Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: METHOD AND APPARATUS FOR APPLYING HOT MIX FOR
TAR SEALED ROADS
This invention relates to a metb.od and apparatus for applying hot mix for tar
sealed
roads_
BACKGROUND OF THE INVENTION
In conventional practice, the surfaces of tar-sealed roads are covered by a
layer of
material comprising a mix of what is known as "aggregate" and bitumen. ()yhen
used
in this specification, the term "mix" will refer to a mixture of these
materials that is
suitable for building and repairing roads, unless it is clear from the context
that another
meaning is intended). The aggregate comprises stone particles of various
graded sizes.
If the mixing has been properly carried out, the stones are randomly dispersed
in a
matrix of the bitumen and the bitumen should be bonded to each stone and
should
cover as much of the surface of the stone as possible. It is of course nearly
impossible
to achieve such an ideal mix in practice but it is at least a goal that is
aimed at.
At the present time when a new tar-sealed road is being conatructed, the mix
is
commonly prepared in bulk at a fixed facility remote from the road building
site or by
a large machine that is transported to, and temporarily set up, at the site:
In either case
the prepared mix is transferred to a machine that lays the mix down in a
continuous
layer that is as wide as the road 'being built. These techniques have been
developed
over many decades in conj un.ction with advances in road building methods and
machinery.
The machines required for building new roads in this way are large and
expensive.
They are satisfactory for the construction of a new road but it would be
impractical and
uneconomic to use them for sinall repairs such as potholes. The repair of
potholes thus
presents particular problems: Potholes are, by their nature, widely spaced
apart and
may be many kilometres away from a facility, of the kind. discussed above, for
preparing an aggregate/biturnen mix. The distance may be such that it is
difficult or
impossible to keep a mix that ha's been pre-prepared and transported to the
site of a
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pothole, at the correct temperature for use. The problem is exacerbated by the
fact that
only a small amount of material is required for ea.ch pothole.
The bitumen and the aggregate are heated when preparing a mix. Bitumen does
not
flow readily at arnbienl temperature, atid it must be heated to enable it to
form a good
matrix for the aggregate. The aggregate is heated to drive off residual
moisture but also
to keep the mix fluent. It is well known that moisture interferes with the
bond between
the bitumen and the particles in the aggregate. The bitumen and the aggregate
are
usually preheated separately especially in the large scale plants of the type
described
above used in the preparation of mix for making new roads. After being
heated,*the
bitumen and the aggregate are mixed together in a mixing vessel designed for
the
purpose.
It is important that the mix should be at the right temperature (1.70-180 C)
when it is
used. It is well established that there is an optimum temperature for good
bonding
between the aggregate particles and the biturnen. One of the most common
causes of
poor road construction or a poor repair is the use of a mix that has cooled
down or that
still contains moisture when it is applied, as this tends to disrupt the
bonding.
The applicant is aware of several mobile machines that are used in the repair
of
potholes. Most of these comprise a truck- or trailer-mounted insulated vessel
for
holding a hot mix that has been preprepared and loaded into the vessel. The
apparatus
may be provided wiih a small heating device, fuelled by LPG or diesel oil, for
keeping
the mix hot. These machines are not able to heat a bitumen mix from cold to
180 and
most of them do not have any mixing devices.
The applicant is aware of two mobile machines that do have mixing devices.
However,
the applicant believes that the disadvantages associated with the use of these
machines,
the construction and operation of which are discussed below, are such that
they have
not found widespread use. In any case, the applicant believes that the mix for
repairing
potholes is still most often prepared by methods that have been used for many
years. In
one such method, cornmonly used in less developed countries, the mix is
prepared by
hand at the site where the potholes occur. The aggregate and the bitutnezt and
placed in
a suitable receptacle that is heated, using a fire or other suitable heater.
The heated mix
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is then shovelled into a wheelbarrow or the like and taken to the pothole. In
bigger
jobs, the mix is prepared in a larger receptacle and loaded into a suitable
truck for
transport to the work site which may sometimes be perhaps 100 km distant.
