US3044717A

US3044717A - Pulverising mills

Info

Publication number: US3044717A
Application number: US777659A
Authority: US
Inventors: Frederick S Tollow
Original assignee: Babcock and Wilcox Ltd
Current assignee: Babcock International Ltd
Priority date: 1957-12-06
Filing date: 1958-12-02
Publication date: 1962-07-17
Anticipated expiration: 1979-07-17
Also published as: GB847281A

Description

July 17, 1962 Filed Dec. 2, 1958 F. S. TOLLOW PULVERISING MILLS 5 Sheets-Sheet l Inventor Frederick 5. Tel low B E Attorney July 17, 1962 F. s. TOLLOW 3,044,717

Y PULVERISING MILLS Filed Dec. 2, 1958 5 Sheets-Sheet 2 In venior Frederick S. Tollow W Attorney July 17, 1962 Filed Dec. 2, 1958 F. S. TOLLOW PULVERISING MILLS 5 Sheets-Sheet 5 Inventor Frederick S. Tolluw W A ttorn e y July 17, 1962 F. s. TOLLOW 3,044,717

PULVERISING MILLS Filed Dec. 2, 1958 5 Sheets-Sheet 4 Inventor Frederick S. Tollow B 3 Attorney I July 17, 1962 F. s. TOLLOW 3,044,717

PULVERISING MILLS Filed Dec. 2, 1958 5 Sheets-Sheet 5 Inventor Frederick S. Tollow A Horn e y United States Patent Qfifice 3,044,717 Patented July 17,.1962

3,644,717 PULVERHSIING MILLS Frederick S. Tollow, London, England, assignor to Bahcoclr & Wilcox Limited, London, England, a Britishcompany Filed Dec. 2, 1958, Ser. No. 777,659 Claims priority, application Great Britain Dec. 6, 1957 9 Claims. (Cl.'241--121) This invention relates to pulverising mills of the kind including relatively rotatable grinding rings affording respective tracks for an intermediate circle of grinding balls and means resiliently urging one ring towards the other ring. Examples of such mills are disclosed, for example, in the specifications of British Patents Numbers 334,058, 396,614 and 523,753.

In mills of the kind in question, the requisite force for urging the grinding rings together is exerted by biassing springs. In the operation of a mill, considerable wear takes place during he useful life of the grinding rings and balls, and the wear is unavoidably accompanied by variation in the forces exerted by the biassing springs. Lessening in the biassing force exerted by the springs adversely affects both the fineness of grinding and the life of the grinding rings. Provision is made for adjusting the forces exerted by the biassing springs, but the requisite adjustments may be effected too infrequently and the adjustments, when made may fail to equalise the forces exerted by the difierent springs.

An object of the invention is the provision of means whereby the bia'ssing force may be maintained automatically at a desired or optimum value, and whereby the necessity of effecting adjustments upon which depends the matching of forces exerted at different locations around the grinding ring is avoided.

In a pulverising mill of the kind described, in accordance with the present invention the mill is provided with hydraulic biassing means for urging the one ring towards the other ring.

The invention will now be described by way of example, with reference to the accompanying partly diagrammatic drawings, in which:

FIGURE 1 is a side view of a mill having a lower grinding ring urged upwardly by hydraulic means the left hand half of the figure being in section; and part of the right hand side of the mill not shown;

FIGURE 2 is a view similar to that of FIGURE lot a mill having a lower rotary grinding ring and an upper ring urged downwardly by hydraulic means;

FIGURE 3 is an enlarged view of part of FIGURE 2 showing an hydraulic cylinder and a plunger for urging the upper grinding ring downwardly;

FIGURE 4 is an end view of FIGURE 3 looking from the left hand side of that figure, and

FIGURE 5 is a modification of part of the embodiment of FIGURE 2-4; and

FIGURE 6 is a detail of a par-t of a mill showing an arrangement of. hydraulic thrust means suitable for use with existing types of mill;

FIGURE 7 is a schematic diagram of a suitable hydraulic loading system for the hydraulic means of the mill of FIGURE 1 or that of FIGURE 2.

The pulverising mill of FIGURE 1 comprises a housing having a substantially cylindrical upper section 1 and a base section 2 mounted in a suitable foundation not shown. The upper section 1 is suitably of welded steel plate construction and is detachably connected to the base section 2, which contains the pulverising mill drive assembly including a vertical drive shaft 3 mounted axially of the housing in roller type journal bearings 4. The drive shaft 3 is supported in roller type thrust bearings 5 adapted to prevent axial movement of the shaft outlet from the classifier.

3. A bevel gear 6 is rigidly mounted on the shaft 3 and is driven from a pinion shaft not, shown for rotation of the drive shaft 3.

The drive shaft 3 extends upwardly into the upper section 1 of the mill housing and rigidly mounted on the upper end of the shaft is a boss 7 to the top of which is rigidly attached the central boss 8 of a spider 9. The spider 9 comprises an annularsupporting ring 10 co axially arranged with respect to the shaft 3 and supported from the central boss 8 by a plurality of circumferentially spaced radial arms 11. Secured to a lower part of the annular supporting ring is a grinding ring 12 which is coaxially arranged with respect to the shaft 3.

