with heat-resistant alloy steel, high compressive strength, strong, wear-resistant, and corrosion-resistant. The barrel cooperates with the screw to achieve the crushing, softening, melting, plasticizing, venting, and compacting of the plastic, and continuously and uniformly conveys the rubber to the molding system. Generally, the length of the barrel is 15 to 30 times its diameter. The principle is to make the plastic fully heated and fully plasticized.
3. Hopper: The bottom of the hopper is equipped with a cutting device to adjust and cut off the material flow. The side of the hopper is equipped with a sight hole and a calibration metering device.
4. Machine head and die: The machine head is composed of an alloy steel inner sleeve and a carbon steel outer cover. The machine head is equipped with a forming die. The function of the machine head is to convert the plastic melt that rotates into parallel and linear movement, which is evenly and smoothly introduced.

In the mold sleeve, the plastic is given the necessary forming pressure. The plastic is plasticized and compacted in the barrel, and passes through the porous filter plate along a certain flow path through the neck of the head and flows into the head forming mold. The core mold sleeve is properly matched to form a circular gap with a decreasing cross-section, so that the plastic melt is in the A continuous and dense tubular coating is formed around the core wire.

In order to ensure that the plastic flow path in the machine head is reasonable and to eliminate the dead angle of the accumulated plastic, a shunt sleeve is often installed. In order to eliminate the pressure fluctuation when the plastic is extruded, there is also a pressure equalizing ring. The head is also equipped with a mold correction and adjustment device, which is convenient for adjusting and correcting the concentricity of the mold core and the mold sleeve.

The extruder divides the machine head into a beveled machine head (with an included angle of 120 °) and a right-angle machine head according to the angle between the head material flow direction and the centerline of the screw. The shell of the machine head is fixed to the fuselage with bolts. The die in the machine head has a core seat and is fixed to the wire inlet port of the head with a nut. The front of the core seat is equipped with the core, the core, and the core seat. There is a hole in the center for passing the core wire. There is a pressure equalizing ring on the front of the machine head for equalizing pressure. The extrusion molding part is composed of a die sleeve and a die sleeve. The position of the die sleeve can be adjusted by the bolt through the support In order to adjust the relative position of the mold sleeve to the mold core, it is easy to adjust the uniformity of the thickness of the cladding layer. The head is equipped with a heating device and a temperature measuring device.

Transmission system

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

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

For the extruder with the same screw diameter, the high-speed and high-efficiency extruder consumes more energy than the conventional extruder, doubles the motor power, and the size of the reducer must be increased accordingly. But high screw speeds mean low reduction ratios. For gearboxes of the same size, compared with gearboxes with low reduction ratios, the gear modulus increases, and the capacity of the gearboxes to withstand load increases. Therefore, the increase in volume and weight of the reducer is not linearly proportional to the increase in motor power. If the amount of extrusion is used as the denominator, divided by the weight of the reducer, the number of high-speed and efficient 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.

Heating and cooling device

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

1. The extruder usually uses electric heating, which is divided into resistance heating and induction heating. The heating sheet is installed in the body, neck, and head. The heating device heats the plastic in the cylinder externally to increase the temperature to reach the required temperature for the process operation.

2. The cooling device is set to ensure that the plastic is in the temperature range required by the process. Specifically, it is to exclude the excess heat generated by the shear friction caused by screw rotation, to avoid the temperature being too high to make the plastic decompose, scorch, or shape difficult. The barrel cooling is divided into two types: water cooling and air cooling. Generally, small and medium-sized extruders are more suitable for air cooling, and large-sized ones are mostly water-cooled or combined with two forms of cooling. To stabilize the amount of glue and improve product quality, but the cooling at the hopper is to strengthen the transport of solid materials, to prevent plastic particles from sticking due to temperature rise, and to ensure the normal operation of the transmission part.

Plastic extrusion machine type

Plastic extruders can be divided into single screw extruders, twin screw extruders, and multi-screw extruders according to the number of screws. At present, a single screw extruder is the most widely used and suitable for the extrusion processing of general materials. The twin-screw extruder has less heat generated by friction, more uniform shearing of the material, larger screw conveying capacity, more stable extrusion capacity, longer material stay in the barrel, and uniform mixing.

The single-screw extruder occupies an important position, whether it is a plasticizing granulation machine or a molding processing machine. In recent years, the single-screw extruder has developed greatly.

The twin screw extruder has good feeding characteristics, is suitable for powder processing, and has better mixing, venting, reaction, and self-cleaning functions than the single screw extruder. It is characterized by processing plastics and blends with poor thermal stability. Shows its superiority when the material. On the basis of twin-screw extruders, in order to more easily process blends with poor thermal stability, multi-screw extruders, such as Guanghua Plastic Extruder, have been developed.

1. According to the number of screws, it is divided into single-screw extruders, twin-screw extruders, and multi-screw extruders.
2. According to whether there is a screw in the extruder, it is divided into screw extruders and plunger extruders.
3. According to the operating speed of the screw:
   1. Ordinary extruder: Rotation speed is below 100r / min;
   2. High-speed extruder: rotation speed is 100 ～ 300r / min;
   3. Ultra-high speed extruder: Rotation speed is 300 ～ 1500r / min.
4. Classification according to the assembly structure of the extruder: there are integral extruders and separate extruders;
5. According to the space position of the screw in the extruder, it can be divided into horizontal extruders and vertical extruders;
6. According to whether the extruder is vented during processing, it can be divided into a vented extruder and a non-vented extruder.