Patent Publication Number: US-2020277854-A1

Title: Strike tip for a pick tool

Description:
FIELD OF THE INVENTION 
     This disclosure relates generally to super-hard strike tips for pick tools, pick tool assemblies comprising the same, particularly but not exclusively for road milling or mining; and methods of making and using same. 
     BACKGROUND 
     International patent application publication number WO2008/105915 discloses a high impact resistant tool has a super-hard material bonded to a cemented metal carbide substrate at a non-planar interface. At the interface, the substrate has a tapered surface starting from a cylindrical rim of the substrate and ending at an elevated flatted central region formed in the substrate. The super-hard material has a pointed geometry with a sharp apex having 1.27 to 3.17 millimetres radius. The super-hard material also has a 2.54 to 12.7 millimetre thickness from the apex to the flatted central region of the substrate. In other embodiments, the substrate may have a non-planar interface. 
     U.S. Pat. No. 8,061,457 discloses a high-impact resistant tool comprising a super-hard material bonded to a carbide substrate at a non-planer interface. The super-hard material comprises substantially pointed geometry with a substantially conical portion, the substantially conical portion comprising a tapering side wall with at least two different, contiguous slopes that form an angle greater than 135 degrees. The thickness from an apex of the super-hard material to the non-planer interface is greater than the thickness of the carbide substrate. The volume of the super-hard material may be 75 to 150 per-cent of the volume of the carbide substrate. The thickness from the apex of the super-hard material to the non-planer interface may be greater than twice the thickness of the carbide substrate. The apex of the super-hard material may comprise a radius between 1.27 to 3.17 millimetres. 
     United States patent application publication number 2010/0263939 discloses a high impact resistant tool comprising a sintered polycrystalline diamond (PCD) body bonded to a cemented metal carbide substrate at an interface. The body comprises a substantially pointed geometry with an apex, and the apex comprises a curved surface that joins a leading side and a trailing side of the body at a first and second transitions respectively. An apex width between the first and second transitions is less than a third of a width of the substrate, and the body also comprises a body thickness from the apex to the interface greater than a third of the width of the substrate. 
     SUMMARY 
     In use, when a high impact tool strikes a formation it is disposed at angle relative to the formation. This can lead to wear of the pick down one side as the trailing edge of the tool though the formation, and can also mean that the sharpest point of the tool tip is not the point that impacts the formation. It is an object to provide an improved strike tip for a pick tool that mitigates some of these problems. 
     According to a first, aspect, there is provided a strike tip for a pick tool. The strike tip comprises a strike structure comprising a super-hard material and a substrate comprising cemented carbide material, the substrate being joined to the strike structure at an interface. The strike tip has rotational symmetry about a main central axis, and the strike structure has a planar apex area and, on a plane on which the main central axis lies, a convex curved side wall depending from the planar apex area towards the substrate. 
     As an option, the curved side wall has a varying radius of curvature. 
     As an option, the planar apex area is 0.5 to 30 percent of a maximum area of a cross-section of the substrate. 
     The apex area is optionally substantially circular, centred upon a central longitudinal axis of the strike tip. 
     The strike structure optionally comprises a skirt structure depending from and surrounding the apex area. 
     As an option, the strike structure comprises a truncated conical surface arranged concentrically with the planar apex area. 
     The super-hard material optionally comprises polycrystalline diamond (PCD) material. As an option, the thickness of the strike structure between the apex area and the interface boundary opposite the apex is between 2.5 and 10 millimetres. 
     According to a second aspect, there is provided an assembly for a pick tool for road milling or mining, comprising a strike tip as described above in the first aspect. 
     According to a third aspect, there is provided a method of making a strike tip as described above in the first aspect. The method comprises:
         providing a pre-cursor construction comprising a strike structure comprising a super-hard material and a substrate comprising cemented carbide material, the substrate being joined to the strike structure at an interface, the strike structure having a non-planar apex and a convex curved side wall depending from the planar apex area towards the substrate; and   processing the super-hard structure to remove a volume of the super-hard structure including the non-planar apex, such that the super-hard structure comprises a planar apex area.       

     As an option, the non-planar apex of the pre-cursor construction is spherically rounded. 
