This article contains everything you need to know about latches.
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Latches are mechanical components that allow the temporary joining of moving parts relative to each other. They are actuated to release the coupling and allow the two parts to separate. They are mostly seen on doors and enclosures. They are used in devices such as seat belts, clamps, straps, and objects with retractable parts. Different designs feature different methods of actuation, holding style, and mounting.
Door latches are a general type of latch used for keeping doors and gates closed. They can be in the form of a sliding bolt that prevents the door from swinging open or a hook for maintaining a closed position for both sliding and swinging motions.
An example of a typical door latch is a doorknob. This type is commonly used for architectural purposes. It is composed of a latching mechanism, a locking mechanism, and two knobs on the interior and exterior sides. The latch is a spring and bolt-type mechanism activated by turning the knob on either side of the door. They are designed to be quarter-turn mechanisms and are fully activated when rotated by 90°.
Other designs use levers instead of knobs for aesthetics and convenience. Using levers improves appearance as levers meld well in some architectural designs. The grip is also better with levers. For doors used as emergency exits, latches called panic bars are used. Panic bars (also known as crash or push bars) are opened by pushing a large bar fitted to the door handle. They are designed to be opened quickly and effortlessly. They aim to prevent people from getting trapped due to panic during emergencies.
All doorknobs also have a locking mechanism that prevents one side from releasing the latch. Modern door knobs are made with electrical and electronic parts that feature sophisticated lock systems and electrically actuated latch release.
Door latches can also be categorized as deadbolts, deadlatches, and deadlocks. Their mechanisms differ in how the latch is locked and unlocked. Their construction and characteristics are explained below.
The unique feature of the deadlatch is the smaller deadlatch bolt. The strike plate of a deadlatch is sized only to accommodate the main bolt and not the deadlatch bolt. Thus, when the door is closed, the deadlatch bolt is retracted. A retracted deadlatch bolt has a mechanism that prevents the main bolt from being pushed or retracted.
Other types of door latches are simple sliding bolts and hooks. They are used on doors that do not get much traffic. They can be made stronger than door knobs since their bolts and latching mechanisms can be thicker and more robust. These door latches are usually accessible only on one side of the door.
A simple latch comprises a base, a bolt, and a box or hole. The base which contains the bolt is typically installed on the door. The box, on the other hand, is installed on the frame. Sliding or moving the bolt into the box activates the latch (such that one end of the bolt holds the door while the other holds the frame).
This basic design is further modified, which brought forth different types of latches. The most distinct types are discussed below.
Bolt latches or latch bolts are simple latching mechanisms that consist of a bolt, a handle, a backplate, a set of barrels, and a box called a striker. The barrels hold the bolt in place and provide locking for the latch. They are formed into a non-continuous loop which allows the handle to pass through. A bolt latch can be locked or unlocked by sliding the bolt into the socket.
The most common type of latch bolt is a barrel bolt. They are used for closing gates, doors, and windows.
A spring latch is similar to a bolt latch but is equipped with a spring for automatic bolt extension. Some designs use the spring to keep the bolt retracted.
Spring latches can have different constructions. A simple spring latch has an L-shaped bolt called a plunger with a small hole for inserting a clip or pin. Its backplate is formed with two-holed lips for holding the plunger. To keep the plunger in an extended position, a spring is fitted between the lip and pin.
The design of a spring latch is also seen on deadlatches and slam latches. Deadlatch and slam latches have unique features that differ from standard spring latches.
Slam latches are also known as push-to-close latches. They are used for doors that require automatic latching when closed. Their design uses cams instead of bolts for latching onto the striker or door frame. They have a rounded or chamfered edge to allow retraction upon impact onto the striker. A spring-loaded mechanism is used to keep the cam raised. When actuated, the cam moves either by turning or sliding.
A slam latch is more robust in construction when compared to an ordinary spring latch. As a result, they can resist more opening and closing cycles without developing damage to their parts. Slam latches are mostly used in high-traffic doors seen in commercial and industrial areas. Emergency exits also feature a slam latch that can easily be released by pushing the handle.
