The usual plastic machinery is generally divided into two types, Extrusion machine is one of them, and the other is an injection molding machine. The extruder is extruded under the action of a screw through a fixed-shaped outlet, and is cut by water-cooling after being pulled by a tractor. Mainly used for a large number of continuous production of various similar cross-section products, such as tubes, rods, profiles, etc., can also be used for plastic modified granulation. The injection molding machine injects molten plastic into the mold and cools it as a product. It is very versatile and varies from plastic to plastic. The main body of the plastic extruder is a press machine, which consists of a pressing system, a transmission system and a heating and cooling system.
1. The pressing system of the pressing system includes a screw, a barrel, a hopper, a machine head, and a mold, and the plastic is plasticized into a uniform melt by a pressing system, and in the process Under the established pressure, the screw is continuously pushed out of the machine head.
(1) Screw: It is the main component of the press machine. It is directly related to the application range and productivity of the press machine. It is made of high strength and corrosion resistant alloy steel. production.
(2) Barrel: It is a metal cylinder, generally made of alloy steel or inner steel with high heat resistance, high compressive strength, strong wear resistance and corrosion resistance. Made of composite steel pipe lined with alloy steel. The barrel is matched with the screw to realize pulverization, softening, melting, plasticizing, venting and compacting of the plastic, and continuously and uniformly conveying the rubber to the molding system. The length of the general barrel is 15 to 30 times its diameter, so that the plastic is fully heated and fully plasticized.
(3) Hopper: The bottom of the hopper is equipped with a shut-off device to adjust and cut the flow. The side of the hopper is equipped with a sight hole and a calibration metering device.
(4) Handpiece and Mold: The machine head consists of an alloy steel inner sleeve and a carbon steel jacket with a forming die. The function of the machine head is to transform the rotating plastic melt into a parallel linear motion, which is evenly and smoothly introduced into the mold sleeve and imparts the necessary molding pressure to the plastic. The plastic is plasticized and compacted in the barrel, and flows into the head forming mold through the neck of the neck through a porous filter plate along a certain flow path. The mold core sleeve is properly matched to form an annular gap with a decreasing cross section, so that the plastic melt is in the A continuous dense tubular coating is formed around the core. In order to ensure the plastic flow path in the machine head is reasonable, and eliminate the dead angle of the accumulated plastic, a shunt sleeve is often placed. In order to eliminate the pressure fluctuation when the plastic is pushed out, a pressure equalizing ring is also provided. A mold correction and adjustment device is also mounted on the handpiece to facilitate adjustment and correction of the concentricity of the core and the mold sleeve. According to the angle between the flow direction of the machine head and the center line of the screw, the press machine divides the machine head into a bevel head (120o angle) and a right angle handpiece. The outer casing of the machine head is bolted to the fuselage. The mold in the machine head has a core sitting and is fixed to the inlet port of the machine head with a nut. The front of the core seat is equipped with a core, a core and a core holder. The center has a hole for passing the core wire; a pressure equalizing ring is arranged at the front of the machine head for equalizing the pressure; the forming part of the bag is composed of a die sleeve and a die sleeve, and the position of the die sleeve can be adjusted by the bolt through the support In order to adjust the relative position of the die sleeve to the core, it is convenient to adjust the uniformity of the thickness of the die layer. The outside of the machine head is equipped with a heating device and a temperature measuring device.
2. 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, usually by motor, reducer and bearing. composition. 3. Heating and cooling device Heating and cooling are necessary conditions for the plastic extrusion process.
(1) Nowadays, the press machine usually uses electric heating, which is divided into resistance heating and induction heating. The heating piece is mounted on the fuselage, neck and nose. Each part. The heating device heats the plastic in the cylinder from the outside to raise the temperature to achieve the temperature required for the process operation.
(2) The cooling unit is set to ensure that the plastic is within 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 temperature being too high, so that the plastic is decomposed, scorched or shaped. The barrel cooling is divided into two types: water cooling and air cooling. Generally, small and medium-sized presses are suitable for air-cooling. Large ones are mostly water-cooled or combined with two types of cooling. Screw cooling mainly uses central water cooling to increase the solids transport rate. Stabilize the amount of glue and improve the quality of the product; however, the cooling at the hopper is to strengthen the conveying effect on the solid material, prevent the plastic particles from sticking and blocking the material due to the temperature rise, and the second is to ensure the normal operation of the transmission part.
Precautions for use of the extruder:
1, the extruder must be running forward to avoid reverse.
2, avoid running on an empty stomach, must be fed by a hot machine, so as to avoid the occurrence of sticking bars.
3. It is strictly forbidden to enter the iron inlet and other holes in the inlet and outlet of the extruder to avoid accidents and affect production.
4, safe power, ground wire.
5, when the machine is running, the rotating parts such as the feeding port, discharge port, belt, gear, etc. are prohibited from touching by hand.
6, the machine should be injected with lubricating oil before use to avoid damage to the machine. The plastics of the extruder as one of the three major synthetic materials have developed rapidly since its inception. It is widely used in agriculture, building materials, packaging, machinery, electronics, automobiles, home appliances, petrochemicals and national defense, extrusion machines and people's daily life in various fields such as plastics and steels, plastics and non-ferrous metals, and plastics. . It can therefore be predicted that in the 21st century, plastic will be one of the more important raw materials for human activities. Extrusion machine design Because extrusion molding is the main form of plastic processing, it is of great significance to develop plastic extrusion molding technology and equipment. There are three main types of new mixing equipment for blending and modifying polymer materials in the world: co-parallel twin-screw extruders, reciprocating mobile screw mixers and tandem disc extrusion machines. Among them, small-scale parallel-parallel twin-screw extruders have been able to produce in China, and the extruder technology, but the 10,000-ton large-scale mixing and pressing granulators all rely on imports. Simultaneously. Reciprocating screw mixer and tandem disc extruder are necessary equipment for preparing high-filled and high value-added polymer alloys. At present, their development in China is just in the prototype stage, with few specifications and incomplete varieties. Prospects.
