Excessive noise during plasticization and its solution
Plasticization is a critical process in injection molding, heating, melting, and uniformly mixing raw materials. Under normal circumstances, the plasticizing system should operate smoothly and with low noise levels (typically below 75 decibels). Excessive plasticizing noise (over 85 decibels) not only impacts the production environment but may also signal equipment failure. Long-term neglect can lead to increased component wear, decreased production efficiency, and even equipment downtime. Excessive plasticizing noise is primarily caused by mechanical component wear, unsuitable raw material properties, and improper process parameter settings. Targeted analysis and measures are necessary to reduce noise and ensure stable equipment operation.
Wear or poor assembly of mechanical parts is a common cause of excessive plasticizing noise. Focus on inspecting the condition of core components such as the screw, barrel, and check ring. Excessive or uneven clearance between the screw and barrel can cause metallic friction noise during plasticizing. Normal clearance should be maintained between 0.1-0.3mm (depending on the screw diameter). If wear causes the clearance to exceed 0.5mm, the screw or barrel must be replaced. Wear on the sealing surface between the check ring and the barrel can cause melt backflow and produce unusual impact noise. Disassemble the sealing surface and inspect for scratches or dents. If wear is severe, the check ring must be replaced. Bearing wear or poor lubrication can cause vibration and noise during screw rotation. Regularly check bearing clearance and add specialized grease to ensure adequate lubrication. Drivetrain faults (such as poor gear meshing or loose belts) can also cause excessive noise. Gear meshing clearance should be maintained between 0.1-0.2mm, and belt tension should be moderate, with a belt deflection of 10-15mm. For example, a certain injection molding machine produced sharp noise during plasticization. Inspection found that the gap between the screw and the barrel increased to 0.6mm due to wear. After replacing the screw, the noise dropped to the normal range.
A mismatch between the raw material properties and the plasticizing system can lead to an uneven plasticizing process and abnormal noise. Oversized or uneven raw material particles can cause “bridging” at the feed port, causing the falling raw material to impact the screw and barrel, generating noise. The raw material particle size should be controlled between 3-5mm, with a uniformity deviation of no more than 10%. Screening should be performed as necessary. Hard impurities (such as metal chips and stones) in the raw material can cause intense friction with the screw and barrel during plasticization, generating harsh noise and accelerating component wear. Magnetic separation devices and filters should be installed during the raw material conveying process to remove impurities. Abnormal raw material viscosity or hardness can also cause noise. For example, glass fiber-reinforced plastics have a high hardness and can rub against metal parts during plasticization, resulting in high noise levels. Specialized, wear-resistant screws and barrels (such as those treated with nitriding or sprayed with tungsten carbide) should be used to reduce wear and noise. Furthermore, insufficient raw material drying, including moisture or volatiles, can generate bubbles during plasticization. The bursting of these bubbles can produce additional noise. Reinforced raw material drying should be strengthened to ensure the moisture content meets the required requirements.
Improper setting of process parameters will lead to unstable plasticizing process and cause excessive noise. Excessive back pressure will increase the resistance to screw rotation, increase the load on the motor, and generate abnormal noise. The back pressure should usually be controlled at 5-15bar, with the lower limit for high-viscosity plastics and the upper limit for low-viscosity plastics. If the back pressure exceeds 20bar, it needs to be reduced to a reasonable range. Excessive screw speed will cause the shear rate of the raw material in the barrel to be too high, resulting in turbulence and vibration, and increased noise. The speed is usually controlled at 50-150rpm, and adjusted according to the characteristics of the raw materials: use low speed for high-viscosity plastics and high speed for low-viscosity plastics, and avoid exceeding 80% of the rated speed of the equipment. Improper barrel temperature setting and local low temperature will lead to uneven plasticization of the raw materials, forming solid particles, which will rub against the screw and barrel and generate noise. It is necessary to set a suitable temperature curve according to the characteristics of the raw materials to ensure that the raw materials are gradually heated from the feeding section to the metering section to avoid local low temperature areas. For example, when processing PP, if the temperature in the middle of the barrel is lower than 160°C, the raw material will not be completely plasticized, which will produce friction noise. After raising the temperature to 180°C, the noise will be significantly reduced.
Abnormalities in the feeding system can lead to poor raw material flow and periodic noise. Components such as the feed port, hopper, and feed screw should be inspected. Improper feed port design, such as a narrow angle or rough surface, can hinder raw material flow, creating a “bottleneck” effect. This can cause noise from the impact of falling raw materials. The feed port angle should be increased to at least 60°, and the surface polished to a Ra of 1.6μm or less to reduce resistance. Insufficient raw material in the hopper or a clogged feed port can cause the screw to run idle or at half capacity, generating irregular noise. Ensure the hopper is fully stocked (at least 1/3 of the hopper volume) and regularly clean the feed port to remove lumps and impurities. Unstable feed screw speed (applicable to loss-in-weight feeders) or improper matching with the main screw can lead to uneven raw material supply and pulsating noise. Adjust the feed screw speed to ensure it matches the plasticizing capacity of the main screw and ensures a stable feed. For example, an injection molding machine uses loss-in-weight feeding. Due to the fluctuation of the feeding screw speed, the raw material supply is uneven, and periodic impact noise is generated during plasticization. By replacing the feeding motor and controller and stabilizing the speed, the noise is eliminated.
Lack of equipment maintenance and servicing can exacerbate plasticizing noise. A regular maintenance system is necessary to prevent this noise. Regularly clean the barrel and screw to remove residual plastic debris and carbonized layers, and to avoid friction noise caused by impurity accumulation. Cleaning intervals are determined based on the characteristics of the raw materials. When processing easily degradable plastics like PVC, this should be done at least weekly, and when processing stable plastics like PE and PP, monthly. Regularly inspect and replace worn parts, such as check rings, bearings, and seals, to prevent excessive wear that can lead to noise and malfunction. Lubricate the drive system regularly, using specialized gear oil for the gearbox and high-temperature grease for the bearings every 1,000 hours of operation, to ensure smooth operation of moving parts. Regularly calibrate equipment parameters, such as screw speed, back pressure, and temperature, to ensure consistency with set values. This can prevent unstable plasticizing and noise caused by parameter drift. Through effective maintenance and servicing, plasticizing noise can be effectively reduced, equipment life can be extended, and production stability and safety can be improved.
