Trolley apparatus with reinforced plastic wheels and interlocking plastic bushings

A trolley assembly is provided including a pair of trolley brackets with an axle extending outwardly from each of the trolley brackets. Bushings adapted to rotatably engage each of the axles are provided with a wheel fixedly attached to each of the bushings. The bushings include an interlock to prevent rotation of the bushing with respect to the wheel. A pendant is attached to the pair of trolley brackets. The components of the trolley assembly can be replaced on a one-to-one basis with parts of prior art trolley assemblies.

BACKGROUND OF THE INVENTION 
This invention relates to conveyor trolley assemblies. More particularly, 
this invention relates to trolley assemblies for overhead roller 
conveyors. 
In most poultry processing plants there are overhead conveyor lines 
including picking lines, eviscerating lines, cut-up lines, and packing 
lines. The average length of a conveyor line is about 150 m. Running speed 
is about 13 m/min and usually the lines are operated two shifts a day. A 
complete overhead conveyor includes a chain, trolley assemblies, and 
H-attachments and pendants. All the parts are assembled and hung from an 
I-beam alloy track. 
A complete trolley assembly is attached every 0.15 m along the line. In 
some cases, a complete trolley assembly is attached only every 0.30 m and, 
in between the trolley assemblies, an H-attachment and pendant are 
attached. Poultry (chickens, turkeys, etc.) having a weight of only about 
3 kg are hung approximately every 0.15 m, although such lines are 
generally rated at about a 50 kg load per trolley. 
The wheels of the trolley assemblies are designed to include ball bearings. 
In some designs, the outside and the inside races of the ball bearings are 
made of plastic material. A disadvantage of such designs is that the load 
which is created on the axle is transferred through the bearing balls 
which are located at any given moment only on the bottom side of the 
wheel. This means that most of the load is transferred only through one or 
two bearing balls. It is well known that a ball creates a very 
concentrated pressure when pressed between two flat panels. Theoretically, 
the load is concentrated on a point. 
The pressure per given area created by the load is higher than permitted 
for any known thermoplastic material. As a result, "creep" occurs in the 
plastic parts. Creep in plastic is a moving of material from one area 
under a constant pressure to another area under less pressure. When creep 
increases during rotation, the distance between the inner race and the 
outer race (i.e., between the stationary and the rotating parts) increases 
to such a degree that a ball can escape from the wheel. As a result, the 
wheel either stops rotating immediately or the remaining balls also escape 
and then the wheel stops rotating. The higher the load, the greater the 
creep, and the shorter the performance life of the wheel. 
There are some designs on the market in which a ball cage is used to 
prevent the balls from escaping. Such a design provides only a marginal 
advantage and increases the working life of the wheel by some percentage. 
Among the disadvantages are that the wheel is more expensive and amount of 
creep is the same. 
Creep occurs all around the outside race (on its inside surface), but only 
on one side of the inner race (the stationary part). The result is that 
the inner race is no longer round in shape and therefore it becomes easier 
for the wheel to slip over the I-beam than to rotate on it. 
An additional disadvantage of wheels designed with ball bearings is the 
high cross-section of the outer race (i.e., the wheel itself). A high 
cross-section is required because both the inner and outer surfaces of the 
outside race must be smooth. The inner surface, because of the bearing 
balls, and the outer surface, because it has to roll against the I-beam. 
This high cross-section poses significant disadvantages: 
(1) A very long thermoplastic injection cycle is required; 
(2) A substantial amount of thermoplastic material is needed; 
(3) A substantial amount of shrinkage and deformation occurs creating lower 
quality plastic properties (increasing creep and outside abrasion of the 
wheel); and 
(4) A complicated assembly process for the ball bearings is required. 
The bracket of the trolley assembly is generally drop forged and coated to 
prevent rusting. The trolley bracket is designed to be strong enough to 
hold a load of about 50 kg per bracket for at least 2 years of operation 
at 2 shifts per day. The weight of the trolley bracket is approximately 
225 gr. The trolley bracket has a coating to prevent rust when working in 
a processing plant having a very high humidity level. Nonetheless, a 
substantial number of trolley brackets rust despite the fact that all the 
conveyor parts are replaced every one to two years. 