The central boss 8 is formed as an annulus of channel section, the sides of the channel forming upper and lower flange parts and the base of the channel forming an upright cylindrical part 13, coaxial with the shaft 3. The upright cylindrical part 13 is formed with a plurality of circumferentially spaced apertures such as the apere ture 14 providing communication between the space within the cylindrical part 13 and the space between the sides of the channel section of the boss 8. Suitably the apertures are adjustable in cross section by movable plates not shown in known manner for example as shown in FIGURE 17 of British patent specification No. 523,753.

Mounted coaxially above and rigidly attached to the central boss 3 is a rotary classifier 15 of well known form, for example substantially as described in said British Patent 523,753, comprising a lower downwardly directed frusto-conical discharge part 15 for returned particles opening at its lower end to the space within the cylindrical part 13.

Disposed above, and rigidly attached to the discharge part 15 is a plurality of classifier blades 16 arranged in a downwardly directed frustum of a cone coaxial with the shaft 3. The blades 16 are obliquely arranged with respect to the axis of the shaft 3, being inclined forwardly in their direction of motion with their leading edges outermost. The upper section of the mill "housing is formed with a central circular aperture 17 in its top 18 adapted to register with the upper entrained material The top of the housing is formed with an inner downwardly projecting flange 19 circumscribing the aperture 17 and the tops of the classifier blades 16 and adapted to provide a seal between the classifier and the housing.

The lower section 2 of the mill housing is formed with an upper inner cylindrical part 20 coaxial with the shaft 3, and the upper cylindrical part 20 is provided with an upper frusto-conical cap portion 21. The cap portion 21 at its upper narrow end part 22 terminates adjacent and closely circumscribes an outer cylindircal peripheral portion of the boss 7. The upper end part 22 is spaced from the periphery of the boss 7 sufiiciently to allow free rotation of the boss 7 within the end part 22 but sufiiciently closely thereto to inhibit the passage of pulverised or ground material between the end part 22 and the boss 7. i

An annular thrust or support ring 23 is slidably mounted on the uppercylindrical part 20, the inner peripheral surface of the annular support ring 23 slidably circumscribing the outer peripheral surface of the cylindrical part 29 so that the support ring is movable axially of the cylindrical part 20 and thus at the same time axially with respect to the shaft 3.

The thrust ring 23 is formed with a flat upper surface 24 and a radially inner upstanding annular flange 25. Supported on the surface 24 and rigidly attached to the thrust ring 23 is an annular grinding ring 26 disposed ooaxially with the shaft 3 with an inner peripheral part of the grinding ring 26 abutting the annular flange 25.

The

grinding rings

12 and 26 are formed at thesame radius from the axis of the shaft 3 with respective tracks for a circular row of spherical grinding balls 27, the upper grinding ring 12 having an annular track 28 in its lower surface and the lower grinding ring 26 having an annular track 29 formed in its upper surface, the tracks 28 and 29 being concave and arcuate in cross section and of the same or substantially the same radius as the grinding balls 27.

The lower grinding ring 26 is formed with a radially outer upwardly convergent frusto-conical taper 30 and radially outwardly and partly above the grinding ring 26 is disposed an annular throat ring 31 rigidly attached to the upper section of the mill housing. The throat ring 31 is formed with a lower upwardly convergent frustoconical portion 32 and an upper, upwardly divergent portion 33. The inner surface of the lower portion 32 is spaced radially outwardly from the frusto-conical tapered portion 30 of the grinding ring 26 to provide an annular passage 34 directed upwardly and inwardly toward the axis of the shaft 3.

The upper portion 33 of the throat ring defines an outwardly flaring path 35 between the portion 33 and the adj acent grinding balls 27.

The upper section of the mill housing is provided with an annular Windbox 36, circumscribing the section 1 of the mill housing between levels adjacent the upper support ring 10 and the lower grinding ring 26. The windbox is supplied with gaseous fluid from a source not shown and is provided with a lower inwardly and downwardly directed annular outlet passage 37 extending to a location within the mill housing below the throat ring 31.

The annular thrust ring 23 is formed in section substantially as a channel with side flanges 39 and extending downwardly, the radially inner flange 39 abutting the outer periphery of the cylindrical part 20 and the base of the channel providing the fiat upper surface 24.

Suitable circumferentially spaced webs such as the web 38 are provided to stiffen the channel section and the radially outer side flange as is of increased thickness compared with the inner flange 39 and the base. The flange 40 is formed in its lower edge with three recesses such as the recess 41 equiangularly distributed about the circumference of a circle centred on the axis of the drive shaft 3.

Each recess 41 is' formed as an upwardly convergent frustum of a cone terminating with a substantially hemispherical upper portion to provide an inverted cup shaped recess.

Three upright thrust rods such as the thrust rod 4-2 are provided slidably mounted in respective guide members 43 equiangularly distributed about a circle centred on the axis of the drive shaft 3 and at the same radius as the recesses 41. The guide members 43 are rigidly mounted in an annular radially outwardly extending flanged portion 45 of the base section 2 of the mill housing at a level below the thrust ring 23 which is so oriented with respect to the axis of the drive shaft 3 that the recesses 41 are disposed immediately above corresponding guide members 43. The upper ends of the thrust rods such as the end 44 of the thrust rod 42 are substantially hemispherical and enter the corresponding recesses to abut the hemispherical portions thereof. Suitably the upper ends of the plungers are hardened to resist wear.

