Machine component and method for manufacturing it

Abstract

A machine component that has a contact area and is designed to move relative to another component and is in contact with the other component in the contact area, wherein the machine component comprises: a carrier material (100) consisting of a first metal; as well as a coating (90) covering the substrate material (100) and forming at least part of the contact area, wherein: a surface (90A) of the coating (90) that forms the contact area has been smoothed; the coating (90) contains a matrix (95) consisting of a second metal, as well as hard particles (91) dispersed in the matrix (95); in an area that includes an interface between the coating (90) and the substrate (100), the coating (90) includes a projection (99) that projects towards the substrate (100); and at least part of a hard particle (91) is incorporated in the projection (99).

Description

Technical area

[0001] The present invention relates to machine components and methods for manufacturing the machine components and in particular to a machine component which is intended to move relative to another component and is in contact with the other component, and to a method for manufacturing the machine component. Technical background

[0002] A coating can be applied to a machine component to improve wear resistance and for other purposes. Coatings that can be used to improve wear resistance include a coating having hard particles dispersed in a matrix made of, for example, steel. Such a coating can be formed, for example, by deposition welding (see, for example, JP 2008 - 000 763 A and JP H08 - 47 774 A).

[0003] JP H09 - 136 136 A describes a method for improving the wear, corrosion, and heat resistance of components such as VTR drums, brake discs, and pistons by using an aluminum alloy substrate with a coating of Al-20-30% Si. Two manufacturing processes are described: machining from extruded bars and forging from disc-shaped blanks. JP H09 - 136 136 A discusses the challenges of material hardness and high production costs and proposes a drop forging technique to improve the interface between the substrate and the coating, ensuring stronger and more durable composite bodies.

[0004] JP 2000 - 343 219 A discusses a reinforcement method for undercarriage components of tracked vehicles, focusing on drive wheels and bushings, which are subject to severe wear from dirt particles. It highlights a method for improving wear resistance in which a coating layer containing hard particles is applied by hardfacing. JP 2000 - 343 219 A criticizes conventional methods that lead to cracks and delamination due to stress and repeated loading and presents a solution aimed at optimizing particle distribution and coating methods to prevent such failures. Summary of the inventionTechnical problem

[0005] If a coating is applied to a machine component that moves relative to another component and is in contact with it to improve wear resistance or for other purposes, the machine component may cause greater damage to the other component. Although the machine component with the coating may exhibit better resistance, it may shorten the service life of the other component.

[0006] An object of the present invention is to produce a machine component with a coating formed thereon, which causes less damage to another component. Solution to the problem

[0007] A machine component according to the present invention is a machine component that has a contact area and is designed to move relative to another component while being in contact with the other component in the contact area. The machine component comprises a substrate material consisting of a first metal and a coating that covers the substrate material and forms at least part of the contact area. A surface of the coating that forms the contact area has been smoothed. The coating contains a matrix consisting of a second metal and hard particles dispersed in the matrix. In a region that includes an interface between the coating and the substrate material, the coating contains a projection that projects towards the substrate. At least part of a hard particle is received in the projection.

[0008] As described above, when a coating is formed on a machine component, although the durability of the machine component with the coating formed thereon may be improved, the service life of another component may be shortened. The inventors have discovered that damage to another component caused by the machine component with the coating formed thereon can be effectively reduced by appropriately controlling the profile of the contact area of ​​the machine component in the manner described below. To form a coating, a material of the coating in a liquid state is applied to a machine component, and this material then solidifies to form the coating. The profile of the coating is affected by surface tension in the liquid state and other factors, so it is difficult to precisely control the profile.If such a coating is formed on a contact area of ​​a component that comes into contact with another component during use, the low accuracy of the profile of the coating may cause a localized increase in contact pressure and other phenomena, so that the component causes greater damage to the other component.

[0009] In the machine component of the present invention, the surface of the coating forming the contact area has been smoothed. This prevents localized increases in contact pressure and other phenomena, so that the machine component causes less damage to the other component. The state in which the surface of the coating has been smoothed refers to the state in which the surface profile created by surface tension in the liquid state, etc., has been removed from the surface of the coating.

[0010] In the machine component according to the present invention, the coating contains the matrix consisting of the second metal and the hard particles dispersed in the matrix. This facilitates the formation of a coating with excellent wear resistance.

[0011] In the machine component described above, the hard particles located in a surface region of the coating, which is a region within an average particle diameter of the hard particles from the surface of the coating forming the contact area, can be embedded in the coating and arranged side by side. This prevents the hard particles from being arranged in such a way that they protrude significantly from the surface of the coating. This prevents the hard particles from falling out during use of the machine component. It should be noted that the average particle diameter of the hard particles can be determined by observing a cross-section perpendicular to the surface of the coating with an optical microscope and calculating an average value of the diameters of ten observed hard particles.

