Patent Publication Number: US-3877897-A

Title: Electric particle precipitator

Description:
United States Patent Glucksman Apr. 15, 1975 [54] ELECTRIC PARTICLE PRECIPITATOR 3,483,672 12/1969 Jahnke 317/4 X Inventor: Dov Z. Glucksman, Newton, Mass. FOREIGN PATENTS OR APPLICATIONS Assignee; Appliance Development 987,220 3/1965 Ul&#39;llllCd Kingdom 55/154 Corporation, Boston, Mass. [22] Filed: Dec. 5 1972 Primary ExaminerDennis E. Talbert, Jr.  
 [21] Appl. No.: 312,392 ABSTRACT An electric particle precipitator includes a stack of ro- [52] US. Cl. 55/111, 5555//l11449,&#39;5555//l14555, tatable plates wherein metal plates alternate with plates of an electric insulating material having conduc- [51] Int. Cl. B03c 3/10 five overlays Intense electrostatic fields are estab [58] Field of Search 55/13, 14, 108, 109, 110, h d b h 1 55M H3 114 115 116 121 149 142 s e etween t e meta plates and the aforementioned conductive overlays. juxtaposed surfaces of the 156 metal plates and of the conductive overlays are scrubbed by fixed brushes or fixed brushlike devices, thus [56] References Cited precluding undue accumulation of particles and elimi- UNITED STATES PATENTS nating the chore of manual cleaning. The surfaces of 2,333,431 1 H1943 Lincoln 55/114 the plates in the process of being cleaned are automat- 2,63 l Dohrer l4 grounded 2,715,944 8/1955 Dohrer 55/111 2,776,724 1/1957 Goldschmied 55/149 X 15 Claims, 11 Drawing Figures ELECTRIC PARTICLE PRECIPITATOR BACKGROUND OF THE INVENTION Conventional electrostatic particle precipitators are still subject to many limitations and drawbacks. These include generation of gases detrimental to the health of human beings, such as ozone and compounds of nitrogene. the need to provide additional ionizing means for ionizing the streams of air or other gases from which particulate matter is to be removed, the danger of electric leakage or breakdown due to the presence of high field concentrations, the need of frequently cleaning the particle-collecting electrodes, and many more.  
  The principal object of this invention is to provide an electrostatic particle precipitator which is compact, can be manufactured at relatively low cost. and is not subject to any of the aforementioned limitations and drawbacks.  
 SUMMARY OF THE INVENTION An electric particle precipitator embodying this invention includes a stack formed by electrically charged spaced plates establishing electrostatic fields between juxtaposed surfaces thereof. Some of the constituent plates of the stack consist substantially of an electric insulating material having discrete areas provided with electrically conductive overlays thereon and being separated from each other by nonconductive surface elements. An electric particle precipitator embodying this invention further includes a frame structure supporting the aforementioned stack, and motor means for moving the stack relative to the frame structure. Fixed brush means engage discrete portions of the constituent plates of the stack to remove particulate matter collected on the surfaces thereof. A switching device removes any significant difference of potential between surfaces of the constituent plates of said stack being acted upon by said brush means.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic representation of a precipitator embodying the present invention;  
  FIG. 2 is a diagram of the circuitry of a precipitator according to FIG. 1;  
  FIG. 3 is an equivalent representation of the circuitry of FIG. 2;  
  FIG. 4 is a side elevation of the precipitator proper of the assembly shown in FIG. 1;  
  FIG. 5 is an end view of the structure of FIG. 4 seen in the direction of the arrow R of FIG. 4;  
 FIG. 6 is a section along 66 of FIG. 4;  
 FIG. 7 is a section along 7-7 of FIG. 4;  
  FIG. 8 is a section along 88 showing several of the constituent plates of the stack of plates according to FIG. 4 and is drawn on a much larger scale than FIGS. 4 and 6;  
  FIG. 9 is a front elevation ofa switching or grounding device or commutator forming part of the structure of FIG. 4 seen in the direction of the arrow S of FIG. 4;  
  FIG. 10 is a side elevation on a larger scale than FIG. 5 of the structure shown on the right of FIG. 5 seen in the direction of the arrow T of FIG. 5; and  
  FIG. 11 is a section along 1l--1l of FIG. 7 showing the sectioned portion in considerable magnification.  
 DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. 1, numeral 1 has been applied to indicate a housing or frame structure wherein all the constituent parts of the precipitator are accommodated. Housing 1 is covered by a top plate 2 and a blower 3 operated by an electric motor 4 is arranged immediately below top plate 2. A charcoal filter 5 is arranged immediately below electromotor 4. The precipitator proper is formed by a stack of discs 6 which are rotatable and form, in effect. a battery of high voltage condensors. The particles collected on the stack of discs are transferred by brushes (not shown in FIG. 1) into a tray 7 arranged below stack 6. Air or other gases admitted through inlets 8 into housing 1 must flow through an upstream filter 9 which may be formed by urethane or an appropriate fibrous matter before reaching the percipitator stack 6. Arrows in FIG. 1 indicate the dual flow of air or gas through the structure of FIG. 1.  
  FIG. 4 shows the stack 6 of FIG. 1 in side elevation and on a larger scale than FIG. 1. The center portion of stack 6 has been deleted in FIG. 4, i.e. but diagrammatically indicated by dash-and-dot lines. The stack 6 is formed by plates or disks 10 of an electric insulating material and metal plates or metal disks 11 which alternate with plates 10. The stack 6 further includes a driving disk 12 having a friction-increasing lining 13 on both sides of its periphery. Driving disk 12 is driven by a gear motor 14 having a friction roller 15 engaging the friction increasing peripheral lining 13 of driving disk 12. This is readily apparent from FIGS. 5 and 10. As shown in FIG. 10 roller 15 has a groove 16 into which the peripheral lining 13 of driving disk 12 projects. Driving disk 12 operates a shaft 17 which is preferably square in cross-section in the area thereof where disks 10, ll, 12 are supported by it. The ends of shaft 17 are cylindrical and are supported in a pair of bearings formed by substantially planar blocks 18 and 19 of electric insulating material. e.g. a synthetic resin. Motor 14 is supported by a vertical plate 23 supported by a vertical plate 20 which, in turn, is supported by the horizontal base plate 21. One end of a helical spring 22 is affixed to plate 20 and the other end to plate 23 pivoted at 24 on plate 20. The extent of the joint pivotal motion of motor 14 and plate 23 is limited by an oblong hole 25 in plate 23. Thus helical spring 22 causes roller 15 to engage under pressure friction rim 13 of drive plate 12. Plate 12 is keyed to shaft 17 and thus causes rotation thereof when driven by motor 14. The angular velocity of plate 12 and shaft 17 is relatively small, e.g. one full revolution per hour. The metal disks 11 have square apertures 11a in the centers thereof conforming to the configuration of shaft 17 at the points where they are supported by shaft 17. As a result metal disks I1 rotate jointly with shaft 17 when the latter is being driven by motor 14. Since metal disks 11 are mounted on metal shaft 17 which is electrically insulated by means of bearing parts 18, 19 of electric insulating material, disks 11 and shaft 17 are always at the same electric potential. This may be, and preferably is, ground potential. The disks 10 of electric insulating material are covered on both sides thereof with overlays of an electri cally conductive material. These overlays are substantially in the shape of sectors of a circle, or pie-shaped, as clearly shown in FIG. 7. As shown in FIG. 7 each insulating plate 10 is provided with five sector-shaped conductive overlays 10a on one side thereof. The side of plate 10 opposite to that shown in FIG. 7 is provided with conductive overlays which are congruent with those shown and are arranged in registry with the conductive overlays shown in FIG. 7. The overlays 10a to both sides of each plate or disk 10 are conductively in terconnected and, therefore, at the same electric potential. The overlays 10a are preferably formed by layers of a sprayed-on conductive substance. Each disk 10 is provided with a plurality of transverse bores 10b of which two are located in the area of each pair of sectorshaped overlays 10a of which each is situated at opposite sides of an insulating disk 10. Bores 10b are internally coated with a conductive overlay or paint as shown in FIG. 11 on a very large scale, this being a simple and effective means of equalizing the electric potential of conductive registering overlays 10a to different sides of insulating plates 10. Each insulating plate 10 is provided with an integral insulating hub member 100 extending to both sides of the plane defined by the respective plate 10. Hub members 10c are square in cross-section and fit tightly upon shaft 17. Hence plates 10 are rotated jointly and synchronously with metal plates 11 from which they are electrically insulated. FIG. 7 shows how the hub members 10c are mounted on shaft 17. It will also be apparent from FIG. 7 that the sector-shaped electrically conductive overlays 