Here, it is
tipped or hand shovelled into the potholes. In another method, the mix
comprises
aggregate added to a proprietary material comprising a bituinen base and
emulsifying
additives which renders the material fluent at a much reduced temperature. The
mix is
at this reduced tenaperature when applied to the pothole.
Both of these methods have their problems. It is practically impossible to mix
the
materials properly by hand in the manner discussed above and the applicant
believes
that the use of cold mixes comprising proprietary materials of the type
discussed above
results in poor quality repairs. Nevertheless, they rernain in widespread use
notwithstanding the availability of mobile mixing machines of the.type
mentioned
above.
One of the mobile machines mentioned above comprises, in essence, three
vessels
mounted on a trailer chassis that can be hooked on to a truck or other towing
vehicle.
'I'he aggregate is heated in one of the vessels and the bitumen is heated in
the second
vesseL The first and second vessels arc thus heating vessels. The heated
materials are
transferred to the third vessel. This is a mixing vessel and in it the
materials are mixed
together by rotating paddles provided for the purpose. The mixing vessel is
provided
with a gate through which the mixed materials can be discharged by gravity
into a
wheelbarrow or the like.
One disadvantage of this machine is that the components that handle the
bitumen, i.e.
the heating vessel, the mixing vessel and the associated pump and pipework by
which
the heated bitumen is transferred to the mixing vessel, must be cleaned after
each use
of the machine. The cleaning operation can typically take an hour or even two.
If the
machine is not cleaned and the hot bitumen or hot mix has been allowed to cool
in the
pump and pipework or the mixing vessel, it is very laborious and time
consuming to
clca.r them.
Another disadvantage of this machine is that the heating vessel for the
aggregate is of
the type that comprises a cylindrical shell that is supported on rollers and
rotates about
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a horizontal axis. A measured quantity of aggregate is charged through an
inlet
aperture formed in a plate located at one end of the shell. The aggregate is
heated as
the shell rotates and is discharged through an outlet aperture formed in a
second plate
at the opposite end of the shell. Both of the apertures have gate-type
closures to retain
the aggregate in the shell as it rotates. The shell is heated by burners that
are located
inside the shell above the aggregate. The outlet aperhue is located adjacent
the bottom
of the shell to allow the aggregate to flow out of the shell by gravity. The
inlet aperture
is located well below the top of the shell. The heated moisture forms steam
and, in the
applicant's experience, it is difficult for the steam to exit the shell
efficiently due to the
fact that the apertures are normatly closed by the gates and are located below
the top of
the shell. The result is that the aggregate is often not properly dry when it
leaves the
shell or, at best, the aggregate must be held in ttxe shell for longer than is
necessary in
order to ensure that it is properly dry._
In the second mobile machine known to the applicant, mentioned above, a truck
is
provided with a tipping body into which.a tpix that has been preprepared is
tipped. The
floor of the body comprises two flat surfaces that run the length of the body
and slope
upwardly on each side of the fore-and-aft centreline of the floor. Two heater
tubes and
two rotating agitator shafts are mounted in the body, running the length
thereof. The
shafts have screw-type flights that convey hot mix material that gravitates
into their
path in the fore-and-aft direction of the body and thus perform a mixing
function. Hot
gas from an LPG burner carried on the vehicle flows through the tubes. The
body has
an open top provided with covers. The body and the covers are insulated. An
aperture
is provided in the rear wall of the body. The hot mix is discharged through
this
aperture when the body is tipped.
This machine has three disadvantages. The heating arrangements are
insufficient to
heat a full load of mix from cold to 180 C in any practical sense and it is
thus again
necessary to ensure that the vessel is cleaned befoie it is allowed to cool.
Second, the
agitator shafts do not perform the mixing function with any great efficiency
with the
result that some parts of the mix are liable to be too cold and other parts
too hot. A
third disadvantage is that the bearings of the agitator shafts are liable to
failure as a
result of the stresses that they undergo due to the thermal expansion of the
agitator
shafts.
