US3184172A

US3184172A - Impact milling apparatus

Info

Publication number: US3184172A
Application number: US98188A
Authority: US
Inventors: Fitz Coleman Dudley
Original assignee: General Mills Inc
Current assignee: General Mills Inc
Priority date: 1961-03-24
Filing date: 1961-03-24
Publication date: 1965-05-18
Anticipated expiration: 1982-05-18

Description

C. D. FITZ IMPACT MILLING APPARATUS May 18, 1965 2 Sheets-Sheet 1 Filed March 24. 1961 IN VEN TOR.

ATTORNEY May 18, 1965 c. D. FITZ IMPACT MILLING APPARATUS Filed March 24' 1961 2 Sheets-Sheet 2 INVENTOR. COLEMAN DUDLEY F ITZ ATTORNEY United States Patent 3,184,172 Ill/{PACT MILLING APPARATUS (Ioleman Dudley Fitz, North Caldwell, NJL, assignor to General Mills, inc, a corporation of Delaware Filed Mar. 24, 1961, Ser. No. 98,188 6 Claims. (Cl. 241-194) The present invention relates generally to pulverizing apparatus and more specifically to improved impact members or hammers for impact mills.

It is known that impact milling requires rapid relative movement between an impact member or hammer and air or another gaseous or fluid medium containing particles of the material to be ground. The resulting impacts between the particles and the impact member are intended to reduce or pulverize the particles by fragmentation.

In known devices of this type the fluid media, upon sensing the relative approach of the usual round pin or fiat-faced impact hammer, move transversely out around the hammer. The heavier, solid particles were previously thought to remain in their original positions or trajectories for impact engagement with the hammer. In reality, however, I have observed that the sidewards motion of the fluid medium exerts a lateral drag upon the particles which tends to deflect the particles from their original trajectories relative to the hammer. This deflecting force was found to be sufiicient to pull some of the smaller particles completely out of the path of relative movement of the hammer. This action appears to establish a minimum particle size which is still capable of impinging upon a given hammer. Particles having sizes below this minimum are not struck and consequently not reduced in size.

The lateral drag of the fluid as it moves around the impact member is also found to deflect some of the larger particles in a manner which decreases the eliectiveness of their impact, even though such particles do still strike the impact member. For example, the impact may be at a more acute angle rather than perpendicular to the impact surface, or it may be at a lower velocity. Thus optimum particle reduction may not occur.

While devices are known for continually tossing particles back into the path of the impact surfaces, there eventually exists a static condition wherein the action of the apparatus no longer overcomes the effect of the aerodynamic drag and except for other possible factors, such as fluid turbulence, the particles are no longer capable of further reduction by further relative movement against the impact surface of the hammer.

With the above problems and findings in view, it is therefore one object of the present invention to provide an impact mill having improved impact members with surface portions oriented to increase the effectiveness of the mill.

Another object is an impact mill hammer design which gives the forces acting upon a particulate material under laminar conditions a greater opportunity of driving the particles against its impact surface.

A further object of the invention is to provide impact hammers for an impact mill, the design of which minimizes the tendency of the surrounding fluid medium to detect the impact surfaces and move particles out of the impact path in advance of particle impingement.

Another object of the invention is to provide improved impact hammers for an impact mill in which the surfaces of said hammers are designed in such a manner as to allow a particulate material to impinge thereon at an angle which is most conducive to fracture.

A further object of the invention is to provide an improved impact mill, the capacity of which is increased through the design of impact hammers which rapidly reduce a particulate material to its minimum particle size.

ice

Other objects and advantages will become apparent in the following specification and the appended drawings in which:

FIGURE 1 is a front elevational view in partial section of an impact mill illustrating one manner in which improved impact members according to the present invention are employed;

FIGURE 2 is a side elevational view taken generally along line 22 of FIGURE 1;

FIGURE 3 is an enlarged isometric view of a preferred form of impact member, as embodied in the device of FIGS. 1 and 2;

FIGURES 4 is a diagrammatic view illustrating the fluid flow and particle impingement with respect to the device of FIGURE 3;

FIGURE 5 is an isometric view of another preferred form of impact hammer according to the invention;

FIGURE 6 is a diagrammatic view illustrating fluid flow and particle impingement with respect to hammer of FIGURE 5;

FIGURE 7 is an isometric view of a modified form of impact member according to another embodiment of the invention; and

FIGURE 8 is a diagrammatic view similar to the diagrammatic view of FIGURES 4 and 6 showing the resultant air flow and particle impingement with respect to the device of FIGURE 7.

