The main machine of plastic extruder is the extruder, which consists of extrusion system, transmission system and heating and cooling system.
1. Extrusion system extrusion system includes screw, barrel, hopper, head, and die, plastic through the extrusion system and plasticized into a uniform melt, and in the process of establishing pressure, by the screw continuous extrusion head.
(1) screw: is the most important part of the extruder, it is directly related to the scope of application and productivity of the extruder, made of high-strength corrosion-resistant alloy steel.
(2) barrel: is a metal cylinder, generally with heat, compression strength, high strength, strong wear-resistant, corrosion-resistant alloy steel or alloy steel lined with composite steel pipe made. Cylinder and screw with the realization of the plastic crushing, softening, melting, plasticizing, exhaust and compaction, and to the molding system continuous and uniform delivery of rubber. Generally the length of the barrel is 15-30 times of its diameter, so that the plastic can be fully heated and fully plasticized as a principle.
(3) hopper: the bottom of the hopper is equipped with a cut-off device, in order to adjust and cut off the flow of material, the side of the hopper is equipped with a sight hole and calibration measuring device.
(4) head and mold: the head consists of an alloy steel inner sleeve and a carbon steel outer sleeve, and the head is equipped with a molding die. The role of the head is to transform the rotary motion of the plastic melt into a parallel linear motion, uniform and smooth introduction into the mold sleeve, and give the plastic to the necessary molding pressure. Plastic in the barrel plasticization compaction, through the porous filter plate along a certain flow channel through the neck of the head into the head molding mold, mold core mold sleeve appropriate coordination, the formation of the cross-section of the ever-decreasing annular gap, so that the plastic melt in the core line around the formation of a continuous and dense tubular cladding layer. In order to ensure that the head of the plastic flow reasonable, to eliminate the accumulation of plastic dead space, often placed in the diversion sleeve, in order to eliminate pressure fluctuations in plastic extrusion, there are also set up pressure equalization ring. The head is also equipped with mold calibration and adjustment devices, easy to adjust and correct the concentricity of the die core and die set.
Extruder according to the head of the direction of material flow and screw centerline angle, the head is divided into angled head (angle of 120o) and right-angle head. The shell of the head is bolted to the body of the machine, the mold in the head has a die core sitting, and fixed with a nut in the head inlet port, the front of the die core seat is equipped with a die core, die core and die core seat in the center of the hole, for the passage of the core; in the front of the head is equipped with an equalizing ring for equalization of pressure; extrusion molding part of the molding by the die set seat and the die sleeve, the position of the die sleeve can be adjusted by the bolt through the support to adjust the relative position of the die sleeve on the core, easy to adjust the relative position of the extrusion package, to facilitate the adjustment of the core The position of the die sleeve can be adjusted by bolts through the support to adjust the relative position of the die sleeve to the die core, which is convenient to adjust the uniformity of the thickness of the extruded layer. The machine head is equipped with heating device and temperature measuring device.
2. The transmission system is to drive the screw and supply the torque and rotation speed required by the screw in the extruding process, which usually consists of electric motor, speed reducer and bearings, etc.
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3. Heating and cooling device heating and cooling is necessary for the plastic extrusion process can be carried out.
(1) now extrusion machine is usually used for electric heating, divided into resistance heating and induction heating, heating pads installed in the body, neck, head parts. The heating device heats the plastic in the barrel from the outside to warm it up to reach the temperature required for the process operation.
(2) cooling device is to ensure that the plastic is in the temperature range required by the process and set up. Specifically, it is to exclude the excess heat generated by the shear friction of the screw rotation, in order to avoid the high temperature of the plastic decomposition, scorching or shaping difficulties. Barrel cooling is divided into water-cooled and air-cooled two kinds, generally small and medium-sized extruder using air-cooled is more appropriate, large-scale water-cooled or a combination of the two forms of cooling; screw cooling is mainly used in the center of the water-cooled, the purpose is to increase the rate of material solids transport, stabilize the amount of rubber, while improving product quality; but in the hopper at the cooler, one in order to strengthen the role of the transport of solids, to prevent the plastic particles due to the temperature of the viscous plastic clogging The second is to ensure that the transmission part of the normal work.
Two, auxiliary equipment
Plastic extrusion unit of auxiliary equipment mainly includes payoff device, straightening device, preheating device, cooling device, hauling device, meter meter, spark tester, take-up device. Extruder unit with different uses of its optional auxiliary equipment is not the same. Such as there is a cutter, blow dryer, printing device.
Straightening device: the most common type of plastic extrusion waste is eccentric, and the core of various types of bending is one of the important reasons for insulation eccentricity. In the sheath extrusion, the sheath surface scratching is also often caused by the bending of the core. Therefore, a variety of extrusion unit in the straightening device is essential. Straightening device of the main types are: roller (divided into horizontal and vertical); pulley type (divided into a single pulley and pulley group); stranded wheel, both drag, straightening, stabilizing tension and so on a variety of roles; pressure wheel type (divided into horizontal and vertical) and so on.