10a on insulating plates 10 neither extend to the centers of insulating plates or disks 10, nor to the periphery thereof. As a result, each sector-shaped conductive overlay 10a is electrically insulated from all other conductive overlays la on the same insulating plate 10, except for reg istering overlays 10a on opposite sides of the particular insulating disks 10 which are conductively connected by the intermediary of bores or holes 10b and the conductive layers therein. The insulating plates 10 are mounted on shaft 17 in such a way that each pair of sector-shaped conductive overlays 10a on each insulating plate 10 is in registry with a pair of sector-shaped conductive overlays 10a on all other plates or disks 10 of insulating material which form the stack 6. Each metal plate or disk 11 is provided with circular aper tures 11b which are spaced radially outwardly from shaft 17 as shown in FIGS. 6 and 8. Apertures 11b are angularly displaced 360/5 72 degrees. The center lines of conductive overlays are angularly displaced 360/5 72 degrees. ,The registering conductive overlays l0a of all insulating plates are conductively interconnected by conductor means which project transversely through the holes or apertures 11b in metal plates 11. As a result, all registering conductive overlays 10a of all constituent insulating plates 10 of stack 6 are at the same electric potential. As shown inFIG 8, each insulating disk 10 has male disconnect contacts 10d extending from the plane defined by the respective insulating disk 10 to the left. FIG. 8 further shows that each insulating disk 10 has a female disconnect contact l0e extending from the plane defined by the respective insulating disk 10 to the right. The male disconnect contacts 10a project through apertures 11b in metal disks 11 into female disconnect contacts l0e in a contiguous insulating plate 10. The male disconnect contacts 10d are slotted as shown in FIG. 8 for increased flexibility. Male contacts 10d may be formed by metal pins, but may also be formed by insulating material as long as the latter is rendered conductive by an appropriate conductive overlay. Each of the conductive overlays 10a on each insulating plate 10 extends over one of the five projections of the respective plate carrying a pin contact 10d, and over and to the inside of one of the five projections of the respective plate forming a female disconnect contact l0e. Consequently each combination of one of the five male contacts 1 1d and of the five female contacts We of one of the five pairs of conductive sectors 10a on each plate 10 is conductively connected to corresponding parts of a contiguous plate 10.  
  The conductive connection of all registering sectors 10a of all plates 10 might also be achieved by means other than the five male disconnect contacts 10d and the five female disconnect contacts l0e forming part of each insulating disk 10, e.g. five rods (not shown) taking the place of parts 10d, l0e. The arrangement of disconnect contacts 10d, 10e best shown in FIG. 8 is, however, particularly desirable because it greatly facilitates the assembly of the constituent disks 10, ll, 10, ll etc. of stack 6, forms effective spacers between contiguous disks 10 of insulating material and greatly contributes to the dimensional stability of stack 6 seen as a subassembly.  
  FIG. 9 is a view of the part of synthetic resin forming the right shaft bearing 18 of FIG. 4. Reference character 26 has been applied in FIG. 9 to indicate the circular bore intended to receive one end of shaft 17. Part 18 is further provided with perforated lugs 18a for attaching part 18 to vertical plate 27 which, in turn, is supported by horizontal base plate 21 (see FIG. 4). The axially inner surface of part 18 is covered by metallic overlays 28 and 29. The former overlay 28 encompasses a relatively large angle and the latter overlay 29 encompasses a relatively small angle. Overlays 28, 29 are fixed contacts intended to cooperate with movable contacts as will be explained below more in detail. Contact overlays 28, 29 are preferably formed by a noble metal, e.g. gold leaf. Contact overlay 28 is provided with a terminal 28a and contact overlay 29 is provided with a terminal 29a. Terminals 28a, 29a are in-.  
 tended to be connected to the terminals of a DC highvoltage power supply. Since the two gaps between contact overlays 28, 29 are relatively narrow, and since the difference in potential between these overlays may be very large, part 18 is provided with ribs 18b coextensive with the aforementioned gaps to increase the creepage paths between contact overlays 28, 29.  
  In FIG. 4 reference character 30 has been applied to indicate diagrammatically the DC high voltage power supply connected to terminals 28a and 29a. Terminal.  
 29a is preferably permanently grounded and a high positive or negative DC voltage is impressed upon terminal 28a. Shaft 17 is maintained at the same potential as contact overlay 29, i.e. preferably permanently grounded.  
