US2531245A - Sifting feeder for powder compressing machines - Google Patents

Description

L; H. BAILEY SIFTING FEEDER FOR POWDER CQMPRESSING MACHINES Filed Feb. 4, 1947 W WY m a H m m m L Fig. 2.

Patented Nov. 21, 1950 :SIETINGsFEEDER EORTOWDER :GOMPRESSING MAGHINES Lawrence :H. mailey, -Cheltenham, Ha, assignor .itoiFlFJ; Stokes Machine Companygrareorporation.

of Pennsylvania fipplication' l 'ebruary 4, 1947, Serial No; 7265336 :1 This invention relates toimprovements in lapparatusafor lthes manufaeture ofcompressed ,p arts from-powdered metahpewdered. ceramic, orother granular 2'01 powderedxmaterials and especially parts :having thin wallseations which are formed in *di'es ihaving narrow sections, suchas 'thinwalled bushings, or -.-other parts with thin sections. 'The inventionl-is. especially concerned with arrangements for feeding thelpowdered material into the dieseof compressing machines.

' The preferred 'form-of .theinventiondescribed herein is applied to the so-callederotary-typeof tablet machinehavingpamultiplicityeof dies set inla rotating head.

Theusualtmethod of 'filling theldi'es. in a rotary machineis .toprovidea feedifrarnc positioned .to rest rupon the lnpper .surface .of the rotary head while the head motates andhaving several openbottom compartments. .Eowidered material :is placed .wi'thinLthese compartmentsandrestsupon therotaryLteihle andifall'siby gravity intothe die cavities .as Lthe .die elements pass beneath the compartments of the .'feeding. 'frame. Powder which does not flow -freely tends to bridge over.

atthe'top'o'f the narrow dies, and will not 'fall into theempty spacebelow. This may be due 'to several causes,.such as fineness of .theppowder, entrapment ofairlin'the die, cohesive'agglomerates 'or lumps in the powdenagglomeration ofv the powder by traces of oil, or the -presence of small piecesof p'artspreviou'sly partly compressed and subsequently insufficiently broken. This condition isaggrava'ted'if the die has a large top section, and a'narr'ow bottom section. In this case-the lumps or agglomerateswvill rest in the larger part of the die; blocking the narrow part below, and cannot be "displaced in the usual fashion by" the "scraping'acti'on of the partitions in theffeed frame. TheIoWersectiOn then remains empty "or partially empty so that very imperfect pieces or not solidly compressed pieces are ,produced.

The foregoing difiiculties are especially troublesome in the handling "oi-powders of a fineness which will pass through ascreen of 100 to 300 mesh. Such fine powders do notallowairltopass readily through them when in a piled condition as exists in the ordinary feed frame-described above. The feeding device'of the presentxinvention overcomes the above-mentioned d'i'fiiculties and permits the use .of such fine powdersin the formation or thin-walled moldedparts.

The preierredform of the invention is illustratedin the accompanying'drawing innvhich I Figure 'lis a-iragmentary plan view, partlyin I section, of a rotary die table oiea tabletting ma chine showing my feeding device associated therewith; and

Figure 2 is an elevational view of the arrange- 2 mentshowrr in Figure :1, 'certain parts being. shown in section.

Referring tto the drawing, only so much of 1a rotary :pressis shownas is necessary tQ'eXplai-n the invention. lindicates theirotary table which carries a =,-plurality.of. .die elements 2 andraicorrespondingtplurali-ty of fixed. core pins}, centeredin the die elements .for iorming thin-walled bushings. .The lower punch elements vareshown at-A, the uppeiuen'dsof .theseelements beingreduced in .sectiento enter thelannular space forming the die .cavity. It will -be understood that other shapes (if-die cavities may be employed, and the particular [cavity illustrated in .the drawing is only .one example. The upper punches and the remaining conventional parts of the rotary press 'are 'n0t;shown.

.Thesifting feeder .of mylinvention is shownii'n planiview in Figure l, The solid'lineportiomof FigureZisa verticalsectional View of Figure 11 takenalongthe cutting plane 2 2 which "follows a circularipath passingthrough the centers of the'dieelemerits z. *The elements'shown'in dotte'd'li'nes inFigure'Zare'located in front of'the cutting-plane "of Figure 1. The-sifting feeder .invoi'ves a "tray-dike structure mounted over the outer peripheral faee 'ofthe rotary table I and having a 'l acttom wall formed of a solid gportion Rand a section h covered with a screeno'ffine mesh, "thescreensection being arranged immediately' above-the path of "travel of the die cavities during rotaticnp'f the' table. "I'h'etray is' provided with a side'wall l which prevents the material fromffaliingout of the tray ontothe rotary table. The tray is also provided withend' walls-"8 and-i] and these wall'seare provided with extensions -'8a and saiwhic'h nonstitute brackets for mounti'ng the :tray from suitable pins iorirods 8b and 9b mounted on a fixed-part of the'ipress.

Thefeeding=trayis-vibrated vertically :or horizontaliy'by anysuitable'vibrator; In the'arrangement shown lIlithG drawing, *thetray iisvibr'ated vertically 1 by meansof a .-.pneumatically--operated vibrator rs mounted on bracket 9a.

