US2108005A - Abrading apparatus - Google Patents

Description

Feb. 8, 1938. w, KEEPER 2,108,005

ABRADING APPARATUS Filed July 25, 1935 2 Shets-Sheet l 3 W0 MM Millie/L. ffiefer Feb. 8, 1938. w L KEEPER 2,108,005

ABRADING APPARATUS Filed July 25, 1935 2 Sheets-Sheet 2 Patented Feb. s, 1938 PATENT OFFICE 2,108,005 ABRADING APPARATUS Walter L. Keefer, Hagerstown, Md., assignor to Pangborn Corporation, Hagerstown, Md., a corpoi-anon of Maryland Application July; 25, 1935, Serial No. 33,185

6 Claims.

The present invention relates to abrading apparatus and it is more particularly concerned with mechanical abrasive projecting or propelling machines of the character wherein an abrasive is projected by centrifugal action against the work operated upon.

A primary object of. the present invention is to provide a machine having all of the desirable characteristics of the successful abrading machine shown in copending application Serial No. 726,188 together with further highly desirable structural and operating features that improve the wearing qualities, life and efficiency of the mechanism materially.

It is a' major object of my invention to provide a novel centrifugal abrading machine that will efficiently utilize all of the abrasive supplied thereto, and have a long useful life in service, which isscconstructed as to provide ready disassembly for servicing, and yet which is low in cost.

It is a further object of. my invention to provide a centrifugal abrading machine having impeller and propeller blades which are properly correlated to produce a uniform flow of abrasive to the propeller blades and to reduce the initial impact of the abrasive therewith and the abrasive wear thereon, while improving the abrasive curtain discharged therefrom by increasing its concentration and reducing the stray abrasive discharge.

It is another object of this invention to provide a novel abrasive feeding assembly for centrifugal abrading machines in which the need for complicated and expensive air and abrasive seals is obviated.

A further object of this invention is to provide an abrasive feeding unit of novel design for abrading machines which may be readily removed from the machine as a unit without disturbing any of the parts thereof.

My invention also aims to provide centrifugal abrading machines with an improved abrasive impeller assembly and generally to refine and improve other features of such machines.

Further objects of the present invention will become apparent as the detailed description thereof proceeds in connection with the annexed drawings, and from the appended claims.

In the drawings:

Figure 1 is a longitudinal sectional view of a centrifugal abrading machine embodying my invention and it is taken approximately on the line l-l of Figure 2. In this view oneof-the propeller blade securing plates has been removed to show a part of the blade securing means.

Figure 2 is a sectional view taken substantially on line 2-2 of Figure 1, and it shows one of. the v propeller blades in section.

Figure 3 is a transverse sectional view through the base of the impeller shown in Figure 1 and illustrates the parts as they appear when viewed from the right-hand side of that figure.

Figure 3A is a sectional view somewhat similar to Figure 3 but the section is taken through the peripheral flange of the cage holder of Figure '1.

Figure 4 is a right-hand end view (Figure l) of the feeding cage with its associated parts removed therefrom.

Figure 5 is a fragmental top plan view of the bracket which holds the feeding assembly in position in the device shown in Figure 1.

Figure 6 is a fragmental sectional view somewhat similar to Figure 2, but illustrates a modified form ofv cage and impeller assembly, also forming part of the invention.

With continued reference to the drawings, wherein like reference characters are employed to designate like parts throughout the several views thereof, the machine is supported upon a base designated generally at l0 and which provides an opening through which the blast wheel or runner assembly projects.

Mounted upon base I0 is a runner wheel housing designated generally at H and which comprises end walls l2 and. I3, side walls l4 and I5, and a cover l6 which is hinged to the housing in a manner to be presently described. Abrasive guard plates l1 and I8 are secured to sidewalls l4 and I5 respectively, by means of nut and bolt assemblies I9. Base I0 is provided with a member 2|] having an opening filled with lead or any other renewable material. A further reinforcing guard plate 2| is secured to plate H by means of a nut and bolt assembly 22. An abrasive guard plate 23 is also secured to the lower side of lid l5 by means of nut and bolt assemblies 24.