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Although the mixing process is apparently simple, well-known techniques have
been
developed in order to achieve a good quality mix. For example, it is knoAn
that the
quality of the mix can be improved by adding the particles of each size in
sequence to
5 a batch of aggregate that is being dried. Often the sequence is starts with
the largest
size and progresses to the smallest size (which is, essentially, dust). The
bitumen is
best added after sotne of the dust has been added and the batch is properly
dry.lvlore
dust can then be added to bring the mix to the right consistency. The sequence
is also
sometimes reversed. It is not possible, in a practical sense; to use these
techniques with
the mobile machines described above.
STATF:.Mf:NTS OF THE iNVENTION
According to the invention, there is provided apparatus for preparing a hot
mix
comprising aggregate and bitumen, the apparatus comprising a vessel
incorporating a
mixing chamber arranged to receive aggregate and bitumen, means for mounting
the
vessel on a vehicle, heating means arranged to heat the aggregate and bitumen,
and
mixing means for innixing the aggregate and bitumen to form a hot mix, the
vessel
comprising a shell and the mixing means comprising a rotor that can be mounted
in the
shelt for rotation about a rotational axis that is disposesi longitudinally in
the shell and
is arranged to carry at least one mixing member that is disposed transversely
to the
rotational axis and, as the rotor rotates, describes a path that substantially
spans the
space between the rotor and the shell.
According to one aspect of the invention, the shell is of right circular
cylindrical shape
and the rotational axis is coincident with.the longitudinal axis of the shell.
In. another aspect of the invention, the shell is mounted on the vehicle in a
vertical
disposition.
In yet another aspect of the invention, the shell comprises a cross member on
which
the rotor is rotatably mounted.
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Advantageously, according to the invention, the cross member is located at
wbat, in
use, is the lower end of the mixing chamber.
In one form of the invention, the rotor comprises a rotatable shaft and the
apparatus
5. comprises a bearing arrangement that is mounted on the cross meritber ain.d
in which an
end of the shaft rotates,
In one aspect of the invention, the bearing arrangement comprises an opening
such that
material from the mixing chamber that passes between the shaft and the bearing
arrangement can pass back into the mixing chamber.
In one form of the invention, the apparatus comprises a drive arrangement for
rotating
the rolor, the drive arrangement comprising a driven rotary member in which is
forned
a passage through which the rotor projects, the passage and the rotor being
eomplemen.tarily out-of-round so that the rotor is able to slide axially in
the passage
while being driven by the rotary member.
According to yet another aspect of the invention, the vessel is mounted so as
to be
stationary on the vehicle when the aggregate and bitumen are being heated and
mixed.
Advantageously, according to the invention, the vessel comprises a second
chamber
located adjacent the mixing chamber, the heating means being located in the
second
chamber.
It is envisaged that the vessel could be mounted on a vehicle that is self
propelled or
that is in the forin of a trailer that is towed by second vehicle. The trailer
would.
advantageously be provided with an engine or other means for powering the
mixer and
tilting mechanism.
The intended use of the apparatus has important effects on variuus aspects of
its
design. A vital feature of the apparatus is that it should be able to
transport the mix
from a locality at which the vessel is charged with the ingredients of the mix
and'the
work site where the mix is discharged. It is highly unlikely that the use of
public roads
could be avoided in this task and the size of both the vehicle and the vessel
will be at
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least partially determined by tlus, since the size of any vehicle that uses a
public road is
limited by regulation. Furthernio'rc, the apparatus is intended primarily for
use in
repairing roads, rather than for building new roads, although a vehicle for
the latter
purpose is not necessarily excluded from the scope of the iunvention.
Consequently, it is
highly desirable that the vehicle sbould be very manoeuvrable at the work site
and this
will also affect the size of the vehicle, the length of its wheelbase and the
like.
