US3544014A - Impact mill - Google Patents

Description

United States Patent 7/1958 Adams 2,917,248 12/1959 Krug.......... 2,981,490 4/1961 0 241/275 24l/299X 241/275 241/275 241/55 241/275X 241/275 onley......... 3,023,973 3/1962 Conley...... 3,149,790 9/1964 Hoffstrom. 3,171,604 3/1965 Conley...... 3,258,211 6/1966 Behnke.......

Primary Examiner-Robert C. Riordon Assistant Exam iner- [72] lnventor Johannes F. E. Kampe Torrance, California [21] Appl. No. 693,561

[22] Filed Dec. 26, 1967 [45] Patented Dec. 1, 1970 [73] Assignee McDonnell Douglas Corporation a corporation of Maryland Donald G. Kelly [54] IMPACT MILL Attorney strauch, Nolan, Neale, Nies & Kurz 4 Claims, 4 Drawing Figs.

1,857,539 5/1932 l-ladsel....................,..... 241/275 away from the rotor periphery.

Patentgd Dec. 1, 1970 INVENTOR Johannes FE Kampe Om m w x om Nm y m/ m o9 w. ow van. 8 9

QNNMVN NM- Patented Dec. 1, 1970 Shoot INVENTOR Johannes FE Kampe ATTORNI IMPACT MILL BACKGROUND or THE INVENTION This invention relates generally to material grinding and comminuting apparatus, and more particularly to a comminuting device of the impact type.

In the past machines of various types including ball mills, hammer mills, impact mills, and jet mills have been used to effect comminution of particles. Each of these'types has its advantages and associated disadvantages. Most of these prior art devices have been very inefficient in that they are generally designed to impart turbulence and more than one impact or breaking force to a particle, thus wasting available energy. Additionally, the hammer, impact, and jet mills normally pump an excessive amount of fluid, thus requiring a high input ener-' The efficiency of apparatus of this type is generally determined by relating the required input energy to the degree of reduction in particle size as measured by the amount of new specific surface created,ge'nerally expressed in cm per gram. Thus, to obtain maximum efficiency, it is desirable to direct all input energy toward creating new specific surface. and to minimize energy losses due to turbulence, friction, and excessive air flow.

One prior proposal to accomplish this is disclosed in U.S. Pat. No. 3,149,790. While thisdevice performed substantially better than other known apparatus, nevertheless, it was subject to wear particularly along the trailing walls of the rotor channels through which the material passed for delivery to the impact area, thus requiring premature and frequent replacement of the wall liners. Additionally, the surface area wear on the impact targets was unduly concentrated. Also wear occurred at the periphery of the rotor because of splashback of the particles and impingement on the rotor after they struck the target impact surfaces.

SUMMARY OF THE INVENTION It is a primary object of this invention to provide a novel comminuting apparatus having an extended service life over whichfull efficiency of operation is maintained.

It is another object of this invention to provide a novel comminuting apparatus in which wear is substantially reduced and generally confined to readily-replaceable parts.

It is another object of this invention to provide a novel impact mill having impact targets so arranged with respect to a particle accelerating rotor to prevent impingement of the crushed particles on the rotor periphery, thus reducing rotor wear.

It is another object of this invention to provide a novel impact mill having a rotor with radial channels lined with wear surfaces, the surfaces being so shaped to spread the material uniformly thereover and thus prevent concentrated wear on the surfaces and the impact targets on which the material imp- Inges.

In summary, this invention accomplishes the above objects and overcomes the disadvantages of the prior art devices by providing an impact mill having a rotor with radially extending channels therein which connects a center annular chamber, to which material is fed, with an impact chamber containing an impact target device. The walls of the channels are lined with replaceable U-shaped wear strips which have a flat-bottomed wearing surface across which the particles are uniformly distributed during rotation of the rotor. The flat-bottomed surface prevents concentrated wear of the strips and also promotes uniform wear across the impact surfaces of the target device. The impact target device comprises a plurality of individual targets carried by upper and lower rings and spaced from each other to providea passage between adjacent targets for escape of the crushed material from the targetimpact surface. The impact face of each target is so positioned with respect to the trajectory of the material leaving the rotor channels, as to cause the material to flow radially outwardly away from the rotor periphery after it strikes the target surface without loss of impact efficiency. Also, pressurized air is introduced above and below the rotor and directed radially outwardly into the impact chamber to prevent crushed material from entering the rotor and bearing areas.

Additional objects and advantages will become apparent as the description proceeds in connection with the accompanying drawings.

THE DRAWINGS FIG. 1 is a front'elevation .view of the comminuting apparatus, partially in section, along line 1-1 of FIG. 2;

FIG. 2 is a top fragmentary view of the apparatus of FIG. 1 partially in'section, showing the spaced arrangement of the impact targets and the radiallyextending channels connecting the material inlet funnel and rotor center to the target chamber; p

FIG. 3 is an enlarged sectional view of the radial .channel and its wear liner taken along line 3-3 of FIG. 2; and

FIG. 4 is an enlarged fragmentary view of the impact or target area.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularly to the drawings, the apparatus of the present invention includes a stand or base 10 supporting a rotor housing 12 and a motor housing 14 in sideby-side relation. The stand is provided with adjustable legs 16 to provide accurate leveling of the assembly.

