Hard surface processing of metal wear parts

Abstract

Methods and related systems are provided for covering a metal component with a hard metal composition, thereby improving wear resistance characteristics of the component. The system comprises an arc welding device, a consumable electrode, a first nozzle, a second nozzle and means for displacing 15 the consumable electrode and the first and second nozzles relative to the metal part or the metal part relative to the arc welding device, the consumable electrode and the first and second nozzles according to a direction of travel, an arc welding device for forming a weld pool on a surface portion of a metal component, the arc welding device having, in use, a direction of travel relative to the metal component, a consumable electrode made of a metallic material or composition, the consumable electrode being melted into the weld pool by the arc welding device in use, a first nozzle adjacent the arc welding device, and a second nozzle adapted to feed at least a first hard metal material in particulate form into the arc upstream of the direction of travel of the arc welding device, the second nozzle being adjacent to the arc welding device, an arc welding device adapted to feed at least a first hard metal material or another hard metal material in particulate form into a cooled weld pool downstream of the arc welding device with respect to a direction of travel of the arc welding device.

Description

Technical Field

[0001] The present invention relates to improvements in the hardfacing of metallic wear components and parts. More particularly, the present invention relates to improved methods and apparatus for depositing hard wear coverings onto metallic articles that are subject to wear in use. Background Art

[0002] Metal parts in heavy-duty processes, such as earth-moving tools, large turbines, steel production and industrial machinery, etc., are generally typically subjected to intense mechanical and abrasive forces in use, often resulting in premature wear. Such parts, which are usually of considerable size, are usually made of mild steel, a material that is a compromise between cost and structural integrity at the expense of durability. It is known to reinforce discrete portions of such parts by applying a hard metal covering comprising hard metal particles, such as tungsten carbide particles, to one or more surfaces of the part that are subject to the greatest wear, impact and other stresses.

[0003] Known techniques for applying hard metal coverings include open arc hard facing machining, in which a matrix covering is applied to a component surface using a tubular wire electrode filled with hard metal and flux; submerged arc hard facing machining, in which a matrix covering is applied to a component surface using a tubular wire electrode filled with hard metal and the covering is deposited beneath a thick layer of powdered liquid continuously fed from a hopper; bulk welding hard facing machining, in which a hard metal covering is applied to a component surface using a solid wire electrode continuously fed into an arc from a hopper, a gas shield, and an external powder supply of hard metal; and gas shielded arc hard facing machining, in which a matrix covering is applied to a component surface using a tubular wire electrode filled with hard metal and a gas shield. In all four processes, most of the hard metal is melted in the arc and reformed into a crystalline structure during consolidation.

[0004] Advantages of these prior art methods include high deposition rates (corresponding to relatively low processing costs) and suitability for large volumes of wear resistant parts for applications where accessibility for replacement is good and the consequences of premature failure are not severe. However, the disadvantages are numerous. For example, in each of these mentioned prior art techniques, the content of hard metal carbides contained in the covering is relatively low, typically 20% to 35%. In addition, each of these prior art techniques operating at very high power levels can use a multi-head welding machine. Therefore, penetration into the component surface material is substantial, typically 2 to 3 mm deep, which results in a significant dilution of the hard metal in the covering by the component material, whereby full hardness can only be achieved when a second or third layer on top of the first layer contacts the component surface.

[0005] Furthermore, in all of these prior art, significant inspection-cracking of the deposits occurs shortly after consolidation, and the deposits tend to be brittle, whereby they lack toughness and impact resistance. Furthermore, the metal microstructure of the component surface closest to the weld layer can be thermally affected and modified, resulting in embrittlement of the component itself, whereby cracks can occur within the component or between the component and the externally facing hard layer and then propagate under load.

[0006] Importantly, as a result of the heat generated in all four prior art techniques, the shrinkage of the machined component surface is very significant and unpredictable. This disadvantage is particularly relevant to applications where the wear component or part itself cannot be hard surfaced, and for these applications, wear plates are used instead, which are covered with the above techniques and then typically secured to the wear component or part using threaded fasteners.

[0007] Fixing methods for hard-surfaced wear plates typically include welding on bolts, welding countersunk inserts, and plasma-cut countersunk drills. Welded studs can be precisely positioned on hard-surfaced wear plates, but there is a risk of separation in use because they rely on the integrity of the attached welds that are in tension. These are not considered to be very reliable for dynamic assembly of components and wear plates. Welded countersunk inserts are also prone to separation, especially if the attached weld is contaminated by hard metal from the edge of the hole in which it is welded. This technology also exposes the bolt head, resulting in preferential wear. The bolt head can then be hard-surfaced, but this still results in preferential wear relative to the bolt head because the bolt head is not hard-surfaced at the same time as the rest of the plate, and because it is manually welded by a different process. Hard-surface machining of the bolt head also subjects the bolt to very high, concentrated heat from the weld pool, thus affecting the material properties and integrity of the bolt. Plasma cut or laser cut countersunk holes can be cut into a wear plate machined hard surface, whereby the countersunk bolt can then be poured into the plate, and covered by the hard surface, although this leads to premature wear and affects the bolt in the same way as when the above welded countersunk inserts are used. The countersunk holes can also be of poor quality because they are not machined but made by a thermal cutting process: this technique results in an unsafe seat for the bolt head, applying uneven stresses to the bolt which can lose tension in use. The combination of welded countersunk inserts and plasma cut countersunk holes with countersunk bolts are sometimes described as "integral bolts", but for the reasons given above they are of inferior quality, durability and safety.

