US3038672A - Pulverizer classifier - Google Patents

Description

P. LANGSET-MO ET AL 3,038,672

June 12, 1962 PULVERIZER CLASSIFIER s Sheets-Sheet 1 Filed May 25. 1958 FIE: l

FIE: E

INVENTOR5 P5252 hmaszrm o -R01F 6: SWAA/JOA/ Z/IYCGai/V Z A/okK June 12, 1962 P. LANGSETMQ ET AL PULVERIZER CLASSIFIER Filed May 25. 1958 3 Sheets-Sheet 2 i \'Q K 1 INVENTORS I I Pam-w bamsasrno a FICi @934 Kly e/g TTORNEYS June 12, 1962 P. LANGSETMO ETAL 3,033,672

PULVERIZER CLASSIFIER a Sheets-Shet 5 Filed May 25, 1958 In: 'I

IL//. \LLUII' INVENTORS Panza (AA/48571910 ROLF 6; SMvm'o/v Ammo/1. 7. WURK United States Patent PULVERTZER CLASSIFEER Peder Langsetmo and Rolf G. Swanson, Minneapolis,

Minn, and Lincoln T. Work, Maplewood, N.J., assignors to Strong-Scott Manufacturing Company, Minneapolis, Minn, a corporation of Minnesota FiledMay 23, 19-58, Ser. No. 7 37,345 70mins. c1. Mir-485) This invention relates to new and novel improvements for apparatus for both pulverizing and classifying matter in a'dry state. Moreparticularly, this invention relates to improved apparatus for realizing a minimum range of particles of the desired particle size in the discharge product.

In the prior art wherein a classifying plate was mounted adjacent the end wall of the casing in which the pulverizing unit is located :and the peripheral edge of the classifying plate was adjacent the peripheral edge of said casing, there has been experienced a problem with respect to the space in the aforementioned area becoming clogged, especially when particles of a fine mesh size were to be ground. Further, it has been hard to obtain a desired classification of "fines when t he classifying chamber is located in the same casing asthe grinding chamber without having undesirable inter-reactions between the particles in the grinding section and the classifying section of the mill when both the classifying plate and the pulverizing apparatus have been mounted on the same shaft.

One of the objects of this invention -is to provide an improved pulverizer-classifier capable of pulverizing either hard or soft'material over a very wide range from thecoarser mesh sizes to the extreme fine particle sizes with a narrow size analysis spectrum. Further, it is an object of this invention to provide a unit having a grinding section that is separated from the classifying section but both located in the same casing, the moving parts of the grinding section being separately controlled and operated from the moving parts of the classifying section.

Additionally, it is an object of this invention to provide a unit for pulverizing materials wherein the material acted on in the pulverizing section is rapidly moved to the classifying section where the coarse are separated from the fines, the coarse being returned to the inlet end of the pulverizing unit and, the fines being moved to a discharge outlet. Still further, it is an object of this invention to provide a classifying section wherein a nonperforated rotary classifying plate is provided, said classifying section being adjacent the pulverizingportions of v the unit. The classifying plate is provided with means mounted thereon to induce turbulence in the outer whirl of the particles adjacent the periphery of the casing, that is, the boundary layer circulating adjacent said periphery; and to aid in imparting a tangential component to the coarse particles to move them into a, tailings conduit to be returned to the grinding section. Additionally, the classifying plate is provided with classifying means on the side opposite the .pulverizing section to centrifugally separate the coarse from the fines and permit the fines to pass therethroug'h into, the discharge opening.

A still further object of this invention is to provide apparatus of the foregoing character that is highly efficient as far. asoverall power consumption-is concerned, that provides for performing combined pulverizing and classifying functions in a compact unit which affords completeaccessibility to allinternal parts in a' -rnaitter of seconds for inspection, maintenance, cleaning, and that provides for adjustable features whereby the particles size of the discharge product may be varied.

Other and further objects are those inherent in the 3, i38,672 Patented June 12, 1962 invention herein illustrated, described in the claims, and will be apparent'as the discussion proceeds.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafiter fully described and particularly pointed out in the claims, the following description setting forth 'in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the. invention may be employed.

The present invention is an improvement on the pulverizing and classifying apparatus specified and claimed in the J. H. Haigh and R. C. Rolotf application, Serial No. 616,443, filed October 17, 1956, now U.S. Patent No. 2,939,638. The aforementioned patent and the present application have a common assignee.

