挤出成型工艺（Extrusion process）

挤出成型工艺（Extrusion process） 挤出成型工艺(Extrusion process) Definition of extrusion In the fiber chemical industry, an extruder is also used to feed the spinneret to melt spinning. Extrusion processing applied to thermoplastic plastics and rubber, for batching, granulation, rubber filtration, continuous production, manufacturing various continuous products such as pipe, profile, sheet (or sheets), film coating, rubber tire, tube noodles barrel, a sealing strip and its production high efficiency. In the production of synthetic resin, can be used as reactor extruder, continuous polymerization and processing, in rubber industry, different compression ratio of extruder can be used to unmasticated natural rubber. Different materials compression extrusion machine than some different. Edit the extrusion principle of this paragraph Feed the material bucket into the barrel, the screw rotates under the action of the cylinder wall and the surface of the screw friction shearing forward delivery to the feeding section, this loose solid transport in the forward is compacted; the compression section, screw groove depth, further compaction, and the external heat and screw and cylinder wall friction material in shear. Cylinder, material temperature melting. The compression section ends; homogeneous section material uniform, constant temperature, constant pressure, quantitative extrusion melt, to die after molding, products are obtained by setting the. 1, extrusion method According to plasticizing methods: dry extrusion and wet extrusion Press the way: continuous extrusion and intermittent extrusion 2, characteristics Continuous production, high efficiency, simple operation and wide range of applications Edit this segment extrusion equipment 1 host Extrusion system: composed of screw and barrel, it is the key part of extruder. Its function is to melt the material, quantitative, constant pressure, constant temperature extrusion melt Drive system: drive the screw to increase the required torque and torque Heating and cooling system: guarantee the temperature of plastic and extrusion system in molding process 2 auxiliaries It is composed of head, setting device, cooling device, traction device, coiling device and cutting 3 、 control system It consists of electric apparatus, instrument and actuating mechanism Purpose: to control the main and auxiliary motor, in order to meet the demands of speed and power; control main engine temperature and pressure and flow, to ensure product quality; to achieve automatic control of the extrusion unit, ensure the coordinated operation of main and auxiliary equipment. Edit an overview of this segment extruder The main frame of a plastic extruder is an extruder, which is composed of an extrusion system, a transmission system and a heating and cooling system. 1. extrusion system of extrusion system includes a screw, barrel, hopper, head, and mould, plastic extrusion system by plasticizing evenly into the melt, establish the pressure in this process and, by continuous screw extrusion die. (1) screw: it is the most important component of the extruder. It is directly related to the application range and productivity of the extruder. It is made of high strength corrosion resistant alloy steel. (2) cylinder: it is a metal cylinder. It is usually made of composite steel pipes of heat-resistant, high compressive strength, strong wear resistance, corrosion-resistant alloy steel or lined with alloy steel. The cylinder is matched with the screw rod to realize the crushing, softening, melting, plasticizing, exhausting and compacting of the plastics, and continuously and evenly transport the rubber material to the forming system. The length of the ordinary cylinder 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 visual hole and a calibration measuring device. (4) head and die: the head is made up of alloy steel inner sleeve and carbon steel coat, and the die head is provided with forming die. The role of the head is to change the rotational movement of plastic melt into parallel linear motion, evenly and smoothly into the mold sleeve, and give plastic to the necessary molding pressure. Plastic in the cylinder plastic compaction, through the porous filter plate along the channel through the head neck into the die mold, mold die sleeve with the appropriate form, the annular space section decreases, the plastic melt formed around the tubular continuous dense core wire coating. To ensure that the plastic channel in the nose is reasonable, In order to eliminate the dead corner of the accumulated plastic, a split sleeve is often arranged, in order to eliminate the fluctuation of the pressure when the plastic is extruded, and the equalizing ring is also arranged. The die head is also provided with a die correcting and adjusting device, which is convenient for adjusting and correcting the concentricity of the die core and the die sleeve. According to the direction of the material flow direction of the head and the center line of the screw head, the extruder divides the machine head into an oblique angle head (an angle 120o) and a right angle head. The head of the shell is fixed on the machine body by bolts, die inside the core seat, fixed in the head line port and nut, a core mold core seat in front of the core and core seat with center hole, used by the core wire; a pressure equalizing ring in the front end, for balanced pressure extrusion; the package consists of forming die and die, die sleeve position by a bolt through the support to adjust, to adjust the relative position of the die sleeve core, adjustable extruded layer thickness uniformity. A heating device and a temperature measuring device are arranged outside the machine head. 2. the drive system of the transmission system is to drive the screw to supply the screw in the extrusion process required torque and speed, usually by the motor, reducer and bearings. 