US2669809A - Sand blasting apparatus and method - Google Patents

Description

Feb. 23, 1954 J. MCGRATH 2,669,809

SAND BLASTING APPARATUS AND METHOD Filed April 18, 1951 2 Sheets-Sheet 1 [Z a INVENTOR.

$411455 E C 6647/4 B 6 Feb. 23, 1954 J c T 2,669,809

SAND BLASTING APPARATUS AND METHOD Filed April 18, 1951 2 Sheets-Sheet 2 fig? ZNVENTOR.

JIM/5 f v M 6m? Patented Feb. 23, 1954 UNITED STATES PATENT OFFICE 9 Claims.

This invention relates to cleaning surfaces and in particular to improved apparatus and method of sand blast cleaning of masonry surfaces and the like.

My invention is concerned with the use of a sand blast in conjunction with water in such a manner as to remove grime and dirt from the masonry surfaces quickly and effectively, without damage to the building surface or injury to the operator from the dust normally generated during sand blasting operations. I achieve these desirable results generally by shooting sand in a dry state from the blast gun while subjecting the building surface immediately adjacent the area of impact of sand therewith to\a continuous flood of water so as to completely saturate the skin or outer layer of the masonry. By s0 saturating the building surface, I tend to prevent the formation of dust and/or effectively allay dust at the impact area of the sand, facilitate the removal of dirt by filling the pores of the masonry with water and maintaining the various areas of the surface in this condition until substantially the instant that the sand is blasted against them, and maintain a condition whereby the building surface is at all times plainly visible to the operator even at the core of the sand stream. Among the objects of my invention is to provide a method for cleaning buildings efficiently, safely and with great facility. Another object is to provide a method of sand blast cleaning masonry and the like in which the area being cleaned directly in the path of the blast is plainly visible to the operator who is thereby enabled to clean more effectively, in less time and with less danger to injury to the building surface through excessive abrading thereof.

Another object of my invention is to provide a method of sand blast cleaning of buildings and the like wherein the dust normally generated i during the cleaning operation is completely eliminated without impairing the overall efficiency of the cleaning operation. A more specific object of my invention is to saturate the surface and subsurface of a building to be cleaned and to maintain it in a saturated condition until the instant it is abraded by the high velocity sand particles so as to facilitate and hasten the removal of dirt, grime and other foreign matter from the building surface.

Another object of my invention is to provide a method of cleaning a building with a sand blast wherein the surface being cleaned immediately adjacent the sand impact area is saturated without reducing the cutting action of the blast, that is without substantially impairing the velocity of the sand particles directed against sand surface. Another object of my invention is to provide a method of cleaning masonry and the like by sand blasting wherein the dust normally generated during such operations is not only allayed but is prevented from forming in the first instance.

Another object of my invention is to provide a simple, inexpensive and yet durable sand blast gun by means of which the several objects set forth above may be accomplished. While the description will largely precede in reference to the cleaning of masonry surfaces, it will illustrate the utility of my invention for the cleaning of other surfaces.

These and other objects of my invention will become apparent from the following description of a preferred form and practice thereof, reference being had to the accompanying drawings in which Figure 1 is a vertical section of the blast gun taken on the line of Figure 2; Figure 2 is an end view of the blast gun; Figure 3 is a partially schematic representation showme the characteristics of the sand blast and water streams as they are projected from the blast gun against the surface being cleaned; Figure 4 is a diagrammatic view of the surface being cleansed showing the flow characteristics of the sheet of water which surrounds the sand impact area; and Figure 5 is a diagram representing the successive positions of the impact area of the constantly moving sand blast stream over the surface being cleaned.

Before discussing the details and precepts of my invention, it will be helpful to an understanding of the principle involved to explain the technique of operators in the sand blast cleaning of masonry in buildings and like structures. The blast, that is, the high velocity stream of air and sand, is caused to move continually over the surface being cleaned to effect uniform abrading or wearing off of the dirt to be removed and preferably a minimum of top layer of the surface to be cleaned. The rate of movement of the core of the blast relative to the surface is determined by such factors as the kind of masonry being cleaned and the physical characteristics of the sand or other abrasive medium used, but in any event the movement should be continuous throughout the cleaning operation to prevent uneven wearing of the surface and to preserve the appearance and beauty of the structure.