The invention is illustrated by reference to. the drawings in which the corresponding numerals refer to the same parts and in which:

FIGURE 1 is an elevational view of the combined pulverizing and classifying unit of this invention with the elimination of the pulverizer section drive motor, the pulley driver of said motor, the guideway for said motor and portions of the belts extended around the pulley driver;

FIGURE 2 is a plan view of the apparatus taken along section lines and in the direction of arrows 22 of FIGURE 1, the view additionally depicting the respective drive means for the pulverizer and classifier sections;

FIGURE 3 is an end view of FIGURE 2, said View showing the classifying end of the unit;

FIGURE 4 is a side elevational view in part crosssection taken along section lines and in the direction of the arrows 4-4 of FIGURE 2 to illustrate the classifying and 'pulverizing sections along with the water jacket sur rounding the pulverizing section;

FIGURE 5 is a cross-sectional end view taken along the section line and in the direction of the arrows 5-5 of FIGURE 4 showing the back side of a classifying plate to illustrate the classifying vanes and classifying lugs mounted thereon, and the water jacket surrounding the pulverizing section of the unit;

FIGURE 6 shows aside view and a front view of the improved form of beater-mounted on a beater plate, said beater being preferably used for pulverizing soft materials;

FIGURE 7 shows a side view and an end View of an addition form of beater, said beater being preferably used for pulverizing hard abrasive materials.

FIGURE 8 is an enlarged fragmentary detailed view, partly in cross-section, illustrating the mounting of the classifying plate on the classifier shaft, the adjacent portion of the pulverizer shaft and axial position of the tailing outlet relative to said shafts.

Referring now to the drawings, and particularly to the FIGURES l4, there is illustrated a pulverizingclassifying unit generally designated as Iii. The pulverizing-classifying unit has an outer circular casingll that is supported above base 16 by legs 15 which are bolted to said base by a mounting bolt 17. The legs are secured to the casing by conventional means such as welding or may be formed integral with the casing, The casing 11 for the, purposes of the description will be considered to be made up of two sections, a pulverizing section 9 and a classifying section 8. At one end'of the casing 11 and formed integral with the peripheral edge is a vertical feed end wall 12 which has a rectangular feed aperture 21 located in the central portion thereof. On the same side'of the mounting base fromtlie casing 11, as the end wall 12, a pedestal'or standard 23 is mounted for supporting other'elements to be described hereinafter.

Formed integral with the casing 1'1 is a feed chute 20 that opens into the casing at the feed aperture 21 and has a top opening wherein the material to be ground is fed therethrough by a worm feed unit generally designated as 22; however, it is to be understood that other types of feeders may be used. One end of the aforementioned worm feed unit is mountably secured to the top portion of the feed chute by mounting bolts 17 and the other end is mountably secured to the pedestal 23 by support 27.

Spaced bearings 24, 25 for journaling a pulverizing shaft 26 therein are secured to the pedestal by mounting bolts 18. A pulley drum 28 is mounted on the end of the shaft opposite the pulverizing section. The shaft is rotatably driven by a motor 31, said motor having a pulley drum 29 drivingly connected to the drum 28 by belts 30 to cause rotation of the shaft. The motor is mounted on the base 16 such that its axis of rotation is parallel to the axis of rotation of the shaft.

The classifying section 8 is pivotally connected to the outer casing 11 on the end opposite the feed chute by a pair of hinges 35, said hinges having a lower hinge arm 35b connected to the main casing 11 and an upper hinge arm 35a connected to the classifying end wall 12. Spaced directly across the end wall 12 from each of the hinges is a swingable hand wheel 36, each of said swingable hand wheels having a shank 37 engageable in a slotted formation or clevis 38 formed integral with the peripheral edge of said end wall.

Secured to the classifying end wall by conventional means (such as welding) is a generally horizontal support base 41. Mounted on the support and secured by U-shaped brackets 53 and bolts 54 are an inboard bearing 42 and an outboard bearing 43, said bearings journaling a classifying shaft 44. Mounted on the outer end of the classifying shaft is a pulley drum 45 which is rotatably driven by a variable speed pulley drive system located under the bracket 46. The variable speed drive system includes a pulley drum 45 and handle 47, said system being conventional and therefore will not be further described. The system under the bracket 46 is in part mounted on a T-support 52, said support being secured to the mounting base 41. The handle 47 provides a means for adjusting the speed of the system.

The motor 48 which drives the variable speed drive system is mountably secured to the support base 41 by a U-shaped bracket 49, said bracket being held in place by conventional means as mounting bolts 50. The motor is so mounted on the support base that its drive shaft is spaced from and parallel to the classifying shaft 44.

