US2752732A - Apparatus for treating surfaces of workpieces - Google Patents

Description

July 3, 1956 M. WALKER 2,752,732

APPARATUS FOR TREATING SURFACES OF WORKPIECES Filed May 26, 1954 C5 Sheets-Sheet l be 5W 1g AOL l, N /W 't PD L- annum-hummm ...-nnnn a h gli INVENTOR.

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July 3, 1956 L. M. WALKER 2,752,732

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4d.. Arran/Eni July 3, 1956 l.. M. WALKER APPARATUS FOR TREATING SURFACES OF' WORKPIECES 3 Sheets-Sheet 3 Filed May 26, 1954 R. l @we bij mf E Y m llmllslfmnlllJllm. m M w WWMH III |ll|.1l\ N A N n n m r O n m@ INN .A N Y n M #wml L A mi A?? lim @m wplanes of rotation APPARATUS FR TREATING SURFACES F WORKPIECES Leon M. Walker, Brooklyn, N. Y. Application May 26, 1954, Serial No. 432,519 7 Claims. (Cl. 51-9) This invention relates to method and apparatus for the treatment of the surfaces of workpieces by means of a stream of particles.

Apparatus of this character suggested in the past has been incapable of regulating the flow of the streams of such particles automatically without the employment of expensive and complicated devices for effecting the recirculation of such particles.

Furthermore, apparatus of this character heretofore suggested has been expensive to operate and to maintain by virtue of the high rate of consumption of the impeller devices for throwing or moving the particles against the 'workpieces Also such prior apparatus have been extraordinarily expensive and complicated and have not satisfactorily solved the problem of obtaining maximum abrasive eti-ect from a given amount of particles.

One of the objects of the present invention is to overcome the aforementioned defects or to reduce same to negligible proportions.

Another object is to provide a single machine of this character which is of high versatility and exibility by virtue of its ability to utilize to best advantage any one of a wide variety of different types of particles, including abrasive particles, thereby to obtain with one machine a wide variety of surface iinish effects upon a wide range of diierent types of workpiece surfaces.

A further object is to provide a device of this character which can be easily adjusted to accommodate and utilize to best advantage the characteristics peculiar to each of a plurality of different types of particles.

A further object of the invention is to provide a novel apparatus of this character for cleaning or descaling or ball peening workpieces which, by means of extremely simple and inexpensive means automatically regulates the stream of descaling or peening matter in such a way that such stream is initiated and the cycle repeated indefinitely until the breakdown of the particles or the wearing away of the impeller for creating such stream, the regulation of the stream of particles being automatic and subject to easy adjustment.

Another object is to provide an apparatus of this character wherein the volume and velocity of a stream of such particles is subject to easy adjustment for the effecting of a desired surface finish of the workpieces.

The invention in one aspect thereof is constituted by .a main outer housing within which there is mounted a rotatable barrel for containing and tumbling the workpieces, the sides of such barrel being constituted by a wide mesh wire screen. One or more impellers may be mounted rotatably beneath such tumbling barrel and each positioned for hurling a stream of particles upwardly towards the barrel and the workpieces therein. Such particles may be abrasive with respect to the workpieces. Preferably a pair of such impellers are employed, the

thereof being substantially in coincidence or parallel but not far removed from one another whereby the streams from each impeller cooperate with 2,752,732 Patented July 3, e

one another in their upward movement toward the workpieces. Each impeller is provided with a casing for partially enclosing the region of movement of the impeller, each casing having an open portion at the top (for the escape of the abrasive stream) and including two side plates, one on each side of the impeller. Each such side plate is provided with an opening near the lower level of the path of movement or the impeller through which the abrasive or surface treating material can be fed into the casing and thus into the path of impeller movement from the side of such impeller. Primary hopper means are employed for holding such comminuted material and for guiding same through such side plate openings into the casing and thence into the path of the impeller. Also each impeller is provided with secondary hopper means which are interposed between the primary hopper means and the tumbling barrel. That is, the secondary hopper means are above the primary hopper means but below such barrel and are so positioned for the purpose of recovering the surface treating material after it has been thrown toward the barrel and falls under gravity therefrom. Such secondary hopper means is in turn provided with suitable outlet means for directing such recovered material from the side of the region of movement of the impeller into the path of such movement, such secondary hopper means also having hopper surfaces of selected inclination which permit the particles of material to accumulate in a selected amount therein prior to a sliding thereof through the outlet means and into the path of movement of the rotating impeller. Such secsecondary hopper impeller.

