US2986772A - Eccentric rolling of powder and bonding agent into spherical pellets - Google Patents

Description

June 6, 1961 PATTON, JR., ETAL 2,986,772

ECCENTRIC ROLLING OF POWDER AND BONDING AGENT INTO SPHERICAL PELLETS Filed May 27, 1959 TO VARIABLE SPEED DRIVE INVENTORS. GEORGE PATTON, JR.

T N Y ZIRINSKY BY 3 A LE A T TORNE Y United. States Patent F 2,986,772 ECCEN'IRIC ROLLING 0F POWDER AND BOND- ING AGENT INTO SPHERICAL PELLETS George Patton, In, Lindenhurst, N.Y., and Stanley Zirinsky, Elkins Park, Pa., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed May 27, 1959, Ser. No. 816,352 2 Claims. (Cl. 18-1) The present invention relates to apparatus for the production of spherical pellets and more particularly to apparatus for the eccentric rolling of powder and bonding agent into spherical pellets of uniform size.

Existing techniques and apparatus for the production of spherical pellets from powdered substances such as carbon black utilize some form of tumbling in which a moistened powder is loaded into a barrel and the barrel rotated about its axis. This action produces tumbling by continuously carrying the powdered substance up to an inclination greater than the angle of repose of the particles so that successive rolling and tumbling of the particles down an inclined surface results. The inclined interior surface of the drum produces pellets of the material generally spherical in shape. However, the use of barrel rolling for the production of spherical pellets produces pellet sizes which vary both from batch to batch and within each batch itself.

This invention improves greatly on prior methods and apparatus by producing pellets which are perfectly spherical with a greater uniformity than heretofore in the sizes of the pellets produced. Briefly described, the novel apparatus of this invention consists of a container or pan having a circular or other convenient cross section mounted to move in a circular orbit in a horizontal plane about an axis displaced from that of the pans central axis without rotating the container about its central axis. The effect of this type of rotation is to keep the pellets rolling around in the container in contrast to the barrel tumbling described above wherein the pellets are alternately carried upward by the moving barrel wall and then dropped back. The powder may be either moistened or mixed with a binder, or used without either, depending upon whether the material itself requires it. The material is then placed into the pan described, while additional material may be added during the operation of the apparatus to provide enlargement of the pellets to the desired size. Pellet size is determined by a combination of factors including the size of the charge and pan, angular velocity of the pan, and duration of oscillation. The apparatus produces pellets of relatively high density having good strength, excellent sphericity, and uniformity of pellet size Within each batch.

It is thus a first object of this invention to provide apparatus for the eccentric rolling of powder and bonding agent into spherical pellets.

It is a further object of this invention to provide apparatus relying on pure rolling motion for the pelletizing of finely divided or powdered material.

It is still a further object of this invention to provide apparatus for the manufacture of pelletized reactor fuel employing metal bonded uranium dioxide.

Other objects and advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the novel apparatus when considered in connection with the accompanying drawing in which:

The figure is a perspective view partially in section of a preferred embodiment of the apparatus of this invention.

Referring to the figure, the inventive apparatus consists of a horizontal stationary platform 12 of conven- Patented Jun G, 1961 ient shape supported by a horizontal member 14 having a plurality of posts 16 for this purpose. Posts 16 may be tapped at their top surfaces for receiving threaded bolts 18 passing through openings in platform 12 to accomplish the rigid support of platform 12. On top of platform 12 there is provided a pair of rotatable link arms 20 and 22 supported rigidly for their rotatable movement with shafts 24 and 26, respectively, passing through one end of each arm 20 and 22'. In the case of arm 20, shaft 24 terminates in a suitable bearing 28 on platform 12 to permit free rotation of arm 20 thereabout. In the case of arm 22, shaft 26 passes through a bearing 30 in platform 12 and terminates in a gear 32 supported by convenient means on support plate 14. The drive for apparatus 10 is provided through gear 32' by a shaft 34 terminating in a pinion 36 which is in toothed engagement with gear 32. Shaft 34 is connected to an appropriate variable speed drive (not illustrated) which can be the usual electric motor or other means available for selectively driving this apparatus.

Mounted on arm 22is a slidable member 38 with a set screw 40 for fixedly clamping slidable member 38 at any predetermined point along the length of arm 22. A scale 42 placed on the top surface of arm 22 permits the fixing of slidable member 38 at a predetermined point which may be recorded for convenience of successive operations. Arm 20 is provided with a similar type slidable member 44 having a set screw 46 and a scale 48 serving the same purpose as arm 22. Bridging across slidable members 38 and 44 is a clamp assembly 54 for supporting a circular container 56 in which the material is placed to be pelletized. Assembly 54 consists of a bridging member 58 which is supported at each end on slidable members 3 8 and 44. To permit rotation of bridging member 58 at each end with respect to slidable member 38 and 44, pins 52 and 50, respectively, or other.