3. heating and cooling equipment heating and cooling is a necessary condition for plastic extrusion. (1) now extrusion machine is usually divided into electric heating, resistance heating and induction heating, heating installed in the fuselage, neck, head of each part. The heating device heats the plastic in the outer barrel to increase the temperature required for the process operation. (2) the cooling device is designed to ensure that the plastic is in the temperature range required by the process. Specifically, to eliminate the excess heat generated by the shear friction of the screw rotation, in order to avoid the temperature is too high, so that plastic decomposition, coke burning or stereotypes difficult. Cylinder cooling water cooling and air cooling is divided into two kinds, small and medium sized extrusion machine adopts air cooling is more appropriate, large use more water or two kinds of combined cooling; cooling water cooling screw mainly adopts the center, the purpose is to increase the solids conveying rate, stable glue volume, and improve product quality; but in the cooling hopper one is, in order to strengthen transport of solid material, prevent warming plastic sticky jam outlet, two is to ensure the normal work of the transmission part. Two, auxiliary equipment The auxiliary units of the plastic extrusion unit mainly include the wire laying device, straightening device, preheating device, cooling device, traction device, meter, spark test machine and take-up device. The use of extruder units is different, and the auxiliary equipment used for matching is different. If there is a cutter, a dryer, a printing device, etc.. Straightening device: one of the most common types of plastic extrusion waste is eccentric, while the core of various types of bending is one of the important causes of insulation bias. In sheath extrusion, the scratches on the sheath surface are often caused by the bending of the cable core. Therefore, the straightening device in various extrusion machines is essential. The main type of straightening device: roller (divided into horizontal and vertical); pulley type (divided into single pulley and pulley); cutter wheel, and drag, alignment, stable tension and other effects; the pressure wheel (divided into horizontal and vertical) etc.. Preheating device: preheating of cable core is necessary for insulation extrusion and sheath extrusion. For the insulation layer, especially the thin layer insulation, the hole can not be allowed to exist. The wire core can completely remove the moisture and oil from the surface before the package is heated at high temperature. For the sheath extrusion, the main function is to dry the cable core and prevent the possibility of air holes in the sheath due to the moisture (or moisture of the wrapped cushion). Preheating can also prevent the extrusion of plastic due to quenching and residual pressure. In the process of plastic extrusion, preheating can eliminate the cold line into the hot head, formed in the die and plastic contact between temperature, avoid plastic temperature fluctuations due to fluctuations in the extrusion pressure and stable extrusion, extrusion quality assurance. The electric heating core preheating device is adopted in the extrusion unit, which requires sufficient capacity and ensures quick heating, The wire core is preheated and the cable core has high drying efficiency. The preheating temperature is controlled by the setting speed, which is similar to the nose temperature. Cooling device: the molded plastic cladding layer should be cooled immediately after leaving the handpiece, otherwise it will deform under the action of gravity. The cooling method is usually cooled by water, and is divided into cold and cold according to different water temperature. The quench is cold water direct cooling, rapid cooling of plastic extruded layer forming favorable, but the crystalline polymer, due to sudden cooling, easy in extruded residual stress remained lamellar, cracks caused in the process of using general PVC plastic layer by quenching. Slow cooling is to reduce the internal stress of products, sub placed different temperature water in the cooling water tank, the product gradually cooling stereotypes, extrusion of PE and PP on the use of slow cooling, hot water, warm water, cold water after three stage cooling. Three 、 control system The control system of plastic extruder includes heating system, cooling system and process parameter measuring system. It mainly consists of electric appliance, instrument and actuating mechanism (control panel and operating table). Its main function is: motor control and regulation of the main auxiliary output, which meets technological requirements of speed and power, and can make the main auxiliary work; temperature, pressure and flow detection and adjusting the plastic extruder; to achieve control of the entire unit or automatic control. Electrical control extrusion unit can be divided into two parts of transmission control and temperature control, to achieve control of the extrusion process including temperature, pressure, screw speed, screw barrel cooling, cooling, cooling and diameter of the products, and traction speed, and ensure the orderly cable take-up reel on constant tension from start to end plates of the wire control. 