The above and further objects and novel features orr the invention will appear more fully when the description given below is read in connection with the accompanying drawings which form a part of the specication. However, the drawings are for purposes of illustration only and are not intended as a definition of the limits of the invention, reference for this latter purpose being had to the appended claims.

In the drawings:

Fig. 1 is a side View, partly in section and with parts broken away, of one form of apparatus embodying the present invention;

Fig. 2 is a plan view of an apparatus shown in Fig. 1;

Fig. 3 is a side view of the impeller shown in Fig. 2;

Fig. 4 is an end view of the impeller shown in Fig. 2;

Fig. 5 is an end View, partly in section and with parts broken away, of the apparatus shown in Fig. l;

Fig. 6 is a top plan View with certain parts omitted for purposes of clarity of the apparatus shown in Fig. 5;

Fig. 7 is a perspective view of a portion of the hopper means employed in the embodiment of Fig. l with certain parts omitted for purposes of clarity;

Fig. 8 is a sectional view, with parts broken away, through an impeller casing employed in the apparatus of Fig. 1; and

Fig. 9 is a side view of the casing of Fig. 8.

Referring to the drawings in greater detail, the invention comprises a device for directing a stream of surface as abrasive material upon workcleaning and descaling same or for for conditioning the surface for other purposes. Various types of abrasive particles may impeller employed in the be employed. For example, the abrasivernay be organic matter, such as pulverized husks or shells, or may be inorganic matter, such as emery, pumice, marble dust, silicon carbide or divided metal. VFor example, steel shot or YCarborundum globules, may be employed. The size of the abrasive particles can vary from very ne powder size up to, for example, y of an inch in diameter. It is possible to employ granules of larger diameter but it is believed that about 3/16 of an inch is as large as normally will be employed. Also, such particles may be mixed with a liquid to form a slurry.

The apparatus is provided with a main outer housing which completely encloses the device in order to prevent the escape of such particles and dust. Extremely line dust can be removed from the housing 10 by means of a suitable blower 11 which is driven by a motor 12 and which is 'connected to an opening 13 in the upper portion of the housing by means of a conduit 14. Suitable battle plates 15 can be employed for preventing the escape of particles of undesired size. The blower or fan 11 is connected at its outlet 11a to a suitable collector (not shown).

In the embodiment shown,` the workpieces, whose surfaces are to be abraded or linished, are tumbled within a rotatable tumbling barrel 16 mounted upon trunnions 17 yand 18 and rotated at a desired speed by means of a motor 19 which is drivably connected thereto by any suitable means, such as a sprocket chain 20, which passes over sprocket wheels 21 and 22 respectively upon the shaft of the motor 19 and the trunnions 17.

The sides of the barrel 16 are constituted by the aforementioned wide mesh wire 23 or any suitable open work material adapted to this purpose.

YSituated beneath the tumbling barrel 16 are the impeller means for urging upwardly with large force the stream or streams of surface treating material. If desired, a single impeller may be employed but in the form shown two impeller's are provided whose planes of rotation are substantially in coincidence, such plane being also preferably positioned parallel to but slightly offset to one side of the axis of rotation of the tumbling barrel 16, although the latter is not entirely necessary. However, it is desirable, in view of the fact that the abrasive stream is directed more efciently along the lower portion of the tumbling barrel, thereby to abrade the surfaces to be iinished in a more efficient manner. The reason for so offsetting or for so positioning to one side the plane of rotation of the impeller means in the embodiment of Fig. l, is that the tumbling barrel 16 urges the general mass of workpieces off to one side due to its rotation. To accommodate this, the impeller is so odset. l

