US2572063A - Pugmill - Google Patents

Description

1951 E. M. SKIPPER 2,572,063

PUG MILL Filed June 6, 1947 3 Sheets-Sheet l EDWHRD "SKIPPER.

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E. M. SKIPPER PUG MILL 3 Sheets-Sheet 2 Filed June 6, 1947 3 Wu wwtov N1 r A/ Enwnren r1. SKIPPER.

E. M. SKIPPER Oct. 23, 1951 PUG MILL Filed June 6, 1947 3 Sheets-Sheet 3 gwu /wfm EDWHRD r1. SKIPPER.

Patented Oct. 23, 1951 :Edward SkippenrBaltimore, Md., assignor to General Electric a Company, a corporation of New .York

Application'June 6, 1947, "Sel'ial NoT7 53,021

I 4 Claims. {:1

'l hisinvention relates toa pug m ill aand is a continuation-impart:of :my co-pendingapPlications, Serial" No. 4991576, "filed August- 23, 1943, nowabandoned, and serial No. '708 ,455;' filed'November '7, 1946, now abandoned.

As -stated in: the aforementioned applications, manufacturers of ceramic materials-and particularly of porcelain insulators. have long been confronted: with large lossfactors in theforming and firingof ceramicbodies. "Theselosses I have discovered to: be" attributable -tothe manner in which' the clayis mixed and extruded, usually in a-pug mill. -I' have round the" principal sources.

*of loss to be the lackof "homogeneity and the existence of linesof force in the'clay-as extruded from the mill,-"for both of which I described solutions' at length in my -co-pendin'g applications.

The pug mills heretofore employed for mixing ceramic materials hav been-of two general types. In'one' the mill"=has but a s'ingle'chamber for botli mixing and 'extruding'the material. In the other these functions are performed in separate chambersfthis' typexb'eing the one most generally used in the insulator industry. However; in both cases the 'mixing and extruding-angers have I either-been mounted on the same shaft or :driven through gearing at fixed relative speeds. As resultagiven pug niill has been capable-of han- 'dling only-relatively. small variations in the consistencyor moi'stur-e contentof the starting material. -Accordingly, it has beencustomary'to adapt one :mill for use-'witl'i so-called soft" *pugs and: to use: a separate machine for "hard pu'gs. Inhave now found that by making: provision for 'both "individual and relative "variations in :the speedszattwhich: theseveral augers' and paddles are :driven, inaconjunction :with' 'my "aforementioned discoveries:- a' single pug mill can be used topug startmg materials oft'a wide range of con- :sistencie's.

.-.The primar object of the invention is to provide an'improvedapparatus for producing homegeneousstress freeceramic mixtures from start- :ing materials-of a: vvide range of consistencies.

SAno-ther 1 object of the invention. is toprovide an: lim-proved apparatus -for pugging ceramic materials having means for varying the individual and'relative speeds of the mixing and extruding 1 angers and means within the vacuum chamber "whereby? a "homogeneous pug is -obtained from i-startingzmaterials of differentconsistencies.

' :Ani'additional' object of-the invention isto p'r'o- :videan improvedtpug mill having meansfor-constrolling? the moisture and air" content2and -elim --inating.:lines :of force'tin startingmaterials of dii ferent consistencies "whereby the: resulting z pug :is homogeneous in' density and :moisture content and; free :fromustresses.

Other' objectsand advantages ofthe invention will :appear hereinafter in" the detailed descripition andvbeparticularly pointed outfin the appended: claims. I In the drawings illustrating -'a preferred embodiment .of the: apparatus of =1 this invention:

Eigure; 1' issa longitudinal sectional View of 'a rug 2min; embodying: my invention.

-Figuret2 is a view; partly 'in 'endel'evation and partly in section taken on amen-:2orEigure 1.

Figure 3 is -a"'vertica1: sectional view taken on line13*3 of Figure 1.

Figure-4 isa side elevational view of theouter end: portion of the extruding auger.

Figure 5 is an end elevational viewer: the "extruding auger. I

Figure 6 1s a perspective-view of the outer end portion or that auger.

Figurel is a sectional "view' taken on line I--l on Figure 4. r

. Referring nowin-"=detail'- to the drawings in which like reference characters designat'e like parts, I indicates a suitable base on Which'the pug mill, :designated generally as- 2, "is' mounted.

Theimixingportionof thepu'g rnill comprises a 'hoppertsi:intowhichthe clay or other ceramic material tobe workedor pugged is dumped. Extendin'gi longitudinally 'throug-h the 'hopper isa mixing 1 shaft :14 carrying, within -'-the hopper, a plurality of substantiallyradialarms or blades 5 iorimixingsand tmascerating 'the' clay introduced into?thezhopper'and feeding-it forward' to an 'upper: auger-' 6: also attached to the shaft .4.

