US2990653A - Method and apparatus for impacting a stream at high velocity against a surface to be treated - Google Patents

Description

2,990,653 VELOCITY July 4, 1961 J. A. BRowNlNG METHOD AND APPARATUS FCR IMPACTING A STREAM AT HIGH AGAINST A SURFACE TO BE TREATED 5 Sheets-Sheet 1 Filed April 2l, 1958 #5M ,41m/wirf July .4, 1961 J. A. BRowNlNG 2,990,653

METHOD AND APPARATUS FCR TMPACTING A STREAM AT HIGH VELOCITY AGAINST A SURFACE To BE TREATED Filed April 21, 1958 3 Sheets-Sheet 2 H6714 F/@J F/ci. 55 /35 /3/ /3/0 July 4, 1951 J. A. BROWNING 2,990,653

METHOD AND APPARATUS FOR TMPACTING A STREAM AT HIGH VELOCITY AGAINST A SURFACE TO BE TREATED Filed April 21, 1958 3 Sheets-Sheet 5 5) Wmw/w/Myfm United States Patent O METHOD AND APPARATUS FOR IMPACTING A `ISTREAM AT HIGH VELOCITY AGAINST A .SUR-

FACE T BE TREATED James A. Browning, Hanover, NH., assgnor to G. H.

Tennant Company, Minneapolis, Minn., a corporation of Minnesota Filed Apr. 21, 1958, Ser. No. 729,725 15 IClaims. (Cl. 51-8) This invention, a continuation-impart of'my pending application, Serial Number 557,100, tiled January 3, 1'95 6, relates tothe treatment of metals and'othe'r materials by such techniques as sandblasting,1steam cleaning and impregnat'ion. Theprinciples of this -invention are particularly applicable to the removal of deposits such as rust, grease, paint and dirt and to the 'impregnation of surfaces with protective `coatings of paint and similar substances.

Sandblasting is a common and extremely efective'technique for the removal of undesirable deposits from the surfaces of structures, machines, ships, castings and the like. The common Sandblasting system uses a stream 4of high velocity air to propel the sand or other abrasive against the work to be cleaned. The usual source for such `a high velocity stream of air is the expansion of Vcompressed air from high pressure through a nozzle toatmospheric pressure. The abrasive or other material is introduced Vinto the air stream at a point ahead of vthe-nozzle. The abrasive is given `high velocity as it is entrained into the air stream. When an abrasive `exhibiting sharp edges and corners is employed, its action upon striking the -material is both of a cutting and impact nature. Whencutting action is not desired, round metal shot is substituted for the sharp abrasive.

The effectiveness of the blasting operation -is directly proportional to the velocity at which the material strikes the work and to the mass of material delivered at that velocity. This is `due to the :higher kinetic energy contained in each particle at the higher velocity. The more particles contained in the stream, the more impacts 'per unit time.

It is current practice to use an air compressor for such blasting purposes whose lcapacity is well above the air requirements of the specific blasting machine being used. Such a recommendation is due to the desire to keep the air .pressure before expansion at a suciently high level to insure sonic exit velocity from the nozzle. A reduction of the inlet air pressure leads to a reduced air jet velocity with subsequent reduction in cleaning effectiveness.

.Steam cleaning is the process in which steam is projected at the surface to be cleaned. The state of the steam may be represented by a mixture of hot vapor in equilibrium with its liquid phase, or superheated. The state is determined by the amount of heat contained in a unit mass of the water. Current types of steam cleaning equipment make use of various cleaning agents such as detergents. Such detergents are effective in removing oil, grease, dirt and similar deposits. However, steam cleaning as it is presently practiced, is not effective in `removing rust and other tenacious deposits.

iIn most steam cleaning applications the effectiveness of the cleaning operation is proportional to the .temperature of the steam or steam-water mixture. Thus, it is desirable in many cases to use the steam at high temperature. However, detergent action may be adversely effected if the temperature is too high. iIt is important that proper control over the quantity and temperature of the mixture flowing be maintained.

The present invention is an internal burner device which make 'use of the combustion of an oxidant and a `fuel to introduced into -an internal combustor where its oxygen ICC combined with Afuel na lcombustion process carried out at very elevated pressure. 'Due to the combustion reaction, the energy level of this airis raised approximately eight fold above that of compressed air expanded through the same pressure differential with no heat addition. Such an energy increase represents a velocity increase of about 21/2 times. Readily iiowable material, such as sand, other particulate matter, and/or liquid, is introduced in-to the ho't products of combustion. The higher velocities attained in such `a system "are very beneficial in many Yap plications. This invention is of great economic importance, as the eightfoldincrease in the energy is obtained by a relatively small addition of inexpensivefuel.

