Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
METHOD AND APPARATUS FOR ELECTRICALLY
HEATING A SCREED ASSEMBLY IN A PAVING MACHINE
FIELD OF THE INVENTION
[0001] The invention relates to paving machines and, more
particularly, relates to an improved method and apparatus for uniformly
heating
a screed plate of a paving machine by providing a conductive plate between an
electrical heating element and the screed plate, and for providing a clamping
mechanism that permits the electrical heating element to be easily replaced
without the need to remove the screed plate.
DISCUSSION OF THE RELATED ART
[0002] Paving machines are well known for working paving materials
into a mat to produce roads and other paved structures. Specifically, the
typical
paving machine transports paving materials from a hopper along a conveyor
system and ultimately to a distributing auger, where the paving materials are
distributed onto a roadway or another surface, where a screed plate then paves
the paving materials into a mat. While the paving materials could be any of
various known materials, hot mix asphalt (HMA) is commonly used and, for the
sake of convenience, the paving materials will hereinafter be referred to as
HMA.
[0003] The screed plates of HMA paving machines are typically
preheated to a temperature of about 200 F to 300 F before paving commences
and are maintained at this temperature during paving to prevent the hot
asphalt
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being levelled by the screed plate from congealing on the face of the screed
plate. Screed plates have traditionally been heated by oil or gas burners
mounted above the screed plate such that the flames from the burners impinge
sheet metal plates on top of the screed plate. Such burners supply intense
heat
to localized portions of the screed plates which results in uneven heating and
congealing of the HMA onto the screed plate. Additionally, if the process is
not
carefully controlled, the screed plate may warp and become ineffective.
Furthermore, as the flames become progressively dirtier, noxious fumes are
emitted for the operator to contend with.
[0004] Systems have been proposed which are designed to avoid or
to at least alleviate some of the problems associated with traditional screed
heaters. In one such system, a heater heats the screed plate of a paving
machine via heat transfer from heating oil stored in a low pressure reservoir
mounted directly on top of the screed plate. Oil in the reservoir is drawn
from
the reservoir, pressurized by a high pressure pump, and then fed through a
pressure release valve or other suitable flow restrictor which creates a
pressure
drop in the range of about 700 to 800 psi, thereby heating the oil to a
temperature of about 275 F. The thus-heated oil is then returned to the
reservoir for heat transfer to the screed plate.
[0005] This heated oil system suffers from several drawbacks and
disadvantages. Most notably, the large pressure drops needed to provide the
necessary heating require that the heating oil be pressurized by a pump to a
relatively high pressure in the range of 800 to 1000 psi before undergoing the
pressure drop in the flow restrictor. This requires the use of high pressure
hoses and connections throughout the system, thus increasing the cost and
complexity of the system and also increasing the dangers of leaks which could
render the system ineffective. Moreover, if for any reason the pump and relief
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valve are not capable of providing a sufficiently large pressure drop to
adequately heat the oil, the system then becomes incapable of boosting the oil
temperature to the required level.
[0006] It therefore became desirable to develop a screed plate
heating system that involves no moving parts, runs clean, emits no noxious
fumes, and is capable of uniformly heating the screed plate.
[0007] One known system that strives to meet at least some of these
goals involves the installation of electrical heating elements that are in
direct
contact with the screed plate to heat the screed plate. Being electrically
powered by a sufficiently sized generator, this system does not have the
disadvantages associated with combustion, and also ensures that sufficient
energy is supplied to the electrical heating elements so that the screed is
adequately heated. Furthermore, the generators associated with the
electrically
heated systems allow the use of higher wattage lights than the conventional
twelve-volt lights used on traditional paving machines, thus facilitating
night
operation. However, the direct contact between the heating elements and the
screed plate gives rise to heat distribution problems similar to those
encountered by oil-heated screeds. Specifically, hot spots develop on the
screed plate at the point where the heating element contacts the screed plate,
and the screed plate cools progressively at points more distant from the
contact. This uneven heat distribution can also lead to relatively high
temperature gradients, and possible warping of the screed plate. Another
disadvantage arises when the electrical heating elements require either repair
or replacement. In order to remove a heating element from this system, the
screed plate must first be removed before an operator is able to access the
heating element. This removal requirement is very time consuming and labor
intensive.
