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Description  |
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BACKGROUND
Systems for transporting cargo in transferable containers, carried on
flatbed trailers towed by a tractor, are becoming increasingly popular.
Such containers, for example, are particularly useful for "partial loads"
where two or more containers may be carried on the same trailer destined
for different destinations. To further increase the utilization of
container/trailer transportation systems, containers have been designed
with rollers or wheels on the bottom to facilitate loading and unloading
of the containers from a trailer.
Three patents which disclose container systems permitting the transfer of
container loads to and from either end of a semi-trailer onto a loading
dock or onto another truck are the U.S. patents to Ault U.S. Pat. No.
2,631,885; Black U.S. Pat. No. 2,986,408; and Cayton U.S. Pat. No.
4,203,697. The Ault patent is directed to a container transfer system
which uses pivot rails on the trailer to permit loading and unloading of
pallets from either side of the trailer, or from either end. The Black
patent is directed to a reversible semi-trailer construction for carrying
two containers, which may be rolled onto and removed from either end of
the trailer.
The patent to Cayton is directed to a trailer which is to be parked near an
agricultural field. Pallets containing agricultural products are loaded
onto a small transfer truck, which then backs up to either end of the
trailer and rolls the pallets onto the trailer. The trailer may be made of
a greater length than the length of the bed of the transfer vehicle; so
that multiple pallets may be transferred from the smaller vehicle onto the
trailer.
Two other patents directed to plural unit trailers having somewhat complex
configurations are Bennett U.S. Pat. No. 3,163,306 and McCleary U.S. No.
3,504,814. The devices of both of these patents permit loading and
unloading from either end of the trailer.
Another industry which has been unrelated to container transportation
systems is the hot mix asphalt (HMA) industry. This industry is composed
of several entities. The heavy tar-like residue, which remains after the
production of gasoline and diesel fuel, is marketed in several grades and
sold as what is called "bitumen" to hot mix asphalt producers (HMAP). The
HMAP store the bitumen in large storage tanks and maintain the temperature
of the bitumen at approximately 300.degree. to keep it in a liquid state.
Whenever bitumen is allowed to cool, it solidifies and is not workable.
The producer has a hot mix plant (HMP) which includes aggregate storage
facilities, conveyors, aggregate dryer drums, aggregate use bins with
weighing devices to proportion different aggregate gradations, and the
like. The producer selects the desired HMA formula and sends the desired
proportions to a heated drum and dries the aggregate to the desired
moisture content. Pugmills or other devices are used to mix the hot
aggregate with asphalt cement (a binder) and bitumen into a well blended,
homogenous mass. The product is called hot mix asphalt (HMA); and the
producer markets HMA in several different formulas or grades.
Asphaltic cement, the binder in HMA, is a thermoplastic material with a
characteristic of being very workable at 300.degree. Fahrenheit and as
hard as concrete at 100.degree. Fahrenheit. Clearly, the workability of
this material varies with temperature. At the job site, the placing crew
typically likes to have the HMA material at close to 300.degree.
Fahrenheit for workable paving. A typical HMA production facility,
however, does not like to exceed 310.degree. to 320.degree. Fahrenheit,
because light end hydrocarbons in the form of smoke and vapors become
abundant at these higher temperatures. In addition, the combination of
high temperatures and exposure to oxygen causes oxidation (hardening) or
rapid aging of the asphaltic cement. Hot mix asphalt is a flexible
pavement; and as long as it remains so, it is serviceable. As asphaltic
pavement ages or hardens, it becomes brittle, cracks, and ultimately no
longer is serviceable as a pavement structure. Consequently, any premature
aging or hardening (oxidation) of asphaltic cement results in shorter
service life of the asphalt pavements.
At HMA production facilities, care is given to protecting the HMA from
rapid high temperature aging. Storage facilities now are available which
are heated, insulated, sealed airtight, and in some cases, held under
slight pressure from an inert gas generator, to avoid any oxygen exposure
to the HMA as it is being stored. Storage facilities of this type have
been approved by various government agencies to store HMA for several
days. Typically, however, HMA is stored in large storage tanks constructed
in this manner at the production facility, and then is transferred from
the tanks to the dump trucks for transportation to the job site.
