Abstract:
A quick change type bit/bit holder includes several different structures for holding the item in a bit block without the necessity of a fastener. The bit portion of the bit/bit holder combination includes a ductile steel insert with a polycrystalline diamond coated tungsten carbide bit positioned therein. The ductility of the steel insert acts as a shock absorber to allow the bit to successfully remove concrete as well as asphalt in a road milling machine.

Description:
This application claims priority to and is a continuation-in-part of provisional patent application Ser. No. 61/716243 filed Oct. 19, 2012, and claims priority to and is a divisional of non-provisional application Ser. No. 13/801,012 filed Mar. 13, 2013 to the extent allowed by law. 
    
    
     This invention relates generally to an integrally formed road milling bit and bit holders for mounting on road milling and other machines and, more particularly, to combinations of bit and bit holders having a polycrystalline diamond cutting tools as a forward leading tip of each. 
     BACKGROUND OF THE INVENTION 
     Originally, road milling equipment was utilized to smooth out bumps in the surface of a roadway or grind down the joinder of two adjacent concrete slabs that may have buckled. However, later these road milling machines, operated with a cylindrical drum having a plurality of bit blocks mounted thereon in herringbone or spiral fashion, and bit holders with bits on top thereof in turn mounted on the bit blocks, have been utilized for completely degrading concrete and macadam roads down to their gravel base. The apparatus can also be used for trenching and mining operations. 
     Bits such as those shown in U.S. Pat. No. 6,739,327 disclose an insert having a conical cutting tip that is mounted in a recess in a frustoconical forward portion of the bit. The insert  88  is surrounded by a hardened annular collar that provides added wear resistance to the cutting tool. The tool has a solid generally cylindrical shank extending axially rearwardly from the body portion. 
     The bit as described in the U.S. Pat. No. 6,739,327 patent fits in a central bore in a bit holder as described in U.S. Pat. Nos. 6,371,567 and 6,585,326. The above-described bit holders, being frictionally seated in bores in their respective bit blocks mounted on drums, and not held therein by retaining clips or threaded nuts provide for ease of removal and replacement when the bit holders are worn through use, or broken because of the harsh road degrading environment they are used in. 
     Additionally, it has been found that because of the harsh use environment, individual bits may wear or be broken off of their shanks and need replacement. Historically, these bits and bit holders have been made of steel with hardened tungsten carbide tips or collars to lengthen their end use service time. 
     Recently, the use of materials harder than tungsten carbide, i.e., polycrystalline diamond, such as shown in U.S. Pat. No. 8,118,371 has been used in certain road milling operations, notably the degradation of asphalt layers on long roadway stretches. While the hardness of the polycrystalline diamond tip lengthens the useful life of the combined bit and bit holder shown in the &#39;371 patent, such that the bit does not have to be removable from the bit holder, the combination includes a somewhat brittle polycrystalline diamond tip that is not suitable for use in degrading concrete highways, or curved highway stretches such as cloverleafs and the like. 
     A need has developed for the provision of a polycrystalline diamond structured combination bit and bit holder that is sturdy enough to withstand the forces found when degrading or breaking up the surfaces of not only macadam (asphalt) roadways but also concrete roadways. 
     SUMMARY OF THE INVENTION 
     The invention resides a bit holder for road milling machinery, a shank comprising an elongate generally cylindrical member having a distal end including an annular axially inwardly extending groove therein defining an interior surface of an annular outer side wall between about ⅛ and ½ inch in thickness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention may best be understood from the following detailed description of a currently preferred embodiment and modifications thereof taken in conjunction with the accompanying drawings wherein like numerals refer to like parts, and in which: 
         FIG. 1  is a front ¼ perspective view of a first embodiment combination bit and bit holder including a conical polycrystalline diamond tip thereof constructed in accordance with the present invention; 
         FIG. 2  is a front elevational view of the combination bit and bit holder shown in  FIG. 1 ; 
         FIG. 3  is a side elevational view of the combination bit and bit holder shown in  FIG. 1 ; 
         FIG. 4  is a front ¼ elevational perspective view of a modification of the first embodiment of a combination bit and bit holder showing a flat top cylindrical polycrystalline diamond tip and constructed in accordance with the present invention; 
         FIG. 5  is a front elevational view of the modification of the first embodiment of the combination bit and bit holder shown in  FIG. 4 ; 
         FIG. 6  is a side elevational view of the modification of the first embodiment of the combination bit and bit holder shown in  FIG. 4 ; 
         FIG. 7 a    is a ¾ top perspective view of a second embodiment of the combination bit and bit holder constructed in accordance with the present invention showing a trepanned shank distal end having 3 longitudinal spaced slots therein; 
