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.
I.Explosion-proof size design considerations
(1) Flat joint surface. Plane joint surface is generally on the line box cover and line box, terminal board and outlet holes, or in the frequency converter machine in the frequency converter shell and motor shell docking applications. 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. are usually installed using a stop joint design. 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 into the normal operation of the structure will not wear.
2.explosion-proof motor pressure design considerations
Explosion-proof motors and ordinary motors is the biggest difference between 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 to 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.