Before a detailed description of the invention is given, an explanation will be presented relative to the general construction and operation of one type of impact mill in which features of the present invention may be used. It will be understood that the improved impact members or hammers of the instant invention are not limited to employment in the particular impact mill herein disclosed and that this mill has been chosen merely as representative of the art in order to illustrate the principal features of the invention.

The impact hammer mill it) as shown in FIGURE 1 includes a supporting frame 12 on which are positioned somewhat cylindrically shaped housing members or castings 14, i6 and 18 which are secured by bolts 20 to the frame 12. A horizontal shaft or rotor 24 extends centrally through suitable openings in the sides of the castings 14, lo and i8 and is journaled in bearings 22 on the frame 12.

the the The castings thus surround the shaft 24 and form annular chambers 26, 28 and Eli which are concentric with shaft 24. The chamber 28 which will be hereinafter referred to as the impact or grinding chamber is located between the castings l4 and 18 within casting 16, while

chambers

26 and 36 hereinafter referred to as discharge chambers are positioned on opposite sides of the grinding chamber 28 in castings l4 and 13 respectively.

The casting 16 is also provided with an integral inlet or opening 32 for admitting material to the impact chamber 28. Similar openings 34 and 36 are provided in the castings l4 and 18 through which material is discharged as explained later in this specification.

Positioned on the shaft 24 within the impact chamber 28 is a rotor unit which includes a pair of separator wheels 38 and 4%) provided with a plurality of radial deflector blades :-2. The deflector blades 4-2 are circumferentially spaced apart on the side surfaces of the separator wheels 38 and 45% generally near the periphery thereof and extend radially outward in planes passing through the axis of the shaft 24. The deflector blades 42 are secured to the separator wheels by screws 44 and together with the separator wheels 38 and 4% form what will later be described as a classifier 56.

Also positioned on the shaft 22 on opposite sides of the separator wheels 33 and within the discharge chambers 26 and 3d are fans 48 and St The fans 43 and 51) have integral hub portions 4) and 51 which, when the fans are positioned on the shaft 24, abut against hubs 39 and 41 of the

separator wheels

38 and 40. As noted in the drawings, shaft 24 is provided generally near the fans 48 and 50 opposite the abutment of said hubs with threaded surfaces 52 (only one is shown). When the separator wheels 38 and 4t) and the fans 48 and 56 are positioned on the shaft 24,.a pair of lock washers 54 and 56 are placed on the ends of the shaft 24 and a pair of lack nuts 57 are secured to the threaded ends of the shaft 14.

to retain the assembly together under compression.

The separator wheels 38 and 49 are provided with an annular opening 58 therebetween which extend; around their outer peripheral edge and in which are positioned a plurality of impact members or hammers 60. The impact members or hammers 60 are equally spaced apart around the circumference of the separator wheels 38 and 4t and are pivotally mounted between the separator plates by cross pins62 which extend into openings 35 and 37 in

plates

38 and 40 respectively. The features of construction of these impact members 60 are described in detail later in this specification.

With reference to the

castings

14, 16 and 18, there are circular openings and 17 along the innerside surfaces of the

respective castings

14 and 18. These openings are positioned adjacent or concentrically within openings 19 and 21 of the casting 16. The openings 15 and 17 are somewhat smaller than the openings 19 and 21 and the portion of the casting which surrounds said openings provides annular orifices 66 and 68 between the two castings. When the millltl is in operation air is drawn in through the orifices 66 and 68 from the outside atmosphere by the fans 48 and 59 and enters the impact chamber 28 being directed inwardly toward the classifier 46 by a plurality of angularly disposed blades 70' spaced circumferentially apart along the side surfaces of the casting 16.

