Patent Application
20050199158
Air cargo pallets are commonly used to support and secure cargo during transportation via aircraft, ground vehicles, and ships. A widely used air cargo pallet is made of a base sheet of aluminum with edge rail extrusions at each side or edge.
The base sheet of a typical air cargo pallet is often subjected to service-induced “oil canning.” Oil canning is a condition where an otherwise substantially flat metal sheet becomes slightly deformed. Oil canning can result from residual stresses induced or redistributed during production, slitting, perforating, forming, or fabrication of the metal sheets. Improper handling, as well as routine service, can also cause oil canning. Oil canning of the base sheet of an air cargo pallet can be detrimental to the pallet's operation. After a certain degree of deformation occurs, the pallet becomes unusable.
Oil canning of the base sheet of an air cargo pallet often results from stresses induced on the bottom surface of the base sheet that occur during repetitive service cycles. Air cargo pallets, and the containers that they support, are typically used to transport up to 15,000 pounds (or more) of cargo, and are generally conveyed over a variety of conveying surfaces and devices. For example, air cargo pallets may be conveyed on roller ball conveyors. These conveyors make rolling point contact with the bottom surface of the base sheet. This rolling point contact induces bending stresses in the bottom surface of the base sheet, which may eventually lead to permanent deformation of the base sheet as the yield strength of the base sheet is exceeded by the compressive forces applied by the roller balls.
To reduce the effects of oil canning, the bottom sheets of air cargo pallets are often made from a high strength aluminum alloy, such as aluminum alloy 7075T6. While this high strength aluminum alloy has been relatively effective at preventing substantial oil canning in a pallet's base sheet, it is typically expensive and/or in short supply. Thus, durable air cargo pallets may be relatively expensive to manufacture. A need exists for a more cost-effective, durable air cargo pallet.
An air cargo pallet includes one or more reinforcing strips attached to a top surface of the base sheet of the pallet. The reinforcing strip divides the unsupported area of the base sheet into two substantially equal sections. This reduces the effects of “oil canning” on the base sheet, and allows the use of lower-cost metals for forming the base sheet. The reinforcing strip may run substantially across the width and/or the length of the base sheet.
Other features and advantages of the invention will appear hereinafter. The features of the invention described above can be used separately or together, or in various combinations of one or more of them. The invention resides as well in sub-combinations of the features described.
In the drawings, wherein the same reference number indicates the same element throughout the several views:
As shown in
The air cargo pallet 10 typically has a length L of approximately 100 to 150 inches, and a width W of approximately 80 to 100 inches. The pallet may also be made to a standard size with a length of approximately 108 inches or 125 inches, and a width of approximately 88 or 96 inches.
Referring to
A reinforcing strip 30 is attached to the upward-facing, or top, surface of the base sheet 14 via screws 32, rivets, or other suitable fastening means. The reinforcing strip 30 in the design shown is located substantially at or near the longitudinal centerline L of the base sheet 14 (or pallet 10), and runs substantially across the entire width X of the base sheet 14. The reinforcing strip is preferably made of metal, such as aluminum or steel, but may also be made from another material. The reinforcing strip 30 may be a tie bar, or any other suitable reinforcing device or structure. The reinforcing strip or strips generally are parallel to the shorter sides of the pallet.
Oil canning of a metal sheet, in general, is inversely proportional to the yield strength of the metal sheet, and is directly proportional to the sheet's unsupported surface area, its moment of inertia (i.e., the cube of its thickness), and the loads applied. The reinforcing strip 30 divides the unsupported surface area of the base sheet 14 into two sections. As a result, oil canning of the base sheet 14 is reduced by approximately one half (assuming that all other factors are equal). This can in principle effectively double the service life of the base sheet 14.
Oil canning also tends to deform the base sheet. This can cause the edge rails to lift up, making the pallet unusable. With the base sheet 14 divided into two pieces, the tendency for the edge rails to lift up is reduced. This prolongs the service of the pallet.
