US2777256A

US2777256A - Apparatus for graining surfaces

Info

Publication number: US2777256A
Application number: US476294A
Authority: US
Inventors: Jens A Paasche
Original assignee: Cline Electric Manufacturing Co
Current assignee: Cline Electric Manufacturing Co
Priority date: 1954-12-20
Filing date: 1954-12-20
Publication date: 1957-01-15
Anticipated expiration: 1974-01-15

Description

1957 J. A. PAASCHE APPARATUS FOR GRAINING SURFACES 8 Sheets-Sheet 1 Filed Dec. 20, 1954 NNN W Jan. 15, 1957 J. A. PAASCHE APPARATUS FOR GRAINING SURFACES 8 Sheets-Sheet 2 Filed Dec. 20, 1954 Jan. 15, 1957 J. A. PAASCHE APPARATUS FOR GRAINING SURFACES Filed Dec. 20, 1954 8 Sheets-Sheet 3 INVENTOR.

H. l h+ m HHHQQ PHHHU m HHHHU W Jan. 15, 1957 J. A. PAASCHE 2,777,256

APPARATUS FOR GRAINING SURFACES Filed Dec. 20, 1954 8 Sheets-Sheet 4 mam?? 76726 31546624 Jan. 15, 1957 J. A. PAASCHE APPARATUS FOR GRAINING SURFACES 8 Sheets-Sheet 5 Filed Dec. 20, 1954 INVENTOR. Jw Qflaaake J- A; PAASCHE APPARATUS FOR GRAINING SURFACES.

' Jan. 15, 1957 '8 Sheets-Sheet 6 Filed Dec. 20, 1954 I 1957 J. A. PAASCHE APPARATUS FOR GRAINING SURFACES 8 Sheets-Sheet 7 Filed Dec. 20, 1954 II I I II I em M 6 w 6 0 w W 5 H 3 Z I I II 1 m 0 II w o w g fl I z I I 6 Z0 0 m A z W 3 m T I a, o w 7 M 11/ Q w a a FINN Jan. 15, 1957 J. A. PAASCHE APPARATUS FOR GRAINING SURFACES 8 Sheets-Sheet 8 Filed Dec. 20, 1954 IN VEN TOR.

United States Patent APPARATUS FoR GRAINING SURFACES Jens A. Paasche, Chicago, 11]., assignor to Cline Electric Manufacturing Company, Chicago, Ill., a corporation oflllinois- Application December 20, 1954, Serial No. 476,294 1 11 Claims. (Cl. 51-14) The present invention relates: to a novel method and apparatus for preparing the surface of sheet metal and the like for the application thereto of a coating andmore particularly to a novel method and apparatus for pre paring printing plates for the application. of printing ink although as willappear from the description given'hereinbelow certain features of the present invention may be utilized for preparing surfaces for the application of various coating materials. i

An object of the present invention is to provide a novel method and apparatus for preparing a surface for the application of a coating material thereto andmore particularly to a novel method and apparatus for cleaning and texturing a surface whereby to obtain an improved bond between the surface and the coating material.

A more specific object of the present invention is to provide a novel method and apparatus for treating sheets of aluminum and the like to be used for printing whereby the printing ink may be applied to the sheets in a predetermined manner without spreading orfiowing over the sheetso-as to destroy the pattern.

Still another object of the present invention isto pro-' vide a novel apparatus for'treatin'ga surface with abrasive particles to prepare the surface for the purposes set forth hereinabove, by which apparatus. the surface may be rapidly, economically and uniformly prepared.

A further object of thepresent invention is to provide a novel apparatus of the type described above which apparatus is adapted to apply the abrasive to and recover the abrasive from the surface being treated for re-use while maintaining the atmosphere around' the apparatus relatively free of the abrasive particles to prevent discomfort to an operator.

Another object of this invention is toprovidea novel apparatus of the above described type whereina suction is provided for not only preventing dust. from entering into the surrounding atmosphere, but also for auto matically retaining the sheet material being processed-on suitable conveyor means.

