US2724145A - Tabletting machine - Google Patents

Description

NOV. 22, 1955 K. w. HALL TBLETTING MACHINE 6 Sheets-Sheet l Filed OCT.. 5, 1950 INVENTOR KE/TH W. HALL Nov. 22, 1955 K. w. HALL. i 2,724,145

TABLETTING MACHINE Filed om. s, 195o 6 sheetsfsheet 2 ROTARY l INVENTOR KEITH W. HALL Va @giri 'TORN Y Nov. 22, 1955 K. w. HALL 2,724,145

TABLETTING MACHINE Filed OGt. 5, 1950 6 Sheets-Sheet 5 im 26 um 26 lm um /V/T/AL PRE- COMPRESS/ON FINAL DOWN RETURN (IP- DOW/V STROKE .Dh/ELL COMPRESS/ON STROKE AND STROKE PREFORM EJECTION /N/ r/A L tu Dow/v STROKE l u RETURN STROKE PRE- COMPREss/ON STROKE PRE- CoM/PRESSION f pwELL [(/RETURN .STROKE :t PosT- cGMP/esss/m/ Dm/ELL U r .....J 2 E l l1 l [t U Qq n COMPRESSION l POST- CoMPREsS/o/v DWELL l b t PRE-FORM Tmc/mess u TIME INVENTOR KE/TH W. HALL Nov. 22, 1955 Filed Oct. 3, 1950 K. W. HALL TABLETTING MACHINE 6 Sheets-Sheet 4 Nov. 22, 1955 K. W. HALL 2,724,145

TABLETTING MACHINE Filed oct. 3, 195o e sheets-sheet 5 FEEDER INVENTOR KE/TH W. HALL BY Y ATOR EV Vinterstices thereof when in its loose condition.

United States Patent TABLETTING MACHINE Keith W. Hall, `Ann Arbor, Mich., assignor to Baldwin- Lima-Hamilton Corporation, a corporation of Pennsyl- Vania Application October 3, 1950, Serial No. 188,233

" 4 Claims. (ci. 1s`1s.s)

This invention relates generally to preform presses for tabletting plastic powders and other materials and more particularly to means for eliminating laminations in and splitting of the preforms.

` When tine plastic powders, having a consistency of flour or talcum powder, are tabletted or preformed on various types of presses, especially conventional high speed mechanical presses, they tend frequently to have laminations 4 therein which makes the preform friable and subject to splitting. This splitting or laminating of the tablet is caused by air becoming trapped in the die cavity when the compressing plunger enters the same, the air being naturally distributed throughout the ne powder in the minute Certain theories have been advanced as to how this trapped air acts in producing the laminations or the splitting and various arrangements have been heretofore proposed and used in an effort to control or eliminate the action of the Mair; For instance the end face of compression punches i a dwell at the end of the compression stroke or the speed of operation of the press has been slowed down or the compressing plunger is lifted to allow escape of air and then its `compression stroke is resumed, or the compression plunger stroke` has a dwell eifected by a predetermined pressure thereby maintaining the material under a constant pressure while `attempting to expel the air. However, none of these or other arrangements has been really satisfactory, and `when it is considered that the material worked upon in my invention is an extremely tine powder, it is seen that this is a highly aggravating factor and that the problem is most serious.

Under other `circumstances a fully compressed tablet, even `though the air has been eifectively eliminated, will shatter or separate when the compression pressure is released.` This is particularly true of preforms made of melamine or other plastics having similar characteristics.

One object of my invention is to provide an improved combination of elements that eliminates laminations in the tablets or preforms or the splitting or shattering thereof, regardless of whether the aggravating condition occurs "prior to the actual compaction or upon release of the compacting pressure. i' A further object is to provide anirnprovedapparatus and method ofoperation for controlling the trapped air in Fig. 2 is a section taken generally along the line 2-2 i of Fig. l with certain parts broken away to show further details of construction.