[0012] In the machine component 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 minimizes the area of ​​a hard particle exposed at the surface of the coating, thereby preventing the hard particle from detaching.

[0013] In the machine component described above, among the hard particles located in the surface area of ​​the coating, any hard particle having an area exposed at the surface of the coating may have an acute central angle (less than 90°) corresponding to the area exposed at the surface of the coating. This makes the area of ​​a hard particle exposed at the surface of the coating small, thereby preventing the hard particle from falling out.

[0014] In the machine component according to the present invention, the coating includes the projection protruding toward the substrate in the region including the interface between the coating and the substrate. This prevents the coating from detaching from the substrate.

[0015] In the machine component according to the present invention, at least a portion of the hard particle is accommodated in the projection. This more reliably prevents the coating from detaching from the substrate.

[0016] In the machine component described above, the surface of the coating forming the contact area can be smoothed by forging. This smooths the surface of the coating, which is affected by surface tension in the liquid state and the like, by forging. This more reliably reduces damage to other components caused by the component.

[0017] A method of manufacturing a machine component according to the present invention is a method of manufacturing a machine component having a contact area and configured to move relative to another component while being in contact with the other component in the contact area.This method for producing a machine component comprises the steps of: manufacturing a support element consisting of a first metal; forming a coating which is in contact with a surface of the support element and covers the surface of the support element, the coating containing a matrix consisting of a second metal and hard particles dispersed in the matrix (95); forming a protrusion within the coating in a region including an interface between the coating and the support material, the protrusion receiving at least a portion of a hard particle and protruding toward the support material; and forging the support element on which the coating is formed so that the coating forms at least a portion of the contact region and the coating is smoothed.

[0018] In the method for manufacturing a machine component of the present invention, the support member on which the coating is formed is forged so that the coating forms at least a part of the contact area, and the coating is machined. Thus, the coating, which has low profile accuracy influenced by surface tension in the liquid state and the like, is machined by forging so that the surface of the coating is smoothed. In the method for manufacturing a machine component of the present invention, the coating is machined by forging so that the surface of the coating is smoothed, thus making it possible to easily manufacture a machine component that causes less damage to another component.

[0019] In the method for manufacturing a machine component described above, the step of forging the support member on which the coating is formed may include hot forging the support member on which the coating is formed. When hot forging is used, this can facilitate forging the support member on which the coating is formed.

[0020] In the method for manufacturing a machine component according to the present invention, the coating forming step includes forming the coating containing the matrix composed of the second metal and the hard particles dispersed in the matrix. This facilitates the formation of a coating with excellent wear resistance. Effects of the invention

[0021] As is apparent from the above description, with the machine component and the method for manufacturing the same of the present invention, it is possible to manufacture a machine component having a coating formed thereon which causes less damage to another component. Short description of the drawings Fig. 1 is a schematic diagram showing the structure of a crawler traveling device; Fig. Figure 2 is a schematic diagram illustrating the function of a drive wheel and bushings; Fig. 3 is a schematic perspective view showing the structure of a socket; Fig. 4 is a schematic plan view showing the contact state of the drive wheel and a bushing; Fig. 5 is a schematic sectional view along the line VV in Fig. 4; Fig. 6 is a schematic sectional view showing the structure of a coating on and near its surface; Fig. 7 is a schematic sectional view showing the structure at and near an interface between the coating and a substrate; Fig. 8 is a flowchart schematically illustrating a method for manufacturing a machine component (drive gear and bushing); Fig. 9 is a schematic perspective view illustrating a method of manufacturing a drive wheel; Fig. 10 is a schematic perspective view illustrating the method of manufacturing the drive wheel; Fig. 11 is a schematic sectional view illustrating a method of forming a coating; Fig. 12 is a schematic perspective view illustrating the method of manufacturing the drive wheel; Fig. 13 is a schematic perspective view illustrating the method of manufacturing the drive wheel; Fig. 14 is a schematic perspective view illustrating a method of manufacturing a bushing; Fig. 15 is a schematic perspective view illustrating the method of manufacturing the bushing; Fig. 16 is an optical micrograph showing a surface of a coating and its surroundings (example); Fig. 17 is an optical micrograph showing a surface of a coating and its surroundings (comparative example); Fig. 18 is an optical micrograph showing an interface between a coating and a substrate and its surroundings (example); and Fig. Figure 19 is an optical micrograph showing an interface between a coating and a substrate and its surroundings (comparative example). Description of embodiments

[0022] An embodiment of the present invention will be described below. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated.

