US3198170A - Ultrasonic-wave painting machine - Google Patents

Description

g 3, 1965 TOSHIO ONISHI 3,198,170

ULTRASONIC-WAVE PAINTING MACHINE Filed March 6. 1962 2 Sheets-Sheet 1 Aug. 3, 1965 TOSHIO ONISHI ULTRASONIC-WAVE PAINTINGMACHINE 2 Sheets-Sheet 2 Filed March 6, 1962 been accomplished by corona discharge.

rapid-drying. paints is also possible.

United States Patent 3,198,170 ULTRASONIC-WAVE PAINTING MACHINE Toshio Onishi, Yamato machi, Kitaadaclii-gun, Saitamaken, Japan, assignor to Kabushiki Kaisha Koparu, Tokyo-to, Japan, a joint-stock company of Japan Filed Mar. 6, 1962, Ser. No. 177,820 Claims priority, application Japan, Mar. 11, 1961, 36/ 8,083; Apr. 27, 1961, 36/ 14,980; July 8, 1961, IMF/24,590; Sept. 22, 1961, 36/34,20

1 Claim. (Cl. 118627) This invention relates to a new painting or coating machine wherein, through the utilization of piezo-electric etfect, magnetostriction effect, and other phenomena, paint is supplied to a vibrating body which undergoes ultrasonic-wave vibration, and the paint is rendered by ultrasonic-wave energy due to this vibration into fine particles of a state of mist and caused to be sprayed uniformly over a wide area onto the article being painted or coated.

It isknown in the prior art that, in general, a film of liquid can be rendered by powerful, ultrasonic-wave energy into fine particles in a state of mist. Based on this phenomenon, the present invention seeks to render paints into fine particles by ultrasonic-wave energy and to utilize this action for industrial painting and coating.

In the ordinary electrostatic painting machines known hitherto, the transformation of the paint into a mist has These painting machines, however, have the disadvantages, due to the fact that the fine particles of paint are propelled by only electrostatic force, of low propulsion velocity of the fine paint particles, consequently, of difficulty in using 'so-called rapid-drying paints, and, furthermore, of difficulty in applying paints wherein such solvents as water, alcohol, and turpentine oil are used. These electrostatic painting machines, moreover, have such disadvantageous features as high prices due to the necessity of using stable, high-voltage, direct-current power source.

The present invention seeks to eliminate the abovedescribed disadvantages of the conventional electrostatic painting machines by fixing a vibrating plate to an ultrasonic-wave vibrating element or transducer of the magnetostriction or electrostriction type excited by an ultrasonic-wave generator, transforming paint, which is caused to flow in a film state onto the surface of this vibrating plate, into fine particles through the vibratory action of this plate, and forcing these fine paint particles to fly in the direction of the sound wave progagation. Accordingly, the paint in a state of fine particles is projected with high eflieciency to the intended points on the article being painted. Moreover, since the propulsion velocity of the paint particles is high, the use of Furthermore, in impressing a direct-current, high voltage in order to promote the projection of the paint in an auxiliary manner,

since, by the present invention, the paint is already transformed into a mist by ultrasonic-wave energy and has ample initial velocity, such a high direct-current voltage (70 to 120 kilovolts) as is required in, the case of the conventional rotating atomizing head cups in electrostatic painting machines is unnecessary, and a direct-current voltage (approximately 35 kilovolts) which is of an order suflicient merely to charge the ejected particles electrostatically is suflicient. Accordingly, the painting machine according to this invention has high industrial worth due to such advantageous features as greatly reduced equipment cost, safe operation for personnel, and reduction. of fire hazard.

. In general, some difiiculties are encountered in the case of atomization of the liquid film supplied to the vibrating plate by the propagated ultrasonic-wave energy with- 3,198,170 Patented Aug. 3, 1965 in the said vibrating plate and the deflection of said vibrating plate due to density of ultrasonic-wave energy concentration in the said vibrating plate. In this case, if the frequency of the ultrasonic-wave which drives the vibrating element is constant, the high and low points of ultrasonic-Wave energy concentration on the vibrating plate become static, and at the points of low concentration of ultrasonic-Wave energy, atomization is not accomplished. The paint which becomes stagnant at such points hardens and sticks, thereby obstructing the free vibrating of the vibrating plate, or moves to a neighbouring point of high concentration of ultrasonicwave energy and is ejected as large drops. If, in order .to accomplish effective atomization, a small quantity of the liquid is caused to flow out onto the vibrating plate, atomization will occur promptly only in the vicinity of the flow-out opening. On the other hand, if the liquid is caused to flow out at a high rate, the liquid film in the vicinity of the flow-out opening will become thick, and large drops will be ejected together with the atomized mist.

