US1842619A - Sheet cleaning apparatus - Google Patents

Description

Jan. 2@, 1932. H, MCCRERY v 1,842,619

SHEET CLEANING APPARATUS Filed Oct. 24. 192? 5 Sheets-Sheet l avwwnto'a uHan. 26, 1932.

H. E. MCCRERY 1,842,619

SHEET CLEANING APPARATUS F iled Oct. 24, 1927 5 Sheets-Sheet 2 Jan. 26, 1932.

H. E. MCCRE'RY 1,842,619

SHEET CLEANING APPARATUS iled Oct. 24, 1927 5 Sheets-Sheet 3 v Jan26, 1932. H, E. MCCRERY 1,842,619

SHEET CLEANING APPARATUS Filed Oct. 24. 1927 5 Sheets-Sheet 4 amoemroz h. E/VCCREW Jan. 26, 11932. H E MCCRERY 1,842,619

SHEET CLEANING APPARATUS Filed Oct. 24, 1927 .5 Sheets$heet 5 till Patented Jan. 26, 1932 UNITED STATES PATENT OFFICE HAROLD E. MCCRERY, .OF APOLLO, PENNSYLVANIA, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO BLAW-KNOX COMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORA- 'I'ION OF NEW JERSEY SHEET CLEANING- APPARATUS Application filed October 24, 1927.

This invention relates to apparatus for cleaning scale and other foreign material from metal sheets, and more particularly sheets of iron and steel. v

in my copending application Serial No. 196,959. filed June 6th, 1927, I have disclosed a scale removing apparatus wherein successive sheets of metal are caused to be fed between spaced parallel series of abrasive impacting nozzles to be cleaned, each series of nozzles being adapted to be slowly reciprocated in alinement with each other transversely of the sheets to be cleaned to evenly distribute the impacting material against the sheets thus effectually cleaning the latter without streaking the sheets. In thestructure referred to,the abrasive material is fed to the nozzles by gravity from a hopper arranged above the nozzles, the greater proportion of the abrasive material being collccted and returned to the hopper by suitable conveying means. Novel means is employed for reciprocating the nozzles referred to, such means being adjustable to vary the distance of reciprocation. Eachv individual nozzle is provided with means to supply fluid pressure to be mixed with the abrasive materiai in the individual nozzles.

The apparatus referred to is adapted to eliminate the objections incident to the usual practice of removing the scale and other foreign material from the sheets by pickling them in an acid bath. The latter practice requires considerable time and is not continuous, it being necessary to immerse and remove successive batches of the sheets. Some of the scale on the sheets adheres more tightly than others, and the pickling operation must be continued until the scale wholly lell'lOVOd from the sheets. Accordingly it has been found that where the scale is relatively loose. the surfaces of the sheets are pitted by the action of the acid when the sheets are left in the pickling bath a suiiicient length of time to remove the tightly adhering scale. lVhen the pickling operation is completed, it is necessary to thoroughly wash the sheets to remove the acid as completely as possible since the presence of acid in the smallest quantities on the sheets causes Serial No. 228,332.

consequently adds to the cost of the process as a whole. Regardless of the thoroughness with which the sheets are washed, it is impossible to completely remove all of the acid since the latter finds its way into the pores of the metal and cannot be readily washed out. As a result it is necessary to coat the sheets by galvanizing, painting or the like within a relatively short time after the complet-ion of the washing operation to prevent corrosion of the sheets.

The apparatus shown and described in my copending application above referred to is adapted to eliminate the use of an acid bath for cleaning the scale from the sheets, the scale being completely removed in a continuous operation without any injury to the sheets, and the subjection of the sheets to the coating operations may be delayed for a considerable period of time without any corrosion appearing on the sheets. ing action of the apparatus referred to is so efficient that relatively heavy sheets after being subjected to the cleaning operation can be cold rolled to reduce their thickness and will be very highly polished in such a rolling operation.

The present apparatus is the same in principle as the apparatus shown and described in my copending application and is adapted to perform its functions in the same efficient manner, but involves improvements thereover.

