A blind hole refers to a hole that is open on one side and closed on the other, commonly used for component connection or positioning.

On a flameproof enclosure for flameproof explosion-proof equipment, a blind hole specifically refers to a threaded hole for installing fasteners such as bolts. Its design must comply with the requirements of GB/T 3836.2 Explosive atmospheres - Part 2: Equipment protected by flameproof enclosures "d".

For blind holes that do not penetrate the wall of the flameproof enclosure (including threaded holes and double-ended stud holes), the remaining wall thickness of the enclosure must meet two conditions simultaneously:

It shall be no less than one-third of the diameter of the bolt or double-ended stud.

It shall be no less than 3 millimeters.

The larger of the two values shall be taken as the requirement during design.

Q: Does the "remaining wall thickness" of the flameproof enclosure wall refer to the thickness directly below the hole, or the thickness around and below the hole?

A: The "remaining wall thickness" of the flameproof enclosure wall is interpreted as follows: When the hole is perpendicular to the enclosure wall, only the thickness of the enclosure wall directly below the hole is subject to the requirement (3 mm or one-third of the diameter, whichever is larger). This interpretation is based on the fact that there are no specific material thickness requirements for the flameproof enclosure itself, so the material around the hole is not restricted. Flameproof tests shall cover most blind holes, such as impact tests and overpressure tests.

For more information on explosion-proof knowledge, please further consult STS!