Method and apparatus for producing rolled metal balls from bars or rods
United States Patent [1 1 Skinner METHOD AND APPARATUS FOR PRODUCING ROLLED METAL BALLS FROM BARS OR RODS lnventor: Kenneth Charles Skinner,  
 Gloucester, England Assignee: Helipebs Limited, Ore, England Filed: Feb. 11, 1974 Appl. N0.: 441,221  
 US. Cl 72/71; 72/98 Int. Cl B21h 1/14 Field of Search 72/71, 98  
 References Cited UNITED STATES PATENTS 672,664 4/1901 Bornemann 72/71 729,519 5/1903 Williams 72/98 1,746,671 2/1930 Munro 72/71 3,466,910 9/1969 Carlsen 72/71 Primary Examiner-Lowell Al Larson Attorney, Agent, or Firm-:lrwin M. Aisenberg 57 1 ABSTRACT The invention provides a method and apparatus for rolling balls from a cylindrical metal workpiece, wherein the workpiece is fed axially along a gap between a pair of generally cylindrical forming rolls havinghelical grooves which act upon the workpiece to form balls therefrom as it moves axially along the grooves. Owing to the particular novel shaping of the grooves in the rolls the quality of the rolled balls is improved and the power required to drive the machine is reduced. Also the shaping of the rolls is such as to enable more economic manufacture of the rolls themselves.  
 7 Claims, 7 Drawing Figures PATENTEEAPR22i95 sum 5 o 5 METHOD AND APPARATUS FOR PRODUCING ROLLED METAL BALLS FROM BARS OR RODS BACKGROUND OF THE INVENTION This invention concerns an improved method and apparatus for producing rolled balls from bars or rods.  
  Prior methods of preparing rolled metal balls use a pair of oppositely disposed rolls having helically formed grooves upon their surfaces. a metal bar being fed longitudinally between the rolls and being held in the gap between the rolls by suitable guide means and the arrangement being such that the profiles of the rolls change progressively along the gap between them in order to work the metal bar from the cylindrical form to the form of a series of spherical balls.  
  These methods. however, have disadvantages&#39;The shape and arrangement of the forming rolls subject the metal bar to undue deformation and lamination. thus leading to a weakening and a porosity in the structure of the balls. Also in some methods the axial length of the forming rolls required to obtain a ball of true shape and consequently the power required to drive the apparatus is excessive. Furthermore the known forming rolls have been of relatively complicated shape and thus costly to produce.  
 SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of rolling metal balls. in which the quality of produced balls is improved It is a further object of the invention to provide an apparatus for rolling metal balls in which the shape of the forming rolls is so defined that the plastic deformation of the metal stock is reduced to a minimum. thus improving the quality of produced metal balls and reducing the.power required to operate the machine.  
  These and other objects and advantages of the invention areachieved. according to one aspect of the invention. by a forming roll in which the shape of a helical groove therein is such that the radius of the base of the groove from the axis of the roll is constant along the length of the roll. that the width of the groove increases progressively along the length of the roll in the direction of feed of the workpiece. and that the height of the rib defined between adjacent helices on the groove increases progressively in the direction of feed of the workpiece. With this shaping of the forming roll the volume of the workpiece enclosed between each of corresponding pairs of opposed helices of the grooves of two forming rolls may be arranged to be substantially constant along lengths of the rolls and to correspond substantially to the desired volume of each finished ball. the workpiece being formed from the cylindrical to the spherical form by compression between the walls of the grooves and corresponding axial expansion.  
  Other features and advantages of the method and apparatus according to the present invention will be readily apparent from the following description and claims taken in conjunction with the accompanying drawings. which illustrate the invention by way of example.  
  BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of one embodiment of an apparatus according to the invention.  
 FIG. 2 is a plan view corresponding to FIG. l,  
  FIG. 3 is a view corresponding to a part of FIG. 1 shown on a larger scale and partly in section (along line IVIV of FIG. 4).  
  FIG. 4 is an end elevation of the apparatus shown in FIG. 3, partly in section.  
  FIG. 5 is an elevation of a part of the profile of a forming roll for use in the apparatus shown in FIGS. 1 4, showing the basic principle governing the shape of a forming roll in accordance with the invention.  
