US2172096A - Rotary hammer mill - Google Patents

Description

Spt. 5, 1939. T. c. ALFRED 2,172,096

ROTARY HAMMER MILL Original Filed Sept. 11, 1933 3 Sheets-Sheet l a 3 T (7p 20 A .34 6

I 364 I 0 4; I o 4/ Q 2 \J] 44 Z? 0 0 o 6 J 1 I wodoitC-ldfired' Sept. 5, 1939 T. c. ALFRED. 2,172,096

- ROTARY HAMMER MILL I Original Filed Sept. 11, 1933 I 3 Sheet s Sheet 2 Sept. 5,1939. T LFR D 7 2,172,096

' ROTARY HAMMERMILL Original Filed Sept. 11, 1933 :5 sne' ts sheet s I Patented gept. 5, 1939 IPATENT- OFFICE ROTARY HAMMER. MILL Theodore 0. Alfred, Lancaster, Ohio Application September 11, 1933, Serial No. 688,970 Renewed May 15, 1937 1 Claim.

This invention relates to improvements. in rotary hammer mills of the character employed in grinding or reducing various products such as grain, stocks, seed, minerals and the like to a desired state of subdivision, the primary object of the invention being to provide a generally improved and more eflicient machine for work of this character and one wherein high grinding capacity is provided with relatively low power consumption.

With these and other objects in view, which will appear as the description proceeds, the invention consists in the novel features of construction, combination of elements and arrangements of parts hereinafter fully described and pointed out in the appended claim.

In the accompanying drawings:

Fig.' 1 is a side elevation .of a rotary hammer mill formed in accordance with the present invention; a Fig. 2 is a front elevation thereof;

Fig. 3 is a vertical longitudinal sectional view taken through the mill;

Fig. 4 is a horizontal transverse sectional view on the line 4-4 of Fig. 3;

Fig. 5 is a perspective view of the mill with the casing plates at one side removed to disclose its interior structure;

Fig. 6 is a vertical transverse sectional view taken through the rotor;

Fig. 7 is a. detailed view of the cam operated fastening means for retaining the cover of the mill casing in secured engagement with the stationary lower section of the casing;

8 is a fragmentary sectional view of the rotor on the line 8--8 of Fig. 6;

Fig. 9 is a detail sectional view taken on the line 99 of Fig. 1.

Referring more particularly to the drawings, the numeral I designates the casing of the reducing mill. Preferably, this casing comprises a stationary lower section. A and a removable cover or hood section B mounted on top of the lower section A when the mill is in operation. This casing may be constructed in any suitable manner from desired materials. In the present form of the invention, however, the lower section A comprises .vertically disposed corner angles I, horizontally extending pairs of top and bottom angles 2 and transversely extending top angles 3. These angles are suitably bolted or otherwise secured in, rigid frame formation and also attached thereto are side and end plates 4 and 5 respectively. The casing may be mounted 'upon any suitable foundation either permanently or removably-in orderthat during operation of the mill a stable working base, free from objectionable vibration, may be provided.

The cover or hood section B also provides corner angles 6 to which is secured in any suitable 5 rigid manner a top plate I, side plates 8, and a vertical end plate 9, the latter being provided, contiguous to its lower edge, with a transversely and horizontally extending exteriorly disposed angle member ID arranged above and in registra- 10 tion with the top angle 3 of the base section A. The other side of the cover or hood B, opposed to the end plate 9, is substantially open, and carries an inclined feed trough ll through or along which themateiials to be reduced are fed into the rotor chamber C of the casing-and below the discharge end of the trough H, the hood section carries a transversely and horizontally extending trap boxing I2 having the wall thereof which communicates with the chamber C slotted as at IS in order to trap'undesirable solids, such as miscellaneous pieces of metal, and prevent their coming into contact with the grinding elements of the mill. Preferably, studs l4 project from the ends of the boxing l2 and serve as fulcrums about which the hood section may turn in order to open or close the rotor chamber. Connected with the top wall 1 of the hood section is a slightly downwardly inclined baffle 15 which actsas a deflector in confining the material undergoing reduction to the limits of the chamber C.

