In the medical injection molding production process, the noise generated by equipment operation not only affects the working environment but may also cause harm to the physical and mental health of operators. Long-term exposure to a noise environment exceeding 80 dB can lead to hearing damage, increased psychological stress, reduced work efficiency, and even interference with the normal operation signals of equipment, affecting product quality. This article will delve into the causes of noise during medical injection molding and propose targeted noise reduction measures.

Causes of Noise During Medical Injection Molding

Hydraulic System Noise
The hydraulic system is the core part of a medical injection molding machine, and its noise sources are diverse. The vibration pump is a major source of noise, with common causes including misalignment of the oil pump motor installation, loose couplings, and internal faults in the oil pump. For example, when the oil pump motor is misaligned during installation, it can lead to increased pump vibration and generate significant noise. A loose coupling can cause unstable power transmission, triggering vibrations and noise. In addition, factors such as a low oil level, air being drawn into the oil through the oil filter screen or joint connections, oil contamination blocking the oil filter screen, loose return oil pipes allowing air to be drawn in or air mixing into the oil above the oil surface can all lead to cavitation in the hydraulic system, resulting in relatively loud noise.

The motor is also an important source of noise in the hydraulic system. Problems such as damaged motor bearings, coil winding faults, and incorrect wiring can cause the motor to generate abnormal noise during operation. For instance, a damaged motor bearing can result in unstable rotation and produce frictional noise, while incorrect wiring can increase noise when the system pressure rises.

The failure of the main relief valve can also cause noise. Issues such as air trapped in the front chamber of the pilot valve, blockage of the orifice in the main spool by oil contaminants, poor sealing between the pilot valve and the valve seat due to wear, deformed or incorrectly installed springs, excessive oil flow at the remote control port, hydraulic oil with viscosity that is too low or too high, and resonance with other components in the circuit can all lead to noise generation by the relief valve.

Mechanical Transmission Noise
Mechanical transmission components are prone to wear after long-term use, such as cracks and thinning on the surface of belts, elongation of chain links, and uneven wear on the tooth surfaces of gears. This wear increases friction between the transmission components, resulting in abnormal vibrations and noise. Moreover, if the connecting components of the transmission mechanism become loose, such as loose connecting bolts between the motor and the transmission device or loose bushings inside the transmission device, abnormal vibrations and noise will also occur during operation.

Insufficient lubrication is another cause of mechanical transmission noise. When there is too little or no lubricating grease, friction between mechanical components increases, leading to noise. At the same time, different mechanical components have different requirements for lubricating grease, and using unsuitable grease may not provide good lubrication and may even generate noise.

Plasticization Process Noise
During the plasticization process of medical injection molding, factors such as excessive back pressure, excessive speed, low temperature in the compression section of the barrel, poor fluidity of the plastic, and a small screw compression ratio can all lead to excessive plasticization noise. For example, excessive back pressure increases the flow resistance of the plastic in the screw, generating noise. Excessive screw speed intensifies the friction between the plastic and the screw and barrel, triggering noise.

Noise Reduction Measures

Hydraulic System Noise Reduction
For vibration pump noise, regularly check the alignment of the oil pump motor installation to ensure it is within 0.1 mm. Promptly correct loose couplings. If there are internal faults in the oil pump, repair or replace it in a timely manner. At the same time, maintain an appropriate oil level to avoid air being drawn in through the oil filter screen or joint connections. Regularly clean the oil filter screen to prevent blockage. Tighten the return oil pipes and extend them to below the oil surface to prevent air from mixing into the oil.

For motor noise, regularly inspect the wear of motor bearings and replace damaged ones in a timely manner. If there are faults in the motor coil windings, replace or repair the motor. During installation and wiring, strictly follow the wiring diagram to avoid incorrect wiring.