At its upper end the housing 12 is closed by a cover plate 18 held in place against an annular shoulder 20 on the housing wall by a snap ring 21. The top wall 18 carriesa central conical material inlet funnel 22 carrying an extension 24 leading into a rotor chamber 26 formed between the top wall 18 and a horizontal wall 28, preferably formed integrally with the housing 12.

The wall 28 carries a downwardly projecting hub 30 formed centrally of the housing which supports upper and lower bearings 32 and 34 separated by a spacer collar 36. The bearings rotatably support a rotor shaft 38, the upper end of which carries rotor-assembly 40 inthe rotor chamber-26 and the lower end of which carries a pulley 42. The motor pulley 44 is drivingly connected to the rotor pulley 42 by a belt 46 which passes over an 'idlerpulley 48 suitably supported on the outer end of an arm 50 projecting from a collar 52 held in placeon the hub 30 by a snap ring 54.

The rotor assembly 40 includes upper and lower plate members 56 and 58, respectively, preferably secured together by screws 60 extending through a discontinuous peripheral flange 62. To impart additional structural rigidity to the assembly the upper rotor plate 56 is provided with a discontinuous inner ring 64, the bottom edge of which engages a replaceable wear plate 66 positioned in an annular recess in the lower plate member 58. The rotor assembly also includes an annular plate 68 interposed between a shoulder 70 on the upper portion of the rotor shaft 38 and the lower rotor plate 58 to protect the bearing assemblies 32 and 34 from dust and other foreign matter, the plate 68 acting as a slinger ring when the unit is in operation.

The rotor assembly 40 and the plate 68 are tightly clamped against the shoulder 70 by a nut 72 threaded into the upper end of the shaft 38, the nut having a conical surface adapted to force a split ring 74 tightly into a recess 76 formed in the rotor plate 58. The upper surface of the nut 72 is suitably formed to facilitate the flow of material from the inlet funnel 22 into the rotor as more fully explained below.

To maintain the upper and lower surfaces of the rotor assembly 40 and the spaces between the rotor assembly and the adjacent stationary parts free from particles these areas are continuously swept by a flow of pressurized air. For this purpose air is supplied -at a pressure of from 40 to 120 psi. through an inlet opening 78 in the funnel 22 and flows through a passage 80 and thence through a series of small orifices 82 in a wear plate 84 carried by the top cover 18 and flows into the space between the plate 84 and the adjacent surface of the upper rotor plate 56.'Similarly, pressurizedair is supplied through an opening 86 in the housing wall 28 and flows through an annular passage 88 in an annular block 90 secured by screws 92 to the upper surface of the housing wall 28.

Air passes from the annular channel 88 through a plurality of ports 93 into the clearance space between the top of the block 90 and the lower surface of the rotor assembly 40 for passage into the chamber 26. Cleanout ports 94 extend through the housing wall 28 for the removal of dirt and dust from the rotor area. Positioned within the chamber 26 is an annular impact or target assembly 96 held against locating surfaces on a support plate 98 clamped between the target assembly 96 and the top. cover 18 by a series of screws 100.

As shown in FIGS. 1 and 2 target assembly 96 comprises individual impact targets or blocks 114 with target surfaces 115, the targets being brazed to upper and lower support rings 116 and 118, respectively, and spaced from each other to provide passages 117 in the device for escape of material radially outwardly away from the'rotor after striking the targets 114. The provision of lower support ring 118 in addition to upper ring 116 adds stability to the target assembly and prevents cracking of the targets 114.

Tangential outlet 119 is provided to exhaust the comminuted material from chamber 106.

Formed within the top plate 56 of rotor assembly 40 are radially extending channels 120 which are open at their outer ends to communicate with impact chamber 26 and at their inner ends to communicate with an annular inlet throat 122 at the center of the rotor immediately below funnel 22. The channels are formed symmetrically about a radius of the rotor and progressively decrease in cross section from the center to the periphery of the rotor to accelerate the air and particles travelling therethrough. At least three channels 120 are provided and, in the preferred embodiment, four such channels are utilized. The walls of channel 120 are formed by ribs 123 which project downwardly from the rotor plate 56. The trail- I ing edges of the channels are lined with replaceable wear plates 124 clamped in place vertically by a force fit between rotor plates 56 and 58 and radially by a protrusion 126 on "As shown in FIG. 3, the wear strips 124 are U-shaped to provide a flat-bottomed wear surface 130 between flanges 132 and 134, which abut against rotor members 56 and 58,respectively. The flat-bottom shape provides for-more uniform wear and longer life of the strips, since the material is distributed over the full width of the strips as it passes through the channel 120; i

It is apparent that the machine may be readily disassembled by removing ring 21 and lifting cover 18 upwardly. This results in the simultaneous removal of funnel 22, sleeve 24, ring 84, and target assembly 96, all of which are attached to cover 18. The rotor and bearing elements are then accessible for repair or replacement. v

Referring to FIG. 4, the angular relationship between the targets 114 and rotor channels 120 has been found to be operationally significant. The trajectory angle A at which the particles leave the channels120 depends upon several factors, including the distance from the center at which the particle acceleration begins and the friction forces between the particles and strips 124. Theoretically, if the particles start at the exact center and there areno friction forces, the trajectory angle would be 45, since the tangential velocity component v would be equal to the radial velocity component u. Another factor modifying the angle A is that the channel walls 123 are not exactly radial but extend along lines which pass a certain distance from the center of the rotor.