Other types of push-to-close/slam latches include:
Swinging latches, or swinging door latches, are similar to slam latches. They are push-to-close latches that automatically activate when the door is shut. They feature a spring-loaded mechanism that keeps the bolt an extended position. The edge of the bolt that impacts the striker is rounded to allow retraction.
Cam latches are commonly used in furniture such as drawers and cabinets. These latches work by turning a knob or key, which also rotates an arm fitted on the other side of the door. Like other knob-activated latches, they are quarter-turn devices. Their assembly does not include a strike plate, box, or hole installed on the frame for receiving the arm. They lock the door or enclosure by barring only one side. Thus, they are not suitable for doors that swing or move past the frame.
Other types of cam latches include:
Aside from hinges, handles, and guide rails, furniture such as cabinets and drawers always has a latch installed. Cabinet latches can be of various forms. The most popular are bolt, spring, cam, and slam latches.
Cabinet latches are usually made from stainless steel, brass, copper, and dyed anodized aluminum. These materials give better aesthetic quality while being durable and resistant to corrosion.
Different metalworking processes such as casting, cutting, and forging are done to produce cabinet latches. As a decorative product, cabinet latch dies and molds are prepared with patterns and shapes much more complex than standard latches.
As the name suggests, gate latches are used for securing gates and large doors. They are made much stronger and thicker than cabinet latches. One thing in common with cabinet latches is that they can also be made with architectural design features.
Common gate latch forms are barrel bolts, bars, and heavy-duty industrial latches. In some instances, slam and spring latches are also used. They are made with thicker gauge sheets or plate metal and are formed by larger compression forces.
Gate latches are usually made with galvanized steel and stainless steel, particularly grade 304. These materials are suitable for the high strength and corrosion resistance required by their application. Gate latches are seen in every industry, whether industrial, commercial, or residential.
This type of latch is similar to a cam latch. It has a simple design wherein the latch is activated when the knob is turned 90°. It uses an arm or a cam that turns when the knob is rotated.
Some turn latches feature a keyed knob design for additional security. Other designs incorporate additional actions for actuation, such as pushing or pulling. These actions are done before turning the knob to release the latch. These double-action devices add a layer of safeguard to prevent accidental releasing of the latch.
A compression latch is a cam latch with a modified arm and is used to provide compression between the door and frame when closed. Compression is created by pushing the door and activating the latch or by turning the latch multiple times using a screw action. In contrast to ordinary cam latches, compression latches have arms that are made in a way that allows for a slight deflection when mated against the frame of an enclosure. The arm of a compression latch is thicker than the ones found on ordinary cam latches.
Compression latches are used on electronic and control equipment enclosures and have gaskets or rubber trim installed along the door or frame, which are squeezed by the compression of the latch. The amount of compression provides a tight seal that protects against the incursion of dust and moisture. Compression latches are used to prevent unapproved access and have a cam that inhibits vibrations that produce noise and fatigue on door hinges.
Other types of compression latches include:
A magnetic door catch consists of a catch body fitted with a permanent magnet and a ferromagnetic strike plate. They are used to provide automatic and convenient latching of furniture doors. Other designs employ two magnets, each fitted on the door and frame. These types are used for light-duty and low-traffic doors.
The magnetic catch has a hollow body typically made of non-ferromagnetic metal or plastic. Inside the non-magnetic body is a bar magnet. Attached on the bottom and top sides of the bar magnet are steel plates used to concentrate the magnetic flux. These steel plates contact the striker plate.
The magnetic catch is mounted on the door jamb or frame while the strike plate is placed on the door edge. They can be surface mounted or concealed. They are installed so there is physical contact between the magnet and the metal strike plate when the door is closed. This is needed to maintain a strong magnetic attraction.
A draw latch, also known as a toggle latch, is characterized by having a component under consistent tension. They are suitable in applications that require strong closing forces to maintain seals against leaks and ingress of dust and water. They are also designed to prevent accidental release of the latch. Examples of applications that use draw latches are electronic enclosures and equipment control panels.
A common design is composed of two hooks. One hook is called a receiver, striker, or catch. It is made from a formed metal plate or sheet metal. The other hook is called a blade or claw. It is also made from sheet metal formed into a hook. Other designs are made from a wire or rod bent to form a loop.
