Latches are ideal for securing machine and equipment parts that must be opened or removed frequently. Many can be easily modified to suit special requirements, thereby eliminating the need for custom designs.
Many parts on industrial and business machines, agricultural and construction equipment, aircraft, and road vehicles must be opened or removed frequently to allow periodic servicing. Examples include hinged panels, doors drawers, windows, and safety guards. All of these components can be secured with latches.
Latches allow quick access because the holding or locking element - a hook, pawl, or bolt releases immediately when a handle knob, or tool socket is actuated. Typically, the holding component spans the joint between a panel or door and the supporting frame. The latch base mounts either on the part to be opened/removed or the supporting frame. To lock a latch, a hook, pawl, or bolt must be engaged with a strike, hole, protruding lip, or directly with the mating joint member.
Most latches are available in adjustable versions to accommodate a range of panel and frame thick-nesses, so manufacturing tolerances usually are not critical. Such latches usually have a self-compensating drawhook made of spring steel, as lotted mounting base, or a threaded element to facilitate manual adjustment. Some adjustable latches can be set to accommodate gaskets in joints. Latches can be attached mechanically with rivets or screws, or they can be welded in place. Latches are usually made of steel, finished with a zinc-chromate coating. Other finishes include chrome, black epoxy or polyurethane paint, and black oxide.Another common latch material is stainless steel. Also, aluminum is sometimes used for latch bases where galvanic corrosion may be a problem.
Actuators on hand-operated latches include knobs, levers, or push buttons; tool-operated latches use a number of different fittings. Such tool-operated latches are opened with screwdrivers or hex wrenches.
A seemingly endless variety of latches is available. The reason for so many different components is that latch suppliers routinely modify standard fasteners to suit special requirements. For instance, a certain overcenter tension latch is available in more than 200 variations. Some of the modifications or options are a secondary lock or hasp, extended drawhook, reversed hook, right-angle mounting base, base with raised pivot, and even special finishes or materials.
Standard latches can be sorted into four general categories:
- Handle-operated latches
- Rotary-actuated latches
- Slide latches
- Panel latches
Latching requirements should be considered at the onset of new product development so that standard fasteners can be selected if possible. If little thought is given to latching until the product design is well underway, the only solution then extensively modify standard latches or design entirely new latches, both of which increase costs.
Today's design standards call for an aesthetically pleasing appearance on the outside of machines and equipment. Consequently, latches often must have flush, unobtrusive actuators.
Human engineering also plays an important role in latch selection. Thus, consideration should be given to who must operate the latch, for what purpose, under what circumstances, and how often. For example, if a door on a piece of heavy construction machinery must be opened often by an operator wearing gloves, a large knob or lever is needed. On the other hand, if an access panel on a computer peripheral need be removed only by a service technician, then an inconspicuous tool-operated latch is appropriate.
Electronic equipment poses special requirements for latches. For instance, latches not only must secure access panels and doors,but also may have to provide sufficient clamping force to com-press RFI/EMI metalized gaskets. These gaskets prevent radiofrequency or electromagnetic interference from entering or being emitted by equipment. In addition, panels on certain electronic equipment must mount flush with outer surfaces, slam closed, and allow only limited access. Such requirements usually can be met conveniently by specifying pull-release and trigger-release panel latches, which are available off the shelf.