US2629207A - Plate blasting machine - Google Patents

Description

Feb. 24, 1953 W. l. GLADFELTER ET AL PLATE BLASTING MACHINE 4 SheetsSheet l Filed Oct. 9, 1950 i f, E,

alxl., l

4 Sheets-Sheet 2 W. l. GLADFELTER ET AL PLATE BLASTING MACHINE Feb. 24, 1953 Filed oct. 9, 195o Feb. 24, 1953 w. l. GLADFELTER ET A1. 2,629,207

PLATE BLASTING MACHINE Filed Oct. 9, 1950 4 Sheets-Sheet 3 I. GLADFELTER RARvER BY w. l. GLADFr-:LTER ET A1. 2,629,207

F eb. 24, 1953 PLATE BLASTING MACHINE 4 Sheets-Sheet 4 Filed Oct, 9, 1950 Patented Feb. 24, 1953 PLATE BLASTING MACHINE Wiltie I. Gladfelter and Ralph R. Garver, Hagerstown, Md., assignors to Pangborn Corporation, Hagerstown, Md., a corporation of Maryland Application October 9, 1950, Serial No. 189,210

15 Claims.

This invention relates to abrading machines, more particularly to machines for blasting with abrasive particles the surface of metal plates such as the lithographie plates used in the printing industry.

Abrasive blasting machines are characterized by the development of clouds of nely divided particles of abrasive and abraded materials which easily pass through small openings and thereby escape from the machines-into their surroundings.

For any effective commercial use of such ma-` chines, it is essential that such discharge be substantially completely prevented, to keep the environment from becoming uncomfortable to the machine operator or attendant and to prevent irritation and possible infection of the respiratory tract of these individuals bythe escaping particles. It has accordingly been an established practice to provide completely closed, dustproof housings for such machines and to station the operator outside of the enclosure.

The blasting of metal plates, which may be as large as 2 by 4 feet in area, does not readily lend itself to the use of completely enclosed housings inasmuch as the provision of suitable loading and unloading mechanism makes the construction and operation of the machine quite awkward. This is particularly serious when the blasting is intended to etect a very uniform abrading of the metal sheet surface, as in the case of lithographie plates. have the individual metal sheets carefully mounted on a movable holder to have their surfaces uniformly moved through an abrading blast.

The fastening of the metal sheets to the mova ble holder has also been a problem in the art. Most blasting machines must be designed to blast sheets that can be varied in size in accordance with other requirements, Lithographie plates used in a single small lithographing establishment, for example, can vary both in length and in width from about inches to about 50 or more inches. A single blasting machine for graining these lithographic plates, should be capable of securely receiving and holding plates having any of these dimensions, and carrying them through the abradant stream. An extremely practical type of plate holding and moving device includes a rotatable drum on the surface of which longi` iently effected, and requires excessive manipulative operations. Y

For such treatment, it is desirable to and a stream of air is arranged to be sucked into Among the objects of the present invention is the provision of plate blasting machines which avoid the above and related difficulties.

Further objects of the invention include blasting machines for uniformly blasting metal plates in which machines the plates are readily loaded and from which they are readily unloaded.

Still further objects of thepresent invention include the provision of plate clamping mechanism that is simple to use and requires very little manipulative treatment to clamp or release a plate.

The above, as well as other objects of the present invention, will be more readily understood from the following description of several of its exemplications, reference being made to the accompanying drawings wherein:

Fig. 1 is a side view of a plate blasting machine embodying the present invention, with parts broken away to better show some of the details;

Fig. 2 is a front elevational view of the machine shown in Fig. l;

Fig. 2a is atop view of the apparatus of Figs. 1 and 2;

Fig. 2b is a detail sectional view taken along line 2b-2b in Fig. 2, and showing the plate clamping mechanism of the apparatus of Figs. 1, 2 and 2a; i

bFig. 2c is a side view of the construction of Fig. 2

Figs. 2d and 2e are views, similar to Figs. 2b and 2c, of a modified form of clamping mechanism;

Fig. 2f is a sectional view taken along the line 2f-2f, of the apparatus of Fig. 2b;

Fig. 3 is a sectional view of a different embodiment of a plate blasting machine exemplifying the invention, this view being taken along line 3 3 of Fig. 4;

Fig. 4 is a front elevational view, with parts broken away, of the machine shown in Fig. 3;

Fig. 5 is a side view of the machine shown in Figs, 3 and 4; and

Fig. 6 is a top view of the machine shown in Figs. 3, 4 and 5.

