US20040031793A1

US20040031793A1 - Plastic load container

Info

Publication number: US20040031793A1
Application number: US10/640,722
Authority: US
Inventors: Marcelo Garcia
Original assignee: Menasha Corp
Current assignee: Menasha Corp
Priority date: 2002-08-16
Filing date: 2003-08-14
Publication date: 2004-02-19

Abstract

A load container is formed of one or more plastic or plastic composite panels so that it is lighter than typical metal load containers and can be easily shipped and repaired. The load container can be part of a vehicle having a vehicle frame and at least one wheel supporting the vehicle frame by engaging the ground or a rail, for example. A load container frame is supported by the vehicle frame, and a plurality of the panels are secured to the load container frame with an edge of each panel adjacent an edge of another panel, possible with sealant or coupling media therebetween. Methods of making such wall panels and vehicles having load containers so formed as well as methods of repairing and assembling such load containers are also disclosed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit to U.S. provisional application Ser. No. 60/404,065 filed on Aug. 16, 2002.[0001]

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to load containers, and more particularly to load containers made of one or more generally plastic panels, and even more particularly to such load containers forming a part of transport vehicles.

2. Description of the Related Art

Containment devices, such as bins, hoppers and large silos, and large containers on transport vehicles, such as trucks and railcars, are often used to contain and transport bulk materials, such as powdered cement. Container trucks, for example, typically include a tractor which pulls a trailer having a load container fixed thereto. The load container is typically formed from a metal skin which defines a load container volume. The load, such as the powdered cement, is contained within the volume while being transported by the truck.

The heavy metal load container increases the overall weight of the vehicle, and thus decreases the load capacity of the truck. Moreover, the increased weight reduces the fuel mileage of the vehicle, thus increasing operating costs for transporting the load. Non fluid loads being transported in the container can stick to the metal which complicates unloading the container. In addition, if a portion of the load container is damaged, the load container must be replaced or repaired.

Replacing the damaged metal load container is very expensive. If the damage is minor, the damaged area can be cut out using a torch and a patch can be welded onto the exterior of the load container. If the load container had been transporting a powder or other explosive material, however, using a torch or welding equipment is extremely dangerous. Moreover, even with a patch, the repaired area is unsightly, and is a constant reminder of the prior damage.

One known solution for reducing the weight of the load container is disclosed in U.S. Pat. No. 6,076,693 which discloses a molded, one piece, completely integral load container for transporting bulk materials. A large, molded, one piece, load container is extremely bulky and expensive to ship from the molder to a vehicle manufacturer for assembling with the vehicle. Moreover, if the load container is damaged, as in metal load containers, the entire container must be replaced or subject to unsightly repairs. Therefore, a need exists for a lightweight load container that can be easily shipped for assembling into a vehicle, and that can be easily repaired without leaving unsightly evidence of the repair.

SUMMARY OF THE INVENTION

The present invention provides a vehicle having a load container which is lighter than typical metal load containers and which can be easily shipped and repaired. One or more plastic or plastic composite panels form a load container having a volume for containing a load, wherein each panel has at least one edge adjacent an edge of an adjacent panel.

A general objective of the present invention is to provide a vehicle having a load container which is lighter than a metal load container having a similar volume and load capacity. This objective is accomplished by providing a vehicle having a vehicle frame supporting a load container frame onto which a plurality of plastic panels are secured to form a load container.

Another objective of the present invention is to provide a load container vehicle suitable for use on existing roadways and railways. This is accomplished by the vehicle frame being a truck frame rotatably mounting a plurality of ground engaging wheels for contacting a ground surface, or a railcar frame rotatably mounting a plurality of rail engaging wheels riding one or more rails.

Another object of the present invention is to provide a method of making a vehicle having a load container. This is accomplished by attaching at least one rotatable wheel and a load container frame to a vehicle frame, and then attaching a plurality of plastic panels in an edge to edge fashion to the load container frame to form the load container. Preferably, at least one of the panels is fixed to the load container frame by at least one bolt received in a countersunk hole formed in a surface of the plastic layer at the interior surface of the load container. The countersunk hole can be formed in the plastic layer so that the bolt(s) are capped by a non-metallic cap that is substantially flush with the interior surface of the load container.