The classifying shaft 44 extends inwardly through an outlet aperture 57 located in the central portion of the classifying end wall 13. A discharge housing 58 having a side wall aperture 59 of the same size and shape as the outlet aperture 57 is mountably secured to the classifying end wall by flat-heated screws 60. In the opposite side wall of the discharge housing from the side wall aperture, a seal ring 62 secured to the side wall by bolts 63 is mounted in an opening 61. The seal ring has an inner opening therethrough which is the size of the shaft, the inner peripheral wall forming said opening having a peripheral groove 64 for mounting an O-ring 65 therein. Thus, the seal ring in combination with the O-ring forms a seal between the shaft and the discharge housing to prevent escape of fines along the shaft. The discharge housing has a flange 58b encompassing the top aperture 580 such that an appropriate conduit (not shown) may be connected thereto to lead to a storage bin. As is conventional a discharge fan (not shown) may be located in said conduit.

The pulverizer shaft 26 previously mentioned extends inwardly through a pulverizing shaft opening 68 located in the central portion of the feed end wall 12, said shaft having a common axis of rotation with the classifying shaft 44. The inner end of the pulverizing shaft 26 extends such that it is adjacent but slightly spaced from the inlet end of the classifying shaft 44. An annular seal 69 is mounted on the pulverizing opening 68 to form a tight fit between the feed end wall and the outer periphery of the shaft to prevent the material to be pulverized from escaping through said opening. A groove 68a is formed in the inner peripheral wall of the seal 69 such that an O-ring 70 may be inserted therein similarly as for the seal ring mounted on the classifying shaft.

As best observed from FIGURE 4, the pulverizing shaft 26 which extends inwardly from the feed end wall 12 has an end plate retainer 89 secured thereon adjacent the ring seal 69. This retainer 89 serves to establish the reference position of the plate which is mounted on said shaft. Since it is desirable that a plurality of spaced disks or beater plates 80, 81, and 82 be removably stacked on the shaft 26, the pair of spacers 87 are positioned between the several disks. A retainer cap 88 held in position by a lock washer 86 and a nut 92 on the inner end of the shaft, maintain the stacked relationship of the aforementioned plates during the operation of the unit.

Each of the plates 80, 81, and 82 have a plurality of spaced heaters 84 mounted on the peripheral edges thereof. Also, each of the plates is provided with a plurality of annularly located apertures 93 spaced peripherally inward.

Spaced radially inwardly from the heaters 84 and secured to the feed end plate side of the beater plate 80 are a plurality of primary beater vanes a, said heater vanes being axially cooperable with annular rear grinding plate which may be of a corrugated configuration, for primary size reduction of the material to be ground or pulverized. The heaters 84 mounted on the beater plates are radially cooperable with a cylindrical liner 91 which may be corrugated. As may be noted in FIG- URE 4 the abutting edges of the annular rear grinding plate and the cylindrical liner have inter-locking edges such that they form a tight fit thus preventing any escape of material at the place of junction between the two aforementioned elements.

On the opposite side of the beater plate 80 from the primary beater vanes 85a are a plurality of secondary beater vanes 85b secured to the beater plate 80. The beater vanes 85b are similarly spaced as the aforementioned beater vanes 85a. The beater vanes 85b perform two functions, that is, they serve to balance the beater plate 80 and at the same time aid to perform the pulverizing function in conjunction with the beater plate 81 and thereby yield a better size reduction of the material.

As may be best seen in FIGURES 4 and 5 a classifying plate 100 is mounted on the inner end of the classifying shaft 44 adjacent the beater plate 82.The classifying plate is held in position on the end of the shaft by fastening a classifier hub 97 to one side of the plate and a classifying plate ring 98 to the opposite side of the plate, there being cap screws extending through appropriate spaced apertures formed in the hub, the classifying plate, and the classifying plate ring to secure said elements in fixed relation to one another. The hub 97 along with the classifying plate attached thereto are axially positionable on the shaft for a purpose to be explained hereinafter.

It may be noted by inspection of FIGURE 4 that the hub 97 is substantially a sleeve having a taper bore extending therethrough. This sleeve or hub encircles a split tapered bushing 99 composed of separate halves 99a and 99b, said hub and split tapered bushing being held in position by tightening bolts 99d and loosening bolts 990 such as those described in application, Serial No. 616,443 which has issued as US. Patent 2,939,638 (see lines 53-75 of column 3 and lines 0 to 28 of column 4 of the printed patent). Only one loosening bolt and one tightening bolt are illustrated, however, a plurality of the aforementioned bolts are provided as described in said patent. The manner in which the bolts and associate elementsare utilized in adjustable axially positioning the classifying plate is fully set forth in the abovementioned lines of Patent 2,939,638 and therefore will not be described herein. The split bushing 99 is splined to shaft 44 by a key 102.

Mounted on the peripheral portion of the classifying plate1-0tl are four spaced elongated lugs 103. Each of these lugs are triangular shaped in vertical cross-section and extend longitudinally on either side of the classifying plate 100. Of course, it is to be understood that either a larger or a lesser number of lugs could be used on the classifying plate, although we prefer to use between two and four to obtain best'results. The purpose of these lugs will be described hereinafter.

