Abstract:
A three roll mill having a feed roll, a center roll, and an apron roll with that are driven so that their cylindrical surfaces move in the same direction but different speeds in each nip. One end of each roll is engaged by a drive shaft at a first side of the mill, whereas the other end of each roll rotates freely at a second side of the mill. Each roll can be removed individually and without tools by moving the roll away from the first side against a spring force in the second side. This disengages the roll from its drive shaft, whereupon it can be lifted out of the mill.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a grinding mill of the type having parallel rolls driven at different speeds so that granular material fed into the nip between adjacent rolls is subjected to both crushing and shear forces. More particularly, it relates to a three roll ointment mill wherein a paste fed into the nip between a feed roll and a center roll is carried by the center roll to the nip formed by the center roll and an apron roll, where it is picked up by the apron roll and removed by a scraper. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Ointment mills are well known to pharmacists. U.S. Pat. No. 915,864 (1909) discloses an ointment mill having a pair of rolls mounted for rotation between a pair of parallel frame members. A first roll is rotated by a hand crank at one end, and a second roll is rotated by a pair of intermeshing gears at the other end. The gears are sized so that that the second roll rotates about three times as fast as the first roll. Since the surface speeds of the rolls are different, particulate in a paste fed into the nip between rolls is subjected to shear force. The second roll is carried in journal boxes that are spring-loaded toward the first roll to provide crushing force. The combination of forces yields an ointment with very fine particulate. 
         [0003]    Modern ointment mills typically have three rolls, so that the particulate is subjected to a second grinding step before the paste is removed by a scraper or doctor blade. One such ointment mill is manufactured by Exakt Vertriebs GmbH of Norderstedt, Germany. The Exakt Model 50 is a three roll mill wherein paste is fed downward between a feed roll and a center roll, whose surfaces in the nip are moving in the same direction at different speeds. The paste adheres to the faster center roll, and is carried upward between the center roll and an apron roll, whose surfaces in the nip are moving in the same direction at different speeds. Unlike the mills of a century ago, modern rolls are not spring loaded to provide compressive force. Rather, the gaps between rolls are adjusted by pivoting plates on which the feed and apron rolls are mounted. However the rolls are still mounted for rotation between a pair of parallel frame members, wherein the apron roll is driven at one end, and the other rolls are driven by intermeshing gears at the other end. The Exakt machine employs pulleys driven by cog belts to drive the apron roll through a two-stage speed reduction from a motor mounted between the frame members at the bottom of the unit. The apron roll, in turn, drives a center roll and a feed roll via intermeshing gears that step down the rotational speed. 
         [0004]    When the rolls need to be removed from the frame members, the cog belts and pulleys must first be removed from the one end, followed by the three gears on the other ends of the roll shafts. This is followed by removal of feathering keys, circlips, and bearing plates from the gear ends, and removal of tensioning springs and bearing plates on the pulley ends. The frame members on both ends must be separated so that the feed and apron rolls can be lifted out as a unit with the pivot plates. Finally, the pivot plates must be removed. 
         [0005]    In an effort to make the task of cleaning rolls easier, Exakt has introduced the Model 50 Easy Clean, wherein the rolls are mounted in a subframe that can be removed as a unit for cleaning. However it is still not easy to remove the individual rolls. 
         [0006]    Other manufacturers of three roll mills include Torrey Hills Technologies, Mikrons, and Charles Ross &amp; Son Co. All have websites where their machines can be seen. None offers easy removal of rolls. 
         [0007]    From the foregoing it will be apparent that removal of the rolls for cleaning requires a number of different tools and is very time-consuming. Indeed, it is an operation that many users would rather not undertake at all. However frequent cleaning is necessary to maintain the high standards of purity required in pharmaceutical preparations. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the invention is to provide a three roll mill, in particular an ointment mill, wherein the rolls may be removed quickly and easily without any tools. 
         [0009]    Another object is to provide a roll drive and differential speed arrangement that is arranged wholly at one end of the rolls, so that the other ends may rotate freely. The three roll mill according to the invention includes a frame having first and second spaced apart support structures in the form of chassis plates, and parallel rolls including a feed roll, a center roll, and an apron roll mounted between the chassis plates. Pulleys are fixed to drive shafts mounted for rotation in the first support structure and fixed against rotation relative to respective rolls by axially releasable connections. Axially movable pins at the second chassis plate are received coaxially in respective rolls, whereby the connections at the first end wall can be released by moving the rolls axially against the pins. These pins are preferably spring-loaded toward the first support structure. 
         [0010]    The pulleys have progressively smaller effective diameters so that a common drive belt will drive the successive rolls at progressively higher speeds. The drive belt is driven by a drive pulley that, in turn, is driven by a motor pulley though a speed reducing arrangement. 