The different HMA products are stored in separate storage bins. Contractors
order the formula they desire. Typically, hot HMA is weighed into dump
truck and the HMA is delivered to the construction site. At the
construction site, the HMA is transferred or dumped from the delivery
truck into a paver, which spreads the HMA to the desired width and
thickness. The HMA then is compacted to a dense mass by using heavy
rollers. After the HMA cools to the ambient temperature, it becomes very
hard and makes an excellent surface for highway pavements, parking lots,
driveways, walking paths, and the like.
In cold climates, typically starting around Labor Day, it is difficult to
place an HMA finish or top course, since the present methods of
transporting and placing HMA allow the HMA to cool, where it becomes
difficult to obtain an ideal paving surface. Since hot HMA cools
relatively rapidly after it is placed in a delivery dump truck, the hot
mix plant typically is located a relatively short distance from the
application site. Presently, permanent hot mix asphalt plants economically
service an area with a radius of approximately 25 miles. Beyond that
radius, paving areas develop which may be considered "soft spots" because
permanent hot mix asphalt plants typically are not located close enough
together to cover all areas of the country. This has created a market for
portable hot mix asphalt plants.
Whenever a contractor requires a large order of HMA (typically several
thousand tons), a portable plant may be set up by the producer near the
distribution site; so that unnecessary cooling of the HMA between the
production site and the distribution site does not take place. This is
done for major highway paving jobs, and the like. For some locations,
however, which fall into the described "soft spots", zoning and aggregate
availability limitations may preclude setting up a portable plant for even
large jobs. In any event, customers who are located in the "soft areas"
generally pay a higher rate for HMA, and frequently receive material which
must be reheated at the distribution site, or which is in risk of being
cooled to a temperature where application becomes difficult.
Another disadvantage of the typical HMA production and distribution system
is that the material must be produced and heated to its application
temperature only a relatively short time prior to its application at the
job site. Consequently, production at an HMA plant typically takes place
in the early morning hours; and the dump trucks which distribute the HMA
material from the plant to the job site travel back and forth between the
plant and the job site. If heavily traveled highways exist between the
plant and the job site, the transportation of HMA material from the plant
to the job site and the return trip of the empty truck can take undue
amounts of time. This is particularly true if delivery is desired during
the typical "rush hour" traffic congestion, which takes place in and
around most large cities in the morning and in the late afternoon.
The size of the HMA industry in the United States is approximately 400
million to 500 million tons of HMA annually. At present market prices,
this constitutes a nearly twenty billion dollar annual industry. In the
United States, approximately 75 percent to 85 percent of HMA is used in
the construction of pavements in highways, streets and airports. The
balance of the HMA produced is used in private work, civil projects,
parking lots, driveways, etc. The foregoing discussion is directed
primarily to the production and delivery of HMA to the large construction
projects constituting highways, streets and airports. Small jobs are
difficult to effectively service; and many of them are located in the
"soft spots". Because of the small size of such jobs, it is not practical
to set up a portable HMA plant at the job site. Consequently, the delivery
and distribution of HMA to many small job sites is inefficient; and the
quality of the delivered HMA frequently is less than desired.
Typically, HMA is transported to paving sites in open dump truck bodies.
During cold weather, truck boxes for transporting HMA are insulated to the
extent possible, and frequently are covered with a roll-out tarpaulin. As
an effort to maintain the HMA at a desired temperature, a system disclosed
in the U.S. patent to O'Brien U.S. Pat. No. 5,120,217 has been developed.
This patent discloses a delivery unit for HMA material. The delivery unit
is mounted on a trailer. The hopper of the unit has hydraulically operated
doors for closing its top; and it incorporates a double walled
construction, with the inner hoppers spaced from the outer walls of the
container. Heated air is passed in the space between the inner and outer
hoppers, and also through a double wall in the doors in the top, to exit
over the material inside the hopper. This unit is designed to be dropped
off at a construction site at the end of a working day. A heater then is
operated overnight; so that the material is at the desired temperature by
the next morning and is then ready for use.
Another effort to provide heating for the hopper or truck used to carry HMA
is disclosed in the U.S. patent to Eldridge U.S. Pat. No. 4,978,068. This
patent discloses the passage of exhaust gases of a vehicle between inner
and outer chambers of a hopper for heating the contents of the hopper. A
different approach for heating the contents of a hopper carried on a truck
is disclosed in the U.S. patent to King U.S. Pat. No. 4,695,186. The
hopper disclosed in this patent is permanently mounted on a truck. The
hopper structure includes a space between the lower walls of the hopper
and an additional plate in the truck. This space provides a chamber for a
heat exchange from a heater located beneath the hopper to transfer heat to
the material within the hopper.