[0023] A machine component according to the present embodiment will be described using a drive wheel and bushings of a crawler traveling device as examples. Fig. 1 is a schematic diagram showing the structure of a crawler track traveling device. Fig. Figure 2 is a schematic diagram illustrating the function of a drive wheel and bushings. Fig. 3 is a schematic perspective view showing the structure of a socket. Fig. 4 and Fig. 5 are schematic sectional views showing the contact state of the drive wheel and a bushing.

[0024] A crawler traveling device 1 in the present embodiment as shown in Fig. 1 is a travel device for a work machine, such as a bulldozer, and includes a crawler track 2, a crawler track frame 3, a deflection sprocket 4, a drive wheel 5 and a plurality (in the present case seven) of track rollers 10 and a plurality (in the present case two) of support rollers 11.

[0025] The crawler track 2 includes a plurality of crawler links 9 connected in an endless manner, as well as crawler plates 6 attached to the corresponding crawler links 9. The crawler links 9 include outer links 7 and inner links 8. The outer links 7 and the inner links 8 are alternately connected.

[0026] The idler sprocket 4, the plurality of track rollers 10, and the plurality of support rollers 11 are mounted on the crawler frame 3 so as to be rotatable about their respective axes. The drive wheel 5 is arranged at one end of the crawler frame 3. A power source, such as a motor, is connected to the drive wheel 5, and the drive wheel 5 rotates about its axis driven by the power source. On an outer peripheral surface of the drive wheel 5, a plurality of projections 51 are arranged, projecting radially outward. The projections 51 engage with the crawler belt 2. The rotation of the drive wheel 5 is thus transmitted to the crawler belt 2. The crawler belt 2, driven by the rotation of the drive wheel 5, rotates in a circumferential direction.

[0027] The idler sprocket 4 is attached to the other end (opposite the end where the drive wheel 5 is arranged) of the crawler frame 3. Furthermore, on the crawler frame 3, in the area enclosed between the drive wheel 5 and the idler sprocket 4, the track rollers 10 and the support rollers 11 are attached, respectively, on the side in contact with the ground and on the side opposite to the side in contact with the ground. The outer peripheral surfaces of the idler sprocket 4, the track rollers 10, and the support rollers 11 each come into contact with the inner peripheral surface of the crawler belt 2. As a result, the crawler belt 2, driven by the rotation of the drive wheel 5, rotates in the circumferential direction while being guided by the idler sprocket 4, the drive wheel 5, the track rollers 10, and the support rollers 11.

[0028] An outer member 7 and an inner member 8 which are adjacent to each other are, as described with reference to Fig. 2, by means of a connecting pin 12 and a bushing 13. Each inner link 8 has two through holes 15 which are formed so as to run in a direction perpendicular to the plane of rotation of the crawler belt 2. One and the other of these two through holes 15 are formed at one end and the other end in the longitudinal direction of the link, respectively. Each outer link 7 has two through holes 15 which are formed so as to run in a direction perpendicular to the plane of rotation of the crawler belt 2. One and the other of these two through holes 15 are formed at one end and the other end in the longitudinal direction of the link, respectively.

[0029] The socket 13 has, as described with reference to Fig. 3, the bushing 13 has the shape of a hollow cylinder. The bushing 13 has a smaller-diameter portion 139 formed at each end, which has a smaller outer diameter. The bushing 13 has an inner peripheral surface 133 that has a constant diameter along its length. In the smaller-diameter portions 139, the thickness of the bushing 13 is reduced.

[0030] Paired outer members 7 are, as described with reference to Fig. 2 and Fig. 3, are arranged so that their two through holes 15 are aligned, as viewed in the direction perpendicular to the plane of rotation of the crawler track 2. Paired inner links 8 are arranged so that their two through holes 15 are aligned, as viewed in the direction perpendicular to the plane of rotation of the crawler track 2. An adjacent outer link 7 and an inner link 8 are arranged so that a through hole 15 of the outer link 7 and a through hole 15 of the inner link 8 are aligned, as viewed in the direction perpendicular to the plane of rotation of the crawler track 2. A bushing 13 is arranged so that it is sandwiched between a pair of inner links 8, and the smaller diameter portion 139 at each end is inserted into a through hole 15 of the corresponding inner link 8.A connecting pin 12 is configured to extend through the through holes 15 of the outer and inner links 7 and 8, which are adjacent to each other, the holes being aligned as viewed in the direction perpendicular to the plane of rotation of the crawler belt 2, and to extend through the space enclosed by the inner peripheral surface 133 of the corresponding bushing 13. The connecting pin 12 is configured to extend through the bushing 13 in the longitudinal direction.

