Abstract:
Improvements in bits, bit holders and bit blocks used in road resurfacing equipment and mining and trenching equipment provide for improved rotatable bit holders in the bit block, ease of removability of bits from bit holders and for predetermined points of desired failure of any member of the combination if the bit should encounter a hard discontinuity while performing its work.

Description:
This invention relates generally to road surface removal or reclaimer-stabilizer equipment and mining equipment, and more particularly, to cutter bit holders and bit blocks used in such road milling, mining, and trenching equipment. 
     BACKGROUND OF THE INVENTION 
     Cutter bits are utilized in road, off-road and mining machinery on the perimeter and across the width of a rotary drum or on the outside of a continuous chain or the like where the bits are moved through an orbit which is intercepted by the face of the material being removed or recycled. Road milling equipment removes the defective surface of a road and smooths the top of all or selected portions of the road surface. The bits include a tip and a shank. The shank is received and may axially rotate in a bit holder which is secured onto a bit block that, in turn, is mounted on the drum. Each of the bits has a hardened tip, preferably made of tungsten carbide or such other hardened material that acts to remove a portion of the surface it contacts. By using a sufficient number of these bits around the outer surface of a rotating drum, a large amount of surface may be worked. Any surface being worked generally has a hardness which can be measured or anticipated prior to the removal operation. However, such road surfaces, or surfaces being removed have hardened irregularities running therethrough. The toughness or hardness of the irregularities may result in the breakage of the bits and holders as they are being run over such irregularities. 
     Additionally, as bits and bit holders wear during the removal process, that wear may be uneven. It would be desirable to be able to selectably change the radial orientation of the bit holder in the bit block. U.S. Pat. No. 5,106,166 discloses a bit retaining sleeve (bit holder) having four flats positioned at 90 degree orientations therearound which fit onto a flat fixation surface on the bit holder to allow the worn bit holder to be positioned in one of four radial orientations in the bit block. A need has developed for an improved means for positioning and mounting a bit holder in a bit block that provides for changing the radial orientation of the bit holder in the bit block as the holder becomes worn. 
     Further, a need has developed for providing ease of removability of bits in their bit holders, especially when the bit becomes worn and need to be replaced. U.S. Pat. No. 5,374,111 discloses an undercut flange at the bottom of a base of a bit that allows a pry bar to be wedged between that flange and the top of the bit block (no bit holder in this patent) to help remove a bit from a bit block. It would be desirable to provide a more efficient means for allowing the removal of a bit from a bit holder or a bit block. 
     Additionally, tightening a small fastener on the bottom of a bit holder to hold it in the bit block concentrates friction forces on a small area of the nut top face and the bottom of the bit block. It would be desirable to spread those friction forces over a larger area. 
     It is, therefore, an object of the present invention, generally stated, to provide an improved means for quickly removing a bit from its bit holder, or a bit block if a bit holder is not utilized. 
     Another object of the present invention is the provision of an improved means for changing the radial orientation of the mounting of a bit holder on a bit block. 
     Another object of the invention is the provision of an improved means for providing for breakage of inexpensive replaceable parts when road resurfacing equipment and mining equipment bits encounter very hard irregularities in the surface being milled or mined. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a bit assembly for use in road milling and mining equipment. The bit assembly includes a bit having a hardened distal end connected to a shank portion and means including a shank receiving bore for mounting the bit on that equipment. The invention resides in an improvement comprising a reduced cross section means on one of the bit and the means for mounting the bit on the equipment. This reduced cross section means provides a predetermined area of failure for when the bit contacts a hard discontinuity in material it encounters. 
