Abstract:
A rotatable cutting insert of improved geometry having a shank depending from a head portion and having a hard insert mounted therein, includes an insert having a conically shaped tip section, a base section contiguous with a first intermediate section, a second intermediate section contiguous with both tip and first intermediate section, and where the diameter of the second intermediate section is equal to the maximum diameter of the tip but is smaller than the diameter of the base section.

Description:
This is a continuation of co-pending application serial no. 756,210 filed on 7/18/85 now U.S. Pat. No. 4,725,099. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a rotatable cutting bit of the type having an improved head portion and depending shank. 
     BACKGROUND OF INVENTION 
     Bits that are used in mining and for removing road surfaces are typically mounted in a machine having a power driven cutting wheel. 
     When employed on abusive material such as concrete, the attack bits encounter high pressures and undergo excessive steel wear around the tip section. Currently employed conically shaped tips not only experience degrees of blunting, thereby reducing machines speed, but also suffer from the presence of manufacturing flaws which can lead to total bit failure. 
     One example of commercially successful bits is described in U.S. Pat. No. 4,497,520, issued on Feb. 5, 1985 to Ojanen and assigned to the same assignee as the present invention. The patent discloses and claims a rotatable cutting bit where the head portion consists of a base section, a conical tip section with a maximum diameter, and an intermediate section contiguous with the base and tip sections. Under manufacturing conditions the dies used in forming these bits experience wear at the point of maximum tip diameter (the seam) resulting in unwanted accumulation of uncompressed carbide material (flashing). Commonly known methods of polishing, such as mechanical tumbling, remove the flashing but generate stress cracks along the same thereby increasing the likelihood of bit failure. 
     As a consequence of the commercial success of assignees Patent No. 4,497,520, consideration has now been given to improvements in construction relative to methods of manufacture for such tooling for better quality and control in production volumes. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided, a rotatable cutting bit comprising a head portion, a shank portion depending from said head portion along a longitudinal axis, said head portion having a socket at the forward end, a hard insert having coaxially aligned and integral sections, said sections comprising a base section, a tip section, a first intermediate section contiguous with said base, a second intermediate section of uniform diameter contiguous with said first intermediate and tip sections, said base being fixedly mounted in said socket and having a first diameter, said tip section being conically shaped and having a maximum second diameter, said first intermediate section having a maximum third diameter, said second intermediate section having a fourth diameter equal to said second diameter, said second and third diameters each being less than said first diameter, said first intermediate section at said base forming a fillet at the junction thereof whereby said base forms a shoulder with said first intermediate section. 
     The present invention alleviates the disadvantages of premature blunting and the formation of manufacturing flaws by providing a small diameter tip and by providing an adjoining cylindrical intermediate section. In production, the tip end plunger completes its compression stroke on a vertical section of the die rather than on the angular seam section of the prior art, thereby reducing die wear and the associated problems of flashing accumulation and stress crack formation. 
    
