US3528704A - Process for drilling by a cavitating fluid jet - Google Patents

Description

Sept. 15, 1970 ENTOR VIRGIL E. JO NSON, JR.

ATTORNEY p 1970 v. E. JOHNSON, JR 3,528,704

PROCESS FOR DRILLING BY A CAVITATING FLUID JET Filed July l7, 1968 3 Sheets-$11991 fl VIRGIL E. JOHNSON, JR.

/4 YWQM ATTORNEY Sept 1970 v. E. JOHNSON, JR 3,528,704

PROCESS FOR DRILLING BY A CAVITATING FLUID JET Filed July 17, 1968 3 Sheets-Sheet INVENTOR VIRGIL E. JOHNSON, JR.

BY heoye $515M ATTORNEY United States Patent 3,528,704 PROCESS FOR DRILLING BY A CAVITATING FLUID JET Virgil E. Johnson, Jr., Gaithersburg, Md., assignor to Hydronautics, Inc., Laurel, Md., a corporation of Maryland Filed July 17, 1968, Ser. No. 745,611 Int. Cl. E21b 7/18 U.S. Cl. 29914 9 Claims ABSTRACT OF THE DISCLOSURE A method for advantageously utilizing the normally destructive forces of cavitation to provide an erosion effect for accomplishing drilling, boring, and like functions of solids which comprises forming a fluid jet by directing the fluid through a restricted orifice at speeds sufiicient to generate vapor-filled bubbles in the jet and impinging the jet against the solid at a distance from the orifice where the vapor bubbles collapse.

Cavitation, as used herein, is defined as the formation growth and collapse of vapor-filled cavities in a flowing liquid which occur at a level where local pressure is reduced below the vapor pressure of the liquid. These vapor cavities, commonly called bubbles, collapse With a violence which damages and erodes material at the area of collapse. For many years, cavitation has been a prime consideration in the choice and design of propellers, hydraulic equipment and other mechanical arts wherein there is a relatively high-speed movement between an article and a surrounding fluid. The primary work of the prior art has been to eliminate the damage caused by cavitation whereas in the instant invention the primary objective is to utilize this turbulent force.

Experimental and theoretical considerations of this problem indicate that pressures as high as 200,000 to 300,000 p.s.i. may be generated during the collapse of the cavities. Some investigations claim pressures as high as 10 p.s.i., but this is questionable. The actual magnitude of the stress is not important, however, as long as it is high enough to cause extensive damage to materials.

Cavitation damages should not be confused with liquid impact erosion The liquid impact phenomenon is related to the cavitation damage problem but it may be regarded inverse-cavitation. Liquid impact damage presents itself when liquid drops exist in a gaseous, or vaporous medium. For instance, the occurrence of this type of damage is found in steam turbine blades which strike tiny droplets condensing from steam and in the leading edge of high speed aircraft wings which strike water droplets in the atmosphere. Against hard surfaces liquid impact erosion has been found to be unsuitable from a time and a power viewpoint.

In the instant invention, a stream of water having vapor cavities therein is projected against a solid surface in such a way that its cavitation bubbles collapse at the area in which the stream has impact with the solid material. Since cavitation bubbles are efliciently produced in water and because efiicient cavitation can be obtained within a wide range of parameters relating pressure, volume, and the like, the apparatus and method disclosed below are conveniently utilized in such environments as underground tunneling. Drilling by cavitation has the advantage of reducing very hard elements such as certain types of rock, to very small particles which are easily removed from the area of drilling by exhaustion with the 'ice propelling water by means well known to those skilled in the art.

A further objective of this invention is to provide a mechanism for efliciently producing vapor cavities and impelling their stream to, or very near, a solid substance at the time of collapse whereby the shock of a cavity collapse will erode the substance.

Another objective of this invention is to provide a system wherein maximum intensity of erosion is obtained by impacting a solid area with a stream of Water at a selected distance of maximum cavity collapse.

A still further objective of this invention is to provide a method and apparatus for obtaining, with a minimum of power, the production of high vapor cavities and impacting these vapors at an area of stagnation wherein the greatest amount of collapsing impact, and thus the greatest amount of erosion, is obtained within selected efficient parameters.

A further objective of this invention is to provide a means for eroding a surface by propelling a stream of water thereon wherein the horsepower expended in propelling the Water is at a minimum because the effects of erosion are primarily obtained by collapsing vapor cavities rather than the inertia or impact effect caused by the velocity of the water itself.