According to the preferred practice of my invention, the surface area which is about to be subjected to sand blasting is first and/or preliminarily wetted and soaked with water. I prefer to fill the pores of the material and saturate the skin or top surface of same to a depth up to about A;" to A" with water before applying the sand blast. After this preliminary wetting, a sand blast consisting of sand or similar abrasive material carried at high velocity in a stream of air is directed against the pre-wet surface and. is moved constantly thereover in the manner described above to wear off dirt engrained in the material. At the same time, a plurality of streams of water arranged concentrically of and flowing substantially parallel to the sand blast are directed towardand against the surface. being cleaned at points substantially on the periphery of the target area, that is, the area of the surface against which substantially all of the sand strikes and within which the abrasive cleaning takes place. Most of this water reaches the masonry surface in a solid state where it isredirected in the form of a thin sheet of water which lays flat against the surface and surrounds the target area and which flows rapidly radially outwardly from the targetfarea. The effect of this radialflow of Water from the target area is to bring the masonry surface up to saturation so that the sand stream being moved continually overthe surface will always be directed against a; part of the surface which the. instant before "was saturated with water. I-have found that by maintaining the surface in such a saturated condition, the dust normally formed by theimpact of the high velocity abrasive particles against the surface is either not generatedor is eifectively allayed. Also, the removal of dirt, grime and. the like from the surface is greatly facilitated by What I believe to be the action of this flood of water in filling the. pores of themasonry and thereby reducing or substantially eliminating the tendency of surface to absorb or suck in the dirt and foreign matter which has been loosened by the sand blast and is suspended in water on the surface.

My improved method of cleaning buildings is dially spaced walls 4 and 5 which define'between' them-an annular chamber-B. Anrelbow' T'communicating with the chamber if is. adapted to be-Tconnected through'a coupling 3' tota'water hose '9 through'which Water under pressure flows from asuitabie' source to the chamber 8;: The

rear end it of chamber 65 is. closed while the Wall ii at'the opposite orfront-end is drilled or otherwise formed with: aiplurality of: longitudinallyextendingholes i2 arranged ina' circle: and

throughwhich the water'admitted to chamber tunder'zpressure will shoot forwardly in as-lmany narrow solid streams. Thehol'es l2 are' drilled with their axes parailel'to the longitudinal axisof thle" casing 2- so. that their axes will also be parallel to the axis of the bore. orpassage in nozzlet in order to insure that thewater streams as they flow forwardly will be substantially equally spaced from and parallel tothe core of the sand blastissuing from the nozzle: 3'. City water at a pressure of about 40 p'oundspe'rsquare in'ch' iss'atisfactoryfor use with the gun I. For such conditions, I have found that about 36 equally spaced water holes drilled on about a 1 inch diametercirclein the end'wall of the casing with a No. 58 drill (0.042" diameter) will give satisfactory results and will furnish asufficient-quantity of water to' the" surface about to be cleaned to-cornpletely'fiood and saturate same according to the precepts of my invention.

' The'casing-2"is iforinedrwithan inwardly ex-' tending annular flange ifilocated at therear iii) end of water chamber 6 which acts as an abutment or shoulder against which the nozzle 3 is seated when the nozzle is assembled with the casing. The rear part 66 of the casing 2 is a cylindrical, single walled extension that isropen and threaded internally as indicated at 1'! to receive the threaded end of a tubular adapter element l8 to which a flexible air-sand hose i9 is adapted to be connected. for delivering sand and high pressure air to the nozzle 3. The hose [9 is connected at'the'other end to a source of high pressure airv and sand, not shown and thus sand delivered to the sand-nozzle 3 for ejection therefrom atv a" high velocity.

The sand nozzle 3 is athick walled hollow tubular member, having an annular flange 2i located at the. rear end of the nozzle, that isg the; end through whichthe air-sand stream enters the nozzle. Flange 2! is adapted to overlie the:

inner flange; i5 onthe casing 2 whenthe nozzle isv inserted therein to locate the longitudinal .as well as the c-caxialposition of the nozzle ini the casing 2. When the nozzle is. initially assembled withthe casing, it is inserted longitudi nially through the rear end it; thereafter, adapter 8 is screwed into the casing so as to press -andseat nozzle flange 2 i .tightlyand firmly against flange it. A resilient washer 22 maybe interposed between flanges 2i and 15 to make the joint air tight. A The opening or central. longitudinal bore 23 through the nozzle 3 is formed so that. the crosssectional area thereof gradually decreases or tapers from the entrance end 2:3 a Off 'the I1OZZle toward the throat 2 3b-thereof as-shown so as to impart a highvelocityto the high pressure airpassing therethrough in a manner wellknown by those skilled in theart of fluidnozzles. Thusthe individual particles of sandentrainedin and carried along by the air-str.eam will likewisembe' greatly accelerated so that they attain a high velocity upon passing through the. nozzle, the velocity beinginthe order of 150 feet per second. Since the sand particles passing through the nozzle at such high velocities tend to rapidly; wear down'the nozzle and enlarge the opening therein,

