Mold Tech

Why is the brightness of ABS mold injection molded parts low

• 2023-08-17

1、 Injection mold

1. Poor processing of mold cavity

If there are defects such as scratches, micropores, wear, and roughness in the mold cavity, it will inevitably reflect on the plastic part, causing poor gloss. Therefore, the mold should be carefully processed to make the surface of the cavity have a smaller roughness, and if necessary, it can be polished and chrome plated.

2. Surface stains on the cavity

If there are oil and water stains on the surface of the mold cavity, or if too much release agent is used, it will make the surface of the plastic part dark and lack luster. Therefore, it is necessary to promptly remove the oil and water stains and limit the use of release agent.

3. The demolding slope of the plastic part is too small

If the demolding angle is too small, it can cause difficulty in demolding, or if the force during demolding is too large, the surface luster of the plastic part will be improved. Therefore, it is necessary to increase the demolding angle.

4. Poor mold exhaust

If the exhaust is poor, it will cause too much gas to stay in the model and also lead to poor gloss. Therefore, it is necessary to check and correct the mold exhaust system.

5. Improper gate or runner design

The cross-sectional area of the gate or runner is too small or suddenly changes, and the melt is subjected to too much shear force when flowing in it, resulting in turbulent dynamic flow and poor gloss. Therefore, the cross-sectional area of the gate and runner should be appropriately increased.

2、 Injection molding process

1. The injection speed is too low

If the injection speed is too low, it can cause the surface of the plastic part to be not dense and exhibit poor gloss. Therefore, the injection speed can be appropriately increased.

2. Insufficient cooling of plastic parts

If the cooling of thick walled plastic parts is not sufficient, their surface will become rough and have a dull luster. Therefore, the cooling system should be improved.

3. Improper pressure maintaining operation

If the holding pressure is too small or the holding time is too short, resulting in insufficient density and poor gloss of the plastic parts, the holding pressure and holding time should be increased.

4. If the melt temperature is too low

When the melt flow is too low, it leads to poor fluidity and poor gloss. Therefore, the melt temperature should be appropriately increased.

5. Uneven cooling of crystalline resin

Plastic parts made of PE, PP, POM, etc., may have poor gloss due to uneven cooling. Therefore, the cooling system should be improved to ensure uniform cooling.

6. Mismatch between injection speed and gate area

If the injection speed is too high and the cross-sectional area of the gate is too small, the area near the gate will become dark and shiny. Therefore, it is advisable to reduce the injection speed and increase the cross-sectional area of the gate appropriately.

3、 Raw materials

1. Significant differences in particle size of raw materials

The difference in particle size makes it difficult to uniformly plasticize, and the gloss is poor. Therefore, the raw materials should be screened and treated.

2. There are too many secondary materials in the raw materials

If too much recycled material or nozzle material is added, it will affect the uniform plasticization of the melt and cause poor gloss. Therefore, the amount of recycled material or nozzle material added should be reduced.

3. Poor temperature resistance of raw materials

Some raw materials may decompose and discolor during temperature adjustment, resulting in poor gloss. Therefore, raw materials with good temperature resistance should be selected.

4. Raw materials contain volatile substances

If the moisture or volatile matter content in the raw material is too high, it will evaporate into gas when heated, and condense in the mold cavity and melt, resulting in poor gloss of the plastic parts. Therefore, the raw material should be pre dried.

5. Poor dispersion of additives

Some additives have poor dispersibility, resulting in poor gloss of plastic parts. Therefore, additives with better flowability should be used instead.

6. Raw materials are impure

If there are foreign objects, impurities, or immiscible materials mixed in the raw materials, they cannot be evenly mixed with the raw materials, resulting in poor gloss. Therefore, these impurities should be strictly excluded in advance.

7. Insufficient lubricant usage

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. Therefore, the amount of lubricant should be appropriately increased.

So, it is also necessary to determine whether the polishing degree of your mold meets the requirements. If there are no problems with the mold itself, it is necessary to determine the characteristics of your ABS. You can choose high mold temperature, high speed, and high pressure; Using chilled water can also achieve a smooth finish.

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