1. temperature control of extruder main engine Plastic extrusion of wires, cables, insulation and sheaths is based on the deformation properties of thermoplastics to make them adhere to a viscous flow regime. In addition to the requirements of screw and barrel external heating, melting to make plastic extrusion, but also consider its own heating screw extrusion plastic, so the temperature of the host should be whole to consider, it is necessary to consider the heater on and off, but also consider the factors of screw extrusion heat to have spillover cooling, cooling facilities effectively the. And requires the correct and reasonable determination of measuring elements, thermocouple location and installation methods, from the temperature meter readings accurately reflect the actual temperature of each section of the host. And requirements of temperature control instrument precision and system coordination, so that the whole host temperature control system fluctuation stability to all kinds of plastic extrusion temperature requirements. 2. pressure control of extruder In order to reflect the needs of extrusion die, extrusion die pressure detection, because no domestic extruder head pressure sensor, is generally the measurement of screw extrusion thrust measurement instead of head pressure, screw load (current or voltage table table table) can reflect the size of the extrusion pressure. The fluctuation of extrusion pressure is one of the important factors that lead to the instability of extrusion quality. The fluctuation of extrusion pressure is closely related to the extrusion temperature, the use of cooling equipment, the duration of continuous operation and so on. When abnormal phenomena occur, the rapid elimination can be ruled out, and the production must be re organized, the machine should be shut down decisively, not only to avoid the increase in waste, but also to prevent accidents. By checking the reading of the pressure gauge, we can know the pressure state of the plastic in extrusion, and generally take the thrust limit value alarm control. 3. screw speed control The adjustment and stability of the screw speed is one of the important technological requirements of the main engine transmission. Screw speed directly determines the quantity of cement and extrusion speed, normal production always hope to achieve the highest speed and achieve high yield as much as possible, the speed of the screw extruder requirements from the start to the work required speed, speed range can be used to. And the stability of the high speed requirements, because the speed fluctuations will lead to fluctuations in the amount of extrusion, affecting the quality of extrusion, so in the traction line speed is not changed, it will lead to changes in cable diameter. Similarly, such as traction device speed fluctuations will also lead to changes in wire diameter, screw and traction speed can be reflected by the corresponding instrument on the operating platform, should be closely observed when extrusion, to ensure high quality and high yield. 4. outside diameter control As mentioned above, in order to ensure the products of cable size, in addition to the requirements of the control core (core) dimensional tolerances, the extrusion temperature, screw speed, traction device line speed etc should be controlled to ensure, and the outer diameter of the comprehensive measurement and control precision and level reflect the above control. In the extrusion unit, especially the high-speed extrusion production line, should be equipped with online diameter tester, at any time to detect the external diameter of the cable, and the ultra poor feedback signal to adjust the traction or screw speed, correct diameter deviation. 5. tension control required for take-up In order to ensure different line speed under constant tension winding, from start to end plates work, hope take-up device storage line tension adjusting mechanism, or considering the constant line speed and constant tension system in electric rolling and so on. 6. electric automatic control of the whole machine This is the production line should have high speed extrusion control requirements, mainly is: boot temperature protection and interlock interlock; work pressure; extrusion and traction two components of transmission ratio of synchronous control; synchronous control and traction wire diameter; online detection and feedback control; according to the different needs of various parts of machine and machine tracking control. Edit this paragraph extruder categories According to the number of points: no screw, single screw, double screw In space: horizontal and vertical Screw speed: ordinary, high speed and ultra high speed Exhaust: exhaust type and non exhaust type According to the assembly structure: integral and separate The most commonly used horizontal single screw non exhaust one-piece extruder Edit the main parts of the extruder Screw rod 1. Evaluate