US3897017A

US3897017A - Grinding mill

Info

Publication number: US3897017A
Application number: US456038A
Authority: US
Inventors: Leo R Rogers; Leo A Rogers
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-07-13
Filing date: 1974-03-29
Publication date: 1975-07-29
Anticipated expiration: 1992-07-29

Abstract

A crushing mill having lower fixed crushing shoe and a crushing assembly having an upper crushing shoe. Matching faces of the shoes consist of cooperable, asymmetrical cam surfaces and the movable shoe rotates about a vertical axis of the movable crushing assembly. Upon rotation of the upper assembly the cam surfaces impart a reciprocal motion to it, which, in turn, will crush and grind material introduced between the matching faces. Feed material is introduced through a hollow central shaft in the upper assembly and processed material is removed through peripheral ports or screens in the walls of a container structure surrounding the shoes. Proper alignment of the movable upper assembly is maintained by a bearing and seal combination which will accommodate the simultaneous rotary and reciprocal motion. Rotary motion is imparted to the rotary head by a drive means capable of adapting to such motion.

Description

United States Patent 1191 Rogers et a1.

[4 1 July 29,1975

1 GRINDING MILL [76] Inventors: Leo R. Rogers, 1182 Browning Ave., Salt Lake City, Utah 84105; Leo A. Rogers, 217 Oleander Way, El Paso, Tex. 79922 [22] Filed: Mar. 29, 1974 [21] Appl. No.: 456,038

Related US. Application Data [63] Continuation of Ser. No. 271,289, July 13, 1972,

abandoned.

[52] US. Cl 241/205; 74/57; 241/257 R [51] Int. Cl. 1302a 1/00 [58] Field of Search 241/203, 205, 206, 212, 241/244, 257 R; 74/57 [56] References (liter! UNITED STATES PATENTS 1,041,569 10/1912 Bade 241/205 UX 2,558,156 6/1951 Pugh 241/205 2,689,094 9/1954 Zaderenko... 241/205 2,834,555 5/1958 Pugh 241/244 3,556,417 1/1971 Newmiller.... 241/205 X 3,599,293 8/1971 Nystrand 241/244 X 1 i i i I l 21 I V 1 F i Primary Examiner-Granville Y. Custer, Jr. Assistant Examiner-Howard 1N. Goldberg Attorney, Agent, or Firm-Criddle & Thorpe [57] ABSTRACT A crushing mill having lower fixed crushing shoe and a crushing assembly having an upper crushing shoe. Matching faces of the shoes consist of cooperable, asymmetrical cam surfaces and the movable shoe rotates about a vertical axis of the movable crushing assembly. Upon rotation of the upper assembly the cam surfaces impart a reciprocal motion to it, which, in turn, will crush and grind material introduced between the matching faces. Feed material is introduced through a hollow central shaft in the upper assembly and processed material is removed through peripheral ports or screens in the walls of a container structure surrounding the'shoes. Proper alignment of the movable upper assembly is maintained by a bearing and seal combination which will accommodate the simultaneous rotary and reciprocal motion. Rotary motion is imparted to the rotary head by a drive means capable of adapting to such motion.

10 Claims, 6 Drawing Figures PATENTED JUL29 1975 SHEET FIG 5 FIG 4 GRINDING MILL This is a continuation of application Ser. No. 271,289 filed July 13, 1972 now abandoned.

BRIEF DESCRIPTION OF THE INVENTION 1. Field of the Invention This invention relates to crushing machines used pri' marily but not exclusively by the mining and mineral industries and particularly to those machines utilizing combined pounding and rotary grinding forces to reduce rock, ore or similar materials.

2. Prior Art Knowledge of this type of machine which incorpo rates both pounding and rotary crushing action has been disclosed as early as 1927 as shown in U.S. Pat. No. 1,627,506. More recently, US. Pat. Nos. 2,558,156, 2,834,555 and 3,556,417 have disclosed certain designs related to the aforementioned concept. To the best of our knowledge, however, none of these prior known machines have proven commercially successful owing to difficulties in keeping them operating properly.

