US2970554A - Tablet press - Google Patents

Description

Feb. 7, 1961 R. R. HAUPT 2,970,554

TABLET PRESS Filed Jan. 9, 1959 5 Sheets-Sheet 1 c D 5 //f 2/ 68 5 INVENTOR. may/2R0 A. luau/ 7- R. R. HAUPT TABLET PRESS Feb. 7, 1961 5 Sheets-Sheet 2 Filed Jan. 9. 1959 53 INVENTOR.

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Feb. 7, 1961 R. R. HAUPT 2,970,554

TABLET PRESS Filed Jan. 9, 1959 s Sheets-Sheet s TABLET PRESS Richard R. Haupt, Salem, N.J., assignor to Bristol-Myers Company, New York, N.Y., a corporation of Delaware Filed Jan. 9, 1959, Ser. No. 785,958

1 Claim. (Cl. 107-17) This invention pertains to an apparatus for making tablets and more particularly to an improved apparatus for handling powder which is fed to a tablet press.

Rotary tablet presses are commonly known to the prior art for the high speed production of pharmaceutical tablets from finely divided particulate material. Such machines generally comprise a fixed base having a circular table rotatably mounted thereupon. The table is provided, adjacent the periphery thereof, with a plurality of die cavities for reception therein of the particulate material. Mounted upon the table and reciprocably movable within each die cavity are opposed, upper and lower punches adapted to compress the particulate material therebetween and thereby to form the tablets. It is also common practice in the prior art to provide a feed frame secured to the base and mounted above the rotatable table in slidable contact therewith. Feed frames are box-like structures, universally open at the top for the reception therein of the particulate material or powder and open at the bottom whereby the powder in the feed frame rests directly upon the upper surface ofthetable. A feed frame is mounted in the path of travel of the die cavities so that as each cavity passes under the feed frame it receives a charge of powder, the lower punches having been retracted or lowered for that purpose.

It is quite ditficult to fill the die cavities by such means with an accurately predetermined quantity of powder. Accordingly, it is common practice in the prior art to-retract the lower punches to an extent greater than that necessary to give the desired final die volume and subsequently to elevate the lower punches to an intermediate height to give a final desired die volume. This elevation of the lower punches and consequent reduction of die volume results in the ejection from the die cavity of a quantity of the initially charged powder. Subsequent passage of the die under a doctor blade riding upon the top surface of the rotatable table scrapes the excess powder from thevicinity of the mouth of the filled die and leaves an accurately determined quantity of powder in the die cavity. The excess or scrape-off powder is commonly directed out of the feed frame and off the table. Forthe sake of economy, it is necessary to recycle this scrape-oil? powder, i.e., to add it to a feed hopper from which the powder was originally fed into the feed frame. The extra handling of the scrape-off powder necessitated by this recycling operation results in added operational costs, aloss of a portion of the reent from that of the bulk of the originally charged powder. 1 Consequently, such, handling of the powderfeed often results in finished tablets having compositions and properties other than those intended.

states {gm cycled powder with consequent increased cost of matea j the filling position.

It is a further object of the invention to provide a powder handling apparatus for eliminating recycled scrape-oil powder in a rotary tablet press. 7

It is another object of the invention to provide apparatus for increasing the rate of production of tablets by a rotary tablet press.

It is a still further object of the invention to provide apparatus for producing tablets of a more uniform composition.

In accordance with the above objects, there is provided a method of handling powder which is fed to a tablet press having a feed frame and rotary table provided with a plurality of dies and opposed, reciprocable upper and lower punches, which comprises initially only partially filling the die cavities, retracting the lower punches to increase the volume of the die cavities, filling the increased volume die cavities, elevating the lower punches to an intermediate height, removing from the vicinity of the dies the excess powder ejected therefrom, confining the ejected excess powder within the feed frame and directing the thus-confined powder into the die cavities of increased volume.

