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Some Uncertainties in Automatic Extrusion Blow Molding

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Time of issue:2022-03-15

Automatic extrusion blow molding machine

During the production of fully automatic blow molding, it is often encountered that the weight of the product is not stable and the weight of the product exceeds the specified deviation. Its main feature is that the material at the bottom of the bottle is in different lengths. In severe cases, the length of the parison is not enough to blow the product. The reasons are as the following:

1. The temperature control is inaccurate or the temperature deviation is large. It is an unreasonable installation point of the temperature measurement point (thermocouple), which causes the temperature to have a periodic deviation. The deviation range increases, and the influence of the weight deviation also increases. When the temperature rises, the extrusion parison stretches, and in the same operating cycle, the outlet material at the bottom of the bottle increases and the weight of the product decreases; as the temperature decreases, the weight of the product increases. When the thermocouple has poor contact, there is a similar problem. If the thermocouple is broken, the amount of extrusion is reduced. When the temperature is lower than the melting point of the plastic, the motor current increases and the material cannot be extruded. Whether the installation position of the thermocouple is reasonable and the area of ​​the thermocouple measuring point of temperature control will directly affect the smoothness of extrusion.

2. The operating time of the two sides of mold platens is inconsistent (the difference is too large). If the flow rate of the parison is constant, when the time between the left and right mold bases varies greatly, the weight of products on both sides is unstable. The faster move of the mold frame  the product is heavier, while the slower move of the mold frame the product is lighter due to stretching. The solution is to adjust the movement of the mold bases on both sides to bring the running time closer.

3. The extrusion volume is unstable, due to the unstable rotational speed of the motor and the unsuitable tightness of the belt.

4. The reason for plastic raw material, due to different plastic raw material or mixing ratio changes that causes the different lenth of parison. If it is often changed for the mixing ratio between new material and recycled material, then it will affect the amount of parison extrusion.

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