the nozzle 3 is made of a very hard wear-resistant material. When the throat 23b in the nozzle becomes enlarged through such abrasion to: anextent that the-velocity of the air-sand stream is reduced to apoint where the blast no longer effectively andefliciently cleans the masonry; a new nozzle, is substituted, by disengaging the adapter I8 from the rear part I6 of the blast gun casing;

removingthe-worn out nozzle and inserting-anew one.

The nozzle-3 is suiiiciently long to permit the;

accelerated stream of air and entrained sand particles to flowevenly and non-turbulently from the mouth 25- of the nozzle; The nozzle projects beyond-the front wall H of the casing 2 as" shown though according to my invention,:a portion" of the'waterorwater vapor'of the water stream may lie-drawn into the air-sandstream before the-latterreaches the surface being cleaned; I prefer to maintain a suitable well defined radial spacing between thewater: streams and the-blast at the) mouth or exit; endzo'f' thegun" sothat relatively" little Water -will=beatomizedby the blast and a.

5 substantial portion, preferably the greater portion, of the water will reach the surface being cleaned in the solid or non-atomized state. By way of example, I have found that an initial radial spacing of about of an inch between the water streams and the core of the blast with the mouth of the sand nozzle projecting about 1% inches in front of the water holes in the gun gives satisfactory results.

In Figure 3 I have shown the gun and a schematic representation of the air-sand stream or blast and the water streams between the blast gun and the surface being cleaned. The airsand stream 3|! diverges slightly as it approaches the target While portions of the surrounding water streams 3| are generally drawn into and atomized by the high velocity blast. This partial atomization of the water streams appears to begin at about 1 /2 to 2 inches in front of the nozzle mouth as indicated at point A in Figure 3. ihe broken lines em represent the portion of the water streams that are separated from the main body of the stream 3i and are pulled and/or induced by gravity to fall inwardly into the air-sand stream 30. At this point, the water and airsand streams are prevaded by a somewhat transparent mist although solid water dib is plainly visible beyond the point A toward the target. A certain portion of the water streams takes a di vergent course as indicated by the broken lines Me. As a result of partial atomization of the surrounding Water streams finely divided water particles are carried by the air-sand stream to the target. The solid constituents til) of water that persist in solid Water streams hit the surface adjacent the target, that is, at substantially the periphery or outer regions of the target area, and are redirected to flow away from the target in a sheet or layer 32 which flows rapidly radially outwardly from the sand impact area or target. I have observed this sheet to appear to be about /8 to /4 inch in depth and to spread outwardly from the target area a minimum distance of about 1% feet. There is substantially no rebound of the water particles, all of it being caused to flow into the sheet 32 and to move over and parallel to the surface of the building, soaking the surface adjacent the target. This is shown in Figure the direction of the flow of water in the sheet 32 being indicated by the arrows. The portions of the water sheet directly above the sand impact or target area T flow in an are under the influence of gravity and finally gather into a perceptible head of water 33 at the outer edge of the sheet 32.

According to my method, the surface of the building not only at the target area T but also immediately adjacent the target area is subjected to a continual flooding of water from the streams 3! which saturate the top layer or skin of the masonry M as indicated in Figure 3 by the heavy shading at M. This saturation process is accelerated by reason of the high pressure of air, indicated by the broken line which forms around the target area when the air in the blast builds up and accumulates. It is my belief that this high pressure area or head of rapidly moving air exerts a pressure against the water sheet 32 in a direction normal to the surface thereby forcing water into the pores of the building surface and aiding the saturation thereof. This pressure will be greatest near the core of the sand stream and will diminish propor tionately at greater radial distances therefrom,

this being indicated by the size and position of the plus signs in Figure 3. The rush of air in the blast as it curves from a direction of flow normal to the surface to one radially outwardly and parallel to the surface induces the water to flow radially outwardly and at the same time presses the resultant sheet fiat against the building surface as shown in Figures 3 and 4. Thus, at all times the portions of the surface imme diately adjacent the continually moving target area, that is, those parts of the surface which v in the next instant will be subjected to the abrasive action and impact of high velocity sand particles are always saturated with water. The air blast cannot dry these portions of the surface because the sheet of water is interposed between the spreading air blast and the building surface. Also, the partial atomization of the solid streams of water results in some water being carried by the air-sand stream to the surface within the target area so that even at the core of the blast some moisture is supplied to the masonry surface to tend to preserve the saturated condition of the masonry against the drying effects of the moving air in the sand blast.

