US1333946A - Grinding-machine - Google Patents

Description

W. TRAVELL.

GRINDING MACHINE.

APPLICATION FILED MAR. 9. 191e.

Patented Mar. 16, 1920.

MAH/uw THA ZIM'CLJQM WARREN TRAVELL, F NEW YORK, N. Y.

GRINDINGr-MACHINE.

Specification of Letters Patent.

Patented Mar. 16, 1920.

Application led March 9, 1916. Serial No. 83,182.

To all whom t may concern Be it known that I, IVARREN TRAVELL, a

citizen ot' the United States, residing at New York, in the county of New York and State of New York, have invented new and useful Improvements in Grinding-Machines, of which the following is a specication.

This invention relates to improvements in grinding machines. More 'particularly it relates to machines in the nat-ure of tube mills wherein balls or pebbles are used for grinding cement or other material which is in relatively line condition.

In the type of tube-mill now in general use, material of twenty to forty mesh size is fed into one endet a rotating cylindrical mill and tumbled therein with a large quantity of pebbles of two or three inches diameter and after thus undergoing crushing and abrasion in the body ot the cylinder is discharged at the other end in inely pulverized form. Tube mills have also been proposed in which there are grooves arranged internally with a single very heavy ball .in each groove. It is an obj ect ot the invention to eliminate cert-ain disadvantages inherent inthe best ot tube mills known to me, among which may be mentioned the requirement ot' a large amount of power during normal operation ior continuously lifting the great mass of pebbles and material in the mill; the requirement of a large amount of additional horse power for overcoming the inertia. of the tube loaded with pebbles and material at the time oi starting; the relatively small amount of grinding done by individual pebbles, owing to their having only point contact with adjacent pebbles; the ineiciency in grinding owing to the greater `part of the pebbles at any given time being in a state ot rest relative to each other and the ineiiiciency owing to the relatively light weight ot the falling pebbles and from the relatively short distance which they travel in tumbling and the rapid wearing away ot the pebbles. It is a further object of the invention to produce mechanism. having the positive advantages characteristic of that herein disclosed, among which may be mentioned the saving ot power and increase of efliciency resulting from improvement in the particular mentioned above; areduction in cost of apparatus both for performing the grinding operation and tor incidental functions, asian illustration of which it may be vmentioned that. the saving ot power requisite tor starting, over and above that requisite for continuing in operation reduces the size of motors required where mills are driven by individual motors; the more thorough grinding, because more systematic, with greater uniformity of product, the superior grinding` e'tlect within a given length ot' tube permitting a mill of given capacity to be constructed in ay shorter length; the possibility of operating the mill at a higher speed than can be used with pebble mills without loss ot elliciency,A thereby increasing the voutput from a particular mill; andl the introduction of a larger proportion of abrasion into the grinding action as contrasted with the pebble mills where the grinding is mainly by concussion and crushing. It is also the object ot theinvention to provide the other advantages that are characteristic ot the mechanism hereinafter set forth. The disclosure herein made embodies inventive ideas which those skilled in the art will readily apply in many ways other than those specilically shown Afor purposes of illustration, without departing from the scope of the in vention. It is intended that the patent shall cover by suitable expression in the appended claims whatever features oft patentable novelty exist in the invention disclosed.

The objects of the invention are accomplished by providing a cylindricalor coni cal shell in which are a number of grooves more or less circular in general course and semi-circular in cross section, inwhich grooves a number ot spherical balls roll or slide and in so doing grind material between themselves and the walls ot the grooves. The partitions between adjacent grooves may Ahave holes which will permit the passage of'material longitudinally of the tube :trom one groove to another. The holes in adjacent partitions may be staggered lwith respect to leach other7 so that material in passing from one end of. the mill to the other is kept by kthese partitions 'from moving too rapidly, yet is permitted to move from the bottom of one groove into another, and withal may travel only in a zigzag path, partly in a circumferential direction along each groove. Such holes may be tapered to prevent clogging. The mill may be set with its longitudinal axis at asuitable inclination to the horizontal, or at least with its under surface inclined so that gravity assists the passage of material. The grooves, ballsl and partitions between grooves may be of such material, size and shape as is most suitable for the particular work to be performed. The metal in which the grooves are formed may be made in removable sections; and other details of construction may be employed as may be found advantageous, some of which are mentioned hereinafter.