Another objective of the present invention is to provide a method for repairing a load container. This objective is accomplished by forming the load container using replaceable panels.

Yet another objective of the present invention is to provide a composite wall panel, and method of making same, for use in making a load container. This is accomplished by pressing a reinforcement layer between two layers of plastic. In one preferred method this includes adhering a pre-pressed sheet to a reinforcement sheet and then pressing a plastic resin together with the adhered pre-pressed and reinforcement sheets so as to form a uniform homogenous composite. Preferably, the reinforcement sheet is metal and the sheet and resin are an ultra high molecular weight polyethylene, such as TIVAR®, preferably having a low coefficient of friction and other flow promoting properties. The plastic layers form the exterior and interior surfaces of the wall panel and thereby the load container. The reinforcement layer is preferably disposed entirely between the plastic layers so as not be exposed and thereby avoid corrosion.

These and still other advantages of the invention will be apparent from the detailed description and drawings. What follows are preferred embodiments of the present invention. To assess the full scope of the invention the claims should be looked to as the preferred embodiments are not intended as the only embodiments within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a vehicle incorporating the present invention; [0017]
FIG. 2 is a perspective view of the vehicle of FIG. 1; [0018]
FIG. 3 is a detailed cross-sectional view of a joint between the panels of FIG. 1; [0019]
FIG. 4 is a detailed cross-sectional view of an alternative joint between panels of FIG. 1; [0020]
FIG. 5 is a detailed cross-sectional view of another alternative joint between panels of FIG. 1; [0021]
FIG. 6 is an exploded perspective view of a connection between the panels and load container frame of FIG. 1; [0022]
FIG. 7 is a detailed cross-sectional view of an alternative joint between panels of FIG. 1; and [0023]
FIG. 8 is a detailed cross-sectional view of a joint similar to that shown in FIG. 5 albeit for panels made of a reinforced plastic composite material.[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an improved plastic load container made of one or more plastic panels joined in an edge to edge fashion. The panels can be entirely plastic, or more preferably, can be a plastic composite having an internal reinforcement layer. The load containers can be used in stationary and transportable applications. For example, the load containers can be storage bins, hoppers, large silos or liners for silos. The load containers can also be part of a vehicle, including any transport machinery suitable for carrying loads, including but not limited to trucks and trailers having wheels engaging the ground or roadway and railcars in which the wheels engage one or more rails or tracks. The figures and the following description disclose a preferred load container vehicle. [0025]
A [0026] vehicle 10, described herein and shown in FIGS. 1 and 2 as a truck, includes a vehicle frame 12 supported by wheels 14 at one end and a tractor 16 at the other end. The vehicle frame 12 supports a load container 18 for containing a load, such as a powder, or other solid, a liquid, a gas, and the like. The load container 18 is formed from a plurality of generally non-metallic wall panels 20 supported by a load container frame 22 fixed to the vehicle frame 12. Advantageously, the panels 20 can be formed from a plastic or reinforced plastic composite (as shown in FIG. 8) material having desirable weight and strength characteristics to reduce operating costs of the vehicle and having flow promoting properties to enhance unloading operations of the container. The term “plastic panel” is defined herein to mean a planar or non-planar wall having opposite face surfaces that are at least in part made of plastic, specifically including, but not limited to, entirely plastic and fibrous or metal reinforced plastic structures and composites.
The [0027] vehicle frame 12 is preferably formed from steel members, as is known in the art, and can be detachable from the tractor 16. If the vehicle frame 12 is detachable from the tractor 16 as shown in FIGS. 1 and 2, landing gear 30 or additional ground engaging wheels can be provided to support the other end of the vehicle frame 12. Of course, the vehicle frame 12 can be fixed to a tractor to form an integral unit, such as a straight truck, without departing from the scope of the invention.
The ground engaging wheels [0028] 14 are joined to the vehicle frame 12 using methods well known in the art. In the embodiment disclosed herein, a pair of ground engaging wheels 14 are rotatably mounted on each end of a pair of axles 24 fixed to the vehicle frame 12. Of course, the number of wheels depends upon the desired load capacity of the vehicle body, and the frame can be supported by one or more wheels without departing from the scope of the invention.