[0008] Therefore, there is a need to provide a more durable cover and an improved connection between the cover and the underlying surface of the wear component. Summary of the invention

[0009] The present invention provides an improved method, and a system embodying the improved method, for covering a component or wear plate with a hard metal composition, wherein the arc technique is applied by a single-head, purpose-built welding machine that is powered at a lower power level relative to the known methods described above.

[0010] According to aspects of the present invention, a system for covering a metal part with a hard metal composition is provided, the system comprising: an arc welding device for producing a weld pool on a surface portion of the metal part, the arc welding device having a travel direction relative to the metal part during use; a consumable electrode made of a metal material or a composition, the consumable electrode being melted into the weld pool by the arc welding device during use; a first nozzle adjacent to the arc welding device, the first nozzle being adapted to feed at least a first hard metal material in the form of particles into the arc upstream of the travel direction of the arc welding device; a second nozzle adjacent to the arc welding device, the second nozzle being adapted to feed at least a first hard metal material in the form of particles or other material into the weld pool downstream of the travel direction of the arc welding device; and a device for displacing the arc welding device, the consumable electrode, the first nozzle and the second nozzle relative to the metal part according to the travel direction or displacing the metal part relative to the arc welding device, the consumable electrode, the first nozzle and the second nozzle.

[0011] The directing elements in the system of the present invention (feeding the hard metal material into the arc at its hottest temperature) greatly increase the ability of the weld pool to accept material added by the downstream feed, effectively enabling the downstream feed to join at a much greater volume percentage than is possible with single or multiple feed techniques without the directing elements or aspects: the addition of cold hard metal rapidly cools the weld pool, thereby reducing the heat applied to the underlying component and thus reducing shrinkage. This technique achieves full hardness and wear characteristics in the first layer, with finer and less significant check cracking of typically 0.25mm to 1.5mm and minimized penetration into the component surface material, and a less brittle deposit, further wherein shrinkage of the component is greatly reduced and predictable relative to the prior art. In some embodiments, the first layer comprises approximately 48% chromium carbide or 53% tungsten carbide.

[0012] In an embodiment of the system of the present invention, the arc welding device, the consumable electrode, and the first and second nozzles can be mounted to a support structure, which is adapted to oscillate orthogonally relative to the direction of travel of the arc welding device when the system layers the components, thereby defining a constant and preferably adjustable width of the weld pool.

[0013] The system of the present invention is advantageously suitable for covering a surface portion of a component multiple times, whereby in an embodiment of the system, the surface portion of the metal component comprises at least a first layer of a hard metal composition, the at least first layer of the hard metal composition comprising one or more first hard metal materials, and the arc welding device is therefore also used to produce a weld pool on the at least first layer on top of the surface portion of the metal component.

[0014] Any hard metal material in the form of particles, powders or granules may be suitable for use with the device, subject to its material properties and their compatibility with the consumable rod material, the component surface and the intended application. In particular, the or each hard metal material in the form of particles may be selected from: chromium, tungsten, carbon, iron, titanium, molybdenum, vanadium, niobium, manganese, silicon, nickel and alloys and compounds thereof. In a preferred variant of this embodiment, the first hard metal material supplied by the first nozzle is ferrochrome and the other hard metal material supplied by the second nozzle is tungsten carbide, ferrochrome or chromium carbide. The deposit according to the present embodiment contains a very high proportion of tungsten carbide or ferrochrome or chromium carbide grit, most of which remain in their original form and are completely integrated into the chromium carbide deposit matrix, wherein the maximum content of tungsten carbide, ferrochrome or chromium carbide in the overburden is evenly distributed throughout the entire thickness of the deposit, in contrast to the prior art, in which heavy tungsten carbide and, to a lesser extent, ferrochrome or chromium carbide in combination with high power levels and therefore large fluid weld pools cause large amounts of relatively low tungsten carbide material content, with the ferrochrome or chromium carbide sinking to the base of the deposit.

[0015] In an embodiment of the system, the arc welding apparatus is a gas metal arc welding apparatus. The gas shield effectively excludes oxygen from the vicinity of the weld pool, thereby enabling complete fusion between the part, the covering and the covering components. An embodiment of the system may further include a wire feeding unit for dispensing a consumable electrode in use. In an embodiment of the system, the consumable electrode is preferably made of carbon steel, stainless steel or nickel.

[0016] In an embodiment of the system, each nozzle is in communication with at least one hopper storing at least a first hard metal material in granular form. In an alternative embodiment of the system, each nozzle may be in communication with a corresponding hopper, each hopper storing the same first hard metal material in granular form or a different corresponding hard metal material. In a variation of any embodiment of the system, the or each hopper may be connected to the nozzle interface by a metering device.