The partial atomization of the water streams 3i while resulting a misty appearance of the air-sand stream does not interfere with the visibility of the target. The light mist is actually transparent and is confined within the air-sand stream. line of demarkation between the dirty and clean portions of the building surface can be easily seen at all times by the operator during the blasting operation. Thus by my method of sand blasting I provide for a complete 7 flooding of the portions of the masonry surface at and adjacent to the target area without lllb pairing the visibility of the target area to any appreciable extent.

The saturation of the building surface the instant before the same is struck by the sand particles appears to be largely responsible for the elimination of and/or the allaying of dust normally created at the point of impact. By saturating the top layer or skin of the material being cleaned, the tendency for harmful dust to be formed during the breaking off of the small surface pieces by the impact thereagainst of high velocity sand particles is at least greatly reduced. The water in the masonry itself thus tends to prevent dust from forming at the target area. The dust that tends to form from the breakup of the abrasive material itself upon impact and/or which results from the finely divided dust lilre particles of abrasive material carried from the source of supply to the gun or are created in the hose or in the gun are also effectively allayed and prevented from filling the atmosphere in. and around the working area by the practice of my invention. Based on observation I believe that this result is brought about by means of the flood of solid parts as well as the atomized parts of the streams St at and adjacent to the target area; that is, as the dust is carried to and/or bounds backward from the masonry surface, it becomes entrained in the rush of various sized water particles directed toward the surface as well as in the accumulation or head Ziid of water which builds up and surrounds the target area. I also believe that the entrainment of this dust in the water at and around the target area is further aided by the how of air in the high pressure area 35 which induces this dust to fly into and become entrained in the water sheet 32 and be carried away from the target area. I have noted fromobservation of sand blasting operations whereingmy inventionzis practioed that .water; sheet. 32 has a .distinctly- .brownishycolor -*:w.hich.-l2 attribute to-the sand anddust as.:well-as l the .dirt andgrime being .carriedeaway from; the wtarget. area and :that nodust of.,-.any visible amount appeared: in or about-the target area. .The only particles that rebounded. from-the sur- ..-face being cleaned were heavy. solid'. grit-like -=-pieces .whichwereheard to strilze against the operators shield. :These. particles were too: large and-heavy tobe breathed by' the operator and .i did not impairvisibility ofthe target area.

The continuous saturation of. the building surcface. according to mywmethod of sand blasting also: contributes to quicker; easier: and: generally 1. more; Efflfilfillll" removal of .dirt and grime from cthe surface Masonry surfaces and particularly uthose of limestone and-sandstoneare quiteporous and thus have agreat aninityfor' water; Based ;qon' observation I. believe. thatwhen water is illtroducedinto the poresofsuchmasonry surfaces, 1 .it is at once drawn rapidlyinwardlyby the force of1-oapillary attraction. Whenever the surface is wetted to any degreeless than-a completexfilling of thesepores, I havenfound that this condi tion exists, that is, there is a tendency for the material to absorber. draw in the water which -..:;laysaon the top of the surface. When the sand :blast is'directed against. the-surfaceand the dirt and grime thereon is loosened, this characteristic of thexsemiewetxsurfa'ces appears and "becomes -:--man-ifest by what I have observed. tobe the tendency' ofathe material to draw the dirt inwardly which-makes thecleaning job. more tedious and -:time consuming-and: results in a'poor quaiity of cleaning. I-a-voidthese effects-by the practice of "1I1YilIl6llhOd because, I. "believe; the surface "immediately adjacent the target-area is so saturated with water..thatntheimaterial has: little. or no affinity for or.;tende.ncy to draw in-more'water and-loosened grime orother foreigrrmatter; To insure that this surface will be in suchaazsaturated condition when theabrasive particles in the blast 1 strike same and begin to'loosen the 'dirt,"lzcause a'floodof water to be: directed atall'time against T' "the portion of the surfacethat are immediately .adj acent the .target area so that the: continually .moving sandblastwill'work ona portion of the ;:surface which the instant' beforezwas completely saturated; .When the'blast 'dislodges', dirt,xthere is"no place for this :dirt togo excepttb follow 't'hewflOVV of water: in" sheet 32;iniwhicb it has lsecome entrainedrand to= be"carriediawayafrom the target --a-rea.f'-Ihus; by saturating thetsurface being;cl.eaned especially .theniornent; before 1 it is'blasted by the sand; particles not..3only is the generation of. harmful dust at' the surface-prevented buthalso aquiekerpmore thoroughand generally better. cleaning .3 ob is realized.

