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Home » Blog » Causes and Solutions of Plastic Molding Shortcomings (3)

Causes and Solutions of Plastic Molding Shortcomings (3)

The last two times have talked about these problems, to understand can click here.

1. Deformation of finished products.

Fault causes and solutions.

(1) The finished product is not yet cooled when topped to reduce the temperature of the mold, extend the cooling time and reduce the temperature of the plastic.

(2) Plastic temperature is too low to raise the plastic temperature, raise the mold temperature.

(3) Finished product shape and thickness asymmetric mold temperature zone control. After remolding, it is fixed with a shaping frame, changing the shape design and filling too much to reduce the injection pressure, speed, time, and dosage.

(4) Uneven feeding several overflow ports, change the overflow port.

(5) Unbalanced ejector system, improve ejector system.

(6) Uneven mold temperature adjusts the mold temperature.

(7) The plastic near the overflow part is too loose or too tight to increase or reduce the injection time.

(8) Poor pressure-holding increases the pressure-holding time.


2. Air holes in the finished product.

The fault causes treatment methods.

(1) The amount of packing is not enough to prevent excessive shrinkage of the finished product.

(2) Finished section, rib, or column is too thick to change the finished product design or overflow location injection pressure is too low to increase the injection pressure.

(3) Insufficient injection volume and time increase the injection volume and time sprue overflow is too tiny, increase the sprue and overflow.

(4) The injection speed is too fast. Slow down the injection speed.

(5) The plastic contains water, and the plastic is thoroughly dried.

(6) The plastic temperature is too high, so decomposition reduces the plastic temperature.

(7) Mold temperature is not uniform. Adjust the mold temperature.

(8) Cooling time is too long to reduce the cooling time in the mold. The use of water bath cooling too quickly reduces the water bath time or increases the temperature of the water bath.

(9) Backpressure is not enough to increase the backpressure.

(10) Improper temperature of the melting cylinder reduces the temperature of the nozzle and the front section and increases the temperature of the rear section. The shrinkage rate of the plastic is too large. Use other plastics with a lower shrinkage rate.


3. Black pattern.

Failure causes treatment methods.

(1) Plastic overheating.

(2) Plastic temperature is too high to reduce the plastic temperature.

(3) Melting speed is too fast to reduce the injection speed.

(4) Screw and melt barrel eccentric and produce very frictional heat to repair the machine.

(5) The injection nozzle hole is too small, or the temperature is too high. Readjust the hole size or temperature.

(6) The injection volume is too large to replace the smaller injection molding machine.

(7) There is a plastic overheating in the melt cylinder * angle, check the contact surface between the injection nozzle and melt Jane. There is no gap or corrosion.


4. Blackspot.

The fault causes treatment methods.

(1) plastic overheating part attached to the inner wall of the melt tube thoroughly empty shot, remove the melt Jane clean up. Reduce the temperature of the plastic. Reduce the heating time, strengthen the plastic drying treatment plastic mixed with debris, paper clips, etc., check the plastic, thoroughly empty shot.

(2) Focal spots are generated when injected into the mold. Reduce the injection pressure and speed, reduce the plastic temperature, strengthen the mold vent, reduce the mold pressure, and change the overflow position. There is a * angle inspection in the melting cylinder to make the plastic overheated whether there is any gap or corrosion on the contact surface between the nozzle melter.

5. Unstable cycle.

Most of the causes and countermeasures for the various molding shortcomings listed above are related to the stability of the cycle or not. Proper plasticization of plastic in the melting cylinder, or temperature control of the mold, results from heat transfer balance. That is to say, during the whole injection cycle, the plastic inside the molten Jane receives heat from the frictional heat of the screw rotation, the heat of the electric heater ring.

The heat energy is injected into the mold with plastic, and heat energy of the mold comes from the plastic and the constant wear of the mold, lost in the remolding of the finished product, dissipated in the air, or taken away in the cooling water. Therefore, if the temperature of the melt or mold remains constant, it is necessary to maintain a balance of heat transfer in and out of the mold. To maintain the balance of heat transfer, it is necessary to maintain a particular stable injection cycle.

If the injection cycle time is getting shorter and shorter, the heat energy in the melting cylinder is not enough to melt the plastic, and the heat energy in the mold is more than out, so the mold temperature is rising. Therefore, in an injection molding operation, especially manual operation, it is necessary to control the stable cycle time and avoid the fast and slow one by one.


If other conditions remain unchanged, then:

A faster cycle time will result in short shots, shrinkage and deformation of the finished product, and sticky mold.

If the cycle time is slowed down, it will cause: overflow, burr, mold, deformation, plastic overheating, and even scorching, and the scorched material left in the mold may cause mold damage. The overheated plastic in the melting cylinder may corrode the cylinder and the finished product with black spots and black lines.

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