In order to eliminate the foregoing problems which adversely affect effective painting, the painting machine of the present invention is adapted to vary the ultrasonic- Wave freqeuncy, which excites the vibrating element or transducer, at a suitable periodv within. a range wherein the ultrasonic-wave output is not greatly reduced, and, by preventing points of low and high concentration of the ultrasonic-wave energy developed on the vibrating plate from becoming static, atomization is caused .to be accomplished at any point on the vibrating plate. Furthermore, the atomization is accomplished uniformly by supplying the paint continuously to the vibrating plate, periodically stopping the supply of ultrasonic-wave energy, then resupplying the ultrasonic-wave energy after a uniform spread of the paint film has been formed over a predetermined area of the vibrating plate, and atomizing and dispersing this paint with one action.

It is an object of the present invention to provide a new ultrasonic-wave painting machine wherein a vibrating plate is fixed to an ultrasonic-wave vibrating element driven by an ultrasonic-wave generator, and paint supplied to the said vibrating plate is caused, by the deflection of the vibrating plate due to the ultrasonic-Wave energy and low and high concentration of the ultrasonic- Wave energy within the vibrating plate, to be atomized in fine particles of uniform size from a wide area of the said vibrating plate so as to be projected onto an article to be painted.

It is another object of this invention to provide a novel vibrating plate which has an extremely effective configuration for the case wherein a direct-current voltage is impressed in an auxiliary manner, and the paint which has been atomized by ultrasonic-wave energy is caused to be projected onto the article to be painted.

It is a further object of the invention to provide a new construction of a vibrtaor for effectively propagating the excitation of a vibrating element to a vibrating plate such as that suitable for the painting machine of this invention.

The nature and details of this invention as well as the manner in which the foregoing objects, other objects, and advantages may best be achieved will be more clearly apparent by reference to the following description when taken in conjunction with the accompanying illustrations in which like parts are designated by like reference numbers and letters, and in which:

FIG. 1 is a perspective View, in diagrammatic form and with certain parts deleted, showing one embodiment of the ultrasonic-wave painting machine according to the invention;

FIG. 2 is a schematic diagram, partly in perspective view and partly as an electrical circuit diagram, for a description of the principle of the painting machine .of the invention;

FIG. 3 is a perspective view showing a vibrator of a extreme end of the frontchamber 3 is adapted to be finely adjustable in a swivelling manner with respect to theinsulative cylinder 2. An ultrasonic-wave vibrating element tor transducer 7, which is fixed'to avibrating plate 5, is disposed within this front chamber 3. Aninsulating transformer 11 is housed within therear chamber 4 of the interrupting device15, by a suitable method, for example, by a method wherein, as shown in FIG. 2, an eccentric cam EC is rotated by a variable-speed motor M causes a switch SW to open and close periodically, thereby causing the suppressor grid G of the oscillatingtube 14 to be subjected periodically to a negative. potential by a storage battery B and an oscillation output to be sent intermittently'to the vibrating element 7. V For example, the rotational period of the eccentric cam maybe varied or the proportion between the exciting time of the vibrating plate during one period and the time when the said excitation does not take place maybe varied. As a result, the paint which is, poured out always forms a uniform filmover a Wide area of thevibrating plate 5, and such defective action as atomization only in the vicinity oftheflow outlet or irregularities in the particle sizedue todiiferences in positions of atomization does not occur. l I

v The ultrasonic-wave generator 8 of the instant embodiment further includes asweep device 16 which varies the oscillation frequency by a suitable method, for example, by rotating a variable condenser-,VC by means of a variable-speed motor M as indicated in FIG. 2. By using thissweep device 16 tocause the ultrasonic-wave frequency to vary, with a suitable period, within a range wherein the In the operation of the painting machine ofthe above constructional arrangement, when. the ultrasonic-wave" vibrating element 7 is excited by the oscillationoutput (at a frequency of approximately kilocycles persecond in the case of the embodiment shown-) 'of the ultrasonic-wave generator 8, the ultrasonic-wave energy propagated by the excitation of the element 7 and deflection of the vibratingplate 5 due to the density of the ultrasonicwave energy concentration in the said vibratingplate 5 cause atomization of the paint supplied from the paint tank 9 and force the paint. particles to be projected onto thearticle 10. A plurality of the articles l'fl'are suspended from an endless belt EB which is driven, in .the arrow direction, by suitable driving wheels DW such as pulleys or chain wheels which in turn are driven by a driving motor not shown. r

a When the high-voltage, direct-current power source 12 is used, in an auxiliary manner, to cause effective projection of the paint which has been atomized .onto thearticle 10, the insulatingtransformer 11 functions to insulate the ultrasonic-wave generator 8 and the vibrating members. 7 The device for atomizing the paint will now be described in greater detail in conjunction with FIG. 2. As shown'in FIG. 2, athin metal plate 13 is interposed betweenthevibra ting plate 5 and the vibrating element or transducer 7. V

