This article will take an in-depth look at magnetic door latches.
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This chapter will explore magnetic door latches, explaining their function and operation.
A magnetic door latch is a device comprising a striking pad and a magnet, designed to secure doors and gates in a closed position. Often referred to as magnetic door stops, magnetic door catches, or door magnets, these latches are commonly used for cabinets and lightweight doors.
A magnetic door latch consists of a magnetized catch body and a ferromagnetic strike plate. It is designed to automatically and conveniently latch furniture doors. Some variations feature two magnets—one mounted on the door and the other on the frame—suitable for low-traffic and light-duty applications.
The hollow body of the magnetic door latch is typically made of non-ferromagnetic metal or plastic. A bar magnet is housed within the non-magnetic body. Steel plates are attached to the bottom and top sides of the bar magnet to concentrate the magnetic flux. The steel plates come into contact with the striker plate. The magnetic door latch is attached to the door jamb or frame, and the strike plate is attached to the door edge. These latches can be surface-mounted or concealed. When the door is closed, they make physical contact between the magnet and the metal strike plate. This process is required to keep a strong magnetic attraction.
Most magnetic catches consist of an armature plate and a magnet. The magnet is fixed to one side of an object, while the armature plate is attached to the opposite side. When installed, the magnetic force holds the two components together. To separate them, you simply pull them apart, breaking the magnetic connection.
Electromagnetic locks represent another form of magnetic latch. These locks operate electrically and are often integrated with an access-control system. They receive signals from devices like motion sensors, exit request switches, or credential readers. Frequently, they are used with exit devices that include built-in signal switches to control the magnetic locks.
Magnetic latches are designed to be fail-safe, meaning that if the power is cut, the latch will remain unlocked. Consequently, continuous power is necessary for the latch to stay locked. These latches can operate on either AC (alternating current) or DC (direct current) power. Once engaged, many magnetic locks can exert hundreds of pounds of holding force. Depending on the location, a higher holding force may be required. Magnetic locks can be used with fire-rated openings if they are connected to a fire alarm system and programmed to release when the alarm is triggered, ensuring that occupants can exit even if the power goes out.
Magnetic locks with holding forces between 500 and 1,000 lbs. are suitable for interior wood and aluminum doors that need lower security. For higher security needs, locks with holding forces ranging from 1,000 to 3,000 lbs. are recommended for heavier gauge, hollow metal doors and frames.
Magnetic locks come in various shapes and sizes, such as round, square, and rectangular, with larger sizes providing greater holding force. They can operate on either AC or DC power, depending on the application, and their efficiency varies with power consumption. Some models include battery backup systems to maintain locking capability during power outages.
An electromagnetic lock works on the principle of using electromagnetism to lock a door when it is energized. To achieve optimal operation, the holding force should be collinear with the load, and the lock and armature plate should be face-to-face. The magnetic lock is based on some fundamental electromagnetism concepts. It consists essentially of an electromagnet attracting a conductor with a force strong enough to prevent the door from being opened. A closer look reveals that these devices make use of the fact that a current flowing through one or more loops of wire (known as a solenoid) generates a magnetic field.
This principle functions in free space, but its effectiveness is significantly enhanced when the solenoid is wrapped around a ferromagnetic core, such as soft iron. This is because the core material's internal magnetic domains align, which greatly increases the magnetic flux density.
This chapter will cover the design of magnetic door latches, their installation, and the materials used. Additionally, it will address various factors to consider when selecting magnetic door latches.
A magnetic door latch consists of a metal plate, typically steel, and a mounted magnet. Although not necessary, most magnets for this application are encased in plastic and feature flanges with holes on three sides to attach the magnetic material to either the door or the door frame.
These magnets are strong enough to keep the door closed but can be easily disengaged with an external force. For instance, after emptying a cupboard or cabinet, the door can be swung shut, and the magnet will return to its original position. This simple mechanism is effective and ensures the door remains securely in place.
Latches can feature various design attributes to enhance their suitability for specific applications. They come in different materials, finishes, thicknesses, and other specifications. Below is a summary of some general characteristics and specifications of latches.
Material: Latches are commonly made from metals like carbon steel, alloy steel, stainless steel, aluminum alloys, and copper alloys. Metals are preferred for their formability, machinability, and strength. Secondary processes, such as finishing and coating, can further enhance their appearance. Plastics and rubbers are often used as trims or wraps to absorb shock or reduce vibration.
