Abstract:
A pick to be used on an earth working roll for mining, construction and public works machines such as crushers, surface miners, milling machines and the like. The pick includes a working end with holes that extend into the pick and inserts are received into the holes. The inserts during operation impact and fracture a consolidated material to separate the material. Impacting the material generates heat in the pick at the working end of the pick which must be dissipated and attenuated to limit thermal fatigue in the inserts that occurs at high temperatures. The inserts in the working end are configured to dissipate the generated thermal energy from the inserts to the body of the pick.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a cutter tool, primarily for use in mineral winning, such as coal mining, but also usable for other underground purposes such as tunnel or roadway driving, or above ground for civil engineering works such as road planing and trench cutting, whether with drums or endless chains, both on land and underwater. 
       BACKGROUND OF THE INVENTION 
       [0002]    A number of machines involved in mining, construction and public works use rolls or drums that are driven for the crushing, mining, milling and the like of earthen materials. These earth working rolls or drums include an array of pick assemblies to engage and separate a consolidated material into smaller portions that can be further separated in subsequent operations. A pick assembly may include a pick releasably attached to a holder secured to the drum or roll. The pick includes a head configured to contact the material and separate it. The picks are wear parts that are replaced after a certain length of use. 
         [0003]    Conventional mineral cutter picks of the shearer type are produced as steel forgings and may include a rectangular section shank whereby the pick is releasably latched in a rectangular receiving aperture of the tool holder or block secured to the roll. The head of the pick projects from the tool holder and above the roll surface. 
         [0004]    The head of the pick is typically notched at its forward end to provide a seat into which is brazed a hard material (usually tungsten carbide) as a tip. The tip may be approximate in width to the head of the pick so as to be capable of cutting clearance for the head. 50 to 100 picks may be attached to a shearer drum of a longwall coal, potash etc. cutting machine. This type of machine has been in use for decades. 
         [0005]    In operation, the impact of the tips can generate significant heat. Dissipation of this heat is critical as the carbide tips are subject to thermal fatigue when they consistently reach or operate at high temperatures. Inefficient operation of the picks due to damage or wear can also generate excessive heat, raising the temperature of proximate parts of the drum and significantly degrading structural properties of components. 
         [0006]    The head of a pick may be damaged by inadvertent collision with a roof support or by hitting hard inclusions in the ore seam such as rocks. When this occurs, a portion of the head of the pick may break away taking the tip with it. The remaining portion of the pick head, without the hardened tip, continues to impact ore material as the machine operates and the drum rotates. The damaged pick then sustains more damage which results in a shortened useful life and lower machine efficiency. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention pertains to an improved pick for use on an earth working roll for mining, construction and public works machines such as crushers, surface miners, underground mining machines, milling machines and the like. The pick includes a head with multiple tips or inserts in a strike face of the pick that impact the worked surface. The inserts are positioned in holes of the pick head that open at a face of the head and the inserts extend beyond the face. The inserts are configured to impact the surface of the consolidated material more efficiently and dissipate generated heat more efficiently to the body of the pick. 
         [0008]    The head of the pick protrudes beyond the tool holder with the head oriented away from the drum and in the direction of rotation of the roll. The inserts are a hard material configured in one construction as elongate rods of any cross-section approximately the same dimension as the holes in the face. The inserts may be held frictionally in the hole, brazed in place, soldered, glued or by any other method that maintains their position in the hole during operation. Multiple small inserts as compared to one relatively large carbide tip positioned in the head presents smaller areas of carbide impacting the target material, generating less heat. 
         [0009]    The pick is configured so that the inserts initially impact the earthen material as the drum rotates. Any number of two or more inserts may be positioned in the head of the pick. Positioning the inserts in the head of the pick with an appropriate configuration and separation between the inserts can more efficiently transfer heat away from the inserts during operation. Where the generated heat can efficiently flow from the carbide tips to the body of the pick and the holder, the life of the inserts can be extended and downtime and expense for replacing the picks can be reduced. 
         [0010]    In a first embodiment, the tips are configured in the head so that they are spaced apart about a central axis of the strike face or contact face of the pick and extend beyond the face. The multiple tips protruding from the face impact the target material over a smaller contact area and generate less heat than a single large tip. 
         [0011]    In a second embodiment the elongate inserts are parallel to each other in the head along their length. Preparing the head of the pick to accept parallel inserts is a less complex and lower cost process than other configurations and the closely spaced tips impacting the material work more efficiently than a single large tip. 