Radially outwardly of the plungers 42 with respect to the axis of shaft 3 and below the lower ends of the plungers are provided respective lever pivot means such as the pivot means, rigidly connected to the base section 2 of the mill housing. There are thus three lever pivot means arranged at equiangularly spaced intervals around a circle centred at the axis of the driving shaft 3 and of radius greater than that of the circle associated with the thrust rods. Each lever pivot means comprises a pair of spaced upstanding flanges 46 through aligned apertures in which passes a horizontal pivot pin 47. Respective levers 48 are pivotally mounted between the flanges 46 of each of the lever pivot means, each lever 48 being rotatably mounted at its mid point on the associated pivot pin 47. The pivot pins 47 are arranged substantially tangential to a circle centred on the axis of the shaft 3 so that the levers are movable in respective planes radially extending from the shaft axis. The radially inner ends of each of the levers 48 are respectively pivotally connected to the lower ends of associated short links such as the link 49, and the short links 49 are respectively pivotally connected at their upper ends to the lower ends of the thrust rods 42.

Circumferentially distributed at equiangularly spaced intervals outside the lower section 2 of the mill housing respectively radially aligned with the pivot means and the thrust rods 42, are three hydraulic cylinders such as the cylinder 51. As is shown for the cylinder 51, each of the cylinders is pivotally anchored at its upper end to flange means rigidly connected to the upper section 1 of the mill housing and to a lower part of the windbox 35. The plungers of the cylinders project downwardly from the cylinders and are respectively pivotally connected to the radially outer ends of the levers 48 of the pivot means 46. Thus the plunger cap 50 of the cylinder 51 is pivotally connected at its lower end to the radially outer end of the lever 48. The arrangement is such that the hydraulic cylinders, as shown for the cylinder 51, are slightly inwardly inclined from the pivots at their upper ends to the radially outer ends of the associated lever 48.

In operation of the mill, material to be pulverised or ground is supplied by means not shown to a Zone radially inwardly of the balls 27 and adjacent the frusto-conical cap portion 21 by way of the spaces between the radial arms 11 of the spider 9. The upper grinding ring 12 rotates with the shaft 3 and the material is ground as it passes radially outwardly between the grinding rings 12 and 26. Gaseous fluid under pressure, suitably air, passes downwardly from the windbox 36 by way of the annular passage 34 to the divergent passage 35 where ring 31 and flows upwardly and inwardly through the annular passage 34 to the devergent passage 35 where it expands and increases in velocity, entraining pulverised or ground material and carrying it upwardly to the classifier 15 whence fine particles pass upwardly through the outlet 17 and coarse particles are returned downwardly to the grinding zone.

The hydraulic cylinders 51 are supplied with fluid at pressure from a source not shown which causes the plunger of the cylinders to be urged downwardly, pivoting the levers 4-8 so that the radially inner ends thereof are urged upwardly consequently urging the thrust rods 42 upwardly against the thrust ring 23. The thrust ring 23 and the associated lower grinding ring 26 are urged upwardly toward the upper grinding ring 12 to provide a desired grinding pressure between the grinding rings 12 and 26 and the balls 27. The lower ring 26 is prevented from rotating by interference of the plunger ends 44 with the sides of the recesses 41.

It will be appreciated that when hydraulic fluid under pressure is supplied to the hydraulic cylinders from the same source the cylinders and the associated link systems being similar, the thrusts on the plungers 42 are equal. Difficulties of equalising forces on the grinding rings is thereby avoided and by choice of suitable pressure of hydraulic fluid an optimum loading may be established between the balls and the grinding rings.

In operation, as wear of the balls and/or rings takes place, there is a corresponding upward movement of the lower ring without change in grinding pressure and the desired loading is maintained throughout the useful life of the grinding rings and the balls.

Conveniently, in order to facilitate access to the balls 27 for replacement purposes, the axial length of the upper cylindrical portion 20 of the lower section 2 of the mill housing is made suflicient for the thrust member 23 and the associated grinding ring 26 to drop, when the hydraulic pressure in the cylinder 51 is released to such a level that the balls 27 may be removed from between the grinding rings 26 and 12 by way of the, spacesbetween the radial arms of the spider 9. It will be appreciated that the radial arms, in this case, must be sufficiently widely spaced to permit removal of the balls.

In the embodiment of FIGURE 2 like reference numerals refer to similar parts in FIGURE 1. In the mill of FIGURE 2, the lower grinding ring 26 is rigidly connected to a rotary supporting ring 25 which forms part of a yoke member 60. The yoke member 60 comprises a central boss 7 rigidly mounted on the upper end of the rotary drive shaft 3 and below the boss 7 a downwardly divergent frusto-conical portion 21' formed at its lower end with anannular radial flange providing the supporting ring 25'. The shaft 3 in this embodiment is provided with thrust bearing means comprising a single roller type thrust bearing 5, adapted to prevent downward movement of the shaft. As will be explained hereinafter the shaft is urged downwardly by a biassing force and the need for the thrust bearing to prevent upward movement of the shaft is thereby obviated.