Due to trolley assembly requirements, the thickness of the pendant should 
be 6 mm. The pendant is made of steel and is also plated to prevent rust. 
Consequently, the pendant is stronger than needed and weighs about 188 gr. 
Similarly, the H-attachment is drop forged or made of sheet metal and is 
coated to prevent rust. Weight of the steel H-attachment is approximately 
89 gr. 
SUMMARY OF THE INVENTION 
With the foregoing in mind, it is an object of the invention to provide an 
improved trolley assembly for use in conveyor systems. 
It is a further object of the invention to provide an improved wheel 
assembly for use in trolley assemblies of conveyor systems. 
In accordance with the invention, a trolley assembly is provided including 
a pair of trolley brackets with an axle extending outwardly from each of 
the trolley brackets. Bushings adapted to rotatably engage each of the 
axles are provided with wheels fixedly attached thereto. A pendant is 
attached to the pair of trolley brackets. 
Further in accordance with the invention, a wheel assembly is provided 
which is adapted to rotatably engage an axle including a wheel providing a 
flange and rib portion. Bushings are provided which are adapted to 
interconnect with the wheel and to rotatably engage the axle. An interlock 
to prevent rotation of the bushing with respect to the wheel is also 
provided. 
Advantageously, the components of the trolley assembly can be replaced on a 
one-to-one basis with parts of the prior art trolley assembly.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIGS. 1 and 2 show perspective and front cross sectional views, 
respectively, of a trolley assembly in accordance with the instant 
invention. The trolley assembly is adapted to work with X-348, X-347 and 
similar overhead conveyors as are available from Greenline Corporation 
(Charlotte, N.C.) and other suppliers. In particular, is shown a standard 
X-348 overhead conveyor I-beam 2 including web portion 4 and flange 
portion 6. 
The trolley assembly includes basically three components; wheel assembly 8, 
trolley bracket 10, and pendant 12. Due to symmetry of the trolley 
assembly, it will be appreciated that two identical wheel assemblies and 
two identical trolley brackets (left and right) are used to make a 
complete trolley assembly. Only a single pendant is required for a 
complete trolley assembly. It will also be appreciated that the trolley 
assembly is adapted to have its wheel assemblies 8 run on flange portion 6 
of I-beam 2. Sufficient space is provided between the right and left wheel 
assemblies 8 to prevent contact with the web portion 4 of I-beam 2. 
Similarly, sufficient space is provided between the right and left trolley 
brackets 10 to prevent contact with flange portion 6 of the I-beam 2. 
In FIG. 3 is shown an exploded view of a wheel assembly in accordance with 
the instant invention. The wheel 14 is made of a thermoplastic material, 
e.g., polyacetal, and is preferably 57 mm in diameter with a face-to-face 
thickness of about 18 mm. A preferred thermoplastic material is 
ULTRAFORM-2320 from BASF. Wheel 14 has an annular surface 16 with a taper 
of approximately 20.degree. with respect to the center line of the wheel. 
It will be appreciated that the annular surface 16 could also have a round 
or flat shape as may be desired for a particular application. On the 
inside of wheel 14 is web portion 18 with ribs 20 which extend radially 
inward toward through hole 24. The web and the ribs are preferably 2.5 mm 
in thickness. It will be appreciated from the figures that ribs 20 may be 
provided on both sides of flange 18. It will be further appreciated that 
the ribs do not extend all the way to the side wall of the wheel. Rather, 
they may be recessed approximately 2.5 mm thereby providing a recess in 
the side wall of the wheel. 
Advantageously, the wheel is designed such that more than 70% of the wheel 
is made of flange and ribs having a wall thickness of only 2.5 mm and only 
at the annular outer surface (the portion which rotates against the 
I-beam) does the wall thickness increase to about 7 mm. In contrast, the 
wall thickness of prior art wheels is about 15-17 mm. 
In FIG. 3 is also shown a bushing of the wheel assembly 8. Bushing 28 
includes face portion 30 and collar 32 and provides a through hole 34. The 
bushing 28 is made of an internally lubricated thermoplastic, e.g., 
polyacetal. A preferred thermoplastic material is Delrin AF313 from DuPont 
which has a lubricant in the material. The face portion preferably has a 
thickness of 2.5 mm and the collar portion preferably has a thickness of 4 
mm. On the back of the face portion is provided at least one rib 36 having 
a thickness of 2.5 mm. 
