Abstract:
Example dock levelers installed at a vehicle loading dock include pivotal or otherwise vertically adjustable deck plates with special coatings on the deck&#39;s upper surface. In some examples, the coating improves traction and addresses various thermal issues, such as condensation and thermal strain between a polymeric coating and a steel deck plate. In some examples, when indoor and outdoor air create a temperature differential across opposite faces of the deck, the coating is designed such that a median temperature of the temperature differential occurs near an interface where the coating bonds to the steel plate&#39;s upper surface. In some examples, the coating includes particles of different sizes and colors embedded within and covered by a polymeric base material. As traffic abrades the coating, the different colored particles become exposed at different levels of wear, thereby providing a visual signal indicating when the coating needs to be touched up or replaced.

Description:
FIELD OF THE DISCLOSURE 
     This patent generally pertains to dock levelers and, more specifically, to dock leveler having thermally balanced traction decks. 
     BACKGROUND 
     Dock levelers are often used to compensate for a height difference that may exist between a loading dock platform and the bed of a truck parked at the dock. A dock leveler typically includes a ramp or deck plate that is hinged at its back edge to raise or lower its front edge to generally match the height of the truck bed. Often an extension plate or lip is pivotally coupled to the deck to bridge the gap between the deck&#39;s front edge and a back edge of the truck bed. The deck and lip provide a path for forklift trucks to travel between the loading dock platform and the truck bed, thus facilitating loading or unloading of the truck. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view of an example dock leveler system. 
         FIG. 2  is a cross-sectional side view of the dock leveler system of  FIG. 1  but showing an example configuration of the dock leveler in a first position. 
         FIG. 3  is a cross-sectional side view of the dock leveler system of  FIG. 1  but showing another example configuration of the dock leveler in a second position. 
         FIG. 4  is an enlarged cross-sectional view taken at circle  4  of  FIG. 1 . 
         FIG. 5  is an enlarged cross-sectional view taken at circle  5  of  FIG. 4 . 
         FIG. 6  is a top view of the example dock leveler shown in  FIG. 1 . 
         FIG. 7  is an enlarged cross-sectional view similar to  FIG. 5  but showing a worn coating with various colors identified by hatching. 
         FIG. 8  is a perspective view showing an example coating being sprayed onto an example deck plate. 
         FIG. 9  is a perspective view showing the coating of  FIG. 8  drying, curing or otherwise setting over time. 
         FIG. 10  is a perspective view showing installation of an example coated deck plate to a dock leveler. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-3  show an example dock leveler system  10  comprising a dock leveler  12  with a deck plate  14  that is vertically movable (e.g., movable via pivoting or translating) between a raised position (e.g.,  FIG. 2 ) and a lowered position (e.g.,  FIG. 1 ).  FIG. 1  shows dock leveler  12  in its stored position with deck plate  14  being generally flush with and/or in generally the same plane as a loading dock platform  16 ,  FIG. 2  shows a vertically moving door  18  opening and dock leveler  12  being deployed, and  FIG. 3  shows dock leveler  12  deployed in an operative position. In the operative position, dock leveler  12  provides an adjustable height bridge across which a forklift  20  or other traffic can travel between a vehicle bed  22  and platform  16 . In some examples, a special coating  24  on the deck&#39;s traffic surface improves traction, impedes corrosion, dampens traffic noise, dampens dock leveler operating noise, and/or serves as a temperature barrier to reduce condensation on deck plate  14 . 
     Although coating  24  can be applied to a wide variety of dock levelers, in the illustrated example, dock leveler  12  comprises a frame  26  installed within a pit  28  of a loading dock  30 . To compensate for a variable height difference that may exist between platform  16  and vehicle bed  22 , a rear edge  32  of deck plate  14  is hinged to frame  26  so that pivoting deck plate  14  adjusts the elevation of the deck&#39;s front edge  34  to generally match the elevation of bed  22 . In this example, an extension plate or lip  36  is pivotally coupled to deck  14  to bridge the gap between the deck&#39;s front edge  34  and the back edge of vehicle bed  22 . When lip  36  is resting upon vehicle bed  22 , as shown in  FIG. 3 , deck  14  and lip  36  provide a path for forklift  20  to travel between platform  16  and vehicle bed  22 , thus facilitating loading or unloading of the vehicle&#39;s cargo. 
