US3066686A - Sonic treating apparatus - Google Patents

Description

Dec. 4, 1962 J. P, @NEM 3,066,686 E soNc TREATING APPARATUS Filed May l0. 1960 t Po- 121-;

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.' SONIC ENERGY GENERATOR Unite i States 3,066,686 SONXC TREATING AlPPARATU .lames P. ONeill, Playa Del Rey, Calif., assigner to The Bendix Corporation, North Hollywood, Calif., a corporation of Delaware Filed May 10, 1969, Ser. No., 28,031 Claims. (Sl. 134-122) This invention relates to apparatus for treating material with sonic energy and, more particularly, to apparatus for sonic cleaning of continuous strips of materials, such as sheets of glass or metal.

The utility of sonic energy for cleaning contaminants from the surface of a variety of articles is well recognized. Cleaning is accomplished by immersing the article in a liquid medium, such as Water, and by introducing sonic energy into the medium in such intensity that caviation occurs in the region of the article. The cavitation effect is associated with the formation of gaseous bubbles Within the cleaning medium upon intense pressure changes in a localized area. Cavitation tends to literally burst contaminants from the surface of the article to be cleaned.

In one cleaning system particularly adapted to the cleaning of residual adhesive from one face of a sheet of glass, it is customary to pass the glass in nearly direct contact with an array of magnetostrictive transducers arranged in a plane with a small amount of liquid confined between the glass and the transducers. Cavitation is produced in the region between the transducer faces and the glass as it moves past, and the contaminant adhesive is removed. Cleaning systems of this type are commonly referred to as contact systems since the transducer faces are practically in contact with the Work piece.

One difliculty which has been encountered in contactcleaning apparatus is that the cavitation produced in the region of the transducers causes erosion of the transducers and requires frequent replacement of the transducer faces.

ln another type of cleaning apparatus, a plurality of transducers are arranged in the walls of a cylindrical tank so that energy produced is focused at a central region. This type of apparatus is particularly useful in the cleaning of small objects which are suspended within the tank in the region of the focus. The transducers are operated at a power level low enough that cavitation does not occur at their faces, but only in the region of the focusing of energy from several transducers. However, such focused sonic energy cleaning systems have not been adaptable to the cleaning of wide strips of material or to continuous cleaning operations because the active cleaning region is comparatively localized along the central axis of the tank.

With this state of the prior art in mind, it is a general object of the invention to facilitate the sonic treatment of continuous strip materials.

A more specific object of the invention is to achieve high eiiciency cleaning of strip materials characteristics of the contact type cleaning apparatus along with the long transducer life characteristic of focused type cleaning apparatus.

Another object of the invention is to improve the efciency of sonic cleaning by employing reinforcement of sonic energy by reflection from selected portions of the cleaning apparatus.

These objects are all achieved in accordance with this invention, one embodiment of which comprises a cleaning tank filled With liquid and including means for driving continuous strips of material through the upper portion of the tank. Within the tank is an enclosure in the form of a sector of a cylinder extending across the tank including converging rigid Walls with horizontal slots of length sufficient to allow the passage of the strip material through the enclosure, a closure at the convergent end, and a cylindrically curved wall at the lower or divergent end of the enclosure. A plurality of transducers are mounted in the lower curved wall with their radiating surfaces arranged or directed toward a common focus at the axis of the cylindrically curved Wall. The slot openings in the side Walls are positioned a short distance below the liquid level Within the tank and are at a distance from the transducer faces which is determined in accordance with a standing Wave pattern established Within the internal enclosure When the transducers are operating. The nature and position of the convergent end closure are designed to utilize the effects of the standing Wave pattern within the cleaning enclosure.

In one embodiment of the invention, the upper closure of the cleaning chamber is a thin metallic diaphragm positioned at a pressure node or point of maximum velocity gradient on the opposite side of strip material passing through the slots from the transducers. The strip material passing through the slots is positioned at a point of maximum pressure gradient or, in other words, a velocity node in the standing wave pattern. The thin metallic diaphragm, exposed on one side to the liquid medium within the internal enclosure and on the other side to the surrounding air, provides a pressure-release reecting surface for sonic energy from the transducers which has passed through the work piece.

ln another embodiment of the invention, the cleaning chamber is of the same size and shape as in the irst embodiment; however, the convergent end has no closure and is exposed directly to the air. in this embodiment there also is an impedance mismatch at the surface causing the rellection of sonic energy back toward the Work piece.