Furthermore, again because of the primary intended use of the vehicle, the
heating
means should advantageously be designed to heat the ingredients from the
ambient to
the minimum mixing temperature in a reasonably short period of time that is
affected
at least partially by the time taken for the vehicle to transport the load
from. the locality
at which the vessel is charged with the ingredients of the mix to the work
site where
the mix is discharged. The maximum kW output of the heater will therefore need
to be
relatively large, and this maximum will increase with the volume of the
ingredients .
that the vessel is capable of holding. However, both the maximum heat output
and the
volume of ingredients vvill be liinited by the size of the vehicle, as already
noted.
A detailed description is given below of a vessel mounted on a vehicle that
are both
considered, at the present time, to be of optimum size. The sizes given are
merely
examples and there is no intention that the scope of the invention should be
limited to a
vehicle and vessel of these sizes. The vessel in the example is smaller than
the
maximum presently envisaged according to the invention or the maximum as
deternnined by the parameters discussed above. One reason for this difference
in sizes
is that, as should be obvious, as the apparatus gets bigger, it also becomes
more
expensive and less manoeuvrable. The size of the necessary heater also
increases and it
may become more difficult to provide a heater with suff'icient output to heat
the mix in
a reasonable time., So the overall usefulness of a larger vehicle and vessel
may be
diminished.
The applicant believes that the road regulations in most countries would limit
the
volume of the vessel to about 8 cubic metres and that a heater for heating the
charge in
a vessel of this size would be of tiie order of 200kW. In the exarnple of the
invention
given below, the appara.tus is provided with a gas heater with an output of
about
75kW. This is considered sufficient to heat a mix having a volume of about 0.7
cubic
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metres. Although not to be excluded from the scope of the invention, it is
considered
unlikely, at the present time, that apparatus constructed according to the
precepts of the
invention and requiring a heater of 200 kW output would be cornmercially or
practically viable, at least for repair work on roads as opposed to the
building of new
roads. At least one reason for this is that it is likely to be difficult and
expensive to
design a vehicle which would be practical to operate, and which would not be
damaged
by the heat radiated by an apparatus of this size
It is also likely that apparatus that is constructed and used in accordance
with the
present invention but that is of less than a certain capacity will be
uneconomic to
operate_ For instance, an apparatus that is of smaller size than that
described with
reference to the drawings should not necessarily be excluded from the scope of
the
invention.
The smallest and largest size of an apparatus that has comrnercial value will
be
determined by demand in the market place.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further discussed with reference to the accompanying drawings
in
which a vehicle for use in road repair. is illustrated by way of example, and
in which
Figure 1 is a somewhat schematic side elevation, partly in section, of a
vehicle
fitted with a vessel for preparing a road mix;
Figure 2 is a plan view of the vehicle also partly in section of the vehicle
shown
in Figure 1;
Figures 3 and 4 are enlarged sectional views of two bearing arrangements with-
which the vessel is provided;
Figure 5 is a view on arrows A-A- in Figure 4; and
Figure 6 is a view in elevation of a paddle ann
In the description that follows, only those parts of the vehicle and vessel
that are
relevant to the present invention will be described in detail. Furthermore,
the design
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and construction of many parts of the vehicle and vessel are either known or
would
present no difficulty to those skilled in the art. In some cases, these parts
are
commercially available. Parts that are not sliown in the drawings fall into
these
categories unless it appears otherwise from the context.
Referring to the drawings, there is shown a vehicle 10 having a pair of front
wheels 12
and a pair of rear wheels 14. The vehicle is propelled by the front wheels and
steered
by the rear wheels. A vessel 16 is mounted on the front of the vehicle 10. The
vehicle
comprises a chassis or frame 18 on which is mounted an engine 20 housed in a
bonnet
22. In the present example, the engine is a diesel engine of 34 h.p. The
engine is
located at the rear of the vehicle and is coupled to a hydraulic pump assembly
24. A
seat 26 for the driver is mounted to one side of the engine_ The driver thuS
sits at the
rear of the vehicle, facing forward in an optimum position to view the
operation of the
vessel. As no cab is provided, the driver sits in the open, behind a steering
wheel 28
supported by a bracket 30. The_vehicle in this example is about 3.3 metres
long and 2.0
metres wide.