Latching is made when both hooks (or when the hook and the loop) clasp each other under tension. One hook is attached to a lever through a pin. Tension is created or released when the lever is pushed or pulled. The lever is carefully designed to produce a mechanical advantage so that sufficient tension can be created while requiring minimal force for releasing the latch.
Subtypes of draw latches include:
Over center latches are types of draw latches described by having minimal actuation force while providing strong closing forces. The lever is carefully designed to produce a mechanical advantage so that sufficient tension can be created while requiring minimal force to release the latch.
The over centre latch derived its name from its characteristic over center lock point. When the lever is moved past its over center position, the latch becomes activated. At this point, the closing force is provided by the hooks.
Cane bolt latches have a simple structure with a single L-shaped spring-loaded bolt that is attached to a bracket by two knuckles. When the spring-loaded bolt is turned and forced forward, it engages with the keeper, a process that can be reversed to disengage the latch. Cane bolt latches are made of steel with finishes that make them resistant to corrosion. They come in left and right orientations with holes for attaching to wood and other surfaces and without holes to be welded to a door.
A pawl latch has a movable rotating cam that can be turned to the latched and unlatched positions. A quarter-turn of the pawl engages the latch with a keeper or the door frame, while a reverse quarter turn disengages the latch. The pawl holds the latch in the latched or unlatched position.
Electronic enclosures, HVAC enclosures, buses, trailers, RVs, and boats have pawl latches mounted on a metal surface.
Multi-point latches have a handle with two long bars that extend from the handle. When the handle is turned, the bars extend to engage the keepers or in a reverse motion to disengage. Multi-point latches, also known as three-point latches, are used in doors and metal cabinets and are ideal for securing tall cabinets with long doors.
The handle for multi-point latches has a rotating mechanism that turns to place the tips of the bars into the upper and lower keepers. It extends them sufficientlyto connect to the frame or edge of a cabinet. The movement of the handle locks all points of a door in a singular smooth motion.
The term quarter-turn latch is a general descriptor for several different types of latches that engage by a quarter-turn of a cam. As may be expected, the wide variety of quarter-turn latches has several kinds of tools, keys, and methods for inserting into the latch to close or open it.
Quarter turn latches are a very secure type of latch designed to prevent tampering and access to enclosures. They are made from zinc, steel, stainless steel, and plastic, with coatings of chrome or baked-on black powder. Quarter-turn latches come in different sizes with different styles of cams. Accessories include various styles of keys, padlock cups, finger pulls, and dust covers.
A trigger latch is a unique type of latch mounted flush to a door or enclosure. They are compression-type latches with a locking mechanism below the trigger. When the latch is unlocked, the trigger of the latch is pushed, and the pawl drops down to release the door.
After being pushed, the lever of the trigger moves upward to take a position as a handle to open the door. Trigger latches are made with or without locks and can have raised trigger buttons for easier opening.
Twist latches, also known as butterfly latches, have a rotating cam attached to a straight piece, referred to as a slide, with a curved end that is rotated by the cam. The keeper for the latch is a flat piece of metal similar to the slide with a curved side that allows the slide and bracket to connect. When they engage, the slide moves over the bracket on the cabinet, cupboard, case, or door and is pulled tight by the rotation of the cam.
There are several different styles of twist latches as well as different methods for mounting them. They are used on closures, cases, containers, shipping containers, and instrument containers. Twist latches can have slides of different lengths and springs.
A rotary latch is composed of a latching mechanism, an actuator, and a cable. A bolt is usually installed on the opposite part that mates with the latching mechanism. When activated, the cams or rotors of a rotary latch turn or rotate. It has a spring-loaded mechanism that enables a push-to-close function, similar to that of a slam latch.
A unique feature of a rotary latch is its remote actuation. A cable connects the actuator and the latching mechanism. This allows the actuator to be located at a distance from the rotary latch. Pulling the actuator causes the rotors to rotate, which releases the latch. The actuator only pulls in one direction. Thus, a spring-loaded mechanism is required to return the rotor to its position.
