How to identify the source of motor noise —— Part three?

Thirdly, Noise control

3.1 Reasonably design the structure of the motor to reduce noise

(1) Correct selection of fan material and structure: a single-rotation high-speed motor can be a streamlined backward-inclined centrifugal fan. For a centrifugal fan, the noise with the reverse ring is lower than that without the reverse ring; in addition, the basin type Fans are quieter than blade fans; aluminum fans are quieter than nylon fans.

(2) Improve the air path: increase the gap between the outer edge of the fan and the fan cover or the inner cavity of the end face, remove the obstacles in the air duct, smooth the direction of the air flow, and improve the noise.

(3) The stator winding adopts a reasonable short moment.

(4) The asynchronous motor rotor adopts a relatively inclined double-slope structure to reduce the axial force; the DC motor adopts an uneven air gap. The AC motor adopts magnetic slot wedge, which can not only reduce the harmonic loss and improve the efficiency, but also reduce the electromagnetic noise caused by the harmonic magnetic field.

(5) When the motor in use produces "sweeping", the air gap can be appropriately increased to reduce the air gap magnetic density. When the motor power has a margin, a part of the rotor circumference can be removed to increase the air gap and eliminate the noise caused by higher harmonics, but at the same time as the reduction, the no-load current is increased and the power factor is improved. reduce.

(6) Appropriately control the ripple, pit, roughness and radial clearance of the bearing rolling surface.

(7) Improve the surface machining accuracy and smoothness of the commutator to reduce brush noise.

(8) Increase the rigidity and balance of the machine base, and use a spirit level to level the foundation if necessary; visually check whether the installation angle of the motor and the machinery being dragged are suitable.

3.2 Ensure that the assembly process is excellent

(1) Choose high-quality bearings. The matching between the bearing and the shaft or between the bearing and the bearing seat should be appropriate, and the temperature and time when the bearing is shrink-fit should be well controlled. (Heating the bearing to about 100°C, the non-sealed bearing can be boiled in oil for about 5 minutes. When the inner ring expands, quickly put the bearing on the journal, and after the bearing cools and shrinks, the inner ring of the bearing will be tightly It is fixed on the journal. For sealed bearings, since the inside is full of grease, do not use oil to heat it. Electric heating can be used to evenly heat the bearing and then put it on the bearing. Our company now uses electric bearing heaters for all heating)

(2) The poor dynamic balance of the rotor is the main cause of mechanical noise, so it is necessary to improve the dynamic balance inspection accuracy of the rotor, minimize the influence of eccentricity, and ensure the concentricity of the coupling when the motor is installed.

(3) The lubricating oil is suitable and free of impurities. The viscosity of the grease is high and the noise is low. But when the viscosity is too large, there will be a stirring sound. Filling amount of grease For non-sealed bearings, the bearing should be filled with grease. The grease can be squeezed in from one end of the bearing and squeezed out from the other end of the bearing, so that the grease is filled in the bearing and wiped with fingers at both ends. flat. The amount of grease applied to the inner cavity of the bearing cover should be 1/3-2/3 of the inner space of the bearing chamber.

(4) Different types of bearings need to be installed according to the requirements of their installation process. In principle, the method of copper rod hitting is not allowed for bearing assembly, otherwise the bearing will be damaged due to uneven force on the inner ring of the bearing. When using the shrink-fit method to assemble the bearing, carefully check the matching size of the bearing and the journal in advance. Because the shrink-fit is different from the cold-fit, it is not easy to find the fit tolerance and interference between the journal and the bearing during the process of shrink-fit into the bearing. whether the degree is appropriate. The motor should not be moved or other accessories assembled to prevent the bearing from shifting after the bearing has been shrunk.