EP3183425B1

EP3183425B1 - Pick assembly, processing assembly comprising it, method of making it and method of using it

Info

Publication number: EP3183425B1
Application number: EP15750034.9A
Authority: EP
Inventors: Bernd Heinrich Ries; Daniel HLAWATSCHEK; Markus Kilian SCHARTING; Peter BUSH
Original assignee: Element Six GmbH; Element Six UK Ltd
Current assignee: Element Six GmbH; Element Six UK Ltd
Priority date: 2014-08-20
Filing date: 2015-08-10
Publication date: 2019-02-27
Anticipated expiration: 2035-08-10
Also published as: US20170234128A1; GB2531125A; GB201414831D0; ZA201700835B; EP3183425A1; CN106795763A; JP2017525876A; GB201513815D0; JP6469866B2; GB2531125B; CN106795763B; WO2016026725A1

Description

This disclosure relates generally to super-hard pick assemblies, methods of providing them and for using them, and processing assemblies comprising them; particularly but not exclusively for pavement milling and texturing, or mining.
United States patent number 7,396,086 discloses a pick comprising a shank attached to a base of a steel body, a cemented metal carbide core press fit into the steel body opposite the shank, and a super-hard impact tip bonded to a first end of the core opposite the shank. A plurality of picks can be attached to a rotating drum connected to the underside of a pavement recycling machine, which will bring the picks into engagement with the pavement in use. A holder or block is attached to the rotating drum, and the pick is inserted into the holder. The holder or block may hold the pick at an angle offset from the direction of rotation, such that the pick engages the pavement at a preferential angle. Picks often rotate within their holders or blocks upon impact with the pavement, which allows wear to occur evenly around the pick, and the impact tip may be angled to cause the pick to rotate within the bore of the holder. A protective spring sleeve may be disposed around the shank both for protection and to allow the high impact resistant pick to be press fit into a holder while still allowing the pick to rotate.
WO 2009/142577 similarly discloses a cutting pick and a hollow sleeve to surround the shank of the cutting pick. The sleeve fits in the bore of a holder block with an optional interference fit.
In WO 97/39221 , the sleeve rotatably receives the shank of the cutting bit, and like US 7,396,086 , no movement of the sleeve relative to the bore is possible.
In US 2009/0200857 , a bolster bonded to a diamond, symmetric, substantially conical shaped tip, is rotatable relative to a stationary block, mounted to a driving mechanism. A compressible element comprising an O-ring is disposed intermediate and in mechanical contact with both the bolster and the block. The compressible element is compressed sufficiently enough to prevent free rotation.
US 2008/0030065 discloses a number of cutting tool assemblies and retention sleeves. Various configurations of sleeve segments are disclosed for non-rotatably supporting the shank of the cutting bit in the tool holder. Furthermore, embodiments include axially extending notches to establish various degrees of interference fit between the sleeve and the tool holder.
Similarly, WO 2010/019361 discloses a cutting tool with a non-rotating wear sleeve mounted in a block. A key is used to intersect with notches in the wear sleeve and the block, to prevent relative rotational movement therebetween.
There is a need for pick assemblies having extended working life, particularly but not exclusively for fine milling (which may be referred to as scarifying, grooving or roughening) pavement, such as concrete pavement, and for efficient ways of providing them.
Viewed from a first aspect there is provided a pick assembly comprising a holder body, a strike body, a base body attachable to a drive mechanism, and an interference assembly comprising a spring sleeve and at least one interference member; in which the holder body comprises a head portion and a shaft depending from the head portion, the strike body comprises a super-hard strike tip, the strike body comprising polycrystalline diamond (PCD) material, or grains of synthetic or natural diamond dispersed in a matrix comprising carbide material, the head portion and the strike body are cooperatively configured such that the strike body is attached to the head portion,, the base body comprises a base bore; the base bore, shaft and interference assembly being cooperatively configured such that the shaft is secured within the base bore, the interference member disposed between the shaft and the bore, frictional interference between the shaft, interference assembly and base bore preventing rotation of the shaft within the base bore in use, the combined radial margin of interference between the shaft, the interference member and the base bore being 10 to 200 microns, and characterised in that the interference member is located between the spring sleeve and the base bore when assembled as for use, the interference member being in the form of an O-ring or quad-ring.
An advantage of this arrangement is that a pick assembly with a holder body and strike body comprising a super-hard strike tip can be non-rotationally attached to a base body that is otherwise configured to rotationally hold a rotating strike body, such as a strike body having a non-super-hard strike tip, for example a carbide strike tip.
Various combinations and arrangements of pick tool assemblies, processing assemblies (which may comprise degradation assemblies) assemblies comprising them, methods for making them and methods for using them are envisaged by this disclosure, of which the following are non-limiting and non-exhaustive examples.
The diameter of the bore may be 10 to 200 microns, or 10 to 100 microns greater than the outermost diameter of the sleeve.