I The Water streams 3| are arranged so asto be entirelyindependent of. and spaced from the airosandstream at the nozzle. The'air-sand stream is therefore dry as it passes through the nozzle and as :such is capable of being accelerated to a r .high velocity which in turn enhances the abrad- .ing action or the sandparticles on the surface about to be cleaned. The partial atomization of these streams does not seem to impair this cutting. action or the sand. The atomized parts of the. water. do strike the surface being cleaned .Wlthil'l the target area and, I be1ieve,..tends to .keep this part of the surface saturated and aids in the allaying of dust. As mentionedabove, the sandblaststream .j..sho.uld be. moved constantly .over the .masonry a surface to preseryeathe z-building; surf ace? against uneven wearing. -I. have shown in .eFigure fizfour positions of theitarget'area 'I!;that is, 11116700738 of the sand-blast;which positions:-; represent; a sequence of movements. of the; blast -.over;,-the

. masonry surface; as for example, fromthe-posi- :tionof T1 in a-clockwise direction to the position T4. Also, there is represented schematicallysthe corresponding areas covered by the sheet132 of water which isrepresented by the concentric circles -W1'through W4; :Whiletheccre of the J sand blast is moved'rfrom T1 toTz; as maywoccur during the cleaningroperation; thesandparticles will at all times strikeagainstportions of the surfaceswhich the instant before, were covered and of T2, thesarne condition of saturation. oithe ital-get area will :exist. T3 is shown aslying-par- =tially within the. circle. .Wz' although it-will, be

. understood that as-the sand blast ismoved from T2 to- T3: the. water sheet=will likewise .move' to thearight and flood-and saturate the surface by .the time the sand blast-reaches T3. In likemanner, the area T4 is shown as havingbeenflooded by the wash oftwater sheet W3 corresponding to the previous position T3 of the sand-blast against the masonry-surface. .The grossresult isthat @the masonry surface surroundingthe continually moving target area is constantly being saturated by the sheet of water 32, which.conditioniacilitates the cleaning of the surfaceand effectively .allaysdust formed :during the sandblast-operation. Throughthe pr-actice of. myinventionl the .cleaning, of irregular-and/or ornamental parts .Inthecase of irregular surfaces, the hood of of buildingsland the C01Il8l5x1lh8160f as vwell as the flatcontinuous surfaces is greatlyfacilitated.

water from streams 3i Willtend to conform generally tothe .contour of the masonrysurface by Lreason of the high pressure area of air around the f: targetarea and will be thereby urged to soaktinto thesub-surface' ofthe material regardless of ...the irregular contours of .same. to saturate it prior tothe impacttherewith by thehigh xeloc- ,ity abrasive particles.v .Referring again to Fig- .ure 5', I have represented by. a. broken. line C ...th,COII16I' of a building being. cleaned. From the foregoingv description, it, will be apparentthat the portions of. the surface adjacent. the. corner C will be .fully soaked by. the: watersheet 32 as the sand blast is moved up, to the corner. edge and the cleaning of these parts of abuilding will be complete.

'While I have illustrated and described a. .preferred embodiment and manner of practicing .my invention, modifications and changes. will occur to those skilled in the art without substantially departing from the substance thereofor precepts of this specificationand therefore I. do. not. care to be limited in the scope' of my patent toithe form herein specifically illustrated. anddscribed nor in any manner notrequired by the. state of the prior art.

I claim: I

' 1. A method of sand blastcleaning comprising projecting a stream of sand at high velocity-from a blasting gun toward thesurface beingcleaned,

simultaneously directing a plurality of individual streams. of water. substantially parallel said sand streamtoward said surface so astdsurround thesand stream in spacedrelation thereto adjacent the gun, causing said water streams to strike said surface immediately adjacent the point of impact of said sand stream therewith and to be thereafter redirected to flow radially outwardly from said impact area to saturate the area of said surface surrounding and immediately adjacent said impact area.