A still further objective of the invention is the generation of vapor cavities within a stream of water by use of a nozzle and so arranging the nozzle components that cavitation bubbles are isolated from the nozzle itself and will be directed and collapsed on the surface of the material to be drilled without concurrent cavitation damage of the nozzle.

A more specific objective of the methods and constructions set forth hereinafter is to provide a convenient method for tunneling underground passages which is less expensive, safer and faster than those methods here tofore known.

These and other objects of the invention will become more apparent to those skilled in the art by reference to the following detailed description when viewed in light of the accompanying drawings wherein:

FIG. 1 is a cross section view showing the principal characteristics of one form of nozzle;

FIGS. 2-6 are diagrammatic views showing other forms of the invention; and

FIGS. 7 and 8 are diagrammatic views showing a working environment of the nozzles of FIGS. 1-6 inclusive.

Referring now to the drawings wherein like numerals indicate like elements, the numeral 10 indicates a nozzle housing. The housing defines a chamber 12 which receives fluid under pressure by way of a conventional fitting 14 near one end of the housing. The interior surface 16 of the housing tapers to an outlet opening 18 at the other end of the housing. As shown in FIG. 1, a stem member 20' is received Within the chamber 12 and is terminated by a lower surface 22 normally located beyond the periphery of opening 18. As shown diagrammatically in FIG. 1, the stem is threadably received through the upper end of housing 10 and is longitudinally adjustable with respect to the housing upon rotation of the stem. The purpose of longitudinally adjusting the stem 20 is to change the position of surface 22 with respect to the opening 18.

In operation, water under pressure is fed to chamber 12 through the fitting 14. As seen by the pattern of flow in FIG. 1, the water is exhausted through the opening 18. Because of the venturi effect of surface 16, the velocity of the water increases as it leaves the housing.

3 As the velocity of the stream increases, pressure within the stream decreases. Because of the reduced pressure, vapor cavities are formed within the water stream. In general terms the velocity of the water is above 350 f.p.s. and the distance d is six inches and the jet nozzle opening is one-quarter inch in diameter.

These vapor cavities will collapse at a distance from opening 18 when the stream velocity is reduced to a point where stream pressure will no longer permit the presence of cavities. This point of collapse can be termed the stagnation point or is sometimes referred to as the point of zero velocity.

The distance from opening 18 at which there is maximum cavity collapse can be determined both mathematically and empirically. As shown in FIG. 1, this distance is labeled as d. The nozzle is located such that the surface 30 is the distance from d to the nozzle. In other words, the surface 30 is located at the area of maximum cavity collapse. As can also be seen from FIG. 1, the location of stem 20 within the opening 18 causes a further increase in the velocity of the stream by reducing its area of exhaust. Additionally, as the water stream passes the surface 22, an evacuated core area 32 is formed which further reduces the pressure within the stream. This, of course, increases the formation of additional bubbles of cavitation. Thus, it can be seen that a nozzle housing has been described which maximizes the formation of cavitation bubbles under certain pressures and velocity and which bubbles are utilized to erode the surface 30.

This invention encompasses various other nozzle geometry for accomplishing a drilling function through erosion. In FIG. 2, for example the lower end of the stem is formed with a tear-shaped ending which can very accurately adjust the annular discharge area of opening 18.

As shown in FIG. 3, a stem member is not utilized but the opening 18b has a cylindrical dimension whereby fluid can be more accurately directed. FIG. 4 utilizes a cylindrical outlet such as 18b in combination with a cavitating disc 36 aflixed to the lower end of a stem member. The cavitating disc maximizes the interior evacuated core 32 as the fluid passes. By locating a grid or screen 34 near the opening 18, as seen in FIG. 5, a plurality of uniformly spaced areas are formed. A still further embodiment of the invention is shown in FIG. 6 wherein flow rotating stator vanes 38 are disposed within the chamber 12 for imparting a vortex movement to the stream as it leaves the nozzle.

It can be seen that each of the nozzles of FIGS. 1 through 6 are adapted to exhaust and direct a stream of water in which cavitation bubbles have been formed. The particular construction of the nozzle to be used will depend primarily on the hardness and consistency of the surface 30 to be drilled and the pressure and velocity at which one chooses to work.