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[0008] The need has therefore arisen to provide an electrically
heated screed assembly, which is capable of uniformly heating the screed plate
while allowing easy access to and replacement of the heating elements without
having to remove the screed plate.
OBJECTS AND SUMMARY OF THE INVENTION
[0009] It is therefore a first object of the invention to provide an
electrically heated screed assembly for a paving machine that heats the screed
plate uniformly, thus preventing both paving material congealing and screed
warping.
[0010] A second object of the invention is to develop an electrically
heated screed assembly that allows for easy removal of the heating elements
of the assembly for repair or replacement without having to remove the screed
plate or otherwise disassemble the screed assembly.
[0011] A third object of the invention is to develop an electrically
heated screed assembly that has one or more of the aforementioned
advantages and that is extendible to widen the screed assembly, thus
permitting paving of a wider area.
[0012] In accordance with a first aspect of the invention, a subframe
attaches to the frame of the screed assembly. A screed plate is mounted onto
the bottom of the subframe and a thermally conductive plate, such as
aluminum, is disposed adjacent to the screed plate in a manner so as to span
the length of the screed plate to a point just short of the midpoint of the
screed
plate's length. An electrical heating element, which may comprise a metallic
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material having a resistive coil wound inside it, is placed onto the thermally
conductive plate. The heating element is wired to a power generator which
supplies energy to the coil, thus heating the heating element. The thermally
conductive plate then becomes uniformly heated and supplies this heat to the
screed plate. The thermally conductive plate therefore effectively acts as a
heating element and, because it is in thermal contact with a substantial area
of
the screed plate, it operates to heat the screed plate uniformly. An
insulation
layer may be placed above the electrical heating element to maximize the
percentage of generated heat that is directed downwards toward the
conductive plate and screed plate. Several electrical heating elements may be
placed in strategic locations throughout the screed plate. To permit the
screed
plate to crown during operation, the heating elements and conductive plate
preferably do not span the entire length of the screed plate. They instead
span
to a point short of the midpoint of the screed plate's length, and a
complimentary assembly is located on the other side of the screed so as to
also
span to a point just short of the midpoint of the screed plate. Several rows
of
heating elements may be installed so that the entire screed plate is
sufficiently
heated.
[0013] In accordance with a second aspect of the invention, a
clamping mechanism is installed on the heating element that, when tightened,
compresses the associated heating element against the screed plate. When
the clamping mechanism is loosened, the compressive force is relieved from
the heating element, thus permitting an electrical heating element to be
removed by an operator simply by pulling it in a longitudinal direction away
from
the screed assembly without first having to remove the screed plate. A new or
repaired heating element may then be inserted into the system before re-
tightening the clamping mechanism.
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[0014] In a preferred embodiment, the clamping mechanism
comprises a tubular beam that is placed above the insulation or,
alternatively,
directly above the heating element. A bracket is mounted on top of the beam
and a vertical hole is created in the bracket's upper horizontal surface.
Likewise, a vertical hole is formed in the upper horizontal surface of the
subframe. The subframe hole is aligned with the hole in the bracket so that a
bolt or other suitable threaded fastener may be inserted into both holes.
[0015] In one embodiment of the invention, the hole through the
subframe surface is tapped and threadedly engages the bolt threads.
[0016] In another embodiment, a first nut is mounted on the
subframe's upper horizontal surface, and the bolt is inserted into both holes.
A
second nut is mounted onto the bolt at a point located between the hole in the
bracket and the beam. Therefore, when the bolt is tightened, the beam is
lowered and provides a compressive force on the screed assembly.