In various example arrangements, the shaft and base bore may be spaced apart by the same distance all the way around the shaft, or the distance by which the shaft and the base bore are spaced apart may vary around the shaft. In some example arrangements, the spacing between the side of the shaft and the inner side of the base bore may be substantially the same all the way around the shaft, with the interference member separating the shaft from the bore by the substantially the same radial distance 360 degrees around the shaft. In other examples, the spacing between the side of the shaft and the inner side of the base bore may vary substantially around the shaft, the interference member separating the shaft from the bore by substantially different distances around the shaft. In other words, the shaft and interference member may be configured such that the shaft may be substantially coaxial or not coaxial with the base bore, when assembled as for use (the respective longitudinal axes being laterally displaced from each other in the latter example arrangement).
In some example arrangements, the head portion may be provided with a head bore, the bore and the strike body being cooperatively configured such that the support body can be retained within the head bore by frictional interference.
In some examples, the strike body may comprise a strike tip joined to a support body. The strike tip may be joined to the support body by means of a join layer comprising braze alloy material, and the holder body may comprise a head bore for accommodating and holding the strike body, configured such that when the strike body is inserted into the head bore as for use, the join layer is contained within the head bore.
In some example arrangements the shaft may be coaxial with the support body and or the strike body when the strike body is attached to the holder body as for use.
In some example arrangements, the base bore may comprise a cylindrical inner surface and have a diameter of 18.00 to 21.00 millimetres (mm). In some example arrangements, at least a portion of the shaft may be cylindrical in shape, and the diameter of the portion of the shaft may be 16.00 to 19.00 millimetres (mm).
In some examples, the base bore may comprise a cylindrical inner surface, at least an area of the side of the shaft may comprise a cylindrical surface, and the interference member may comprise a resilient sleeve configured to be capable of accommodating the cylindrical area of the shaft and clamping it with sufficient compressive force that the shaft will not rotate relative to the sleeve in use. In some examples, the maximum (radial) thickness of the sleeve or ring may be at least 1.20 millimetres (mm); and or at most 1.60, 1.45 or 1.35 millimetres (mm). The mean thickness of the sleeve may be such as to allow it function as a clip in relation to the shaft, by being capable of expanding radially sufficiently to receive the shaft and to apply compressive, clamping force onto the shaft to restrict, retard or prevent its rotation within the sleeve.
In some example arrangements, the interference member may comprise or consist of elastomer material, such as synthetic or natural rubber. Example interference members (comprising elastomer or other material) having various shapes in cross section are envisaged, including circular, polygonal, square, rectangular shaped cross sections. In some examples, the ring may be generally square in cross section (the corners may be rounded), such as of a kind that may be used in hydraulic or pneumatic pistons, and which may be referred to as 'quad-rings'. The shape of an interference member in the general form of a ring may affect its stiffness, and quad-rings may likely be stiffer than O-rings, all else being equal.
In some example arrangements, the interference assembly may comprise a laterally (or radially) extending portion that will be located outside the base bore when assembled as for use, and which may protect the base body in use.
In some example arrangements, the interference assembly may be configured such that the shaft is spaced apart from the base bore, solid material not being present to connect that portion and the base bore. In other words, a substantially annular volume may surround at least a portion of the shaft, the volume being empty of solid material connecting the shaft and the base bore.
In some example arrangements, the interference assembly may be configured such that a volume between the shaft and the base bore contains material from a body being degraded by means of the pick.
In various examples, the interference member may comprise or consist of material that is sufficiently deformable or compliant and sufficiently resilient that it can be forced into a volume between the shaft and the base bore, and then resist rotation of the shaft within the bore with sufficiently large force that the shaft will not rotate in use. Example materials may include elastomer and various polymer materials, and or relatively soft alloys or metals such as copper or aluminium. In some example arrangements, the interference member may comprise a relatively hard and non-compliant material, the interference assembly being configured such that it can be inserted between the shaft and the base bore and substantially prevent the shaft from rotating in use.
In some examples, the interference member may comprise material, the coefficient of friction of which when in contact with the base bore steel is greater than the coefficient of friction between the material comprised in the shaft in contact with the material comprised in the base bore.
In some example arrangements, the interference assembly may comprise a plurality of interference members.
Viewed from a second aspect there is provided a processing assembly comprising a plurality of disclosed pick assemblies, each capable of being attached to a drive mechanism or carrier body. Example processing assemblies may be suitable for processing pavement in order to provide it with a substantially uniform surface roughness and or to break up at least part of the pavement (in other words, to degrade it). Example processing assemblies may be suitable for use in mining or boring into the earth, such as for breaking rock formations.