Other objects and advantages of the presentiinvention will become apparent from the following'description"and the accompanying drawings wherein:

Fig. 1 is aside elevational view showing an apparatus embodying the features of this invention;

Fig. 2 is an elevational view showing the-end of the apparatusinto which sheet material to be treated is fed;

Fig; 3 is=a plan view reduced in-scale' of the apparatus Ofi'this invention;

Fig. 4'is anend elevational view reduced in-scale,:sliow-' ing. the end of the apparatus from which treated-sheet material isdischarged;

Fig. 5 is across sectional view taken along'line-E5 in'Fig. 1;

, Fig. 6 is a fragmentaryperspective. view showing the. structure. of a portion. of. the a. apparatus? in; greater detail;

Fig. 7 is a fragmentary perspective view showing the partially broken away to show the structure in greater detail;

Fig. 10 is a side elevational view of the apparatus shown in Fig. 8;

Fig. 11 is an enlargedcrosssectional view taken along the line 1111 in Fig. 10;

Fig. 12 is an enlarged fragmentary sectional view taken along the line 12 -12 in Fig. 13;

Fig. 13is a plan view of: the apparatus shown in Figs. 8 and 10;

Fig. 14 is an enlarged fragmentary elevational View of a spraying headused' inuthe apparatus of this invention;

Fig. 15 is an enlarged. fragmentary perspective View partially broken away to show the novel structure in greater detail; and

Fig. 16 is an enlargedfragmentary sectional view showinga nozzle tip used. in the spraying'head and a valve for controlling the flow of abrasive material therethrcugh.

In accordance with the. present invention the surface of sheet material is prepared for the application of a coating by directing a blast of fine abrasive particles against. the surface sothat the surface is clean-and textured orv roughened, whereby an improved bond between the surface and the coating material is-obtain'ed. While the principles ofthepresent invention may beutilized'to preparev surfaces for. the application of coatings of paint or othersimilar materials, the invention has particular utility for preparing sheets to be used for printingplates for the application of ink; Such sheets may, for example, be in the form of aluminum foil which is applied to' to spread or not adhere uniformly to the surface so as to destroy the pattern. This tendency has been overcome in the past by chemically treating the sheets to obtain'the grainsurface necessary'to obtain the pattern or illustration formed by the printing ink so that the ink will not run or spread. It has been found that by graining or roughening the sheet surface to a very fine and uniform pattern in accordance with the present invention such chemical treating of the surface, Which is slow andcostly, may be omitted.-

Referring-now more specifically to the drawings, wherein like'parts are designated bythe same numerals through out-the various figures, an apparatus 10 embodying the novel features of this invention is illustrated in Figs. 1 through 7. The apparatus lilincludes a pair of spaced side frame members 12and14 which may be connected together by spacer bars 16- and 18.

Rolls

20 and 22 are: journaled between the frame members atone end thereof and

similar rolls

24 and 26 are journaled between the-opposite ends of the frame members. A foraminous continuousbelt or. web 28 encircles the rolls for conveying sheet material through the apparatus. A motor 30 is suitably'supported within the frame for driving at least one of the rolls and thus the endless foraminous' belt. In the specific'embodiment illustrated the motor is connected with a speed reducer 32 which drives the roll 24 by means'of sprockets 34 and 36-and an endless chain 33. In addition, the roller 26 is driven from the roller 24 by 'a chain 39 wrappe'daround suitable sprocket wheels. In: order to. insure the proper frictional: driving engagement: between the belt and the roller 24' the

belt tensioning devices

40 and 42 are mountedon the frame aseshownbe'st inFig. 1. These devices maybe-ofiany known construction and neednot be described in detail.

A guide and support table 44 is mounted at the left hand end of the apparatus as viewed in Fig. 1 for guiding sheet material to be treated onto the continuously moving foraminous belt 28. If desired individual sheets of the material to be treated may be fed successively onto the belt or on the other hand the apparatus may be utilized to treat anelongated strip of sheet material which is fed from a roll, not shown, at the left hand end of the apparatus as viewed in Fig. 1 and received on a second roll, not shown, at the right hand end of the apparatus. In any event, the sheet material is continuously advanced on the foraminous belt and means generally designated by the numeral 46 is provided 'for directing a blast of abrasive particles against the surface of the sheet material so that the surface is uniformly treated and textured. If a continuous strip of sheet material is processed, it is understood that the strip may be subsequently severed by means not shown to provide a plurality of individual sheets for printing plates.