According to the present invention a work piece blasting machine is provided in the form of a housing, blasting structure mounted within the housing and connected for projecting :a stream of blasting particles towards exchangeable work pieces and an uncovered work-piece-loading and unloading opening in the housing. To keep the blastant particles from emerging through the uncovered opening, the housing is arranged to closely fit against the movable plate-holding structure the machine through this spacing during blasting. In addition, sealing elements can be extended between the housing and the plate-holding structure at some or all of the margins of the opening. Work-piece-holding clamps can be provided to hold these pieces in the path of the abrasive stream. The y clamps preferably include quickly ladjustable vspring catches and are arranged to hold one or more individual plates along any portion of a holder such as the periphery of a rotatable drum thereby simplifying the replacements of the work pieces.

Referring to the constructicn'shown in Figs. 1, 2 and 2a, it will be seen thatgthe,machineincludes a housing I supported on legs .I2 4and carrying y bearings I4' in which is journaled va drum |76 on shaft I5. In the rear of the hous'ing is secured a traversing mechanism indicated generally at I8 and shown as including a threaded enclosed .She-f.;t joorheled er -loohh ends .epd Coupled ro' @more 2,2 there@ erhoehen geef rex 24! 'Threeregl'vehsegedhytheiehefto 1S .erelidehlehloek or .herir held' hre eerrreee .21 .Whieh is dipped with rollers 28, y.22) guided along fixed traeks 3l, .33.Ay O n thecarriage ismonnted a set of 'blasting' nozzles 325 directed toward a portion of the erom. periphery! Ih rhe-formrholwh, .eeeh hoehe -ieloohheeredpye hoses? fro. .e compressed eir .line through eh ehv hrehifold 3.5- ,Aleo rohe peered tothe' hdiyrduel nozzles .ere abrasive mixture supply" lin`es`38, which entend down to the lower portion .of t.he .ho-hehe AWhere they ,ere ,heid irifpleee er' by .Clamps L49 eo their the heee. opeh at '42 into ya dependent portion of the housingin the 1general shape of a, hopperd. `lThe hoses are of iieicibleconstrntion so that they remain connected at theirrespective fends and,- at the same timefperniit the lnozzles to be carried b y the traversing mechanism to and fro longitudinally across the drum. In (this type of construction the nozles are of a socalled suction type s o that thepasseee of eorhpreesed oir .through ,themv eoueee thenblasting mixture to be sucked up freni the hopper where .it .is ih doeted .et .46, and forcefully eiw lied aga'nststhie'drnm surface with the oomp .Se'ee err! eheh nozzles ere Well known, ohe very effective construction being described in U. S. parent go,- -rpeaer sented February 1e. 19115- Theabrasive mixture is preferably a suspension of finely .divided grit perholes oooh es send/ih ehehe soph-:esperen The hopper 44 is equipped with an agita-ting de vice shown as a slurry circulating arrangement including Aa centrifugal pumpffl having an outlet line 4l .eohheered to the. bottom 'of the hopper and aninlet line i3 opening at a point in the. hQlpeif .abovefthe level at` which the abrasive particlesY generally settle. Anfoverow conduit 39 is arranged to fix the maximum liguid'level above slurry Aby automatically permitting heherfstreta ,of hoord to .dieeherse to waere An additional overow line 59 adjusted to a suitably higher level may he provided as for indicating obstruction of line 39. A slurry drain 6L liquid drain 72, drain reeptacle 63 and hopper isolating valve 64 are also included to simplify the cleaning of the hopper and the initiation of slurry eiroolahoh.

fIAhe housing I AIl has an .uncovered opening 48 on .the ls ideof `the drum opposite the nozzle assembly. As shown, the housing walls about the opening may be somewhat curved to more closely follow the cylindrical wall surface of the drum. Through theopennsil plates to be `blasted may be conveniently loaded onto the-,drum ,It-.and unf loaded from it when the treatment is completed. A grating 5@ may be provided between the lower portion of the opening and the drum to serve as a support or rest as, for example, to hold a tool or sheet while it is being mounted or dismounted.

For rotatably driving the drum I5 around its longitudinal axisthe shaft'IS is coupled by means of clutch v,latoa clutch shaft 5I which is impelled by electric motor 53 via belt driven reducer 55 and chain-and-sprocket drive 5l. A clutch operating handle ci is shown as projecting out beside the housing opening 128 for `convenient manipulation to engage and disengage the clutch and thereby startend stop thedrum rotation as desired. Adjustablelpositioningmounts are shown for motors `2 2 and 53 to compensate for variations in drive belttension.

Therdrum I5 carries on its periphery clamping devices one of which is indicated at 52. The clamps are shown as vincluding ,a rod 54, to vthe ndsof whicha're fastened as by welding'rclamping jaws 55,` 58. `Jaw 58' Vis shown as fixed in position with an inwa'rdlydirected tooth b5 engaged against the tapered undersurface 66 of thedrum end which is flanged as more clearly shown'in Fig'. 2b. The theriaw 'has a xed boss 61 which pivotally carries a tooth 68; as Yby the pivot pin '69. A manuallyoperable clamping screw ,60' is threadedly received in'bossV 4l and the end of this screw engages the `pivoted tooth 58 and holds it in l'engagement with '.a :corresponding Vtapered undeiwsurfaceit, atthe zopposite vend of dru'rri` I6.

