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Causes and solutions of dents in plastic products of injecti

1、 Causes of dents
1. The thickness of each part of the product is different
2. Insufficient internal pressure of mould
3. Insufficient mold cooling
4. Deformation due to insufficient cooling time
2、 Associated knowledge
1. In the process of producing products, dents are the most frequent defects, which are injected into the mold
When the material is cooled, the volume shrinks. In the early cooling part, the surface hardens first, and bubbles will be generated inside
Dent refers to that the part with slow cooling produces a conspicuous dent in the direction of bubble contraction.
2. Materials with high shrinkage are also prone to dents. When the forming conditions are to be changed to eliminate dents, the
The setting conditions should be set in the direction of shrinking. That is to say, the mold temperature and barrel temperature are reduced, and the injection pressure is increased
It should be noted that this may cause residual internal stress.
3. Because the dent is better to be inconspicuous, if it does not affect the appearance, it is intentionally placed in the mold
It is processed into a corrosive pattern, such as striation, graininess, etc. Also, if the molding material is hips, use
Reducing the mold temperature to reduce the finish also has an effect. But once these methods have dents, they want to repair and polish them
There are difficulties with the product.
3、 Solution
1. Instant: injection molding machine increases injection pressure, prolongs injection holding time, reduces barrel temperature and mold temperature,
Force cooling where dents are created.
2. Short term: fill up the flow edge where the dent occurs. In the place where the dent occurs, the material has
When the place is small, the edge of this part is thick.
3. Long term: the thickness difference of the designed products should be completely avoided. Dented stiffeners, narrow
The long shape should be as short as possible.
4、 Differences in materials
Forming materials with large shrinkage and large dents. For example, PE, PP, even if only a small amount of stiffener
There will be dents.
Material forming shrinkage
PS 0.002~0.006
PP 0.01~0.02
PE 0.02~0.05
5、 Reference:
1. When the temperature of the injection molding machine is reduced to no dent, if the material in the cavity still has pressure, it should be considered
It won't dent. The pressure around the material in the mold is the static pressure, no matter where
Fang is not necessarily. The pressure near the gate section is high if the material has a wide through edge because it reaches every corner
The pressure difference between the near gate and the far gate is very small compared with that of the whole gate
There is no dent, and the products without residual internal stress can be obtained. And part of the material is having trouble flowing in
When the pressure in this place is high, the pressure in other places will be reduced to produce dents. This part
The residual of high pressure is that the internal stress of products is also large. Under the ideal condition, the material temperature is the same as the mold temperature
The fluidity of the material is better, and the injection is at the bottom of static pressure.
2. When changing the forming conditions, the combination of temperature, pressure and time shall be prepared in advance according to
In order, we can know the result early. First of all, after a long period of time, every small change in pressure also allows
Easy to know. It should be noted that the result of temperature change should be obtained after the injection material, and the temperature should be reduced
Results at post reproduction