Overview of extrusion molding machine
Plastic extrusion molding machine is abbreviated as extruder. It uses screw pressure to continuously extrude the plasticized material from the extruder barrel through the mould mouth, so that it is in a molten state and cooled and shaped. The product continuously extruded from the mould mouth is pulled by the traction device or the forming device to the cutting machine for fixed-length cutting. Currently our company uses single/twin screw extruder.
The main components and functions of the extruder.The extruder is mainly composed of host and auxiliary machines.
The host is mainly composed of: rotating system, temperature control system, feeding system and vacuum exhaust system. The functions of each part are as follows:
Rotation system: adopts direct current or frequency conversion speed regulation, the screw speed is steplessly regulated from 0-31r/min or 0-43r/min, so that the screw extrudes the molten raw material through the mold mouth.
Temperature control system: Use an automatic temperature regulator with corresponding heating coils, thermocouples and thermostats (air-cooled, oil-cooled) to indirectly heat the raw materials as required to make them melt.
Feeding system: The material is continuously and evenly supplied to the screw of the extruder by the stepless speed regulation device or the weight of the raw material itself plus the hopper sealing plate to achieve quantitative feeding and continuous extrusion through the mold mouth.
Vacuum exhaust system: The vacuum pump is equipped with a particle separator to extract water vapor and volatile generated when the material in the barrel is melted to achieve the effect of removing water and volatile.
Auxiliary machine is mainly composed of: shaping box (set) or forming machine, tractor, cutting machine, printing machine, turning frame, etc. The functions of each part are as follows:
Shaping box (set): The sizing sleeve (mold) is equipped with spray or bubble-type cooling water, and the vacuum pump is used to generate negative pressure in the sizing box (mold) to shape and solidify the molten products into qualified products.
Forming machine: It is composed of a certain specification and number of modules. After the product extruded by the mold is shaped and cooled, it is continuously drawn to the cutting machine for fixed-length cutting (usually a special unit for corrugated pipe).
Tractor: Utilize crawler type or roller type tractor to smoothly and continuously pull the products extruded from the mold mouth to the cutting machine and turning frame. The change of the tractor speed will directly affect the cross-sectional wall thickness and shape of the produced product.
Cutting machine: Use pneumatic mechanical device and length counting device to automatically or manually cut products according to the required length.
Printer: Continuously print or jet-print the name, model, specification, etc. of the molded product on the produced product.
Turnover table: Use pneumatic device to make the product out of the length counting station to achieve the purpose of re-counting length.
Mold operation and maintenance: Correct process conditions, reasonable formulas, applicable process parameters, skilled operators, correct operation and use methods are the keys to invisible maintenance of molds.
Frequently Asked Questions
Answer: Original (mixed) materials → feeding → extrusion → shaping and cooling → traction → cutting → inspection → packaging → storage and stacking.
Answer: Single-screw and partial twin-screw extruders are determined by their structure, plasticizing capacity, and whether to use porous plates according to actual conditions.
Answer: The plasticization of the material in the barrel is related to the heating and the rolling shear of the screw. Under the same conditions, the higher the heating temperature, the greater the shear strength and the better the plasticization.
Answer: It is better to fill the screw with 2/3 of the material. Because there are too few filling screws, there is no material at the bottom of the screw, and there is no material above the screw. The material has low shear strength and poor plasticization, which affects the product quality. On the contrary, if it is too much, it will cause the material to enclose the screw with poor exhaust. Even the material from the vent will affect the quality of the product.
Answer: Too good or insufficient plasticization will weaken the impact performance. Therefore, if the impact performance is unqualified, the correct measures must be taken in the adjustment of the process parameters based on the symptoms of the cross section of the inner wall of the product appearance.
Is the process temperature too high or too low for the roughness of the inner wall of the product? How to judge?
Answer: Both will cause the inner wall to be rough. If the inner wall is shiny or rough, and the outer surface is discolored, the temperature is higher, especially the third and fourth sections of the barrel; if there are raw meal particles on the inner wall and the surface is dark, the temperature is lower. Therefore, if the small product is rough, it must be cut and judged clearly to avoid mis-breaking.
What measures can be taken when the product enters the sizing sleeve to be easily blocked? What are the side effects of the reform measures?
Answer: The product entering the sizing sleeve is easy to be blocked. Available: A. Check whether the cooling water is blocked; B. Dripping water can solve it or speed up the traction; C. Reduce the vacuum pressure or turn off the vacuum pump to reduce the traction resistance.
Answer: A, the product is easy to be blocked; B, the product wall thickness deviation is caused.
Because it is close to the side of the sizing sleeve, it is first drawn by cold shrinkage to pull the surrounding materials closer to it. This effect can adjust the wall thickness deviation or concentric line without causing blockage.
Answer: It is determined by the gap between the mold and the mandrel, the pulling speed and the extrusion speed (extrusion amount).
Answer: A. The recycled material contains decomposed material or other red crushed materials; B. The accumulated material falls and is brought out after the vacuum exhaust hole is blocked for a period of time; C. The material temperature is too low or the machine processing temperature is not enough; D Screw clearance Change, the uneven part decomposes and the part is not plasticized.
Answer: A. If the temperature of the mold is too high or too low, the surface gloss will be dim; B. The inner surface of the mold is rough and the accuracy is too low; C. The extrusion speed is too fast and the vacuum is not enough.
Answer: A. The temperature of the mold or mandrel is too low; B. The extrusion speed is too fast, and the melt is not plasticized in the mold body; C. The mold structure design is unreasonable and the compression ratio is too small; D. The ingremoldnt structure is unreasonable , The liquidity is too good.
Answer: A. There are impurities in the raw materials; B. The processing temperature is too low, it is not plasticized or the temperature is too high, and it is caused by the gas after decomposition; C. The ingremoldnt structure is not ideal.