In accordance with one embodiment of the apparatus contemplated by the invention, there is provided a tablet press of the type having a fixed base and a circular table rotatably mounted upon the base and provided with a plurality of dies and opposed upper and lower punches reciprocably movable within the dies. A totally enclosed feed frame is provided into which powder may be fed, through a feed spout, from a supply hopper mounted upon the base. Lower cam means are provided to control the sequential elevation and retraction of the lower punches with respect to the feed frame and feed spout. The position of the feed spout is adjustable along the path of travel of the dies in order to control the amount of powder fed into each die at a filling position thereof. By predetermined positioning of the feed spout with respect to the dies and the lower punch cam means, the die cavities may be either overfilled or underfilled at Means are provided to thereafter overfill the dies and doctor blades are provided to scrape off the excess powder from the dies, to confine the scrapeoifpowder within the feed frame and direct it immediately back into succeeding dies.

A fuller understanding of the invention may be had by reference to the-following description and to the accompanying drawings wherein:

Fig. 1 is a top plan view of a rotary tablet press, a portion thereof being partially cut away to more clearly illustrate the associated feed frame, feed spout and hopper; a r

Fig. 2 is a schematic development, partially in crosssection, of a portion of the tablet press and associated dies, punches and cam means in operative association with the feed hopper, spout and feed frame, a single upper punch being shown in a retracted position;

Fig. 2A is a fragmentary side elevation partially in cross-section, of a portion of the apparatus illustrated in Fig. 2 and showing an upper. punch in a closed, or tabletforming position; i a l .Fig. 3 is an enlarged plan view of the feed frame, spout and hopper illustrated in Fig. 1;-- i i Fig; 4 is a slightly enlarged side elevation, partially in cross-section, taken along line 44 of Fig. 1 and showing the feed hopper and spout in operative associationwith an upper and a lower in the filling position;

- Fig. 5 is a view taken along line 5-5 of'Fig. 3 and punch and a die cavity shows, partially in cross-section, a suitable means for mounting within the feed, frame a'doctor blade to scrape excess powder from the dies;

Fig. 6 is a view taken along line 66 of Fig. 3 and shows, in cross-section, another blade for retaining and directing the flow of scrape-off powder within the feed frame, and

Fig. 7 is an exploded perspective view of the feed frame, feed hopper and spout and a portion of the rotatable table of the tablet press.

Referring now to the drawings, and in particular to Figs. 1 and 4, the numeral 11 designates generally a fixed base of a tablet press. Rotatably mounted upon the base is a circular table, designated generally by the numeral 12. Serially spaced, in a circular pattern adjacent the periphery of the table is a plurality of cavities 13 extending through the table. Inserted within each cavity is a die 14 in the form of a generally cylindrical sleeve. The dies 14 may be retained within the cavities 13 by abutment against a radially inwardly projecting shoulder 16 formed by a reduced diameter portion 17 of the cavities 13 (Fig. 2). Slidably mounted within the cavity of each of the dies 13 is a generally cylindrical lower punch designated generally by the numeral 18. Each punch 18 has a head portion 19 which, when the punch is mounted in a lower die, projects beneath the die and is engageable with the base 11 in a fully retracted, or lowermost position of the lower punch. Mounted upon the base and underneath the dies is a circular cam track denoted generally by the numeral 21 and adapted, at predetermined positions, to elevate and to retract the lower punches 18 as the same are carried along the track by the rotating table.