[0031] The drive wheel 5 rotates in a circumferential direction, with its outer peripheral surface 53 engaging with outer peripheral surfaces 131 of the bushings 13 that form the crawler belt 2. The outer peripheral surface 53 of the drive wheel 5 and the outer peripheral surfaces 131 of each bushing 13 must therefore have high wear resistance. The drive wheel 5 is a machine component that slides relative to another component or the bushing 13 and is in contact with the bushing 13 or the outer peripheral surface 53 in the contact area. The bushing 13 is a machine component that slides relative to another component or the drive wheel 5 and is in contact with the drive wheel 5 or the outer peripheral surface 131 in the contact area.

[0032] The drive wheel 5 contains, as described with reference to Fig. 4 and Fig. 5, a base material 50 made of metal (steel) and a coating 52 covering the base material 50 to form the outer peripheral surface 53, which is the contact portion. The outer peripheral surface 53, which is the surface of the coating 52, has been smoothed. Here, the state in which the outer peripheral surface 53, i.e., the surface of the coating 52, is smoothed refers to the state in which the surface profile, which was created by surface tension and the like when the coating 52 was formed in the liquid state, has been removed from the surface of the coating 52. In the present embodiment, the outer peripheral surface 53, which is the surface of the coating 52, is a forged surface. The outer peripheral surface 53, orThe surface of the coating 52, which was formed by surface tension and the like during the formation of the coating 52 in the liquid state, has been smoothed by forging. As the metal constituting the base material 50, for example, carbon steel for machine use or alloy steel for machine use specified according to the JIS standard (e.g., S45C or SCM435, as well as manganese steel (SMn), chromium steel (SCr), or chromium-molybdenum steel (SCM) containing an equivalent amount of carbon) can be used.

[0033] A bushing 13 includes a base material 134 and a coating 132 covering the base material 134, thus forming the outer peripheral surface 131, which is the contact area. The outer peripheral surface 131, which is the surface of the coating 132, has been smoothed. In the present embodiment, the outer peripheral surface 131, which is the surface of the coating 132, is a forged surface. The outer peripheral surface 131, or the surface of the coating 132, which has been affected by surface tension and the like during formation of the coating 132 in the liquid state, has been smoothed by forging. As the metal forming the base material 134, for example, carbon steel for use in machinery or alloy steel for use in machinery specified according to the JIS standard (e.g.S45C or SCM435, as well as manganese steel (SMn), chromium steel (SCr) or chromium-molybdenum steel (SCM), which contains an equivalent amount of carbon).

[0034] In the drive gear 5 and the bushings 13, which are the machine components in the present embodiment, the surfaces of the coatings 52 and 132 forming the contact areas have been smoothed. This prevents a localized increase in contact pressure and other phenomena, so that the components cause less damage to the other components (bushes 13 and drive gear 5).

[0035] The following is a description of the structure of a coating formed on the drive wheel 5 and the bushings 13. Fig. Figure 6 is a schematic sectional view showing the structure of a coating at and near its surface. Fig. Figure 7 is a schematic sectional view showing the structure at and around an interface between the coating and a substrate. A coating 90 (coating 52 and coating 132) formed on the drive wheel 5 and the bushings 13 includes, as described with reference to Fig. 6 and Fig. 7, 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 originating from a welding wire and the metal (first metal) forming the carrier material 100 (carrier material 50 and carrier material 134). Particles having a higher hardness than the matrix 95, such as particles made of cemented carbide, can be used as the hard particles 91. The coating 90 has greater wear resistance than the carrier material 100.

[0036] The surface 90A of the coating 90 as shown in Fig. 6 is a forged surface. The hard particles 91 located in a surface area 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 while being arranged adjacent to each other. This prevents the hard particles 91 from being arranged to significantly protrude from the surface 90A of the coating 90. This, in turn, prevents the hard particles 91 from falling out during use of the drive gear 5 and the bushings 13, thereby improving the wear resistance of the drive gear 5 and the bushings 13.

[0037] The hard particles 91 located in the surface area 90B of the coating can, as in Fig. 6, be arranged in contact with the surface 90A of the coating 90. This makes the area of ​​a hard particle 91 exposed at the surface 90A of the coating 90 small, thereby preventing the hard particle 91 from falling out.

[0038] Of the hard particles 91 located in the surface area 90B of the coating, as shown in Fig. As shown in Figure 6, each hard particle 91 having a portion exposed at the surface 90A of the coating 90 must have an acute central angle θ (less than 90°) corresponding to that exposed portion. This makes the area of ​​a hard particle 91 exposed at the surface 90A of the coating 90 small, thereby preventing the hard particle 91 from falling out.

