Explosion-proof motors, as the main power equipment, are usually used to drive pumps, fans, compressors and other transmission machinery. Explosion-proof motor is the most basic type of explosion-proof motor, because of its shell non-sealed structure characteristics, the main flammable gas gas in the coal mine to reach a certain concentration limit, when in contact with the shell of sparks, arcs, dangerous high temperatures and other sources of ignition may explode; reasonable design is to ensure that the motor’s explosion-proof shell is not only will not be damaged or deformed, and the explosion of flames or hot gases through the gap between the joints Passed out, but also can not ignite the surrounding explosive gas mixtures. This paper combines the national standards and basic requirements of mechanical design, talk about the structural dimensions of such motors, pressure, cooling, three aspects of the design considerations.
1.The explosion-proof size design considerations
The type of joint plane joint, cylindrical joint or stop joint, and explosion-proof motor because of its driving needs also has its own unique shaft joint. Explosion-proof joint design should mainly consider the joint width, clearance and roughness of the three elements. Class Ⅰ shell joint minimum width and maximum gap are referenced to GB3836.2 in the table specific data, the following four kinds of joints to elaborate.
(1) plane joint surface. Plane joint surface is generally online box cover and line box, terminal board and outlet holes, or in the inverter integrated machine in the inverter shell and motor shell butt application. Large and medium-sized explosion-proof motor shell plane joint surface is generally milling, boring process, less grinding process, the general design roughness Ra 3.2μm, design flatness tolerance of not more than 0.2mm. design accuracy requirements are often higher than the standard requirements for machining accuracy is slightly less than the national standard, but still meet the national standards.
(2) Cylindrical joint surface. Cylindrical copper jointing surface in the explosion-proof motor can be applied to the installation of cable connectors, the installation of terminals and so on. If the cylindrical joint contains a sealing groove, the width of the groove can not be calculated, the width of the part of the groove partition can not be added. The most economical and reliable means of realizing the cylindrical joint surface for turning, the accuracy of its selection is generally hole machining level 8 or 7, shaft machining is to improve the accuracy of a corresponding level, the general design of roughness Ra 3.2μm. Note: cylindrical joint surface of the explosion-proof clearance refers to the hole, the shaft diameter difference.
(3) stop joint surface. In the design of explosion-proof motor structure, end caps, bearing end caps, etc., the installation is usually used to stop the design of the joint surface. Stop joint surface is actually a combination of the characteristics of the plane joint surface and cylindrical joint surface. It should be noted that, if the stop cylinder part of the gap is too large or small width, or the corresponding corner chamfer more than 1mm, that is, by the chamfer partition, then only calculate the width of the plane joint surface L and the distance l; while the distance l of the plane joint surface is too small or with the cylindrical joint surface between the partition (more than 1mm chamfer or sealing groove, etc.), then only calculate the width of the cylindrical joint surface.
(4) Shaft joint surface Shaft joint is an inherent feature of rotating motors, in addition to the motor shaft and end caps with the application, in some of the need to install the knob of the explosion-proof electrical equipment is also used. Shaft joint is a special kind of cylindrical joint, the difference is that the rotating motor shaft of the explosion-proof surface needs to be designed in normal operation will not wear the structure.
2.The explosion-proof motor pressure design considerations
Explosion-proof motors and ordinary motors is the biggest difference is that the shell must be able to withstand the internal explosion pressure, explosion should not occur when the explosion should not affect the explosion-proof type of permanent deformation or damage, any part of the gap should not be a permanent increase. Usually use the static pressure method test: in the shell filled with water, pressurized to 1MPa, holding pressure for more than 10s, such as no leakage through the shell wall or permanent deformation, it is considered to be overpressure test qualified.
Explosion-proof motor pressure components mainly by the explosion-proof shell, shell end caps, flanges, etc., the design should focus on their strength and coordination. According to the explosion-proof shell structure: cylindrical explosion-proof shell, square explosion-proof shell, etc., the calculation method is different; the main method of theoretical calculations and finite element analysis of the two methods; theoretical calculations are difficult to accurately calculate the local stress; but finite element analysis is more rapid and intuitive to get the whole structure of the stress situation, optimization of the design, so as to avoid the explosion of the experiments caused by the local stress concentration of the shell Failure.
3.Explosion-proof motor cooling design considerations
General motor cooling methods are air-cooled, liquid-cooled, air-liquid cooled and so on. In view of the characteristics of the coal mine application environment, more coal dust is not conducive to air-cooled, so the coal mine equipment is commonly used liquid cooling. Now the explosion-proof motor waterway mainly has two types of folding and spiral, the following comparative discussion.
(1) Fold back waterway structure. Folding waterway processing can be used in two ways: one is directly in the thick-walled shell with a CNC boring machine to cut out the folding of the waterway, and then outside the welded cover, the advantages of a smooth waterway, water resistance is small, no cascade of water between neighboring waterways, which is conducive to improving the cooling effect; the disadvantage of the boring process is inefficient, troublesome programming, high cost. Another is welded on the periphery of the cylinder rib plate, spacing out the continuous waterway folded back, and then weld the cover; advantage is that the production process is simple; disadvantage is that the quality of the welder’s level of operation with the welder, weld channel water resistance, easy to scale.
(2) spiral waterway structure. Spiral waterway is mainly composed of auxiliary cover plate and socket shell two methods; because of the spiral “buckle cover” operation up time-consuming and difficult, generally do not use, usually use the method of interference heat set shell. According to the expansion coefficient of the material and the actual elevated temperature calculated shell diameter can be expanded out of the size of the design of a larger amount of surplus, to prevent the string of water between adjacent waterways. The structure of the watercourse water resistance is small, the best cooling effect; its disadvantage: watercourse once the water pressure accidentally too high, resulting in shell expansion package, the shell gap between the shell, resulting in the shell can not be repaired and scrapped. Therefore, generally set up in the water inlet pressure reducing valve to ensure normal operation.
High-power motors due to shaft heating is more serious, will be considered to the bearing cooling, and in the bearing end cap design ring-shaped waterway. When several parts of the same equipment have waterways, parallel water supply is generally used; or use the water port plus sealing ring directly butt the way to make access to water more simple and convenient.
Post time: Jul-06-2024