     In some examples, deck plate  14  is a generally smooth plate comprised of steel with a generally uniform plate thickness  38  ( FIG. 1 ). Referring to  FIG. 4 , plate thickness  38  is defined by an average distance between an upper surface  40  and a lower surface  42  of plate  14 . Example values or dimensions of thickness  38  include, but are not limited to, 3/16 inches, ¼ inches, 5/16 inches, and ⅜ inches (nominal dimensions). In some examples, a plurality of stiffeners  44  (e.g., beams, joists, ribs, etc.) are attached to lower surface  42  to provide deck plate  14  with greater rigidity. 
     Referring to  FIG. 5 , to address issues of traction (e.g., traction between forklift  20  and deck plate  14 ), corrosion, noise dampening, and/or thermal considerations (e.g., condensation and thermal expansion), some examples of coating  24  comprises a plurality larger particles  46  and a plurality of smaller particles  48  mixed, coupled to, covered by, or embedded within a polymeric base material  50 . Material examples of larger particles  46  include, but are not limited to, polypropylene, sand, silica, glass, and/or metal and/or any combination thereof. Material examples of smaller particles  48  include, but are not limited to, polypropylene, sand, silica, glass, and/or metal and/or any combination thereof. Material examples of polymeric base material  50  include, but are not limited to, polyurethane, acrylic, enamel, and/or epoxy and/or any combination thereof. The terms, “larger” and “smaller” are being used solely in comparison to each other, i.e., larger particles  46  are relatively larger than smaller particles  48 . 
     Although the actual shape and sizes of particles  46  and  48  may vary, in some examples of coating  24 , most of larger particles  46  have an average large particle thickness  52  of between approximately 440-510 microns, and most of smaller particles  48  have an average small particle thickness  54  of between approximately 160-180 microns. The terms, “average large particle thickness” and “average small particle thickness” are defined as the cube root of an individual particle&#39;s volume (V) multiplied by 1.25 (i.e., 1.25×V 1/3 ). Thus, in examples where the particle is spherical, the average large particle thickness  52  or average small particle thickness  54  is the sphere&#39;s diameter. In some examples, the particles are irregularly shaped and not spherical. However, the average large or small thickness of an irregularly shaped particle is still defined as the particle&#39;s volume multiplied by 1.25. 
     In some examples, prior to being dried, cured and/or otherwise set, coating  24  is comprised of, by weight, one part smaller particles  48 , three parts larger particles  46 , 36 parts polymeric base material  50 , and 17 parts volatile liquid that evaporates as coating  14  sets. Examples of such volatile liquid include, but are not limited to, water, solvent, ketones and/or acetone and/or a combination thereof. 
     In the example formulation of one part smaller particles  48 , three parts larger particles  46  and 36 parts polymeric base material  50 , particles  46  and  48  are broadly distributed in polymeric base material  50  to create, as shown in  FIGS. 5 and 6 , a plurality of protrusions  56  intermingled with or otherwise distributed on deck  14  to provide a plurality of coating areas  58  void of particles (e.g., void of particles  46  and  48 ). The term, “broadly distributed” means that many of particles  46  and  48  are sufficiently spaced apart to create coating areas  58  void of particles  46  and  48 . In some examples, as shown in  FIG. 6 , the plurality of protrusions  56  create a plurality of raised areas  60 , and the plurality of coating areas  58  void of particles cover relatively more area on the deck&#39;s upper surface  40  than do the plurality of raised areas  60 . The term, “void of particles” specifically means void of particles  46  and  48 . Coating areas  58  void of particles may include other particles of inconsequential size. 
     In the illustrated example, most of particles  46  and  48  are completely embedded within and thus fully covered by polymeric base material  50 . This helps ensure that traffic on deck plate  14  does not readily dislodge particles  46  and  48  from deck  14  and/or polymeric base material  50 . 