The vessel 16 comprises an inner steel shel132 with a right circular
cylindrical body
and, atits upper end, a dome shaped cross member that will be referred to as
the top
wail 36. A cylindrical outer shel138 surrounds the inner shell with a space
therebetween forming an annular passage 40 between the two shells. The shell
32
incorporates an upper chamber 42 that in use functions as a mixing chamber in
which
aggregate and bitumen are.mixed together, as will be desciibed. The upper
chamber is
separated from a second, lower, chamber 44 by a floor comprised of two dome
shaped
-cross members that will be referred to as cross walls 46, 481ocated one above
the
other. Mixing means is the form of rotor comprisi.ng a paddle assembly 50
mounted on
a shaft 60 is located in the upper chamber and heating means in the form, in
this case,
of a=gas ring 52 is located in the lower chatnber, suppoA-#ed by a cross
member 54.. In
the lower chamber, apertures 56 are formed in the wall of the shell 32. Via
the annular
passage 40, the apertures connect the lower chambei to chimneys 58 spaced
around the
domed top 36.
The paddle assembly 50 comprises a pair of mixing members in the form of
paddle
arms 50a, 50b. The paddle arms are mounted in alignment with each other on
opposite
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sides of the shaft 60, which is of square cross section. The shaft is disposed
longitudinally the shell. The shaft is carried in bearing arra-ngements
mounted on the
upper cross wall 46 and in the top wall 36 respectively and rotates about a
rotational
axis X that is coincident with the longitudinal axis of the shell that, in the
present
5 example, is vertical.
The upper end 60a of the shaft projects through a drive arrangement 62 that,
in this
exatnple, corriprises a driven rotary member in the form of a gear wheel 66
driven by a
worm. The worm is coupled to a hydraulic motor 70 driven, through suitable
hydraulic
10 lines and controls to the pump assembly 24. The gear wheel 66 is integral
with the
outer race 72a of a roller bearing assembly 72 the inner race 72b of which is
bolted to
tlie floor of the gearbox housing 74. The gearbox in turn is bolted to'the top
of a
pedestal assembly 36a that is mounted on the top wal136 of the vessel. The
outer race
is bolted to a circular collar plate 76. The bearing assembly 72 and the
collar plate are
parts of the upper bearing arrangement for the shaft 60. The collar plate is
provided
with a central passage 78 that is of square cross sectional shape of size
complemental
to the shaft 60 and such I.hat, when the gear wheel rotates, the collar plate
engages the
shaft, forciiig it to rotate also. However the s.haft is also able to slide up
and down in an
axial direction in the passage 78. This is important as the sha.ft undergoes
considerable
such axial movement up and down as the apparatus heats up and cools down. This
axial movement is as much as 30 mm in the present example. It is not essential
that the
shaft 60 and lhe passage 78 be of square cross sectional shape but this shape
is
probably the most practical. Any suitable out-of-round shape could be used.
The lower end 60b of the shaft is machined so that it is round and is received
in the
lower bearing arcangement 64. This arrangement comprises a vertically disposed
sleeve 80 that in use functions as a bearing bush for the lower end of the
shaft. The
sleeve is supported above the cross wa1146 on four legs 82 that are welded to
the
sleeve and to the~ cross walI 46. The legs are equally spaced about the
periphery of the
sleeve. There is thus a space 84 between ihe lower end of the sleeve and the
cross wall
and there are gaps 86 betweeTi each pair of the legs. Additionally, openings
in the form
of vertical slits 88 are formed in the lower end of the sleeve 80. These slits
are open to
the gaps 86 between the legs 82.