This thin metal plate.13 has;anarea which is somewhat greater thanthe area of the 'vibrating surface ofthe vi: brating'element 7 and; a thickness which is slightly greater than that of the vibrating plate 5 (in this embodiment, the

thickness ofthe vibratingplate. is 0.3 mm., andthat o f the thin metal plate is 1 mm.) .l It is necessary that thisthinmetal plate 13 have a relatively/high thermal capacity and be a thin plate which will not. cause great variation in the resonance frequency (approximately 40 kilocycles {per second) of .the vibrating element 7 when only thismetal 'plate is bonded to the. vibrating element. Such athin metal plate 13 functions'to prevent separation of the vi brating element 7 andthevibrating plate 5 and,1at the same time, facilitates the acoustic matching of these. two parts.

One example circuit diagram of FIG.. 2. .This ultrasonic wave ,generator includes, in a'ddition to a high-frequency.'o'scillating tube 14,'an,oscillation interrupting device 15 forcaus 'ing the supplied paint to assume the form of a uniform fil on the entire surface of thevibrating plate 5.; This of an ultrasonic-wave generator euitable l 'forexciting the vibrating element 7 is represented by the ftration of ultrasonic-wave energy becoming static as in the case of operation with constant frequency.

. In FIG. 3, .a'vibrator with amodifiedvibr'ating' plate 17 :of dish form differing from the configuration of thevibrating plate 5 of FIG. 2 is shown. In the case wherein, in order to coat, effectively, an article tobe painted with paint which has been atomizedby means of a vibrating plate, a direct-current voltage (approximately 35 kilovolts) is impressed as an auxiliary measure, the distribution of lines'of electric force will'become dense at the peripheral parts of the vibrating plate if thevibrating plate is a flat plate, and its emission positions, being readily affected by outside influences, will become astatic. For this reason, the projection, directions of 'the atomized paint will become greatly disturbed, and painting operation will become unstable. In the case of the dish-shaped "vib'ratingplate 17, however, since the lines of electric force are almost entirely concentrated in the central portion; theatomized particles of paint arejnot readily affected-by external influences and' are projected in a stable manner directly to the article bein'g'painted; Moreover, since the electric charge of the fine particles which are projected from the central portion is high, their projected velocity becomes high. v a j A vibrator having a construction'which differs from those of the vibrators of FIG. 2-and FIG. 3 is shown in FIG.,4. In this vibrator, by interposing a coupling element in the form of ahorn 18 between the vibrating element or transducerf7 andthe vibrating paint-projectingplate 5, the excitation of theultrasonic-wavevibrating element ortransducer 17 generated by the ultrasonic-wave generator. 8 is propagated with even greater effectiveness to the vibrating plate 5'." I a v Although this invention'has been described with respect to a particular embodiment and a few modification thereof,'it is not to be so limited as further changes and modifications may be made therein'which are within. the full intended scope of the invention, as defined by the appended Claim-g, 1 What is claimed is:. I, V I v An ultrasonic-wave spray painting apparatus comprising in combination'an ultrasonic-wave generator, an interrupting device for. periodically interrupting; the output 'of said generator, 'a sweeping dvice for continuously varying the oscillation frequency ofsaid generator 'witha relatively smallreduction infoutput, a transducer connected to the output of said ,generator, a horn-shaped coupling element fixed at one end to said transducer, a thin metal acoustic matching element fixed to the opposite end of said coupling element, a paint projecting plate fixed on one side surface to said matching element, means providing a continuous flow of paint in film form over the surface of said plate opposite said matching element and a high voltage direct current power source connected to said plate for providing an auxiliary electrostatic field between said plate and an article to be painted, whereby upon operation of said generator to energize said trans ducer said plate will vibrate at a varying frequency corresponding to the output frequency of said generator to project paint from said plate in the form of a spray to an article to be painted.

ICHARD References Cited by the Examiner UNITED STATESPATENTS FOREIGN PATENTS 8/59 France.

D. NEVIUS, Primary Examiner.

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