[0017] According to another aspect of the present invention, a method for covering a metal part with a hard metal composition is also provided, the method comprising the following steps: using an arc welding device to melt a consumable electrode made of a metal material or composition into a weld pool on a surface portion of the metal part, the arc welding device having a travel direction relative to the metal part during use; using a feeding device (such as a metering device) to feed at least a first hard metal material in the form of particles into the arc upstream of the travel direction of the arc welding device; using a feeding device to feed at least a first hard metal material or other material in the form of particles into the weld pool downstream of the travel direction of the arc welding device; and moving the arc welding device and the supply device relative to the metal part according to the travel direction; or moving the metal part relative to the arc welding device and the supply device according to the travel direction.

[0018] Embodiments of the method may include the further steps of melting the consumable electrode and feeding one or more hard metal materials onto the layer of hard metal composition atop the surface portion of the metal component upstream and downstream in the direction of travel of the arc welding device.

[0019] In an embodiment of the method, the melting step preferably comprises heating the consumable electrode in the range of 1490 to 1550 degrees Celsius.

[0020] In an embodiment of the method, the step of feeding the or each hard metal material further comprises metering the or each hard metal material in dependence on the displacement rate of the arc welding apparatus, the feeding means and the components relative to each other. In a variation of this embodiment, the step of metering the first hard metal material at the first nozzle further comprises generating a feed rate of the first hard metal material in dependence on the volume of the weld pool. In a variation of either embodiment, the step of metering the first or second hard metal material at the second nozzle further comprises generating a feed rate of the first or second hard metal material in dependence on the volume and / or volume of the weld pool.

[0021] For any of the above embodiments of the method, the or each hard metal material in particulate form is selected from the group consisting of: chromium, tungsten, carbon, iron, titanium, molybdenum, vanadium, niobium, manganese, silicon, nickel, and alloys and compounds thereof. In a preferred variant, the first hard metal material is preferably ferrochrome, the second hard metal material is preferably tungsten carbide, the feed rate of the ferrochrome is approximately 55 grams per minute, the feed rate of the tungsten carbide is approximately 180 grams per minute, and the feed rate of the consumable electrode is approximately 78 grams per minute.

[0022] According to a further preferred embodiment of the present invention, a method for covering a metal component with a hard metal composition is such that the component comprises an integral fastening device, such as a bolt or the like, and the method comprises the following steps: machining at least one countersunk through hole in the metal component and fitting a countersunk bolt in the countersunk hole.

[0023] In this manner, the method of the present invention is therefore preferably applied to wear plates because the relatively small shrinkage associated with the covering of the first method and the predictability of the shrinkage that does occur facilitates the production of bolted wear plates that effortlessly pierce holes in the component or structure, where the fasteners are secure, robust, and simple to use with conventional tools.

[0024] Preferably, the machining step may include machining a plurality of countersunk through holes and the fitting step includes fitting fewer bolts than the machined countersunk holes.

[0025] Preferably, the step of fitting the or each countersunk bolt may include the further steps of chamfering the bolt head, welding the bolt into the hole and grinding any excess weld metal material together with the surface portion.

[0026] Preferably the or each bolt is made from carbon steel or stainless steel.

[0027] Suitably, the features of the invention as set out in accompanying claim 1 may be provided as a kit of parts for a welding system.

[0028] Preferably, such a set of parts including the features of the attached claim 1 may further include a wire feeding unit for dispensing consumable electrodes during use, at least one hopper for storing at least a first hard metal material in granular form and at least one dosing device for connecting the or each hopper to the first nozzle and the second nozzle interface.

[0029] Other aspects are as set out in the claims herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to better understand the present invention and to show how the present invention may be effected, specific embodiments, methods and processes according to the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0031] Figure 1A A first embodiment of a system for coating a metal component with a hard metal composition according to the invention is shown.

[0032] Figure 1B A second embodiment of a system for coating a metal component with a hard metal composition according to the invention is shown.

[0033] Figure 1C A third embodiment of a system for coating a metal component with a hard metal composition according to the invention is shown.

[0034] Figure 1DA fourth embodiment of a system for coating a metal component with a hard metal composition according to the invention is shown.

[0035] Figure 2 Illustration of the formation of a weld pool on a surface portion of a metal component according to the direction of travel Figure 1A-Figure 1D An arc welding device according to any one of the items, wherein the first nozzle is adjacent to and adjacent to the front of the arc welding device relative to the direction of travel during use, and the second nozzle is adjacent to and adjacent to the rear of the arc welding device according to the direction of travel during use.

[0036] Figure 3 Indicates Figure 1A-Figure 1D The system of any of the above covers embodiments of the method of forming a metal component with a hard metal composition as discrete logical steps.

[0037] Figure 4 The second embodiment is shown in use covering a surface portion of a metal component according to a first covering process. Figure 1B The second embodiment of the present invention.

[0038] Figure 5 FIG. 1 shows a method of covering a surface portion of a metal component according to a second covering process. Figure 4 system.

[0039] Fig. 6A shows a hard metal composition having a single layer Figure 4 or Figure 5 parts.

[0040] Figure 6B A second layer of hard metal composition is shown on top of the first layer. Figure 4 or Figure 5 parts.