The upper grinding ring 12 is non rotary and is rigidly attached to a support ring 10, coaxially arranged with respect to the axis of the shaft 3, but independent thereof as regards rotation.

The support ring 10 is formed with a plurality of circumferentially distributed radially outwardly projecting lugs such as the lug 10. An equal number of lugs 10" are similarly circumferentially distributed around the inner surface of the upper section 1 of the mill housing, and rigidly attached thereto. Each of the lugs 10" is formed with an upright radially inner slot 10' in which the associated lug 18' is slidably located so that the support ring 10 is free to move axially of the shaft 3 with the lugs 10' sliding in the slots 10' of the lugs 10" but prevented from rotation by the lugs 10 interfering with the sides of the slots 10". The lugs 10" are of such length and are so disposed that the slots 10" provide guides for the associated lugs 10' over a range of movement at least equivalent to the range of movement of the thrust ring 10 from the maximum expected upward displocement thereof due to the passage of coarse material between the grinding rings 12 and 26, and the maximum expected downward displacement thereof when the balls and the grinding rings are all worn to their useful limits.

Rigidly attached to the top 18 of the upper section 1 of the mill housing are three guide members 62 equiangularly spaced about a circle centred on the axis of the drive shaft 3. As is shown more clearly in FIGURE 3, each guide member 62 comprises an upright cylindrical housing 63 extending through an associated circular aperture 63 formed in the top coverplate 18 of the upper section 1 of the mill housing. Each guide member housing 63 is formed intermediate its ends with a flange 64 which is disposed above and rigidly attached to the top 18 of the mill housing by bolts not shown. The flanges 64 are so disposed that relatively short portions such as the portion 62 of each cylindrical housing 63 extend through and below the top 18 of the mill housing, and a relatively long portion such as the portion 62" extends above the top 18 of the mill housing.

Respective thrust rods are slidably mounted in the guide members, thus as shown in FIGURE 3 for one of the guide members an upright thrust rod 65 formed as a hollow cylindrical rod is slidably mounted in a guide member 62. An upper end part 65' of the thrust rod 65 substantially longer than the cylindrical housing 63 is of enlarged outer diameter compared with a lower end part 65" of the thrust rod and slidably fits within and extends at either end beyond the ends of the guide member housing 63 and is suitably nickel plated on its outer surface. The lower end part 65" of the rod is disposed within the mill housing below the guide member 62. The housing 63 is provided .at its upper and lower ends with annular gland caps 66 threaded on to the ends of the housing and packed with suitable material to prevent upward escape of hot gaseous entraining fluid through the housing 63 from within the mill housing. At its upper end the thrust rod is provided with a lifting eye 79. p

At its lower end the thrust rod 65 is provided with a replaceable wear resistant head 68 comprising a substantially cylindrical plug formed at its lower end with a hemispherical convex surface 68' and intermediate its ends with an annular flange 68" of outer diameter equal to that of the lower portion 65" of the rod 65. The upper end 68" of the plug 68" tightly fits within the bore of the lower end of the thrust rod 65 with the flange 68 abutting the lower end of the rod.

The lower end 68 of the plug is adapted to engage a f-rustro-conical recess 69 having a hemispherical bottom and formed in the top of the supportring 10 of the upper grinding ring 12. Thus the support ring is formed with three recesses such as the recess 69 equiangularly spaced about a circle centred on the axis of the drive shaft 3, and each recess is adapted to receive the head 68' of the lower end of a thrust rod 65.

Each of the three thrust rods and their associated guide members is associated with an individual hydraulic cy1inder and a link mechanism connecting the plunger of the 7, cylinder to the thrust rod. There are thus provided three hydraulic cylinders disposed at equiangularly spaced intervals circumferentially of the upper section 1 of the mill housing and each is arranged as shown in FIGURES 3 and 4.

As shown in FIGS. 3 and 4 radially outwardly extending from the guide member housing 62 with respect to the axis of the drive shaft 3 is an upright flange 71 formed as a web between the flange 64 and the upper portion of the housing 63. At a radially outer part of the flange 71, spaced above the annular flange 64 and below the top of the housing 63 the flange 71 is formed with a boss 72 provided with a horizontal bore through which passes a pivot pin 73 arranged tangential to a circle centred on the mill drive shaft axis and passing through the mid point of the pivot pin. The ends of the pivot pin protrude from the ends of the boss and at each end is pivoted one of a pair of similar levers 74. Each lever 74 is pivoted at its mid point and is suitably cranked at its ends in a plane including the axes of the levers 74 and that of the pivot pin 73 so that the upper ends of the lever 74 are spaced apart a distance greater than the outside diameter of the guide member cylindrical housing 63. The upper end of each of the levers 74 is pivotally connected to an individually associated link 75 and the links 75 extend upwardly to respective locations on either side of the lifting eye 70 of the thrust rod 65. A horizontal pivot pin 70' passes through the lifting eye 70 and through respective apertures in the upper ends of the links 75. The arrangement is such that the upper ends of the levers 74 embrace the cylindrical housing 63.

Radially outwardly of the thrust rod 65 and outside the upper section 1 of the mill housing is provided an hydraulic cylinder pivotally anchored at its lower end to rotate in a direction radially of the axis of the shaft 3.