The impellers employed in the embodiment of Fig. l are indicated at 24 and 25, respectively. I have found one desirable form of an individual impeller is vtypified Vby means 24 which are shown in detail in Figs. 2, 3 and 4 and constitute a pair of impeller 4rods 24a and 24b (Fig. 3). Such rods are of any suitable metal and preferably aie'in the form of flat metallic strips, for example, of normal commercial construction steel and therefore of relatively low cost. As is well shown in Fig. 3, the impeller strips 24a and 2417 are mounted parallel to one another in a hub generally indicated at 26 consisting of a central hub element 27 through which passes a rotatably mounted shaft 2S, such central hub element being preferably substantially rectangular in cross section and thereby holding the impeller strips 24a and 24b in parallel relationship under the iniluence of a pair of opposite outer hub plates 29 and 30 which are urged tightly together by means of 'a suitable pair of bolts 31 and 32 (Fig. 4) to each of which is 'threadedly engaged a'converiti'onal threaded nut.

"In View lof the simplicity and low cost of the impeller, such as 24,l a`substantial 'rate of consumption of the strips 24a 'and .Z417 'is of no great consequence. Furthermore,

it is a 'simple matter Ato adjust the length ofthe s't'rips'Ziin and 24h, that is, to move same radially outwardly from the hub as they are worn down, Y outer path of the impeller wherein the periphery of such path is positioned to give the desired coaction with the abrasive particles and also to adjust peripheral (or tangential) velocity of the impeller blades. The volume of the stream of particles, of course, can be controlled by adjusting the width of the impeller strips 24a and 24h, the wider the Strip the greater the volume of such material that will be picked up and flung at Workpieces. Also the velocity ot such stream can be controlled by adjusting the angular velocity of the impeller.

Each of the impeller means is driven by a suitable power means, for example, the impeller 24 is drivably connected to an electric motor 33 (Fig. 5). Although it is desirable for each of the impellers to be driven by its individual electric motor, including the aforementioned motor 33 for the impeller 24 and also the motor 34 for the impeller 25, it is, of course, possible to employ a single motor for driving both impellers.

Each of the impellers is provided with an impeller casing which is substantially box-like in conformation but with substantially one upper quadrant thereof removed for the purpose of permitting the abrasive stream to escape upwardly. However, the outlines of the portion of the casing kwhich are removed are of speclal conformation in l order tofacilitate the recycling of the abrasive stream as will more fully appear hereinafter.

Consider for example an impeller housing 35 for'the impeller 24 which will now be described and which vis identical to an impeller housing 36 for the impeller 25, such impeller casings being in alignment with one another, as is well shown in Fig. '6, and with kthe open quadrants thereof adjacent one another.

Referring again to the impeller casing 35, the latter is provided with a pair of side plates 37 and 38 which, in the form shown, are vertical and thus substantially parallel. Such side plates 37 and 38 comprise the vertical and principal sides of the box-like impeller casing from which substantially one quadrant has been removed, such removed quadrant being schematically shown in broken lines at 39 (Fig. 1). Thus an opening exists in an upper quadrant region of the impeller casing.

The pulverulent material is fed into the impeller casing 35 via a pair of openings 40 and 41 (Fig. 5) which are located near the lower level of the path of movement of the impeller 24. Such openings 40 and 41 are 4controllable by suitable valve plates 42. and 43 respectively, thereby controlling the exent of the openings. Such valve plates may be controlled by means of a suitable handle positioned externally of the housing. For f'example, the valve plate 42, as shown in Fig. 1, may be shifted under the influence of 'a handle 44 pivotally secured to the housing 10.

The comminuted or pulverulent material is fed'through the openings 40 and 41 from suitable primary hopper means into which the material initially is stored. Such primary hopper means are Well shown in Fig. 5 and, in the formshown, constitute hoppers 45 and 46 respectively. yThe hopper 45, which is identical to hopper y46 but reversed in attitude 'relative thereto, will now be described. This hopper is constituted by an inclined plate 47 which, cooperating with the vertical side plate 37, forms a trough having a V-shaped cross section. The inclined plate 47 cooperates with one ofthe end surface plates of the housing 10 and with another surface to appear below to form such trough.

The pulverulent material is fed into the primary hopper 45 via a removable window 48.

