US2590576A - Abrading apparatus - Google Patents

Description

March 25, 1952 Filed May 17, 1934 w. A. ROSENBERGER ET AL 2,590,576

ABRADING APPARATUS 3 Sheets-Sheet l :jnuentoz March 25, 1952 w. A. ROSENBERGER ET AL 2,590,576

ABRADING APPARATUS Filed May 17, 1954 3 Sheets-Sheet 2 Mar h 25, 19 w. A. ROSENBERGER ETAL 2,590,576

ABRADING APPARATUS 3 Sheets-Sheet 3 Filed May 17, 1934 ||llllllllrTrllllllllllll IIIIIIIIIIII/l Zhwentor VIM/dim A .Rwenb e/ye/ Walter L.Keef/ ayw /mm (Ittornegs Patented Mar. 25, 1952 ABRADING APPARATUS William A. Rosenberger and Walter L. Keefer,

Hagerstown, Md., assignors to Pangborn Corporation, a corporation of Maryland Application May 1'1, 1934, Serial No. 726,188

8 Claims.

The present invention relates to abrading apparatus, more particularly the present invention is concerned with abrading machines of the character wherein an abrasive is picked up and directed against the work operated upon, by centrifugal action.

Machines of this general character have been heretofore proposed, but they have not been commercially successful for the reason that they have failed not only to efficiently perform the functions required of such machines, but also to stand up in use, due to parts thereof rapidly wearing away under the influence of the abrasive handled thereby. Such prior machines discharge abrasive throughout 360 degrees of the impeller, and since the article operated upon by the machine must be held to one side of the impeller only a small proportion of the abrasive handled by the machine is utilized for useful work, with the result that the greater part of the abrasive is directed against the casing or housing that may enclose the machine, causing it to wearaway rapidly in use. It has been found that the impeller elements in such prior proposed machines also wear away rapidly, particularly near their inner ends, where they initially contact th abrasive.

It is accordingly a primary object of our invention to devise a novel centrifugal abrading machine that will efficiently utilize the abrasive supplied thereto, and which will have a long life.

It is another major object of our invention to devise a novel centrifugal blasting machine that will -efiicientlydirect substantially all of the abrasive supplied it against the work that is being handled thereby. It is another important object of the present invention to devise a centrifugal blasting machine having means for supplying abrasive to a limited angular portion of the inside of the impelle'r, so as to limit the centrifugal discharge thereof to. a limited angular region.

It is a further object of this invention to provide a centrifugal abrading machine of the character having a plurality of outwardly extending blades which terminate short of the center of rotation to define a central space, with means for selectively supplying abrasive to predetermined limited portions of the central space.

i It is another object of our invention to provide the abrasive impelling mechanism of a centrifugal blasting machine with an abrasive impelling blade assembly that will not impede air or abrasive flow therefrom, and also with means for supplying abrasive to a limited angular region of the inner ends of the blades.

A further object of our invention is to so construct a centrifugal blasting machine of the character having rotary abrasive impelling surfaces, that an initial velocity of considerable magnitude is imparted to the abrasive prior to its being picked up by the abrasive impelling surfaces.

It is another object of the present invention to equip a blasting machine of the character having a plurality of radially outwardly extending blades which terminate short of the center of rotation, to define a central space with means for supplying abrasive to a limited portion of the central space to thereby predetermine the angular discharge of the machine.

It is a further object of our invention to provide a blasting machine of the character having a plurality of outwardly extending blades, which terminate short of the center of rotation to define an abrasive supply space, with novel means for introducing abrasive to the abrasive supply space.

A further object of this invention resides in the provision of a centrifugal blasting machine with novel means for securing the abrasive impelling elements in place in such manner that it is possible to readily remove them when they are worn out, and yet which will securely hold them in place when the machine is in operation.

It is another object of our invention to so construct a centrifugal blasting machine that wear of the parts thereof will not result in substantial dynamic or static unbalance of the machine.

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 plan view of a blasting machine embodying our invention.