The blasting or spring means 46 includes a pair of standards 48. and 50 disposed on opposite sides of the foraminous belt as shown best in Fig. 2. A pair of spaced horizontal rods or

track members

52 and 54 are mounted between the upper ends of the standards, and a carriage 56 is supported on the track members for movement between the standards. The carriage is operatively connected with an endless chain 58 which is carried by sprocket wheels 60 and 62 suitably mounted on a transverse support bar 64 extending between the standards. A motor and speed reducing unit 66 is provided for driving the endless chain 58 through a chain 68 encircling a sprocket wheel, not shown, connected to the sprocket wheel 60 and another sprocket wheel at the speed reducer. The specific details of the carriage 56 and the connection between the carriage and the endless chain 58 form no part of this invention and need not be specifically described. It suffices to say that the endless chain 58 is continuously driven in one direction and the connection between the chain and the carriage is such that the carriage will be moved back and forth across the foraminous belt 28.

Carried by and extending from the carriage 56 is a rigid arm 70 having an abrasive spraying head at its free end. While the spraying head may consist of a single spraying nozzle it preferably includes two or more spraying devices 72 since it has been found that by using two spraying devices the sheet material may be treated about twice as fast as when using only one spraying device. The nozzle 72 is constructed so as to deliver a uniform. spray of fine abrasive particles. While numerous well known abrasives may be used a preferred abrasive in accordance with the present invention is finely powdered aluminum oxide, which is supplied to the nozzles from a container 74 through a flexible hose 76. The finely powdered abrasive has a tendency to cake or stick in the container and in the hose and .in order to provide a continuous flow of the abrasive to the nozzles the container is continuously jiggled or oscillated. To accomplish this the container 74 is fixed on a support arm 78 journaled in a bearing 80 mounted on an upstanding pedestal 82. The pedestal 82 is disposed on and centrally of the transverse support bar 64 so that as the nozzles are moved back and forth with the carriage 56 the hose 76 pulls on and oscillates the container 74. In order to limit the oscillating movement of the container 74 a pin 84 is fixed to the support rod 78 and extends upwardly between spaced fingers of a bifurcated bracket 86.

As shown best in Figs. 1, 14, 15 and 16, the abrasive material flows by gravity through the hose 76 into a container 81. From the container 81 the abrasive material flows under the influence of gravity through suitable passageways 83 to nozzle tips 85. The abrasive material is drawn from the tips by streams of air under pressure passing out through annular openings 87 surrounding the tips. As shown in Fig. 15 this jet of air and abrasive material is broken up and fanned out by streams of air directed from openings 89. With this arrangement it is seen that the abrasive particles flow through the nozzle merely under the force of gravity and are not acted upon by the air under pressure until they leave the nozzle whereby excessive abrading of the nozzle is prevented. Furthermore, the air jets from the opening 89 serve to form the abrasive particles into a uniform oblong pattern extending in the direction of movement of the sheets being treated whereby this treating operation may be accelerated. As shown in Fig. 16, the spraying devices are provided with valve members 91 for controlling flow of abrasive material through the nozzles.

The air under pressure is directed to the nozzles through the support arm 70 which also serves as an air conduit. Thesupport arm or air conduit 70 is connected to a source of air under pressure, not shown, by means including an air line 88 fixed to the upstanding pedestal 82. A flexible conduit is connected to the upper end of the conduit 88 and to valve means 92 mounted on the carriage 56. Another flexible conduit 94 connects the valve means 92 and and an end of the conduit 70. In order to prevent overtreating of the sheet material when the carriage pauses at both ends of its travel or stroke across the sheet material, means is provided for closing the valve means 92 to shut off the air and discontinue the spray. This means includes a cam member 96 mounted on the carriage and operatively connected to the valve means 92 to open and close the valve and

cam actuating fingers

98 and 100 mounted on a rod 102 and similar

cam actuating members

104 and 106 mounted on a rod 108. The cam 96 and the actuating fingers need not be described in detail and it suffices to say that as the car riage moves toward the left end of its travel as viewed in Fig. 2 one of the fingers actuates the cam to close the valve 92 and as the carriage reverses the direction of its movement the other of the fingers operates the cam to open the valve. The

cam actuating fingers

104 and 106 operate the cam 96 and the valve in a similar manner when the carriage is at the right hand end of its travel as viewed in Fig. 2.