     In addition to traffic, deck  14  and coating  24  can experience adverse thermal loads, temperature differentials and/or thermal shocks due to a number of factors. In some installations, as shown in  FIG. 1 , coating  24  is exposed to indoor air  62  at an indoor temperature (e.g., room temperature), and the deck&#39;s bottom side or lower surface  42  is exposed to outdoor air  64  at an outdoor temperature (e.g., different than the indoor temperature). Lower surface  42  being exposed to the outdoor temperature means that at least some outdoor air  64  reaches lower surface  42 . Dock lever  12  being exposed to both indoor and outdoor air can create a temperature differential between coating  24  and the deck&#39;s lower surface  42 . Depending on the positive or negative magnitude of the temperature differential and the dew points of the indoor and outdoor air, condensation might accumulate on either coating  24  or on the deck&#39;s lower surface  42 . Condensation on coating  24  can reduce traction, and condensation on lower surface  42  can promote corrosion. 
     Additionally, repeatedly opening and closing door  18  in proximity with deck plate  14  and repeatedly raising and lowering deck  14  can create air currents that suddenly change the temperature of coating  24  and lower surface  42 . Such temperature changes create thermal expansion in coating  24  and deck plate  14 , which might urge coating  24  to separate from the deck&#39;s upper surface  40  if there is an imbalance in the relative thermal expansion between coating  24  and deck plate  14 . 
     In some examples, to mitigate the unfavorable effects of various thermal adversities, a coating thickness  66  (thickness at coating areas  58 ), the thermal conductivity of base material  50 , plate thickness  38 , and the plate&#39;s thermal conductivity are such that for a given temperature differential between the indoor air temperature at the coating&#39;s topside  68  and the outdoor air temperature at the deck&#39;s lower surface  42 , the median temperature of the temperature differential is focused near the deck&#39;s upper surface  40 , which is at the transition between coating  24  and deck plate  14 . This allows coating  24  and deck plate  14  to share more equally a given temperature differential, rather than coating  24  or deck plate  14  having to endure nearly all the thermal load. In examples where base material  50  has a lower thermal conductivity than deck plate  14 , it may be beneficial to have the median temperature above the deck&#39;s upper surface  40 . However, if the median temperature is excessively above the deck&#39;s upper surface  40 , that may be the consequence of an excessively thick coating  24 , and an excessively thick coating  24  might be too soft to withstand heavy traffic. 
     In some examples, to have the median temperature occur at or somewhat above deck surface  40 , coating thickness  66  at area  58 , the thermal conductivity of base material  50 , plate thickness  38  and the plate&#39;s thermal conductivity are chosen such that a first thickness/conductivity ratio (defined as plate thickness  38  divided by the plate&#39;s thermal conductivity) is less than a second thickness/conductivity ratio (defined as coating thickness  66  at area  58  divided by the thermal conductivity of base material  50 ). Thus, the second thickness/conductivity ratio divided by the first thickness/conductivity ratio is, in some examples, greater than one. Although the units of measure for thickness and thermal conductivity are irrelevant per se, the units of measure, of course, are the same for meaningful comparison of two like features of thickness, thermal conductivity, and ratios thereof. For example, thickness comparisons may involve comparing inches to inches, or millimeters to millimeters, but not millimeters to centimeters. 
     In one example, deck plate  14  has a plate thickness  38  of about ¼ inches, a thermal conductivity of about 43 W/m-K, and a coefficient of thermal expansion of about 13×10 6  m/m-K; and coating  24  has a coating thickness  66  of 0.002 inches, with polymeric base material  50  having a thermal conductivity of 0.2 W/m-K and a coefficient of thermal expansion of about 70×10 6  m/m-K. This particular example provides deck plate  14  with a first thickness/conductivity ratio of 0.0058 (0.25/43=0.0058) and provides coating  24  with a second thickness/conductivity ratio of 0.0100 (0.002/0.2=0.0100), whereby the second thickness/conductivity ratio (0.0100) divided by the first thickness/conductivity ratio (0.0058) equals 1.7, which is greater than one. 