Preheating device: core preheating for insulation and sheath extrusion are necessary. For the insulation layer, especially the thin layer of insulation, can not allow the existence of air holes, the core in the extrusion of the package before the high temperature preheating can be completely removed from the surface of the water, oil. For the sheath extrusion, its main role is to dry the cable core, to prevent the role of moisture (or moisture around the package cushion layer) so that the sheath in the possibility of air holes. Preheating can also prevent the plastic extrusion due to sudden cooling and residual internal pressure effect. In the process of extrusion of plastic, preheating can eliminate the cold line into the high temperature head, in contact with the plastic at the die mouth of the formation of the disparity between the temperature difference, to avoid fluctuations in the temperature of the plastic and lead to fluctuations in the pressure of the extrusion, so as to stabilize the amount of extrusion, to ensure the quality of extrusion. Extrusion unit are used in electric heating core preheating device, required to have sufficient capacity and to ensure that the temperature rises quickly, so that the core preheating and cable core drying efficiency. Preheating temperature is subject to the constraints of the release speed, generally similar to the head temperature can be.
Cooling device: molded plastic extruded layer in the head after leaving the machine, should be immediately cooled and shaped, otherwise it will be deformed under the action of gravity. Cooling is usually water cooling, and according to the different water temperatures, divided into rapid cooling and slow cooling. Rapid cooling is cold water direct cooling, rapid cooling of the plastic extrusion layer shaping is beneficial, but for crystalline polymer, because of the sudden hot cooling, easy to residual internal stress in the organization of the extrusion layer, leading to cracking in the process of use, the general PVC plastic layer using rapid cooling. Slow cooling is in order to reduce the internal stress of the product, in the cooling water tank segments placed in different temperatures of water, so that the product is gradually cooled down and shaped, PE, PP extrusion on the use of slow cooling, that is, after the hot water, warm water, cold water, three sections of cooling.
Three, the control system
Plastic extruder control system, including the heating system, cooling system and process parameter measurement system, mainly by the electrical appliances, instruments and actuators (i.e., control panels and operating stations). Its main role is to: control and regulate the main and auxiliary drag motor, output speed and power in line with the process requirements, and can make the main and auxiliary coordinated work; detect and regulate the temperature of plastic in the extruder, pressure, flow rate; to achieve the control of the whole unit or automatic control.
The electrical control of the extrusion unit is roughly divided into transmission control and temperature control of the two major parts of the realization of the extrusion process, including temperature, pressure, screw speed, screw cooling, barrel cooling, product cooling and the control of the outer diameter, as well as the hauling speed, neatly lined up and to ensure that the take-up of the reel from the empty disk to the full disk of the constant tension take-up control.
1. Extruder host temperature control
Wire and cable insulation and sheath plastic extrusion is based on the deformation characteristics of thermoplastics, so that it is in a viscous flow state. In addition to the requirements of the screw and barrel external heating, to the plastic melting extrusion, but also consider the screw extrusion of plastic when its own heat, so the temperature of the host should be considered as a whole, not only to consider the heater heating on and off, but also consider the extrusion of the screw heat spillover factors to be cooled to have an effective cooling facilities. And requires the correct and reasonable determination of the location of the measuring element thermocouple and installation methods, can be read from the temperature control instrumentation to accurately reflect the actual temperature of the host section. As well as the requirements of the accuracy of the temperature control instrumentation with the system with a good, so that the entire host temperature control system fluctuations in stability to achieve a variety of plastic extrusion temperature requirements.
2. Extruder pressure control
In order to reflect the extrusion of the head, it is necessary to detect the extrusion of the head pressure, due to the domestic extruder does not have a head pressure sensor, generally on the screw extrusion thrust measurement instead of the measurement of the head pressure, the screw load table (ammeter or voltmeter) can correctly reflect the size of the extrusion pressure. Extrusion pressure fluctuations, is also one of the important factors causing extrusion quality instability, extrusion pressure fluctuations and extrusion temperature, the use of cooling devices, the length of continuous operation time and other factors are closely related. When the anomaly occurs, can be excluded from the rapid exclusion, must be re-organized production should be decisive shutdown, not only can avoid the increase in scrap, but also to prevent accidents. Through the detection of the pressure gauge readings, you can know the plastic in the extrusion of the pressure state, generally taken after the thrust limit value alarm control.
3. Screw speed control
Screw speed regulation and stabilization is one of the important process requirements of the host drive. Screw speed directly determines the amount of glue and extrusion speed, normal production always hope to achieve the highest possible speed and achieve high yield, the extruder requires screw speed from the start to the required working speed, the speed range available to be large. And the stability of the speed of high requirements, because fluctuations in speed will lead to fluctuations in the amount of extrusion, affecting the quality of extrusion, so in the case of traction line speed does not change, it will cause changes in the outer diameter of the cable. Similarly, such as the traction device line speed fluctuations will also cause changes in the outer diameter of the cable, screw and traction line speed can be reflected through the corresponding instrumentation on the operating table, extrusion should be closely observed to ensure high quality and high yield.