Housing top or lid I6 is hingedly connected to the housing for ready access to the interior by means of a hinge comprising a pair of. lugs 25 secured to the lid, a pair of lugs 26 secured to the casing and a pivot pin assembly 21. The lid is releasably held in place by a plurality of bolts 28 having special dustproof or blind-ended nuts 29 threaded thereon. Bolts 28 fit through slots 30 in a pair of cross pieces 3| secured to lid l6, and are received with considerable clearance in lugs 32' secured to housing H so that nuts 29 need carried upon a shaft 38,'which maybe mounted of counter-sunk screws 49.

merely be loosened and bolts 29 rocked out of slots 38 in cross pieces 3| to permit the lid to be lifted into opened position.

' Secured to side wall I2 of housing H by means of nut and bolt assemblies 33 and angle brackets 34, is an abrasive rebound guard 35 whose funcfor rotation in any suitable manner, but which is supported in the present instance by means of a pair of axially spaced bearings 39 which are provided with arms 4| for securing them to the base. As. the shaft and bearing arrangement forms no part of the present invention, only one bearing assembly has been shown in order to simplify the disclosure.

Power may be applied to shaft 38 in any suitable manner and it extends into housing H through an opening defined by notches 42 and 43 formed respectively in base l8 and housing side wall l2. Supported on the shouldered end of shaft 38 is a heavy disc 45 and it is preferably keyed thereto in any suitable con'ventional manner. Disc 45 is restrained against axial displacement from shaft 38 by means of a plate 48 which bears against the end face of disc 45 and is 'secured to shaft 38 by two machine screws 41.

The abrasive propelling elements of my machine are carried by a rotatable runner head or rotor 48 which is secured to disc 45 by a plurality Runner 48 is provided with a peripheral flange which operates to restrain the abrasive propelling blades against outward movement in response to centrifugal force. The abrasive propelling blades are preferably four in number and are designated generally at B. Blades B are secured in place in preferably symmetrical relationship on runner 48 in a manner similar to that employed in the aforesaid copending application, and with reference to Figures 1 and 2, four sector-shaped guide plates 53 are secured in place on head 48 by means of counter-sunk screws 54, and their edges are beveled so that adjacent sides of each pair of guide plates will form a dove-tail groove. The side edge of each blade B is provided with a correspondingly beveled face 55, so that when blades B are inserted in the center of the machine and I and with reference to Figures 1 and 2, each blade slid outwardly into position between the guide plates they will be flrmly held against movement. Annular flange 5| prevents the blades from moving outwardly in response to centrifugal force and a bowed leaf spring 58, fitting in a groove 51 provided in each blade, frictionally restrains each blade against inward movement. As the blade restraining means forms no part of the present invention it will not be further described.

Referring to the configuration of the blades,

B is provided with a substantially flat abrasive propelling surface 59, which extends from .the outer end of the blade to a region near the inner end thereof. The inner end of each blade is preferably provided with a curved abrasive pickup surface 8| for a purpose that will presently appear. With reference to Figure 1, each blade (in this instance upper blade B) is provided with a pair of abrasive guiding flanges 82 and 83. Flange 82 is substantially parallel to runner head 48 whereas flange 83 inclines toward the runner head at its outer end. Flange 83 is inclined in view of the fact that the velocity of the abrasive increases as it-approaches the outer end of the blades and accordingly'narrows down to a thinner stream. Hence theblade is wider at its inner end in order to insure that the abrasive will not escape laterally from the blade as it is initially contacting therewith and is in a less contracted condition.