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In use, material firom the aggregate and bitumen that is being mixed in the
mixing
chamber migrates, principally under the force of gravity, between the lower
end 60b of
the shaft and the sleeve 80. It has been found that this material has a
tendency to build
up in the sleeve and, in the absence of means to prevent it, eventually causes
the shaft
to seize. The build up is prevented by the presence of the space 84 and the
slits 88
which function as openings through which the material is able to exit the
sleeve
through the gaps 86 and back into the mixing chamber.
In the present example the diameter of the lower end of the shaft is about 58
mm and
the internal diameter of the sleeve 80 is about 61 mm. There is thus
considerable
clearance therebetween. This is necessary to accommodate the considerable
ehatiges in
size of the components due to thermal expansion and contraction. It has been
found in
practice that, at it's centre, the cross wall 46 is typically lifted by about
30 .mrn due to
thennal expansion as it heats up to working temperature.
The paddle arms 50a, 50b that are similar to each other and only one is
described in
detail. The ann 50a is fabricated from a steel plate 98, tapered inwardly from
its inner
end to its outer end and reinforced by a rib 100 that is welded to the
approxiniate
centre of the face 102 of the plate and runs along the entire length thereof_
At its inner
end, the plate 98 is welded to an upstanding rectangular mounting plate 104
with
boltholes drilled in each corner. The paddle arms are mounted on the shaft 60
by
means of bolts 108 that pass through the holes and clamp the respective
mounting
plates against opposite faces of the shaft. Two upstanding paddle plates 110a,
110b of
approximately trapezoidal shape are welded to the face'i 12 of the plate 98.
Wearing
shoes 114 may be welded to the lower edges of the respective paddle plates_
The width
of each paddle plate is about a quarter of the length of the plate 98. The
paddle plates
11 0a, I I Ob on the arm 50a aremounted on the plate 98 with a space 116
between them
approximately equal to the width of each paddle plate. The paddle plate l 10a
is
mounted at the outer end of the plate 98. The space 118 between the paddle
plate 1.10b
and the mounting plate 104 is thus again approxi.mately equal to the width of
each
paddle plate.
The paddle arm 50b is substantially simila.r to tlie paddle arm 50a with the
exception of
the positioning of the pa.ddle plates. While the paddle plates of the arm 50b
are also
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mounted with a space 116a between them approximately equal to the width of
each
paddle plate, the inner paddle plate of the arm 50b is located close to the
mounting
plate 104 of that arm. The result of this arrangement is that, when the shafl.
60 is
rotated, the paddle plates between them sweep the entire diameter of the shell
32 and
the cross wall 46. The paddle plates are shaped and mounted on the arms 50a,
50b in
such positions that the wearing shoes are located close to, and parallel with,
the domed
upper cross wall 46. The outer ends of the paddle arms are located close to
the inner
face of the shell 32.
As the rotor rotates, each paddle arm thus sweeps through a path that
substantially
spans the space between rotor and the shell 32. Furthernlore, the path swept
by the
paddle arms jointly is substantially coincident with the upper surface of
shell floor.
The tops of the paddle plates are located close to the top of a full load of
aggregate in
the mixing chamber. Virtually all of the load is thius subject to the mixing
action of the
paddle assembly during each revolution of the rotor and the mixing acEion is
thus
highly efficient. This action is most efficient when the shell is right
circular cylindrical.
A shell of this shape is also likely to be the most economical to produce.
However,
shells of other shapes are not necessarily excluded from the scope of the
invention.- A
shell of square shape could also conceivably be used. In this case, the path
swept by
the paddle atms would best span the smallest space between the rotor and each
vertical
wall of the shell. This space would extend between the rotor and the centre of
the
vertical wall.
An aperture in the form of a manhole 120 is provided at the ft-oni. of the
domed top
wall 36. Aggregate and lumps of bitumen in solid condition are shovelled into
the
upper chaniber through this manhole, as will be described.