An important feature of the present invention resides in the construction of the rotor D. This rotor comprises, in the preferred form of the invention, an axial support in the form of a shaft I6 which is suitably journaled for rotation in connection with bearings I! mounted upon the upper surfaces of the top angles 2 of the base or lower section A. One end of this shaft carries a suitable form of belt wheel l8 by means of which power, obtained from any suitable form of prime mover, may be applied to the mill, whilethe opposite end of the shaft is connected with a suctional fan 20, the latter being disposed in a casing 2| arranged exteriorly and to one side of the mill casing, as shown more particularly in Fig. 2. The shaft I6, between the bearings i1, is threaded as at 22 for the reception of clamping nuts 23, which function to retain in assembled and clamped order a plurality of spaced flat bars, comprising secondary hammers and designated generally by the numeral 24, in rotatable connection in unison with the shaft I 6. If desired, the rotor shaft between its threaded portions 22 may be of polygonal design in tr'a'n sveisiegcros s 5? section for reception within similarly formed openings provided in the intermediate portions of the bars 26 which comprise the secondary hammers.

It will be observed that these secondary hammers comprise a multiplicty of flat substantially rectangular bars of uniform length which have their intermediate portions connected for unitary rotation with the shaft or other form of axial support I6. Further, these bars are disposedin sets extending radially from the shaft l6 and are spaced substantially equidistantly at their outer ends to provide a plurality of relatively -V-shaped pockets 25 therebetween, which pockets open to the periphery of the rotor as shown in Fig. 3. These bars may be of any suitable length and-are compactly secured together in side by side relationship on the shaft for rotary movement in unison with the shaft, with the different sets of bars spaced equidistantly around the orbit of travel of the rotor, and the advantages of this construction over the usual disc type of mounting, commonly found in grinding mills of this character, will be more fully described herein after.

Each set of bars at' positions spaced from the axis l6 has the individual bars thereof provided with registering perforations for the reception of transversely extending cross pins 26 which may be retained in connection with the bars by having their outer ends equipped with cotter keys 21.

-The pins 26 are employed to provide pivotal mountings for the reception of primary hammers 28.- Each of these hammers comprises a metallic casting or stamping of a thickness to be freely received within the spaces provided between adjoining bars of a set, and the opposite ends of these primary hammers are formed with perforations 29 for the reception of the cross pins 26 by means of which the said primary hammers are pivotally connected for independent swinging movement to the outer portions of the secondary hammers, so that while the primary hammers revolve with the secondary hammers and the axial support l6, yet they are permitted to respond freely to centrifugal forces, set up by the rapid rotation of the rotor, usually a speed of 3300 R. P. M., to assume extended grinding positions wherein the outer ends of the primary hammers project beyond the corresponding squared ends of the secondary hammers. These primary hammers may be of the type disclosed in my prior Patent No. 9,325, which have here been selected for illustration and include somewhat tapering, stepped or shouldered ends 30, which have been found to be very effective in grinding operations of this character. Following a certain amount of use of the primary hammers with resulting wear, the positions thereof in connection with the secondary hammers or bars 24 may be reversed-to restore their normal operating efficiency.

One of the serious disadvantages in the ordinary reducing mill as heretofore constructed has been the lack of proper rotor weights, which have been seriouslylacking in adequate fly wheel action. As a consequence, rotors of prior design with which I have exeprimented are not considered to possessa desired state of efficiency for the reason that they require an excessive amount of power for a given output of ground material. In the design of the present rotor, however, I have discovered that by employing the grouped bars arranged in the compact fashion disclosed, the weight of the rotor may be increased to augment this fly wheel action and secure smoothness, lack of vibration, low power consumption and into the emciency of the mill, as a much harder blow is struck on the material being reduced than when a rotor of smaller diameter is used and, moreover, there is no loss in the actual number of blows struck per minute. This is a marked contrast with the usual type of rotor employing spacing discs for the centrifugal hammers. Such discs do not in the ordinary mill function to strike blows upon the material being reduced, as do the secondary hammers or bars, here disclosed. In the present rotor, with the power input remaining constant, the arms or bars provide increased diameter 'over the ordinary disc type rotor, adequate weight for the desired fly wheel action, grinding or reducing operation from the bars or secondary hammers, and augmented peripheral velocityof the outer or primary hammers carried thereby.