FIG. 3 further shows an axle of the wheel assembly 8. The axle 38 is 
preferably made of reinforced nylon. A preferred reinforced nylon material 
is RTP-205 from Fiberit Corp. Axle 38 includes side bearing surface 40, 
beveled head 42, and shoulder 44. The axle provides through hole 46 with 
recess 48 adapted to contain a bolt head therein. (See FIG. 2.) If 
desired, the recess may be adapted to capture the bolt head and prevent 
its rotation by making recess 48, for example, six sided. Alternatively, 
the recess may be adapted to capture the nut of a bolt. It will be 
appreciated that the recess 48 may be designed to capture any 
configuration of bolt head or nut. On the opposite side of axle 38 from 
recess 48 is mating face 50 which includes at least one pin 52 having a 
preferred diameter of 3 mm. For applications wherein the wheel assembly of 
the invention is intended to replace prior art wheel assemblies and to be 
used with a metal trolley bracket, it is preferable to produce the axle 48 
without pins 52. 
It will be appreciated that, when assembled with a bushing 28 and a wheel 
14, cylindrical bearing surface 40 and shoulder 44 of axle 38 are adapted 
to rotatably contact the inside of collar 32 and the front of face portion 
30 of bushing 28. Advantageously, shoulder 44 prevents axial movement of 
the wheel 14 and beveled head 42 of axle 38 provides a smoother profile to 
the wheel assembly when in use. 
FIG. 2 shows a cross sectional view of a complete wheel assembly. As may be 
appreciated from FIG. 2, a bushing 28 is inserted on either side of the 
wheel 14 and due to symmetry of the inside configuration of the wheel, two 
identical bushings may be used for each wheel. When the bushing is 
inserted into the wheel, ribs 36 of bushing 28 interlocks with ribs 20 of 
wheel 14 preventing rotation of the bushing with respect to the wheel. It 
will be appreciated that face portion 30 of bushing 28 recesses into the 
recess in the side wall of wheel 14 to present a substantially smooth 
surface to the bushing/wheel interface. 
It may be appreciated that there are distinctly different physical 
requirements for the inside and outside surfaces of the wheel. The outside 
surface (the circumference of the wheel) must be smooth in order to roll 
well against the I-beam. The outside surface should also preferably be 
from a material with a low wear factor and the proper friction to prevent 
the wheel from slipping against the I-beam rather than rolling. The inside 
surface must be very smooth, but with a minimum possible coefficient of 
friction and abrasion, in order to permit excellent rotation against the 
axle. 
In order to meet these different physical requirements, the wheel/bushing 
assembly in accordance with the invention is provided. The bushing is 
produced from a special plastic material having an inherent lubricant, 
such as Delrin AF313 from DuPont. The bushings interconnected with the 
wheel. The bushing has integral ribs which are located between the ribs of 
the wheel. The wheel with the two bushings (one on each side) may then act 
as one part which is made of two different materials. 
An additional advantage of the invention is that the bushing also prevents 
friction and abrasion between the wheel and the trolley bracket and 
between the wheel and the axle-both in the axial direction. Axial forces 
are created because of the horizontal distance between the load and the 
wheels and because of the sloped flange portion of the I-beam. 
Advantageously, the wheel assembly according to the invention creates a 
chamber between the bushing 28 and the wheel 14. This chamber not only 
saves material and improves the properties of the parts, but also can be 
used as a vessel for grease or other lubricants for trolley applications 
other than in processing plants. For such applications, the bushing 28 may 
be designed to be sealed around the wheel 14, and a clearance provided 
between the two bushings to allow lubricant to exit from the chamber 
through the clearance between bushings 28 and the axle 38. For such an 
application, a special greasing thread as are known in the art may also be 
provided. 
The wheel assembly according to the invention overcomes numerous 
disadvantages of prior art wheels: 
(1) The thermoplastic injection cycle for production of wheels is reduced 
by about 300-500%; 
(2) A very high quality product is attained due to having a uniform and low 
wall thickness all over the product (shrinkage is 300-500% less when 
compared to the prior art) because excellent filling of the part can be 
obtained; 
(3) The wheel weighs less than 50% of the weight of the prior art wheels; 
and 
(4) There is no need for a ball bearing assembly process. 
