|
Open and Shut Case for High-Speed Doors
A stopwatch-wielding efficiency expert determines that extensive equipment modifications can shave several seconds from a minutes-long production operating cycle, and the plant engineering department implements the prescribed modifications. The efficiency expert receives a rousing "Hurrah!" and a feather in his cap. In Contrast, a plant engineer cuts almost an hour from work-in-process transport time by installing more efficient traffic doors, and hardly anyone seems to notice. Thus is the life of the plant engineer and the attention to "behind the scene" products like high-speed doors. In addition to external doors needed for shipments and deliveries, almost every manufacturing facility has internal doorways connecting rooms that must be kept closed to block out noise, dust, odors or vapors; or to maintain proper temperatures. These internal doors are not considered production equipment, but can affect the cost of product manufacture. And contrary to production equipment specifications, responsibility for doors lies with the plant engineer. Slow Doors Increase Costs The cost of producing a product can be affected by how frequently and rapidly doors open and close - and productivity can suffer severely if malfunction or damage prevents them from operating at all. Very real productivity losses can occur from the idle time waiting for doors to open. While slight delays might not have made much difference a few years ago, time management has taken on increased significance in today's environment of increased competition and leaner workforces. Time simply must not be wasted. Many doors must be opened hundreds of times per day. Assuming that a door opens at the rate of 8 in./sec., it takes 15 sec for 10-ft-high door to fully open. If a single worker transporting material passes through 25 times/hr, he collectively spends 50 min/8-hr workshift waiting for the door to open. The purpose of most doors in industrial receiving, shipping, warehousing, and manufacturing areas is not to control access, but to provide a seal between adjacent areas. Slow-operating doors compromise this role with increased migration of dust, fumes, and noise between areas; and by reduced effectiveness in maintaining desired temperatures. Slow Doors Invite Damage Any door that is heavily used by fork lift trucks and other motorized vehicles is a prime candidate for vehicular damage. Impatient drivers (and especially those working on an incentive pay basis) frequently misjudge the opening speed of doors, causing serious damage - and the slower the operating speed, the greater the margin for miscalculation. Preventable door repairs diminish the productivity of plant maintenance forces, and sometimes disrupt the flow of product ingredients and finished items while repairs are in process. Often, steel roll-up doors are used in areas with moderate-to-heavy motorized traffic. Even if automatically-activated, this does not increase their operating speed; they rise at the sluggish rate of about 8 to 12 in./sec. This slow pace contributes to accidents, prompting hasty or careless drivers to proceed before the door rises to the top. Furthermore, most operating systems for steel roll-up doors are not designed for high-traffic areas. They can be severely taxed, requiring frequent maintenance. Cement bollards and other precautionary obstacles can protect steel doors and frames from being accidentally struck by vehicles, but they provide little protection against drivers who are on a straight course and too impatient to ensure that the door has fully opened. Strip and impact/bump doors can be installed when traffic must move frequently and quickly through doorways. Both styles move out when vehicles contact them, so drivers don't have to wait. These designs, however, raise issues of safety and excessive maintenance. High-Speed Door Construction To ensure a tight seal between adjoining rooms, construction typically incorporates vinyl seals in side columns, and a vinyl bottom edge that hugs the contour of the floor. Personal safety features include controls that raise the door to the open position if the bottom edge contacts an object before reaching the floor. The system must be manually reset to resume operation. Photocontrols are also used to sense obstructions in the door's operating path. Although increased door operating speed reduces the likelihood of vehicular damage, most manufacturers acknowledge that accidents will happen, and design their high-speed doors to accept hits without sustaining serious damage. High-speed doors are available in a variety of styles, but most common are rolling and folding versions. The rolling types can be programmed to operate at speeds ranging from 3 to 8 ft/sec. Most are made of flexible, durable, and puncture-resistant vinyl fabrics; and are available with transparent PVC windows. The vinyl fabric is fully tensioned to withstand high exterior winds or interior negative pressure. A key feature of some rolling doors is a release system, or breakaway bar on the bottom. If the door is hit, the bar breaks free, fabric flexes, and door operator motor automatically shuts off. The bar, usually made of extruded aluminum, is easily reset without tools, and the door is restored within minutes. High-speed folding doors open at speeds up to 7 ft/sec, and also incorporate design features to withstand the impact of a fork lift with little or no damage. When closed, their transparent PVC panels overlap as much as 12 in. to ensure a tight seal. Actuation Options Classic methods of activating vehicular traffic doors call for the approaching driver to operate either a pendant pushbutton control or a pullcord-operated switch as he nears the door. Operating efficiency of high-speed doors is further enhanced by going beyond these basic actuation methods. Motion detectors and photoelectric controls can be applied to open and close the door as the driver approaches and passes through; hand-held radio controls are another option. Several operating methods can be combined and are programmed through a wall-mounted controller. One such system can be programmed to let the door open only high enough to accommodate pedestrians when actuated by persons walking. The most effective system utilizes an induction loop embedded in the floor to sense metallic objects passing over it to activate the door. The control is tuned to discriminate between vehicular traffic and objects of lesser metallic mass. The permanence of this type of actuating system is superior to portable devices that can get misplaced. An induction loop can be installed in existing floors as well as in new construction, positioned at whatever distance and in whatever configuration is optimum for the application. Installing high-speed doors may not be a sure path to fame and fortune. But selection of the right door and options can make a big difference in plant operating efficiency. Rytec Corporation One Cedar Parkway Jackson, WI 53037-0403 United States Toll-Free: 888-GO-RYTEC (888-467-9832) |