Mounted on. the table concentrically thereof and rotatable' therewith is an upper punch holder 22 provided about the periphery thereof with a plurality of passageways 23 receiving sleeves 24 for the slidable reception therein of upper punches designated generally by the numeral 26. The upper punches are alignable with the die cavities in the table 12 and are adaptable for entry therein in cooperation with the lower punches 18 to compress the powder in the die cavities into the form of tablets (Fig. 2A). One extremity of each of the upper punches 26 is provided with an expanded head portion 27 whereby the upper punches maybe held in a retracted or uppermost position by engagement of the head portions 27 of the upper punches with a beveled edge 28 of an upper cam member denoted generally by the nu meral 29 which is mounted concentrically of the table above the upper punch holder 22 and secured against rotation by attachment to the base 11. At one orImore intervals the edge 28 is depressed, thereby permitting the upper punches to fall into a lower position and to enter the cavities'of the dies 14 whereupon the expanded head portions 27 of the upper punches are engaged by a rotatable upper compression roller 31 to force the upper punches against the powder charges in the die cavities to compress the same into tablet form. The roller 31 may be adapted for powered rotation by any suitable means (not shown), as through a gear 32 upon axle 33. Simultaneously, with the actuation of the upper punches by the upper compression roller 31, the lower punches are forced upwardly within the die cavities by a l'ower com'pression roller (not shown) similar in construction to the upper compression roller 31 and mounted in opposition thereto cavities.

generally by the numeral 37, is secured, as 'bymeans of a bolt 38, to the fixed base 11. A portion of the feed frame projects from the base and is positioned over the rotatable table 12 and slidably rides against the upper surface thereof. The feed frame 37 is provided with an elongated well 39 the center line of which coincides with the path of travel of the vertical center lines of the dies. The well 39 is enclosed on all sides by the body of the feed frame so that powder fed into the well can escape therefrom only by falling into the die cavities which pass under the Well.

A scraper or first doctor blade 41 is slidably mounted within a groove 42 in the feed frame 37 and forms one end wall of the well 39. The lower edge of the doctor blade 41 bears against the surface of the table 12 and extends in a direction normal to and across the path of travel of the dies. The doctor blade 41 is forcibly and resiliently maintained in contact with the surface of the table by means of two spring bars 43 each of which is .to a. maximum height to eject the'tablets fro'mtlie die The thus-formed tablets, after their ejection from the die' cavities may be removed from the table as by means of a deflector 34 into a discharge chute 36 mountedlon thebase 11.. 1 1 v Referring now. to Figs. 3 and7, a feed frame, denoted secured at one extremity thereof to the feed frame as by screws 44 (Fig. 5). The other end of each of the spring bars 43 bears against one extremity of a pin 46 which is slidably mounted in a hole 47 within the feed frame. The other extremity of each of the pins 46 bears against the upper edge of the doctor blade 41 to bias the same against the table to maintain scraping contact therewith.

Mounted upon the feed frame adjacent the first doctor blade 41 is a second blade denoted generally by the numeral 48 (Fig. 6) for containing and directing the flow, within the well 39, of powder scraped from the dies. This second blade comprises an apertured first arm 49 which is secured, as by means of a screw 51, to the feed frame above the Well 39, and a second arm 52 which de pends, at an angle to the surface of the table, into the Well 39 and has an extremity 53 thereof Which may ride against the upper surface of the table 12 adjacent the first blade 41. The depending arm 52 or the entirety of the second blade 48 is formed of a suitably resilient material so that the depending arm 52 may be held in contact with the surface of the table at all times. Thedepending arm 52 extends across substantially the entire width of the well 39. Certain powders of relatively soft sub stances tend to compact when subjected to pressure and,

consequently, to form solid aggregations in the triangular space defined by the upper surface of the table 12 within 1 the feed frame 37 and the under surface of the arm 52 of the blade 48. In such instances, this undesirable occurrence may beavoided by spacing the extremity 53 slightly from the table. For example, in the case'of a granulation comprising a mixture of magnesium carbonate and dihyd'roxyaluminum aminoacetate, it has been found that'a spacing of about inch between the table and the extremity 53 effectively precludes compaction.

