Electrodynamic Apparatus For Controlling Flow Of Particulate Material

Abstract

Flow of particulate material along a defined path is controlled electrodynamically by means of elongated electrodes curved concentrically to the path, as axially spaced rings or interwound spirals. Each electrode is axially spaced from its neighbors by a distance about equal to its diameter and is connected with one terminal of a multi-phase alternating high voltage source. Adjacent electrodes along the path are connected with different terminals in a regular sequence, producing a wave-like non-uniform electric field that repels electrically charged particles axially inwardly and tends to propel them along the path.

Parent Case Text

This application is a continuation-in-part of each of the applicant's copending applications Ser. No. 366,655, filed June 4, 1973 as a continuation of Ser. No. 151,789, filed June 10, 1971; and Ser. No. 237,822, filed Mar. 24, 1972 now Pat. No. 3806763; and inasmuch as the present application contains only subject matter disclosed in those applications, this application constitutes a consolidation of portions of those applications. There is being filed in connection with this application a terminal disclaimer which effects expiration of the patent issuing hereon concurrently with expiration of the patent issuing on applicant's copending allowed application, Ser. No. 226,750, filed Feb. 16, 1972 now Pat. No. 3,778678.

Description

This invention relates to apparatus for controlling the movement of particulate material along a defined path while confining the material to a zone near the centerline of that path; and the invention is more particularly concerned with apparatus whereby such control of the movement of powder-like material is effected substantially without permitting contact between the material and a solid surface and while the material is maintained in a loose and uncompacted state, that is, with its particles not adhering or cohering to one another.

The general object of the present invention is to provide apparatus by which powder-like particulate material can either be transported along a defined elongated path or stopped or otherwise controlled in its movement along such a path, at the same time that such material is confined to a zone near the centerline of the path and against lateral dispersion into contact with surface areas of solid material which are substantially concentric with that centerline.

Thus one of the specific objects of the invention, achieved in certain embodiments of it, is to provide means for causing coloring powder or other particulate material to move along a substantially horizontally disposed tube at a controlled rate, from a source of the material near one end of the tube to a destination zone or point of application near the other end of the tube, with the material uncompacted and loose in the tube and more or less levitated to be substantially out of contact with the tube surfaces.

Another specific object of the invention, realized in other embodiments thereof, is to provide apparatus by which a stream of particulate material, dropping from a source thereof under the influence of gravity, can be caused to flow intermittently, with flow being controlledly started and stopped as desired, so that a valve-like operation can be obtained although the apparatus includes no valve element or its equivalent, and with the material being at all times more or less levitated in a loose, cloud-like condition so that free and steady flow of the material is obtained at times when discharge is desired.

It will be apparent that the apparatus of the present invention is useful, in general, for transporting a variety of kinds of particulate material and metering or feeding such material out of a source or supply thereof, and that the apparatus is thus generally useful for such varied purposes as powder spray painting and coating, printing and decorating various articles, classifying particles as to size, and otherwise guiding and controlling the flow of powder and particulate materials.

In general the objects of the invention are achieved with apparatus comprising elongated concentrically curved electrodes that are so connected with the terminals of a multi-phase alternating voltage source as to produce a constantly changing electric field that has a wave-like variation along the axis about which the electrodes are curved, which field tends to repel charged particles in a manner that confines them to a zone near the axis of the electrodes as well as tending to impart to them a net motion in one direction along that axis.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplifying the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate several complete examples of embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a more or less diagrammatic view, partly in longitudinal section and partly in side elevation, illustrating apparatus which embodies the present invention and which enables particulate material to be controlledly propelled along a defined generally horizontal path in a substantially steady stream;

FIG. 2 is another somewhat diagrammatic view, partly in side elevation and partly in section, illustrating a modified form of the general type of apparatus illustrated in FIG. 1, particularly intended for use in electrostatic powder coating and decorating applications; and

FIG. 3 is a generally diagrammatic illustration of another embodiment of the invention comprising apparatus by which a gravity produced flow of particulate material downwardly from a source thereof to a delivery zone can be controlled.

Referring now more particularly to the accompanying drawings, the numeral 26 designates generally a cylindrical tube of dielectric material that defines an elongated generally horizontal path along which powder-like particulate material can be caused to flow in a substantially steady stream. The tube has a partial closure 27 at its rear end that leaves an opening 50 through which the lower end portion of a supply duct 48 projects obliquely downwardly and forwardly for delivery of particulate material into the rear end portion of the tube. It will be understood that the supply duct communicates at its upper end with a source (not shown) of particulate material and that it conducts such material into the tube 26 by gravity.