On the discharge side of the classifying plate spaced radially from the shaft 44 and located approximatelymidway between the shaft and the outer peripheral portions of the classifying plate are a plurality of classifying vanes 105. The vanes are positioned between /2 to of the radial distance out from the axis of rotation of shaft 44. If they arelocated further out, they disturb the classifying zone (in the area of arrow 140) and if too far in, the coarse are not subjected to sufficient centrifugal force.

As may be noted in FIGURE 5, the flat surface of each vane is perpendicular to the classifying plate and has an elongated dimension that is located radially from the axis of rotation of the classifying plate. Although for fine grindings, we have found that best results may be obtained with the use of 20-24 spaced classifying vanes, it is to be understood that either a larger or lesser number of vanes may be used. The vanes may be attached to the classifying plate by any conventional means such as flat headed rivets 106 as shown in FIGURE 5.

The inner wall of the classifying end plate 13 has a shallow annular recessed portion 139 formed therein, said recessed portion extending radially outward from the edge of the outlet aperture 57 to form an annular shoulder 141 adjacent the lugs 103, the purpose of said structure will be explained hereinafter.

As may be noted in FIGURE 4, a relatively wide shallow groove 110 is formed in the inner peripheral wall of the outer casing 11. The groove in conjunction with a portion of the outer peripheral wall of the cylindrical liner 91-forms an annular water channel 111.

A hollowed-out water inlet chamber 112 is formed integral with the bottom portion of the casing 11, said inlet chamber having spaced grates 113 adjacent to and across the width of the water channel to distribute the water across the width of said channel and to prevent foreign objects from flowing into the water channel. The side Wall portion 112a of the chamber adjacent the classifying end plate 13 has a threaded aperture 1121) formed therein such that the water inlet pipe 114 may be threaded into said aperture. Thus water may flow through the pipe into the hollow portion 112c, pass between the grated sections of said chamber into the water channel 111.

Formed in the-top of the outer casing and integral therewith is a water outlet chamber 118, said water outlet chamber having a top annular flange 118k: and a hollow portion 118:: with spaced grates 113 mounted therein adja'ce'nt the water channel 111. The width of the hollow portion of 118 'is the same as the width of the water channel, and thence narrows to the diameter of the flange portion. The top inner surface of the flange portion is threaded such that the water outlet pipe 119 may be secured therein. Thus, it may be seen that water may be passed through the inlet pipe 114 to the water inlet chamber where it separates and flows along both sides of the inner cylinder liner through the water channel 111 and upwardly to the water outlet chamber 118 and thence through the water outlet pipe, to provide means for cooling the outer wall of the pulverizing section without having to rely on air flow through said section.

Three spaced O-rings are positioned in grooves 120 one of said grooves being located adjacent the intersection of the outer casing with the feed end wall, a central groove being formed adjacent the water channel in the area between the classifying section 8 and pulverizing section 9, and the third groove being formed adjacent the classifying end wall 13. The O-rings 121a, 12112, and 121a are each positioned in the respective grooves; the O-rings 121a and 121b forming a water seal on either side of the water channel. The O-ring 121C provides a seal to prevent the fines from passing out of the casing at the place of intersection of the classifying end wall with the cylindrical liner and the outer casing.

Referring now in particular to FIGURE 6, a side view and an end view of our new and improved beater plate 84 are illustrated. The beater plate is made up of a beater section 125 and legs 126. The beater section has an elongated rectangular face 125a. and is relatively narrow in cross-section. Formed integral with the bottom edge of the beater section are two legs 126, each having a generally flat surface lying in a vertical plane that is perpendicular to a plane passing through the rectangular face 125a and having inner faces 126a that are spaced apart from each other such that they may be passed over the edge of any one of the beater plates 80, 81, or 82. The fiat face of the legs are generally triangular in shape with the upper apex thereof narrowing to the width of the bottom edge of the beater portion. Two spaced apertures are formed in the base portion of the generally triangular face in either leg such that bolts 128 may be passed through said apertures to secure the beater to the beater plate. Since the slot formed by the two inner faces 126a of the legs is midway between the length of the beater portion and both legs are identical in shape and in cross-section except that one leg is rotated 180; the heaters when mounted are balanced such that the weight is distributed on either side of the beater plate. Thus, a heater is formed having a substantial impact surface and means for readily attaching said beater to a heater plate whereby the beater may be secured to the beater plate and still not disturb the balance thereof.

The heaters 130 shown in FIGURE 7 are quite similar to conventional types already used and there-fore will not be described. It has been found that beaters 130 are better for pulverizing hard abrasive material whereas the new type heaters 84 shown in FIGURE 6 are superior for pulverizing non-abrasive material.