Finishing and Coating: Finishing and coating are secondary processes that enhance the surface quality of latches and similar products. Common techniques include plating, powder coating, and painting. Plating applies a thin layer of metals like zinc, silver, or chromium through electrochemical deposition. Powder coating involves applying a protective layer of coating material using a spray gun. These processes aim to improve corrosion resistance and make latches suitable for outdoor applications.
Polishing and Buffing: These processes are used to achieve a smooth surface and a bright finish by removing burrs and microscopic imperfections from latches. Polishing can be performed mechanically or electrochemically, such as through electropolishing.
Powder Coating and Painting: These processes apply a protective layer of polymer material to the surface of the part. Similar to metal plating, powder coating and painting enhance corrosion resistance while also allowing for color customization to improve the product's appearance.
Strength: Latch strength is classified into light, medium, or heavy-duty categories based on the thickness of the material used, typically metal, in the latch's components such as plates, barrels, and rotors. Different thicknesses are also present in cams and bolts. Latches are designed to withstand shearing effects and bending stresses effectively.
Mounting: Latches can be installed using various mounting types. In architectural applications, latches can be flush-mounted, mortised, or surface-mounted. Flush-mounted latches align with both the latch and door surfaces. Mortise latches are installed inside the door's cavity, with only the handle and keyhole visible. Surface-mounted latches are fixed directly to the door and frame, requiring no additional bores or holes.
Handedness: Some latches, including deadlatches and certain bolt, rotary, and slam latch designs, are available in left-handed or right-handed configurations. Many designs are adaptable with minor adjustments. If handedness options are not provided, it can be determined by inspecting the hinge position: left or right hinges indicate the corresponding handedness for the door and latch.
Magnetic locks can be used for both doors that swing inward and those that swing outward. To ensure proper alignment of the armature, various brackets such as L brackets, LZ brackets, and U brackets are employed. In cases where the electromagnet's size exceeds the available mounting space on the door frame, filler plates are used to expand the mounting area. Always mount the magnetic lock on the secure side of the door. Most installations involve surface mounting. For safety reasons, cables and wires for magnetic locks should be routed through the door frame or be installed flush with wire molding. Here is the procedure for installation.
For doors that swing inward, the electromagnet is generally mounted on the header of the door frame at the corner of the opening. When a magnetic lock features full-length housing, it can be installed vertically within the door frame. In this setup, the armature is bolted through the door and aligned to interact with the electromagnet's face. Proper locking force is achieved when the armature plate makes contact with the electromagnet.
In outward-swinging door configurations, the electromagnet is usually fixed on the side of the door header. The armature is attached to a Z-shaped bracket, positioning it to align with the electromagnet. Magnetic locks are frequently integrated into comprehensive electronic security systems, which can range from simple keycard readers to sophisticated setups linked to a central security monitoring system. Fire safety considerations are crucial irrespective of the locking mechanism in use.
Advancements in electromagnetic locks include variations such as the shear lock. Unlike traditional direct-pull magnetic latches, which operate in either in-swing or out-swing directions, the shear lock functions by shearing the load, much like a mechanical stop. This design allows the door to swing in both directions. The shear lock achieves its holding force through two pins that secure the armature onto the magnet, ensuring that the magnet remains firmly in place.
Regardless of their exact configuration, all door latches are made using both the metalworking process known as stamping, and the spot-welding process. Flat sheet metal is stamped or pressed into shapes during the stamping process. These shapes are later organized, assembled, and spot welded into full latches to complete the job. Manufacturers typically construct door latches with durable and sturdy materials to ensure that they can withstand the potential stress loads and heavy use that they may encounter. Included below are a few examples of such materials:
Aluminum: Aluminum is an excellent, lightweight material for door latches. Aluminum latches are long-lasting and rust-resistant. Aluminum is also one of the least expensive latch materials, so these latches are very affordable to consumers. However, because of its lightweight, this metal is more brittle than other latch materials.
Brass: Brass is often chosen by homeowners for its elegant appearance and ability to enhance design aesthetics. However, it is not commonly used for door latches and can be challenging to find depending on the location. Additionally, brass latches require regular polishing to maintain their visual appeal and ensure proper functioning.
Bronze: Latches made from bronze are generally more costly compared to other materials. Despite the higher price, bronze latches offer a versatile look that suits various interior designs. They are durable, resisting both chipping and rust. To maintain their condition and prevent patina, bronze latches should be waxed annually.