The mechanism I preferably employ for feeding abrasive into the space defined by the inner ends of the propelling blades will now be described. a

Bridging a semi-circular recess 88 provided in base I8 is an arm or bracket 81 which is provided with a forwardly and downwardly curving portion 88. Portion .88 is reinforced by means of a plurality of webs which join it to arm 81. Arm 8! may be secured to base l in any suitable manner, but I preferably employ a r pair of studs 89 which are secured in base I8 and tioning set screws 14 for cooperation with studs.

89, each having a locknut l5 turned thereon. To properly adjust positioning screws 14, arm or bracket 81 is put in place on base l8, nuts II are taken up lightly, and arm 81 is then by experiment or measurement brought into the proper position. Nuts 12 are then taken up tight. Positioning screws 14 are then screwed up to take up the lost motion between them and studs 89,

and locknuts 15 are then screwed into place to maintain the positioning screws in the proper set position. If desired, however, positioning screws 14 may be manipulated while nuts 12 are partially loosened and arm 81 is, being maneuvered into proper position.

The forward face of the curved portion 88 of arm 81 is provided with a circumscribing flange 11 having vertical and horizontal portions. Secured to the forward face of portion 88 by three nut and bolt assemblies 19 and having a rabbeted portion 18 conforming to the flange of portion' 88, is a holder 8|. Holder 8| provides a combined'spout and cage or distributor support.

Holder 8| is accordingly stationarily but removably secured to base l8, and it is provided with a preferably integral spout portion 82 which has an overhanging lip 83 for cooperation with the impeller in a manner to be hereinafter pointed out. Spout portion 82 is provided with a funnel or spout extension 84, and although these parts may be integrally formed, I preferably form them in two pieces to facilitate casting of the parts.

They are fastened together by pairs of lugs 85 formed on the respective members and nut and bolt assemblies 88.

Abrasive introduced into spout 84 is conveyed into a cage or receptacle which is carried by holder 8|, and which is designated generally at C. Cage C is provided with a generally cylindrical portion 81, a deep, preferably imperforate flange 88 anda shallower flange 9| in which four notches 89 are provided. Notches 89 correspond in number and spacing to the blades of the impeller, to be described hereinafter. Cage flange 9| is plloted or centered upon a cylindrical hub or flange 92 provided on holder 8|. Cage-C is also provided with a recessed face 98, and an element 98 covers slots 98 in holder 8|. Cage C is-preferably adjustably supported for angular rocking movement about the axis of the machine upon holder 8i in the following manner:

Preferably a pair of diametrically opposite studs 91 are secured in flange SI of cage C and extend through apertures in slot cover 84. Studs 91 extend through arcuately-shaped slots 98 in holder 8|, as shown in Figure 3', and a pair of.

nuts 99 are turned thereon to releasably clamp cage C to holder 8|. As seen in Figure 1, nuts 99 are of special form as their ends are closed to exclude dust and abrasive from the threads, and they provide hex" manipulating heads which are disposed a considerable distance from cage C in order that the nuts may be readily loosened and. manipulated during the cage adjusting operation. Nuts 99 also provide convenient operating handles which may be grasped for rocking cage C into proper angular adjusted position after they are loosened. Cage C is also provided with a discharge slot or opening I00, which inclines forwardly with respect to the direction of rotation of the runner, as seen in Figure 2.

the heads of machine screws 41.

I preferably employ an impeller or agitator within cage C which rotates synchronously with runner 8; for insuring a proper feeding of the abrasive to the propeller blades B. The impeller. or agitator is preferably equipped with the same number of blades as are present on runner 40, v

and in the present case they are four in number. Impeller blades IOI are joined at one end by. a cone-shaped cylindrical portion I02 providing a truncated cone-shaped internal abrasive feeding face, and into which lip 83 of spout 82 projects. Blades Il are joined at their other ends by'a generally cup-shaped member preferably providing a circular abrasive ballling flange I03, and a deep cylindrical flange or hub I04 in which a pair of diametrically opposed slots I05 are formed.