In some example arrangements, the base bodies may be attached, such as welded, to a drum, which may be configured for being attached to and driven to rotate by a drive vehicle.
In some example, the processing assembly may be suitable for use in texturing (which may also be referred to as 'scarifying' or increasing the roughness of) structures such as pavement, and which may comprise or consist of asphalt or concrete. The texturing may involve breaking and removing material from a pavement to form a plurality of grooves into it, corresponding to the respective pick assemblies. After texturing, the grooves may exhibit a substantially uniform roughness substantially, in which the mean distance between the highest peak and lowest valley in each sampling length may be at least about 3 or at least about 5 millimetres (mm); and or at most about 15 or at most about 10 millimetres (mm). The drive mechanism may comprise a drum, in which a plurality of pick tools attached to the drum will be caused to strike the pavement (or other body to be processed) as the drum is driven by a vehicle to rotate (a pick assembly in the assembled condition may be referred to as a pick tool).
Drums for pavement milling may be available in various diameters and lengths, and may be capable of holding various numbers of picks, depending on the drum dimensions and the nature of the milling process to be carried out. For example, drums for fine milling may have lengths of about 2.2 or 2 metres (m) and be capable of holding about 748 or 672 pick tools, respectively. The pick tool will likely be sufficiently small for use on drums configured for achieving a relatively finely-structured texturing, such drums potentially capable of at least 800 pick tools attached to them.
In some example arrangements, a processing assembly may comprise a drum capable of attachment to most about one pick tool per 400 or per 100 square millimetres (mm²) over the surface area of the drum the cylindrical side area). In other words, the spacing between picks attached or attachable to the drum may be at most about 20 or at most about 10 millimetres (mm). In some examples, the drum may be capable of attachment to at least about 70 or at least about 90 pick tools per square metre (m²) of the cylindrical side of the drum; in some example arrangements, the drum may be capable of attachment to at most about 230, at most about 160 or at most about 120 pick tools per square metre (m²) of the cylindrical side of the drum. In some example arrangements, the drum may be capable of attachment to 90 to 110 pick tools per square metre (m²) of the cylindrical side of the drum. In various example arrangements, the drum may be configured to be capable of attachment to a number of pick tools per unit area (of the cylindrical side) such that the processing apparatus is suitable for micro- or fine-milling of pavement.
In some example arrangements, the processing assembly may comprise a plurality of pick assemblies attached to a drum suitable for use cutting a plurality of substantially parallel grooves, providing a surface roughness of up to 15 millimetres (mm) or up to 10 mm; and or at least 3 or at least 5 mm.
In some example arrangements, each of the shafts of all of the pick assemblies may have the same diameter and the dimensions of the respective interference members differ from each other to account for differences in a base bore dimension.
In some example arrangements of processing assemblies, at least some of the pick assemblies may be attached to the drive mechanism such that when the strike body strikes a body to be degraded with a force, the reaction force on the strike body will result in the strike body experiencing an asymmetric torque about a central cylindrical axis of the strike body. The frictional interference force between the shaft, interference assembly and base bore will be sufficient to defeat (in other words, to resist, or be equal to or exceed) the torque and avoid rotation of the strike body.
Viewed from a third aspect there is provided a method of making a disclosed pick assembly, the method including providing a first pick assembly comprising a first holder body and a base body, attachable to a drive mechanism, and a rotation member; in which the first holder body comprises a first shaft and the base body comprises a base bore; the base bore, the first shaft and the rotation member being cooperatively configured such that the first shaft can be inserted within the base bore, the rotation member is disposed between the first shaft and the base bore, such that the first shaft is capable of rotation relative to the base bore when in use; the method including removing the rotation member and the first holder body; providing a second holder body and an interference assembly comprising an interference member; in which the second holder body comprises a head portion and a second shaft depending from the head portion, the head portion and a strike body being cooperatively configured such that the strike body is attached to the head portion, the strike body comprising a super-hard strike tip; the strike body comprising polycrystalline diamond (PCD) material, or grains of synthetic or natural diamond dispersed in a matrix comprising carbide material, the second shaft and interference assembly being cooperatively configured such that the second shaft is secured within the base bore, the interference member disposed between the shaft and the bore, frictional interference between the shaft, interference assembly and base bore preventing rotation of the second shaft within the base bore in use; the combined radial margin of interference between the shaft, the interference member and the base bore being 10 to 200 microns, the pick assembly comprising the base body, the second holder body, the strike tip and the interference member. The method may include assembling the pick assembly to provide a pick tool.
Non-limiting example arrangements to illustrate the present disclosure are described hereafter with reference to the accompanying drawings, of which:

Fig. 1 shows a schematic, partly cut-away side view of an example pick assembly attached to a drum (only a small part of which is included in the illustration);
Fig. 2A shows a schematic side view of an example pick assembly, partially cut-away to show a side view of the strike body;
Fig. 2B shows a schematic side view of assembled components of the example pick assembly, excluding the base body;
Fig. 2C shows a schematic side view of assembled components of the example pick assembly excluding the base body, partially cut-away to show part of a side view of the strike body; and
Fig. 2D shows a schematic cross section view of part of an example base body for the example pick assembly of Fig. 2A;
Fig. 3 shows a schematic exploded side view of an example holder body and an example strike body;
Fig. 4A shows a schematic side view of assembled components of the example pick assembly excluding the base body, partially cut-away to show a side view of the strike body;
Fig. 4B shows a schematic exploded side view of an example holder body and an example strike body;
Fig. 5 shows a schematic perspective view of an example interference assembly; and
Fig. 6 shows a schematic perspective view of an example interference assembly attached to an example holder body.

With reference to Fig. 1, an example pick assembly may comprise a holder body 10, a strike body 20, a base body 50 welded to a drive mechanism 60, which may comprise a drum that can be driven to rotate, and an interference member in the form of a spring sleeve 30. The holder body 10 may comprise a head portion 12 and a cylindrical shaped shaft 14 depending from it, the shaft 14 and the spring sleeve 30 being cooperatively configured such that both can be accommodated substantially non-rotatably within a base bore 52 of the base body 50, having an inner diameter W0. The strike body 20 may comprise a strike tip 22, comprising polycrystalline diamond (PCD) material defining a rounded conical end surface for engaging a body to be degraded, the strike tip 22 joined to a cemented carbide support body 24 attached to the head portion 12 of the holder body 10.
With reference to Fig. 2A, Fig. 2B, Fig. 2D and Fig. 2C, an example pick assembly may comprise a steel holder body 10, a strike body 20, a base body 50 attachable to a drive mechanism (not shown), and an interference member in the form of a spring sleeve 30. The holder body 10 may comprise a head portion 12 and a cylindrical shaped shaft 14 depending from it, the shaft 14 and the spring sleeve 30 being cooperatively configured such that both can be accommodated non-rotatably within a base bore 52 of the base body 50, having an inner diameter W0. The strike body 20 may comprise a strike tip 22, comprising a polycrystalline diamond (PCD) structure joined to a cemented carbide substrate 24. The outermost, exposed end of the strike tip 22 is defined by the PCD material and an opposite end of the strike tip 22 is coterminous with an end boundary of the substrate 25. In this example, the end PCD surface has the shape of a blunted cone. The end boundary of the substrate 25 is joined to an end of a generally cylindrical cemented carbide support body 24 by a layer 23 consisting of braze alloy material. In this example, the strike body 20 is fixed by shrink fitting into a bore provided in a proximate end of the head portion 12, coaxial with the shaft 14 depending from the opposite end of the head portion 12. The bore in the head portion 12 (which may be referred to as the 'head bore') is sufficiently large that the layer 23 of braze material is contained within the head bore.
A proximate end of the base bore 52 will have a bore mouth 54 for receiving the shaft 4 and the spring sleeve 30 (in combination). In a particular example, the base bore diameter W0 may have a diameter about 50 microns larger than the outer diameter W2 of spring sleeve (in other words, the interference margin may be about 50 microns). In various examples, the overall margin of frictional interference between the spring sleeve 30 (when clamping the shaft 14 as for use) and the base bore 52 may be 10 to 100 microns, in order to prevent substantial rotation of the shaft 14 within the base bore 52 in use.
The proximate end of the base body may comprise or consist of a generally annular surface area 56 surrounding the mouth 54 of the base bore 52 and having an outer diameter W4. In various examples, the surface area 56 may be substantially planar or non-planar. In some examples, it may lie on a transverse plane substantially perpendicular to the longitudinal axis of base body, which will be coaxial with the inner surface of the base bore 52; in other examples, at least a region of the surface area 56 may lie at a non-zero angle to such a plane; for example, the surface area 56 may depend away from the mouth 54 at a non-zero angle to the transverse plane. An annular washer 40 may be disposed between an under-side of the head portion 12 and the surface area 56, which extends radially in the example illustrated. The washer 40 may consist of steel, have substantially the same outer diameter W4 as the surface area 56 and thickness T1, which may be about 3 to 5 millimetres (mm). In a particular example, it may be about 4 mm. It may function to provide a degree of wear protection for the surface area 56.
In the particular example illustrated in Fig. 2A to Fig. 2D, the shaft 14 may have a length L2 of about 39.5 mm, the head portion may have a L1 of about 41.1 mm, the base bore 52 may have a diameter W0 of 19.85 millimetres (mm) and the spring sleeve 30 may have a generally annular wall thickness T of 1.30 millimetres (mm). The spring sleeve wall thickness T may be sufficiently thin that it will be sufficiently flexible to be capable of being radially expanded to receive the shaft 14 and sufficiently resilient to hold the shaft 14 by a radial frictional force in use. In general, the thicker the annular wall of the spring sleeve 30, the more force will likely be required to expand it to receive the shaft 14. The flexibility and resilience of the spring sleeve 30 will likely be affected by the mechanical properties of the material of which it is formed, for example by the type of steel used. In some examples, the inner diameter of the spring sleeve 30 may be at least approximately 5 microns greater than the diameter W3 of the shaft 14. The largest diameter W3 of the cylindrical portion of the shaft 14 to be accommodated by the spring sleeve 30 is about 17.15 millimetres (mm). When the shaft 14 is accommodated by the spring sleeve 30 as for use, the outer diameter W2 of the spring sleeve 30 will be the sum of the shaft diameter W3 and double the wall thickness T of the spring sleeve 30. In this specific non-limiting example, W2 will be 17.15 mm + 2 x 1.30 mm = 19.75 mm, which is 0.1 mm (100 microns) less than the inner diameter W0 of the base bore 52. This example arrangement will thus provide a margin of radial interference of about 100 microns (0.1 mm) between the shaft 14 and spring sleeve 30 on the on hand and the base bore 52 on the other.
