Latches

View A Video on Latches- A Quick Introduction

Latches are mechanical devices used in the closing and fastening of doors, windows, cabinets and other types of items which can be open or closed. Latches are particularly efficient in applications which call for the controlled operation of closing and releasing two adjacent surfaces. They are fabricated for a variety of specific functions and common types of latches include door latches, cabinet latches, gate latches and paddle latches. The functioning requirements of a latch will be dependent on the specifics of its intended use in terms of applied force, intensity of operation and potential exposure to environmental elements and weather. These factors should all be taken into consideration when determining the best materials for and design type of industrial latches. Stainless steel latches offer high strength and corrosion resistance and are useful in any applications exposed to elements of moisture and high frequency use. Plastic latches are typically made from high strength thermoplastics and are light weight latching options which can easily be fabricated for custom design and fit. Other types of latches include compression latches, draw latches, bolt latches, spring latches and slam latches. The wide range of contexts in which latches are used necessitates a great variety of different industrial latch types and capabilities.

Most latches consist of plates or brackets which are placed at corresponding points on two adjacent surfaces. A pin or post is attached to one bracket and the other bracket holds a notch, groove, or seal for the pin to be fed into. Once the pin is joining the brackets of the latch, the door, cabinet, gate or lid cannot be opened. The simplest types of latches are bolt latches or spring latches. Bolt latches can be single bolt, double bolt and are typically used on doors and gates. Spring latches incorporate an angled bolt edge that engages the spring when the door is closed to secure it. In order to disengage the latch, a handle is turned which then retracts the spring, allowing the door to be opened. Draw latches, also known as tension or toggle latches, are designed to pull surfaces together and secure them. Consisting of two plates and a joining strap or pin, this type of latch is versatile and can be used in a variety of household and office products such as suitcases and briefcases, trunks, tool and jewelry boxes. They can also be used in corners and hinges. Compression latches are similar to draw latches which form a tight connection, and in addition are often used in applications requiring a seal along the two edges of the adjacent components. Paddle latches utilize a specific flip-out latch handle mechanism that allows the operator to close the latch tightly and open it when required. Industrial latches are typically large and durable, making them well suited to transportation uses which include latches for the aerospace and automobile industries, as well as for recreational vehicles, railway, marine and off-highway uses.

Material choice is an important consideration for latch type. Metal is a high strength material that can withstand repeated use and is resistant to impact. Many latches are required to be heavy duty as they receiver tremendous wear due to high frequency and high stress use and so are constructed from different types of metals. Stainless steel, steel, aluminum alloy, cast iron and brass are all commonly used to make durable and long lasting latches. Using thermoplastics in the formation of latches offers the added benefits of flexibility and increased shock and impact resistance as plastic materials absorb vibrations better than metals. In addition, both the use and spatial availability of the mounting surface must be considered when selecting a latch type and there are a number of different mounting options available for latches. This choice is also based on the function and performance requirements of the latch itself. Concealed mounting refers to the setup in which the latches and corresponding mounting hardware are hidden behind the panel. Edge mounting installs the latch components along the edge of the mating panels. When the latches are mounted directly on the front of the panel, this is called face mounting. Side mounting is when both the latch and the keeper are mounted on the back of the connecting panels and cannot be viewed from the cabinet or door front. Lastly, single-hole mounting involves mounting the latches in a single hole on the panel face. Latching position is also important. Primary latching position means that the door is securely held in a closed position, while secondary latching position refers to a latch that holds the door in a position that is not fully closed.

The different types of latches are widely used in almost every industry and especially in applications for transportation, home and building related fields. Important considerations when choosing latches for a specific use include the number of latches required, the material choice based on intended use and intensity of performance (plastic, rubber, stainless steel or other metals). The mounting surface composition of the latch mechanism also needs to be considered in terms of compatibility. This applies to applications using compression latches, spring latches, draw latches or slam latches. Some surfaces are more suitable to heavy duty latches than others and it is important that the latch mechanism is not too cumbersome or heavy for the mounting surface to handle. The majority of latches are manufactured using die casting, stamping or forging metals with additional components being assembled or spot-welded as needed.

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Latches Types

• Bolt latches, also known as crossbars, use a bolt to physically prevent two surfaces from parting.
• Bored latches are latches with components that are used for installation in bored holes on a door.
  
• Cabinet latches secure cabinet doors to their frame or adjacent doors.
  
• Catches are mechanisms used to hold doors closed.
• Compression latches are a self-adjusting type of latch.
  
• Cylindrical latches are bored latches that have a cylindrical case into which another latch bolt case may fit.
  
• Door latches are mechanisms that hold doors shut.
• Draw latches are designed to draw together and hold two panels.
  
