US2205414A - Abrading apparatus - Google Patents

Description

June 25, 1940. w. L. KEEFER ABRADING APPARATUS Filed Oct. 15, 1957 3 Sheets-Sheet 1 1 ML su- MM ,1 X

Jlm 1940. w. 1.. KEEFER ABRLDING APPARATUS Filed Oct. 13. 1937 5 Sheets-Sheet 2 ill 1 a" m "EH7 lHl llY/ Wo/zer L Keefer Snow/aw June 25, 1940. w. L. KEEFER ABRADING APPARATUS Filed on. 1a, 1957 3 Sheets-Sheet 3 a rtouwyp Patented June 25, 1940 UNITED STATES PATENT OFFICE 2,205,414 ABRADING APPARATUS poration of Maryland Application October 13, 1937, Serial No. 168,799

18 Claims.

The present invention relates to abrading apparatus and it is more particularly concerned with apparatus for mechanically picking up abrasive and centrifugally discharging it at abrading I velocities in any desired direction to surface clean castings and other articles of work.

Abrading machines are in use today embodying bladed rotors for propelling abrasive, wherein the abrasive is fed over the inner end of lothe blades and they require the use of an impeller and impeller cage for securing proper directional control of the propelled abrasive. Although these machines are successful from a commercial standpoint they are not perfectly satisfactory because the impeller and impeller cage add a complication and also are further elements to wear out and require replacement. Impeller machines also require more power to operate them by reason of the frictional loss in churning the abrasive within the impeller cage.

Also machines are known to the art in which no impeller or impeller cage is used, but in all cases in such machines the abrasive feeds across the sides of the blades and not to the inner ends as in the present invention: Feeding over the sides of the blades so blocks or interrupts the flow of the abrasive from the feed spout that such wheels are relatively inefiicient due to the large percentage of splashed abrasive and can only be fed in small quantities, not suitable for production demands.

It is accordingly the primary object of this invention to provide an abrasive propelling machine capable of throwing abrasive in any desired direction and yet which does not require the use of an impeller and impeller cage for feeding abrasive to the blades.

It is a further object to provide an abrading machine having a gravity abrasive feed device in combination with a rotor designed to effect discharge of the abrasive from the rotor in the desired direction.

Another important object is to provide an abrasive propelling rotor having blades which retard movement of the abrasive thereover so as to predetermine the direction in which the abrasive is discharged from the rotor.

My invention also aims to provide a novel mechanism for releasably holding the blades of an abrasive propelling rotor in place and which securely maintains them in proper position during operation and yet which may be readily operated to release the blades for replacement when desired.

Another object is to provide a centrifugal blades.

A further object is to provide novel abrasive propelling blades for use with rotors of centrifugal abrading machines.

It is another object to provide novel blades for use in abrading machines and embodying a surface designed to retard outward movement of the abrasive thereover, the blade having a pocket thereon adapted to gather or concentrate the abrasive before it is propelled by the retarding surface of the blade.

This application is a continuation-in-part of my copending application Serial No. 33,185, filed July 25, 1935, now Patent No. 2,108,005 and further objects of the invention will become apparent as the specification thereof proceeds in connection with the annexed drawings, and from the appended claims. In the drawings:

Figure 1 is a vertical sectional view of one form of apparatus embodying the invention and shows the feeding device mounted in cooperating relationship with the rotor.

Figure 2 is a sectional view taken on the line 22 of Figure 1, looking in the direction of the arrows.

Figure 3 is an end elevational view of another form of machine embodying the invention and 30 parts have been broken away to show the constructlon.

Figure 4 is a vertical sectional view of the machine shown in Figure 3 but the spout and cage have been shown in. elevation in order to clarify the illustration.

Figure 5 is a fragmental top plan view of the face plate employed in the machine shown in Figures 3 and 4.

Figure 6 is a vertical fragmental sectional view illustrating the outer edge of the rotor and shows one form of vane locking ring that may be used in the machine.

Figure 7 is a view similar to Figure 6 but illustrates a modified form of locking means for the vanes.

Figure 8 is a fragmental face view of the rotor employed in the machine and illustrates one blade mounted thereon and shows a portion of the feed cage in section.