  FIG. 6 is an elevation corresponding to another embodiment of forming roll for use in the apparatus of FIGS. 1 6, for the production of bearing balls. and  
 FIG. 7 is a section on the line A A of FIG. 6.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 of the drawings. a ball rolling machine comprises a forming head. indicated generally at 1, including a pair of forming rolls 2. A motor 3 is arranged to drive the rolls 2 by way of a pulley 4, a driving belt 5, a pulley 6, a variable speed gearbox 9. Output shafts 10, ll of the gearbox 9 are coupled to the rolls 2 via conventional flexible couplings I2 and drive shaft 13, which allow for adjustment of the axes of the forming rolls 2 as described below. Handwheels 14 are provided for adjustment of the axes of the rolls 2 in the horizontal plane. and a hand-wheel I5 is provided for adjustment of a guide means for metal stock. in the vertical plane. as described in greater detail below.  
  As shown in more detail in FIGS. 3 and 4. the forming head 1 comprises a main supporting frame 16 in which are journalled the hand-wheels 14, 15. Each of the rolls 2 is supported at its opposite ends in a U- shaped yoke member 17 which is mounted for horizontal sliding movement in a generally cylindrical member 18. The member 18 is in turn mounted for rotation about a horizontal axis in the frame 16 but is held against axial movement. Rails 19 are secured at each side of member 18 and serve to locate and guide the member 17 as well as providing abutment means for locking screw 20 which serve for adjustment of the member 18 about its horizontal axis. The hand-wheel 14 is coupled by gears. not shown in detail. to a pair of screw-threaded rods 21 which engage screw threadsin the frame 16. The free ends of the rods 21 can abut against the member 17 and thus by means of the handwheel 14 the member 17 and the roll 2 can be urged in a direction towards the cooperating roll 2.  
  A further hand-wheel 22 is screw threaded on a rod 23 having a widened head portion 23a which engages in a recess 17a of the member 17. Thus by the handwheel 22 the member 17 can be drawn firmly into engagement with the ends of rods 21 and locked in position.  
  Adjacent the peripheries of the cooperating parts of the rolls 2, there are arranged a pair of oppositely disposed guide plates 24, 25 which extend along the length of the rolls 2 and serve to support metal stock during its passage between the forming rolls. The plates 24, 25 are radiused as shown to extend between the rolls 2, and are supported in mounting blocks 26, 27 respectively. The mounting blocks 26, 27 are horizontally adjustable between clamping screws 28 threaded in the members 18, and are also vertically adjustable for location of the metal stock. The block 27 is clamped to the frame 16 by screws 29 and clamping jaws 30, and is vertically adjustable by way of shims insertable between it and the frame 16. The block 26 is slidable in the frame 16 and is vertically adjustable by way of a lead screw 31 threaded therein and coupled to the hand-wheel 15.  
  The operation of the machine as described above is basically as follows. as shown in the drawings the two forming rolls 2 are located with their axes in parallel vertical planes and the distance between them is adjusted to the appropriate requirements as explained in more detail below. By means of the members IS. the rolls 2 are set at opposite angles to the horizontal plane also as described below. Finally the guide plates 24. 25 are set at the required positions to guide the metal stock between the rolls. A heated metal bar is then fed between the guide plates 24, 25 to the driven forming rolls and is drawn between the rolls by the helical grooves therein. The method in which the metal bar is formed to the spherical shape is a function of the novel 7 shape of forming rolls in accordance with the present invention. and this will now be described in more detail with reference to two examples of forming roll.  
  FIG. 5 shows-one example of the profile of a forming roll 2, in which the end 20 of the roll corresponds to the end from which a metal bar to be worked is fed to the roll in the direction of the arrow X. The profile of the roll can best be described by referring to the method of forming the roll. A cylindrical blank is initially pro vided with a helical groove of constant pitch and constant semicircular cross-section. as indicated in the right hand side of the drawing and continued to the left in broken lines. The pitch of the helix is slightly greater than the diameter of the balls to be produced. and the radius of the semicircular crosssection is equal to or slightly greater than that of the balls to be produced. Thus the centres of curvature of the consecutive helices of the semicircular groove are located at a series of nodes X. X X X equally spaced along the length of the roll and at a constant distance from the axis thereof. Then the helical groove is modified by cutting a further helix to the same semicircular cross-section as the first but having a different pitch which is initially smaller than the first but increases to the same value. The centres ofcurvature of the helices of the second groove are thus located at second series of nodes .v. x X the nodes X. .v. X .v,. etc. being spaced apart in the direction ofthe axis of the roll by a distance v which progressively decreases along the direction of feed of the metal stock until the nodes coincide. The decrease in the distance v is not regular. but varies with the change in pitch of the secondary helix,  
  The two helical grooves are then blended together to form a common groove. and the crest of the projecting rib defined by the groove is finished to the desired profile. The resulting groove has a shape such that the height of the ribs bounding the groove and the width of the groove are both initially small but increase towards the end of the roll defining the finally desired crosssection of a rolled ball. The change in profile is such that the volume of the metal bar enclosed between the cooperating grooves of the two rolls is substantially constant along the length of the roll. the rolls initially accepting a relatively short axial length of the cylindrical metal rod. and allowing the axial length of the worked metal rod to increase as it is compressed between the rolls to a spherical form.  