Three insulated elongated electrodes 62, 63, 64 are curved along their lengths to the form of concentric spirals that surround the tube 26 and closely embrace its outer periphery. Each of the spiral electrodes extends along the full length of the tube and has a uniform axial pitch along its length. The three electrodes are spaced apart by small but uniform axial and circumferential distances, as more fully described below.

The three electrodes 62, 63, 64 are respectively connected with the terminals U, V, W of a three-phase a.c. voltage source. Attention is directed to the fact that each electrode is connected with only one of the voltage source terminals, and that the connections to the several electrodes are such that the alternating voltage applied to each of them is 120.degree. out of phase with that applied to its adjacent electrodes.

As a result of this connection of the electrodes to an a.c. voltage source, a constantly varying nonuniform electric field is generated by the several electrodes. Such a field is nonuniform and varying in the sense that its intensity varies from point to point within it at any given instant, and, at any given point within it, varies from one instant to another during the voltage cycle. As a result, a small electrically charged particle in that field is subjected to repulsive forces that set it into oscillatory motion along curved paths. As more fully explained in the applicant's above mentioned copending application Ser. No. 366,655 (continuation of Ser. No. 151,789), with proper connections of the electrodes to a multi-phase alternating voltage source, the intensity of the field thus produced changes in a wave-like fashion, so that the oscillations of a charged particle in that field will tend to be unequal, that is, the particle will always tend to move farther in one direction of its oscillation than in the other, and will thus tend to have a net motion in one direction or another transversely to the several electrodes producing the field.

The values required for satisfactory operation with charged powder particles having diameters on the order of one to 100 microns are approximately as follows:

The electrodes should be of fairly uniform diameter; their diameter should be not more than about 5 cm., and for particles of less than 30 microns the electrode diameters should be less than 1 cm.; and the spacing between adjacent electrodes should be about equal to the diameter of an electrode.

Preferably the peak voltage of the applied alternating voltage should be high, but should be just low enough to insure that no sparking or arcing takes place between electrodes. Coating the electrodes with a suitable insulation (e.g., teflon or epoxy resin) is desirable because it tends to raise the applied voltage at which arc-over occurs.

The frequency of the alternating voltage should be on the order of 10 to 120 Hz. For particles of less than 30 micron diameter the frequency is preferably below 120 Hz; for particles of less than 10 micron diameter the frequency is preferably below 60 Hz; for particles of less than three microns the frequency is preferably below 30 Hz.

It will now be apparent that powdered material that is delivered into the rear of the tube 26 from the duct 48 tends to fall down onto the inner bottom surface of the tube. But owing to the constantly changing electric field which exists there, the particles pick up an electric charge and are repulsively acted upon by the electric field in the manner explained above. Such repulsion confines the particles to a zone near the axis of the tube, owing to the fact that the particles are urged away from the spiral electrodes that surround the tube; and because the repulsively produced oscillations of the particles are unequal, as explained above, the particles also have a net motion along the axis of the tube. If the connections of the several electrodes to the several terminals of the alternating voltage source are in the correct sequence, the direction of such net motion of the particles will be forwardly, and the particulate material will move to the front end of the tube in a stream and at a controlled rate of flow that depends upon the parameters of the electrodes and the a.c. applied to them. While so moving, the stream of particulate material will be more or less levitated in being confined to a zone near the tube axis and repelled away from contact with the inner surface of the tube.

FIG. 2 illustrates apparatus generally like that shown in FIG. 1, but in a form which particularly adapts it to applying to a solid article 101 a coating of particulate material obtained from a source 120 thereof. The apparatus illustrated in FIG. 2 is thus in the nature of an electric field pump that can be utilized for electrostatic painting, coating, dyeing, pile planting and similar processes. In this case a tube 26' of electrical insulating material that defines a path along which the particulate material is to be controlledly transported can be a flexible one, and the elongated electrodes 62, 63, 64 that spiral all along the exterior surface of the tube are secured to it by a flexible insulating cover or coating that not only insulates them from one another but substantially fixes them in relation to the tube and one another while constraining them to flex with the tube. The dimensions and spacing of the electrodes are as described above.