Air under pressure is directed from a suitable source, not shown, through a conduit 110 to an air filter and dehumidifier 112 (Figs. 2 and 3) or, if necessary, to a plurality of such filters which may be connected both in series and in parallel and thence to a manifold 114. The air line 88 is connected to the manifold in any desired manner. In order to remove any loose foreign material on the sheet before the sheet is passed on to the foraminous belt a hand operated air nozzle 116 is provided and this nozzle is also connected to the manifold by a flexible conduit 118. A hook 120 may be provided for supporting the nozzle when the nozzle is not in use. A similar hand operated nozzle, not shown, may be provided at the discharge end of the apparatus if desired. In addition, another air conduit 122 is connected to the manifold and supplies air under pressure to a pair of

nozzles

124 and 126 which are arranged as shown best in Figs. 1 and 3. These nozzles are directed across the foraminous belt and along opposite sides of the abrasive spraying devices 72 in order to blow dust and abrasive material off of the sheet being treated and to help confine the dust and abrasive material within the apparatus as will be described more fully below.

In accordance with the present invention, novel means is provided for confining dust and abrasive particles within the apparatus, thereby preventing contamination of the surrounding atmosphere. This means includes a blower 128 (Fig. 4) driven by a motor 130 for drawing air over the sheet material while it is being treated with the abrasive particles, then drawing the dust and abrasive laden air through a series of ducts, filters and chambers wherein the air is cleaned, and finally discharging the uncontaminated s air through an opening 132 (Fig. 3) into the surrounding atmosphere. More particularly, a hood 134 (Figs. 1-5) is mounted on the

frame members

12 and 14 and encloses the upper course ofthe foraminous belt andthe abrasive,

metal bafile structure 144 located beneath the hood 134.

The bafflestructure 144 includes downwardly

inclined side sections

148 and 150 extending inwardly from the opposite

longitudinal frame members

12 and 14 respectively. A downwardly inclined bottom section 146 extends from the margin of the section 148 and beneath the section 150, and a section 147 extends from the margin of the section 150 over the section 146. At the entering end of the apparatus there is provided a downwardly and inwardly inclined end section 152 and at the discharge end of the apparatus the baffle structure 144 is provided with a verticalend section 154. As shown best in Fig. 7, an upwardly and inwardly inclined bafile plate 168 extends from the vertical end section 154.

The-upper course of the foraminous belt is supported over the battle structure 144 by means of aplurality of longitudinally extending

rails

174, 176 and 178 which are mounted at their opposite ends on the

transverse frame members

16 and 18. With the hood and baffle structure described above it has been found that air will be drawn into the hood through the

openings

136, 138, 140 and 142 and then directed uniformly over and around the foraminous belt and a sheet of material thereon so that this incoming air in combination with the jets of air di reoted by the nozzles 1-24 and 126 effectively prevent dust or abrasive particles from escaping out of the hood. In addition, these streams of air effectively clean the dust and abrasive particles from the treated sheet of material and carry the dust and abrasive particles in the manner indicated' by the arrows in Fig. 5. The dust laden air is drawn through a duct 180 provided by the

sections

146 and 147 and suitable end panels 181 and upwardly to a chamber 182. However, substantial deposits of heavier abrasive particles tend to accumulate on the bottom section 146, and these particlesare conveniently collected and removed by slidably mounting a drawer-like receptacle 183 in a suitable opening in the section 146. It will be appreciated that the suction applied to the hood by the blower for removing the dust also reduces the air pressure at the back of the upper course of the foraminous belt so that the sheet material is securely held on the belt by the differential in the air pressures at the opposite sides of the sheet.

The, chamber 182 has disposed therein a number of spaced

filtering bags

186, 188, 198, 192 and 194 (Figs. 1 and 3). Each of the wide flat filtering bags has a closed upper end and is supported in an expanded condition by one of a plurality of forms or frames 195, as illustrated bestin Figs. and 9'. The open bottom ends of the bags are each connected with one of a plurality of ducts 198. The filtering bags may. be made of cloth or any other suitable material capable of filtering the abrasive particles from the air. Preferably the filtering material of the bags. is such that the abrasive particles collected thereby are of a size that they may be re-used in the sheet treating process. Most of the abrasive particles collecting on the exterior of the bags will fall to the bottom of the chamber 182, and more praticularly into a. collecting drawer 200 (Fig. 2) so that they may be removed for re-use. the/particles will adhere. to the exterior surfaces of the Of course a certain amount of 3 bags, but since such surfaces are readily accessible they may be easily cleaned at periodic intervals.

