Detailed explanation of material accumulation and production speed in the PVC calendering production process

PVC calendering film is one of the commonly used base films for color modification film, which has the characteristics of light weight, high mechanical strength, good insulation performance and easy processing, and its calendering process is mainly as follows: mixing - hot extrusion - calendering (extrusion, extraction, embossing) - cooling - winding.

Today, we will take you to understand two important influencing factors in the PVC calendering production process: material accumulation and production speed.

First, the impact of material accumulation on production

Poor rotation of the accumulated material will cause uneven transverse thickness of the product, bubbles in the film, and cold scars on the hard sheet.

Reasons for poor stock rotation:

1. The material temperature is too low or the material has poor fluidity due to the formula

2. The roll temperature is too low

3. Improper adjustment of roll distance

The size of the first accumulation and the raw and cooked material affect the size of the second and third accumulations, resulting in variations in thickness and circumference.

By appropriately adjusting the size of the second deposit, the influence of changes in the first accumulation (e.g., changing the die) on the thickness and circumference can be reduced.

Second, the advantages of making the accumulation material properly larger:

1. Make the temperature of the accumulation more uniform and reduce the influence of heat accumulation;

2. Better control of the circumference of 4 points (outward movement of the inflection point);

3. Reduce the impact of the change of the first accumulation on the third accumulation (the degree of influence is mitigated by the second accumulation);

4. When there is a lot of edge rising in the second accumulation (about 20cm or above), the missing edge caused by the raw material of the first accumulation material, due to the buffer of the second accumulation material, the material missing to the next round is not much, and the deviation of the bait is reduced.

Thirdly, the size of the accumulation material affects the height of the lower wheel lifting material and the stability of the lifting material

1. The temperature change of the accumulated material;

2. The change of the area of the roller in contact with the accumulated material causes the temperature change of the roller

The role of accumulation:

Proper accumulation can make the film smooth and reduce air bubbles, and the film has good density, which will increase the calendering effect. On the contrary, the no-accumulation rule is suitable for plastics or rubbers with high plasticity.

Second, the impact of production rate on production

Excessive speed:

1. Cause internal friction shear force and a large amount of "heat accumulation" may occur between the roll gaps, resulting in the orientation of the entire molecular chain (the molecular orientation and relaxation degree are different), causing poor flattening (the degree of molecular chain orientation is different, resulting in different retraction, even if the circumference is good) and the winding gas package (the degree of orientation is different, the immediate control of the circumference is very good, but because some points are tightened, the gas cannot be discharged)

2. The elastic potential energy increases (the elastic deformation becomes larger), the internal stress release of the material decreases when in the equipment, and the melt strength becomes smaller (the melt strength decreases with the increase of the melt flow rate, the higher the speed, the material is easy to melt and sag, and the melt strength is low).

(Increasing the stress or strain rate within a certain range will increase the reversible elastic deformation in the flow channel and aggravate the out-of-mold expansion; Decreasing the temperature of the polymer melt increases the elastic strain entering the die area, and the extension of the relaxation time will also increase the expansion from the mold) (elastic deformation, relaxation degree, melt strength)

3. The separation force becomes larger, which leads to the change of roller rapidity, resulting in medium and high temperatures.

4. It has an impact on the metal detachment, the speed is too fast, the transverse material temperature is unstable in the lower wheel due to the point of "heat accumulation" and heat dissipation, and the lifting material fluctuates, affecting the circumference, and the bait is easy to run, causing the circumference problem. (It is related to the size of the metal detachment of PVC) (the first accumulation material becomes unstable at a high production rate, and the edge is easy to grow)

5. The vehicle speed is high, although the shear force increases, the heating time of the material is shortened, which is more likely to cause the uneven temperature of the accumulated material and the material attached to the wheel surface, so that the mixed system contains raw meal and produces deep air spots; At the same time, there were inconsistencies in the degree of molecular orientation.

Knowledge

Detailed explanation of material accumulation and production speed in the PVC calendering production process

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