Discharge means are provided in the form, in the present example, of a
closable
aperture or manhole 122 is provided low down at the front of the shell,
adjacent the
upper cross wall 46. The manhole is closed by a manually operated, guillotine
type
gate 124. A chute 126 is mounted adjacent the manbole 122. VJhen the aggregate
and
bitumen have been properly mixed and heated to the correct temperature in the
upper
chamber, the mix can be.discharged through the manhole and onto the chute.
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The heater 52 is a two ringed gas burner fed from twin gas cylinders 128
through
suitable hoses. Zn the present example, the heat output 'of the burner is of
the order of
75 kVd, as already noted. The domed shape helps to prevent thermal distortion
of the
cross walls 46, 48. Notwithstanding the domed shape, in the absence of the
lower cross
wali 48, the heat from the burner would be likely to overheat the upper cross
wall 46,
causing it to distort. The two cross walls are located close together in order
to
maximise heat transfer and the presence of the lower cross wal148 helps to
spread the
heat and avoid hot spots in the upper cross wa1146.
A layer 130 of suitable insulating material is placed around the outside of
the shell 38
to reduce heat loss. The insulating material is held in place and protected by
a steel
sheU 132. The hot gases from the bumer pass through the apertures 56 in the
shell 32
and out through the chimneys 58 via the annular passage 40_ These gases heat
the wall
of the shell 32 and the heat is transferred to the mix in the upper chamber.
The vessel 16 is mounted on the frame 18 so as to be capable of tilting
forward about
a hinged connection 134 located at the front edge of the frame. The tilting is
brought
about by a hydraulic ram 136. The lower end of the ram is mounted on the fxame
through a pin seated between trunnions 138 welded to the frame. The upper end
of the
ram is similarly mounted on the vessel through a pin seated between trunnions
140
welded to the shell 38. The ram is actuated by the driver through suitable
controls, not
shown. As should be clear, the vcssel remains stationary on the frame while
the
aggregate and bitumen are being heated arid mixed.
A safety barrier may be monnted on the fr6nt of the vehicle, surrounding the
front of
the vessel 16. The barrier comprises a series of steel stanchions 144 welded
to the
frame 18 at their lower ends and carrying rails 146 welded to their upper
ends. The
barrier is intended primarily to prevent damage to the vessel in the event
that the -
vehicle collides with objects around a work place. One example af such an
object is
the back of a delivery vehicle that carries aggregate and/or raw bitumen. It
would often
be convenient to shovel the aggregate or bitunen directly into the vessel from
the
delivery vehicle and the two vehicles would be brought together for the
purpose.
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14
The vehicle is obviously provided with the controls necessary for its
operation. These
controls would include a temperature gauge, visible from the driver's seat,
for
checking the temperature of the i ix; and a regulator for controlling the flow
of gas to
the burner.
In use, stocks of raw bitumen and stones for aggregate are brought to a
convenient
place in the vicinity of wherc there are potholes in a tar-sealed road. For
practical
purposes, raw bitumen is solid at ambient temperature and the bituunen in the
stock is
broken into lumps that can pass through the manhole 120. The stones should
advantageously, but not essentially, be graded according to their size and
left in
separate stockpiles. All this is well known to experieneed operators. The
vehicle 10
illustrated in the drawings has a maximum tra.velling speed of about 12 km/h.
This
would be one of the factors that would determine how far away the stockpiles
can be
from the furthest pot hole that must be repaired. If the travelling speed
renders the
working range of the vehicle unacceptably low, the vehicle 10 can be carried
to the
work place on the back of a truck or trailer capable of a higher speed. An
alternative
exarnple of an apparatus according to the invention would be a vessel similar
to the
vessel 16 rnounted directly on a vehicle in the form of a trailer that is
towed by a
second vehicle. This second vehicle could be a cornmercial.ly available truck
and
would usually be capable of a much higher speed than 12 km/h.
The vehicle 10 is taken to the stockpiles where, in one method of use, first
the
aggregate is loaded into the upper chamber 42 through the manhole 120, while
the
muxer 50 is rotating and the burner lit. An experi.enced operator will know
the
sequence in which the material should loaded. This has been discussed above.