[0041] Figure 7 Indicates the use of hard metal composites to cover metal parts Figure 1A-Figure 1D Embodiments of alternative methods of any system in the invention as discrete logical steps.

[0042] Figure 8 Shows that according to Figure 7 Two example components of a layer of a hard metal composition deposited by the method are shown, wherein each component is a wear plate including a fastening device.

[0043] Fig. 9 Shows Figure 3 and Figure 7 The inherent processing temperature of the method shown allows for alternative configurations. Figure 8 The same example parts of . DETAILED DESCRIPTION

[0044] The specific modes envisioned by the inventors will now be described by way of example. In the following description, many specific details are set forth to provide a thorough understanding. However, it is clear to those skilled in the art that the present invention can be implemented without being limited to these specific details. In other cases, well-known methods and structures are not described in detail to avoid unnecessary fuzzy descriptions.

[0045] The words “comprises / comprising” and the words “having / including” when used herein with reference to the present invention are intended to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0046] Now refer to the drawings and the initial Figure 1A , shows a first embodiment of a system 1001 for covering a metal part with a hard metal composition, comprising an arc welding device 110, a consumable electrode 120, a first nozzle 130, and a second nozzle 140, the consumable electrode 120 being made of a metallic material or composition, the first nozzle 130 being adjacent to and in front of the arc welding device 110 according to a travel direction 190 of the system in use, and the second nozzle 140 being adjacent to and behind the arc welding device 110 according to a travel direction 190 of the system 1001 in use. The arc welding device 110 is a gas metal arc welding device, and in a preferred embodiment is a metal inert gas (MIG) welding device. The consumable electrode 120 is dispensed by a wire feeding unit 150. In this first embodiment, each of the first nozzle 130 and the second nozzle 140 is fed by gravity from a common hopper 160 located above the welding device 110 and the nozzles 130, 140. The shielding gas required for the MIG device 110 is supplied from a gas source 170 through a gas nozzle 175. The height of the welding device relative to the lower component and the distance of the welding point from each of the guide nozzle 130 and the tail nozzle 140 are preferably in the range of 15 mm to 30 mm.

[0047] See now Figure 1B, wherein like reference numerals correspond to like features, shows a second embodiment of a system 1002 for coating a metal component with a hard metal component, again comprising an arc welding device 110, a consumable electrode 120 made of a metallic material or composition, a first nozzle 130 adjacent to the arc welding device 110 and in front of it in use according to the direction of travel of the system, and a second nozzle 140 adjacent to the arc welding device 110 and in rear of it in use according to the direction of travel of the system 100. In the second embodiment, each of the first nozzle 130 and the second nozzle 140 is fed by gravity from a respective hopper 160 1,2 Supply, wherein both hoppers are located above the welding device 110 and the nozzles 130 , 140 .

[0048] See now Figure 1C , wherein like reference numerals still correspond to like features, illustrates a third embodiment of a system 1003 for coating a metal component with a hard metal composition, generally corresponding to Figure 1A The first embodiment 1001 shown in FIG. 1 further comprises a metering device 180 in this embodiment, which interfaces the common hopper 160 with the conduits to the front nozzle 130 and the rear nozzle 140 for metering the hard material feed rate to the nozzle rather than by gravity.

[0049] Next reference Figure 1D , wherein like reference numerals still correspond to like features, illustrates a fourth embodiment of a system 1004 for overlapping a metal component with a hard metal composite, generally corresponding to Figure 1B The second embodiment 1002 shown in FIG. 1 , however, further comprises two metering devices 180 1,2 Each metering device will correspond to the hopper 160 1,2 The conduit interface therewith to its associated nozzle 130, 140 is used to feed the hard material to the nozzle rather than by gravity, and each metering device is independent of the other.

[0050] For any of the above embodiments, the angle of the welding head 110 should preferably be in the range of 83 degrees to 90 degrees, the angle of the guide nozzle 130 is in the range of 40 degrees to 50 degrees from the horizontal plane, and the angle of the tail nozzle 130 is in the range of 50 degrees to 70 degrees from the horizontal plane.

[0051] From one or more hoppers 160 1,2The hard metal material in the form of particles, powder or granules fed to the nozzles 130, 140 is selected from chromium, tungsten, carbon and alloys and compounds thereof. For most applications tested by the inventors, the hard metal material supplied by the first nozzle 130 in front of the welding head 110 is ferrochrome, and the other hard metal material supplied by the second nozzle 140 behind the welding head 110 is tungsten carbide or ferrochrome or chromium carbide. See Figure 2 , showing a close-up view of a component 200, the surface 210 of which, in use, is formed according to any of the embodiments 100 of the present invention. 1-4 A single welding head 110 and a combination of a front nozzle 130 and a rear nozzle 140 are depicted moving relative to a part 200 and a delamination surface 210 of the part 200 according to a direction of travel 190 , wherein the arc welding device 110 generates a weld pool 220 directly beneath the welding head 110 by melting the consumable rod 120 .

