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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, etc. When using cast aluminum alloy, the total content of aluminum, titanium, and magnesium in the shell of Class I electrical equipment 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 enclosures, the magnesium content is not allowed to exceed 6% (by mass). The thickness of the metal shell: For explosion-proof shells, it should be able to withstand the assessment of internal explosive pressure and external impact energy; For other explosion-proof types of enclosures, they should be able to withstand external impact energy assessment.
1.2 Plastic materials
Plastic casings are commonly used in increased safety electrical equipment 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 the key defects of plastic products. Some plastics can overcome the above drawbacks, such as DMC and SMC plastic products, which have been widely used in the casings of explosion-proof electrical products. When selecting plastic grades, 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 equipment's operating environment temperature, it can withstand the specified impact or drop test without damage. The influence of electrostatic 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 in Table 2.
2Fasteners
2.1 Design Principles
2.1.1 The size and material of fasteners should meet the structural requirements of explosion-proof types, such as the tensile strength of fasteners for explosion-proof equipment that can withstand explosive pressure; Fasteners for increased safety and other equipment should ensure that the casing is fully compressed to achieve the specified level of protection.
If bolts made of light metal or plastic are used as fasteners for aluminum alloy and plastic shells, 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 that only specialized tools can be used to open the structure.
2.2 Special fasteners shall comply with the provisions of Article 9.1 of GB3836.1-2000.
3Adhesive materials
When resin composite is required to bond explosion-proof electrical components to achieve the specified bonding strength, the formula and process of the composite should be considered, and the maximum 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 wiring cavities, 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 of the wiring terminals set in the wiring chamber should have a margin.
5Connecting components
Internal and external grounding connectors should be installed on the metal casing of explosion-proof electrical equipment. External grounding connectors should be placed as close as possible to the cable entry device, while internal grounding connectors should be located within the wiring compartment. The size of the connector should be able to reliably connect with a protective wire of at least 4mm2, 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 connected by metal conduits 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 made into explosion-proof components (Ex elements) fixed on the 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 casing, wiring terminals, ammeters, small switches, small buttons, indicator lights, instrument display introduction devices, and other components, if made into Ex components, can be easily installed in the increased safety casing, achieving the purpose of lightweight structure and convenient installation and maintenance.
8.Interlocking devices and warning signs
To prevent the explosion-proof enclosure from being electrified and opening the cover, 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 should be set up stating 'Do not open the lid with power on'.
9, Logo
There should be a general marking of "Ex" or "Ex explosion-proof level temperature group" on the obvious part of the explosion-proof electrical equipment casing. Explosion proof electrical equipment should have nameplates made of brass or stainless steel materials, with no specific thickness requirements. Plastic nameplates for foreign instruments have been widely used, and the quality of their adhesive materials is quite good. The nameplate should include at least the following information:
9.1 Manufacturer 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:- When the ambient temperature is between -20 ℃ and 40 ℃, there is no requirement for this item.
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