1.Explosion proof shell material
1.1 Metal Materials
Commonly used materials include cast steel, cast iron, welded steel plates, cast aluminum alloys, stainless steel, and so on. When using cast aluminum alloy, for Class I electrical equipment casings, the total content of aluminum, titanium, and magnesium is not allowed to exceed 15% (mass ratio), and the total content of titanium and magnesium is not allowed to exceed 6%; For Class II electrical equipment casings, the magnesium content is not allowed to exceed 6% (mass ratio). The thickness of the metal shell: for explosion-proof shells, they should be able to withstand the assessment of internal explosion pressure and external impact energy; For other types of explosion-proof enclosures, they should be able to withstand external impact energy assessment.
1.2 Plastic materials
Plastic casings are commonly used in increased safety and intrinsic safety electrical equipment. Mainly considering the characteristics of lightweight structure and excellent resistance to environmental chemical corrosion. But the aging and deformation of materials are key defects in plastic products. Some plastics can overcome the above drawbacks, such as DMC and SMC plastic products, which are widely used in explosion-proof electrical product casings. When selecting a plastic grade, the thermal stability of the material should be considered to be at least 20K higher than the surface temperature generated by the equipment; Under the condition that the low-temperature characteristics are at least 5-10K lower than the lower limit of the ambient temperature for equipment use, it can withstand the specified impact or drop test without damage. The influence of static charges should be considered for mobile electrical equipment and plastic surfaces that may be rubbed or wiped, which can be designed according to the requirements of Table 2.
2Fasteners
2.1 Design Principles
2.1.1 The size and material of fasteners must meet the structural requirements of explosion-proof types, such as the tensile strength of explosion-proof equipment fasteners that must withstand explosive pressure; The fasteners of increased safety and other equipment should ensure that the casing is fully compressed to achieve the specified protection level.
2.1.2 If the fasteners of aluminum alloy and plastic shells are made of light metal or plastic bolts, the material and thread shape of the bolts must meet the fastening requirements before they can be used.
2.1.3 The fastening of fasteners should ensure a structure that can only be opened with specialized tools.
2.2 Special fasteners shall comply with Article 9.1 of GB3836.1-2000.
3Adhesive materials
When resin composites are required for bonding between explosion-proof electrical components to achieve the specified bonding strength, the formula and process of the composites should be considered, and the ultimate temperature of the bonding material should be at least 20K higher than the surface temperature of the equipment.
4Electrical connectors and wiring cavities
The introduction of external cables or conduits for explosion-proof electrical equipment, except for the use of * cable method, is mostly carried out in the wiring chamber. When designing the wiring cavity, sufficient size should be ensured to facilitate reliable connection of wires. The explosion-proof type of the shell should comply with the explosive hazardous environment used. The specifications of the conductive bolts for the wiring terminals installed in the wiring chamber should have margin.
5Connection piece
Internal and external grounding connectors should be installed on the metal casing of explosion-proof electrical equipment. The external grounding connector should be as close as possible to the cable entry device, and the internal grounding connector should be inside the wiring compartment. The size of the connector should be able to reliably connect with a protective wire of at least 4mm2 or more, and there should be anti loosening measures to ensure reliable compression. A grounding symbol should be set at the grounding connector to indicate correct connection. Electrical equipment with double insulation and reinforced insulation; Electrical equipment with metal conduit connections does not require the installation of grounding connectors.
6Cable and conduit entry devices
Cable and conduit entry devices can be integrated with explosion-proof enclosures, or can be made into explosion-proof components (Ex components) fixed on explosion-proof enclosures. The technical requirements for cable and conduit entry devices can be found in Appendix D of GB3836.1-2000. The through-holes on electrical equipment without cables and conduits must be sealed with sealing components.
7. Exelement
Explosion proof housing, wiring terminals, ammeters, small switches, small buttons, indicator lights, instrument display entry devices, and other components, if made into Ex components, can be easily installed in increased safety housing, achieving the goal of lightweight structure and convenient installation and maintenance.
8.Interlocking devices and warning signs
To prevent the live opening of the explosion-proof shell, an interlocking device should be installed, which should ensure that the mechanism cannot be opened by non specialized tools. If there is no interlocking device, a warning sign "Do not open the cover with electricity" should be set up.
9Logo
There should be a general sign indicating "Ex" or "Ex explosion-proof level temperature group" on the shell of explosion-proof electrical equipment. Explosion proof electrical equipment should have nameplates, which are made of brass or stainless steel materials with no specific thickness requirements. Plastic nameplates for foreign instruments have been widely used, and their adhesive material quality is quite good. The nameplate should at least include the following content:
9.1 Manufacturer's name or registered trademark;
9.2 Product name and model specifications;
9.3 Explosion proof signs;
9.4 Explosion proof certificate number;
9.5 Manufacturing date or factory number
9.6 Environmental temperature: -20 ℃ Ta 60 ℃ * When the environmental temperature is between -20 ℃ and 40 ℃, there is no requirement for this item.
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