US3408963A - Tablet machine - Google Patents

Description

Nov. 5, 1968 J, ALEXANDER, JR ET AL 3,408,963

TABLET MACH INE Filed May 2, 1967 FIG.2

INVENTORS v. E dm "8 N "H R 0 M 4 T Am T A MR m n vW J United States Patent 3,408,963 TABLET MACHINE John M. Alexander, Jr., and William H. Hamilton, Philadelphia, Pa., assignors to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed May 2, 1967, Ser. No. 635,534 9 Claims. (Cl. 10717) ABSTRACT OF THE DISCLOSURE A tablet machine has an auxiliary roll, between the lower pressure roll and the ejection cam surface, for actuating the lower punch to dislodge a compressed tablet from the die. The auxiliary roll is carried by mounting means permitting vertical adjustment of the roll simultaneously with, or incident to, vertical adjustment of the lower pressure roll; and the positional relationship of the rolls to each other is maintained in their various vertical positions.

DISCLOSURE OF THE INVENTION This invention relates to tablet machines, such as rotary tablet presses, which employ a traveling tool assembly including opposing upper and lower punches which cooperate in a die to form tablets between them as they are passed between upper and lower pressure rolls and thereafter move to eject the tablets from the die. The invention in particular provides a novel construction for actuating the lower punch to dislodge a compressed tablet held tightly by the die prior to its ejection from the die.

Conventional rotary tablet machines of the type employing traveling tool assemblies are shown in US. Patent No. 1,289,570, issued Dec. 31, 1918 in the name of F. I. Stokes; US. Patent No. 2,043,085, issued June 2, 1936 to C. I. Westin et al.; and US. Patent No. 2,839,015, issued June 17, 1958 to R. G. Frank. These machines are conventionally arranged to eject the tablet after it leaves the lower pressure roll by passing the lower punch onto an ejection cam which forces the lower punch upwardly in the die to lift the compressed tablet and eject it from the die. The pressure roll may have its vertical position adjustable by journalling it eccentrically on a horizontal shaft, or by journalling it on an eccentric horizontal shaft according to the cited Frank patent, so that the vertical position of the punch-contacting surface of the pressure roll may be set by adjustment of the angular position of the shaft.

One of the problems with conventional apparatus to which the present invention is addressed is excessive wear of the ejection cam surface. This problem is more acute in situations where tablets are highly compressed and thus make such tight contact on their edges with the die that they resist ejection. This resistance is transmitted by the lower punch to the steeply inclined, ejection cam surface and produces a high normal force there with the punch head. As a result, high friction forces are developed and the contacting parts wear so rapidly as to require all too frequent replacement.

In order to overcome this problem the present invention proposes to employ a freely rotatable auxiliary roll at or adjacent the leading or first-contacted portion of the ejection cam surface to effect breakaway, or initial dislodgement of the tablet to break or loosen its tight grip on the die. In carrying out this concept, the contact surface of the auxiliary roll is set a small fixed distance above the vertical position of the contact surface of the pressure roll, for example .085 inch. Normal ejection of the tablet, wherein the lower punch head travels up the ejection cam surface with a minimum of resistance, can then follow.

It is a feature of the present invention that the mentioned vertical distance between the contact surfaces of the auxiliary roll and the pressure roll is maintained by mounting the auxiliary roll so that it maintains its position relative to the compression roll during vertical adjustment of the latter to various vertical positions.

In the drawings:

FIG. 1 is an enlarged fragmentary elevational view of a tablet machine, illustrating one pair of punches in four positions and the adjusting mechanism, constructed according to the invention.

FIG. 2 is a vertical rectilinear development of a rotary tablet machine embodying the invention, taken through the arcuate series of punches along arcuate line A--A of FIG. 3.

FIG. 3 is a fragmentary plan view of the apparatus showing the feeder framein detail.

Referring to the drawings for a detailed description of the invention, the tabletting machine includes a rotary tool head 12 which is rotated on a central vertical spindle (not shown). The tool head 12 includes three superposed tiers which move as a unit. The top tier 14 is a horizontal annular disc provided at arcuate intervals adjacent to its periphery with a series of vertical sockets or openings receiving upper punches 16. The middle tier 18 is a horizontal annular disc positioned beneath disc 14 and spaced therefrom. Tier 18 is provided at arcuate intervals with a series of vertical die openings 20 which are vertically aligned with the longitudinal vertical axes of the upper punches 16 and their sockets. The bottom tier 22 is an annular disc positioned immediately beneath the disc 18 and provided at arcuate intervals with a series of vertical sockets or openings for respective lower punches 26 aligned vertically with the die openings 20 in disc 18 and also the vertical axes of the upper punches 16 and their sockets.

As best seen in FIG. 1, a series of upper and lower cams 27 and 28, respectively, are mounted on a pedestal 29. The lower cam series 28 is disposed immediately below the rotary tool head 12; and it cooperates with the heads of the lower punches 26 to move the lower punches 26 up and down in the conventional manner.

