Analysis and solution to the causes of bubbles and voids in TPE injection molded products

TPE bubbles and voids mostly refer to the voids generated inside the thick wall of the molded part. The outer casing of the molded part is condensed and solidified by injection molding, and the amount of the melt is insufficient relative to the entire part, thereby generating vacuum holes, which generally occur. In places where the product is thick and at the sprue. It is called a bubble or a void. Generally speaking, if a bubble is found at the moment of opening, it is a gas interference problem. 
The formation of vacuum bubbles is due to insufficient filling or low pressure. Under the rapid cooling of the mold, the molten material in contact with the cavity is involved, resulting in a volume loss. 

In this sense, the term “bubble” is not appropriate, at least in the moment after the formation, there is no air in the hole. Bubbles generated by this reason cannot be said to be defects of molded parts, but most of them are not problematic as opaque or colored parts. However, it is necessary to eliminate the bubbles in the roots of the main runner of the transparent part and the sprue.

1. Injection molding machine: (similar to the sink marks)

2. Mold: thick-walled parts.

3. The process: this is the same as the reason for the lack of compression to produce sink marks. Therefore, it is necessary to increase the diameter of the main runner, sprue and gate, reduce the temperature of the melt, raise the temperature of the mold, and use a plastic with poor fluidity to ensure sufficient injection and holding time and reduce the injection speed. However, for thick-walled parts and crystalline plastics, most of them cannot eliminate the voids even if necessary measures are taken. Non-transparent parts produce several shrinkage holes without any hindrance. For parts that do not allow bubbles, the shrinkage holes are not considered, so that no bubbles are generated inside, the mold can be demolded before the wall thickness portion is fully hardened, and then immersed in slow cooling in warm water, this method is sometimes effective in preventing bubbles. 

For this reason, the bubble is exactly the same as the reason why the uneven cooling produces a shrinkage cavity. Therefore, the method of preventing defects is also the same, and eliminating bubbles is theoretically difficult. Therefore, it is important to avoid designing the desired part into a shape that is prone to bubble formation. Slow cooling in warm water is also effective.

4. Plastics: When TPE plastics contain moisture or volatile components, and plastics or added components are decomposed into gas in the cylinder, bubbles are injected into the cavity as the melt is injected. When bubbles are generated due to volatile components or moisture, the bubbles can be eliminated by improving the back pressure and sufficiently cooling the lower portion of the hopper to improve the exhaust in the cylinder while sufficiently drying the raw material. Bubbles can be eliminated by overheating decomposition, lowering the melt temperature, and shortening the residence time of the melt in the barrel.
5. Some TPE plastic parts quickly swell or swell on the back of the metal insert or in a particularly thick part after the mold is demolded. 
This is because the plastic that is not completely cooled and hardened is caused by the release of gas under the action of internal pressure.

 Solution:

1. Effective cooling. Reduce the mold temperature, extend the mold opening time, and reduce the drying and processing temperature of the material.
2. Reduce the filling speed, reduce the forming cycle and reduce the flow resistance.
3. Increase holding pressure and time.
4. Improve the condition that the wall of the part is too thick or the thickness changes greatly.

About JasonMould Industrial Company Limited

Jasonmould is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.

Contact:
Person: James Yuan
Company: JasonMould Industrial Company Limited
Add:  LongGang Village,LongXi Town,BoLuo County,HuiZhou City,GuangDong Province, China
Tel: 86-752-6682869
Email: [email protected]

Site: https://www.jasonmolding.com/low-volume-manufacturing/