Along with the continuous acceleration of the process of urbanization in our country, the contradiction between the development of the petrochemical industry and urbanization construction is becoming increasingly prominent, and the unexpected incidents of production safety have caused serious threats to people's life and property safety. According to authoritative data, 2016. In 2018, there were 620 chemical accidents nationwide, resulting in 728 deaths. In 2019, the top 10 safety accidents in the chemical industry resulted in 112 deaths and 717 injuries. Behind these cold figures, the whole industry sounded a heavy alarm!

In summary, then some people ask, why not use explosion-proof products in such inflammable and explosive places? Some people say that the use of explosion-proof products at the same time, some people also asked, explosion-proof products really have explosion-proof function? Then on this issue to give you a science popularization of what materials are used in explosion-proof products.

In the oil, natural gas and other energy industries, as well as a variety of mining, chemical, fire rescue, hazardous chemicals management, airports and other fields, there is a normal flammable and explosive environment, a little spark or energy will cause an explosion, in these environments need special explosion-proof equipment to ensure safe operation. As a high-risk production industry, enterprises involved in explosion-proof requirements face many challenges in real-time communication and management.

1. Explosion-proof shell material

1.1 Metal Materials

Commonly used are cast steel, cast iron, welded steel plate, cast aluminum alloy, stainless steel and other materials. If cast aluminum alloy is used, the total content of aluminum, titanium and magnesium for Class I electrical equipment enclosures is not allowed to be greater than 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%(mass ratio). The thickness of the metal shell: for the flameproof shell, it should be able to withstand the assessment of internal explosion pressure and external impact energy; For other explosion-proof shell types, it should be able to withstand the external impact energy assessment.

1.2 Plastic Materials

Plastic shell is used more in increased safety electrical equipment and intrinsically safe electrical equipment. The main consideration is the characteristics of light structure and excellent resistance to environmental chemical corrosion. However, the aging and deformation of materials are the key defects of plastic products. Some plastics can overcome the above shortcomings, such as DMC, SMC plastic products have been widely used in the shell of explosion-proof electrical products.

When selecting a plastic grade, consider that the thermal stability of the material is at least 20K higher than the surface temperature generated by the equipment; Low temperature characteristics At least 5-10K lower than the lower limit of the ambient temperature of the equipment can withstand the specified impact or drop test without damage.

The effect of static charge on mobile electrical equipment and plastic surfaces that may be rubbed or wiped should be considered, which can be designed according to the requirements in Table 2.

2. Fasteners

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 of flameproof equipment to withstand explosion pressure; Fasteners for increased safety and other equipment should ensure that the housing is sufficiently compressed to achieve the specified protection level.

2.1.2 Fasteners of aluminum alloy and plastic shell, such as bolts made of light metal or plastic, can be used if the material and thread shape of the bolts meet the fastening requirements.

2.1.3 Fasteners should be tightened to ensure that only special tools can be used to open the structure.

2.2 Special Fasteners

According to Article 9.1 of GB3836.1-2000.

3. Bonding material

When a resin compound is required for bonding between explosion-proof electrical components to achieve the specified bonding strength, the formulation and process of the compound should be considered, and the limiting temperature of the bonding material should be considered to be at least 20K higher than the maximum surface temperature of the equipment.

4. Electrical connectors and wiring cavities

The introduction of external cables or conduits of explosion-proof electrical equipment, except for the introduction of permanent cable methods, is mostly carried out in the connecting cavity. When designing the wiring cavity, it should be ensured that there is sufficient size to facilitate the reliable connection of the wire. The explosion-proof type of the shell shall conform to the explosive hazardous environment used.

The specification of the conducting bolt of the terminal set in the connecting cavity shall have a margin.

5. Connecting parts

The metal shell of explosion-proof electrical equipment shall be provided with internal and external ground connectors. The external ground connector should be as close as possible to the cable lead-in device, and the internal ground connector should be in the connecting cavity.

The size of the connector should be able to reliably connect with the protection cable of at least 4mm2, and the anti-loosening measures should be taken to ensure reliable compaction. The grounding symbol should be set on the ground connector to show correct connection.

Electrical equipment with double insulation and reinforced insulation; Electrical equipment with metal conduit connection may not have a ground connection.

6, cable and conduit introduction device

The cable and conduit lead-in devices can be integrated with the explosion-proof housing, or can be made into explosion-proof components (Ex components) fixed to the explosion-proof housing. The technical requirements for cable and conduit introduction devices are shown in Appendix D of GB3836.1-2000. The through holes on the electrical equipment that are not equipped with cables and conduits must be sealed with plugging pieces.

7. Ex components

Explosion-proof shell, terminal, ammeter, small switch, small button, indicator light, instrument display introduction device, and other components, such as Ex components, can be easily installed in the increased safety shell, to achieve the purpose of lightweight structure, easy installation and maintenance.

8. Interlocking devices and warning signs

In order to prevent the explosion-proof shell from opening the cover with electricity, an interlocking device should be provided, and the device should ensure that the mechanism cannot be opened by non-special tools. If there is no interlocking device, “ It is strictly forbidden to open the lid with electricity” The warning sign.