In addition, pallet designs including a reinforcing strip allow for the use of lower strength, lower cost, and more readily available aluminum alloys as the base sheet material. For example, the base sheets of many conventional air cargo pallets are made from heat-treated aluminum alloy 7075T6, with a thickness of approximately 0.160 inches. By including a reinforcing strip 30 on the base sheet 14, similar resistance to oil canning can be achieved using other aluminum alloys having lower yield strength, with only a slightly greater base sheet thickness.
Other aluminum alloys are typically significantly less costly than aluminum alloy 7075T6 and is also more easily obtained (regardless of cost). Thus, the use of other aluminum alloys provides substantial cost savings, particularly when several air cargo pallets are being produced. Since other aluminum alloys have lower strength in comparison to aluminum alloy 7075T6, base sheets made of other aluminum alloys can be made slightly thicker, to achieve equivalent strength. This increase in thickness, however, does not also result in a proportional increase in weight, because other aluminum alloys typically weigh less than aluminum alloy 7075T6. As one example, a base sheet of aluminum alloy 5083H24P is used instead of aluminum alloy 7075T6. The 5083H24P base sheet is 8% thicker than the 7075T6 base sheet. The aluminum alloy 5083H24P, however, is approximately 4.5% lighter than aluminum alloy 7075T6. Accordingly, using the lower cost and more abundant aluminum alloy 5083H24P as the base sheet increases the overall weight by only approximately 3.5%. This is relatively insignificant compared to the considerable cost savings that are realized by using the lower cost alloy. Various other examples using other lower cost aluminum alloys can also be made. The term other aluminum alloys as used here means aluminum alloys having a yield strength less than the yield strength of 7076T6 aluminum alloy.
In an alternative embodiment, the overall base sheet structure of the air cargo pallet 10 includes two coplanar smaller base sheets 14′, as illustrated in
The interior adjoining sides 34 of the two smaller base sheets 14′ may abut or contact each other, and are joined together via the reinforcing strip 30. As shown in
Any suitable number of base sheets and/or reinforcing strips may be included in the air cargo pallet 10. For example, a single base sheet 14 may include a single reinforcing strip 30, or may include two or more reinforcing strips 30. If two or more reinforcing strips 30 are used, the reinforcing strips 30 can be spaced approximately equidistantly from one another, and from the outer edges of the pallet 10. However, the reinforcing strips 30 may be arranged in other ways as well, to better meet the design requirements of any specific pallet.
The pallet's overall base sheet structure may include one base sheet 14, two base sheets 14′, or three or more base sheets. Each pair of adjacent base sheets is preferably, but not necessarily, joined by a reinforcing strip 30. Alternatively, only a single reinforcing strip 30 may be included on the overall base sheet structure of the air cargo pallet 10, regardless of the number of base sheets used. Thus, various combinations and numbers of base sheets and reinforcing strips 30 may be used. The base sheet thickness when using other aluminum alloys will generally be about 0.16 or 0.17 to about 0.25 inches. As shown in
In another alternative embodiment, one or more reinforcing strips may run lengthwise across the one or more base sheets of the air cargo pallet 10, as opposed to, or in addition to, running widthwise across the one or more base sheets. The lengthwise reinforcing strip(s) may run substantially across the entire length of the base sheet (or of the combined base sheets), or may run a shorter distance.
The inclusion of one or more reinforcing strips substantially reduces the unsupported area of the one or more base sheets of an air cargo pallet, and therefore significantly reduces oil canning in the base sheet(s). As a result, the service life of the base sheet, and the pallet itself, may be dramatically increased. Furthermore, lower cost materials, having a lower yield strength than conventional base sheet materials, may be used to form the base sheet(s), thus significantly reducing the total cost of the air cargo pallet.
The preferred dimensions and materials of the various components of the air cargo pallet 10 may vary depending on specific design requirements. Accordingly, any pallet having one or more base sheets having a reinforcing strip or element is within the scope of the invention.
While embodiments and applications of the invention have been shown and described, it will be apparent to one skilled in the art that other modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except to the following claims and their equivalents.