Again, the electrodes are connectable with the terminals U, V, W of a three-phase alternating voltage source, but in this case a switch 40 that provides for such connection is so arranged that it can be thrown to an alternative closed position at which the sequence of connections of the electrodes to the terminals is the reverse of that in the illustrated switch-closed position. By reason of such alternative closed positions of the switch 40, the direction of wave-like variation of the electric field with time can be reversed, which is to say that, depending upon the position of the switch, particles can be caused to move either forwardly or rearwardly through the tube 26'.

At its rear end the tube has an upwardly curved end portion or elbow 138, and on this elbow portion are arranged electrodes 141, 142, 143 . . . that extend generally parallel to the tube axis and are spaced from one another at intervals circumferentially around the tube. These axially extending electrodes are connected, in a regular sequence around the tube, with the terminals U, V, W of the alternating voltage source, and they serve to produce a field that repels charged particles from the wall of the elbow portion of the tube, tending to confine them to a zone near the longitudinal centerline of the elbow as they move through it by gravity.

In this case it is not desired to have the particles contact the tube wall to pick up the electrical charge that they need for repulsion by the electric fields in the tube, and therefore a charge must be impressed upon them before they enter the tube. Apparatus for imparting such a charge to the particles (e.g., known corona discharge apparatus) is designated by 120. Upon leaving the charging apparatus, the particles 121 are introduced into an electric field hopper 78 of the type illustrated in FIG. 3 and described hereinafter, from which they are controlledly permitted to fall into the open upper end of the elbow 138.

As shown, the a.c. voltage source comprises step-up transformer means 29 that has the neutral side of its secondary connected with a.d.c. voltage source 102. The voltage of the d.c. voltage source is preferably adjustably variable, as denoted by the oblique arrow through the symbol for it. Since the d.c. voltage source is grounded to the workpiece 101 that is to be coated with particulate material, as well as being connected to the spiral electrodes 62, 63, 64 as just described, there is a d.c. potential difference between the workpiece 101 and the electrodes, hence also a potential difference between the workpiece and the particles; and by reason of this potential difference the particles tend to be attracted to the workpiece, across the space between it and the front end of the tube.

The hopper illustrated in FIG. 3 provides for control of the gravity flow of particulate material from a source or inlet located above the hopper to a point or zone of use below it. In this case charged particles 121 are introduced into the top of the hopper from an outlet at the bottom of an upright inlet duct 77. Near the level of the lower end of the duct 77 and concentric with it is a disc 54 of dielectric material or electric insulating material that supports a plurality of elongated electrodes 56, 57, 56' 57' 56". These electrodes are bent along their lengths to an annular shape, and they are secured to the underside of the insulating disc 54, by means of screws 55, in concentric electrodes so differ in diameter from one another that each is radially spaced from its neighbors by a distance substantially equal to its diameter. These several electrodes are so connected with two of the terminals U and W of a three phase alternating current source that each is connected with only one of said terminals, which terminal is other than the one that both of its radially adjacent electrodes are connected to. Hence there is a single-phase alternating voltage field beneath the disc 54.

As brought out in more detail in the above mentioned copending application Ser. No. 366,655, the effect of a single-phase alternating field upon charged particles is to set them into an oscillation along curved paths, which oscillation carries them substantially equal distances in both directions of their oscillatory motion so that they have no net motion as a result of the electric field itself. However, the single-phase alternating electric field does serve to repel the particles from the electrodes, forcing them downwardly out of the inlet duct 77 and into the body portion of the hopper, and preventing them from settling on the disc 54 and the several electrodes that it carries.

The hopper itself is defined by annular electrodes 59, 60, 59' . . . 60" and 65, 66, 67 . . . 74. These are generally similar to the above described annular electrodes that are secured to the disc 54, and, like them, they are concentric to the upright axis of the hopper. But the electrodes 58-60" and 65-74 are vertically spaced from one another, although, again, the vertical distance between each electrode and those adjacent to it is equal to its diameter. The several vertically spaced electrodes can be supported by means of a pair of diametrically opposite upright pillars or standards 63 of insulating material that also serve to support the disc 54. Conducting arms 61, secured in an obvious manner by screw threaded elements 62, extend through the standards 63 and provide for connection of the vertically spaced apart electrodes with the a.c. voltage source terminals.

Note that the electrodes 59-60" that define the upper portion of the hopper are of substantially equal diameters; whereas each of the electrodes 65-71 in the medical portion of the hopper has a slightly smaller diameter than the one above it; while the electrodes 71-74 that define the lowermost part of the hopper are again of uniform diameter and smaller in diameter than those above them. Thus the hopper as a whole that is defined by the several vertically space apart electrodes is more or less funnel-shaped.