         FIG. 7 b    is a ¾ bottom perspective view of the second embodiment of the present invention showing the longitudinally slotted trepanned shank thereon; 
         FIG. 8 a    is a side elevational view of the second embodiment of the present invention shown in  FIGS. 7 a    and  7   b;    
         FIG. 8 b    is a bottom plan view of the second embodiment shown in  FIG. 8 ; 
         FIG. 9 a    is a bottom ¾ perspective view of a third embodiment of the present invention showing a trepanned shank constructed in accordance with the present invention; 
         FIG. 9 b    is a side elevational view of the third embodiment of the present invention shown in  FIG. 9   a;    
         FIG. 10  is a side elevational view of a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1-6 , a first embodiment of a bit holder  10  and a first modification of a bit holder  12  of the present invention are shown in perspective view in  FIGS. 1 and 4 , respectively. The invention resides in a unitary bit and bit holder construction that includes a bit holder body  13 , generally constructed in accordance with the teachings of U.S. Pat. No. 6,585,326, and a generally cylindrical hollow shank  14  which in this embodiment of one side thereof has an elongate first slot  15  extending from a generally annular distal end  20  of the shank  14  axially upward or forward to an upper termination  16  adjacent the upper or forward end of the shank  14 . In this embodiment, the shank  14  also includes a internally oriented second slot  17  180 degrees around the annular shank  14  from the first slot  15 . This second slot  17 , first disclosed in U.S. Pat. No. 6,685,273, is parallel to the first slot  15  and is an internal slot having a rearward semicircular termination  18  inwardly adjacent the distal end  20  of the shank  14  and a forward semicircular termination  22  generally coinciding longitudinally and axially with the upper termination  16  of the first slot  15 . 
     In this first embodiment, the shank  14  preferably includes a lower or first tapered portion  23  running axially from a stepped shoulder  24  adjacent the distal end  20  of the shank  14  upwardly or axially from the top or front of the shank  14  where it terminates generally mid slot longitudinally, and includes an annular shoulder  25  separating this lower tapered portion  23  from an upper or second tapered portion  26  which extends from that shoulder  25  generally to the top of the shank  14  or forward terminations of the slots. From a position adjacent the top or upper termination of the slots, a generally cylindrical upper portion  27  of the shank  14  extends towards a generally annular back flange  28  denoting the base of the bit holder body  13  of the bit holder  10 . 
     In the preferred first embodiment of bit holder  10 , this generally annular flange  28  includes a pair of horizontal slots  30 - 30  generally perpendicular to the longitudinal axis of the combination bit/bit holder, one on either side of the generally annular flange  28  into which bifurcated fork tines may be inserted between the base of the body portion of the bit holder and a bit block (not shown) into which the shank of the bit/bit holder combination is inserted and retained by outward radial force in use. 
     An enlarged upper body  32  of the bit holder body  13  of the bit/bit holder combination  10  includes a generally cylindrical base  33 , termed in the trade ad a tire portion, having a cylindrical side wall extending upwardly approximately ½ inch to a generally frustoconical, but in this embodiment a convex surfaced upper body  32 , which is a solid structure. 
     In this first preferred embodiment, a central bore  34  longitudinally and axially through the shank  14  of the bit holder body  13  of the bit/bit holder combination  10  terminates  35  approximately at the upper end of the shank  14 . This allows the generally C-shaped annular side wall of the shank  14  to radially contract when the shank  14  is mounted in one of a tapered or cylindrical bore in a bit block (not shown). 
     In this first preferred embodiment, the bit holder body  13  of the bit/bit holder combination  10  provides added bulk and strength to the entire unitary assembly which allows the bit/bit holder combination  10  of the present invention to withstand substantial forces and stress superior to heretofore known bit holders or bit/bit holder combinations. The present invention may be utilized not only in the degrading and removal of macadam or asphalt from long straight stretches of roadway, but may also provide for the removal of concrete and other materials both in straight long stretches and in curved sections such as at corners, cloverleaf intersections, or the like. Also the flat top design is less expensive to make and is a readily available part stocked by many suppliers. 
     Adjacent the top of the preferred first embodiment of the present invention shown in  FIGS. 1-6 , the generally convex sided bit holder body  13  has a generally flat annular top surface  36  therearound positioned perpendicular to the axis of the bit holder from the interior of which axially extends a smaller radially oriented annular tapered upper or forward extension  37 . Around this tapered upper extension  37  is fitted an annular tungsten carbide ring  38  which may preferably be braised into unitary construction with the remainder of the bit holder. The top or forwardmost portion of the tungsten carbide ring  38  and the annular tapered upper extension  37  of the upper body portion terminate generally at the top of the bit holder body  13  of the combination bit/bit holder  10 . 