The impeller is preferably secured to the runner assembly by means of a long cap screw I 06 which passes through an aperture in the central part of the impeller and plate 48, andis threaded into shaft 38. Cap screw I 06 pulls the impeller with its flange I04 into tight engagement with plate 48 and with its slots I05 embracing By reason of slots I05 in the impeller flange fitting over screws 41, it is impossible to improperly assemble the impeller with the runner assembly, as these parts mustbe in alignment before cap screw I06 may be brought into its final tightened position. With reference to Figure 1, flange I03 of the impeller extends outwardly beyond flange 88 of cage C,

with the result that they are radially overlapped and abrasive leakage is minimized, because the abrasive in cage C would have to take a tortuous path in order to escape therefrom. In order to minimize abrasive leakage over flange 9|, one wall I01 of each of slots 89 formed therein is beveled, and as seen in Figure 4 they are beveled in a direction to assist in maintaining the abrasive in cage C.

Although I have termed blades B propeller blades, and blades IOI impeller blades, their action upon the abrasive is somewhat similar because in each instance the abrasive is picked up by the inner end of the blades and is impelled or propelled outwardly over the blade and is smoothly and continuously accelerated without abrupt changes in a substantially radial direction" Blades IOI until it reaches the tips of. the blades. are also distributor blades as they serve to break up the abrasive stream entering cage C into a readily distributable form, and to impart an initial velocity to the abrasive prior to its being picked up by the propeller blades, and the latter it is seen that each impeller blade IOI- is dis-- posed at a predetermined angle of advance in the direction of rotation of the runher with respect to its propelling blade B. This relationship is established between the impeller and propeller blades so that --the abrasive .which is churned around in cage C will be discharged through slot I00 a predetermined angle in ad- Vance of each blade B. This synchronized or coordinated action of 'the impeller and propeller blades insures that the abrasive will be positively thrown out into the path of the propeller blades, and by reason of the angular velocity component of the-abrasive, and the rearward inclination of the inner ends of the blades, the abrasive is picked up with a minimum impact. This also results in a more restricted or contracted discharge from the wheel. Impeller blades IOI are also provided with concave faces I08 which face forwardly with respect to the direction of rotation of the runner assembly so that the abrasive impelled thereby will be confined to the width of the blades, and Will accordingly be discharged through slot I00 onto blades B in a more contracted form. By confining outward flow of the abrasive over blades B to a narrower lateral area, less power is required to drive the wheel. and the discharge from the runner is of a more concentrated character.

Operation The work is placed under the machine opposite the discharge opcning and it is to be understood that the work may assume. various forms and may be moved in various ways while it is treated. For instance. the work may be located in a tumbling device or may be mounted on a truck to be moved about under the machine to expose various parts to the blast. Moreover, the

work may be passed through a cabinet, and the machine mounted for oscillation about different axes in order to subject the work to the blast at various angles. Also, the work may be passed through a suitable cabinet or housing in strip or sheet form and subjected to the action of one or Y portions of the various parts as shown, and with ably metal grit) is preferably allowed to drop by gravity into spout 84, and it is preferably medrawings, I find that a speed of approximately 2500 R. P. M., in the direction indicated in Figure 4 is suitable for satisfactory operation of the machine. Cage C is mounted on holder 8| in the position shown in, the drawings at the factory, and it has been found that. with the prothe discharge opening I00 located as shown in Figure 2, the discharge from the machine will be properly located when the machine is rotated at the proper speed.

However, if it is found upon operating the machine that the .discharge is not directed as desired, nuts 99 may be loosened and manipulated to rock cage C and thereby change the angular relationship of abrasive discharge slot I00. As the point at which the abrasive stream leaves the wheel is determined by the point at which the abrasive is admitted to the inner ends of the propeller blades, and as the time it takes for an abrasive particle to traverse the blade depends upon the length of the blade and to some extent upon the nature of the abrasive, it is apparent that by rocking cage C so as to vary the angular position of slot I00, the angular range over which the discharge from the machine will occur may be correspondingly varied.

