GB2030599A - Method and Apparatus for Ultrasonically Cleaning Articles - Google Patents

Abstract

An ultrasonic cleaning method and apparatus in which the articles (16) to be cleaned are moved along and in mechanical contact with a transport path member (12) having ultrasonic transducers (10) mounted on or near the opposite surface thereof, the member being immersed in a liquid bath (13). The member (12) may be inclined at an adjustable angle so that the articles (16) slide down the path by virtue of the vibration in a controllable time period. <IMAGE>

Description

SPECIFICATION Method and Apparatus for Cleaning Articles This invention comprises a method and an apparatus for cleaning with ultrasonic vibratory energy. The invention is especially suitable for cleaning, with ultrasonic vibrations or energy, mass produced parts such as screws, nuts, bolts and similar fasteners, ballbearings, machine parts, parts for instruments, watches and other precision products.

The need for cleaning often exists at the end of a production line to remove fats, oils, dirt, carbon particles, soot, metal particles, oxides, etc. Also, within a production cycle there are needs for cleaning of component parts such as, for instance, those which in a later production step will go through electrolytic surface coating. Different apparatuses on the market at the present time for cleaning of component parts using ultrasonic vibrations or energy are built for a liquid as a medium in which the component parts are immersed during the cleaning. In these apparatuses one utilizes the force that develops at the intermediary surface between a liquid and a solid body when an ultrasonic field is put through the liquid bath. This force is primarily the result of a very high acceleration of the sound at the transition from the liquid to the solid body.Solid body is for this purpose defined not only as the component part which is to be cleaned, but also as the partictesof-different kinds which are to be removed from the component part. Also, fats, oils and similar substances on the surfaces of component parts cause such acceleration forces.

These forces are normally stronger than the forces that exist between the adhering particles and the component parts to be cleaned.

In many liquids there also develops cavitation in addition to the acceleration forces under the influence of an ultrasonic field. Cavitation generates air or gas bubbles at the intermediary surfaces between solid bodies and the liquids. The bubbles are exposed to very high pressures, often 100 times higher than the dynamic pressure of the ultrasonic field. This cavitation plays an important role also in the cleaning of component parts because of its explosion effect. Cavitation, however, is only at hand at relatively low frequencies of the ultrasonic field. It is also enhanced by those liquids which have the ability to dissolve gases. The cavitation effect has one disadvantage, namely that it highly corrodes most materials. This fact puts a limit on the time such component parts which are susceptible to corrosion can be exposed to the cleaning process.

This is one of the problems this invention is meant to solve.

In the apparatuses for cleaning of component parts using ultrasonic which are on the market, the component parts to be cleaned are often placed in baskets which are moved through an ultrasonic field. A disadvantage of this method is that parts which are located in the shadow of other parts in the ultrasonic field receive significantly weaker ultrasonic power than those which are directly exposed to the ultrasonic energy. Other types of apparatuses contain a drum of perforated plate in which rotation of the drum tumbles the parts to better expose the parts to the ultrasonic energy. In a third type of apparatus, the parts sink vertically down in a liquid bath and pass through an ultrasonic field.

All of these types of apparatuses have in common the fact that the ultrasonic energy reaches the particles to be cleaned from a liquid bath. The loss of ultrasonic energy is substantial in passage through the liquid bath, which means that the ultrasonic energy has to be generated by relatively high energy transducers, and has to be used in combination with long treatment times, in order to achieve the desired degree of cleaning.

It is intended that this invention shall result in a more efficient cleaning at lower energy levels and at a shorter treatment time. The means of achieving this are characterized by the fact that the parts to be cleaned are brought into mechanical contact with a free surface of one or more plates, discs, tubes, pipes or similar objects, located close to each other, and that on the opposite free surface is mounted at least one ultrasonic transducer. This is done as the parts are moved through a bath.

The invention will be further described in relation to the following exemplary embodiments and reference is made to the attached drawings.

Figure 1 is a diagrammatic illustration showing, in cross section, cleaning apparatus according to the invention.