As is well known, in tabletting machines of the type set forth herein the punches 16 and 26 oppose each other in die cavity 20 to form tabletted products between their adjacent ends. Referring again to FIG. 1, the general operation commences in a fill position (at the right hand end of the illustration) in which upper punch 16 is completely withdrawn from die cavity 20 and in which lower punch 26 is depressed toward the bottom of the die cavity 20. In the fill position the powdered material which is to be tabletted flows fr-o a hopper 30 downwardly into a feed frame 32, and from there into the upwardly opening cavity 20 above punch 26. Thereafter as head 12 rotates the operation progresses (toward the left as shown in FIG. 1) and a selectively positionable weight adjusting cam 33 raises the lower punch 26 slightly to lift some of the powdered material out of the die, and the excess is scraped off. Next, the lower punch 26 is relowered and then travels straight, while at the same time the right hand portion of upper cam 27 lowers upper punch 16 into cavity 20 to close the upper end of the die cavity 20.

The feed frame 32 is shown in FIG. 3 in relation to a broken line 35 indicating the arcuate path of travel of the punches 16 and 26.

The pair of opposing punches 16 and 26 are then passed between vertically aligned, upper and lower pressure rolls 34 and 36 which are also supported by the pedestal 29. Upper pressure roll 34 is freely rotatable about a horizontal axis and is positioned such that the lower portion of its edge rides over the head of upper punch 16, forcing punch 16 down in die cavity 20. At the same time, lower pressure roll 36 which is also mounted for free rotation about a horizontal axis, rides under the head of lower punch 26, thereby forcing lower punch 26 up in die cavity 20 and opposing the downward movement of punch 16 to compress the powdered material in die cavity 20 between the punches.

After the compression operation, the rotation of head 12 carries upper punch 16 again onto cam 27 the left hand end of which lifts it from die cavity 20. As this action takes place, lowerpunch 26 proceeds toward the ejection of the compressed tablet; and this will now be described in detail with reference especially to FIG. 2.

It is to be noted in FIG. 2 that the punches 16 and 26 are not equally spaced, as in FIG. 1. This is because FIG. 2 illustrates one punch out of the entire series, in four selected positions proceeding from compression through complete ejection. In actual practice of the invention, therefore, a series of equally spaced punches are shown in their various positions.

The numeral 40 in FIG. 2 designates a stationary ejection cam of the lower cam series 28 which forces the lower punch 26 upwardly and further into die opening 20 until the upper end thereof is in registry with the upper surface of a disc 18, thereby lifting the compressed tablet out of the die opening 20 in position to be intercepted by an abutment surface 42 for delivery to a discharge chute (not shown).

According to the invention, there is disposed between the lower pressure roll 36 and the ejection cam 40 a breakaway or auxiliary roll 44. The roll 44 is mounted for free rotation on a movable guide block 46 adjacent the leading or first-contacted portion of the ejection cam 40. As best seen in FIG. 2 the upper or contact surface of the auxiliary roll 44 is slightly closer to the rotatable head 12 than is the upper or contact surface of the lower 1 pressure roll 36, preferably by a distance of .085 inch. It is the function of the auxiliary roll 44 to engage the head of the lower punch 26 and deliver thereto a sudden upward force which is transmitted to the compressed tablet 48 in order to loosen the grip of the tablet 48 on the die cavity.

It is to be appreciated that the high compression forces employed to press the powdered material into tablet form exerts a high lateral force at the interface between the die and the periphery of the tablet, so that the tablet offers appreciable resistance to ejection. It has been found, however, that the delivery of a sharp blow to the tablet at the beginning of the ejection stroke facilitates ejection thereafter by a conventional ejection cam 40 having a steeply inclined surface, with the further advantage of minimizing wear on the ejection cam surface. In addition, the roll 44 experiences a minimal amount of wear as the result of contact with the head of the punch 26 because its engagement therewith is rolling contact involving a relatively small amount of friction and considerably less force than is required for compression by the pressure rolls.

It is also to be noted from FIG. 2 that a bridging surface 50 extends horizontally within the space between the contact surface of the lower pressure roll 36 and the contact surface of the roll 44. It is the function of the bridging surface 50 to prevent a sudden drop in the punch 26 as it travels between the rolls 36 and 44. The bridging surface 50 may be rigidly attached to the pedestal 29 or it may be arranged to be moved with the lower pressure roll 36 during any vertical adjustment thereof according to the teachings of the previously cited Frank Patent 2,839,015. The Frank patent may also be referred to for a description of one means for effecting vertical adjustment of the lower pressure roll 36, also to show how the roll 36 is held against movement from the position to which it has been adjusted. The lower pressure roll 36 is preferably rotatably mounted on a horizontal shaft 52 so as to be driven by a circular gear 54 keyed to the other end of shaft 52. By eccentrically 4 mounting the lower pressure roll 36 on the shaft 52, the vertical position of the roll contact surface may be varied and set by adjustment of the angular position of the shaft 52. Such adjustment may be desired to vary the compressive force imposed upon the material to be tabletted.