Assuming that the machine is properly adjusted, and the rotor has been brought up to speed, .an abrasive of any suitable form, (prefertered as by means of a screw or other conveyor operating at a predetermined constant speed.

Rotation of runner head 48 causes blades B and impeller blades i0l to establish a partial vacuum in the axially extending passage defined by the inner ends of the impeller blades and in the lower end of spout 84, so that the abrasive entering the spout is picked up by a rapidly moving air stream and enters the impeller with a predetermined degree of initial velocity. The abrasive is then impelled outwardly over concave portions of the impeller blades, and when it reaches the blade tips it is churned around or agitated within cage C. A dispersion of' air and abrasive which rotatesforwardly with respect to the direction of rotation of the runner assembly is thereby established, and also a stationary or slowly moving film of abrasive lodges on the interior of cylindrical portion 81 of cage C, and thereby protects it from excessive wear. Cage flanges 88 and 9| serve to confine the abrasive within the cage as it is being agitated.

The forwardly rotating dispersion of sand and air is of fairly uniform intensity but it is naturally of somewhat more concentrated character immediately in front of the leading face I 000i each impeller blade. By reason of the angular advance of each impeller blade with respect to its corresponding propeller blade, the concentrated streams of abrasive on the leading faces of the impeller blades are thrown outwardly through slot I00 in such manner, and at such a time that the inner curved end SI of blade B will properly pick them up with a minimum of impact and splash. As the abrasive is exhausted through slot I00, it possesses angular as well as radial velocity in view of the impelling action of blades IN. This feature, when taken in connection with the fact that the inner ends of blades B are curved, operates to minimize any abrading action that may take place as blades B initially pickup the abrasive. The abrasive accordingly travels outwardly and angularly,

and as the tangential component of the velocity of an individual particle of abrasive is not greatly lower than the velocity of the inner ends of blades B, wear of the latter is minimized.

As the abrasive is forwardly rotated in cage C under the influence of impeller blades l0l it is confined by flanges 80 and 9| and it will be seen that if any stray abrasive should leak between cage C and holder 8| and the sides of spacer member 94, the abrasive so escaping can do no harm as it is located within housing H and hence will merely gravitate or be impelled out of the discharge opening thereof. Moreover, as these parts merely function as a funnel or chute for introducing the abrasive into the impeller, there is no tendency for an air or abrasive leak to develop due to the arrangement and location of the parts. It is accordingly unnecessary to provide an air or abrasive tight joint between the cage and the holder.

In view of the fact that disc 45 and runner head 48 ,are permanent parts, as distinguished from certain other parts of the device, which are frequently replaced and hence are replacement parts, it is desired to completely protect these permanent parts against abrasion. The end of disc 45 is protected by wear plate 46, which may be replaced in a manner to be hereinafter described when it has become worn excessively by stray abrasive. The impeller and cage and blades B may likewise be replaced and in connection with blades B, it should be observed that as the abrasive travels outwardly over surfaces 59 of each blade, it is prevented from laterally escaping from the free edge of the blade by flange 63, and it is prevented from abrading runner head 48 or guide plates 53 by flange G2, which keeps the abrasive, spaced a considerable distance from these parts;

The abrasive is therefore supplied to the inner ends of blades B in a predetermined limited angular region, and as it travels outwardly, each particle defines a spiral path and is directed against the work over a definite region. Therefore, none of the abrasive, properly discharged from the opening I00, strikes any of the stationary parts of the device. However, a minute amount of stray abrasive is sometimes admitted to the blades in a region other than that ad- ,jacent discharge slot I00, and this abrasive, as it is discharged from blades B (Figure 2), strikes ing H, the abrasive is given a chance to expand I ner head 40. If it is desired to inspect the runner blades or other parts of the device located in the upper portion of housing H, nuts 28 may be loosened and lid l6 lifted to expose the interior of the cabinet.