The air passing through the filtering bags may still contain a considerable amount of fine dust or powder and therefore this dust laden air is directed by the duct 198 into a water chamber 214 (Figs. 3 and 4). The air is directed over and against the surface 216 of the water within the chamber 214' and so that the heavier particles in the air impinge against the water. The air then passes upinto an air Washing chamber 218 wherein the remaining finer dust particles are removed from the air. This is accomplished by washing the air passing through the chamber 218- with a water spray 220 directed downwardly by a series of nozzles 222; Water is supplied to the nozzles 222' by means of a motor driven pump 224 having its discharge side connected to the nozzles by a pipe 226. Preferably the inlet of the pump is connected to the water chamber 214' so that the level'of the water in this chamber remains substantially constant. From the washing chamber-the air is directed to a chamber'230 from where it is drawn through the fan housing anddischarged into the atmosphere.

In the operation of the above described apparatus the blower 128" is first started so as to obtain a flow of air through the apparatus. A sheet of material such as aluminum having a smooth surface is then fed into the apparatus and the foraminous belt is driven to advance the sheet material through the apparatus at a: uniform rate of speed. As pointed out above, the material to be treated may be in the form of'separate sheets which are preferably placed on the belt in substantially abutting relationship or in the form of a continuous strip. The carriage carrying the abrasive spraying nozzle 72 is then driven back and forth, and suitable control valves, not shown, are opened to admit air under pressure to the

air lines

88 and 122 and thenceto the abrasive spraying nozzles 72 and the

air jet nozzles

124 and 126; The speed reducers. of both the foraminous belt and the carriage drive mechanisms are preferably adjustable, and it is understood that these speed reducers are adjusted to correlate the rates of movement of the belt and the carriage so that the entire surface ofthe sheet material carried by the belt will be uniformly subjected to the action of the abrasive spray. The dust and abrasive particles are, of course, removed'from the treated sheet material and then recovered in the manner fully set forth above.

In Figs. 8 and 10 through 13 there is illustrated an apparatus 250 which embodies a modified form of the present invention. This apparatus is especially adapted for treating a continuous strip 252 of sheet material and is similar to the above described apparatus as indicated by the application of identical reference numerals with the suffix a added to the corresponding elements. The apparatus 250 includes sheet material supply and receiving

spindles

256 and 258 rotatably supported between the

frame'meinbers

12a and 14a.

rollers

260 and 262 are supported between the frame members and the sheet material is directed from the supply spindle over these rollers and then downwardly between tensioning and feedrollers 264 and 266. In addition, the sheet material is directed between a pair of rotatably supported brushes 260 and 270'which serve to clean abrasive particles and dust therefrom. In order to feed'the sheet materialcontinuously, the spindle 258is driven by the means shown in Fig. 12, whichis similar tothe above described driving means and the tensioning and feed rollers 264 and 266 are driven by a chain 272 which extends around a sprocket on the shaft of the speed reducer 32a and a sprocket on the shaft of the roller 266. The roller 264 is driven by a gear 274 fixed'thereon and meshing with a gear 276 on the roller 266. The brush 270 is driven by a chain 278 wrapped around sprockets on the brush shaft and the roller 264 shaft, andrneshing gears, not shown, are providedon the shafts Sheet material guidefor driving the brush 268 from the, brush'270. The apparatus 250 is provided with an abrasive spraying mechanism 286 which is similar to the above described spraying mechanism 46 and, therefore, need not be described in detail. However, it should be noted that instead of supporting the carriage track between a pair of standardslocated at opposite sides of the sheet material, the mechanism 286 has a cantilever track 288 mounted on a single pedestal 290. With this arrangement, the track may be positioned directly over the portion of the sheet material to be sprayed and, therefore, the spraying device 7211 may be connected directly with the carriage 560. In this embodiment the variable speed drive mechanism 66a for the carriage actuating fan 58a is supported on top of the pedestal 290.