Figure 9 is a view looking at the outer end of the blade shown in Figure 8.

Figure 10 is a top plan view of the blade shown in Figure 8.

Figure 11 is a side elevational view of a modifled form of blade and which may be used in the machine previously described.

Figure 12 is a side elevational view of a further modified form of blade, together with a guard or baille cooperating therewith.

Figure 13 is a side elevational view of a still further modified form of blade, and

Figure 14 is a side elevational view of another modified form of blade together with a baille cooperating therewith.

With continued reference to the drawings, wherein like reference characters have been employed to designate like parts throughout the several views thereof, and with particular reference to Figures 1 and 2, I have somewhat diagrammatically illustrated one form of abrasive propelling wheel embodying the invention, and the component parts will be taken up separately.

A rotor I is supported on a shaft H and the latter is carried by bearings in any suitable manner. One or more blades may be mounted upon rotor ill, but in the present instance I have shown four blades l2 as being carried by the rotor, each blade having a short, substantially radially disposed surface I3 and a long propelling surface H of preferably curved configuration. Each blade is preferably rounded at its inner end at l5, to reduce the abrasive blocking action of the blades as they pass the discharge opening in the feed mechanism, and each blade is'also provided with an abrasive retaining flange i6.

Supported for adjustable rocking movement in any suitable manner adjacent the rotor is a feeding device l8, which is of generally cylindrical form and extends into the central space between the inner ends of the blades, and it is provided with an outer cylindrical surface IS; an abrasive feeding passage 2| having a mouth 22 terminating adjacent the inner ends of the blades; and a spout 23 into which the abrasive may be fed by any suitable mechanism.

The machine accordingly embodies no impeller and the abrasive may gravitate freely down through spout 23 and be picked up by the inner ends of the blades. Assuming that the rotor is operating at the desired speed (preferably from 2000 to 2500 R. P. M.), and that spout 23 is supplied with abrasive, the latter gravitates through passage 2| and on through the inner ends of" blades l2, and by reason of the substantially radial disposition of surface l3 of each blade the abrasive is picked up with a: minimum of "backwash and splash, and is given an initial outward acceleration.

When the abrasive reaches curved surface H of each blade it is subjected to an accelerating influence of smaller magnitude because, as seen in Figure 2, this part of the blade surface is disposed at an angle too, or is inclined outwardly and forwardly with respect to the direction of rotation of the rotor.

The effect of centrifugal force upon the abrasive is therefore counteracted by the inclination of surface i4 and abrasive accordingly travels more slowly over the blades than when radially or rearwardly inclined blades are used. The abrasive accordingly may be said to be retarded, when the term is employed in a comparative sense using a radial bladed rotor as a standard.

It accordingly takes more time for the abrasive to travel outwardly over the blades, and advantage is taken of this fact to adjust the point of discharge of the machine by selecting the inclination of the blades to give the desired discharge. In other words, the feeding mechanism,

being of thegravity type, must always feed generally downwardly, and therefore the angle through which the the abrasive is carried by the blades must be computed from the downward position as a starting point.

In the present instance the discharge from the rotor is seen to be horizontal, as at 24, or at a point about 180 from the point of admission of abrasive to the blades. It is of course understod that minor adjustments in the direction of the discharge may be eflected by rockably adjusting feeding device 23 so as to properly adjust the point of admission of the abrasive to the blades.

Irrespective of the inclination of the blades in a particular installation, the abrasive is discharged from the blades at a speed which is substantially equal to the linear speed of the blade tips, and the abrasive discharge means takes a direction substantially tangential to the path of the blade tips, because the radial component of the final velocity has been suppressed or reduced by the forward inclination of the blades.

In Figure 2 the tip of each blade I2 is seen to be disposed at an angle a: with respect to a radius r drawn through its inner edge, and it is to be understood that this angle may be increased or decreased depending upon whether it is desired to have the machine discharge at a greater or less distance from the point of admission of abrasive to the blades. Angle a: may assume a wide variety of values, but its upper limit is determined by value at which the abrasive, after admission to'the blades, will not be propelled outwardly thereon. This limiting value will vary with the type of abrasive used and the condition of the surfaces of the blades, and therefore is governed by the angle of repose of the particular abrasive used and upon the surface of the blade employed.