         [0011]    The drive shafts for the feed and apron rolls are mounted for rotation in bearings fixed to pivot plates that are pivotably mounted on the first chassis plate. The drive shaft for the center roll rotates in a fixed plate, so that the two gaps can be adjusted by moving the pivot plates. Likewise, the axially movable pins for the feed and apron rolls are mounted for axial movement in sleeves fixed to pivot plates that are pivotably mounted on the second chassis plate, whereas the axially movable pin for the center roll is mounted for axial movement in a fixed sleeve. The gaps can thus be adjusted at both ends and made uniform along their lengths. 
         [0012]    According to a preferred embodiment, each axially releasable connection is formed by a drive plate fixed to the respective drive shaft, means for centering the roll coaxially with respect to the drive plate, an offset pin fixed to the roll, and a radially extending slot in the drive plate, the pin being received in the slot to prevent relative rotation. 
         [0013]    The coaxial pins at the second chassis plate preferably have conical tips received in coaxially arranged conical recesses in respective rolls. This acts as a simple bearing arrangement that permits the rolls to rotate relative to the pins. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0014]      FIG. 1  is a perspective view of a three roll mill according to the invention, showing the rolls, scraper, and control panel; 
           [0015]      FIG. 2  is a plan view of the mill with the side covers and rolls removed; 
           [0016]      FIG. 3  is a simplified plan view of the rolls and bearings; 
           [0017]      FIG. 4  is a section view of a bearing arrangement for a single roll; 
           [0018]      FIG. 5  is a schematic view showing the first step for removing a roll; 
           [0019]      FIG. 6  is an end view showing the drive arrangement for the rolls; 
           [0020]      FIG. 7  is an end view showing the spring plates; and 
           [0021]      FIG. 8  is an end view of the scraper mechanism for the apron roll. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    Since the mounting arrangement for the rolls is substantially identical, components associated with respective rolls will utilize the same reference numerals. Those associated with the feed roll will be unprimed, whereas those associated with the center roll will have a single prime, and those associated with the apron roll will have a double prime. 
         [0023]      FIG. 1  shows the three roll mill with the left side cover  4 , right side cover  5  and scraper  70  in place on box frame  10 . The feed roll  20 , center roll  20 ′, and apron roll  20 ″ are exposed as in other three roll mills. A pair of spring-loaded guide blocks  6 ,  7  extend closely into the nip between the feed and center rolls to prevent the escape of material from the ends of the rolls. These are well known and will not be shown again. A platform  3  catches any material that falls off the rolls, and can be easily removed for cleaning. Knobs  59 ,  59 ″ are used to control the gaps between rolls, as will be described. Finished ointment is removed from apron roll  20 ″ by scraper  70  which can be tilted using handle  75  mounted in support block  74 . 
         [0024]    A control panel  80  is used to control the roll speed, time, and direction of rotation. The panel  80  includes a timer  81 , speed display  82 , run switch  83 , stop switch  84 , speed increase switch  85 , speed decrease switch  86 , timer reset  87 , and roller reverse switch  88 . These controls and the attendant wiring are conventional and will not be described further. 
         [0025]      FIG. 2  is a plan view showing the inside of the frame with the rolls and platform removed. The basic support structure is a box frame  10  to which a first chassis plate  12  and a second chassis plate  13  are fixed on opposite sides. Four posts  11  are fixed to each of plates  12 ,  13  for mounting side covers  4 ,  5 . AC power is provided to a power supply  14  that rectifies it for DC motor  16  that drives pulleys  34 ,  34 ′,  34 ″ via cog belts  60 ,  64  ( FIG. 6 ). Control panel  80  can be used to regulate the current, and thus the RPM, as well as the polarity, and thus the direction of rotation. The motor is preferably a low profile Maxon brushless motor rated for 50 w at 4500 RPM. A shaft  63  journaled in a bearing  63 ′ above the motor  16  carries a pulley arrangement ( FIG. 6 ) that transfers power from the motor  16  to the roll pulleys  34 ,  34 ′,  34 ″. The drive shafts  32 ,  32 ′,  32 ″ rotate in bearing housings  33 ,  33 ′,  33 ″ fixed to plates  30 ,  30 ′,  30 ″ on the outside of first chassis plate  12 . Pulleys  34 ,  34 ′,  34 ″ are fixed to the outer ends of respective drive shafts, whereas the conical inner ends  36 ,  36 ′,  36 ″ stand proud of plate  12 . Pins  42 ,  42 ′,  42 ″ are arranged to slide axially in sleeves  43 ,  43 ′,  43 ″ fixed to plates  40 ,  40 ′,  40 ″ on the outside of second chassis plate  13 , whereas the conical inner ends  47 ,  47 ′,  47 ″ stand proud of the plate  13 . Camshaft  50  is used to pivot plates  30 ,  40 , whereas camshaft  50 ″ is used to pivot plates  30 ″ and  40 ″. 
