US2846723A - Rotary tablet press - Google Patents

Description

Aug 12, 1958 R. G. FRANK 2,846,723

ROTARY TABLET PRESS Filed Feb. 27, 1957 3 Sheets-Sheet 1 INVENTOR. Raymond G. F rank MM YWd/MW ATTORNEYS Aug. 12, 1958 R. G. FRANK ROTARY TABLET PRESS 3 Sheets-Sheet 3 Filed Feb. 27. 1957 "'IIHI Q II FIG.?

' INVENTOR. Raymond G. Frank AIR flm7mwwzd%@ 84 LA\ \F 65 ATTORNEYS United States Patent Ofiice 2,846,723 Patented Aug. 12, 1958 ROTARY TABLET PRESS Raymond G. Frank, Ambler, Corporation, Philadelphia, sylvania Pa., assignor to F. J. Stokes Pa., a corporation of Penn- My invention relates to tablet presses, such as rotary tablet presses, which employ a traveling tool assembly including opposing pairs of punches and a die disposed between each pair of punches in which such punches cooperate to form tabletted products. My invention has particular application to rotary tablet presses in which a single rotation of a traveling tool assembly is carried through two or more distinct tabletting operations and in which more than one set of pressure rolls are employed.

It is an important object of my invention to provide a loading device for controlling the force applied at each of at least two separate pres-sure rolls by providing a floating mount for such pair of pressure rolls. It is particularly contemplated that the floating mount will be employed to support the upper pressure rolls of a double sided rotary press.

It is a further object of my invention to provide an overload release which will hold a constant tabletting thickness as opposing pairs of punches pass between a set of pressure rolls which will release the rolls and permit them to float over the punches as a preselected tonnage is exceeded. Such an overload release is singularly valuable in preventing jamming and damage to punches and dies in the event of an overcharge, e. g., caused by failure of ejection in a previous cycle, in permitting pressing of tapered pieces with controlled punch entrance and in permitting pressing of flanged pieces with dimension control and directional control of overload release. Such an overload release arrangement, since it can be employed to press to constant thickness, will evidently have obvious advantage wherever dimensional control of the tabletted products is a prime consideration.

It is a further object of my invention to provide a pressure roll mounting arrangement in which total tonnage applied can be set to any preselected value by relatively simple adjustment in order to permit rapid change-over from one tabletting operation to another, where different tonnages are required.

It is yet another object of my invention to provide a pressure roll mounting arrangement which is capable of pressing to constant density, i. e., constant unit Inolding pressure, despite variations in thickness which can be caused by non-uniformity of the powder charge and the like.

It is still another object of my invention to provide a loading arrangement for pressure rolls in a rotary press which can be preset to yield a constant force on the punches as they pass between the pressure rolls regardless of the displacement of the rolls. This arrangement has'particular advantage where the diameter of the punches is small such that an overload, if roll displacement gradient were substantial, would damage the punches.

It is also an important object of my invention to provide a pressure roll loading arrangement which by simple change at the factory or in the field can be converted from one type of compression means to another. Since pressing requirements vary for 'diflerent products and a single user of one machine may produce various types of tabletted products on the machine, such flexibility is particularly advantageous.

These and other objects of my invention which will become more apparent hereinafter are fundamentally obtained, for example in a double sided rotary press, by supporting a set of corresponding pressure rolls, e. g., the upper pressure rolls, for eccentric rotation about separate rotatable axles which carry eccentric cams, e. g. cranks, which bear against a loading beam positioned to oppose movement of the rolls away from the punches as they cooperate with the rolls, and by supporting and loading the beam intermediate of its hearing points against the cams. In a more particular aspect the loading beam is suppoIted on the end of arecip'rocable plunger which is interchangeably loaded by a spring, a hydraulic cylinder or an air cylinder or combinations of these. In still a more specific aspect of my invention the reciprocable plunger is loaded by a cylinder and piston carrying the lunger in which the cylinder forms a vertical spindle for the traveling tool assembly, i. e. rotary head of the press.