  The shape of the forming roll as described above has a number of important advantages. Firstly. since the forming roll is basically cylindrical the periphery of the metal rod being worked is not subjected to differing rolling speed along its length and the tendency of the rolls to cause relative twisting of the adjacent parts of the metal bar about its axis during the progress of the bar along the rolls. with corresponding lamination and porosity of the structure of the ball. is reduced as compared to known methods. Secondly since the grooves of the rolls initially accept substantially only that volume of metal necessary to form the final ball excess metal is not discharged from the grooves during the compression of the bar to the shape ofa ball and is thus not laminated into the surface of the next ball to be formed. Thirdly. as a result of the elimination of the first two disadvantages and the corresponding ease of formation of the final shape of the ball. the axial length of the forming roll required to produce a ball of true shape can be reduced as compared with some known forming rolls and the power required to drive the rolls can also be reduced. Finally. in view of the fact that the forming rolls can be produced from a basic workpiece of simple shape. the cost of fabrication of the rolls and thus the cost of producing and maintaining a ball rolling machine can be considerably reduced.  
  The shape of roll shown in FIG. 5 can be used for the production of balls for use in ore crushing. in which case a greater tolerance in the finished size of the ball. and a small amount of lamination of metal at the surface of the ball. can be tolerated. In the case of balls to be used for the production of ball bearings. however. a more accurate finish and a higher quality is required. A forming roll suitable for the production of bearing balls is shown in FIGS. 6 and 7.  
  Referring to FIG. 6, a forming roll is shown which is constructed upon the same basic principle as described with reference to FIG. 5. In this case however. the semicircular cross-section of the basic groove is accurately dimensioned to correspond exactly to the required cross-section of the balls to be produced. and in order to ensure that an adequate volume of metal for each ball is drawn from the metal bar the initial part of the groove is designed to accept a slightly greater volume of metal than necessary. As shown at 2b. the flanks of the final part of the helical groove are relieved at the outside of the groove. During the final formation of the ball excess metal can accumulate in the relieved portion of the groove to form a small pip on the ball. which is either parted therefrom as it passes the final parting edges of the cooperating rolls or is easily removable during finishing of the ball. The relieved portions of the groove also serve to hold the metal ball about a single axis of rotation during the final formation and parting thereof from the metal bar. and tend to prevent skidding of the ball within the groove. It is such skidding of the ball within the grooves of the forming rolls that tends to cause lamination of metal into the surface of the ball during the final shaping thereof.  
  The setting up of a machine as described above for use with forming rolls as described above varies slightly depending upon the shape of the roll.  
  In the case of the roll as shown in FIG. 5 for producing crusher balls. the whole of the metal bar is to be used for producing balls. there being no surplus metal. and the crests of the rolls are relatively flat and do not serve to part the balls from one another. this being accomplished by deliberately imparting a degree of skidding to the balls during the initial working steps so that the balls are broken from one another by. relative twisting motion and the severed edges are rolled into the surface of the ball. This is achieved by making one forming roll to a slightly greater diameter than the other and displacing the rolls slightly relatively to one another in the longitudinal direction so that in addition to causing rotation of the metal bar about its axis rotation of the metal balls is caused about a further axis at an angle to the bar. The different diameters of the forming rolls also serve to urge the metal bar downwards towards the lower guide plate 25. and to further assist this action the guide plates 24, are adjusted so that the axis of the metal bar is slightly below those of the forming rolls. 1  
  In the case of the roll as shown in FIG. 6, it is important that the metal bar is rotated only about its own axis, and parting of the metal balls from one another is achieved solely by the final parts of the helical ribs of the forming rolls, the rolls being adjusted so that these ribs are close enough together to have a cutting action. In this case both rolls are identical and are accurately dimensioned to the shape of the final ball, and the axis of the metal bar is fed on the centre line between the two forming rolls. The metal bar is again caused to be urged downwardly onto the lower guide plate 25 by means of a slight axial displacement of the rolls relatively to one another, although the axial displacement is not sufficient to cause skidding of the balls within the groove or to distort the shape of the finished ball.  