In the steam cleaning :application the oxidant and fuel are burned at elevated .pressure in an internal combustor. Water is added to the products of combustion. Heat is extracted from these hot products turning a portion, or lall of the water into steam. The combined steam and products of combustion form amixture which exhausts at .high velocity from the chamber through the nozzle. A very effective cleaning jet -is thus formed. 'I'he present invention when -used for steam cleaning, clearly exhibits the value of the additional kinetic energy contained in the jet. Conventional steam cleaners have low jet velocities and arenot nearly so effective `in the removal of thick deposits.

The impregnation of surfaces for protection from corrosive action requires that the impregnating materialcompletely coat the surface. For example, high Velocityprojection of paint particles is known to result in the deeper penetration of the paint into-surface imperfections than when brushed on. Such penetration leads to better bonding Abetween the surface `andthe paint film.

When a particle in plastic condition .impinges on a surface at high velocity the particle spreads out radially to anextent determined by its size and velocity at impact. Such later spreading is conducive to good bond strength between adjacent particles when subsequently solidified. Mechanical bonding is proportional to the impact velocity.

iParticle size also .effects the tendency of particles in both the liquid and plastic state to deform on impact. The smaller the particle, the more difiicult such deformation becomes. This is due to the increase of surface tension with diminishing radius. The extremely high velocities of my internal burner jet assures the desired high particle velocity.

An additional advantage of the internal burner as a propelling device lies `in the heat content of the iet. Such liquid materials as lacquers and plastics, which after :application solidify, are commonly heated prior to spraying. This heating is vaccomplished batchwise or `in continuous fashion by heating the Iliquid prior to introduction into the propelling medium. The temperature to which this -material may be heated when in spray form, is limited by the tempera-ture Ao-f the relatively cool propellant air. Although `the liquid may have sucient heat content lbefore spraying, much of this heat is extracted by the propelling gases.

In some cases ya thinner must be added to provide proper Viscosity values. The ratio of thinner to paint may be greatly reduced when elevated spraying temperatures are used. This allows for the deposition 'of thicker dry films. vSolvents notrrequired for flowout disappear between the spray gun and target. By allowing the material to be deposited to remain at a relatively low temperature por to its introduction into the thermal jet, the material can be brought lto its most desirable tempenature within a vmatter of a few milliseconds. A comparable period of time -is 4required to deposit the material. In this manner, `it is possible to decrease the Y time for the drying -or setting of such materials. This Y fact, plus the high velocities imparted, `makes' 'the internal fha burner a valuable addition to the plastic and paint spraying elds.

It is .apparent that the internal burner is well suited to impart both kinetic and thermal energy to particles introduced into its jets. Such particles may be composed of solids, liquids, and plastics as well as suspensions of solid particles in a liquid medium-a slurry.

The denition of particles as herein used refers to any readily owable material introduced into agaseous jet for the purpose of raising the kinetic and/ or thermal energy level of the added material. The material may be in a form other than particulate when introduced, and in such case it is transformed by thermal and shearing means into such particles.

To lower the jet temperature of a suspension of particles contained in the products of combustion of an internal burner it may be necessary to add diluent air, or liquid, to the jet. For example, such a diluent may be added tothe jet prior to the introduction of the material to be sprayed. Such a system is applicable to the spraying of paint by means of a jet composed of the products of combustion of a flame and a substantial proportion of superheated steam.

The structure, functions and advantages of my internal burners will be more apparent from the following description made in connection with the accompanying drawings, wherein:

FIG. l is a longitudinal sectional view of an embodiment of my internal burner;

FIG. 2 is a cross section taken on the line 2-2 of FIG. l, showing the structure of the combustion chamber and the relationship between saidchamber, the inner and outer tube, and thenozzle; l j K FIG. 3A is a cross sectional view` taken on the line 3A-3A of FIG. 1, showing the injector piece;

l FIG. 3B is` a detail vertical section showing theatrangement of the fuel-inlet-system within the injector prece;

FIG. 3C is a detail section showing the air-atomization provided for breaking up a liquid fuel;

FIG. 4 is a rear elevation of the burner showing the injector piece;

FIG. 5A is' a detail vertical section showing the use of 4an aspirating section for inducing water into the exiting jet; A FIG. 5B -illustrates in vertical, longitudinal section. a water-cooled nozzle employing pressure-fed water;

FIG. 6 is a longitudinal cross section of the rear portion of a burner system utilizing a principle of this invention for the axial injection of liquid through the combustion chamber;

FIG. 7 is a graph showing the results of tests conducted to determine the effectiveness of the burner when used Vfor Sandblasting as compared with conventional blasters;