The inner end of thesha it is mounted 1 within a casing or the like 1 housing suitable gearing (not shown) driven by a variable speed motor-of the usual'type (not shown) for imparting' rotation to the shait'over-a-nyde'sird range of speeds. The shaft preferably extends continuously to the front walll'8'of the machine and 'is'rotatably supported at itsiront end by a suitable bearin'gfl mounted in: the-wall. I

The upper-ormiXingauger-G ispinned or otherwisesecured to the s-haft' l. Thisauger has-a single continuously extending "helical vane or blade ill, 'thediameter ofwhich progressively decreases toward its -forward end. The forepart'oi the mixing chamber ln which the auger is'housed isformed as a tubular casing or housing "I! of frusto-oonical configuration which progressively effectively seal both openings and thus prevent air from being drawn into the chamber when suction is applied.

From the vacuum the clay is fed into the extrusion device or outlet portion of the pug mill. Forming a part of this device is a lower or extruding auger H which extrudes the clay from the mill and the inner end of which is arranged within the lower portion of the vacuum chamber in substantially vertical alignment with the shaft 4. The forward end of this auger is housed within a cylindrical casing or extrusion chamber which is preferably provided with a water-cooled jacket "5. Bolted or otherwise secured to the forward end of the casing is a nozzle or die I! of truncated cone-shape through which the clay is discharged from the mill.

The extruding auger I4 is formed with a shaft or hub portion l8- which is removably splined or otherwise keyed to an aligned with a drive shaft 19, as by inwardly projecting ribs 2|. At its forward end the shaft l9 isrotatably journaled in the rear wall of the vacuum chamber through suitable bearings. The rear end of the shaft l9 extends into and is journaled within the casing 1. As in the case of the shaft 4, the shaft 19 is adapted to be driven through suitable gearing (not shown) by a variable speed motor of the usual type (not shown), separate motors being provided for the two shafts to enable their relathreaded into the end of the shaft IS.

The shredded clay forced into the vacuum chamber l3 by the upper auger 6 is driven down toward the lower auger l4 by a pair of laterally spaced paddles or the like 26. These paddles may be mounted on the forward ends of the shafts 21, the rear ends of which extend into the casing I and are there connected to a suitable source ofpower (not shown) through which the desired rotation is transmitted to the paddles. The paddles are preferably connected through suitable gearing (not shown) to a single source of power, the latter desirably being a variable speed motor of the usual type (not shown) to enablethe speed of the paddles relative to the mixing and extrusion augers to be controlled at will.

As described in my aforementioned co-pending application, Serial No. 499,676, the extruding augeris provided with a plurality of spaced sets of flat blades 28, the radii of rotation of which are substantially equal to the-inner radius of the extrusionchamber [5. Each of theblades lies normally to the axis of theshaftglB of the auger and within each set the blades are diagonally or obliquely disposed such that each lies in a plane intersecting the other blades of the set. Additionally, the blades of each set are positioned to interrupt the flights of the blades of the next preceding set. In each set, with the exception of the outermost set, the trailing edge a of each blade is spaced laterally from and in advance of the leading edge I) of the next adjacent blade of its set. In the outermost set the trailing and leading edges, a and b, respectively, of the adjacent blades overlap in part.

Utilizing an extruding auger of the above construction, the clay extruded from the pug mill is driven at a substantially uniform speed throughout the free area of the extrusion chamber. At the same time any lines of force or cleavage set up in the clay by'the flights of the blades of each set are cut or interrupted by the blades of the next succeeding set such that the clay, as extruded, is in substantially stress-free condition. By enlarged the leading and trailing edges of the blades of the outermost set the clay is prevented from backing up into the extrusion chamber.

As previously mentioned, the apparatus of the present invention is designed to handle ceramic materials or clays of different consistencies and is particularly adapted to handle clays in which the moisture content is controlled. Accordingly, instead of utilizing the usual filter cake as the starting material, there is preferably employed, the controlled moisture content mixture of my aforementioned co-pending application, Serial No. 708,455. As therein described,- the starting material is a bone-dry ceramic mixture. As preferred, water may be added to this mixture either immediately preceding or as the mixture is introduced into the hopper 3, in the latter case by such means as a dispenser indicated at: 29 in Figure 1. In either case a measured quantity of water relative to the weight of-the clay is added, the exact quantity depending on the consistency desired in the clay as extruded from the mill. The ceramic materials and added water are then thoroughly mixed by both the paddles 5 and the mixing auger blade it into a mass of homogeneous moisture content which, after shredding by the member I2, is fed into the vacuum chamber l 3. Utilizing the variable speed motor, previously described, the speed at which the materials are mixed and fed forward by the mixing auger l0 will be controlled depending upon the amount present and its consistency. After,

entering the vacuum chamber the ceramic mixture or clay is freed of its entrapped air and driven downwardly by the paddles 26 at the speed required to keep the mouth or entrance ofthe extrusion chamber filled and the vacuum chamber sealed against the entrance of outside air, the paddles also serving to agitate the clay and expose a maximum of its surface to the vacuum. Thereafter, the clay is driven through the extrusion chamber and extruded from the mill by the extruding auger I4, the speed of the latter being at varying speeds determined by its quantity and consistency, ,it is possible to -obtain from start= ing materials of diiierent consistencies an extruded mass or pug which is both stress-free and homogeneous. Thereby, the use of different mills as well as the high percentage of losses, under present practice in the subsequent drying and firing stages as the result of non-control of these factors, are practically eliminated.

