The motor is the driving system of industrial fans, and the motor gear will generate varying degrees of vibration and noise during operation. Gear transmission noise is also the main source of transmission system noise. In the gear transmission system, noise can be divided into two categories based on mechanism: acceleration noise and self-resonance noise. On one hand, when the gear teeth are engaged, the impact causes the gear to have a large acceleration, which can cause disturbance to the surrounding medium, resulting in noise radiation caused by this disturbance, known as gear acceleration noise. On the other hand, under the dynamic meshing force of the gear, various components of the system will vibrate, and the noise radiation caused by these vibrations is called self-resonance noise. The usage scenario for industrial fans requires the use of enclosed gear transmission motors, with self-resonance noise being the main noise source. To solve gear noise, it is necessary to consider the type, material, and processing of the gear.
Gear type - From the perspective of smooth transmission and low noise, helical cylindrical gears have more tooth pairs in simultaneous contact, and the change in total meshing stiffness is relatively smooth. Therefore, vibration noise may be lower than that of the same spur gear, sometimes as low as about 12dB. For herringbone gears, due to strict requirements for alignment, minor errors or uneven wear can affect their load-bearing and transmission smoothness. Therefore, among cylindrical gears, helical cylindrical gears are the better gears for reducing noise.
Gear material - Generally speaking, using materials with good damping performance to manufacture gears can reduce noise. However, materials with good damping performance typically do not have high strength and cannot be used in all situations. For example, phenolic resin and nylon are often only used to make lightly loaded gears for sewing machines and other light machinery. To reduce noise, steel gears can be case-hardened or copper-plated on the bearing surface. The purpose of sulfur-carburizing the tooth surface is to reduce the coefficient of friction on the tooth surface, and copper-plating the tooth surface has been used to improve the contact accuracy of gear teeth in steam turbine gears. Gear heat treatment also affects noise. For example, after quenching, damping performance worsens, and noise can increase by 3-4 dB. Therefore, gears that do not require high strength and wear resistance do not need to be quenched.
Regarding the impact of lubricating oil and refueling methods, it is generally believed that noise decreases as the amount and viscosity of oil increase because lubricating oil has a damping effect that prevents direct contact between meshing tooth surfaces. When oil-bath lubrication is used, the gear noise also varies with the oil level because the oil level is different. Gear machining accuracy has an important influence on gear transmission system noise. Generally speaking, improving machining accuracy helps reduce gear system noise. However, improving machining accuracy is limited by processing costs, and the higher the initial machining accuracy, the less obvious the noise reduction effect of improving accuracy. Among the various single-wheel tooth errors, tooth shape error has the greatest influence on noise. If the tooth shape error is large, the gear noise will be large, but their relationship is not a simple linear one. Because noise not only depends on the size of the tooth shape error but also mainly depends on the tooth shape. Experiments have shown that tooth shapes with a slightly bulged shape are conducive to reducing noise. In terms of the impact of gear backlash on noise, if the backlash is too small, the noise will increase sharply, and if it is slightly larger, it will not have much impact on noise.
Although most industrial fan manufacturers use standard motors from mature brands, understanding the principle of noise generation, and demands from suppliers since the design phase, is necessary to minimize the noise experience caused by gear meshing in industrial fans.