Figs. 3 to 6 are diagrammatic views of the upper punch,`

lower punch, and die cavity of the press, showing four phases in the cycle of operation of the punches to compress a tablet in accordance with the invention disclosed herein;

Fig. 7 is a time vs. punch-movement diagram;

Fig. 8 is a sectional view of the air clutch and brake flywheel control taken substantially on line 8-8 of Fig. 2;

Fig. 9 is a sectional view of a solenoid-operated air valve for controlling the clutch and brake;

Fig. l0 is a horizontal sectional view of an adjustable commutator type timing switch for controlling the solenoid valve;

Fig. 1l is a transverse section of the switch taken on line 11--11 of Fig. l0; and

Fig. l2 is a wiring diagram of the electric circuits for operating the press and for creating a pre-dwell in each cycle of operation as well as a post-compression dwell.

In the particular embodiment of my invention which is disclosed herein merely to illustrate one specific form among possible others that the invention might take, I have generally shown in Figs. 1 and 2 a high speed preform press of the type described in Patent 2,214,505. The press has a main housing 10 and a head 12 mounted on four vertically reciprocating tie rods 13 guided at their upper ends by the housing and at their lower ends by lugs 14 of a stationary gear bracket 1S. The rods are connected in pairs to equalizing members 16, Fig. 1, and thence to connecting rods 18 on a double overhung crank shaft 19 journaled in the gear bracket 157. A gear 20 and pinion 21 drives the crank shaft. A suitable die 22, Fig. 2, is held in a recess 23 while an ejector rod 24 is carried by an ejector ram 25, the ejector rod also forming the bottom of the die opening. A compression punch 26 is carried by a punch ram 27 mounted in the head 12. Inasmuch as the punch and ejector ram devices, as well as the means for feeding material to the die cavity, do not per se form a part of the present invention, further description thereof has been omitted for sake of clarity. These devices, however, and other details of the press are disclosed in said patent.

I have found that laminations or splitting of the pre-` may be slightly tapered preferably throughout its 1ength and then continuing the downward advance of the upper punch to complete the compression stroke. As the length Patented Nov. 22, 1955 l of this pause during the pre-compaction dwell or during the post-compaction dwell, as they might be respectively called, and the positions of the upper punch at the times of the dwells may be varied with the particular type of material being used or with the size of the tablet being made, or with both, l provide means for making adjustmcnts towards this end. It will be understood that the dwells may be selectively or simultaneously used as is necessary.

Figs. 3 to 6 illustrate diagrammatically four phases in a cycle of operation of upper punch 26 as it compresses nely powdered material into tablet form according to the pre-compaction principles of my invention, it being understood that reference herein to powdered material includes varying degrees of tineness up to granular material. Fig. 3 shows upper punch 26 beginning its downward stroke into die cavity 11 whose walls are slightly tapered. Fig. 4 shows the point at which upper punch 26 has been stopped during its compression stroke. lt is seen that while the material in the die cavity may be momentarily compressed yet in accordance with one possible theory of operation of my invention this compression is only suflicient to squeeze out the air naturally present in the powder, the air escaping from between the sides of the upper punch and the tapered walls of the die cavity, as shown by the arrows in Fig. 4. It is believed that after expulsionof the air the bulk factor of the material has been reduced only to the point where no compaction of the material has actually taken place, or if so, it is not suicient to effect laminations. After a pause or dwell of a predetermined length of time has elapsed, upper punch 26 continues its downward stroke to the point shown in Fig. 5 when the material is finally compressed to the necessary degree of density and evenness. As there is little or no air in the material during this final compression stage which etfects compaction, the release of pressure on the material by the withdrawal of upper punch 26 from the die cavity, as shown in Fig. .6, does not result in any fracture of the tablet or in the formation thereof. lt has been found that the finer the material, the longer the pre-compression dwell should be although usually one-half second is the maximum.