FIGS. 1 and 2 show perspective and cross sectional views respectively of 
the trolley bracket in accordance with the instant invention. The trolley 
bracket is preferably made of reinforced nylon. A preferred reinforced 
nylon material is Nylon 6/6 ADEL AR-16 from Adel Plastics. At the upper 
end of trolley bracket 10 is provided through hole 56 and axle face 58 
which is designed to allow free rotation against face portion 30 of 
bushing 28 of the wheel assembly 8. In axle face 58 is provided at least 
one pin recess 60 which is adapted to accept pin 52 from axle 38 in the 
trolley assembly creating an interlock to prevent rotation of the axle 
should the connecting bolt loosen. It will be appreciated that the upper 
portion of trolley bracket 10 is generally U-shaped in cross-section and 
includes an essentially flat portion preferably 5 mm in thickness with 
stiffening ribs on either side, again preferably 5 mm in thickness. On the 
lower portion of trolley bracket 10 is provided pendant face 70 which is 
adapted to mate with a pendant. The face-to-face distance between axle 
face 58 and pendant face 70 is preferably about 26 mm. On the lower 
portion of trolley bracket 10 are provided bolt holes 66 for attaching the 
trolley bracket to another similar trolley bracket and a pendant to form a 
trolley assembly. 
The trolley bracket has been designed to have a moment of inertia such that 
the bending stresses are maintained low enough to permit carrying a 
continuous load of at least 100 kg per bracket. The surface of the trolley 
bracket is preferably very smooth with high radii in order to prevent any 
accumulation of dirt. As the conveyor chain moves and pushes the trolley 
assembly, substantial friction is created between the chain and the 
trolley bracket. Since the prior art trolley bracket was made of steel, 
substantial abrasion occured. Such abrasion is reduced when using a 
plastic bracket against a metal chain. 
FIGS. 5 and 2 show perspective and cross sectional views, respectively, of 
a pendant 12 of the trolley assembly. The pendant has a preferred 
thickness of 5 mm. In order to conform with standard pendant dimensions, 
there is an additional peripheral rib 72 of 0.5 mm on both sides to create 
a 6 mm thickness. Pendant 12 is preferably made of reinforced nylon. A 
preferred reinforced nylon material is ADEL AR-16 from Adel Plastics. 
Pendant 12 provides through holes 74 for connection with trolley brackets 
10. Pendant 12 is adapted to be mated between two pendant faces of 
opposing trolley brackets. Pendant 12 presents a rounded lower end 78 to 
the trolley assembly. The weight of the pendant made according to the 
invention is about 29 gr. 
FIGS. 1 and 6 show perspective and cross sectional views, respectively, of 
an H-attachment assembly, including two H-attachments and a pendant, as 
may be used with the trolley assembly. The H-attachment is preferably made 
of a reinforced nylon. A preferred reinforced nylon is ADEL AR-16 from 
Adel Plastics. The H-attachment 80 has a substantially planar surface 
preferably 4 mm in thickness with stiffening ribs 82 and including bolt 
holes 86 to attach one such H-attachment on each side of a pendant 12. 
Stiffening ribs 82 also define a channel portion 88 for the conveyor chain 
similar to the channel portion in the trolley assembly. The weight of the 
H-attachment made according to the invention is only 18 gr while a prior 
art metal H-attachment weighs about 80 gr. 
Advantageously, the components of the trolley assembly--i.e., the wheel 
assembly, the trolley bracket, the pendant and the H-attachment 
assembly--can be replaced on a one-to-one basis with parts of prior art 
trolley assemblies. 
While the invention has been described in its preferred embodiments, it is 
to be understood that the words which have been used are words of 
description, rather than limitation, and that changes may be made within 
the purview of the appended claims without departing from the true scope 
and spirit of the invention in its broader aspects. For example, although 
the axle and trolley bracket are described herein as being two separate 
components, the trolley bracket may be integrally formed with the axle as 
shown in FIG. 7. This arrangement may be preferable for certain 
applications and results in fewer individual components for the trolley 
assembly.