For a more complete understanding of the practical application of the principles of my invention reference is made to the appended drawings in which:

Figure 1 is an isometric view of the basic operating parts of an upper pressure roll loading arrangement for a double sided rotary press in accordance with my invention;

Figure 2 is a plan view of a double sided rotary tablet press showing the loading arrangement of Figure 1 and omitting non-operating parts which are unessential to an understanding of the invention;

Figure 3 is a cross-sectional view of the press shown in Figure 2 taken at line 3-3 in Figure 2; p I

Figure 4 is a fragmentary view illustrating the basic operation of the loading system of the press shown in Figures l-3;

Figure 5 is a fragmentary view similar to Figure 4 and of the same parts illustrating the operable motion of the loading system;

Figure 6 is a schematic diagram of a hydraulic loading system for the press shown in Figures 13;

Figure 7 is a schematic diagram of a pneumatic pressure loading system for the press shown in Figures 1-3; and

Figure 8 is a schematic diagram illustrating a combined loading system for the press shown in Figures 1-3.

Referring to Figures 1, 2, and 3 the reference numeral 10 designates a double sided rotary tablet press includ= ing a base 11, a rotary r001 head 12 and a fixed cap 13. It will be noted for clarity of illustration cap .13 is not shown in Figures 1 and 2. 7

Rotary head 12 is mounted for rotation about a vertical axis on an upright spindle l4, afiixed at its lower end on base 11, by means of two sets of tapered roller bearings, upper bearings '15 and lower bearings 16. Cap 13 is supported on the upper end of spindle 14 in fixed position above rotary head 12.

Rotary head 12 includes a lower horizontal flanged portion 17 which is provided with a plurality of vertical apertures 18 carrying vertically reciprocable lower punches 19. Rotary head 12 similarly carries an upper horizontal flanged portion 20 provided with a plurality of vertical apertures 21 receiving vertically reciprocable upper punches 22 and registering with apertures 18. Intermediate of and spaced between flanged portions and 20 is a third flanged portion extending horizontally from rotary head 12 forming a die table 23 and provided with a plurality of vertical apertures 24 receiving vertical apertured dies 25 which register with punches 19 and 22 to receive the inner, i. e., confronting, ends thereof. A worm 26 driven from an external power source (not shown) is mounted to engage with worm gear teeth 27 extending about the lower peripheral edge of lower flanged portion 17 of rotary head 12 to drive rotary head 12 about spindle 14 carrying punches 19 and 22 in a single rotation of head 12 through two distinct tabletting operations. Punches 19 and 22 are thus reciprocated vertically by cams (not shown) cooperating with their outer ends in a conventional manner to carry them through two sequences involving filling, compression and ejection.

The sequence and location of these operations is schematically suggested in the plan view Figure 2 which shows a pair of loading hoppers 28 and 29, conventionally affixed to cap 13 and positioned diametrically opposite each other with their lower discharge ends riding just above die table 23. In Figure 2, for convenience, the portion of rotary head 12 located above the die table 23 has been shown removed. Scraper blades 30 and 31 are positioned immediately after each of hoppers 28 and 29, respectively, as die table 23 rotates in a counter-clockwise direction, to remove inwardly the surplus powder charge distributed on die table 23 over dies 25 leveling in the bore of each die 25 a quantity of powder charge volumetrically determined by the depth of lower punch 19 in such bore. During the filling operation, of course, upper punches 22 are raised clear of blades 30 and 31.

Thereafter, as head 12 continues to rotate in a counterclockwise direction, upper punches 22 are lowered into dies 25 and the outer ends of punches 19 and 22 are carried between the peripheral edges of upper and lower pressure rolls, one pair of pressure rolls, upper roll 32 and lower roll 33 being diametrically positioned from the other set of pressure rolls, upper roll 34 and lower roll 35. Lower rolls 33 and 35 are respectively mounted on axles 36 and 37 which are mounted in base 11 for rotation about horizontal axes. Upper rolls 32 and 34 are similarly mounted on horizontal axles 38 and 39, respectively.