To reduce noise from the main relief valve, enhance sealing and raise and lower the pressure several times to discharge air from the front chamber of the pilot valve. Regularly clean the valve body to keep the orifice unobstructed. If the pilot valve and valve seat are worn and do not seal properly, repair or replace them in a timely manner. Inspect and replace deformed springs. Reduce the oil flow at the remote control port to avoid excessive flow generating noise. Select appropriate hydraulic oil according to the working environment and requirements of the equipment to avoid oil with viscosity that is too low or too high. Adjust the pressure settings of other components to avoid resonance with the relief valve pressure setting.

Mechanical Transmission Noise Reduction
Optimizing the mechanical structure design is an effective way to reduce mechanical transmission noise. Arrange the layout of transmission components such as belts, chains, and gears reasonably to minimize crossovers and interferences between them, ensuring smooth power transmission and reducing noise caused by uneven collisions or friction between components. When designing the layout, consider isolating components that generate relatively loud noise from other components or enclosing them in a closed structure to reduce noise propagation.

Add elastic buffer structures made of rubber, polyurethane, and other elastic buffer materials at key parts of the transmission mechanism, such as the connections between the motor and the transmission device and between transmission components and the machine body. These buffer structures can cushion vibrations and reduce noise transmission. For example, use elastic elements of couplings to buffer vibrations and reduce noise transmission.

Regularly maintain and service mechanical transmission components, and promptly replace worn belts, chains, and gears. For belt drives, regularly check the belt tension using a tension meter and adjust it to ensure appropriate tension. Check whether the pulleys are installed parallelly and adjust them if not. Also, clean foreign objects from the pulley surfaces and replace severely worn pulleys. For chain drives, promptly adjust the chain tensioning device. If the chain pitch elongation exceeds the allowable range, replace the chain. When replacing sprockets, ensure they match the chain in terms of parameters such as pitch and pay attention to the installation position accuracy of the sprockets.

Plasticization Process Noise Reduction
Reasonably adjusting the plasticization process parameters is crucial for reducing noise during the plasticization process. According to the characteristics of the plastic and product requirements, appropriately reduce the back pressure and screw speed to avoid excessive noise caused by high back pressure and fast screw speed. At the same time, control the temperature of the compression section of the barrel to ensure that the plastic is plasticized at an appropriate temperature, improving the fluidity of the plastic and reducing noise caused by poor fluidity. In addition, selecting an appropriate screw compression ratio also helps reduce plasticization noise.

Comprehensive Noise Reduction Measures
The use of soundproofing materials can to some extent reduce the noise of medical injection molding machines. Using sound-absorbing cotton, soundproofing tape, and other soundproofing materials around the machine or inside the machine can absorb and reduce noise propagation, thereby lowering the overall noise level of the machine. For example, pasting sound-absorbing cotton on the inner wall of the injection molding machine's casing can effectively reduce noise propagation to the outside.

Controlling vibrations and resonance is also an important noise reduction measure. Vibration dampers and shock absorbers can be used to reduce machine vibrations and thus lower noise. For example, installing shock-absorbing pads at the bottom of the injection molding machine can reduce the transmission of machine vibrations to the ground and lower noise. At the same time, avoid having the operating frequency of the machine close to or the same as the natural frequency of the equipment to prevent resonance. If resonance occurs, methods such as adjusting the installation position of the transmission mechanism or adding rubber shock-absorbing pads can be used to avoid it.

For medical injection molding machines with relatively loud noise, consider setting up soundproof compartments. Isolate the machine and personnel to reduce the impact of noise on people. Soundproof compartments can be decorated with special sound-absorbing materials to improve sound insulation.

Operators are exposed to a noisy environment for a long time during medical injection molding production. Wearing anti-noise earmuffs or earplugs can effectively reduce the impact of noise on the ears. Enterprises can provide operators with appropriate anti-noise earmuffs or earplugs and require them to wear them correctly during work.

The noise problem during medical injection molding should not be underestimated. By analyzing the causes of noise and adopting targeted noise reduction measures, the noise level can be effectively reduced, the working environment can be improved, the physical and mental health of operators can be protected, and production efficiency and product quality can be improved.