Patent Publication Number: US-6702393-B2

Title: Rotatable cutting bit and retainer sleeve therefor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates primarily to the retention of mining, trenching and construction tools or bits which are comprised of a hardened steel body with a hard tip and which are retained by a hardened steel retainer sleeve. These tools are mounted to drums, chains and wheels in various orientations and quantity. The bit is then engaged in soft rock formations ranging from asphalt to sandstone. The hard tip fixed to the end of the tool directly engages the material being mined or cut. 
     Typically the retainer sleeve retains the tool axially while allowing free rotation of the tool during service, as disclosed for example in Hedlund et al., U.S. Pat. No. 4,921,310. 
     For example, as shown in accompanying FIG. 1, a retainer sleeve  10  is disclosed for retaining a rotary tool  14  in a bore  16  of a holder  18 . The sleeve includes tongues  20  that are deformed radially inwardly from a cylindrical portion  22  of the sleeve to engage in an annular groove  24  of the tool. The cylindrical portion  22  continues rearwardly past the tongues  20  and is situated between the outer periphery of a rear flange  26  of the tool and a wall  28  of the bore in order to prevent the flange from contacting the bore wall. The inner diameter of the retainer sleeve is larger than the outer diameter of the tool, to ensure that the tool can freely rotate relative to the stationary retainer sleeve. 
     It has been discovered that during cutting operations, especially the cutting of gummy materials, such as hot asphalt, fines such as dirt and cuttings can become trapped and packed within the annular groove  24 , thereby filling the gap and opposing free rotation of the tool. As a result, a wear flat will develop on the hard tip of the tool progressing down onto the steel body. After developing a wear flat, the tool rotation generally stops, whereby the remaining useful tool life is lost. 
     Another prior art arrangement described in the Hedlund et al. patent is depicted in accompanying FIG.  2 . In that arrangement, the entire rear edge portion of a cylindrical retainer sleeve  32  is bent inwardly to form a flange  30  which is inclined in an axially rearward, radially inward direction and is received in an annular groove  34  of a tool  36 . It will be appreciated that an inward bending of the entire rear portion of the sleeve causes the material of the sleeve to bulge radially outwardly at the annular junction between the cylindrical portion  38  of the sleeve and the bent portion  30 . That protrusion becomes squeezed between the bore wall and the tool when the tool/sleeve assembly is forced into the bore, thereby applying considerable friction against the tool tending to resist free rotation thereof. Also, since the flange extends continuously in the circumferential direction there is less ability for fines trapped between the flange  30  and a front surface of the groove  34  to escape rearwardly. 
     One additional prior art arrangement is disclosed in German Patent Document 3712 427 and depicted in the accompanying FIG.  3 . In that arrangement, a rear portion of a retainer sleeve  42  is deformed to form tongues  40  that are bent radially inwardly into an annular groove  44  of a tool  46 . The deformation step for producing each tongue is performed after a short sleeve-weakening slit has been formed in a cylindrical portion of the sleeve, the slit extending in the circumferential direction. The slits associated with respective tongues are spaced apart from one another in the circumferential direction. Each tongue thus forms a shoulder  48  extending perpendicular to the center axis of the sleeve. That shoulder extends parallel to an opposing front surface  50  of the annular groove  44  to form a gap therebetween from which fines have difficulty exiting, and can result in the above-mentioned opposition to tool rotation. 
     It is, therefore, an object of the present invention to provide a tool/sleeve assembly which facilitates free rotation of a tool and minimizes a tendency for fines to become packed in a manner preventing such free rotation. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a cutting assembly which comprises a holder, a cutting tool body, and a retainer sleeve. The holder includes a bore having a cylindrical bore wall of a first diameter. The cutting tool body defines a longitudinal center axis and includes a front head, a shank, a rear flange, and an annular groove. The front head has a cutting tip, and the shank extends rearwardly from the front head and into the bore. The shank includes an outer cylindrical surface of a second diameter smaller than the first diameter. The rear flange is disposed at a rear end of the shank and is situated within the bore. The rear flange includes an outer cylindrical surface of a third diameter no greater than the second diameter. An annular radial gap is formed between the bore wall and the outer cylindrical surface of the rear flange. The annular groove is formed in the outer cylindrical surface of the shank immediately in front of the rear flange. The groove includes a forwardly facing stop surface. The retainer sleeve retains the tool body axially within the bore while permitting the tool body to rotate freely about the axis. The retainer sleeve includes a cylindrical portion which is slit longitudinally in half and situated radially between the outer surface of the shank and the bore wall. The cylindrical portion is elastically compressed radially by engagement with the bore wall to tightly engage the bore wall. An inner surface of the radially inwardly compressed cylindrical portion has a fourth diameter greater than the second diameter. The retainer sleeve includes circumferentially spaced tongues bent inwardly from the cylindrical portion and extending into the groove to axially retain the tool body in the bore, while permitting the tool body to rotate freely about the axis. Each tongue is inclined in a direction axially rearwardly and radially inwardly from the cylindrical portion, to form an oblique angle with the axis. A longitudinal length of the retainer sleeve is dimensioned such that when the tool is rearwardly pressured during a cutting operation, the tongues are essentially out of continuous contact with the surfaces of the groove, and a rear edge of the cylindrical portion and rear edges of the tongues are spaced forwardly from the forwardly facing stop surface. 