A bracket .81 is rigidly mounted on the outside of the upper section 1 of the mill housing formed with an upright bore through which passes a stud 82; The stud 82 is threaded and is provided with a pair of clamping nuts threaded on the stud, an upper clamping nut 83 above the arm of the bracket 81 and a lower clamping nut 84 below the arm of the bracket 81 the arrangement being such that the stud may be adjusted axially to a desired position by adjustment of the clamping

nuts

83 and 84. The upper end of the stud 83 is formed with an eye member 85 which is located between a pair of eye members 86 formed at the lower end of the hydraulic cylinder 80. A pivot pin 87 passes horizontally through the

eye members

86 and 85 and is arranged tangential to a circle centred on the axis of the shaft 3 and passing through the mid point of the pivot pin 87.

The hydraulic cylinder extends upwardly from the bracket 81 and slightly outwardly with respect to the axis of shaft 3. The cylinder is provided with a plunger cap 90 formed at the upper end of the plunger rod with an eye member 91 which is located between the lower ends of the levers 74. A pivot pin passes through respective apertures formed in the lower ends of the lever 74 and through the eye member 91 pivotally to connect the upper end of the plunger to the levers 74.

Each of the three hydraulic cylinders and its associated thrust rod is arranged as described in connection with and shown in FIGURES 3 and 4. All of the hydraulic cylinders are connected to a common source of hydraulic pressure fluid, so that in operation, the hydraulic cylinder and the link mechanism being similar for each of the thrust rods 65, the downward forces on the thrust rods are equal and difficulties in equalising the forces are avoided. By choice of a suitable hydraulic pressure an optimum loading may be established on the upper grinding ring 12. As wear of the grinding rings 12 and 26 and balls 27 takes place, such wear is compensated by corresponding downward projection of the thrust members 65 under the influence of a corresponding upthrust of the plunger caps 90 of the hydraulic cylinders 80 due to the hydraulic pressure in the cylinders 80. The desired loading on the upper grinding ring 12 is thus maintained automatically throughout the useful life of the grinding rings and balls.

When foreign material for example tramp iron, passes through the mill with the material to be ground, it does not cause an excessive rise in grinding pressure, but the upper ring 12 may lift to allow passage of the body of foreign material Without increase in the downthrust of the thrust rods 65 on the upper ring 10.

In the embodiment of FIGURES 2 to 4, if it is desired to lift the upper ring 12 with its support ring 10 for access to the balls for replacement purposes, the pivot pins 70 may be removed, and the thrust rods 65 lifted out by means of tackle connected to the lifting eyes 70. In this way access may be had to the support ring 10 and the associated upper grinding ring 12, without obstruction from the thrust rods 65.

Alternatively, in a modification of the embodiment of FIGURES 2 to 4, the thrust rods 65 may be pivotally connected at their lower ends to the support ring 10 so that lifting of the thrust rods 65 causes lifting of the support ring 10 and the associated upper grinding ring 12.

Thus as is shown in FIGURE 5 for one of the thrust rods 65, the lower end of each thrust rod 65 is formed with an eye 681 and the adjacent upper part of the support ring is formed with a spaced pair of upstanding flanges 683. The eye 681 enters the space between the flanges and a pivot pin 632 passes through aligned apertures in the flange 683 and the eye 681.

In this embodiment, lifting of the rods 65 causes lifting of the support ring 10 and the associated upper grinding ring 12. If desired the lifting may be performed by tackle connected to the eyes 70 at the upper ends of the thrust rods. Alternatively, the hydraulic cylinders 80, associated with the thrust rods 65 may be made double acting, in which case the thrust rods 65 and the support ring 10 with its grinding ring 12 may be lifted under hydraulic action.

It will be appreciated that if it is desired to lift the support ring 10 through a substantial distance under hydraulic action, the plungers of the hydraulic cylinders associated with the thrust rods will need to have a suitable travel and the link and lever system connecting the plunger to the associated thrust rods will be adapted to permit the travel of the plungers whilst lifting or lowering the thrust rods 65.

In an embodiment suitable for application to existing mills, for example of the nature disclosed in said British Patent Number 523,753, where it is desired to replace the conventional coil spring biassing means, hydraulic power devices are adapted to operate directly on an upper non- Cir rotary grinding ring. As is shown in FIGURE 6, the hydraulic power devices are mounted upon and extend through apertures in a top part of the mill housing.

FIGURE 6 shows the arrangement of one hydraulic power device in relation to a mill of the general type shown in FIGURE 2 to 4. Suitably the mill is provided with 4 power devices arranged at right angle intervals about the axis of the mill drive shaft, and spaced an equal radial distance therefrom.

In FIGURE 6 a lower grinding ring 131 is disposed as described for the ring 26 with reference to FIGURE 2 within a mill casing and supports a circular row of grinding balls such as the balls 132. An upper grinding ring 133, cooperating with upper surfaces of the balls 132, is rigidly attached to an upper annular support ring 134. The support ring 134 is formed at right angle spaced in- .ervals with respect to the drive shaft axis with radially outer projections such as the projection 135 which support respective thrust pads for the hydraulically operated plungers of the power devices.