Figure 2 is an elevational view of the machine illustrated in Figure 1.

Figure 3 is a longitudinal sectional view on an enlarged scale of the machine shown in Figure 1, and illustrates the handle disposed in its vertical position in order to more clearly show the structure involved, and the sectional part of the runner-head is taken substantially in line 3-3 of Figure 4.

Figure 4 is a sectional view taken substantially on the line 44 of Figure 3.

Figure 4A is a fragmental sectional view illustrating the device employed for holding the cone in place in the machine shown in Figure 3.

Figure 5 is a side elevational view of one of the main impeller blades employed in the device shown in Figure 1.

Figure 6 is a detailed sectional view taken substantially on the line 66 of Figure 4.

Figure '7 is a longitudinal sectional view of a modified form of blasting machine also forming part of our invention when viewed apart from the machine, and

Figure 8 is a top plan view illustrating the abrasive supply conduit of the machine shown in Figure 7 as it appears when viewed apart from the machine.

With continued reference to the drawings wherein like reference characters have been employed to designate like parts throughout the several views thereof, the machine is supported upon a base designated generally at I0, and although the base may be supported in any desired manner, we have in the present instance shown it as being secured to the upper side II of a sand 7 blasting cabinet (not shown) by means of cap screws I2 or the like.

Cabinet top I I is provided with a comparatively large opening through which an impeller housing I3 projects. Housing I3 is secured to the lower side of base II] by means of cap screws I4, and a complemental housing member I is secured to base In in spaced relation to housing I3 by means of cap screws I6. Housings I3 and I5 house the lower part of the impeller of the machine that n will be hereinafter described.

An upper housing member I1 is secured to the upper side of base In by means of nut and bolt assemblies I8 and is provided with a pair of handles I9 by which it may be lifted when it is detached from the base. Housing II encloses the upper portion of the centrifugal impeller and is preferably provided with a removable wear element which takes the form of a semi-cylindrical ring 2 I, which may be detachably secured thereto in any suitable manner.

As seen in Figures 1 and 3, base I 8 is of hollow construction and is provided with a pair of bearing recesses 22 and 22a which are interconnected by a trough-like portion 23. A shaft is disposed in trough portion 23 and extends longitudinally of the base. Shaft 25 constitutes the impeller driving shaft, and it is journaled in bearings which in the present instance preferably take the form of anti-friction ball bearings of conventional design.

Clamped between a shoulder 26 provided on shaft 25, and a nut 21 is the inner race of a bearing 28. The outer race of bearing 28 is supported in a bearing support 29, which is provided with a pair of laterally extending arms 3|. Arms 3| bridge bearing recess 22 and are secured to the top side of base II] by means of bolt and nut assemblies 32.

Bearing 28 is secured within support 29 by means of a cap member 33, which is secured to support 29 by means of cap screws 34. Frictionally clamped between a flange formed on cap member 33, and a nut 35 threaded into the cap, is a sealing member 31, which in the present instance takes the form of a hard felt ringmember. Also frictionally clamped between a flange 38 provided on bearing support 29 and a nut 39 threadedly connected thereto, is a similar sealing member 40.

The chamber defined by bearing support 29 and cap 33 is preferably filled with lubricant prior to assembly to provide lubrication for bearing 28, and the seal rings 31 and 40 operate to prevent lubricant from escaping from the reservoir and also prevent any abrasive that may be present in the air from entering and causing wear of the bearings. The right hand end of shaft 25 is supported in a bearing and sealing assembly that is identical (except for size) with that just described, and corresponding reference characters with the subscript a have accordingly been applied to designate like parts.

Shaft 25 is accordingly mounted for rotation upon base It], and power may be applied to it in any suitable manner, as for instance by means of a pulley 4I secured thereto. Shaft 25 is provided with an annular groove 42 and extends through semi-circular recesses 43 and 44 located respectively in housing I1 and base I0. Secured to a reduced portion 45 of shaft 25 by means of a key 46, is a runner-head 41, which supports all of the rotating elements of our blasting machine. Runner-head 41 is provided with an annular flange 48 that cooperates with the impeller blades in a manner to be hereinafter described.