Conversely, when the bolt is loosened, the second nut exerts an upward force
on the bracket, thus raising the beam and relieving the compressive force. The
tapped hole through the subframe surface, mentioned above and preferred,
achieves the same effect.
[0017] Additionally, a series of pusher bolts may be added to the
clamping mechanism, that extend through the upper horizontal surface and
contact the beam to provide uniform pressure throughout the screed assembly.
[0018] In accordance with a third aspect of the invention, an
extension is provided that can be attached to the pre-existing screed
assembly.
Specifically, the extension includes a subframe having a vertical wall that is
bolted onto a vertical wall of the frame of the paving machine. The extension
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also includes an electrical heating element and a thermally conductive plate,
as
well as the aforementioned clamping mechanism. This is particularly useful
when an operator needs to pave a wider surface than usual.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Preferred exemplary embodiments of the invention are
illustrated in the accompanying drawings in which like reference numerals
represent like parts throughout, and in which:
[0020] Figure 1 is a side elevation view of a paving machine that
incorporates an electrically heated screed assembly constructed in accordance
with a preferred embodiment of the present invention;
[0021] Figure 2 is a sectional side elevation view of the screed
assembly of the paving machine of Figure 1, on an enlarged scale relative
thereto;
[0022] Figure 3 is a sectional rear elevation view of the screed
assembly with the exterior frame removed;
[0023] Figure 4 is a fragmentary sectional side elevation view of one
of the clamping mechanisms of the screed assembly with a cutaway portion of
the frame, taken along the plane 4-4 in Figure 2 and on an enlarged scale
relative thereto;
[0024] Figure 5 is an exploded perspective assembly view of the
screed assembly;
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[0025] Figure 6 is an exploded perspective view of one of the
heating elements and the associated clamping mechanism of the screed
assembly;
[0026] Figure 7 is a sectional side view of a portion of the heated
screed assembly, on an enlarged scale relative to Figure 2;
[0027] Figure 8 is a sectional end elevation view of a portion of the
screed assembly, taken along the plane 8-8 in Figure 7 and on a slightly
reduced scale relative thereto;
[0028] Figure 9 is a rear elevation view showing the two halves of
the screed plate of the screed assembly, on a slightly reduced scale relative
to
Figure 3;
[0029] Figure 10 is a fragmentary sectional side elevation view
showing an extension mounted onto the screed assembly, on an enlarged
scale relative to Figure 9; and
[0030] Figure 11 is an exploded perspective view of the extension.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0031] Pursuant to the invention, a paving machine is provided
which employs an electrically heated screed assembly including a screed plate
and electrical heating elements that are in contact with a thermally
conductive
plate which is in contact with the screed plate. In this manner, the screed
plate
is uniformly heated. Clamping mechanisms are also installed in the screed
assembly which, when loosened, allow for easy removal and replacement of
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the electrical heating elements without removing the screed plate. When
tightened, the clamping mechanisms supply a compressive force to the heating
elements, thereby preventing removal of the heating elements in the tightened
state.
[0032] Referring to the drawings and initially to Figure 1 in particular,
a paving machine 20 is illustrated that includes a self-propelled chassis 22
on
which is mounted an engine 24; a hopper 26; and a paving apparatus including
a distributing auger mechanism 28 and a screed assembly 30. The chassis 22
is mounted on two front axles 32 and rear axle 34, receiving front steering
wheels 36 and rear driving wheels 38, respectively. The front 32 and rear 34
axles are steered and powered hydrostatically by engine 24 in a known
manner.
[0033] The hopper 26 preferably has a total capacity of about twelve
tons to conform with industry standards and is designed to receive the paving
materials 40 and to temporarily store them pending their delivery to the
paving
apparatus. While the paving materials 40 may comprise any known material,
HMA is typically used and, for the sake of convenience, the paving materials
40
will hereinafter be referred to as HMA. A conveyor assembly 42 transports the
HMA from a rear discharge opening of the hopper 26 to the auger mechanism
28 of the paving apparatus.