In common with prior hammer mills of this general character, I employ a semicircular perforated plate or screen 3| beneath the lower half of the rotor. In contrast, however, with previous screens, the screen 3| is set so that it is disposed slightlyeccentrically of the axis .of the rotor, or conversely the axis of the rotor is eccentric to that of the screen. This eccentricity issuch that the screen is spaced roughly at approximately of an inch from the outer orbit of the rotor at the front of the mill, tapering to approximately of an inch at the botom and to about A; of an inch at the rear. These figures are of course approximate and are subject to variation if found desirable. By this eccentricity of the rotor with respect to the screen, I have been able to secure a more eflicient grinding or reducing operation and have increased materially the capacity of the mill over the usual construction wherein the screen exactly conforms to the orbit of the rotor. In the operation of a screen of this character. it is important that it should shed finely divided materials through the openings or perforations thereof rapidly so that the ground materials may pass freely therethrough. To this end I mount the screen 3| in arcuate guides 32 in which the screen is free to move until one end thereof con-' tacts with a stationary abutment 33 disposed adjacent to the trap l2. The opposite edge of the screen is then so disposed as to engage with the lower portion of the cover or hoodB when the latter is closed, so that upon the final clamping of the hood in its closed position, the screen will be placed under compression, the purpose of this being to maintain the screen in what may be termed a tuned state when the mill is in operation so that the minute and rapid vibration thereof will serve to cause a rapid and effective passage of the finely ground materials through the perforations thereof.

To obtain thelocking of the hood in its closed position and the screen under compression as described; the angle 3 of the base section is formed intermediately of its length with an opening for the reception of a swinging eye bolt 34. This eye bolt, as shown in Fig. 7, is receivable within an open ended slot provided in the angle member In of the hood section. Also formed with the bolt 34 is a stationary cam enlargement 36, which cooperates with a movable cam 31 which is turnable about the axis of the bolt shank. The outer or upper end of the bolt maybe provided with a nut 38 and a spring may be positioned between the nut 38 and the movable cam 31. The cam is'provided with a lateral handle extension 40, and also a stop lug 4i. When this fastening is positioned in hood securing relationship, the handle 40 is actuated to rotate the movable cam until the stop lug 4| contacts with the end plate 9. Due to the inclined plane action downward pressure will then be imparted to the hood causing it to exert a considerable force on one of the upper horizontal edges of the screen to maintain the latter under compression and at the same time to securely retain the hood section in closed operative relationship with the stationary lower section of the mill casing.

The ground material drops into a trough 42 formed withinthe confines of the base section of the mill and is discharged therefrom by way of a conduit 43 by the suction created through the operation of the fan or blower 20. The divided material may then be delivered from the fan to a suitable form of separator (not shown) or other position of material deposit.

As set forth in my prior Patent No. 1,829,325, I

' there is a decided tendency for ground material to clog the openings provided in the upper portion of the screen at the front of the mill. Due to the curvature of the screen, the openings which extend therethrough at this portion thereof are substantially horizontal, or more nearly the horizontal than the vertical and, therefore, material which collects in these openings does not so readily respond to gravity and as a'consequence the screen clogs in this area. To take care of this condition, the front of the mill in the present invention is provided with a slot-open to the atmosphere and formed between the adjoining edges of the laterally offset walls of one of the end plates 5 and the vertical'end plate 9, and through which slot air from the atmosphere may be drawn. By the operation of the mill and the suction developed by the operation of the fan 20, air drawn into the mill through the slot 44 travels at a high velocity past the forward upper edge area of the screen, creating suction forces by which materials which normally clog that particular part of the screen arepositively removed from obstructing positions and delivered to the trough 42 for subsequent discharge from the mill.

Attention is directed to the cross sectional configuration of the hood section as more particularly disclosed in Fig. 3. The angles of the top plate I, the vertical end plate 9 and the deflector plate l5 are such that th'ematerial in this portion of the rotor chamber is kept moving back and forth on the rotor between the ends of the hammers and the angular walls of the hood, For example, theoretically, material falling on a set of hammers when the latter are in a horizontal position, will be thrown against the deflector bafiie I5 in the hood above the feed table. While this material will not lose all of its rotary and forward motion, nevertheless, it will be deflected back onto ,the hammers to then strike the slanting top wall 1 of the hood, thence again back upon the hammers and into contact with the forward wall 9, being constantly reduced by this agitation and contact with stationary or moving surfaces, so that the material will be divided to a desired state by the time it reaches the screen area. Preferably, the inner surfaces of the walls I and 9 are provided with a screen lining as indicated at 45. This lining not only changes the direction of the material contact therewith from a deflecting standpoint but it also has a certain cutting eifect on the material at the edges of its openings, and, in addition, the lining serves to slow up or retard the forward motion of the feed or'other material undergoing reduction.