[0052] A first hard metal material 230, in this example ferrochrome, is fed by the front nozzle 130 into the weld pool 220, wherein ferrochrome particles melt within the weld pool 220 and form a ferrochrome matrix layer 250. The relatively low temperature of the weld pool and the maximum input of granular hard material minimize the penetration of the matrix layer 250 through the surface 210 into the substrate material 200, wherein penetration into the surface portion 210 is in the range of 0.25 mm to 1.5 mm and is depicted by the dashed line 260 in the figure.

[0053] A second hard material 240 in the form of particles, powder or granules (in the example, tungsten carbide, chromium iron or chromium carbide) is deposited by the second nozzle 140 into the cooling weld pool 220 downstream of the welding head 110, as depicted by the top dashed line 270 in the figure. Therefore, the second hard metal particles 240 are not subjected to the same high temperature as the first hard material particles 230, and are generally uniformly dispersed throughout the matrix 220, wherein the first hard metal material particles and the second hard metal material particles 240 are represented as in the system 100. 1-4 The particles are all (as a continuous line) in the cooling section of the layer 250 downstream of the travel path and then gradually fuse (as dotted lines with increasing intervals), ultimately forming a covering 250 composed of a homogeneous matrix filled with hard metal particles in the cold section downstream of the travel path.

[0054] See now Figure 3 The method followed to cover a metal component 200 with one or more layers 250 of a hard material composition is described. The metal component, typically made of steel, is initially fixed to the system 100 at a first step 301. 1-4At the next step 302, the surface portion of the component to be delaminated with the hard material matrix 250 is defined and input into a motion controller that drives the arc welding device 110 and its associated front nozzle 130 and rear nozzle 140 combination.

[0055] It will be readily understood by those skilled in the art that embodiments of the present invention can also be implemented in which the system 100 1-4 relative to the component 200 fixed to the fixture, or vice versa, wherein the fixture to which the component 200 is fixed is relative to the fixing system 100 1-4 moves without departing from the scope of the invention as disclosed and described.

[0056] At the next step 303, the process for the system 100 relative to the component 200 fixed on the fixture is programmed so that the welding head 110 can travel over the entire surface portion 210 of the component 200 to be delaminated. It will be noted that the surface portion 210 can correspond to the entire surface of the component 200 or to one or more discrete portions thereof, depending on which surface portion(s) of the component 200 requires hard surface machining according to its final application.

[0057] At step 304, a feed rate of one or more hard metal materials is calculated based on several factors, notably including the temperature of the weld pool, the melting point of each hard metal material fed by the first nozzle 130 and the second nozzle 140, respectively, the melting point of the consumable electrode 120, the displacement speed of the welding device relative to the part, the cooling rate of the substrate, the desired thickness of the deposit 250, and the size and shape of the part 200.

[0058] For the granular hard materials indicated herein as examples, experiments have indicated that the feed rate range for the guided powder feed 130 (for grain size -20+60 BS mesh) is 60 to 130 g / min, and the feed rate range for grain size -20+60 BS mesh to -14+40 BS mesh is 90 to 260 g / min. Experiments have shown that the consumption rate of the electrode 120 at 414 to 526 amperes is 85 to 140 gr. / min. Experiments have shown that the travel speed is 300 to 450 mm / min.

[0059] A variety of applications and contexts are known for which a component may require multiple (1-N) layers 250 on top of the surface portion 210 of the component 200, wherein each additional layer covers the underlying layer. Thus, at step 305, N layers are input, corresponding to the number of hard metal composition layers 250 desired for the hard facing component 200.

[0060] At step 306, the controller programmed according to steps 302 to 305 drives the system 100 relative to the component 200. 1-4 , or mutually drive the system 100 depending on the embodiment 1-4 , wherein the wire feeding unit 150 feeds the consumable rod 120 at step 3061, at step 3062, the welding head 110 melts the consumable rod 120 into the weld pool 220, and as the system follows the programmed process along the travel direction 190, at step 3063, the front nozzle 130 feeds the first hard metal granular material 240, and at step 3064, the rear nozzle 140 feeds the same or another hard metal granular material 240.

[0061] When the process calculated at step 303 is completed, the controller interrupts the system 100 1-4 , and at the next step 307 a question is asked as to whether the layer counter N has a null value. This question effectively corresponds to a check as to whether there are further layers 220 to be welded to the layered element 200, 250. If the layer counter N does not have a null value, the value of the counter is decremented at step 308, and control returns to step 306, wherein the controller drives the system 100 on the same process as previously programmed at step 303. 1-4 , which ultimately results in a layer component having an additional layer 2502 superimposed on top of the previously deposited layer 2501. In the alternative, the question of step 307 is answered affirmatively, indicating that the covering of the component 200 fixed to the fixture at step 301 is complete, so that the method can be repeated on the next component, whereupon control returns to step 301.

[0062] Figure 4 and Figure 5 Provides common Figure 1B A second embodiment of the system 1002 is shown, covering a continuous surface portion 410 according to steps 301 to 307. 1,2 Each surface portion 410 1,2 The width 420 corresponds to the effective coverage width of the welding head 110 in use.

