Generally speaking, there are many reasons for such problems, but if they are not dealt with in time, they will not only cause bad plastic molding but also may produce more defects.

Therefore, when there are bubbles in injection molding products, it is important to solve the problem in time. In addition, we also know how to solve the problem of air bubbles in injection molding products. Here is a detailed introduction.

Types of air bubbles divided

There are two causes of bubbles in the plastic injection molding process: one is vacuum voids and other water vapor.

(1）Bubbles due to the presence of moisture

Cause: insufficient drying of plastic material and cause plastic material for hydrolysis.

Solution: Adequate pre-drying pay attention to the hopper insulation management.

(2）Vacuum bubble

Causes of vacuum bubbles:

a. The thick-walled part of the material flow freezes quickly, the shrinkage is prevented, and the mold is not filled enough to produce a vacuum bubble in the injection molding process parameters.

b. The melt temperature setting of the injection mold is not suitable. The barrel temperature is not suitable, and the injection pressure and holding pressure are not enough.

Solutions:

a. Avoid uneven wall thickness structure of plastic product design. Fix the gate position so that the plastic flow material is injected vertically into the thick wall part.

b. Increase the temperature of the injection mold. Lower the barrel temperature. Increase the injection pressure and pressure-holding pressure.

What causes bubbles in injection molded products?

Equipment

The nozzle hole is too small, the material is salivating or drawing at the nozzle, there are obstacles or burrs in the barrel or nozzle, and the high-speed material flow path through the past produces frictional heat to make the material decompose.

Mould

(1) Due to design defects, such as poor gate position, too small gate, asymmetric gate arrangement for multi-gate parts, small runners, the unreasonable cooling system of the mold to make the difference of mold temperature too big, etc. cause the molten material to flow discontinuously in the mold cavity and block the passage of air.

(2)The mold parting surface lacks the necessary exhaust orifice or exhaust orifice is insufficient, blocked, poor location, and there is no insert, ejector, and other processing gaps exhaust, resulting in the air in the cavity can not leave at the same plastic and cycle time when the plastic enters.

(3) Poor surface roughness of the mold, friction resistance, resulting in local overheating, so that the plastic through decomposition.

Process

(1) The material temperature is too high, causing decomposition. The barrel temperature is too high or the heating is out of adjustment, and the barrel temperature should be reduced section by section.

The temperature of the charging section is too high, so that part of the plastic melts prematurely and fills the screw groove, and the air cannot be discharged from the charging port.

(2) Small injection pressure, and short holding time, so that the molten material and the surface of the cavity are not close to each other.

(3) Injection speed is too fast so that the molten plastic is decomposed by large shear, resulting in decomposition trapped gas; injection speed is too slow, can not fill the cavity in time to cause the product surface density is not enough to produce silver lines.

(4) Cooling time is too short (especially for thick-walled products), the solution can be outside the machine with cold water and cold pressing mold for cooling.

(5) The product has the phenomenon of decomposition black line, which is formed due to the high temperature. If the situation is not serious, the temperature can be properly reduced, if the entire barrel decomposes, it must be disassembled and cleaned.

Raw material

(1) Raw materials mixed with foreign plastic or granules mixed with a large amount of powder melt easily in entrapped air, and sometimes silver lines will appear. Raw materials are contaminated or contain harmful crumbs when the raw materials are easily decomposed by heat, poor melt flow pattern is a major cause of bubbles.

(2) Recycled material grain structure is loose, the amount of air stored in the microporous; recycled material regeneration too many times or too high with the proportion of new material (generally should be less than 20%)

(3) Raw materials containing volatile solvents or raw materials in the liquid additives such as dyeing aid white oil, lubricant silicone oil, plasticizer dibutyl ester and stabilizer, antistatic agent, etc. too much or mixed unevenly, to accumulate state into the cavity, the formation of the silver pattern.

(4) Adding too much or too little material, and the injection pressure is too high, will also produce this phenomenon.

How to solve bubbles in injection molded products?

1. Some bubbles are mainly caused by material degradation, which can be solved by reducing the speed, increasing the back pressure, and reducing the injection molding temperature and molding speed. Also, do a good job of exhaust.

2. PC transparent product bubbles are generally caused by the exterior cooling faster, the resin will face outward, that is, to the cold direction shrinkage, so that the products form a vacuum, from the appearance of the bubble.

The solution is to raise the mold temperature, lower the material temperature, find the location of the product where the bubble is formed, and shoot the glue in sections.

The speed of injection is adjusted according to the structure of the injection mold, and the appropriate pressure-holding is adjusted to ensure that the products are full and prevent shrinkage.

Auxiliary conditions: the raw material should be well dried, the temperature of the injection nozzle should not be too low, and the injection nozzle should not be too small.

3. Slow injection molding system, the product feels full after the high pressure holding atmospheric pressure pushing for a few seconds, and the speed of holding pressure can be adjusted to about 15. The pressure must be large, the holding time can be longer, and the injection time should not be too long.

Summary

Through the above introduction, I believe that you have a certain understanding of the causes of bubbles in injection molding products, there are many reasons for bubbles in injection molding products, when such a situation arises, exclude them one by one.

In addition, there are ways to solve, in the use of methods to solve the injection molding products with bubbles, but also can not be careless, do not know can also consult the professional plastic manufacturing injection molding machine tuning personnel operation.