Chrome: Chrome is a popular choice for latches due to its shiny, reflective finish. However, it is generally less durable compared to stainless steel. Chrome latches tend to be more susceptible to chipping and scratching over time, making them less resilient than some other materials used for latches.
Iron: Iron latches are characterized by their black powder-coated finish, which shields the metal from environmental damage and complements various design aesthetics. Despite this protective layer, iron latches are prone to rust. However, in environments where rust is not a significant issue, these latches can be quite durable. To maintain their appearance, regular maintenance is necessary. It is advisable to use steel wool to scrub away any rust before applying a protective spray. Additionally, the coating can be refreshed with spray paint if needed.
Stainless Steel: Stainless steel has a similar appearance to aluminum. Stainless steel, on the other hand, is known for its high durability and resistance to pressure. While powder-coated stainless-steel latches are available, the natural silver color of uncoated stainless steel provides a great modern look. Stainless steel is also already corrosion resistant on its own, making it an excellent material choice for those who are constantly plagued by rust. To keep the stainless-steel gate latch material in good condition, wash it with mild dish soap and warm water, then wipe it dry.
Plastics: For door latches requiring less robustness, high-strength thermoplastics can be employed. These plastic latches offer comparable performance to metal latches in lighter-duty scenarios, featuring advantages like superior impact resistance and flexibility.
When choosing magnetic catches, the material is a crucial factor. Typically, these catches feature a magnet encased in a protective covering, which is often made from plastic. Plastic magnetic catches are affordable, versatile, and durable. Alternatively, aluminum is a popular choice due to its lightweight and rust-resistant properties.
The shape of the magnetic catches is also important. While rectangular designs are most common, there are other shapes available, including cylindrical options known as barrel magnetic catches. These can accommodate multiple magnets. Ensure that the magnetic catches are the right size for the objects they will be used with, considering both material and shape.
For magnetic door catches, it's essential to assess their height, depth, and width. These dimensions should be compared with those of the items they will be paired with to confirm a proper fit. Additionally, there are other factors to consider when selecting magnetic latches, such as:
Both traditional and electric door latches offer distinct advantages and drawbacks. Traditional locking mechanisms, such as metal keys, key cards, or remote controls, are susceptible to being lost or damaged. In contrast, numerical key codes can be forgotten or potentially compromised if learned by unauthorized individuals. However, key codes offer the benefit of easy modification by the user, whereas altering physical locks and keys typically involves complex procedures and specialized tools. On the other hand, purely electronic locks may face issues during power outages, as they will remain either locked or unlocked until power is restored or batteries are replaced, unlike traditional door latches which are not affected by such power interruptions.
Many electronic door locks combine both physical and electronic control systems on the same door. For instance, you might use a physical key for initial setup or as an emergency backup, while primarily relying on a remote or keypad for everyday locking and unlocking. This dual approach enhances user convenience and adds an extra layer of security and functionality. Electronic locks are widely available for traditional swing doors, and electronic locks for sliding doors are also increasingly common.
Traditional key locks typically use a "pin and tumbler" mechanism. In this system, the lock cylinder is held in place by a series of metal pins, each consisting of an upper and lower segment. The key’s serrated edge aligns the pins to the correct height, allowing the cylinder to turn only when all pins are properly aligned to form a straight line between the upper and lower sections.
Electronic door locks feature "actuators" that connect the lock’s bolt or cylinder to a concealed motor within the door or its frame. The motor is controlled by an electrical impulse, which can be triggered through various methods, such as an electronic card reader, keypad, or wireless remote control. The lock is programmed to activate the motor-driven actuator only after receiving the correct electronic input.
Magnetic door latches come in various types, each tailored to different levels of complexity and application needs. It is important for engineers, technicians, and users to thoroughly assess the specific requirements and match them with the available latch designs. Fortunately, a wide range of latch types is available, offering solutions for diverse design and functional needs.
Surface-mounted magnetic door latches are among the most widely used magnetic locks. These latches can be installed on the header of a door frame for both single and double door openings or on the strike jamb for single doors. While they are ideally positioned on the push side of the door, they can also be installed on the pull side if necessary.
Surface-mounted magnetic locks come in different sizes and finishes to suit various needs. While these locks are primarily designed for indoor use, they can also be used for exterior openings. However, if installed outside, they will require more frequent maintenance due to exposure to the elements.