         [0012]    In a third embodiment the holes with inserts are spaced apart in the head of the pick and the inserts converge toward the face to a closely spaced configuration. Heat generated at the tip of the insert from impacting the target material is more efficiently transferred to the head and body of the pick in this embodiment by dissipating the heat over a larger body area than would occur with the picks in a parallel configuration. 
         [0013]    A pick assembly configured to operate and dissipate heat more efficiently from the inserts to the head would be advantageous by reducing insert thermal fatigue, machine downtime and power consumption. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a depiction of an earth working operation including a roll drum with picks. 
           [0015]      FIG. 2  is a side cross section view of a pick with inserts in accordance with the present invention including a tool holder mounted to a drum. 
           [0016]      FIG. 2A  is a side cross section view of an alternative configuration of a pick with inserts in a carrier received by the head of the pick. 
           [0017]      FIG. 3A  is a perspective view of a pick with three inserts. 
           [0018]      FIG. 3B  is a perspective view of a pick with four inserts. 
           [0019]      FIG. 4  is a cross- section view of a pick with three inserts along line  4 - 4  of  FIG. 2 . 
           [0020]      FIG. 5  is a side cross section view of a pick with inserts. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]      FIG. 1  depicts an earth working operation including a face miner with pick assemblies for extracting earthen material such as coal in a mining operation. The operation is shown as including a mining machine  4  with a driven drum, roll or cylindrical body  6  mounted with pick assemblies  8  including picks  10  for impacting the ore seam or consolidated earthen material  12  as drum  6  rotates. Picks  10  are mechanically attached or secured to rotating drum or cylindrical body  6 . Earthen material  12  to be extracted is typically in a seam and rotating drum  6  passes across the mine face so the picks impact the face and dislodge material from the seam in manageable portions. Picks  10  impinge on the material with adequate speed and force to fracture the material. 
         [0022]    The spacing of the picks determines the size of the dislodged material, but also is a factor in stress on individual picks and heating of components. The mined material is typically dropped onto a conveyor and transported away to a roll crusher or other processing. Pick assembly  8  is one of many similar assemblies attached to drum  6 , often in staggered rows. 
         [0023]    In all figures, like components use similar numbering.  FIG. 2  is a cross section view of pick assembly  8  mounted to drum  6 . Drum  6  has a direction of rotation R and a radial direction r away from the axis of drum  6 . Pick assembly  8  as shown includes a pick  10  and a tool holder or base  14 . Pick  10  has a proximal end  10 A and a distal end  10 B. Pick  10  is shown with a shank  18  at proximal end  10 A which is the portion of pick  10  received by holder  14 . Pick  10  is shown with a head  22  at distal end  10 B and a body  16  generally between shank  18  and head  22 . 
         [0024]    Head  22  tapers forward and away from body  16  and is configured to contact consolidated materials to be separated. In  FIG. 2  head  22 , indicated by a dotted line, generally extends away from the drum and in the direction of rotation R. Head  22  defines a longitudinal axis  20  and includes a strike face or contact face  22 A. The pick body  16  is shown with a pry point  16 A at a forward portion of body  16  configured to receive a pry bar for removing pick  10  from holder  14 . At a rear portion body  16  includes an opening  16 B associated with a water spray system not shown in this embodiment. 
         [0025]    Head  22  includes face  22 A with holes  24  configured to receive inserts  26 . In a preferred embodiment, holes  24  with inserts  26  are shown inclined to each other and converging toward face  22 A. Each hole  24  and insert  26  may define an axis and the inclination of the holes may be defined by an angle between the axis of the hole and the longitudinal axis  20  of head  22 , preferably between 5 and 20 degrees. Alternatively, the inclination of the holes may be defined by an angle α between holes in the head  22 . Hole  24  may be inclined an any angle α that fits within the envelope of head  22 , but preferable is between 5 and 40 degrees. 
         [0026]    In one embodiment, the axes of adjacent holes  24  may be substantially parallel to the longitudinal axis  20  as shown in  FIG. 4 . In another embodiment the inserts may be distributed about the longitudinal axis, each insert  26  with the same inclination to axis  20  as shown in  FIG. 2 . In another alternative embodiment, inserts  26  may be parallel to each other and axis  20  in one perspective. Then from an orthogonal perspective one or more inserts  26  are inclined to axis  20 . 
         [0027]    Holes  24  may extend more than a quarter of the distance between head  22  and the top of shank  18 . Preferably, hole  24  extends 30 to 50 millimeters in depth. The length of inserts  26  and depth of hole  24  affects heat propagation, structural integrity of the inserts and transfer of impact forces from the inserts to head  22  and body  16  of pick  10 . Holes  24  and inserts  26  may be round, triangular, rectangular or square in cross section or any other shape and can be manufactured by several processes. 
