US2437147A - Colloidal mills of the multiple grinding unit type - Google Patents

Description

March 2, l948- E. B. A.'ZWOYER COLLOIDAL .MILLS OF THE MULTIPLE GRINDING UNIT TYPE Filed May 12, 19 44 2 Sheets-Sheet l V INVENTOR. Z2 zin a/zr/e jfl Z n ome BY 8 I March 2, 1948. E. B. A. ZWOYER COLLOIDAL MILLS THE MULTIPLE GRINDING UNIT TYPE 2 Sheets- Sheet 2 Filed May 12, 1944 INVENTOR.

flash 02MB. 5W0 VE/Z WITNESS ATTORNEYS Patented Mar. 2, 1948 COLLOIDAL MILLS OF THE MULTIPLE GRINDING UNIT TYPE Ellsworth B. A. Zwoyer, Perth Amboy, N. J., assignor to Fuel Research Corporation, New York, N. Y., a corporation of Delaware Application May 12, 1944, Serial No. 535,237

8 Claims. (01. 241-146) This invention relates to grinding mills and more particularly to the type of mills which are known as colloid mills. These mills are high speed disintegrators which operate with close clearances of the grinding surfaces and are arranged for wet grinding. In their usual form, they include within a cylindrical casing, a stator and a rotor driven at a very" high speed. The grinding faces of the stator and rotor are usually either disc or conically shaped.

The term "colloid applied to these mills is a misnomer in the sense that these mills are usually not capable of reducing the solid particles of material to colloidal size, namely, between 1. (micron) and 1 pp. in diameter. Many of them are not even capable of reducing solid material, such as coal, to a size of 325 mesh which is considerab-ly above colloidal size. These mills, however, are capable of producing small quantities of mixture in which the particle size of the solid element is 100% under 200 mesh. To accomplish this result with known mills, however, requires that the rotor be driven at an extremely high peripheral speed and this in turn causes excessive wear at the grinding faces of the discs. If an attempt is made to increase the diametrical dimensions of the grinding discs with a view of decreasing the rotational speed of the rotor, it has been found that excessive wear will take place at the peripheries of the discs. Ordinarily wear is compensated for by a. take-up device desi ned to move the stator toward the rotor until the proper desired clearance is reached. If, however, discs over 4 inches in diameter are used; the freedom from wear near the shaft as compared with that at the periphery is such that the metal of the discs close to the shaft is practically unworn, while the metal of such discs at the peripheries thereof is substantially worn. Thus, the machine action will be braked to a stop by the less worn portions thereof and the machine rendered useless until new discs are substituted. This wear of known types of grinding discs especially in the grinding of hard materials, such as, coal, is so rapid that under continuous operation of the mill, they must be replaced every few days if the mill is to be kept functioning and this is a highly unsatisfactory condition.

Theprincipal purpose of the present invention is to provide a grinding mill whose operational characteristics are considerably improved over those of the mills heretofore made and will make possible a quick and low cost method for grinding solid materials.

Another object of the invention is to provide a grinding mill capable of disintegrating the solid material readily and reliably to particle sizes below that capable of being produced by known mills of the type indicated, i. e., capable of reducing material such as coal with one pass so that the coal particles will pass through a sieve of 325 mesh or finer and of which particles at least 50%, by weight, will be less than 10 microns in size.

Another object of the invention, is to provide a grinding mill capable of producing in large quantity a substantially uniform product.

A further object of the invention is to provide a grinding mill which is cap-able of being constructed in large sizes and of employing a large number of grinding discs and yet which can be simply and readily adjusted to produce a substantially uniform product from all of such grinding discs.