[0039] In a region including an interface between the coating 90 and the carrier material 100, as described with reference to Fig. 7, the coating 90 has protrusions 99 that protrude toward the carrier material 100. The protrusions 99 provide an anchoring effect that prevents the coating 90 from detaching from the carrier material 100. A protrusion 99 receives at least a portion of a hard particle 91. This more reliably prevents the coating 90 from detaching from the carrier material 100. The matrix 95 of the coating 90 is located between the carrier material 100 and the hard particle 91 received in the protrusion 99. The hard particle 91 received in the protrusion 99 is not in contact with the carrier material 100. The center of the hard particle 91 is located outside the protrusion 99 (i.e., a portion of the hard particle 91, which has a volume of less than half of that of the hard particle 91, is received in the protrusion 99). A hard particle 91 is received in a protrusion 99.Each projection 99 has a depth that is smaller than the radius of the hard particle 91 received in the projection 99.

[0040] A method of manufacturing a drive wheel 5, which is the machine component in the present embodiment, will be described below with reference to Fig. 8 to 13 described. Fig. 8 is a flowchart schematically illustrating a method for manufacturing a drive wheel which is the machine component. Fig. 9, Fig. 10, Fig. 12 and Fig. 13 are schematic perspective views illustrating the method of manufacturing the drive wheel. Fig. 11 is a schematic sectional view illustrating a method of forming a coating.

[0041] In the method for manufacturing a drive wheel 5 in the present embodiment, first, as described with reference to Fig. 8, a step for manufacturing a support element is carried out as a step S10. In this step S10, as described with reference to Fig. 9, a support member 61 is manufactured, which becomes a support material 50 of the drive wheel 5. The support member 61 is made of a metal that forms the support material 50. The support member 61 has a cylindrical shape. The support member 61 includes a pair of end surfaces 61B and a side surface 61A connecting the end surfaces 61B.

[0042] Subsequently, a step of forming a coating is carried out as a step S20. In this step S20, as described with reference to Fig. 9 and Fig. 10, a coating layer 63 is formed to cover a part of the side surface 61A of the support member 61 manufactured in step S10. The coating layer 63 is formed over the entire length in the longitudinal direction of the support member 61. The coating layer 63 is formed in a part in the circumferential direction (approximately one half in the circumferential direction) of the support member 61. The coating layer 63 has a structure in which beads 62 extending in the longitudinal direction of the support member 61 are adjacent to each other without gaps between them in the circumferential direction.

[0043] The coating 63 can be formed, for example, by means of deposition welding using CO2 arc welding, as described below. First, an apparatus for forming a coating is described. The apparatus for forming a coating includes, as described with reference to Fig. 11, a welding torch 70 and a nozzle 80 for supplying hard particles. The welding torch 70 includes a welding nozzle 71 having a hollow cylinder shape, and a contact tip 72 arranged 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 supplied to the front end side of the welding nozzle 71. For the welding wire, JIS YGW12, for example, can be used. 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 ejected from the front end of the welding nozzle 71. The nozzle 80 for supplying hard particles has a hollow cylinder shape. Inside the hard particle supply nozzle 80, hard particles 91 are supplied and ejected from the front end of the hard particle supply nozzle 80.

[0044] This coating forming apparatus can be used to form a coating 63 using the method shown below. With a support member 61 as one electrode and the welding wire 73 as the other electrode, voltage is applied across the support member 61 and the welding wire 73. This creates an arc 74 between the welding wire 73 and the support member 61. The arc 74 is protected from the ambient air by the shielding gas emitted from the front end of the welding nozzle 71 along the arrows β. Carbon dioxide, for example, can be used as the shielding gas. The heat in the arc 74 melts a part of the support member 61 and also melts the front end of the welding wire 73. The thus melted front end of the welding wire 73 forms droplets that are transferred to the molten portion of the support member 61.This forms 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 hard particle supply nozzle 80 are supplied to this melt pool 92.

[0045] When the welding torch 70 and the nozzle 80 for supplying hard particles constituting the build-up welding device move relative to the support member 61 in the direction shown by the arrow α, the position at which the molten pool 92 is formed shifts accordingly. The previously formed molten pool 92 solidifies to form a bead 62. The bead 62 contains a matrix 95 formed by solidification of the molten pool 92 and hard particles 91 dispersed in the matrix 95. A plurality of such beads 62 are formed side by side in the width direction without any gap between them, so that a desired area on the side surface 61A of the support member 61 is covered, thus completing the formation of the coating 63 (see Fig. 10). It should be noted that hardfacing can be performed, for example, under the following conditions: welding current of 230 A, welding voltage of 17 V, hard particle feed rate of 110 g / min, and bead protrusion length of 4 mm. JIS YGW11 can be used as the welding wire. WC- or W2C-based particles can be used as the hard particles.