Rotary latches can have single or double rotors. A single rotor rotary latch provides the basic function of keeping a door or panel closed. On the other hand, double rotor rotary latches have two mirrored single rotors placed adjacent to each other. Intuitively, an advantage of a double rotor type is better rigidity attributed to the two rotors holding the bolt. Another advantage is their better tolerance to misalignment. Double rotor types have wider catch openings than single rotor types.
Another classification of rotary latches is the number of latching stages. They can either be single or two-stage. Again, a single-stage rotary latch only has the basic latching function. However, in a two-stage rotary latch, there are two latching positions. One is a secondary, partially closed (false close) position, while the other is a primary, fully closed latch. A two-stage rotor must always be fully closed. But if the primary stage fails, the secondary stage prevents the door from suddenly opening. This type of rotary latch is frequently seen in cars and other vehicles.
A hasp is a simple latch that consists of a strap and a staple. The strap is a metal plate punched on one end with a slot that fits over the staple. Its other end has a hinge used to attach the strap to the door or door frame that allows it to swing. The other part, called a staple, is a loop made of a bent metal rod or formed plate.
A pin is inserted through the loop of the staple to secure the strap. Padlocks are commonly used instead of pins for better security. Other types of hasps, called hasp locks, use built-in locks in place of a staple. Latching is achieved when the lock is rotated, which secures the strap in place.
This is one of the earliest forms of latches. A hook and eye latch are commonly made from bent wires and rods. They can also be made from cast metals. Through casting, they are formed into intricate shapes intended to be used as decorations. The hook becomes the arm of the latch attached to the door. The eye functions like a catch that receives the hook when the latch is closed.
A bar is another form of primitive latch. They are made from wooden or metal beams much larger than bolts. Because of their ruggedness, they are used to hold gates and large doors. They are built to withstand high bending forces to prevent forcing the door open. The bar is held by a set of cleats or hooks that are equally strong. A door is closed by sliding the bar into the hole or lifting and manually placing the bar onto the cleats.
Cam locks are cam latches combined with a key instead of an ordinary knob. Their main feature is the added security provided by the lock. The base of the cam is a cylinder fitted into a hole on the door or cabinet. On the lateral side of the base, external threads are cut. A nut mates with these threads for holding the cam lock firmly on the door.
A cam lock can only be actuated with the correct key for turning the cam. Cam locks are available with different forms of locks and keys. The lock assembly can be generally classified as mechanical or electronic.
Another type of lock used in cam locks is a tubular lock. Instead of being positioned radially towards the plug's axis, the tubular lock's pins are arranged circularly. These pins also have varying lengths that match the profile of the key. A tubular lock key is cylindrical and has half-cylinder notches to align the pins.
Other cam locks feature a lock that a common or universal key can release. These types of cam locks are usually seen in utility cabinets and control boxes in which more than one person is permitted to access. Also, using these types allows multiple cabinets to be accessed with just one key. These keys have standard shapes and profiles. Examples of key profiles are square, triangle, and double-bit keys.
Electronic cam locks offer better features than mechanical types. First is convenience since it is easier to input a code or perform a fingerprint scan than using a physical key. Another advantage is being programmable. The key can easily be changed without changing the lock. Other features of electronic cam locks are remote control, events history, and blacklist functions.
Latches can have different design features, which makes them more suitable for a particular application. They can be made with different materials, finishes, thicknesses, and other features. Summarized below are some of the general features and specifications of latches.
Polishing and buffingare done to create a smooth surface and bright finish. Polished latches are free from burrs and other microscopic defects. Polishing can be done mechanically or through an electrochemical process called electropolishing.
Powder coating and painting add a layer of polymer material to the surface of the part. These processes add corrosion resistance to the metal latch, similar to metal plating. Moreover, coatings can have different colors to improve the product's appearance.
A gate latch is a locking mechanism that is used to secure gates on fences or stakes on truck beds using a metal bar and lever that is raised to open the latch and lowered to close it. Although they do not have...
A magnetic door latch is a type of latch that consists of a striking pad and a magnet and is used to keep doors and gates closed. Magnetic door latches are also known as magnetic door stops, magnetic door catches, and door magnets...
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