A still further object of the invention is to provide an improved grinding mill in which the material to be ground, can be fed under substantial pressure and which will operate satisfactorily with such material without leakage and at relatively low cost.

a Other objects of the invention as well as the novel details of constructibn of the mill by which such objects are accomplished, will become apparent from a perusal of the following description when read in connection with the accompanying drawings, in which, Fig. 1 is a vertical sectional view of a grinding mill embodying the features of this invention; Fig. 2 is a side elevational View of such mill and Fig. 3 is a sectional view taken along the line 3 3 of Fig. 2.

In the drawings, the reference numeral l designates the sub-base of the mill. Secured upon the sub-base l is a base 2 having a plurality of integrally formed, spaced block portions 2 defining a centrally disposed'longitudinal area of a size to receive a supporting frame 4 (see Figs. 2 and 3) and enabling such frame to be moved longitudinally with respect to the base 2, movement of the frame 4 in a transverse direction being.

prevented by the block portions 2. The frame 4 is movably supported on the base 2 by means of a plurality of transverse shafts 3, which extend through apertures in the front and rear sides of the frame 4, and ball bearing units 1 provided on one end of such shafts. As is shown more clearly in Figs. 2 and 3 of the drawings, the shafts 3 of which there are three in the embodiment disclosed, each have reduced end portions which extend through the walls of the frame land one of which is threaded to receive a locking nut 6. The other ends of such shafts are provided with ball bearing units 1, the units of the two outer shafts 3 being mounted on the ends thereof which project through the front wall of the frame 4 while the ball bearing unit of the intermediate shaft 3 is on the end of the latter which projects through the rear wall of the frame 5. The outer race 8 of each unit 1 (see Figs. 1 and 2) rests on a machined surface provided at the bottom of a recess 9 formed in the upper inner end portion of an associated block portion 2, the longitudinal dimension of each of the recesses 9 being such that the outer races 8 of each of the units 1 and consequently the frame 4 have a limited movement in a longitudinal direction with re;-' spect to the base 2. A cover plate Ill is bolted to the upper surfaces of the block portions 2' to retain the units 1 in the recesses 9.

The mill proper has a central, cyli'ndrlbally shaped body 5 which is closed at its ends by heads H, II, these three parts being securely fastened together by means of the longitudinally extending tie bolts l2 and forming the shell of the mill.

.The body 5 of the mill is secured upon the frame 4 and it will accordingly be understood from the foregoing that the shell of the mill is capable of movement in longitudinal directions with respect to the base 2 and sub-base I through the ball bearing units 7, but is restricted against movement in a transverse direction by the inner Walls of the block portions 2 or the base 2.

Extending through the shell composed of the central cylinders 5 and heads H and l l is a shaft l3 which is supported at its ends by the bearings 15, I5. The shaft l3 has an enlarged central portion Id of a length substantially equal to the length of the central cylinder 5 as is shown more clearly in Fig. 1 of the drawings. The reduced ends M, M of the shaft are further reduced within the bearings 15, Iii to prevent movement thereof in a longitudinal direction. The right hand end of shaft I3, as viewed in Fig. 1 of the drawings, is connected to any suitable source of power capable of rotating such shaft at the speed desired.

The mill includes an inner cylinder l6 provided on its outer end with an exterior flange I! which is secured intermediate the head II and central cylinder 5 by means of the tie bolts 12. The inner cylinder 16 also includes a reduced cylindrical portion [3 which is bounded at its outer end by an inwardly extending annular flange l9 and at its other or inner end by an inturned annular flange or end wall 20 so that such reduced portion I8 together with flange l9 and end wall 20 forms a cylindrically-shaped chamber designated 32 in Fig. l of the drawings. The inner edge of end wall 26 is provided with an outwardly projecting annular flange or lip 2|, upon which rests for rotational movement relative thereto, the flanged end portion of a worm wheel 22. A retaining ring 23 is secured to the end surface of the lip 2i and maintains the flanged end portion of worm wheel 22 in position on such lip. The worm wheel 22 is in engagement with a worm 24 secured to a transverse shaft 25 having at one end a hand wheel 25 by which the shaft 25 and consequently worm 24', and worm wheel 22 may be rotated in one direction or the other. The worm wheel 22 is internally threaded and is in threaded engagement with the exterior surface of an annular adjusting member or nut 27 provided at its outer end with a flange 28 which at its periphery is keyed to the interior surface ofthe central cylinder 5 to permit longitudinal movement of the member 21 within the shell but preventing such member 2'! from partaking of the rotative movements of the worm wheel 22. The flange 23 extends inwardly of the cylindrical wall of member 21 and, together with an inturned end wall portion provided on the other side of such member, forms a cylindricail'y shaped chamber which is designated in Fig. l of the drawings by the numeral 33. The inturned end wall of member 2? is provided with a longitudinally disposed cylindrical sleeve 29 which extends across the inner surfaces of ring 23 and lip 2! and into the chamber 32 and which is of substantially greater diameter than the central portion M of shaft i3 '50 that it is in spaced relation thereto.