An important object of the present invention is to provide means for mixing the compressed air or other fluid with the abrasive material prior to conveying it to the nozzles whereby the usual drop in pressure incident to mixing the air and abrasive in the individual nozzles is eliminated, the initial relatively high pressure of the air being substantially entirely preserved thus economizing in the use of air and permitting the device to be operated at a lower cost.

A further object is to provide an apparatus of the character referred to wherein the sup ply of abrasive material is maintained beneath the impacting nozzles and is fed thereto The cleanby air or other fluid pressure, the abrasive material from the lower nozzles being returned to the source of supply by gravity.

A further object is to provide novel means for picking up the abrasive particles from the upper faces of'the sheets being cleaned and returning the abrasive to the source thereof.

A further object is to provide an improved form of abrasive nozzle manifold whereby eflicient distribution of the abrasive to the various nozzles is effected.

A further object is to provide a plurality of the manifolds referred to, and to provide single conduit means for supplying air and abrasive material toeach manifold, thus eliminating the use of separate pipes or con duits to each nozzle.

A further object is to provide novel means for returning the abrasive to the source thereof after it has been impacted against a sheet, to be mixed again with air under pressure and returned to the sheets for further abrasive action.

A further object is to provide a supply tank for the abrasive and an abrasive collecting hopper arranged thereabove, the tank being provided with an upper intermediate compartment into which abrasive is adapted to be fed from the hopper when atmospheric pressure is present in the hopper and upper compartment, and from which the abrasive is adaptedtobe fed downwardly into the lower portion of the tank when the pressure in the upper and lower portions of the tank is equalized, valve means being employed for changing the pressure conditionsvreferred to and effecting movement of the abrasive from the hopper to the main or lower tank and adapted to be controlled by automatic means.

Other objects and advantages of the invention will become apparent during the course of the following description.

In the drawings I have shown one embodiment of the invention. In this showing,

Figure 1 is a vertical tranverse sectional View through the apparatus, parts being shown in elevation,

Figure 2 is a side elevation,

Figure 3 is an enlarged central vertical sectional view through a portion of the apparatus, p

Figure 4 is a front elevation of a portion of the actuating means for the moving parts of the apparatus, parts being shown in sec tion,

I Figure 5 is a plan view of one of the abrasive noz'zle units, Y

Figure 6 is a central vertical sectional view through one of the nozzle manifolds and associated elements,

Figure 7 is an enlarged transverse sectional view of the abrasive tank and associated elements, and,

Figure 8 is an enlarged transverse sectional view of one of the manifolds.

Referring to Figures 1, 2, and 3, the numeral 10 designates a casing as a whole which may be arranged on the floor 11 or other suitablevfoundation. The casing is provided in one side with an inlet opening 12 into which the sheets are fed and in its opposite side with a discharge opening 13 through which the sheets pass after the cleaning operation has been completed. A pair of shafts 14 and 15 is arranged transversely of the casing, these shafts preferably being square for a purpose to be described.

A plurality of manifolds 16 is carried by each of the shafts 14 and 15, each of these manifolds preferably being an integral casting and provided on one side wiah a boss 17 having an angular recess 18 therein, as shown in Figure 8. The shafts are preferably angularly arranged whereby one corner portion of each shaft is adapted to be arranged in the corresponding recesses 18. The outer corner of each shaft is provided with flattened portions 19 and screws 20 pass through the shafts and are threaded in the bosses 17. It will be apparent that the heads of the screws are adapted to engage against the flattened portions of the shafts.

Any suitable number of manifolds may be employed, and in the drawings I have shown four upper and fourlower manifolds, the two sets of manifolds being inverted with respect to each other. The manifolds are shown in detail in Figures 5, 6 and 8 of the drawings. Each manifold is provided with a cylindrical end 21 to which is connected a pipe 21, the lower end of which is connected to a four-way connection 22 having a closure plug 22 in two branches thereof. The fourth branch of each connection 22 is connected to one endof a flexible hose 23 for a purpose to be described. Inwardly of the connection 21, each manifold is flared as at 24 to provide a relatively large flat inner end 25 having at spaced intervals a plurality of openings 26 therein.' Transversely, each manifold is relatively fiat as indicated in Figures 3 and 8, thus providing a reduced passage 27 adjacent the connection 21 for a purpose to be described. The manifold gradually increases in width toward its inner end as shown in the figures referred to.

