Drive wheel and method for manufacturing it

Abstract

drive wheel (5) which has a ring shape and a plurality of projections (51) formed on an outer circumferential surface (53) for transmitting a driving force to a crawler track (2), wherein the drive wheel (5) comprises: a carrier material (50, 100) consisting of a first metal; and a coating (52, 90) covering the carrier material (50, 100) and forming at least a part of the outer circumferential surface (53), wherein the coating (52, 90) contains a second metal, wherein: the coating (52, 90) is formed with a metallic structure that extends continuously in a circumferential direction and connects adjacent projections (51); and the coating (52, 90) contains a matrix (95) consisting of the second metal and hard particles (91) dispersed in the matrix (95), wherein at an interface between the coating (52, 90) and the support material (50, 100) the coating (52, 90) has projections (99) which project towards the support material (50, 100), and wherein each projection (99) accommodates at least a part of a hard particle (91).

Description

Technical field

[0001] The present invention relates to drive wheels and methods for manufacturing the drive wheels, and in particular to a drive wheel having a coating formed on its outer circumferential surface, and to a method for manufacturing the drive wheel. Technical background

[0002] A drive wheel, which transmits power to a crawler track in a crawler undercarriage, rotates and engages with the track's bushings in an environment containing soil and sand. The outer circumferential surface of the drive wheel, which engages with the bushings, must therefore exhibit high wear resistance. One way to improve wear resistance is to apply a coating to the drive wheel's outer circumferential surface. Such a coating could, for example, consist of particles dispersed in a steel matrix. The coating could be applied, for instance, by weld overlay.To form a coating on an outer circumferential surface of a drive wheel by means of overlay welding, it has been proposed to form the coating in such a way that the beads forming the coating extend in a direction perpendicular to the circumferential direction or in a tooth-lateral direction of the drive wheel (see, for example, JP 2000 - 343 219 A, JP 2008 - 000 763 A and JP H08 - 47 774 A).

[0003] US 2005 / 0090347 A1 describes a drive gear featuring a wear-resistant coating that is metallurgically bonded, emphasizing improved service life and performance. In the context of improving wear resistance, US 2005 / 0090347 A1 addresses common shortcomings, noting that even hardened steels are susceptible to abrasive environmental factors such as sand, which limits their service life despite surface treatment. The document describes a solution in which a base steel component is provided with an external tooth profile onto which a coating material is applied that enhances wear and corrosion resistance.

[0004] US 2009 / 0019783A1 deals with wear-resistant particles and structural components, focusing on methods for the uniform distribution of wear-resistant particles such as carbides within a molten weld pool to produce wear-resistant structural components. It describes conventional methods in which such particles are embedded in molten metal during various welding processes and discusses the challenges of these methods, such as the uneven settling of particles due to differences in specific gravity, which leads to inconsistent wear resistance. Summary of the invention: Technical problem

[0005] On the drive wheel, projections formed on the outer circumferential surface engage with the bushings to rotate the crawler track. These projections absorb a force that causes them to tilt circumferentially. If the projections are designed to extend perpendicular to the circumferential direction, as in the aforementioned JP 2000 - 343 219 A, the force acts perpendicular to the interface between adjacent projections. When such a force acts on the interface where the metallic structures are interrupted, cracks can form and propagate along this interface. The formation and propagation of such cracks leads to gaps in the coating and impairs the wear resistance of the drive wheel.

[0006] One object of the present invention is to improve the wear resistance of a drive wheel by preventing the occurrence and propagation of cracks in the coating. Solution to the problem

[0007] A drive wheel according to the present invention is a drive wheel having a ring shape and a plurality of projections formed on an outer circumferential surface for transmitting a driving force to a crawler track. The drive wheel comprises a carrier material consisting of a first metal and a coating containing a second metal, which covers the carrier material and forms at least a portion of the outer circumferential surface. The coating has a metallic structure that extends continuously in a circumferential direction and connects adjacent projections. The coating contains a matrix consisting of the second metal and hard particles dispersed in the matrix. At an interface between the coating and the carrier material, the coating has projections that project onto the carrier material. Each projection accommodates at least a portion of a hard particle.