In order that the difference between the vertical distances of the respective contact surfaces of the rolls 34 and 36 to the heads of the punches 26 may be maintained uniform, for example, .085 inch, it is desired that they maintain their relative positions to one another throughout various vertical adjustments of the roll 36. Stated another way, it is desired that the roll 44 be moved a corresponding vertical distance whenever a vertical adjustment of the roll 36 is effected. Preferably this is accomplished simultaneously with, or incident to, vertical adjustment of the roll 36. In carrying out this concept, the guide block 46 is carried for vertical movement in vertical grooves in the pedestal 29, and it is provided with a lower cam surface 56 which is engageable with a generally circular cam 58 eccentrically mounted on one end of a horizontal shaft 60 and keyed thereto. The cam 58 is driven for angular movement through shaft 60 by a circular gear 62 similar to gear 54; and both gears 54 and 62 are simultaneously driven through the same amount of angular movement by respective Worm gears 64 and 66 rigidly mounted on a common shaft 68, as shown in FIG. 2. The radial distances between the contact surfaces of the cam 58 and the roll 36, and also the corresponding angular inclinations of the maximum and minimum distances are such as to effect the same degree of vertical movement of the contact surfaces of the rolls 34 and 36 relative to the heads of the punches 26 and the rotary tool head 12.

It can be seen that angular rotation of the shaft 68 produces the same degree of angular rotation of the gears 54 and 62, their respective shafts 52 and 60, and the roll 36 and cam 58, with the result that the guide block 46 and roll 44 are driven upwardly or downwardly to the same extent that the contact surface of the roll 36 is elevated or depressed.

From the foregoing it can be seen that a tablet can now be ejected from a die with a minimum amount of wear on the lower punch head and the ejection cam, and yet the required ejection forces are obtained with a minimum amount of frictional head. It is a further advantage of the invention that wear on the punch sockets is reduced because lateral movement of the punches is minimized as a result of the small friction forces encountered during the ejection operation. It is also to be noted with reduced wear of the punch sockets the punches are maintained in good alignment, thus further ensuring the production of a quality tabletted product.

What is claimed is:

1. In a tablet machine having structure rotatable about an axis including a disc provided with a die cavity extending therethrough and a pair of opposed punches coacting therewith and one another to receive and compress material to be tabletted and eject the same in tablet form, with pressure rolls on opposite sides of said disc to force said punches toward one another during compression of said material, and a stationary cam following one of said pressure rolls relative to the direction of movement of said structure for moving one of said punches further into said cavity during ejection of the tablet, the improvement comprising an auxiliary roll positioned between said one pressure roll and said stationary cam and having a contact surface disposed closer to said disc than said one pressure roll for contacting said one punch in rolling engagement to loosen a tablet in said die cavity following its compression and prior to its ejection.

2. A tablet machine according to claim 1 wherein said disc is horizontally disposed, said axis extends vertically, said die cavity and said punches are vertically elongated, and said pressure rolls and said auxiliary roll are vertically spaced from said disc.

3. A tablet machine according to claim 2 further including stationary cam means for raising the other of said punches following compression of said material.

4. A tablet machine according to claim 2 further including a horizontal earn surface bridging the space between said one pressure roll and said auxiliary roll and being no closer to said disc than the contact surface of said one pressure roll.

5. A tablet machine according to claim 1 wherein the contact surface of said auxiliary roll is .085 inch closer to said disc than the contact surface of said one pressure roll.

6. A tablet machine according to claim 1 further including means for adjusting the spacing between said disc and said one pressure roll while maintaining said auxiliary roll and said one pressure roll in the same positions relative to one another.

7. A tablet machine according to claim 1 further including a shaft upon which said one pressure roll is eccentrically mounted whereby the position of the punch-contacting surface of said one pressure roll is set and the distance thereof to said disc is varied by angular rotation of said shaft, means for transmitting angular rotation to said shaft, and means responsive to angular rotation of said shaft for moving the punch-contacting surface of said auxiliary roll the same distance and in the same direction as the punch-contacting surface of said one pressure roll.

8. A tablet machine according to claim 7 wherein said last-mentioned means includes a movable mount for said auxiliary roll, and an eccentrically mounted c am engaging said mount and driven by said transmitting means through the same amount of angular rotation as said shaft for varying the distance of said mounting means and said auxiliary roll to said disc in like direction and amount as said one pressure roll.

9. A tablet machine according to claim 1 further including first and second rotatable means each eccentrica'lly mounted relative to said auxiliary roll and said one pressure roll and being ang-ularly rotatable, said first and second rotatable means being in respective driving relation to said auxiliary roll and said pressure roll for effecting like amounts of movement of their contacting surfaces toward or away from said disc for like angular rotation, and common driving means for said first and second rotatable means for effecting like angular rotation thereof.

References Cited UNITED STATES PATENTS 2,949,082 8/1960 McCarley 107--17 2,997,741 8/1961 Crossley 107--17 XR 3,158,111 11/1964 Raff 10717 XR 3,230,905 1/1966 Gajda 107-17 WALTER A. SCHEEL, Primary Examiner.

A. O. HENDERSON, Assistant Examiner.

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