     The invention also pertains to a cutter tool assembly comprising the body and the retainer sleeve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof in connection with the accompanying drawings in which like numerals designate like elements and in which: 
     FIG. 1 is a longitudinal sectional view of a first conventional cutting assembly: 
     FIG. 2 is a longitudinal sectional view of a second conventional cutting assembly; 
     FIG. 3 is a longitudinal sectional view of a third conventional cutting assembly; 
     FIG. 4 is a longitudinal sectional view of a cutting assembly according to the present invention; 
     FIG. 5 is a front end view (i.e., taken from the left in FIG. 6) of a retainer sleeve according to the present invention, in a relaxed state; 
     FIG. 6 is a side elevational view of the retainer sleeve of FIG. 5; 
     FIG. 7 is an enlarged fragmentary longitudinal sectional view taken through a tongue portion of the retainer sleeve; 
     FIG. 8 is a side elevational view of the tongue portion shown in FIG. 7; and 
     FIG. 9 is a rear end view of the tongue portion shown in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
     Depicted in FIG. 4 is a tool holder  40  adapted to be mounted, e.g. bolted or welded, to a vehicle (not shown), and a cutting tool or bit  42  mounted in the holder. There would normally be a plurality of holders  40  and bits  42  mounted on a carrier, such as a rotary drum disposed on the vehicle. 
     The holder can be formed of steel and includes a cylindrical bore  44  extending through a front face  46  of the holder. The bore  44  has a front bevel  48  at the front face  46  (the bevel preferably being about 40-50 degrees). 
     The tool  42  includes a body formed for example of hardened steel, the body including a front head  50 . A hard cutting tip  52  (e.g., formed of cemented carbide) is mounted in a front end of the head  50 . The body defines a longitudinal center axis A. 
     The head  50  includes a front annular flange  54  of larger diameter than both the cutting tip  52  and the bore  44 . The body further includes a shank  56  extending rearwardly from the head  53 , the shank  56  having a smaller diameter than the bore  44 . 
     The body further includes a rear cylindrical flange  58  situated at a rear end of the shank  56  and having a diameter no greater than (preferably equal to) that of the shank. Thus, an annular radial gap  59  is formed between an outer cylindrical surface of the rear flange and the cylindrical wall of the bore  44 . A rear end  61  of the flange  58  is chamfered to facilitate entry into the bore. 
     The shank includes an annular groove  60  formed therein immediately in front of the rear flange. That groove  60  includes a bottom surface  65 , a forwardly facing surface  62  and an opposing rearwardly facing surface  63 . The rearwardly facing surface  63  is inclined in a direction extending axially rearwardly and radially inwardly, thereby promoting the rearward travel of fines that engage the surface  63 . The forwardly facing surface  62  defines a rear stop surface. 
     A retainer sleeve  70  formed preferably of hardened steel is disposed radially between the shank  56  and the cylindrical wall of the bore  44 . The retainer sleeve includes a cylindrical portion  72  which has a chamfer  73  at its rear end edge and includes a longitudinal slit  75 . In a relaxed state, the cylindrical portion has an outer diameter larger than that of the bore  44 . Thus, after being radially compressed and positioned in the bore, the cylindrical portion attempts to rebound outwardly and makes tight contact with the bore wall, while the inner diameter of the compressed cylindrical portion  72  remains greater than the diameter of the shank  56  to minimize any obstruction to free rotation of the tool. 
     The retainer sleeve  70  includes circumferentially spaced tongues  74  bent in a direction extending axially rearwardly and radially inwardly from the cylindrical portion along the rear end edge thereof and extending into the groove  60 . Each tongue thus forms an oblique angle α with the axis A. Thus, in response to forward axial movement of the tool  42  relative to the bore, the tongues are abuttable with the rear stop surface  62  of the groove  60  to axially retain the tool in the bore. The direction of bending B of each tongue  74  includes two faces  74   a ,  74   b  converging inwardly from the outer cylindrical surface of the portion  73  of the sleeve, wherein each tongue is V-shaped as viewed along the axis A (see FIGS.  5  and  9 ). The two faces  74   a ,  74   b  intersect along a line  100  which is inclined in a direction axially rearwardly and radially inwardly from the cylindrical portion to form the oblique angle α with the axis A as viewed in a direction perpendicular to the axis (i.e. as viewed in FIG.  7 ). During a cutting operation, when the tool  42  is pressed rearwardly, the tongues  74  are, for the most part, spaced from all surfaces  62 ,  63  and  65  of the groove  60 , to enable the tool to freely rotate about its center axis. Due to being inclined axially rearwardly and radially inwardly, the tongues are less obstructive to the rearward travel of fines attempting to escape from between the tongue and the rearwardly facing surface  63  of the groove, as compared to tongues that are oriented perpendicularly to the axis A. 