  Referring now to FIG. 4, it will be apparent that the disk 11 immediately adjacent part 18 is a metal plate perforated as shown in FIG. 6. The male contacts or pins 10d of the insulating plate 10 immediately adjacent to that metal plate project through the holes 11b provided therein and engage the axially inner surface of part 18. Those pins 10d which engage contact surface 28 impart a predetermined high voltage to all registering sectors 10a of insulating plates 10 of stack 6 which are conductively interconnected by cooperating disconnects 10d, l0e with the pins engaging contact 28. On the other hand, the pin 10d which engages contact surface 29 imparts another voltage. e.g. ground potential, to all registering sectors a of insulating plates 10 which are conductively interconnected by cooperating disconnects 10d, 10e with the pin 10a that engages contact surface 29. As a result, intense electrostatic fields are established between all plates 11 and the areas of juxtaposed sectors 10a of all plates 10 which are at a different potential. There are no electrostatic fields between plates 11 and the areas of juxtaposed sectors 10a of all plates 10 which are at the same potential as plates 11, e.g. ground potential. If all metal plates 11 are at ground potential and if surface 29 is maintained at ground potential, there will be no electrostatic field between any of plates 11 and the regions or sectors 10a of any of insulating plates 10 which are grounded by a set of serially arranged disconnect contacts 10d. l0e of which one male disconnect contact 10d engages the grounded contact surface 29.  
  Reference character 31 has been applied to indicate brushes for removing particulate matter from the surfaces of the constituent plates of stack 6. The brushes 31 are preferably formed by channel-shaped bristle supports 32 arranged back to back as shown in FIG. 10 and extending substantially radially inwardly into the gap formed by contiguous plates or disks 10, 11, 12. The bristle supports 32 support soft bristles 33 which engage all surfaces on which particulate matter may have been deposited. The lower ends of bristle supports 32 are held by a common supporting bar member 34 allowing simple simultaneous insertion or removal of all brush means or of a complete set of brushes from the particle collecting capacitor stack 6. Reference character 35 has been applied to indicate spacers extending from the periphery of plates 10, ll radially inwardly into the gaps formed between contiguous plates 10, 11. These spacers are made of soft electric insulating material and are supported on horizontal base plate 21 in a similar fashion as brushes 31. The principal difference between brushes 31 and spacers 35 resides in the fact that the former are, and that the latter are not. in physical engagement with the particle collecting surfaces of disks 10 and 11. In FIG. 10 the spacers 35 have been deleted to give full visibility to brushes 31.  
  It will be noted from FIG. 4 that the male and female disconnect switch means 10d, l0e form columns (five columns) extending transversely across the stack formed by plates or discs 10., 11. At the left side of column 6 (as seen in FIG. 4) the male disconnect contacts or pins 10d project beyond the stack 6 into engagement with contact surfaces 28, 29 (FIG. 9). The female contact extensions We of insulating plate 10 immediately adjacent drive plate 12 have been cut away or reduced in height since there is no need of conductively connecting the conductive sectors 10a of that plate with drive plate 12. FIG. 4 shows clearly in the right portion thereof the aforementioned way of deleting or shortening the female disconnect extensions in the gap formed between drive disk 12 and the immediately adjacent insulating disk 10.  
  FIG. 2 shows a preferred circuitry for the highvoltage DC power supply 30 of FIG. 4. In FIG. 2 reference character 36 has been applied to indicate a plug intended to cooperate with a conventional receptacle or outlet (not shown). The plug 36 has three prongs of which one is intended to be connected to ground and to the grounded contact 29. The step-up transformer 37 has a primary winding protected by a fuse 38 connected in series with the primary winding. The circuit of the primary winding of step-up transformer 37 is controlled by a switch 39. The motor 4 for operating the fan 3 (see also FIG. 1) is connected in parallel to the primary winding of step-up transformer 37 and controlled by a switch 40. The motor 14 for operating or rotating the stack 6 and shaft 17 is also connected in parallel to the primary winding of step-up transformer 37. One terminal of the secondary winding of step-up transformer 37 is connected to ground. The secondary circuit of step-up transformer 37 includes capacitor 41, the diodes 42 and 43, contact surface 28 described more in detail in connection with FIG. 9, resistor 44 and grounding switch 45. In FIG. 2 the five contact rods or male disconnect contacts 10d which rotate with shaft 17 and engage contact surfaces 28, 29 have also been shown in one of their possible positions. As shown in FIG. 2, four of the contact rods or male disconnect contacts 10d engage the contact surface 28 which is at an elevated voltage. and one contact rod 10d engages the contact surface 29 which is grounded. As a result. all conductive sectors 10a of insulating plates 10 conductively connected by disconnect means 10d, 10e with contact surface 28 are at an elevated voltage. and all conductive sectors 10a of insulating plates 10 conductively connected by disconnect contact means 10d, 10e with contact surface 29 as well as shaft 17 and metal plates 11 are grounded. In other words, four pairs of sectors 10a of each plate 10 are at an elevated voltage and one pair of sectors 10a of each insulating plate 10 is at ground potential. The brushes 31 for removing particles electrostatically precipitated upon plates or disks 10, 11 are arranged in such a fashion that they en gage in addition to grounded metal plates 11 sectors 10a of insulating plates 10 which are grounded at the time. To put it in another way, the configuration of switching means 28, 29 and 10d, 10e is such that the sectors 10a of the plates 10 engaged by brushes 31 are always at ground potential.  
