In the injection molding process, the main reasons for the poor gloss of the injection molded parts are: mold, injection molding process, raw materials, etc. Let's take a look at the following:
First, the injection mold
1. Mold cavity processing is poor
If the mold cavity is flawed, microporous, worn, rough, etc., it will inevitably reflect on the plastic parts, so that the gloss of the plastic parts is poor. In this case, the mold must be carefully processed to make the surface of the cavity have a small roughness. It can be polished with chrome.
2. Cavity surface stains
If the surface of the cavity is oily or watery, or the release agent is too much, the surface of the plastic part will be dark and dull. To do this, remove the oil and water stains in time, and use the release agent in a limited amount.
3. The stripping angle of the plastic part is too small
If the draft angle is too small, the mold release is difficult, or the force is too large when the mold is released, so that the surface gloss of the plastic part is not good, and the draft angle is increased.
4. Die exhaustion
If the exhaust gas will cause too much gas to stay in the model, it will also lead to poor gloss. In this case, the mold exhaust system should be checked and corrected.
5. improper gate or runner design
The cross-sectional area of ​​the gate or runner is too small or abruptly changed. When the melt flows therein, the shear force is too large, and the turbulent flow is dynamic, resulting in poor gloss. For this, the gate and runner cross-sectional area should be appropriately increased.
Second, the injection molding process
1. The injection speed is too small
If the injection speed is too small, the surface of the plastic part is not dense, and the gloss is poor, and the injection speed can be appropriately increased.
2. Plastic parts are not fully cooled
If the thick-walled plastic parts are not sufficiently cooled, the surface will be hairy and the gloss will be dark. For this, the cooling system should be improved.
3. Improper pressure holding operation
If the holding pressure is too small and the holding time is too short, the density of the plastic parts is not enough and the gloss is poor. In this case, the holding pressure and the holding time should be increased.
4. If the melt temperature is too low
When the melt flow is too low, the fluidity is poor, which tends to cause poor gloss. For this, the melt temperature should be appropriately increased.
5. Crystalline resin is unevenly cooled
For plastic parts made of PE, PP, POM, etc., if the cooling is uneven, the gloss will be poor. For this, the cooling system should be improved to make it evenly cooled.
6. Injection speed does not match gate area
If the injection speed is too large and the gate cross-sectional area is too small, the vicinity of the gate will be dark and the gloss is poor. For this, the injection speed and the gate cross-sectional area can be appropriately reduced.
Third, raw materials
1. The difference in raw material particle size is large
The large difference in particle size makes it difficult to uniformly plasticize and the gloss is poor. For this, the raw materials should be sieved.
2. There are too many secondary materials in the raw materials
If the recycled material or the nozzle material is added too much, the uniform plasticization of the melt is affected and the gloss is poor. Therefore, the amount of the recycled material or the nozzle material to be added should be reduced.
3. The raw material has poor temperature resistance
Some raw materials will decompose and change color when the temperature is adjusted, resulting in poor gloss. For this, raw materials with good temperature resistance should be used.
4. Raw materials contain volatiles
If the content of moisture or volatile matter in the raw material is too high, it will volatilize into a gas when heated, and condense in the cavity and the melt, resulting in poor gloss of the plastic part. For this, the raw material should be pre-dried.
5. The dispersion of additives is not good
Some additives have poor dispersibility and poor gloss of plastic parts. For this, additives with better flow properties should be used instead.
6. Raw materials are not pure
If the raw materials are mixed with foreign materials, miscellaneous materials or incompatible materials, they cannot be uniformly mixed with the raw materials to cause poor gloss. For this, these impurities should be strictly excluded in advance.
7. Too little lubricant
If the amount of lubricant is too small, the fluidity of the melt is poor, and the surface of the plastic part is not dense, resulting in poor gloss. For this, the amount of the lubricant should be appropriately increased.
Therefore, according to whether your mold polishing degree meets the requirements, if the mold itself has no problem, determine the characteristics of your ABS to determine, you can choose high mold temperature, high speed and high pressure; with chilled water can also achieve smoothness.
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