     There are preferably four tongues  74 , that are spaced circumferentially apart by an angle ∞ of preferably 86 degrees, except for the two tongues that are separated by the longitudinal slit  75 ; the two latter tongues would be separated by an angle of preferably 102 degrees. It will be appreciated that more or fewer tongues could be provided, and at a different angular spacing. 
     A longitudinal length L of the retainer sleeve  70  is dimensioned such that a rear edge  76  of the cylindrical portion and rear edges  78  of the tongues are spaced forwardly from the rear stop surface  62  when the tool is pushed rearwardly during a cutting operation. In particular, the body of the tool forms a rearwardly facing shoulder  80  (see FIG. 4) at a front end of the shank, the shoulder  80  opposing a front edge  82  of the cylindrical portion  72  of the retainer sleeve. A dimension L′ between the rear stop surfaces  62  and the shoulder  80  is longer than the longitudinal length L of the retainer sleeve. 
     Since the diameter of the rear flange  58  is no greater than the diameter of the shank  56 , the radial gap  59  permits the rearward passage of fines exiting the groove  60 . The exiting of fines from the groove  60  is possible since the rear edges  76 ,  78  of the cylindrical portion  72  and the tongues  74  are spaced forwardly from the rear flange  58  during a cutting operation. 
     Installation of the tool  42  is performed in a conventional manner by first inserting the retainer sleeve  70  onto the shank  56 , with the tongues  74  disposed in the groove  60 . Then, the rear flange  58  of the tool is inserted into the bore  44 . That is, the chamfered rear flange  58  is able to easily enter the bore since it is not covered by the retainer sleeve, and thus functions as a guide or locator to properly position the tool. Thereafter, the tool/sleeve unit is hammered into the bore manually by an operator. In so doing, the cylindrical portion  72  of the retainer sleeve becomes radially compressed, whereupon the cylindrical portion is elastically biased outwardly into firm contact with the bore wall while remaining in loose engagement with the tool shank. The tongues  74  remain disposed within the annular groove  60  to prevent the bit form becoming accidentally dislodged axially from the bore. 
     A conical washer  90 , commonly known as a Belleville washer, is disposed between the tool shoulder and the holder face to aid in keeping fines such as dirt and cuttings from reaching the bore during a cutting operation, as described in detail in U.S. Pat. No. 6,113,195. 
     During a cutting operation, the tool  42  is pressed rearwardly, and the tongues  74  are out of contact with all surfaces of the groove  60 . The tool  42  is free to be rotated by forces applied to the cutting tip by the material being cut, whereby the tool is self-sharpening and wears evenly. Fines may find their way into the groove  60  during the cutting operation. However, instead of becoming packed in the groove and thereby impeding free rotation of the tool, the fines are able to pass rearwardly past the bit since: (i) the cylindrical portion  72  and the tongues  74  stop short of the rear stop surface  62 , (ii) the rear flange  58  forms an open radial gap with the bore wall, and (iii) the tongues  74  and the rearwardly facing surface  63  of the groove  60  are inclined axially rearwardly and radially inwardly. Thus, the inclined nature of the tongues  74  and the rearwardly facing surface  63  promotes a rearward migration of the fines. Those fines are able to pass radially outwardly from the groove  60  between the stop surface  62  and the rear end of the cylindrical portion  72 , and then axially rearwardly through the radial gap formed between the rear flange  58  and the bore wall. It has also been found that the rear flange  58  will not contact the bore wall, due to the presence of the cylindrical portion  72 , which restricts the extent to which the bit can become skewed relative to the axis A. 
     It will be appreciated that the cutting forces are not applied to the tool in a direction that is exactly aligned with the center axis of the tool. Rather, the forces are inclined somewhat relative to the axis. Thus, the forces cause the shank  56  to become slightly skewed within the bore  44 . Thus, each tongue may become intermittently contacted by a surface of the groove  60 . However, the contact at any given tongue will not be continuous, thereby enabling fines to migrate out of the groove. 
     It will be appreciated that the retainer sleeve according to the present invention retains the advantages of prior art retainers in that the tool is held in the bore, and is able to freely rotate without the rear flange  58  coming into direct contact with the bore wall. In addition, however, the tendency for fines to become packed in the annular groove of the tool and hamper free rotation of the tool is minimized. Also, since the rear flange  58  is uncovered by the retainer sleeve, the rear flange can freely enter the bore during a tool installation procedure, and thereby act to locate the tool relative to the bore. In addition, less material is needed to manufacture the retainer sleeve, due to its longitudinally shortened nature. 
     Although the present invention has been described in connection with a preferred embodiment thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.