A threaded fitting 28 is arranged over each opening 26 and is provided at opposite sides with ears 29 through which are passed bolts 30 by means of which the fittings are secured against the upper end 25 of the manifold. A jet or nozzle 31 is associated with each fitting 28, each nozzle having an annular flange 32 seating upon the end of its associated fitting. The inner end of each nozzle projects into one of the fittings and the nozzle has an opening 33 passing therethrough passages 33 through the nozzles slightly inzontal tank crease in diameter toward the outer nozzles for a purpose to be described.

A hopper 36 comprising a pair of outwarly flared side walls is arranged beneath the casing of the apparatus, as shown in Figure 3. A plurality of short pipe sections 33 extend through one wall of the hopper 36, and each pipe section is connected to one of the flexible hoses- 23, as shown in Figure 3. A preferably cylindrical hori- 39 is arranged beneath the lower end of the hopper, the lower extremity of the latter extending downwardly through an opening 40 formed in the tank 39 and being rolled as at 41 to form av valve seat in a manner to be described. Brackets 42 are adapted to secure the tank 39 and hopper 36 together, as will be apparent.

The valve seat 41 extends substantially throughout the length of the tank 39, While the latter is co-extensive with the'hopper 36. A valve indicated as a whole by the numeral 43 is adapted to engage the valve seat 41. This valve is elongated and obviously coextensive with the valve seat 41, and includes a preferably hollow body 44 which is triangular in cross section. A valve 45 is arranged over the upper faces of the body 44 and is preferably formed of rubber or other similar material. Arms 46 are connected to the valve 43 and are secured to a longitudinally extending shaft 47 journalled in brackets 48 arranged within the tank 39. This shaft extends through oneend of the tank and is provided at its extremity with an arm 49 for a purpose to be described. A suitable stuffing box 50 preferably surrounds the shaft 47 at the point where the latter extends through the end wall of the tank 39.

A relatively small substantially cylindrical tank 51 is arranged within the tank 39 and divides the latter into upper and lower cornpartments 52 and 53. The tank 51 is open at its top and the upperedge portions of the tank are bolted or otherwise secured to the upper portion of the tank 39 as at 53. The bottom portions of the tank 51 are turned to form a valve seat 54, similar to the valve seat 41 previously described. A valve 55 is adapted to engage the seat 54. This valve is similar to the valve 43 and need not be referred to in detail.

Arms 56 are connected to the valve 55 and are secured to a longitudinally extending shaft 57 journalled in brackets 58 carried by the tank 51. The shaft 57 also extends beyond the end of the tank 39 through a suitable stuffing box 59, and is provided at its projecting end with an arm 60. A-spring 61 is connected between the arms 49 and tending normally to urge these arms toward each other and thus close the valves 43 and 55. A shaft 62 is arranged between the arms 49 and 60 and is provided with a cam 63 adapted to engage these arms. The shaft 62 is adapted to be rotated slowly by any suitable drive means, thus causing the cam 63 alternately to engage the arms 49 and 60 and thus alternately open the valves 43 and 55. When the valve 43 is open, atmospheric pressure is present in the hopper 36 and the intermediate compartment 52, and accordingly abrasive will flow from the hopper to the compartment referred to. Air or other fluid under pressure is adapted to be supplied to the lower compartment 53 through a supply pipe 64, thus maintaining air under pressure in the compartment 53. Under such conditions, it will be apparent that when the valve 55 is opened, fluid pressure will escape into the compartment 52 thus balancing the pressure in the two compartments and permitting the abrasive in the compartment 52 to flow clownwardly into the compartment 53.