Secured to head 41, by means of bolt and nut assemblies 49 are a plurality of guide blocks 5I Which are provided with inclined faces 52. With particular reference to Figure 6, the neighboring sides of blocks 5I form dove-tail grooves in which the abrasive impelling blades are adapted to be retained.

A plurality of blade members 54 are mounted upon head 4! and are provided with dove-tailed portions 55 which are disposed within the guide grooves defined by blocks 5I. As indicated in Figure 4, blade members 54 are inserted from the center of the assembly and are slid outwardly until they engage flange 48 of head 41, which restrains them from outward displacement in response to centrifugal force. Any suitable means may be employed to restrain blades 54 from sliding inwardly under the influence of gravity when the head is at rest, but we preferably employ frictional means which takes the form of fiat leaf springs 56 which seat in recesses 51 located in portions 55 of blades 54, and bear against the radial face of head 41.

Referring more particularly to Figures 4 and 6, blades 54 are provided with substantially fiat abrasive-impelling surfaces 58, which extend from the outer periphery of the blades to a point near the inner ends thereof. The inner ends of the blades are provided with curved impelling sur faces 59 for a purpose that will presently appear. As seen in Figure 3, the blades decrease in width toward their outer periphery in view of the fact that the velocity of the abrasive increases as it approaches the outer periphery of the blades, and in order to prevent the abrasive from escaping laterally from the blades we preferably provide blades 54 with ribs BI, which are coextensive with their impelling surfaces.

The abrasive may be fed into the center of the blade assembly by any suitable means, but we preferably employ the following mechanism for this purpose. A short shaft 62 is mounted for rocking movement in a bearing 63, which is provided with a .pair of diametrically opposed arms 64. Arms 54 bridge a bearing recess located in the left hand end of base Ill and are provided with recesses 65. A pair of nut and bolt assemblies 66 extend through recesses and secure member 63 to the top of base I0.

Secured to the right-hand end of shaft 62, by means of a set screw 6'! or the like, is an armately shaped bracket 68, to which a substantially cylindrical abrasive distributing member 69 is secured by means of cap screws 10. Member assume i9 is provided with an annular boss H, having preferably four notches l2, and a preferably single abrasive outlet 13. A plurality of teeth 14 are provided on the inner cylindrical wall of member 69 for a purpose that will presently appear.

In view of the fact that member 69 may undergo rocking movement with shaft 62, abrasive outlet or distributing aperture 13 may be angularly adjusted with respect to blades 54 so as to predetermine a point at which the abrasive shall enter the abrasive receiving space defined by blades 54 and head ll. Abrasive is supplied to member 69 by means of a cone member 75 having a flange 16 which frictionally rests against a gasket Tl disposed in contact with boss 12. Cone member 15 may be secured in place by any suitable means, but we preferably employ a plurality of eccentric members 18, having pivot portions 19 extending through apertures in member 69. Members 18 bear against flange l6 and maintain cone 15 in fluid-tight relationship with gasket 11. This action is also augmented by the vacuum developed within cone '15 when the machine is in operation. When it is desired to remove cone 15, members 18 are rocked about portions l9'as axes by means of handles 8c and are removed from their apertures.

Cone 15 is provided with an aperture 8! through which a spout member 82 projects. 3'

Spout 82 is provided with a hopper portion 83, through which abrasive may be sup-plied in any suitable manner, and a distributing, or nozzle portion 84 through which abrasive is supplied to member 69. Spout member 32 is preferably provided with a gasket '85 which rests in frictional engagement with the top face of cone 15 to prevent air from leaking directly from the atmosphere into member 69, Spout member 82 is provided with an arm 86 which is secured to bearing member 63 by means of cap screws Bl or the like.