[0034] The distributing auger mechanism 28 of the paving apparatus
may be any conventional mechanism and, in the illustrated embodiment, is of
the type employed by the paving machine manufactured by Roadtec of
Chattanooga, Tennessee under the Model No. RP 180-10. The distributing
auger mechanism 28 thus includes a hydrostatically driven bolt-type
distributing
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auger extending transversely across the chassis 22 and mounted on a slide
(not shown) which is raiseable and lowerable with respect to a stationary
frame.
[0035] The screed assembly 30 comprises a pair of transversely
spaced apart tow arms 44 (only one of which is shown in Figure 1), and a
heated (and preferably vibratory) screed plate 46 pivotally suspended from the
rear ends of the tow arms 44. Each tow arm 44 is raiseable and lowerable with
respect to the chassis 22 at its front end via a first hydraulic cylinder (not
shown) and at its rear end via a second hydraulic cylinder 48. The front of
each
of the tow arms 44 is also pivotally connected to the chassis 22 at a tow
point,
formed from a bracket assembly, so as to permit vertical adjustment of the
screed assembly 30 using the hydraulic cylinders mentioned.
[0036] In operation, the paving machine 20 is positioned on the
surface to be paved 50, and the hopper 26 is filled with the preferred paving
material 40, HMA. The conveyor assembly 42 then is activated to transport the
HMA to the paving apparatus. An operator (not shown), when seated at a
station or console 52, then controls the engine 24 to propel the paving
machine
forward, in the direction of the arrow shown in Figure 1. Paving is commenced
by discharging HMA 40 from the hopper 26 to the distributing auger 28, which
then remixes and distributes the HMA 40. The screed assembly 30 then works
the HMA into a mat 54 on the paving surface 50.
[0037] Referring now also to Figure 2, the screed assembly 30
further includes a main frame 56 and a subframe 58 mounted on the bottom of
the main frame 56. A screed plate 46 is then mounted on the bottom of the
subframe 58, thereby providing the foundation for the installation of the
heating
elements 60. The screed plate 46 is covered by, and is in direct contact and
thermal communication with, a thermally conductive plate 62. The thermally
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conductive plate 62 is in thermal communication with the screed plate 46,
preferably by direct contact. In the present embodiment, the thermally
conductive plate 62 is formed from aluminum, but it should be noted that any
suitable thermally conductive material would suffice.
[0038] Turning next to Figure 5, it will be noted, when the thermally
conductive plate 62 is placed onto the screed plate 46, that studs 64 in the
screed plate 46 are able to extend through corresponding holes 66 in the
thermally conductive plate 62, enabling the plates 62 and 46 to be fixed to
the
subframe 58. This manner of assembly not only fixes the thermally conductive
plate 62 to subframe 58 but also prevents relative movement with respect to
the screed plate 46. A plurality of heating elements 60 are disposed directly
above the thermally conductive plate 62, and an additional insulation layer 68
is
disposed between the subframe 58 and the conductive plate 62. Each heating
element 60 is held in place by a dedicated clamping mechanism 74, as is
shown in Figure 8.
[0039] Referring back to Figure 2, the several illustrated electrical
heating elements 60 are shown as being arranged in four rows of laterally-
disposed heating elements 60, so spaced longitudinally relative to the front
and
back of the paving machine 20 (Figure 1) as to effectively span the width and
a
major portion of the length of the screed plate 46.
[0040] As shown in Figures 3 and 8, each row of heating elements
includes two electrical heating elements 60, disposed on opposite lateral
sides
of the screed plate 46, in a known manner, to form a gap midway along the
length of the screed plate 46, thereby allowing the screed plate 46 to crown
during operation. Of course, the number and location of heating elements 60
may vary depending on, for example, the size of the screed plate 46.
