(1) Defect characteristics
(2) Causes and elimination methods of defects
The reason why bubbles appear in the plastic parts is that a large amount of gas is mixed into the plastic melt and solidified with the melt. The specific analysis is as follows.
1) Injection mold
(1) If the mold of the injection molding manufacturer has poor or blocked exhaust system, the excess gas will mix into the melt and become bubbles. To this end, the exhaust system should be carefully checked, or the blocked channels should be cleared.
(2) If the mold of the plastic supplier has a long or narrow runner or a dead corner in the runner, it will cause poor mold venting and bubbles. To this end, the runner should be shortened and enlarged, and the dead corners in the runner should be removed.
(3) In a multi-cavity mold, if the sizes of the various cavities are not the same, it is necessary to pay attention to the fact that the size of the gate is proportional to the quality of the plastic part, otherwise, the larger plastic part is prone to bubble defects.
2) Plastic molding process
(1) If the injection speed is too fast, the gas in the cavity will not be discharged in time and enter the melt to produce bubbles. To this end, the injection speed should be appropriately reduced.
(2) If the melt temperature is too high, it will cause melt degradation, which will produce a large amount of gas and form bubbles. To this end, the melt temperature should be lowered.
(3) If the melt temperature is too low, the fluidity is poor, which will cause insufficient filling, and the internal space of the plastic part will produce voids, forming bubbles. To this end, the melt temperature should be appropriately increased.
(4) If the melt is not cooled evenly or not cooled enough, it will cause bubbles in the plastic part. To this end, the cooling conditions should be improved.
(5) If the mold temperature is not properly controlled, too high or too low, it is easy to produce bubbles. To this end, the mold temperature should be selected according to the different plastics.
(6) If the feeding is too much or too little, it is easy to cause bubbles in the plastic part. To this end, the feeding should be controlled to an appropriate level.
(7) If the holding pressure is not enough or the holding time is not enough, bubbles are likely to appear. To this end, the holding parameters should be controlled.
(8) If the temperature of the barrel feed section is too high, it is easy to cause the melt to flow back and return to the material, which will produce bubbles. To this end, the feed section temperature should be controlled.
3) Plastic part
(1) If there are special thick parts on the plastic part, this position is prone to bubbles. To this end, special thick parts should be avoided on the plastic part.
(2) If there are parts with too much thickness difference on the plastic part, it is also a place where bubbles are easily generated. To this end, attention should be paid when designing the plastic part.
4) Raw materials
(1) If the diameter of the raw material particles is too different, a large amount of air will be mixed into the melt and bubbles will appear. To this end, the size of the raw material particles should be controlled and the difference should not be too large.
(2) If the powder material in the raw material is too much, it will make the melt difficult to plasticize evenly and easily generate bubbles. To this end, the powder material should be removed.
(3) If the raw material contains a lot of water, it will produce a large amount of gas after heating, which is easy to cause air flow. To this end, the raw material should be pre-dried.
(4) If too much recycled material is added, the recycled material contains a lot of impurities, which is easy to produce bubbles. To this end, the amount of recycled material added should be controlled.
(5) If some raw materials contain a lot of volatile substances, they will produce a lot of gas after heating, which will cause bubbles. To this end, this type of raw material should be replaced.