Continuous geared hinges help prevent doors from pulling away from their frames.

School officials have a common complaint about doors: "We thought we got top-quality door hardware for our new building, but now the doors are beginning to sag after only six months."

Medium- and high-traffic doors at schools and universities often show wear after only a few months because the frequent use and stresses are more than some traditional hinges can handle. Sagging doors occur most commonly when the top butt hinge or pivot has started to pull out from the frame. One way to prevent this condition is to begin with a full-length continuous geared hinge that distributes the door weight and stresses over the full length of the door and frame.

Continuous geared hinges are used with aluminum, wood and hollow metal doors and frames. This product is being specified more and more for medium- to high-traffic interior and exterior school doors. Continuous geared hinges are well-suited for keeping entrance components in alignment while withstanding the pressure of many thousands of cycles per year and, in some cases, even thousands per day.

New school and university building entrances are usually designed with full-length continuous geared aluminum hinges. The continuous hinge can be anodized or painted to match nearly any exterior design.

Constructed of three interlocking, anodized extrusions (two geared leaves and a cover channel), a continuous geared hinge installs on the full length of a door and frame, and uniformly distributes the opening and closing force of the door. The vertical door loads are carried on a series of either plastic or steel bearings along the full length of the hinge.

Continuous geared hinges can be manufactured in light-duty, standard-duty, heavy-duty or extra-heavy-duty versions. The heavy-duty and extra-heavy-duty models have additional bearings and fasteners to support added door weight, extra-wide doors, lead-lined doors, or any doorway having unusually high traffic.

The full-length design seals the gap between door and frame, offering security, privacy, noise reduction and weatherproofing. The dispersal of opening force along the length of the door also greatly reduces the amount of stress on a door caused by misaligned butt hinges or pivots, which by their nature localize door weight and stress at the upper portion of the door. Most important, continuous geared hinges serve to reduce or eliminate door sag.

Continuous geared hinges are installed on the surface of the door and frame. Because of the rapidly growing usage of continuous geared hinges, most door manufacturers now prepare their doors for continuous hinges. This eliminates the additional expense of a "custom" undersized door. Also, because a continuous geared hinge is designed to support the door along its entire length, the need to reinforce the frame is reduced. When the door is closed, most profiles have no exposed screws, bolts, pins or knuckles to be vandalized. All of these points are important factors for school building owners and architects to consider when deciding what kinds of doors to install.

Hinge application

Here are descriptions of the three main applications for continuous geared hinges.

- Concealed mounting. Instead of being "mortised," the concealed type of continuous geared hinge is mounted on the hinge stile of the door and on the rabbet of the frame. This profile normally is specified for use in new school construction, but also can be used with new doors in existing frames.

A new square-edge door must be undersized by the amount of clearance needed at the lockside, plus 5/16-inch for the hinge (1/8-inch leaf + 1/8-inch leaf + 1/16-inch clearance between leaves = 5/16-inch).

A new bevel-edge door must be undersized by the amount of clearance needed at the lockside, plus 11/32-inch for the hinge (1/8-inch leaf + 1/8-inch leaf + 3/32-inch clearance between leaves = 11/32-inch).

The hinge cap on the profile requires a 7/16 -inch rotational clearance at the jamb side. The hinge opens to a full 180 degrees and is usually designed for either 13/4-inch or two-inch doors. The concealed hinge is engineered to work with a closer having a butt-hinge-type pivot point. Existing concealed floor or concealed overhead closers having a fixed center pivot point must be replaced with a traditional overhead surface closer.

Concealed continuous geared hinges are normally installed with either 10-24 or 12-24 undercut head, self-tapping fasteners. A pilot hole needs to be drilled, and the fastener then forms its own threads. Some installers use self-drilling fasteners, but they are not recommended for installation in mortar- or grout-filled door frames. The drill point in all probability will hit the mortar and create a "jacking effect" on the frame. It is recommended to first remove the mortar with a masonry bit. If possible with contract work, some form of mortar guard should be specified behind slushed-in frames. Security fasteners, wood screws and other fasteners also are available.

- Full surface mounting. Full surface continuous geared hinges are installed on the face of a door and frame. This profile usually is used in retrofit situations, but also can be used with new doors and frames. The hinge is installed with 12-24 fasteners in the frame leaf, and fastened with sexnuts and 1/4-20 shoulder screws through the door. Full surface hinges also usually are designed with four locator holes per hinge to aid in the adjustment of the door to fit plumb and square in the entrance opening before installation of the door and frame fasteners. This profile can be used on aluminum, wood and hollow metal doors up to 21/4-inch thick. A common use for full-surface hinges is on school building doors that have sagged due to damage or wear on the original butt hinge or pivot.

- Half-surface mounting. Half-surface continuous geared hinges are installed on the face of a door, with the frame leaf concealed. This profile usually is used in retrofit situations, but also can be used with new doors and frames. The new door must be undersized by the clearance needed at the lock side of the door, plus 3/16-inch (1/8-inch frame leaf + 1/16-inch clearance = 3/16-inch) on the hinge side. The frame leaf is installed on the rabbet of the frame with 12-24 fasteners, and the door leaf is through-bolted to the door surface with sexnuts and 1/4-20 shoulder screws. This profile can be used on aluminum, wood and hollow metal doors up to 21/4 inches thick. A common use for half-surface hinges is on school building doors that have been weakened at the hinge edge, but the door itself is still serviceable.

Continuous geared hinges are available with fire ratings ranging from 20 minutes to 3 hours. Some concealed, full- and half-surface hinges need pins or studs to be fire-rated. Most manufacturers have gained approvals for positive pressure fire ratings.

Continuous geared hinges have improved since they were introduced more than 25 years ago. Modern continuous geared hinges have templated hole patterns, lubricated bearings, permanent lubricants on the geared areas (which nearly eliminate maintenance needs), extended wear life, non-handed design, stainless-steel fasteners, security features, electrical modifications and decorative hinge caps.

The Builders Hardware Manufacturers Association (BHMA) is working on establishing a cycle test standard for continuous geared hinges.

Continuous geared hinges are manufactured in standard industry lengths (79, 83, 85, 95 and 119 inches) that allow for threshold clearance in most openings. Mounted flush with the top of the door and allowing 1/8-inch header clearance, standard length hinges allow 7/8-inch clearances at the bottom. Hinges can be cut to exact lengths on site, or at the factory. After cutting, a non-handed new continuous hinge may become handed, depending on the model. Most hinges are finished in 628 (US28) clear anodized aluminum, or 313AN dark bronze anodized duranodic colors. Custom anodizing and painting allow the hinges to be matched with other hardware finishes.

A properly installed continuous geared hinge can easily last 10 to 20 years or longer in an entrance and tolerate a great deal of abuse and heavy traffic with little or no maintenance required.