Axles 38 and 39 are mounted for rotation about horizontal axes in fixed cap 13 and carry eccentric portions 40 and 41, respectively, which rotatably receive pressure rolls 32 and 34, respectively. At their inner, confronting ends axles 33 and 39 carry cranks 42 and 43, respectively, which are bored and slotted to permit them to be mounted on the ends of their respective axles and clamped in position by suitable devices, such as bolts 44 and 45 and nuts 46 and 47 which are tightened down on cranks 42 and 43 to clamp them on the ends of axles 38 and 39, respectively. As is shown best in Figures 1 and 2, cranks 42 and 43 are disposed at the inner ends of axles 38 and 39 with the outer ends of the cranks extending horizontally away from each other and with their inner ends closely adjacent. Normally eccentrics 40 and 41 will have their centers offset from the axis of rotation of axles 38 and 39 approximately horizontally, such that eccentric 40 is ofiset in the opposite direction of crank 42 which is associated with the same axle 38 as eccentric 40. Similarly the center line of eccentric 41 will be offset in the opposite direction from crank 43. Accordingly, as pressure rolls 32 and 34 move upwardly the consequent rotation of their respective axles 38 and 39 caused by raising the ofiset portions of eccentrics 40 and 41 will lower the outer ends of crank 42 and 43.

As head 12 continues to rotate carrying punches 19 and 22 past the two sets of pressure rolls upper punches 22 are drawn clear of dies 25 above the surface of table 23. At the same time lower punches 19 are raised to level their upper ends with the upper surface of die table 23 carrying the tabletted products above table 23. Thereafter the raised tablets are carried into engagement with diametrically disposed ejection blades 48 and 49 which remove the tablets outwardly from the table. As head 12 continues to rotate lower punches 19 are again dropped and passed under hoppers 23 and 29 for repetition of the filling operation. Surplus material scraped inwardly by leveling blades 30 and 31 is scraped outwardly to the paths of dies 25 in the vicinity of hoppers 28 and 29 by diametrically disposed collector blades 50 and 51.

It will be noted, referring again to the upper roll supporting arrangement, that each of cranks 42 and 43 is provided with a crank pin 52 and 53, respectively, which extend inwardly parallel with axles 38 and 39 and to each other. Beneath pins 52 and 53 extends a normally horizontal loading beam 54 which at its ends is provided with a pair of flats 55 and 56, receiving respectively the undersides of crank pins 52 and 53. Centrally beam 54 is provided with a recess 57 in its undersurface. Recess 57 receives the upper flatted end of a vertical plunger 58 which is pivotally secured to beam 54 by a pin 59 extending across recess 57 parallel to pins 52 and 53.

Referring more particularly to Figure 3, it will be noted that plunger 58 has afiixed at its lower end a keeper 60 mounted for vertical reciprocation within hollow spindle 14. A piston 61 is positioned for vertical reciprocation in fluid-tight contact with the inner walls of spindle 14 beneath keeper 6%. A guide stem 62 afiixed at its upper end in the underside of kcepcr 60, extends vertically down partly into the upper end of a vertical bore 63 in the upper end of piston 61 which slidingly receives guide stem 62. A helical coil spring 64 is positioned between keeper 60 and piston 61 within spindle 14 and about guide stem 62. Beneath piston 61 spindle 14 is provided with a suitable port 65 for connection to pneumatic or hydraulic pressure circuits.

Threadedly affixed in the top of cap 13 are a pair of threaded vertical studs 66 and 6'7. Stud 66 is located immediately over crank pin 52, and stud 67 is located immediately over crank pin 53. Both studs 66 and 67 are of suitable length to permit their being screwed down to abut at the lower ends against their associated crank pins. A lock nut 68 is provided on stud 66 to secure it in position and similarly a lock nut is provided to retain stud 67 in position.