In the accompanying drawings which represent more or less diagrammatically an enibodiment of the invention:

Figure 1 is a side elevation of a tube mill showing the grinding cylinder but with bearings, driving mechanism and other incidental parts omitted, partly in section;

'F ig. 2 is an end elevation of the same in section on the line 2 2 of Fig. 1;

Fig. 3 is an end elevation of the same in section on the line 3 3 of Fig. 1;

Fig. l is a longitudinal section of a detail with a modification in certain respects; and

Fig. 5 is a fragmentary diagram of the interior.

Referring to the drawings, 1() indicates the shell of a cylinder or tube -mill having an axial discharge orifice 11 and an axial inlet 12 fed from a hopper 13. Any suitable means may be employed to support and to rotate this cylinder upon its axis. The interior of the shell 10, as illustrated, is lined with metallic blocks 14 formed with depressions and ridges such that when assembled together they maire grooves 15 whose bottoms are substantially of semi-circular cross sectionv and whose sides 16 rise in straight vlines approximately tangent to the semi-circles as high as may be desired. In the bottom portions of the partitions betweenV grooves are holes 17 through which material may pass from one groove to the next. vThese holes may be tapered as illustrated clearly in Fig. -1 with their larger ends toward the lower part of the mill so that if 'any material becomes lodged therein it will automatically be cleared under the concussion and general jar that characterizes the operation of the apparatus; and the holes in successive partitions may be staggered with respect to each other so that material coming through one hole must travel somewhat longitudinally in the groove where it is before it can escape to the next groove. In these grooves are balls 20 about equal in diameter to the diameter of the semi-circular cross section of the groove, but enough smaller so that they roll freely therein with whatever clearance be desired for best grinding action upon the material between themselves and the walls of the grooves. The grooves may be covered over by cylindrical plates 19 which will keep the balls in position and prevent the material from going over the partitions.

At the delivery end of the tube may be a screen 21 to prevent balls, broken castings, etc., from passing out of the mill. In order to have the material discharged at the axis, lifting vanes 22 may be employed in the space between the screen and the axial discharge 11. lThese are illustrated as spiral vanes, as seen clearly in F ig. 3, but par- .titionsor vanes of other shape may be employed, as for example radial partitions.

In operation balls remain approximately in the position shown in Fig. 2 while the shell rotates past them in the direction of the arrow. y gradually along from the entrance 1Q to the axial discharge 11. The partitions between the grooves prevent the material from moving too fast. The staggering of the holes 17 further delays it and compels the material to be subject to a certain amount of grinding in the circumferential direction in each groove'. llfhile en route the material is subject to heavy crushing pressure and also to abrasion resulting the balls'relative thereto and relative to the grooves in which the balls are. The balls may be of hard metal, either rough -or smooth, and all of approximately the same size; or, they may be graded in various sizes, as for example balls 12 in diameter in the grooves nearest to the receiving' end, grooves and balls then diminishing through 10, 8, 6 and finally to 4t diameter in the grooves nearest the delivery end. In either event the weight of these individual balls is many times greater' than that of the individual pebbles in a pebble mill, because of their greater size and greater specific gravity; and also there is a superior grinding effect resulting from the greater area of available grinding surface, the diverse character of theaction between two grinding surfaces, being part sliding and part rolling, and the superior speed at which the grinding surfaces may movewith respect to each other and the material. llhile the machine is being started far less power is required. The contrast here is between a mill such as that described where the balls are free to roll, so that their inertia does not greatly affect the starting torque, a pebble mill where the inertia of a large mass of material and pebbles must be overcome, at starting, which in practice is considerable. A point of practical value resulting from this is that where mills of the ball and groove type are driven by individual electric motors the requisite size of motorv is reduced. There is also a saving of power during operation because there is not so great a mass which must be constantly lifted as the mill turns, with attendant friction to be overcome.