. FIG. 8 is a graph contrasting test results showing the effectiveness of slurry cleaning when using my internal burner against conventional slurry cleaning;

FIG. 9A is drawn to show a typical sand feeding system; and

FIG. 9B is a detail view of an orifice system for regulating the air flow propelling the sand to the burner unit. The use of such internal burners for these purposes can better be understood by reference to the drawings. FIG. 1 is a longitudinal sectional view of the complete burner for use in blasting operations where an abrasive grit is introduced into the products of combustion. The air for combustion is also used to cool the hot walls of the burner and the nozzle 27. This air enters the burner from a hose (not shown) attached to the projection sleeve 13 by means of the threads 12. The air passes through the passage 29 into passage 70, shown in FIG. 3A. Still referring'to FIG. 3A, the air is metered into the passage 72 by the annular area contained between the valve seat 71 and the valve 75. The metered air then passes through the short circular passage 73 into the large annular supply-passage 16 at the rear of the burner, whence it is distributed forwardly to the elongated, narrow, annular passage 17 contained between the large outer 4tube 40 `and the middle tube 42. The air travels to the front diminished end of the burner where it transfers through the circumferentially spaced ports 18 to a second, elongated, annular cooling passage 19 contained between the middle tube 42 and the nozzle 27. The air passes at high velocity over this nozzle providing the effective cooling required. The air next passes around the reducer section 25 which is of an annular, truncated conical form, into the annular region 24a contained exteriorly and around the combustion chamber 24. The high velocity `air passing between a multiplicity of external, longitudinal -fns 28 (see FIG. 2) cools the combustion chamber 24. The air is then distributed into the annular well 21 through a plurality of radial ports 20 rat the rear of the burner and thence into the rear of the combustion chamber 22. In passing into the chamber 22 a recirculation of the air is realized due to the larger cross sectional larea of the chamber 22 in comparison with the well 21. This recirculation, near the rear injector piece 10, helps stabilize the combustion reaction.

When liquid fuel such as number 2 fuel oil is used, thorough atomization is required for reliable ignition at low temperature. The `use of a small llow of high pressure lair is very etfective in producing good fuel atomization. Referring to FIG. 3B, `the fuel oil is rst metered and enters the injector piece 10 through the threaded, circular passage 90. The fuel is conducted through the relatively small, forwardly extending passage 91 to a small injector port 92. Atomizing air passing at high velocity from the passage 61 (FIGURE 3C) intersects the fuel flow producing the desired fuel droplets of small size. The passage 60, which conducts the air to passage 61, connects with air passage 29 (see FIGS. 3A and 3B), which is on the high pressure side of the metering valve used to control the combustion air ilow.

Combustion is initiated by a spark produced across the annular area 35 (see FIG. 1) contained between the electrode 31 and the plug body 33. A small amount ofair enters 'the plug through the small radial ports 36 communicating with the upper portion of the annular cooling passage 19, to pass through the annular area 35 into the combustion chamber 22. This flow of air serves a dual purpose. It lengthens the arc path into the gases to be ignited and serves to cool the plug body 33 and the electrode 31. The plug body 33 is attached by means of threads to the spud 34 which is welded to the outer tube 40. The ceramic section 32 of the ignition plug provides electrical insulation between the electrode 31 and the plug body 33. The threads 37 are provided for the attachment of a shield lead housing (not shown). A conventional high voltage transformer (not shown) of 10,000-volt secondary voltage is used to provide the spark energy. This transformer may be located well away from the burner and does not have to be carried when the burner is being hand-held. Combustion is essentially completed within the charnber 22. The products of combustion travel through the reducer section 25 into the nozzle 27 from which expansion to atmospheric pressure produces a high velocity jet.

The abrasive particles or other material are introduced through the rear axial passage 53 contained in the piece 50. For blasting purposes a small How of air carries these particles through the hose length 114 (see FIG. 9A) which is connected by means of the threads 52 to the piece `50. This secondary ow of air is consumed in the combustion reaction along with the air used for cooling the burner. The abrasive becomes entrained in the Yuse `with air cooling due to their oxidation at the elevated temperature of operation. used.

The nozzle is detachably held in place between the reducer section 25 and the retainer ring 45, which has an 'externally 'threaded sleeve.

The piece 50 must project beyond the point of intersection of the air entering the well Z1 (see FIG. 1) through the radial ports 20. In this fashion the recircution of the `primary combustion air is not deleteriously inuenced by the `secondary flow of air :and its contained particles. For best operation, the annular face 54 of piece V50, should project slightly beyond the face of injector piece 10.