Thus the projection 135 is provided on an upper surface with a removable thrust pad 138 formed with a lower spigot engaging a corresponding recess in the projection 135. The thrust pad 133 is formed in an upper surface thereof with a slot 135? arranged radially with respect to the axis of the mill drive shaft, not shown, and extending from a radially outer part of the pad to a location radially outwards of a radially innermost part thereof, the slot extending part way only through the radial thickness of the pad 133.

The slot 139 is formed at its radially inner portion with a lower concave recess 139 adapted to provide a seat for a corresponding convex lower end 140 of a thrust face of a thrust member 140. The thrust member 146 is rigidly connected to the lower end of a thrust rod 141 and is suitably hardened to reduce the effect of wear.

The top casing 136 of the mill housing is formed vertically above the projection 135 with a circular aperture 137 adapted slidably to engage an annular shoulder 141 formed on the lower end of an hydraulic cylinder 142. The hydraulic cylinder 142 is formed with a cylindrical upper body part 142 disposed above the top plate 136 of the mill housing and at its lower end is formed with a lower annular shoulder 143, of diameter larger than the aperture 137 and an upper annular shoulder 141 of diameter slightly less than that of the aperture. The shoulder 141 slidably fits within the aperture 137 with the shoulder 143 abutting against the lower face of the top cover 136 of the mill housing.

An annular collar or extension piece 144 formed with an upper annular recess 144 adapted to cooperate with the lower peripheral edge of the shoulder 143 is coaxially arranged with respect to the hydraulic cylinder 142 and is mounted below the top cover plate 136 of the mill housing to which it is rigidly attached by bolts not shown. The arrangement is such that the shoulder 143 of the hydraulic cylinder 142 is clamped between the walls of the recess 144' and the lower surface of the top cover 136 of the mill.

The extension piece 144 is provided with a lower extension member 145 of substantially frusto-conical form with its Wider end uppermost and rigidly attached to the lower end of the extension piece 144 by respective mutually cooperating flanges 144 and 145' and suitable bolts not shown. The extension piece 145 is hollow and is formed with a lower annular internal shoulder 146 and an annular internal shoulder 147 intermediate its ends. The shoulders 146 and 147 are bored to take upright aligned bearing

sleeves

149 and 148, respectively, and an upright thrust rod 150 is slidably supported in the

bearings

148 and 149.

The lower end of the extension piece 144 is formed with a gland recess 151 for packing material adapted to withstand the temperature of gases within the mill and the recess is closed by an annular cover plate 152 mounted at the lower end of the extension piece 145 and retained by bolts not shown. Within the extension piece 145 and between the intermediate and lower internal shoulders 147 and 146 is a space 153 surrounding a portion of the thrust rod 150, and an inlet 154 is provided, closed by a removable plug 155, for the introduction of suitable lubricant to the space for supply to the relatively sliding surfaces between the thrust rod 150 and the

sleeve bearings

149 and 148.

The hydraulic cylinder 142 is provided with a plunger cap 160 movable under the influence of hydraulic pressure within the cylinder and the plunger is adapted to register at its lower end with the upper endof the thrust rod 150, so that on application of hydraulic pressure within the cylinder 142, the plunger cap 160 is urged downwardly, forcing the thrust rod 150 downwardly against the thrust pad 138 and urging the support ring 134 and the associated upper grinding ring 133 downwardly toward the lower grinding ring 131. ably chosen to give a desired grinding pressure between the upper and lower grinding rings 133 and 131 and the grinding balls 132.

It will be appreciated that the three other power devices are arranged and adapted to operate in a similar way to the arrangement described in connection with FIG- URE '6, and that the four hydraulic power devices are actuated by hydraulic fluid at the same pressure from a common source. Equal forces are thus supplied to the upper grinding ring 133 and difliculty of equalising the forces is avoided. An optimum load may be established on the grinding rings by suitable choice of the hydraulic pressure and, in operation as wear of the balls and the grinding rings takes place, such wear is compensated by a corresponding downward movement of the plungers of the hydraulic power devices. Thus the desired loading on the upper grinding ring is maintained automatically throughout the useful life of the grinding rings and balls.

Adjacent the extension piece 145, the casing 130 of the mill is formed with an aperture 161 for access purposes. The aperture 161 is normally closed by a removable cover plate 162 in fluid tight manner.

Should it be desired to lift the ring 134 for the removal of a ball or balls for replacement purposes the cover plate 162 is removed and the hydraulic pressure is reduced. The bolts connecting the cooperating flanges 144 and 145 are removed and the extension piece 145 with its associated thrust member 150 is removed radially from the mill chamber 130, by way of the aperture 161, the thrust member sliding in the slot 139 of the thrust pad 138. Similarly the extension pieces associated with other hydraulic cylinders of the mill are removable and the upper grinding ring 133 of the mill may thus be lifted without obstruction from the thrust rods such as the thrust rod 150.

Furthermore the provision of the extension pieces such as the piece 145 stiitens the associated thrust rods such as the thrust rod 150, and the upper grinding ring 133 is prevented from rotating solely by the interference of the thrust members, such as the member 140, at their lower ends with the thrust pads, such as the pad 138.