The [0029] load container 18 is supported by the vehicle frame 12, and includes the plurality of panels 20 secured to the load container frame 22. Preferably, the load container frame 22 is formed from spaced steel structural members 26 joined by cross members 28 which maintain the spacing between the structural members 26. The cross members 28 and structural members 26 form a framework for attaching the panels 20 thereto. The members 26, 28 can be joined to the vehicle frame 12 and each other using methods known in the art, such as bolting, welding, and the like.
The [0030] panels 20 are secured to the load container frame members 26, 28, and in one preferred embodiment, are formed from a solid plastic material. Forming the panels from a High Density Polyethylene (HDPE) or more preferably from an Ultra High Molecular Weight Polyethylene (UHMW-PE), such as TIVAR® 88 and TIVAR 88-2 available from Poly Hi Solidur Inc. of Fort Wayne, Ind., is preferred for its high strength, light weight, and flow promoting characteristics. The TIVAR preferably has a low coefficient of friction, in the range of about 0.1 to 0.2, with a preferred dynamic coefficient of friction between about 0.1 and 0.15. Strengthening members (not shown), such as metal, glass fibers, and the like can be embedded in the panels 20 to provide additional strength, if required for a particular application. In addition, panel thickness can vary depending upon the particular application.
As shown in FIG. 8, the [0031] panels 20 can be formed of as a uniform homogenous composite including a plastic layer 70, a layer 72 of reinforcement material and another plastic layer 74. The composite material is formed by pressing the reinforcement layer between two layers of plastic. The reinforcement layer 72 is disposed between the plastic layers 70 and 74, and thus is not visible. The plastic layer 70 of the composite panel 20 forms an exterior surface 80 of the panel 20 and thereby of the load container 18 and the plastic layer 74 forms an interior surface 48 of the panel 20 and load container 18.
Preferably, the [0032] reinforcement layer 72 is expanded or perforated metal, however, fiberglass or other non-metal rigidifying materials could be used. In the case of a metal reinforcement layer, the plastic layers 70 and 74 preferably entirely encapsulate the reinforcement layer 72 to prevent corrosion from moisture within the load container or to its exterior. The plastic layers 70 and 74 are preferably an ultra high molecular weight polyethylene, such as TIVAR described above.
In one preferred form, the plastic layer [0033] 70 is a pre-pressed plastic, preferably TIVAR, sheet. The pre-pressed plastic aids in forming the composite and helps provide a constant thickness of plastic on each side of the reinforcement layer, particular at the side that faces the bottom of the mold. Thus, in one preferred method, the pre-pressed sheet is inserted into the bottom of the mold. The sheet preferably has an adhesive backing, which could be an ultra high molecular weight adhesive tape, that allows the reinforcement to be adhered to the pre-pressed sheet either before or after it is placed into the mold. Plastic resin powder is than poured onto the reinforcement and pre-pressed sheet as needed to achieve the desired wall thickness of the composite panel. A top part of the mold is closed against the bottom part to enclose these materials. These materials are then heated and pressurized using a known pressing operation to form a uniform homogenous reinforced plastic composite. It should be noted that plastic layer 70 could be formed with powdered resin, rather than a pre-pressed sheet, provided suitable techniques were employed to ensure that the reinforcement layer was disposed between two plastic layers. Inserting spacers or risers between the bottom of the mold and the reinforcement layer would be one such technique.
The composite panel construction of FIG. 8 offers several advantages over conventional steel skin and even some advantages over the plastic only panels described herein. The composite material, like the all plastic panels, does not corrode and is smoother at the interior of the [0034] load container 18 than conventional steel skins so as to reduce the occurrence of the load sticking to the panels, and thereby promote dispensing of the load in the load container. It is also stronger than steel skins and is stronger and has improved anti-sagging characteristics than plastic only panels. The composite panel can be configured for various strengths not only by changing the thickness of the plastic but also by changing the thickness, type or configuration of the reinforcement. The pressing operation forms a consistently thick, homogeneous monolithic panel, flat or of any mold formed non-planar configuration, such that there are no problems with expansion and contraction of different materials as would be the case if a separate metal reinforcement was simply mechanically mounted to the plastic.