A tailings conduit .137 having a tailings outlet 136 formed in the cylindrical liner 91 is provided, there being a tailings conduit mounted on either side of the casing. The respective tailings outlets are formed in the cylindrical liner wall on a level that lies in approximately the same horizontal Zone that the shaft 44 is locatedin, and are located in the peripheral portion of the casing such that they are adjacent the peripheral edge of the classifying plate. The tailings outlets are made of a width such that they normally extend on either side of a vertical plane passing through the vertical surfaces of the classifying plate. Mounted in the tailings conduit adjacent the tailings outlet but on the outside of the casing is a gate valve which is controlled by the handle 138. The gate valve 135 is adjustable such that the effective width of the tailings conduit may be varied from a fully closed to a fully opened position.

The tailings conduit 137 extends in an outward direction from the tailings outlet then is bent such that its side walls run parallel to the casing, said conduit running to the feed end of the casing whereat it is bent in an inward direction. The conduit then extends to tailings inlet openings (not shown) which are located on either side of the shaft 26 and adjacent thereto. Thus, the coarse may be passed from the classifying section back to and through the feed end wall to be further pulverized.

Although the classifying plate with classifying lugs and vanes mounted thereon is described as being used in a beater mill, it is to be understood'that it may be used in other comminuting mills to effectuate classification. Further, it is to be understood that the unit would function without the provision of a recessed portion in the classifying end wall as described but the unit would not operate as effectively and there would be a far greater danger of clogging. In addition, the spacing of any classifying vanes may be varied from each other and from the shaft 44, and that the planes of the surfaces of the vanes may be offset planes extending radially outwardly from the shaft; but it is preferred that said vanes be located between /2 and of the radial distance outward from the axis of rotation as previously mentioned.

The structural elements of our new and improved apparatus having been set forth, a typical operation will be set forth. The exact theory by which the present invention operates to effectuate the results obtained is not entirely under-stood, however, it is believed to be as set forth hereinafter in the description of a typical operation.

Considering now a typical operation, we will assume that all adjustments have been made for the fineness desired and that the variou members are in the relative positions pictured in the drawings. The material to be pulverized is advanced through worm feed unit 22 to the inclined chute through which it falls into the pulverizing section 9 of the casing 11. As the material enters into the casing 11, it encounters the primary beater 85a. Centrifugal forces produced by the rotating 'beaters 85a distribute the entering material such that the material is effectively dispersed between the corrugated back grinding plate 90 and the heaters 85a to yield a primary reduction in particle size.

Since the centrifugal forces act upon the larger and heavier particles more forcibly than the smaller and lighter weight ones, the greater bulk of the material at this initial stage moves radially outward, only a small fraction passing to the apertures 93 in the plate 80. After subjection to the action of the primary beaters 85a, the particles are thrown against the cylinder liner wall 91 where they first pass between and encounter the heaters 84 on the plate 80. Owing to the presence of the liner and attrition between particles more size reduction takes place. Centrifugal forces will tend to keep the larger particles adjacent the liner 91, although part of the fines and the coarse will be rebounded into the area between the plates 80 and 81 wherein the coarse will encounter the secondary beater vanes 8512 on the inner side of the beater plate 80. The latter mentioned vanes will aid in eifectuating further pulverizing action on the coarse material and also to throw said particles outwardly against the cylindrical liner. Those particles remaining next to the liner 91, and of course, those advanced between the heaters 84 are further pulverized to a smaller size. Similarly, the coarse particles are passed by the heaters 84 mounted on the plate 82 where they receive further grinding treatment. The fines are moved in a longitudinal direction through the unit at a faster rate than the coarse due to the longitudinal air flow through said unit.

The next step is to expose the pulverized material to the action of the classifying plate 100. Since the classifying plate 100 is driven by the motor 48, and the beater plates 80, 81, and 82 are driven by the motor 31, it follows that the speed of the classifying plate is fully independent of the pulverizing plates. However, the output whirl of the particles of the pulverizing section becomes the input whirl of the classifying section and thus as the pulverized material approaches the classifying plate, the larger particles are retained adjacent the inner side of the cylindrical liner by centrifugal forces. Where apertures 93 have been provided in the beater plates, a portion of the fines may be drawn therethrough by any air currents that pass through the apertures 93 of said plates. Since the classifying plate has no perforations therein, the air currents carrying both the fines and the coarse have to pass around the peripheral edges of said plates. A portion of the coarse particles adjacent the peripheral wall of the casing will be induced to leave the casing through the tailings outlets to be returned to the inlet end of the pulverize section for regrinding. The main adjustments governing the quantity of material passing through the tailings conduits are the axial position of the classifying plate on the shaft, the degree of closure of the gate valve 135 in the tailings conduit 137, and the adjustments which affect the static air pressure differential in the unit.