Secured to the outer faces of flanges l9 and 28 are two stators 35 and 35, respectively. Each of the stators 35 and 35', which are substantially identical in construction, includes a flat discshaped body portion provided on its outer face with a grinding ring. The inner diameter of the body portion of each stator 35 and 35' is greater than the exterior diameter of the central portion M of shaft l3 and substantially the same as the inner diameter of the flange on which it is mounted to form an annularlyshaped' passageway around the portion of the shaft it surrounds. The outer peripheries of stators 35 and 35 are cut back to facilitate the discharge of material from the grinding rings thereofinto the annularlyshaped discharge passages 39 and 39' (see Fig. 1).

Adjacent to the outer faces of stators 35 and 35, are floating rotors Eli and 43, respectively. Each of the rotors 4t and includes a hub, provided with two diametrically opposed key slots which engage with longitudinally extending keys 4% provided on the outer ends of the central portion M of shaft l 3. Thus rotors 40 and 46' are driven by shaft f3 and also are capable of movement in a longitudinaldirection relation to shaft l3 and stators 35 and 35. On each face of the body portions of rotors 416 and 49' is provided a grinding ring. The inner rings of these rotors cooperate with the grinding rings of stators 355 and 35', while the outer grinding rings thereof cooperate with the inner grinding rings of a pair of adjacently positioned stators 50 and 5d. The bodies of the floating rotors id and 40, intermediate the hubs '4! and grinding rings thereof, are provided with a-plurality of apertures 65 through which the material to be ground may flow from the annularpa'ssageways formed by stators 35, 35", flanges IQ and '28 and shaft I3'to the succeeding grinding discs, will be hereinafter more fully explained.

The stators 50 and 5B are also of the floating type in that they are mounted for longitudinal movement within the shell. These stators each include a body portion provided with a pair of diametrically opposed flange portions having keyways adapted 'to receive the keys 5E provided on the inner surfaces of the mill to enable longitudi= nal movement of such stators but to prevent any rotational movement thereof such as may be caused by the rotors through the material being ground. The faces of each body of the floating stators 5t and 58 are provided with annular grinding rings, the inner rings thereof cooperating with the outer grinding rih'gsof rotors 553 and it and the outer rings thereof cooperating with grinding rings of a pair of adjacently positioned rotors 55, 5'5. V