Although surface H has been illustrated as of curved concave configuration, it is to be understood that it may be of plain or convex shape or assume the forms of the subsequently described blades without departing from the spirit of the invention. A further important advantage secured by reducing the outward radial velocity of the abrasive resides in the fact that blade wear is materially reduced.

Referring now to the machine illustrated in Figures 3 to 10, inclusive, and with particular reference to Figures 3 and 4, the wheel is mounted within the housing having a rear plate 30 which isv covered by the wear plate 3| and a front plate 32 which is in turn covered by a wear plate 33. The housing is mounted upon a base 34 in any well known manner.

A shaft 35 is journaled in bearings (not shown) and carries a flange 36 to which the rotor proper 31 is secured by means of a plurality of screws 33.

Secured to rotor or head plate 31 by means of a central screw 39 and a plurality of screws 4| located adjacent the periphery of the head is a guide plate 42. As seen in Figure 5, plate 42 is provided with a plurality of non-radial slots 43, each of which terminates in a large end 44 which provides clearance for the inner ends of the blades. Theside walls of slots 43 function as guides for the abrasive propelling blades and to this end they are provided with bevelled or inclined faces 45. The guides are preferably one thirty-second of an inch wider at their outer end than at their inner end in order to facilitate removal of the blades, especially when fine ab asive finds its way between the blades and guides. As indicated at 4B the plate may be cored out if desired to lighten it.

As bestillustrated in Figure 9, a plurality 'of abrasive propelling blades B are associated with the rotor and they each are provided with aflat base 48 which abuts head plate 31. They are also provided with inclined side faces 49 and 5| which cooperate with inclined faces 45 of plate 42. The face 48 of the base of the blade is preferably-disposed at approximately 88 with respect to the abrasive propelling face of the blade, and suflicient clearance is provided so that when the machine is in operation and the blades are placed under load they will rock into the position shown and dispose their abrasive propelling surfaces substantially normal to'the face of the rotor. By proceeding in this manner sufllcient clearance may be provided between the parts so as to allow the blades to be slid freely out of the machine and yet when the machine is in operation they will be disposed accurately in abrasive propelling position. The base of the blade is preferably so formed as to provide a recess 53 for a blade retaining spring (not shown).

As best seen in Figures 8 and 9, each blade is provided with an abrasive retaining flange 54, which is comparatively straight for the major part of the length of the blade, and which merges into a deeper retaining flange 55 at the inner end of the blade.

The inner extremity of the blade provides an abrasive propelling pick-up surface 55 which curves sharply back with respect to the direction of rotation of the rotor and merges with a curved gathering surface or pocket 51. and the latter in turn merges with a substantially straight abrasive propelling surface 58. As shown in Figure -8, the rear surface of the inner blade tips, designated as 56a, recedes so as to avoid contact with the severed end of the abrasive ribbon.

As the abrasive is fed on to the blade by the feeding means to be hereinafter described, surface 55 rapidly picks it up and in view of the rearward inclination of this surface the impact at the moment of pick-up is comparatively small. Just subsequent to pick-up the abrasive is "gathered or concentrated on curved surface 51 and then starts to move outwardly comparatively slowly over straight surface 58. In View of the factthat in this form of wheel the abrasive is retained on the blades for approximately one revolution, if the abrasive were not ='gathered" it would spread out during discharge so as to undesirably increase the discharge angle from the rotor. By providing a pocketed end on the blade the portion of the abrasive ribbon that is cut off is maintained substantially intact until it attains the main propelling surface 58.

Blade locking mechanism The preferred form of blade retaining means is illustrated in Figure 6 and with continued reference to this figure, rotor 31 is provided with a plurality of short plugs 6| which are secured in place in the periphery of the rotor in any suitable manner. Mounted for axial sliding movement upon plugs 6| as bearings, is a comparatively massive locking ring 62, having an,

inclined abutment surface 63 and a radial abutment surface 6 1. Each blade B is provided at its outer end with an inclined surface 65 and it is preferably of frustro conical shape, so as to cooperate in full surface engagement with abutment wall 53.

