US3222221A

US3222221A - Ultrasonic cleaning method and apparatus

Info

Publication number: US3222221A
Application number: US809718A
Authority: US
Inventors: Norman G Branson
Original assignee: Branson Ultrasonics Corp
Current assignee: Branson Ultrasonics Corp
Priority date: 1959-04-29
Filing date: 1959-04-29
Publication date: 1965-12-07
Anticipated expiration: 1982-12-07
Also published as: GB946863A

Description

Dec. 7,1965 so 3,222,221

ULTRASONIC CLEANING METHOD AND APPARATUS Filed-April 29, 1959 INVENTOR JWnmarz .Branson ATTORNEYS United States Patent 3,222,221 ULTRASONIC CLEANING METHOD AND APPARATUS Norman G. Branson, Revonah Woods, Stamford, Conn,

assignor, by mesne assignments, to Branson Instrumerits, Incorporated, Stamford, Conn., a corporation of Delaware Filed Apr. 29, 1959, Ser. No. 809,718 5 Claims. (Cl. 1341) This invention relates to a method and apparatus for ultrasonic cleaning of small articles and particulate materials. More particularly, it relates to the cleaning by ultrasonic means of sand, grinding wheel particles, tumbling media, ball bearings, nuts and bolts, and all other small articles and small machine parts.

There has been developed in the past ten years a Whole new technology of cleaning using the effects produced by so-called ultrasonic energy. Generally, sonic vibrations ranging in frequency from kilocycles to 1 megacycle have been used for ultrasonic cleaning of the surfaces of objects. Sonic vibrations of approximately 20 kilocycles, which is just above the range of audibility for most persons, have been found to be effective for many surface cleaning operations.

In ultrasonic cleaning, a sonic field is set up in a liquid cleaning medium and the objects to be cleaned are introduced into the medium; where the cleaning action takes place at their surface. It is believed that cavitation, caused in the liquid medium by the extreme pressure differentials produced in the medium by the ultrasonic waves, causes the cleaning action. It has been discovered that the cavitation bubbles are more likely to form around small nuclei in the liquid or on the surfaces of objects in the liquid and that these bubbles or cavities may be made to form and then to implode during one complete pressure cycle of an ultrasonic wave. It has also been found that caviation will occur in liquids from induced sonic fields having frequencies ranging from 3 kilocycles to 2.5 megacycles. The present invention, although particularly directed to the preferred 20 kc. frequency now used, is applicable to the full range of ultrasonic cleaning frequencies.

When an object is introduced into the ultrasonic field in an ultrasonic cleaning medium the cavitation bubbles form at and around the surface contaminants and the contaminants seem to literally explode off the surfaces of the object. Various other chemical reactions have been found to be accelerated by the application of ultrasonic energy to chemical reagents. The use of a combined chemical reaction and ultrasonic field for cleaning the surfaces of objects is disclosed in the co-pending application of Frank W. Hightower and Walter J. Bleistein Serial No. 645,477, filed March 12, 1957, now Patent No. 3,033,710 relating to Method and Apparatus For Surface Cleaning Using Ultrasonic Energy, and assigned to the same assignee as the invention herein.

It has been one of the anomalies of the ultrasonic art that many of the objects and materials to which application of ultrasonic cleaning is most desirable have in the past not lent themselves to the existing methods of ultrasonic cleaning. In particular, it is most desirable that sand and other hard particulate materials should be cleaned by ultrasonic methods. When such materials are used in the manufacture of grinding wheels, any impurities or contaminants left in the material will interfere with the bonding of the particles together into the grinding Wheel units, and such poor bonding has sometimes in the past caused the wheels to explode, thus presenting a danger to operators and to machines using the grinding wheels. Also, when sand, gravel, metal scraps, etc., are

Patented Dec. 7, 1965 used as tumbling media for debnrring, boning and polishing, it is desirable that these media should be capable of being cleaned by ultrasonic methods. The characteristics of the tumbling media are adversely affected by the vari ous particles, grease and other contaminants removed during the tumbling process. The present non-ultrasonic, chemical and agitation, cleaning methods have proved insufficient to properly clean these materials for re-use. The application of ultrasonic cleaning methods to such materials provides the opportunity for complete cleaning so that the materials may be re-used.