The U.S. patent to Dillingham U.S. Pat. No. 4,944,632 also discloses the
use of a double wall construction in a hopper for transporting asphalt
repair materials from one place to another. The hopper is open at the top;
but the heat source is located to supply heat to the space between the
walls for heating the asphalt in the hopper.
Accordingly, it is desirable to provide an improved distribution system,
particularly suited for the delivery and distribution of HMA, which
overcomes the disadvantages of the prior art, which is simple and
effective to execute, and which is reliable in operation.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved transportation
system.
It is another object of this invention to provide an improved container
transportation system for delivery of containers to a job site and for
facilitating the removal of containers from a transporting vehicle to a
delivery vehicle.
It is an additional object of this invention to provide an improved
delivery system for storing and protecting hot mix asphalt (HMA).
It is a further object of this invention to permit the transportation of
HMA at off-peak traffic hours.
It is yet another object of this invention to provide a delivery system for
HMA which permits storage of HMA at the job site to increase the
efficiency of the paving application.
It is yet another object of this invention to provide an HMA transportation
system utilizing smaller, lighter weight delivery containers at the paver
location.
In accordance with a preferred embodiment of the invention, a
transportation system includes a tractor with a fifth wheel for towing a
trailer loaded with a roll on/roll off container on the load carrying
surface of the trailer. The towing tractor carries a supplemental
platform, which normally is held in a storage position when the trailer is
being towed by the tractor. The supplemental platform is moved to a use
position after the tractor is detached from the trailer. A lift device
then is provided on the tractor for engaging a mating member on a
container placed on the supplemental platform to lift one end of the
container relative to the other to facilitate unloading of the container.
In a particular application of the system, a plurality of containers is
provided for transporting heated materials, such as hot mix asphalt, from
a production site to a job site. Each container comprises an outer shell
spaced from an inner shell; and the space between the two shells is filled
with insulation. After the container is emptied, it is returned to the
transporting trailer, readying it for the return to the plant for
refilling.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic representation of a preferred embodiment of the
invention;
FIG. 2 is a diagrammatic representation of another preferred embodiment of
the invention;
FIG. 3 is a cross-sectional detail of a container used in the embodiments
of FIGS. 1 and 2;
FIG. 4 is a partially cut away cross-sectional view of a portion of the
embodiment shown in FIG. 3 illustrating a different operating position of
some of the parts thereof;
FIG. 5 is an end view of the container shown in FIG. 3;
FIGS. 6A to 6E illustrate different stages in the operation, of the
embodiment of the invention shown in FIG. 2; and
FIG. 7 is a detail of a portion of the operation of the embodiment shown in
FIGS. 6B through 6E.
DETAILED DESCRIPTION
Reference now should be made to the drawings, in which the same reference
numbers are used throughout the different figures to designate the same
components. FIGS. 1 and 2 are directed to two different embodiments of a
transporting system fop moving containers from a loading site to a
delivery site.
FIG. 1 shows a tandem axle tractor 10 towing a flatbed trailer 12 attached
to the tractor 10 through a standard fifth wheel connector 14. The flatbed
trailer 12 has an upper load carrying surface on it, which may include
spaced guide rails or channels or, depending upon the type of containers
to be carried, the load carrying surface may be entirely flat. The trailer
12 of FIG. 1 may be a typical forty foot long flatbed trailer; and it is
illustrated hauling four container boxes 16. The boxes 16 have an overall
length of approximately eight feet, and typically are eight feet, 10
inches wide and six feet to seven feet high. Standard tie-down devices
hold the containers in place during transit.
In the embodiment illustrated in FIG. 1, the containers 16 preferably are
insulated containers for carrying hot mix asphalt (HMA) or any material
that requires to be kept either hot or cold such as any liquid, fruits or
vegetables, etc. In order to maintain the elevated temperature of the HMA
within the containers 16, the exhaust from the tractor 10 is applied
through an exhaust pipe 18 and coupled through couplers 20 to external
pipe connections on each side of the container which lead to an internal
air space 21 at the bottom of the container formed by the lower curved
inner wall and the outer wall. The exhaust passes through the bottom of
the container 16 and is discharged directly to the atmosphere through two
bottom outlets (not shown). The heated air in this area 21 conducts heat
upward to the contained air between the inner and outer wall and maintains
the heat in the side and end walls.