The following description is applicable for [0035] panels 20 having the plastic only or the reinforced plastic composite construction. As shown in FIGS. 1-3 and 8, the panels 20 are arranged in an edge 32 to edge 32 relation forming a joint 36 between the panels 20, and defining a volume for containing the load. Each panel 20 is formed using methods known in the art, such as molding, shaping, and the like, to provide a portion of an interior surface 48 of the load container 18 defining the load volume. The panels 20 can be planar or non-planar depending upon the desired load container shape and volume. For example, as shown in FIG. 2, an end panel 34 can be cup shaped to form an end of a closed container.
Preferably, the [0036] panels 20 are formed such that the joints 36 between adjacent panels 20 are aligned with, or adjacent to, a load container frame member 26, 28 for attachment of the adjacent panels thereto. In the embodiment disclosed herein, the panels 20, 34 define an enclosed volume for carrying a powder, liquid, and or gas. Of course, the defined volume can have an open top or ends to accommodate bulky, solid materials without departing from the scope of the invention.
Advantageously, if the [0037] load container panels 20, 34 are damaged, individual damaged panels 20, 34 can be removed and replaced to provide a repaired load container without obvious evidence of the repair. Moreover, each individual panel 20, 34 can be formed more easily than a larger, single piece, molded load container. In addition, shipping panels 20, 34 which form part of the load container 18 to a vehicle assembler or repair site is easier and less expensive than shipping an entire replacement load container molded as a single piece.
If a fluid-tight load container is not required, such as when transporting a powder, adjacent edges [0038] 32 of adjacent panels 20 can abut one another to form the load container joint 36, such as shown in FIG. 3. Of course, if a tighter joint 36 is requires, a tongue 38 in groove 40 construction, such as shown in FIG. 4, can be used. Advantageously, if a tongue and groove construction is used with at least some of the panels, not all of the panels need be secured to the load container frame 22. To provide an even more impervious joint 36 for transporting fluids, such as a gas or liquid, a gasket 42, or other sealant, such as a pourable caulk, can be provided between adjacent panels 20, such as shown in FIG. 5. Of course, the panels 20 can be welded together to close the joint 36.
As shown in FIGS. [0039] 3-6 and 8, the panels 20 are secured to the load container frame 22 using countersunk bolts 44 which do not protrude into the volume defined by the panels 20. Preferably, each bolt 44 includes a cap 46 which is substantially flush with the load container interior surface 48 to minimize obstructions on the load container interior surface 48. Most preferably, the cap 46 is formed from a flow promoting material, such as HDPE or UHMW-PE. Of course, protrusions into the volume may be desired when transporting fluid loads, for example ridges can be provided in load containers transporting slurries to minimize surging. Accordingly, bolts, and other structure can extend into the load container volume without departing from the scope of the invention. A nut 60 and washers 62, preferably the washer adjacent to the nut 60 is steel and the other is plastic (such as TIVAR), are provided to secure the bolt 44 in place.
In the embodiment disclosed herein, as shown in FIGS. 1 and 2, funnels [0040] 50 or hoppers formed in the bottom 52 of the load container 18 provide discharge ports for unloading the load container 18. Each funnel 50 is formed from a flow promoting material, such as HDPE or UHMW-PE, and is joined to, and forms part of, the load container 18. Preferably, support structure fixed to the truck and/or load container frame 12, 22 supports each funnel 50. Most preferably, each funnel 50 is formed from panels 20, such as used to form the load container 18. Valves (not shown) fixed to each funnel bottom are provided to control the flow of material through each funnel 50, as is known in the art. Although a plurality of funnels are disclosed, any number of funnels an be provided, as required for the particular application, without departing from the scope of the invention.
In an alternative embodiment shown in FIG. 7, [0041] flanges 56 formed proximal the panel edges 32 can be provided for attachment to the structural members 26, 28. Advantageously, bolts 58 extending through a pair of adjacent flanges 56 can be provided to draw the panel edges 36 together to form a tight joint 36 between the adjacent panels 20.
In another embodiment, at least a portion of the load container frame is disposed inside the container volume to provide a relatively smooth exterior load container surface. In this embodiment the countersunk bolts do not protrude outwardly from the panels. Preferably, caps are fixed to the countersunk bolt to provide the relatively smooth exterior load container surface. [0042]
It should be appreciated that merely preferred embodiments of the invention have been described above. However, many modifications and variations to the preferred embodiments will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiments. To ascertain the full scope of the invention, the following claims should be referenced. [0043]