In other examples in which the inner diameter of the base bore W0 may be about 19.85 millimetres (mm), the diameter of the portion of the shaft 14 to be inserted into the spring sleeve may be greater than 17.15 and the thickness T of the wall of the spring sleeve may be less than 1.30 mm. Many arrangements are envisaged, in which the diameter W0 base bore 52 may not have the value 19.85 mm (in some examples, the diameter W0 may be 18 to 22 mm), the diameter W3 of the portion of the shaft 14 to be inserted into the spring sleeve 30 may not have the value 17.15 and the thickness T of the wall of the spring sleeve 30 may have the value in the range of about 1.2 to about 1.6 mm, other than 1.30 mm. In such example arrangements, the diameter W2 of the spring clip 30 when the shaft 14 has been inserted into it as for use may be 10 to 200 microns less than the diameter W0 of the base bore 52. For example, the inner diameter W0 of the base bore 52 may be 19.00 mm, the thickness T of the wall of the spring sleeve 30 may be 1.20 mm, the outer diameter W2 of the spring sleeve 30 when the shaft 14 is inserted into it may be 18.75 mm and the diameter W3 of the shaft 14 may be 16.35 mm. In this example, the margin of frictional interference between the spring sleeve 30 and the shaft 14 will be 25 microns.
In practice, dimensional tolerances of the diameters of shafts and or the bore diameters may be 0.05 to 0.1, or up to about 0.20 millimetres (mm), which may need to be taken into account when selecting or configuring interference members, and or in combining particular holder bodies, interference members and base bodies.
In some examples, a plurality of holder bodies 10 may need to be secured within a corresponding plurality of base bodies 50, which may be secured by welding or other means to one or more drums for road milling or mining, for example, and in which the base bores 52 may have different diameters W0 from each other. One example approach may be to provide the plurality of holder bodies 10 having substantially the same shaft diameters W3, and a corresponding plurality of spring sleeves 30 having different wall thicknesses T, each selected for a respective base body 50 according to its bore diameter W0 and the overall margin of frictional interference required. In some circumstances, such an approach may be relatively more efficient than using spring sleeves having the same wall thicknesses T as each other and providing the plurality of holder bodies 10 having different respective shaft diameters W3. However, the latter approach or a combination of approaches, in which the spring sleeve wall thicknesses T and the shaft diameters W3 are different from each other within the respective pluralities, are also envisaged within the scope of this disclosure.
About 35 example pick tools as described with reference to Fig. 2A to Fig. 2D were tested by using them to form chamfers on a concrete road pavement. The base holder and drum were commercially available products. For comparison, commercially available pick assemblies configured to allow the holder body to rotate within the base bore and in which the strike bodies comprised cemented carbide tips were also used. The example pick assembly appeared to be effective in substantially preventing the holder bodies from rotating in use and in penetrating the concrete to a depth of up to 10 mm, under relatively high stress owing to the fact that they were relatively widely spaced apart from each other on the milling drum (the spacing between the example pick assemblies was substantially greater that they would be on a drum to be used for 'fine' milling operations in practice). In this trial, the example pick tools exhibited at least about 6 to 10 times longer working life than comparison pick assemblies, the tips formed by the super-hard material substantially maintaining their shapes over the extended working life.
In various kinds of applications such as pavement grooving, the aspect of super-hard tips maintaining their desired shape for an extended period will likely result in the shapes and sizes of the grooves to remain substantially constant throughout the operation, with fewer changes of picks.
With reference to Fig. 3 an example pick assembly may comprise a holder body 10 and strike body 20. The holder body 10 comprises head portion 12 provided with a head bore 16 at a proximate end for accommodating the strike bod 20, and a shaft 14 extending from a distal end of the head portion 12. The strike body 20 may comprise polycrystalline diamond (PCD) material 22 defining a dome-shaped end surface for striking a body to be degraded. The lengths L1, L2 of the head portion 12 and shaft 14, respectively, may be 39 mm and 38 mm, and the largest diameter W0 of the shaft may be 17.35 mm.
With reference to Fig. 4A and Fig. 4B, an example pick assembly may comprise a holder body 10 having a head portion 12 and a shaft 14 extending from a base of the head portion 12, as well as a spring sleeve 30 and wear protection ring 40, in which the thickness T1 of and outer diameter W2 of the wear protection ring 40, and the lengths L1, L2, L3 of the head portion 12, shaft 14 and spring sleeve 30, respectively, had the same values as in the pick assembly described with reference to Fig. 2A to Fig. 2D. The head bore 16 for accommodating the strike body 20 had a depth of 2.9 mm. The strike body 20 may comprise polycrystalline diamond (PCD) material 22 defining a blunted cone end surface and bonded to a cemented carbide substrate 25, which is joined by a layer 23 of braze material to the support body 24. In this example, proximate end of the support body 24 adjacent the braze layer 23 is substantially the same as the diameter of the substrate 25, which may be about 12 mm, and the distal end to be joined to the head bore 16 of the holder body 10 may have a substantially greater diameter of 21.8 mm, the side of the support body 24 connecting the opposite end curving divergently outward (transversely, or radially). In this example, the distal end of the support body 24 may be joined to a bottom surface within the head bore 16 by braze material or adhesive, for example.
