Calculation formula for the tension of the fastening bolts of explosion-proof electrical appliances

In addition to the necessary locking force, the fastening bolts of the explosion-proof electrical appliance are also subjected to the explosion pressure. This paper mainly introduces the calculation formula of the tension bolt of the explosion-proof electrical appliance, as follows:

Q=1.3Qo(N)

For the stop structure

Q=1.1Qo(N)

Qo=QP/Z(N)

QP=PA

Where Qo - the calculated stress of each bolt, N;

QP - the total pressure the bolt is subjected to during the explosion, N;

Z——the number of bolts;

P——includes the compressive stress to be subjected to the explosion, MPa, 1.5 MPa for the IIC, and 1.0 MPa for the rest;

A - the effective area under pressure, m2.

The spacing of the fastening bolts of the explosion-proof electrical enclosure is related to the shape, material and presence or absence of the outer casing. For the planar structure, the IIC level is generally not more than 70-80 mm, and the other explosion-proof grades are generally not more than 120 mm. When the structure is stopped, it is generally not more than 140mm. The number of bolts is generally not less than 4 for a planar structure, and the number of anchors should not be less than 3.

The screw-in depth of the explosion-proof electrical bolts is 1.25 to 1.5 times the bolt diameter for the cast iron casing; the steel casing is less than 1.0 times the bolt diameter.

Thread allowance for the outer casing fastening bolts: The remaining threads of the washer clearance greater than 2 times must be left after the bolts are tightened so that the outer casing can be tightened after the gasket is lost.

In addition to the necessary locking force, the fastening bolts of the explosion-proof electrical appliance are also subjected to the explosion pressure. This paper mainly introduces the calculation formula of the tension bolt of the explosion-proof electrical appliance, as follows:

Q=1.3Qo(N)

For the stop structure

Q=1.1Qo(N)

Qo=QP/Z(N)

QP=PA

Where Qo - the calculated stress of each bolt, N;

QP - the total pressure the bolt is subjected to during the explosion, N;

Z——the number of bolts;

P——includes the compressive stress to be subjected to the explosion, MPa, 1.5 MPa for the IIC, and 1.0 MPa for the rest;

A - the effective area under pressure, m2.

The spacing of the fastening bolts of the explosion-proof electrical enclosure is related to the shape, material and presence or absence of the outer casing. For the planar structure, the IIC level is generally not more than 70-80 mm, and the other explosion-proof grades are generally not more than 120 mm. When the structure is stopped, it is generally not more than 140mm. The number of bolts is generally not less than 4 for a planar structure, and the number of anchors should not be less than 3.

The screw-in depth of the explosion-proof electrical bolts is 1.25 to 1.5 times the bolt diameter for the cast iron casing; the steel casing is less than 1.0 times the bolt diameter.

Thread allowance for the outer casing fastening bolts: The remaining threads of the washer clearance greater than 2 times must be left after the bolts are tightened so that the outer casing can be tightened after the gasket is lost.