The rotors 55, each include a body provided on its inner surface withja grinding ring. The bodies bf rotors 5'5 and 55" "are-bolted or otherwise secured to a pair of exterior flanges 58 and 58', respectively, formed on the hubs 59 and 59' respectively, the latter of which are mounted on the reduced end portions I4, M of shaft l3 adjacently to the ends of the enlarged portion I4 5 of such shaft (see Fig. 1). The inner surfaces of hubs 59 and 59 are provided with longitudinally extending keyways which interengage with keys 6!] and 65' provided on the inner ends of the reduced portions 14' of shaft l3 so as to secure 10 such hubs to the shaft for rotational movement therewith. The hubs are secured against longitudinal movement on shaft l3 by the shoulders formed between the reduced portions 14' and the central portion [4 of shaft I3, and nuts 6| and 15 2 Surrounding the sets of nuts 6|, B2 and 6|" and 62 are a pair of tubular sleeves 63 and 63', respectively, which extend within the shell of the mill to the outer ends of hubs 59 and 59 and at their outer ends are provided with external 5 flanges 54 and 54', respectively, by which they are secured in position within the central openings of the heads II and H, respectively. Secured to the outer faces of the flanges 58 and 58', respectively, are a pair of funnel-shaped members 55 and 65' which project outwardly from such flanges so as to enclose the inner ends of the sleeve members 63 and 63, respectively. Outlets 55 and 56' are provided at the lower ends of the heads II and I! and are in communication with the chambers of such heads. The walls of the heads H and H and the central cylinder 5 of the mill are formed to. provide a water cooling jacket around the shell formed by such parts,

the sections of such jacket being supplieclwith cooling water in any suitable manner.

From the foregoing description, it will be understood that in the operation of the mill, the

material to be ground is fed through the intake pipe 3| and through the port 30 into the chamber 32. The material is fed into the mill under substantial pressure. For example, if the mill is to grind a coal-oil mixture for the production of liquid fuel, the oil mixed with coal of 100 mesh is fed into the mill at a pressure of from 125 to 150 pounds per square inch. After the material to be ground, enters the chamber 32, it travels to the right and left, as viewed in Fig. 1 of the drawings, to the sets of stators and rotors at each end of the central cylinder 5. Thus, a portion of the material fed under pressure into chamber 32 travels to the right to pass through the cylindrical sleeve 29 into the chamber 33 and from the latter, through the annular space between the shaft I3 and the stator 35, As the material travels up between stator 35' and rotor 40' a portion thereof is fed between the grinding rings thereof and discharged into the discharge passage 39', while another portion of the material passes through the openings 45 of rotor 40'. The portion of material that travels through the openings 45 of rotor 40 is further divided, part of it passing between the opposed grinding rings of rotor 45' and stat-or 511' and part of it passing between shaft [3 and the inner periphery of stator 50 and thence up between the opposed grinding rings of stator 50' and rotor 55' to be discharged into the discharge passage39, the

ground material fed into the discharge passage 39' passin into the chamber formed in the head ll.

The portion of the material entering the intake port 30 which travels to the left, as viewed in Fig. 1 of the drawings, pursues similar courses, though in opposite directions, between the grinding surfaces of stator 35, rotor 40, stator 50 and rotor 55 to the discharge-passage 39 and thence to the chamber formed in the head ll.

When the material reaches the chambers of heads I I and l l', some of it falls upon the rapidly revolving funnel-shaped deflecting members 65 and 65' and is forced by the centrifugal action of such members against the outside walls of such heads and away from the central shaft of the machine. The material is therefore compelled to avoid areas, such as the places where shaft l3 emerges from the shell, Where leakage might occur until it passes out of the exit pipes 65, 66' at the bases of the heads H, H, respec- 0 tively. Not only do the members 65, 65' and the tubular sleeves 63, 63" prevent the fuel from going out of the shell around the shaft, but their construction and arrangement are such that they cause the circulation of cool air from the atmosphere, through such members and into the chambers on the heads II and I l, thereby assisting the water jacket system in the removal of the heat generated by the action of the grinding rings. The material passing out of the conduits 65, 65' may be conducted off separately or merged into one conduit for conduction to a place of use or storage.