SUMMARY OF THE INVENTION Principal objects of the present invention are to provide a crushing and abrading forces to a stream of feed material continuously passed through the machine and a machine capable of long periods of operation between maintenance shut downs.

Other objects are to provide such a machine having a simple rugged and easily maintained drive system for applying the necessary power to the operating parts and lubricated bearings and seals arranged to accommodate combined rotary and reciprocal motion while maintaining the cooperating grinding shoes in the proper orientation with respect to each other.

Another object is to provide such a machine with covers, seals and traps such that harsh or foreign materials cannot contact the bearings to cause their untimely failure and that lubricants or foreign materials cannot easily enter into the machine to contaminate the material being processed therein.

Still another object is to provide a machine which can be easily disassembled and reassembled to replace the grinding shoes, which of necessity wear out, and other parts which need to be adjusted or sized according to the particular application of the machine.

To achieve these objects we have provided as principal features of the invention, a fixed base structure which maintains the lower crushing shoe assembly in proper orientation with respect to a containing tank and associated structures; a movable upper drive and crushing shoe assembly that mates with the lower crushing shoe assembly; a superstructure which attaches to the base structure and provides a mount for the movable upper drive and crushing shoe assembly; a central cylindrical drive shaft containing an axial opening for admission of feed material to be crushed between shoes of the shoe assemblies; and, a drive means to apply rotary motion to the shaft while allowing for reciprocation thereof.

With the present invention the material to be crushed, along with any required carrier or processing fluids, is fed into the upper end of the axial opening in the drive shaft and drops to the bottom of the mill where it is deflected between the crushing shoes as the upper shoe is rotated. During rotation of the upper crushing shoe with respect to the lower shoe the camming surfaces thereof repeatedly raise the upper shoe and allow it to drop under the force of gravity onto the surface of the lower shoe. The asymmetrical shape of the cams and the rotary speed of the upper shoe assem bly are adjusted with respect to each other such that proper crushing and grinding action is achieved consistent with the nature of the material being processed.

The cylindrical drive shaft passes through a lubricated bearing contained in the supporting superstructure. Seals are provided for the bearings so that dirt, dust or other foreign material cannot enter the bearings. The upper end of the drive shaft is affixed to the power source. The lower end of the drive shaft is attached to the upper grinding shoe. A cylindrical grease trap is provided around and is attached to the drive shaft to catch any lubricant or foreign material that attempts to enter the crushing chamber by means of a pathway around the drive shaft.

The bearing seals may be of several designs, depending on the particular intended application of the machine. One design consists of a packing ring and bolt circle which compresses an elastomeric packing material as the bolts are tightened. With this design foreign materials that adhere to the shaft are wiped off by the packing ring as the shaft reciprocates. Another design consists of a floating circular seal combined with a bellows or rolling diaphragm. With this design one side of the seal assembly is attached to the bearing shaft and the other side of the seal assembly is attached to the drive shaft at a position beyond the range of reciprocal travel. Reciprocal motion is absorbed by a bellows or rolling diaphragm while rotary motion is allowed by the circular seal.

The superstructure consists of the bearing and seal support assembly with multiple support arms extending from the bearing housing to vertical walls of the base assembly. The number of supporting arms used is de pendent on the size and use to be made of the particular mill. The ends of the supporting arms are fastened to the walls with bolts or other mechanical devices which can be readily removed for disassembly of the mill.

In some respects, the base structure of the invention is similar to that disclosed in US. Pat. No. 2,558,156. However, lids or covers are fastened to the base, superstructure and movable assembly sealing mechanisms, so as to affect containment of material processed. The outer containment wall also provides mechanical support for the superstructure. Fittings around the upper rim of the outer containment wall permit attachment of the arms of the superstructure. Inside the outer containment wall is an inner containment wall which is shorter in height and fitted with multiple screen covered ports that pass the processed material. The outer containment wall has one or more discharge ports, as required by the particular application, to remove the processed material from the mill. The tank walls are normally cylindrical in shaped, but are not restricted to this shape.