2. A method of cleaning masonry and the like consisting of the steps of projecting a stream of finely divided abrasive particles at high velocity from a gun against the surface being cleaned, simultaneously directing water from said gun in a direction substantially parallel to the sand stream, said water being radially spaced from said sand stream at the gun, and causing a substantial portion of said water to hit said surface at points at least as close to the area of impact of said sand stream thereagainst as said spacing between the water and the sand stream at the gun.

3. A method of sand cleaning masonry and like surfaces consisting of the steps of projecting a stream of sand at high velocity from a gun to- Ward the surface being cleaned, simultaneously directing a plurality of streams of water from said gun toward said surface, said streams of water being concentric with and spaced from and flowing substantially parallel to said sand stream at least at the mouth of the gun and ultimately striking said surface at points approximately as close to said sand stream as the spacing between the water and the sand stream at the gun and thereafter causing said water to flow radially outwardly from the sand impact area in contact with said surface to wet portions of said surface completely surrounding the sand impact area.

4. A method of sand blasting masonry and the like consisting of the steps of pre-wetting a portion of the surface to be cleaned, directing a stream of sand at high velocity toward said prewet portion of said surface, simultaneously directing a plurality of streams of water from said gun toward said surface in a direction substantially parallel to the sand stream, said water streams being spaced from said sand stream at least at the mouth of the gun and ultimately striking said surface at points approximately as close to said sand stream as the spacing between the water streams and the sand stream r at the gun, causing said water after striking said surface to be redirected to flow radially outwardly from the point of impact and to saturate the surface over which it flows, and continually moving the sand and water streams transversely of said surface.

5. A method of cleaning a masonry surface by sand blasting consisting of the steps of prewetting a portion of the surface to be cleaned. directing a continuous blast of abrasive particles from a gun at high velocity generally toward said pre-wet surface and continuously moving said gun so as to move the core of said blast continually over the surface being cleaned, simultaneously directing a plurality of streams of water from said gun initially concentrically of and spaced from and substantially parallel to the core of the blast and in a direction toward said pre-wet surface, said water streams ultimately striking portions of said surface proximate to and completely surrounding the area of impact of the abrasive particles, and thereafter 10 causing said water streams to be converted into a thin sheet of water on said surface and flowing rapidly radially outwardly from said area of impact so as to constantly and thoroughly soak the portions of said surface against which the abrasive particles will next be directed.

6. The method according to claim 4 which includes the step of causing at least a portion of said water to strike the surface within said area of impact.

7. A method of sand blast cleaning compris ing projecting a stream of sand at high velocity from a blasting gun toward the surface being cleaned, simultaneously directing a plurality of individual streams of water substantially nondivergently toward said surface and surrounding the sand stream in spaced relation thereto substantially throughout the length of the sand stream, causing said water streams to strike said surface immediately adjacent the point of impact of said sand stream therewith and to be thereafter redirected to flow radially outwardly from said impact area to saturate the area of said surface surrounding and immediately adjacent said impact area.

8. A method of sand blasting cleaning comprising projecting a stream of sand at high velocity from a blasting gun toward the surface being cleaned, simultaneously directing a plurality of streams of water toward said surface and surrounding the sand stream in spaced relation thereto, causing said water streams to strike said surface immediately adjacent the point of impact of said sand stream therewith and to be thereafter redirected to flow radially outwardly from said impact area to saturate the area of said surface surrounding and immediately adjacent said impact area.

9. A sand blast gun for use in cleaning surfaces comprising a hollow cylindrical casing, one portion of said casing having radially spaced walls defining an annular chamber, mean for supplying water under pressure to said chamber, the end of said one portion of said casing having about 36 openings, each approximately 0.042" in diameter and communicating with said chamber, said openings being substantially equally spaced from each other and formed on a circle having a diameter of about 1 and concentrically of the longitudinal axis of the casing, the axes of said openings being substantially parallel to the axis of the casing, a nozzle removably mounted within said casing and extending beyond said one end of said casing and having a longitudinal bore therethrough, the axis of said bore coinciding with the longitudinal axis of said casing, and means connected to another portion of said casing for supplying sand and air under pressure to said nozzle, the sand being projected at high velocity from said nozzle in radially spaced relation to the water issuing from said openings in the casing.

JAMES RICHARD MCGRATH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 699,838 Evans May 13, 1902 2,114,573 Rhodes Apr. 19, 1938 2,324,250 Voerge July 13, 1943 2,376,287 Sorrentino May 15, 1945

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