• Flexible latches are made from rubber or another elastomer, and are used in situations when vibration isolation or panel misalignment problems occur.
  
• Floating strike latches are rotary latches that have a vertical clearance pawl.
  
• Flush latches have little or no protrusion from the mounting panel.
• Gate Latches fasten and secure adjacent segments of fencing that ordinarily function as an entrance or exit.
  
• Industrial latches often require a large and particularly sturdy design.
  
• Integral latches have a cylinder in the knob.
  
• Mortise latches are not applied to a door's surface, but rather installed in a mortise.
  
• Narrow case latches are rim latches that are very narrow, generally less than 75mm.
  
• Nightlatches are either mortise or rim latches with a ‘snib' to hold the latch back if needed. Typically, these latches are not very secure.
  
• Overcenter latches are secured with a member traveling beyond the center.
  
• Paddle latches have flat, flip-out handles used for actuation.
  
• Pin-type latches have a cylindrical pin that is used to strike.
  
• Plastic latches may offer some flexibility in a latch, but can also be manufactured as strong, rigid fasteners.
  
• Rim latches are old-fashioned latches that are mounted on the inside of a door instead of inserted into the door edge.
  
• Roller latches use a roller latch head under spring tension to reduce friction. This engages a strike and forms a recess to receive the roller.
  
• Rotary latches have one or more rotating members that are used to secure the door.
  
• Slam latches are activated by the slamming of a door.
• Sliding latches use actuation to push or slam the door closed.
  
• Spring latches make use of a spring for the latching operation.
  
• Stainless steel latches offer a very durable option for mechanical fasteners.
  
• Thumb latches, like rim latches, are another old-fashioned type of latch.
  
• Tube latches have a tubular body, which is inserted into a drilled hole in the door edge.

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Latches Terms

Actuation - The movement of the handle or latch portion, which is what causes the latch/unlatch function.

Alike Change - Multiple latches or locks that are able to use the same key.

Anti-Friction Latch Bolt - A latch bolt that is specifically designed to reduce friction.

Architectural Hardware - Hardware used in construction on movable components, such as doors, windows and cabinets.

Axle - A component that provides the bearing surface of the rotating rotor and latch mounting on a rotary latch.

Back Plate - The protective plate on the door onto which the moving parts of the latch are attached.

Bevel - A term that indicates the direction the latch bolt is inclined.

Cam - A tongue on the end of the plug of a latch.

Case - The part of the latch that contains the mechanism.

Catch - The part of the latch that allows for pawl retention.

Clamping Force - The force that is exerted from a latch, in order to draw two panels together.

Coaxial Mount - Allows for maximum strength of rotary latches by combining the standard mount with a second pivot on the bottom of the back plate.

Deadlocking Latch Bolt - A latch bolt with a plunger that is used to prevent the bolt from retraction by end pressure when the door is closed.

Direct Release Actuation - Unlatching by moving the handle or latch directly at the mechanism.

Dogging Device - A device used to fasten the cross bar in the depressed position to keep the latch bolt in the retracted position. This allows for free operation of the door on both sides.

Drop Ring - A ring handle that is attached to a spindle and is used to operate a latch. When not in use, the ring stays in the dropped position.

Four-Point Actuation - Unlocking by moving the handle or latch portion at multiple points.

Front - The area through which the latch bolt projects.

Hinged/Swinging Latch Bolt - A latch bolt that is hinged to the front and retracted by a swinging action.

Hook - A component that allows for a slam action function on a latch.

Latch Bolt - A spring bolt with a beveled edge that may be operated by a handle, knob or turn.

Lip - The projecting piece that the latch bolt strikes when the door is shut.

Mortise - The door cavity that receives the mortise latch.

Plate - The body of the latch, which provides the structural strength.

Plunger - A sliding component of a latch that provides retention for a strike.

Roller Strike - A strike with a rolling member that reduces friction at the point of the latch bolt contact.

Snib - A small switch on a nightlatch, which prevents the latch from being operated when closed.

Springbolt - A bolt that can be pushed back into the lock case and is able to return to the original position without assistance.

Stop - The button that locks or unlocks the latch bolt against the outside knob.

Strike - A metal plate used for protection, which is placed in the doorjamb and receives the latch when the door is closed. This is usually "t"-shaped and has a single hole.

Template Hardware - Hardware that is made exactly to template, precisely matching the spacing of holes and dimensions.

Throw - The maximum projection at which a bolt is fully extended.

Transom Catch - A fastener that is applied to the transom, and has a ring that is used to retract the latch bolt.

Universal - A latch or other piece of hardware that can be used on any door.

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