    
     DRAWINGS 
     FIG. 1 is a partially sectioned view of a bit mounted in block. 
     FIG. 2 is a side view of a tip; 
     FIG. 3 is an end view of a tip; and 
     FIG. 4 is a cut-out side view of the fillet section joining the first intermediate section and the base section. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, FIG. 1 shows a rotatable bit  11  having a head portion  13  and a depending shank portion  15 . The head portion  13  and shank  15  are coaxially aligned with the head  13  having an enlarged section  17  which prevents the head  13  from being forced into the opening in the mounting block  19 . The shank portion  15  which is a cylindrical configuration includes a sleeve  21  which is radially contracted when present in the opening so as to hold the bit  11  in the block  19 . 
     A hard insert  23  typically made of a carbide material is fixedly secured to the forward end of the head  13 . Preferably the base section  25  of the insert  23  is positioned in the socket and brazed in such a manner that the braze flows over and around the base section  25 . 
     In accordance with the principals of the present invention, the insert  23  includes a plurality of sections coaxially aligned with the head  13  and shank  15  of the bit  11 . The sections include a base section  25 , a tip section  27 , a first intermediate section  29  contiguous to both the base  25  and a second intermediate section  28 , and a tip section  27  contiguous with the second intermediate section  28 . 
     The tip section  27  tapers outwardly at an included angle “c” of from about 83 degrees to about 93 degrees. Preferably the angle is about 88 degrees. The point portion of the tip may be rounded to promote even wearing. Preferably the tip  27  extends downwardly in an axial direction toward the base  25  a distance of from about 0.12 to about 0.18 inches. The maximum diameter of the tip  27  is from about 0.36 to about 0.44 inches, and most preferably about 0.40 inches. 
     The second intermediate section  28  extends downwardly from the junction with tip  27  or forwardly from the junction with the first intermediate section  29  along a longitudinal direction a distance of about 0.02 to about 0.05 inches and most preferably about 0.03 inches. The second intermediate section  28  is cylindrical in shape and exhibits a uniform diameter equal to the maximum diameter of the tip  27 . 
     The first intermediate section  29  extends downwardly from the juncture with the second intermediate section  28  or forwardly from the juncture with the base  25  along a longitudinal direction a distance of about 0.22 to about 0.28 inches. Preferably the first intermediate section  29  has a frusto-conical shape and tapers outwardly to the base section  25  at an included angle “d” of from about  17  to about  23  degrees. The taper is outwardly from the junction with the second intermediate section  28  to the junction with the base  25 . The first intermediate section  29  has a maximum diameter less than the diameter of the base  25 . 
     The base section  25  preferably has a diameter of from about 0.60 to about 0.66 and most preferably about 0.63. The extension of the base  25  in the axial direction or the height of the base is from about 0.05 to about 0.11 inches preferably about 0.08. As illustrated in FIG.  3  and FIG. 4, a fillet  30  may be utilized to give a smooth transition from the base  25  to the first intermediate section  29  whereby the base  25  forms a shoulder with the first intermediate section  29 . The transition is in the form of an arc of radius between about 0.15 inches and about 0.25 inches which sweeps out a distance starting from the base section  25  forwardly to a diameter in the first intermediate section  24  of between about 0.54 to about 0.60 inches and preferably about 0.60. A more severe transition between the first intermediate section  29  and the base  25  often results in the formation of stress cracks along the fillet thereby increasing the likelihood of bit failure. 
     The total axial length of the hard insert is the sum of the axial lengths of the tip section (   0 . 12  inches to  0 . 18  inches ) , the second intermediate section  (   0 . 02  inches to  0 . 05  inches ) ( which is a fifth distance ) , the first intermediate section  (   0 . 22  inches to  0 . 28  inches ) , and the base section  (   0 . 05  inches to  0 . 11  inches ) . It can this be seen that the axial length of the hard insert, which is a sixth distance, can range between  0 . 41  inches to  0 . 62  inches. Using the preferred dimensions, the axial length ranges between about  0 . 45  inches and about  0 . 57  inches.    
     
       The ratio of the fifth distance, which is the axial length of the second intermediate section, to the first diameter of the base section ranges between about  0 . 03  and about  0 . 08 . Based upon the preferred dimensions, this ratio of the fifth distance to the first diameter equals about  0 . 05 .  
     
       The ratio of the fifth distance  ( the axial length of the second intermediate section )  to the sixth distance  ( the overall axial length of the hard insert )  has a range between a minimum ratio and a maximum ratio. The minimum ratio is the ratio of the minimum fifth distance  ( i.e.,  0 . 02  inches )  to the maximum sixth distance that uses the minimum fifth distance. This sixth distance  ( i.e.,  0 . 59  inches )  used to arrive at the minimum ratio equals the sum of the maximum axial length of the tip section  (   0 . 18  inches ) , the minimum axial length of the second intermediate section  (   0 . 02  inches ) , the maximum axial length of the first intermediate section  (   0 . 28  inches ) , and the maximum axial length of the base section  (   0 . 11  inches ) . This minimum ratio equals about  (   0 . 02 / 0 . 59   )    0 . 03 . The maximum ratio is the ratio of the maximum fifth distance to the minimum sixth distance that uses the maximum fifth distance. The sixth distance equals the sum of the minimum axial lengths of the tip section  (   0 . 12  inches ) , the first intermediate section  (   0 . 22  inches ) , and the base section  (   0 . 05  inches ) , and the maximum fifth distance  (   0 . 05  inches ) . This maximum ratio equals about  (   0 . 05 / 0 . 44   )    0 . 11 . Based upon the preferred dimensions to the extent they are set forth, the preferred ratio of the fifth distance to the sixth distance ranges between about  (   0 . 03 / 0 . 57   )    0 . 05  and about  (   0 . 03 / 0 . 45   )    0 . 07 .   
     Since variations of this invention will be apparent to those skilled in the art, it is intended that this invention be limited only by the scope of the appended claims.