The drive mechanism may be one of many different designs, that will allow continuous transmission of rotary motion to the cylindrical drive shaft even as it reciprocates. In one embodiment, a sprocket or pulley is attached to the upper end of the drive shaft. A drive chain or belt is then attached between the driving head of the mill and an adjacent power supply fitted with matching sprockets or pulleys. The flexible nature of the drive chain or belt accommodates the reciprocal motion of the mill drive shaft while at the same time imparting rotary motion to the mill. In another embodiment, the drive shaft forms a hollow center shaft of an electric motor. The armature of the motor is attached to and surrounds the center shaft so that it reciprocates with the drive shaft. The field poles of the motor are contained in a housing attached to the superstructure of the mill and surround the armature and drive shaft. With this arrangement the reciprocating motion of the armature is accommodated in the electromagnetic field between the field poles and armature of the motor. Additional bearings, gears or splines may be used in the motor assembly, as necessary.

Additional objects and features of the invention will become apparent from the following detailed description and drawings, disclosing what is presently contemplated as being the best mode of the invention.

THE DRAWINGS FIG. 1 is a front elevation view of the invention with one embodiment of drive mechanism, shown fragmentarily;

FIG. 2, a perspective cut-away view of the invention as shown in FIG. 1;

FIG. 3, a fragmentary vertical section taken on the line 3-3 of FIG. 2;

FIG. 4, a view like FIG. 3, but showing another embodiment of the invention;

FIG. 5, a similar view showing still another embodiment; and

FIG. 6, a similar view of yet another embodiment of the invention.

DETAILED DESCRIPTION Referring now to the drawings:

In the illustrated embodiment of FIGS. 1-3, the mill of the invention shown generally in FIGS. 1 and 2 includes a base structure having a base plate and an upright outer circular side wall 11 supporting a superstructure shown generally at 12. The side wall may be rolled steel welded to the base plate. The superstructure may be cast or may be fabricated from welded parts. Support arms 12a of the superstructure form spaced cross bars with a bearing housing 13 contained in the center thereof. The support arms rest on a flange 14 welded to the side wall and are fixed in place by means of bolts 15, inserted through matching holes in the flanges and the arms, and nuts 15a threaded thereon.

A side wall has a discharge opening 16, FIG. 1, therethrough for exit of processed material, as will be further explained. Inside the superstructure supporting outside side wall 11 is an inner screen wall 17 and a lower grinding shoe 18 is fastened to the base plate 10 by hold down flanges 19 engaging a lip of the shoe and bolts 20 inserted through the flanges and threaded into the base plate. The face of the grinding shoe has a plurality of cam surfaces 18a and, as shown herein, has four identical such surfaces, one in each quadrant thereof. The cam surfaces 18:: match similar cam surfaces 21a on the lower face of an upper grinding shoe 21. Thus, rotation of the grinding shoe 21 will cause the cam surfaces 21a to ride over the cam surfaces 18a. The cam surfaces are asymmetrical, but matched, such that sloped faces thereof are in contact with material between the faces and during rotation the upper shoe will rise until the high points 18b and 21b pass each other. As will be explained, rotary speed of the upper shoe is adjusted such that when the high points 21b of the upper shoe travel past the high points 18b of the lower shoe, the surfaces part and the upper shoe is thrown into free fall under the force of gravity until it impacts feed material which has been deflected between the shoes from the hollow drive shaft 23. Continued rotation will repeatedly cause the upper shoe 21 to impact material injected between the shoes and this will be followed by an abrading and grinding action as the shoe face 21a rides over face 18a with the crushable material contained therebetween. The crushing shoes of the present invention can be made in monolithic pieces or formed from assembled sections in a manner disclosed in U.S. Pat. No. 2,834,555, and the rotary reciprocating motion and the crushing-grinding action of the shoes is essentially the same as that described in the aforesaid U.S. Pat. No. 2,834,555.