     With the bit holder body  13  of the present invention preferably made of  4340  or equivalent steel, the top of the upper extension  37  of the upper body  32  includes a generally radially declining tapered bore  40  extending from the co-terminal upper wall of the body axially inwardly thereof which defines a declining radial taper. This tapered bore  40  extends a short distance longitudinally axially inwardly of the annular extension  37  that defines the base for the tungsten carbide protective ring  38 . 
     This declining taper bore  40  provides a space for receiving a complementary shaped positive declining tapered outer surface of a solid base insert  42  for the bit/bit holder combination. The base insert  42  can be made of solid steel or tungsten carbide. The base insert  42  also extends upwardly and outwardly axially longitudinally from the co-terminal annular tapered upper extension  37  of the bit holder body  13  and includes an upper annular ring portion made of a protective material, which in this embodiment is made of tungsten carbide. 
     This top portion of the bit base insert  42  includes a generally cylindrical bore  44  positioned centrally therein into which a base  45  of the bit tip may be positioned and braised therein to provide a unitary structure. This base  45  may be made of steel or tungsten carbide and includes at the outer or upper end thereof a tip  46  which is preferably made of polycrystalline diamond structure which, in this embodiment, may be frustoconical in shape  47 , sown in  FIGS. 1-3 , or a flat generally cylindrical puck shape  48 , as shown in the first modification in  FIGS. 4-6 . 
     The conical tip  46  shown in  FIGS. 1-3  is of the type which has been used in degrading straight long stretches of asphalt or macadam, and which is sufficiently brittle not to be used in more strenuous applications such as degrading concrete and degrading curved sections of highway surface construction. 
     The flat generally cylindrical puck shaped tip  48  of the bit of the first modification of the bit holder  12  shown in  FIGS. 4-6  provides a substantially stronger tip that is able to withstand the added forces and peak jolts found in degrading concrete and the like, and together with the added bulk of the bit holder body  13  of the preferred bit/bit holder combination is capable of removing or degrading concrete surfaces with the added life expectancy shown in prior bit/bit holder constructions with polycrystalline diamond (PCD) tips that have heretofore been utilized only in removing long straight stretches of macadam. The steel member  41  holding the puck is an impact absorbing member that can stretch and compress without fracturing. A road milling machine can travel faster with forward speed using the instant bit/bit holders than it can with bit holders having a strictly tungsten carbide forward end. The remainder of the first modification is identical to the first embodiment. 
     A second embodiment of a bit holder  50  of the preferred invention, shown in  FIGS. 7 a , 7 b , 8 a  and 8 b   , includes a bit  51 , tip  52  and bit holder body  53  that is similar to that shown in  FIGS. 4-6 . A shank  54  of the bit/bit holder combination  50  provides an important aspect of the present invention. In the second embodiment of bit holder  50 , the outer surface of a side wall  54   a  of the shank  54  is substantially similar to that shown in  FIGS. 1-6 , with the exception that the a distal first tapered portion  62  of the shank  54  includes three evenly spaced slots  65 ,  66 ,  67  longitudinally formed axially through the side wall  54   a . It should be noted that the first tapered portion  62  may be constructed with either a slight taper of one degree or less or down to a cylindrical (no-taper) configuration. The second embodiment may include more or fewer slots. 
     In this second embodiment, not only is the generally frustoconical, convex side wall of the bit holder body  53  solid in construction, with the exception of a bore  56  for mounting the bit  51  at a forward end  57  thereof, the shank  54  that extends from a generally annular flange  58  of the bit holder body  53  is also largely solid in construction. Similar to the first embodiment of bit holder  10 , the upper or forward portion of the shank  54 , adjacent the generally annular flange  58  of the body portion, includes a cylindrical portion which has a second tapered portion  60  extending axially from the border thereof and a shoulder portion  61  that extends radially outwardly of the base of the second tapered portion  60  that defines the top of the first tapered portion  62  which extends axially to a distal end  63  of the shank  54 . 
     As indicated previously, this first tapered portion  62  may include a taper of about 1 degree or less, down to having a cylindrical outer surface. Whereas the shank in the first embodiment shown in  FIGS. 1-6  was hollow at its center, the shank  54  of the second embodiment is solid at its center core  64  completely from the bit holder body  53  to a distal end  63  of the shank  54 . The first tapered portion  62 , which in this embodiment includes three equally spatially circumferentially related longitudinal slots  65 ,  66 ,  67 , defines a generally annular ring with the exception of the equally spaced slots  65 ,  66 ,  67 . This slightly radially inwardly deformable first tapered portion  62  has an inner annular surface  68  defined by a trepanned or hole saw type groove  69  extending inwardly of the shank  54  from the distal end  63  to the top of the first tapered portion  62 . The depth of the trepanned groove  69  may by varied to obtain the proper preformability of the sidewall and the number of slots may be varied depending on the design parameters desired. 