It will be apparent from the above detailed description that there has been provided an improved apparatus for mixing clay which, while particularly suited for the production of ceramic insulators, is of wide application in clay mixing. It should be understood that the described and disclosed apparatus is merely exemplary of the invention and that all modifications are intended to be included which do not depart either from the spirit of the invention or the scope of the appended claims.

I claim:

1. A pug mill adapted to handle ceramic materials of different moisture consistency whereby so-called soft pugs and hard pugs can be obtained from the same pug mill, said pug mill comprising a mixing chamber, a vacuum chamber, and an extrusion chamber, said respective chambers being connected in serial relation whereby material fed into said mixing chamber will be discharged from said extrusion chamber, a mixing auger positioned in said mixing chamber, means positioned in said vacuum chamber for impelling material therefrom into said extrusion chamber, an extrusion auger positioned in said extrusion chamber, and a variable speed drive means connected to each of said augers and the impelling means, there being an independent drive means for each of said augers and the impelling means whereby any one of said augers or the impelling means may be driven at a predetermined rate of speed as desired, the relative rates of speed of said auger drives and the impelling means drive being determined in accordance with the consistency of the ceramic materials fed into said mixing chamber to permit discharge of said materials from said extrusion chamber without breaking the vacuum in the vacuum chamber.

2. A pug mill adapted to handle ceramic materials of different moisture consistency whereby so-called soft pugs and hard pugs can be obtained from the same pug mill, said pug mill comprising a mixing chamber, a vacuum chamber, and an extrusion chamber, said respective chambers being connected in serial relation whereby material fed into said mixing chamber will be discharged from said extrusion chamber, a mixing auger positioned in said mixing chamber, an extrusion auger positioned in said extrusion chamber, a paddle positioned in said vacuum chamber for impelling material from said vacuum chamber into said extrusion chamber, and a variable speed drive means connected to each of said augers and the paddle, there being an independent drive means for each of said augers and the paddle whereby said augers and paddle may be driven at independent rates of speed, said rates of speed being determined in accordance with the consistency of the material fed into the mixing chamber to permit discharge of said material from the extrusion chamber without breaking the vacuum in the vacuum chamber.

3. A pug mill adapted to handle ceramic materials of difierent moisture consistency whereby so-called soft pugs and hard pugs can be obtained from the same pug mill, said pug mill comprising a mixing chamber having a discharge opening, a vacuum chamber having an inlet opening and a discharge opening, and an extrusion chamber having an inlet opening, means connecting said vacuum chamber to said mixing chamber whereby the inlet opening of said vacuum chamber is positioned in registry with the discharge opening of said mixing chamber, means connecting said extrusion chamber to said vacuum chamber whereby the inlet opening or said extrusion chamber is positioned in registry with the discharge opening of said vacuum chamber, means positioned in said mixing chamber to feed material into the inlet opening of said vacuum chamber to keep said opening filled, means positioned in said vacuum chamber to force material therefrom into the inlet opening of said extrusion chamber to keep said opening filled and thus prevent loss of vacuum, and means to feed material through said extrusion chamber, said mixing chamber feed means, vacuum chamber forcing means, and extrusion chamber feed means each having connected thereto an independent variable speed drive means whereby, depending upon the consistency of the material fed into said mixing chamber, the rate of feed of said material through the pug mill can be adjusted so that vacuum is maintained in said vacuum chamber.

4. A pug mill adapted to handle ceramic materials of different moisture consistency whereby so-called soft pugs and hard pugs can be obtained from the same pug mill, said pug mill comprising an elongated mixing chamber having a discharge opening at one end thereof, a mixing auger positioned axially of said chamber, a shredder connected to said mixing auger and positioned at the discharge opening of said mixing chamber, a vacuum chamber positioned in extension of said mixing chamber, said vacuum chamber having an inlet opening positioned in registry with the discharge opening of said mixing chamber, means connecting said respective openings, said vacuum chamber also having a discharge opening positioned substantially at right angles to the inlet opening of the vacuum chamber and opening downward from the vacuum chamber, a plurality of paddles positioned in said vacuum chamber, said paddles being constructed and arranged to impel material within said vacuum chamber toward the discharge opening thereof, an extrusion chamber having an inlet opening positioned below and in registry with the discharge opening of said vacuum chamber, an extrusion auger positioned in said extrusion chamber and adapted to force material from the inlet opening of said extrusion chamber, and variable speed drive means connected to said paddles whereby said paddles may be driven at a rate of speed sufficient to keep the discharge opening of said vacuum chamber filled and thus prevent loss of vacuum in said vacuum chamber.

EDWARD M. SKIPPER.

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

UNITED STATES PATENTS Number Name Date 1,614,526 Lambie et a1. Jan. 18, 1927 1,879,367 Lotz i Sept. 27, 1932 1,987,358 Bonnot Jan. 8, 1935 1,987,359 Brown Jan. 8, 1935

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