It will be evident when press 10 is in operation that the positions of studs 66 and 67 can be set to limit the maximum entrance of upper punches 22. Similarly it will be evident from the preceding description that the force applied upwardly on plunger will be divided equally by crank pins 52 and 53, assuming pin 59 is, as illustrated, centered between crank pins 52 and 53 and hence will be divided equally by cranks 42 end 43 and by eccentrics 40 and 41 as equal Forces exerted by rolls 32 and 34 against diametrically opposite upper punches 22 as these pass beneath rolls 32 and 34. Should an odd number of punches be employed rather than an even number, such that one punch at a time will be beneath either roll 32 or 34, the force applied will nevertheless be equally divided because of the limited movement permitted by studs 66' and 67.

Hydraulic l0ading-0verload release Referring also to Figure 6, it will be noted that press 10 can be equipped with a hydraulic system including a gear pump 70 for pumping oil from a reservoir 71 through line 72 into line 73 which leads to a foot valve 74 having a relief drain line 75 leading back to reservoir 71. On its discharge side, foot valve 74 is connected by line 76 to port 65 at the lower end of spindle 14 beneath piston 61. A pressure gauge 77 is suitably installed in line 76 and calibrated in terms of loading tonnage.

In operation with the press rotating and supplied with tabletting material in hoppers 28 and 29, gear pump 70 is turned on to pump oil from reservoir 71 through line 72 line 73 and line 76 into the space in spindle 14 beneath piston 61, forcing piston 61 upwardly to compress spring 64 and .hence load keeper 60 and plunger 58 with a spring force which is transmitted through pivot pin 59 to loading beam 54. Spring force is increased to the desired tonnage indicated on gauge 77 whereupon gear pump 70 is shut off. The tonnage thus applied to beam 54 'by compression of spring 64 is divided equally between crank pins 52 and 53 of cranks 42 and 43, respectively. Studs 66 and 67 limit the upward travel of crank pins 52 and 53, respectively, and hence of spring 64 and other associated components. Since cranks 42 and 43 are clamped to axles 38 and 39 respectively (and desirably are keyed as well), rolls 32 and 34 rotate about the centers of eccentrics 40 and 41, respectively, which are thus set (diametrically offset from crank pins 52 and 53, respectively) by the positions of studs 66 and 67 (see particularly Figures 1 and 4).

In constant thickness tabletting the press tonnage indicated by gauge 77 is set at or above the maximum tonnage required for the particular volume of powder charge in dies 25 to compact the charge to the tablet thickness set by the position of studs 66 and '67. The press tonnage indicated by gauge '77 is set at or below the hydraulic pressure in line 76 which will cause foot valve 74 to open and discharge fluid from line 76 into drain line 75.

From the foregoing it can be seen that in normal constant thickness tabletting the pressing force on the punches is at or less than the tonnage which is available from spring 64 which in turn is at or less than the release tonnage. Consequently rolls 32 and 34 remain in fixed vertical position as punches 22 pass beneath them and the material in dies 25 is compacted to a constant thickness. Should an overload occur, for example, by failure of tablet ejection from the previous cycle, the upper pressure roll under which the overloaded die is passed rises as the tonnage at the punch equals that delivered by spring 64 thereby lowering its associated crank pin and tipping beam 54 (see Figure 5). This overload movement of the roll drives plunger 58 downwardly thereby increasing the compression of spring 64. If the overload is sufiiciently great, foot valve 74, because of the increased pressure on spring 64, opens, releasing the hydraulic pressure against piston 61 thereby preventing tonnage applied to the press from exceeding any predetermined safe limit set by the release pressure of valve 74. Suitably, where required, provision can be made to stop the press upon overload causing movement of beam 54, or alternatively, if required, upon actuation of valve 74.

In constant thickness tabletting since the upper punch entrance is set by the position of studs 66 and 67 conversion to different requirements of upper punch entrance is accomplished simply by changing the position of studs 66 and 67. Desirably the hydraulic system shown in Figure 6 also includes a pressure release line 78 connected to line 76 controlled by a manually or mechanically operated valve 79. Thus in changing from one setup to another the tonnage exerted against piston 61 can be varied upwardly by operation of pump 70 and downwardly by opening valve 79.

