Abstract
A road finisher comprising a screed plate extending at right angles to the working direction of the road finisher, and a tamper bar disposed rearwardly and/or forwardly of the screed plate in the working direction, wherein at least one electrically operated heating element is present, which is configured so as to heat up a heating surface facing a road subsurface, and wherein the heating element comprises a heating layer at least partially obtained through thermal spraying onto a substrate surface, wherein the tamper bar is made from two parts with an upper tamper bar member and a lower tamper bar member assembled together. Further, a tamper bar for a road finisher and a method of manufacturing a tamper bar are provided.
Claims
1. A tamper bar for a road finisher, the tamper bar comprising: an upper tamper bar member and a lower tamper bar member assembled together, at least one electrically operated heating element, which is configured to heat a heating surface facing a road subsurface, wherein the heating element comprises at least one heating layer at least partially comprising a thermal spray coating, obtained through thermal spraying onto a substrate surface, wherein the upper tamper bar member has a lower surface which, in the assembled state, contacts an upper surface of the lower tamper bar member, wherein a groove is provided in the lower surface of the upper tamper bar member, and wherein the thermal spray coating is disposed in the groove of the upper tamper bar member.
2. The tamper bar according to claim 1 wherein: the at least one heating layer is a multilayered heating layer comprising an insulating layer, a strip conductor and a sealing layer, and the thermal spray coating of the at least one heating layer provides at least one of the insulating layer, the strip conductor and the sealing layer.
3. The tamper bar according to claim 2 wherein: the thermal spray coating of the at least one heating layer is a multi-layered thermal spray coating, and each of the insulating layer, the strip conductor and the sealing layer of the at least one heating layer is provided by a layer of the multi-layered thermal spray coating, respectively.
4. The tamper bar according to claim 1 wherein: the substrate surface is provided by a surface of the groove in the lower surface of the upper tamper bar member.
5. The tamper bar according to claim 1 wherein: the thermal spray coating is at least one of a plasma spray coating or a high velocity oxygen fuel spray coating.
6. The tamper bar according to claim 1 wherein: the groove, in the assembled state of the upper tamper bar member and the lower tamper bar member, provides an encapsulated cavity for the at least one heating layer.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a side view of a road finisher;
(2) FIG. 2a is a side view of a paving screed comprising a tamper bar and a screed plate according to prior art;
(3) FIG. 2b is an enlarged detail of the tamper bar according to prior art of FIG. 2a;
(4) FIG. 3 is a perspective view of a piston rod and a tamper bar according to an embodiment of the invention;
(5) FIG. 4 is a perspective view of the piston rod and the upper tamper bar member of the tamper bar shown in FIG. 3;
(6) FIG. 5a is a vertical cross-sectional view of a metallic support plate of a tamper bar;
(7) FIG. 5b is a horizontal cross-sectional view of the tamper bar shown in FIG. 5a;
(8) FIG. 5c is an alternative embodiment relating to FIG. 5b;
(9) FIG. 5d is a further alternative embodiment relating to FIG. 5b;
(10) FIG. 6 is a perspective cross-sectional view of a first end portion of the tamper bar shown in FIG. 3;
(11) FIG. 7 is a perspective view of the first end portion of the tamper bar shown in FIG. 6; and
(12) FIG. 8 is a vertical cross-sectional view of an upper tamper bar element with the heating layer being positioned in a groove.
DETAILED DESCRIPTION
(13) As shown in FIG. 1, the essential components of the road finisher 1 are a machine frame 2, driving devices 3 for the traveling operation (track systems can also be used in this context, in part), a bunker 15 for accommodating paving material, a transporting unit (not shown in detail), by means of which the paving material accommodated in the bunker is transported rearwardly contrary to the working direction a to the paving section, a spreading screw 4, by means of which the paving material is distributed across the paving width of the road finisher 1 at right angles to the working direction a, and a paving screed 5 that is trailed after the road finisher 1 during the paving operation in a floating manner on the bituminous paving material. The paving screed is mounted on the road finisher 1 so as to be vertically displaceable and can be lowered from its raised starting position towards the road subsurface for execution of the operating mode. Furthermore, a control platform 6 and a drive motor 7 are provided. In the operating mode, the road finisher 1 moves in the working direction a and deposits a layer of bituminous paving material of a desired thickness on the road subsurface for execution of the operating mode. Furthermore, a control platform 6 and a drive motor 7 are provided. In the operating mode, the road finisher 1 moves in the working direction a and deposits a layer of bituminous paving material of a desired thickness on the road subsurface U.
(14) FIG. 2a illustrates the essential components of the paving screed. These include a tamper bar 8, a smoothing plate 9 disposed rearwardly of the same in the working direction a, and a carrier housing 10 comprising an exciter unit 11. The carrier housing 10 and the smoothing plate 9 together form the screed plate. The tamper bar 8 is capable of being moved vertically in the direction of the arrow b and thus of carrying out stamping movements in the direction of the arrow b during the paving operation. In its front region, the tamper bar 8 comprises an obliquely extending guiding surface (lead-in slope 12) in the working direction followed by a horizontally extending tamping surface 13. The tamper bar 8 is followed by the smoothing plate 9. Above the smoothing plate 9 there is disposed an exciter unit 11 by means of which an oscillating movement can be induced in the paving screed 5. This basic structure of the paving screed 5 is known in the art. Further, the smoothing plate 9 comprises an underside 14 that slides over the paving material and levels the same during the operating mode. The smoothing plate 9 and the part having the lead-in slope 12 are each configured to have a first and a second heating layer 18, 18, respectively, as part of a heating element.