When it becomes necessary to replace blades B it is merely necessary to loosen nuts I2, remove nuts 99, so as to detach cage C, from the holder,

and pull the entire feeding assembly (with the exception of cage C) axially to the right, and remove it from the machine. It is then possible to reach into the comparatively large opening and remove the single cap screw I86 which holds the impeller in place and remove the impeller and cage C as a unit from the machine. After the impeller and cage have been removed from the machine they may be disassembled by aligning impeller blades ml with notches 89 of flange 9|.

After cage C and the impeller have been removed in the manner just described, blades B maythen be individuallyslid inwardly to the large central space and then withdrawn and replaced by new blades. At this time, wear plate 46 may also be renewed, if necessary, by removing machine screws 41. After the new blades are in place and plate 46 is secured to shaft 38, the impeller (or a new one if it requires replacement) is then put in place with cage C and the impeller and aligned with screws 41 as previously described. Although as illustrated I preferably employ a wear plate 46 which is separately formed from the impeller because these parts wear at different rates of speed, they may if desired be made integral without departing from the spirit of the present invention. In the event that plate 46 and the impeller are integrally formed, screws 41 are dispensed with and dowel pins or the like employed to cooperate with openings in member 45 for properly positioning the impeller in-the device, and also notches 89 will be formed in flange 88 instead of flange 9|, in order to facilitate assembly of the impeller with the parts. Moreover, in the two part construction shown, notches 89 may be provided in flange 88 instead of flange BI, and in such case the entire feeding assembly, including cage C may be removed by merely loosening nuts 12 and aligning the impeller with notches 89.

After the parts just described have been put in place, the remaining parts of the feed assembly may be slid to the left toward the opening in the machine. The cage is then secured to the holder by nuts 99 and the holder assembly is slid over studs 69 until it is arrested by contact of positioning screws 14 with the'studs. Nuts 12 are then tightened and the machine is ready for operation. In this connection it should be observed that the horizontal contacting bearing faces provided on bracket 61 and base III are of considerable area, which forms an adequate support for the feed assembly.

Although I have illustrated and prefer to employ a runner assembly'embodying four impeller blades and four propeller blades, it is to be understood that if desired the number of blades in each set may be one or more blades, depending upon the'size of the wheel and the abrading characteristics desired. In any event, however, an equal number of blades is employed in each set, in order that the impeller may discharge the abrasive through slot Hill a predetermined angular degree in advance of the inner ends of the propeller blades and bring about the beneficial results previously discussed. It is to be understood, however, that insofar as the other novel features of my machine are concerned, an

unequal number of impeller and propeller blades may be used without sacrificing the advantages of those features. .7- r

. Although Ihave illustrated cage Gas-being adjustably mounted upon spout holder 8|, and I prefer to employ this arrangement as it makes it possible to maintain the spout in a fixed position irrespective of the adjusted position of the cage, it is to be understood that if desired these parts may be permanently connected or'integrally formed, and arcuately-shaped slots provided,

and determined the proper angle of advance of the impeller blades with respect to the propeller blades, and which remains fixed throughout the life of the machine, it is to be understood that if it is desired to operate the machine in a manner that requires it, slots I85 in impeller flange I84 may be elongated so as'to provide a predetermined range ofadiustability of the impeller with respect to the runner, and the appended claims are intended to embrace my machine when it assumes this form. Moreover, I prefer to use the positioning means shown as it is of simple form and does not entail the use of additional parts, but I may if desired, especially if an adjustable impeller is used, employ a dowel pin on one of the parts which may be selectively engaged with one, or with one of a plurality of holes located in another of the parts for positively or selectively adjusting the impeller respectively, without departing from the spirit of the present invention.