[0008] In the drive wheel of the present invention, the coating is formed with a metallic structure that extends continuously in the circumferential direction and connects adjacent projections. This prevents the formation of cracks in the coating due to the force that causes the projections to tilt in the circumferential direction and improves the wear resistance of the drive wheel. Thus, with the drive wheel according to the present invention, it is possible to improve the wear resistance of the drive wheel by preventing the formation and propagation of cracks in the coating.

[0009] In the drive wheel described above, the coating can be designed with a metallic structure that extends continuously in a direction that intersects the circumferential direction. If the coating is designed to have a metallic structure that extends continuously not only in the circumferential direction but also in a direction that intersects the circumferential direction, the formation and propagation of cracks against forces acting in different directions can be prevented.

[0010] In the drive wheel according to the present invention, the coating comprises a matrix consisting of the second metal as well as hard particles dispersed in the matrix. This facilitates the formation of a coating with excellent wear resistance.

[0011] In the drive wheel described above, the hard particles located within the surface area of ​​the coating—defined as an area within the average diameter of the hard particles measured from the coating surface—can be embedded in the coating and arranged side by side. This prevents the hard particles from protruding significantly from the coating surface and thus prevents them from falling out during operation of the drive wheel. It should be noted that the average diameter of the hard particles can be determined by examining a cross-section perpendicular to the coating surface with a light microscope and calculating the mean diameter of ten hard particles examined.

[0012] In the drive wheel described above, the hard particles located in the surface area of ​​the coating can be arranged in contact with the surface of the coating. This reduces the area of ​​each hard particle exposed at the surface of the coating, thus preventing the hard particle from detaching.

[0013] In the drive wheel described above, any hard particle located in the surface area of ​​the coating that has an exposed area can have an acute central angle (less than 90°) corresponding to the exposed area. This reduces the exposed area of ​​the hard particle, thus preventing it from falling out.

[0014] In the drive wheel according to the present invention, the coating in an area that includes an interface between the coating and the substrate material has projections that extend onto the substrate material. This prevents the coating from detaching from the substrate material.

[0015] In the drive wheel according to the present invention, at least a portion of a hard particle is incorporated in each projection. This more reliably prevents the coating from detaching from the substrate material.

[0016] A method for manufacturing a drive wheel according to the present invention is a method for manufacturing a drive wheel having a ring shape and a plurality of projections formed on an outer circumferential surface for transmitting a driving force to a crawler track. This method for manufacturing a drive wheel comprises the following steps: manufacturing a carrier element consisting of a first metal; forming a coating containing a second metal in contact with a surface of the carrier element to cover at least a portion of the surface; and hot forging the carrier element with the coating formed thereon, such that the coating forms the outer circumferential surface, the plurality of projections on the outer circumferential surface are formed to project radially outwards, and the coating is machined.

[0017] In the method for manufacturing a drive wheel according to the present invention, the carrier element on which the coating is formed is hot-forged, thus processing the coating. This causes the metal forming the coating to recrystallize, resulting in a continuous metallic structure within the coating. Using the method for manufacturing a drive wheel according to the present invention, it is readily possible to produce the drive wheel of the present invention shown above by continuously forming the metallic structure within the coating.

[0018] In the above-described process for manufacturing a drive wheel, the coating formation step can include forming a coating containing a matrix of the second metal as well as hard particles dispersed within the matrix. This facilitates the formation of a coating with excellent wear resistance. Effects of the invention

[0019] As can be seen from the description above, with the drive wheel and the method for manufacturing it according to the present invention it is possible to improve the wear resistance of the drive wheel by preventing the occurrence and propagation of cracks in the coating. Brief description of the drawings Fig. Figure 1 is a schematic representation showing the structure of a caterpillar track vehicle; Fig. Figure 2 is a schematic representation illustrating the function of a drive wheel and bushings; Fig. Figure 3 is a schematic perspective view showing the structure of a socket; Fig. Figure 4 is a schematic top view showing the contact state of the drive wheel and a bushing; Fig. Figure 5 is a schematic sectional view along line VV in Fig. 4; Fig. Figure 6 is a schematic sectional view showing the structure of a coating on its surface and in its vicinity; Fig. 7 is a schematic sectional view showing the structure at and near an interface between the coating and a substrate material; Fig. Figure 8 is a flowchart that schematically illustrates a process for manufacturing a drive wheel; Fig. Figure 9 is a schematic perspective view illustrating a method for manufacturing a drive wheel; Fig. Figure 10 is a schematic perspective view illustrating the process for manufacturing the drive wheel; Fig. Figure 11 is a schematic sectional view illustrating a method for forming a coating; Fig. Figure 12 is a schematic perspective view illustrating the process for manufacturing the drive wheel; Fig. Figure 13 is a schematic perspective view illustrating the process for manufacturing the drive wheel; Fig. 14 is an optical micrograph showing a surface of a coating and its surroundings (example); Fig. Figure 15 is an optical micrograph showing a surface of a coating and its surroundings (comparative example); Fig. 16 is an optical micrograph showing an interface between a coating and a substrate material and its surroundings (example); and Fig. 17. It is an optical micrograph showing an interface between a coating and a substrate material and its surroundings (comparative example). Description of embodiments