The inclination of the plate 47 is selected for the purpose of insuring that the pulverulent material can slide through the opening 40 into the bottom region 49 within the impeller casing 35 Where it can build up 'to a level where the rotating 'impeller will entrain same 'and hurl the particles upwardly toward the workpiec'es.

thereby to insure a desired The rotating impeller not only may physically strike the abrasive particles in the lirst instance and thereby hurl them upwardly, but it createfL a vacuum due to its high angular velocity and thereby agitates the accumulated pulverulent material in the bottom of the casing and causes same to be thrown upwardly into the path of the rotating blades or impeller strips under the influence of such a vacuum which is created by the high angular velocity.

Thus as the pulverulent material is needed to create a stream thereof in suspension it is fed into the region 49 and thrown upwardly with large force toward the Workpieces within the tumbling barrel 16 and thereafter such particles fall downwardly into a secondary hopper 50 which is outside of the impeller casing and interposed between the primary hopper 4S and the tumbling barrel 16. That is, the secondary hopper 50 is above the primary hopper but below the tumbling barrel 16.

The function of the secondary hopper 50 it to permit the accumulation of the particles which have fallen under gravity toward the hopper means to permit same to build up above certain inclined surfaces of selected inclination whereby when a desired depth has been built up a landslide of the particles will occur to cause same to be fed to the rotating impeller via a suitable passage or opening which is positioned well above the opening 40 and preferably approximately on the same level as and near the shaft 28 which supports the impeller 24.

On the opposite side of the impeller 24 a similar and corresponding hopper 51 is located which serves a similar purpose. However, only the single hopper 50 will now be described.

Referring now to Fig. 7, the upper portion of the impeller casing 35 is illustrated which includes a roof member 35a mounted between side plates 37 and 38. The hopper 50 is constituted by an inclined plate 52 which directs the pulverulent material downward toward an opening 53 through which such material can pass onto a channel or chute 54. The opening 53 is formed within a plate 37a which preferably is at and constitutes a portion of the side plate 37. The plate 37a may be removed, if desired, and thus is separable from the main side plate 37.

Such plate 37a may be formed from a suitable rectangular plate from the top of which is cut a V-shaped portion and in the bottom of the V the 4opening 53 may be formed. However, the invention is not limited to such particular type of side plate, it being suicient if merely a suitable opening is provided for the feeding of the pulverulent material from the secondary hopper 50 into the side of the region of rotation of the impeller 24.

In order to assist the pulverulent material in reaching the opening 53 and thence the channel 54, not only is the inclined plate 52 employed, but a second inclined plate, as at 55, is also provided which is angularly disposed with the inclined plate 52 thereby jointly forming therewith an inclined sub-trough, the association of the surfaces thereof being somewhat similar to that of the roof of a gable with the inclined roof proper of a house from which the gable protrudes.

In operation, the pulverulent material is fed into the respective primary hopper means via the windows, as at 48, and the valve plates, as at 42, are suitably adjusted. The impeller means are rotated by energizing the motors 33 and 34 and such irnpellers are driven at high angular velocity, thereby creating a vacutun in the rotational region thereof which tends to draw inwardly the pulverulent material through the openings, as at 40 and 41, thereby to cause same to build up in the region 49 and eventually to be entrained by the rotating impellers and hurled upwardly with large force and high velocity against the workpieces within the rotating barrel 16. After striking the Workpieces and rebounding many times, for example, to other parts of the workpieces and to other workpieces, the particles then, under ythe inuence of gravity, fall back into the secondary hopper means, as at 50, thereby building up to a point Where a landslide thereof can occur through the opening 53 and the chute 54 and thence again into the path of the rotating impeller 24, the chute 54 directing such material into the impeller path at about the level of the rotating shaft 2S and near the latter. The particles thus again are thrown upwardly and the cycle is repeated with such particles again falling into the secondary hopper means. Small quantities of such particles may fall from the workpiece region directly into the lower region 49 in the impeller casing where the particles are struck by the rotating impeller and again hurled upwardly into the workpiece area. Furthermore, such particles which may fall directly into the region 49 not only may be hurled upwardly but may be hurled against other particles which have collected in such region thereby agitating same and forcing such other particles into the path of the rotating impeller.

lt is not necessary for the workpieces to be tumbled within a barrel, such as barrel 16, although in one form thereof, as above described, such barrel is provided. The', workpieces may be moved into the stream of particles by any suitable means, or, if desired, such workpieces may be turned as upon a spit. Any suitable conveyor means, may move the workpieces in succession, if desired, into and out of such stream or, if desired, such pieces may beiy held stationary in the stream as upon a stationary wire: mesh table. Also a turntable may be employed for sup-- porting the workpieces in the stream.