In Figure 6 I have shown a modified form of cage C for use in the machine shown in Figures 1 to 5, inclusive. Cage C is provided with an abrasive discharge slot a, having a preferably plane wall H0, which is substantially tangentially disposed with respect to the path of the tips of blades IN, and a preferably plane inclined wall Ill.

This cage assembly has been found to have an extremely long life by reason of the abrasive striking the parts in such manner as to avoid recurrent rebounding of the abrasive on the inner surface of cylindrical portion 81a of cage 0', thereby avoiding the wearing of pits or other surface irregularities in the cage. Assuming that the machine is operating at the proper speed and that abrasive is fed into the cage in the manner described in connection with the first form of my invention, the abrasive is churned around in the cage and when each blade reaches opening I 00a it discharges a predetermined quantity of abrasive therethrough and onto the inner end of its corresponding propeller blade. A small quantity of abrasive however fails to be discharged through opening lllfla and strikes wall III of opening 18a, and this abrasive, by reason of the inclination of wall III, is smoothly guided back into cage C and is carried around therein, without rebounding against wall 81a, until it is brought around into the proper position to be discharged through opening lfliia. With this structure I have found that the cage, when it has worn sufficiently to require replacement, is uniformly worn throughout the extent of the inner surface of its cylindrical portion 81a of the cage without the formation of pits or other sur face irregularities.

The terms runner and rotor" employed in the appended claims are intended to embrace the blade carrying member irrespective of whether it is made in one piece or is as a matter of fact integrally formed with shaft 38, or is made up of two members and 48 and secured to shaft 38 vs shown in the drawings. Moreover, I prefer to support the propelling blades at one edge only, but it is to be understood that the invention embraces runner assemblies having an apertured side plate secured to the other edges of the blades or other similar constructions.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by 'United States Letters Patent is:

1. In an abrading machine, a rotor having a plurality of blades terminating short of the axis of said rotor to define an abrasive admitting space, an abrasive feeding device of an external diameter less than the radius of the rotor extending into said space and having a discharge opening therein disposed to one side of the axis of said rotor and located between the planes of rotation defined by the sides of said blades for delivering abrasive to the inner ends of said blades, said blades terminating sumciently close to said feeding device to pick up the abrasive with a minimum impact and said blades having substantially smooth and uninterrupted abrasivepropelling surfaces of suificient length to accelerate the abrasive smoothly and continuously and without abrupt changes in a substantially radial direction and discharge it from the outer ends of said blades at an abrading velocity when said rotor is rotated, a rotatable impeller mounted for synchronous rotation with said rotor and comprising a plurality of impeller va'nes disposed within said feeding device, said' vanes being equal in number to said blades and extending to a region closely adjacent the axis to define a comparatively small axially extending passage, and means for introducing abrasive into said passage and over the inner edges of said vanes, said vanes being operable to impel predetermined quantities of abrasive through said discharge opening and into the path of the inner ends of said blades in timed relationship thereto.

2. In an abrading machine, a rotor having a plurality of blades terminating short of the axis of said rotor to define an abrasive admitting tion defined by the sides of said blades for delivering abrasive to the inner ends of said blades,

radial direction and discharge it from the outer ends of said blades at an abrading velocity when said rotor is rotated, a rotatable impeller comprising a plurality of impeller vanes disposed within said feeding device, said vanes extending to a region closely adjacent the axis to define a comparatiyely small axially extending passage, the forward face of each impeller vane being concave in transverse section, and means for introducing abrasive into said passage and over the inner edges of said vanes, said vanes being operable to impel a contracted stream of abrasive through said discharge opening.