     The method optionally further comprises processing the super-hard structure to remove a volume of the super-hard structure including the non-planar apex to leave a planar apex area having an area of 0.5 to 30 percent of a maximum area of a cross-section of the substrate. 
     As an option, the method further comprises processing the super-hard structure to remove a volume of the super-hard structure including the non-planar apex to leave a planar apex area that is substantially circular and centred upon a central longitudinal axis of the strike tip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting example arrangements are described with reference to the accompanying drawings, of which: 
         FIG. 1  shows a first exemplary strike tip in side elevation and perspective view; 
         FIG. 2  shows a second exemplary strike tip in side elevation and perspective view; 
         FIG. 3  shows a third exemplary strike tip in side elevation and perspective view; 
         FIG. 4  is a graph of wear scar area for exemplary strike tips after a vertical borer test; 
         FIG. 5  is a perspective view of an exemplary pick tool assembly; and 
         FIG. 6  is a flow diagram showing exemplary steps for making a strike tip. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a first exemplary strike tip  1 . The strike tip  1  comprises a strike structure  2  that is manufactured from a super-hard material. The strike structure  2  is joined to a substrate  3  manufactured from a cemented tungsten carbide material. The strike tip  1  has rotational symmetry about a main central axis  4 . A planar apex area  5  is provided at an apex of the strike structure. The strike structure, when viewed in side elevation (or on a plane on which the main central axis  4  lies) has a curved convex side wall  6  depending from the planar apex area  5  towards the substrate. 
     In the example of  FIG. 1 , the substrate  3  has a diameter of 15 mm, and the planar apex area  5  has a diameter of 2 mm. 
       FIG. 2  shows a second exemplary embodiment in which the planar apex area  5  has a diameter of 3 mm. 
       FIG. 3  shows a third exemplary embodiment in which the planar apex area  5  has a diameter of 3.5 mm. 
     In the three exemplary embodiments of  FIGS. 1 to 3 , the strike structure  2  comprises polycrystalline diamond (PCD) material comprising inter-grown diamond grains. The interstices between the diamond grains are substantially filled with filler material comprising cobalt, the content of the filler material being between 1 and 18 weight percent throughout the strike structure. In other examples, the content of the filler material in a volume of the PCD material adjacent the planar apex area  5  may be substantially less than 10 weight percent, and may be less than 2 weight percent. The substrate  3  comprises a cobalt-based cemented carbide material. 
     Each strike end  2  is defined by the PCD material and includes the planar apex area  5  bounded by an edge  7  extending all the way around the periphery of the apex areas  5 . With reference to  FIG. 1 , the edge  7  of the planar apex area  5  is formed between the apex area  5  and a rounded surface area  8  (or skirt structure) of the strike structure  2 , in which the rounded surface area  8  is arcuate in a longitudinal plane parallel to the main central axis  4 . The rounded surface area  8  has a radius of curvature of about 2.25 mm and is intermediate the apex area  5  and the side wall  6 . Note that instead of being a rounded surface area  8 , it may be chamfered or simply a sharp change from the planar apex area  5  and the side wall  6 . 
     Several strike tips were made with different conditions, as follows: 
     Sample 1: A strike tip  2  formed from PCD diamond material on a cemented tungsten carbide substrate  3  having a diameter of 15 mm. The strike tip did not have a planar apex area, but instead had a rounded apex with a radius of curvature at the apex of 3.8 mm. 
     Sample 2: Same as sample 1, except that the strike tip  2  had a planar apex area of 2 mm, as shown in  FIG. 1 . 
     Sample 3: A strike tip  2  formed from PCD diamond material on a cemented tungsten carbide substrate  3  having a diameter of 15 mm and using diamond enhanced carbide layers at the interface between the substrate  3  and the strike tip  2  to account for differences in thermal expansion between the PCD and the cemented tungsten carbide. The strike tip did not have a planar apex area, but instead had a rounded apex with a radius of curvature at the apex of 3.8 mm. 
     Sample 4: Same as sample 3, except that the strike tip  2  had a planar apex area of 2 mm, as shown in  FIG. 1 . 
