There is no problem with mold polishing, why is brightness of ABS injection molded parts low?

Time:2020-06-24 08:20:04 / Popularity: / Source:

First, injection mold

1. Poor machining of mold cavity

If mold cavity has defects such as scars, micropores, wear, roughness, etc., it will inevitably be reflected on plastic parts, which will make plastic parts have poor gloss. For this, mold must be carefully processed to make surface of cavity have a small roughness, and if necessary, it can be polished and chrome plated.

2. Surface stains on the cavity

If surface of cavity has oil stains, water stains, or too much release agent, it will make surface of plastic parts dark and dull. In this regard, it is necessary to remove oil stains and water stains in time, and use a limited amount of release agent.

3. Mold release slope is too small

If stripping slope is too small, it will cause difficulty in demolding, or force will be too large during demoulding, which will make surface gloss of plastic parts poor. For this, stripping slope should be increased.

4. Poor mold exhaust system

If exhaust is bad, it will cause too much gas to stay in model, and it will also lead to poor gloss. For this, mold exhaust system should be checked and corrected.

5. Improper design of gate or runner

Cross-sectional area of gate or runner is too small or changes suddenly. When melt flows in it, shear force is too large, flow is turbulent, resulting in poor gloss. For this, cross-sectional area of gate and runner should be appropriately increased.

Second, injection molding process

1. Injection speed is too low

If injection speed is too low, surface of plastic part is not dense and gloss is poor. For this, injection speed can be appropriately increased.

2. Insufficient cooling of plastic parts

If cooling of thick-walled plastic parts is insufficient, surface will be fluffy and gloss will be dark. For this, cooling system should be improved.

3. Improper holding operation

If holding pressure is too small and holding time is too short, density of plastic parts is insufficient and gloss is not good. For this, holding pressure and holding time should be increased.

4. If melt temperature is too low

When melt flow is too low, fluidity is poor, which easily leads to poor gloss. For this, melt temperature should be appropriately increased.

5. Uneven cooling of crystalline resin

For plastic parts made of PE, PP, POM, etc., uneven cooling will result in poor gloss. For this, cooling system should be improved to make it evenly cool.

6. Injection speed does not match gate area

If injection speed is too high, and gate cross-sectional area is too small, gate will be dark and poor gloss. For this, injection speed can be appropriately reduced and gate cross-sectional area can be increased.
ABS injection molded parts 

Third, raw materials

1. Size of raw materials varies greatly

Large difference in particle size makes it difficult to uniformly plasticize, and gloss is poor. For this, raw materials should be sieved.

2. Too much secondary material in raw material

If too much recycled material or sprue material is added, it will affect uniform plasticization of melt and gloss will be poor. For this reason, amount of recycled material or sprue material should be reduced.

3. Poor temperature resistance of raw materials

Some raw materials will decompose and change color during temperature adjustment, resulting in poor gloss. For this, raw materials with better temperature resistance should be selected.

4. Raw materials contain volatile substances

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

5. Dispersibility of additives is not good

Some additives have too poor dispersibility and make plastic parts have poor gloss. For this, additives with better flow properties should be used instead.

6. Impure raw materials

If raw materials are mixed with foreign materials, miscellaneous materials or incompatible materials, they can not be uniformly mixed with their raw materials and cause poor gloss. For this, these miscellaneous materials should be strictly excluded in advance.

7. Too little lubricant

If amount of lubricant is too small, fluidity of melt is poor, and surface of plastic part is not dense, which makes gloss poor. For this, amount of lubricant should be appropriately increased.
Therefore, according to whether polishing degree of your mold meets requirements, if there is no problem with mold itself, you must determine characteristics of your ABS. You can choose high mold temperature, high speed and high pressure; using chilled water can also achieve smoothness.

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