injection common sense sharing

How to increase the brightness of injection products from process and mold

How to Increase the Brightness of Injection Products from Process and Mold

1. Why Surface Gloss Matters

So why do we even care about surface gloss? Well, it's not just about looking pretty. A nice, even gloss tells you the mold is well-made, the melt is flowing smoothly, the packing is good, and the cooling is on point. If the gloss is bad, it's usually a sign that something's off—like trapped gas, uneven cooling, too much shear stress, or poor density. And those things can hurt the part's strength, dimensional stability, and chemical resistance. Plus, for stuff you actually see—like pipe elbows, faucet connectors, and plumbing fittings—a smooth surface looks better, collects less dirt, and resists corrosion more. So yeah, keeping that gloss good is important for both how the part works and how it looks.

2. Injection Mold

Problem: If the mold cavity isn't processed well—scratches, tiny holes, wear, rough surface, all that stuff—it's gonna show up on the plastic part, and the gloss will be bad.
Solution: Machine the mold carefully so the cavity surface is smooth. If needed, polish it and chrome plate it.
Problem: Oil or water stains on the cavity, or using too much release agent, will make the plastic part look dark and dull.
Solution: Clean off the oil and water stains right away, and don't use too much release agent.
Problem: If the demolding slope is too small, it's hard to pop the part out, or you need too much force—and that messes up the surface gloss.
Solution: Increase the demolding slope.
Problem: If the mold can't exhaust properly, too much gas gets trapped inside, and the gloss turns out bad.
Solution: Check the exhaust system and fix it.
Problem: If the gate or runner cross-section is too small or changes too abruptly, the melt flows too turbulently under shear force, and the gloss suffers.
Solution: Make the gate and runner cross-section a bit bigger.

3. Injection Molding Process

Problem: Injection speed too slow? The part surface won't be dense, and the gloss will be poor.
Solution: Speed up the injection a bit.
Problem: For thick-walled parts, if cooling isn't enough, the surface gets hairy, and the gloss goes dark.
Solution: Improve the cooling system.
Problem: Not enough holding pressure or too short a holding time means the part isn't dense enough, so the gloss isn't good.
Solution: Increase holding pressure and holding time.
Problem: Melt temperature too low? Then the flow is poor, and the gloss is usually bad.
Solution: Raise the melt temperature a little.
Problem: For crystalline resins like PE, PP, POM—if cooling isn't uniform, the gloss turns out bad.
Solution: Improve the cooling system so it cools evenly.
Problem: Injection speed too high and gate cross-section too small? You'll get dark, glossy patches near the gate.
Solution: Slow down the injection a bit and make the gate cross-section bigger.

If you have such items, please contact us: contact@yxplasticmolding.com

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injection common sense sharing

How to increase the brightness of injection products from process and mold