[0046] Subsequently, a hot forging step is carried out as a step S30. In this step S30, the support member 61 with the coating 63 formed in step S20 is hot forged. The support member 61 with the coating 63 formed thereon is, as described with reference to Fig. 10 and Fig. 12, heated to a temperature that enables hot forging, and then placed in a mold for forging, which has a cavity corresponding to a 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 later step to produce the annular drive wheel 5. The coating 63 formed in step S20 is processed by hot forging. The support member 61 is hot forged so that the coating 63 covers the outer peripheral surface of the drive wheel 5. Thus, a coating 52 is produced which has a smooth surface on which the surface profile caused by surface tension in the liquid state and the like has been removed. By hot forging, as shown in Fig. 12, ridge 59 is formed. Subsequently, as described with reference to Fig. 12 and Fig. 13, punching is carried out to remove the burr 59, so that a part is created that forms the drive wheel 5 (see Fig. 13).

[0047] When the support member 61 with the coating 63 formed thereon 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 (beads 62) during the formation of the coating 63, are pressed into the coating 63 (beads 62). As a result, in the drive gear 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 arranged in contact with the surface 90A of the coating 90. Of the hard particles 91 located in the surface region 90B of the coating, any hard particle 91 that has a portion exposed on the surface 90A of the coating 90 has an acute central angle θ (less than 90°) corresponding to the exposed portion. This prevents the hard particle 91 from falling out during use of the drive gear 5, thereby improving the wear resistance of the drive gear 5.

[0048] When the support member 61 with the coating 63 formed thereon is hot forged, protrusions 99 are formed in the coating 90 due to the hard particles 91 that were present near the interface between the coating 63 (beads 62) and the support member 61 at the time of formation of the coating 63. At least a portion of a corresponding hard particle 91 is received in each protrusion 99. With the above-described process, the surface portion of the coating 90, which has excellent wear resistance because the hard particles 91 are arranged in contact with the surface 90A, and the protrusions 99 that prevent the coating 90 from separating from the base material 100 are simultaneously formed.

[0049] Subsequently, as explained with reference to Fig. 8, a heat treatment step is performed as a step S40. In this step S40, the pinion 5 (the part constituting the pinion 5) manufactured by hot forging in step S30 is subjected to heat treatment. The heat treatment performed in step S40 is, for example, quenching and tempering. This imparts desired hardness and toughness to the base material 50 of the pinion 5. Subsequently, in order to attach the pinion 5 to a support body (not shown), a portion where no coating 90 has been formed is subjected to machining to improve dimensional accuracy, form a mounting hole, and so on. The pinion 5 (the part constituting the pinion 5) in the present embodiment is thus completed.

[0050] In the following, with reference to Fig. 8, Fig. 14 and Fig. 15, a method of manufacturing a bushing 13, which is the machine component in the present embodiment, is described. Fig. 8 is a flowchart schematically illustrating a method for manufacturing a bushing. Fig. 14 and Fig. 15 are schematic perspective views illustrating the method for manufacturing the bushing. The bushing 13 in the present embodiment can be manufactured using a method similar to that of the drive gear 5 described above.

[0051] In the method of manufacturing a bushing 13 in the present embodiment, as described with reference to Fig. 8, first, a step for manufacturing a carrier element is carried out as a step S10. In this step S10, as described with reference to Fig. 14, a support member 64 is manufactured, which becomes a support material 134 of the bushing 13. The support member 64 is made of a metal that forms the support material 134. The support member 64 has a cylindrical shape. The support member 64 includes a pair of end surfaces 64B and an outer peripheral surface 64A connecting the end surfaces 64B.

[0052] Subsequently, a step of forming a coating is carried out as a step S20. In this step S20, as described with reference to Fig. 14 and Fig. 15, a coating layer 63 is formed to cover part of the outer peripheral surface 64A of the support member 61 formed in step S10. The coating layer 63 is formed in the central portion in the longitudinal direction of the support member 64. No coating layer 63 is formed at both end portions in the longitudinal direction of the support member 64. The coating layer 63 is formed over the entire surface in the circumferential direction of the support member 64. The coating layer 63 has a structure in which beads 62 extending in the longitudinal direction of the support member 64 are juxtaposed with each other in the circumferential direction without gaps between them. The coating layer 63 can be formed, for example, by deposition welding using CO2 arc welding, as in the above-described production of the drive gear 5.It should be noted that the coating 63 may be formed in a part in the circumferential direction of the support member 64 corresponding to the area that comes into contact with the drive wheel 5, for example, over half of the circumference.