The apparatus 250 is provided with a hood structure 134a having a narrow slit-like inlet and outlet opening for the sheet material. The top of the hood structure 134 may be left open since the air being drawn into the hood by the blower will prevent dust from escaping. Since the top of the hood is open, the pedestal 290 may be shifted to position the spraying head over any desired portion of the sheet material within the hood. In this embodiment the space beneath the sheet material and the hood 134 is enclosed by a simple box-like sheet material structure .or bin 292 which communicates directly with the chamber 182a, A pair of

access doors

294 and 296 may be provided in the box-like structure at opposite sides of the pedestal 290 to permit the collected dust to be removed from the bin.

As shown best in Figs. 10, 11 and 12, the rotatable brushes are enclosed within a housing 298 having inlet and outlet slots 300 and 302 for the sheet material. One end of the housing is connected by duct means 304 with the upper end of the filtering chamber 182a and the opposite end ofthe housing 298 opened as at 306. Thus, air is drawn into the housing through the open end 306 and directed to the filtering chamber so that abrasive particles and dust removed from the sheet material by the brushes are delivered to the filtering chamber.

The operation of the apparatus 250 is substantially the same as the operation of the apparatus described above and need not be set forth in detail. Therefore, it suffices to state that the continuous strip of sheet material is fed through the housing structure 134:: at a continuous uniform rate and the drive mechanism 66a is adjusted so that the carriage 56a is reciprocated in a manner which will assure uniform treatment of all portions of the sheet material. In addition, the blower is continuously operated to draw dust-retaining air from the housing structure 134a, from the housing 298 surrounding the brushes into the filtering chamber 182a, through the filtering bags, over the water chamber, and up through the Washing chamber. In order further to insure complete cleaning of the air passing through the washing chamber, inclined bafile means 308 is mounted in this chamber. The bafile means 308 is preferably formed from screen-like sheet material such as sheet metal which has been slit and expanded in a known manner. In addition, the expanded sheet material is formed so that it has the zigzag cross sectional configuration shown in Fig. 8. Furthermore, the spray nozzles 22211 are arranged inttwo rows which are angularly disposed with respect to each other as shown in Fig. 8 so that the entire surface of the bathe means is flooded. With this arrangement intimate contact by substantially all portions of the air passing through the bafile means and the cleaning water is obtained so as to insure substantially complete removal of dust and the like from the air. Preferably, additional bafi le means 310 is disposed in the chamber 218a above the spray nozzles. This battle means includes a plurality of sheet metal plates arranged to provide a plurality of zigzag passageways so that air passing therethrough comes into contact with the plates and a substantial portion of the moisture in the air f5 condenses on the plates and drips, down into the water chamber.

From the above description it is seen that the. present invention has provided a novel. method and apparatus whereby surfaces may be rapidly and economically treated and prepared for the application thereto of coating materials. More specifically, it is seen that the present invention has provided a novel method and apparatus for rapidly and economically preparing surfaces of sheet ma,- terial to be used as printing sheets for the application thereto of printing ink and the like. In addition, it is seen that the present invention has provided a novel apparatus for spraying sheet material with abrasive particles by which apparatus the surface of the sheet material may be uniformly treated and the abrasive particles are confined within the apparatus to prevent contamination of the surrounding atmosphere and are collected for reuse.

While the preferred embodiments of the present invention have been illustrated and described herein, it is obvious that many changes may be made without departing from the spirit and scope of the appended claims.

The invention is claimed as follows:

1. An apparatus for preparing surfaces of flat sheets for the application of a coating thereto comprising means providing a substantially enclosed chamber, means for conveying a sheet having a surface to be prepared through said chamber, said conveying means including an endless foraminous belt for supporting a sheet on one course thereof, spray means for directing a spray of abrasive particles against said surface of a sheet within said chamber, means for recovering reusable abrasive particles from said chamber, means admitting atmospheric air to said chamber on an outer side of said foraminous belt course, means including a blower and air confining means for exhausting air from said chamher and for creating a suction at an inner side of said foraminous belt course for retaining a sheet on said course, and means for cleaning said exhausted air so as to prevent contamination of the atmosphere surrounding said apparatus.