Ultrasonic cleaning methods have been somewhat imperfectly applied to the cleaning of ball bearings for high precision machines, such as gyroscopes, in which it is absolutely necessary that all contaminants be removed from the bearings and associated small parts in order for the machine to properly operate over a reasonable lifetime. Nuts and bolts for such high precision machines must also be perfectly clean; otherwise, the use of contaminated nuts and bolts may introduce into the machine contaminants which would adversely affect the lifetime and operation of the device. The same is true for all small parts in high precision machinery, and to some extent for small parts for use in any machines which are contaminated during the manufacturing process.

In the prior art the methods of treating small parts and particulate materials have been two in number. The cleaning of ball bearings and other small parts for high precision machines can be done on an individual basis, if only a few of such machines are to be built. This of course is impratcical for any high volume production. If large quantities of small parts and particulate materials are desired to be cleaned by the ultrasonic methods of the prior art, a batch of such material is placed in the sonic field, in an ultrasonic medium, and the batch is occasionally stirred. By this technique the parts or particles near the outer surfaces of the batch are cleaned ultrasonically but those in the middle are not subjected to ultrasonic caviation, which causes the cleaning, because the sound intensity is too low at the middle of the batch, having been attenuated by its passage through the outer portions of the batch. Also, air and other gases collect on the surfaces of the material being cleaned due to the cavitation process and, in a batch, this gas is prevented from escaping. Cavitation no longer occurs on those surfaces to which the gas attaches itself, and cleaning stops there. Dirt and other contaminants are caught in the center of the batch since the flow of the cleaning liquid through the batch is inhibited, thereby preventing the removal of free dirt and contaminants. This inhibited fluid motion also reduces the action of solvents, acids or other chemicals used in combined chemical and ultrasonic cleaning. The above problems of the prior art batch cleaning method are eliminated when large parts are cleaned, or when small parts are cleaned on an individual basis, since all surfaces of the object can be subjected to ultrasonic energy in the ultrasonic medium. The method and apparatus of the present invention solves these problems of the prior art in cleaning small articles and particulate materials by doing so on a semi-individual basis,

thus allowing the cleaning of large volumes of material.

It is therefore an object of this invention to clean small parts and other small articles by ultrasonic methods. Another object of the invention is to clean particulate materials by ultrasonic methods. A further object of the invention is to clean small parts, small articles and particulate materials ultrasonically on a semi part-bypart, article-by-article or particle-by-particle basis. A still further object of the invention is to accomplish the above objects in a continuous process.

Another object of the invention is to provide means for placing each part, article or particle into a sonic field for cleaning individually. Yet another object of the invention is to accomplish objects of the above character in such a way that each part, article or particle is in total contact with the ultrasonic cleaning fluid when it is in the ultrasonic field. Still another object of the invention is to accomplish objects of the above character and rovide a continuous flow of cleaning fluid around each part, article or particle during cleaning. Another object of the invention is to permit the continuous free escape of gas formed on the surfaces of parts, articles or particles while they are being cleaned. Still another object of the invention is to accomplish objects of the above character and to subject all of the surfaces of each part, article or particle being cleaned to direct sonic vibrations.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements, and arrangements of parts, which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

FIGURE 1 is a cross sectional side view of an apparatus adapted to ultrasonic cleaning according to the method of the present invention;

FIGURE 2 is a partial top view of the apparatus of FIGURE 1; and,

FIGURE 3 is a top view of a portion of the apparatus of FIGURE 1, showing a modification in the ultrasonic transducer configuration.

Similar reference characters refer to similar parts throughout the several views of the drawing.

In general, according to the method of the present invention for cleaning small articles and particulate materials, the particles, parts or articles are introduced into a bath of ultrasonic cleaning fluid, preferably at a constant rate, and allowed to fall freely in the medium, tumbling as they do, through the ultrasonic field in the medium where they are subjected to surface cavitation over their entire surface due to the random nature of their tumbling and falling motion.

More particularly, referring to FIGURES 1 and 2, an apparatus for cleaning sand, gravel, grinding wheel particles and the like comprises a tank containing an ultrasonic cleaning fluid 12 which may be any convenient solvent or other chemical reagent. The cleaning fluid 12 is continuously circulated in the tank 10, entering through inlet 14 at the bottom of the tank and exiting from the top of the tank through the outlet 16. The used cleaning fluid may be filtered, distilled or treated in any other convenient manner to remove the impurities which it has taken up during the cleaning process and may then be reused. The placement of the outlet 16 at the top of the fluid level in the tank 10 allows any accumulated scum on the surface of the cleaning fluid 12 to be rather quickly drained off through the outlet 16.