  it has been found that tilting of the axes of the rolls 2 in opposite directions by means of the members 18 is important in ensuring effective feeding of the metal bar into the gap between the rolls, and in practice an effective control of the size and quality of the rolled balls has been found possible by this adjustment in conjunction with an adjustment of the relative axial displacements of the rolls. The axes of the rolls advantageously form an angle in the vertical plane of up to 5, and preferably in the region of 2 3.  
  From the above description it will be seen that the invention provides a novel method of rolling balls. together with a novel construction and arrangement of forming rolls for a ball rolling machine, that substantially reduces the disadvantages of the known methods. In particular the invention provides for the formation of balls of bearing quality that have hitherto been unobtainable by a rolling process.  
 1 claim:  
  1. An apparatus for rolling balls from metal stock, the apparatus comprising a pair of generally-cylindrical forming rolls, each of which has a rotary axis and a helical groove of progressively changing profile, means for supporting the rolls in spaced relation so that the axes thereof are parallel to a median plane between them and the helical grooves register to define between them a space for receiving a workpiece fed axially into the space along an axis lying in the median plane. means for driving said forming rolls to roll the workpiece, the groove of each forming roll having a base of substantially constant radius with reference to the rotary axis of the forming roll and being defined by a helical rib with leading and trailing edges having a concave partcircular profile tangential to the base of the groove and having the same, substantially-constant, radius of curvature, the trailing edge of the helical rib. as defined by the point at which the part-circular profile thereof becomes tangential to the base of the groove, having a pitch which is substantially constant along the length of the roll, the leading edge of the helical rib. as defined by the point at which the part-circular profile thereof becomes tangential to the base of the groove, having a pitch which is substantially less than the pitch of the trailing edge and gradually increases along the length of the roll until the pitches of the trailing and leading edges of consecutive helices of said rib coincide and become substantially constant to define a portion of the groove of constant semicircular profile.  
 2. Apparatus according to claim 1 having a discharge end and in which the groove of each roller, adjacent the discharge end, has margins which are relieved so that during final ball formation. any excess metal is accommodated in the relieved part of the groove as a projection which is easily removable from the ball.  
  3. Apparatus according to claim 1 in which the axes of said forming rolls are inclined so that projections of said axes onto said median plane define an angle of up to about 5.  
  4. Apparatus according to claim 3 in which the said angle between said projections of said axes is about 2 to 3.  
  5. A forming roll for rolling balls from metal stock and having a helical groove and a helical rib of progressively-changing profile around its periphery; the groove having essentially the shape of an arc of a circle of substantially-constant radius and having a progressively increasing pitch, the forming roll having a central axis which is at a constant distance from the groove throughout the length of the groove and the same distance from the surface of the forming roll at one end of the helical groove. the other end of the helical groove having an essentially semicircular cross-section:  
 the helical rib having leading and trailing edges in sectional profile and the distances between such leading edges increasing successively from materially less to slightly more than two times the radius of the circle.  
  6. A pair of cooperating rolls, each of which is a forming roll according to claim 5, the corresponding helical ribs and grooves defining between them substantially constant volumes of the metal stock along the length of the rolls.  
  7. A forming roll for rolling balls from metal stock and having a helical groove and a helical rib of progressively changing profile around its periphery and having a central axis; the helical groove and helical rib constituting a composite of a. a first helical groove of constant pitch and constant semi-circular cross-section, the pitch being slightly greater than the diameter of the semi-circular cross-section and the helical groove being at a constant distance from the central axis throughout the length of said helical groove, and  
 b. a second helical groove in the same direction, of  
  the same and constant semi-circular cross-section and at the same distance from the central axis. but displaced from the first helical groove at one end thereof and having a progressively decreasing pitch until the two helical grooves coincide at the other end thereof; the composite of the two helical grooves being blended together as a single groove which, in cross-se ction, has points separated by the pitch of the first helical groove which are at a distance from the central axis equal to the distance of the first helical groove from the central