Figure 2 is an enlarged diagrammatic illustration, in cross section along the line 2-2 of Figure 1 showing a vibrator and vibratory plate or member that forms a part of a channel or gutter along which parts move as they are cleaned in a bath.

Figure 3 is an enlarged diagrammatic and fragmentary cross sectional view of an embodiment of the invention adding a protective plate to the gutter or channel of Figure 2.

Figure 4 is a diagrammatic cross sectional view of an embodiment of the invention adding an endless conveyor for moving parts as they are cleaned.

Figure 5 is another enlarged cross section of an embodiment of the invention diagrammatically illustrating a wiper arrangement for moving parts along the vibratory plate.

Figure 6 is a further enlarged cross sectional view of an embodiment wherein the vibratory plate is in the form of a pipe through which the parts move.

Figure 1 shows a cross-section of a device according to the invention. A series of ultrasonic vibration generating transducers 10 is mounted on the underside of a member or plate 12. This plate 1 2 can preferably be the bottom of an inclined channel or gutter 11 down which parts 1 6 to be cleaned slide. Two upright gutter sides 1 7 complete the gutter 11. The parts are fed into the gutter at location A in any suitable manner, and at location B the parts, now cleaned, are collected for discharge, again in a known manner.

Parts 1 6 pass immediately over the ultrasonic transducers and in mechanical contact with these during a short period of time by virtue of the plate 12 being driven by the transducers 10 and forming the energy transmitting output member of these transducers, as discussed below. Time of contact can be adjusted by changing the angle of inclination of the plate 12. Figure 1 illustrates, very generally and in block diagram form, inclination adjusting means 15; numerous arrangements for this purpose will be apparent.

That part of the gutter or channel 11 along which the parts move and to which the ultrasonic transducers are mounted is immersed in a liquid bath 13, commonly water. The transducers 10 are water tight by virtue of their enclosure in a shell or housing 14.

As shown diagrammatically in Figure 2, the ultrasonic transducer 10 is mounted with its vibratory member 18 to the plate 12. For purposes of illustration only, the transducer 10 is shown as magnetostrictive with coils 1 9 and with a core that is the vibratory member 1 8. The transducer may be either magnetostrictive or piezoelectric. Both are known in the art.

The plate 12 is both the bottom of the gutter 11 and the ultrasonic vibrator that imparts ultrasonic vibrations to the workpieces or parts 1 6 and to the surrounding bath. Good contact between the vibratory member 16 of the transducer 10 and the plate 12 results in a high transfer of energy with low losses. Plate 12 should be made of fairly thin sheet. For example, at a thickness of one millimeter of this plate, about 85% of the energy that is fed to the plate will leave its upper side. If the plate, however, is five millimeters thick, then only 20% of the energy applied to the plate will be passed therethrough.

Substantial wearing of the plate can occur both by the sliding of the parts 1 6 and by cavitation.

Therefore, in some cases, an easily replaceable additional plate or member 20 protecting the bottom of the gutter can be added as shown in Figure 3. With the addition of the plate 20, however, transmission losses of the ultrasonic energy increase. In a further embodiment of the invention, the extra plate can be an endless metal conveyor 21 as generally, schematically shown in Figure 4. With this arrangement, the conveyor preferably moves the parts horizontally through the liquid bath.

In yet another arrangement according to the invention, as illustrated in Figure 5, the plate or plates can be located horizontally in a liquid bath, and the parts can be transported thereon by the use of a scraper 22. Although the plate 12 that applies the ultrasonic vibration to the parts is preferably made of metal, it is possible to employ nonmetallic materials, for example layers of plastic materials. The plate need not be planar, but may be configured as is suitable for the particular parts to be treated. For example, in one embodiment, the gutter can be made of corrugated sheet. In another embodiment the plate constitutes a pipe 12' of, for example, plastic, and this is very generally illustrated in Figure 6.In this context then, the word "plate", or "member", means, broadly, a part, whether of metal or nonmetallic material, having a surface available for ultrasonic energization, and another for imparting ultrasonic energy therefrom.