Such an
operator will also know how long mixing and heating of the aggregate should be
continued. Mixing is continued until the mixed aggregate is dry and has been
brought
up to the correct temperature. At this stage lumps of solid bitumen,
conveniently at
ambient temperature, are loaded by hand through the manhole 120. When the
bitumen
has melted and is well mixed with the aggregate, a further small quantity of
dust may
be added to bring the rnix to the correct consistency for use.
It should be stressed that, instead of loading one grade of aggregate after
the other, it is
possible to use a premixed composition of several aggregate sizes and dust and
then
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add the bitumen. It is also possible, instead of adding the bitumen in solid
(cold) form,
it can be added in preheated, liquid form.
It is an advantageous feature of the present inverition that the matnhole 120
is located
5 close to the top'of the vessel. This enables substantially all of the
moisture driven off
the aggregate to escape to atmosphere as efficiently and quickly as possible.
This
feature is made possible by the fact that the vessel is stationary in use.
Based on these
parameters, the vessel and the shaft are most suitably vertically, or at least
uprightly,
disposed.
The mixer 50 continues to rotate while the vehicle is driven or taken to a
selected one
of the potholes to be repaired. The burner remains lit to keep the mix at the
correct
temperature. At the work site, the driver manoeuvres the vehicle so that the
chute 126
is over the selected pothole and actuates the ram 136 to tilt the vessel 16
upwards and.
forwards about the hinge 134. A second operator lifts the gate 124 to allow
the
required amount of hot mix to flow out of the vessel and over the chute from
where it
,=t
is deposited in the pothole. The driver returns the vessel to the upright
positiozi and
backs the vehicle away from the pothole. The hot mix in the selected pothole
is worked
in known manner to complete the repair.
In the present example, the i.nternal diameter of the shell 32 is 126 cm. The
vertical
distance between the upper cross plate 40 and the domed top 36 is 75 cm, and
the
distance from the bottom of the shell to the upper cross plate 40 is 30 cm.
These
dimensions are taken at the centre of the shell. The volume of the upper
chamber 36 is
thus about 930 litres. This is su.ff-icient for a charge of about 700 litres
of aggregate and
bitumen. The width of the annular passage 40 is 30 mm and the distance between
the
shell 38 and the shell 132 is 60 mm. The wall thicknesses of the shells 32, 38
and 132
are 6, 3 and I mm respe3ctiveiy. The overall diameter of the vessel is thus
about,156
cm. This is less than the maximum width of the vehicle 10. The highest point
on the
vehicle, with the vessel mounted in place, is at the top of the vessel and is
about 203
cm above the road surface: The vehicle is thus well within the height.and
width limits
for vehicles to be allowed on the public roads of most countries without a
special
permit.
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16
The manhole 120 for filling the vessel is about 177 cm above the ground and
the
manhole 122 through ~Nrhich the mix is discharged is about 73 cm above the
ground.
There is no serious disadvantage in allowing any mix remaining in the mixing
chamber when a job is eompleted to cool and become solid as the mix can be
made
fluent again simply by heating. There is no pump or pipework to be cleaned at
the end
of a shift and, if necessary, the mixing chamber can easily be cleared by
working
through the manholes.
It may be noted that the machines consiructed according to the precepts of the
invention can be used to heat bitumen only or bitumen mixed with quarry dust
in a
certain percentage to repair, fill or seal cracks in the bitu.men.layer.of
roads to prevent
water from destabilizing the roadbase. The same machines can also be used to
seal
roofs, expansion gaps in concirete roads and slabs.
It is not intended that -xecognised mechanical equivale.nts of and/or
modifications of
and/or improvements to any matter described and/or illustrated herein should
be
excluded from the scope of.a patent granted in pursuance of any application of
which
this specification forms a part or that claims the priority thereof or that
the scope of
any such patent should be limited by such rnatter further than is necessary to
distinguish inventive matter disclosed herein from the prior art.
