This article takes an in depth look at Concealed Hinges.
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A concealed hinge, also known as a hidden or European hinge, is a hinge that lays flush on the interior of a cabinet door and the surface of the cabinet to provide a smooth outer appearance. There are several varieties of concealed hinges with different leaf designs, pin sizes, and lengths. Concealed hinges for industrial applications are capable of supporting doors weighing 50 lbs up to 90 lbs., which makes it possible to install short wide panels.
Modern concealed hinges are engineered to be installed on different door types and have a variety of features such as soft-close, adjustable arms, and easy dismount. They are produced using several types of metal including steel, zinc, stainless steel, and aluminum. Heavy duty hinges are made of aluminum, stainless steel and cold-rolled steel, with zinc-plated, passivated, or electropolished finishes.to be able to withstand the necessary weight and stress requirements of industrial applications.
Concealed hinges follow the same design pattern as all forms of hinges with a pin, leaves, and knuckle. Each of the various types attach to a cabinet in different ways and may require adjustments to the cabinet during installation. A unique type of concealed hinge is a cup hinge that does not have the traditional pin, leaf, and knuckle design. When it is installed, the interior wall of a cabinet has to be adjusted.
Another form of concealed hinge is an enclosure hinge that has the pin, leaf, and knuckle design with a quick lease pin, which makes it easy to remove the door to an enclosure. Enclosure hinges are a form of industrial hinge for electrical enclosures. The quick release pin makes it possible for workers to access an electrical cabinet without the inconvenience of a door blocking their way.
The hinge cup is the part mounted on the door of the cabinet. The typical bore diameters for receiving the cup are 26, 35, and 40 mm. The depth of the bore varies depending on the construction of the hinge arm. The hinge cup has two flanges for screwing the metal at the backside of the door.
The hinge arm usually refers to the main hinge piece. This is the part where most of the design features are applied. The hinge arm connects the hinge cup installed at the backside of the door to the mounting plate installed at the frame of the cabinet. It has different forms depending on the type of cabinet door and the required travel or end play.
The hinge cup and hinge arm form the main hinge and are typically assembled together. Thus, a full concealed hinge set is typically composed of only two separated components: the main hinge and the mounting plate. One-piece sets are also available for compact applications.
The mounting is installed at the edge, side, or frame of the furniture. It has either two or four mounting holes depending on the weight or load imposed by the door. It has notches, clips, or holes for receiving the hinge arm.
Industrial enclosure concealed hinges are designed to keep enclosures and cabinets secure and safe and are an essential part of the efficiency of an operation. They come in a wide variety of styles from very simple ones with holes for screws and a curved bracket to more complex ones with brackets, special screws, quick release removable pins, and uniquely designed leaves.
The curved pivot allows the door of a cabinet to easily swing open and can come with holes to attach it to a wood cabinet or without screw holes for it to be welded to a metal cabinet.
The brackets of a concealed hinge are similar to those of conventional hinges and come with or without holes.
The key to industrial enclosure hinges is the pin that can be easily removed such that the brackets remain in place as workers open and access the contents of a cabinet.
Electrical box concealed hinges are especially designed for use with cabinets and boxes that contain electrical circuits, connections, and breakers. They are designed for quick and easy removal when electrical connectors need to be repaired or replaced. Electrical box concealed hinges have a complex design with several engineered parts. They are exceptionally sturdy made of materials capable of withstanding exposure to the elements and various corrosive substances.
The important components of an electrical box concealed hinge are:
The quick release pin made of heavy duty steel has an element on top that makes it easy to remove the pin and detach the door of a box or cabinet.
The box leaf has holes for the bolts that attach the body of the hinge to the utility bracket.
The hex bolts securely attach the hinge body to the utility bracket.
Depending on the type and design of the box or cabinet, the lid leaf is held in place by the quick release pin around which the lid leaf rotates when the box or cabinet is opened. It attaches to the hinge body in the traditional fashion of all hinges with a knuckle that fits into the knuckle of the body of the hinge.
Overlay and reveal are the two most commonly used terms in specifying the cabinet door design and concealed hinge specifications. These two dimensions affect the door position and the overall appearance of the cabinet doors.