[0020] One embodiment of the present invention is described below. In the following drawings, the same or corresponding parts are identified by the same reference numerals, and their description is not repeated.

[0021] A drive wheel according to an embodiment of the present invention is described with reference to Fig. 1 to 5 described. Fig. Figure 1 is a schematic representation showing the structure of a caterpillar track vehicle. Fig. Figure 2 is a schematic representation illustrating the function of a drive wheel and bushings. Fig. Figure 3 is a schematic perspective view showing the structure of a socket. Fig. 4 and Fig. Figure 5 are schematic sectional views showing the contact state of the drive wheel and a bushing.

[0022] A tracked driving device 1 in the present embodiment, as described in Fig. Figure 1 shows a driving device for a working machine, such as a bulldozer, and includes a track 2, a track frame 3, a deflection wheel 4, a drive wheel 5, and a plurality (in this case seven) of running rollers 10 and a plurality (in this case two) of support rollers 11.

[0023] The caterpillar track 2 comprises a multitude of caterpillar track links 9 connected in an endless configuration, as well as caterpillar plates 6 attached to the corresponding caterpillar track links 9. The caterpillar track links 9 include outer links 7 and inner links 8. The outer links 7 and the inner links 8 are connected alternately.

[0024] The deflection pulley 4, the multiple track rollers 10, and the multiple support rollers 11 are mounted on the crawler track frame 3 in such a way that they can be rotated about their respective axes. The drive sprocket 5 is located at one end of the crawler track frame 3. A power source, such as a motor, is connected to the drive sprocket 5, and the drive sprocket 5 rotates about its axis, driven by the power source. A multiple of projections 51 are arranged on an outer circumferential surface of the drive sprocket 5, projecting radially outwards. The projections 51 engage with the crawler track 2. The rotation of the drive sprocket 5 is thus transmitted to the crawler track 2. The crawler track 2, driven by the rotation of the drive sprocket 5, rotates in a circumferential direction.

[0025] The deflection pulley 4 is attached to the other end (opposite the end where the drive wheel 5 is located) of the track frame 3. Furthermore, the track rollers 10 and the support rollers 11 are attached to the track frame 3 in the area enclosed between the drive wheel 5 and the deflection pulley 4, respectively, on the side in contact with the ground and on the side opposite the side in contact with the ground. The outer circumferential surfaces of the deflection pulley 4, the track rollers 10, and the support rollers 11 each come into contact with the inner circumferential surface of the track 2. This causes the track 2, driven by the rotation of the drive wheel 5, to rotate circumferentially and be guided by the deflection pulley 4, the drive wheel 5, the track rollers 10, and the support rollers 11.

[0026] An outer member 7 and an inner member 8, which are adjacent to each other, are, as with reference to Fig. As shown in Figure 2, the inner link 8 is connected by means of a connecting bolt 12 and a bushing 13. Each inner link 8 has two through holes 15, which are designed to extend in a direction perpendicular to the plane of rotation of the track 2. One and the other of these two through holes 15 are formed at one end and the other end, respectively, in the longitudinal direction of the link. Each outer link 7 has two through holes 15, which are designed to extend in a direction perpendicular to the plane of rotation of the track 2. One and the other of these two through holes 15 are formed at one end and the other end, respectively, in the longitudinal direction of the link.

[0027] The socket 13 has, as with reference to Fig. Figure 3 shows the shape of a hollow cylinder. The bushing 13 has a smaller diameter section 139 at each end, which has a smaller outer diameter. The bushing 13 has an inner circumferential surface 133 that has a constant diameter along its length. The thickness of the bushing 13 is reduced in the smaller diameter sections 139.