The powdered-material isrsupp'lied-to thetsifting tray from a suitable supply (not shown)- through an inclined-chute which may also be vibrated by any suitable means. In Figure: 2 the .powdered .material in the rchute -is shown at mlandlat 12a in the'itray. lAs XVfl-Lbe secn from Figure Tlthe end of the chute .H. ispositioned so, that the powdered tmaterialis deposited on the screenedlseotionof the trayandis :more or .-less evenly-.distributedalong the length 01 misses-- tion.

.Therscreen 45- is selected to have. armesh which is smaller than the smallest wall th-ickness to :be molded. .-For example, if a ftubularisleevea-is 'to be molded having .a wall thickness of 0f :an inch,v the screen 6- would :be 'iormed :of mesh preferably not less than 30 per inch. Since the wire of the screen is of appreciable thickness, the mesh openings will be considerably smaller than the wall thickness of the molded article. The length of the screen 6 along the path of travel of the dies will be determined by the speed of movement of the table I and the rate at which the powdered material passes through the screen. It should be of sufiicient length so that each die cavity will be completely filled by powdered material as it falls directly from the screen 6 in a free and unconfined condition, The screen 6 screens out any lumps or other particles which are too large to pass into the narrow die cavity or which might cause bridging of the material over the entrance of the cavity. Furthermore, since the upper part of the die cavity is not covered or sealed off by a pile of powdered material, the freely falling and separted grains of material will pass down to the bottom of the cavity, and the air will be freely displaced from the cavity, thereby avoiding trapping of air in the cavity.

The excess material deposited on the face of the rotary table between the die cavities and above the filled cavities is first deflected inwardly on the surface of table I by the end wall 8 which extends down and has contact with the upper face of the table I as shown in Figure 2. This arrangement causes the accumulation of a pile of powdered material as shown at I2b in Figure 2, and the wall 8 causes this material to move in the direction shown by the arrow I2b in Figure 1. The direction of rotation of the table I is indicated by the arrow I. The excess material is finally removed from the rotating table by means of a scraper plate I3 which is arranged in contact with the upper face of the table I and at an angle to the radius of the table as shown in Figure 1 This scraper plate accumulates the excess material into a pile shown at I in Figure 2 and the accumulated material is moved outwardly and discharged over the edge of the rotary table in the direction shown by the arrow I2c in Figure 1. It will be noted that the excess material is deflected across the path of travel of the die cavities in two directions, first inwardly and then outwardly. This will insure complete filling of the cavities in case the screen should not be functioning properly.

From the foregoing it will be seen that my improved feeding device involves an arrangement I for dispersing the finely powdered material at a point directly above the die cavity, the material being dispersed into freely falling, separated particles having a maximum dimension which is only a fraction of the distance of separation of the die walls, and the entire die cavity is filled by the falling particles which pass directly into the die cavity and continue to the lowermost part thereof in a continuous falling movement from the time they leave the sifting tray.

I claim:

1. In a press for molding articles from finely powdered material in the cavities of a plurality of die elements carried by a rotary die table, the transverse dimensions of said die cavities being so small as to cause bridging of said powdered material across the cavities when the cavities are filled by scraping a pile of said material across the top surface of said table, an improved feeding device for filling said cavities with powdered material without causing bridging of said material and without entrapping air in said cavities comprising, in combination, a relatively shallow tray-like element mounted above said rotary table in spaced relation to the face of said table and having a screened bottom section elevated above saidtable and extending over the path of travel of said die elements, the mesh openings of said screened section being less than the distance of separation of the walls forming each die cavity, and the screened section of said tray being extended along the path of travel of said die elements for a distance sufficient to completely fill each die cavity as it passes beneath said screened section, said powdered material passing directly and freely from said elevated screen section into each die cavity, a chute positioned above said tray for supplying a powdered molding material to said tray, and means for continuously vibrating said tray during rotation of said table.

2. A feeding device according to claim 1 wherein said tray-like element is provided with an end wall at the trailing end thereof, said end wall being extended downwardly into contact with the upper face of said rotary table and is arranged at an angle to the radius of said table whereby said end wall serves as a scraper for collecting excess material on the face of the table and defiects the same inwardly across the path of travel of said die cavities.

3. A feeding device according to claim 1 and including a scraper arranged at the trailing end of -said tray-like element, said scraper being in contact with the upper face of said rotary table and at an angle to the radius thereof for collecting excess material on the face of said table and deflecting the same inwardly across the path of travel of said die cavities, and a second scraper spaced from said first scraper and arranged with an opposite angular relation for deflecting said excess material outwardly across the path of travel of the die cavities and beyond the outer edge of said table.

4. A feeding device according to claim 1 wherein said tray-like element is provided with an end wall at the trailing end thereof, said end wall being extended downwardly into contact with the upper face of said rotary table and is arranged at an angle to the radius of said table whereby said end wall serves as a scraper for collecting excess material on the face of the table and deflects the same inwardly across the path of travel of said die cavities, and a second scraper element positioned in contact with the face of said table on the trailing side of said tray-like element and arranged to deflect the excess material outwardly across the path of travel of said die cavities and beyond the outer edge of said table.

LAWRENCE H. BAILEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 51,050 Hotchkiss et al Nov. 21, 1865 260,444 Allen July 4, 1882 1,990,634 Brown et al Feb. 12, 1935 2,043,086 Westin et a1 June 2, 1936 2,260,456 Johnson Oct. 28, 1941 2,329,948 Shallock Sept. 21, 1943 FOREIGN PATENTS Number Country Date 13,019 Denmark July 1, 1909

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