The blades are removed from the apparatus simply by moving them inward a slight distance sufficient toallow the inner periphery of abutment-surface 63 to clear the blades and ring 62 is then moved to the right into the dotted line position. The blades may then be freely moved outwardly from their guides.

In view of this comparatively small bearing surface presented by plugs 6|, any abrasive that finds its way between the ring and the, periphery of the rotor cannot set up a binding action and resist ring removal. Also, in order to reduce the amount of abrasive that rebounds between the parts, rotor 31 and ring 62 are provided with step formations 66 and 61 respectively. Therefore,

should stray abrasive in its movement outwardly certain features in common with that just described because it embodies a ring 62a mounted on the periphery of rotor 31a and has an inclined abutment face 63a disposed in the path of movement of blades B. inclined outer ends 650. and ring 62a, rather than being slidably mounted upon the outer portion of the rotor, is provided with an annular flange 1| which seats in annular groove 12 in the rotor.

The blades are removed in this form of the invention by moving them inwardly sufliciently to allow ring 62a to clear their outer ends and then the ring 62a is moved axially to the left and completely removed from the machine. Blades B may then be freely moved outwardly in their guides.

Feeding mechanism Any desired form of feeding mechanism may be employed to introduce abrasive over the inner ends of the blades but I prefer to employ the novel feed assembly shown in Figures 3, 4 and 8 as it has proven very satisfactory in service. The feeding device preferably comprises a generally cylindrical cage 15 which is disposed in the central space defined by the inner ends of blades B and it is provided with a plurality of rebound surfaces 16 for a purpose that will presently appear.

Cage 15 terminates in a flange 11 and is secured, by means of studs and nuts, toa member having a flange 18. The assembly extends through aligned openings in wall 32 of the housing and liner 33.

As seen in Figure 3 the opposite sides of flange 18 are enlarged to provide for the formation of a pair of arcuate slots 19 and 8|, a pair of studs 82 are secured to wall 32 and extend through openings 19 and 8|. By turning a pair ofnuts 83 on studs 82 it is apparent that cage 15 may be secured to casing 32 in any desired adjusted position within the range of movement permitted by slots 19 and 8|.

Preferably, though not necessarily formed integrally with cage 15, is a diagonally disposed feed conduit 85 which as seen in Figure 3 is substantially bisected by a diametrical plane passing through the cage and yet, in Figure 4 it is observed to be disposed diagonally or at an angle of approximately 45 with the axis-of the mechanism. The lower end of feed conduit 85 terminates in an opening 86 which is observed to incline outwardly and forwardly with respect Blades B are provided with to the direction of rotation of the rotor and is provided with a sharply curved forward wall 81 and a less sharply curved rearward wall 88.

Abrasive is introduced into feed conduit 85 by means of a spout 88 having a pair of lugs 8| secured to housing sidewall 82 by means of a pair of cap screws 82.

As seen in Figures 3 and 4 the lower end of spout 88 is tapered and the upper end of conduit in 85 assumes a hopper-like form so that the cage may undergo a small range of adjustment without interference from spout 88. Abrasive is preferably admitted to the upper end of spout 88 by means of a metering mechanism in order to provide auniform blasting action and this mechanism may assume any suitable form well known in the art.

It is accordingly apparent that when the machine is brought up to operating speed; for

instance, speeds ranging from 2000 to 2500 R. P. M., and abrasive is fed through spout 88, it flows into conduit 85 and in issuing from opening 88 it is promptly picked up by the inner ends of the blades B, which pass fairly close 2 to the feed opening.

-The abrasive that is properly picked up by the blades moves outwardly over the surfaces of the blades and is discharged from the wheel in the manner previously described. In view of the fact that as a practical matter it is impossible to perfectly pick up all of the abrasive issuing from slot 86, surfaces I5 are employed to rebound back toward the discharge opening any abrasive that may strike the inner extremity of the blades and ricochet toward the'cage.

