Method for making a hollow-bodied caster wheel

A hollow-bodied caster wheel is produced by casting a pair of wheel body halves with flanges which do not fit over one another at equal temperatures, cooling the inner half while keeping the outer half hot, fitting the two halves over one another in that condition, and then allowing the temperatures of the two halves to become equalized so as to cause the flanges of the two halves to bond together as the outer half shrinks during cooling. A tire is then vulcanized over the outer surfaces of the assembled wheel body halves, and bearings are press-fitted into the inner surfaces of the assembled wheel body halves to complete the wheel.

BACKGROUND OF THE INVENTION 
In a number of applications, such as in food handling and other 
circumstances where cleanliness of equipment is important, it is desirable 
to build caster wheels in such a way that the tire and hub when assembled 
together, form a relatively recess-free surface which is easy to clean. 
This objective is normally accomplished by providing a hollow wheel of 
generally rectangular cross-section whose width is generally equal to the 
width of the tire which is vulcanized onto the rolling surface of the 
wheel. In the highly competitive caster industry, it is imperative to 
manufacture a caster conforming to these requirements at the least 
possible cost. 
Currently, two principal ways of manufacturing a wheel of this type are in 
use: stamping followed by press-fitting (which is undesirable because the 
press-fit tends to work loose in use), and stamping followed by welding. 
In the first method, two generally symmetrical halves of the wheel are 
stamped from flat stock by a series of successive stamping operations, and 
then press-fitted together. In the second method, two identical stampings 
forming the two havles of the outer portion of the wheel, and a sleeve 
forming the hub portion of the wheel, are all welded together to form a 
unitary hollow wheel. In either method, a subsequent plating operation is 
often necessary to produce an estehtically acceptable wheel body surface. 
In view of the need for cost-effective manufacture of high-quality caster 
wheels for the above-mentioned applications, it has therefore become 
necessary to devise a wheel body structure of the type described which 
lends itself to easy assembly in a single step without further processing, 
yet provides a sturdy, well-sealed hollow wheel body. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a wheel body of the type described is 
manufactured by precision molding or die-casting the two halves of the 
wheel from aluminum, allowing the inner half to cool, and dropping the 
outer half over it while still hot. As the outer half cools, it shrinks 
into an extremely tight, solid fit with the inner half. By selecting 
appropriate grades of aluminum or other materials, and appropriate surface 
finishes on the molds, no further manufacturing operations other than the 
vulcanizing of the tire and the insertion of the wheel bearings are 
required. 
It is therefore the object of the invention to provide a wheel construction 
for hollow-bodied caster wheels which produces a sturdy, unitary, and 
esthetically satisfactory wheel body in a single, simple manufacturing 
operation. 
It is another object of the invention to provide a method of manufacturing 
a caster wheel by precision molding or die-casting the wheel in two 
halves, cooling the inner half, dropping the outer half over the inner 
half while still hot, and allowing the outer half to shrink tightly onto 
the inner half as it cools.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 and 2 show, respectively, the currently used methods of making 
hollow caster wheel bodies by stamping (FIG. 1) and welding (FIG. 2). It 
will be noted that in order to produce the press-fitted wheel halves 10, 
12 of FIG. 1, separate stamping operations have to be performed to form 
the blank itself, the outer flange 14, and the inner flange 16. The 
three-part wheel body of FIG. 2 requires two assembly operations in which 
the stampings 20, 21 are welded together at 23, and the hub sleeve 18 is 
then welded, as at 22, to the stampings, 20, 21 forming the outer portion 
of the wheel body. 
It is therefore desirable to build the wheel body in such a manner as to 
make it capable of being formed and assembled with a minimum of effort, 
while at the same time obviating the need for a plating operation. 
These objectives are accomplished in accordance with the invention, as 
shown in FIGS. 3 through 5, by casting two wheel body halves 24, 26 (FIG. 
3) in such a manner that the inside surfaces 28, 30 of the flanges 32, 34 
of the outer half 24 are slightly closer to the wheel axis A than the 
outside surfaces 36, 38 of the flanges 40, 42 of the inner half 26. Thus, 
the outer half 24 does not normally fit over the inner half 26 of the 
wheel body. 
In order to assemble the wheel of the invention, the outer half 24 is 
maintained at an elevated temperature (e.g. about the temperature at which 
it is taken from the casting mold), while the inner half 26 is allowed to 
cool to room temperature. The resultant shrinkage of inner half 26 is 
sufficient to bring surfaces 36, 38 closer to axis A than surfaces 28, 30. 
In this condition, the flanges 32, 34 of the outer half 24 of the wheel 
body readily slip over the flanges 40, 42 of the inner half 26 (FIG. 4). 
As the outer half 24 also cools to room temperature, it shrinks 
sufficiently to cause surfaces 28, 30 and 36, 38, respectively, to become 
tightly bonded to each other in a sturdy, uniform bond. The hub 44 (FIG. 
5) and tire 46 can now be press-fitted and vulcanized, respectively, onto 
the completed wheel body in a manner well-known in the art. The heating 
involved in the vulcanizing operation is not sufficient to separate the 
two wheel halves, particularly because the vulcanizing heat is applied 
equally to both halves so that both halves will expand with no significant 
effect on the bond formed by the shrink fit.