[0063] Embodiments of the system may include a transverse oscillation device adapted to oscillate the welding head 110 perpendicular to the travel direction 190, in particular when a deposit of variable width is desired, either on (multiple) identical or different surface portions 210 of a component 200 or between corresponding surface portions 210 of different components 200N having corresponding uses and wear requirements, wherein both the oscillation width and the speed can be varied independently of each other for optimal results.

[0064] System 1002 performs a process 430 on each surface portion 410 according to process 430 programmed at step 303 and processed at step 306. 1,2 Delamination is performed, wherein the movement of system 1002 relative to component 200 secured to fixture 440 according to process 430 is represented by arrow 440 in the figure.

[0065] Depending on the intended application and use of the component 200, the surface hardening requirements for the component 200 may require the process 430 programmed at step 306 to include only a single layer 250 of hard metal composition, which is Fig. 6A 6 as having a height 610 extending between an underlying surface portion 210 of the component that is minimally penetrated by the component and a substantially planar surface portion 620 of the deposited layer 250 .

[0066] However, depending on the wear characteristics sought for the component 200, the process 430 programmed at step 306 may include one or more additional layers 250 of hard metal composition. 1+N , this is Figure 6B In this example, a second layer of hard metal composition 2502 is shown having approximately the same height 610 extending between an underlying substantially flat surface portion 620 of the initial layer 2501 of the component and a substantially flat surface portion 620 of the second deposited layer 2502, wherein the underlying surface portion 610 of the initial layer 2501 of the component is again minimally penetrated by the composition to the low temperature of the weld pool.

[0067] The specific details of process programming and actuation are not provided for the purpose of unnecessarily obscuring the description, as they are considered to be readily understood and implemented by readers of industrial automation. Likewise, those skilled in the art will readily appreciate that the above principles can be implemented with a fixture 440 movable relative to the system 1002 or conversely with a system 1002 movable relative to the fixture 440, and include independent movement of each of the system 1002 and the fixture 440 relative to each other.

[0068] One or more layers 250 having a hard metal composition N The relatively low temperature of the weld pool inherent in the operating parameters of the method of subjecting the component 200 to hard surface machining provides an opportunity to both increase the number of component types susceptible to hard surface machining and to modify the configuration of known components to improve their operating life. Particularly advantageous areas of application of the invention are complex or semi-complex modular components having removable wear plates secured by fasteners which are subjected to non-insignificant pressure levels of gases or liquids in use and typically in aggressive environments, such as wear plates for turbine blades and vanes.

[0069] For such removable parts, whose assembly configurations typically require fasteners to be engaged in apertures therein prior to hardfacing, elevated temperature ranges of prior art methods and systems are known to alter the geometry of the apertures, the attitude of the fasteners therein, and the structural integrity of the fasteners. The relatively low temperatures of the weld pool of the hardfacing method disclosed herein, enabled by the opposing configuration of the dual particle feeds 130, 140, advantageously avoid these undesirable effects.

[0070] Accordingly, and now see Figure 7 , a method for covering a metal part with a hard metal composition is provided, the metal part comprising an integral fastening device, such as a bolt engaged in a portion or through hole therein; wherein the method comprises: a first preliminary step 701, which first preliminary step 701 is to machine at least one countersunk through hole in the metal part; and a second preliminary step 702, which second preliminary step 702 is to install a countersunk bolt in the countersunk hole before subjecting the metal part comprising the countersunk through hole and the bolt engaged or threaded in the metal part to steps 301 to 307, wherein steps 301 to 307 include multiple overlaps according to the interaction of steps 307 and 308.

[0071] A practical example of the application of the above method is Figure 8 and Fig. 9 It is shown in Figure 8 The diagram shows the reference Figure 7 The described method combines two known configurations of modular wear plates with fastener hard surfaces, Fig. 9 Pictured Figure 8 Two new configurations of modular wear plates, which are modified to improve their operational life.

[0072] The first example is shown in cross section in the body portion of a turbine blade 888 having a surface hardened for use by mounting a wear plate component 800 thereon. The blade and the adjacent wear plate each have a coaxial through hole defining a single through hole 820 extending between a surface portion 810 of the wear plate component 800 to be hard surfaced according to steps 301 to 307 and a surface portion 880 which is the rear wall of the turbine blade. The inner wall of the wear plate through hole 820 is a countersunk bore 830 adjacent to the surface portion 810. A countersunk bolt 885 is inserted into the wear plate through hole 820, wherein the top surface of the bolt head is flush with the surface portion 810 of the wear plate. A washer 890 is fitted around the bolt shaft to abut against the opposing surface portion 880 of the turbine blade, and a nut 895 is threaded around the bolt shaft to abut against the washer 890 for securing the bolt in place. In the first example, both the nut 895 and the washer 890 protrude from the opposing surface portion 880 of the turbine blade and thus to the turbine blade rear wall.

