Plastic Injection Mold Components Resemble Vacuum Bubbles

Basic phenomenon of vacuum bubbles

Plastic product vacuum bubbles, also known as shrinkage cavities or cavities, generally appear on plastic parts where a large amount of melt accumulates, which is caused by sufficient replenishment of the melt during cooling and shrinkage. Shrinkage cavities often appear in the thick-walled areas of plastic parts, such as the junction of stiffeners, support columns, and the surface of plastic parts.

Defect causes and improvement methods

The reason for the shrinkage of plastic parts is that when the melt turns into a solid, the volume of the thick wall shrinks slowly, resulting in tensile stress. At this time, if the surface hardness of the plastic part is not enough and there is no melt supplement, a cavity will be formed inside the plastic part.

The reason for the shrinkage of plastic parts is that the shrinkage is concave on the surface of the plastic part, while the shrinkage cavity forms a cavity inside. Shrinkage cavities usually occur in thick-walled parts, which are mainly related to the cooling speed of the mold. The cooling rate of the melt in the mold is different, and the degree of shrinkage of the melt in different positions will be different. If the mold temperature is too low, the melt surface will be rapidly cooled, and the hot melt in the thick-walled part will be pulled to the surrounding surface. It will shrink and cause holes inside.

Shrinkage of plastic components

Plastic parts’ strength and mechanical characteristics will be impacted by the phenomenon of shrinkage cavities. The shrinkage cavity will also impair the products’ look if they are made of clear plastic. The regulation of mold temperature is the main goal of reducing product shrinkage.

*These are the precise causes and remediation techniques:

1. The ribs or columns in the finished product segment are overly thick.

2. The temperature of the mold is too low,

3. Either the injection speed or the injection pressure is too low.

4. The gate size is too tiny or in the wrong place.

5. The runner is excessively tall or skinny (the melt is easy to cool).

6. Inadequate holding force or holding duration.

7. The runner’s cold slug hole is too small or insufficient.

8. Either the injection volume is too small or the melt temperature is too low.

9. Too much time is spent chilling the mold.

10. The water bath cools off too quickly (the water temperature is too low).

11. Back pressure is insufficient (low melt density).

12. A glue leak or a clogged nozzle (the heating ring is burned out).

*Matching improvement strategy:

1. Make the product’s design better and work to make the wall thickness uniform.

2. Raise the temperature of the mold (use a mold temperature machine).

3. Boost the injection pressure or speed.

4. Modify the gate size or gate position (thick wall).

5. Make the runner wider or shorter as appropriate.

6. Boost the holding force or extend the holding period.

7. Enlarge the cold material hole or make it accessible.

8. Increase the melt temperature or the melt stroke, as appropriate.

9. Use a hot water bath to speed up the mold’s cooling process.

10. Raise the water’s temperature to stop the bath from cooling too quickly.

11. Properly raise the melt density and back pressure.

12. Straighten, clean, or remove the nozzle.

Basic phenomena of Bubbles.

Bubble defects, also known as air defects. occur when the plastic melt fills the cavity formed by the multiple melt front wrapping or the melt filling end. Because the gas cannot be discharged, it is wrapped in the melt and will remain in the melt. Air bubbles form on plastic parts.

*Causes of bubble generation and improvement methods

1. The back pressure is too low or the melt temperature is too high.

2. The raw materials are not sufficiently dried.

3. The screw speed or injection speed is too fast.

4. Poor mold exhaust.

5. The residual amount of melt is too much, and the time for the melt to stay in the barrel is too long.

6. The gate shape is too large or the shape is not suitable.

7. The thermal stability of plastic or toner is poor.

8. The glue in the glue barrel is trapped by air.

*Matching improvement strategy

1. Lower the material temperature or raise the back pressure.

2. the materials are completely dried.

3. Lower the injection or screw speed.

4. To enhance the exhaust effect, widen or extend the exhaust groove.

5. Lessen the remaining volume of a molten substance in the barrel.

6. To enable the gas to stay in the runner, reduce the size of the gate or alter its design.

7. Select materials or toners that have higher thermal stability.

8. Lower the feeding area’s temperature to enhance degassing.

What is different about the vacuum bubbles between the bubbles?

Bubbles are not the same as vacuum bubbles (shrinkage cavities). Bubbles refer to small bubbles existing in plastic parts, while vacuum bubbles are cavities that have been emptied of gas. They are cavities generated by uneven shrinkage when the melt is cooled and shaped. There is no gas present.

During the injection molding process, if the material is not sufficiently dried, the injection speed is too fast, the air is trapped in the melt, the mold exhaust is poor, the thermal stability of the plastic is poor, etc., small bubbles may appear inside the plastic part. When there are fine air bubbles inside the plastic parts, the surface of the plastic parts is often accompanied by silver streaks (material flowers).

The air bubbles in the transparent parts will affect the appearance quality. At the same time, it also belongs to the poor material of plastic parts, which will reduce the strength of plastic parts.