     The samples were tested using a vertical borer (VB) test at an angle of 50°. In the VB test, a workpiece of Santa Eulalia granite was rotated at a speed of 55 revolutions per minute (rpm). The strike tip was used to cut through the workpiece at a feed rate of 5.0 mm/revolution and a cut depth of 0.15 mm. After 50 passes through the workpiece, the area of wear on the strike tip was measured. 
       FIG. 4  is a graph showing the area of wear of the strike tip for each sample. It can be seen that truncation reduces the wear scar area for sample 2 compared to sample 1, and sample 4 compared to sample 3, indicating that the provision of a planar apex area improves the tool performance and life. It is thought that locating the transition between the planar apex area  5  and the side wall  6  closer to the point at which the strike tip  1  cuts the workpiece improves the efficiency of the cutting operation. 
     WO2014/049162 describes a conical strike tip for a pick tool with a flat apex area having an area between 1 and 25 square millimetres. However, being conical in shape, the side wall appears to be flat from a side elevation view. It is thought that having a convex curved shape improves the impact resistance of the strike tip by providing more material between the substrate  3  and the transition between the planar apex area  5  and the side wall  6  to support the strike tip  1 . 
     With reference to  FIG. 5 , an exemplary, example pick tools  9  comprises a strike tip  1  joined to a support body  10  at a join interface boundary, and the support body  10  comprises an insertion shaft, which is shrink fit into a bore formed into a steel base  11 . The base  11  has a shank  12  for mounting the pick  9  onto a drum (not shown) via a coupling mechanism (not shown). In the example arrangement shown in  FIG. 5 , the shank  12  is substantially not aligned with a main axis of the support body  10 . 
     The volume of the support body  10  may be about 30 cm 3  and the length of the support body  10  may be about 6.8 cm. As used herein, a shrink fit is a kind of interference fit between components achieved by a relative size change in at least one of the components (the shape may also change somewhat). This is usually achieved by heating or cooling one component before assembly and allowing it to return to the ambient temperature after assembly. Shrink-fitting is understood to be contrasted with press-fitting, in which a component is forced into a bore or recess within another component, which may involve generating substantial frictional stress between the components. In some variants, the support body  10  comprises a cemented carbide material comprising grains of tungsten carbide having a mean size of at about 2.5 microns to about 3 microns, and at most about 10 weight percent of metal binder material, such as cobalt (Co). Shrink fitting the support body  10  into the base  12  may allow relatively stiff grades of cemented carbide to be used, which is likely to enhance support for the tip  1  and reduce the risk of fracture. In order to reduce stresses, sharp corners at points of contact may be avoided. For example, edges and corners may be radiused or chamfered, and the edge of the bore may be provided with a radius or chamfer to reduce the risk of stress-related cracks arising. 
     In use, the strike end of the strike tip will be driven to impact a body or formation to be broken up. The strike tip may be comprised in a pick tool may be driven to impact a body or formation to be degraded. In road milling or mining, a plurality of picks each comprising a respective strike tip may be mounted onto a drum. The drum will be coupled to and driven by a vehicle, causing the drum to rotate and the picks repeatedly to strike the asphalt or rock, for example, as the drum rotates. The picks may generally be arranged so the each strike tip does not strike the body directly with the top of the apex, but somewhat obliquely to achieve a digging action in which the body is locally broken up by each strike tip. Repeated impact of the strike tip against hard material is likely to result in the abrasive wear and or fracture of the strike tip and or other parts of the pick. 
     Synthetic and natural diamond, polycrystalline diamond (PCD), cubic boron nitride (cBN) and polycrystalline cBN (PCBN) material are examples of super-hard materials. As used herein, synthetic diamond, which is also called man-made diamond, is diamond material that has been manufactured. As used herein, polycrystalline diamond (PCD) material comprises an aggregation of a plurality of diamond grains, a substantial portion of which are directly inter-bonded with each other and in which the content of diamond is at least about 80 volume percent of the material. Interstices between the diamond grains may be at least partly filled with a filler material that may comprise catalyst material for synthetic diamond, or they may be substantially empty. As used herein, a catalyst material for synthetic diamond is capable of promoting the growth of synthetic diamond grains and or the direct inter-growth of synthetic or natural diamond grains at a temperature and pressure at which synthetic or natural diamond is thermodynamically stable. Examples of catalyst materials for diamond are Fe, Ni, Co and Mn, and certain alloys including these. Bodies comprising PCD material may comprise at least a region from which catalyst material has been removed from the interstices, leaving interstitial voids between the diamond grains. As used herein, a PCD grade is a variant of PCD material characterised in terms of the volume content and or size of diamond grains, the volume content of interstitial regions between the diamond grains and composition of material that may be present within the interstitial regions. Different PCD grades may have different microstructure and different mechanical properties, such as elastic (or Young&#39;s) modulus E, modulus of elasticity, transverse rupture strength (TRS), toughness (such as so-called K 1 C toughness), hardness, density and coefficient of thermal expansion (CTE). Different PCD grades may also perform differently in use. For example, the wear rate and fracture resistance of different PCD grades may be different. 
