Plastic extrusion processing is a widely used manufacturing technique in the plastics industry. However, during this process, several issues can arise that affect the quality of the final product and the efficiency of production. This article will explore the common problems encountered in plastic extrusion processing.
Raw material related issues
Excessive moisture content in raw materials
Even plastics with low water absorption, like HDPE, are vulnerable to moisture. When exposed to moisture, during the extrusion process, the vaporization of water forms bubbles and voids in the product. If HDPE raw materials aren’t fully dried before processing, internal bubbles may appear in the pipe. These bubbles reduce the strength and sealing performance of the product, making it less suitable for its intended use.
Mixing of impurities in raw materials
The presence of metal particles, sand, and other impurities in raw materials can cause significant problems. They can aggravate the wear of the screw, barrel, and mold. For instance, when impurities enter the die mold, scratches and pits will appear on the surface of the pipe. This not only seriously affects the appearance of the product but also its quality, potentially leading to product rejection.
Unreasonable raw material formula
An improper proportion of additives can have a negative impact. For example, if there is too little antioxidant, the plastic is prone to oxidation and degradation during processing and use. On the other hand, an excessive amount of lubricant will result in oil spots on the surface of the product, affecting both its appearance and performance. Moreover, large performance fluctuations among different batches of raw materials can also lead to unstable product quality.
Equipment failure issues
Screw wear
After long – term use, the screw thread wears due to friction. This wear leads to a decrease in material conveying capacity and a poor plasticizing effect. As a result, the extrusion volume becomes unstable, the wall thickness of the pipe is uneven, and unmelted particles may be present in the pipe due to insufficient plasticization. These issues can lead to sub – standard products.
Failure of the heating and cooling system
A malfunctioning heating device can cause the temperature to drop too low, preventing the material from being fully plasticized. This results in a rough and defective surface of the extruded product. Similarly, a failure in the cooling system, such as a leakage in the cooling water tank, high cooling water temperature, or insufficient cooling of the pipe, will affect the dimensional accuracy, cause deformation, and shrinkage problems.
Damage to the head mold
Over time, the gap between the core mold and the die changes after long – term use of the mold. This change leads to an uneven wall thickness of the pipe. Wear or corrosion on the mold surface also causes defects on the surface of the pipe, such as stripes and roughness, which reduce the overall quality of the product.
Process parameter problems
Improper temperature control
If the barrel temperature is too high, the plastic will decompose, producing a pungent odor, changing the product color to yellow, and deteriorating its performance. Conversely, if the temperature is too low, the material will not be fully plasticized, the fluidity will be poor, and the extrusion pressure will increase. This can cause equipment overload, high internal stress in the product, and make it easy to break.
Abnormal screw speed
A too – fast screw speed will cause the material to be sheared and overheated, leading to plastic degradation and a decrease in the pipe’s performance. A too – slow screw speed, on the other hand, will result in insufficient extrusion volume, low production efficiency, and the material staying in the barrel for too long, which may also cause performance changes.
Fluctuation of extrusion pressure
An unstable extrusion pressure will cause appearance defects such as uneven wall thickness and bamboo – joint – like formations on the pipe. Sudden pressure changes can also create stress concentration points inside the pipe, reducing its pressure – bearing capacity.
The traction and extrusion speeds do not match
If the traction speed is too fast, the pipe will be over – stretched, resulting in a thinner wall thickness and reduced strength. If the traction speed is too slow, the pipe will accumulate, which may cause blockages and affect production continuity. Additionally, the pipe may be deformed due to untimely cooling.
In conclusion, being aware of these potential problems in plastic extrusion processing is crucial. By identifying and addressing these issues promptly, manufacturers can improve product quality, enhance production efficiency, and reduce production costs.