[0028] Paired outer members 7 are, as with reference to Fig. 2 and Fig. As shown in Figure 3, the inner links 8 are arranged such that their two through-holes 15 are aligned when viewed in the direction perpendicular to the plane of rotation of the track 2. Paired inner links 8 are arranged such that their two through-holes 15 are aligned when viewed in the direction perpendicular to the plane of rotation of the track 2. An outer link 7 and an inner link 8 adjacent to each other are arranged such that a through-hole 15 of the outer link 7 and a through-hole 15 of the inner link 8 are aligned when viewed in the direction perpendicular to the plane of rotation of the track 2. A bushing 13 is arranged such that it is enclosed between a pair of inner links 8 and the smaller-diameter section 139 at each end is inserted into a through-hole 15 of the corresponding inner link 8.A connecting bolt 12 is arranged such that it extends through the through holes 15 of the outer and inner links 7 and 8, which are adjacent to each other, the holes being aligned in the direction perpendicular to the plane of rotation of the caterpillar track 2, and it extends through the space enclosed by the inner circumferential surface 133 of the corresponding bushing 13. The connecting bolt 12 is arranged such that it extends longitudinally through the bushing 13.

[0029] The drive wheel 5 rotates in a circumferential direction, its outer circumferential surface 53 engaging with outer circumferential surfaces 131 of the bushings 13 that form the track 2. The outer circumferential surface 53 of the drive wheel 5 must therefore exhibit high wear resistance. The drive wheel 5 is a machine component that slides relative to another component, namely the bushing 13, and is in contact with the bushing 13 in the contact area, which is the outer circumferential surface 53.

[0030] The drive wheel 5 has, as with reference to Fig. 4 and Fig. Figure 5 shows a ring shape. A plurality of projections 51 are formed on the outer circumferential surface 53 of the drive wheel 5. These projections serve to transmit a driving force to the bushings 13 of the crawler track 2. The drive wheel 5 comprises a carrier material 50, which consists of a first metal, and a coating 52 that covers the carrier material 50 and thus forms the outer circumferential surface 53, which is the contact area. The coating 52 comprises a second metal. The coating 52 has a metallic structure that extends continuously in the circumferential direction and establishes connections between adjacent projections 51. For example, the first metal forming the carrier material 50 can be carbon steel for use in mechanical engineering or alloy steel for use in mechanical engineering, specified according to the JIS standard (e.g., JIS 1000).S45C or SCM435, as well as manganese steel (SMn), chromium steel (SCr) or chromium-molybdenum steel (SCM), which contains an equivalent amount of carbon), can be used.

[0031] Furthermore, the outer circumferential surface 53, which is the surface of the coating 52, has been smoothed. The state in which the outer circumferential surface 53, i.e., the surface of the coating 52, is smoothed refers to the state in which the surface profile, which arose from surface tension and the like during the formation of the coating 52 in the liquid state, has been removed from the surface of the coating 52. In the present embodiment, the outer circumferential surface 53, which is the surface of the coating 52, is a forged surface. The outer circumferential surface 53, or the surface of the coating 52, which arose from surface tension and the like during the formation of the coating 52 in the liquid state, has been smoothed by forging.

[0032] A bushing 13 contains a carrier material 134 and a coating 132, which covers the carrier material 134 and thus forms the outer circumferential surface 131, which is the contact area.

[0033] In the present embodiment of the drive wheel 5, the coating 52 is formed with a metallic structure that extends continuously in the circumferential direction and connects adjacent projections 51. This prevents the formation of cracks in the coating 52, which would otherwise be caused by the force that causes the projections 51 to tilt in the circumferential direction, and improves the wear resistance of the drive wheel 5. Thus, with the drive wheel 5 in the present embodiment, it is possible to improve the wear resistance of the drive wheel 5 by preventing the formation and propagation of cracks in the coating 52. The condition in which the metallic structure of the second metal extends continuously in the circumferential direction represents the condition in which the metal has a microstructure that extends continuously in the circumferential direction.The coating 52 can be formed with a metallic structure that extends continuously in the direction intersecting the circumferential direction. This makes it possible to prevent the formation and propagation of cracks against forces acting in different directions.