[0073] A second example is shown at the edge portion of the same turbine blade 888, where like reference numerals correspond to like features in the figure, where the corresponding edge portion of the covering wear plate component 800 surrounds and covers the turbine edge. The blade and the adjacent wear plate each again have a coaxial through hole 820 extending between the surface portion 810 of the wear plate component 800 to be hardfaced according to steps 301 to 307 and the opposite surface portion 880 of the blade 888, and then through the bottom of the volume 877 defined by the peripheral wall 878, which projects away from the opposite surface portion 880 of the turbine blade 888, and the peripheral wall 878 defines a countersunk well on the top of the opposite surface portion 880 of the periphery of the aperture of the blade through hole 820. The inner wall of the wear plate through hole 820 is again a countersunk hole 830 adjacent to the surface portion 810. Countersunk bolt 885 is again inserted into wear plate through hole 820, however in the second example, see Figure 7 The method described includes the further steps of chamfering the edge of the bolt head 883, welding the bolt head 883 to the appropriate position of the wear plate 800, and then grinding any resulting weld that protrudes upward from the plane of the top surface to achieve flushness of the welded bolt head with the surface portion 810 of the wear plate. In addition, in this second example, the washer 890 is assembled and the nut 895 is threaded around the bolt shaft within the counterbore well so that both are protected to some extent from the environment by the peripheral wall 878 during use.

[0074] In both examples, after bolts 885 are tightened in place, wear plate component 800 is hard faced with a single layer of hard material composition 250 in accordance with steps 301 to 307, either by a flush fit or by chamfering and welding bolt head 883 and grinding the weld flush, wherein wear plate through hole 820 and fastening features are substantially unaffected by the hard facing process performed at a temperature near surface portion 210 of wear plate component 800 that is substantially below the material temperature range that is susceptible to modifying or otherwise affecting its material properties and geometry.

[0075] By referring to Figure 8 The two example configurations shown in Fig. 9 The scope provided by this effect for improving the design of parts and components, such as the exemplary turbine blades, is best illustrated.

[0076] A third example shows the same body portion of a turbine blade 888, wherein like reference numerals correspond to like features in the figure, the body portion having a surface hardened for use by mounting a wear plate component 800. The blade and the adjacent wear plate each again have a coaxial through hole. However, in this example, while a first threaded hole 820 having a first diameter corresponding to the thread diameter of a bolt 885 again extends from a first surface portion 810 of the wear plate to be hard faced toward an opposing surface portion 880 according to steps 301 to 307, a second hole 910 having a second diameter greater than the first diameter is provided, the second hole 910 extending from the opposing surface portion 880 toward the first surface portion 810, wherein the two holes are coaxial and thus define a countersunk through hole, the well of the countersunk through hole being located within the opposing surface portion 880 at a depth between the first surface portion 810 and the opposing surface portion 880.

[0077] Countersunk bolt 885 is again inserted into first through hole 820, wherein the top surface of the bolt head is flush with the surface portion 810 of the wear plate, optionally by chamfering and welding the bolt head 883 and grinding the weld flush. In this example, washer 890 is assembled and nut 895 is tightened around the bolt axis within countersunk borehole 910 so that relative to reference Figure 8 The first example described is completely devoid of any shielding, both being protected from the environment by the body of the turbine blade 888 around the countersunk bore 910 .

[0078] A similar internal countersunk bore configuration adjacent to an edge portion of a turbine blade 888 and a wear plate component 800 is shown in a fourth example to illustrate how this alternative configuration 910 protects the washer 890 and nut 895 to the same extent as the third example above and therefore to a better extent than the protruding holes 877, 878 of the second example, and how this alternative configuration 910 simplifies the design and machining of the turbine blade 888 when integrally protruding countersunk bores 877, 878 are no longer required.

[0079] Experiments have shown that a chromium carbide layer consisting of chromium carbide particles in a chromium-iron matrix according to the method described herein, in a proportion of about 5% carbon, about 43% chromium (the balance being made of iron and alloying elements), achieves a hardness of 82 on the HRA scale, and should therefore be beneficial for specialized applications involving high abrasion, erosion and impact type wear, for example on impeller blades, vibrating screens and feeders, crusher drums and auxiliary equipment, and also as high quality wear plates for many applications in the mineral processing industry.

[0080] Experiments have shown that a sintered tungsten carbide alloy layer consisting of particles of sintered tungsten carbide in a chromium-tungsten-iron matrix according to the method described herein, in a proportion of approximately 5% carbon, approximately 53% tungsten carbide, approximately 9% chromium, the balance being iron and alloying elements, achieves a hardness of 83 on the HRA scale and should therefore be beneficial for professional applications involving very high wear, erosion and medium impacts, such as sinter plant exhaust gas impellers, coal exhaust fan impellers, blades and screen bars.

[0081] The present invention is not limited to the embodiments described above, but may be varied in both construction and detail. In this specification, the terms "comprise, comprise, comprised and comprising" or any variant thereof and the terms "includes, includes, included and including" or any variant thereof are considered to be fully interchangeable and should all be given their broadest possible interpretation, and vice versa.