With reference to Fig. 5, the interference assembly 30 may comprise a spring sleeve 32 and an interference member 34 that will be located between the spring sleeve 30 and the base bore (not shown) when assembled as for use. The interference assembly 30 may comprise a laterally extending portion 40 at a proximate end, which may abut or be spaced apart from the surface area of the base body surrounding the base bore when assembled as for use, potentially providing a degree of protection for the base body against wear in use. The spring sleeve 32 will clamp around a shaft of a holder body (not shown in Fig. 5) inserted into it, such that the shaft will be unable to rotate substantially relative to the spring sleeve 32 in use. The interference member 34 may comprise or consist of material having a relatively high coefficient of friction when in contact with steel and may be ring (for example, an 'O-ring') or cylindrically shaped, and may be referred to as an 'interference ring' 34. For example, the interference ring 34 may comprise or consist of elastomeric material such as rubber (for example, natural rubber). The interference ring 34 will be configured such that the area of contact between the spring sleeve 32 on the one side and the base bore on the opposite side is sufficiently great that the spring sleeve 32 containing the shaft of a holder body will not substantially rotate within the base bore in use. The configuration of the interference ring 34 to achieve this effect will likely depend on the material comprised in it, and more particularly, the friction properties of the material. In the example arrangement illustrated in Fig. 5, a major side area of the spring sleeve will be spaced apart from the inner surface of the base bore, since the interference member 34 contacts only a minor side area of the spring sleeve 32. In use, a gap between the side of the spring sleeve 32 and the inner base bore surface may become filled with material removed from a body, which may increase the frictional forces between the spring sleeve 32 and the base bore and contribute to the effect of preventing the spring sleeve 32 from rotating within the base bore. In some examples, more than one interference member 34 may be present.
With reference to Fig. 6, an example interference assembly may comprise one or more interference rings 30A, 30B in contact with the shaft 14 extending from a head portion 12 of a holder body. In such examples, a spring sleeve may not be required and the interference rings 30A, 30B will function substantially as described above with reference to Fig. 5.
In examples such as described with reference to Fig. 5 and Fig. 6, there may be a risk of the interference member 34, 30A, 30B becoming less effective during use, by being compressed or deformed. However, the potential accumulation of debris in the gap or gaps between the base bore and the spring sleeve or the shaft, as the case may be, may have a significant effect in some examples in reducing or preventing the holder body rotating relative to the base body. In such examples, the interference member 34, 30A, 30B may not need to function optimally throughout the entire working life of the pick assembly, but potentially only for a sufficiently long period for a sufficient amount of debris to accumulate in the gap between the spring sleeve 32 or shaft 14 and the base bore.
In certain example applications, such as fine milling of pavement (in which the pick tools are relatively closely spaced apart), pick assemblies attached to drive mechanisms such as drums may be used to cut series of substantially parallel and relatively shallow grooves into a body. For example, pick assemblies attached to drums may be used to cut a plurality of substantially parallel grooves having a depth of up to 15 or up to 10 mm into concrete pavement. It may be desired for the grooves to have substantially the same cross sectional profile and depth as each other, and for these features to remain substantially unchanged throughout the operation, with as few replacements of pick tools as possible. However, the shapes of the pick tips that engage and degrade the body will tend to change with use, as they are abrasively worn by the material comprised in the body being processed. It may be desired that the pick tips wear slowly, at substantially the same rate and in substantially the same way as each other, so that changes in the shapes and sizes of the grooves that may occur over time will be as consistent as possible. If a pick breaks, for example by fracturing on striking a relatively harder object within the pavement, or due to imperfections in the material comprised in the pick tip, then all the pick tools on a drum may need to be replaced. If only the fractured pick tool is replaced, its shape profile will likely differ from that of the other picks because it will not have undergone abrasive wear; consequently, the groove that it will produce may have different characteristics from the other grooves. Replacement of all pick tools may be time consuming and costly because in some applications, each drum may hold several hundred pick tools (for example, in excess of 700 pick tools). In order for cemented carbide tips to wear evenly and at similar rates, pick assemblies for various applications may be configured such that the holder body will be capable of rotating about its longitudinal axis within the base bore in use. Promoting rotation of carbide pick tips when they engage the body may result in more even wear around the axis of rotation and extend the working life of the carbide-tipped pick. In general, this may be promoted by mounting the base bodies onto a drum at a slight angle (for example, about 5 degrees) to the direction of travel of the pick tip in use, and a spring sleeve between the shaft of the holder body and the base bore may have the effect of permitting rotation of the holder body in use. Promotion of rotation of super-hard tipped picks may not be as effective as for carbide tips, and may not be necessary.
Since super-hard material such as polycrystalline diamond (PCD) material is substantially more resistant to abrasive wear then cemented carbide material, pick tools comprising super-hard tips will likely have the aspect of substantially extended working life, during which their initial shapes will be preserved for substantially longer periods of time. Unfortunately, super-hard material is generally substantially more brittle than cemented carbide and the risk of fracture when used in impact applications such as pavement milling may generally be very substantially higher than that for cemented carbide material. In addition, super-hard tips for picks will likely be substantially more costly to provide than cemented carbide tips. In order for super-hard tipped pick tools to be viable in certain example applications, the risk of fracture and or of differential wear will likely need to be reduced as much as possible.