To create a pause or dwell in the cycle of operation lof the press, I have provided as one element of my combination a well-known type of air clutch-brake-tlywheel mechanism generally indicated at 28 and shown in particular in Fig. 8. This mechanism includes a shaft 29 `connected to the driving pinion 21, Fig. l, and carries a rotatable brake shoe disk 30 and a clutch backing plate 31 formed on a common hub 32 which is fixed to shaft .29 to rotate therewith. A stationary brake disk 33 is axially slidably mounted on a series of stationary pins 34 secured in press housing 10. A second brake shoe disk 35 is slidably keyed to hub 32 and is normally biased by springs 36 to bring the two brake shoe disks into Contact with the brake disk 33. inasmuch as this mechanism is to alternately apply the brake and to transmit power from a belt driven iiywheel 37 to pinion shaft 29 the `shiftable brake shoe disk 35 is provided with a clutch disk portion 38 which is biased to its unclutched position by the springs 36. interposed between clutch disk 38 and clutch backing plate 31 are clutch disks 39 secured to ywheel 37 to rotate therewith and a clutch disk 40 slidably keyed to hub 32. To apply the clutch, a series of axially extending cylinders 41 are placed yaround the axis of shaft 29 and are formed in the rear of clutch plate 38 while suitable pistons 42 are formed on the brake shoe disk 3i). An operating uid medium such as air is admitted or exhausted through a pipe 43 .and passages 44 to the cylinders 4l. Upon admission of air to these cylinders the clutch plate 3S engages the various clutch disks and clutch shoes with each other to cause the flywheel 37 to transmit power to pinion `shaft 29. Upon release of such air pressure the springs k36 simultaneously disengage the clutch disks and shift brake shoe disk 35 against brake disk 33 to stop rotation of pinion shaft 29 substantially instantaneously. The clutchand brake may be thus alternately engaged or disengaged with a high degree of rapidity suitable for eecting necessary ram dwell at the proper point in the press cycle as well as to continue the press after the dwell.

To coordinate this clutch and brake operation with the ram movements as well as to be able to vary the timing of the cycle events I provide a rotary commutator type switch generally indicated at 45, Figs. 2, l0 and 1l, comprising a slip ring shaft 46 journaled in a housing 47 and suitablyl connected to the crank shaft 19 by a pin 48, Fig. 2 mounted upon the side of a material feeder cam 49 in axial alignment with the crank shaft axis.

A pre-compression timing slip ring 51 and a postcompression timing slip ring 52 are mounted on shaft 46 to rotate therewith. Theserings can be relatively angularly adiusted by releasing a clamping nut 51' which holds the rings on the shaft. Brushes such as 53, Fig. 1l, are provided, two for each of the slip rings. The position of these brushes is indicated in dotted circles in Fig. l0. The brushes are supported in the housing 47 which in turn is bolted to a flange 54 projecting axially from an adjusting disk 55. This disk is held on the side of the press frame 10 by a series of clamping studs 56 extending through arcuate slots 57 concentric with the crank shaft axis whereby upon loosening the studs the disk may be angularly rotated to the desired extent and then clamped in position. In this manner the relation ofthe brushes 53 is changed with respect to insulated segments 58 of the respective slip rings which, of course, are also insulated from the shaft 46. The timing slip ring assembly controls ow of air to the clutch and brake cylinders 41 by a solenoid-controlled air valve generally indicated at 60, Fig. 9, suitably mounted on the press at any convenient location.