[0034] The following is a description of the structure of a coating formed on the drive wheel 5. Fig. Figure 6 is a schematic sectional view showing the structure of a coating on its surface and in its vicinity. Fig. Figure 7 is a schematic sectional view showing the structure at and around an interface between the coating and a substrate material. A coating 90 (coating 52) formed on the drive wheel 5 contains, as described with reference to Fig. 6 and Fig. Figure 7 shows a matrix 95 consisting of a second metal and hard particles 91 dispersed in the matrix 95. The second metal forming the matrix 95 can, for example, be a mixture of a metal derived from a welding wire and the metal (first metal) forming the carrier material 100 (carrier material 50). The hard particles 91 can be particles with a higher hardness than the matrix 95, such as sintered carbide particles. The coating 90 exhibits higher wear resistance than the carrier material 100.

[0035] The surface 90A of the coating 90, as described in Fig. Figure 6 shows a forged surface. The hard particles 91, located in a surface region 90B of the coating, which is an area within an average particle diameter of the hard particles 91 from the surface 90A of the coating 90, are embedded in the coating 90 and arranged side by side. This prevents the hard particles 91 from protruding significantly from the surface 90A of the coating 90. This, in turn, prevents the hard particles 91 from falling out during use of the drive wheel 5, thereby improving the wear resistance of the drive wheel 5.

[0036] The hard particles 91 located in the surface area 90B of the coating can, as in Fig. Figure 6 shows that the hard particle 91 is arranged in contact with the surface 90A of the coating 90. This reduces the area of ​​a hard particle 91 exposed at the surface 90A of the coating 90, thus preventing the hard particle 91 from falling out.

[0037] Of the hard particles 91, which are located in the surface area 90B of the coating, as shown in Fig. As shown in Figure 6, each hard particle 91 that has an area exposed at the surface 90A of the coating 90 has an acute central angle θ (of less than 90°) corresponding to this exposed area. This makes the area of ​​a hard particle 91 exposed at the surface 90A of the coating 90 small, thus preventing the hard particle 91 from falling out.

[0038] In an area that includes an interface between the coating 90 and the substrate material 100, as described with reference to Fig. Figure 7 shows the coating 90 with projections 99 that extend onto the substrate 100. The projections 99 create an anchoring effect that prevents the coating 90 from detaching from the substrate 100. Each projection 99 encloses at least part of a hard particle 91. This more reliably prevents the coating 90 from detaching from the substrate 100. The matrix 95 of the coating 90 is located between the substrate 100 and the hard particle 91 enclosed in the projection 99. The hard particle 91 enclosed in the projection 99 is not in contact with the substrate 100. The center of the hard particle 91 is located outside the projection 99 (i.e., a portion of the hard particle 91, which has a volume of less than half its volume, is enclosed in the projection 99). A hard particle 91 is enclosed in a projection 99.Each protrusion 99 has a depth that is smaller than the radius of the hard particle 91 contained in the protrusion 99.

[0039] A method for manufacturing a drive wheel 5 in the present embodiment is described below with reference to Fig. 8 to 13 described. Fig. Figure 8 is a flowchart that schematically illustrates a process for manufacturing a drive wheel. Fig. 9, Fig. 10, Fig. 12 and Fig. Figure 13 are schematic perspective views illustrating the process for manufacturing the drive wheel. Fig. Figure 11 is a schematic sectional view illustrating a method for forming a coating.

[0040] In the method for manufacturing a drive wheel 5 in the present embodiment, first, as described with reference to Fig. As can be seen in Figure 8, a step in the production of a support element is carried out as step S10. In this step S10, as described in reference to Fig. Figure 9 shows a carrier element 61, which becomes a support material 50 of the drive wheel 5. The carrier element 61 consists of a metal that forms the support material 50. The carrier element 61 has a cylindrical shape. The carrier element 61 includes a pair of end faces 61B and a side face 61A that connects the end faces 61B.

[0041] Subsequently, a step to form a coating is executed as step S20. In this step S20, as described in reference to Fig. 9 and Fig. As shown in Figure 10, a coating 63 is formed such that it covers part of the side surface 61A of the support element 61 manufactured in step S10. The coating 63 is formed over its entire longitudinal extent in the longitudinal direction of the support element 61. The coating 63 is also formed in a portion of the circumferential direction (approximately half) of the support element 61. The coating 63 has a structure in which beads 62, extending in the longitudinal direction of the support element 61, lie adjacent to each other in the circumferential direction without gaps between them. The beads 62 are formed such that they extend in a direction corresponding to the circumferential direction of the drive wheel 5.