     Example methods for making a tip comprising a PCD structure formed joined to a substrate will now be described. 
     In general, a strike tip may be made by placing an aggregation comprising a plurality of diamond grains onto a cemented carbide substrate in the presence of a catalyst material for diamond, thus providing a pre-sinter assembly, which may then be subjected to an ultra-high pressure and high temperature at which diamond is more thermodynamically stable than graphite, to sinter together the diamond grains and form a PCD structure joined to the substrate body. Binder material within the cemented carbide substrate body may provide a source of the catalyst material, such as cobalt, iron or nickel, or mixtures or alloys including any of these. A source of catalyst material may be provided within the aggregation of diamond grains, in the form of admixed powder or deposits on the diamond grains, for example. A source of catalyst material may be provided proximate a boundary of the aggregation other than the boundary between the aggregation and the substrate body, for example adjacent a boundary of the aggregation that will correspond to the strike end of the sintered PCD structure. 
     In some example methods, the aggregation may comprise substantially loose diamond grains, or diamond grains held together by a binder material. The aggregations may be in the form of granules, discs, wafers or sheets, and may contain catalyst material for diamond and or additives for reducing abnormal diamond grain growth, for example, or the aggregation may be substantially free of catalyst material or additives. 
     In some example methods, aggregations in the form of sheets comprising a plurality of diamond grains held together by a binder material may be provided. The sheets may be made by a method such as extrusion or tape casting, in which slurries comprising diamond grains having respective size distributions suitable for making the desired respective PCD grades, and a binder material is spread onto a surface and allowed to dry. Other methods for making diamond-containing sheets may also be used. Alternative methods for depositing diamond-bearing layers include spraying methods, such as thermal spraying. The binder material may comprise a water-based organic binder such as methyl cellulose or polyethylene glycol (PEG) and different sheets comprising diamond grains having different size distributions, diamond content and or additives may be provided. For example, sheets comprising diamond grains having a mean size in the range from about 15 microns to about 80 microns may be provided. Discs may be cut from the sheet or the sheet may be fragmented. The sheets may also contain catalyst material for diamond, such as cobalt, and or precursor material for the catalyst material, and or additives for inhibiting abnormal growth of the diamond grains or enhancing the properties of the PCD material. For example, the sheets may contain about 0.5 weight percent to about 5 weight percent of vanadium carbide, chromium carbide or tungsten carbide. 
     In some versions of the example method, the aggregation of diamond grains may include precursor material for catalyst material. For example, the aggregation may include metal carbonate precursor material, in particular metal carbonate crystals, and the method may include converting the binder precursor material to the corresponding metal oxide (for example, by pyrolysis or decomposition), admixing the metal oxide based binder precursor material with a mass of diamond particles, and milling the mixture to produce metal oxide precursor material dispersed over the surfaces of the diamond particles. The metal carbonate crystals may be selected from cobalt carbonate, nickel carbonate, copper carbonate and the like, in particular cobalt carbonate. The catalyst precursor material may be milled until the mean particle size of the metal oxide is in the range from about 5 nm to about 200 nm. The metal oxide may be reduced to a metal dispersion, for example in a vacuum in the presence of carbon and/or by hydrogen reduction. The controlled pyrolysis of a metal carbonate, such as cobalt carbonate crystals provides a method for producing the corresponding metal oxide, for example cobalt oxide (Co 3 O 4 ), which can be reduced to form cobalt metal dispersions. The reduction of the oxide may be carried out in a vacuum in the presence of carbon and/or by hydrogen reduction. 