Therad 'is also' longitudinally grooved on opposite faces, as shownrnoreclearly at *59 `in Fig. 2f. At thefurthest portion from the drum surface, thes'groofves are undercut into therod to provide a seat 78 .for a readily attachable and detachable spring holder 1I. The holder 7| hasl v a generally UA-shaped body 12 `and through both.

arms of the U are' aligned openings in which r'are slidably receivedv a plunger 13. A biasing force urgesv the plnnger to slide in one direction, and in 'the "formV shown is provided by a coil spring 'I4 compressed between one arm of the body vand a, pin carried bythe plunger.A 'The other arm of the body is entended to forma claw 16 shaped to t in theseat lil. A friction grip 'l1 of rubber or similar material is` heldin a socket at the plunger end 'towards'which' it is spring biased to rrnlyhold a portion of a'work sheet ksuch as litho graphic vplate Ille in .place against the drum. At thother end ofthe plunger the' bofdy 'E2 is open to vperilit retraction .of the plunger so .that'the linger can be conveniently depressed againstthe 55VV action of Ispring i4 for mounting and dismounting purposes. tapereddrum .flange surface 66 can be extended entirely around the drum 'to ena-ble mounting o f the clamp 52 in any radial position. Similarly, the gOOl/e 59 may be arranged to extend along the entire length of rod 54 to accommodate one or more fingers 1I in any distribution.

Figs. 2d and 2e show a somewhat different form of clamp 'I8 in which a rod rs' is grooved in a manner generally similar vto rod 5.4, but clamping jaws 30 at each end of rod 'i8 are arranged for quick anchoring or release by a single manipulative movement. lThe `clamp jaws 80 Aat each end of rod I9 can be of identical constructionincluding a C-member 80 pivotedv at one end by a pin 82 to a handle BI, the handle in turn being pinned for rotation about the end of rod 73. The other end of C-member SI Vcarries a 'positioning element'shown Yas a set-screw 83 threadedly received in member t1 and ,equipped 'with `alocking nut 84. The tip of screw 83 is shown as pointed and as received in a correspondingly shaped groove 85 in the inner surface of the drum ange. y

By merely rotating handle 8| outwardly around the end of bar 19, the C-member can be disengaged from the drum flange. This simple operation at both ends of clamp 18 completely frees the clamp so that it can then be removed. For attachment of the clamp, the procedure is reversed. To improve the ease of clamp manipulation, the pin'82 can be arranged to be tightly received Vin handle 8|, and `easily rotatable in C-member 81.

To keep particles of the blasting mixture and/or abraded material from escaping from the machine, it is equipped with an air iiow actuating device arranged to suck air in through all openings in the machine housing. As shown in Figs. 1, 2 and 2a, a set of air conduits 88 are connected to filter chambers 89 that open into the top of housing I0.v These conduits 88 are led through symmetrical manifolds 90 to the intake of a motor-driven blower 9|, the discharge outlet of which is open to the surrounding atmosphere or is led away to venting means not shown.

t has been discovered that a one horsepower suction device will give the desired absence of leakage when used with an apparatus in which openings in the housing total not more than about 10 square` feet. This simple expedient makes it unnecessary to carefully seal openings or provide air-tight closures. Where advisable, the housing openings can be effectively reduced in size as by bringing the housing walls relatively close to the drum I6. Thus the shaping ofthe front of the housing so that it follows the contour ofthe drum as shown more clearly in Fig. 1, serves to restrict the effective cross section of the air passageway there provided. Another effective technique for restricting the air intake is by the addition of a baffle or vane 31 which extends across the housing so that its lower end dips below the hopper overflow level and its upper edge is relatively closely adjacent to the drum periphery. In the chamber 89 there may be mounted dust obstructing air filters such as the cylindrical fabric tubes 92. Screens 93 are advantageously used to support the fabric tubes and to cover the intake to each chamber 89 so as to trap the coarser particles such as those of the abrasive. Baffie rings 94 and perforated bafile cups can beprovided to spread out the air sucking action and permit more of the coarser suspended particles to settle in the housing without being sucked against the screens.

The chambers 89 also carry a water supply line 96 through which washing Water may be delivered for spraying the iilter elements and removing the particles which are filtered out by them. This rejuvenates the filters so that they can be directly reused after the washing step without any handling.

