Analysis of quality problems in profile extrusion
DATE：2022/10/19 9:00:56 / READ： / SOURCE：This station
Analysis of quality problems in profile extrusion
The temperature is too high, the product molding is difficult, and the raw materials are easy to decompose. ④ During the extrusion molding production, the barrel and molding die temperature and process temperature are low, and the raw materials plasticization cannot meet the requirements. The molding is also difficult. The surface of the products is rented, and sometimes the gas and products cannot even be produced normally.⑤ , and then directly use water to cool and finalize. During vacuum setting, the vacuum degree is 0.06~0.08MP, and the temperature of water is controlled at 15~20 ℃. The vacuum degree is too high, and the traction resistance increases. Output of government products; The vacuum degree is low, the geometric accuracy of the product is low, and the overall dimension error is large. The flow direction of water should be from the extrusion end of the product to the mold end.
⑥ It is appropriate to control the screw speed at 15~25r/min, the higher speed is taken when the wall thickness is less than 1mm, and the lower speed is taken when the wall thickness is greater than 2mm.
⑦ The speed of the feeding screw should match the speed of the extrusion screw. Generally, the speed of the feeding screw is controlled to be about twice the speed of the extrusion screw.
⑧ The pulling speed should match the extrusion speed of the product from the die mouth. Generally, the pulling speed is slightly faster than the extrusion speed of the product from the die mouth, usually within the range of 1.05~110 times.
(6) Analysis of quality problems in profile extrusion
① Longitudinal shape fluctuation of profile
a. The feeding fluctuation (refers to the unstable rotation of the feeding screw or the uneven feeding of the hopper) may lead to the bridging of the powder.
b. The barrel heating temperature control is unstable.
c. The traction speed is uneven, fast and slow.
② The product is warped
a. The working center lines of each equipment on the production line are not in the same straight line.
b. The parison cooling speed is inconsistent.
C. The vacuum degree and cooling water temperature of the finalized cooling jacket are not controlled reasonably.
d. The screw speed is too fast, and the parison shaping cooling is insufficient.
③ There are longitudinal streaks
a. The mold structure design is unreasonable, the molten material molding pressure is insufficient, and the length of the molding section is insufficient.
b. The raw material selection in the product formula is unreasonable.
c. There are scratches on the die part.
④ The shrinkage of products after molding is relatively large
a. The traction speed is too fast.
b. Short shaping cooling time.
c. The temperature is too high during molten metal forming.
⑤ Large shrinkage of reinforcement
a. The flow rate of molten material in the rib part of the die forming part is slow, and the drawing amount is large.
b. B. The cooling water temperature is too high.
c. The working vacuum or pressure of the sizing sleeve is adjusted improperly.
⑥ Cracks in products
a. The raw materials are plasticized unevenly, and the barrel temperature is low.
b. The mold temperature is low.
⑦ The product surface has spots, fish eyes or bubbles
a. There are impurities in the raw materials.
b. There is water or volatile matter in the raw materials.
c. Insufficient venting of molten materials during extrusion.
d. The working temperature of the screw is too high.
⑧ There are yellow lines on the surface of the product
a. The melting material has a high plasticizing temperature and is decomposed.
b. The molten material in the inner cavity of the molding die does not flow smoothly, and partial decomposition residues remain.
c. The selection of raw materials in the formula is unreasonable, and some raw materials have poor thermal stability.
⑨ Stripes or cloud patterns on the surface of the product
a. The mixing temperature and time of raw materials are unreasonable. b. Too much lubricant is added in the formula.
c. The raw materials in the main raw material PVC resin are impure and mixed with materials of different brands.
Chapter 9 Plastic Wire Extrusion Molding
9.1 Polyethylene wire
Polyethylene wire is extruded with high-density polyethylene resin. The fineness (diameter) of the filament can be 0.15~0.30mm; It can be divided into fishery silk, industrial silk and civil silk according to their uses. Polyethylene wire has the characteristics of high strength, light weight, good abrasion resistance and chemical corrosion resistance, good elasticity, good flexibility in low temperature environment, no influence on the strength in water and excellent dielectric properties. The polyethylene wire is mainly used in the manufacture of dragnet, purse seine and fixed net in fishery; Used as filter screen and various ropes in industry; It is mainly used for window screening.
(1) The main raw material for extrusion molding of polyethylene monofilament is high-density polyethylene resin with a melt flow rate of 0.4~1.0g/10min. The application brands include SR5000 produced by Sinopec Beijing Yanshan Petrochemical Co., Ltd. No. 1 Chemical Plant, 5000S produced by PetroChina Daqing Petrochemical General Plant, GF7750 and GF7750J produced by Liaohua, which can be used to form monofilament.
(2) Equipment conditions The production line for polyethylene filament extrusion molding is shown in Figure 9-1.
Figure 9-1 Polyethylene monofilament extrusion process flow 1-single screw extruder; 2 - Forming mould; 3 - Cooling water tank;
4 - First tension device; 5 - Hot stretching water tank; 6 - Second stretching device;
7 - Heat treatment oven; 8 - Third tension device; 9 - Winding device
The equipment on the production line mainly includes single screw extruder, molding die and auxiliary machine.
Author：admin