For operation of the impact mill 10, the rotor 24 is connected to and driven by a high speed motor (not shown) and asthe shaft 24 revolves, it carries therewith the

separator wheels

38 and 40 and the fans 48 and 50. As the shaft 24 rotates the impact hammers 60 are thrown radially outward and their impact surfaces traverse a circular path within the grinding chamber 28. Material to be pulverized is admitted through the inlet opening 32 and enters the path of the

impact surfaces

61, 63 and 65 of the impact hammers 60.

Clearance is provided between the outersurfaces of the hammers 60 and the inside of the impact chamber 28 which serves as an area for the free circulation and passage of the material admitted to the chamber. The centrifugal force created by the movement of the impact hammers causes the material to remain substantially in suspension in the air or other fluid medium in the path of the

impact surfaces

61, 63 and 65 and the particles impinge 'thereon by virtue of the relative movement between the impact members 60 and the air and particles. As their size and gravitational weight become smaller as a result is provided which includes a plurality of associated impact surface portions having different relative angular orientations with respect to the path of relative movement between the impactmember and the fluid medium within the housing. The angular orientation of at least one of the surface portions is adapted to resist lateral deflection The latter particles are subsequently withdrawn The preferred impact hammers 6%) of the instant invention, as shown in FIGS. l-4, are provided with a pair of deflectors or inclined

impact surface portions

61 and 63 which are spaced apart to define an air passage between them. The hammers 60 move in a counterclockwise direction, as viewed in FIG. 2, along a circular path determined by the rotational movement of the shaft 24, as indicated by the arrow 64. The preferred impact members 60 also include a third impact surface 65, located rear- Wardly of the

inclined surfaces

61 and 63, against which some of the particles are channeled at increased velocities when the hammer member is moved along its path Within the impact chamber. It is against these impact surfaces 61, 63 and 65 that the particles impinge and are reduced by fragmentation.

FIGURE 3 illustrates further details of the combination of the impact hammer 60 of FIGURES 1 and 2.

I through the opening 69, when the hammer is employed in The impact hammer 69 includes a shank 67 and a plurality of impact bars161, 163 and 165 which are provided with the angularly oriented

impact surface portions

61, 63 and 65. The supporting shank 67 is also provided on its inner end with a cross pin 62 for attaching the hammer to a suitable moving or rotating device, as already described with reference to the mill 10 of FIGURE 1. The impact bars 161, 163 and 165 having

surfaces

61, 63 and 65 are located normal to and extend transversely and symmetrically on each side of the central or radial axis of the shank 67. Each is spaced apart from the other to provide in effect, a tortuous path for the passage of the particle-containing fluid medium. The impact surfaces or

vanes

61 and 63 are radially spaced apart on the shank 67 and are inclined inwardly at an angle tending to deflect fluid and particles toward each other, and thus toward the passage 69 between them. Thus surfaces 61 and 63 provide a substantially concave impact zone adjacent the opening 69 therebetween.

The fluid medium and the particles which thus pass an impact device, then encounter the impact surface 65, which is the front surface of another cross bar 165 secured to the shank 67 by set screws 70. This cross bar 165 is located in a positioning slot 72 rearward of the opening 69. The impact bars 161 and 163 having

surfaces

61 and 63 may be integral with'the shank as shown or attached thereto by other suitable means. Thus particles encountering the hammer member 66 are forced to take a tortuous path around impact surfaces 61, 63 and 65 of the impact member.

The resultant air flow and subsequent particle impingement against the hammer can be readily understood by viewing FIGURE 4. The fluid medium indicated generally by the solid lines of numeral 76 passes primarily through the. opening 69 and only a small portion is deflected outwardly around and out of the path of the impact member. Most of the particles 78 thus move inwardly toward the opening 69 and against one or more of the

impact surface portions

61, 63 and 65. In so doing of the particles out of the path of the impactmembenand preferably to deflect the fluid and particles into the path of an impact surface portion.