There is contained within the tank 10 a vertically aligned chute 18 of generally parallelopiped construction. The chute 18 is supported within the tank 10 by supporting bracket structures 2020 which are mounted on

opposite side walls

21 and 23 of tank 10. A number of electro-acoustical transducers 22 are mounted on

opposite walls

15 and 17 of the chute 18. The transducers 22 are driven by an ultrasonic generator (not shown) and acoustically coupled to the

walls

15 and 17 for transmission of ultrasonic energy through the walls into the central portion 19 where the ultrasonic energy is concentrated. The transducers 22 may be electrostatic, piezoelectric, or magnetostrictive and are constructed in a manner well known in the prior art.

A continuous endless conveyor belt 24 operates from below the chute 18 to the upper edge of the tank 10, as shown in FIGURE 1. The belt 24 passes over and around horizontally disposed roller 26 which is rotatably mounted in bushings 27 and 29 affixed to

opposite walls

21 and 23 of tank 10. As shown in FIGURE 2, the belt 24 passes under and is bent around four parallel horizontally disposed guide rollers 30 and proceeds upwardly in a diagonal direction to a terminal roller 32 which is mounted above the fluid level on end wall 33 of tank 10. Rotary motion is imparted to belt 24 by driving roller 32 by means of shaft 28. Upstanding portions 34 along the belt 24 are spaced at equal intervals and faciliate the transport of fine material diagonally upwards towards the terminal roller 32. The material leaving the belt 24 at the terminal roller 32 is deposited on the chute 36 which directs it to the next operation. When the apparatus is used to clean fine particulate material such as sand and the like, the belt 24 is chosen to be impervious to the passage of such material through it and preferably is a non-porous webbing. When machine parts or other aggregations of larger objects are cleaned the belt 24 is a fine mesh webbing so that any fine impurities will fall through it and not be carried to the next operation.

Above the transducer chute 18 there is located a storage bin 38 and a constant feed mechanism 40. The constant feed mechanism 40 feeds a constant flow of material to above the transducer chute 18 and may be of the wellknown vibrator type. The material 42 which is to be cleaned may be pre-wetted in the storage bin 33 to facilitate its sinking through the surface level 44 of the cleaning fluid 12 above the chute 18 or it may be introduced into the fluid 12 just below the surface level 44 to prevent suspension of the material 42 by surface tension on the surface 44.

The surface level 44 of the cleaning fluid 12 is preferably arranged to be slightly above the top of the chute 18 so that any accumulated scum is allowed to escape from the chute and pass through the outlet 16. A vertical barrier wall .-6 is mounted between

opposite tank walls

21 and 23, extends above the belt 24 and above the cleaning fluid level separating the surface 44 above the chute 18 from the surface 45 through which the belt 24 passes and prevents scum accumulating on the surface 44 from spreading to the surface 45 through which belt 24 passes, thus preventing scum from being deposited on the cleaned material as it passes upwardly through the liquid surface.

As is well known in the ultrasonic art, the arrangement of the electro-acoustical transducers 22 along opposite sides of the transducer chute 18 as shown in FIGURES 1 and 2 will produce a substantially uniform sonic field within the chute 18. If higher sonic intensities are (esired at the surfaces of the material to be cleaned, the transducers may be arranged to focus their energy as shown in FIGURE 3. In this circular arrangement, the tranducers 22 are arranged within a chute of circular cross section 48. The transducers 22 are coupled at their inner faces 50 directly to the ultrasonic fluid 12 within the chute 48 and the arrangement of the transducers 22 produces a focusing effect whereby the ultrasonic intensity within the chute is greatest at its center. When a chute of this nature is used the stream of falling material 42 should preferably be restricted to a relatively narrow stream through the central portion of the chute, where the ultrasonic energy is concentrated.

The apparatus shown in FIGURES 1 and 2, with or without the modification shown in FIGURE 3 operates substantially as follows. The material 42 to be cleaned, which in this example is sand, gravel, or other fine particulate material, but with minor modifications of the apparatus may be any aggregation of small objects, or

other aggregative material, is constantly dropped into the ultrasonic cleaning fluid 12. The material then freely falls, tumbling in a random way, through the chute 18 (FIGURES 1 and 2) where it is subjected to surface cavitation caused by the ultrasonic field of energy, produced by the transducers 22. This cavitation causes the entire surface of each individual particle or part of the material to be thoroughly cleaned. After passing through the chute 18, the material is caught on the conveyor belt 24 and is carried out of the tank and deposited onto the chute 36. The material is partially subjected to some rinsing action as it is drawn through the cleaning fluid 12 by the belt 24. The cleaning operation may be performed several times using a plurality of cleaning tanks as heretofore described.