  It will be apparent from the above that parts 18, 28 and 29 are in effect a stationary or fixed commutator and that the pins 10d sliding over the above parts are, in effect, movable or rotatable brushes.  
  The step-up transformer 37 may increase the available line voltage of volts or more to several kilovolts. The power consumption of the entire electrical system is negligible. In FIG. 3 reference character C has been applied to indicate the internal capacity of the stack 6 of plates 10, 11. The peak voltage at the ends of the secondary winding of step-up transformer 37 may be, for instance, +3 Kv and -3 Kv as indicated in FIG. 3. The capacitor 41 having a small capacity is intended as an impedance limiter for protecting the stepup transformer 37 and the diodes 42 and 43. The voltages between diodes 42 and 43 is an undulating DC voltage having peaks which may be 3 Kv. This has been diagrammatically indicated in FIG. 3. The peak voltage between the interleaving plates l0, 11 of stack 6 is about as high as that of the secondary winding of stepup transformer 37 measured between peaks.  
  When dust collected in tray 7 (FIG. 1) is emptied switch 45 is automatically closed and discharges the sectors 10a of plates 10 through resistor 44. In other words, switch 45 is a safety means for protecting personnel maintaining the particular precipitator.  
  In the particular embodiment of the invention shown and described above means for ionizing the air or gas to be departicularized are dispensed with. This&#39;greatly contributes to the simplicity and compactness of the device and tends to eliminate the generation of ozone. It has been found that particulate matter contained in the surrounding atmosphere is generally more or less ionized so called Langevin ions or formed by dipoles to allow electrostatic precipitation without additional ionization means such as, for instance, electric high voltage gas discharges.  
  The precipitator which has been described above is particularly intended for household applications, i.e. as an appliance. It may, however, readily be adapted for other and in particular industrial applications. Such an adaptation may include the addition of a pre-ionizing device. e.g. a high-voltage gas discharge means for increasing the ionization of air or other gases preparatory to their processing in precipitation stack 6.  
  As a general rule plates 10 may be made of any suitable thermoplastic or thermosetting resin. In instances where it is desired to remove particles from hot gases, e.g. hot fumes, the plates 10 ought to be made ofa heat resistant electric insulating material such as, for instance, a ceramic material.  
  Other brush means or particle removing means may take the place of brushes including bristles. Plastic wipers. jets of fluid or vacuum brush means may also be used to remove particulate matter from plates 10 and 11.  
  The time during which an electrically charged particle is subjected to an electrostatic field in a particle precipitator is referred to as the dwell time. The structure embodying this invention involves relatively long dwell times on account of the relative large size which may be imparted to disks l and 11, and the relatively large cross-sectional area of a flow of air or gas through the gaps formed between plates and 11. The long dwell time of particles in the high electrostatic field formed between charged plates or disks 10 and 11 is a crucial factor which makes it possible to dispense in many cases with pre-ionization means for pre-ionizing the air or gas from which particulate matter is to be removed.  
  The number of five sectors 10a has been found to be desirable for home appliance type particle precipitators. This number may be increased or decreased depending upon the particular circumstances of any other application, or applications.  
  The electrostatic fields between electrically conductive sectors 10a of insulating plates 10 and metal plates 11 has a high degree of homogeneity, i.e. there are no regions of excessive field concentration therein. This minimizes the danger of formation of ozone by low current electric gas discharges and of total breakdown at points of high field concentration resulting in destructive high current arc discharges.  