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[0041] In this embodiment, each heating element 60 comprises a
rigid hollow bar of steel or another metallic material having a resistive coil
wound inside it that heats when energized, as is well known in the art. The
heating element is wired to an electric generator (not shown) by lead wires 70
(shown in Figures 3 and 8) in a known, conventional manner to supply energy
to the coil. The generator also provides additional power for high voltage
lighting, thus facilitating night operation. An insulation layer 72 (shown in
Figures 7 and 8) is disposed directly above the electrical heating elements 60
to inhibit heat transfer to the associated clamping mechanisms 74 (detailed
below), thereby maximizing the transfer of energy downwards toward the
thermally conductive plate 62 and screed plate 46, thus increasing the
efficiency of the system. While the insulation layers 68 and 72 are not
essential
for the operation of the present invention, their non-use will decrease the
efficiency of the system. It must also be noted that the thermally conductive
plate 62 is not necessary to comply with all aspects of the invention, but it
is
implemented in this embodiment to supply heat uniformly to the screed plate
46. If the thermally conductive plate is not used, the electrical heating
elements
60 will be in direct contact with the screed plate 46, and a higher number of
more closely spaced heating elements would likely be employed.
[0042] Turning next to Figures 7 and 8, each clamping mechanism
74 is seen to include a pair of clamps 76 located at both ends of a tubular
beam
78, which is mounted above the insulation layer 72. Mounted directly to the
underside surface of the beam 78 is a bent plate 95 that is designed to
captively retain the insulating layer 72 and electrical heating element 60
relative
to conductive plate 62 when the clamps 76 are tightened.
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[0043] As shown in Figure 7, one such clamp 76 can be used to pull
the beam 78 upwardly (as depicted by the arrow) away from the heating
elements 60, when loosened, thereby allowing the heating elements 60 to be
easily removed from the paving machine, as desired, without first removing the
screed plate 46.
[0044] As shown in Figures 2-4 and 7, the clamps 76 are seen to
exert a downward force on the beam 78 when tightened, thereby providing a
compressive force to the associated heating element 60. Each clamp 76
preferably includes a bracket 80 that is welded to or otherwise mounted on
beam 78. Both the subframe 58 and bracket 80 (Figures 2 and 4) comprise
horizontal surfaces 92, 94, respectively, shown in Figure 4, in which aligned
holes 82, 84 exist, respectively, as shown in Figures 5 and 7.
[0045] In the illustrated embodiment of Figure 4, a nut 86 is shown
as welded to or otherwise mounted on the underside of the hole 82 in the
subframe 58. To achieve the same effect, the illustrated hole 82 may be tapped
in a known manner to form a threaded hole through the upper surface of
subframe 58.
[0046] As shown in Figure 4, a bolt 88 is inserted through the hole
82 in the subframe 58 and accompanying nut 86 and is further inserted through
the hole 84 in the bracket 80. If holes 82 of the subframe 58 are tapped, as
noted above, the nuts 86 will not be necessary if the threads of hole 82 mesh
with the threads of bolt 88.
[0047] Once the bolt 88 is inserted into the bracket 80, a nut 90 is
mounted onto the bolt 88 at a point between the bracket 80 and the beam 78.
As shown in Figures 4 and 7, the bolt 88 may then be tightened relative to
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subframe 58 until such bolt 88 buttresses up against beam 78. After that, a
nut
90, threadedly engaging bolt 88 between surface 94 and tubular beam 78 (as
shown in Figure 4), may be raised along the bolt 88 until such nut 90 is
closely
adjacent the underside of the horizontal surface 94 of the bracket 80, after
which such may then be fixed to the bolt 88 using a spring pin (not shown) or
any other known method of fastening.
[0048] In this manner, when clamp 76 is tightened, the downward
movement of each beam 78 provides a compressive force to associated
heating elements 60. Conversely, when the clamp 76 is loosened, the nut 90
exerts an upwards force on the bracket 80, thus raising the beam 78 away from
the associated electrical heating element 60. Once the beam 78 is raised, the
electrical heating element 60 can be removed by sliding it in a longitudinal
direction that is generally parallel to the beam 78 until it is free from the
system,
as shown in Figure 8. A second electrical heating element may then be
installed by sliding it into the system in a direction generally parallel to
the
beam 78. Alternatively, the electrical heating element 60 may be repaired and
reinstalled into the assembly 30. Note that the screed plate 46 is not removed
during this process. Referring to Figure 7, the clamping mechanism 74 on the
left is shown in the open position while the remaining clamping mechanisms 74
are shown to be tightened.
