The extrusion system includes a screw, barrel, hopper, head, and mold, through which the plastic is plasticized into a homogeneous melt, and under the pressure established in this process, the head is continuously extruded by the screw.
(1) Screw: It 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, which is generally made of alloy steel with high heat resistance, high compressive strength, strong and wear-resistant, corrosion-resistant alloy steel or composite steel pipe lined with alloy steel. The barrel cooperates with the screw to crush, soften, melt, plasticize, vent and compact the plastic, and continuously and evenly conveys the rubber material to the molding system. Generally, the length of the barrel is 15~30 times of its diameter, so that the plastic can be fully heated and fully plasticized.
(3) Hopper: The bottom of the hopper is equipped with a cut-off device in order to adjust and cut off the material flow, and the side of the hopper is equipped with a sight 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 in rotational motion into parallel linear motion, which is evenly and smoothly introduced into the mold sleeve and gives the plastic the necessary molding pressure. The plastic is plasticized and compacted in the barrel, and flows into the head forming mold through a certain flow channel along the perforated filter plate through the nose neck, 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 and dense tubular coating layer around the core. 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 a pressure equalizing ring is also set to eliminate the pressure fluctuation during plastic extrusion. The machine head is also equipped with a device for mold correction and adjustment, which is convenient for adjusting and correcting the concentricity of the mold core and mold sleeve.
According to the direction of material flow of the machine head and the angle of the center line of the screw, the extruder divides the machine head into an inclined angle head (including angle 120o) and a right-angle machine head. The shell of the machine head is fixed on the fuselage with bolts, the mold in the machine head has a mold core sitting, and is fixed on the head inlet port with a nut, 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 a hole for passing through the core wire; The front part of the head is equipped with a pressure equalizing ring for equalizing the pressure; The extruded forming part is composed of a mold sleeve seat and a mold sleeve, and the position of the mold sleeve can be adjusted by a bolt through a support to adjust the relative position of the mold sleeve to the mold core, so as to facilitate the uniformity of the thickness of the extruded cladding layer. The outside of the 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 an electric motor, a reducer and a bearing.
3. Heating and cooling device
Heating and cooling are necessary for the plastic extrusion process to take place.
(1) At present, the extruder usually uses electric heating, which is 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 cylinder 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 high temperature that makes it difficult for the plastic to decompose, scorch, or set. Barrel cooling is divided into two types: water-cooled and air-cooled, generally small and medium-sized extruders are more suitable for air-cooling, and large-scale extruders are mostly water-cooled or two forms of combined cooling; The screw cooling mainly adopts central water cooling, which is to increase the solid conveying rate of materials, stabilize the amount of glue, and improve product quality. However, the cooling at the hopper is to strengthen the conveying effect of solid materials, prevent the plastic particles from sticking and blocking the material mouth due to the rising temperature, and ensure the normal operation of the transmission part.