In still another embodiment, the closure of the cleaning chamber at the convergent end is a solid member which acts as a rigid reflector, and that member is positioned directly above the work piece at a pressure antinode.

In each of these embodiments, the treating or cleaning action on the Work piece is enhanced iirst by the focusing effect of the arrangement of the transducers; second, by the restriction of the sonic energy within the chamber by the rigid convergent side walls; and, third, by the reflection of the energy to produce standing waves.

An advantage of the invention is that these enhanced cleaning characteristics are obtained in apparatus adapted to the treatment of continuous strip material which heretofore has been successfully cleaned by sonic energy only in contact type apparatus. Another advantage of the invention is that the transducers may be operated at an amplitude insuiiicient to produce cavitation at the faces of the transducers, thereby minimizing the wear on the transducer while, through the focusing elfect, producing cavitation in the region of the work piece.

These advantages are all achieved in accordance with the invention, one feature of which is the arrangement of converging boundary walls of the cleaning enclosure forming a segment of a cylinder with transducers mounted to radiate energy toward the axis of the cylinder and with openings to pass continuous strip or sheet material through the enclosure.

Another' feature of this invention involves the positioning of the strip or sheet material guiding means so that it passes through a pressure anti-node region resulting from a standing wave pattern established within the cleaning enclosure.

Another feature of this invention resides in the use of a sonic energy reliector positioned beyond the work piece 4at a predetermined distance in order to produce standing waves and achieve reinforcement of the sonic energy in the region of the material to be cleaned.

A full understanding of the invention may be had from n the following detailed description with reference to the drawing in which:

FIG. 1 is a longitudinal, vertical sectional View of a cleaning apparatus employing this invention taken in the plane I-I of FIG. 2;

FIG. 2 is a transverse section through the apparatus of FIG. l taken along the line 2-2 of FIG. l;

FIG. 3 is a fragmentary sectional view similar to FIG. l, showing another embodiment of the invention; and

FIG. 4 is a fragmentary sectional view similar to FIG. l, showing still another embodiment of the invention.

Referring now to FIGS. 1 and 2, apparatus for the cleaning of strips of semirigid material includes a tank having sidewalls and bottom of relatively thin metal and including a curved lip 11 at one side over which a strip 13 to be cleaned enters the tank and a curved lip 12 at the opposite side of the tank 10' where the strip 13 emerges. In the drawing, the curvature of lips 11 and 12 is greatly exaggerated. The strip may be, for example, sheet metal or other material capable of slight deflection in order to enter the tank 10. The strip is driven through the tank 10 by a pair of rollers 14 and 15.

Contained within the tank is a secondary or cleaning enclosure 16 made up of a pair of converging rigid side walls 17 and 20. For ease of manufacture, the rigid side walls 17 and 20 are made up of comparatively heavy steel plate, 1%" in thickness, backed by a crosswork of stiifening ribs 21 and 22. This arrangement is desirable since, in sonic cleaning employing the frequency range of 100 to 30,000 cycles per second with a preferred operating frequency of 10,000 cycles per second, in order for the side walls of the internal enclosure to react as rigid members at such an operating frequency, they should have an equivalent thickness of approximately two inches; that is, in excess of one-tenth of the wavelength of the radiated energy. This equivalent thickness is obtained by means of stiifeners 21 and 22.

At the upper convergent region of the side walls 17 and 13 are a pair of elongated slots 19 and 20 for introducing the strip material 13 into the inner enclosure 16. The side walls have extensions 23 and 24 for guiding the strip material 13 into the chamber 16, which chamber extends above the level of the slots 19 and 20 a distance of one-half wavelength of the sonic cleaning energy. The upper end of the inner chamber 16 in the embodiment of FIG. l is open to the air. A source of cleaning liquid which may simply be a water pump 2S, as shown in the drawing, delivers a flow of liquid into the chamber 16 through an inlet pipe 26 so as to maintain the chamber 16 full at all times. Excess liquid spills over the sides of the cleaning enclosure 16 into the tank 10 proper, maintaining a constant level within the inner enclosure 16.