4. Outer diameter control
As mentioned above in order to ensure that the products of the outer diameter of the cable size, in addition to the requirement to control the size of the core (core) tolerance, in the extrusion temperature, screw speed, hauling device speed should be controlled to ensure that the measurement of the outer diameter of the control of the integrated reflection of the above control of the accuracy and level. In the extrusion unit equipment, especially high-speed extrusion production line, should be equipped with online OD detector, at any time on the cable OD detection, and will exceed the signal feedback to adjust the traction or screw speed, correct the OD overrun.
5. winding requirements of the tension control
In order to ensure that different line speeds under the winding, from the empty disk to the full disk of the work of the constant tension requirements, I hope that the winding device has a storage line tension adjustment mechanism, or in the electrical consideration of the constant line speed system and constant tension system of the winding and so on.
6. Electrical automation control of the machine
This is the realization of high-speed extrusion line should have process control requirements, mainly: boot temperature interlock; working pressure protection and interlock; extrusion, hauling the two major components of the proportion of synchronous control of the drive; take-up and hauling of synchronous control; online detection of the outer diameter and feedback control; according to a variety of different needs to be composed of components of the machine and the entire control of the tracking. Tracking control. According to the number of points: no screw, single screw, twin-screw
According to the space position: horizontal and vertical
According to the screw speed: ordinary, high speed and ultra-high speed
Can be vented: exhaust and non-exhaust
According to the structure of the assembly: the whole type and the separate type
The most commonly used single-screw horizontal non-exhaust integral extruder, a screw
1, evaluation of the performance of the screw
According to the number of parts of the whole machine and the tracking control. p>1, evaluation of screw performance standards and design screw should be considered
1) evaluation of screw performance standards
① plasticizing quality: must meet the quality requirements. Product quality and head, auxiliary machine related, but with the screw plasticizing quality is more relevant, such as uneven temperature, axial pressure fluctuations, radial temperature, dyeing and other uneven dispersion, which directly affects product quality.
②Production: under the premise of quality assurance, the amount of extrusion through the head. Good screw, should have a high plasticizing capacity
③ Nominal power consumption: each extrusion of 1Kg of plastic consumed by the output that P / Q (power / production), to ensure that the quality of the less consumption, the better.
④Adaptability: the processing of different plastics, matching the adaptability of different machine heads and different products. But generally adaptable, often low plasticizing efficiency.
⑤Easy to manufacture: must be easy to manufacture, low cost
2) Design screw should be considered
①Material properties and processing geometry, size, temperature conditions. Due to different physical properties of different materials, so different processing performance, the screw structure and geometric parameters have different requirements.
②Mouth mold geometry and head resistance characteristics. The screw shape should match them.
The structural form of the barrel and heating and cooling. If the taper and longitudinal grooves are machined and cooled on the inner wall of the barrel in the charging section, the solids conveying efficiency is improved, and the screw should be designed to improve the melt rate and homogenization capacity to match the conveying of the charging section.
③Screw speed
④Extruder use: for mixing, pelletizing and feeding, etc., the screw structure is different
2, conventional all-threaded three-section screw design
refers to the screw by the charging section, compression section, homogenization of three sections of the threaded composition of the extruder process relies solely on the threaded form of the completion of a screw.
1) Screw type determination
According to the depth of the spiral groove from the charging section of the deeper to the homogenization section of the shallower transition:
① Gradual change type: the depth of the spiral groove changes in a longer distance gradually become shallower. Used for amorphous, heat-sensitive plastics processing, can also be used for crystallization.
② mutation type: used for sudden change in melting point, low viscosity plastics. Such as PA, PE, PP, not suitable for PVC and other heat-sensitive plastics
2) screw diameter
has been standardized, its size is generally based on the cross-section size of the processed products, the type of plastics processed, the required amount of extrusion to determine
3) screw L/D ratio L/Db
Length and diameter ratio of the larger, the longer the plastic stays in the barrel, the plastification of the more fully The larger the screw diameter, the more time the plastic stays in the barrel, the more fully and evenly plasticized it will be to ensure the quality of the system. 1, single-screw extruder technical parameters
Screw diameter Db: refers to the large diameter, the series of standard 20, 30, 45, 65, 90, 120, 150, 165, 200, 250, 300
Screw length-to-diameter ratio L/Db: the ratio of the length of the screw's working part to the screw's diameter
Screw rotational speed range: nmin-nmax r/min
Driving screw motor power P: KW Extruder production capacity Q: the amount of plastic extruded per hour
Specific flow rate per hour per week of extruder production capacity
Nominal specific power Motor power required to process kg of plastic per hour
2, model number
SL-150 indicates that the screw Diameter of 150mm, L/D ratio of 20:1 plastic extrusion