What are the types and compositions of commutators commonly used in single-phase series motors?

Update:22-07-2022
Summary:

The commutator is a key component of the air conditione […]

The commutator is a key component of the air conditioner motors, and its technical performance indicators and product quality directly affect the overall performance of the motor. When the motor rotates, the brushes commutate on the surface of the commutator, and frequent friction generates heat. The higher the speed, the higher the surface temperature. At this time, the radial direction of the commutator and the deformation between the adjacent pieces are larger, and the spark The larger the grade, the shorter the motor life. There are many structural forms of plastic commutators, which are mainly determined by the power, voltage, speed and size of the motor. Practice has shown that choosing a reasonable commutator structure is an important prerequisite for ensuring motor performance and improving product productivity. Most of the commutators are semi-plastic commutators, which are composed of plastic shells, commutator segments (or copper bars), insulation between mica sheets and metal bushings.

Due to the difference in the structure of the connection between the commutator piece and the coil head, it can be divided into two types: slot commutator and hook commutator. The slot commutator is shown in Figure 2. Its characteristic is that the groove is milled in the raised part of the commutator segment, the coil head is embedded in this groove, and then spot welded (hot pressure welding), the paint film of the enameled wire melts and dissipates at the high temperature during spot welding, making the wire head and the wire head. And form a good electrical connection with the commutator slot wall. The hook commutator is shown in Figure 3. When winding the rotor coil, the coil head is wound on the hook of the commutator segment, and then the hook is pressed down during spot welding to form a good electrical connection between the wire head and the commutator. The hook-shaped commutator is used to automate the process of connecting the coil head to the commutator, but it is mostly used in the occasions where the number of commutators is small and the motor power is small. Winding is difficult, and when the number of commutator segments is large, the width of the hook becomes narrower, and the adjacent wire ends are easily short-circuited.

When the motor speed is high and the speed reaches 30~60m/s, certain measures can be taken on the structure to improve the mechanical strength. Figure 4 shows the structure of a U-shaped dovetail groove with a reinforcing ring. The reinforcing ring can be made of steel rings (which can be machined from seamless steel pipes) or welded with steel wires, covered with a layer of insulating material, or organic insulating materials such as glass fiber reinforced plastics.

The shell of the commutator is made of glass fiber reinforced thermosetting plastic or asbestos plastic, which has high requirements on the heat resistance and mechanical strength of the plastic, and the thermal expansion coefficient is required to be as close as possible to the commutator copper material, and phenolic resin is often used. bakelite powder. The role of the metal bushing is to prevent the plastic from being mechanically stressed when the commutator is pressed against the shaft. Small commutators generally do not have metal bushings due to size constraints. Metal bushings include brass bushings, spring bushings, etc.

Mica plate or mica powder is used for inter-chip insulation. Because mica has strong wear resistance, it is necessary to pull grooves so that the mica plate between the chips is lower than the commutator plate, so as to avoid the wear-resistant mica plate protruding from the commutator plate. It affects the contact between the brush and the commutation piece, causing the commutation to deteriorate, and the motor cannot run.

The commutator copper bar materials can be roughly divided into two categories: one is oxygen-free copper or electrolytic copper; the other is silver-copper alloy. The first type of oxygen-free copper or electrolytic copper is mainly used in occasions with low speed, such as small home appliance motors, automobile starter motors, etc. The second largest category of silver-copper alloys is mainly used in vacuum cleaners and power tools. Due to the high linear speed of vacuum cleaners and power tools when reversing, the sparks during reversing continue to ablate the surface of the commutator, causing the temperature of the surface of the commutator to rise sharply, which can be increased by adding a certain amount of silver to the copper. The high temperature resistance of silver-copper alloy makes the surface of the commutator less likely to cause deformation, and can effectively control the occurrence of defects such as sparks and floating rows.

0
Views: 158