The overlay is the term used to denote how much of the edge of the cabinet or cabinet frame is covered by the door. Opposite the overlay is the reveal which specifies the portion of the edge or frame of the cabinet that is not covered by the door.
The different amounts of overlay and reveal lead to the three main classifications of concealed hinges.
This type of concealed hinge is used in cabinets where the door is positioned at the front of the cabinet box or frame. When closed, the periphery of the door‘s backside mates against the edge of the cabinet panels.
A full overlay does not necessarily mean that the door completely covers the entire cabinet box. Some designs allow some amount of reveal. The datasheet of most commercially available concealed hinges gives mounting plate dimensions, so the desired amount of overlay and reveal can be achieved.
With a half overlay concealed hinge, two doors of a cabinet sit on top of the cabinet‘s frame and meet in the center of the frame. Where the two doors meet is a partitioning wall or center post that is the portion of the cabinet to which the concealed hinge is attached. The concealed hinges are placed such that the two doors can be opened together without hitting each other.
Curved pivot concealed hinges are ideal as half overlay concealed hinges because of their small size and ability to be easily connected to wood or metal cabinets.
To achieve a half overlay installation, half overlay hinges use a cranked hinge arm and a raised mounting plate. These two features reduce the overlay taken by a single door.
Doors that use inset concealed hinges fit inside the cabinet panel or frame. Thus, the installation has no overlay. This design has the outer face of the door flushed on the outer surface of the frame or edge of the cabinet box.
The hinge arm of an inset concealed hinge is highly cranked. Also, the mounting plate is raised to fully eliminate the overlay.
Pivot concealed hinges are used with cabinets that have inset doors and the hinges need to be invisible. They have two flat leaves, a L bracket attached to one of the leaves and the knuckle, and a permanent or removal pin with the removal pin type used for industrial applications. They open and close smoothly and are designed to hold lightweight doors in industrial applications.
Aside from the desired overlay, cabinets can also have different frame constructions. The corresponding hinge type must be employed for proper attachment.
This type of hinge is used in cabinets with plain or bare side panels. It uses mounting screws that are fixed perpendicularly to the mounting plate. Frameless-type concealed hinges can also be a full overlay, half overlay, or inset hinges.
A face frame cabinet has a small amount of fascia installed on the side panels of the cabinet. The mounting plate design of face frame-type concealed hinges is different for full overlay and inset concealed hinge types. The mounting plate of a full overlay type has screws oriented perpendicularly to the plate. The screws on the inset types are aligned at an angle and fixed at the backside of the frame.
Special concealed hinge designs are also available for less common cabinet types. Most of the other cabinet types are located at the inside and outside corners of the furniture. Examples of concealed hinges used in these areas are:
This type of hinge is used in double doors of L-shaped corner cabinets. Ordinary overlay or inset concealed hinges are used to attach the door assembly to the cabinet frame while bi-fold concealed hinges are used to attach the two doors together. The result is a folding door with one side hinged on the cabinet.
These hinges are used in inside-corner cabinets with a side panel inline and flushed with the door. Most blind corner hinge arm designs allow a full 90° opening of the cabinet door.
Also known as an angled concealed hinge, corner concealed hinges are used in doors hinged at the outside corner of the furniture. Most furniture outside corners are angled at 90°, but 30° and 45° angles also exist. For these types of furniture, a corner concealed hinge with the corresponding angle is available.
There are several reasons that concealed or invisible hinges are used for industrial enclosures, doors, and cabinets. The first and primary reason is security, safety, and prevention of tampering with sensitive or valuable equipment. In such applications, concealed industrial hinges are hidden and inaccessible.
Concealed industrial hinges are commonly found on interior doors and various types of security doors as well as commercial refrigerator doors and tightly sealed enclosures and cabinets. Unlike typical hinges that are completely visible, concealed hinges for industrial use are hidden, flush, and invisible offering exceptional security and protection.
With hold door closed concealed hinge, spring tension closes the door after it is opened and keeps it closed without the need of a latch. They are used for work locations where there is heavy and constant use and doors have to remain closed to be out of the way of workers.