The electrodes 59-60" that define the large diameter upper portion of the hopper are connected with the terminals U and W of the three-phase voltage source, each with only one terminal, which terminal is different from the one that its adjacent electrodes are connected to. Hence electrodes 59-60" repel the charged particles toward the hopper axis and tend to levitate them in the upper portion of the hopper, where they form a clould-like accumulation 79.

Since the individual particles of this accumulation 79 have like charges, they repel one another. Furthermore, the constantly changing intensity of the electric field at any point in the interior of the hopper tends to maintain the particles in a state of agitation while repelling them radially. Hence the particulate material of the accumulation 79 will neither compact into a cohesive mass nor settle on the solid surfaces of the hopper.

Of course gravity also acts upon the particles, and under its influence they tend to move downwardly in the hopper.

The electrodes 69-74 that define the lower outlet portion of the hopper are so connectable with all three terminals U, V, W of the voltage source as to provide a constantly varying potential difference between every pair of adjacent ones of those electrodes, and, as explained above, this variation in potential difference produces a wave-like moving field that tends to repel the particles either upwardly or downwardly, depending upon the sequence of connection of the several terminals with the terminals U, V, W as established by the two-position switch 40.

It will now be apparent that with the switch 40 in one of its closed positions, the moving field produced by the electrodes 69-74 propels particles downwardly out of the hopper, in effect drawing them down out of the cloud-like accumulation and causing them to be discharged in a controlled stream, at a rate dependent upon the parameters of the electrodes and the charging voltage source. A workpiece 101 located beneath the outlet of the hopper can thus be smoothly and evenly coated with the particulate material by moving it steadily in a direction transverse to the hopper axis, as indicated by the arrow to the left of the workpiece. Preferably the workpiece and the lowermost electrode 74 are respectively connected with the opposite terminals of a.d.c. voltage source that is also connected with the a.c. terminal U to which said electrode is connected, to provide for electrostatic attraction of particles to the workpiece.

To terminate discharge of particles from the bottom of the hopper, the switch 40 is thrown to its other closed position. The constantly changing field now produced by the electrodes 69-74 has a repulsive effect upon the particles that tends to impart to them a net upward motion, which is to say that said electric field overcomes the force of gravity upon the particles and confines them to the interior of the hopper, where they remain in a cloud-like accumulation as described above. The switch 40 thus provides for control of the flow of particulate material with a sort of valving action, although, as contrasted with a conventional valve, the particles are maintained out of contact with solid surfaces while they remain in the hopper and, by being kept in a state of agitation and mutual repulsion, they are substantially prevented from cohering to one another so that compaction of the material is prevented and controlled discharge can be resumed as soon as the switch 40 is thrown over to its material discharging position.

Since the principles of this invention can be applied to controlling the flow of particulate material either in supplementing or overcoming the force of gravity upon the particles, it will be obvious from a consideration of the last described embodiment of the invention that it is also possible to use apparatus according to the invention for either supplementing or overcoming the viscous force which a flowing gas imposes upon particulate material carried in it.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

Claims

1. Apparatus for controlling the movement of powder-like particulate material along an elongated path which is defined by surface areas of solid material that surround a longitudinal centerline of said path, and for confining the particulate material to a zone near said centerline and against substantial lateral dispersal therefrom into contact with said surface areas, said apparatus comprising:

A. a plurality of elongated electrodes, each curved along its length to be substantially concentric to said centerline, said electrodes being spaced from one another along said path by substantially uniform distances, and adjacent electrodes along said path being curved to radii about said centerline that differ no more than slightly; and

B. means for connecting each of the electrodes with only one of the several terminals of a polyphase alternating high voltage source, and with each of said electrodes connected to a different one of said terminals than the electrodes that are longitudinally adjacent to it along said path, so that a constantly varying electric field is produced by each pair of the electrodes that are so adjacent whereby particles are urged toward said centerline, and so that the several electrodes cooperate to produce a net electric field of wave-like character that urges the particles in one

2. The apparatus of claim 1 wherein each of the electrodes is substantially

3. The apparatus of claim 2 wherein the number of said annular electrodes is larger than the number of different terminals at said alternating voltage source, and wherein said means for connecting electrodes with said terminals provides for connection of a plurality of electrodes with each

4. The apparatus of claim 1 wherein each of said electrodes is in the form of a spiral extending a substantial distance along said path, and wherein the number of such spiral electrodes is equal to the number of different terminals at the alternating voltage source.