Where it is desired to provide a relatively smooth 1in ish to the workpieces, the velocity of the stream prefer. ably is reduced, such velocity being increased Where the finish is desired to be relatively more rough.

It will be understood that although only the single secondary hopper means 50, with its chute or channel 54, have been described above, each impeller preferably is provided with a pair of such hopper means and channel. However, it is within the purview of the invention to employ but a single such hopper and chute or channel with a single impeller.

The aforementioned odset position of the impeller casings and the impellers with respect to the axis of rotation of the tumbling barrel 16 is well shown in Fig. 5 wherein it is seen that the plane of rotation of the impeller means is directly beneath a region 56 which in turn is not di rectly beneath the axis of rotation of the barrel 16. The general mass of the workpieces being tumbled in the barrel 16 will be in the region 16a by virtue of the counterclockwise rotation of the barrel, as viewed in Fig. 5.

Referring now to Figs. 8 and 9, the adjustment of the point of introduction of the stream of particles to the impeller will now be described. As is well shown in Fig. 8, the chute 54 can be adjusted with its lowermost extremity toward or away from the rotating impeller 24. In the position of the chute 54 shown in solid lines, it will be seen that the trajectory of the falling stream is such that it will encounter the rotating impeller 2411 approximately at the region S6 whereas if the chute 54 is in the position shown in broken lines at 54a wherein its lower ertremity is closer to the rotating impeller, the trajectory of such falling stream is such that the point of impact with the rotating impeller is at region 57. The reason for the importance of the correct location of the point of impact between the falling abrasive stream and the impeller is that such point of impact must be adjusted in such a way that the stream is thrown off from the impeller in generally an upward direction towards the region of the workpieces.

Referring to Fig. 9, it will be seen that the optimum region of departure of such stream from the impeller is` approximately at 58 wherein the stream is thrown upwardly assuming generally the form, as at S9. lf the point of entry of the stream is improperly adjusted, such streammay be `thrown olf ina direction, as at' 60 or 61, which obviously willenot accomplish the purpose of the device but; will. result inwearing away of wear plate 6,2.

Thechute- 54lthus1is adjustable by any suitable means toward; or awayfrom the' impeller 24.

:In: addition to: the aforementioned adjustment of the spaced' relationship of: the'chute and the-impeller, there should@ be `carefully adjusted the position of the chute with respect .tolh'orizonta'l and-vertical coordinates having azerofpositon ati the axis ofthe impeller shaft 28. ln'the form-tof. the invention-shown in Figs. l 4and 5, the level of the. lowermost extremity of the chute 54 is slightly be low-thehorizontalplane passing through' the axis-ofthe shaft l28; y However, such level is adjustable to accommodate' ther-particulartype of surface treating particlesy employed', with particularl reference to-the speed of the impellersand. they density .of such particles. ln general, the lower the density thereof, the closer it may be introduced: toward the axis ofi theshaft 2,8. For example, pulverized walnut shells may be introduced much closer to the shafttZS than, for example, steel shot.

Furthermore, the speed of the impeller has an inuenceupon the level at which such particles are introduced. thereto, that is, considering the vertical coordinate as' shown in Fig. 9 passing through the center of tho shaftuZS and `measuring from such center downwardly, the lower the revolutions per minute of the impeller, thel lower` itis necessary to introducev the stream ofparticles into the impeller.

Thefactorswhich may be adjusted in the present in vention for the purpose of controlling suchstream are asfollows:

(l) The angular velocity of the impeller;

(2) The length of the impeller;

(3) The width of the impeller;

(4); The point of initial impact between the abrasive stream with the impeller;

(5) The horizontal distance between the lowermost extremity of the -chute 54 and the impeller;

(6) The distance between the axis of the impeller and the workpieces.