     The invention is further directed to a bit holder for retaining a bit therein as a part of a bit assembly. The bit holder comprises a generally frustoconical bit mounting portion including a top surface, a mediate portion tapering outwardly from the top surface and a radial flange defining the bottom thereof. The shank portion extends axially from the radial flange and terminates in a fastening portion adjacent a distal end of the shank. An axial bore is in communication with and extends inwardly from the top surface and is adapted for mounting a bit therein. The invention resides in indent means extending radially inwardly from an outer surface of the mediate portion and in communication with the top surface. The indent means provides access to an underside of any bit mounted on the bit holder and resting on the top surface thereof to aid in any removal of a bit from the bit holder and provides for axially turning the bit holder with respect to the bit block. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention which are believed to be novel are set forth with particularity in the attached claims. The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which like numerals refer to like parts, and in which: 
     FIG. 1 is a side elevational view of a bit block, bit holder and bit assembly constructed in accordance with the present invention; 
     FIG. 2 is an exploded side elevational view of the assembly shown in FIG. 1; 
     FIG. 3 is a front elevational view of a bit holder constructed in accordance with the present invention; 
     FIG. 4 is a top plan view of the bit holder shown in FIG. 3; 
     FIG. 5 is a bottom plan view of the assembly shown in FIG. 1; 
     FIG. 6 is a perspective view of a bit holder tightening-loosening socket constructed in accordance with the present invention; 
     FIG. 7 is a front elevational view of the socket of FIG. 6 shown mounted on the bit holder of the invention; 
     FIG. 8 is a side elevational view of a modification of the bit holder of the present invention mounted in a bit block and including a modification of a socket mounted over the bit holder to engage notches in the bit holder radial flange; 
     FIG. 9 is a bottom plan view of a modification of a socket having three equally spaced cylindrical detents therein; 
     FIG. 10 is a side elevational view of a second embodiment combination bit holder/bit block constructed in accordance with the present invention having a bit mounted therein and showing a pneumatically operated impact tool positioned to remove the bit utilizing the notches of the present invention. 
     FIG. 11 is a top plan view of the combination bit block/bit holder shown in FIG. 10 showing the notches therein constructed in accordance with the present invention; 
     FIG. 12 is a view similar to FIG. 1 of a third embodiment of a bit holder further including a half tapered shank on the bit holder; 
     FIG. 13 is a side elevational view of a fourth combination bit block/bit holder having a slot formed therein for breakage purposes; 
     FIG. 14 is a side elevational view of a bit holder having a bit mounted therein and showing the breakage slots of the invention formed thereon; 
     FIG. 15 is a perspective view of a sixth embodiment combination bit block and bit holder shown having a breakage slot of the invention formed thereon. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-5, a bit mounting assembly, generally indicated at  20 , constructed in accordance with the present invention, includes a bit, generally indicated at  21 , which is mounted on a bit holder, generally indicated at  22 , which, in turn, is secured on a bit block, generally indicated at  23 . The bit block  23  is one of a plurality of such blocks mounted around the outside of the generally circular drum (not shown) or on a movable chain or track (not shown). 
     Referring to FIG. 2, the bit, generally indicated at  21 , includes a forward end  24 , and a shank  25  or rear end thereof. The forward end  24  includes a hardened nose  26 , preferably made of tungsten carbide or the like material, a middle tapered portion  27  including a reduced diameter area  27   a  and a bottom flange portion  28  which is made so as to rest on the bit holder, generally indicated at  22 . A spring steel retaining clip  30  is positioned over the shank  25  of bit  21  and is shaped so that when the bit  21  is inserted in the bit holder  22 , the retaining clip  30  will secure the bit therein while allowing it to rotate from external forces. 
     The bit holder  22 , constructed in accordance with the present invention, includes a generally flat annular leading surface  31  on which the rear side of the bit flange  28  rests when inserted therein. Adjacent the annular leading surface  31  is a middle or tapered portion  32  that ends in an enlarged flange portion  33 . In the preferred embodiment of the invention, a plurality of notches, flats or indents  32   a-d  extend radially inwardly of the middle tapered portion from top surface  31  toward the flange  33 . The back side  34  of flange  33  is an annular flat surface which rests on the bit block  23  when mounted thereon, and includes one aspect of the present invention to be discussed below. Rearwardly adjacent the flange portion  33  is a reduced diameter cylindrical shank portion  35  and a tapered portion  36  which may vary in length depending on its function, an undercut portion  37  is next to the tapered portion  36 , and the bit holder terminates in a threaded portion  38  adjacent the distal end  44  thereof. If the nose  26  of bit  21  hits a hard discontinuity, bit  21  will fail first, the bit holder in this embodiment may be engineered to fail next across reduced diameter section  37 . The long tapered shank portion  36  allows the bit holder to tumble out of bit block bore  49  after failure. 
     Also shown in FIGS. 2 and 4 is a bore  40  that extends axially through bit holder  22  from a chamfer  41  in communication with the front face  31 , through the tapered portion  32 , the flange portion  33  and a substantial portion of the shank  35 ,  36  where it narrows at chamfer  42  to a smaller diameter bore  43 . Bore  43  extends the remainder of the bit holder to its distal end  44 , or it may be increased in diameter partly along its length to decrease the cross sectional reduced diameter section  37 , if desired. The length of the bore  40  is determined partly by the length of the shank  25  on bit  21 . The shank  25  fits within bore  40 , and is retained therein by the spring steel retainer  30 . If the bit  21  should break at the shank  25 , a rod, punch, etc. (not shown) may be inserted into the bottom of the bore to push the shank out of the holder. 
