A sectional door is a door on a opening that opens either manually or by an electric motor. Sectional doors are frequently large enough to accommodate automobiles and other vehicles. Sectional doors may be made in a single panel that travels up vertically or back across the opening ceiling. Larger doors are usually made in several jointed panels that roll up on tracks across the opening ceiling, or into a roll above the doorway. The operating mechanism of a sectional door is spring-loaded or counterbalanced to offset the weight of the sectional door and reduce human or motor effort required to operate the sectional door. Less commonly, some sectional doors slide or swing horizontally.Sectional doors are made of wood, metal, or fiberglass, and may be insulated to prevent heat loss. The size of sectional door can very from a domestic garage size to bus garages size and bigger.
Torsion spring lift mechanism
A torsion spring counterbalance system consists of one or two tightly wound up springs on a steel shaft with cable drums at both ends. The entire apparatus mounts on the header wall above the opening and has three supports: a center bearing plate with a steel or nylon bearing and two end bearing plates at both ends. The springs themselves consist of the steel wire with a stationary cone at one end and a winding cone at the other end. The stationary cone is attached to the center bearing plate. The winding cone consists of holes every 90 degrees for winding the springs and two set screws to secure the springs to the shaft. Steel counterbalance cables run from the roller brackets at the bottom corners of the door to a notch in the cable drums. When the door is raised, the springs unwind and the stored tension lifts the door by turning the shaft, thus turning the cable drums, wrapping the cables around the grooves on the cable drums. When the door is lowered, the cables unwrap from the drums and the springs are rewound to full tension.
Some manufacturers advertise very high insulating values for some of their garage doors (R-15 to R-17), but it may be true for only for some central sections. The actual R-values – for the entire door – are often 1/2 or 1/3 of the advertised value.
Maintenance of sectional door is described in the manufacturer's instructions and consists of periodic checks for correct operation, visual inspection of parts, and lubrication.
Sectional Doors cause injury and property damage (including expensive damage to the door itself) in several different ways. The most common causes of injury from sectional door systems include falling doors, pinch points, improperly adjusted opener force settings and safety eyes, attempts at do-it-yourself repair without the proper knowledge or tools, and uncontrolled release of spring tension (on extension spring systems).
A sectional door with a broken spring, or the wrong strength spring, can fall. Because the effective mass of the door increases as the sectional door sections transfer from the horizontal to vertical door tracks, a falling sectional doors accelerates rapidly. A free falling sectional door can cause serious injury or death.
The sections and rollers on sectional door represent a major pinch hazard. Pedestrians should never be allowed near a moving sectional door for this reason. On manually operated sectional doors, handles should be installed vertically, to promote "vertical orientation of the hand".
Mechanical sectional door openers can pull or push a garage door with enough force to injure or kill people and pets if they become trapped. All modern openers are equipped with “force settings” that make the door reverse if it encounters too much resistance while closing or opening. Any sectional door opener requires safety eyes—sensors that prevent the door from closing if obstructed. Force settings should cause a door to stop or reverse on encountering more than approximately 20 lbs (9.07 kg) of resistance. Safety eyes should be installed a maximum of six inches above the ground. Many sectional doors injuries, and nearly all sectional doors related property damage, can be avoided by following these precautions.
Certain parts, especially springs, cables, bottom brackets, and spring anchor plates, are under extreme tension. Injuries can occur if parts under tension are removed.
Extension spring systems should always be restrained by a safety cable that runs through the middle of the spring, tying off to a solid point at the rear and front of the horizontal door track. Extension springs represent a hazard to bystanders when a spring, pulley, or cable breaks under tension. Metal parts from extension spring systems can suddenly be launched.
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