`Any -action which interferes with the lstabilization process will extinguish the llame, thus obviating the use of such a system as a practical heat source. This adverse condition is 'particularly true when water is injected into a combustion chamber. VSuch water is able to extract a sutlicient amount of `heat from the reacting gases to reduce the heat output from these gases to below that necessary to :keep the combustion going.

It is possible to `avoid `this problem of quenching of the flame reactions by injecting the water into the products of combustion at a point well removed 'from the injector end ofthe unit. Such avsystem is shown and described in my pending application, ySerial No. 557,100, ledJanuary 3, 1956.

'I'he present invention allows for the vembodiment of axial injection; thus, a longer path is provided for the injected material. This leads to Xlonger residence time of the particles within 'the hot gases allowing .more complete heat and momentum-transfer.

It has been found that the injection `of water `axially down the combustor leads to `an extremely critical situation. If the water `jet should break into droplets which disperse `through *the chamber 22 at Ya position not suiiciently far `removed from `the injector piece, the flame may be extinguished. `It is possible to veliminate this initial break-up f the water jet by controlling the momentum of said jet. If the water riiow is lprojected axially downstream in a stream of suicient momentum, the break-up process does not occur yuntil a position is reached well down the chamber length. FIG. 6i illustrates an internal burner as used for steam cleaning, or for other liquid injection into the hot gases. It `has been found that the liquid injector tube 103 should extend Well into the chamber 22. The liquid is rst metered 'by a valve (not shown) and passes through a hose (not shown) threaded to tube 103 by means -of the threads 104. The axial passage 105 conducts this liquid tothe smaller injector port 106. The size of the port 106 is important with respect 'to producing a jet 107 which retains its identity until a point well down the combustor length is reached. At this `point the jet suddenly breaks into droplets `108. The diameter vof the injector port 106 together with the mass flow-of the liquid determine the `momentum contained in the jet 107.

When -air expands into the atmosphere from a pressure at -least ldouble that of the atmosphere, it is possible for the result-ing jet to reach sonic-orrhigher velocity. Under perfect conditions, a nozzle which contracts` to its '-iinal opening size, or lfor a tube, the resulting velocity -is sonic. For a nozzle, which contracts 'to fits minimum section and then expands, 'the `-jet velocity "can reach higher than Titanium `carbide may be sonic value `provided the inlet pressure is sutlicientl-y great. The sonic velocity of a gas at the gas temperature is Vson ic R T 10:@ cv

g is'the acceleration of gravity R is the gas constant T is the temperature.

It is thus seen that the sonic velocity for any one gas is a function of the absolute temperature alone. For an air jet at 65 F. the sonic velocity is 1125 feet per second. The static temperature of the products of combustion for an air-fuel internal burner is about 2800" F. This gives a sonic velocity of about 2500 feet per second. It is this increase in 'jet velocity Which makes the internal burner so eifective in increasing the eiciency of the Sandblasting operation.

Although a delivery pressure double that of the atmosphere leads `to sonic velocity of the jet, an additional pressure lhead must be provided to accelerate the particles to high velocity. It is for this reason that the compressor is `required to deliver air at a pressure of at least 90 p.s.i.g. for maximum blasting effect.

FIG. 7 correlates results obtained from tests conducted on the use ofinternal burners for Sandblasting operations. The ordinate represents the increased cleaning effectiveness of the higher particle velocities with respect to that for conventional compressed air blasting. 'Ihe internal burner of this invention is thus compared with conventional blasting systems for a range of comparable air flows. The abscissa represents the particle velocity. The relative effectiveness represents the area cleaned using my burner system, divided by the area cleaned using 'compressed air with no heat addition. No attempt has been made to include -the qualit-y of the resulting cleaning, al-

though in all cases vthe nish produced with the internal burner was superior to that by conventional means.

Particle velocity has been calculated assuming that ithe final velocities of the gaseous jet and entrained particles are the same. The combustor jet velocity with no particle entrainment -attains a momentum value which is conserved. This momentum is distributed between the Vgaseous medium and the abrasive in relation to their relative mass flows to produce the particle velocity plotted.

The top curve of FIG. 7 (for nearly constant sand flow) shows the effect of particle velocity on cleaning effectiveness. A fourfold increase in the area cleaned per unit mass `of abrasive results. Increase in particle velocity has a nearly Llinear effect on the cleaning eiectiveness.

The lower curve of FIG. 7 represents the increase of effectiveness -per unit of air consumption. The energy level of a flow of compressed air is increased approximately eightfold 4when the available oxygen contained in that air is burned. This added energy arises from the heat of combustion which is released to increase both the temperature level and the specific volume of the gas. The energy equation contains the velocity to the second power. The eight-fold energy increase would thus be expected to increase the throat velocity of a cold air stream by about 21/2 times.

