US2398989A - Air swept ball mill system - Google Patents

Description

Amin 23, 194, F; T AG1-HE 39,89

AIR SWEPT BALL MILL SYSTEM 23, F. T. AG1-HE I AIR `SWEIQT BALL MILL SYSTEM l f Filed Sepb. 1., 1943 2 Sheets-Sheet 2 Patented Apr. 23, 1946 l 2,398,989 Am swEP'r BALI. MILL SYSTEM Frederick T. Agthe, Milwaukee, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application September l, 1943,` Serial No. 500,779

' 4 Claims. (Ci. 241-52) This invention relates to air swept tube and ball mills for dry grinding to obtain a ne product.

Ordinarily material discharged from the mill is a mixture of finished material of the requisite size and coarser insufficiently ground materials. This discharged material is classified or separated into finished product and tailings to be returned to the mill for further grinding.

It is known to carry on a portion of the classiflcation process within the mill by causing the material being ground to fall through a current of air which carries off the finer ground particles.

It is also known to return particles too coarse these devices is Well known and will be readily apto be carried by the current of air to the grinding space for further grinding. 'g

This invention concerns a specific 'internal classifying and discharge chamber` construction in which material passes through a grid in the mill into a cascading space, isshowered over a coaxial screen and through it into a current of air being drawn axiallyI through the screen.

Ari object of the invention is to provide for im,- proved classification capacity in an air swept mill.

Another object is to provide a control of coarse material returned to the grinding space from the cascading space.

Still another object is to Provide for a return of coarsematerial settling in an upcast duct to the grinding space through the discharge trunnion but out of contact with the air current in the mill.

Still other objects will be apparent from the parent to any person skilled in the art.

air seal valve I1 of any known type and transmitted to join the stream of raw material moving to feeder 4. Conveyors I 8 and I9 of 'any known type convey the finished ground product to a product outlet 2l.

following description with reference to the acings.

A rotating mill I is, provided with a hollow feed trunnion 2 at one end. A controllable stationary fluid inlet hood 3 and a feeder 4 of suitable known construction are arranged to introduce fluid and material to be ground through the trunnion 2. A hollow discharge trunnion 5 on discharge end plate 6 supports the other end .of the mill. Trunnions 2 and 5 rest in suitable bearings of any known type (not shown) to support the mill The invention resides in the internal structure of mill I and its relation to upcast duct 9 as hereinaf ter described.

The ball or tube mill I is provided with an annular, foraminous grid or screen 22 axially spaced from the discharge end plate 6' to form a division between the grinding space 8 and a constant dischargev chamberor cascading space 23. Lifters 24 of any known suitable type, such as the radial plates shown in the drawings, are spaced around the periphery of the mill between grid 22 and the end plate 6. Openings 26 are provided in the periphery of the mill between the lifter-s 24 for reasons hereinafter disclosed. A foraminous tubular liner 21 which may be flared or funnel-like as shown is attached at one end to the annular grid 22 adjacent its central opening and vextends through trunnion 5 radially spaced relation thereto. The portion of the tubular liner 21 axially within the space 23 is provided with perforations as shown at 28. A helical fin 29 which may be formed integrally with liner 21 is arranged to occupy the space between the inner surface of trunnion 5 and liner 21 to serve as.a material conveying means as hereinafter further described. Fin 29 may also support liner 21 within trunnion 5. The pitch and direction of helical iin 29 are so designed as to feed material into the space 23 when the mill I is revolving in its normal direction. The stationary upcast duct 9 is arranged to have an area somewhat larger than the discharge end of liner 21,

in coaxial.`

and to seal in any known manner with the end of rotating trunnion 5.

Surrounding the mill adjacent openings 26 is an` annular box or collector 3| secured to the periphery of mill Each opening 26 is provided with a seat 32 for a valve 33, and these seats and valves, or either of them, may be formed of or covered with resilient, tough, wear-resistant material such as rubber. The valve 33 may be carried on a threaded stem 34 passing in sealing relation through the box 3|. The stem 34 may engage a stationary, threaded guide or nut 36 and may be provided with any known means for adjustment to variably positionvalve 33 with relation to its seat 32, such as a gear 31. A pinion 36 may be turned by hand or may be controlled during mill operation by an electric motor 39 mounted on box 3| and energized by connection to slip rings 4l and 42 which may be energized in an obvious manner. A helical conduit 43 connects box 3| with an opening 44 in the mill l, and communicates with the grinding space 8 for reasons to appear hereinafter.

In the modification shown in Fig. 3 a second set of openings |26 is provided, opening into box 3|. Conduits 46, which may be formed integrally with lifters 24 on the trailing sides thereof, connect'holes |26 With an annular breast or diaphragm 41 separating the space 23 surrounding the perforated portion of liner 21 within the mill, from a space 48 freelycommunicating with the annular space between the unperforated portion of the liner 21 and the inner surface of trunnion S.

