Rotary implement having hard metallic layer and method therefor

A rotary implement includes a metallic body that is rotatable around an axis. The metallic body includes a tapered leading edge having an interface surface and an opposite, free surface. The metallic body has a first composition. A metallic layer has a first side surface that is attached to the interface surface and a free, second side surface opposite from the first side surface. The metallic layer has a second, different composition from the first composition. A rotary machine can include an actuator and the rotary implement operably coupled to the actuator. A method for making a rotary implement includes providing the metallic body that has the tapered leading edge having the interface surface and the opposite, free surface. The metallic layer is then attached to the interface surface of the metallic body.

BACKGROUND

This disclosure relates to rotary implements that have a hard protective layer. Rotary implements, such as mower blades, coulter blades and the like, typically have one or more leading edges that serve as working surfaces. For example, the working surface of a mower blade is a cutting edge. The working surface of a coulter blade may have a wavy, notched or plain/smooth geometry and may be blunt to interact with soil for planting and seeding. To protect the working surfaces from stones, wear and the like, such implements may include a protective coating.

SUMMARY

Disclosed is a rotary implement that includes a metallic body that is rotatable around an axis. The metallic body includes a tapered leading edge that has an interface surface and an opposite, free surface. The metallic body has a first composition. A metallic layer has a first side surface that is attached to the interface surface and a free, second side surface opposite from the first side surface. The metallic layer has a second, different composition from the first composition.

In another aspect, a rotary machine includes an actuator and the rotary implement operably coupled to the actuator.

Also disclosed is a method for making a rotary implement. The method includes providing a metallic body that has a tapered leading edge having an interface surface and an opposite, free surface. The metallic body has a first composition. A metallic layer is then attached to the metallic body. The metallic layer includes a first side surface that is attached to the interface surface and a free, second side surface opposite from the first side surface. The metallic layer has a second, different composition from the first composition.

DETAILED DESCRIPTION

FIG. 1illustrates selected portions of an example rotary implement20. For instance, the rotary implement20may be a mower blade, a coulter blade or the like that is configured for use on a rotary machine. As will be described in more detail, the example rotary implement20has features for enhanced durability.

In the illustrated example, the rotary implement20includes a metallic body22that is rotatable, as indicated at R, about an axis A. For example, the rotation can be powered, such as direct-drive by an actuator, or unpowered, such as a “rolling” rotation. The metallic body22includes a tapered leading edge24, which generally narrows in geometry from a base to a tip (from right to left inFIG. 1). The tapered leading edge24serves as a working surface of the rotary implement20. That is, the tapered leading edge24is the primary location at which the rotary implement20cuts, strikes, meets or otherwise engages the material worked upon during its normal intended use.

The geometry or angle of tapered leading edge24may be relatively acute to form knife or cutting edge. Alternatively, the geometry or angle may be larger to provide a more blunt working surface. As can be appreciated, other tapered geometries may alternatively be selected based upon the intended end-use of the rotary implement20.

The metallic body22is made of a first composition and has an interface surface26and an opposite, free surface28. The free surface28is “free” with respect to having any additional metallic or other hard protective layers thereon. Thus, the free surface28may include paint or other similar polymer-based layers thereon.

A metallic layer30is attached to the tapered leading edge24, in this case a bottom or backside of the tapered leading edge24, and is harder than the metallic body22. The metallic layer30has a first side surface32that is attached to the interface surface26and a second, free side surface34located opposite from the first side surface32. The free side surface34is “free” with respect to having any additional metallic or hard protective layers thereon. The free side surface34may, at least initially, include paint or other similar polymer-based layers thereon. The metallic layer30has a second, different composition from the first composition of the metallic body22.

In some examples, the metallic layer30is on the bottom of the rotary implement20relative to the orientation of the rotary implement20in its normal intended use, while the free surface28of the metallic body22is on top. The disclosed arrangement of the metallic layer30on the bottom of, or at least on only one side of, the tapered leading edge24provides a self-sharpening effect. Due to the difference in hardness' between the first composition and the second composition, the metallic body22at the tapered leading edge24wears and erodes away more rapidly than the metallic layer30. The dissimilar wear and erosion rates of the metallic body22and the metallic layer30maintain a cutting edge on the metallic layer30at the tip of the tapered leading edge24. For non-cutting working surface the effect is self-maintaining geometry.

The first composition of the metallic body22and the second composition of the metallic layer30are selected to cooperate with respect to the protection provided by the metallic layer30and the resistance of the metallic layer30to cracking, spallation and the like. In one example, the first composition is a steel composition and the second composition is one of a nickel-based composition, a cobalt-based composition or an iron-based composition. The steel composition of the metallic body22can be heat treated to enhance hardness and toughness. For example, the steel can be austempered to a bainitic microstructure.

In a further example, the steel of the first composition is a boron-containing steel composition. The nickel-based composition, cobalt-based composition or iron-based composition of the second composition can include alloy elements in individual amounts of 0.1-20% by weight of boron, silicon, chromium, iron (for nickel- and cobalt-based alloys), carbon, manganese, nickel (for iron- and cobalt-based alloys), tungsten and combinations thereof. In further examples, the second composition is a composition set forth in the Table below.

In a further example, the metallic body22defines a first hardness H1(hardness Vickers) and the metallic layer30defines a second hardness H2(hardness Vickers) such that a ratio of H2/H1is from 1.0 to 4.5. In use, because the hardnesses of the metallic body22and the metallic layer30are different, the harder metallic layer30does not wear as rapidly as the metallic body22. However, if the hardness' of the metallic body22and the metallic layer30are close, the metallic body22and the metallic layer30will wear at approximately equivalent rates, thus blunting or otherwise changing the geometry of the tapered leading edge24. Alternatively, if the hardness of the metallic layer30is too high, the metallic layer30can crack from stone impact or the like, and thus provide less protection. The disclosed range of the ratio of H2/H1therefore represents a favorable combination of resistance to cracking/impact and relative wear/erosion between the metallic body22and the metallic layer30, which thus enhances durability of the rotary implement20.

