Trolley wheel tread and flange

BACKGROUND OF THE INVENTION

The invention relates to trolley wheels, and more particularly to trolley wheels for an overhead load lifting apparatus such as a monorail hoist. Conventional overhead lifting apparatus such as monorail hoists include trolleys supported by trolley wheels that ride on a rail. Typically, the rail is some variation of an I-beam that includes a substantially horizontal supporting surface with a flat tread supporting surface on which a trolley wheel rolls. To keep the wheel in the proper position on the tread supporting surface, the wheel includes a flange. If the wheel deviates too far from the proper rolling position on the rail, the flange contacts the sidewall of the rail and forces the wheel to move back into the proper rolling position.

While the tread surface of a trolley wheel is often flat, it has been known to crown the tread surface to produce better rolling contact with the supporting surface of the rail. It is also common to linearly taper the flange of the trolley wheel such that only the flange portion nearest the tread surface would ever contact the sidewall of the rail. Examples of these types of trolley wheels are disclosed in U.S. Pat. Nos. 4,236,456 issued to Schreyer et al., 2,997,996 issued to Chapin et al., 2,584,610 issued to Pearson, and 1,367,706 issued to Loudenslager.

It has also been known to use a gradual non-linear tapering on the flange of the trolley wheel. An example of this type of trolley wheel is disclosed in U.S. Pat. No. 1,869,422 issued to Harris.

SUMMARY OF THE INVENTION

Improper and premature trolley wheel wear is a common problem in many monorail hoist systems. Systems that utIlize a wheel with a flat tread surface rolling on a flat supporting surface often encounter various problems created by a mismatch at the rolling interface. Small variations in the surfaces themselves often cause the wheel to wear unevenly due to mismatched contact between the rail supporting surface and the usually softer wheel tread surface. Interface mismatches are also caused by the forces exerted on the trolley that cantilever the wheel off-center, causing the harder rail to dig into the wheel's tread surface.

This common problem can be alleviated by crowning the wheel's tread surface. Mismatches at the rolling interface are significantly or totally eliminated since the crown reduces the surface areas actually in contact. Variations in the surfaces and cantilevering actions of the wheel do not cause uneven or premature wearing. Crowning the wheel's tread surface will allow the wheel to track and fit itself to the rail as it is being used.

A second common problem associated with the trolley wheels of monorail hoists occurs when the sidewall of the rail comes into excessive contact with the flange. Whether the wheel's tread surface is flat or crowned, forces on the trolley cantilever the wheel such that the sidewall of the rail, and especially the corner where the flat supporting surface meets the sidewall, rubs against or digs into the flange. Ideally, a flange should quickly realign the wheel and stabilize it back into the proper position on the rail. Unfortunately, common tapered flanges achieve this objective only after the rail digs into the flange, or the taper causes the wheel to first “ride-up” on the rail. This excessive contact, often known as “scrubbing,” usually occurs at the point on the flange nearest to the wheel's tread surface.

To alleviate these problems, the present invention provides a heat treated trolley wheel having both a crowned tread surface that prevents uneven and premature wear, and a non-tapered flange that prohibits the rail from digging into the flange and also prohibits the wheel from riding-up on the rail. The flange design incorporates an undercut directly adjacent the wheel's tread surface that prevents the corner of the rail from contacting the flange. The flange design also incorporates a “kick-back” feature; a substantially crowned realigning portion that prevents the wheel from riding-up on the rail. This flange design is extremely effective in realigning the trolley wheel on the rail with minimal scrubbing.

Specifically, the invention provides a trolley wheel for a load lifting apparatus movable along a rail having a horizontal supporting surface. The wheel includes a tread surface for rolling contact with the rail and a flange for stabilizing the tread surface in position on the rail. The flange includes either a substantially crowned realigning portion for realigning the wheel to its proper rolling position with minimal contact, or an undercut adjacent the tread surface for minimizing contact between the rail and flange, or both.

Preferably, the tread surface of the wheel is crowned, and the radius of curvature of the crowned realigning portion is less than the radius of curvature of the crowned tread surface. Furthermore, the crowned tread surface, crowned realigning portion, and undercut may all be heat treated, preferably to 450 BHN, for improved toughness and wear resistance.

Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a perspective view of a monorail hoist embodying the invention.

FIG. 2

is an enlarged cross-sectional view taken along line

2

—

2

in FIG.

1

.

Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrated in the drawings is a load lifting apparatus

10

embodying the invention. The invention can be embodied in various lifting apparatus, such as cranes, weighing systems, and hoists. The illustrated embodiment is a monorail hoist.

As best shown in

FIG. 1

, the lifting apparatus or hoist

10

generally comprises a horizontally extending overhead rail

14

. A trolley

18

is supported on the rail

14

. The trolley

18

includes spaced wheel assemblies

22

and

26

. The wheel assembly

22

includes a wheel bracket

28

having a pair of opposed wheels (not shown) that are mounted therein for rotation about a horizontal axis and that roll along the rail

14

and support the wheel bracket

28

. The wheel assembly

26

includes a wheel bracket

30

having two spaced pairs of opposed drive wheels

34

mounted therein for rotation about respective horizontal axes. The drive wheels

34

roll along the rail

14

and support the wheel bracket

30

. A drive motor

38

is operably connected to the wheels

34

for moving the trolley

18

in opposite directions along the rail

14

.