22 and 20 are provided with freely rotating wheels '68 and 70 for supporting the ends thereof, respective, and

thereby maintaining arms 20 and 22 in a horizontal plane parallel to platform 12 during their rotation. The directions of rotation of arms 22 and 20 are indicated by arrows A and B, respectively. It is understood that the rotation of shaft 34 by the driving means (not illustrated) causes the rotation of arm 22 through pinion 36 and gear 32 and that this action transmits forces through bridging member 58 to arm 20 to cause the latter to ro-, tate as well. Thus, the whole assembly, consisting of arms 22 and 20, support assembly 54, and container 56, rotate in a horizontal plane above platform 12 in a manner to be described in connection with the process.

The operation of apparatus 10 is as follows: An initial charge of the powder with binder, if required, is placed in powdered form into container 56. Motion of the apparatus is commenced either before or after the initial charge is placed in container 56. The motion of container 56 in a plane parallel to platform 12 follows a circular course which has been found to cause a distribution and changes in direction of the centrifugal forces on the material in container 56 such as to result in the powdered material rolling around the inside of the outer edge of container 56 causing a spherical build-up of the pellets. Additional material is added either continuously or from time to time to build up the pellets to the desired size, and experience has shown that within each batch of pellets produced all the pellets produced will have exactly the same size.

The method and apparatus are suitable for use in the manufacture Oi spherical pellets made from any powdered material which has suitable characteristics such as the materials described in US. Patent No. 2,674,522, issued April 6, 1954, to Takewell et al. In addition, however the inventive apparatus can be used in the pro-' duction of metal bonded uranium dioxide pellets for use in, a reactive bed through which a fluid coolant, such as helium is pumped. A specific example is moistened powder composed of screened-325 fractions of which 25% is derived from an alloy powder of A.I.S.I type 347 stainless steel and 75% derived from hydrogen reducible oxides of iron, nickel and chromium. The binder consists exclusively of water.

Experience with the inventive rolling machine shows that the degree of moistening and type of rolling action (i.e. diameter of pan, radius of curvature of eccentric circular motion plus period of this motion) dictate the number and size of pellets that will form. The control of the motion will vary as to whether further pellet nuclei will form or enlargement of the residual nuclei will occur upon addition of the moistened charge. In other Words, the results obtained depends to a considerable (legee, upon the skill and developed experience of the operator. For a particular set of operating conditions (motions of the roller) the results will vary with physically different powders and different binders.

It will be seen that this apparatus is particularly advantageous in that it is of simple construction, relatively small in size and economical to build. In addition, it is possible to automate this apparatus to produce any preselected size of pellets desired. This would be accomplished. by determining the particular size of pellets produced by the use of certain positions of slidable members 38 and 44 along their respective rotating arms 22 and 20, the particular size of container 56 and the speed of rotation of shaft 34 and arms 22' and, as well as the length of operating time. By determining in this manner the sizes of pellets produced under certain conditions, it is possible in effect to automate the operation of this device by either putting a sufficient initial charge in container 56 if the pellets are not to be too large or providing in some convenient, wellknown manner means to feed, the predetermined amount of the charge into container 56 slowly or in measured amounts during the operating cycle.

The. use of this apparatus is particularly advantageous because, as already noted, it produces a pellet size for each batch which is more uniform than can be produced by prior techniques known and also because the pellets have excellent sphericity which would be important for certain uses of such pellets. Also, the pellets produced as a result of this process have proven to have excellent mechanical strength as well as high densities.

It will, of course, be understood that the specific embodiment of the apparatus shown in the drawing is but one form. Hence it will be seen that the particular apparatus described above and the particular modes of operation given are for illustrative purposes only, and obviously many variations and modifications of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Whatis claimed is:

1. Apparatus for pelletizing powdered material comprising in combination, a pair of parallel extending arms mounted each on a rotatable shaft at one end, a member bridging corresponding points on said arms, a pan for containing said material mounted rigidly on said bridging member, and means driving at least one of said arms thereby causing the circular translational motion of said pan with the material therein rolling around the inner periphery thereof and building up into high density spherical pellets of uniform size.

2. Apparatus for pelletizing powdered material comprising in combination, a pair of parallel extending arms mounted each on a rotatable shaft at one end, a member bridging corresponding points on said arms, a fiat cir cular pan for containing said material mounted on said bridging member, and means driving at constant rotational speed at least one of said arms thereby causing the circular translational motion of said pan with the material therein rolling around the periphery thereof and building up into high density spherical pellets of uniform size.

References Cited in the file of this patent UNITED STATES PATENTS 1,661,681 Rood Mar. 6, 1928 2,860,598 Loesche Nov. 18, 1958 2,876,491 Meyer Mar. 10, 1959 2,889,576 Selig June 9, 1959 OTHER REFERENCES Chemical Eng. Prog. Agglomeration, pages 291- 295, vol. 51, No. 6, 1955.

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