The structural characteristics of the screw and barrel of the film blowing machine

Update: 2021/09/02

The screw section of the film blowing machine is a scre […]

The screw section of the film blowing machine is a screw groove with a fixed groove depth. In addition to its main functions of mixing, output and measurement of the melt, it must also provide sufficient pressure to maintain a uniform temperature of the melt and stabilize the flow of the molten plastic. Metering section Long, the mixing effect is good; too long the metering section will easily make the melt stay too long and cause thermal decomposition; too short will easily make the temperature uneven.

Film blowing machine screw length to diameter ratio = screw working length (mm) ÷ screw diameter (mm)

If the aspect ratio is large, the food is easy to eat evenly, but it is easy to overheat. For plastics with better thermal stability, a longer screw can be used to improve mixing performance without scorching; for plastics with poor thermal stability, a shorter screw or no screw at the end of the screw can be used.

Film blowing machine screw compression ratio = feeding tooth depth (mm) ÷ measuring tooth depth (mm)

Consider the compressibility of the material, the degree of filling, the return flow, the compactness of the product, the heat transfer and the exhaust. A proper compression ratio can increase the density of the plastic, make the molecules and molecules more tightly bound, help reduce the inhalation of air, reduce the temperature rise due to pressure, and affect the difference in output, which is not appropriate. The compression ratio will destroy the physical properties of the plastic. The higher the compression ratio, the higher the temperature rise of the plastic during the plasticization process in the barrel, and the better mixing uniformity for the plastic in the gelatinization, and the relative output volume Greatly reduced. When the tooth depth of the feed section is deeper, the conveying capacity will increase, but the required torque of the screw of the film blowing machine is larger; the tooth depth of the feed section is too shallow, the conveying capacity is not enough, and the compression ratio is insufficient. When the metering section is too deep, the compression ratio is insufficient, and the required feeding force is greater; when it is too shallow, it is easy to overfire and burn. High compression ratio is suitable for non-meltable plastics, especially plastics with low melting viscosity and thermal stability. Low compression ratio is suitable for fusible plastics, especially high melting viscosity, heat-sensitive plastics.

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