The effect of these factors is to modify the trajectory angle A to produce in practice an angle of approximately as discussed in the Hoffstrom patent.

It can be established theoretically that every particle entering the rotor is given the same velocity and leaves the rotor at the same angle A, thus containing the same specific energy.

each wear plate which engages a circular recess 128 in ribs 1 This invention uses the kinetic energy of the particles to produce the comminuting effect by directing the particles against stationary targets 114 which are constructed of any hard material, preferably tungsten carbide. Theoretically, the greatest force of impact and most efficient conversion of the kinetic energy occurs when the particles strike target impact surface 115 at an angle B of It has been discovered, however, that improved performance is obtained when the targets 1 14 are arranged to provide an angle B of approximately 1 20, preferably 1 15 or 25 away from the perpendicular of the particle trajectory. The grinding efficiency of the device is not substantially reduced because the friction angle of the material to be ground when moved over the target surface is larger than 25.

This arrangement of targets 114 causes the crushed fragments of material to flow away from the rotor radially outwardly through passages 117, thus preventing wear on the rotor periphery.

In operation, the rotor 52 is rotated to create a rotor rim velocity within the range of 5,000-l0,000 in./sec., it being apparent that the higher speed of rotation produces particles of smaller size. The material to be ground is fed through funnel 22 to rotor annular chamber 122 and outwardly through channels 120. The flat surface 130 of channel liner 124 causes the material to be spread uniformly over the entire width of the surface and to impinge evenly across the entire target surface 115 to avoid localized wear on these parts.

The rotation of the rotor also draws air along with the material through .funnel 22, which air serves as a carrying medium for the material. Additionally, air is introduced at a pressure of 40- l 20-p.s.i.into the area below the rotor by port 86 and passageways 88 and 92 and above the rotor by port 78 and passageways 82. Substantially all of this pressurized air passes radially away from the rotor axis and into chamber 26, thus preventing any ground material from collecting within the rotor and bearing areas.

As the material strikes target surface 115, it is reduced in size and directed radially outwardly through passages 117 because of the angular relationship noted above between targets -114 and the material trajectory angle A. The ground material and the pressurized air is then exhausted from chamber 106 through tangential outlet 119.

The number of channels provided in the rotor is a variable depending upon the desired capacity of the apparatus. The material entering annular chamber 122 must immediately find an-exit channel therefrom to prevent clogging of the rotor. Also, the size of the channels must be sufficient'to pass the largest particle to be ground However, as Hoffstrom notes, the number of channels .should be kept to the required minimum to reduce the air flow through the system, since the more air that flows, the greater will be the input energy required to move the air. Although the moving air performs a material carrying function, most of it represents lost energy, and thus should be minimized.

It is understood then that the present invention accomplishes the desired high efficiency and in addition provides a more stable and longer lasting impact mill. The novel design of liner strips 124 results in uniform distribution of wear across surface and increases the area of impingement of the particles on target surface 115, thus preventing any concentrated gouging or wearing of these elements which would require premature, early discard and replacement thereof. Also, the specific structure of the target assembly 96 maintains the high degree of efficiency desired, while preventing wear on the periphery of the rotor by directing the comminuted particles outwardly through passages 117.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefor, the present embodiment is to be considered illustrative and not restrictive, the scope of the invention being I claim:

1. Apparatus for reducing the size of particles comprising a housing, a rotor mounted in said housing, said rotor having a plurality of channels connecting a center inlet section with the periphery thereof, said inlet section being open to the exterior of said housing to permit the inflow of air and particles thereto, means for rotating said rotor whereby particles delivered to said inlet will be moved in an airstream through nicating with the region adjacent said target means, said airstream delivering broken particles to said outlet means.

2. Apparatus according to claim 1, wherein the impact surfaces of said targets extend at an angle of substantially more than with respect to the path of particles issuing from said 7 channels.

3. Apparatus according to claim 1, wherein the impact surfaces of said targets extend at an angle of from to with respect to the path of particles issuing from said channels.

4. Apparatus according to claim 1 together with means for introducing pressurized air above and below said rotor and for directing said air radially outward to the region adjacent said target means, at least the flow of air below said rotor being guided along said rotor closely adjacent the surface thereof in the region of the outer periphery of said rotor, said flow of air preventing the passage of broken particles radially inwardly towards said rotor center.

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