Air pressure from any suitable source is admitted through pipe 61 and then continuously through passages 62 of a piston guide and upwardly past a ball valve 63 to the right end of a piston 64 to move the piston andan attached valve 64a, whereupon air is admitted to a charnber 64b from which it ows to the clutch brake cylinders. Simultaneously with the opening of valve 64a the left end of the piston acting as a valve closes communication between the chamber 64b and an exhaust chamber 64e which leads through a suitable exhaust pipe to the atmosphere. The ball valve 63 is depressed to the position shown in Fig. 9 when the solenoid is energized but when the solenoid is de-energized a spring 63a raises the ball to a seat to shut off flow of air to the right end of piston 64 and a spring 63b continues to raise the solenoid stem 63e` to a stillfurther upper position. The stem has a vent passage 63d whose lower end is closed when in engagement with the ball valve 63 but when this ball is seated and the stem 63e is raised, air pressure at the right end of piston 64 is then vented to the atmosphere through passage 63d thereby allowing a spring 63e to move the piston and valve 64a to the right position shown in Fig. 9. In this position air pressure in the clutch cylinders is vented to the atmosphere through chambers 64b and 64e.

To control the clutch air valve and the press drive I have provided a circuit diagrammatically shown in Fig. l2. A main `motor 65 for driving the press pinion 21 is supplied with current from a main line L controlled by a switch 66. To start t-he motor a switch 67 normally biased to open position is momentarily closed thereby energizing a solenoid 68 which closes a holding circuit 69 to maintain main switch 66 closed. There are now. three possible press operations: l-continuous .operation (without dwell), Z-inching, and S-pre-compression and/or post-compression dwells,

In continuous operation a run `switch 70 is rst .closed manually and .then a start clutch switch 71 normally biased open is manually closed thereby energizing a solewheel to drive the press plunger.

. noid 72 which is maintained energized by a holding circuit `which breaks the circuit through air valve solenoid 75 and holding circuit 73, although allowing press motor `65 to continue driving the flywheel 37. T o stop the press rnotor a switch 67 is opened.

Inching of the press plunger is effected by throwing the clutch in and out. To do this, switch 78 is now manually closed which by being mechanically connected to switch 70 causes the latter to open. Inching switch 79, normally spring biased open, is manually held closed for such length of time as the operator desires. Closure of inching switch 79 energizes the air valve solenoid 75, it being understood that the stop clutch switch 77 is closed by reason of being normally biased to closed position.

To obtain a pre-compression dwell it is first necessary to manually close running switch 70 and open inching switch 78. A pre-compression switch 81 is also manually closed. The clutch starting switch 71 is now closed which energizes solenoid 72 to close air valve switch 74 whereupon the clutch is engaged with the ily- As the press crank shaft rotates, the commutator slip ring 51 is rotated and so long as the two brushes S3 of that ring are in contact with the conducting segment of the slip ring a circuit is maintained to energize a time delay relay coil 82 which closes a switch 83, normally biased open, thereby to energize a solenoid 84 which closes an air valve switch 85. The switch' 74 in series with switch 85 has been previously closed by the start clutch switch 71. When the insulated segment 58, Fig. ll, of commutator ring 51 engages one or both of brushes 53 soas to break the circuit tothe time delay relay coil 82, the latter then starts its timed cycle to open switch 83 to release Ithe clutch and then after a predetermined time to reclose switch 83 to engage the clutch. The press plunger may be thus stopped at any selected `point prior to compaction of the material to allow escape of air entrapped in the material and thereafter continue the compression stroke. The time delay relays shown herein may be of any conventional and well known type and hence need not be further described.

It is sometimes desirable, as previously pointed out, to have in one cycle both a pre-compression dwell as well as a post-compression dwell, although under certain circumstances either dwell alone may be used. To obtain a post-compression dwell alone it is only necessary to close a manual switch 88 and open switch 81. The remainder of the post-compression circuit is then identical to the pre-compression circuit including a time delay relay 89 and a relay switch 90. Inasmuch as these two time delay circuits are identical further description is not necessary of the latter one, it being understood, of course, that the slip lrings for the post-compression dwell are shown at 52 on the same shaft with rings 51. The post-compression dwell occurs slightly after the compression plunger `retracts from the preform so that the preform can expand upwardly against the plunger which thus acts to restrain any shattering force within the preform. The dwell continues until the stresses in the preform have been sufficiently relieved or dissipated, which usually requires from one-fourth to one second. The preform thus is allowed to expand under controlled conning limits to a point where it will not shatter when the plunger is completely withdrawn and the ejector plunger ejects the preform.