The. influence of the density of theparticles upon the point of entry of the stream into the impeller may gcnerally be summarized as follows:

If theparticles are of relatively low density, the stream thereof should be introduced into the side of the-rotatingimpeller at a relatively low` poi-nt as measured on the coordinateszshown in Fig. 9, that is, a relatively low` point belowthe horizontal'as measured along' the vertical coordinate O(-)Y and relatively close to. such vertical coordinate, that is, of a relatively low value with respect to the coordinate OX. Conversely if the particles are of relatively highdensity, the stream should be introduced with respect to suchvertical coordinate at a much higher location than that of the .relatively light abrasive and may be introduced at or slightly above the horizontal plane passing through the axis of the shaft 28. With respect to the coordinate OX (Fig. 9), such relatively highzdensity material may be introduced either substantially at'thevertical planeV passing through such shaft, or near the tipof the impeller, that is,` such material may be. introduced between the limits: (a) at the hub or (b) at the tip, the precise point of impact beingdetermined by theconsideration of the several factors enumerated above, together with the desired finish of the workpiece.

Referring particularly to Fig. 9, further description of the` special'characteristics of an impeller housing, such as 3S, will now be set forth. One of the important aspectsof such impeller housing and any of the others, such as-housing 36 employed in the embodiment of Fig. l, is that the housing* as a unit is removable from the overall housing of the apparatus. Referring now 'to' Fig. 6,iit is seen thatanopening at 63 is formed inthe main'` removable' impeller housing housing 10 of th'e-apparatus for the purpose of receiving Such* opening 63 .may .be com the impelle'rf housing 35, Y pletely closed and: sealed by means-ofi asuitablerern'v-A able panel or door 64.

One of theimportant advantages of employing such is thatsuoh housing isI in' effecta'n expendable element ofthelcombinatio'n and thus canendure.` severe abrasionbutcan be easil'yf replaced by merely removing same without appreciably disturbing the balance off the apparatus.- Such` abrasion yprincipally is undergone by the aforementionedwear plates, one of which has been described atf 62. An` opposit'ely facing' wear plate is eniployed atf65- whchis parallel to' plate` 62. Also upper and lower wear plates 35h and 6'6 (Fig. 9i respectively, comprise' the' roof and floor of theA impeller housing 35.

The wear plate 35aprevents abrasive particles from' falling into the downwardly moving impeller andthereby protects the' bottom wear plate 66 and the' two wear plates 62v and 65fby preventing abrasive particles from being hurled tliereagainstv after so falling from above the plate 35a.

If desired, each o'f the aforementioned wear plates 35a, 62, 65" and 66 may be removably attached to the impeller casing' 35 whereby anyv one or more can bev quickly replaced whenever required.

The wea'rplatev 62whicl' is substantially'in the lower center region of the. apparatus (Fig. l), together with* a corresponding wear plate 67 `ofthe impeller housing 36, both extend to the peak of the inverted' V comprisingA the upper terminus thereof, that is, both plates extend to a point 68. One of the reasons for so locating the wear plates 62 and 67 is to prevent -particles from being thrown from one impeller, for example, 24, into the path of the other impeller, e. g; 215. If-the streams of thc two` impellers 24 and 2S were not so separated, there would be a substantial tendency for the impellers mutually to destroy one another by abrasion.

What is claimedis:

l. In apparatus'oftheclass described, `a main housing,v

which such material is fed into such casing and thus'v from the side of the impeller into the path-of impeller movement; .-primaryhopper means for holding such pulverulent-material andy guiding same through such side plateopenings into ysuch casing; secondary hopper means abovesaid primary hopper means and also positioned at onev side of said impeller butl below said barrel into which vfalls such material after being thrown toward said barrel, such secondary hopper means havingoutlet means for directing material vfrom the side thereof intoV the path of movement of such rotatable impeller from the` side thereof, and also having inclined hopper surfaces ofselected inclination for permitting such material to accumulate in a. selected amount-prior to sliding through saidoutlet means.

2; In apparatus of the class described, a main housing; an impeller mountedV for rotation in the lower regionof suchhousing-and positioned for hurling a stream of particles upwardly; an impeller casing for partially enclosingv the region of rotation of said impeller, such casing having -a-n open' top quadrant region and including two `sideplates:onlopposite sides of the plane of r rotation ofthe impeller, each suchsidepl'ate` havinguan yopening therethrough nearl thewlower levelofthepath oftmoveparticles fromv ment of the impeller and through which such particles are fed into the casing and thus into the path of impeller movement from the side of the impeller; primary hopper means for holding such particles and guiding same through such side plate openings and into such casing; secondary hopper means above said primary hopper means but substantially below the top of the housing for recovering such particles falling therein by gravity after being thrown upwardly toward the top of the housing, such secondary hopper means having outlet means for directing material from the side of the plane of rotation and the path of movement of the impeller into such path of movement, and also having inclined hopper surfaces of selected inclination for permitting such abrasive material to accumulate in a selected amount prior to the sliding thereof through such outlet means.