(15) FIG. 2b illustrates the enlarged detail IIb of the tamper bar 8 as shown in FIG. 2a according to prior art. The tamper bar 8 has an L-steel rail 28 comprising a vertical and a horizontal leg and a part with the lead-in slope 12 connecting the two legs. The steel rail or metallic support plate 28 is covering the front edge of the tamper bar 8. On the back side of the part having lead-in slope 12 there is provided the second heating layer 18. It is also possible to have a heating layer (not shown) on the back side of the horizontal and/or vertical leg of the tamper bar 8. The term back side in each case designates the outside surface facing away from the paving material. Thus, according to this configuration known from prior art, arrangement of the heating element is restricted to the back side of the tamper bar 8.
(16) FIG. 3 is a perspective view of a piston rod 15 and a tamper bar 8 according to an embodiment of the invention. As can be seen here, the tamper bar 8 comprises two parts, namely, an upper tamper bar member 8 and a lower tamper bar member 8. The lower tamper bar member 8 at its lower side comprises the tamping surface 13 which during operation contacts the ground and is subject to high stress and thus, strong wear. Therefore the lower tamper bar member 8 is made from hardened steel. The upper tamper bar member 8 which does not contact the ground surface during tamping operation is not necessarily made from hardened steel but can be made from for example a less expensive kind of steel. The upper tamper bar member 8 and the lower tamper bar member 8 are connected to each other by a plurality of screws 16 whereby the lower surface 23 of the upper tamper bar member 8 contacts the upper surface 24 of the lower tamper bar member 8 (see FIG. 6). Inbetween the upper tamper bar member 8 and the lower tamper bar member 8, there is arranged a heating element 17 (see FIG. 6) comprising a multi-layered structure of layers (see FIGS. 5a to 5d and FIG. 8) applied to either one of the upper surface 24 of the lower tamper bar member 8 or the lower surface 23 of the upper tamper bar member 8 by thermal spraying whereby the latter case is more preferable, since upon replacement of the lower tamper bar member 8, the heating element 17 does not have to be replaced together with it but rather remains unaffected by the replacement procedure of the lower tamper bar member 8 on the lower surface of the upper tamper bar member 8.
(17) At the upper surface 25 of the upper tamper bar member 8, the latter is connected to two piston rods 15 such that the upper tamper bar member 8 functions as a spacer or intermediate part between the lower tamper bar member 8 and the piston rod 15. The piston rod 15, at its upper end, has connecting means 26 for connecting the tamper bar 8 to a part of a drive means not shown here. In particular, an exciter shaft may be supported in the connecting means 26 of the piston rods 15.
(18) FIG. 4 is a perspective view of the piston rod 15 and the upper tamper bar member 8 of the tamper bar 8 shown in FIG. 3, disassembled from the lower tamper bar member 8 which is not shown here. As can be seen, the lower surface 23 of the upper tamper bar member 8 is provided with a groove 29 in which the heating layers 18 of the heating element 17 are applied by thermal spraying. Further, a plurality of screws 17 can be seen running through the upper tamper bar member 8 and projecting from its lower surface 23. In an assembled state, the screws 17 are in engagement with corresponding holes (not shown) provided in the upper surface 24 of the lower tamper bar member 8 at corresponding positions.
(19) As shown in FIG. 5a, the first heating layer 18 of the heating element 17 applied to the tamper bar 8 is composed of a total of three layers including an electrically insulating layer 19, a sealing layer 20, and a metallic strip conductor 21. Each of these layers has been applied successively and on top of each other by thermal spraying. An intermediate anchor layer 22 is, likewise by thermal spraying, optionally applied directly to the lower surface 23 of the upper tamper bar member 8. The metallic strip conductor 21 is applied to the surface of the insulating layer 19 facing the sealing layer 20 and is covered by the sealing layer 20. The metallic strip conductor 21 serves as an electrical heating member to heat the sealing layer 20 and forms part of an electric heating circuit which is connected to an electrical power supply system (not shown).