These magnetic locks, known as "shear locks," are hidden within both the door and the frame, as implied by their name. Unlike surface-mounted locks, shear locks operate with a pull force applied in a "shear" direction rather than directly. They can be installed within the door frame, inside the door itself, or even at the bottom of the door and on the floor.
Shear locks need a specific minimum distance between them, so it's important to carefully prepare the installation area, particularly if they are being mounted on the floor. These locks connect to hardware similar to that used for surface-mounted magnetic locks and are compatible with the same types of access control systems.
Fail-secure latches require power to unlock. During a power outage, these locks will remain engaged, preventing entry even for users with valid credentials. Fail-secure locks are essential in environments where constant security is crucial, such as server rooms, IT suites, secure storage areas for sensitive information or valuable equipment, and research laboratories.
While fail-secure magnetic locks provide robust security, it's important to ensure that authorized users can still gain access if needed. To accommodate this, the lock should be equipped with a backup power source, such as a battery. During a power outage, fail-secure locks will prevent unauthorized entry but allow users to exit from the inside to maintain safety.
Fail-safe locks rely on power to stay locked. During a power outage, these locks will unlock automatically, allowing access to anyone regardless of their credentials. Fail-safe locks are crucial in situations where safety takes precedence, such as in locations where users must be able to open doors under any conditions.
Consequently, fail-safe locks are well-suited for emergency exits and stairwell doors. In situations where stringent security is necessary, backup power sources can be added to ensure that unauthorized access is prevented even during power outages.
Magnetic touch latches operate with a magnet connected to a spring-loaded plunger that holds the door shut. When the door is pushed, the plunger springs open, releasing the door. To secure the door again, the user simply pushes it once more, which compresses the plunger and reattaches the magnet to the metal door or striker plate.
This chapter will explore the different uses and advantages of magnetic door latches.
Magnetic door catches are ideal for lightweight doors made from materials like plywood, plastic, or certain metals that cannot accommodate or do not need a more substantial latching mechanism. They offer versatility in commercial settings, securing both interior and exterior entry points and fitting a wide range of doors. Commonly used on emergency exits, delayed-egress doors, and controlled-egress doors, magnetic catches are also employed in the automotive and construction industries. Below is a list of various applications where magnetic locks prove useful:
The main advantages of using magnetic catches and plates are their simplicity and reliability. Unlike mechanical door catches, these specially designed latching devices are durable and require no replacements. Once properly aligned, they securely hold lightweight doors in place, eliminating the need for complex locking mechanisms or moving parts.
Magnetic door catches are particularly well-suited for keeping doors closed in environments like kitchens, laboratories, workshops, or storage rooms due to their unique design. They operate with a straightforward pull and swing action toward the catch plate. Key benefits include:
Remote Operation: Magnetic locks can be controlled remotely by adjusting the power source, enabling on/off functionality from a distance.
Easy Installation: With no interconnecting components, magnetic locks are generally simpler to install compared to other types of locks.
Quick Release: Magnetic locks (excluding fail-secure types) unlock immediately when power is cut, providing a faster release compared to traditional locks.
Durability: Magnetic locks are often more resistant to physical tampering than conventional locks. When subjected to force, such as with a crowbar, the lock or door is less likely to sustain damage. Additionally, electromagnetic locks have no moving parts that can break down.
Magnetic door latches have their drawbacks as well. Some of these disadvantages include:
The magnetic door latch is based on the basic electromagnetic concept that the electronically charged particles in certain materials are attracted to bond to one another. 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. Though not required, most magnets for this type of door are encased in plastic and have flanges for holes on three sides to attach the magnet to the door or the door frame. An electromagnetic lock works on the principle of using electromagnetism to lock a door when it is energized.
To achieve optimal operation, the holding force should be collinear with the load, and the lock and armature plate should be face-to-face. Magnetic door latches are used throughout a variety of industries and for different purposes. The automotive industry, for example, relies on these devices for use in door locks, seatbelts, and with shifting and braking applications. Magnetic door latches are commonly used to close various cupboards and drawers. You most likely pass right by magnetic door latches every time you walk by your washing machine or refrigerator. Both commercial and home security systems frequently rely on magnetic door latches. There are several magnetic latch types available to meet the needs of various designs and applications and these latches differ significantly depending on their complexity and purpose. When analyzing the requirements of their specific needs, one should carefully evaluate these different types of latches.
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