The system according to the invention operates as follows:

Constant weight feeder I6 feeds raw material to be ground into mill feeder 4 which conveys the material through trunnion 2 into grinding space 8. Here the material is tumbled about, with or without a charge of steel balls or other grinding media,

being comminuted or ground as in known ball and tube mills. As the material reaches grid 22, such material as is line enough ito pass the apertures is passed into space 23. Air or other gaseous fluid medium is drawn into the mill through hood 3. The current of uid entrains particles in the space 8 which are ne enough to be suspended in the current of fluid and passes at an increased velocity through the central opening of grid 22 and liner 21. A minor ow throughthe apertures of grid 22, space 23 and perforations28 may also occur. The mixture of finished and insuiciently 'passing openings 26 can be controlled according to the invention by adjustment of valves 33. Such control will cause more or less material to be carried in the cascading space or constant discharge chamber 23, which will iniiuence the passage of material through grid 22 and thusV control the neness of grinding in the mill. Control of valves 33 may be coordinated in any known manner with control of feed by feeder I6, and control of volume of air by control of blower 1 or an inlet con trol valve as shown at 49 in hood 3.

ground material passing the apertures of grid 22 into space 23 will be lifted by lifters 24 and showered over the perforated portion of tube or liner 21. Some, particularly the finest of this partially ground material, will be dispersed in streams through the perforations 28 and will fall into the rapid main current of :duid passing through the restricted passage within liner 21. Here the rapidly moving tluid will entrain substantially all sufficiently ground material and carry it out of the mill into upcast duct 9. As the stream changes direction and also is decreased in velocity due to the fact that the area of duct 9 is larger than that of liner 21, some coarser material will settle in duct 9 and tend to build up at the joint with trunnion 5. Material gathering here will be conveyed by the helical fin 29 back to'space-23.

- From space 23 a. portion ofthe partially ground The operation of the form of the invention shown in Fig. 3 dilers only in that material settling in upcast duct 9 is returned directly to box 3| through space 48, conduits 46 and openings |26, bypassing the constant discharge chamber 23 and valved openings 26, thus permitting a return of coarse material without further contact with the stream of air in chamber 23.

It will be noted that in either form of the invention as disclosed, material settling in duct 9 is returned to the mill out of contact with the maintstream of uid sweeping through tubular liner 21, as in the form of Figs. l and 2 the n 29 will impede if not altogether prevent any now of fluid at any appreciable velocity through the space in trunnion 5 surrounding liner 2l.

Use of the ilared liner 21 will permit some coarser materials entering perforations 26 to be deflected back into the grinding space 3 against the stream of air.

The abovedescribed mill construction affords a great advantage over prior constructions in that all ground product is cascaded through and contacted by the fluid stream at substantially its maximum velocity and good product removal is obtained with a minimum of power consumed in fluid blowing as comparedwith iluid swept mills in which the air must entrain the product paricles in the grinding space when its velocity is ow. l

.It will be understood that the specic structure shown is susceptible to modiiication by substitution of equivalents within 'the scope of the invention, for instance by useof other well known types of valves at openings 2B, other known types of valve control for motors 39, and other well known devices for the product classifying and collecting devices |I, |3,. I4, |8 and I9, etc. It is intended that such modifications and others which will readily occur to persons skilled "in the art be included within the scope of the invention, which is limited only by the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In anair swept ball mill, having `a grinding space and a hollow discharge trunnion, a tubular liner for said trunnion having an imperforate portion extending through said trunnion and coaxially spaced therefrom and a .foraminous portion extending within said mill, an annular grid dividing the space within said mill surrounding said foraminous portion from said grinding space, a wall dividing the annular space between said imperforate portion of said liner and the inner surface of said trunnion from direct communication with the interior of said mill surrounding said foraminous portion, and conduit means in said mill for conducting materials from the inner end of said annular space to said grinding space.

2. A ball mill comprising a grinding chamber, feed and discharge trunnions, an annular grid dividing said grinding space from the discharge end wall of said mill, a perforated tubular member circumferentially connected with said grid and extending coaxially through said discharge trunnion, said grid and tubular member dening with, said end wall an annular ground material discharge chamber radially surrounding said,

perforated tubular member, liiters in said discharge chamber for showering ground material over said perforated tubular member, a conduit arranged to conduct ground material from the periphery of said discharge chamber to said grinding space, and load control means comprising a valve adjustable to control the flow of material through said conduit.

3. In a ball mill having a discharge end wall and a discharge trunnon, a grid spaced from said discharge end wall to form a discharge chamber in said mill, a perforated tubular member extending from said grid into said discharge trunnion and having an mperforate section extending coaxially through said trunnion in radially spaced relation, means for depositing insuiiiciently ground material discharged from said tubular member in the outer end .of the space between said trunnion and said tubular member, a material returning helix arranged in-and extending through said space, a conduit connecting said discharge chamber with the grin g space of said mill, a valve arranged to restric ow of material from said discharge chamber to saidconduit, and means for conducting into said conduit material which is returned into said mill by said helix, said last meansbypassing said valve.

4. In a ball mill having a discharge end wall and a discharge trunnion, a grid spaced from said end wall to define a discharge chamber in said mill, a perforated tubular member extending from said grid through said discharge chamber into said' discharge'trunnion and having an im"- perforaie section extending through said trunnion in coaxially spaced relation, means for depositing insufficiently ground material discharged from said tubular member in the outer end of the space between 4said trunnion and the imperforate -section of said tubular member, a material returning helix arranged in said space, means for drawing a current of gaseous iirid through said mill and out through said tubular member and means in said discharge chamber for lifting and showering materials therein over the perforated surface or said tubular member.

FREDERICK T. AGTHE.

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