The lower end of the inner chamber is closed by a curved wall member 2.7 in the form of a section of a cylinder mounting a plurality of transducers 28 with their working faces 29 within the inner enclosure 16 and their driving elements 30 outside of the tank 10. Although transducers of various types are satisfactory for use in this apparatus, the magnetostrictive transducer and mounting arrangement preferred as disclosed in Patent No. 2,- 864,592 to L. W. Camp, issued December 16, 1958. The transducers 28 are energized from an electrical generator 31 of suitable frequency.

Examining now in more detail the enclosure 16 in which the sonic treatment or cleaning takes place, it may be seen that the array of transducers 28 in the lower cylindrical wall 27 are directed so as to focus the sonic energy produced in approximately the region beyond the end of the side walls 17 and 18. As indicated in the drawing by the letter P0, a surface of highest pressure variation exists directly at the faces 29 of the transducers 28. The chamber 16 is approximately two and one-half wave lengths high from the face 29 of the transducers 28 to the upper free surface 32 of the cleaning liquid. The free surface 32 constitutes a boundary between the liquid medium within the enclosure 16 and the ambient air. The impedances of the two media differ by a factor of about 3,600 to 1, so the boundary constitutes a useful reflector for the sonic energy radiated toward the surface 32. With the side walls 17 and 18 rigid at the frequency of sonic energy within the enclosure 16, little or none of the energy is transmitted to the outer tank 10. The chamber 16 including the transducer faces 29 as sources of sonic energy at the lower end of the rigid side walls 17 and 18, along with the reflective surface 32, causes the establishment of a standing wave pattern as indicated in the drawing. Above the first region of maximum pressure variation P0 adjacent to the faces 29 of the transducers 23 is a region of maximum velocity V, at a half wavelength distance from the transducer faces, and two other levels of maximum pressure variation labeled P1 and P2 at one and two wavelengths, respectively, from the faces 2S. It should be noted that the material to be treated, strip 13, is positioned at two wavelengths distance from the faces 29 of the transducers 28. At this point the converging or focusing effect of the array in combination with the side walls exceeds the attenuation of the energy passing through the medium; therefore, high intensity sonic pressure changes sufiicient to produce cavitation exist over the area of the strip 13 within the enclosure 16. The material being relatively thin compared with the wavelength, c g., six inches, of the sonic energy in the medium allows the transmission of the energy through the strip 13 into the liquid contained above and within the enclosure 16. The free surface 32 at the upper end of the enclosure positioned at a pressure node (and a velocity anti-node) labeled V, reflects the transmitted energy back to produce the standing wave pattern as previously indicated.

Referring to FIG. 2, at the distance two wavelengths from the transducer faces 29 is the elongated slot 19 through which passes the strip of material 13 to be treated. The strip 13 passes into the slot 19 after riding over a roller 14 which is journaled in bearings 31 and 32 to be driven by power applied to a pulley 33.

In the plane of FIG. 2, the transducers 28 are arranged with their working faces 29 parallel to the strip 13 so that their energy is equally distributed over the entire width of the strip 13 passing through the tank. The inner chamber 16 of the tank 10 in which the treatment or cleaning takes place is actually shaped like a sector of a cylinder with the faces 29 of the transducers 20 forming a major part of the outer curved wall. The end walls 36 and 37 of the inner chamber 16 are subject to sonic energy and, therefore, are of re-enforced design similar to the side walls 17 and 18 of enclosure 16 in order to achieve an effective thickness in excess of two inches.

The embodiment of FIG. l and FIG. 2 is adapted for the sonic treatment of semirigid materials, such as sheet metal. One particular useful application is in the removal from plate glass of plaster of Paris adhering there to from the bed used to support the glass in the grinding step of manufacture.