[0042] The coating 63 can, for example, be formed by overlay welding using CO2 arc welding, as described below. First, a device for forming a coating is described. The device for forming a coating contains, as referenced in Fig. Figure 11 shows a welding torch 70 and a nozzle 80 for feeding hard particles. The welding torch 70 contains a welding nozzle 71, which has the shape of a hollow cylinder, and a contact tip 72, which is located inside the welding nozzle 71 and connected to a power source (not shown). A welding wire 73, which is in contact with the contact tip 72, is continuously fed to the side of the front end of the welding nozzle 71. JIS YGW12, for example, can be used for the welding wire. A gap between the welding nozzle 71 and the contact tip 72 is a flow path for shielding gas. The shielding gas flowing through the flow path is expelled from the front end of the welding nozzle 71. The nozzle 80 for feeding hard particles has the shape of a hollow cylinder. Inside the nozzle 80 for feeding hard particles, hard particles 91 are fed in and ejected via the front end of the nozzle 80 for feeding hard particles.

[0043] This device for forming a coating can be used to form a coating 63 using the method described below. With a carrier element 61 serving as one electrode and the welding wire 73 as the other electrode, voltage is applied across the carrier element 61 and the welding wire 73. This generates an arc 74 between the welding wire 73 and the carrier element 61. The arc 74 is shielded from the ambient air by the shielding gas, which is expelled from the front end of the welding nozzle 71 along the direction indicated by arrows β. Carbon dioxide, for example, can be used as the shielding gas. The heat in the arc 74 melts part of the carrier element 61 and also melts the front end of the welding wire 73. The melted front end of the welding wire 73 forms droplets that are transferred to the molten area of ​​the carrier element 61.This creates a melt pool 92, which is a liquid region in which the molten support element 61 and the molten welding wire 73 are mixed together. The hard particles 91, ejected via the nozzle 80 for the purpose of supplying hard particles, are fed into this melt pool 92.

[0044] When the welding torch 70 and the nozzle 80, which supply hard particles forming the device for cladding, move relative to the carrier element 61 in the direction indicated by arrow α, the position at which the molten pool 92 is formed shifts accordingly. The previously formed molten pool 92 solidifies, forming a bead 62. The bead 62 contains a matrix 95, which is formed by the solidification of the molten pool 92, as well as hard particles 91 dispersed in the matrix 95. A plurality of such beads 62 are formed side by side in the width direction without a gap between them, so that a desired area on the side surface 61A of the carrier element 61 is covered, thus completing the formation of the coating 63 (see Fig. 10) It should be noted that weld overlay can be carried out, for example, under the following conditions: welding current of 230 A, welding voltage of 17 V, feed rate of 110 g / min, and bead overhang of 4 mm. JIS YGW11 can be used as the welding wire. WC or W2C-based particles can be used as the hard particles.

[0045] Subsequently, a hot forging step is performed as step S30. In this step S30, the carrier element 61 with the coating 63 formed in step S20 is hot forged. The carrier element 61 with the coating 63 formed on it is then, as described in [reference to] Fig. 10 and Fig. As shown in Figure 12, the component is heated to a temperature that enables hot forging and then placed in a mold for forging. The mold has a cavity corresponding to the desired shape of the drive wheel 5. In the present embodiment, a plurality of arc-shaped parts forming an annular drive wheel 5 are produced by hot forging. The resulting parts are assembled in a subsequent step to produce the annular drive wheel 5. The coating 63 formed in step S20 is processed by hot forging. The carrier element 61 is hot forged such that the coating 63 covers the outer circumferential surface of the drive wheel 5. In this way, the second metal forming the coating 63 recrystallizes, so that the microstructure of the metal extends continuously even in the area that formed the interface between the adjacent ridges 62.This results in the microstructure of the metal in the forged coating 52 being continuous not only in the circumferential direction of the drive wheel 5, but also in a direction that intersects the circumferential direction (for example, in the direction perpendicular to the circumferential direction). Furthermore, the coating 52 is produced with a smooth surface from which the surface profile, which arose due to surface tension in the liquid state, etc., has been removed. Hot forging, as described in... Fig. 12 shown, ridge 59 formed. Subsequently, as with reference to Fig. 12 and Fig. 13 shows that punching was carried out to remove the burr 59, so that a part is created that forms the drive wheel 5 (see Fig. 13).