In other words, the stream of abrasive issuing from opening 88 may be regarded as a continuous abrasive ribbon and if it were possible to employ a blade that would maintain con- 9 tinuously a very sharp pick-up edge, then practically all of the abrasive would be properly picked up. However, as a practical matter, it is impossible to maintain a sharp edge on the inner ends of the blades and applicant has accordingly provided rebound surfaces for compensating for the action of the comparatively dull blades that must be used in practice. For instance, if a cage having a smooth cylindrical surface were used, and an abrasive particle 5 was struck by the inner end of the blade so as to ricochet toward the cage, it would leave the cage at an angle of reflection equal to the angle of incidence and would again be picked up by the blade at a point angularly remote'from the proper pick-up zone adjacent opening 86. By providing surfaces I6 they cause the ricocheting abrasive to be thrown back toward the pick-up zone and hence cause them to be picked up in the proper angular position. Otherwise, an angularly delayed pick-up of the abrasive would eifect a similar angularly delayed discharge of the stray abrasive, which would occur beyond the useful range of the wheel and would not strike the work, and would probably abrade the cabinet or other stationary parts of the machine.

With the form of blade illustrated in Figures 8, 9 and 10, I have found that when the wheel is fed with abrasive downwardly as seen in Figures 3 and 4, the abrasive is retained in the wheel 70 substantially a whole revolution and is discharged downwardly. In other words, the wheel may be said to possess a one-hundred per cent degree of retardation, because the abrasive is discharged from the same angular portion of l the rotor as it is admitted to the blades. It is accordingly apparent that by reason of the feed mechanism and blade design of my machine, I am able to provide a blast wheel having directional control and which is operable to blast downwardly and yet it issnot necessary to em- I ploy an impeller because the abrasive is fed downwardly by gravity. 1

Blade design The exact dimensions and proportions of the 10 various parts of the blade may vary somewhat depending upon the particular characteristics desired and the degree of retardation of delivery of the abrasive which is to be effected.

Referring particularly to Figure 8, this shows 15 a so-called one-hundred per cent retarding vane, and it is so termed because it is so shaped as to require substantially a full revolution of the rotor to discharge the abrasive from it. -The axis of rotation of the wheel is indicated at C and it 90 will be observed that a radius R1 passing through the center Cand the innermost end of straight surface 58 makes an angle of approximately 57 with respect to surface 58. It is to be understood that applicant is not limited to 25 this particular angle, but that it may be increased or decreased to vary the characteristics of the machine desired. It is also observed that straight surface 58 which inclines rearwardly with respect to the direction of rotation makes 00 an angle of approximately 13 with respect to a radius R2 passing through the center C. It is also seen that the inner surface 56a of the inner end of the blade makes an angle of approximately 30 with respect to surface 58 of the 85 blade;

The blades of the present invention incline outwardly and forwardly with the result that the final or discharge velocity, which they impart to the abrasive, is higher than in a radial- 0 bladed machine of comparable size when operated at the same speed. The increase in velocity is dependent upon the degree of forward inclination of the blades, the greater the inclination the greater the final velocity. 45

For instance I have found that when the rotoi is provided with the form of blade shown in Figure 8, and wherein the propelling surface 58 makes an angle of 25 to a radius passing through the blade tip, the rotor need be operated at only 83 per cent of the velocity required in a radial bladed rotor to develop the same abrading efflciency.

Referring to Figure 8, the abrasive moving outwardly over the tip of surface 58 possesses an 08 outward velocity component V0 and a tangential or forward velocity component Vf and completing the parallelogram, the final or resultant velocity Vr is shown. Also shown, in this figure, is the velocity diagram for a radial blade having 80 the same speed of rotation and it is observed that although V0 is silghtly greater than Vo, the diagram assumes the form of a rectangle and the final or resultant velocity V1" is lower than Vr for the forwardly inclined retarding blade. I 05 Referring now to Figure 11 of the drawings, I have illustrated a somewhat modified form of blade which possesses a somewhat less degree of retardation than the blades just described.

With continued reference to this figure, the blade comprises a base or web porti 11 IM terminating in a pair of cars I02 whic are provided with curved slots I03. The blade is clamped to rotor 31 by means of a pair of cap screws I04, and by reason of the elongated slots I03 the blade I may be secured to the rotor in a plurality of adiusted angular positions.