It will be obvious to anyone skilled in the ultrasonic cleaning art that the crux of the method herein described is allowing each part, article or particle which is to be cleaned to free fall in a tumbling manner through an ultrasonic cleaning field, so that all surfaces of each part, article or particle will be subjected to ultrasonic cavitation. Many variations of apparatus for practicing the method of the invention will occur to persons skilled in the art; for example, the material to be cleaned may be mixed with the ultrasonic cleaning fluid and sprayed horizontally out of a nozzle through an ultrasonic cleaning field; or to clean material which is less dense than the liquid and hence will float in the ultrasonic cleaning fluid, provision may be made for introducing such material into the bottom of the vessel and allowing the material to float to the surface of the fluid through an ultrasonic cleaning field. Therefore, in the following claims the terms free fall or freely falling are intended to mean any free unsupported motion through an ultrasonic cleaning field.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efliciently attained, and, since certain changes may be made in carrying out the above method and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A method for removing contamination from small objects comprising the steps of dropping said objects into a solvent for the contamination, permitting said objects to fall freely through said solvent, and ultrasonically activating said solvent to the degree necessary to cause cavitation in the solvent as the objects fall through it.

2. A method for cleaning the surface of particulate elements, said method comprising the steps of introducing said elements below the surface of a sonic cleaning liquid, said elements having a density less than the density of said liquid, permitting said elements to rise through said liquid toward the surface thereof, and ultrasonically activating said liquid to the degree necessary to cause cavitation in the liquid as the elements rise through it.

3. The method of cleaning particulate elements which comprises dropping said elements into a sonic cleaning liquid, permitting said elements to fall freely through said liquid, and ultrasonically activating said liquid to the degree necessary to cause cavitation in the liquid as the elements fall through it.

4. The method of removing oil from oil bearing elements which comprises dropping said elements into a solvent for oil, permitting said elements to fall free through said solvent, and ultrasonically activating said solvent to the degree necessary to cause cavitation in the solvent as the elements so fall through it.

5. Apparatus for cleaning aggregative material comprising, in combination, a tank for containing cleaning fluid, a plurality of ultrasonic transducers to create a field of ultrasonic energy in a vertical portion of the cleaning fluid in said tank, said plurality of ultrasonic transducers vertically and oppositely positioned in said tank to subject materials in said vertical portion to ultrasonic energy from at least two directions, and means for dropping a stream of the aggregative material into said portion of the cleaning fluid above said field of ultrasonic energy whereby the material freely falls during cleaning under the influence of gravity through said ultrasonic field of energy.

References Cited by the Examiner UNITED STATES PATENTS 898,954 9/1908 Baker 134-73 1,544,894 7/1925 Farnsworth 134-25 X 1,580,723 4/ 1926 Hapgood 134-25 X 1,791,797 2/ 1931 Clark 208-11 2,460,919 2/ 1949 Bodine. 2,578,505 12/ 1951 Carlin. 2,620,894 12/ 1952 Peterson. 2,635,614 4/1953 Ford 134-74 X 2,722,498 11/ 1955 Morrell et a1. 208-11 2,735,795 2/1956 Weiss 134-25 2,742,408 4/ 1956 La Porte 208-146 2,845,936 8/ 1958 Boynton 134-25 X 2,871,180 1/1959 Lowman et al. 208-11 2,919,215 12/1959 Neuhaus 134-1 2,972,997 2/1961 McCown 134-1 X 2,973,312 2/ 1961 Logan.

FOREIGN PATENTS 1,011,301 4/1952 France. 1,052,776 3/ 1959 Germany.

MORRIS O. WOLK, Primary Examiner.

SIDNEY JAMES, CHARLES A. WILLMUTH, AL-

PHONSO D. SULLIVAN, MILTON STERMAN, DONALL H. SYLVESTER, Examiners.

Claims

1. A METHOD FOR REMOVING CONTAMINATION FROM SMALL OBJECTS COMPRISING THE STEPS OF DROPPING SAID OBJECTS INTO A SOLVENT FOR THE CONTAMINATION, PERMITTING SAID OBJECTS TO FALL FREELY THROUGH SAID SOLVENT, AND ULTRASONICALLY ACTIVATING SAID SOLVENT TO THE DEGREE NECESSARY TO CAUSE CAVITATION IN THE SOLVENT AS THE OBJECTS FALL THROUGHT IT.