61 and 63 while others near the center of the fluid flow are carried forward into the path of the impact surface. Since the fluid medium is in effect funneled through the impact zone, the construction provides increased relative velocity which accelerates the particles toward impact surface and enables the inertia of the particles to have a greater influence. Thus impingement efiiciency, impactionangle and impaction velocity are'all substantially maximized to produce rapid and eflicient reduction of particle size. 7 a

In certain applications or situations other embodiments Y are also useful such as the one shown in FIGURE 5.

Another embodiment of animpact harrnner according to the invention is indicated generally by the numeral 80 of FIGURE 5. This modification is somewhat like the previous embodiment, but without the rearward impact surface 55 thereof. The impact hammer 8i accordingly is provided with a similar supporting shank 82 and a like cross pin 84. The lower end of the shank. 82 and the cross pin 84 are identical to the previous embodiment and are therefore interchangeable in the impact mill 1%.

The impact hammer Si) is provided opposite the pin 84 with a first and a second impact bar or

vane

186 and 188 having inclined impact surfaces 86 and S8. The impact bars 186 and 183 are radially spaced apart as in the previous embodiment and their inclined surfaces 85 and 88 face inwardly to deflect particles and fluid somewhat toward a central opening 90 thereoetween, which is created by their spaced relation. The combined impact surfaces 86 and 88 thus form a recessed impact surface or zone, which minimizes the tendency of fluid to escape outwardly around the impact member and drag particles laterally out of the path of the hammer. Here the fluid flow remains chiefly within the path of movement of impact member 80 so that particles will be struck by surfaces 86 and 83. Moreover, the increased relative velocity of the fluid passing through the narrow opening or slot 90 as in the previous embodiment further accelerates the rate of relative movemnt of the particles 92 without tending so strongly to drag them out of the path of the hammers. Thus greater impact velocities may be achieved.

FIGURE 6 is a diagrammatic View illustrating this fluid flow and particle impingement on the hammer 80 of the embodiment of FIGURE 5. The fluid or air stream is indicated generally by the numeral '76 and is deflected somewhat inwardly and through the opening 90 at higher relative velocity. The particles 7 S are therefore projected from the fluid stream at greater impact speeds and a large share of them impinge upon the impact surfaces 86 and 88. Those particles which pass through the opening 9%, with or without striking either of

surfaces

86 or 88 of one hammer member, will have further opportunities for impact against the similar surfaces of successive hammers.

Another modification of the invention is seen in FIG- URE 7 wherein improved particle impingement is ob tained by the use of a single hammer head or member having a concave impact surface. The inner and outer impact surface portions which are angularly oriented to deflect material toward each other are thus parts of a single total impact surface. This impact hammer indicated generally by the numeral 98 includes a supporting shank 1%, an integral hammer head 162, and a support pin E4. The impact hammer head 162 is positioned normal to the shank parallel to the pin 1% and extends transversely and symmetrically with respect to the central or radial axis of the shank as shown. The impact hammer head 1G2 is substantially elongated, is somewhat narrow in cross section and is provided with a recessed or concave impact surface 1%, that is coextensive with its transverse length.

The diagrammatic view in FIGURE 8 illustrates the air flow and resultant particle impingement upon the concave impact surface 166. The air flow is indicated by the numeral 76. While the fluid medium in this case must necessarily flow around the impact hammer head 1532 rather than through a passage at its center, the relative angular orientation of the concave leading edges minimizes the distance at which the fluid starts such lateral movement ahead of the impact surface. The particles of material, indicated generally by the numeral 78, are thus subjected to lateral aerodynamic drag for as little time as possible.

Moreover, any particles which are drawn outwardly toward the edges of the concave impact surface 1% by such drag, tend to impinge upon the impact surface more nearly perpendicularly to such surface, in View of the angular orientation thereof. Also, in view of the minimum time during which particles are drawn outwardly by the air stream, many of the particles have suflicient momentum to continue toward the center of the impact surface 106 and impinge thereon. Thus the concave impact surface 106 also offers advantages in more efiicient and effective impact reduction.