The blade is provided with a comparativelystraight abrasive pick-up surface IIIIi which inclines slightly rearw'ardly with respect to the direction of rotation and it smoothly merges with a straight abrasive propelling surface I06. The blade is provided with an abrasive retaining flange III! at its free edge and with a somewhat higher abrasive flange I08 at its inner edge for protecting the rotor against wear.

It is accordingly apparent that when this blade is used the abrasive will be picked up by surface I05 somewhat less rapidly than in the form of blade shown inFigure 8 and that it will be propelled outwardly over surface I06 and discharged from the wheel as described in the other forms of the invention. Also, by loosening screws III the blade may be rocked to present its propelling surface I06 at a different angle or as to possess a different degree of retardation. The abrasive may be fed to this blade in the same manner as that, described in connection with the previously illustrated forms of the invention.

In Figure 12 I have shown a further modified form of blade embodying a web portion Na and having lugs I02a for securing it to the rotor, and is secured to the rotor by means of cap screws as previously described. This blade embodies a straight pick-up surface IIO which is rearwardly inclined with respect to the direction of rotation of the rotor and it is disposed approximately normal to a long propelling surface III of the blade. Surfaces III) and III are joined by a smoothly curved portion II2 which constitutes an abrasive-gathering pocket. This blade is also provided with an abrasive retaining flange H3.

In connection with this blade I have illustrated a guard or baflie member embodying a flat web portion II4 secured to the rotor by a pair of cap screws H5. The guard member is provided with an abrasive baffle surface H6 and at its free edge is provided with a. flange I II.

It is accordingly seen that as the abrasive issues from opening 86 in cage I5 it will be picked up by surface III! and gathered in pocket H2 and propelled outwardly over surface III and discharged from the rotor as previously described. Also, when the abrasive issues from the discharge opening in the cage a part of the ribbon that has been severed by the proceeding vane may be deposited on surface II6 and will flnd its way to propelling surface I I I by the time or shortly after pick-up surface IIIl attains the discharge slot, thereby utilizing all of the abrasive issuing from the slot and insuring that it will be deposited on the blade at the proper point during rotation.

In Figure 13 there is disclosed a further modified form of blade embodying a comparatively straight pick-up surface III, a straight propelling surface I22 and a smoothly curved surface I23 which connects surfaces I2I and I22. The junction with surfaces I23 and I2I defines a comparatively smooth pocket I24 for gathering the abrasive and surface I23 which constitutes a transition between the pocket and surface I22 effects a gradual increase of speed of the abrasive prior to the time the abrasive attains the inner end of surface I22.

In Figure 14 I have shown a blade having a straight pick-up surface I21 and a long propelling surface I28. Surfaces I 21 and I28 are joined by a. smoothly curved surface I29 and a surface I3I of comparatively short radius. Surface I27 inclines rearwardly with respect to the direction of rotation of the rotor to a considerable degree with the result that the abrasive picked up by the inner ends of the blade comparatively rapidly attains the curved surface I3I and is then comparatively smoothly picked up on surface I29 prior to admission to surface I28.

In this form of the invention I have also shown a baille member I32 having a vertical portion I33 and a horizontal portion I34. This baffle functions substantially in the same manner as that previously described, and-in addition surface I34 prevents rebound of the abrasive upwardly from the abrasive propelling surface I28.

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 the United States Letters Fatent is:

1. In an abrading apparatus, a runner head mounted for rotation; an abrasive propelling blade mounted on said runner head; means for feeding a stream of abrasive downwardly over the inner end of said blade adjacent the axis of rotation of said runner head, the inner end of said blade having a comparatively short abrasive propelling surface inclining outwardly and rear wardly with respect to the direction of rotation of said runner head, and the outer portion of said blade having a comparatively long abrasive propelling surface inclining outwardly and forwardly with respect to the direction of rotation of said runner head, said long abrasive propelling surface being sufficiently inclinedto a radius so that upon rotation of said runner head the abrasive is given an outward acceleration of requisite magnitude to cause it to be discharged in a predetermined direction from said runner head approximately 360 degrees from the point of feeding of said stream of abrasive to said blade.