Shaft 62 maybe rocked in any suitable manner, but we preferably provide a handle 89, having the hub portion 89 mounted upon shaft 62,

and which is secured thereto in any suitable manner. Bearing member 53 is provided with an upstanding flange 9! having an arcuate slot 92 formed therein. A nut and bolt assembly 93 extends through slot 92 and through an aperture in handle 88 and may be taken up to maintain handle 88 and shaft 62 in any desired adiusted position.

In view of the fact that rotation of head l! causes blades 54 to function as a centrifugal fan, ahigh vacuum is developed within the member 69 and spout 82, with the result that any abrasive'supplied to spout 82 will be drawn into member 69 and thence through aperture 13 to the blades. We preferably, however, provide head 41 with an auxiliary rotor or fan mechanism for more intimately mixing the incoming sand with the incoming air prior to delivery to aperture 13, and it preferably takes the form of a generally cylindrical boss 95 which fits into a recess in head 41 and it is secured to shaft2'5 by means of a cap screw 95. Member 95 consists of a plurality, preferably four, heavy blade members 91, which are joined at their ends by cylindrical portions 98 and 99. Member 95 is assembled within member 69 by aligning blades 91 with two recesses I99 formed in the flange provided on member 69, which are preferably disposed in angular alignment with recesses or notches 72 formed in boss H. Member 95 is then slid into place, with blades 91., which project beyond portions 98, 99, passing. through recesses I00 and 12, and bolted to head 41. Although we preferably associate the parts in this manner, so as to provide an annular abrasive chamber that extends inwardly beyond blades 91 at either end of auxiliary rotor 95, it is to be understood that if desired, notches similar to 72 may be provided in flange (02 of casing 69, so that the latter may be removed without first detaching member 95, and the appended claims are intended to embrace our machine when it is constructed in this manner. As seen in Figure 3, portion 98 of member 95 provides a conical chamber which is aligned with cylin' drical chamber I0! defined by the inner edges of blades 91 and also is axially aligned with the delivery end 84 of spout 8.2,, and communicates with the spaces between the blades 91.

Operation The work is placed under the cabinet in registry with the discharge opening of the device and it is preferably mounted on a truck or conveyor or the like so that it may be moved around to expose various areas of it to the blast. Shaft 25 may be rotated at any desired speed, but we find that with the machine illustrated, aspeed' of approximately 2400 revolutions per minute, in the direction indicated in Figure 4, is suitable for satisfactory operation of the machine. assembly 93 is then loosened and handle 88 is actuated to bring member 69, and hence aperi ture I3 into the proper abrasive delivering position, as dicated by the type of abrasive used, the shape and size of the blades, and the nature of the work. For instance, with reference to Figure 4, the point at which the abrasive leaves the wheel is determined by the point at which he abrasive is admited to the wheel, and as the time it takes for a particle to traverse the blades depends upon the length of the blade and nature of the abrasive, it is obvious that it is necessary to adjust the point of admission of the abrassive to cause it to discharge through the bottom of the machine.

Bolt and nut assembly 93 is then tightened and the machine is ready for operation. If desired however, the adjustment of handle 88 may be deferred until the machine is actually in operation, as the operator can then, by observing the character, and the discharge point of the blast, properly manipulate the handle to give the best results.

Sand or other abrasive is preferably allowed to drop by gravity into hopper portion 83 of spout 82 and it is preferably supplied thereto in uniform quantities as by means of a screw or like conveyor operating at a predetermined constant speed. Rotation of head 41 causes blades 54 to establish a partial vacuum within member 69 and the interior of spout 82, so that the sand entering the spout is picked up by an air stream and enters passage l0! in auxiliary rotor 95. Blades 91 of rotor 95 cause the abrasive to pass outwardlybetween them to their periphery, where it is agitated or churned around within member 69. Sand lodges within teeth M and the abrasive thus accumulated protects the interior of member 69 from excessive wear.

A forwardly rotating dispersion of air and abrasive is accordingly established in the annular space defined by member 69 and member 9'5, and it is uniformly Withdrawn from member 69 Nutthrough aperture I3 by virtue of its velocity and the suction effect of blades 54.

