What type of defect will occur in the custom plastic extrusion manufacturing process?

H.D.Plastics is a premier specialist of plastic extrusion profiles and extrusion pipe & tubing with customized service. Quality is our top priority in those long years of business.

How to recognize the defects during manufacturing will save us a lot of trouble.

The defect is any form of deviation of the product’s characteristic from the required specification defined by the manufacturing process. It can be caused by a single source or the cumulative effect of several factors, which may arise at any stage of the extruded process.

The common failure or defects which are normally occurring in the custom plastic extrusion process are due to three main causes: mold design, material selection, and extrusion processing. Some of the common extrusion defects are Improper operation such as Resin Defects, Trapped air, Overheating, Melt fracture, Moisture absorption, Poor Mixing, Surging. Some are Improper Material Addition, Improper system engineering, and installation.

Improper Operation in the custom plastic extrusion process.

There is a molecular orientation change, resulting in a variation in the machine direction versus the transverse direction properties. Depending on the orientation change, the properties in the machine direction may increase or decrease, with the corresponding properties in the transverse direction varying in the opposite direction. In other words, if the tensile properties in the machine direction increase, they will decrease in the transverse direction, and vice versa. A potential cause for the change in molecular orientation is the draw ratio has changed between the extruder and the puller. This only occurs with a die with an adjustable gap, where the die lip setting has been changed. As the die lips are opened, a higher draw ratio is required to maintain the final product dimensions.

In processes with nonadjustable die lip openings, the product dimensions are changed as the puller speed or the extruder screw speed is changed. With an adjustable die opening, the product thickness exiting the die can be increased or decreased through die adjustments. As the die is opened, the puller speed is adjusted to maintain the product dimensions, causing the product draw ratio to be increased and changing the product orientation.

Gauge variations are defined as thickness nonuniformities in the final product. These variations are due to the no uniform melting temperature that results in polymer viscosity variations and causes of nonuniform melt temperature with poor melt mixing, and unevenly clogged screen pack. This is due to the polymer flowing through one part of the pack to another.

If take-off equipment is not functioning properly, the product slippage can cause thickness variations. Slippage in the puller allows the product dimensions to rise. The reason lies in that the product is not being pulled away from the extruder at the proper rate. The caterpillar or puller pressure has to be adjusted to prevent the product from slipping without causing any distortion or damage to the final product. Here we also have some solutions.
Verify puller speed correctly.
Verify screw speed is properly set.
Check extruder temperature and adapter set points.