Surface mounted concealed hinges are necessary where durability, size, flush fit, and smooth operation are a necessity. They are a single action hinge that opens 180o and can be attached to wood or metal surfaces of industrial cabinets.
Quick release concealed hinges are a necessity for electrical enclosures, cabinets, and boxes where quick removal of doors makes it easier and more efficient to work on the contents of an enclosure. There are several styles of pin quick release concealed hinges that vary in accordance with the type of pin, length of the hinge, and strength of the hinge.
Most quick release concealed hinges are surface mounted to make the pin more accessible and its removal easier without having to negotiate around a door.
In addition to type, concealed hinges are selected according to different specifications and features.
For cup concealed hinges, the cup can come in different sizes. Each size represents a type of application.
The attachment type refers to how the hinge arm attaches to the mounting plate. There are two main types: clip-on or slide-on.
The design of a concealed hinge with a clip-on attachment makes for effortless door mounting and dismounting. This is useful on doors with multiple hinges as it allows door installation in one movement. There is no need to use screws and screwdrivers.
A typical clip-on hinge has a clip tab located at the rear end of the hinge arm right next to the depth adjustment screw. Mating the hinge arm on the mounting plate latches both parts in place using the clip-on assembly. The attachment can be released by pressing or pulling the clip tab.
This is the traditional attachment type of concealed hinges. Slide-on hinges are much simpler in construction: a slot or notch on the hinge arm and a hole on the mounting plate. The two parts of the hinge are set by a fixing screw.
The slot on the slide-on design is not just for fixing the hinge arm on the mounting plate but also for adjusting the depth of the hinge.
Manufacturers usually provide a chart for determining the recommended number of hinges to use. The number of hinges needed depends on the height, weight, and in some cases, the width of the door.
A 40 inch (101.6 cm) tall door typically requires two hinges. Adding another 20 inches (50.8 cm) to its height adds another hinge. Thus,
This is all true regardless of the weight of the door.
In terms of the weight or load applied on the door, a 15 pound (6.8 kg) door usually requires two hinges. Adding another 15 pounds (6.78 kg) necessitates another hinge, and so on. This is applied regardless of the door height. Note that this 15-pound value is highly likely to vary depending on the design, material, and thickness of the hinge. The specified weight varies more than the height when comparing product datasheets.
When considering both height and weight, if the two yield different requirements for the number of hinges, the larger number is always followed.
The closing action refers to the manner in which the door closes without the aid of any external force. There are three popular options: self-close, soft close, and free swing.
As the name suggests, a self-closing concealed hinge automatically closes the door and keeps it from creeping open. This is done mechanically through the design of the hinge arm. The hinge arm has a small spring mechanism that returns the hinge to its resting or closed position. The spring is carefully designed so that when the door is opened to a certain degree, there is not enough torque or force to pull the door.
The closing action only occurs at the "tipping point" of the hinge arm. The tipping point is at the 10 to 20-degree position of a partially opened door.
This type of concealed hinge has an integrated hydraulic damping mechanism. When the door is left partially opened and over the tipping point of the closing mechanism, the damper activates to gradually and silently closes the door. This prevents unwanted slamming that can damage the furniture. The damper offers significant resistance that even makes it hard to force close the door. The soft closing feature is considered a self-closing design but with additional technology.
Some soft-close mechanisms allow adjustments to the damping or closing resistance. The damping system can be adjusted to have high resistance and long closing action or low resistance and faster closing action.
Free swing concealed hinges are the simplest among the three types. They do not have a self-closing mechanism. Thus, the door can freely swing on its entire range of opening without encountering resistance or a tipping point. Doors fitted with free swing hinges rely on magnetic and mechanical latches for keeping the door closed.
This specification is defined as the angle made by the door and the frame of the cabinet at the door‘s fully open position. The degree of opening is sometimes called the range of opening or door swing.
The minimum degree of opening of concealed hinges is about 100°. Concealed hinges with opening angles below 100° are considered low angle types. Depending on the hinge design, the most common hinges have an opening of 100° to 120°. Going beyond 120° results in more expensive hinges with complex hinge arm mechanisms. The maximum degree of opening is 270°, which allows the door to swing back against the cabinet.
