Are your dock doors hindering plant productivity?

Advancements in material handling technology have translated into significant cost savings and efficiency for manufacturing plants and distribution centers. These developments work together to make it easier to load/unload trucks and sort, pick, store, and move increasing volumes of product more accurately and efficiently.


Advancements in material handling technology have translated into significant cost savings and efficiency for manufacturing plants and distribution centers. These developments work together to make it easier to load/unload trucks and sort, pick, store, and move increasing volumes of product more accurately and efficiently.

Yet, despite all of this forward thinking, a major area of neglect remains — the sectional dock door. These doors often throw a roadblock into the efficiency provided by modern material handling systems, while doing a poor job of protecting one of the facility's most significant investments — the HVAC system and it's related costs.

Basic functions

A door has a number of rudimentary, yet crucial, tasks to perform:

  • Contain interior energy

  • Stop entry of debris, contamination, wind, and vermin

  • Enable doorway access

  • Protect facility against intrusions.

    • While a door is ready to perform these tasks, it's natural enemy — the fork lift truck — stands in the way (Fig. 1). Moving these heavy, bulky, relatively high-speed vehicles in confined spaces around the dock is an accident waiting to happen. The door is a constant target. The damage certainly impacts door operation, but the affect also telescopes throughout the facility.

      Fig. 1. Dock doors are continually abused by fork lift impacts.

      Resulting problems

      After a typical accident, damage is assessed, the driver is reprimanded and may be written up, and the call goes out to maintenance for emergency patch-ups. Facilities with dozens of doorways report these types of accidents occur daily.

      Costs begin with the repairs (see "Door cost comparison" sidebar) and build from there. Following the accident, the driver loses three or four loading cycles. The traffic manager has to juggle schedules to reroute trucks to available doorways. If this is an intricately scheduled just-in-time or crossdock operation, benefits of the system are jeopardized.

      About 95% of these minor accidents affect the sheet metal door tracks. The hammering finally leads to maintenance problems, with a door typically needing replacement every 5 yr.

      Standard doors eventually have difficulties containing HVAC energy, which creates problems in controlling temperature and humidity. Even the smallest gap between a slightly out-of-alignment door and the frame could mean hundreds of dollars of energy loss annually if temperature differentials between inside and outside are significant. These same openings enable insects, rodents, and other vermin to find their way inside.

      Over time, misalignment causes the door to become more difficult to operate. As opening/ closing becomes harder, workers tend to leave the door open all the time, which creates a serious energy loss. Also, a hard-to-operate powered door eventually experiences motor burnout.

      Seals are the main guardians of energy loss, and the most vulnerable portion of the door. As vehicles pass through the doorway, the fork lift or pallet load often rip the side and top seals. Many facilities find they have to do this replacement job so often the crew frequently ignores the task. Constant door repair becomes viewed as a losing battle when considering all of the other demands on their time.

      No matter how well organized the material handling flow, loaded pallets end up resting on the dock while staged for delivery, which creates an obstacle course. On some docks, the path narrows to just the width of a lift truck.

      The clock becomes another villain in door damage. To beat demanding schedules, drivers are traveling faster than their ability to judge turns in the confined spaces. It is just a matter of time before they clip or collide into a door.

      Dock human resources is an ongoing problem for doors, with turnover rates typically high. New hires receive one or two-day fork lift safety classes, but after graduating, many of the drivers end up on graveyard shifts where supervision is light, horseplay and sloppy driving are more common, and accidents often result.

      One answer

      Material handling modernization aside, loading docks remain rough places. Conditions in this very important area of the plant prompted the development of the knockout style sectional door to help overcome potential problems.

      Fig. 3. Knockout doors withstand fork lift impacts and are back in operation in just seconds.

      Traditionally, soft panel roll-up doors with bottom bars that broke away upon impact protected interior doorways. On a standard door, guide rollers enclosed in a sheet metal track were a source of constant maintenance. The knockout door replaces rollers with a quick-release mechanism. In some models, this can be a 3/4-in. steel pin in a spring-loaded housing. The mechanism is engineered to enable impact release of the door panel while being strong enough to take a direct hit.

      The metal track encasing the rollers is replaced with a modified V-groove design, which allows more spring when hit. The track is a thick section of plastic, heavy gauge metal, or heavy gauge metal encased in plastic.

      When the door is hit, pins slide out of the V-groove track to release the impacted sections, enabling the door to remain on the wall. The driver simply yanks the panel to reset the pins in the track and the door is ready to operate.

      Track design leads to other solutions. At ground level, the track is shaped so the door can be knocked out, but not pushed in by intruders or wind. The panel can be locked to the track for security.

      The track also remedies one of the more common forms of accidents — fork lift masts clipping the lower panel when the door is raised. Knockout tracks often include a special feature that enables the panels to be pushed if a fork lift hits the door. The double knockout track is at the upper section so the door can be pushed in when fully open, but not when the door is fully closed, to maintain doorway security.

      To combat the problem of ripped seals, some knockout door models have the seal attached to the door panel rather than the doorway. When the panel rises, the seal goes up with it, pulling out of the way of passing traffic.

      Many standard doors are solid metal panels or hollow metal, offering security but little or no insulation. Knockout door panels have insulated foam cores, some as thick as 4 in. and rated R-25.

      Insulated panels also increase dock safety. Temperature differentials can form moisture on the panels and around the threshold if the doorway is not fully sealed and properly insulated. The slippery floor is a safety hazard for personnel and leads to more door accidents, as lift trucks may not be able to brake in time.

      A major consideration in using these doors is cost. With a price two or three times a standard door, the decision comes down to whether a doorway experiences enough damage to warrant replacement.

      Key concepts

      Fork lift trucks are the natural enemy of doors.

      Damaged doors dramatically increase operating and maintenance costs.

      Knockout style sectional doors feature a quick- release mechanism that minimizes damage and downtime.

      Door cost comparison

      Cost itemStandard sectional doorEntry-level knockout doorMiddle-level knockout door
      Initial purchase price is based upon an average 8-ft x 8-ft loading dock door opening installed in a retrofit application.
      Two years of preventive maintenance includes spring lubrication, roller wheel replacement, and replacement of weather seal. The knockout doors do not use roller wheels and it's weather seal cannot be damaged or worn within a 2-yr period.
      Few, if any, door repair companies carry the parts for all makes, models, and sizes on their truck or in their shop. Most door damage requires two service calls — the first to get the door running and the second to replace the parts.
      Initial purchase price$900$1500$2500
      Two years of preventive maintenance$230$100$100
      First panel replacement
      First service call to order parts and get door running$200
      Second service call to install new parts$300
      Second panel replacement
      First service call to order parts and get door running$200
      Second service call to install new parts$300$280
      Track replacement$364
      Two years cost of ownership$2494$1880$2600

      More info
      The author is willing to answer technical questions concerning this article. Mr. Hare is available at 414-820-1217. The company web site is

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