In a further example, the ratio of H2/H1is greater than at least 1.67 and the metallic layer30has an average thickness t that is one millimeter or less. In further examples, the average thickness t of the metallic layer30is approximately 0.7 millimeters or less than 0.7 millimeters. In other examples, the thickness t can be greater than 1 millimeter.

In further examples, the metallic layer30can have a hardness H2of no less than 700 HV (Vickers hardness) and the metallic body has a hardness H1of 300-600 HV. In a further example the hardness H2is no less than 1000 HV. In one further example, the hardness H2is 700-1300 HV.

In this example, the metallic body22extends from a tip24aof the tapered leading edge24to an opposed end36. The metallic layer30extends along only the tapered leading edge24and not along the remainder of the metallic body22toward the opposed end36. That is, the metallic layer30extends from approximately the tip24ato a location L that aligns with a transition of the metallic body22from a tapering shape to a non-tapering shape, such as to a uniform thickness portion22aof the metallic body22.

In the illustrated example, the metallic layer30is directly attached to the interface surface26of the metallic body22. For example, the metallic layer30is directly metallically bonded to the interface surface26of the metallic body22.

As discussed above, the second composition of the metallic layer30can include a nickel-based composition, cobalt-based composition or iron-based composition.FIG. 2shows an example microstructure40of the metallic layer30. In this example, the microstructure40includes tungsten carbide42that is dispersed in a matrix44. For example, the matrix44can be a nickel-based composition, cobalt-based composition or iron-based composition. In another example the overall composition of the metallic layer30includes, by weight, 10-90% of the tungsten carbide and a remainder of the matrix44. In a further example, the metallic layer30includes, by weight, 10-50% of the tungsten carbide and a remainder of the matrix44. As can be appreciated, other example can exclude the tungsten carbide42such that the metallic layer30has only the nickel-based composition, cobalt-based composition or iron-based composition.

As can also be appreciated, the overall geometry of the rotary implement20can vary depending upon the intended end-use.FIG. 3illustrates a top view of an example of a rotary implement20′, where like reference numerals designate like elements that are understood to incorporate the same features and benefits of the corresponding elements. In this example, the rotary implement20′ is an elongated blade that has a connection feature50in a central portion thereof and tapered leading edges24′ at opposed ends thereof. The metallic layer30(not in view) is located on the opposite, backside of the rotary implement20′.

FIG. 4Aillustrates a top view of another embodiment of a rotary implement20″ that also has two tapered leading edges24″. In this example, the rotary implement20″ is configured to be used to rotate either a clockwise or counterclockwise direction. For example the rotary implement20″ can be rotated in one direction such that one of the tapered leading edges24″ is used and then flipped over such that the other of the tapered leading edges24″ is then used. The metallic layer30(not in view) is located on the opposite, backside of the rotary implement20″. The rotary implement20″ can be attached to a cutter bar52or a rotary machine, as shown inFIG. 4B.

FIGS. 5 and 6illustrate schematic views of another example rotary machine60that, in this example, includes multiple rotary implements20′. As can be appreciated, the rotary machine is a non-limiting example and can vary from the design shown. In simple form, the rotary machine60includes an actuator62and the rotary implement20′ operably coupled to the actuator62. In this case, the rotary implement20′ is connected through a known type of connection feature64. In use, the actuator62drives the rotary implement20′ to rotate about axis A by way of the connection feature64.

FIG. 7schematically illustrates an example method70for making a rotary implement, such as any of the rotary implements disclosed herein. In this example, the method70includes at least step72and step74. Step72includes providing the metallic body22including the tapered leading edge24having the interface surface26and the opposite, free surface28. Step74includes attaching the metallic layer30to the interface surface26.

The method or techniques that are utilized to attach the metallic layer30to the metallic body22are not limited to any particular type but can include, for example, powder cladding or slurry deposition to produce a dense layer as the metallic layer30. Thermal spraying can also be used to produce a porous layer as the metallic layer30. In another alternative, the metallic layer30can be attached to the metallic body22by welding (e.g., electrical or plasma transfer arc) or inductive heat fusing. Given this description, one of ordinary skill in the art will be able to recognize other suitable attachment techniques to meet their particular needs.

In the powder cladding technique, a powder of the second composition (for the metallic layer30) is applied onto the interface surface26and then consolidated (i.e., fused together) using an energy beam. For example, the energy beam is a laser. In one example the laser is a diode laser and the control parameters thereof with respect to laser power, traverse speed and the like can be controlled to achieve a desirable thickness of the metallic layer30. For example, the laser power is 4-6 kilowatts, the traverse speed is 1.5 meters per minute and the powder application rate is 28 grams per minute. One or more deposition passes of applying and fusing the powder can be used to achieve a desired thickness.

In slurry deposition, the powder of the second composition (for the metallic layer30) is included in a slurry with a carrier fluid. The slurry is then applied onto the interface surface26of the metallic body22and the carrier fluid is then removed through evaporation. The deposited powder is then consolidated to fuse the powder thereby form the metallic layer30. The consolidation can be conducted by subjecting the implement to a heat treatment at a fusing temperature approaching the melting temperature of the composition. In a further example, the slurry can additionally include a binder such that a self-supporting green body is produced once the carrier fluid is removed. The green body can then be machined to a desired geometry or thickness prior to consolidation. Thus, the metallic layer30, which is very hard, can be formed to near-net shape with minimal or no machining of the metallic layer30.

The preceding description is for explanation rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.