Example disclosed pick assemblies have the aspect of extended working life and retention of their shape in certain example applications. While wishing not to be bound by a particular theory, this may arise from achieving substantially reduced risk of fracture and differential wear of the super-hard tips; which may arise from reduced scope for movement of the shaft within the base bore. Configuration of the shaft, interference member and base bore such that the holder body is prevented from substantial rotation in use appears to reduce the potential amount of transverse or radial movement that the holder body can experience in use. In other words, if these dimensions permit rotation of the holder body about its longitudinal axis, other movements within the base bore will likely be permitted to some extent; for example, a kind of 'rattle fit' or 'chatter' of the holder body may be permitted. This may permit sufficient lateral movement for the super-hard tip to engage the body being degraded at slightly varying contact angles, which may increase the risk of fracture and or uneven wear of the super-hard material. Consequently, the mean working life of the picks may be reduced and or the statistical distribution of their working lives may widen, making their performance relatively less predictable. In addition, the risk of the shaft wearing as a result of rotation against the wall of the base bore and or a spring sleeve will be negligible if the shaft is substantially prevented from rotating. This risk would likely be higher for super-hard tipped picks since the tips will tend to wear much more slowly and the potential working life of the pick tool will be correspondingly higher.
An aspect of an example method of making an example pick assembly may be that a processing assembly comprising a plurality of cemented carbide-tipped pick tools, in which the pick tips are urged to rotate about their own longitudinal axes in use, can be adapted relatively efficiently and quickly to comprise a plurality of super-hard tipped pick tools, in which the pick tips do not rotate relative to the base body in use.
When picks comprising super-hard tips are used in at least some applications, the aspect of reducing or eliminating movement of the holder body relative to the base body appears to exceed potential benefits of allowing the picks to rotate in use. Disclosed example pick assemblies may have the aspect of extended working life and or improved quality and consistency of the surface finish of the processed body.
Certain terms and concepts as used herein are briefly explained below.
In general, as used herein, 'super-hard material' has a Vickers hardness (HV) of at least about 28 gigapascals (GPa). 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 per cent of the PCD 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 (which may also be referred to a solvent / 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, PCBN material comprises grains of cubic boron nitride (cBN) dispersed within a matrix, which may comprise metal, alloys, intermetallic materials, Ni-based super-alloy material or ceramic material, for example.
Other examples of super-hard materials 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, as described in United States patents numbers 5,453,105 or 6,919,040 ). For example, certain SiC-bonded diamond materials may comprise at least about 30 volume per cent diamond grains dispersed in a SiC matrix (which may contain a minor amount of Si in a form other than SiC). Examples of SiC-bonded diamond materials are described in United States patents numbers 7,008,672 ; 6,709,747 ; 6,179,886 ; 6,447,852 ; and International Application publication number WO2009/013713 ).
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 head bore or recess within another component, which may involve generating substantial frictional stress between the components and potentially some surface deformation.
As used herein, the phrase 'radial margin of interference' is the difference in a radial dimension between a bore and a body accommodated by the bore, the bore dimension being greater than the corresponding dimension of the body. For example, if the respective lateral (radial) cross sections of the bore and of the part of the body inserted into the bore are circular, the radial margin of interference will be the difference in diameter between the circular cross sections, provided that the diameter of the bore will be greater than that of the body and that the diameters are sufficiently similar for a degree of frictional interference to be evident between the bore and the body. In various other examples, the transverse or radial cross section may be non-circular, such as polygonal or elliptical, or different regions of the cross section shape may be different shapes. In such examples, the radial margin of interference will refer to the corresponding dimensions of the bore and body for which the difference between them is smallest.
In example arrangements in which an assembly, body or part or a body has a generally cylindrical shape (a degree of cylindrical symmetry), the use of terminology associated with a cylindrical coordinate system may be helpful for describing the spatial relationship between features. In particular, a 'cylindrical' or 'longitudinal' axis may be said to pass through the centres of each of a pair of opposite ends and the body or a part of it may have a degree of rotational symmetry about this axis. Planes perpendicular to the longitudinal axis may be referred to as 'lateral' or 'radial' planes and the distances of points on the lateral plane from the longitudinal axis may be referred to as 'radial distances', 'radial positions' or the like. Directions towards or away from the longitudinal axis on a lateral plane may be referred to as 'radial directions'. The term 'azimuthal' will refer to directions or positions on a lateral plane, circumferentially about the longitudinal axis.
As used herein, the term 'surface texture' (which may be referred to simply as 'texture') includes surface roughness, which is quantified by the vertical deviations of a real surface from a substantially planar ideal form. Pavement may be mechanically treated to provide it with texture and exhibit a degree of roughness. As used herein, roughness will mean the average distance between the highest peak and lowest valley in each sampling length.

