Time was when enclosure hinges were basically pivoted connections between doors and frames. But modern hinges often do much more: They can make a door easily removable, close a door automatically when it reaches a minimum opening angle, hold it open at a particular angle, or prevent unauthorized access. Selecting the correct hinge for the job can be a challenge so here are some basic guidelines.
Hinges for industrial enclosures, for example, come in a range of opening angles. Side-by-side enclosures in a row require hinges with an opening arc of 120° to prevent the doors of one enclosure from striking and damaging the one beside it. An opening angle of 180° makes sense when it is critical to keep aisles in front of enclosures free of obstructions. Hinges for free-standing enclosures should let doors open to 270°. This puts doors flush against the enclosure sides and out of harm's way.
Another hinge type stops at multiple angles less than the maximum opening angle. An enclosure containing switchgear is one application for such a hinge. A 90° door opening is wide enough for normal operations, but for big jobs, doors open 180°, leaving a clear path in front of the enclosure.
So-called detent hinges pull doors closed when the opening angle falls within a defined minimum. The design works especially well for enclosures facing emergency exit routes. For example, a detent-type hinge can automatically close a door when the angle falls below 85° and assume an angle of -5° when the door is fully closed. This acts as a catch to prevent the door from being opened unintentionally, from say strong drafts, or jarring of the enclosure. Detent hinges also offset the effects of enclosure door gaskets taking a set over time.
In most industrial applications, ease of operation is a key goal of hinge design. Hinges should allow one person to easily install or remove a door and have few loose components. However, security concerns may override ergonomics in some cases. Latches and locking mechanisms typically secure most cabinets, though hinge design also plays an important role. For maximum security, hinges should be either weld-on, concealed, or fastened with screws that are inaccessible from the outside of the enclosure. Obviously, strength of the hinge material is also important.
How a hinge mounts is another design consideration. Screw-mounted 2D hinges, for example, adjust in two planes. Oblong slots in the hinge leaves let the hinge shift slightly both vertically and horizontally. Screws are secured in the oblong holes with an adjustment bushing. Ribbing on the bushing back and in the oblong slots prevents unintentional shifting once the screws are tightened. These hinges let doors open 270°.
A 120° inside-mounted hinge has no loose parts and works when doors must be easily removed and installed. It contains a frame part with an integral pin that screws to the enclosure frame. The mating component welds (or attaches with threaded fasteners or rivets) to the door, but lets the door rotate around its center point. A locking cam rotates 90°, securing the pin on the frame when the hinge is assembled. To remove the door, rotate the cam 90° to its vertical position, clearing the pin on the frame component. Then lift the door off. To re-hang the door, reverse the operation by joining the door and frame and turning the locking cam to its horizontal position to engage the pin.
Other hinges mount through cut-outs in enclosure doors. The frame part fastens with screws to the enclosure frame. The door has an "incomplete" cut-out with material left on the door edge to boost strength of the door near the door bend. The door component of the hinge seats in this cut-out and secures to the frame component with a pin that is inserted when the door is hung. This pin functions as the hinge pin.
Surface-mounted hinges attach with screws from inside of both the door and frame. Screws are not accessible from outside the enclosure which prevents tampering. Such hinges are especially suitable for cabinets with narrow frames because they require a mounting surface roughly 17.5-mm wide. Surface-mounted hinges have four basic components to handle multiple applications. All combinations of components permit a 180° opening angle. A frame part with the foot and hinge pin both in line can combine with an in-line door part for both right and left-hand doors. This setup also works for overlapping doors. Left and right-hand, L-shaped door parts work with the frame-mounted part or another L-shaped frame part. These are intended for flush doors but can be used for surface-mounted doors with a wide bend at the edge.
Hinge selection criteria
- Position of the door (left hand, right hand)
- Type of door -- surface mounted or flush
- Door opening angle -- 90, 120, 180, or 270°; with or without adjacent doors
- Lift-off capability
- Concealed or visible
- Enclosure material
- Environment -- moisture, vapors, corrosives
- Required security of the enclosure (such as Bellcore spec)
- Enclosure safety class (such as NEMA/IP rating, etc.)
- Hinge forces
- Door size and swept area
- Mounting -- screws, welded, clipped on
- Grounding features