Referring to Figure 7, the numeral 63 designates a mixing chamber preferably in the form of an integral casting having flanges 66 by means of which the mixing chamber may be secured against the bottom of the tank 39 by rivets or the like 67. One of the chambers is provided for each of the lower manifolds 16, and for each pair of upper manifolds, and thus it will be apparent that six of the mixing chambers preferably are employed in the construction illustrated, as shown in Fi ure 1. Each chamber 65 communicates with the interior of the tank 39 through a relatively large opening 68, as shown in Figure 7 the top of the chamber 65 being provided with a spider 69 through which such communication takes place. A central threaded member 70 is carried by the inner ends of the arms of the spider and supports a vertically extending tube 71 having perforations 72 therein. The pipe 71 is adapted to supply air under pressure from the tank 39 to the corresponding mixing! chamber 65, as will be apparent. An aux-. iliary air supply pipe 71' also communicates with each chamber 65. Each mixing chamber is provided in one side with a tubular portion 73 extending laterally with respect to the tank '39, this tubular portion communicating with one end of a'pipe 74. A fourway connection is arranged at the outer end of each pipe 74 and is closed in two of its branches by plugs 76. The remaining branch of the connection 75 extends vertically and is connected with a pipe 72'. The upper end of each pipe 72 is connected to a four-way fitting 73'. one branch of this fitting being connected to one of the pipes 38. The remaining two branches of the fitting are provided with plugs 74. If desired,

a valve 75 may be arranged in each pipe 7 2. It has been found inadvisable from a practical standpoint to curve the various pipe connections from the mixing chambers to the pipes 21, for the reason that the abrasive, traveling at a high velocity, tends rapidly to wear off such curved pipe sections. Accordingly the various four-way fittings have been employed so that the impact action will be taken up by the plugs which are arranged in the path of travel of the abrasive. The abrasive materials tends to pile up to a certain extent in the corners of the fittings thus protecting to some extent the plugs which receive the impact. All of the plugs are adapted to be removed for replacement purposes and to permit the various pipes to be cleaned out if necessary.

The two mixing chambers 65 at the end of the tank 39 are connected to vertically extending pipes 77 which preferably are arranged outwardly of the ends of the casing 10, thus permitting the latter to be shortened. The upper ends of these pipes also are provided with four-way connections 78 having plugs 79 therein, for the same purpose as the connections and plugs 76. Each connection 78 has one branch connected to an inwardly extending horizontal pipe 80, as shown in Figure 1, the latter pipe being provided with a pair of depending branches 81. The inner ends of thepipes 80 are provided with impact plugs 82. Each branch pipe 81 is connected to one of the upper manifolds 16 through a flexible connection 83..

Successive sheets 84 are adapted to be fed through the apparatus in a manner to be described to pass between the sets of nozzles 31,

as shown in Figure 1. Abrasive material will be impacted against the sides of the sheet, and the abrasive from the lower nozzles will fall downwardly into the hopper 36 after striking the sheets. Means are provided for picking up the material impacted against the upper face of the sheet and returning it to the hopper 36. As shown in Figures 1 and 3, a hood 85 surrounds the 'upper set of'manifolds 16, being provided with openings 86 through which the connections 21 extend. The hood 85 is provided with end walls 87 and side walls 88 which preferably extend downwardly somewhat beneath the lower ends of the upper nozzles 31. The hood 85 is connected to a plurality of flexible hoses 89, the upper ends of which connect to branches 90 carried by a pipe 91. The branches 90 extend into the pipe 91 at a sharp angle, and the left end of the pipe 91, as viewed in Figure 1, is connected to a high speed fan or blower to project air through the pipe 91 at a high velocity. This air per-.v

forms an ejector action on the branches 90, thus maintaining a partial vacuum in the hood 85 to pick up the abrasive particles ejected from the upper nozzles 31. It will be apparent that as the abrasive particles strike the sheet, they will bounce upwardly therefrom thus easily being collected by the hood 85. The right hand end of the pipe 91 communicates with a downwardly extending pipe 92 which has its lower end arranged in the hopper 36 to discharge the abrasive mate-- rial thereinto.