Claims

1. A system for coating a metal part with a hard metal composition, comprising: an arc welding apparatus for forming a weld pool on a surface portion of the metal component, the arc welding apparatus having a direction of travel relative to the metal component in use; a consumable electrode, the consumable electrode being made of a metallic material or a composition, the consumable electrode being melted into the weld pool by the arc welding device during use; a first nozzle adjacent to the arc welding device, the first nozzle being adapted to supply at least a first hard metal material in the form of particles into the arc upstream in a direction of travel of the arc welding device; a second nozzle, the second nozzle being adjacent to the arc welding device, the second nozzle being adapted to feed at least the first hard metal material or another hard metal material in the form of particles into a cooling weld pool downstream of the arc welding device relative to a direction of travel of the arc welding device; as well as A device for displacing the arc welding device, the consumable electrode and the first and second nozzles relative to the metal part or displacing the metal part relative to the arc welding device, the consumable electrode and the first and second nozzles according to the travel direction.

2. The system according to claim 1, wherein: The means for displacing is further configured to oscillate the arc welding device, the consumable electrode, and the first and second nozzles orthogonally relative to the direction of travel.

3. The system according to claim 1 or 2, wherein: The surface portion of the metal component comprises at least a first layer of a hard metal composition comprising one or more of the first hard metal materials, wherein the arc welding device is further operable to form a weld pool on at least the first layer on top of the surface portion of the metal component.

4. The system according to any one of claims 1 to 3, wherein: The or each hard metal material in particulate form is selected from chromium, tungsten, iron, titanium, vanadium, molybdenum, niobium, manganese, nickel and alloys and compounds thereof.

5. The system according to claim 1, wherein: At least the first hard metal material in the form of particles supplied by the first nozzle is ferrochrome, and the other hard metal material in the form of particles supplied by the second nozzle is tungsten ferrochrome carbide or chromium carbide.

6. The system according to any one of claims 1 to 5, wherein: The arc welding device is a gas metal arc welding device.

7. The system of claim 6, further comprising a wire feeding unit for dispensing the consumable electrode in use.

8. The system according to any one of claims 1 to 7, wherein: Each nozzle is in communication with at least one hopper storing at least said first hard-metal material in the form of particles.

9. The system according to any one of claims 1 to 7, wherein: Each nozzle is in communication with a respective hopper, each hopper storing the same first hard-metal material or a respective hard-metal material in granular form.

10. The system according to claim 8 or 9, wherein: The or each hopper is connected to the nozzle interface via a metering device.

11. A method for coating a metal part with a hard metal composition, comprising the steps of: melting a consumable electrode made of a metallic material or composition into a weld pool on a surface portion of the metal part using an arc welding apparatus having a direction of travel relative to the metal part in use; feeding at least a first hard metal material in the form of particles into the arc upstream in the direction of travel of the arc welding device by means of a first feeding device; feeding at least the first hard metal material or another hard metal material in the form of particles into a cooling weld pool downstream of the arc welding device relative to the direction of travel of the arc welding device using a second feeding device; as well as moving the arc welding device and the feeding device relative to the metal part according to a direction of travel; or The metal part is moved relative to the arc welding device and the feed device according to a direction of travel.

12. The method according to claim 11, further comprising the steps of: The arc welding apparatus, the consumable electrode and the feed device are oscillated orthogonally relative to the direction of travel.

13. The method according to claim 11 or 12, further comprising the steps of: The consumable electrode is melted and one or more hard metal materials are fed upstream and downstream in the direction of travel of the arc welding device onto the layer of hard metal composition on top of the surface portion of the metal component.

14. The method according to any one of claims 11 to 13, wherein: The melting step includes heating the consumable electrode in a range of 1490 degrees Celsius to 1550 degrees Celsius.

15. The method according to any one of claims 11 to 14, wherein: The step of feeding the or each hard metal material further comprises metering the or each hard metal material in dependence on the rate of displacement of the arc welding apparatus, the feeding device and the component relative to one another.

16. The method according to claim 15, wherein: The step of metering a first hard metal material further includes establishing a feed rate of the first hard metal material.

17. The method according to claim 15 or 16, wherein: The step of metering a feed of the or each hard metal material with the feed device further comprises generating a feed rate of the or each hard metal material.

18. The method according to any one of claims 11 to 17, wherein: The hard metal material or materials in particulate form are selected from the group consisting of chromium, tungsten, iron, titanium, molybdenum, vanadium, niobium, manganese, nickel and alloys and compounds thereof.

19. The method according to claim 11, wherein: At least the first hard metal material in the form of particles supplied by the first nozzle is ferrochrome, and the other hard metal material in the form of particles supplied by the second nozzle is tungsten carbide or ferrochrome or chromium carbide.

20. The method according to claim 11, comprising the steps of: Select metal parts that include integral fastening devices; machining at least one countersunk through hole in the metal component; and Install countersunk bolts in the countersunk holes.

21. The method according to claim 20, wherein: The machining step includes machining a plurality of countersunk through holes, and wherein the assembling step includes assembling fewer bolts than the machined countersunk holes.

22. The method according to claim 20 or 21, wherein: The machining step further comprises countersinking the or each through hole in a surface portion of the metal component opposite the or each countersunk through hole.

23. The method according to any one of claims 20 to 22, wherein: The step of fitting the or each countersunk bolt may further comprise the steps of chamfering the bolt head, welding the bolt into the hole and grinding any excess weld metal flush with the surface portion.

24. The method according to any one of claims 20 to 23, wherein: The or each bolt is made from carbon steel or stainless steel.

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