Why Do Pet Bottle Preform Have Cracks?

Cracks are narrow cracks or cracks that appear on the surface of Pet Bottle Preform, possibly due to injection molding machines, molds, processes, or raw materials.

(1) Injection molding machine
Mainly because of insufficient plasticizing ability, that is, the plasticizing ability is too low, resulting in insufficient plasticization. It is necessary to replace an injection molding machine with a large plasticizing capacity.

(2) mold
1 poor exhaust gas is easy to cause flow marks and reduce the strength of parts;
2 The size of the gate is too large, so that the pressure of the plastic injection molded part is too large; the gate size should be reduced;
3 water leakage in the cavity or core – check for fine cracks;

4 plastic parts are designed too thin – need reinforcement;

5 Check the cavity to see if the core has enough draft angle;

6 thimble oil spreads to the cavity surface – the mold needs maintenance and repair;

7 increase the diameter of the ejector pin and reduce the ejection speed;

(3) Injection molding process
1 Adjust the barrel temperature. If the temperature is too high, the material will decompose; if it is too low, sufficient welding strength cannot be guaranteed;

2 Adjust the injection pressure. Increase the temperature to ensure smooth filling and reduce the viscosity; if the pressure is too high, the crack will be caused by internal stress, so the pressure needs to be reduced;

3 reduce the preform back pressure and screw speed to avoid material decomposition;

4 appropriately increase the injection speed;

5 increase the cooling time. If the cooling time is too short, sufficient solidification cannot be guaranteed, resulting in spray cracks or spray marks;

(4) Raw materials
1 to ensure that the raw materials are completely dry;

2 the raw materials are contaminated; find out the cause and take control measures;

3 Add too much recycled material – determine the appropriate proportion of recycled material through the test results.

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