3. In apparatus of the class described, a main housing in which workpieces are positionable for abrading the surfaces thereof with abrasive particles; impeller means mounted in the lower region of such housing and beneath the region wherein the workpieces are positionable, such impeller thus being positioned for hurling a stream of abrasive particles upwardly at the workpieces; primary hopper means for holding pulverulent abrasive material and guiding same from the side of the plane of rotation of the impeller means into the path of movement thereof, thereby to be entrained and hurled upwardly in the workpiece region of the housing; secondary hopper means positioned above such primary hopper means but below the workpiece region of the housing for recovering the abrasive particles after being thrown toward the workpieces and falling therefrom under the inuence of gravity, such secondary hopper means having outlet means for directing material into the path of movement of the rotatable impeller and from the side of such rotatable impeller means, and also having inclined hopper surfaces of selected inclination.

4. Apparatus in accordance with claim 3 wherein the outlet of said primary hopper means is at the lower region of the path of movement of the impeller means and the outlet means for the secondary hopper means is substantially at the level of the axis of rotation of such impeller means.

5. In apparatus of the class described, a main housing; means for supporting workpieces within such housing in the upper region thereof; an impeller mounted for rotation beneath such workpiece supporting means and positioned for hurling a stream of abrasive particles upwardly at such supporting means; an impeller casing for entirely enclosing the region of movement of the impeller except for one upper quadrant region thereof, such casing thus having an open top quadrant region and including two side plates on opposite sides of the impeller and of its plane of rotation; primary hopper means for holding pulverulent abrasive material and guiding same into the path of such impeller near the lowermost region of its motion and through one of said side plates; secondary hopper means positioned to one side of said plane of rotation and above said primary hopper means but below the workpiece supporting means for recovering the abrasive material after being thrown upward toward such supporting means, such secondary hopper means having outlet means for directing the abrasive pulverulent material into the path of movement of the rotatable impeller.

6. In apparatus of the class described, a main housing; an impeller mounted for rotation in the lower region of such housing and positioned for hurling a stream of abrasive particles upwardly; wear plate means positioned spaced from but about the path of peripheral movement of the impeller, such wear plate means having an opening therein for the passage of the upwardly directed stream of abrasive particles, such opening being located in an upper quadrant region about said impeller; primary hopper means for holding such abrasive particles and guiding same into the region of lowermost movement of the impeller means whereby such abrasive particles are entrained by the impeller and hurled through the aforementioned opening; secondary hopper means above such primary hopper means but below the top of such housing for recovering the abrasive particles after being thrown upwardly toward the top of the housing, such secondary hopper means having adjustably positioned outlet means for redirecting the abrasive material into the path of movement of said impeller.

7. In apparatus of the class described, a main housing having a top covering; an impeller mounted for rotation in the lower region of such housing and positioned for hurling a stream of particles upwardly; an impeller casing of generally box-like conformation for partially enclosing the region of rotation of said impeller, such casing having an opening in the top region thereof through which such upwardly hurled stream of particles can pass, such impeller casing having a roof member over that portion of the path of such impeller wherein such impeller moves downwardly, thus preventing particles which have been hurled by said impeller upwardly out of said impeller casing through such casing opening, from falling downwardly from the top covering of such housing and being engaged by the downwardly moving portions of said imcasing roof member being spaced below the top coverlng of said housing thereby providing space for the positioning therein of workpieces above the aforementioned opening in such casing; hopper means having a chute-like outlet, such hopper means being positioned for collecting the particles after having been thrown upwardly by the impeller, such chute-like outlet being positioned for directing a stream of abrasive particles directly therefrom into the path of movement of the rotatable impeller from the side thereof.

References Cited in the le of this patent UNITED STATES PATENTS

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