[0046] When the carrier element 61 with the coating 63 formed on it is hot-forged, as described with reference to Fig. 11 and Fig. As can be seen in Figure 6, hard particles 91, which protrude from a surface of the coating 63 during its formation (beads 62), are pressed into the coating 63 (beads 62). As a result, in the drive wheel 5, the hard particles 91 located in the surface region 90B of the coating are embedded in the coating 90 and arranged side by side. The hard particles 91 located in the surface region 90B of the coating are in contact with the surface 90A of the coating 90. Of the hard particles 91 located in the surface region 90B of the coating, each hard particle 91 that has a region exposed at the surface 90A of the coating 90 has an acute central angle θ (of less than 90°) corresponding to the exposed region. This prevents the hard particle 91 from falling out during use of the drive wheel 5, thereby improving the wear resistance of the drive wheel 5.

[0047] When the carrier element 61 with the coating 63 formed on it is hot-forged, projections 99 are formed in the coating 90 due to the hard particles 91 that were located near the interface between the coating 63 (beads 62) and the carrier element 61 at the time of the coating 63's formation. At least a portion of a corresponding hard particle 91 is incorporated into each projection 99. The process described above simultaneously forms the surface area of ​​the coating 90, which exhibits excellent wear resistance because the hard particles 91 are in contact with the surface 90A, and the projections 99, which prevent the coating 90 from detaching from the carrier material 100.

[0048] Subsequently, as with reference to Fig. As shown in Figure 8, a heat treatment step is carried out as step S40. In this step S40, the drive wheel 5 (the part forming the drive wheel 5), produced by hot forging in step S30, undergoes heat treatment. The heat treatment carried out in step S40 consists, for example, of tempering. This gives the carrier material 50 of the drive wheel 5 the desired hardness and toughness. Subsequently, in order to mount the drive wheel 5 onto a support body (not shown), an area where no coating 90 has been formed is machined to improve dimensional accuracy, create a mounting hole, etc. The drive wheel 5 (the part forming the drive wheel 5) in the present embodiment is thus completed. Examples

[0049] A test piece was produced by forming a coating on a substrate element by weld overlay, as described in the embodiment shown above, and then hot-forging the substrate element to process the coating (Example). For comparison, another test piece was produced by forming a coating after hot forging (Comparative Example). The dies used for hot forging were of the same shape in both the Example and the Comparative Example. Each test piece was sectioned, and the condition of the coating was examined using a light microscope.

[0050] Fig. Figure 14 is an optical micrograph obtained by imaging a surface of the coating of the example and its surroundings. Fig. Figure 15 is an optical micrograph obtained by imaging a surface of the coating of the comparison example and its surroundings. In the case of the coating of the comparison example, which was formed by weld overlay and subsequently not machined by forging, the following are available, as shown in Fig. Figure 15 shows that hard particles 91 are significantly separated from the surface 90A of the coating. In the coating of the example, which was formed and subsequently machined by forging, hard particles 91 located in the surface area are, as shown with reference to Fig. As can be seen in Figure 14, the hard particles 91 are embedded in the coating (matrix 95) and arranged side by side. They are aligned in contact with the surface 90A of the coating. A hard particle 91 with an area exposed at the surface 90A of the coating 90 has an acute central angle θ (of less than 90°) corresponding to the exposed area. This is presumably due to the fact that during the forging process, the hard particles 91 protruding from the surface 90A of the coating are pressed into the matrix 95, which has relatively low hardness.