The hydraulic system connected to the hydraulic power devices may be of any suitable form adapted to supply liquid at a pressure limited substantially to the desired value. The pressure limiting means may take any suitable form of elastic or weight loading device which permits flow of liquid to or from the hydraulic cylinder of The hydraulic pressure is suitthe power devices as the axially movable ring performs up and down movements consequent upon the grinding operation.

In FIGURE 7 is shown a suitable hydraulic system adapted to operate 3

hydraulic cylinders

100, 101 and 102.

The hydraulic cylinders are supplied with hydraulic fluid from the high pressure hydraulic fluid outlet of a pressure intensifier 104 by way of a common supply line 103 having

respective branch lines

103', 10 and 103" to the cylinders. Hydraulic fluid is supplied to the inten- 10 sifier 104 by way of a suction line 105 from a supply tank 106 and intermediate the tank 106 and the intensifier 104, the suction line 105 is provided with an isolating valve 107 and between the valve 107 and the intensifier 104 with .a suitable filter 108.

The high pressure supply line 103 is connected for the return of fluid to the supply tank 106 by return line 109 including a needle control valve 110 which is normally closed. Between the intensifier 104 and the return line 109, the supply line 103 is provided with a relief valve 111 with a discharge line 112 leading from the relief valve 111 to the return line 109 at a location between the needle valve and the supply tank 106. On a side of the return line 109 remote from the intensifier 104, the supply line 103 is connected to an accumulator 113 by way of line 114, suitably a spring loaded accumulator of suflicient capacity to maintain the pressure in the line 103 whilst the intensifier is on its suction stroke.

On the side of the accumulator 113 remote from the intensifier 104 the supply line 103 is connected to a pressure gauge 115. The pressure gauge 115 is provided with two contacts 116 and 117 suitably arranged in the control system of the driving motor of the mill and adapted to operate to shut the mill down when the pressure in the line 103 falls below a minimum operational value or exceeds a maximum operational value.

The intensifier 104 is of the type having a piston of large area exposed to low pressure fluid and rigidly connected to a piston of small area exposed to high pressure fluid, the ratio of the respective fluid pressure being equal to the ratio of the piston areas. The intensifier 104 is supplied with low pressure fluid, suitably air from the supply of entraining air to the mill, by way of a supply line 120 having a shut oif valve 121 and a filter 122, and connected to the low pressure fluid side of the intensifier by way of a pressure reducing valve 123. The intensifier 104 is provided with a suitable control system arranged and adapted to operate so that when the hydraulic high pressure fluid is exhausted from below the piston of small cross sectional area, and the piston is at the bottom of its travel, the low pressure fluid is supplied below the piston of large area so as to raise the piston of small area and suck in hydraulic fluid by way of the line 105 and filter 108 from the supply tank 106, and when the piston is at the top of its travel the low pressure fluid supply is disconnected from the underside of the piston of large area and connected to the intensifier above the piston of larger area so as to raise the pressure on the hydraulic fluid below the piston of small area. To this end the suction line 105 andthe supply line 103 are connected to the intensifier by respective. one way valves adapted to permit the hydraulic fluid to flow from the suction line to the intensifier and from p the intensifier to the supply, line. 103 but not to permit the reverse flow of fluid from the supply line 103 to the intensifier 104 or from the intensifier 104 to the suction line 105.

In operation of the hydraulic system, air from the mill entraining air supply is supplied to the underside of the piston of large area of the intensifier, and the piston is raised, raising the piston of small area and causing hydraulic fluid to be sucked from the supply tank 106 by way of line 105 intothe intensifier. When the pistons are at the top of their travel, and the intensifier hydraulic fluid capacity is filled with hydraulic fluid, the air supply below the piston of large area is cut otf, and the air is supplied above the piston of large area to raise the pressure of hydraulic fluid below the piston of small area. Hydraulic fluid is discharged from the intensifier 104 by way of line 103 to the three

hydraulic cylinders

100, 101 and 102 until these cylinders exert a fluid back pressure substantially equal to the hydraulic fluid pressure in the intensifier 104. When this condition is reached, it will be appreciated that a similar hydraulic pressure will exist in the accumulator 113 and the press sure gauge 115 will register a pressure corresponding to the hydraulic pressure in the intensifier. Suitably this pressure will be substantially midway between pressure levels equivalent to the positions of the contacts 116 and 117 and it will be appreciated that when the hydraulic pressure rises under starting up conditions and the pressure gauge pointer reaches contact 116, the drive motor for the mill will be energised and start to rotate.

During operation of the mill, should the hydraulic fluid pressure fall below a level corresponding to the position of contact 116 of the pressure gauge 115, the pressure gauge pointer in passing the contact 116 deenergises the mill drive motor and operation of the mill ceases. There is thus provided a protection against operation of the mill at too low a grinding pressure which may, for example, be unsafe due to the minimum forces necessary to maintain the grinding rings and balls in their safe operational position not being achieved and may arise by leakage of hydraulic fluid from the system.

It will be appreciated that the intensifier 104 and accumulator 113 will minimise the effect of small leaks of hydraulic fluid from the system since the accumulator 113 will act as a reservoir for excess fluid pumped into the high pressure side of the system from the intensifier 104, and small losses of hydraulic fluid will be made up from the accumulator 113 without significant pressure change in the system.