When the tractor-trailer rig 10/12 arrives at the delivery destination, the
containers 16 may be unloaded in any suitable manner. As illustrated in
FIG. 1, the containers are on wheels or rollers; so that they may be
pushed or pulled off the trailer 12 in any suitable manner. The design of
the trailer 12 is such that when the trailer is unhitched from the tractor
and the landing gear is lowered to place the trailer in its "parked"
position, the containers 16 may be removed from the flat trailer bed from
either end, that is, from the end which is attached to the towing tractor
10, or from the rear end (the right end, as shown in FIG. 1). When the
containers 16 are used to transport HMA, the connector pipes 20 first are
disconnected from the connections to the internal air spaces 21 of the
containers 16 to permit unimpeded removal of the containers from the
flatbed trailer 12.
After a container has been emptied, it then may be returned to the opposite
end of the trailer 12, pushing the loaded containers 16 toward to the
unloading end, so that the next container 16 may be removed. This sequence
is repeated until all four of the containers 16 have been removed,
unloaded and returned to the trailer 12. This type of operation is the one
which is employed whenever the containers 16 are used to carry HMA. It
should be noted, however, that containers 16 carrying various types of
cargo may be employed with this system, and loaded and unloaded in this
manner, as desired.
In FIG. 2, a tandem trailer arrangement is employed. In the transportation
system of FIG. 2, a single axle tractor 30 pulls a first semi-trailer 32
through a fifth wheel hitch 31. As illustrated in FIG. 2, a fifth wheel
assembly 15 is attached to the first trailer 32 for towing a second
trailer 32. Each of the trailers 32 are capable of carrying two of the
containers 16 of the size described above in conjunction with the
embodiment of FIG. 1. As an alternative to the use of the exhaust pipe 18
from the towing tractor, however, the embodiment shown in FIG. 2 employs a
separate heater 34, which may be electric, bottled gas, or gasoline fueled
to supply heated air to the connections to the air spaces 21 through
center-connecting ducts 36, 37 and 38 in a recirculating manner. A
separate heater 34 is employed for each of the trailers 32 in the
embodiment shown in FIG. 2.
In both of the embodiments shown in FIGS. 1 and 2, the containers 16, with
the dimensions given above, each are capable of holding a seven ton
payload of HMA. Consequently, the single forty foot trailer 12 of FIG. 1
may be used to haul 28 tons of HMA material. The two trailers 32 of FIG. 2
each haul a payload of fourteen tons of HMA. In some states, a third
trailer 32 may be used to haul an additional 14 tons of HMA with a single
tractor 30.
When HMA is carried in the containers 16, transfer of each container 16 to
a delivery vehicle is effected one at a time. The delivery vehicle may be
any suitable smaller truck, capable of removing the container 16 and
carrying it to the paver. Once the delivery truck reaches the paver, the
HMA is dumped into the paver hopper from the container 16, as described in
greater detail later. The first container then is returned to the opposite
end of the trailer 12 (or 32), as described above, and the process is
repeated. By using relatively small, seven-ton containers, the lighter
weight delivery at the paver results in less damage to the subgrade and
the area encroached on by the delivery vehicle. In addition, the smaller
size container enhances placement of the HMA into the hopper of a paver by
permitting the use of a more maneuverable delivery vehicle. This results
in a lower HMA placement cost.
FIGS. 3, 4 and 5 show a typical container 16 used to deliver HMA to a job
site by means of either the semi-trailer 12 or the trailers 32, shown in
FIGS. 1 and 2, respectively. As shown in FIGS. 3, 4 and 5, the container
16 includes a double-walled inner shell or housing having a pair of spaced
apart steel walls 40 and 42. The space between the walls 40 and 42 is
developed by means of a network of 2 inch by 2 inch by 12 gauge square
cross section steel tubing 44, arranged in a grid-like pattern between the
walls 40 and 42. The distance between the different tubing sections 44
typically is between one foot and two feet to provide the desired
structural integrity to the inner shell or inner housing of the container
16.
The container 16 has an aluminum outer shell 46, which covers both sides
and the two ends, and a bottom 48. The space between the outer shell 46
and the bottom 48 and the inner shell 40/42 is filled with air or a
suitable insulation 52. At the bottom, between the outer shell bottom 48
and the bottom of the double-walled inner shell 40/42, transverse and
longitudinal suppor | | |