         [0026]      FIG. 3  shows the mounting arrangement for the rolls  20 ,  20 ′,  20 ″. Each roll is formed by a tube that may be made of stainless steel or a ceramic such as porcelain or alumina. The roll  20  has a first end formed by a first end piece  21 , and a second end formed a second end piece  26 . The end pieces  21 ,  26  are molded of durable plastic such as polyoxymethylene (POM), also known as acetal. POM is characterized by high strength, hardness, rigidity, and a low coefficient of friction. The end pieces  21 ,  26  are bonded in the tube to form the complete roll  20  having a cylindrical surface  25 . The first end piece  21  has a central conical recess that receives the conical tip  36  of the drive shaft  32 , and a radially offset drive pin  23 . The second end piece  26  has a steel spigot  27  located centrally and bonded in place; the spigot  27  has a central conical recess that receives the conical tip  47  of axially movable pin  42 . The conical recesses are also useful for centering the roll while the cylindrical surface  25  is machined for concentricity with the central axis. This assures a uniform gap between rolls. The gap  29  between rolls  20 ,  20 ′ and the gap  29 ′ between rolls  20 ′,  20 ″ are adjusted using the camshafts  50 ,  50 ″ ( FIG. 2 ). Rolls  20 ′ and  20 ″ are identical to and interchangeable with roll  20 . 
         [0027]    The pin  42  is axially loaded toward the roll  20  by a pair of tension springs  46 . This loads the roll  20  toward the first chassis plate  12  so that it rotates with the drive shaft  32 . Each spring  46  has one end attached to a stud  44  fixed in sleeve  43 , and another end attached to an ear  79  on plate  45  fixed on the outer end of pin  42 . The pin  42  is preferably made of polyether ether ketone (PEEK), a semicrystalline thermoplastic with mechanical and chemical resistance properties that are retained to high temperatures. Since the pin  42  does not rotate, this makes it suitable for the bearing surface where the conical tip  47  engages the recess in spigot  27 . Each assembly of a drive shaft  32 ,  32 ′,  32 ″ in a respective bearing housing  33 ,  33 ′,  33 ″ is identical, but for the diameter of pulleys  34 ,  34 ′,  34 ″. Each assembly of a pin  42 ,  42 ′,  42 ″ in a respective sleeve  43 ,  43 ′,  43 ″ is also identical. In lieu of springs, it is also possible for the axially movable pin  47  to positively engage the roller  20 , e.g. by a latch effective between plate  45  and sleeve  43 . 
         [0028]      FIG. 4  shows the construction of the drive side and idle side bearing assemblies in greater detail. On the drive side, the bearing housing  33  has a pair of ball bearings  90  that are axially fixed, each bearing having an outer race against the housing  33  and an inner race against the drive shaft  32 . The housing  33  is machined with a flange  93  that is held against plate  30  by a pair of diametrically opposed fixing plates  94  secured by nuts  96  on studs  95 . The inner end of the bearing housing  33  is machined to fit closely in hole  92  in the plate  30 . The outer end of the drive shaft  32  is fitted with a pulley  34  that is fixed by set screw  91 . The inner end of the drive shaft  32  is fitted with a round drive plate  35  that is also fixed by a set screw  91 . The drive plate  35  is provided with a recess or slot  37  that receives drive pin  23  to prevent relative rotation. The plate  35  is dimensioned to rotate freely within hole  92  in the plate  30 . 
         [0029]    On the idle side, the slide housing  43  is machined with a flange  98  held against the plate  40  by a pair of diametrically opposed fixing plates secured by nuts on studs. The inner end of the sleeve  43  is machined to fit closely in hole  97  in the plate  40 . Since the associated roll has been removed, the conical tip  47  is fully extended beyond the plate  40 , and spring plate  45  bears against the sleeve  43  under the action of springs  46 . 
         [0030]      FIG. 5  shows the roll  34  moved against the action of springs  46  so that the cone  36  disengages the central recess  22  in the first end  21 , and the drive pin  23  disengages the recess  37  in drive plate  35 . From this position the first end  21  can be pivoted upward until it clears the first chassis plate  30 , then moved axially until the cone  47  disengages the recess  28  in spigot  27 . The spring plate  45  will then be against the slide housing  43 . 