The results obtained by' test agree with the above theoretical discussion. Per unit of air ow, the cleaning eiectiveness would be expected to be somewhat less than 21/2 times.

It has been found that the cleaning of deposits too diiiicult for lpresent steam cleaning methods may be accomplished with the internal burner if a small quantity of abrasive Ipowder is suspended in the water. The use of such an abrasive suspension is not practical in the conventional type of steam generator due to the formation of deposits on the inside of the heat exchanger tube walls. Only small Vquantities 'of such powders as aluminum oxide, pumice, or even common cement are required. In some cases, it may be desirable to mix the' abrasive with a detergent to utilize the beneficial features of each.

I'he use of small amounts of abrasive powder in steam cleaning applications is differentiated from slurry cleaning in this invention. Slurry cleaning makes use of much larger quantities of abrasive suspended in the water. The cleaning action is dependent on abrasive action rather than steam, although in some cases the steam may play a part. In the former case the abrasive is added to increase the effectiveness of steam cleaning. In the latter case, the major role is played by the abrasive.

When the use of such suspensions is required, it is recommended that the water and abrasive be thoroughly mixed within a pressurized tank. The mixture is then fed to the burner under a pressure greater than that in the combustion chamber. It is desirable to feed this suspension longitudinally through the combustor from an injector such as 103 of FIG. 6, although injection beyond the combustor, but ahead of the nozzlev exit, is also possible.

Feeding of such a mixture'of liquid containing a suspended abrasive may be accomplished by the aspirating action of the high velocity exiting jet. Such an aspiration system is shown in FIG. A. The jet from the nozzle 26 issues into the region 99 causing a partial vacuum to form. Water, or a mixture of water and abrasive is drawn through a hose connected to the fitting 97 into the region 99 via the small distribution ports 98. To obtain higher particle velocities, the length of the cylindrical passage in piece 94 may be extended. The maximum velocity obtainable is considerably less than that obtained by pressure feeding ahead of the nozzle orice 26. Formost steam cleaning applications it is quite suitable to use the aspiration technique for drawing the liquid into the stream of hot gases. The water and detergent may be mixed and placed in au open container obviating the use of more complex pressure-feed systems.

The effectiveness of slurry cleaning is shown by the curves of FIG. 8, which compare the results of slurry cleaning using the burner of this invention with conventional slurry cleaning where no heat addition is used. Per unit of air flow, the cleaning effectiveness of the burner system, removing thick layers of enamel paint baked on metal, is approximately 11 to l when compared to the same air flow with no heat addition. The figures are heavily in favor of the burner system and it is thought that in this case the heat contained in the hot water plays an important part.

Sand blasting leads to the formation of large quantities of dust. Such dust can be a hazard to both personnel and equipment. It is desirable in many cases to introduce water into the exiting jet for the purpose of suppressing the formation of this dust. When using an air-cooled nozzle, the aspiration system shown in FIG. 5A and described for steam cleaning, may be used very effectively.

In many cases where water is to be used for such dust suppression, it is desirable to make additional use of the water for nozzle cooling. This allows the use of tungsten carbide nozzles which have an extremely long, useful life. FIG. 5B shows such a system. A burner adapted to water cooling of the nozzle requires different outer and middle tubes than in the case of the air-cooled burner. The outer tube is fitted with an internal ring 131a to contain the 0ring 136 which serves the function to separate the water from the cooling air. It is desirable to use air cooling for the combustion chamber as an elevated combustor wall temperature leads to better combustion eciencies. The air passes through the annular passage 132 contained between the tubes 131 and 130 to a joint just ahead of the O-ring location. The air then passes through the combustor ns as before. Water is either drawn by aspiration action or supplied under pressure through the fixture 138 into the annular volume 139 contained between the nozzle and the forward, diminished end of tube 131. The nozzle is kept quite cool by the water passing over its outer surface. The water, for the case shown, is forced under pressure through the circumferentially spaced, forwardly and inwardly extending ports 142 contained in the retainer ring 141 into the exiting jet. A retainer piece similar to induction piece of FIG. 5A is suitable for aspiration use coupled with nozzle cooling.

An additional advantage of the aspiration of water into the region containing the boundary of the exiting high velocity jet is its effect on reducing the noise level of that jet. For example, actual sound level measurements show a reduction of the sound intensity of 116 db without water injection to 96 db with water injection. Pressure feeding of the water ahead of the nozzle section does not reduce the noise level.

It is seen that the aspiration of water may serve several functions. First, it is useful for steam cleaning. Secondly, it provides a simple technique for dust suppression. Thirdly, the noise level of the jet is reduced to a much lower level.