the standard of screw performance and the factors that should be considered in designing screw 1) evaluate screw performance standards Plasticizing quality: quality requirements must be met. The quality of the products is related to the head and the auxiliary machine, but it is more related to the plasticizing quality of the screw, such as uneven temperature, axial pressure fluctuation, radial temperature, uneven dyeing and so on, which directly affect the quality of the products. Output: under the premise of guaranteeing the quality, the extrusion quantity is through the head. Good screw, should have high plasticizing ability Nominal specific power unit consumption: the output per extrusion of 1Kg plastic is P/Q (power / output). Under the guarantee of quality, the less unit consumption, the better. Adaptability: adaptability to processing different plastics, matching different machine heads and different products. But generally adaptable, often plasticizing efficiency is low. Manufacturing is difficult: it must be easy to manufacture and low in cost 2) the design screw shall be considered Material characteristics and geometry, size and temperature conditions during processing. Because of the different physical characteristics of different materials, the processing performance is different, and the structure and geometry parameters of the screw have different requirements. Geometric form of die and resistance characteristic of die head. The shape of the screw should match them. The structure of the barrel and the heating and cooling conditions. If the taper and the longitudinal groove are machined and cooled in the inner wall of the feeding section, the solid conveying efficiency will be improved. The design of the screw should consider increasing the melting rate and homogenizing ability so as to match the feeding section. Screw speed Extruder use: mixing, granulation and feeding, the screw structure is different 2 、 conventional full thread three section screw design The finger screw is composed of feeding section, compression section and homogenizing section three section screw, and its extrusion process completely depends on the form of thread to complete a screw. 1) screw type determination According to the depth of the spiral groove, from the feeding section to the shallow transition section: Gradual change: the depth of the spiral groove changes gradually in the long distance. For amorphous, heat sensitive plastics processing, can also be crystalline. Mutant: a plastic used for melting point change and low viscosity. Such as PA, PE, PP, PVC is not suitable for heat sensitive plastics 2) screw diameter Has been standardized, and its size is generally determined according to the cross-section size of the processed products, processing plastics and the amount of extrusion required 3) screw length diameter ratio L/Db The longer the diameter diameter ratio is, the longer the plastic stays in the barrel, and the plasticization is more adequate and uniform to ensure the quality of the product Edit the technical parameters and models of this single screw extruder 1. Technical parameters of single screw extruder Screw diameter Db: refers to the big diameter, series standards 20, 30, 45, 65, 90, 120, 150, 165,, 200, 250, and 300 Screw length to diameter ratio L/Db: screw work length and screw diameter ratio Screw speed range: nmin-nmax r/min Drive screw motor power P:KW Extruder capacity Q: the amount of plastic extruded per hour Specific throughput per hour, RPM, extruder capacity Nominal specific power required for processing kg plastic motor per hour 2, model SL-150 indicates that the screw diameter is 150mm and the ratio of length to diameter is 20:1 plastic extrusion Edit the paragraph and extrude the process parameters 1, temperature Extrusion temperature, cylinder temperature, plastic temperature, screw temperature, we generally measure the cylinder temperature. The temperature is controlled by heating and cooling system, heating and cooling system, because the structure of screw instability, screw speed change causes extrusion material temperature in axial and radial direction are fluctuations, thus affecting the quality of products, the product strength is not the same, residual stress, surface dull gray. In order to ensure the quality of products, the temperature should be stable. 2, pressure Because of the screw and barrel structure, the resistance of the head, filter screen and filter board causes the pressure inside the plastic. As the pressure changes, the pressure fluctuates as well. 3, extrusion rate The quality or length of a plastic extruded out of an extruder die in unit time. Factors affecting extrusion rate are head resistance, screw and barrel structure, screw speed, heating and cooling system, plastic characteristics. However, when the product has been set, the extrusion rate is only related to the screw speed. The extrusion rate also fluctuates, affecting the geometry and size of the product. Temperature, pressure and extrusion rate all fluctuate. In order to ensure the quality of products, the screw should be properly designed, the heating cooling system and screw speed stability should be controlled to reduce the fluctuation of parameters. Edit the extrusion process According to the general types of products and processing of polymer or semi-finished shapes, selected extruder, die and die, and