Should the hydraulic fluid pressure in the line 103, for any reason rise to a level equivalent to the position of the contact 117 of the pressure gauge, the drive motor for the mill will be deenergised, and cease rotating. There is thus provided a protection against overloading of the mill due to too high a grinding pressure.

In operation of the mill, should any large particles or foreign bodies such as tramp iron, pass through the grinding zone urging the upper and lower grinding rings to move apart, the grinding ring loaded by thrust rods associated with the hydraulic cylinder as in the embodiments described in connection with FIGURES 1 to 5 or the plungers of the hydraulic cylinders as in the embodiment of FIGURE 6, may move to permit the passage of the large particle or foreign body. This has the efiect of displacing the plungers of one or more of the hydraulic cylinders and tends to increase the pressure of the hydraulic fluid with the result that hydraulic fluid is forced into the accumulator 113, against the biassing force loading the accumulator without significant rise in hydraulic fluid pressure. Consequently the large particle or foreign body is passed through the mill without causing a significant rise in grinding pressure and endangering the grinding rings and balls due to a local rise in grinding pressure to an unsafe value.

The application of hydraulic biassing means to grinding mills as has been described advantageously eliminates the need for constant adjustment of the grinding pressure in order to maintain the fineness of grinding and to obtain the maximum useful life for the grinding rings and the balls.

It will be appreciated by those skilled in the art that further changes may be made in the form of the apparatus without departing from the scope of the invention covered by the subsequent claims.

I claim:

1. A pulverizer comprising a housing, a plurality of rolling grinding elements arranged for rotational movement in a horizontal circular path between the grinding surfaces of opposed grinding rings, means for rotating one of said rings about the axis of said circular path, and means for resiliently urging said other ring toward said rotating ring to exert a selected and adjustable grinding pressure on said grinding surfaces including a plurality of circumferentially equally spaced thrust rods positioned in and slidably axially movable with respect to said housing, the axis of each of said rods being normal to said other ring, hydraulic cylinders externally attached 12 to said housing a piston operable within each of said cylinders, means connecting each of said pistons with one end of one of said rods and with the opposite end of each of said rods engaging said ring.

2. A mill as claimed in claim 1, wherein the hydraulic means are connected to an hydraulic system of suitable form adapted to supply liquid to the said means at a pressure limited substantially to a desired value.

3. A mill as claimed in claim 2 wherein the hydraulic system includes a pressure intensifier supplied with air from the mill entraining air supply as low pressure fluid and adapted to supply hydraulic fluid at high pressure.

4. A mill as claimed in claim 3 wherein the hydraulic system between the intensifier and the hydraulic biassing means is provided with a spring or weight loaded hydraulic fluid accumulator.

5. A mill as claimed in claim 2, wherein means are provided adapted to shut down the motor driving the mill when the pressure of the hydraulic fluid supplied to the power devices falls below a lower predetermined value or rises above an upper predetermined value.

6. A pulverizer according to claim 1 wherein said other end of each of said rods is attached to said ring and the pistons'are double acting so as to lift said ring when desired.

7. A pulverizer comprising a housing, a plurality of rolling grinding elements arranged for rotational movement in a horizontal circular path between the grinding surfaces of opposed upper and lower grinding rings, means for rotating said lower ring about the axis of said circular path, and means for resiliently urging said upper ring toward said rotating ring to exert a continuous selected grinding pressure on said grinding surfaces and simultaneously resisting rotational movement of said upper ring including a plurality of circumferentially equally spaced external power cylinders rigidly mounted on the top of said housing, a piston vertically movable in each of said cylinders, a plurality of vertical axially movable thrust rods in said housing having their upper ends operatively connected to corresponding pistons, and means associated with the lower end of said thrust rods arranged to transmit the pressure on said thrust rods to said upper ring and yet permit limited tilting movement of said upper ring relative to said thrust rods.

8. A pulverizer comprising a housing, a plurality of rolling grinding elements arranged for rotational movement in a horizontal circular path between the grinding surfaces of opposed upper and lower grinding rings, means for rotating said upper ring about the axis of said circular path, and means for resiliently urging said lower ring upwardly toward said rotating ring to exert a selected grinding pressure on said grinding surfaces including a plurality of circumferentially equally spaced thrust rods positioned in and slidably axially movable with respect to said housing, the axes of said rods being normal to said lower ring, a hydraulic cylinder and piston for each of said thrust rods and externally attached to the lower portion of said housing, lever and linkage means connecting each of said pistons with one end of each of said rods and with the opposite end of each of said rods engaging said lower ring.

9. A pulverizer comprising a housing, a plurality of rolling grinding elements arranged for rotational movement in a horizontal circular path between the grinding surfaces of opposed grinding rings, means for rotating one of said rings about the axis of said circular path, and means for resiliently urging said other ring toward said rotating ring to exert a selected grinding pressure on said grinding surfaces and simultaneously resisting rotational movement of said other ring including hydraulic biasing means attached to the exterior of said housing, a plurality of circumferentially equally spaced thrust rods positioned to engage said other grinding ring, linkage means connecting each of said hydraulic biasing means and each of said rods, and means for simultaneously adjusting the force exerted by said hydraulic biasing means.

References Cited in the file of this patent UNITED STATES PATENTS Peck Sept. 21, 1909 King Nov. 29, 1932