The hoist

10

also comprises a load engaging mechanism supported by the wheel assemblies

22

and

26

for engaging a load. In the illustrated embodiment, the load engaging mechanism is a bottom block

46

including a hook

50

. In other embodiments the load engaging mechanism can include a grapple, magnet, bucket or scoop suitably adapted for engaging a load.

The hoist

10

also comprises a mechanism for raising and lowering the bottom block

46

. Such mechanism preferably includes a hoist mechanism

54

. The hoist mechanism

54

includes a hoist drum (not shown) rotatable about a horizontal axis. A conventional hoist motor

62

is operably connected to the hoist drum for rotating the hoist drum in opposite directions to raise and lower the bottom block

46

. A cable or lifting rope

66

supports the bottom block

46

. In the illustrated embodiment, the lifting rope

66

includes opposite end portions received around the hoist drum and bottom block

46

as is known in the art.

As shown in more detail in

FIG. 2

, the rail

14

includes a lower horizontal portion

68

including a horizontal supporting surface

70

. The lower horizontal portion

68

is supported by a vertical web

74

, which is in turn supported by an upper horizontal mounting portion

76

(FIG.

1

). The rail

14

is a variation of a standard carbon-steel I-beam known in the art and typically has a hardness of 375-425 BHN. Preferably the horizontal supporting surface

70

is symmetrical about the vertical web

74

, but this need not be the case.

In the illustrated embodiment, the horizontal supporting surface

70

includes tread supporting surfaces

78

that extend horizontally over the length of the rail

14

for rolling contact with the trolley wheels

34

. The outer edges of the horizontal supporting surface

70

and tread supporting surfaces

78

are defined by vertical sidewalls

82

. Squared corners

86

(

FIG. 1

) are defined by the intersection of the tread supporting surfaces

78

and the sidewalls

82

.

Each trolley wheel

34

is preferably made of carbon-steel and includes a hub

90

which surrounds an axis of rotation

94

of the wheel

34

. The hub

90

is part of a radially inner portion

98

which consists of a body or core material

102

of the wheel

34

. The wheel

34

further includes a radially outer portion

106

which includes a tread surface

110

and a flange

114

with an inner surface

118

adjacent and substantially perpendicular to the tread surface

110

for stabilizing the tread surface

110

in position on the rail

14

. The tread surface

110

and the flange inner surface

118

make up a wear area

122

of the trolley wheel

34

. The radially outer portion

106

also includes a toothed surface

126

for driving engagement with a drive gear (not shown) operably connected to the drive motor

38

.

The tread surface

110

extends circumferentially around the radially outer portion

106

for rolling contact with the tread supporting surface

78

. The tread surface

110

is slightly crowned for improved wear resistance. In one embodiment, a tread surface

110

having a diameter of 117 millimeters has a radius of curvature of approximately 305 millimeters. Furthermore, the tread surface

110

is preferably heat treated to approximately 450 BHN for additional wear resistance.

The inner surface

118

includes an undercut

130

that provides added clearance between the inner surface

118

and the squared corner

86

. The undercut

130

may also be heat treated to approximately 450 BHN for improved toughness, but this need not be the case. The inner surface

118

is crowned to form a realigning portion (also referred to by reference numeral

118

) adjacent the undercut

130

. In the embodiment described above, the realigning portion

118

has a radius of curvature of approximately 6 millimeters; notably smaller than the 305 millimeter radius of curvature of the tread surface

110

. The realigning portion

118

is also heat treated to approximately 450 BHN for superior toughness and wear resistance.

In normal operation, the tread surfaces

110

of opposing wheels

34

roll smoothly in the respective normal tracks on the tread supporting surfaces

78

. The respective realigning portions

118

and sidewalls

82

are separated by a clearance ranging from approximately {fraction (1/16)} to {fraction (3/32)} of an inch. This clearance is sufficient to prevent “scrubbing” or more severe binding between the inner surfaces

118

and the sidewalls

82

. The crowning and heat treating of the tread surfaces

110

minimize wear on the tread surfaces

110

.

Should the opposing wheels

34

cantilever due to a bending moment caused by an uneven load on the trolley

18

, the tread surfaces

110

may deviate from the normal tracks on the tread supporting surfaces

78

. When this occurs, one of the opposing trolley wheels

34

will move laterally inward toward the vertical web

74

until a point on the crown of the realigning portion

118

contacts the associated sidewall

82

and “kicks” both of the tread surfaces

110

back into the normal tracks on the tread supporting surfaces

78

. This “kick-back” will occur with minimal contact and without the wheel

34

riding-up on the rail

14

. Furthermore, the squared corners

86

will not contact the inner surfaces

118

due to the clearance created by the undercuts

130

. Likewise, the squared corners

86

will not dig into the crowned tread surfaces

110

.

When the above-described deviation occurs, uneven or excessive wear on the tread surfaces

110

is minimized due to the crowning and heat treating of the tread surfaces

110

. The heat treating also improves the impact toughness of the crowned realigning portion

118

, thereby reducing the wear and maintaining the effectiveness of the realigning portion

118

.

It is important to note that the trolley wheels

34

embodying the present invention need not include both the undercut

130

and the crowned realigning portion

118

, but could rather incorporate one or the other as needed for the particular application. Furthermore, it is not a necessity of the present invention that the heat treating occur, or that the preferred hardness values be achieved. Alternatively, other methods of hardening and other hardness values could be substituted.

Various features of the invention are set forth in the following claims.