As has been prevously mentioned, all of the stators and rotors with the exception of the rotors 55, 55 which are secured to the shaft iii, are of the floating type, that is, they can be shifted longitudinally relative to the shaft I3. The spaces between the coacting grinding rings of the stators and rotors may be adjusted for the type of grinding required. For instance, if the material being ground is a coal-oil mixture in which the coal is to be reduced to a particle size where it'passes one hundred percent through a 325 mesh sieve, the spaces between the grinding surfaces should be of the order of one thousandth of an inch. It is quite essential where such close' grinding is required that the spaces between the grinding elements be at all times equal. Also, as in the grinding of coal the metal of the grinding discs is rapidly worn away, adjustments must be made quite frequently,

about every one-half hour, and to stop the mill for individual adjustments of the grinding discs, or even to do this by separate adjustments with the mill in operation would be impractical and even impossible. The mill of this invention takes- .care of these requirements by providing a single adjustment mechanism which by reason of the fact that it takes advantage of the pressure of the material being ground, enables the grinding surfaces in one operation to be correctly and equally spaced while the machine is in operation. As was previously described, adjustment of the stators and rotors is made by the hand wheel 26, which through shaft 25, worm 24 and worm wheel 22 causes the adjusting nut or sleeve 2'! which is fixed against rotation, to be moved longitudinally within the shell. In taking up wear, the control or hand wheel is turned to cause stator 35' carried by the adjusting nut 21 to be moved to the right, as viewed in Fig. l of the drawings, toward rotor 45'. Due to the decreased space between stator 35' and rotor 40', the pressure of the coal-oil mix between such grinding anaare? elements increases, causing the rotor 4i!- to shift to the right to equalize the pressures of the coaloil mix onboth faces thereof. The shifting of rotor 40' unbalances the pressures on both faces of stator 5c" in the same manner, thus causing stator 58 to shift to the right towards the fixed rotor 55'. When the grinding elements have shifted so that the pressures on the faces thereof become balanced, the pressure of the mix on such faces is greater than on the faces ofthe grinding elements on the left hand side of the machine. As fixed rotorhfi bars any further movement to the right, this inequality of pressure causes the shell as a unit to shift to the left bringing the stator 3'5 closer to rotor 49. In a manner similar to that explained with respect to rotor 20 and stator 5t", rotor 40 and stator '50 will be shifted. toward fixed-rotor 55' until the pressures and consequently the spaces between the grinding faces of such elements will be equal. The wheel 26 is turned until the proper clearance between the grinding faces of stator SW'and rotor it is obtained, the other elements shifting relative to each other in the manner explained by the pressures of the material on their faces until they assume the same clearance when the'pressure on all the faces will be equalized. Thus by merely moving stator 35 towards rotor 46, all of the grinding elements are automatically shifted relative to each other by the pressure of the material being ground until all of the grinding surfaces therebetween are equally spaced and have the same clearance. This is made possible by making the shell and the adjusting mechanism free from the shaft l4 and in not fixedly attaching the shell to the base but making it capable of endwise movement relative thereto, as has been explained.

While I have described and shown a preferred form of my invention, it will be evident to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. A colloidal disc grinding mill for material fed thereto under pressure comprising a shell, a rotatable shaft extending through said shell, means supporting said shell to enable movement thereof in the direction of the central axis of said shaft, a pair of spaced groups of cooperating grinding elements contained in said shell, the grinding elements of each group including a rotor mounted on said shaft and a stator supported by said shell, means intermediate said 1 groups for feeding the material under pressure to both of said'group's, the grinding elements in said groups being constructed andarranged with relation tosaid shaft andshell to shift the la or relative to each other when the pressures between the elements of each group become unbalanced to a relative position where such pressures will be balanced between the elements of both groups.

2. A colloidal disc grinding-mill for material fed thereto under pressure comprising a shell, a rotatable shaft extending through said shell, a plurality of cooperating grinding elerrients con tained said shell, said grinding elements including a rotor secured to said shaft, a stator movably mounted on said shell, a second rotor and stator positioned intermediate said stator and rotor and being movabiy mounted onsa ld shaft and shell, respectively, said second men tione'd movable rotor and stator being construc ted and arranged to enable material flowing toward said first mentioned stator to pass between the grinding surfaces of all of said ele ments, and means for adjusting said first-mentioned stator relative to the other elements without interrupting the flow of material, whereby the pressures of the material between said elements will effect an adjustment of said second mentioned stator and rotor.

