How to control film quality in blowing process?

Whether the plastic is complete and uniform, the bubble shape is stable, temperature is one of the main technological conditions.
In the production of polyethylene blown film, it should be based on the melt index of raw materials (I M) and different product specifications, select the different temperature, the general melt index, the lower the temperature of the processing time, the opposite is high. Such as extruding machine temperature is low, the plastic viscosity, transparency of the films, prone to not plasticizing the eutectic point and cloud, the film is easy to pull off, the elongation at break of the film decreased.
If the extruder temperature is high, the plastic viscosity is reduced, the fluidity is very big, the opening of the film is poor, and it is easy to cause the production is not stable, but the transparency is improved. Continue to heat up, the material is overheated decomposition, thin film yellow, yellow and black focus. So the temperature instability will make the bubble shape is irregular, affect the quality of products, and even cause defective.
Thickness control of blown film
Film thickness is one of the main indicators of quality control:
1. The head design cavity structure is smooth, no dead angle, so that the material flow rate is uniform and uniform.
2.The die gap is uniform, not biased, and can be easily adjusted to control the amount of the uniform material.
3. Cooling wind ring blowing flow and flow rate also should be stable. Otherwise, poor film cooling to extension thinning and anti thickened, to regulate the use of wind thickness.
4. The head heating device: head heating distribution should be uniform, to ensure equality at the resin flow of the die. Otherwise, the high temperature part of the film extends, the expansion becomes thin; otherwise, it becomes thicker.
5. The normal operation of the host, to ensure the discharge uniformity, traction speed should be uniform.
6. Influence of the incoming flow, in the blown film tube under cooling line parts, does not allow foreign wind power fluctuations caused by the disturbance of air flow, the used plastic film curtain set.
The effect of screw speed on the quality of film production:
Rod speed increases, plastic in the machine tube residence time is short, poor plastic, thin film appear plastic is not complete, or because of extrusion, cooling parts is not compatible, also can make the film appearance quality is not good. There are special circumstances in the production and increasing screw speed, feed will increase, and the temperature of the heater is not continue to heat up, production is still normal. This is due to shear heat, but must and traction ratio matching, the quality of the products to be stable. Screw rotational speed is lower, it is advantageous to the membrane tube cooling. In the case of incomplete plastic, reducing the screw speed is conducive to improving the quality of products, but the speed is low, plastic in the barrel of a long time, easy to break down. In short, the screw speed and processing raw materials, finished product specifications, temperature and other process conditions to ensure product quality.