     Referring to FIGS. 1,  2  and  5 , the bit block  23  consists of a base portion  45  that mounts to a drum (not shown) or chain (not shown) and an angled bit holder mounting portion  46  extending from the base  45  that includes a top face  47 , and a bottom recessed slot  48  which provides the opposing ends for a bore  49 , which may be tapered, and a reduced bridging portion  51  extending from a bottom of bore  49  to the recessed slot  48 . Bore  49  is sized to receive the cylindrical shank  35  and tapered shank portion  36  of the bit holder  22  with the annular flat surface  34  on the bottom of the flange portion  33  resting on the top surface  47  of the bit block mounting portion  46 . In one important aspect of the present invention, the surface area of contact between flange bottom  34  and bit block top  47  is much greater than the surface area of contact between the top  52   a  of nut  52  and nut contacting surface on slot  48  and will be discussed in greater detail below. The threaded portion  38  adjacent the distal end  44  of bit holder  22  extends through the reduced passageway  51  where a nut  52  may be threaded thereon by rotating the bit holder until its top surface  52   a  engages the surface of the recessed slot  48  to retain the bit holder  22  on the bit block  23 . 
     Referring to FIG. 1, the distal end of a pneumatically operated chisel is shown in dotted line at  55 , inserted in one of the notches  32 C as more fully shown in FIGS. 3 and 4. The notches  32   a - 32   d , constructed in accordance with the present invention, allow for the quick removal of the bit  21  from the bit holder  22  by applying a force having a substantial axial component thereto to the bottom side of the bit flange  28 . In the preferred embodiments there may be three or four notches or indents  32   a-d  (FIG. 4) on the bit holder  22  positioned at 120 degree or 90 degree intervals, respectively, around the circumference thereof. Each notch may be straight vertically or slightly wider at surface  31  and narrows as the notch descends toward flange  33 . While the use of the punch  55  on one notch is usually sufficient to remove the bit, the punch may be utilized sequentially in differing notches to balance the axial force, if necessary, to move the bit  21  out of the bit holder  22 . The notches also provide for better rotation by removing debris that may work into the bottom of flange  28 . When the bit rotates, the notches will urge debris out of this area. 
     In its preferred operation, even though the bit can rotate axially, it is not unusual for the tip  26  and the surrounding tapered portion  27  of the bit  21  to wear unevenly on one side thereof. The bit holder  22  may also become worn unevenly during its use in the operations of milling a road or in use as a mining bit. In one aspect of the present invention, the recessed slot  48  helps to protect nut  52  from wear since the nut protrudes out of the assembly less than if there was no recess. The ability to rotate the bit holder  22  in the bit block  23  provides for extending the usable life of the assembly by being able to index the holder in 60 degree increments. 
     Referring to FIGS. 6-8, a bit holder socket, generally indicated at  60 , includes a generally hollow annular cylindrical wall  61  having an enclosing end wall  62  at one end thereof with a square drive receiving passageway  63  therethrough and a generally hollow cylindrical interior surface  64  extending from the end wall  62  to an opposing annular opening surface  65 . In the first preferred embodiment, four cylindrical inserts  66   a - 66   d  are positioned in respective cylindrical recesses at 90 degree intervals around the interior hollow cylindrical surface  64  so as to extend radially inwardly of that surface. As shown most clearly in FIG. 6, each of the cylindrical inserts  66   a - 66   d  is sized to fit in one of the notches  32   a - 32   d  when the socket  60  is positioned over a bit holder  22 . With a ratchet, breaker bar or pneumatic impact wrench (not shown) mounted on socket  60  and the shank portion  35  of the bit holder  22  positioned in bore  49  of the bit block (FIG. 2) the combination socket  60  and bit holder  22  may be rotated to one of six desired orientations to be discussed in greater detail below, with respect to the bit block  23  and maintained in that position as the nut  52 , while retained in slot  48 , is threaded onto the distal end  44  of the bit holder  22  until it is securely fitted in the bit block. Nuts of varying hardness will be utilized. Also, lock nuts may be used depending on the application. 