The plaster of Paris is Va particularly tenacious material and must be removed from each side after grinding. The plate glass may be in the order of inches wide, one-half inch in thickness, and continuous lengths. Plate glass, being a relatively rigid material, is not capable of bending enough to enter the cleaning tank as shown in FIG. 1. Therefore, an arrangement is required in which the strip does not have to bend. Such an arrangement is shown in FIG. 3, in which the cleaning chamber 16 is positioned with the slots 19 at transport table height for the passage of the rigid strip 13 through the chamber 16. Because of the problem of constant loss of cleaning liquid and since the enclosure is not immersed in a surrounding tank, the cleaning enclosure is closed in its upper end in contrast with the embodiment of FIG. l and FIG. 2. This apparatus is identical with that of FIG. 1 and FIG. 2 in most other respects, and the same reference numerals are used when the elements are identical. It employs a pair of converging side walls 17 and 18 defining chamber 16. The divergent end of the chamber 16, as in FIG. .1 and not shown in FIG. 3, is closed by a sheet metal member and mounts an array of transducers. In the upper region of the chamber 16 at a distance two wavelengths from the faces of the transducers are a pair of extensions 23 `and Z4 defining slots 19 and 20 for allowing the passage of the strip material 13 lto be cleaned through the cleaning chamber 16. Above the slot 1S and 19 level, at one-half wavelength distance, is an upper closure in the form of a thin diaphragm 40 which may be planar or may be slightly concave to conform to the standing wave pattern within the chamber 16. A positive pressure of liquid within the chamber is maintained in the same manner as in FIG. 1 by a pump. This source for liquid will compensate of the loss of liquid owing to escape through the slots 18 and 19, in particular the outlet slot 19.

The upper closure or diaphragm '40 maintains a constant, smooth reflecting surface for sonic energy within the chamber 16. No turbulence at the surface, as may be encountered in the embodiment of FIG. l, is present since the liquid is restrained within the chamber 16 by the diaphragm 40. 'I'he acoustic impedance mismatch between the liquid medium in the chamber and the air without still exists so that the boundary provides etticient reflection of energy back into the chamber and toward the strip to be cleaned. The closure 40 forming the boundary for reflection is positioned at one-half wavelength beyond the strip 13, so that reflected energy reaching the strip 13, after striking the boundary, will again be at a pressure anti-node -to reinforce the direct energy vat the strip 13.

Another embodiment of this invention employing a rigid upper closure Sil may be seen in FIG. 4. In this embodiment, the closure 50 is positioned directly above the strip material 13 to be cleaned. In this case the closure 50 is a rigid reflector of the same general nature as the side walls. Reflection is thereby accomplished not by the liquid-air boundary, but by a liquidsolid boundary. In order to obtain reinforcement, the rigid closure is positioned directly, or as nearly as possible, -at a pressure anti-node; in other words, at an incremental wavelength distance from the transducers. In the embodiment of FIG. 4 the rigid reflector 50 is positioned directly in contact with the strip to be cleaned.

In all the embodiments of this invention, sonic treatment is accomplished in a chamber so arranged to provide focusing of sonic energy from remote transducers with openings arranged to pass the material lto be treated through the chamber. The openings are at a predetermined distance from the working faces of the transducers. As shown, this distance is two wavelengths at the operating frequency of the transducers. Of course, with proper proportioning of the walls of the chamber, this distance may be one, two, three, or any integral wavelength distance. In addition to the effect achieved by focusing, the chamber is designed to enhance the cleaning effect owing to energy reflected from the end of the converging chamber back to the work piece, or strip. The reflecting surface may be the boundary between the liquid contained within the chamber and air, and in these circumstances the boundary would be at a half-wavelength distance beyond the work piece. The reflecting surface, alternatively, may be the air-solid boundary at the outside of a thin metal skin 40 as shown in FIG. 3. That reflecting boundary should also be placed at a wavelength distance beyond the workpiece. A liquid-solid boundary 50 as shown in FIG. 4, however, should be positioned directly on the Work piece. Employing the concept of this invention, improved cleaning of strip material is readily achieved without the problem of undue wear because of cavitation at the faces of the transducers.

Although for the purpose of explaining the invention va particular embodiment thereof has been shown and described, obvious modications will occur vto a person skilled in the art, and I do not desire to be limited to the exact details shown and described.

Iclaim:

1. Sonic treating apparatus comprising:

a chamber including rigid converging side walls;

a curvilinear end wall at the divergent end of Ithe chamber;

a plurality of transducers mounted in the end wall with radiating elements directed to introduce sonic vibrations into the chamber toward a common focus beyond the convergent end of the chamber;

the convergent end of the chamber positioned at an odd multiple of half-wavelengths of the acoustic energy radiated by the transducers into the chamber;

and means for positioning articles to be treated within the chamber at substantially a point an incremental wavelength distance from the radiating surfaces of the transducers.