Claims

What is claimed is:

1. A wall panel of a load container having a volume defined by one or more of the wall panels, comprising:

a first plastic layer forming one surface of said wall panel;

a second plastic layer forming an opposite surface of said wall panel; and

a reinforcement layer at least in part disposed between said first and second plastic layers;

wherein said first and second plastic layers and said reinforcement layer form a uniform homogenous composite wall panel.

2. The wall panel of claim 1, wherein said load container is defined by a plurality of said wall panels arranged in an edge to edge fashion.

3. The wall panel of claim 2, wherein said one surface of said wall panel formed by said first plastic layer is an exterior surface of said load container and wherein said opposite surface of said wall panel formed by said second plastic layer is an interior surface of said load container.

4. The wall panel of claim 1, wherein said load container is selected from the group of containers including hoppers, storage bins and silos.

5. The wall panel of claim 1, wherein the load container is selected from a group of transportable containers including a truck mounted load container and a railcar mounted load container.

6. The wall panel of claim 5, wherein said load container is a truck mounted load container and further including a vehicle frame mounting a load container frame mounting said load container.

7. The wall panel of claim 1, wherein at least one of said first and second plastic layers is polyethylene.

8. The wall panel of claim 7, wherein said polyethylene is an ultra high molecular weight polyethylene.

9. The wall panel of claim 8, wherein said ultra high molecular weight polyethylene is TIVAR.

10. The wall panel of claim 9, wherein the first and second plastic layers are TIVAR.

11. The wall panel of claim 1, wherein said reinforcement layer is metal.

12. The wall panel of claim 11, wherein said reinforcement layer is an expanded metal.

13. The wall panel of claim 1, wherein said first plastic layer is made from a pre-pressed plastic sheet.

14. The wall panel of claim 13, wherein said pre-pressed plastic sheet is adhered to said reinforcement layer.

15. The wall panel of claim 14, wherein an ultra high molecular weight plastic tape adhesive is disposed between said pre-pressed plastic sheet and said reinforcement layer.

16. The wall panel of claim 15, wherein said first and second plastic layers are ultra high molecular weight polyethylene.

17. The wall panel of claim 16, wherein said first and second plastic layers are TIVAR.

18. The wall panel of claim 1, wherein said second plastic layer defines a surface of said wall panel defining an interior surface of said load container and has a coefficient of friction of no more than about 0.2.

19. A method of making a composite wall panel for a load container, wherein said load container is formed from a plurality of panels defining a load container volume, said method comprising:

inserting a pre-pressed plastic sheet into a mold;

setting a reinforcement layer against said pre-pressed plastic sheet;

inserting plastic resin into said mold at least onto said reinforcement layer; and

closing said mold with said plastic sheet, said reinforcement layer and said plastic resin inside;

heating and pressurizing said mold to form a composite wall panel having said reinforcement layer disposed between a plastic layer formed of said pre-pressed plastic sheet and another plastic layer formed of said plastic resin.

20. The method of claim 19, wherein said reinforcement sheet is metal.

21. The method of claim 20, wherein said plastic resin is an ultra high molecular weight polyethylene.

22. The method of claim 21, wherein said pre-pressed plastic sheet is an ultra high molecular weight polyethylene.

23. The method of claim 22, further including adhering the reinforcement layer to said pre-pressed plastic sheet.

24. A method of repairing a load container, wherein said load container is formed from a plurality of plastic panels defining a load container volume, said panels being secured to a load container frame, and at least one of said panels is damaged, said method comprising:

detaching the at least one damaged panel from the load container frame; and

replacing said at least one damaged panel with at least one undamaged panel; and

securing said at least one undamaged panel to the load container frame.

25. A method of making a vehicle having a vehicle frame supporting a load container frame in turn supporting a load container, comprising the steps of:

rotatably mounting at least one wheel to said vehicle frame;

mounting said load container frame to said vehicle frame; and

attaching a plurality of plastic panels in an edge to edge fashion to said load container frame and forming said load container having a volume for containing a load.