A feed spout, denoted generally by the'numeral 54,

secu'redto the lower end of a feed hopper 55, is provided with flattened surfaces 57 (Fig. 7) adapted to be clamped by shoes 58 whenthe spout extends between the arms 59 of a' generally U-shaped yoke denoted generally by the numeral 61. The shoes 58 aresecured to the yoke 61 as by screws 62. The subassembly comprising the yoke 61, shoes 58, 'feed spout 54 and hopper 55 is secured, as

by means of screws 63, through the yoke 61 to a 64' and the associated hopper and feed, spoutmay be moved-a limited d1stance .along the pathof travel 'described :bythe dies. I i

The cam track 21'.is designed so that when the lower punches 18 pass beneath the leading end wall of'the' The .slots'67 are in the form of arcs of a feed frame 37 (the left end wall in Fig. -2), the lower punches 18 are in an uppermost position (position A of Fig. 2) thereby substantially completely occluding the die cavities as the same pass beneath the leading wall of the feed frame. The floor of the cam track ll is further provided with a gradually inclined surface 68 whereby the lower punches 18, after they pass under the leading wall of the feed frame are gradually retracted or lowered. The feed spont 54 extends into the well 39 of the feed frame adjacent the leading wall thereof and above the lower punches 18 when the same are at an intermediate position in their travel down the inclined surface 68 of the cam track 21 (position B of Fig. 2). The mouth of the feed spout is spaced a predetermined distance a above the upper surface of the table 12 so that the powder does not flow out of the feed spout and fill the well 39, but instead, when no die is beneath the feed spout, rests upon the upper surface of the table filling substantially only the volume defined by the area of the feed spout open ing and the distance a. For example, it has been found that when a has a value of about inch, this powder choke-off" feature obtains. Of course, when a die is moved into a filling position underneath the feed spout, the powder falls into the die cavity. The feed spout 54 is desirably positioned at an angle with respect to the vertical center line of the dies (Fig. 4). It has been found that by such means the powder feed, entering the die cavities at an angle thereto and, for the most part, directed against the wall of the die opposite the feed spout, has the desirable effect of pushing before it the air within the die cavity. Consequently, less air is entrapped within the powder charge in the die cavities than is common in prior art procedures and devices and hence more uniformity in charge quantities is achieved.

With further movement along the cam track 21, the lower punches 18 are retracted to a lowermost position (position C of Fig. 2) wherein the volume of the die cavity is increased to an extent greater than the final desired volume. Still further movement of the lower punches along the cam track 21 results in their elevation, by means of an inclined portion 69 of the cam track 21 to a final desired height corresponding to a final desired die cavity volume (position D of Fig. 2). The excess powder is ejected into the well 39 where it is scraped from the mouth of the die by the doctor blade 41. This scrapeoff powder is directed by means of the resilient blade 48 back into the well 39 where it falls into a succeeding die cavity as in position C of Fig. 2. Thereafter the dies, containing accurately predetermined quantities of powder pass beneath the trailing edge (the right hand edge in Fig. 2) of the feed frame after which the powder in the dies may be compressed by the punches into tablets of a uniform size, weight and composition (position E of Fig. 2).

In operation, powder is fed from the hopper 55, through the feed spout 54 into a die in the filling position "B (Fig. 2), the feed frame having been previously primed with a quantity of powder for completely filling the dies in position C when the lower punches are completely retracted. The scrape-off powder removed from the dies in position D is added to the supply of powder within the feed frame available for filling the dies. If the volumes of the die cavities at positions B and D, i.e., the filling position and scrape-off position, respectively, are substantially equal, there will be no net accumulation of powder within the feed frame and continuous operation is insured without the necessity of recycling any of the powder feed from the hopper to the tablet press.

If, however, there is a net. accumulation or depletion of the supply of powder in the feed frame and available feed spout-is moved to the left (Fig. 2) thereby decreasing the amount of powder initially filled and consequently increasing the amount of powder which must be supplied to the dies in position C. Accordingly, this adjustment increases the rate of depletion of the powder supply in the feed frame. Conversely, if there is a net depletion of scrape-off powder within the feed frame, the feed spout may be moved to the right (Fig. 2) whereby the amount of powder initially filled into the die cavities in the filling position is increased. Consequently, the amount of scrape-off powder to be filled into the dies in position C is smaller and, since the amount of scrape-off powder removed from the dies in position D remains the same, this results in an accumulation of scrape-oft powder within the feed frame. A few adjustments of this nature serve to balance the input to and output of powder from the feed frame.