FIGS. 7 and 8 diagrammatically show a use for nozzles of the type described. A drilling apparatus is generally indicated by the numeral 50. The apparatus includes a water manifold 52 which receives water under pressure through a fitting such as that indicated by the numeral 54. Rotatably received within the manifold is a shaft 56 which is rotated by a motor 58. Aflixed to the shaft 56 and extending outwardly from the manifold 52 are a plurality of tubular members 60 having nozzle housing 10 aflixed at their outer ends. The interiors of the tubular members are communicated with the manifold 52 and deliver the water under pressure to the nozzles.

As the arms 60 are rotated, it can be seen that the nozzle will follow the circular dotted-line path indicated by the numeral 62. With the nozzle disposed at a correct distance D from the surface to be drilled, an annular groove will be formed in the surface along path 62. When this groove reaches a selected depth, the core thereof is removed by conventional drilling and mining methods. It is, of course, contemplated that arms 60 can be of various lengths such that a plurality of concentric grooves can be formed during a single mining operation. It is also to be appreciated that the disclose of FIGS. 7 and 8 are merely illustrative. It should, of course, be understood that sealing members are necessary to inhibit leakage from manifold 52.

It has also been found that by heating the work surface, the water or both there is some increase in drilling result. The heating can be accomplished in any suitable manner.

However, where space is a premium the additional equipment required for heating may not justify its use.

Additionally pulsing the stream also adds to the effectiveness of the method and this can be done by valving the inlets from the water chamber (FIG. 8) to the nozzle carrying spider arms.

Summarizing, it is seen that the several embodiments of the nozzle are venturies having an annular outlet so constructed and designed that as the water is discharged therefrom the velocity increases and the pressure decreases to produce vapor cavities. In the embodiments shown in FIGS. 1, 2 and 4 dividing means are associated with the nozzle outlet whereby, a cylindrical tubular stream is discharged thereby further increasing velocity and establishing a vacuum area axial of the dividing means but terminating short of the work face. In FIGS. 5 and 6 the stream dividing means are respectively the screen and rotor. In FIG. 3 a divider is not utilized, but increase in velocity and decrease in pressure results in the formation of the vapor cavities.

In a general manner, while there has been disclosed an effective and efficient embodiment of the invention, it should be well understood that the invention is not limited to such embodiments, as there might be changes made in the arrangement, disposition, and form of the parts with out departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

I claim:

1. A method of drilling through a relatively hard solid substance with a pressurized fluid comprising the steps of forming a fluid jet by directing said fluid through a restricted orifice to restrict the flow of the fluid jet and increase its velocity and decrease its pressure below the vapor pressure of the fluid to form vapor cavities of the fluid therein and impinging said jet against the solid at a distance from the orifice where said vapor cavities collapse.

2. The method of drilling defined in claim 1 including the step of isolating said cavities from said nozzle after the formation thereof.

3. The method of drilling defined in claim 1 to include the step of heating said solid prior to the impingement thereof.

4. The method of drilling defined in claim 1 to include the step of pulsing said jet during the formation of said cavities.

5. The method of claim 1 to include the step of inducing a vortex movement to said jet in said nozzle.

6. The method of claim 1, wherein the flow of the fluid jet is restricted by passing the jet through an annular orifice to form an evacuated core area beyond the orifice which further reduces the pressure of the fluid and increases the formation of the vapor cavities within the fluid.

7. The invention of claim 1 to include the step of traversing said jet in a fixed geometric pattern with respect to said surface.

8. The invention of claim 7 wherein a plurality of jets are traversed in said same geometric pattern.

9. A method of drilling a relatively solid substance which comprises:

forming a high pressure and velocity water jet,

restricting the flow of the water jet to increase its velocity and decrease its pressure below the vapor pressure of the water to form water vapor cavities therein whereby the jet will collapse at a predetermined 3,373,752 3/1968 Inove 134-1 distance from the point of restriction; and 3,387,672 6/ 1968 Cook 17569 impinging the jet against the solid substance at the point 3,402,075 9/1968 G ld s t a1, 134 1 of collapse.

eferences C te 5 ERNEST R. PURSER, Primary Examiner UNITED STATES PATENTS Us 1 R 2,018,926 10/1935 Schroepfer 299-17 3,174,561 3/1965 Sterrett 175-65 299-17; 175-67, 422; 239-499; 1341

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