(20) The heating layer 18 can be obtained by successively applying the three layers 19, 20 and 21 by means of thermal spraying, in particular, by means of a thermal plasma spraying technique or HVOF, onto the tamper bar 8 (more specifically its metallic support plate 28, see FIG. 2b). Any remarks made hereinafter with reference to thermal plasma spraying is to be understood to likewise apply, within the scope of the present invention, to other thermal spraying techniques such as, in particular, HVOF. Thermal plasma spraying technique is a surface coating technology known in the industry. For this purpose in a first step, the intermediate anchor layer 22 is sprayed onto the surface of the support plate 28 following preparation of the surface by sand blasting. In particular, a defined surface roughness enables particularly stable, essentially mechanical anchoring of the optional intermediate anchor layer 22 on the support plate 28 of the tamper bar 8. Then, the insulating layer 19 is deposited onto the intermediate anchor layer 22 by thermal plasma spraying technique. Next, the strip conductor 21 is deposited on the insulating layer 19 also by thermal plasma spraying technique. Finally, the sealing layer 20 is deposited to seal the insulating layer 19 and the strip conductor 21 from the environment and, in particular, to provide mechanical protection towards the environment. In this specific exemplary embodiment, the strip conductor 21 is deposited on the insulating layer 19 and embedded in the sealing layer 20. Thus, at least three successive steps of the plasma spraying procedure are performed to obtain the heating layer 18. The sealing layer 20 and the insulating layer 19 are each composed of alumina based material, whereas the strip conductor 21 is preferably composed, for example, of a nickel-chromium alloy, or of another material composition, in particular, as described above. The heating layer 18 has a thickness D. The single layers including the insulating layer 19 and the sealing layer 20 are substantially of the same size and of the same thickness, and strip conductor 21 can be of a substantially smaller thickness than, for example, the sealing layer 20.
(21) FIG. 5b is a horizontal cross sectional view of the metallic support plate 28 of the tamper bar 8 along the line A-A in FIG. 5a. FIG. 5b illustrates that the strip conductor 21 extends in a meandrous pattern across the surface of the insulating layer 19. When implemented in practice, the strip conductor 21 is not visible on the metallic plate 28 of the tamper bar 8, as it is covered towards the top by the sealing layer 20. Thus, FIG. 5b shows the course of the strip conductor 21 as being underneath the sealing layer 20 merely for the purpose of clarification.
(22) The strip conductor 21 terminates at both ends at contact points 27 that are connected to an electrical power supply system (not shown). To this end, provision is made, in particular, for contact pins or comparable connecting means, for example, to lead away from the tamper bar 8.
(23) FIGS. 5c and 5d show further exemplary embodiments of a possible run of the strip conductor. In FIG. 5c, the strip conductor is arranged in a linear pattern of webs across the metallic support plate 28 of the tamper bar 8 with a number of individual webs 21a, 21b, 21c running parallel to each other. By contrast, FIG. 5d shows two webs 21d, 21e of the strip conductor that are interconnected with each other. It is essential for the configuration of the strip conductor that the underside of the support plate 28 facing the paving material, apart from heating up rapidly, should also heat up at the same time over its entire surface as far as possible in order to prevent any bituminous paving material from sticking thereto.
(24) FIG. 6 is a perspective cross-sectional view of a first or left hand side end portion of the tamper bar 8 shown in FIG. 3 according to which it can be seen how the screws 16 penetrating through the upper tamper bar member 8 engage the lower tamper bar member 8 in the assembled state of the tamper bar. Further, it can be seen that on the upper surface 25 of the upper tamper bar member 8, on the left hand side, a housing or cap 30 is provided in which the electrical connections can be accommodated. Also, it can be seen here that the screws 16 provided in the region of the piston rod 15 have a longer shaft than the screws 16 so as to also penetrate through a base member 31 of the piston rod 15 so as to connect the latter to the tamper bar 8.
(25) FIG. 7 is a perspective view of the first end portion of the tamper bar 8 shown in FIG. 6. As can be seen in the assembled state, the tamper bar 8 forms a compact structure whereby if the lower tamper bar member 8 has to be replaced, the upper tamper bar member 8 comprising the heating element 17 remains connected to the piston rod 15 and does not have to be replaced. Further, only the lower tamper bar member 8 is made from hardened steel, reducing production costs. Also, it can be seen that the cap 30 fully protects the electrical connections of the heating element 17.
(26) FIG. 8 further clarifies the positioning of the heating layer 18 in the groove 29, in the shown example in the upper tamper bar 8. FIG. 8 is a partial cross-sectional view along line I-I of FIGS. 3 and 4. The groove comprises a groove bottom 29a and groove side walls 29b, wherein the groove side walls 29b extend between the groove bottom 29a and the lower surface 23 of the upper tamper bar member 8. As can clearly be seen, the heating layer 18 is accommodated with all of its layers within the groove 29. Thus, the heating layer 18 does not protrude over the surrounding surface of the lower surface 23 of the upper tamper bar member 8. In the shown example, there is furthermore provided a gap 31 between the outer surface of the heating layer 18 and the upper surface of the lower tamper bar member 8. Thus, in the assembled state of the upper tamper bar member 8 and the lower tamper bar member 8, the heating layer is not directly contacting the opposite tamper bar member, in the present case the lower tamper bar member 8. It is however possible and part of the invention as well, to fill up the groove 29 up to that the heating layer is essentially flush with the lower surface 23 of the upper tamper bar 8 (per definition, the surface of the groove is not part of the lower or upper surface of the upper or lower tamper bar member 8, 8, respectively). For example the material of the outer sealing layer 20 may be used for this purpose.