When facing the cabinet door, adjusting this screw moves the position of the hinge arm either left or right. It affects the reveal, or the portion of the cabinet not covered by the cabinet door for a frameless cabinet. Also, if the cabinet type is a two-door cabinet, the lateral adjustment changes the space or gap between the two doors. The lateral adjustment typically allows 5 mm of movement.
Correcting the lateral adjustment is one of the hardest tasks when installing a concealed hinge. Most of the time, this is when the imperfections of the furniture structure are revealed. Luckily, this is done mechanically by turning the screw. Thus, adjustment can be done incrementally. The lateral adjustment of one concealed hinge is accomplished in tandem with the other hinge installed on the door. The coordinated adjustment of the concealed hinge pair slightly tilts the door. Too much adjustment can lead to a door appearing to sag on one side.
Turning a depth adjustment screw allows an in-and-out or front-to-back movement of the door from the cabinet. This feature is used to control the gap between the frame and the backside of the door when the cabinet is closed.
The typical design of the depth adjustment is an elongated slot or notch punched near the rear end of the hinge arm or piece. This slot mates to a hole located on the mounting plate. Loosening the fixing screw on the mounting plate allows the hinge arm to slide in and out. This configuration allows 3 to 5 mm of movement. Other high-tech designs, like Blum‘s proprietary Spiral Tech, do not use a fixing screw. Instead, the depth is changed by turning the adjustment screw with a preset number of revolutions. Spiral Tech allows 5 mm of movement by turning the depth adjustment screw one and three-quarter revolutions.
The height adjustment feature of a concealed hinge allows for changing the position of the door in the vertical direction. This is used to ensure the top and bottom edges of the door match properly on the corresponding edges of the cabinet.
The height adjustment is integrated into the mounting plate. Some designs feature a mounting plate with elongated slots. These slots match up with holes drilled on the edge of the cabinet. Loosening the fixing screws allows a small amount of movement by sliding the mounting plate up or down. The height adjustment is typically small and can range from 2 to 3 mm.
There are two basic types of mounting screws for both the hinge cup and mounting plate:
This is the traditional style of mounting hinge. As the name suggests, it uses screws to fasten the hinge onto the door and side or frame of the cabinet.
This was developed to ease the installation of concealed hinges. Concealed hinges with this feature have pre-fitted dowels integrated into the hinge assembly. Installation is tool-free and only requires pressing the dowels ito the holes in the cabinet.
Concealed hinges are typically made of stainless steel. Stainless steel has excellent mechanical properties, a variety of surface finishes, and inherent corrosion resistance. Other materials used for fabricating concealed hinges are nickel-plated steel, galvanized steel, and brass.
Below is some additional information for specifying concealed hinge requirements. It is recommended to look into charts and tables that specify these values for precise and accurate mounting.
The door gap is the space between the edge or frame of the cabinet and the backside of the door. A small door gap is desired to create a continuous appearance for the cabinet. However, too small a door gap can lead to clashing and unwanted scraping of the hinged side of the door. The default door gap is typically 3/16 inches (4.8 mm). This can be adjusted by turning the depth adjustment screw.
The bore refers to the recess on the door for receiving the hinge cup. Measuring the distance between the perimeter of the bore and the edge of the door gives the bore distance. The bore distance is selected along with the mounting plate thickness and amount of hinge crank to achieve the desired overlay.
Some concealed hinge datasheets also specify the mounting plate thickness. Choosing the right mounting plate thickness, along with the predetermined bore distance, helps achieve the desired overlay. Common manufacturer standards for this measurement can range from 0 to 9 mm. A 0 mm mounting plate thickness does not mean that the mounting plate has no thickness. The 0 mm value means the hinge is neutral and does not contribute to reducing the overlay.
The hinge crank specifies the amount of offset built into the hinge arm. This offset can be either the left or right direction which makes the value either positive or negative. Like the mounting plate thickness, the hinge crank affects the resulting overlay. A zero crank hinge arm is neutral or flat with a full overlay hinge. The crank can vary from -3 to +19 mm.
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