For best operation it is desirable that the ltering action be continuous as long as the machine is in operation. Accordingly, the manifolds 90 are shown as equipped with dampers 91 which are connected for out-of-phase simultaneous operation, as by the hydraulically driven air cylinder 90. Air pressure lines 99 are connected inthe conventional manner to the cylinder and solenoid-operated valves (not shown) in these lines can be actuated by time-controlled circuits to close one damper, while the other is opened,` and at `the same `time suplying wash liquid to the lines 96 in the chambers connected to the manifold having the closed damper. At regular or irregular intervals the cylinder 98 is reversed to shift the dampers so that the previously inactive manifold circuit is put into operation while the other is subjected to the washing step in preparation for the next shift. Any convenient motor such as that for blower 9| or traversing carriage 26 can be used as the aircylinder timing motor.

The filter washings drain through the baffles and housing into the slurry in hopper 44. Finely divided particles or lithographie coating materials iioat or do not settlerapidly in the slurry and are preferentially removed by the automatic overflow arrangement, so that the slurry can be arranged to keep contamination quite low.

The operation of the machine may be controlled by a solenoid valve in the compressed air line 34 and this valve may be electricallyl or mechanically connected with nozzle traversing motor 22 and the motor for blower 9| so that air filtering and movement of the nozzles begin when the blasting is starting and continue so long as blasting is being maintained. It is usual-ly advisable to energize the circulating pump 45 somewhat in advance of the blasting so as to stir up the blasting mixture as indicated by the arrows in Fig. 1 and put this mixture in' such condition that it will beeffective to produce the desired blasting characteristics as soon as the blasting has begun. If desired, the drum rotation can also be interlinked with the nozzle traverse so that the blasting is uniformly distributed at all times. However, it is desirable to be able to rotate drum I6 independently of the blasting as, for example, when mounting lor replacing the plates to be abraded. It is accordingly advisable to have the clutch 49 or other mechanism for such independent drum rotation either manually by the machine attendant or by suitable actuation of the drum rotating motor.

Figs. 3 to 6 inclusive show a diierent embodiment of the present invention. Here an external casing H0, supported on legs ||2, rotatably carries an internal wheel ||3 journaled as by shaft ||5 in bearings H4. The wheel ||3 includes outwardly projecting vanes ||1 which extend outwardly and in an axial direction to form partitioned compartments indicated respectively at 20|, 202,` 203, 204, and 205. On each side the vanes ||1 are secured to differently sized side plates 9, |39. Journaled between these side plates on shafts ||I in each compartment is a drum as indicated at 2H, 2I2, 2|3, 2|4, and 2I5. These drums may be identical with drum i6 shown in Fig. 1. Most of the drum details are accordingly omitted in the interest of clarity. One end of each drum carries an outwardly projecting cylindrical flange |2| by which it can be rotatably driven.

Into compartments 202, 203, and 205 there is fitted, beyond the smaller side plate I|9, a drum driving mechanism shown in the form of a friction roller |23 held on a spur shaft |25 suitably .arranged for rotating by an electric motor. Motors for compartments in positions 202, 203, 295 are shown respectively (Fig. 5) at 222, 223 and 225 as mounted externally of the housing on conveniently :positioned brackets |21. The drum driving mechanisms are fixed with respect to the housing so that the compartment positions referred to above indicate the portion of the housing in which these'compartment-s are located or maybe` moved to. In othervwordsaas the wheel aeeaaov ||3 isrotated inthe direction shownby. the arrow |39 in Fig. 3 the .compartment at position 20|'will move to the position of compartment 202,.then successively to the positions 203, 204, 205 and from there on to position 20 l. During such wheel movement the drums will `be engaged by androtatably driven. when in positions 202, 203,205 by reason of frictional .contact with the rollers |23. At positions 20| and 20.4 the drums will be disengaged from the drum rotating mechanism.

The lower portion vof the housing il!! ,iS Shown as shaped to providev hQDpers |54 andv|45 Vbelow the compartments I202 and 2,03 respectively. These compartments also contain nozzle blasting equipment A|30 which .may be generally similar to that shown in the construction` ofFig. l

and also provided with a threaded shaft |25, connected for rotation by an external electric vmotor |22 (Fig. 5). Hoppers-IM, .|45 contanblast mixture ietf. and areitted with agitating mechanism |94 as in the construction of Fig. 1.

At one end, leach compartment 252,253. communicates. by means of duct |14 (Fig. 6) with an individual separator |15 both of which may be identical with the separator 89 shown in Fig. l but may be operated with a common exhaust bl-ower 52.

Compartmentv ..205 carries at its top a.k spray washing line l! connected to a suitable .source of washing liquids such as water. The floors of each of the compartments 20| to 205 inclusive taper towards shaft H5 adjacent the side plate |30, as shown more clearly in Fig. 4 at |43. Side pl-ate |39 carries a drain connection |45 adjacent the floors |43, and the housing H5 has an internal trough |111 positioned just below compartment 205 and connecting vwith a discharge line |5|. This construction enables a drum to be washed at yposition 255 and directs the washing into trough l'l and 4out of the machine so that the wash material is kept from mixing with the abrasive mixture |45 in hoppers Ill-4, |45.

