Failure and analysis of injection molding (1)

>>Failure and analysis of injection molding (1)

Failure and analysis of injection molding (1)

Injection molding is the plastic raw material after granulation, dying, adding additives and other processing of granular materials) into the cylinder, after heating plasticizing, making it the high viscosity of the fluid (melt), pressurized with piston or screw as a tool, make the melt with high pressure (about 25 ~ 80 Mpa) through the nozzle injection mold cavity, after cooling, solidified and demoulding, become plastic products. Defects caused by plastic forming may affect the assembly efficiency or the performance of the whole machine. These defects may be caused by mold, raw materials, process parameters, equipment, environment, personnel and other reasons. Here we summarize the defects as follows:

 

Moisture Streaks

Some imfusible layers of material are created on the surface of the mold to separate the parts (possibly water, gas) or to prevent the plastic from completely copying the original mold surface when it enters the mold.

Glass Fiber Streaks

Based on the length of glass fiber, or the relationship between the direction before melting flow and the direction, the change of flow speed and cooling speed, the bad arrangement of glass iron, and the appearance of float surface of glass domain (uneven distribution of glass fiber) due to vertical and oblique reasons, this situation will not only affect the appearance, but also reduce the engineering structure of injection parts.

Gas Trap Effect

This condition is caused by the presence of poor air emissions in the mold, which can be caused by design, material or poor injection molding conditions.

Silver Marks

This situation is caused by the fact that the hot melt plastic in the mold or the injection cylinder has a large amount of gasified water or the gas/water caused by the chemical reaction of the additive, which is injected into the mold cavity and pressed to radiate to form the silvery ridges during the injection molding process.

Weld Line

In the process of injection molding parts in the inflow of bad clamping produced bonding line, in the process of flow will also produce a similar fusion line. Both of them basically have the same original trap. Whether the plastic parts are poorly designed or the injection molding conditions are not good enough, the most important reason is that the confluence flow peak produces a temperature of = or >10 degrees.

Water Wave Effect

Injection parts in the process of the inflow of bad cooling conditions, injection speed or melt temperature are too low, which will produce water ripples. Or the plastic side into the side of rapid cooling, that is not the smooth movement of the plastic pressure to the wall and the plastic into the form of radiation propulsion after cooling the surface so that the formation of like water ripples/finger pattern.

Dark Spots

The black spots on the injection parts are all made of impurity. This person has many problems such as injection molding operation control, mold cleaning and wear, injection molding machine barrel cleaning and wear, raw material pollution/turn over abrasive pollution.

Visible Ejector Marks

Visible Ejector Mark is caused by ejection difficulties. And the demoulding difficulty is basically due to the plastic parts in the mold was pushed to cure insufficient and mold design/poor production.

Deformation During Demolding

The deformation of the injection parts does not occur until/after demoulding. The first is deformation due to poor curing conditions/poor die design, and the second is deformation due to poor injection pressure conditions provided during the injection molding process.

Short FiIling

Insufficient filling occurs in the following environments, one is a poor injection molding operation, the other is a poor injection molding part design. Most defects caused by injection processing factors are caused by excessive temperature drop and pressure drop during the injection process from the gate to the completion of filling. Defects caused by poor design of injection parts, most of which are caused by gate opening too far away, uneven thickness, overall thin glue level, special design restrictions, poor exhaust, etc.

(to be continued…)

By | 2019-03-13T06:46:13+00:00 February 25th, 2019|Industry News|0 Comments

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