Rotary tablet presses provided with the improved powder feed handling apparatus contemplated by the invention will produce tablets of a uniformity superior to those produced by those known to the prior art. There is no alteration of the character of powders or granulations fed to the tablet press in accordance with the in vention as so often happens in prior art devices where the scrape-off often amounts to as much as fifty percent of the material originally fed to the press. There is a consequent increase in rate of production when the apparatus of this invention is used since one hundred percent of each batch of powder feed is converted directly into tablets without the necessity of recycling. These advantages are especially desirable in those instances where the material fed to the feed frame is in the form of friable particles or granulations which tend to be reduced in size by the mechanical operations entailed in filling the die cavities, scraping off the excess powder and subjecting it to the additional handling necessitated by recycling. The scrape-off fraction of such materials, when handled by prior art devices, generally had to be completely reworked in order to convert it to the original particle size before mixing with the main portion of the feed. This disadvantage has been eliminated by the present invention by reducing the number and severity of the mechanical operations to which the powder is subjected before compression into tablet form.

In the embodiment illustrated in the drawings, only one feed frame has been shown. Manifestly, however, two or more feed frames could be mounted on a single tablet press. Such a construction is particularly desirafor filling the diecavities in position C, a correction l may be easily made by adjusting the position of the feed spout in the filling position B. .Thus, if there is a net accumulation of scrape-01f powder within the feed frame the ble in the production of multilayer or core tablets.

Although the foregoing description and drawings are directed to a single embodiment of the invention, it is obvious that other embodiments, modifications and additions may be made by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

An improved tableting apparatus comprising a fixed I base, a circular table rotatably mounted upon said base, said table having a plurality of die cavities adjacent the periphery thereof and extending therethrough, upper and lower punches mounted upon said table and reciprocably movable into and out of said die cavities, a feed frame secured to said base and positioned above and adjacent said die cavities, said feed frame defining a completely enclosed well, apowder feed hopper mounted upon said base and positioned above said table, a spout on said hopper extending into said well adjacent to the side of the feed frame from which the die cavities are first introduced within said well upon rotation of the table and spaced from said table above thepath of travel of said die cavities, means to rotate said table so that the die cavities are successively positioned beneath said spout to receive powder-from said hopper, 'means to lower said lower punches after powder has been received in the die cavities from said spout, means to there-after elevate said lower punches, a rigid spring-biased first doctor blade arr-#0554 7 mourned on said teed frame adjacent the side of said frame from which the die cavities move out of the well upon" rotation of the table and bearing against the upper surface of said table whereby excess powder is scraped from said cavities after said lower punches are elevated, a resilient second doctor blade for retaining and directing the flow of the scrape-off powder within said feed frame, said second blade being secured at one extremity thereof to said feed frame above said well and having a depending portion thereof extending into said well and substantially completely thereacross at an angle to said table, a free extremity of said depending portion resting upon said table adjacent said first blade whereby the scrape-off powder is directed by said second blade into the die cavities wherein the lower punches are lowered,

8 means for adjusting the spacial relationship'between said hopper" and said die cavities in the powder-receiving p0 sition thereof whereby the amount of powder received in said die cavities and, consequently, the amount-of scrape-off powder accumulated within the feed frame may be controlled, and means to reciprocate said upper and lower punches to compress the powder in said die cavities into tablet form.

References Cited in the file of this patent UNITED STATES PATENTS 901,937 Scott Oct. 20,1908

2,043,086 Westin a a1. June 2,1936

FOREIGN PATENTS V 158,643 Australia Sept. 6, 1954

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