         [0028]    Holes  24  may not extend substantially into head  22 . Holes  24  in an alternative embodiment may be of adequate depth to accept an insert configured as a tile and to limit transverse movement of the tile on strike face  22 A. 
         [0029]    In a preferred process, holes  24  are drilled into head  22  and inserts  26  inserted into the drilled holes. Round holes are most easily drilled, but square and other cross-sectioned blind holes can be produced using more sophisticated machining processes. 
         [0030]    In another embodiment pick  10  includes a carrier for inserts  26  as shown in  FIG. 2A .  FIG. 2A  includes a pick  10  with a shank  18  and a head  22  similar to the pick of  FIG. 2 . In this embodiment pick  10  further includes a carrier  30  and a carrier opening  32 . Holes  24  are machined in carrier  30  and inserts  26  are positioned into each hole  24 . Head  22  then receives carrier  30  with the inserts in carrier opening  32 . As an example, a square hole can be configured in carrier  30  by square swaging through the carrier to configure the hole and a square insert  26  positioned in the swaged square hole  24 . Carrier  30  can then be mounted to head  22  by any of various means including threading the carrier and carrier opening, brazing or welding. Swaging a hole in carrier  30  is a lower cost process than other forms of machining for some hole configurations. 
         [0031]    In still another embodiment, carrier  30  of  FIG. 2A  could be formed around inserts  26 . Inserts  26  could be held in position in a carrier mold or in a carrier opening  32  in head  22 . A casting material such as bronze, aluminum, epoxy or other compatible material is then poured around inserts  26 . If a carrier mold is used, the carrier  30  is separated from the mold and received by carrier opening  32  of head  22 . 
         [0032]    Casting around inserts  26  would provide for any shape of insert  26  to be used, as well as inserts that vary in cross section along their length. Heat transfer characteristics, wear and structural properties in head  22  can be modified by appropriate selection of casting materials. 
         [0033]    Returning to  FIG. 2 , tool holder  14  is shown with an aperture or opening  14 A configured to receive shank  18 . Shank  18  is preferably rectangular in cross-section, but may be oval or round or any other shape which is compatible with the holder. Holder or base  14  is secured to the surface of drum  6  or in a depression or indentation for a lower profile by any means that reliably retains the holder such as welding or bolting. Pick  10  may further include a shoulder  14 B. With shank  18  fully inserted in opening  14 A, shoulder  14 B abuts an edge of opening  14 A limiting the depth of insertion. 
         [0034]    Pick assembly  8  is shown with a resilient retention feature  28  in shank  18 . Retention feature  28  may be a button inserted into a hole of shank  18  and configured to work cooperatively with a feature of holder  14  to retain pick  10  in holder  14 . Shank  18  may be inserted and extracted from tool holder  14  along radial direction r. Longitudinal axis  20  may be may have an angle of inclination between the direction of rotation R and the drum radial direction r so that is it is inclined in the direction of rotation. Pick  10  may not have a shank. Pick assembly  8  may be secured to roll  6  by another means such as welding or bolting holder  14  or pick base  16  to roll  6 . 
         [0035]    The portion of head  22  proximate to face  22 A may be configured with a narrower cross section, acutely angled surfaces, sharper edges and smaller radii of curvature than sections of pick  10  and head  22  farther from face  22 A. This forward area is also more exposed to impact from material separated by inserts  26 . This makes the area around face  22 A more prone to fatigue cracking, chipping and fracture. Having the end of insert  26  abut the body of pick  10  at the bottom end of hole  24  farther from face  22 A, allows impact forces to be transmitted to an area of pick  10  less prone to damage. This reduces stress in the area proximate to face  22 A and increases service life of pick  10 . 
         [0036]    When pick  10  is damaged, a portion of head  22  may be broken off from pick  10 . With multiple inserts, a remaining portion of head  22  may retain one or more inserts that continue to efficiently impact earthen materials  12 . In previous configurations with a single large tip, any damage to head  22  tended to separate the tip from the head, severely reducing the efficiency of the pick. 
         [0037]    Pick  10  and tool holder  14  may be composed of iron, steel or any other material that is durable enough to withstand continuous impacting and abrading of the surface by the fractured materials. Inserts  26  are selected to be a much harder material than pick  10  and are preferably cemented carbide, diamond or ceramic, but other materials can be used. The inserts may vary in hardness. One insert may have a different hardness than the other picks in the same pick head. 