[0049] Referring to Figures 6 and 8, optional pusher bolts 96 are
installed at spaced apart locations longitudinally between the clamps 76 in
accordance with the preferred embodiment of the invention. These pusher bolts
96 function to provide uniform compression to the beam 78 if the beam 78 is
sufficiently long that the clamps 76 alone might not adequately compress the
heating elements 60. The number of necessary pusher bolts 96 is indicative of
the length of the associated beam 78. Thus, if the beam 78 is sufficiently
short,
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no pusher bolts 96 will be necessary. If necessary, one such pusher bolt 96
can
be installed by drilling a vertical hole 97 in the subframe 58. Preferably,
the hole
97 is tapped in a known manner so as to have threads that mesh with the
threads of pusher bolt 96. As still another and alternative embodiment, nut 86
may be welded to or otherwise mounted on the underside surface of subframe
58. In the illustrated alternative embodiment, the pusher bolt 96 is shown to
be
inserted through the hole 97, threaded through the nut 86 and, when tightened,
buttressed up against the beam 78. Further tightening of the pusher bolts 96
compresses the associated electrical heating element 60, thereby holding the
heating element 60. Note that if the pusher bolts 96 are installed, they are
first
loosened before the clamps 76 are raised.
[0050] Lateral clamps 98, best seen in Figures 2, 4 and 6-8, are also
integrated into each clamping mechanism 74 (Figures 6 and 7) to prevent the
clamping mechanism 74 from collapsing while the bolts 88 and 96 are
tightened against the beam 78. Otherwise, the compressive force from clamp
76 and pusher bolts 96 could cause the base of beam 78 to slip out from
underneath of the screed assembly 30. Each lateral clamp mechanism 98 is
seen to include: 1) a hole 104 (Figures 2 and 7) in a vertical surface 100 of
subframe 58; 2) vertical slots 102 (Figure 6) in the side walls of the beam 78
that are laterally aligned with the holes 104 in the subframe 58; and 3) a
bolt
114 inserted into the slots 102 so as to extend into hole 104. Nuts 105 and
washers are installed as shown (Figure 6) to secure the beam's lateral
position
with respect to the subframe 58, as shown in Figures 7 and 8. The vertical
slots
102 in the beam 78 (Figure 4) permit beam 78 to be raised and lowered, as
desired, during operation of the clamping mechanism 74, as shown in Figures 7
and 8. In this manner, lateral movement of the clamping mechanism 74 is fixed
with respect to the subframe 58.
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[0051] It must be further noted that while a clamping mechanism 74
in accordance with the preferred embodiment has been described, any
clamping device that can be loosened to permit the easy removal of the
electrical heating element without removal of the screed plate 46 may be used.
[0052] Turning now to Figures 9, 10, and 11, a lateral extension
component 106 having an electrically heated screed assembly 130 (Figures 9
and 10) is shown connected to the above-described screed assembly 30 by
bolts 108 (Figure 9) extending though holes in a side wall 110 (Figure 10) of
main frame 56 and through mating holes in a corresponding side wall 112 of
frame member 156 of extension 106. The extension 106 is particularly useful
when a wider surface area than normal is to be paved. Extension 106
comprises a screed plate 146 with studs 164 (Figure 11) extending through
holes 166 in a conductive plate 162 that are fixed to holes 192 in the frame
156. Electrical heating elements 160 and insulation layers 172 are positioned
above the thermally conductive plate 162. The extension 106 is shown further
to include two clamping mechanisms 174 (Figure 9), one of which is provided
for each heating element 160. Each clamping mechanism 174 (Figure 11)
includes a beam 178 and two clamps 176. An alternative embodiment may
further include a bent plate (not shown), as previously described above in
connection with Figures 2, 4 and 6-8. Each illustrated clamp 176 (Figures 10
and 11) is seen to include bolts 188, brackets 180, and nuts 190. Also as
mentioned above, bolts 188 can threadedly engage threaded holes in the frame
156, or may threadedly engage nuts 186. As shown in Figure 10, the clamping
mechanism 174 on the left is loose while the clamping mechanism 174 on the
right is tightened, as previously described. However, in the extension 106,
the
clamping mechanism 174 and heating elements 160 extend laterally of the
above-described screed assembly 30. Note also that the heating elements 160
and clamping mechanisms 174 are sufficiently short that pusher bolts (none
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shown) are accordingly not needed to ensure that the heating elements 160 are
sufficiently compressed, nor are lateral clamps necessary.