It should be observed, referring more particularly to Figure i, that as the abrasive is exhausted from aperture I3, it possesses angular as well as radial velocity in view of the impelling action of blades 91. This initial velocity feature, when taken in connection with the fact that the inner ends of blades 54 are curved, operates to minimize any abrading action as blades 54 pick up the abrasive. In other words, the abrasive exhausted from aperture 'I3 travels outwardly and angularly, defining a spiral, and as the angular component of the velocity of an individual particle of abrasive is not greatly lower than the velocity of the inner portions of blades 54 that picks it up, and as these portions of blades 54 are curved, they strike the abrasive a glancing blow and wear thereof under such action is minimized.

The abrasive is accordingly supplied to blades 54 in a predeterminedlimited angular position, and as it travels outwardly each particle defines a spiral path as indicated in Figure 4, and is directed against the work over a definite region, none of the abrasive striking housing I! or base I0. In view of the fact that the abrasive passing outwardlyover blades 54 is increasingly accelerated until it leaves the blades, and it also possesses an angular velocity due to the rotation of the-blacles, it leaves them at an angle thereto. With reference to Figure 4, the velocity of the abrasive under discharge conditions is diagrammatically illustrated, wherein the radial or outward velocity is represented as V1 and the instantaneous angular velocity of the sand as it is about to leave the tip of the blade is represented as V2. These component velocities when combined result in a velocity V1 and although the values indicated have not been computed they are thought to fairly well represent the conditions existing in the machine during operation. It should be observed that as abrasive is delivered from only a small angular region of the rotor, which in the present case is below the axis of the members and through the openings between the housings I3 and I5, all of the abrasive is utilized for useful work, as no energy whatever is lost by abrasive being thrown against stationary housing I'I.

Although we have illustrated our blast machine as discharging the sand blast downwardly against the work to be cleaned, and we prefer to utilize the device shown as it has proven to be the most convenient, it is to be understood that the device may be designed to discharge at any other angular point by properly rocking member 69 into the proper position to cause the abrasive stream to be delivered to the desired point, and the opening in the housing members may be properly angularly modified to meet the changed conditions, and the appended claims are intended to embrace our device when it is used in this manner.

Prior to assembling blades 55 upon head 4? they are carefully tested for hardness. Eight blades of substantially identical hardness are then selected and assembled upon head. The blades are selected in this manner so that when they are in use in the machine they will wear away evenly, and hence lose mass uniformly, with the result that dynamic and static balance of the runner-head assemblyis maintained until the blades become so worn as to require replacement.

t should be particularly observed that runner-head i! is of considerable mass, with the result that should blades 54 wear .slightly unevenly, despite the fact that they are selected in sets of eight of substantially equal hardness, the change in the dynamic balance of the blades will not seriously affect the dynamic balance of the runner-head assembly as a whole. However, when it does become necessary to replace-blades 54, it is only necessary to loosen bolt and nut assemblies BB and slide the bearing support 63 to the left, after removing cap screw 96. This leaves the central space of the rotor unobstructed and blades 54 may accordingly he slipped inwardly and removed and new blades substituted therefor; Wear element 2I may be readily replaced by removing housing I'I.

With reference now to Figures 7 and 8, we have illustrated a modified form of centrifugal blast machine, and the major diiference thereof over the machine just described resides in the fact that the auxiliary impeller is omitted and a compressed air stream is employed for agitating the abrasive air mixture and for imparting an initial velocity thereto.

With continued reference to these figures, a hopper I05 is supported upon base I0 in any suitable manner and member I06, which divides it into an abrasive passage I0! and an air passage I08. Abrasive is adapted to be supplied to pase sage III'I by means of a pipe I09, and the abrasive so supplied is adapted to be picked up by an air stream set up by an air jet III, which is connected to any suitable source of compressed air. The action of air jet III sets up an aspirating effect and causes a partial vacuum to be established in the bottom of the hopper, which causes air to enter passage I08 and carry the abrasive gravitating into passage IB'I into the blast of air issuing from jet I I I.