     Various examples of dock leveler system  10  include, plate thickness  38  ranging between about 3/16 to ⅜ inches, a thermal conductivity of deck plate  14  ranging between about 20 to 80 W/m-K, a coefficient of thermal expansion of deck plate  14  ranging between about 5×10 6  to 30×10 6  m/m-K, a coating thickness ranging between about 0.001 to 0.006 inches, base material  50  having a thermal conductivity ranging between about 0.1 to 0.4 W/m-K, a coefficient of thermal expansion of base material  50  ranging between about 30×10 6  to 140×10 6  m/m-K, and the second thickness/conductivity ratio of plate  14  divided by the first thickness/conductivity ratio of coating  24  ranging between approximately one and four. In examples where base material  50  has a coefficient of thermal expansion greater than that of deck plate  14 , and the indoor temperature is warmer than the outdoor temperature (e.g., in colder climates), the relative coefficients of thermal expansion allows coating  24  to readily expand as the deck&#39;s upper surface  40  expands more than its lower surface  42 . 
     In some cases, after prolonged use of dock leveler system  10 , it can be beneficial to identify one or more stages of coating wear caused by, for example, forklift  20  repeatedly traveling over coated deck plate  14 . To this end, in some examples, polymeric base material  50  is of a different color than that of particles  46  and/or  48  so that coating  24  provides color changes as coating  24  wears down, as shown in  FIG. 7 . In some examples, for instance, base material  50  is green, larger particles  46  are red and smaller particles  48  are blue. In this particular example, coating  24  initially is green but begins turning red as larger particles  46  are exposed due to abrasion or wear of green base material  50  that had been covering the red larger particles  46 . In this example, further abrasion or wear will exposes the smaller blue particles  48 , so coating  24  will begin turning blue as coating  26  wears and exposes the smaller particles  48 . 
     The timing or degree of color changes, in some examples, is dependent on the relative sizes of the larger and smaller particles. To provide an appreciable time span between the first exposure of red particles and subsequent exposure of blue particles, in some examples, the average large particle volume of larger particles  46  is more than ten times greater than the average small particle volume of smaller particles  48 . Consequently, in some examples, the color changes indicate various degrees of coating wear and serve as signals that coating  24  may need to be reapplied or touched up. 
       FIGS. 8-10  show various methods associated with dock leveler system  10 .  FIG. 8  shows a spray nozzle  70  being used for spraying simultaneously base material  50  and particles  46  and  48  onto upper surface  40  of deck plate  14 . To reduce the chance of one or two particles plugging an orifice  72  of nozzle  70 , orifice  72  has an open cross-sectional orifice area that is more than two times greater than a maximum cross-sectional area of an average sized particle of the plurality of larger particles  46 . In some examples, the orifice area is round with a diameter of 2.5 millimeters (about 0.1 inches) to spray a larger particle  46  having an approximate diameter of 0.02 inches.  FIG. 8  with further reference to  FIGS. 5 and 6  illustrate distributing particles and  46  and  48  within base material  50  to create the plurality of protrusions  56  intermingled with and/or distributed relative to the plurality of coating areas  58  void of particles  46  and  48 .  FIGS. 9 and 10  with further reference to  FIGS. 5 and 6  illustrate the polymeric base material  50  completely covering most of particles  46  and  48 . Clock  74  in  FIG. 9  schematically illustrates allowing polymeric base material  50  to set, thereby creating coating  24  on the deck&#39;s upper surface  40 . Arrow  76  in  FIG. 10  illustrates installing deck plate  14  in proximity with vertically movable door  18  at loading dock platform  16 . Arrow  78  in  FIG. 10  and arrows  80  in  FIG. 1  illustrate repeatedly opening and closing door  18 . Arrows  82  in  FIG. 2  illustrate repeatedly lifting and lowering deck plate  14  relative to loading dock platform  16 . In  FIG. 1 , arrows representing indoor air  62  and outdoor air  64  illustrate simultaneously exposing coating  24  to a first temperature and exposing lower surface  42  of deck plate  14  to a second temperature, thereby subjecting deck plate  14  and coating  24  to a temperature differential. Arrows  84  in  FIG. 3  with further reference to  FIGS. 5 and 7  illustrate abrading coating  24  by repeatedly traveling over deck plate  14  and coating  24  changing color as a consequence of the abrading and exposing at least some of the plurality of larger particles  46 . 
     It should be noted that references to “thickness” means an average thickness. Values of thermal conductivity for given materials are with reference to the materials being at 25 degrees Celsius. Values of coefficient of thermal expansion for given materials are with reference to the materials being at 21 degrees Celsius. 
     Although certain example methods, apparatus and articles of manufacture have been described herein, the scope of the coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.