On cleaning metal parts, there is often a need to remove a layer or flakes of oxides, for instance in the production of screws, nuts, and bolts.

Ultrasonic cleaning according to the invention is then preferably combined with a pretreatment using pickling for a short period of time in a suitable acid bath. As an alternative, the liquid bath 13 in which the ultrasonic cleaning takes place can be a weak acid pickling bath.

Because of the mechanical contact between the generator and the parts to be cleaned, via the plate 12 or plates 12 and 20, a much faster and more efficient cleaning is achieved than in previously known equipment where ultrasonic energy is directed to the parts through the bath.

The short treatment time and the comparatively low amount of energy that is required from the ultrasonic generator in order to achieve an efficient cleaning reduces the risk for cavitation damage to the equipment and to the parts being cleaned. In addition, an advantage of using an ultrasonic cleaning method according to the invention is high cleaning efficiency achieved at lower energy input and shorter treatment time.

In operation, the workpieces 1 6 can for instance be dropped into a funnel and onto the vibratory plate 121. Depending on the amount of cleaning necessary, an adjustable support can be arranged to provide the correct degree of inclination to the plate 12 whereby the workpieces 1 6 move slowly or quickly down the vibratory surface of the plate. As they reach the end of the plate 12, the workpieces 1 6 can for instance be dropped onto a conveyor and transported by the conveyor to for instance a chute. There they leave the apparatus and are taken to an assembling or packing station, for example. By virtue of combining the movement of the workpieces with the ultrasonic cleaning directly from the vibratory plate 12, no tedious timing of individual workpieces is required, but each proceeds through the bath 1 3 in the requisite time.

The versatility of the invention is demonstrated by the several embodiments set forth above. The direct application of vibratory energy to the parts by their resting on the plate 12 as they move enhances cleaning, shortens cleaning time, reduces input electrical energy necessary to drive the transducers, and thus results in a much improved cleaning device.

The foregoing details of specific embodiments are illustrative only. The foregoing description of preferred embodiments is not to be constructed as limiting the scope of protection of the invention, which scope is set forth in the appended claims.

Claims (12)

Claims

1. A method of cleaning articles by exposing the articles in a bath of liquid to an ultrasonic field generated byan ultrasonic vibration generating transducer, said method comprising transporting the articles along and in mechanical contact with a transport path defined by the first surface of a member, and vibrating said member by means of said transducer mounted to a second surface of said member opposite to said first surface.

2. A method as claimed in claim 1 including controlling the time duration of passage of said articles along said path.

3. Apparatus for cleaning articles by exposing the articles in a bath of liquid to an ultrasonic field generated by an ultrasonic vibration generating transducer, said apparatus comprising a member having a first surface defining a transport path for transport of the articles to be cleaned through said liquid in mechanical contact with said first surface, said transducer being mounted to said member on a second surface thereof opposite to said first surface.

4. Apparatus as claimed in claim 3 wherein said transport path is inclined within said bath whereby articles being cleaned slide down the said path.

5. Apparatus as claimed in claim 4 including adjusting means operable to alter the inclination of said path.

6. Apparatus as claimed in any one of claims 3 to 5 wherein said member is in the form of a gutter.

7. Apparatus as claimed in claim 3 wherein said transport path is disposed horizontally within said bath, and means is provided to move articles being cleaned along said path.

8. Apparatus as claimed in any one of claims 3 to 5 wherein said member is in the form of a pipe'

9. Apparatus as claimed in any one of claims 3 to 8 wherein said transport path is formed by a replaceable protective layer on said member, an upper surface of said layer supporting said articles to be cleaned.

10. Apparatus as claimed in any of claim 3 to 7 wherein said transport path comprises an endless belt conveyor.

11. A method as claimed in claim 1 and substantially as described herein with reference to the accompanying drawings.

12. Apparatus for cleaning articles substantially as described herein with reference to the accompanying drawings.