  The invention is not limited to two voltage levels, i.e. ground potential for the metal plates 11 and a potential different from ground potential for the sectors 10a on insulating plates 10. As an alternative the sequence of potential may be positive, negative, positive, etc. One pair of sectors 10a in the process of being cleaned from adhering particles would still be grounded in that particular instance.  
  The bristles 33 of brushes 31 may be made of wool and silicone coated.  
  In tests conducted with an air cleaner of the aforedescribed character particles as small as 0.1 micron were removed from the air stream and up to 99 percent of pollen, dust and fungus spores were eliminated from it. The urethane filter 9 of FIG. 1 is intended to eliminate relatively coarse particles such as strips of lint, hair and ashes. The charcoal filter 5 of FIG. 1 is intended to absorb undesirable gases and vapors and to eliminate undesirable odors. A unit of the kind illustrated and described has a power consumption of but 60 watt. Using a National Bureau of Standards dust elimination test method, the air cleaner shown has an efficiency rating of 93 percent at cu. ft./min. air flow.  
  Another important feature of the structure shown resides in the fact that the plates 10 and 11 are cleaned in relatively short intervals of time or semicontinuously. In electrostatic air cleaners the build-up of particulate matter on the electrode decreases the efficiency of particle precipitation, tends to cause electrical leakage or even breakdown, and the generation of ozone by electric gas discharges between the electrodes. It is apparent from the foregoing that all these limitations are nonexistent in air cleaners embodying the present invention because of their automatic platecleaning means.  
  A slight modification of the particles precipitator illustrated and described lends itself to application in central air conditioning systems.  
  The ends of male contacts 10d intended to establish electrical contact with surfaces 28, 29 (FIG. 9) are preferably not in direct or physical contact with these surfaces. As shown in FIG. 8, springbiased metal caps 10d are mounted on male contacts 10d immediately adjacent fixed contact surfaces 28, 29, and these caps 10d rather than male contacts 10d physically engage contacts 28, 29.  
  Parts 31 and 35, in addition to forming spacers between plates 10, 11 and brushes for removing particulate matter from the plates 10, 11 have the important function of forming baffles for preventing the flow of gas established by fan 3 (see FIG. 1) from obtaining access to a predetermined zone extending along the stack formed by plates 10, 11 which zone extends along the entire stack in a direction of the shaft 17 thereof. The quiescent flow zone formed by parts 31 and 35 is readily apparent from FIGS. 1 and 5 where the direction of gas flow has been indicated by appropriate arrows. There is no air or other gas flow inside the space substantially V-shaped in cross-section bounded by parts 31 and 35. As shown in FIG. 1 housing 1 is provided with baffles la tending to control the flow of air or other gas through housing 1 as indicated by the ar-.  
 rows in FIGS. 1 and 5. It will be apparent from FIG. 1 that the receptacle or container 7 for collecting particulate matter removed from plates 10, 11 is arranged between baffle means 31, 35 and at a lower level than baffie means 31, 35.  
  The. switching means formed by fixed contacts 28, 29 and spring-biased metal caps 10d operate in such a way that the electrostatic field normally prevailing between surfaces of plates 10, 11 is removed from the surfaces thereof while in the process of rotating through the plate cleaning zone bounded by baffles 31, 35 and receptacle 7.  
  The corrugations 18b (FIG. 9) on insulating plate 18, in addition to increasing the creepage path between contact surfaces 28 and 29, serve the function of precluding a smear of conductive particles across the gaps formed between contact surfaces 28 and 29.  
  if desired insulating plates 10 could be provided with shallow substantially sector-shaped recesses for receiving conductive overlays which would then also be conductive inlays. Plates 11 are preferably of metal but might be formed by plates of insulating material having conductive surfaces. e.g. metallized surfaces.  
 I claim as my invention:  
 1. An electric particle precipitator including a. a stack formed by electrically charged spaced plates establishing electrostatic fields between juxtaposed surfaces thereof, some of the constituent plates of said stack consisting substantially of an electric insulating material having discrete areas provided with electrically conductive overlays thereon and being separated from each other by non-conductive surface elements;  
 b. a frame structure supporting said stack and motor means moving said stack relative to said frame structure;  
 c. fixed brush means engaging discrete portions of the constituent plates of said stack to remove particulate matter collected on the surfaces thereof; and  
 d. a switching device for removing any significant difference of potential between surfaces of the constituent plates of said stack being acted upon by said brush means.  