As the grinds pass over the peripheral edge of the classifying plate they pass between the rotating lugs 103 which are mounted on said classifying plate. The longitudinal lugs tend to impart a component of force to the coarser particles such that said particles will pass through the outlet 136 into the tailings conduit to be returned to the feed end of the pulverizer. Also these lugs tend to stir up and create a high degree of turbulence in the boundary suspensional layer that tends to be formed in the area adjacent the cylinder liner. This action aids in separating the coarse from the fines, thereby minimizing the quantity of fines passing through the tailings outlet.

The air sweep is sufficiently strong so that the majority of fines and a portion of the coarse are carried over the peripheral edge of the classifying plate into the area between the end wall and the classifying plate adjacent the classifying vanes. As may be noted, an annular shoulder M1 is formed on the end wall 13 adjacent the lugs 103, said shoulder decreasing the effective area between the vertical peripheral edge of the classifying plate and the end wall 13. The provision of a shoulder adjacent the lugs increases radial velocity of the air sweep passing between said shoulder and the classifying plate and thereby prevents classification from taking place at this point. This has a two-fold effect, namely, a better separation of grinds may be obtained and also clogging is prevented from taking place in the aforementioned area. Also the coarse will be projected off the shoulder and subjected to classifying action in the free space and will not creep along the wall part in the classifying zone.

The vanes which are mounted on the classifying plate tend to create a high degree of turbulence, thus much of the classifying action takes place in the area between the lugs and the classifying vane. The classifying plate is generally rotated at a lower speed than the primary plate so that a pumping and an inter-Washing action near the outer radial portion of the blades is created. That is, the larger particles that come in contact with or close to the blades have a centrifugal force imparted thereto which throws them in an outward direction adjacent the classifying plate. The larger particles of course will be brought into the area of the lugs or will be directly thrown to the outer peripheral portion wherein they will enter the tailings outlet due to the large centrifugal force that is imparted to them. The cross-flow of particles resulting from the coarse and fines being drawn inwardly by air current and the coarse being impelled outwardly by the classifying vanes tends to set up a circular flow as indicated by the arrows 140. The fine particles of the desired range of sizes will not be significant-1y effected by the classifying vanes and will be drawn therethrough by the inward air wash to be passed through the discharge housing 58.

The inward air flow velocity and the centrifugal force acting outwardly adjacent the classifying end wall is much less than it is in the area between the vanes and the wall; but there is still sufficient turbulence to break the inward movement of the large particles to the discharge outlet. The air flow angular velocity at the outer periphery of the classifying plate is lower than it is adjacent the shaft but the linear velocity is the same. As a result of the aforementioned factors, by moving the classifying plate close to the end wall, a sharper cut is obtained.

Also with the vanes mounted such that their edges are adjacent to the classifying walls, they tend to break up the suspension layer and thereby operate to prevent caking or clogging. Further by mounting the vanes on the back of the classifying plate, a pumping action is obtained,

b said action operating to prevent clogging. However, sufficient distance has to be left between the classifying end wall and the classifying plate so that the previously mentioned cross flow may take place such as represented by arrow 140.

If the vanes are mounted such that their edges are too great a distance from the classifying end wall, poor classifioation is obtained since many of the particles escape through the space between the outer edges of the vanes and said wall without being subjected to proper classifying action.

If the vanes used are too large in area, poor classification is obtained. A possible reason is that the vanes tend to operate as a scoop rather than to reject the oversize. However, the vanes have to have sufficient radial length to separate the coarse from the fine.

In making adjustments on the unit to vary the product size and/or range, it is preferable not to change the position of the vanes since it is diflicult to obtain fine control. A small change in the position of the vanes will produce a large change in the product sizes obtained and thus result in poor classification.

In most cases, the finest of grinds is most conveniently changed by changing the rate of air passage through the unit and by changing the rotation speed of classifying plate. The classifier unit is equipped with the variable drive located under 46 for making the latter adjustment. By increasing the classifier speed, the larger particles will be subject to a greater centrifugal force and will be rejected by the classifier to be returned through the tailings conduit for the regrinding. Various adjustments which may be made to control product sizes are the classifier speed which is inversely proportioned to product sizes, the clearance between the beater tip and the cylinder liner, the r.p.m. of the main rotor, the number of beater plates, the amount of grinds recirculated through the tailings return, and the type of liner-corrugated, smooth, or perforated. The aforementioned factors are some of the adjustments used to control the degree of fineness of the product to obtain the most economical grinding. A more complete description of the various adjustments and their effect on particle size is set forth in US. Patent 2,939,638.