The upper grinding shoe is attached to a flange 22 on the lower end of a hollow drive shaft 23 by means of bolts 24 inserted through holes in the flange 22 and threaded into the shoe 21. The flange 22 is fixed, as by welding, to the hollow drive shaft 23 and is suitably reinforced with a radiating web 22a coupling the flange to the hollow drive shaft so as to obtain a rigid connection between the drive shaft 23 and the shoe 21 which is secured to the flange 22.

The opening through the hollow drive shaft 23 is aligned with corresponding central openings formed through flange 22 and and upper shoe 21.

Attached to and surrounding the drive shaft 23 above the webs 22a there is provided a grease trap 25 for catching and retaining leaked lubricant or foreign material that might otherwise enter into the region of the grinding shoes from above and that could contaminate the material being processed. Such entrapped foreign material is manually removed as frequently as necessary to maintain the effectiveness of the trap.

Superstructure 12 includes the support arms 12a that each have their ends resting on and bolted to the top of side wall 11 and the central cylindrical bearing housing 13 formed at the other ends of the arms surrounding the drive shaft 23. A central shoulder 28, (FIG. 3) is formed on the inner surface of bearing housing 13, intermediate the length of the housing. The shoulder extends partially into the space between the drive shaft and the bearing housing and acts as a divider between upper and

lower bearings

29 and 30, respectively.

The

bearings

29 and 30 are each of ring shape, made of bronze alloy or other suitable solid or porous material having sufficient rigidity to withstand the forces imparted to it by the operating mill and capable of accepting a lubricant and maintaining a lubricanted surface between the bearing rings and the drive shaft 23. At least one port 31 is provided through the wall of bearing housing 13 and shoulder 28 to interconnect the exterior of the housing with a lubricant receiving space 32 formed between bearings and between the bearing housing and drive shaft. A fitting 33, which may be a conventional Zirk fitting, is provided each such port 31 to allow lubricant under pressure to be applied therethrough and to be retained in the lubricant receiving space.

In the embodiment shown in FIG. 3, upper and lower elastomeric seals 34 and 3S closely surround the drive shaft 23 above the bearing 29 and below the bearing 30, respectively, to provide a wiping contact with the drive shaft and to prevent leakage of lubricant along the drive shaft. Upper and lower packing rings 36 and 37, each having a ring shaped seal engaging leg and an outwardly projecting flange are used to compress the seals to the extent necessary to maintain the desired wiping contact. Bolts 38 are threaded through the packing ring flanges and into the bearing housing to hold the seal engaging leg of each packing ring against its seal. The seals are thus compressed between the adjacent bearing and a packing ring and expand into wiping engagement with the drive shaft.

In the embodiment shown in FIG. I, the structure is essentially the same as that previously described. However, the

elastomeric seals

34 and 35 are not used and a ring 39 is held to the inner, lower wall of bearing housing 13 by bolts 40 inserted through the wall of the bearing housing and threaded into the ring 39. The ring 39 serves as a support, holding the lower bearing 30 in place. Ring 39 and bolts 4-0 may be omitted if the

bearings

29 and 30 are press fitted into the bearing housing 13. In this embodiment, convolute diaphragm seals 41 surround the drive shaft 23 above and below the bearing housing and one end of each seal is anchored to the bearing housing and the other end is anchored by a compression band 4-4 to the drive shaft.

One or both ends of each seal are arranged to slide with respect to its anchor means, so that free rotation of the drive shaft can be maintained, and the convolute configuration of the seals allows for simultaneous reciprocation of the drive shaft as the upper shoe moves over the face of the lower crushing shoe. As illustrated, one end of each seal is fixed at 42 to the drive shaft 23 and the other end of each seal extends into a slot 43 formed in the bottom of bearing housing 13. In operation, as the seals 41 turn with the drive shaft 23 the ends of the seals slide within sealing slots 43.