[0053] Subsequently, a hot forging step is carried out as a step S30. In this step S30, the support element 64 with the coating 63 formed in step S20 is hot forged. The support element 64 with the coating 63 formed thereon is, as described with reference to Fig. 15 and Fig. 3 to 5, heated to a temperature that enables hot forging, and then placed in a mold for forging, which has a cavity corresponding to a desired shape of the bushing 13. With hot forging, the coating 63 formed in step S20 is processed. The support member 64 is hot forged so that the coating 63 covers the outer peripheral surface 131 of the bushing 13. Thus, a coating 132 is produced that has a smooth surface on which the surface profile caused by surface tension in the liquid state and the like has been removed. The two ends of the support member 64 in the longitudinal direction where no coating 63 has been formed become the smaller diameter portions 139 of the bushing 13. Subsequently, a bolt hole is formed into which a connecting bolt 12 for connecting the links 7 and 8 is inserted (see Fig. 2). The bolt hole is drilled as described with reference to Fig. 3, is formed by the inner peripheral surface 133 and extends in the axial direction.

[0054] When the support member 64 with the coating 63 formed thereon is hot forged, hard particles 91 that protrude from a surface of the coating 63 (beads 62) when the coating 63 is formed are pressed into the coating 63 (beads 62). As a result, in the bushing 13, the hard particles 91 located in the coating surface region 90B are embedded in the coating 90 while being arranged side by side. The hard particles 91 located in the coating surface region 90B are arranged in contact with the surface 90A of the coating 90. Of the hard particles 91 located in the coating surface region 90B, any hard particle 91 that has a portion exposed on the surface 90A of the coating 90 has an acute central angle θ (less than 90°) corresponding to the exposed portion.This prevents the hard particle 91 from falling out during use of the bushing 13, thereby improving the wear resistance of the bushing 13.

[0055] When the support member 64 with the coating 63 formed thereon is hot forged, the bushing 13 develops projections 99 in the coating 90 due to the hard particles 91 that were present near the interface between the coating 63 (beads 62) and the support member 64 at the time the coating 63 was formed. At least a portion of a corresponding hard particle 91 is received in a projection 99.

[0056] Subsequently, as explained with reference to Fig. 8, a heat treatment step is performed as a step S40. In this step S40, the bushing 13 produced by hot forging in step S30 is subjected to heat treatment. The heat treatment performed in step S40 includes, for example, quenching and tempering. This imparts the desired hardness and toughness to the base material 134 of the bushing 13. Subsequently, the smaller-diameter portions 139 of the bushing 13 are machined to improve dimensional accuracy, reduce surface roughness, etc. The bushing 13 in the present embodiment is thus completed.

[0057] It should be noted that in the method for manufacturing the machine component in the above-described embodiment, when forming the coating on the support member, a surface portion of the support member corresponding to the area of ​​the support member where the coating is to be formed may be removed in advance, or a stepped portion may be formed on the support member before forming the coating. This reduces the degree of deformation of the coating during forging, thereby preventing, for example, wrinkling of the forged coating. Examples

[0058] A test piece was manufactured by forming a coating on a support member by deposition welding, as in the manufacturing method described in the above-described embodiment, and hot forging the support member to process the coating (Example). For comparison, another test piece was manufactured by forming a coating after hot forging (Comparative Example). The dies used for hot forging had the same shape in the Example and Comparative Example. Each manufactured test piece was cut, and the coating condition was examined with an optical microscope.

[0059] Fig. Figure 16 is an optical micrograph obtained by imaging a surface of the coating of the example and its surroundings. Fig. Figure 17 is an optical micrograph obtained by imaging a surface of the coating of the comparative example and its surroundings. In the coating of the comparative example, which was formed by deposition welding and subsequently not processed by forging, as shown in Fig. 17, hard particles 91 protrude significantly from the surface 90A of the coating. In the coating of the example, which was formed and then processed by forging, hard particles 91 located in the surface area, as shown with reference to Fig. 16, are embedded in the coating (matrix 95) and arranged side by side. The hard particles 91 are aligned in contact with the surface 90A of the coating. A hard particle 91 having a portion exposed at the surface 90A of the coating 90 has an acute central angle θ (less than 90°) corresponding to the exposed portion. This is presumably because, during the process of forging the coating, the hard particles 91 protruding from the surface 90A of the coating are pressed into the matrix 95, which has a relatively low hardness.