A product with particle size distribution in a narrow spectrum along with the most economical grind is usually desirable. A narrow spectrum of particle size is obtained in applicants invention by a high recirculation rate through the tailings conduit and by using the loosest setting possible in the grind, thus allowing the particles of an acceptable size to be removed as produced without excessive grinding. The factors contributing to a loose setting are low r.p.m., large clearance between heaters and liners and a small number of beater plates.

For tough resilient materials and for fine grinding high speed is used together with small beater-liner clearance. The number of these beater plates-is kept low as possible, Without getting too coarse a product, and without plugging tailings conduit by too high recirculation rate. The circulation rate may also be governed by using one or both tailings returns. Tailingsreturns may be shut olf individually by the gate valve in each of the tailings conduits. For abrasive materials it may be desirable to use a low grinding speed and maximum number of beater plates in order to reduce wear on heaters and liners.

Increasing the air flow through the pulverizing section will give a coarser grind, and conversely, a decrease in the air flow will produce a finer grind. Many times, however, air flow is determined by other factors, such as conveying velocity. Enough air must move through the mill fast enough to convey the amount of material fed and not so fast as to flush the mill without adequate grinding. Another factor in determining the air flow used in the unit is the amount of air flow required for cooling purposes. However, with the use of applicants new and improved water jacket provided for circulation of a cooling fluid around an outer peripheral portion of the cy1init der liner, the need for air flow cooling is minimized and at the same time permitting higher grindingspeeds.

As many apparently widely diiferent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments herein.

What is claimed is:

1. A combined pulverizer and classifier comprising a pulverizing section including a pulverizing casing provided with an inlet at one end for introduction of material into the casing and being substantially open at its other end, a first shaft journalled for rotation in said casing, pulverizing means mounted on said first shaft for causing size reduction of material introduced into the pulverizing casing, drive means for rotating said first shaft; and a classifying section including a classifying casing provided with an outlet opening at one end and being substantially open at its other end for cooperation with the open end of said pulverizing casing, and a second shaft journalled for rotation in said classifying section, second drive means for rotating said second shaft, a classifying plate mounted on a second shaft, and means mounted on said classifying plate for classifying the material passing through the classifying section, said classifying casing including an end wall having an annular shoulder extending inwardly into the interior of the easing, said shoulder being located adjacent the peripheral edge of the classifying plate, the outlet opening being formed in the end wall and being of a diameter substan tially less than the minimum diameter of the annular shoulder formed on said end wall.

2. A combined pulverizer and classifier comprising a pulverizer section having a pulverizer casing with an inlet formed in one end and an open ended outlet, and pulverizer means rotatably mounted in said pulverizer casing for causing size reduction of material introduced into the pulverizer casing, and a classifying section comprising a classifier casing having an open inlet end of the same size and shape as the outlet end of the pulverizer section so that material pulverized in the pulverizer casing can pass directly into the classifying section, and an end wall on the opposite side of the classifier casing from the inlet, said end wall having a central outlet aperture of a size substantially smaller than the classifier casing inlet, a shaft rotatably mounted in said classifier casing portion concentric with the outlet aperture, said shaft having an axis of rotation that extends through said aperture, a classifying plate mounted on said shaft, said classifying plate being of substantially larger size than the size of said aperture, and a plurality of spaced elongated axially extending classifying lugs mounted on the peripheral portion of the classifying plate, said classifying casing end wall having an annular shoulder formed on the outer peripheral portion thereof, said shoulder extending into the casing, the inner diameter of the shoulder being substantially greater than the diameter of said outlet.

3. The apparatus of claim 2 further characterized in that a plurality of spaced vanes are mounted onthe classifying plate, said vanes mounted to extend in a generally radial direction relative to the shaft and located a suflicient distance outwardly from the shaft to rotate in the general area intermediate the shoulder and the outlet.

4. A combined pulverizer and classifier comprising a pulverizer section having a pulverizer casing with an inlet formed at one end and an open ended outlet, and pulverizing means rotatably mounted in said pulverizing casing for causing size reduction of material introduced into the pulverizer casing; and a classifying section comprising a classifying casing having an open inlet end for cooperation with the pulverizer outlet so that the material pulverized in the pulverizer casing can pass directly into the classifying section and an end wall on the opposite side of the classifier casing from the inlet, said end wall having a central outlet formed therein, a shaft rotatably mounted in said classifier casing, means for driving said shaft independent of the rotation of the pulverizing means said shaft having an axis of rotation that extends through said central outlet, a classifying plate mounted on said shaft, said classifying plate being of a substantially larger size than the size of said central outlet, a plurality of spaced elongated axially extending lugs mounted on the peripheral portion of the classifying plate to extend axially outwardly of either side of said plate, said lugs being triangular shaped in cross section and mounted on the plate to have the apices thereof pointed outwardly of the plate, and elongated classifying vanes mounted on the classifying plate intermediate said shaft and the outer peripheral portion of said classifying plate for classifying the pulverized material, each of said elongated vanes mounted on the plate to extend substantially radially relative to the said shaft and axially closely adjacent to said end wall, each of said elongated vanes being mounted on the classifying plate a greater radial distance from said axis of rotation than any portion of the end wall forming said central outlet and a lesser radial distance than said lugs, said end wall having an annular zone radially beyond the vanes that is substantially planar.

