Regarding dust explosion-proof motors

Dust explosion-proof motors are widely used in factories and enterprises with a lot of dust, which can prevent flammable dust from being ignited. Many textile manufacturers are equipped with dust explosion-proof motors in their operating equipment, with the aim of preventing the generation of flammable and explosive substances from dust. So, what are the precautions for dust explosion-proof motors? How to understand dust explosion-proof motors?

Dust explosion-proof motor

It refers to a motor whose casing is designed and manufactured under specified conditions, which can prevent dust from entering the motor casing or, although it cannot completely prevent dust from entering, the amount of dust entering does not affect the safe operation of the motor, and the accumulation of dust inside is not likely to cause an ignition hazard, and it will not cause an explosion of the surrounding explosive dust mixture during use. (1) The enclosure has a high degree of sealing to reduce or prevent dust from entering the enclosure. Even if dust does enter, the amount is not large enough to pose an ignition hazard. (2) Control that the maximum allowable surface temperature of the enclosure does not exceed the specified temperature group. It has been used on the mechanical equipment of the national grain reserve depots.

Characteristics of the sealing structure of dust explosion-proof motors

The sealed type connects the various components of the inner and outer cavities of the explosion-proof motor, and achieves the dust-proof effect by adding sealing gaskets. The sealing gasket must be made of asbestos board, rubber board or other durable high-quality materials, and it should be suitable for the load conditions of the electrical equipment and the expected working life temperature; otherwise, it will affect the performance of the explosion-proof motor. The sealing parts of a sealed dust explosion-proof motor mainly refer to the junctions between the motor base and the end cover, the end cover and the outer cover, the base and the junction box, and the box base and the box cover, etc.

Due to the long circumference of the mating surface between the base and the end cover, the sealing requirements are also high. To achieve sealing performance, the gasket should have a certain degree of elasticity. In order to keep the bearing distance of the motor stable, there must be a positioning structure between the frame and the end cover, and it cannot be positioned by the strength of the sealing gasket. When the connecting bolts between the end cover and the base are tightened, the gasket is compressed and thinned, causing the end cover to move inward and the entire bearing housing to move accordingly. In mild cases, this will reduce the axial clearance reserved in the design and the axial clearance of the bearing. In severe cases, it may cause the bearing to get stuck. Even if it does not get stuck, after the explosion-proof motor starts running, it will inevitably lead to high bearing noise, high bearing temperature and short service life.

Division of hazardous areas for dust explosion

Before delving into dust-proof and explosion-proof motors, let's first understand how dust explosion hazardous areas are classified. Dust explosion hazardous areas are classified into two zones based on the frequency and duration of the occurrence of explosive or flammable dust environments.

Zone 10: An area where dust clouds or dust layers that may or may occur during normal processing, handling or cleaning, when mixed with air, can reach explosive concentrations.

Zone 11: Areas not classified as Zone 10, but where dust clouds occur under abnormal conditions and the mixture of dust and air can reach explosive concentrations.

Selection of dust explosion-proof motors

In order to operate normally in the above-mentioned areas, the enclosures of dust explosion-proof motors are also classified into two types based on their ability to restrict dust: dust-tight enclosures, with an enclosure protection grade of IP6X and a marking of DT; Dust-proof housing, with a protection grade of IP5X and a marking of DP. When choosing a dust explosion-proof motor, the appropriate type of dust explosion-proof motor can generally be selected based on two aspects.

First, select the type of protection based on the motor corresponding to different hazardous locations

2. Then, make a selection based on the nature, category and temperature group of the dust

1. IIIA  is combustible flying dust, Class IIIB is non-conductive dust, and Class IIIC is conductive dust.

2. Ex  represents the equipment of explosion-proof motors.

3. tD  indicates that the enclosure can be applied to electrical equipment for dust explosion-proof purposes.

4. B21  indicates that it is suitable for dust in Zone 21. The explosion-proof grade for dust in Zone 21 is relatively high, and it is also applicable to Zone 22.

5. B  indicates that the explosion-proof joint surface of the motor is a straight joint surface. The explosion-proof structure is safer than the flat joint explosion-proof structure.

6. IP65  represents the protection level. The number 6 indicates that no dust can enter the dust-tight motor, and the number 5 indicates that the motor is waterproof.

7. T135℃(degree)  indicates that the maximum temperature of the equipment casing must not exceed 135 degrees.

1. Explosion-proof type: Ex dI Mb suitable for coal mines \ n

2. Explosion-proof type: Ex d IIB T4 Gb It is applicable to places in factories where flammable gases (propane and ethylene) are present.

3. Explosion-proof type: Ex d IIC T4 Gb, suitable for places in factories with flammable gases (hydrogen, propane, ethylene).

4. Explosion-proof type: Ex tD B21 T135° C. It is suitable for places in factories with flammable dust and flammable flying flocs (such as feed, textile, flour, cement and other places that generate dust).

5. Explosion-proof type: Ex d IIC T4 Gb/Ex td B21 T135° C. It is suitable not only for places with flammable gases in factories, but also for places with flammable dust and flammable flying flocs (such as feed). Textile, flour, cement and other places that can generate dust.

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