Claims

A pick assembly comprising:
a holder body (10),

a strike body (20),

a base body (50) attachable to a drive mechanism, and

an interference assembly (30) comprising a spring sleeve (32) and at least one interference member (34);
in which:
the holder body (10) comprises a head portion (12) and a shaft (14) depending from the head portion (12),

the strike body (20) comprises a super-hard strike tip (22), the strike body (20) comprising polycrystalline diamond (PCD) material, or grains of synthetic or natural diamond dispersed in a matrix comprising carbide material,

the head portion (12) and the strike body (20) are cooperatively configured such that the strike body (20) is attached to the head portion (12),

the base body (50) comprises a base bore (52);

the base bore (52), shaft (14) and interference assembly (30) being cooperatively configured such that the shaft (14) is secured within the base bore (52), the interference member (34) disposed between the shaft (14) and the bore (52), frictional interference between the shaft (140 interference assembly (30) and base bore (52) preventing rotation of the shaft (14) within the base bore (52) in use, the combined radial margin of interference between the shaft (14), the interference member (34) and the base bore (52) being 10 to 200 microns, and

characterised in that the interference member (34) is located between the spring sleeve (32) and the base bore (52) when assembled as for use, the interference member (34) being in the form of an O-ring or quad-ring.
A pick assembly as claimed in any of the preceding claims, in which the shaft (14) is coaxial with the strike body (20) when the strike body (20) is attached to the holder body (10) as for use.
A pick assembly as claimed in any of the preceding claims, in which the base bore (52) comprises a cylindrical inner surface and has a diameter of 18.00 to 21.00 millimetres (mm).
A pick assembly as claimed in any of the preceding claims, in which the base bore (52) comprises a cylindrical inner surface, at least an area of the side of the shaft comprises a cylindrical surface, and the interference member comprises a resilient sleeve configured to be capable of accommodating the cylindrical area of the shaft and clamping it with sufficient compressive force that the shaft will not rotate relative to the sleeve in use, the thickness of the sleeve being 1.20 to 1.45 millimetres (mm).
A pick assembly as claimed in any of the preceding claims, in which the interference assembly (30) is configured such that a portion of the shaft (14) is spaced apart from the base bore (52), the portion and the base bore (52) not being connected by solid state material.
A processing assembly comprising a plurality of pick assemblies as claimed in any of the preceding claims, attachable to a drive mechanism.
A method of making a pick assembly as claimed in any of claims 1 to 5, the method including:
providing a first pick assembly comprising
a first holder body and

a base body, attachable to a drive mechanism (60), and

a rotation member;

in which the first holder body comprises a first shaft and the base body comprises a base bore;

the base bore, the first shaft and the rotation member being cooperatively configured such that when the first shaft is inserted within the base bore, the rotation member is disposed between the first shaft and the base bore, such that the first shaft is capable of rotation relative to the base bore when in use;

removing the rotation member and the first holder body;

providing a second holder body (10) and an interference assembly (30) comprising an interference member (34); in which
the second holder body (10) comprises a head portion (12) and a second shaft (14) depending from the head portion (12),

the head portion (12) and a strike body (20) being cooperatively configured such that the strike body (20) is attached to the head portion (12),

the strike body (20) comprising a super-hard strike tip (22); the strike body (20) comprising polycrystalline diamond (PCD) material, or grains of synthetic or natural diamond dispersed in a matrix comprising carbide material,

the second shaft (14) and interference assembly (30) being cooperatively configured such that the second shaft (14) is secured within the base bore (52), the interference member (34) disposed between the second shaft (14) and the bore (52), frictional interference between the second shaft (14), interference assembly (30) and base bore (52) preventing rotation of the second shaft (14) within the base bore (52) in use; the combined radial margin of interference between the shaft (14), the interference member (34) and the base bore being 10 to 200 microns,

the pick assembly comprising the base body (50), the second holder body (10), the strike tip (22) and the interference member (34), wherein the interference assembly (30) comprises a spring sleeve (32) and the interference member (34) is located between the spring sleeve (32) and the base bore (52) when assembled as for use, the interference member (34) being in the form of an O-ring or quad-ring.
A method of using a processing assembly as claimed in claim 6, the method including striking a work body by an end of the strike body coterminous with the super-hard material and removing material from the work body to provide a corresponding plurality of grooves, each having a depth of at most 15 centimetres (cm).