来源：http://www.jnmcd.com 发布时间：2019-06-12 浏览：次
1 collector ring structure collector ring structure is divided into: all plastic die-casting collector ring (suitable for small micro-motors); assembly collector ring (medium-sized micro-motors); screw assembly collector ring (medium and low-speed large micro-motors); hot sleeve collector ring (suitable for high-speed micro-motors).
According to the conductive function, sliding touch with brush, it is necessary to have wear resistance, stable sliding touch characteristics and mechanical strength. The sliding ring can be made of brass, bronze, low carbon steel or medium carbon steel. The sliding ring of high speed micro motor is made of high strength alloy steel (such as 35SMin). For corrosive places, stainless steel sliding rings can be used, but the sliding characteristics of stainless steel are not stable, and the inappropriate combination with brushes usually causes the brush to jump, which simply constitutes excessive temperature rise or abnormal wear of brushes, so as not to use this raw material as far as possible.
The diameter and width of the metal ring on the collector ring are related to the current passing through, the number of brushes, the scale of brushes, the heat dissipation area and the acceptable circumferential velocity of brushes. The interval between metal rings shall be determined according to the insulation interval required for winding voltage and the space required for installing brush holders, brushes and other parts. When the circumferential velocity of the metal ring surface is 3070m/s, the gas film on the metal ring surface will cause the brush to float, making the brush and the metal ring touch badly, and the current distribution is uneven, showing sparks and erosion, accelerating the wear and heat of the metal ring. The spiral groove can be machined on the surface of the metal ring to avoid the occurrence of such a situation. When the current passing through the collector ring exceeds 1000A, the metal ring should be ventilated or equipped with fans to enhance the cooling of the metal ring.
3 There are many kinds of brushes for brush materials, which can be roughly divided into carbon brushes and metal brushes. Because metal graphite brushes permit large current density, they can meet the needs of low speed micro motors. For high-speed micro-motors (such as 2p micro-motors), natural graphite brushes with good sliding and stability characteristics should be selected.
When choosing brushes, it is necessary to consider the technical requirements of micro motors for brushes and the technical characteristics of brushes. The technical characteristics of brushes include touch characteristics and physical and chemical characteristics. The main factors affecting the touch characteristics of brushes are circumferential velocity, current density, unit pressure applied to brushes and surrounding media. The touch characteristics of brush mainly include touch voltage drop and resistance coefficient.
Touch voltage drop is the voltage drop of current passing through brush, touch point film and collector ring. The touch voltage drop of each brush has its limit value. The touch voltage drop of metallic graphite brushes is lower than that of graphite brushes and graphite brushes. Assuming that the threshold value of touch voltage drop is exceeded, the electric loss of sliding touch point will be too large and cause overheating.
For collector ring, brush with lower touch voltage is more suitable.
Conflict is an important factor to be considered in the normal operation of brushes. It is one of the reasons for heat attack. The composition and function of the film on the collector ring surface have a significant impact on the resistance, and it is also affected by the raw materials, touch surface and operation conditions of the brush and collector ring. The conflict situation is usually weighed by the resistance coefficient of the brush. The larger the number of brushes, the larger the resistance coefficient and the higher the circumferential velocity, the greater the resistance loss. From the point of view of mechanical loss, the demand conflict coefficient of brushes used in high-speed micro motors is the smallest.
Violent conflict can cause the brush to oscillate, announce noise and unstable touch during operation. In severe cases, brushes can be broken.
The physical and chemical properties of brushes include resistivity, hardness and ash impurities. The applicability of brushes can be roughly determined according to the size of resistivity. Brushes with high resistivity are suitable for micro motors with difficult commutation, brushes with medium resistivity are suitable for ordinary DC micro motors, and brushes with low resistivity are suitable for low voltage micro motors. The hardness and resistivity of the brush can be summed up to reflect the general situation of the quality and function of the brush.
High resistivity and low hardness indicate that the brush has low density and is prone to wear. The brush contains a small amount of very fine ash, which can improve the wear resistance of the brush. However, assuming that there are a few hard abrasive particles in the ash impurities, such as iron carbide and silicon carbide (i.e. diamond), the surface of the collector ring will be grooved, which will cause great damage to the micro-motor.