Rotary power may be applied to the drive shaft in several ways. As shown in the embodiment of FIGS. 1-3, a sprocket 45 is fixed around the upper end of drive shaft 23 and a chain 46, shown fragmentarily connects the sprocket 45 and a sprocket, not shown, on a drive assembly, not shown, which may typically include an electric motor and transmission unit.

As shown in the embodiment of FIG. 4, a pulley 47 is fixed to the upper end of drive shaft 23 and V-belts 48 interconnect the pulley 57 and another pulley, not shown, driven by a drive means, not shown. With either the chain drive of FIG. 3, of the belt drive of FIG. 4, the chain or belts are made sufficiently long that they have the necessary flexiblity to allow for reciprocation of the drive shaft, without coming off the sprockets or pulleys.

Alternatively a direct drive of the drive shaft can be provided as shown in FIGS. 5 and 6, for example.

In the embodiment shown in FIG. 5, drive shaft 23 is journaled for both reciprocating and rotary motion through a motor housing as that is supported on the superstructure 12. An armature coil 50 is fixed to and moveswith the drive shaft 2.3 and a field coil SI is fixed to the inside of the motor housing 49, a spaced distance from the armature. A flange 52, fixed to the drive shaft extends over the journal assembly of the motor housing through which drive shaft 23 passes to prevent en- .trance of damaging foreign material into the housing 49. It should be apparent that other seal means, especially such as have been heretofore described, could be used. Naturally, electrical energization of the field coil will rotate the armature coil and the drive shaft 23 attached thereto. The armature is arranged to be within the field coil during full reciprocation of the drive shaft.

In the embodiment of FIG. 6, the motor housing and protective flange are the same as shown in the embodiment of FIG. 5. In this embodiment, however, the armature coil 53 is spline connected to the drive shaft 23.

A removable cover 54 is fitted over the top of the inner screen wall 17 to keep material being crushed that is around the crushing shoes from splashing over the top of the wall. Thus the material, which generally is in slurry form, is continually ground and reduced until it is small enough to pass through screen windows 55 in wall 17, and then through the discharge opening 16 in the outer, supporting side wall 11. Additional covers 56 extend across the upper end of side wall 11 and cover the upper portions thereof not covered by the superstructure 12, thereby keeping crushed material from splashing out and helping to keep contaminants from entering the mill.

In operation, slurreyed ore or other material to be crushed, is dropped down the hollow central opening of drive shaft 23. As the upper grinding shoe rotates and the shoes separate the slurry moves between them to be crushed when the upper shoe drops and to be ground as the rotation continues. The crushed material moves out of the shoes andl when it has been sufficiently reduced passes through screens of windows 55. Until such time as the material has been reduced to a size capable of passing the screens it is repeatedly drawn back into the space between the crushing shoes as the upper shoe is rotated and reciprocated.

Whereas there is here illustrated and specifically described a certain preferred construction presently regarded as constituting the best mode of the invention, it should be understood that changes can be made and other constructions can be adapted without departing from the inventive subject matter particularly set out and claimed herebelow.

We claim:

1. A grinding mill having a fixed lower grinding shoe with a plurality of asymmetrical camming surfaces on an upper face thereof;

a movable upper grinding shoe positioned above the fixed lower grinding shoe and having a plurality of asymmetrical camming surfaces on a lower face thereof, in mating relationship to the camming surfaces on the lower grinding shoe and a hole centrally through said upper shoe;

a cylindrical drive shaft fixed to and extending above the upper grinding shoe on the face opposite to the camming surfaces thereof and surrounding the hole therethrough, whereby ore fed into the drive shaft is fed by gravity between the grinding shoes;

a bearing housing surrounding and spaced from a portion of the drive shaft;

at least one bearing in the bearing housing closely surrounding the drive shaft to allow rotation and reciprocation of the drive shaft;

seal means at each end of the bearing housing and providing a seal between the drive shaft and the bearing housing;

means for adjustably compressing the seal means in the bearing housing, whereby said seal means is expanded into wiping engagement with the drive shaft and with the bearing housing;

at least one passage through the wall of the bearing housing;

fitting means for each passage, whereby lubricant can be applied through the passage to each bearing; and

means for rotating said drive shaft and the upper grinding shoe affixed thereto about a vertical longitudinal axis through the drive shaft.

