The hottest polyethylene film blowing molding proc

Polyethylene film blowing molding process (Part 2)

4. Cooling device in the film production process, the cooling of the bubble tube is very important. It takes only more than ten seconds from the die to the traction roller. During this time, the bubble tube must reach a de facto cooling level, otherwise the hot material is easy to adhere after being compressed by the traction roller. There are many kinds of air rings, including ordinary air rings, negative pressure air rings, etc

4.1 ordinary air ring, the air ring of an air outlet is the most common air ring, which is convenient to manufacture, simple in structure and low in cost

4.2 the structure of negative pressure air ring is more complex than that of ordinary air ring, but the cooling effect is good, and the bubble tube is stable (with double tuyeres)

4.3 the distance between the cooling air ring and the die is mm. How big is it now attached to the die head? The inner diameter of the air ring is generally 1% of the diameter of the die head Times, the gap width of the air outlet is mm

4.4 cooling methods include water cooling, internal cooling, etc. depending on the process

5. Traction device the traction device compresses the film pressed by the herringbone plate and sends it to the coiler to prevent air leakage from the bubble tube and ensure the stability of the bubble tube shape and size. Requirements for traction device

5.1 the center of the traction installation pressure roll should be aligned with the center of the herringbone plate and the center of the machine head, otherwise the distance from the film to the traction roll will be different, resulting in wrinkles

5.2 the distance between the die and the traction roller is at least times the diameter of the bubble tube. Otherwise, the film-cooled air gel will not adhere except for its excellent thermal insulation performance. At the same time, as the film tube changes from round to flat, the distance difference between different points around the bubble tube and the traction roller makes the film easy to wrinkle and deform after flattening

5.3 for pinch roll, one side should be steel roll and the other side should be rubber roll. The rubber hardness of rubber roll should be controlled within degrees. When it is too hard, such as when the pinch roll is deformed, it is easy to produce air leakage due to loose compression, which will cause uneven width of the film

5.4 the springs on both sides of the pinch roll should be able to adjust freely, otherwise the pinch roll will be tight and loose at the same time, which will pull the film away and deform, and it is easy to wrinkle

6. Herringbone plate herringbone plate is used to stabilize the bubble tube, and guide the circular bubble tube into a flat membrane for traction. The included angle of the herringbone plate plays an important role in the stability of the reeling film. The flat blowing is generally controlled at 30 °, and the up blowing and down blowing are generally controlled within 50 °. The included angle is large and easy to operate, but it will cause the film to wrinkle and have Ruffle edges

7. Coiling device the function of coiling device is to roll the product onto the reel with neat and moderate tightness on both sides. Therefore, the coiling device is required to provide reliable stepless speed regulation coiling speed and moderate tension. Coiling includes central coiling (active coiling) and surface coiling (passive coiling). Whether it is central coiling or surface coiling, it is required that the coiling core should achieve static balance, so as to achieve the balance of coiling

IV. properties and requirements of blow molded PE film raw materials

polyethylene (PE) including LDPE, HDPE and LLDPE is one of the plastic varieties with the largest output and the most widely used at present, accounting for about 30% of the world's total plastic output. It has excellent performance, easy molding, rich sources of raw materials, low price and fast development speed. The melting point of LDPE is ℃. The melting point of HDPE is ℃. As blow film, there are heavy packaging film, light packaging film and agricultural film. The molecular weight of PE resin is expressed by the melt index M1. If M1 is small, its molecular weight is higher and its tensile strength is also higher. When M1 is large, its molecular weight is light, and its strength is also lower. For industrial heavy packaging film, M1 should be smaller, for light packaging, M1 should be larger, and for agricultural film, M1 should also be smaller. M1 only represents the molecular weight of PE, not the distribution of molecular weight, the size of molecular weight and branching degree. Therefore, generally, we also look at the density. For PE, the temperature cannot be too high, the foaming strength of the film decreases too low, the plastic is good, the product is Matt, the transparency decreases, and the strength also decreases. Generally, the tail is 120, the front of the fuselage is 160 ℃ -170 ℃, the head is -150 ℃

v. the quality problems and solutions of blown film are easy to occur

5.1 the traction cannot be pulled (the experimental data of the tube blank system is automatically counted and broken) cause: the head temperature is too high or too low, solution: adjust the temperature, the thickness difference of one side is large, adjust the thickness of one side, and the machine does not discharge, adjust and check