3. In acolloidal disc grinding mill, the combinationof a longitudinally movable shell, a rotatable shaft extending through said shell, a pair of spaced groups of cooperative grinding elements contained in said shell, the grinding elements of each group being mounted for relative adjustment and including a rotor mounted on said shaft anda stator supported by said shell, means intermediate said groups for feeding the material to be ground to both of said groups, grinding elements positioned inter-mediate the outer elements of 'both' groups constructed to enable the material to be ground to pass between the grinding surfaces of all of the elements in each group, and a single adjusting means for adjusting the relative position of the grinding elements in both groups, said means including a pair ofmovable cooperating members adjustable relative to each other, one of said adjusting members being mounted within said shell intel-mediate said groups and connected to a movable grindingelement in at least one' of said groups and the other adjusting member being mounted on said shell and operable to actuate said first mentioned adjusting member.

4; In a colloidal disc grinding mill for material fed thereto under pressure, the combination of ashell, a rotatable shaft eXtending through said shell, means fixedly supporting said shaft against lon itudinal movement, means supporting said shell'to enable automatic movement thereof in the direction of the central axis of said shaft, a pair of spaced groups of grindingelements contained in sa id shell, means for feeding the material intermediate said spaced groups, the outer grinding element in each group being a rotor securedto said shaft and the inner grinding element of'e-ach group being a stator supported by said shell; one of said stators being adjustably mounted on said shell for'movement axially of said shaft and the other stator being secured to said such, a secondurotor and stator positioned intermediate the said stator and rotorof each group and being 'tloatingly mounted on said shaft and shell; respectively, for movement axially of said shaft, the grinding elements positioned intermediate the outer secured rotors being constructed to' enable the material to pass between the grinding surfaces of all of said elements, and means for adjusting the grinding elements in both-groups relative to each other by adjustmerit of said adjustable stator, :said means including a pair of cooperating, relatively movable adjusting members, one of said adjusting membersbei-ng secured to said adjustable stator and the other of said adjusting members being mounted on said shell and capable of causing said first mentioned adjusting member to move said adjustable stator towardits associated rotor, whereby the increased pressure of the material between'sa'id adjustable stator and its associated rotor due to the adjustment of the former, will cause said'she'll and the stator secured thereto to shift relative to said shaft to a position where the pressures of the-m'aterlalbetween bot-hgroups o'f'grindmgelementswiil be balanced;

5. In a colloidal disc grinding mill for material fed thereto under pressure, the combination of a shell, a rotatable shaft extending through said shell, a pair of spaced groups of cooperative grinding elements contained in said shell, the outer grinding element in each group being a rotor secured to said shaft and the inner grinding element of each group being a stator supported by said shell, said stators being mounted on said shell for relative adjustment in a direction axially of the shaft, a second rotor and stator positioned intermediate the stator and rotor of each group and being floatingly mounted on said shaft and shell, respectively, for movement axially of said shaft, means intermediate said groups for feeding the material to be ground to both of said groups, the grinding elements positioned intermediate the outer secured rotors being constructed to enable the material to pass between the grinding surfaces of all of said elements, and means for adjusting the grinding elements in both groups relative to each other, said means including a pair of cooperating relatively movable adjusting members, one of said adjusting members being mounted intermediate said groups and connected to the first mentioned stator in at least one of said groups and the other of said adjusting members being mounted on said shell and operable to actuate said first mentioned adjusting member to cause said first mentioned stators to move toward said fixed rotors and thereby to cause thesecond mentioned rotor and stator in each group to shift axially of the shaft to positions where the pressures of the material on the grinding surfaces thereof will be balanced.