Housing H0 is provided with uncoyeredopene ings |45, l|49, by which the compartments 20|, Y205 are exposed'A sovthat the cylindrical surface `ci? their drums in the position shown are readily accessible. be completely enclosed andA sealed against leakage of suspended-particles. Vanes H1 are shown 4as carrying sealing strips |611 which cooperate with arcuate depressions |55 inv the housing Vto seal the compartments from each other andreduce the possibili-ty of suspended particles linding their way from the blasting zones to the openings |40, |43. The sides of the compartments can be sealed from each other `by side sealing stripsv as shown in Fig. 1 or by ,using .addition sealing flaps held so as to project from` the side edge of the vane and engaging the inside vsurface of adjacent portions of the housing. To simplify the, side sealing,l the mating portions of the housing walls may be carried inwardly v.adjacent the side sealing portions of the respective -vanes particularly at the side of the housing which iacesthe cylindrical flanges l2 l inasmuch as at these positions the side sealing flaps ,must clear the inwardly projectingv drive rollers |23.

To further simplify the sealing problem the drum carrying wheel ||3 is arranged` to rotate only in distinct-.and spaced steps rather than in a continual manner. Bythis technique,l the blasting can be arranged-to take place only between the steps while the wheel is in such position that the compartments are substantially sealed from each other. Suitable wheel stepping The remainder of the housing may.'

trio motorv `24,5 is connected to rotate a crankpin 241. J ournaled in an outervportion of the crank pin, as indicated at 25|, is an adjustable advancing arm 253 which in turn pivotally connects at 254 to a ratchet arm 255 rotatably held by shaft H5. A ratchet dog 251 is carried by ratchet arm 255 and is urged by a spring, not shown, lin clockwise direction as seen in Fig.5 around p in 254. Fixed to shaft.||5 is a ratchet Wheel 259 the periphery of which has a plurality of spaced dog engaging grooves 25|. One orY more holding lugs 263 may be provided as shown to releasably engage in the ratchet wheel grooves and assure that the ratchet wheel does not rotate between steps.

`Rotation of pin 241 causes advancing arm253 to move through cycles of to and fro. oscillation, carrying ratchet 'arm 255 and -ratchetdog 251 through to and fro oscillating movement-'round shaft H5. The groove engaging end of dog 251 has its sides so shaped that a counterclockwise movement of dog 251 causes the dog to be lifted out of the groove 26| while the ratchet Wheel'is held in place by the lugs 253. |The counterclockwise dog travel is arranged to be of sufficient extent to bring the driven end of thev Vdog into the next groove 26S. The engaging end; of the dog is so shaped that clockwiser movementof the dog from this position will cause the dog to overcome the holding forces of lugs 263 and` rotate the ratchet Wheel 259 one step. At the endk of this step the lugs 253 again seat themselves into grooves while the ratchet 'dog 251 is returned in counterclockwise direction for the next'advancing step.

In the machine shown in Figs. 3 to 6 inclusive, plates to be abraded may be loaded on a ydrum in compartment 20 I.. From this position' the rst step of the wheel I I3 will carry the plates tothe compartment at position 202. Here they will be rotated by the drum 2|2 under the drivingv inuence of roller |23, while blasting is `elected by the nozzle assembly |30. The blasting nozzles are arranged to traverse longitudinally of the drum 2 I2 during the drum rotation in the-manner explained in connection with Fig. l."'After the' desired blasting treatment at position 202, the wheel i3 is stepped bringing the plates lnow to position 203 where another blasting treatment is elfected ina similar manner. At the end of the second blasting treatment, the plates are stepped to position 204 where they can be unloaded. The subsequent advancing step of wheel.

||3 carries the unloaded drum to position 205 where it iswashed. The final step in the drum rotation carries the washed drum to position 20| where it is ready to receive the next set of plates.

sibility of confusion'between the supply of plates to be blasted and the withdrawal of the treated plates. One operator may be assigned the 'duty of loading while an entirely different operator does the unloading.

. The blasting at positions 202 and 203 may be of identical or of different characteristics. lIfde` sired, the hopper |44 may be supplied with ab.- rasive of different size and/orhardness so that mechanism isshownyin, Eigs. 4 Aand 5.l ,Appletsy 75- the dual abrasion can be. ofryariednature.;

ternatively, only one of the compartments 2112-- 203` may be used for abrasion at a time with the other held in reserve.

The present invention also encompasses modifications of the above machine. Thus, for example, a washing position may be inserted between the two successive blasting operations or after all blasting is completed and before articles blasted are unloaded.

