Your Basic Guide to Avoiding Plastic Injection Molding Flash

injection mold

One of the most common defects in injection molding is flash, which can directly affect the amount of scrap you run as a processor.

Here's our basic guide to avoiding plastic injection molding flash.

Adjust the sprue bushing length and offer adequate support in the mold for the sprue bushing

See if the sprue bushing's face is sealing off on the parting line. If yes, adjust the length to ensure that thermal expansion or nozzle pressure doesn't hold the mold open while allowing the plastic to flow out.

Once the press nozzle seals on the sprue bushing, it can produce 5-15 tons of force. If there's no adequate support in the mold, this pressure may shift to the parting line, which may allow the plastic to flow out. However, you can overcome this by adding appropriate support in the mold for the sprue busing.

Rule out improper venting as a cause of flash

Making vents as deep as the material viscosity will allow you to remove air from the mold as fast as possible. The vent's depth is determined by the viscosity of the plastic being molded. While stiff materials can use deeper vents, fluid materials need thinner vents.

a gray connector

Check if the mold vent size is in accordance with the supplier's recommendations. If not, get recommended vent sizes from the supplier of the plastic resin you're using.

It's important to correct the vent size if the existing vents aren't the recommended size. If the tool is showing wear, re-machine the vents. 

Prevent parting line mismatch

Clean off any contaminants, dirt, or plastic that could keep the mold from closing properly, especially inside the leader pin bushings and behind slides.

Plus, ensure proper mold seal and mold plate fit by:

§  Giving the mold plates sufficient surface areas that seal off at the parting line, thereby distributing the clamping force evenly during molding. Don't forget to offer an adequate 'land' of sufficient, even seal-off area around the part cavity.

§  Checking to see molding pressure during injection and packing have deformed the mold plates. Correct this by reducing/thickening mold plates or using pillar supports.

§  Cleaning the molding press from any obstructions.

PTMS likes to produce top-quality custom plastic injection molding parts for its clients

PTMS offers mold design, mold making, plastic injection molding, metal parts, and products assembly.

Reach out to them directly for more information on their plastic injection molding service!

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