2. Sonic treating apparatus comprising:

a chamber including rigid converging side walls;

a curvilinear end wall at the divergent end of the side walls;

a plurality of transducers mounted in the end wall with radiating elements directed to introduce vibrations into the chamber;

the convergent end of the chamber defining a reflecting boundary of the liquid within the chamber;

the reflecting boundary being at an odd multiple of half-wavelengths of the energy radiated by the transducers;

the side walls of the` chamber including restricted openings for introducing material to be treated through the chamber;

the restricted openings being positioned to introduce the material at a point substantially an incremental wavelength from the radiating surfaces of the transducers.

3. Sonic treating `apparatus comprising:

a chamber including rigid converging side walls;

a curvilinear end wall at the divergent end of the side walls;

a plurality of transducers mounted in the end wall with radiating elements directed to introduce sonic energy into the chamber;

a closure at the convergent end `of the chamber constituting a reiiecting surface for sonic energy directed thereagainst;

the walls of said convergent chamber including aligned openings at an incremental wavelength distance from the radiating elements of said transducers for the passage of continuous strip materials through the treating apparatus.

4. Sonic treating apparatus comprising:

a chamber including rigid converging sidewalls;

a curvilinear end wall at the divergent end of the sidewalls;

a plurality of transducers mounted in the end wall with radiating elements directed to introduce sonic energy into the chamber;

a closure at the convergent end of the chamber constituting a reflecting surface for sonic energy directed thereagainst;

said closure constituting a thin diaphragm exposed on one face to the liquid medium within the chamber and on the opposite face to air;

and means positioning articles to be treated in the chamber at substantially an incremental wavelength distance from the radiating surfaces of the transducers.

5. The combination in accordance with claim 4 wherein said diaphragm closure is positioned at an odd multiple of half-wavelengths of the energy introduced into the chamber bythe transducer.

6. Sonic treating apparatus comprising:

a chamber including converging rigid sidewalls;

a plurality of transducers positioned to radiate sonic energy into said chamber in the direction of convergence Iand toward a common focus beyond the convergent end of said chambers;

said sidewalls including restricted openings at integral wavelength distance therealong from said transducers for passing continuous strips of material to be treated through said chamber in a direction generally transverse to the direction of propagation of energy within said chamber;

and means'including a closure at the convergent end of said chamber maintaining 'a liquid medium within said chamber at least between said transducers and said material to be treated.

7. The combination in accordance with claim 6 wherein the closure for the convergent end of the chamber comprises a rigid reflective surface.

8. The combination in accordance with claim 6 wherein said closure is positioned at an incremental wavelength distance from the radiating surfaces of the transducers.

9. Sonic treating apparatus comprising:

a chamber;

an array of transducers mounted within said chamber with radiating elements directed to introduce vibrations into the chamber toward a common focus at a point outside of a boundary of the chamber, the boundary of the chamber between the transducers and focus defining a reecting boundary of liquid medium within the chamber;

the reflecting boundary being in an odd multiple of half wavelengths of the energy radiated by the transducers;

said chamber including restricted openings for introducing material to be treated through the chamber;

the restricted openings being'positioned to allow the introduction of material in a direction generally transverse to the direction of radiation of sonic energy and at a point substantially an incremental wavelength distance from the radiating surfaces of the transducers.

l0. Sonic treating apparatus comprising:

a chamber including converging rigid side walls;

a plurality of transducers positioned to radiate sonic energy into said chamber in the direction of convergence and toward a common focus beyond the convergent end of said chamber;

a sonic energy-reflecting boundary positioned at an odd number of half wavelengths from the working surfaces of said transducers;

and means for passing material to be treated through said chamber at substantially 4an incremental wavelength distance from the operating surface of said transducers and means maintaining a liquid medium within said chamber between said transducers and said material to be treated and between said material and the convergent end wall of the chamber;

whereby sonic energy passing through the material treated is reflected into the chamber to reinforce the directly propagated sonic energy.

References Cited in the le of this patent UNITED STATES PATENTS 2,484,014 Peterson Oct. l1, 1949 2,522,071 Tait Sept. l2, 1950 2,632,634 Williams Mar. 24, 11953 2,950,725 Jacke Aug. 30, 1960 2,987,068 Branson June 6, 19611

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