Extruders and injection molding machines

The usual plastic machinery is generally divided into two types, extruder is one of them, the other is injection molding machine. The extruder is to extrude the molten plastic through the extruded outlet of a fixed shape under the action of the screw, and cut it after being shaped by water cooling under the action of the tractor, which is mainly used for the mass continuous production of a variety of products of the same section, such as tuberodprofile, etc., and can also be used for plastic modification and granulation.
The injection molding machine is to inject molten plastic into the mold, and after cooling, it is a product, which is very widely used, and the place of use is different depending on the plastic. The main machine of the plastic extruder is the extruder, which is composed of an extrusion system, a transmission system and a heating and cooling system.
1. Extrusion system The extrusion system includes screw, barrel, hopper, machine head, and mold, and the plastic is plasticized into a uniform melt through the extrusion system, and under the pressure established in this process, the screw is continuously extruded head.
(1) Screw: is the most important component 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.
(2) Barrel: It is a metal cylinder, generally made of alloy steel with high heat resistance, high compressive strength, strong wear resistance and corrosion resistance or composite steel pipe lined with alloy steel. The barrel and screw cooperate to achieve crushing, softening, melting, plasticizing, exhausting and compaction of plastics, and continuously and uniformly convey the rubber to the molding system. Generally, the length of the barrel is 15~30 times of its diameter, so that the plastic is fully heated and fully plasticized as the principle.
(3) Hopper: The bottom of the hopper is equipped with a truncating device to adjust and cut off the material flow, and the side of the hopper is equipped with a viewing hole and a calibration metering device.
(4) Machine head and mold: The machine head is composed of alloy steel inner sleeve and carbon steel outer jacket, and the machine head is equipped with a forming mold. The function of the machine head is to transform the plastic melt of the rotating movement into a parallel linear motion, evenly and smoothly into the mold sleeve, and give the plastic the necessary molding pressure. The plastic is plasticized and compacted in the barrel, and flows into the head forming mold through the neck of the machine head along a certain flow channel through the porous filter plate, and the mold core mold sleeve is properly matched to form an annular void with a decreasing cross-section, so that the plastic melt forms a continuous dense tubular coating layer around the core wire. In order to ensure that the plastic flow channel in the machine head is reasonable and eliminate the dead angle of the accumulated plastic, a shunt sleeve is often placed, and in order to eliminate the pressure fluctuation during plastic extrusion, there is also a pressure equalizing ring. The machine 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 mold sleeve.
The extruder divides the head into an angled head (angle 1200) and a right-angle head according to the direction of the head flow and the angle of the screw centerline. The shell of the machine head is fixed on the fuselage with bolts, the mold in the machine head has a mold core seat, and is fixed in the head wire entry port with a nut cap, the front of the mold core seat is equipped with a mold core, and the center of the mold core and the mold core seat has holes for passing through the core wire; A pressure equalizing ring is installed in the front of the machine head for equalizing the pressure; The extrusion forming part is composed of a mold sleeve seat and a mold sleeve, and the position of the mold sleeve can be adjusted by bolts through support to adjust the relative position of the mold sleeve to the mold core, which is convenient to adjust the uniformity of the thickness of the extruded cladding layer. The outside of the machine head is equipped with a heating device and a temperature measuring device.
2. Transmission system The function of the transmission system is to drive the screw and supply the torque and speed required by the screw in the extrusion process, which is usually composed of motor, reducer and bearing.
3. Heating and cooling device Heating and cooling are necessary conditions for the plastic extrusion process to be carried out.
(1) Now the extruder usually uses electric heating, divided into resistance heating and induction heating, and the heating sheet is installed in the body, neck and head. The heating device heats up the plastic inside the external heating cylinder to reach the temperature required for 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 exclude excess heat generated by the shear friction of screw rotation to avoid excessive temperature and make it difficult to decompose, scorch or set the plastic. Barrel cooling is divided into two types: water cooling and air cooling, generally small and medium-sized extruders use air cooling is more suitable, large ones mostly use water cooling or two forms of combined cooling; Screw cooling mainly adopts central water cooling, the purpose is to increase the solid conveying rate of materials, stabilize the amount of glue, and improve product quality; However, the cooling at the hopper, one is to strengthen the conveying effect of solid materials, to prevent the plastic particles from sticking and blocking the material mouth due to heating, and the other is to ensure the normal operation of the transmission part. Precautions for the use of extruder:
1. The extruder should run in a positive direction to avoid reversal.
2. Avoid running on an empty stomach, and must heat the machine to add materials, so as to avoid the phenomenon of sticky rod (shaft).
3. It is strictly forbidden to enter the iron and other miscellaneous in the feed port and air vent of the extruder, so as not to cause accidents and affect production.
4. Safe use of electricity, grounding wire.
5. When the machine is running, it is forbidden to touch the rotating parts such as feeding port, discharge port, belt, gear, etc. by hand.
6. Lubricating oil should be injected before the machine is used to avoid damage to the machine.
Extruders, as one of the three major synthetic materials, have developed rapidly since their advent. Plastic instead of steel, plastic instead of non-ferrous metals, plastic instead of cement, etc., are widely used in agriculture, building materials, packaging, machinery, electronics, automobiles, home appliances, petrochemical and national defense, extruders and people's daily life and other fields. Therefore, it can be predicted that in the 21st century, plastic will be one of the most important raw materials for human activities. Extruder design Since extrusion molding is the most important form of plastic processing, it is of great significance to develop plastic extrusion molding technology and equipment. There are three main categories of new mixing equipment used in the blending and modification of polymer materials: co-directional parallel twin screw extruder, reciprocating mobile screw mixer and tandem grinding disc extruder. Among them, the small and medium-sized co-directional parallel twin screw extruder can be produced in China, and the extruder technology but the 10,000-ton large-scale mixing and extrusion granulation unit all rely on imports. Meantime. Reciprocating mobile screw mixer and tandem grinding disc extruder is a necessary device for the preparation of high filling, high value-added polymer alloy, at present, the domestic development of them is just in the prototype stage, the specifications are not much, the variety is not complete, has broad development prospects.