Sealing And Heat Dissipation Of Explosion-proof Distribution Boxes

Sealing and heat dissipation are a core contradiction in explosion-proof distribution boxes. Explosion-proof requirements necessitate a completely sealed enclosure to prevent internal sparks from igniting the external explosive environment, while the heat generated by electrical components needs to be effectively dissipated. Resolving this contradiction is one of the core technologies in explosion-proof electrical design.

I. Sealing

The sealing of an explosion-proof distribution box is not primarily for waterproofing or dustproofing, but rather to prevent the propagation of an explosion.

1. Flameproof Type ("d") Sealing Principle:

This is the most common type of explosion-proof enclosure. Its sealing does not rely on rubber gaskets, but rather on precise flameproof mating surfaces, such as flange faces and stops. When an explosion occurs inside the enclosure, high-temperature, high-pressure gases are ejected through the gaps in the mating surfaces, and are cooled to below the ignition temperature of the external explosive environment during the ejection process.

2. Increased Safety Type ("e") Sealing Principle:

This type does not rely on flameproofing, but rather on a high protection level (IP65/IP66) seal to prevent external dust or moisture from entering and to prevent dangerous temperatures and electric arcs from forming inside. Its sealing primarily relies on integrally cast sealing strips, such as silicone foam strips and stainless steel cable connectors.

3. Common Sealing Failure Points：

Box Cover: Aging of the sealing strip, uneven compression, and deformation of the sheet metal box can lead to failure.

Bolts: Electrochemical corrosion between stainless steel bolts and the aluminum alloy box can cause them to seize, making them impossible to tighten.

Inlet Devices: Failure to use explosion-proof plugs to seal unused cable inlets, or ordinary cables being passed directly through without being properly secured.

II. Heat Dissipation: Under the premise of ensuring explosion-proof performance, heat dissipation typically follows these paths

1. Structural Heat Dissipation (Suitable for low power)

Thickened Housing: Utilizing an aluminum alloy or cast aluminum housing, which has a higher thermal conductivity than carbon steel, and increasing the convection area through heat dissipation fins on the outer wall of the housing.

Heat Conduction Path: The heating element is directly mounted on a mounting plate on the inner wall of the housing, transferring heat to the housing surface for dissipation through metal conduction.

2. Heat Pipe Technology (Suitable for medium power)

Explosion-proof Heat Pipe Radiator:

This is a compliant solution. The evaporation section of the heat pipe is located inside the explosion-proof enclosure, absorbing heat. The condensation section of the heat pipe is located outside the enclosure, cooled by forced airflow from a fan. The portion of the heat pipe passing through the explosion-proof enclosure must be sealed or have an explosion-proof structure to ensure that the explosion-proof performance is not compromised in extreme situations such as heat pipe breakage.

3. Water-Cooled Plate (Suitable for high power)
A water-cooled plate is installed inside the enclosure, with the heating element mounted on it. Heat is carried away by circulating cooling water. Explosion-proof through-wall terminals must be used at the inlet and outlet water pipe interfaces to ensure explosion-proof isolation between the water passage and the electrical cavity.

4. Ventilation and Filtration System (for specific conditions)

In some special explosion-proof types, ventilation and heat dissipation can be used. Protective gas is introduced into the enclosure to maintain an internal pressure higher than the external pressure, preventing the entry of hazardous external gases.

III. Balancing in Practical Design

1. Derating
In explosion-proof environments, electrical components cannot be used at their rated current under normal conditions. According to standards such as GB/T 3836.3 (increased safety type), derating by 10%-25% is typically required. For example, a circuit breaker rated at 100A should ideally be used with only 80A in an explosion-proof enclosure to reduce heat generation.

2. Rational Layout and Airflow Simulation
Mounting high-heat-generating components in the upper part of the enclosure allows heat to rise naturally.

Even if ventilation holes are not possible, sufficient space for heat convection must be provided internally. High-power explosion-proof enclosures often incorporate explosion-proof axial flow fans to force internal airflow, distributing heat evenly to the heat dissipation fins on the outer shell and preventing localized overheating.

3. Material Selection
Aluminum alloy offers significantly better heat dissipation than carbon steel/stainless steel. For explosion-proof enclosures requiring high heat dissipation, cast aluminum alloy shells are the preferred choice. While stainless steel is corrosion-resistant, its poor thermal conductivity can lead to heat accumulation inside.