In Sandblasting, the use of water not only supresses dust, but also takes an effective part in the cleaning action. The heat contained in the water has a softening effect on many deposits. For example, some paints are more easily removed when warmed. In some cases, it is desirable to add a stripper to help in the paint removal. When live organisms are being removed by blasting, the elfect of the hot water and steam are very desirable. An example of this is represented by the cleaning of barnacles from ship hulls. In many cases, they may be removed whole due to their less tenacious grip on the hull when subjected to high heat. Such deposits as Thiokol and other organic substances are more easily removed when rst subjected to the heat contained in the hot water and steam.

It is possible with the Sandblasting system shown to make use of the different features of the internal burner as best adapted to the job. For example, where thick encrustations of `barnacles and other marine life are encountered, it may be desirable to stop the abrasive ow to use steam action alone to loosen the deposit. Such a step would then be followed by Sandblasting. A time interval between the heating and blasting is desirable to insure maximum heat effect on the organisms. In other cases the steam and grit are combined.

Another desirable feature of the heat contained in the blaster jet is in the cutting of concrete containing an aggregate of high silica content. Concrete is quickly severed by the high velocity particles. The heat action tends to split the larger aggregate particles helping the cutting action.

FIG. 4 is a rear view of the injector piece 10. The small valve 93 meters the fuel. The larger valve meters the air for combustion. The valve knob 81 is directly connected to the valve stem 74. Referring to FIG. 3A, it is seen that the piece 79 guides the valve stem by means of the threads 82. The nut 76 holds the valve disc 75 tothe stem 74. The O-ring 78 and the gasket 80 prevent the escape of the pressurized air to the atmosphere.

Gaseous fuels are more easily ignited than liquid fuels. The fuel injection system for such gases as propane and natural gas is shown in FIG. 6. The fuel is metered by a valve attached by means of the threads 101 to the injector piece 100. The fuel passes directly into one of the radial passages 20 to the wall 21.

To operate the internal burner using a liquid for the fuel, the unit being used for blasting purposes, the main air valve 116 (FIG. 9A) is turned on. Air passes into air hose from the main air line i125. With the valve 81 closed, a small amount of atomizing air flows through the passages 60 and 61. With the ignition spark turned on the fuel valve 113` is opened. The unit experiences ignition of the combustible mixture within the chamber 22. The air valve 81 is next turned to the desired value of air ow with the fuel flow adjusted to its corresponding best value. The spark system may then be turned 0E.

`V9 When the burner is adapted to sand blasting, it is necessary thaftacertainminimum owvof air be allowed to ow through the hose =114 and .then through the passage 53 (see FIGS. 1 and 4), into the chamber 22. Without this flow `of air, hot gases from the combustion region may enter lthe hose through the passage 53 resulting in overheating of the hose'material. The same air ow is used vtopropel the sand Aor other abrasive through the hose 114. 4As soon as ignition is effected, the valve 119 is turned on. An aoritce y124 (PIG. 9B) controls the air ow to the `desired value.

The 'amount of air required to yprevent heating of the hose 11'4 by the backflow of combustion gases and to propel the abrasive through the same hose, is small in relation to the amount of air which passes through the abrasive-feed hose of conventional blaster units. 'I'he particle velocity is thus reduced during passage through the feed hose 114. The `extreme wear of the feed hose yin conventional units is reduced considerably when the system of this `invention is used. The major ow of air for the `blasting process is represented by that air required for combustion which passes through the hose 115.

When the abrasive is pressure-fed to the burner unit, an :arrangement as shown in FIG. 9A .may be used. The tank 118 is first illed with the abrasive. With the abrasive feed valve 121 Vin the closed position, the tank 118 is pressurized with air by opening the air valve 126. To feed abrasive vto the tmit with valve 1119 open, all that is necessary is to open valve '121 to a position which will deliver the desired abrasive iiow.

A sketch `of the burner with the necessary hoses and lines attached is shown in FIG. 9A. The burner 110 under `full combustion intensity has 'a cool outer wall due to the flow of cooling air between the tubes 40 and 42 (see FIG. 1). To further reduce heat transfer from the combustion region to the outer tube, it has been found desirable to coat the combustor 24 `(see FIG. 1) with a flame-applied coating of aluminum oxide 30. This coating, which ranges from 0.010 inch to 0.020 inch, by virtue of its low heat conductivity reduces the temperature of the combustors outer circumference. The ns 28 (PIG. 2) offer maximum cooling of the combustor 24, reducing i-ts temperature even further. A coating 43 (FIGS. l and 2) similar to that on the inner wail ofthe combustor further reduces heat ow. The outer surface of rthe tube '40 thus is maintained at a temperature which is not uncomfortable to the bare hand.