To obtain both pre-compression and post-compression dwells both switches 81 and 88 will be closed and then it is only necessary to have the slip rings 51 and 52 so angularly related to each other that the insulated segments of each will not simultaneously engage the brushes of the respective rings which, if it occurred, wouldresult in both circuits being open at the same time.

It is thus seen from the foregoing disclosure that I have provided an improved combination of elements that is highly eiective and relatively economical in construction, operation and maintenance, to accomplish the result of forming preforms of solid, uniform texture throughout, free of laminations or the possibility of shattering in the case of certain plastics whose internal stresses may cause the preform to shatter upon release of the compression pressure. My improved combination not only accomplishes this result but also permits a high degree of ilexibility of operation whereby the dwell cycles may be conveniently varied with a high degree of precision, this being accomplished notwithstanding the inertia and momentum forces involved in a press of the type necessary for this kind of work.

lt will of course be understood that various changes in details of construction and arrangement of parts may be made by those skilled in the art without departing from the spirit of the invention as set forth in the appended claims.

I claim:

l. In combination, a press having a die cavity and a plunger for compressing powdered material therein and whose relative dimensions provide air escape clearance when the plunger enters the cavity, means for reciprocating the plunger through compression and return strokes, control means responsive to a predetermined position of the press operation for stopping and maintaining the plunger at a predetermined position after entering the cavity but before completing its compression stroke thereby to effect a pre-compression plunger dwell during which time the plunger remains stationary within the cavity for allowing escape of air from the cavity prior to compaction of material therein, means for automatically restarting the plunger compression stroke from said stationary position after a predetermined time interval and continuing the stroke to completion, and additional control means responsive to a predetermined position of the press operation for stopping the plunger at a given position within the die cavity and maintaining the plunger stationary at that position after it has started its return stroke upon completion of its compression operation thereby to effect a post-compression plunger dwell to allow controlled expansion of the compressed material, and means for automatically restarting the plunger return stroke from said position after a pre-determined time interval allowed for such expansion.

2. In combination, a press having a die cavity and a plunger for compressing powdered material therein, means for reciprocating the plunger through compression and return strokes, control means responsive to a predetermined position of the press operation for stopping the plunger at a given point in the die cavity and maintaining it stationary at that point during its return stroke after compressing the material thereby to effect a post-compression plunger dwell to allow controlled expansion of the compressed material, and means for automatically restarting the plunger return stroke from said point after a predetermined time interval allowed for such expansion.

3. The combination set forth in claim 2 further characterized in that the means for reciprocating the plunger includes a clutch and brake, and the control means includes a commutator type slip ring driven in synchronism with the plunger movement and an electrical circuit controlled by said commutator ring for effecting operation of the brake and clutch to produce the post-compression dwell.

4. The combination set forth in claim 2 further characterized in that the automatic restarting means for the plunger includes a time delay relay whose operation is initiated by the control means.

References Cited in the f lle of this patent UNITED STATES PATENTS Apfelbaum Oct. 15, 1929 Bradley Feb. 17, 1931 Winegar June 6, 1939 Mitchell July 9, 1940 Lewis Oct. 1, 1940 Winegar Nov. 26, 1940 Zelov et al. May 13, 1941 Emst et yal May 9, 1944 8 Stacy --,--,-.-4-7,--- Mf'iY 301 1944 Y Sfacy 14n. 16, '1945 Hermann Aug, 7, 1945 Piperoux et aL Oct. 28, 1947 Hatch et a1. Dec. 16, V1947 Hess Jan. 20, 1948 Eisen Sept. 21, 1948 Whitmore et a1. Nov. 23, 1.948 Carter Septf25, 1951 Wissman Dec. 4, 1951

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