6. In a colloidal disc grinding mill for material fed thereto under pressure, the combination of a shell, a rotatable shaft extending through said shell, a pair of spaced groups of cooperative grinding elements contained in said shell, the outer grinding element in each group being a rotor secured to said shaft and the inner grinding element of each group being a stator supported by said shell, said stators being mounted on said shell for relative adjustment in a direction axially of the shaft, a second rotor and stator positioned intermediate the said stator and rotor of each group and being floatingly mounted on said shaft and shell, respectively, for movement axially of said shaft, means intermediate said groups for feeding the material to be ground to both of said groups, the grinding elements positioned intermediate the outer secured rotors being constructed to enable the material to pass between the grinding surfaces of all of said elements, and means for adjusting the grindingelements in both groups relative to each other in an axial direction, said means including an externally threaded member mounted in said shell intermediate said groups and directly connected to a stator in one of'such groups, a worm wheel provided with a female thread in ranged to enable the material to be fed from such intermediate means to between the grinding surfaces thereof, the outer grinding element of each group being a rotor secured to said shaft and the inner grinding element of each group being a stator supported by said shell, one of said stators being secured to said shell and the other stator being movable relative thereof, a discharge passageway associated with each group, and a single adjusting means for both groups of grinding elements, said means including a pair of cooperating, relatively movable adjusting members, one of which is connected to said movable stator and the other of which is permanently positioned on said shell.

8. A colloidal disc grinding mill comprising a shell, a horizontally disposed rotatable shaft extending through said shell, means separately supporting said shell and shaft, a plurality of cooperating grinding elements contained in said shell, a discharge chamber atone end of said shell and formed in partby an end wall of said shell through which said shaft extends, means for preventing the discharging material from passing through the shaft opening in such end wall including a fixed annular member provided on said end wall and extending inwardly into said discharge chamber to form a sleeve through which the shaft extends in spaced relation, and

having an outer end portion constructed and arengagement with the external thread of said member, a worm engaging said worm wheel and means operable to actuate said worm.

7. In a colloidal grindin mill, the combination of a shell, a rotatable shaft extending through said shell, means supporting said shell to enable movement thereof in the direction of the central axis of said shaft, a pair of spaced groups of cooperating, grinding elements contained in said shell, means intermediate such groups for feeding the material to be ground and said grinding elements being constructed and arranged to substantially close the space between the inner end of said sleeve and said shaft, and a funnel-shaped centrifugal member surrounding said rotatable member and having its wider projecting end extending beyond the outer end portion of said rotatable member and enclosing the inner end of said first mentioned fixed member.

ELLSWORTH B. A. ZWOYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 214,243 Due Apr. 15, 1879 234,010 Fahs et a1 Nov. 2, 1880 260,750 Gratiot July 11, 1882 323,561 Cadwgan Aug. 4, 1885 353,710 Raymond Dec. 7, 1886 380,180 Cadwgan Mar. 27, 1888 826,711 Davis July 24, 1906 1,079,465 Bausman Nov. 25, 1913 1,135,017 Hiller Apr. 13, 1915 1,213,149 Bodey Jan. 23, 1917 1,248,814 Craig Dec. 4, 1917 1,251,905 Martin Jan. 1, 1918 1,409,238 Punteney V Mar. 14, 1922 1,537,759 Fleming et al May 12, 1925 1,556,764 Daniel Oct. 13, 1925 1,614,409 Surtees Jan. 11, 1927 1,728,178 Eppenbach Sept. 17, 1929 1,937,788 Ross Dec. 5, 1933 2,128,226 Atwood Aug. 30, 1938 2,244,996 Laird June 10, 1941 2,255,071 Marco Sept. 9, 1941 2,412,680 Fisher et a1 Dec. 17, 1946 FOREIGN PATENTS Number Country Date 145,676 Germany Oct. 31, 1903

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