What are the reasons and adjustment methods for the decomposition of the inner and outer walls of the product?
Answer: 1. Reasons for the decomposition of the inner wall of the product and adjustment methods
- If the product temperature is too high, reduce the temperature of each area of the fuselage and the mixing material; B. The screw oil temperature is too high, reduce the screw oil temperature; C. Too much feeding, vacuum feeding, reduce feeding speed, control feeding; D , Body string temperature, reduce the synchronization speed and look for machine repair; E. The synchronization speed is higher, and the synchronization speed should be reduced appropriately;, F. The temperature of the mandrel is too high, and the temperature of the mandrel should be appropriately reduced; G. The formula is
- Reasons for the decomposition of the outer wall of the product and adjustment methods
- The heating ring of the machine head is out of control. Frequently measure the temperature of each zone. Pay attention to whether the thermocouple is completely inserted at the bottom of the hole or whether there is debris in the thermocouple hole to make the contact bad, or whether the AC contactor is stuck; B. Mold Leaking material causes the outer wall to decompose and disassemble the mold; C. Extrusion speed is too slow to cause the outer wall to decompose, increase the synchronous speed appropriately; D. The formula is unreasonable, ask a technician to deal with it.
Answer: The function of the filter plate: A. Establish the head pressure; B. Transform the screw head material from spiral flow to axial flow along the filter hole.
Answer: Prevent the material from being heated and agglomerate, causing the material at the screw feeding section to be unable to be transported forward in time, which is the so-called ‘’not eating material’’
Answer: The shear strength of the same material depends on the filling degree of the material in the screw groove. The size of the screw gap, the larger the diameter of the screw and the depth of the screw groove, the faster the screw speed, the greater the shearing effect.
Answer: A. Promote the partial plasticization of PVC materials before the exhaust section, which is beneficial to the escape of water vapor volatiles, but when the plasticization is too good, it is not conducive to full exhaust. B. Avoid dry powder being pumped away in the exhaust section. C. The torque can be appropriately reduced, and the material can be prevented from sticking to the barrel at high temperature.
Answer: If the temperature of the screw and the material is too high or the speed is too fast, regular screw marks may appear on the inner wall.
Answer: A. The vacuum is too large; B. The cooling effect is poor; C. The product wall thickness is uneven; D. The product is immersed in cooling water.
Answer: A. Wall thickness deviation; B. The center of the machine head cooling water tank (bracket) traction and cutting equipment is not in the same straight line; C. The shaping cooling water is not uniformly cooled; D. The discharge speed is inconsistent; E. The inner wall of the product has water.
Answer: A. The center of the mold and the mandrel is not aligned, adjust the mold and the mandrel to be concentric; B. The head is unevenly heated, and check whether the heating ring is tightly wrapped or partially damaged; C. The molten material is decomposed in the head Materials should be cleaned up.
Answer: A. The gap between the screw and the barrel is too small or the screw barrel is severely worn, and the friction causes the pattern to be regular and linear (this phenomenon is generally that the white product usually appears on the bottom after it comes out of the mold); B. The screw leaks Oil; C. The problem of raw materials is mainly the pollution of recycled materials. When the materials containing sulfur organic tin and materials containing lead salt are mixed, sulfur pollution will occur.
Answer: A. The sizing sleeve itself is deformed, and the sizing sleeve should be replaced or corrected; B. The setting water is too small and the vacuum is not large enough, causing the product to fall out of round without setting. The setting water or vacuum degree should be increased; C. Traction pressure If the squeeze is too tight, the gap of the traction track should be adjusted appropriately; D. The position of the supporting roller in the shaping box is too high, which causes the lower end of the product to be flat. The tug should be adjusted to make it concentric; E. The impact of the cooling water is too large to be cooled without being vacuum shaped. Therefore, the water flow should be appropriately reduced.
Answer: A. The problem of the raw material itself; B. The screw is severely worn and the gap has changed; C. The material in the head is decomposed and there is sticky material.
Answer: A. There are impurities in the raw materials; B. The processing temperature is too low; C. The traction speed is too fast (the product is thinned with a large gap); D. The ingremoldnt structure is not ideal.
Answer: A. Regardless of the material temperature, the temperature of each zone should be appropriately lowered in advance; B. When changing the material, pay close attention to the current or torque changes. If the torque is found to rise rapidly, you need to immediately reduce the feed or stop the feed; C. If the torque is basically unchanged, the vacuum device of the barrel should be opened at this time to observe the vacuum plasticization and the filling of the material in the screw groove; D. Control the material amount in an appropriate range so that the volume of the material accounts for 2/3 of the volume of the screw groove Turn left and right to make it in a semi-plasticized state; E. Observe its condition when the product is extruded from the mold, and then adjust the speed and temperature of each zone to make the material plasticize well and meet the production requirements.
Answer: 1. Rough inner wall: This phenomenon is the most serious phenomenon that causes the product to be brittle. Even a little roughness will have a great impact on the product. Therefore, it is better to make the product wrinkle rather than rough during production. Improvement method: A. Increase the vacuum of the main engine to control the amount of filling material within an appropriate range and do not cause it to take off; B. Reduce the temperature of the body and the synchronous speed; C. If the formula has not changed, the mixing time should be shortened ; D. Avoid fuselage string temperature.
- Poor plasticization: Solutions: A. Improve the formula; B. Increase the temperature of each zone or extend the mixing time to increase the mixing temperature
- Third, the mold compression ratio is too small: the compression ratio is too small to make the material plasticized uniformly, and it is easy to cause the product to be less dense and make the product brittle. The mold compression ratio should be increased.
; C. Reduce the synchronous speed so that the material is plasticized in the machine before being pushed out .