The screw and barrel are key components of a plastic pelletizing machine. Their condition affects material conveying, plasticization, product quality, and production efficiency. Over time, wear, mechanical overload, or unsuitable processing conditions can damage these components and reduce the performance of the extrusion system.
The main causes of screw damage include progressive wear, sudden torque overload, and abrasion from fillers in the processed material.
Wear of the screw and barrel
As the screw rotates inside the barrel, friction and contact with the processed material gradually wear the working surfaces of both components. Over time, the screw flight diameter decreases and the barrel bore diameter increases, resulting in greater clearance between the screw and barrel.
As this clearance increases, more molten polymer can leak backward through the gap from higher-pressure areas toward the feed side. This reduces conveying efficiency and can lower the machine's output. Wear may also increase melt temperature and extend the material's residence time in the barrel, raising the risk of polymer degradation.
The resulting degradation can further damage the equipment, particularly when the processed material releases corrosive compounds. For example, overheating or prolonged processing of polyvinyl chloride (PVC) can release hydrogen chloride (HCl), which can attack susceptible metal surfaces. Polyethylene (PE), by contrast, does not contain chlorine in its polymer structure and does not generate HCl from the degradation of the pure polymer itself.
Progressive screw and barrel wear can therefore affect both production efficiency and equipment service life. Regular inspection and measurement of the screw dimensions and barrel bore help determine when repair or replacement is necessary.
Screw fracture caused by excessive torque
The screw can also fail when the torque applied during operation exceeds its mechanical capacity.
One possible cause is inadequate plasticization. If the material has not reached the required processing temperature, its flow resistance may remain high, increasing the load on the screw and drive system.
Foreign objects, particularly metal fragments, can also obstruct screw rotation or become trapped between the screw and barrel. This may cause a sudden increase in torque and lead to severe mechanical damage. Other contributing factors include excessive feeding, blocked flow passages, and incorrect screw assembly.
The risk is greater when the machine starts before the barrel has reached the specified operating temperature. Insufficient preheating can increase the resistance encountered by the screw and place excessive stress on the drive system.
Before restarting the machine after an abnormal torque increase, operators should identify and correct the cause. The inspection should include the feed material, screw and barrel condition, die and screen restrictions, drive components, and relevant temperature settings.
Abrasive wear caused by fillers
Fillers and reinforcing materials can accelerate wear of the screw and barrel. Common examples include calcium carbonate, glass fibers, silica, and other hard particles used in plastic compounding.
As the material moves through the screw channels under pressure, these particles can abrade the metal surfaces. Wear may be particularly severe in areas where the filler concentration is high or where solid particles accumulate and restrict material movement.
The rate of wear depends on the type, hardness, particle size, and loading of the filler, as well as the screw geometry, operating conditions, and materials used to manufacture the screw and barrel.
When processing highly filled or reinforced polymers, the screw and barrel should be selected for the expected abrasive conditions. Suitable wear-resistant materials, surface treatments, or replaceable wear components may help extend service life.
Other factors that can contribute to screw damage
In addition to the three main causes above, several mechanical and operating conditions can accelerate wear or lead to premature failure.
Incorrect alignment between the screw, barrel, and drive system can create uneven loading and unwanted contact between components. Uneven barrel heating can also cause differential thermal expansion, affecting the clearance between the screw and barrel.
A bent screw, worn support components, incorrect assembly, or unsuitable screw and barrel materials can further increase the risk of damage. Corrosive ingredients or degradation products may also attack metal surfaces when the selected materials are not compatible with the process.
To identify the cause of a failure, inspect the damaged surfaces and review the machine's operating history. The wear pattern, abnormal noise, changes in output, temperature fluctuations, and sudden increases in motor load can help distinguish abrasive wear, corrosion, misalignment, and torque overload.
Custom machining for plastic processing equipment
Beyond plastic pelletizing machine components, Hansheng Automation provides custom precision machining for non-standard industrial parts according to customer-supplied drawings. Our services also cover parts for filling machinery and tobacco packaging equipment, precision components for yacht equipment, and parts for remote control racing cars. Each component is manufactured according to the specified dimensions, structural requirements, and drawing details.