A pair of upper and lower vacuum hoods 93 and 94 is arranged at opposite sides of the sets of nozzles 31, as shown in Figure 3. The adjacent edges of the hoods of each pair are spaced from each other to permit the sheets to pass therethrough, and suitable uide rolls 95 are associated with each pair 0 hoods to assist in properly positioning the sheets for passage therethrough. The hoods are connected to any suitable source of suction whereby a partial vacuum is maintained therein to pickup any loose particles ofabrasive and foreign material from the sheets which .fail to fall downwardly into the hopper 36, or to be picked up by the hood 88. Wear plates 96 are arranged in the end portions of the pairs of hoods to assist in guiding the sheets in a straight line through the apparatus, and to prevent the sheets from wearing against the side walls of the casing 10. Suitable flaps 97 are arranged at opposite sides of the vacuum hoods to minimize the outward passage of abrasive material as the sheets are being subjected to the action of the nozzles 31. The passage of each successive sheet through the apparatus obviously is adapted to open the flaps. If desired, a pair of wear plates 98 also may be arranged at op-' posite sides of the apparatus adjacent the end portions of the sets of nozzles 31.

Upper and lower feeds rolls 99 and 100 are arranged in the inlet and outlet openings of the apparatus, these rollers being mounted upon shafts 101 and 102 respectively. The roll 99 is preferably provided with a coating of rubber or other similar material 103 which is adapted to engage the surface of each sheet fed into the apparatus. The shaft 101 is journalled in bearing blocks 104 which are normally urged downwardly by springs 105, screws 106 being adapted to adjust-the tension of the springs 105. v

The shafts 14 and 15 are adapted to be longitudinally reciprocated in a manner tqbe described to effect movement of the nozzles 31 transversely of the sheets. These shafts extend through and are secured to flexible elements 107 secured at their edges within openings 108 formed in the'walls of the easing. It will be apparent that these flexible elements permit the reciprocating action of the shafts 14 and 15 to take place without permitting the escape of abrasive from the apparatus.

Supporting frames 109 are arranged at opposite sides of the apparatus. These frames and their associated elements are identill tical and only one need be referred to in detail. Referring to Figures 1 and 4, the numeral 110 designates two'pai-rs of rollers associated with each shaft 14 and 15 and arranged at right angles with each other, whereby it will be apparent that each roller engages one face of its associated shaft 14 or 15. The rollers 110 are journalled between ears 111 carried by disks 112, each of these disks being arranged in a support 113 which is vertically adjustable by means of a screw 114 whereby it will be apparent that the distances of the nozzles 31 from the sheets may be varied. The disks 112 are adapted to be circumferentially adjusted by loosening bolts 115 which secure plates 116 against the supports 113. Thus it will be apparent also that the angularity of the nozzles 31 may be varied with respect to the surfaces of the sheets. The ends of the shafts 14 and 15 are swivelly connected as at 117 to heads 118 preferably formed integral with frames 119 having vertical slots 120 therein. These slots receive blocks 121 which are eccentrically connected to gears 122, whereby itwill be apparent that rotation of the gears referred to is adapted to effect reciprocation of the shafts 114 and 115, vertical movement of the blocks being taken up in the slots 120. The latter slots are sufficiently long to permit the vertical adjustment of the shafts 14 and 15 in the manner previously described. Each block 121 is pivotally connected as at 123 link 124, the opposite end of this link being pivotally connected as at 125 to a shaft 126. Each of these shafts carries a piston 127 mounted to reciprocate in a cylinder 128, the piston and cylinders acting as dash pot means to cushion the movement of the shafts 14 and 15 adjacent the ends of their strokes.

rtn intermediate gear 129 meshes with the gears 122 and is mounted upon a shaft 130 which also carries a large gear 131 meshing with pinion 132. This pinion is carried by a shaft 133 journalled in bearings 134, and the opposite end of the shaft is provided with a gear 135, as shown in Figure 2. The, latter gear meshes with a pinion 136 driven by a motor 137. v

