Insulation parts used in explosion-proof positive pressure cabinets are mostly made of plastic materials. In order to ensure the reliable explosion-proof safety performance of the explosion-proof positive pressure cabinet, these plastic material products must have good insulation performance and reliable mechanical properties. To this end, the selection of plastic materials and the design of the insulating structure are crucial.

There are many types of plastic insulation materials that can be used in explosion-proof positive pressure cabinets, and here are only a few commonly used ones for people's reference, as shown in the table.

Table Several plastic insulating materials commonly used in explosion-proof positive pressure cabinets

Name Code Continuous working temperature Heat deflection temperature Flammability Arc resistance Dielectric strength

Melamine formaldehyde resin MF 150~200 177~199 Self-extinguishing — —

Epichlorine resin EP -89~155 124~288 — 45~120 160~200

Phenolic plastic PF less than 140 149~188

Polycarbonate PC -10 - 130 121~132 Self-extinguishing 10~20 150~180

Acrylonitrile. Butadiene. Styrene copolymer ABS -40 ~90 93~118 Self-extinguishing 130~200

Polymethacrylic acid ① PMM^ 70~80 flame retardant

Polyethylene PE -70~100 Flammable

Polytetrafluoroethylene PTEE -180~260 Less than 121 Non-combustible Less than 200 160~200

① Commonly known as: plexiglass.

In addition to the properties shown in the table, the plastic insulating materials listed in Table 6.4 also have some characteristics that people should consider when choosing materials, which are briefly introduced here.

(1) Melamine formaldehyde resin (MF)

This is a thermosetting plastic with melamine formaldehyde resin as the main material, cellulose as the auxiliary material and various additives. It has good arc resistance and can self-extinguish after being ignited, but its impact resistance and dimensional stability are low, so it can be used to make electrical insulation parts of explosion-proof positive pressure cabinets.

(2) Epoxy resin (EP)

This is a composite thermosetting plastic with epoxy resin as the main material and different additives as auxiliary materials. It has good insulation properties, mechanical properties and adhesive properties, and is resistant to seawater (salt water) erosion and small shrinkage. It is suitable for making electrical insulation parts and printed circuit boards.

(3) Bakelite (PF)

This is a thermosetting plastic with phenolic resin as the main material and other additives as auxiliary materials. For example, when the additive is glass fiber, its product is called phenolic FRP, which has high strength, good heat resistance and corrosion resistance; when the additive is wood powder, its product is called bakelite, It has good mechanical properties and insulation properties.

These products of phenolic resin are often used to make electrical insulation parts. Some phenolic plastic products have good ablation resistance. For example, phenolic resin products with asbestos fiber additives can withstand high temperatures of several thousand degrees Celsius instantaneously, and are optional materials for making explosion-proof positive pressure cabinet parts for high-temperature environments.

(4) Polycarbonate (PC)

This is a thermoplastic with good light transmission properties. It has good insulation performance, heat and cold resistance, corrosion resistance and wear resistance, but has low thermal conductivity and large thermal expansion coefficient. Its products can be used as transparent parts of observation windows in explosion-proof positive pressure cabinets.

(5) Acrylonitrile-butadiene-styrene copolymer (ABS)

This is an excellent engineering thermoplastic. It has good mechanical properties, insulation properties, heat resistance, corrosion resistance, and the impact resistance of the material is good and the dimensional stability of the molded parts is good. It is widely used in the manufacture of structural and insulating parts of various equipment, such as special Battery compartment for explosion-proof storage battery (Exs: U).

(6) Polymethyl methacrylate (plexiglass, PMMA)

This is a thermoplastic based on acrylic plastic. It has good insulation performance and secondary processing performance, and high transparency; however, it is brittle and cannot withstand high stress, for example, it is easy to crack when drilling or (and) screwing into screw holes. In engineering, people often use it as a transparent part instead of quartz glass, such as the transparent part of the observation window in the explosion-proof positive pressure cabinet.

(7) Polyethylene (PE)

This is a thermoplastic of ethylene polymer crystals, usually divided into low-density polyethylene (LDPE) and high-density polyethylene (HDPE).

Low-density polyethylene has good flexibility, ductility and transparency, and is suitable for making various "plastic cloths" such as films, such as the separator between the positive and negative plates in the battery; high-density polyethylene has good Excellent mechanical properties and a wide operating temperature range, suitable for the manufacture of various profiles such as pipes, such as the casing of small electrical appliances, the battery tank of special explosion-proof batteries (Exs.U), etc.

Whether it is low-density polyethylene or high-density polyethylene, they all have good electrical insulation properties and have been well applied in the manufacture of explosion-proof positive pressure cabinets.

(8) Polytetrafluoroethylene (PTEE)

This is a thermoplastic that contains fluoroplastics. It has excellent insulation performance, high and low temperature resistance, corrosion resistance, and low friction coefficient, but has a large temperature expansion coefficient and poor thermal conductivity. Its products are often used in chemical equipment, low temperature equipment and various wear-resistant and sealing structures, such as shaft sealing rings (such as V-rings) of explosion-proof motors.

Of course, in addition to the materials shown in the table, there are many plastic insulating materials available, and people can choose the best according to the specific situation.