         [0031]      FIG. 6  shows the drive arrangement and gap adjustment mechanism. The motor shaft  17  is fitted with a motor pulley  18  that turns speed reduction pulley  61  via a primary drive belt  60 . The pulley  61  is mounted coaxially with drive pulley  62  on shaft  63 , which is also visible in  FIG. 2 . The drive pulley  62  turns the feed pulley  34 , center pulley  34 ′, and apron pulley  34 ″ via roller drive belt  64 . As can be seen from the relative pulley sizes, this results in a large reduction in RPM from the motor to the rolls. The motor operates at speeds up to 4500 RPM, while the apron roll turns at speeds up to 420 RPM. All pulleys have teeth, and both belts  60 ,  64  are cog belts that positively engage the pulleys so there is no slippage. The motor pulley  18  and reduction pulley  61  have a first tooth spacing, whereas the drive pulley and roll have a second (larger) tooth spacing. The feed pulley  34  has 36 teeth, the center pulley  34 ′ has 20 teeth, and the apron pulley  34 ″ has 13 teeth. This results in relative speeds in a ratio of 1:1.80:2.77. 
         [0032]    Tension is maintained on roll drive belt  64  by jockey pulley  65  journaled on the end of swing arm  66 . This tension can be adjusted by pivoting the swing arm  66  about pivot pin  67 , which is fixed in chassis plate  12 . The swing arm  66  has a slot  69  for screw  67  that is used to lock the position of the swing arm. 
         [0033]    The drive shafts  32 ,  32 ″ have axes that are fixed in respective pivot plates  30 ,  30 ″. The plates  30 ,  30 ″can pivot about pins  31 ,  31 ″ fixed in first chassis plate  12 . The first chassis plate  12  is provided with slots (not shown) that accommodate lateral movement of the drive plates  35 ,  35 ″. The center drive shaft  32 ′ is carried in fixed plate  30 ′ and cannot be moved laterally. Referring to  FIG. 7 , a mirror image arrangement is provided on second chassis plate  13 , where the plates  40 ,  40 ″ can pivot about fixed pins  41 ,  41 ″. The second chassis plate  13  is provided with slots (not shown) that accommodate lateral movement of the pins  42 ,  42 ″. 
         [0034]    The gap  29  between rolls  20 ,  20 ′ is adjusted by rotating camshaft  50  that is journaled for rotation in chassis plates  12 ,  13  and passes through slots  38 ,  48  in respective pivot plates  30 ,  40 . The camshaft  50  carries a cam  51  that contacts a cam follower  52  in the form of a thumbscrew received through a block  54  fixed to pivot plate  30 . The camshaft  50  carries another cam  55  that contacts a similar cam follower  56  mounted on opposing pivot plate  40 . Rotating the camshaft  50  causes the plates  30 ,  40  to pivot due to eccentricity of the cams. Fine calibration is achieved by turning the thumbscrews  52 ,  56 , which can be locked by turning nuts  53 ,  57  against blocks  54 ,  58 . 
         [0035]    The gap  29 ′ between rolls  20 ′,  20 ″ is adjusted by rotating camshaft  50 ″ that is journaled for rotation in chassis plates  12 ,  13  and passes through slots  38 ″,  48 ″ in respective pivot plates  30 ″,  40 ″. The camshaft  50 ″ carries a cam  51 ″ that contacts one end of a rocker arm  89  whose other end contacts a cam follower  52 ″ in the form of a thumbscrew received through a block  54 ″ fixed to pivot plate  40 ″. This is similar to the arrangement on pivot plate  30 , but for the interposition of rocker arm  89  mounted on the pivot plate  30 ″, which is necessary to make room for the control panel  80 . The camshaft  50 ″ carries another cam  55 ″ that contacts a cam follower  56 ″ mounted on the opposing plate  40 ″, as shown in  FIG. 7 . Rotating the camshaft  50 ″ causes the plates  30 ″,  40 ″ to pivot due to eccentricity of cams  51 ″,  55 ″. Fine calibration is achieved by turning the thumbscrews  52 ″,  56 ″, which can then be locked by turning nuts  53 ″,  57 ″ against blocks  54 ″,  58 ″ on the respective pivot plates  30 ″,  40 ″. 
         [0036]    The presence of cams and a calibration mechanism at both ends of each roll  20 ,  20 ″ assures that the gaps  29 ,  29 ′ can be precisely controlled and made uniform along their length. The pivot plates  30 ,  30 ″ are loaded toward each other by a tension spring  39 , and the pivot plates  40 ,  40 ″ are also loaded toward each other by a tension spring  49 . The camshafts  50 ,  50 ″ encounter enough friction that they will not turn without the use of knobs  59 ,  59 ″. The gaps  29 ,  29 ′ are typically in a range of 20 to 600 microns. 
         [0037]      FIG. 8  is a schematic view of the scraper  70 , which is mounted on locator pins  72  on a pivot block  71  which pivots about shaft  73  in support blocks  74  on the front of box frame  10 . A lever  76  extending through an aperture in the frame is urged downward by a tension spring  77  fixed to a hanger  78  on the floor of the frame. 
         [0038]    The foregoing is exemplary and not intended to limit the scope of the claims which follow.