Any suitable means may be employed for driving the pinch rolls 99 and 100, and the guide rollers 95 and in practice it is preferred that the shafts which carry these elements be provided with sprockets about which passes a signal endless chain 138, as shown in Figure 4. The drive means described is similar to that shown in my copending application previously referred to. The chain 138 is adapted to be driven by a chain 139 passing around a. by a shaft 141, the latter sprocket 140 carried shaft carrying a bevel gear 142 meshing with a bevel gear 143 mounted upon a shaft 144.

it worm wheel 145 also is mounted upon the shaft 144 and meshes with a worm 146 mounted upon a shaft 147. The sprocket 148 is to one end of a carried by the shaft 147 and is adapted to be driven by a chain 149 the upper end of which passes around a sprocket 150. Any suitable variable speed drive may be employed for rotating the sprocket 150 and in the drawings I have shown an ordinary commercial form of Reeves unit 151, the inlet side of which is connected to a-motor 152 by a drive belt 153. 1 The operation of the apparatus is as folows:

The forward edge of each successive sheet is fed between the rolls 99 and 100 at the inlet side of the apparatus, and rotation of the roll 100 is adapted to feed the sheet into the apparatus. The advancing sheet is guided in its movement by the Various rollers 95 and the forward edge of the sheet is adapted to lift each successive flap 97. The forward edge of the sheet as it reaches the outlet side of the apparatus is engaged by the rolls 99 and 100 to be discharged from the apparatus.

Any suitable quantity of abrasive material is initially placed in the hopper 36 and the lower compartment 53 of the tank 39 is conuected to a suitable source of air pressure by the pipe 64. As the shaft 62 (see Figures 2 and 3) slowly rotates, the cam 63 will lift the arm 49, thus swinging the valve 43 downwardly to establish balanced pressure within the tank 51 and hopper 36. Thus abrasive material will flow downwardly into the tank 51 until the latter is full, or until the cam 63 releases the arm 49. Continued movement of the cam causes the arm 60 to be swung downwardly, thus opening the valve 55 and permitting pressure to escape from the compartment 53 to the tank 51 until a balanced pressure is established between these compartments, whereupon the abrasive in the tank 51 will be fed downwardly by gravity into the lower compartment 53. The abrasive flows into the various mixing chambers 65, and will be picked up by air under pressure therein, this pressure being suppliedthrough pipe 71. The pipe 71 is arranged in alinement with the pipe 74 and assists in feeding the abrasive material, and in keeping the chamber 65 clear. The air and abrasive thus will be mixed and will be forced through the various pipe connections of the different manifolds. The supply of the abrasive and air through clearly understood from the foregoing description. The flexible hoses 23 are provided to permit the reciprocating motion of the manifolds and nozzles, as will be understood. Passage of the air and abrasive through the restricted portion 27 in each manifold causes the abrasive to be spread out for passage to each of the individual nozzles 31. However, it has been found that there will be a slightly greater feed of air and abrasive to the central nozzles 31, and accordingly nozzles are employed, the passages 33 of which, progressively increase in diameter toward the outer the piping connections will be nozzles. Thus an even feed of abrasive against the sheets is obtained to provide an e cient cleaning action.

The abrasive impacted by the lower set of nozzles will strike against the lower face of the sheets and then will fall downwardly directly into the hopper 36. The abrasive from the upper nozzles will strike the sheet and bounce upwardly to be picked up by the hood 85 and thus returned to the hopper 36 through pipes 91 and 92. Thus it will be apparent that the same body of abrasive material may be used continuously. Since the air under pressure and abrasive is fed directly in a mixed condition to the nozzles, it has been found that there is a very slight decrease in the pressure of the air between the tank 39 and the impacting nozzles. Thus lower air pressure may be employed than in the form of the apparatus disclosed in my copending application, and a smaller quantity of air will bere uired. It will be obvious therefore that t e apparatus is adapted to be very economically operated. The large hood 85, and the auxiliary vacuum hoods 93 and 94 also serve the purpose of carrying off excess pressure generated within the casing 10, thus minimizing the flow of abrasive material out-. wardly from the casing. The shafts 14 and 15 are reciprocated by rotation of the gears 122, these elements being connected eccentrically to the blocks 121 to transmit their rotary movement into reciprocating movement. The angularity of the nozzles readily may be varied by loosening the nuts 115 and rotating the disks 112 to the desired degree. The distance between the nozzles and the sides of the sheet also may be adjusted by proper operation of the screws 114. The adjusting and reciprocating means for the shafts 14 and 15 are fully disclosed in my copending application previously referred to, as are also the means for driving the rolls 99 and 100, and the rollers 95. It will be apparent that the Reeves unit 151 may be controlled to vary the speed ratio between the motor 152 and shaft 147, whereby the pinch and guide rolls may be rotated at any desired speed. The pinch rolls are adapted to feed the sheets through the apparatus at a slow rate of speed, as will be apparent.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same and that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of the invention or the scope of the subj oined claims.