[0053] A method of assembling the screed assembly 30 will now be
described. First, the clamping mechanism is assembled as follows. Such
assembly includes positioning the subframe 58 and brackets 80 in a manner
such that their respective holes 82 and 84 are aligned, and securing the
brackets 80 to subframe 58 using bolts 88 and nuts 90, as shown in Figure 7.
Next, the conductive plate is placed on top of the screed plate 46, as shown
in
Figure 3. Then, with the conductive plate 62 on screed plate 46 (as shown in
Figure 7), with the heating elements 60 placed on the top of conductive plate
62 in spaced-apart fashion (see, e.g., Figures 5 and 7), and with insulation
layers 72 longitudinally placed on top of corresponding associated heating
elements 60 (see, e.g., Figures 6 and 7), the clamping bar portion of the
clamping mechanism 74 is sub-assembled by first aligning bolts 114 with
opposite slots 102 through beam 78, then passing the bolts 114 through the
holes 102, and using nuts 105 and washers (as shown in Figure 6) in a known
manner, to position the plural (or several) tubular beams 78 (shown in Figure
5)
onto subframe 58 relative to the insulation layers 72 mounted on the heating
elements 60 that have been placed on plate 62, as shown in Figure 7. Next, the
heating elements 60 with insulation layers 72 on top are together laterally
slid
inwardly, as can be appreciated by referring to Figure 8. Finally, the several
bolts 88 are separately rotated about their longitudinal axes in a known
manner
relative to subframe 58, to cause the tubular beam 78 to move toward the
screed plate 46. The several heating elements 60 and corresponding
supermounted insulation layers 72 are separately longitudinally aligned with
the
bent plate 95 of each respective tubular beam 78 (see, e.g., Figure 6) before
each tubular member 78 is brought into abutting engagement with a respective
insulation layer 72, for purposes of fixedly urging the insulation layer
against
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conductive plate 62, as shown in Figure 7. While the longitudinal axes of
bolts
88 are preferably disposed perpendicular to upper horizontal surface of
subframe 58, those skilled in the art can appreciate that bolt orientation
that is
somewhat offset from the perpendicular may, on occasion, be desirable for
certain design purposes. Such bolt orientation is within the scope of the
present
invention.
[0054] To remove an electrical heating element 60, the associated
pusher bolts 96 are first loosened, and the bolts 88 of the two clamps 76 are
also then loosened to raise the beam 78. The electrical heating element 60 to
be replaced or repaired is then removed by sliding it longitudinally out of
the
screed assembly 30. A second heating element may then be inserted into the
assembly 30 by sliding it in longitudinally above the thermally conductive
plate
62. If necessary, the insulation layer 72 may be placed on top of the
replacement heating element before insertion. Once the new heating element
60 is in place, the clamping mechanism 74 is tightened to lower the beam 78
onto the heating element 60, thus rendering the system operational. Note that
replacement of the heating element 60 takes place without removal of the
screed plate 46.
[0055] Many changes and modifications may be made to the
invention without departing from the spirit thereof. The scope of these
changes
will become apparent from the appended claims.