- 3. In an abrading machine, a rotor having a plurality of blades terminating short of the axis of said rotor to define an abrasive admitting space, an abrasive feeding device of an external diameter less than the radius of the rotor extending into said space and having a discharge opening therein disposed to one side of the axis of said rotor and located between the planes of rotation defined by the sides of said blades for delivering abrasive to the inner ends of said blades, said blades terminating sufliciently close to said feeding device to pick up the abrasive with a minimum impact and being operable to discharge it from the outer-ends of said blades at an abrading velocity when said rotor is rotated, a rotatable impeller comprising a plurality of impeller vanes disposed within said feeding device, said vanes being joined adjacent said rotor by a generally circular flange, said vanes extending to a region closely adjacent the axis to define a comparatively small axially extending passage, and means for introducing abrasive into said passage and over the inner edges of said vanes, said vanes being operable to impel abrasive through said discharge opening, said feeding device having an inwardly extending abrasiveretaining flange disposed between said generally circular flange and said rotor and having an internal diameter which is less than the external diameter of the latterflange, whereby they are radially overlapped to minimize abrasive leakage.

4. In an abrading machine, a housing, a rotor mounted for rotation in said housing and having a plurality of blades thereon, said blades terminating short of the axis of rotation of said rotor to define a central abrasive admitting space, an abrasive feeding device having an external diameter less than the radius of the rotor disposed in said space and having a discharge opening therein disposed toone side of the axis of said rotor and located wholly between the planes of rotation defined by the sides of said blades for delivering abrasive to the inner ends of said blades, said feeding device being located wholly within said housing and having an axial length which is only slightly greater than the width of said blades, said blades being operable to pick up said abrasive and discharge it from the outer ends of said blades at an abrading velocity'when said rotor is rotated at a predetermin'ed speed, a stationarily supported conduit extending into said housing for delivering abrasive to said feeding device, said conduit and feeding device having a joint located wholly within said housing for placing them in fluid communication, and a rotatable means disposed in said feeding device for impelling abrasive through said discharge opening.

5. In an abrading machine, a housing, a rotor mounted for rotation in said housing and having a plurality of blades terminating short of the axis of rotation of said rotorto define a central abrasive admitting space, an abrasive feeding device having an external diameter less than the radius of the rotor disposed in said space and having a discharge opening therein disposed to one side of the axis of said rotor and located wholly between the planes of rotation defined by the sides of said blades for delivering abrasive to the inner ends of said blades, said feeding device being located wholly within said housing and having an axial length which is only slightly greater than the width of said blades, said blades being operable to pick up said abrasive and discharge it from the outer ends of said blades at an abrading velocity when said rotor is rotated at a predetermined speed, a stationarily supported conduit extending into said housing for delivering abrasive to said feeding device, said conduit and feeding device having a joint located wholly within said housing for placing them in fluid communication, and a rotatable means disposed in said feeding device for impelling abrasive through said discharge opening,-

said joint comprising means for securing said feeding device and said conduit together in angularly arUustable relationship, whereby said feeding device is supported upon said conduit.

6. In an abrading machine, a rotor having a plurality of blades terminating short of the axis 0! said rotor to define an abrasive admitting space, an abrasive feeding device of an external diameter less than the radius oi the rotor extending into said space and having a discharge opening therein disposed to one side of the axis of said rotor and located between the planes of rotation defined by the sides of said blades for delivering abrasive to the inner ends of said blades, said blades terminating sufliciently close to said feeding device to pick up the abrasive with a minimum impact and arranged to discharge it from the outer ends of said blades at an abrading velocity when said rotor is rotated, a rotatable impeller mounted for synchronous rotation with said rotor and comprising a plurality of impeller vanes disposed within said feeding device, said vanes being equal in number to said blades and being so angularly positioned with respect thereto as to impel abrasive through said discharge opening onto the inner ends or said blades in a predetermined timed relationship thereto, a single centrally disposed fastening device extending through said impeller and secured to said rotor for firmly holding the said impeller to the latter, and means for preventing said impeller from being assembled in said rotor in any position other than its proper angular position, comprising a projection provided on said rotor and extending into a recess provided in said impeller remote from said impeller securing means, and means for introducing abrasive into said feeding device.

WALTER L. KEEFER.

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