2. A grinding mill having a fixed lower grinding shoe with a plurality of asymmetrical camming surfaces on an upper face thereof;

a bearing housing surrounding and spaced from a portion of the drive shaft;

seal means at each end of the bearing housing and providing a seal between the drive shaft and the bearing housing comprising convolute diaphragms having one end connected to the drive shaft and one end connected to the bearing housing, at least one of said ends being slidably connected whereby said drive shaft can rotate with respect to said bearing housing;

at least one passage through the wall of the bearing housing; 1

3. A grinding mill having a fixed lower grinding shoe with a plurality of asymmetrical camming surfaces on an upper face thereof;

a bearing housing;

a cylindrical drive shaft fixed to and extending above the upper grinding shoe on the face opposite to the camming surfaces thereof and surrounding the hole therethrough, said shaft extending upwardly through the bearing housing;

drive means for rotating said drive shaft and the upper grinding shoe affixed thereto about a vertical longitudinal axis through the drive shaft, said drive means being fixed to the drive shaft above the bearing housing; and

flexible means extending at least partially around the means for rotating said drive shaft to rotate said shaft while allowing for reciprocation thereof. 4. A grinding mill as in claim 3, wherein the drive means comprises a sprocket. 5. A grinding mill as in claim 3, wherein the drive means comprises a pulley.

6. A grinding mill having a fixed lower grinding shoe with a plurality of asymmetrical camming surfaces on an upper face thereof;

a bearing housing surrounding and spaced from a portion of the drive shaft;

at least one passage through the wall of the bearing housing;

means for rotating said drive shaft and the upper grinding shoe affixed thereto about a vertical longitudinal axis through the drive shaft, said means including drive means comprising an armature surrounding the drive shaft and affixed to the upper end of the shaft above the seal means.

7. A grinding mill as in claim 6, further including means for electrically exciting the armature to thereby operate the drive means.

8. A grinding mill as in claim 7, wherein the means for operating the drive means includes an electrically excited field coil surrounding said armature and fixed with respect to the bearing housmg.

9. A grinding mill as in claim 8, wherein the armature is fixed within the field coil and is positioned to be within said field coil during reciprocation of the drive shaft.

10. A grinding mill as in claim 8, wherein the drive shaft extends axially slidably through the armature and the armature is fixed for rotation with the drive shaft; and

means mounting the armature to rotate with respect to the field coil.

Claims

1. A grinding mill having a fixed lower grinding shoe with a plurality of asymmetrical camming surfaces on an upper face thereof; a movable upper grinding shoe positioned above the fixed lower grinding shoe and having a plurality of asymmetrical camming surfaces on a lower face thereof, in mating relationship to the camming surfaces on the lower grinding shoe and a hole centrally through said upper shoe; a cylindrical drive shaft fixed to and extending above the upper grinding shoe on the face opposite to the camming surfaces thereof and surrounding the hole therethrough, whereby ore fed into the drive shaft is fed by gravity between the grinding shoes; a bearing housing surrounding and spaced from a portion of the drive shaft; at least one bearing in the bearing housing closely surrounding the drive shaft to allow rotation and reciprocation of the drive shaft; seal means at each end of the bearing housing and providing a seal between the drive shaft and the bearing housing; means for adjustably compressing the seal means in the bearing housing, whereby said seal means is expanded into wiping engagement with the drive shaft and with the bearing housing; at least one passage through the wall of the bearing housing; fitting means for each passage, whereby lubricant can be applied through the passage to each bearing; and means for rotating said drive shaft and the upper grinding shoe affixed thereto about a vertical longitudinal axis through the drive shaft.

