Heat passage tunnel for screed burner

Abstract: A heating device for heating a substantially planar screed plate (24) for a paving machine comprising a plate (48) being spaced from the screed plate, a space (50) being defined therebetween. A heated gas inlet (28) feeds into a tunnel (36) connecting to the space. At least some of the heated gas is directed from the tunnel substantially parallel to the screed plate. The tunnel is formed from a plurality of tunnel branches (36, 40) with an orifice (46, 44) attached to the end of each tunnel orifice determining the direction where the heated gas will be directed.

Description: This invention relates generally to road paving machines and more particularly to heat tunnels to apply heat efficiently to a paving screed prior to operation of the paving machine. During operation of paving machines, the heat of the pavement maintains screed plate temperatures roughly equivalent to the pavement temperature. However, when the machines are being used after a period of inactivity, the temperature of the screed plate is at a much lower temperature than the pavement. Operation of the screed plate on pavement having a considerably higher temperature may result in inefficient operation of the screed and possible warping or other damage to the screed plate itself. More importantly, the paving material tends to adhere to the colder screed, possibly ruining the final paving material finish. To remedy this situation, burner units have been installed to apply heated air to the interior of the screed, raising the screed plate temperature prior to screed operation. These burner units are typically removably mounted in an upper surface of the screed and are directed towards the screed plate. Based on the relatively small heating area of the burner units compared to the relatively large screed plate area, only a small portion of the screed plate is often heated prior to screed operation. This increased heating of only a small portion of the screed plate can also result in damage to the screed plate. To illustrate the above, US-A-2 589 257 discloses a road paving machine which includes a heating apparatus to heat a screed for the machine. The screed includes a screed plate having substantially planar inner and outer surfaces and another plate located substantially parallel to the screed plate so as to define a space between them. A heated gas inlet is connected via a tunnel to the space between the plates and some of the gas is directed from the tunnel substantially parallel to the inner surface of the screed plate. According to one aspect of the present invention, there is provided a heating apparatus to heat a screed for a paving machine, comprising a screed plate having a substantially planar outer surface and an inner surface opposite thereto; a second plate spaced substantially parallel from the screed plate defining a space therebetween; a heated gas inlet; a tunnel communicating the heated gas inlet with the space at a first and second aperture; wherein a divider plate is in the tunnel opposite the heated gas inlet to divide heated gas into a first stream that exits the first aperture into the space and a second stream that exits the second aperture into the space; and at least one of the apertures is disposed to direct one of the heated gas streams to flow along the inner surface of the screed plate substantially parallel to the outer surface of the screed plate. According to a second aspect of the present invention, there is provided a method of heating a screed for a paving machine comprising the steps of providing a screed plate having a substantially outer and inner planar surface, spacing an insulating means a distance from the planar surface; creating a space between the insulating means and the planar surface; supplying a heated gas through a tunnel to a location distant from the space, in a non-coplanar direction relative to the planar surface; and directing the heated gas supply from the heated gas supply to the space in a direction substantially parallel to the inner planar surface, wherein a divider plate in the tunnel opposite a gas inlet divides heated gas into a first stream that exits a first aperture into the space and a second stream that exits a second aperture into the space; at least one of said apertures being disposed to direct one of the heated gas streams to flow along the inner surface of the screed plate substantially parallel to the outer surface of the screed plate. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a side view illustrating an embodiment of a paving machine pulling a screed; Figure 2 is an underneath view of the screed with a screed plate removed; Figure 3 is a view similar to Figure 2 with the screed plate and an insulating plate removed; Figure 4 is a sectional view taken along lines 4-4 of Figure 3 and is based on Figure 3 except with the screed plate and the insulating plate in position; Figure 5 is a sectional view taken along lines 5-5 of Figure 4; and Figure 6 is a sectional view of a prior art screed illustrating a similar view to Figure 5. In this application, similar reference characters are used to illustrate identical elements in different embodiments. As illustrated in Figure 1, a paver 10 is used to pave roads or pavement 12. The paver 10 includes a hopper 14, a tractor 16, an auger 18 and a screed 20. The tractor 16 propels the paver 10. The hopper 14 contains loose paving material 22 to be distributed along a length of pavement 12. The hopper feeds the loose paving material to the auger 18 which disperses it along a width of the pavement 12. Once the loose paving material 22 is laid by the auger 18, the screed 20 passes over it to compress it into the desired density, and to give it a final contour. One prior art screed 20 illustrated in Figure 6, includes one or more screed housings 22, a screed plate or planar surface 24, a burner recess or aperture 26 formed in the screed housing and a burner unit 28 which interfits within the burner aperture 26. A space is defined within the screed housing 22 by the walls of the screed housing 22 and the screed plate 24. A burner exhaust outlet 30 may be formed in the screed housing permitting a flow of heated gas through the space in the housing and out of the outlet 30 which spreads heat produced by the burner unit over a sizeable portion of the screed plate 24. In this configuration, the entire space must be heated by the burner unit 28 which leads to inefficient heating. It is desirable for the temperature of the screed plate to be approximately the same as the loose paving material. This produces more efficient paving and reduces the damage to the screed plate which may result from exposure to considerably higher temperatures than the plate itself. During the normal operation of the paver 10, the temperature of the screed plate 24 is roughly equivalent to the temperature of the loose paving material 22. However, when the paver 10 is being used for the first time after a period of non-use, the initial screed plate temperature will be considerably lower than the pavement. The burner unit 28 raises the temperature of the screed plate 24 prior to use. The burner unit 28, as utilised in the known screed illustrated in Figure 6, does not heat the screed plate evenly. A first portion 32 of the screed plate 24, being close to the burner unit 28, will be at a much greater temperature than a second portion 34 of the screed plate more distant from the burner unit. This temperature differential can result in possible damage to, as well as inefficient heating of, the screed plate 24. To provide a more even heating of the screed plate 24 prior to screed 20 use, a tunnel 36 as illustrated in Figure 4 may be installed. The tunnel 36 includes an inlet portion 38 (which interfits over the burner unit), one or more tunnel branches 40, 42 and an orifice 44, 46. Each tunnel branch 42, 44 preferably has a lesser cross-sectional dimension adjacent the inlet portion than at the orifices 44, 46 as illustrated in Figure 3. The orifice 44 of the tunnel branch 40 discharges heated gas in a direction parallel to the screed plate 24, while the orifice 46 of the tunnel branch 42 extends in a direction perpendicular to the screed plate 24. Since the flow length 49 of the tunnel branch 40 is shorter than the flow length 51 of the tunnel branch 42, the tunnel branch 42 thereby provides greater resistance. More gas will thereby pass through tunnel branch 40 than tunnel branch 42 due to decreased resistance to flow. Heated gas 53 passing from orifices 44 and 46 will distribute heat from the heated gas to the screed plate 24 much more efficiently than the prior art burner unit 28 as illustrated in Figure 6 since a majority of the heated gas is travelling parallel to the surface in the present configuration. Heated gas 52 passing from orifice 46 of tunnel branch 42 will travel radially from the axis of the orifice. This will cause the heated gas 53 passing from orifice 46 to expand outwardly as it exits the orifice 44 as illustrated in Figure 2, further contributing to an even transfer of heat throughout the screed plate 24. An insulating plate or insulation retainer 48 is substantially parallel to the screed plate 24 and forms a space 50 therebetween. The insulating plate 48 performs two functions. Initially, the heated gas passing through the orifices 44, 46 will remain close to the screed plate 24 instead of rising away from the screed plate. The width 55 of the space 50 (see Figure 5) is selected to ensure that the heated gas will pass through the entire space 50. The second function of the insulation plate or retainer 48 is to retain an insulating material 54 in position. The insulating material is placed in the parts of the screed removed from the space 50. The insulating material 54 has to withstand the temperatures of the heated gas 52 and 53 which passes through the tunnel 36. The insulating material prevents heat loss not only from the tunnel 36, but also from the insulating plate 48. The overall purpose