2. In an abrading apparatus, a runner head mounted for rotation; an abrasive propelling blade mounted on said runner head, said blade terminating short of the axis of rotation of said runner head, whereby the inner edge of said blade generates a surface of revolution; means for feeding a stream of abrasive downwardly over said inner edge of said blade adjacent the axis of rotation of said runner head when said blade is moving through a predetermined portion of each revolution; the inner portion of said blade having a comparatively short abrasive propelling surface inclining outwardly and rearwar'dly with respect to the direction of rotation of said runner head, and the outer portion of said blade having an abrasive propelling surface inclining outwardly and forwardly with respect to the direction of rotation of said runner head, said outer portion being a plurality of times longer than said inner portion and being so inclined to a radius that movement of the abrasive over said blade consumes a suflicientlylong period of time to allow said runner head to turn substantially a full revolution from the time of pick-up to the time of discharge of the abrasive from the runner head.

3. In an abrading apparatus, a runner head mounted for rotation; an abrasive propelling blade mounted on said runner head; means for feeding a stream of abrasive over the inner end of said blade adjacent the axis of rotation of said runner head; the inner end of said blade having a comparatively short primary abrasive propelling surface inclining outwardly and rearwardly with respect to the direction of rotation of said runner head, and the outer portion of said blade having a comparatively long secondary abrasive propelling surface inclining outwardly and forwardly with respect to the direction of rotation of said runner head at an angle to a radius sumciently great to effect outward acceleration of the abrasive over the blade at a rate sufficiently lower than that of a radial blade to eifect discharge of the abrasive from the runner head in a predetermined direction angularly remote from the point of feeding of said abrasive stream to said blade, said primary and secondary abrasive propelling surfaces merging into each other so as to provide an abrasive pocket for gathering the abrasive subsequent to pick up but prior to discharge thereof over said secondary surface.

4. The abrading apparatus set forth in claim 3, wherein said primary and secondary abrasive propelling surfaces merge into each other along a curved surface.

5. In an abrading apparatus, a rotor, at least one utwardly extending guideway provided on said rotor, said guideway being open at its outer end, an abrasive propelling blade mounted for sliding movement in said guideway, and means for releasably locking said blade against outward displacement in said guideway comprising a ringlike element mounted for sliding movement adjacent the periphery of said rotor in a direction parallel to the axis of rotation of said rotor, said element being movable into the path of outward movement of said blade and engageable therewith, for locking said blade against outward movement.

6. The apparatus set forth in claim 5, wherein said rotor is of disc-like'form and said element slidably cooperates with the periphery thereof.

7. The apparatus set forth in claim 5, together with means for locking said element against axial movement when said blade is engaged therewith.

8. In an abrading apparatus, a rotor, at least one outwardly extending guideway provided on said rotor, said guideway being open at its outer end, an abrasive propelling blade mounted for sliding movement in said' guideway, said blade having an inclined abutment face provided on its outer end, means for releasably locking said blade against outward displacement in said guideway, comprising a ring mounted for axial sliding movement on the periphery of said rotor and having an inclined surface engageable with said inclined abutment face of said blade.

9. The apparatus set forth in claim 8, wherein said'ring is provided with a surface disposed at an acute angle to said inclined surface and is engageable with a side portion of said blade whereby said ring is locked against axial movement.

10. In an abrading apparatus, a rotor member having a plurality of outwardly slidable blades mounted thereon, said rotor member having a plurality of bearing-forming projections provided on the periphery thereof, and a locking ring member mounted for axial sliding movement on said projections into and out of locking cooper:- ation with said blades, said projections spacing said ring member from the periphery of said rotor member for preventing'abrasive from becoming wedged therebetween.

in at least one of said members is provided with a plurality of reversely inclined abrasive baflle faces for preventing abrasive from freely rebounding through the space between said rotor member and said ring member.

