Explosion proof measures for flameproof electrical

2022-08-09
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Explosion proof measures for explosion-proof electrical equipment

explosion proof electrical equipment is mainly used in workplaces with explosion hazards in underground coal mines. Its use environment is narrow, it is difficult to handle, and there is a risk of rock and coal falling and impact. Its shell should not only have explosion resistance, but also have sufficient mechanical strength, so as to ensure that the shell of the equipment will not be seriously deformed or damaged in case of internal explosion or impact by foreign objects. Therefore, the flameproof shell of flameproof electrical equipment that often works in the underground mining face of coal mines must be made of steel plate or cast iron, but other parts or electrical equipment that cannot be impacted after assembly or whose volume does not exceed 2L can be made of HT gray cast iron. For class I non mining working face, the flameproof shell can also be made of HT gray cast iron. For the shell with a volume not greater than 2L, it can also be made of engineering plastic. This material has the advantages of easy molding, easy cutting, light specific gravity, easy manufacturing, etc., but when using this material as an explosion-proof shell, we must pay attention to the nature that plastic is prone to decomposition and deformation at high temperature. Therefore, plastic enclosures should not be used on electrical equipment with a large number of heat sources and large arcs. The geometry of the flameproof shell is diverse. A large number of theoretical research and practice have proved that: in the flameproof shell with the same volume and different shapes, the explosion pressure in the non spherical shell is lower than that in the spherical shell, that is, the explosion pressure of the spherical shell is the largest, while the explosion pressure of the rectangular shell is the smallest, and the explosion pressure in the shell changes with the shape of the container. This is because the explosion pressure is reduced with the increase of the external heat dissipation surface area. Therefore, the explosion-proof shell should adopt a rectangular shape, which can improve the explosion resistance of the shell. The volume of flameproof enclosure is also the key to the design of flameproof enclosure. Both theory and practice have proved that under certain other conditions, the volume of the flameproof shell has nothing to do with the explosion pressure in the shell, and the volume has little effect on the pressure. Therefore, when designing and manufacturing the flameproof shell, on the premise of meeting the technical requirements of the equipment, the volume of the flameproof shell can be reduced as much as possible, which not only ensures the explosion resistance of the shell, but also reduces the volume and weight, which is more convenient for use in the special environment under the coal mine. Generally, the explosion-proof shell is mostly composed of two or more cavities, and the cavities are connected. Therefore, when the explosive mixture in the shell explodes, the pressure overlap phenomenon will occur, that is, when the explosive mixture in one cavity explodes, the explosive mixture in the other cavity will be compressed and the pressure will increase. If this cavity explodes again, you will be welcome to learn about our company's relevant experimental machine knowledge. Overpressure will occur, forming multiple cavity pressure overlap, and the explosion resistance of the flameproof shell will be threatened. Therefore, when designing construction projects to manufacture flameproof shells for construction projects of non public issuance of shares by listed companies, we should try to avoid the use of multi cavity structure. If this structure cannot be avoided, we should try to increase the area of connecting holes between cavities. Because the overpressure of multi cavity pressure overlap accounts for 34.7% of the high-tech industry, which is related to the volume ratio of the two cavities and the sectional area of the connecting hole. When the volume ratio of the two cavities is constant, the larger the sectional area of the connecting hole, the smaller the overpressure, thereby increasing the explosion resistance of the shell. In addition, the ratio of length, width and height of the shell should not be too large to avoid pressure overlap in the shell. The flameproof enclosure of flameproof electrical equipment should not only have explosion resistance, but also have explosion resistance. How to realize the flameproof function of flameproof enclosure is the key to the study of flameproof electrical equipment. We know that due to the needs of processing, manufacturing, use, maintenance and other aspects, the flameproof shell of any shape cannot be a "seamless" whole, but consists of several parts and various parts. All parts and parts need to be connected, and the joint gap is bound to become the way for explosive products in the shell to pass through. If there are no special regulations and technical requirements for the gaps of these connections, the explosive products in the shell passing through the gap will ignite the explosive mixture around the outside of the shell, and the consequences are unimaginable. In order to prevent the explosive mixture inside the shell from igniting the explosive mixture around the outside of the shell, some special and effective measures must be taken at the joints of the shell, that is, the connection gap, to realize the explosion-proof performance of the shell. Usually, the joint surface connected with each other is called "flameproof joint surface", which is called "flameproof surface" for short. The gap between the flameproof surfaces is called "flameproof joint surface gap", which is referred to as "flameproof gap". The size of the flameproof gap is the key to whether the flameproof shell can be flameproof. Usually, the flameproof surface adopts the flameproof protection method of flange connection. There are many kinds of structures for the gap between the flameproof joint surface: planar structure (switch cover and shell, junction box and shell), cylindrical structure (motor end cover and base, rotating shaft and rotating hole), planar plus cylindrical structure (coal electric drill junction box cover and junction box), curved (labyrinth) structure (switch cover and shell imported from the former Soviet Union), threaded structure, gasket structure (lighting lampshade and metal shell), Laminated structure (explosion-proof structure on old battery box), microporous structure (copper based and stainless steel based powder metallurgy sheets for analytical instrument sensors, stainless steel ball explosion-proof structure, foaming stainless steel plate), metal explosion-proof structure (multi-layer copper, stainless steel), etc., are shown in Figure 1. The theory of using the gap of the shell for flameproof is similar to the principle of metal on flame extinction. The flameproof function of the flameproof shell is to realize flameproof by using the flange gap of the shell. There are still two views on why the flange gap can achieve explosion-proof in theoretical research: one view is that the flange gap has the effect of extinguishing the explosive products (flames) in the shell, and the flame automatically extinguishes in the narrow flange gap, so the flange gap has the effect of explosion-proof; the other view is that the flange gap can not only extinguish the flame in the shell, but also reduce the temperature of the explosive products in the shell, These products are explosion-proof, so the flange gap can play a role in explosion-proof. In a word, theoretical research and practice have proved that using the flange gap of flameproof shell can play a flameproof role. Since the flange gap can play the role of flameproof, what is the relationship between the size of the gap and the size of the flameproof effect? The research shows that the larger the flange gap is, the more biological energy produced by explosion passing through the gap is, the stronger the detonation transmission is, and the worse the flameproof performance is. On the contrary, the smaller the flange clearance is, the weaker the explosion propagation is and the better the flameproof performance is. The length of flange flameproof surface is also related to the flameproof of flange gap

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