The nozzle traverse of either of the above machines can be arranged so that with each turn of the drum shaft, the blast moves longitudinally a relatively small amount to give the `desired overlap between successive turns of the spiral blasting trace. In this way `one entire traverse of the nozzles will complete the abrading treatment. If desired, however, the plate to be treated may be given one or more repeat operations. The traverse mechanism may have a manual or automatic reversing arrangement, One suitable form for automatic `traverse reversal is the reversible motor type of construction shown, for example, in Patent No. 2,495,269, granted January 24, 1950. Another convenient reversing mechanism is provided by having the thread on shaft 2G arrangedin endless formso that it extends uniformly from one end to the other and then bends back and runs uniformly back to the rst end where it again bends back and joins the beginning. In this construction the block 25 may be provided with a rotatable thread claw which is arranged to t into the thread of shaft 2l] and be carried by it from one end to the other and be rotated by the reversal of the thread `to then follow the thread return path back along the shaft. This is the well known reversing mechanism commonly used in level Winding mechanisms and needs no further description; l

In the place of the threaded traversing shafts the machines may have a reciprocating belt drive for the nozzles, as shown in copending Huyett application Serial No. 103,710, filed July 8, 1949 which issued as Patent No. 2,590,819 on March 25, 1952.

By way of additional modification, the drums having the construction of Figs. l and 3 may be arranged for rotation in small steps with a complete traverse of the blasting nozzle assembly between steps to trace across the drum a set of parallel blasting lines having the desired overlap. This will also provide a uniformly abraded finish. If desired steam may be used as a blasting gas instead of all or part of the air. Alternatively, water under pressure will also do a good `iob of projecting the blasting mixture. The use of' water as an impellant will dilute the mixture and make it advisable to withdraw the mixture collecting in the housing, separate out most of thewater and supply the separated portions for reuse so that the grid is not subject to excessive dilution. For this purpose the blasting mixture is conveniently kept external of the housing and fed directly to the nozzles.

Either or both types of machines described above may have a viewing window which, as shown at I I in Fig. l, may be. hinged in place and provided with a suitable locking device I3. This enables the window'to be opened for simplifying maintenance such as replacement of the nozzles. To improve observation through the window, a window washing line I'I can be supplied to continually or periodically supply a washing uid such as water over the transparent sections. f l

Figs. 1 and 2 also show a sheet washing line I9 equipped with nozzles 2| through which a washing liquid can be sprayed over the surface of the drum and any plate mounted througih.- As indicated above in connection with the construction of Figs; Sito 6 inclusive, this simplifies clamping and unclamping of the Work sheets and reduces the amount of abrasive clinging to `the unlocked sheet after graining is completed.

In abrasive blasting 'machines such as those described` above, it is highly desirable to protect mechanical drive elements such as the traverse shaft 20 and engagedblock 26, against the abrading action. These elements are according- .1y mounted externally of the housing in which `the blasting iseifecte'd.` This type of construction however calls for "a communication passage- Way of some sort through which the external drive elements arecorinected to the internal nozzles. The constructionof Fig. 1 has such a slot shown at 2:3. Although the use of a suction device as indicated above will keep back all airsuspended particles from escaping out through this slot, the presence of liquid in the blastant stream as well as the drum and filter washings will causeliquidto be throwni about the housL ing and to drain from the walls such as the rear housing wall 25;` The draining liquid tends to escape through a conventional slot as by reason of `surface tension effects and to carry along abrasive particles which work their way into closely fitting parts suchas the threaded drive, and rapidly erode the threads. I

A feature ofthe present invention is the offsetting of. the slot in Wall 25 so that the wall portion defining the lower edge of the slot extends `further out from the center of the housing than the Wall portion defining the upper edge ofthe slot. This serves to catch and trap all materials dripping down on wall 25 and prevents tliese materials from reaching the carriage traverse mechanism in any appreciable quantity.

To provide an abrasion-resistant and uniform work surface against whichA the plates are clamped and abrade'd, the drums such as drum I6 may have' a suitably hard outer periphery of stainless4 ste'el for example. This is shown more clearingin Figs. Zb'to 2f inclusive Where an external coating sheet 35 of stainless steel is illustated' as fixed to the drum periphery," as by welding the stainless steel sheet around a suitably prepared drum surface. l

An additional feature vof the present invention is the ease with which work sheets of substantially any different size can be mounted in place on" the drum by the mounting clamps. The clamping bar itself can, as pointed outabove, loeI readilyshifted to any portion of the drum periphery,y while the individual fingers are easily and rapidlyxed anywhere along these rods. In other words, all that is needed is that a pair of `clamping bars be applied to the drum and adjusted inposition so that the length of the work sheet Will be received between them. As many fingers are then applied to these bars as considered necessary tohold the longitudinal margins of the sheet in a suitable number of places.

'I'he clamping is readily accomplished in a few seconds and the unclamping is even more rapidly effected. l t l As many apparently widely different embodiments of this invention maybe made without departing from the spirit and scope hereof, it is to be understood that Nit is not limited to the lilspeciiic einbodinie'ntshereof,V except'as defined in the:appendedV- claims.