[0051] Fig. Figure 16 is an optical micrograph obtained by imaging an interface between the coating and the substrate of the example, as well as its surroundings. Fig. Figure 17 is an optical micrograph obtained by imaging an interface between the coating and the substrate of the comparison example, as well as its surroundings. In the comparison example, where the coating was formed by weld overlay and subsequently not machined by forging, as shown in Fig. As shown in Figure 17, the interface between the coating (matrix 95) and the substrate 100 is flat. In the example, which was machined by forging after the coating was formed, the area encompassing the interface between the coating (matrix 95) and the substrate 100 is flat, as shown in Figure 17. Fig.Figure 16 shows projections 99 formed with the coating (matrix 95) that project onto the substrate material 100. A portion of a corresponding hard particle 91 is incorporated into each projection 99. It is assumed that the projections 99 were formed due to the presence of the hard particles 91 near the interface with the substrate element while the coating was being processed by forging. A hard particle 91 that contributed to the formation of a projection 99 has at least one portion incorporated into the projection 99. Industrial applications

[0052] The drive wheel and the method for manufacturing it according to the present invention can be used particularly advantageously in a drive wheel where improved wear resistance is desired, and in the method for manufacturing it. Description of reference symbols

[0053] 1: Crawler track drive device; 2: Crawler track; 3: Crawler track frame; 4: Deflection wheel; 5: Drive wheel; 6: Track plate; 7: Outer link; 8: Inner link; 9: Crawler track link; 10: Running roller; 11: Bearing roller; 12: Connecting bolt; 13: Bushing; 15: Through hole; 50: Carrier material; 51: Projection; 52: Coating; 53: Outer circumferential surface; 59: Burr; 69: Carrier element; 61A: Side surface; 61B: End surface; 62: Bead; 63: Coating; 70: Welding torch; 71: Welding nozzle; 72: Contact tip; 73: Welding wire; 74: Arc; 80: Nozzle for feeding hard particles; 90: Coating; 90A: Surface; 90B: Surface area of ​​the coating; 91: Hard particle; 92: Melt bath; 95: Matrix; 99: Projection; 100: Substrate material; 131: Outer circumferential surface; 132: Coating; 133: Inner circumferential surface; 134: Substrate material; and 139: Smaller diameter section.

Claims

[1] Drive wheel (5) having a ring shape and having a plurality of projections (51) formed on an outer peripheral surface (53) for transmitting a driving force to a crawler belt (2), the drive wheel (5) comprising: a carrier material (50, 100) consisting of a first metal; and a coating (52, 90) covering the carrier material (50, 100) and forming at least part of the outer peripheral surface (53), the coating (52, 90) containing a second metal, wherein: the coating (52, 90) is formed with a metallic structure which extends continuously in a circumferential direction and establishes a connection between adjacent projections (51); and the coating (52, 90) contains a matrix (95) consisting of the second metal and hard particles (91) dispersed in the matrix (95), wherein at an interface between the coating (52, 90) and the carrier material (50, 100), the coating (52, 90) has projections (99) which project towards the carrier material (50, 100), and wherein each projection (99) receives at least a portion of a hard particle (91). [2] Drive wheel (5) according to claim 1, wherein the coating (52, 90) is formed with the metallic structure which also extends continuously in a direction which intersects the circumferential direction. [3] Drive wheel according to claim 1 or 2, wherein the hard particles (91) located in a surface region (90B) of the coating (52, 90) are embedded in the coating (52, 90) and arranged side by side, and wherein the surface region (90B) of the coating (52, 90) is a region within an average particle diameter of the hard particles (91) from the surface (90A) of the coating (52, 90). [4] Drive wheel (5) according to claim 3, wherein the hard particles (91) located in the surface region (90B) of the coating (52, 90) are arranged in contact with the surface (90A) of the coating (52, 90). [5] Drive wheel (5) according to claim 3, wherein of the hard particles (91) located in the surface region (90B) of the coating (52, 90), any hard particle (91) having a region exposed at the surface (90A) of the coating (52, 90) has an acute central angle (θ) corresponding to the region exposed at the surface (90A) of the coating (52, 90). [6] A method for manufacturing a drive wheel (5) having a ring shape and having a plurality of projections (51) formed on an outer peripheral surface (53) for transmitting a driving force to a crawler belt (2), the method comprising the following steps: Producing a support element (61) made of a first metal; Forming a coating (63) containing a second metal in contact with a surface (61A) of the support member (61) to cover at least a portion of the surface (61A); and Hot forging the support member (61) with the coating (63) formed thereon such that the coating (63) forms the outer peripheral surface (53), the plurality of projections (51) are formed on the outer peripheral surface (53) so as to protrude radially outward, and the coating (63) is machined. [7] A method of manufacturing a drive wheel (5) according to claim 6, wherein the step of forming the coating (63) includes forming the coating (63) containing a matrix (95) made of the second metal and hard particles (91) dispersed in the matrix (95).

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