It will be observed that the feed chute or trough H enters the rotor chamber at a point just.above the plane of the axial center of the rotor. This is a considerably lower point than has been custom-\ ary in previous hammer mill designs, and a dc?- clded advantage is obtained by this lowering of the feed chute, in that it provides for a more extended contact between the primary and secondary hammers in the upper portion, of the rotor chamber, or in the hood area, with consequent greater reduction of the material before the screen area is reached. It is in this portion of the rotor chamber that the arms or .secondary hammers function as reducing agents since the large material readily drops into the V-shaped spaces formed between the adjoining sets of bars or arms comprising the secondary hammers, but this is accomplished with but a negligible consumption of power. Where power is largely expended is in passing the primary hammers through the bed of finely ground material retained on the upper surfaces of the screen, but

since this bed rarely exceeds a depth in excess,

of of an inch, it will be seen that the secondary hammers or bars during their travel through the lower half of the rotor chamber will be out of contact with the material being acted upon and thence will not consume any appreciable power in this portion of the mill operation.

Any desired grouping of the primary hammers on the several sets of bars may be provided. It is important however that the primary hammers should be placed in such sequence between said bars that the rotor will be substantially statically and dynamically balanced. Preferably, each set of bars carries eight hammers, four at each end,

as shown in Fig. 4.' By laterally offsetting the cation with the rotor chamber C so that as the' rotor revolves, any foreign particles, such as bits of metal or the like will, by centrifugal force, be advanced into the boxing where such foreign particles will be imbedded in the reduced mate rial which collects in this boxing during the operation of the mill. Preferably, the boxing is provided with a removable rear wall 41, which may be instantly removed by the mere loosening of the wing nut 48 shown in Fig. 4, so that in the event of fire in the boxing, the'same may be readily extinguished by the removal of the rear wall 41. The latter is ordinarily used for removing accumulated'particles of matter from the boxing.

The eccentricity of the screen mounting is such that in one of the commercial forms of my improved hammer mill, the clearance between the ends of the hammer and the screen proper at the forward upper end of the screen is approximately three-fourths of an inch. This eccentricity provides a clearance of approximately onehalf of an inch at the bottom of the screen and approximately one-fourth of an inch at the upper rear end of the screen. While this degree of eccentricity may be varied, the eccentricity thus afforded provides more freedom between the ends of the hammers and the screen in the threequarter inch space and allows ,further reduction without as much drag or power consumption. In other words, the tapered circle admits larger portions at one end than would a concentric circle only one-half an inch away from the ends of the hammers, doing away with shock loss at the point of entry over the screen because of the greater space provided. At the other end, the reverse is true. However, by this time the materials are finely divided and by operating the hammers closer to the screen, a greater output is obtained.

Heretofore hammer mills of this character have I been formed to include heavy cast metal casings which have been considered necessary in order to minimize vibration in the operation of the rotor at high speeds and to preserve bearing alignments. In the design of the present mill, however, I use a separate angle construction or subframe composed of structural metallic members to which are bolted or otherwise secured the v wall plates. Normally, it would be thought that this construction would be ample to avoid defiection but if unprotected such deflection would exist. enough in the operation of the mill, even up to 75 H. P. application, to distort this frame structure permanently or really damage it in any way,

While almost no force would be great arcades yet there is an initial deflection before the full resistance of the steel is obtained, which would be very detrimental and cause trouble with shafts and bearings.

To overcome this, I use the braces 69 which are connected as shown in Figs. 1 and 2 with the upper and lower sets of angle members 2. In order to make these braces effective and produce a rigid solid frame construction, the lower frame is assembled including the members I, 2, 3, l and'i'a, and an expander (not shown) is inserted to spread apart the upper and lower angles until there is produced a decided buckle in the side sheets. The braces 59 are then cut to such length that when they are inserted and secured, this deflection of the frame will be maintained following the removal of theexpanding means. In this way, I overcome entirely any tendency of flexure in the frame. By the employment of these pressure braces, the middle is relieved entirely from this initial fiexure which would otherwise be present and also I am enabled to avoid the use of inordinately heavy steel members. What is claimed is: .In a rotary hammer mill, a casing comprising a structural steel frame of substantial cubical form, including rigidly united upper and lower sets of horizontally disposed rails and vertically extending post rails, sheet metal plates secured to the sides and ends of said rails and defining a rotor chamber, a rotor arranged in said chamber and including a shaft mounted for rotation in bearings carried by' the upper set of horizontally disposed rails, and brace members under compression uniting the upper and lower sets of horizontally disposed rails and arranged to deflect said frame structure and hold it under tension.

THEODORE C. ALFRED.

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