The reasons of breakage of WPC granulator screw

Sometimes, when the WPC granulator machine is running, the screw may suddenly break.

The main reasons maybe: material performance is not up to standard, improper operation, lack of maintenance and design defects. Targeted investigation is needed to avoid frequent failure.

WPC granulator Screw Material mismatch: When screw segments are made of ordinary steel  instead of specialized wear-resistant alloys, they may lack sufficient strength and toughness during high-temperature and high-pressure wood-plastic processing, leading to brittle fracture.

Defects of heat treatment process: if the quenching temperature is not proper and the tempering is not sufficient during heat treatment, the internal stress concentration of the material or the imbalance between hardness and toughness (such as high hardness but poor toughness) will be caused, and the fracture will be caused by impact during operation.

Insufficient machining accuracy: the root of the screw is too small, burrs or cracks exist, which will form stress concentration points, and gradually expand to fracture after long-term operation. Improper use Non-standard behavior in daily operation will make the threaded block bear the load beyond the design range.

Unstable feeding: the feeding amount of wood-plastic raw material (such as wood chips and plastic particles mixture) fluctuates, resulting in drastic fluctuations in screw load, and the screw alternately bears overload and impact, and fatigue fracture under repeated stress.

Foreign matter in the material: metal blocks, stones and other hard objects are mixed in the raw material, which will be stuck in the screw groove, and the screw will be subjected to a great torque instantly, resulting in cracking or shear fracture.

Improper startup/shutdown procedures: Failure to preheat or feed at low speed during startup causes excessive stress on the threaded block at low temperatures. Failure to empty the material during shutdown leads to solidification after cooling. Forced startup during subsequent operations may cause the threaded block to fracture due to overload.3、Maintenance is missingLong-term lack of scientific maintenance will accelerate the aging of the rebar block and cause fracture.

Wear and tear: The hard particles in the wood-plastic raw material will continue to wear the thread surface, resulting in shallow thread tooth type, reduced force area, increased local stress, and finally fracture.

Abnormal assembly clearance: after long-term use, the clearance between the screw and the screw and barrel becomes larger, and radial jumping occurs during operation. The screw is subjected to additional radial force, and it is easy to break from the root.

Insufficient lubrication: if the lubrication fails in the connection between the screw and the drive shaft, dry friction will be generated, which will not only increase the running resistance, but also lead to local overheating, reduce the strength of the material and induce fracture.

Unreasonable structure design: the thread angle and pitch of the thread block are not matched with the characteristics of wood-plastic raw materials, or the root of the thread is not strengthened (such as not increasing the rounded corner), which is easy to form a stress weak area.

Power and load mismatch: If the selected thread block specification is not matched with the power of the host (such as a small thread block with a high-power motor), the processing is easy to exceed the load limit of the thread block due to overload.

To reduce WPC granulator screw breakage, it is recommended to control the source: prioritize bimetallic thread blocks with strict heat treatment during purchase; ensure uniform feeding and regular cleaning of foreign matter in raw materials during use; inspect screw wear and assembly clearance every 100-200 hours of operation.

Yongte WPC granulator machine equip with special designed wear-resistant WR4 material for screw, The main carbide of WR4 is vanadium carbide (VC microhardness HV2600), which has higher hardness and better wear resistance; the carbide form of WR4 is dispersed, spherical or nearly spherical carbide, which has better impact toughness. In addition, it was found in heat treatment that under the same quenching conditions, WR4 hardly deformed during the heat treatment process, and the hardness was more uniform after quenching. The metallographic structure has fine grains, good anti-stripping and outstanding wear resistance. It is used in working conditions with large wear, especially in high-filling fields, such as nylon fiber-reinforced, wood-plastic composition, aluminum-plastic, modified nylon reinforced, mica reinforced, PA6, PA66, etc., with outstanding effects;