Spark ignition energy is supplied 'through the 'shielded lead cable -111 from a transformer located at a remote position. Successful `ignition may be obtained with the transformer location being as far as '100 feet from the burner.

Fuel is supplied under pressure to the burner 110 through the hose 112. When propane is used, it is convenient to use the tank pressure of the fuel to act as the pressure source. YWhenoil is used, a gear pump has been found to be quite satisfactory. During cold weather conditions the air-atomization system for the fuel `oil is to be recommended. During warm weather, oil may be used satisfactorily Vwith the injection system shown in FIG. 6. |In this lease the same injector piece 100 lis suited for both liquid -and gaseous fuels.

This invention supplies a simple and very inexpensive means gfor Aincr-easing the energy of `a stream of 'compressed air. As shown, .by the tests reported here, without any increase in air flow it is possible to obtain up to twelve times the cleaning effectiveness using a slurry, up to 3 times the effectiveness for abrasive blasting, and it provides. a steam cleaning system which is much simpler than conventional units which require a large and expensive steam generator.

From the foregoing description, it will be apparent that I have conceived and provided a widely variable, new method of very substantially increasing the discharge velocity of astream which mayconsist fin `a `number .of readily iiowable materials for use in impacting operations 'against .a surface to be treated. The impacting loperations may consist in sand or grit blasting withor with- -out addition .of steam `or other detergent owable material; or it may constitute steam cleaning operations with or without other detergents; or it may constitute impregnation, spreading and coating of pigment, bonding and .other materials into and upon a surface to be treated.

My novel method, while `embracing a number of selectively applicable and sequel steps, in its basic principle consists `in producing a confined stream )for subsequent impact discharge through the utilization kand ymovement of combustible fluid media and introducing into such a lconfined stream, readily suspendable material and the step of igniting and reacting combustible fluid ymedia to add thermal energy to the stream with the suspended material therein, whereby the discharge and impact velocity is very `substantially increased.

In distinguishing from the prior'art, my invention appears to be of Vsuch broad scope as to include the addition of thermal energy to a confined, moving stream whether combustion of uid media is effected actually within the main moving stream or transmitted into said streamand also, whether the combustion -is effected prior to the introduction of the suspendable material or after such introduction.

Within the scope of my method as described herein, the introduced, suspendable material may constitute solid particulate material, steam, chemicals, gaseous or :liquid detergents, pigments, bonding `and other surface-coating materials.

My method within its important ramifications, includes the introduction of the readily suspendable materials under the aspirating action of the main gaseous stream which is discharged from a duct of relatively small cross section into a larger duct.

In most instances (not necessarily), the combustion of an oxidant gas and fuel is effected prior to the introduction of the additional, readily ilowable materials.

In use of my novel method for steam cleaning operations against a Lsurface to be treated, Water is introduced Vinto the main gaseous stream composed of an oxidant gas `and fluid fuel. The thermal'energy obtained from the combustion of said-oxidant gas and fuel prior tothe discharge converts the water to steam (usually superheated steam). The water is preferably either injected into the chamber substantially axially of the ow of the combusting Huid media towards a restricted discharge and at high velocity Vor the water `may be aspirated by the action of the gaseous stream after combustion, `entering the ow near the ultimate area of ydischarge and 'in fact, after the main discharge of the products of combustion.

It will of course `be understood that various apparatus and media for carrying o-ut my novel multi-purpose methods may be employed, all within the scope of the broad, patentable aspects of the method invention.

It will further be understood that internal burner apparatus of the several basic structures disclosed herein, are particularly applicable for carrying out ymy methods and such structures and apparatus are quite closely linked with lthe essential method steps.

What is claimed is:

l. 'Ihe method of impacting at high velocity, a stream against a surface to be treated, which consists in producing Va confined and `selectively continuous `stream through movement of combustible fluid media, introducing into said coniined stream, readily owable, suspendable material of a class comprising hard particulate material, liquids, and suspension of solid particles in liquid media, combusting and reacting said iiuid media in said movement to add thermal energy to said stream and said material suspended therein in travel, then continuously and directly discharging the ultimate stream produced lagainst the surface to be treated, whereby the discharge l l Y 'velocity 'thereof is very substantially increased as contrasted with said original'continuous stream.

2. The method of producing and discharging a blasting stream against a surface, which consists in continuously moving a. combustible fluid through a confined burner space, combusting said uid in its movement within said space to materially increase the thermal energy and velocity of the resultant stream, introducing and suspending in such stream, readily flowable material, and without interruption of the travel of said stream, discharging the same against a surface to be treated.