of the insulating material 54 and the insulating plate 48 is to maximize the heat transfer from the burner unit 28 directly to the screed plate 24. Since the insulating plate 48 is insulated on one side by an insulating material 54, the insulating plate 48 maintains most of the heat applied to it. Whatever heat is contained in the insulating plate will be passed through the entire plate by conduction. If the temperature of the insulating plate exceeds the temperature of the screed plate, much of the heat contained within the insulating plate 48 will be radiated to the screed plate, further adding to even heating of the screed plate. As illustrated in Figure 2, the insulating plate 48 is formed from two insulating plate portions 56, 58 which intersect at approximately ninety degrees. There are recesses 60, 62 in the insulating plate portions 56, 58 permitting the tunnel branches 40, 42 to extend through the insulating plate 48. The screed plate 24 is formed from two screed plate portions 64, 66 (Figure 5) which intersect at approximately ninety degrees. The space 50 includes the areas between the insulating plate portion 56 and the screed plate portion 64, as well as between the insulating plate portion 58 and the screed plate portion 66. The screed plate 24 is removably affixed to the screed housing 22 by a plurality of fasteners 68, 70. The fasteners 68, 70 are mounted on flange portions 72, 74 which are formed on the screed plate portions 64, 66, respectively. When the screed plate 24 is attached to the screed housing 22, there will be a slight space between these two members to permit the heated gas which is passing through the tunnel branches 40, 42 to escape from the space 50 and permit a constant flow of heated air throughout the space 50. Alternately, apertures 76 may be formed in the screed housing 22 to allow this flow of heated gas. A divider plate 78 is inserted in the tunnel 36 opposite the burner unit 28. The divider plate 78 divides the heated gas flow from the burner unit into the two tunnel branches 40, 42 while minimising the turbulence in each of the two branches.

Claims: A heating apparatus to heat a screed for a paving machine, comprising a screed plate (24) having a substantially planar outer surface and an inner surface opposite thereto; a second plate (48) spaced substantially parallel from the screed plate (24) defining a space (50) therebetween; a heated gas inlet (38); a tunnel (36) communicating the heated gas inlet (38) with the space (50) at a first and second aperture (44, 46); wherein a divider plate (78) is in the tunnel (36) opposite the heated gas inlet (38) to divide heated gas into a first stream that exits the first aperture (44) into the space (50) and a second stream that exits the second aperture (46) into the space (50); and at least one of the apertures (44, 46) is disposed to direct one of the heated gas streams to flow along the inner surface of the screed plate (24) substantially parallel to the outer surface of the screed plate (24). An apparatus according to claim 1, wherein the heated gas is air. An apparatus according to claim 1 or 2, wherein the screed plate forms a portion of the tunnel. An apparatus according to claim 1, 2 or 3, wherein the other further aperture (46) is arranged to direct gas perpendicularly towards the screed plate (24). An apparatus according to any one of the preceding claims, wherein some heat contained within the plate (48) will be radiated to the surface (24). An apparatus according to any one of the preceding claims and wherein said second plate is an insulator retainer (48) and there being insulating means (54) inserted on the side of the insulator retainer opposite the space (50), resisting heat transfer from the insulator retainer and the tunnel. A method of heating a screed for a paving machine comprising the steps of providing a screed plate (24) having a substantially outer and inner planar surface, spacing an insulating means (54) a distance from the planar surface; creating a space (50) between the insulating means and the planar surface; supplying a heated gas through a tunnel (36) to a location (28) distant from the space, in a non-coplanar direction relative to the planar surface; and directing the heated gas supply from the heated gas supply to the space (50) in a direction substantially parallel to the inner planar surface, wherein a divider plate (78) in the tunnel opposite a gas inlet (38) divides heated gas into a first stream that exits a first aperture (44) into the space (50) and a second stream that exits a second aperture (46) into the space (50); at least one of said apertures being disposed to direct one of the heated gas streams to flow along the inner surface of the screed plate (24) substantially parallel to the outer surface of the screed plate (24).

Inventors: LANGLEY DAVID P, RICHTER KURT W, LANGLEY, DAVID P., RICHTER, KURT W.
Applicants: INGERSOLL RAND CO, INGERSOLL-RAND COMPANY
Application year: 1991
Main classification: E01C19
IPC codes: E01C19