I claim:

1. Apparatus of the character described comprising a source of abrasive material, a

- pair of nozzles facing and spaced from each other, means for supplying fluid under pressure and abrasive material from said source to said nozzles for discharge therethrough against a sheet passing therebetween, a hood arranged over one of said nozzles, a conduit communicating between said hood and said source, and means for creating a partial vacuum in said hood to pick up discharged abrasive material and return it to said source through said conduit.

2. Apparatus of the character described comprising a source of abrasive material, upper and lower sets of alined nozzles arranged parallel to each other, means for supplying fluid pressure and abrasive material from said source to said nozzles for discharge therethrough against a'sheet passing between the sets of nozzles, a hood having an open bottom portion surrounding said upper set of nozzles, a conduit communicating between said hood and said source, and injector means associated with said conduit for creating a partial vacuum in said hood to pick up abrasive material discharged against the upper face of the sheet and return it to said source through said conduit.

3. Apparatus of the character described comprising a source of abrasive material including a hopper, upper and lower sets of alined nozzles arranged parallel to each other above said hopper, means for supplying fluid pressure and abrasive material from said source to said nozzles for discharge therethrough against a sheet passing between said sets of nozzles, a hood having an open bottom portion surrounding said upper set of nozzles, a conduit communicating between comprising a fluid tight tank constituting a source of abrasive material, upper and lower sets of manifolds each provided with a plurality of relatively small closely arranged nozzles, the nozzles of the upper and lower sets being substantially parallel to and directed toward each other, means for conveying a sheet of material between said sets of nozzles, means for supplying fluid under pressure to said tank, a conduit connected between the bottom of said tank and each of said manifolds, a hopper arranged beneath said nozzles to collect abrasive material impacted through the latter against the lower surface of a sheet. passing between said nozzles, means for returning abrasive material from said hopper to said tank, and means for returning to said tank abrasive material impacted against the upper surface of the sheet,

said last named means including a hood in which a partial vacuum is maintained for collecting the impacted abrasive.

5. Apparatus of the character described comprising a tank constituting a source of 5 abrasive material, upper and lower sets of abrasive impacting nozzles, the nozzles of the upper and lower sets being substantially par allel to and directed toward each other, means for conveying a sheet of material be- 1 tween said nozzles, means for supplying abrasive material from said tank to said nozzles under pressure, a hopper arranged beneath the lower set of nozzles to collect abrasive impacted against the lower surface of a sheet 1 by the lower set of nozzles, means for returning abrasive material from said hopper to said tank, and means for collecting abrasive material impacted against the upper surface of the sheet by the upper set of nozzles and returning it to said tank.

6. Apparatus of the character described comprising a tank constituting a source of abrasive material, upper and lower sets of abrasive impacting nozzles, the nozzles of the upper and lower sets being substantially parallel to and directed toward each other, means for conveying a sheet of material between said nozzles, means for supplying abrasive material from said tank to said nozzles under pressure, a hopper arranged beneath the lower set of nozzles to collect abrasive impacted against the lower surface of a sheet by the lower set of nozzles, means for returning abrasive material from said hopper to said tank, and means for returning to said tank abrasive material impacted against the upper surface of the sheet by the upper set of nozzles, said last named means including a hood in which a partial vacuum is maintained tor collecting the impacted abrasive.

lln testimony whereof ll afiix my signature.

HAROLD E. MQORERY.

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