3. The method of continuously producing and continuously discharging a blasting stream against a surface, which consists in continuously moving a combustible fluid through a confined burner space, combusting said iluid in its movement through said space to materially i11- crease thermal energy and velocity of the resultant stream, continuously introducing and suspending -in such stream, material of a class comprising hard particulate material, liquids and suspensions of solid particles in liquid medium, and without interruption of the travel of said stream, discharging the same against a surface.

4. The method set forth in claim 3 wherein aqueous moisture yis introduced into said resultant stream.

5. The method set forth in claim 3 wherein water and hard particulate material is introduced into said resultant stream and suspended thereby.

6. The method of impacting a blasting stream against a surface which consists in continuously moving a fuel and also an oxidant into and through a confined burner duct, cooling the exterior of said duct by impingement of said oxidant thereagainst prior to introduction into said duct, combusting said fuel with the aid of said oxidant within said duct during movement of said oxidant and `fuel to substantially increase thermal energy and velocity of the 'resultant stream, introducing and suspending in said resultant stream, readily flowable blasting material and without interruption of the travel of said stream, discharging the same against a surface to be treated.

7. 'Ihe method of vimpacting at high velocity, a stream containing suspended material against a surface to be treated, which consists in producing a combustible stream at elevated pressure by continuously introducing and moving an oxidant gas and a fuel into a duct system having a discharge nozzle, combusting said oxidant gas and fuel prior to discharge and suspending readily flowable material in the resulting products of combustion and directly discharging the ultim-ate stream against the surface to be treated.

8. 'Dhe steps set forth in claim 7 in which the oxidant gas is air and 4in which the combustion reaction takes place within said duct system at a pressure greater than l5 pounds per square inch gauge.

9. In apparatus -for producing and impacting at high velocity, a stream against a surface to be treated, a medium deiining a combustion chamber, a diminished discharge nozzle constantly communicating with the forward portion of said combustion chamber, means for continuously introducing a combustible fluid medium at elevated pressure into the rear portion of said combustion chamber, means for igniting said medium within said chamber and means for continuously introducing readily lowable and suspendablematerial into the resultant products of combustion produced in said combustion chamber whereby a continuous, direct discharge of a resultant stream with 'chamber directionally disposed in a manner favorable to the flame stabilization of the combustion processes therein.

11. The structure set forth in claim 9 whereby combustion within said chamber substantially adds thermal energy to the combustible iuid media and products of combustion moving through said chamber and wherein said means for introducing readily ilowable material includes a jet orifice directed generally axially and forwardly of said chamber and protruding slightly in advance of the entrance area of said combustible uid media, whereby flame stabilization of combustion is not impaired.

12. In apparatus for producing and impacting at high velocity, a mixed stream against a surface to be treated, a longitudinal combustion chamber, a tapered reducer element communicating with the forward end of said chamber, a discharge nozzle communicating with the forward end of said reducer element, means for introducing at elevated pressure, a combustibleuid media into the rear portion of said combustion chamber, means for facilitating ignition of -said medium within said chamber, said combustion adding substantial thermal energy to the materials within said chamber and substantially increasing discharge velocity from said nozzle and means for introducing readily flowable material into the stream discharged from said nozzle through aspiration action produced by said discharging stream.

13. In apparatus for producing and impacting at high velocity, a mixed stream against a surface to be treated, a longitudinal combustion chamber including a diminished discharge nozzle communicating generally axially with the forward portion of said chamber, means for introducing at elevated pressure a combustible fluid mixture into the rear por-tion of said chamber and entering from a generally annular rear area disposed generally concentric with the axis of said chamber, means for providing ignition of said mixture within said chamber and means for introducing readily owable material into the products of combustion emanating from said chamber, the area of communication of said last mentioned means being Vdisposed forwardly of said iirst mentioned area.

14. The structure set forth in claim 13 wherein said means for introducing readily flowable material includes a discharge element extending forwardly and generally axially within said chamber.

15. The structure set forth in claim 13 further charac terized by an annular cooling duct surrounding at least a portion of, said overall combustion chamber, means for communicating a cooling tiuid medium to said duct adjacent one end thereof and means for communicating said duct with the interior of said overall combustion charnber,k and the cooling fluid medium employed constituting one of the owable materials previously referred to in claim 13.

References Cited in the tile of this patent Y UNITED STATES PATENTS 1,227,007 Shea May 22, 1917 1,890,164 Rosenberger Dec. 6, 1932 2,114,573 Rhodes Apr. 19, 1938 2,399,680 Keefer May 7, 1946 2,714,563 Poorman Aug. 2, 1955 jimi- 1""

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