     Referring to FIGS. 8 and 9, a second embodiment of the bit holder, generally indicated at  70 , is constructed similarly to bit holder  22  with the exception of a shorter tapered shank portion  71  and having a plurality of additional notches  72   a-c  providing equally spaced semicircular indentations around the outside of the bit holder radial flange portion  33 . A second embodiment of a socket, generally indicated at  74 , is larger than socket  60  and has a central recess  75   a  at the open end thereof that is large enough to fit over the outside of the bit holder radial flange  73 . Socket  74  includes a plurality of cylindrical inserts  76   a-c  positioned in semicylindrical recesses  77   a-c  in evenly spaced relation around the outside of hollow recess  75   a , complementary to notches  72   a-c . With this structure, socket  74  may be inserted over bit holder  70  and the bit holder rotated by driving the socket with an impact wrench (not shown) or the like. 
     In operation, the mounting and removal of both bit holders  22  and  70  from their respective bit blocks  23  and  78  is an important aspect of the present invention. Rather than the bit holder being fixed (non-rotatable) on the bit block, and the fastener  52 ,  79 , respectively, being turned on the threaded end of the bit holder, the reverse happens in applicant&#39;s invention. Taking the first embodiment as an example, nut  52  is positioned in recessed slot  48  (FIG. 5) so that it does not rotate. Since the threads inside nut  52  are fixed in position, each of the six hex surfaces of nut  52 , when positioned against one of the respective flat sides of recessed slot  48  will position the threads therein in a differing radial or arcuate orientation with respect to the start and end of the threads. As a result, when the bit holder threaded portion  38  is turned on the nut  52 , it will stop turning in one of six rotational positions when the bottom  34  of flange  33  contacts the top  47  of bit block  23 , give or take slight movement when the rotational force, in foot-pounds, on the bit holder is increased or decreased. While the turning force may vary from 100 to about 1100 foot-pounds, within the strength of the material, a preferable range of torque to securely mount the bit holder on the bit block ranges from 400-600 foot-pounds. 
     As mentioned previously, since the area of contact between the bottom  34  of flange  33  against the top  47  of bit block  23  is substantially greater than the area of contact between the top  52   a  of nut  52  and the face of slot  48 , there is a substantial increase, in the range of 3 to 4 times, in frictional surface grabbing between the holder and block tending to prevent rotation of the holder when the holder is rotated during mounting over prior methods used when the holder was held still and the fastener turned during mounting of the holder on the block. 
     Referring to FIG. 8, when the bit holder  70  is rotated to a new position on bit block  78 , it is not necessary to fully remove the nut  79  from the threaded end  71   a  of the bit holder. The back of bit block  78  is notched at  78   a  to provide clearance when hex nut  79  is loosened so that surface  79   a  on nut  79  moves beyond surface  130  to allow the indexing of hex nut  79  in slot  78   c  without the nut being completely off the threads  71   a . Thus, fast and safe adjustments of the rotational mounting position of the bit holder in the bit block according to applicant&#39;s invention provides for superior change of positioning of the bit holder in the bit block over prior such combinations. 
     Referring to FIGS. 2 and 3, when the leading end or hardened nose  26  of the bit  21  encounters a hard discontinuity in the surface it is removing, something has to give and quickly. In this respect, it is desirable to engineer the shapes of the bit, bit holder and bit block to assure that the part or parts destroyed in the process are chosen to be broken or destroyed rather than having the same happen by accident. If it is desirable to have the bit  21  break during such an occurrence in order to maintain the bit holder  22  and bit block  23  in working order, a reduced diameter portion  27   a  of the bit may be made a diameter such that upon the hardened end  26  striking a hard discontinuity, the bit  21  will break at the reduced diameter portion  27   a  thus saving the remainder of the assembly for future use. If it is desired that the bit block  23  remain usable and the bit holder  22  be replaceable, the reduced section  37  of the bit holder between the shank  35  and the threaded portion  38  may be made of a diameter and the shank tapered as shown in FIG. 1 so that any breakage will occur at the reduced diameter section  37 . As will be shown hereafter, it may, in certain instances, be desirable to have the bit holder nose break. Additionally, an annular groove  99  (FIG. 12) between the notches and the radial flange may be sized to provide for failure between groove  99  and the central bore when the hardened end  26  of the bit  21  encounters a hard discontinuity, thus allowing the bit to tumble out of the top of the bit holder  22 , while the remaining radial flange protects the top surface of the bit block. 