Hydraulic l0ading-C0nstant density pressing The requirements for constant density pressing are essentially those described above for constant thickness tabletting except that studs 66 and 67 are backed away from crank pins 52 and 53 a sufiicient distance to permit the powder charges in dies 25 to limit the downward travel of rolls 32 and 34 during compression. This permits pressing compacts of uniform density irrespective of thickness and the upper pressure rolls float over the punch heads rather than remaining vertically stationary.

Pneumatic loading In many cases the vertical displacement gradient of the upper pressure rolls is such that an overload might damage the punches because of the significant increase in loading tonnage as spring 64 is compressed. For a spring system the roll gradient can be demonstrated to be equal to the square of the lever ratio multiplied by the spring rate, where the lever ratio is fixed. If an air cylinder is substituted for the spring, the spring rate is reduced substantially to zero and accordingly the roll gradient likewise approaches zero.

Figure 7 shows an arrangement by which the present press can be converted to pneumatic loading, in which case guide stem 62 is pinned in position in piston 61. Referring to Figure 7 and considering the numeral v60 to represent a solidly connected arrangement of keeper 60 and piston 61, the pneumatic loading system includes a line 31 connected to a suitable air supply at one end and connected at its other end to a relieving type pressure regulating valve 82. On its discharge side valve 82 is connected to a line 83 which leads to port 65. A pressure gauge 84 is tapped in line 83 and suitably is calibrated in terms of total press tonnage. An expansion chamber 85 is also connected to line 83.

With the press in operation valve 82 is opened and set to the desired air pressure under piston 60' yielding the preselected press tonnage required as indicated on gauge 84. Since the volume of the pneumatic loading system is large an overload causing downward movement of plunger 58 as indicated in Figure 5 produces only a small incremental change in volume of the pneumatic system, and, accordingly, even with large overloads, the increase in force applied to plunger 58 is small. With the use of a relieving type pressure regulating valve the increase in force at overload is further reduced, thus the system can be designed to approach assentially zero roll gradient which is extremely desirable particularly in low tonnage applications involving small punch areas.

Pneumatic loading can of course be adapted to constant thickness tabletting by making the loading pneumatic pressure higher than the pressure normally required to compress the compact in dies 25 to the limiting thickness determined by studs 66 and 67. If studs 66 and 67 are backed off when using a pneumatic system constant force pressing is obtained since the roll gradient is essentially zero.

Hydraulic equalizer In installations where it is desired to utilize the advantages of a pneumatic system but air is not available at pressures sufficient to achieve higher press tonnages required, a combination of pneumatic and hydraulic loading can be obtained employing the pressure loading system of Figure 8.

Figure 8 shows an arrangement for converting the press described in Figures 1-3 to hydraulic loading controlled by a pneumatic system. In the arrangement of Figure 8, as in Figure 7 the reference numeral 60 designates a solidly connected piston arrangement which is vertically reciprocable within the bore of spindle 14. The lower end of spindle 14 is connected at port 65 to a conduit 86 which leads to a rubber bladder type airoil accumulator 87. A pressure gauge 88 calibrated in terms of press tonnage is connected to conduit 86. The input side of accumulator 87 is connected by, successively, a conduit 89, check valve 90, a line 91, a pressure regulating valve 92 and a conduit 93 to a source of air pressure. An auxiliary oil release line 94 is connected to line 86 through a manually or automatically operable valve 95. The output line 86 from accumulator 87 is connected by a line 96 to a gear pump 97 the intake side of which is connected to an oil reservoir.

In operation air is admitted from air line 93 to accumulator 87 through check valve 90, and conduits 89 and 91 by valve 92. Thereafter the air in accumulator 87 is compressed and higher pressures are achieved in the system by pumping oil through pump 97 and line 96 into conduit 86 until the pressure indicated by gauge 88 is at a desired level. Although piston 60 is thus hydraulically loaded the operation of the press is essentially the same as described above for pneumatic loading and accordingly the displacement gradient of the rolls loaded by beam 54 is substantially negligible.