2. An apparatus for preparing surfaces of articles for the application of a coating to said surfaces comprising means providing a substantially enclosed chamber, means for conveying an article having a surface to be prepared through said chamber, spray means disposed for directing a spray of abrasive particles against a surface of an article within said chamber, and means for recovering sprayed abrasive particles from said chamber, said last named means including a chamber communicating with said first mentioned chamber and having outlet means, means for exhausting abrasive particle laden air from said chambers through said outlet means, a filter bag having a substantially closed end disposed in said second mentioned chamber and an open mouth connected with said outlet means, and means for maintaining said bag in an expanded condition, the air passing through the filter bag from the outside to the inside thereof whereby abrasive particles carried by the air are deposited on the outer surface of the bag.

3. An apparatus as defined in claim 2 which includes a plurality of adjacently disposed spaced filtering bags covering said outlet means and having open mouths communicating with said outlet means and closed ends, and means maintaining said bags in an expanded condition and in spaced relationship.

4. An apparatus as defined in claim 2 which includes means for cleaning any dust from said air after the abrasive particles have been recovered therefrom, said cleaning means including means for providing a spray of liquid during the operation of said blower, and means for directing said air through said liquid spray.

5. An apparatus for preparing surfaces of articles for the application of a coating to said surfaces comprising means providing a chamber, means for conveying an article having a surface to be treated through said chamber, spray means for directing a spray of abrasive particles against said surface of an article within said chamber, means for exhausting air from said chamber, and means for cleaning any dust and abrasive particles from said exhausted air to prevent contamination of the atmosphere surrounding said apparatus, said last named means including means providing an air washing spray and means for directing said air through said washing spray, said air Washing spray and said air exhausting means being operated simultaneously.

6. An apparatus as defined in claim wherein said means for cleaning said air includes means for retaining a body of liquid, and means for directing said exhausted air downwardly against the surface of said body of liquid so that heavier particles carried by said air will impinge against the surface of said liquid.

- 7. An apparatus for preparing surfaces of sheet material for the application of a coating thereto comprising means providing a substantially closed chamber, means for continuously moving sheet material having a surface to be prepared through said chamber, means for directing a spray of abrasive particles against said surface of the sheet material within said chamber so as uniformly to roughen said surface, a pair of rotatable brushes disposed adjacent said chamber for cleaning abrasive particles and the like from the sheet material, means for directing the sheet material between said brushes, housing means closely surrounding said brushes and enclosing a portion of said sheet material engaged by said brushes, means for moving air through said housing means to remove abrasive particles and the like from the housing means with said air, and means connected with said housing means for subsequently removing the abrasive particles from the air.

8. An apparatus for preparing surfaces of articles for the application of a coating to said surfaces comprising means for advancing an article along a path of travel, means for spraying abrasive particles against said surface of an article moving along said path of travel, said spraying means including a nozzle, means supporting said nozzle for movement back and forth transversely of said path of travel, means for so moving said nozzle, a container spaced above said nozzle for holding a supply of abrasive particles, a supply conduit connecting said container and said nozzle for feeding abrasive particles from said container to said nozzle, and means pivotally sup porting said container above said nozzle for oscillating movement whereby said container is oscillated by said supply conduit upon the back and forth movement of said nozzle to insure a flow of abrasive particles from the container to the nozzle.

9. An apparatus as defined in claim 8 wherein the abrasive material flows through the nozzle substantially only under the influence of gravity to eliminate abrading of the nozzle, and which nozzle includes means for directing air under pressure against the abrasive particles after the particles have passed out of the nozzle.

10. An apparatus for preparing surfaces of articles for application of a coating thereto comprising means providing a chamber, means for moving an article with a surface to be treated through the chamber, a nozzle for directing a spray of abrasive particles against said surface of an article within said chamber, and means for directing a supply of abrasive particles through said nozzle substantially only by the force of gravity to eliminate abrasion of the nozzle, said nozzle having means for directing streams of air under pressure against the abrasive particles only after the abrasive particles have passed out of the nozzle.

11. An apparatus as set forth in claim 10 and further including additional air stream directing means on said nozzle for shaping the pattern of the air borne abrasive particles.

References Cited in the file of this patent