  2. An electric particle precipitator as specified in claim 1 including a blower for producing currents of gas through the gaps formed between the constituent plates of said stack wherein means for ionizing said currents of gas are dispensed with.  
  3. An electric particle precipitator as specified in claim 1 wherein a. said stack is arranged inside of a housing;  
 b. a motor-driven blower is provided inside said housing at a level thereof above said stack adapted to establish upwardly directed currents of gas through the gaps formed between the constituent plates of said stack;  
 c. said housing has gas-intake-openings arranged at a lower level than said stack and a first filter is interposed between said gas-intake openings and said stack; and  
 d. a second filter is interposed between said stack and said motor-driven blower.  
 4. An electric particle precipitator as specified in claim 1 wherein a. said stack is formed by substantially disk-shaped plates of metal alternating with substantially diskshaped plates of an electric insulating material, each of said plates of an electric insulating material having on both sides thereof substantially sectorshaped overlays having a smaller diameter than said plates of an electric insulating material and being electrically isolated from each other by substantially radially extending non-conductive surface elements, said sector-shaped overlays of the constituent plates of an electric insulating material of said stack being arranged in registry;  
 b. wherein said motor means are adapted to rotate said stack around the axis thereof; and  
 0. wherein said fixed brush means extend substantially radially in the direction from the periphery of the constituent plates of said stack to the axis thereof and engage juxtaposed surfaces of said plates of metal and of said plates of an electric insulating material.  
  5. An electric particle precipitator as specified in claim 4 wherein said plates of an electric insulating material are of a ceramic nature.  
  6. An electric particle precipitator as specified in claim 4 including a substantially disk-shaped plate having a friction-increasing means around the periphery thereof being frictionally engaged by drive wheel means operated by an electric gear motor to rotate said stack.  
  7. An electric particle precipitator as specified in claim 4 wherein said plates of metal are mounted on a rotatable metal shaft equalizing the electric potential between the constituent plates of metal of said stack, each of said plates of metal having a plurality of angularly displaced perforations arranged radially outwardly from said metal shaft, and wherein said sectorshaped overlays of each of said plates of an electric insulating material is provided with a connector means projecting through one of said perforations in said plates of metal of said stack to equalize the potential of overlays being arranged in registry.  
  8. An electric particle precipitator as specified in claim 7 wherein said metal shaft has a non-circular cross-sectional area, wherein the constituent plates of metal of said stack have a shaft-receiving aperture in the center thereof conforming to the shape and size of the cross-sectional area of said metal shaft, and wherein each of said plates of an electric insulating material is provided with an insulating hub-section in the center thereof extending in a direction longitudinally of said metal shaft and having a shaft-receiving aperture conforming to the shape and size of the cross-sectional area of said metal shaft.  
  9. An electric particle precipitator as specified in claim 7 wherein said connector means of each of said sector-shaped overlays are formed by a disconnect switch which includes a male portion and a female portion.  
  10. An electric particle precipitator as specified in claim 7 wherein said connector means extend axially outwardly beyond said stack toward a fixed switching device, said switching device having a plurality of substantially planar contact surfaces electrically isolated from each other, maintained at substantially different electric potentials and adapted to be engaged by ends of said connector means extending beyond said stack.  
  11. An electric particle precipitator as specified in claim 10 wherein said switching device includes a substantially plate-shaped member of electric insulating material having an aperture forming a bearing for the shaft supporting the constituent plates of said stack and having contact surfaces formed by overlays of a noble metal in leaf form.  
 12. An electric particle precipitator including a..a stack formed by electrically charged plates establishing electrostatic fields between juxtaposed surfaces thereof, some of the constituent plates of said stack consisting substantially of an electric insulating material having discrete electrically conductive areas thereon separated from each other by nonconductive surface elements;  
 b. a shaft supporting said stack and electric motor means for rotating said stack about said shaft;  
 c. means for establishing a flow of gas through the gaps formed between said plates of said stack;  
  12 plates alternating with said plates of electric insulating material.  
  14. An electric particle precipitator as specified in claim 12 wherein said baffle means extend substantially radially from the outer periphery of said stack to said shaft.  
  15. An electric particle precipitator as specified in claim 14 wherein a receptacle for particles removed from said stack of plates is arranged between said baffle means and at a lower level than said baffle means.