[0060] Fig. Figure 18 is an optical micrograph obtained by imaging an interface between the coating and the support material of the example and its surroundings. Fig. Figure 19 is an optical micrograph obtained by imaging an interface between the coating and the substrate of the comparative example and its surroundings. In the comparative example, in which the coating was formed by deposition welding and subsequently not processed by forging, as shown in Fig. 19, the interface between the coating (matrix 95) and the substrate 100 is flat. In the example that was processed by forging after the coating was formed, in the area that includes the interface between the coating (matrix 95) and the substrate 100, as described with reference to Fig.37, projections 99 are formed with the coating (matrix 95) that project toward the substrate 100. Each projection 99 accommodates a portion of a corresponding hard particle 91. It is assumed that the projections 99 were formed due to the presence of the hard particles 91 near the interface with the substrate while the coating was being forged. A hard particle 91 that contributed to the formation of a projection 99 has at least a portion accommodated in the projection 99.

[0061] Although the drive gear and bushings have been described as examples of the machine components of the present invention in the above-described embodiment, the machine components of the present invention are not limited thereto. The present invention can be applied to various machine components, including, for example, rollers (support rollers, idler rollers) and idler pulleys that constitute a crawler undercarriage of a work machine, which are intended to move relative to another component while being in contact with the other component. Industrial applications

[0062] The machine component and the method for producing the same according to the present invention can be used particularly advantageously in a machine component which is intended to cause less damage to another component and the method for producing the same. Description of reference symbols

[0063] 1: Crawler track traveling device; 2: Crawler track; 3: Crawler track frame; 4: Idler sprocket; 5: Drive wheel; 6: Crawler plate; 7: Outer link; 8: Inner link; 9: Crawler link; 10: Idler roller; 11: Support roller; 12: Connecting pin; 13: Bushing; 15: Through hole; 50: Backing material; 51: Projection; 52: Plating; 53: Outer peripheral surface; 59: Burr; 69: Backing member; 61A: Side surface; 61B: End surface; 62: Bead; 63: Plating; 64: Backing member; 64A: Outer peripheral surface; 64B: End surface; 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 pool; 95: Matrix; 99: Protrusion; 100: Substrate; 131: Outer peripheral surface; 132: Coating; 133: Inner peripheral surface; 134: Substrate; and 139: Smaller diameter portion.

Claims

[1] A machine component having a contact area and being designed to move relative to another component and to be in contact with the other component in the contact area, the machine component comprising: a carrier material (100) consisting of a first metal; and a coating (90) covering the carrier material (100) and forming at least part of the contact area, wherein: a surface (90A) of the coating (90) forming the contact area has been smoothed; the coating (90) contains a matrix (95) consisting of a second metal and hard particles (91) dispersed in the matrix (95); in a region including an interface between the coating (90) and the carrier material (100), the coating (90) contains a projection (99) projecting toward the carrier material (100); and at least part of a hard particle (91) is accommodated in the projection (99). [2] The machine component according to claim 1, wherein the hard particles (91) located in a surface region (90B) of the coating (90) are embedded in the coating (90) while being arranged side by side, and the surface region (90B) of the coating (90) is a region within an average particle diameter of the hard particles (91) from the surface (90A) of the coating (90) forming the contact region. [3] Machine component according to claim 2, wherein the hard particles (91) located in the surface region (90B) of the coating (90) are arranged in contact with the surface (90A) of the coating (90). [4] A machine component according to claim 2, wherein, of the hard particles (91) located in the surface region (90B) of the coating (90), any hard particle (91) having a region exposed at the surface (90A) of the coating (90) has an acute central angle (θ) corresponding to the region exposed at the surface (90A) of the coating (90). [5] Machine component according to one of claims 1 to 4, wherein the surface (90A) of the coating (90) forming the contact area has been smoothed by forging. [6] A method for producing a machine component having a contact area and designed to move relative to another component and to be in contact with the other component in the contact area, the method comprising the following steps: Manufacturing a support element (100) made of a first metal; Forming a coating (90) in contact with a surface of the support element (100) and covering the surface of the support element (100), the coating (90) containing a matrix (95) consisting of a second metal and hard particles (91) dispersed in the matrix (95); Forming a projection (99) within the coating (90) in a region that includes an interface between the coating (90) and the carrier material (100), wherein at least a portion of a hard particle (91) is received in the projection (99) and the projection (99) projects toward the carrier material (100); and Forging the support element (100) on which the coating (90) is formed, so that the coating (90) forms at least part of the contact area and the coating (90) is smoothed. [7] A method of manufacturing a machine component according to claim 6, wherein the step of forging the support member (100) on which the coating (90) is formed includes hot forging the support member (100) on which the coating (90) is formed.

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