The impact members or hammers shown and described in the foregoing examples have a plurality of angularly oriented impact surface portions, at least one of which is oriented to deflect fluid medium and entrained particles toward at least one other such surface portion. These hammers or impact members are constructed in such a manner that the forces acting upon the particles will have the greatest opportunity to drive them against the hammers. These constructions minimize those adverse effects of lateral aerodynamic drag which might tend to pull the particles laterally out of the paths of the impact members. Thus the inertial forces which tend to project the particles in their original path or direction against the impact members are used to better advantage.

In summary, the features described make it possible to provide such advantages as increased impingement efiiciency (i.e. a higher percentage of the particles originally in the path of the impact member will actually be struck by that member), more effective angles of impact, and higher impact velocities. In the foregoing specification a disclosure of the principles of the invention has been presented together with some of the embodiments by which the invention can be carried out.

Now, therefore, I claim:

1. In an impact mill having an impact chamber with inlet and outlet means for admitting and discharging material to be pulverized, and a rotor means mounted within said chamber for rotation on a given axis, the improvement comprising impacting means on said rotor means for pulverizing the material admitted to said chamber in response to rotation of said rotor means around said axis, said impacting means including a plurality of impact hammers circumferentially spaced apart on said rotor means and movable circumferentially within said impact chamber when said rotor is actuated, each of said impact hammers including a radially extending supporting shank, means securing said shank to said rotor means, first and second radially spaced impact plates extending symmetrically from said shank and parallel to the rotor axis, said impact plates defining an opening between them and each being provided with an inclined impact surface having an angular orientation at the outer edge of its effective impact area adapted to deflect material from that surface toward said opening, and including a third impact plate on said shank, said third plate having an impact surface located rearwardly of the opening between said first and second impact plates for engagement by material passing through said opening.

2. The device of claim 1 wherein each of said impact surfaces is substantially rectangular in shape and is bounded by acute peripheral edges.

3. In an impact mill having an impact chamber with inlet and outlet means for admitting and discharging material to be pulverized, and a rotor means mounted within said chamber for rotation on a given axis, the improvement comprising impacting means on said rotor means for pulverizing the material admitted to said chamber in response to rotation of said rotor means around said axis, said impacting means including a plurality of impact hammers circumferentially spaced apart on said rotor means and movable circumferentially within said impact chamber when said rotor is actuated, each of said impact hammers including a radially extending supporting shank, means securing said shank to said rotor means, first and second radially spaced impact plates extending symmetrically from said shank and parallel to the rotor axis, said impact plates defining an opening between them and each being provided with an inclined total effective impact surface having an angular orientation adapted to deflect material from that surface toward said opening.

having an axis perpendicular to said path, first and second impact plates positioned substantially near one end of said supporting shank perpendicular to and symmetrical with said axis of said shank, said plates being integral with said shank and each provided with an angularly disposed impact surface having an angular orientation with respect to said path adapted to deflect such fluid medium transversely of said path toward the other plate. 5. An improved impact hammer for an impact mill including in combination a supporting shank provided with means for pivotally attaching said supporting shank to a rotor member of an impact mill, said shank provided with an impacting member adjacent one end thereof, said impacting member including first, second and third substantially planar impact surfaces, each of said surfaces being spaced apart from the others and having different angular orientations and locations such that the planes of said surfaces intersect along a common line centrally and longitudinally of one of said surfaces.

6. In an impact mill comprising a housing for a fluid medium containing particles of material to be ground, an impact member within said housing, and means for causing rapid relative movement between said impact member and said particle containing medium along a predetermined path, the improvement in which said impact member comprises a plurality of impact surfaces spaced with respect to each other transversely and longitudinally of said path and providing a tortuous passage for relative movement of the fluid medium through said impact member, at least two of said impact surfaces being spaced from each other transversely of said path and defining at least a portion of said passage between them for relative movement of said fluid movement therebe tween, each of said two last mentioned impact surfaces having a total effective impact area, substantially all of which is angularly oriented with respect to said path to deflect the fluid medium transversely toward said passage.