     A substrate body comprising cemented carbide in which the cement or binder material comprises a catalyst material for diamond, such as cobalt, may be provided. The substrate body may have a non-planar or a substantially planar proximate end on which the PCD structure is to be formed. For example, the proximate end may be configured to reduce or at least modify residual stress within the PCD. A cup having a generally conical internal surface may be provided for use in assembling the diamond aggregation, which may be in the form of an assembly of diamond-containing sheets, onto the substrate body. The aggregation may be placed into the cup and arranged to fit substantially conformally against the internal surface. The substrate body may then be inserted into the cup with the proximate end going in first and pushed against the aggregation of diamond grains. The substrate body may be firmly held against the aggregation by means of a second cup placed over it and inter-engaging or joining with the first cup to form a pre-sinter assembly. 
     The pre-sinter assembly can be placed into a capsule for an ultra-high pressure press and subjected to an ultra-high pressure of at least about 5.5 GPa and a temperature of at least about 1,300 degrees centigrade to sinter the diamond grains and form a construction comprising a PCD structure sintered onto the substrate body. In one version of the method, when the pre-sinter assembly is treated at the ultra-high pressure and high temperature, the binder material within the support body melts and infiltrates the aggregation of diamond grains. The presence of the molten catalyst material from the support body and or from a source provided within the aggregation will promote the sintering of the diamond grains by intergrowth with each other to form a PCD structure. 
     There are many ways that a planar apex area  5  may be provided to the strike tip  1 . For example, the strike tip  1  could be sintered at high pressure and temperature as described above in a capsule that provides the shape of the planar apex  5 , which would require very little post-sintering processing to obtain the final shape. Alternatively, the strike tip  1  could be sintered to have a curved apex and then processed to remove the curvature at the apex, leading to a planar apex area  5 . Examples of such processing techniques include grinding, electrical discharge machining (EDM) cutting or laser cutting. Any suitable processing can be used. It is thought that during sintering, impurities in the precursor powders migrate toward the apex of the strike tip  1 . An advantage of sintering a strike tip with a curved apex and subsequently processing the apex to remove the curvature is that such impurities are removed. 
       FIG. 6  is a flow diagram illustrating an exemplary method of making a strike tip. The following numbering corresponds with that of  FIG. 6 : 
     S 1 . A pre-cursor construction is provided, which comprises a strike structure comprising a super-hard material and a substrate comprising cemented carbide material. The strike structure has a non-planar apex and a convex curved side wall depending from the planar apex area towards the substrate. The non-planar apex of the pre-cursor construction may be spherically rounded. 
     S 2 . The super-hard structure is processed to remove a volume of the super-hard structure including the non-planar apex, such that the super-hard structure comprises a planar apex area. It is thought that the processing should be sufficient to produce a planar apex area having an area of 0.5% to 30% of a maximum area of a cross-section of the substrate. Any less than 0.5% would not provide much benefit from the flat apex area, and any more than this may weaken the strike tip  1 . It is also preferred that the non-planar apex is substantially circular and centred upon a central longitudinal axis of the strike tip. However, while the plane of the planar apex area  5  is shown in  FIGS. 1 to 3  as being substantially perpendicular to the main central axis  4 , it will be appreciated that the planar apex area  5  could be disposed at an angle relative to the main central axis  4 . 
     While the examples above refer to PCD strike structures  2 , the super-hard material may include certain composite materials comprising diamond or cBN grains held together by a matrix comprising ceramic material, such as silicon carbide (SiC), or cemented carbide material, such as Co-bonded WC material. For example, certain SiC-bonded diamond materials may comprise at least about 30 volume percent diamond grains dispersed in a SiC matrix (which may contain a minor amount of Si in a form other than SiC). 
     Disclosed strike tips and picks comprising them may have the aspect of good working life and efficient degradation capability. A relatively sharp geometrical transition between the apex area and an outer surface of the strike end may allow for greater efficiency in removing material from a body to be degraded, since the this feature may allow for greater penetration of the edge of the strike structure into the body on impact (in other words, there may be an enhanced digging action). This effect may be greater