Explosion proof typeExplosion proof certificationtechnology
1、 Explosion proof principle of explosion-proof type "d"
Explosion proof typeExplosion proof type is to enclose all components of the equipment that may ignite explosive gas mixtures in an enclosure, which can withstand the explosive mixture that penetrates into the interior of the enclosure through any joint surface or structural gap of the enclosure without damage, and will not ignite the explosive environment formed by one or more gases or vapors on the outside(Refer toGB/T 3836.2standard)Put all components that may generate sparks, arcs, and dangerous temperatures into a flameproof enclosure, which separates the internal space of the equipment from the surrounding environment. There are gaps in the explosion-proof shell, and due to the breathing and gas permeation of electrical equipment, there may be explosive gas mixtures inside. When an explosion occurs, the shell can withstand the generated explosion pressure without damage. At the same time, the gaps in the shell structure can cool the flame, reduce the flame propagation speed, or terminate the acceleration chain, so that the flame or dangerous flame products cannot penetrate the explosion-proof gap and ignite the external explosive environment, thereby achieving the purpose of explosion-proof.
2、 Main explosion-proof measures:
1. Requirements for material of explosion-proof shell
（1）The explosion-proof shell needs to withstand the explosion pressure generated by the internal explosive gas explosion, and cannot rupture or deform to damage the explosion-proof performance, such as the gap at the joint surface becoming larger during the explosion.
（2）The explosion-proof shell must meet two basic conditions:
A、 The shell has sufficient mechanical strength to withstand internal explosive pressure without damage, and does not produce permanent deformation that affects explosion-proof performance.
B、 All seams and pores on the outer shell wall that are connected to the outside are smaller than the corresponding maximum experimental safety clearance
2. The gap length and width of the explosion-proof joint surface, as well as the surface smoothness requirements.
The casing of electrical equipment is generally composed of a shell and a cover, and there are often rotating shafts (such as rotating motors), control levers, and other components on the casing wall. The seams between the cover and the shell, as well as between the aforementioned components and the shell, form a pathway from the inside out. Combustible gases enter the interior of the equipment casing through these gaps. When an explosion occurs inside, the explosion flame will be transmitted to the outside of the casing through these gaps, igniting the surrounding explosive environment. If the gap is small and the path from inside to outside is relatively long, the flame cannot reach the outside of the shell. The standard defines such a joint as a flameproof joint surface.
3. Requirements for fasteners and threaded holes
The fasteners of the explosion-proof shell should withstand the tensile force generated by the explosion inside the shell, such as a side length of0.5mThe cube explosion-proof shell, when hydrogen gas inside the shell explodes, the pressure borne by the lid is22Ton. If the lid is used8If one fastening screw is tightened, the tensile force that each screw can withstand during the overvoltage test is4Ton. As can be seen from the above, the requirements for the fasteners and screw holes of the explosion-proof shell are very high.
4. Requirements for Transparent Components
5. Requirements for adhesives and sealants
6. Grounding
7. Cable and conduit entry device
8. Chain and warning signs, etc.
3、 Applicable standards:
1GB/T 3836.2-2021-Explosive Environment2Part: Composed of explosion-proof shell“d”Protected equipment
4、 Classification of explosion-proof equipment
Explosion proof type "d" is classified according to the types of explosive gas environments allowed for useIClass andIIA、IIB、IICClass. This explosion-proof type of equipment is suitable for1、2District venue.
Class II explosion-proof electrical equipment according to maximum test safety clearanceMESG（mm）Divided intoIIA、IIB、IICThree levels:
The so-called maximum test safety gap is at a length of25mm, in accordance withIEC79-1Aof8Rising ball describes the gap in the internal testing of the product
MESG。
Note: Class IIC electrical equipment can replaceIIA、IIBGrade equipment;
IIB level electrical equipment can replaceIIAGrade equipment;
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