2. A grinding mill having a fixed lower grinding shoe with a plurality of asymmetrical camming surfaces on an upper face thereof; a movable upper grinding shoe positioned above the fixed lower grinding shoe and having a plurality of asymmetrical camming surfaces on a lower face thereof, in mating relationship to the camming surfaces on the lower grinding shoe and a hole centrally through said upper shoe; a cylindrical drive shaft fixed to and extending above the upper grinding shoe on the face opposite to the camming surfaces thereof and surrounding the hole therethrough, whereby ore fed into the drive shaft is fed by gravity between the grinding shoes; a bearing housing surrounding and spaced from a portion of the drive shaft; at least one bearing in the bearing housing closely surrounding the drive shaft to allow rotation and reciprocation of the drive shaft; seal means at each end of the bearing housing and providing a seal between the drive shaft and the bearing housing comprising convolute diaphragms having one end connected to the drive shaft and one end connected to the bearing housing, at least one of said ends being slidably connected whereby said drive shaft can rotate with respect to said bearing housing; at least one passage through the wall of the bearing housing; fitting means for each passage, whereby lubricant can be applied through the passage to each bearing; and means for rotating said drive shaft and the upper grinding shoe affixed thereto about a vertical longitudinal axis through the drive shaft.

3. A grinding mill having a fixed lower grinding shoe with a plurality of asymmetrical camming surfaces on an upper face thereof; a movable upper grinding shoe positioned above the fixed lower grinding shoe and having a plurality of asymmetrical camming surfaces on a lower face thereof, in mating relationship to the camming surfaces on the lower grinding shoe and a hole centrally through said upper shoe; a bearing housing; a cylindrical drive shaft fixed to and extending above the upper grinding shoe on the face opposite to the camming surfaces thereof and surrounding the hole therethrough, said shaft extending upwardly through the bearing housing; drive means for rotating said drive shaft and the upper grinding shoe affixed thereto about a vertical longitudinal axis through the drive shaft, said drive means being fixed to the drive shaft above the bearing housing; and flexible means extending at least partially around the means for rotating said drive shaft to rotate said shaft while allowing for reciprocation thereof.

4. A grinding mill as in claim 3, wherein the drive means comprises a sprocket.

5. A grinding mill as in claim 3, wherein the drive means comprises a pulley.

6. A grinding mill having a fixed lower grinding shoe with a plurality of asymmetrical camming surfaces on an upper face thereof; a movable upper grinding shoe positioned above the fixed lower grinding shoe and having a plurality of asymmetrical camming surfaces on a lower face thereof, in mating relationship to the camming surfaces on the lower grinding shoe and a hole centrally through said upper shoe; a cylindrical drive shaft fixed to and extending above the upper grinding shoe on the face opposite to the camming surfaces thereof and surrounding the hole therethrough, whereby ore fed into the drive shaft is fed by gravity between the grinding shoes; a bearing housing surrounding and spaced from a portion of the drive shaft; at least one bearing in the bearing housing closely surrounding the drive shaft to allow rotation and reciprocation of the drive shaft; seal means at each end of the bearing housing and providing a seal between the drive shaft and the bearing housing; at least one passage through the wall of the bearing housing; fitting means for each passage, whereby lubricant can be applied through the passage to each bearing; and means for rotating said drive shaft and the upper grinding shoe affixed thereto about a vertical longitudinal axis through the drive shaft, said means including drive means comprising an armature surrounding the drive shaft and affixed to the upper end of the shaft above the seal means.

8. A grinding mill as in claim 7, wherein the means for operating the drive means includes an electrically excited field coil surrounding said armature and fixed with respect to the bearing housing.

10. A grinding mill as in claim 8, wherein the drive shaft extends axially slidably through the armature and the armature is fixed for rotation with the drive shaft; and means mounting the armature to rotate with respect to the field coil.