         [0038]    Carbide may have twice the thermal conductivity of steel. With the higher thermal conductivity, insert  26  acts as a radiator and the entire length of the insert will tend to stay at a higher temperature than the surrounding steel. This temperature differential in turn drives a higher rate of heat transfer or heat flux along the entire surface of the insert. 
         [0039]    Three smaller inserts  26  with a larger surface area will dissipate the heat more readily than the single larger tip. For the purpose of illustration only and as an example, insert  26  may be round with a diameter of 1 millimeter (mm) and a length of 10 mm. The total circumference of 3 tips, each with a diameter of 1 mm is 9.4 mm and a typical single large tip may have a diameter of 1.85 mm inserted in the head for a circumference of 5.8 mm. The inserts significantly increase surface area for transfer of heat from the insert to the steel body. Making insert  26  longer than a standard single tip also significantly increases the surface area for heat transfer to the steel body. Drilling insert holes  24  so they diverge from face  22 A into the head of pick  10  provides a further advantage in dissipating the heat over a greater volume of pick  10 . 
         [0040]    A pick operates over a wide range of temperatures and mismatch of thermal expansion between components can cause internal stresses. The coefficient of expansion of the carbide, 5×10−6 m/m-K, is less than that of steel which is 13×10−6 m/m-K. Using three smaller diameter tips results in less tension between the steel and carbide as the contact area is greater. The brazing and soldering materials also act as an interface between the inserts and the head and compensate for mismatch at the interface. 
         [0041]    The service life of a pick is a function of the volume of carbide removed during operation (wear rate) as well as the susceptibility of insert  26  falling out of pick  10 . When the portion of insert  26  remaining in the head is small, it is more susceptible to leverage from side impacts that can extract the insert from head  22  and face  22 A. The smaller diameter insert is less likely to be extracted by side forces because of the mechanical advantage that it has over the larger tip. For example, when both tips wear down to 5 mm long, there is a higher extracting force exerted by side or angled impacts on the large tip than the smaller insert because of its larger diameter. 
         [0042]    A large single tip is usually sized to the same general width as head  22  to limit wear to the head. The smaller diameter inserts  26  leave the head  22  of pick  10  more exposed to the abrasive materials even though inserts  26  make the primary impact on the consolidated materials to separate it. This results in more wear of head  22 . Insert  26 , a much harder material than head  22  and body  16  of pick  10 , has a lower wear rate. 
         [0043]    With an optimal tip length (the portion of insert  26  extending beyond the face  22 A), wear and erosion of head  22  and insert  26  are minimized. If insert  26  extends beyond head  22  too far, it is susceptible to lateral forces and portions of the insert tend to break off. Where exposed tip lengths of inserts  26  are short, head  22  wears at a higher rate, exposing the inserts. Pick  10  can continue in service as long as inserts  26  are retained in head  22  with an adequate tip length. 
         [0044]      FIG. 3A  is a perspective view of an embodiment of pick  10  with three inserts  26  and longitudinal axis  20  passing through the center of head  22  of pick  10 . The three inserts are distributed about longitudinal axis  20  with 120 degrees between each insert. 
         [0045]      FIG. 3B  is a perspective view of an alternative embodiment of pick  10  shown with four inserts  26  and longitudinal axis  20 . Inserts  26  are distributed about longitudinal axis  20  with 90 degrees between each insert. There can be any number of two or more inserts  26  in head  22  and in any configuration. The two configurations shown are examples for illustration. 
         [0046]      FIG. 4  shows an alternative configuration of pick  10 . Pick  10  in  FIG. 4  is a section view from  FIG. 2  showing a top view of inserts  26  and longitudinal axis  20 . In this embodiment in this perspective inserts  26  are parallel to longitudinal axis  20  while from the orthogonal perspective of  FIG. 2  each insert is inclined to longitudinal axis  20  at the same angle. 
         [0047]      FIG. 5  is a side view of an alternative pick  10  in cross section, again showing three inserts  26 . In this view, orthogonal to a top view such as  FIG. 4 , and in contrast to  FIG. 2 , one or more inserts are inclined to axis  20  with other inserts parallel to axis  20 . 
         [0048]    The present invention pertains to picks for an earth working roll or roller such as used in roll crushers, surface miners, milling machines and the like. The use of relative terms such as forward, front, rear or sides or the use of specific shapes is not intended to be limiting, but rather to more clearly illustrate the invention. Also, picks as described here are shown primarily in the context of mining machines. Nevertheless, the invention is not limited to this operation. Picks in accordance with the invention are also suitable for use in conjunction with other earth working machines involving the use of driven rolls with picks such as single roll crushers, scroll crushers, surface miners, underground mining machines, milling machines and the like.