Although the discussion in the preceding description of the drawings has been confined to a double sided rotary tablet press employing two pairs of opposing pressure rolls, it will be evident that the loading arrangement of my invention is applicable with proper construction of beam 54 to loading any desired number of pressure roll pairs. It will be further evident, although the preceding description has been confined to employment of opposing pairs of pressure rolls, that in many instances the pressure roll of a given pair which is not loaded in accordance with the present invention can take the form of a simple cam or any other device for governing the position of a punch. In particular I prefer to employ an opposing pressure roll mount of the type described in my copending application, Serial No. 552,494, filed December 12, 1955.

I claim:

1. In a tablet press including a plurality of punches, a pair of pressure rolls and means for moving said punches relative to said rolls to bring each said punch in endwise bearing contact against the peripheral surface of one said roll and thereafter against the peripheral surface of the other said roll, the improvement which includes a first axle rotatably carrying said one roll and supported for rotation about an axis eccentric to the axis of rotation of said one roll, a second axle rotatably carrying said other roll and supported for rotation about an axis eccentric to the axis of rotation of said other roll, a first means affixed to said first axle defining a bearing surface eccentric to the axis of rotation of said first axle, a second means affixed to said second axle eccentric to the axis defining a bearing surface of rotation of said second axle, a loading beam bearing against each said bearing surface in a direction tending to rotate said axles and thereby the axes of rotation of said rolls to bias said rolls into said bearing contact with said punches, and pressure means forcing said loading beam against said bearing surfaces.

2. The improvement according to claim 1 which further includes first stop means positioned to limit movement of said first means defining a bearing surface under biasing of said loading beam, and second stop means positioned to limit movement of said second means defining a bearing surface under biasing of said loading beam.

3. The improvement according to claim 1 in which said pressure means includes a pneumatically loaded cylinder and piston.

4. The improvement according to claim 1 in which said pressure means includes a hydraulically loaded cylinder and piston.

5. The improvement according to claim 1 in which said pressure means includes a spring.

6. In a tablet press including a plurality of punches mounted in a rotary head, a pair of pressure rolls and means for rotating said head to move said punches relative to said rolls to bring each said punch in endwise bearing contact against the peripheral surface of one said roll and thereafter against the peripheral surface of the other said roll, the improvement which includes a first axle rotatably carrying said one roll and supported for rotation about an axis eccentric to the axis of rotation of said one roll, a second axle rotatably carrying said other roll and supported for rotation about an axis eccentric to the axis of rotation of said other roll, a first crank affixed to said first axle, a second crank affixed to said second axle, a loading beam bearing against each said crank in a direction tending to rotate said axles and thereby the axes of rotation of said rolls to bias said rolls into said bearing contact with said punches, a reciprocable plunger atfixed pivotally to said beam intermediate the places of contact thereof with said cranks and extending centrally of said rotary head, and pressure means biasing said plunger to force said loading beam against said cranks.

7. The improvement according to claim 6 which further includes first stop means positioned to limit movement of said first crank under biasing of said loading beam, and second stop means positioned to limit move ment of said second crank under biasing of said loading beam.

8. The improvement according to claim 6 in which said pressure means includes a pneumatically loaded cylinder and piston connected to said plunger.

9. The improvement according to claim 6 in which said pressure means includes a hydraulically loaded cylinder and piston connected to said plunger.

10. The improvement according to claim 6 in which said pressure means includes a spring connected to said plunger.

11. The improvement according to claim 6 in which said pressure means includes a cylinder forming a spindle on which said rotary head is rotatably mounted, and a piston vertically reciprocable in said cylinder and alfixed to said plunger.

References Cited in the file of this patent UNITED STATES PATENTS 610,029 Clark Aug. 30, 1898 1,698,852 Miller et al. Jan. 15, 1929 2,043,086 Westin et a1 June 2, 1936

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