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Common Injection Defects and Solutions in PP Injection Molding

In the injection molding process, polypropylene (PP) is a widely used plastic material, and its molding process often faces various challenges and defects. This article will provide a detailed analysis of 13 common injection molding defects in PP injection molding, and provide corresponding solutions to help enterprises improve product quality and production efficiency.

1.Insufficient annotation

Phenomenon description: The product is not fully filled in the mold, resulting in short shots or missing parts.

Solution:

·Adjust the process conditions to ensure appropriate injection pressure, time, and temperature.

·If the injection capacity of the injection molding machine is less than the weight of the plastic part, a larger specification injection molding machine should be used instead.

·Increase the cross-sectional area of the runner and gate, and optimize the mold design.

·Set up cold material holes, improve the mold exhaust system, and reduce residual air inside the mold cavity.

2.Flying edge

Phenomenon description: Excess plastic appears at the edge of the product, commonly known as "burrs".

Solution:

·Reduce injection pressure and speed.

·Check and adjust the joint surface of the mold to ensure good sealing.

·Raise the mold temperature, but be careful not to overheat and cause other problems.

3.Shrinkage marks

Phenomenon description: There are depressions or shrinkage holes on the surface of the product.

Solution:

·Raise the temperature of the material barrel and mold to increase the fluidity of the molten material.

·Extend the cooling time to ensure that the product is fully cured.

·Optimize mold design to reduce uneven wall thickness and shrinkage differences.

4.Pores

Phenomenon description: Bubbles or pores appear inside or on the surface of the product.

Solution:

·Reduce the molding temperature appropriately and increase the injection pressure.

·Check whether the raw materials contain excessive moisture or volatile substances, and perform pre drying treatment.

·Optimize the mold exhaust system to ensure smooth gas discharge.

5.Silver bar mark

Phenomenon description: Silver stripes or spots appear on the surface of the product.

Solution:

·Raise the temperature of the material barrel and mold to increase the fluidity of the molten material.

·Accelerate the injection speed and reduce the residence time of the molten material in the mold.

·Check if there are any scratches on the surface of the mold and repair them.

6.Welding marks

Phenomenon description: Traces formed when multiple streams of molten material converge in the mold.

Solution:

·Adjust the gate position and optimize the runner design.

·Improve injection pressure and speed to enhance the fusion effect of the melt.

·Add exhaust grooves or push out rods at the weld seam to promote gas discharge.

7.Cracking

Phenomenon description: Cracks or fissures appear on the surface of the product.

Solution:

·Check the mold design to ensure that the demolding slope and surface finish are appropriate.

·Properly increase the mold temperature and injection pressure to reduce stress generation.

·Shorten injection and holding time to avoid stress concentration.

8.Deformation

Phenomenon description: The product shape does not match the mold, resulting in distortion or bending.

Solution:

·Optimize mold design to ensure even and effective cooling system.

·Adjust the molding conditions, such as reducing injection pressure, increasing mold temperature, etc.

·Increase the number or area of push rods to improve the demolding effect.

9.Warping

Phenomenon description: The product undergoes warping and deformation after leaving the mold.

Solution:

·Balance the cooling rate of each part of the mold to ensure even cooling of the product.

·Increase the cooling time appropriately to ensure complete solidification of the product.

·Check if the mold design is reasonable and make necessary corrections.

10.Spray pattern

Phenomenon description: Serpentine or spray like marks appear on the surface of the product.

Solution:

·Expand the cross-section of the sprue or adjust the sprue position.

·Reduce the injection speed and slow down the flow rate of the melt.

·Raise the mold temperature and reduce the difference in cooling rate of the melt.

11.Burning

Phenomenon description: The product surface has burnt or black spots.

Solution:

·Clean the components such as the material cylinder, nozzle, and screw to avoid burning of any residue.

·Reduce back pressure and screw speed to avoid overheating.

·Check if the exhaust system of the mold is unobstructed.

12.Bubbles

Phenomenon description: There are voids or bubbles inside the product.

Solution:

·Fully pre dry the raw materials to remove moisture and volatile substances.

·Raise the temperature of the material barrel and mold to enhance the fluidity of the molten material.

·Extend the injection time to ensure that the molten material completely fills the mold.

13.Adhesive mold

Phenomenon description: The product is difficult to detach from the mold.

Solution:

·Check if the mold design is reasonable, increase the demolding slope and the number of push rods.

·Adjust the molding conditions, such as reducing the mold temperature and injection pressure.

·Use release agents or increase the ejection area to improve the demolding effect.