What' is claimed` is: j 1

y 1. ,Aj lithograrihicf,l plate graining' x-'nachinev for holding a plurality tlf lithographie plates and graining atleast one plate' While another is ex"- changed, said machine'comprising a housing; a wheel rotatably mounted on a horizontal axis within the housing, saidv wheel presenting a plurality of axially-extending compartments disposed around the wheel periphery and having vanes4 partitioning the compartments from each other; af plurality of drums, each positioned in a different compartment with'y its axis horizontal and each journaledy for rotation' about its axis, said drums having clamping elements for holding lithographie plates against their cylindrical external surface; blasting elements mounted within the housing for projecting a graining mixture toward portions of at least' one drum when it is held by the Wheel in a rst part of the housing; dri-ving mechanism connected for rota-ting the Wheel, rotating the individual drums when they are in said part of the housing, and also traversing the blasting elements across the rotating drum to bring substantiallyv all partsv of a plate held on said drum in the path of the blast; and an uncovered opening in a second part of the housing opposite a portion of the wheel periphery,` said opening being large enough to admit a lithographie plate for replacing a plate held on a drum when the drumv is brought by the wheel to said second Apart of the housing.

2. The machine as dened by claim 1 and further including a second uncovered opening in a part of the' housing approximately opposite the rst opening,- said second opening being also large enough tov admit a lithographie plate, the driving mechanismv being connected for rotating the Wheel in steps, for rotatingth individual drums when they reach the blasting position, and for automatic disengagementJ fron'r the drums when' they are stepped to positions adjacent the housing openings.

3.V The machine as defined by claim 1 and further including a' Washing mechanism mounted Within a portion of thehousing for washing the drums when they are brought by the' wheel to a position at an opening. g. t j

l4. Themachine as dened by claim 3 in which the blasting elements are positioned adjacent the low portion of the wheel; the housing includes a yhopper at its rlower portionA to catch and collect blasting mixture dropping from the compartment having the drum being blasted; and all the coinf partments having sloping floors for guiding the Washed-'on mixture to .a Wash collector and preventing dilution of the collected blast mixture by the washing. I I. t A

5. The machine as-deflned by claim l in which the compartr'nentY partitions carry sealing elements cooperating withthe housing toreduce the leakage of blasting miiituife f'rrfnhA the blasting' compartment to the plate-replacing compartment M6 n1 anl adjustameciaiiipi" i iampig sheisfprf vai es ended eiiwih .m edges o 'f the area, Aan elongated rodlong enough to catena frcro of said 'flanges toy the other, clamping jaws secured to each end of the rod Afor selectively clamping the rod to the surface at any portion of the flanges; 'said rod having an elongated longitudinally eteiding seat; and a spring finger having a seat-*engaging anchoring broadly. sur@ if claw portion', a sheet-'holding gripportori and` a resilient structure connected to-v urge the claw portion into anchoring engagement with these'at and the grip portion in gripping engagement'with a sheet held on said surface to fix the finger in place againstany longitudinal portion of the' seat and clamp in place correspondingly positioned portion ofthe' sheet, and exposed manipulating structure connected to the resilient structure for manipulation t'o release the finger from anchoring engagement with the seat and enable rapid positioning and adjustment of theA iinger.

, 7. In an adjustable clamping device for rapidly clamping lithographie sheets of varying sizes to an elongated abrasive blasting machine drum having a flange on eachV end, 4an elongated rod long enough to extend from one of said .flanges to the other,f clamping jaws secured to each end of the rod for selectively clamping the rod to the surface at any portion of the flanges, at least one of the jaws being pivotally held on the rod for rapid engagement with and` disengagement from a drum flange, said rod having an elongated longitudinally extending seat in the form of a pocket having its* blind end facing the drum when the rod is clamped in place, and a spring finger having aseat-engaging anchoring claw portion,v a sheet-holding grip portion land a resilient structure connected between the claw portion and the grip portion to urge the cla-W portion into anchoring engagement with the seat and the grip portion in gripping engagement with ai sheet held on said drum to iixV the linger i-n place against any longitudinal portion ofthe seat yand clamp in place correspondingly positioned portion of the sheet', a portion of the grip structure being exposedfor manipulation to release the nger' fromanchor'- ing engagement with the seatand enable rapid positioning and adjustment of the finger.