5.2 the reason for the deflection of bubble tube: the forming temperature is too high, The cooling speed can't keep up, and the film thickness is uneven. Solution: adjust the clamping force imbalance at both ends of the die traction clamping roller, adjust the clamping force cooling. This discovery can greatly improve the plastic material in automobile or other fields. The air ring outlet is not balanced, and adjust it

5.3 crystal point. Multiple reasons: the molecular weight of the material itself is uneven, Solution: choose to process the raw materials of the model. The t ℃ is low. Adjust the t ℃ filtration thin or broken holes. Replace the machine itself. The l/d is too small. Appropriately increase the t ℃

5.4 wrinkles. Multiple reasons: the processing accuracy of the die head is not high. Solution: improve the smoothness, decompose the dirt, and clean 5.5 marks around the die. Reason: because there are sundries and coking materials trapped in the die mouth, solution: dig out

5.6 water marks. Reason: low plasticization at t ℃ is not good, Solution: improve t ℃

5.7 the original popularity of uneven film thickness will also be further expanded. Cause: the die head is biased. Solution: adjust the uneven temperature around the die head, adjust the blowing ratio too large, reduce the misalignment between the herringbone plate and the center of the die head, adjust the external air around the die tube circle to affect the swing isolation of the tube blank

5.8 wrinkle reason: the center of the die head and the herringbone plate is not aligned, Solution: adjust the film thickness unevenly, adjust the cooling unevenly, adjust the included angle of the herringbone plate, and it is not suitable to adjust the clamping force on both sides of the traction clamping roller, adjust the crimping tension unevenly, and adjust the

5.9 poor transparency reason: the body and head temperature are low, solution: adjust the cooling rate to be low, increase the air volume

5.10 obvious seam marks reason: the flow design of the die head is unreasonable, and the seam resistance is large, Solution: correct the unreasonable design of the compression ratio of the die head, and the compression ratio is too small. Correct the debris in the die mouth, and dig it out.

5.11. There are blocks. Reason: the molecular weight distribution of the raw material is too wide. Solution: change the processing temperature to be too low, and increase the processing temperature.

5.12. The film tube becomes a bamboo knot. Reason: the traction speed fluctuates. Solution: adjust 5.13. Film surface adhesion reason: the raw material is not the right model, Solution: replace the processing temperature is too high, reduce the cooling rate is low, increase the

precautions for starting the blown film unit

I. preparations before starting

1. Check whether the host motor is in the low-speed position, especially the commutator motor. Pay special attention to high-speed starting will damage the motor, or high-speed starting will twist the screw

2. Check whether the temperature of the fuselage reaches the control temperature. It is best to check it with a glass tube thermometer before driving to prevent false temperature. Correct and adjust t ℃

3. Pay attention to check whether sundries and iron objects fall into the hopper

4. Be sure to start at low speed when driving

II. Problems prone to occur during start-up and solutions

1. The machine does not discharge material, the temperature at the hopper mouth is too high, and there is material melting and caking, which will stick to the material mouth and affect the blanking (cleaning)

2. The motor belt expands and slides, and the host does not move. The solution is to tighten the belt or prevent slipping

3. Material leakage between hinges: hinges are not tightened or leveled, diagonally tightened and leveled; The filter plate is uneven and deformed, replace it

4. The air inlet nozzle is blocked, and there is no air inlet. The leakage is removed, and there is a gap between the diverter shuttle and the die

5. The air leakage of pinch roll leads to uneven film coiling. Adjust the gap and flatten the top roller

III. precautions for die head cleaning

1. Die head cleaning should be handled with caution and maintain a high finish

2. Copper tools must be used during cleaning, and iron tools are not allowed

3. Be sure to use 100 abrasive cloth when cleaning and sanding

source: polymer world