The abrasive air mixture enters a hollow member H2 which in the present instance takes the form of a pipe and it is preferably adjustably secured to hopper I05 by means of a set screw H3 or the like. Member II2 extends into the central space defined by the inner ends of blades 54, and is flattened to provide an elongated opening I I4 terminating adjacent blades 54.

Member I I2, adjacent opening I I4, is preferably provided with a plurality of steps II5, which exert an agitating effect upon the abrasive-air mixture and cause it to be evenly distributed over the faces of blades 54. As seen in Figure 8, the passage in member II2 decreases in Width with the result that the velocity of the abrasive-air mixture increases as it approaches opening H4.

The operation of this machine is similar to that of the machine previously described as set screw I I3 may be loosened and member I I 2 rocked within hopper I to bring into the desired angular position. The quantity of abrasive supplied the machine may be regulated by regulating the flow of abrasive through pipe I09, and the degree of agitation, and the initial velocity of the abrasive may be controlled by varying the quantity of air supplied jet III.

Although we have illustrated member II2 as being constructed of a cylindrical pipe or tube, it may be of cast construction or be formed in any other suitable manner, so long as it provides a discharge opening adjacent the inner ends of blades 54, without departing from the spirit of our invention. Moreover, if desired the compressed air blast nozzle may be omitted and the suction set up by rotation of head 41 relied upon to agitate and carry the abrasive to blades 54, and the appended claims are intended to embrace our machine when it is used in this manner.

'Also member H22 may extend loosely through recesses in housing Ila and base [0a. but it. is shown as fitting. fairly closely therein in order to provide a substantially air-tight joint so as to enable the suction set up by blades 54 to be utilized in assisting in feeding the abrasive from member H2.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is 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 a centrifugal blasting machine, a rotatably supported member having a plurality of outwardly extending abrasive impelling blades projecting therefrom, the inner ends of said blades terminating short of the axis of rotation of said member and defining an abrasive supplying space, acylindrical sleeve element non-rotatably held within said space and having an inwardly extending flange adjacent the rotatably supported member defining an abrasive impelling chamber, and a passageway in the cylindrical wall of the sleeve element defining a communication opening of limited peripheral extent to discharge abrasive from the chamber into the blades over a limited range to efiect directional control of the abrasive combination, a stationary sleeve, said stationary sleeve having a peripheral aperture, means for feeding an uninterrupted supply of abrasive through the peripheral aperture in said stationary sleeve, a rotary impeller mounted peripherally of said stationary sleeve, said rotary impeller having at least one throwing blade mounted for rotation around the sleeve to engage the abrasive fed through the aperture and impel it at high speed from its periphery, said blade having an abrasive engaging surface which extends substantially radially from its periphery to a zone adjacent its inner terminus, and in this zone smoothly and gradually inclines forwardly with respect to the direction of rotation, said surface shape accelerating the abrasive smoothly and continuously and without abrupt change, from the initial contact to the final discharge.

'4. A centrifugal blasting device comprising, in

blades having an abrasive engaging surface which by the revolving blades, and a plurality of rotatable abrasive impelling vanes on said member and disposed within said sleeve, said vanes extending outwardly beyond the inner periphery of said flange.

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 space, driving mechanism connected to rotate the rotor about its axis, a non-rotatable 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 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 being joined adjacent said rotor by a generally circular flange structure, said vanes extending inwardly, 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 driving mechanism being comiected to rotate the vane-carrying impeller to impel abrasive through said discharge opening, said impeller vanes being axially spaced from said rotor and said feeding device having an inwardly extending abrasive-retaining fiange disposed between said impeller and said rotor, and having an internal diameter which is less than the overall external diameter of said impeller vanes.

3. A centrifugal blasting device comprising, in

extends substantially radially from its periphery to a zone adjacent its inner terminus, and in this zone smoothly and gradually inclines forwardly with respect to the direction of rotation, said surface shape accelerating the abrasive smoothly and continuously and without abrupt change, from the initial contact to the final discharge.