setting and traction corresponding auxiliary device, and then determine the extrusion process conditions such as screw speed, die pressure, material temperature and setting temperature, traction speed. In the extrusion process, the material is generally subject to plastic refining, but the method of setting is different. For example, the extruded plastic often needs to be cooled and shaped so that it can be cured, while the finished product of the extruded rubber needs further vulcanization. Different extrusion equipment and process can be used to obtain different products. Aggregate When the polymer is mixed with various additives, it is melted into the extruder and further mixed. Through the porous die, a plurality of strips are formed and then cut into pellets. Cut between the hot and cold cuts. The former strips are cooled by air or water after leaving the mold and are immediately removed with a rotating knife. The latter is to strip all after cooling, and then into the granulator grain. Sheet and film Where the thickness is above 0.25mm, the length is greater than the width of many flat products called sheets; thickness less than 0.25mm is called film. A flat film can be made by cooling a film through a cooling drum with a very smooth surface, and this method is also called an extrusion casting method. This is a common method for making polypropylene film. If the flat film is fed into a stretching machine and stretched 4~10 times at a time, either longitudinally or transversely, and then longitudinally stretched and then stretched transversely, a biaxially oriented film can be made. Because of the orientation of macromolecules when stretched, the film has a high strength, but the permeability and permeability decrease. Often used in making polypropylene and polyester films. If the foaming agent is added to the material and the special screw and die are adopted, the low foamed plastic sheet can be prepared. Covered wire When the metal wire through a T shaped die, the molten plastic is around the bare form coating layer (with head] Figure 3[coating line, coating line) is cooled after winding, which have a variety of wire and cable products. Edit the tube extrusion process Equipment: extruder, head, setting device, cooling tank, traction equipment and cutting equipment 1, forming Realized by extrusion die. The melt passes through the filter screen and the filter plate, the diverging zone, the compression zone, and the molding zone. 2, stereotypes Methods: internal diameter determination and external diameter sizing (internal pressure and vacuum method) 3 、 pipe extrusion process condition control Temperature: the temperature of the barrel, the head and the die is the main factor affecting the quality of the plasticizing and the products. Extrusion pipe temperature is generally low, high viscosity, is conducive to stereotypes. Extrusion rate: impact on Yield and quality, depending on screw speed Traction speed: the accuracy of pipe wall thickness and diameter to be adjusted to the extrusion speed. Compressed air pressure: internal pressure, pressure 0.02~0.05MPa Edit this section of blown film molding process 1, extrusion and blow up Equipment: extruder and head, cooling device, plywood, traction roller, guide roller, coiling device. 2, extrusion film extrusion process conditions Temperature: barrel, head and neck temperature. When the temperature is too high, the film is brittle, the tensile strength decreases, the tensile strength is too high, the surface gloss is poor, the transparency is decreased, and there is weld line. Blow up ratio and draft ratio: ratio of blow up ratio to film diameter and die ratio (2-3); draft ratio film elongation factor (4-6). Cooling rate: regulated by the cooling device. Freezing line - the line on which the film has been cooled; the farther away the line is, the slower the cooling rate is, and the film is torn laterally. Edit this segment extrusion process application Several extruders are used to supply several plastics at the same time, and then they are extruded through a common die head to form a whole composite product. For example, A, B, C three plastic extrusion, can produce a variety of composite films, composite sheets, plates, profiles and tubes. Rubber filtration In the manufacture of thin rubber products, in order to prevent the occurrence of leakage, Water Leakage products, rubber can not contain impurities, generally add vulcanizing agent before filtration rubber extruder, which is placed in one or more layers of filter in the nose, to filter out impurities in plastic material. Tyre tread and inner tube make tread, whole extrusion and lamination extrusion. The whole extrusion can be extruded by one extruder through a flat die, and also can be extruded with two kinds of rubber material (tire crown material and tire side material) and two extruders, and a whole tread is formed in the extrusion die. Two layers of extruder are used to squeeze two kinds of rubber into crown and sidewall respectively, and then heat it on the conveyor belt. The inner tube extrusion is similar to the tube extrusion. After the tyre tube is pressed, it is cut and welded again. Melt spinning Some resins with high viscosity usually melt the material in the melt when they are spinning. The molten material passes through the filter directly into the spinneret, or with a spinneret pump into the spinneret.