26. The method of claim 25, wherein said plurality of plastic panels are a composite material including a reinforcement layer disposed between two plastic layers.

27. The method of claim 26, wherein said reinforcement layer is metal.

28. The method of claim 27, wherein said plastic layers are made of an ultra high molecular weight polyethylene.

29. The method of claim 28, wherein the ultra high molecular weight polyethylene is TIVAR.

30. The method of claim 28, wherein at least one of said plastic layers is formed from a pre-pressed plastic sheet.

31. The method of claim 25, wherein at least one of said panels is fixed to said load container frame by at least one bolt received in a countersunk hole formed in a surface of one of said plastic layers at an interior of said load container.

32. The method of claim 31, wherein said at least one bolt is capped by a non-metallic cap which is substantially flush with said surface.

33. A load container for mounting to a vehicle, said load container comprising:

a load container frame formed from spaced apart structural members supported by said vehicle frame; and

a plurality of plastic panels arranged in an edge to edge fashion secured to said load container frame, and forming a load container having a volume for containing a load.

34. The load container of claim 33, wherein a sealing material is interposed between at least one pair of adjacent panels.

35. The load container of claim 34, wherein said sealing material is a gasket.

36. The load container of claim 33, wherein at least one edge of at least one panel includes a tongue received in a groove formed in an edge of an adjacent panel.

37. The load container of claim 33, wherein at least one of said panels of said plurality is made of polyethylene.

38. The load container of claim 33, wherein at least one of said panels is made of a reinforced polyethylene composite having a reinforcement layer disposed between two plastic layers.

39. The load container of claim 33, in which at least one of said panels is non-planar.

40 The load container of claim 33, wherein at least one joint between at least one pair of adjacent panels is welded together.

41. The load container of claim 33, wherein at least one of said panels is fixed to said load container frame by at least one bolt received in a countersunk hole formed in a surface of said load container.

42. The load container of claim 41, wherein said at least one bolt is capped by a non-metallic cap which is substantially flush with said surface.

43. The load container of claim 33, wherein said load container frame includes cross members joined to said structural members to space said structural members apart.

44. A vehicle comprising:

a vehicle frame;

a load container frame supported by said vehicle frame; and

45. The vehicle of claim 44, wherein sealing material is interposed between at least one pair of adjacent panels.

46. The vehicle of claim 44, wherein at least one edge of at least one panel includes a tongue received in a groove formed in an edge of an adjacent panel.

47. The vehicle of claim 44, wherein at least one of said panels is formed from ultra high molecular weight polyethylene.

48. The vehicle of claim 44, wherein at least one of said plurality of plastic panels are a plastic composite material including a reinforcement layer disposed between two plastic layers.

49. The vehicle of claim 48, wherein at least one of said plastic layers is an ultra high molecular weight polyethylene and said reinforcement layer is metal.

50. The vehicle of claim 49, wherein one of said plastic layers is formed from a pre-pressed sheet.

51. The vehicle of claim 44, wherein at least one hopper forms a part of said load container.

52. The vehicle of claim 51, wherein said at least one hopper is formed from at least one non-metallic panel supported by at least one of said vehicle frame and said load container frame.

53. The vehicle of claim 44, wherein at least one of said panels is non-planar.

54. The vehicle of claim 44, wherein at least one joint between at least one pair of adjacent panels is welded together.

55. The vehicle of claim 44, wherein at least one of said panels is fixed to said load container frame by at least one bolt received in a countersunk hole formed in a surface of said load container.

56. The vehicle of claim 55, wherein said at least one bolt is capped by a non-metallic cap which is substantially flush with said surface.

57. The vehicle of claim 44, wherein said load container frame is formed from spaced apart structural members supported by said vehicle frame.

58. The vehicle of claim 57, wherein said load container frame includes cross members joined to said structural members to space said structural members apart.

59. The vehicle of claim 44, wherein said vehicle frame is a truck frame rotatably mounting a plurality of ground engaging wheels for contacting a ground surface.

60. The vehicle of claim 59, further including a tractor is joined to said vehicle frame.

61. The vehicle of claim 44, wherein said vehicle frame is a railcar frame rotatably mounting a plurality of rail engaging wheels for riding on one or more rails.