5. In an abrading apparatus, a rotor comprising a disc-like member mounted on a shaft and having a plurality of blades terminating short of the axis of said rotor to define an abrasive admitting space; a normally stationarily supported abrasive feeding device of an external diameter less than the diameter of the abrasive admitting space, extending into said space and having a discharge opening therein disposed to one side of the axis of said rotor for delivering abrasive to the inner ends of said blades; said blades ter- =minating sufficiently close to said feeding device to pick up the abrasive with a minimum of impact, driving mechanism connected to rotate the rotor shaft, said blades having substantially straight, smooth and uninterrupted abrasive propelling surfaces of sufficient length to accelerate the abrasive smoothly and continuously without abrupt changes in direction and discharge it from the outer ends of said blades at an abrading velocity when said rotor is rotated; means for introducing abrasive into said feeding device; and an impeller disposed within said feeding device and being rotatable about the axis of said rotor and having abrasive impelling surfaces connected for rotation by the driving mechanism to .f impel abrasive through said discharge opening,

-- and extending outwardly from said axis, said blades being spaced from said axis to define a central abrasive inlet, a non-rotatable tubular control member fixed in said inlet and having a discharge opening positioned to supply abrasive and direct the supply substantially radially into the path of rotation of said blades, and air blast structure connected to the tubular member for forcing supplied abrasive out through the discharge opening.

7. In a. centrifugal blasting machine, a discshaped rotor journalled for rotation about an axis perpendicular to the plane of the disc and passing through its center, a plurality of throwing blades carried by said rotor and extending from its periphery close to, but short of its center, to define a central abrasive feed opening, driving mechanism connected to the rotor to rotate it about said axis, abrasive feed structure in said opening having control elements positioned close to the outer portion of said opening to feed abrasive to the blades in a limited segment of the rotating travel to cause the rotating blades to engage, accelerate and discharge the abrasive at high velocity from their periphery over a relatively short arc, and supply elements connected to deliver abrasive to the feed structure, said control elements including a tubular member adjustably held in fixed position in said feed opening coaxially of the rotor and having an abrasive feed passageway of limited peripheral extent in its side wall and within the span of the blades to limit the pick-up of the abrasive by the rotating blades to a small segment of the rotation and thereby effect directional control of the abrasive thrown out from the periphery of the blades, and a set of impelling vanes rotatably mounted about the rotor axis within the tubular 'member and in the span of its passageway, said driving mechanism being connected to rotate the impelling vanes to discharge through this passageway the abrasive delivered by the supply elements, said tubular member having the inner surface of its peripheral wall provided with inwardly directed ridges extending axially to reduce the erosion by the abrasive rotated by the impelling vanes.

8. In a centrifugal blasting machine, a discshaped rotor journalled for rotation about an axis perpendicular to the plane of the disc and passing through its center, a plurality of blades each extending generally radially of the disc from adjacent its periphery close to, but short of its center, to'define a central abrasive feed opening, driving mechanism connected to the rotor to rotate it about said axis, abrasive feed structure thickened dovetail portion holding the blade in place in a, mating dovetail groove in the rotor to provide a detachable flush blade mounting with the blades otherwise.

WM. A. ROSENBERGER. WALTER L. KEEFER.

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

UNITED STATES PATENTS Number Name Date 554,473 Beeg Feb. 11, 1896 716,268 McPhee et al Dec. 16, 1902 772,606 Brossmann Oct. 18, 1904 1,010,929 Loetzer Dec. 5, 1911 1,457,113 Langworthy May 29, 1923 1,789,874 Lilly Jan. 20', 1931 1,953,566 Peik Apr. 3, 1934 1,971,535 Parkins Aug. 28, 1934 2,224,647 Grocholl Dec. 10, 1940 2,254,234 Minich Sept. 2, 1941 FOREIGN PATENTS Number Country Date 155,979 Great Britain Dec. 3, 1919 519,837 Germany Mar. 5, 1931

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