     Referring to FIGS. 10 and 11, a differing shape combination bit holder/bit block, generally indicated at  80 , includes a mounting surface  81  and a bit holding body  82  extending therefrom including a bore  83  into which a bit, generally indicated at  21 , is retained by the spring steel retainer  30  previously discussed. The bit flange  28  rests on a top flat surface  84  of the combination block/holder  80 . In this embodiment, three notches  85   a-c  are positioned at 90 degree intervals around the body  82  and extend upwardly to be in communication with top surface  84  of the combination block/holder. When the bit  21  is retained in the combination block holder  80 , as shown in FIG. 10, a pneumatic punch  86  may be used similarly to the pneumatic punch  55  shown in FIG. 1 by being inserted into one of the slots  85   a-c  until it contacts the underside of the bit flange  28  to provide a substantial axial component of force to move the bit  21  upwardly out of the bore  83  of the combination block/holder  80 . 
     Referring to FIGS. 12 and 13, bit blocks, generally indicated at  89  and  91 , while having a differing appearance, both provide for mounting the bits  21  the same distance from the mounting drum and at the same angle. Bit block  89  retains therein a bit holder generally indicated at  90 . The smaller tapered shank (in comparison to longer tapered shank  36  of the first embodiment) avoids having a concentrated corner stress point that would be present if the cylindrical shank  92   a  extended to the bottom of the bit block bore. 
     It should be noted that while the mounting surface  94  of bit block  89  is not quite the same as the curved mounting surface  95  of bit block  91 , both surfaces are mountable on the flight (outer wall) of a drum which makes the bit blocks interchangeable in use. It should be noted that the mounting holes  94   a-b  are positioned in the same alignment as threaded holes  95   a-b  on bit block  91  for complete interchangeability. 
     The bit block/holder  91  includes a mounting body  96  extending upwardly from the circular mounting surface  95  and ends at a bit mounting portion  97  having a bore  98  therethrough into which the bit  21  is retained by the spring retainer  30 . In order to provide for the intended failure of the holder  92  if the bit  21  encounters a hard discontinuity, an indentation type slot  100  is formed between the body  96  and the bit mounting portion  97 . In the event the bit  21  encounters a hard discontinuity, the bit holder  92  is engineered to fail across the bit mounting portion from the inner end of slot  100  to the bore  98 , thereby saving the mounting body  96 . In FIG. 12, bit holder  90  is engineered to fail first in order to save the bit block  89 . 
     Referring to FIG. 14, a sixth embodiment of a bit mounting body is shown, generally indicated at  110 , and includes a shank portion  111  and a bit receiving portion  112  having a bore  113  therethrough into which a bit  21  is retained by a spring steel retainer  30 . The bit block is not shown. As shown most clearly in FIG. 14, slots  115  and  116  are positioned in the bit receiving portion  112  and the shank portion  111 , respectively, to provide for failure of the bit mounting body at one of those positions when the bit  21  encounters a hard discontinuity. One or both slots may be used. The failure of the bit receiving portion from the base of slot  115  through to the opposing side of the bit receiving portion designated  117  or from the base of the slot  116  through to the opposite side of the bit receiving portion  117  will save the bit block (not shown) in the event of such an occurrence. 
     FIG. 15 shows a seventh embodiment of a bit holder, generally indicated at  120 , that includes a rectangular mounting portion  121  and a terminal distal bit mounting surface  122  having a bore  123  extending inwardly therefrom through the bit holder  120  for mounting a bit  21  therein (not shown). As shown most clearly in FIG. 15, a slot  124  extends part way through the bit holder  120  between the mounting portion  121  and the bit mounting surface  122  to provide for failure of the bit holder from the bottom end of slot  124  through to the opposing side  125  of the bit holder, if the bit  21  (not shown) should encounter a hard discontinuity. Failure of the bit holder  120  at the slot  124  will save the expensive bit holder mounting configuration and allow the replacement of inexpensive bit holder. 
     Improvements in bit holders and bit holder/blocks have been shown that provide for rotating the bit and bit holder in a bit block and mounting the holder in the block in a superior and more secure manner, ease of removability of bits from bit holders and for providing for the engineered failure of parts of less expensive parts of the bit, bit holder, bit block combination if the bit should encounter a hard discontinuity while working. 
     While seven embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the true spirit and scope of the present invention. It is the intent of the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.