5. A combined pulverizer and classifier unit comprising a pulverizer casing with an inlet formed in one end and an open ended outlet at the other end, and pulverizer means rotatably mounted in said pulverizing casing for causing size reduction of material introduced in the pulverizer casing; and a classifying section comprising a classifier casing having an open inlet end for cooperation with the pulverizer outlet so that the material pulverized in the pulverizer casing can pass directly into the classifying section; and an end wall in the opposite side of the classifying casing from the inlet, said end wall having a central outlet aperture formed therein, a shaft rotatably mounted in said classifier casing, means for driving said shaft, independently of the pulverizing means, a classifier plate mounted on said shaft, and classifying vanes mounted on the classifier plate to extend generally radially relative to the shaft and axially toward said end wall, the outer axial edges of said vanes being located inwardly of the peripheral edge of the plate a distance substantially A of the outer radial dimension of the plate and inner axial edges located outwardly of the axis of rotation of the shaft a distance substantially /2 of the outer radial dimension of the plate, said classifier casing having a tailings outlet port located closely adjacent the peripheral edge of the classifying plate, a tailings conduit connected to said port for returning the tailings from the classifier section to the pulverizer section, and control valve means mounted in the tailings conduit near the inlet of the tailings conduit for controlling the flow of tailings through the tailings conduit.

6. A combined pulverizer and classifier comprising a pulverizer section having a pulverizer casing with an inlet formed at one end, an open ended outlet, pulverizer means rotatably mounted in said pulverizer casing for causing size reduction of material introduced into the pulverizer casing; and a classifier section comprising a classifier casing having an open inlet end for cooperation with the outlet of the pulverizer casing to permit material pulverized in the pulverizer casing to pass directly into the classifier section and an end wall on the opposite side of the classifier casing from the inlet, said end wall having a central outlet aperture, a shaft rotatably mounted in said classifier casing portion, means for driving said shaft independent of the rotation of the pulverizer means, said shaft having an axis of rotation that extends through said aperture, an imperforate classifying plate mounted on said shaft, said classifying plate being of a substantially larger size than the size of said apertures, a plurality of spaced elongated lugs mounted on the classifying plate close to the inner periphery of the pulverized casing and a plurality of spaced elongated classifying vanes mounted on the classifying plate, said vanes extending radially relative to the shaft and axially outwardly from the classifying plate toward the end wall, said vanes being located between only /2 and of the distance from the axis of rotation of the shaft to the peripheral edge of the plate.

7. In a combined pulverizer and classifier, a generally cylindrical casing having an inlet formed at one end and an end wall at the opposite end from the inlet, said end wall having a central outlet aperture, pulverizing means mounted rotatably in the inlet end of the casing for causing size reduction of material, first means for driving said pulverizing means, a shaft rotatably mounted in the outlet end of the casing having an axis of rotation and extending through said outlet aperture, second means for driving said shaft independent of the rotation of the pulverizing means, an imperforate classifying plate of a substantially larger size than said aperture mounted on said shaft in proximity to the end Wall, and a plurality of elongated radially extending classifying vanes mounted on the side of the plate adjacent the end wall and extending axially within closer proximity to the end wall for classifying the pulverized material as it moves radially inwardly to the outlet aperture, said vanes having outer axial edges located a distance radially inwardly of the peripheral edge of the plate about A of the outer radial dimension of said plate and inner axial edges located a distance radially outwardly of the axis of rotation of said shaft about /2 of the outer radial dimension of the plate, the interior of the end wall being substantially planar through an annular zone from said aperture to a location a substantial distance radially outwardly of the outer axial edges of said vanes.

References Cited in the file of this patent UNITED STATES PATENTS 529,874 Parker Nov. 27, 1894 745,075 Schutz Nov. 24, 1903 938,923 Walker Nov. 2, 1909 1,260,406 Lachmann Mar. 26, 1918 1,628,295 Wickland May 10, 1927 1,840,380 Andrews Jan. 12, 1932 1,855,171 Holbeck Apr. 19, 1932 1,971,314 Lauenstein Aug. 21, 1934 2,042,042 Frisch May 26, 1936 2,939,638 Haigh et al. June 7, 1960

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