8. In an abrasive blasting machine for graining lithographie plates of all sizes Within a range of dimension limits,l a cylindrical drum having an outer surface large Venough to receive the largest plate, said drum being mounted for rotation about its cylindrical axis and having at each end axially directed flanges extending entirelyaround its periphery,- the internal face of each flange having a tapering clamp guiding portion,1 a blasting structure for projecting a stream of abradant toward a` portion of the cylindrical periphery of the drum, impelling mechanism connected to axially rotate the drum with respect to the blasting structure for presenting substantially the 'entire cylindrical periphery to the abradant` stream,v at least one adjustable clamp mounted on the drum to hold both ends of a lithographie plate in plaat,l said clamp including an elongated rod extending from one of said flanges to the other, clamping jaws secured to each end of the rod and holding the rod against the drum by engagement against the tapering portiono'f the' internal flange surface, said rod having an elongated longitudinally extending seat in the form of a pocket having' its blind emi facing the drum When the rod is 'clamped in place; and a spring linger having a seat-en-` gaging anchoring claw portion, a sheet-holding grippcrtion and resilient structure eonnectcd between the claw portion and the' gili iiio'rtioh to urge the claw portion into anchoring engagement with the seat and the grip portion in gripping engagement with a sheet held on said drum to fix the finger in placeagainst any longitudinal portion of the seat and clamp in place a correspondingly positioned portion of the sheet, a portion of the grip structure being exposed for manipulation to release the finger from anchoring engagement with the seat and enable rapid positioning and adjustment of the finger'.

9. In a wet blasting machine having automatically traversing nozzle mechanism extending through a traverse slot in the upwardly extending wall of a housing and externally driven for projecting a fluid stream of slurried abrasive particles against a wide surface contained in the housing to automatically sweep the stream over the surface, the improvement for reducing the passage of projected material from the housing through the slot to the nozzle driving mechanism outside of the slot, which improvement comprises the offsetting of the upwardly extending housing wall so that the portion defining the lower edge of the slot extends further out from the center of the housing than the wall portion defining the upper edge of the slot to catch all materials dripping down this wall.

10. The combination as defined by claim 9 in which the machine includes a suction device connected to suck air out of the housing and thereby draw air into the housing through the slot, and the slot provides a restricted air passageway which, together with all other openings in the housing walls, totals not more than about 10 square feet of passageway cross section per horsepower of the suction device.

11. In a wet abrasive-particle blasting apparatus, an enclosed housing, a wall surface in said housing, an uncovered loading port formed in said wall surface, a Work carrier positioned Within said housing adjacent said port but spaced therefrom at all points to form a continuous uncovered gap between said carrier and said wall all around the periphery of said port, blasting means including abrasive particles and liquid supply elements positioned within said housing on the side of thecarrier opposite to the side facing said port, for projecting a slurry of abrasive particles at said carrier, and suction means connected to the interior of said housing for producing an air current stream from outside the housing through said port and said gap to the interior of the housing, said air current opposing and preventing egress of debris and abrasive particles from said housing through said uncovered port.

12. The combination set forth in claim l1 in which said work carrier is a drum and has clamping structure positioned on the periphery thereof for removably securing work articles thereto.

13. The combination set forth in olairn 12 in which said port is about as large as said drum and the gap is large enough to pass the clamping structure.

14. In an abrasive-particle blasting apparatus,

an enclosed housing, a wall surface in said housing, an uncovered loading port formed in said wall surface, a cylindrical work carrier positioned within said housing adjacent said port but spaced therefrom at all points to form a continuous uncovered gap between said carrier and said wall all around the periphery of said port, blasting means positioned within said housing on the side of the carrier opposite to the side facing said port for projecting a slurry of abrasive particles at said carrier, and suction means connected to the interior of said housing for producing an air current stream from outside the housing through said port and said gap to the interior of the housing, said air current opposing and preventing egress of debris and abrasive particles from said 'housing through said uncovered port, and an additional egress-blccking structure within the housing in the form of a vane xed in place with an edge positioned adjacent the work carrier to provide an additional baille restricting the path for the escape of particles from the blasting zone.

15. In a wet abrasive particle blasting apparatus, an enclosed housing, a wall surface in said housing, an uncovered loading port formed in said wall surface, a cylindrical work carrier positioned within said housing with part of its cylindrical face adjacent said port but spaced therefrom at all points to form a continuous uncovered gap between said carrier and said wall all around the periphery of said port, blasting means including abrasive particle and liquid supply elements positioned within said housing on the side of the carrier opposite to the side facing said port for projecting a slurry of abrasive particles at said carrier, and suction means connected to the interior of said housing for producing an air current stream from outside the housing through said port and said gap to the interior of the housing, said air current opposing and preventing egress of debris and abrasive particles from said housing through said uncovered port, a portion of the housing adjacent the port being curved to follow the cylindrical contour of the carrier and also limit the width of the gap.

WILTIE I. GLADFELTER. RALPH R. GARVER.

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

UNITED STATES PATENTS Number Name Date 398,497 Currier Feb. 26, 1889 2,005,654 Fritsche June 18, 1935 2,351,272 LeTourneau June 13, 1944 2,495,269 Lindmark Jan. 24, 1950 2,532,136 Zahn Nov. 28, 1950

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