     This annular trepanned groove  69  is formed to provide a side wall for the first tapered portion  62  having a thickness which may vary from about ⅛ inch to about ½ inch depending upon the desired elastic flexibility of the side wall of the first tapered portion  62 . 
     In construction, the trepanned groove  69  is a less expensive forming operation than is the bore  34  found in the first embodiment of bit holder  10  of  FIGS. 1-6 , although the center portion of the shank may be removed if desired. Additionally, the trepanned groove  69  leaves the center core  64  of the shank  54  intact in the preferred second embodiment to provide a stronger overall construction for the combination bit/bit holder  50 . Further, with the additional mass of the bit holder portion of the bit/bit holder combination, the entire bit holder may be made of less expensive steel than is necessary for the first embodiment of bit holder  10  shown in  FIGS. 1-6 . Generally, steels of the type  4140  may be utilized for construction of the second embodiment of the present invention. 
       FIGS. 9 a  and 9 b    show the third embodiment of bit holder  70  of the present invention which has a combined bit  71  and an upper body  72  of the holder portion being identical to that shown in  FIGS. 7 a , 7 b , 8 a  and 8 b   . The difference between the third embodiment of bit holder  70  and the second embodiment of bit holder  50  is in the trepanned first tapered portion of the shank  73 , and slots shown in the second embodiment. Similar to the second embodiment of bit holder  50 , the third embodiment of bit holder  70  includes an annular trepanned groove  74  that extends axially inwardly in a first tapered portion  75  of the shank  73  from a distal end  76  of the shank  73  generally to the shoulder at a top  77  of the first tapered portion  75 . 
     The difference between the second embodiment and the third embodiment is that the third embodiment does not include the slots shown in the second embodiment. The thickness of the outer side wall of the annular first tapered portion  75  (which may also be cylindrical) will be thinner than that disclosed in the second embodiment of bit holder  50  shown in  FIGS. 7 a , 7 b , 8 a  and 8 b    and may be on the order of 1/16 to ¼ inch wall thickness for the embodiment shown in  FIGS. 9 a  and 9 b   , having a nominal 1-½ inch outer diameter. As a result, while the typical interference fit for severe or extreme uses such as concrete degradation might have a solid shank interference of 0.001 to 0.003 of an inch thickness for the nominal 1-½ inch diameter shank, the interference fit for the thin side wall in the trepanned first tapered portion  75  of the shank in the third embodiment of bit holder  70  would approximate two to four times the previously mentioned interference fit. 
     With such a fit, the shank side wall may wrinkle when a shank is inserted in a bit block bore. Again, the third embodiment of bit holder  70  shown in  FIGS. 9 a  and 9 b    would be less expensive to manufacture than even the second embodiment of bit holder  50  shown in  FIGS. 7 a , 7 b , 8 a  and 8 b   . In this third embodiment of bit holder  70 , the core or central portion  78  of the shank may be left intact, or removed, and the combination of that mass in the shank together with the solid upper body and integrally formed bit  71  braised thereon provides a structure which can be utilized to degrade not only macadam or asphalt but also concrete pavement. 
     The use of the flat puck shaped polycrystalline bit tip, the bit/bit holder combination provides added use life for the structure and sturdiness thereof which would be superior to the bit and bit holder combinations heretofore known. The shorter use life for a tungsten carbide tipped bit has resulted in a design necessity of allowing the bit to be removed and replaced numerous times prior to replacing the bit holder. 
     Referring to  FIG. 10 , a fourth embodiment of bit holder  90  of the present invention is similar to the prior embodiments disclosed herein with 2 differences. First, in order to provide superior brazing of the tungsten carbide ring to the forward end of the bit holder, a forwardly extending annular collar  91  is created on the bit holder body  92  to provide an annular trough  93  onto which the annular ring  94  is mounted. The vertical outer wall of the trough  93  will keep brazing material from flowing outwardly of the joinder between the base of the ring  94  and the annular flange on which the ring  94  is positioned. After the brazing is complete, the outer portion of the trough may be left as is, or may be removed and generally conformed to a shape similar to that shown in  FIGS. 1-6 . 
     The second difference between the fourth embodiment of bit holder  90  and the preceding embodiments is an annular cylindrical outer wall portion  96  adjacent the top of to first tapered portion  98  of the shank  97 . When it has been determined that the design parameters for the outward forces at the shank first tapered portion  98  have been met utilizing less than the whole available surface area, an annular cylindrical area  100  may be formed adjacent the upper end of the first tapered portion  98  that keeps that area from contacting the bit block bore. The axial width of the cylindrical band may be varied to meet design criteria. 
     While the invention herein has been shown in three embodiments, and a modification of the first embodiment, it will be understood by those skilled in the art that changes and modifications may be made within the aspect of the present invention 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.