In a mill of the ball and groove type herein described, each ball is in the groove in which it runs through nearly its semi-circumference. The contact between the ball and the wall of the groove at the bottom of the groove is a rolling confrom slidino` of contact with Y The material meanwhile moves tact, producing a simple crushing action; the contact at the extreme edges of the semieircle of cross section is a sliding contact with a somewhat different and abrasive action on the material; while contact between the points mentioned is partly sliding and partly rolling.

The entire surface of each groove comes into rolling` or sliding contact with each ball during each revolution of the mill. If a mill is constructed with thirty grooves and contains ten balls in each groove, it is evident that the total effective grinding area during each revolution is 800 times the surface area of a semi-circular groove.

In the drawing, at the right of Fig. l, the grooves are represented as being parallel to each other, each lying in a plane perpendicular to the axis of the tube. It would be possible to get somewhatof a lateral pressure of the balls against the sides of their grooves by setting the grooves with their planes inclined to the axis of the main shell, as illustrated at the left in Fig. 1, in which case there would at each revolution be a lateral thrust of one or the other side of a groove against the balls therein, tending to deiect those balls first to one side and then to the other side, and thus providing more of a crushing effect for those larger particles of material which may be nearer the top of the groove than the particles over which the balls roll directly. This would set up some endwise thrusts in the mechanism as a whole, which however might be approximately balanced by providing an equal number of the grooves and balls oppositely inclined.

In Fig. 5 the holes 18 through the partitions between grooves are shown making an angle with the longitudinal axis of the mill, thereby assisting in the passage of material through the mill in a forward direction from the receiving to the delivery end. Y

When the mill is revolved, there is possibilit-y of the balls being carried so high that some will fall down over the other balls, also, any sudden movement of the balls in a groove due, for instance, to temporaryr wedging of particles, may cause the ne material to be thrown out of the groove over the partition and into an adjoining groove.

Either of these vactions would be detrimental to best action of mill. Means to prevent it is illustrated in Fig. l, and' at the left in Fig. l, consisting of an inner shell which would cover these grooves. Such anV inner shell may be cylindrical in shape as illustrated at 19 in Fig. 4, or it may have grooves corresponding to and opposite those on the outer shell as at 19 in F ig. 1, in which case the balls would be contained in conduits of circular cross section. Also, and particularly if it be cylindrical, it may be perforated with holes of such size as would permit passage of the material easily, but not the balls as illustrated in Fig. 4.

Many variations from the specific embodiment of the invention as set forth herein will suggest themselves to engineers trained in handlingthis kind of machinery and the patent is ltherefore vnot to be limited to the specific arrangement shown,

I claim as my invention:

1. A mill, comprising a shell, provided with partitions having central openings and forming internal circumferential grooves; and grinding rollers in said grooves; adjacent partitions having communicating openings therethrough permitting passage of material, the openings in adjacent partitions of a groove being staggered with respect to each other.

2. A mill, comprising a shell, provided with partitions forming internal circumferential grooves; and grinding rollers in said grooves; some of said partitions being arranged in planes oblique to the axis, thereby oscillating past the perpendicular plane during the revolution of the shell and causing the rollers to grind somewhat laterally; some of said partitions being inclined oppositely to others, thereby neutralizing their thrust effect on the mill.

3. A mill, comprising a shell, having within it partitions having central openingsl and forming circumferential grooves; andV grinding rollers in said grooves; said partitions havingy openings between said grooves, affording direct and open communication between adjacent grooves, and extending at an oblique angle with the diametric plane of the shell.

i. A mill, comprising an external shell, provided with internal circumferential grooves; an internal cylindrical shell; `and grinding rollers in said grooves; the partitions between said grooves extending inward to said shell, whereby conduits are constituted forming clearance space for material in process of reduction; and being provided with communicating openings between them.

A millcomprising a shell, provided interiorly with circumferential vpartitions forming tubular conduits; and Vgrinding rollers therein; adjacent partitions having openings at the periphery permitting passage of material between adjacent conduits, and said conduits having an inner screen wall affording communication with the inner chamber of the shell.

Signed by me at New York, N. Y., 6th day of March, 1916.

WARREN TRAVELL.

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lVitnesses z' linx lVIN'rHRor TRAVELL,A FRANK Pannen BALnwix.

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