12. In an abrading apparatus, arotor mounted for rotation about a substantially horizontal axis, said rotor having a plurality of blades thereon terminating short of the axis of rotation of said rotor to define a central abrasive admitting space, a stationarily supported abrasive feeding device projecting into said space and operable to feed abrasive over the inner ends of said blades-said device comprising a hollow member of generally cylindrical form disposed closely adjacent the inner ends of said blades and having a peripheral opening located in the lower side thereof and being of a width substantially equal to the width of the inner ends of said blades for delivering abrasive thereover, and a conduit disposed within said feeding device and extending substantially diagonally downwardly and being in communication withsaid peripheral opening, and means for feeding abrasive to said conduit, the outer surface of said feeding device, forwardly of said peripheral opening, being provided with a plurality of angular rebound surfaces for rebounding back toward said peripheral opening any abrasive that may be improperly picked up by the inner ends of said blades, each of said surfaces being disposed at an obtuse angle with respect to a radial line passing through said surface, said ohtuse angles facing rearwardly with respect to the direction of rotation of said rotor.

13. In an abrading apparatus, a rotor-mounted for rotation about a substantially horizontal axis; said rotor having a plurality of blades thereon terminating short of the axis of rotation of said rotor to define a central abrasive admitting space; a stationarily supported abrasive feeding device projecting into said space and operable to feed abrasive over the inner ends of said blades, said device comprising a hollow member of generally cylindrical form disposed closely adjacent the inner ends of said blades and having a peripheral opening located in the lower side thereof and being of a width substantially equal to the width of the inner ends of said blades for delivering abrasive thereover; a conduit disposed .within said feeding device and extending substantially diagonally downwardly and in communication with said peripheral opening; and means for feeding abrasive to said conduit; said blades being provided with a comparatively long, smooth and straight abrasive propelling surface for smoothly and continuously accelerating the abrasive, said abrasive propelling surface inclining outwardly and forwardly with respect to the direction of rotation of said runner head and being sufliciently inclined to a radius to effect outward acceleration of the abrasive of requisite magnitude to cause it to be discharged in a predetermined direction approximately 360 degrees from the point of feeding of abrasive to said blade.

14. In an abrading apparatus, a rotor mounted for rotation, said rotor having at least one abrasive propelling blade mounted thereon, said blade having an abrasive propelling surface inclining outwardly and forwardly with respect to the direction of rotation of said rotor and having an abrasive gathering pocket at its inner end, means for.feeding abrasive over the inner end of said blade, and a bafllespaced from the abrasive propelling surface of said blade adjacent said abrasive gathering pocket, for preventing abrasive from being improperly fed to said blade.

15. In an abrading apparatus, a disc-like runner head mounted for rotation, an outwardly extending guideway provided on said head,'an abrasive propelling blade mounted for sliding movement in said guideway, means for releasably locking said blade against outward movement in said guideway, said blade having a base portion of considerable area designed to seat against said head when said blade is in place in said guideway, said base being disposed at slightly less than a right angle to said abrasive propelling surface and sufflcient spacing being provided between said blade and said guideway whereby when said apparatus is placed in operation and said blade is placed under load said blade will be disposed in a position with its abrasive propelling surface substantially normal to said runner head.

18. An abrasive propelling blade for use in the rotor of a centrifugal abrading apparatus comprising a member having a comparatively long,

substantially straight abrasive propelling surface at its outer end, a short abrasive pick-up surface located at its inner end and disposed at an angle greater than 45 and less than 100 with respect to said abrasive propelling surface, and a surface portion of concave formation between said surfaces and merging them together.

17. The abrading apparatus described in claim 2, together with means for adjustably securing said blades to said runner head with said abrasive propelling surface disposed at various selected inclinations on said runner head, for varying the accelerating action thereof upon the abrasive.

18. In an abrading apparatus, a disc-like rotor carried by a. shaft mounted for rotation, a disc detachably secured to one face of said rotor and operable to protect the entire face thereof against abrasion, said disc having a plurality of outwardly extending slots therein and cooperating with the face of said rotor to define guideways for a plurality of outwardly extending abrasive propelling blades, said rotor forming the bottoms of said guideways and adapted to be protected against abrasion by said blades, and wherein the walls of said slots form the sides of said guideways, the inner ends of said slots being closed to limit inward movement of said blades.

WALTER L. KEEFER.

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