References Cited by the Examiner UNITED STATES PATENTS r 696,628 4/02 Dickson 241 X 845,171 2/07 Gardner 241-194 1,203,314 10/16 Day 241195 1,366,512 1/21 Blum 241195 X 1,646,752 10/27 Kimber 241191 X 1,753,473 4/30 POISter 241195 X 1,850,244 3/32 Shelton 241-195 2,237,510 4/41 Tankersley 241195 2,467,865 4/ 49 Smith 241-194 X 2,700,511 1/55 Denovan 241-494 2,822,138 2/58 Olive 241194 7 t FOREIGN PATENTS 175,145 6/53 Austria. 958,520 2/57 Germany. 388,337 2/33 Great Britain.

70,780 7/46 Norway.

J. SPENCER OVERHOLSER, Primary Examiner.

ROBERT A. OLEARY, JOHN C. CHRISTIE,

. Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,184, 172 May 18, 1965 Coleman Dudley Fitz It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 8, for "lack" read lock line 45, after "hammers 60." insert As shown, these

surfaces

61, 63 and 65 serveas angularly oriented impactsurface portions of each impact member or hammer 60. line 67, after "is" insert thus line 75, for "an" rea'd-- another column 4, line 19, after 3"bars" insert orplates column 5?, line 10, after "surfaces" insert or surface portions line 25, for "movemnt" read movement line 44, after "portions" insert of this concave impact surface, line 45, after "other" insert a comma; column 6, line 6, after "have" insert their impact surfaces constructed and arranged to provide same column 6, line 74, before "adapted" insert at the outer edge of its effective impact area Signed and sealed this 14th day of December 1965;

(SEAL) \ttest:

ERNEST W. SWIDER EDWARD J. BRENNER \ttesting Officer Commissioner of Patents

Claims

1. IN AN IMPACT MILL HAVING AN IMPACT CHAMBER WITH INLET AND OUTLET MEANS FOR ADMITTING AND DISCHARGING MATERIAL TO BE PULVERIZED, AND A ROTOR MEANS MOUNTED WITHIN SAID CHAMBER FOR ROTATION ON A GIVEN AXIS, THE IMPROVEMENT COMPRISING IMPACTING MEANS ON SAID ROTOR MEANS FOR PULVERIZING THE MATERIAL ADMITTED TO SAID CHAMBER IN RESPONSE TO ROTATION OF SAID ROTOR MEANS AROUND SAID AXIS, SAID IMPACTING MEANS INCLUDING A PLURALITY OF IMPACT HAMMERS CIRCUMFERENTIALLY SPACED APART ON SAID ROTOR MEANS AND MOVABLE CIRCUMFERENTIALLY WITHIN SAID INPACT CHAMBER WHEN SAID ROTOR IS ACTUATED, EACH OF SAID IMPACT HAMMERS INCLUDING A RADIALLY EXTENDING SUPPORTING SHANK, MEANS SECURING SAID SHANK TO SAID ROTOR MEANS, FIRST AND SECOND RADIALLY SPACED IMPACT PLATES EXTENDING SYMMETRICALLY FROM SAID SHANK AND PARALLEL TO THE ROTOR AXIS, SAID IMPACT PLATES DEFINING AN OPENING BETWEEN THEM AND EACH BEING PROVIDED WITH AN INCLINED IMPACT SURFACE HAVING AN ANGULAR ORIENTATION AT THE OUTER EDGE OF ITS EFFECTIVE IMPACT AREA ADAPTED TO DEFLECT MATERIAL FROM THAT SURFACE TOWARD SAID OPENING, AND INCLUDING A THIRD INPACT PLATE ON SAID SHANK, SAID THIRD PLATE HAVING AN IMPACT SURFACE LOCATED REARWARDLY OF THE OPENING BETWEEN SAID FIRST AND SECOND INPACT PLATES FOR ENGAGEMENT BY MATERIAL PASSING THROUGH SAID OPENING.