Patent Publication Number: US-7717984-B1

Title: Electrostatic precipitator unit

Description:
FIELD OF INVENTION 
   This invention relates to electrostatic precipitator units which are electrically constructed so as to minimize, if not eliminate, shortening to ground by liquid pathways. 
   BACKGROUND OF THE INVENTION 
   Electrostatic precipitator devices are used with machine tools for removing and collecting liquid coolant and particles generated during operation of the machine tool. The electrostatic precipitator may be mounted on the machine tool and coolant and particles are entrained in a stream of air drawn through the electrostatic cell plates where the drops of coolant and particles accumulate and drain downwardly. The electrostatic precipitator device may also be mounted on the floor, ceiling, wall, etc. and ducted to the machine tool. 
   In conventional electrostatic precipitators the electric contacts to the cell plates or fins and cell ionizer are mounted on dielectric elements to insulate the conductive portion of the contact to ground. However, these contacts are susceptible to tracking by conductive fluid (coolant) to ground. This produces shorting and damage to the cell and loss of performance. 
   The power and ground fins of the cell are arranged vertically in alternating fashion and the air entrained ionized fluid and particles collect on the ground fins and flow downwardly by action of gravity. As the drops accumulate on the lower edge portions of the ground fins, the coolant drops may grow or agglomerate sufficiently to extend across and engage the adjacent power fins before dropping from the ground plate. This also produces shorting and damage to the cell and loss of performance. 
   The present invention is directed to improvement of the electrostatic precipitator unit for eliminating these problems. 
   SUMMARY OF THE INVENTION 
   An object of this invention is to provide an electrical contact assembly for supplying current to the ionizer and collector fins of an electrostatic precipitator cell for an electrostatic precipitator unit which is insulated from any ground portions of the unit by an air gap thereby minimizing, if not eliminating, shorting to ground by liquid tracking. 
   Another object of this invention is to provide shortened power fins having their lower edges spaced above the lower edges of adjacent ground fins to avoid globules of coolant at the bottom of the ground fins contacting adjacent power fins. 
   The electrostatic precipitator unit includes a cabinet containing an electrostatic precipitator cell or cells. The unit is designed to be positioned upon or adjacent a conventional machine tool and communicates with the cutting chamber of the machine tool. When the unit is mounted on the wall, ceiling, etc. adjacent a machine tool, it will be connected to the tool via ducting. A stream of air entrained coolant and particles flows upwardly through the precipitator unit. Ionized coolant and particles collect on the ground plates or fins of the cell. An electrical contact assembly providing high voltage (about up to 4,700 volts DC) current to the collector cell is mounted within the cabinet but isolated from ground by nylon sleeves which provide an electrically insulating air gap which, in effect, eliminates the occurrence of unwanted liquid tracking pathways to ground. One contact of the electrical contact assembly contacts the ionizer bar of the ionizer grid and supplies high voltage (about up to 9,600 volts DC) current thereto. Another contact of the electrical contact assembly contacts the power fins. The power fins have shortened lower edge to prevent tracking across from the adjacent ground fin by agglomerating liquid coolant droplets. 

   
     BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
       FIG. 1  is a perspective view of the novel electrostatic precipitator unit mounted on a machine tool; 
       FIG. 2  is a perspective view of a an electrostatic precipitator unit with the access door opened and a an electrostatic precipitator cell withdrawn from the cabinet; 
       FIG. 3  is a fragmentary, exploded perspective view of a portion of the electrostatic precipitator unit illustrating the novel electrical contact assembly; 
       FIG. 4  is a cross-sectional view taken approximately along line  4 - 4  of  FIG. 3  and looking in the direction of the arrows; 
       FIG. 5  is a cross-sectional view taken approximately along line  5 - 5  of  FIG. 4  of the electrical contact assembly illustrating the manner in which the contact members of the contact assembly engage electrical contact elements on the precipitator cell; 
       FIG. 6  is a fragmentary top plan view, partly in section, of the electrical contact member of the electrical contact assembly engaging the contact element for the ionizer grid; 
       FIG. 7  is a fragmentary perspective view of the bus bar and phosphor-bronze strip engaging the ionizer wires of the ionizer grid; 
       FIG. 8  is a diagrammatic view of a precipitator cell illustrating the collector fins in a conventional commercial cell or prior art cell; and 
       FIG. 9  is a diagrammatic view of the precipitator cell of the present invention also depicting the collector fins. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The novel and improved electrostatic precipitator unit, designated generally by the reference numeral  10 , is shown mounted on a machine tool  11 . The machine tool  11  may be an automatic screw machine, lathe, metal turning machine or similar type machine tool. The operation of the machine tools are controlled by computer programs in a manner well-known in the industry. 
   During operation of the machine tool, liquid coolant is sprayed on the work piece in the work area  13  in the chamber  12 . Access to the chamber  12  is by way of an access door  14 . The electrostatic precipitator unit  10  serves to remove liquid coolant and particles generated during operation of the machine tool  11 . 
   The electrostatic precipitator unit  10  includes a generally rectangular shaped (parallelopiped) cabinet  15  having opposed side walls  16 , a top wall  17 , a front wall  19  and a rear wall (not shown). The top wall  17  includes a grill  18  to permit air to flow out of the chamber  23  of the cabinet. The bottom wall (not shown) of the cabinet is provided with an inlet opening through which the stream of air-entrained liquid coolant and particles pass. An evacuation impeller or fan  22   a  is mounted in the top portion of the cabinet chamber  23  adjacent the grill  18  and produces an upwardly flowing air stream for entraining the liquid coolant and particles therein as best seen in  FIG. 2 . Mechanical mist impingers  83  are positioned in the lower portion of the cabinet chamber  23  below the ionizer grid as a first stage for removing substantial quantities of the coolant and particles. In the embodiment shown, the mist impingers  83  have thickness dimension of several inches. 
   In the embodiment shown, a single electrostatic precipitator cell  24  is the collector for the coolant and particles, but larger units will use more than one cell. The cell  24  includes a frame comprised of a front wall or plate  25  and a rear wall  26  interconnected by upper side rails  27  and lower side rails  28 . The cell is provided with a plurality of identical, vertically disposed ground fins or plates  29  and a plurality of identically disposed power plates or fins  30  as best seen in  FIGS. 3 and 7 . The power fins and ground fins are arranged in alternate fashion. 
   Referring again to  FIG. 2 , it is pointed out that a plurality of rods  33  extend through openings in the front and rear plates of the cell and are supported by rivets and bump offsets  34  in the front and rear walls  25 ,  26  of the cell. The rods  33  are connected to ground and pass through openings in the ground fins  29  to provide support for the ground fins. The cell  24  is also provided with a plurality of rods  35  extending through the front and rear plates of the cell and through openings in the power fins  30 . The rods  35  are supported in ceramic insulators  36  and provide support to the power fins. 
   The electrostatic precipitator cell  24  is also provided an ionizer grid  31  which is positioned below the ground fins and power fins and includes a plurality of ionizer wires  32 . The ionizer grid  31  is diagrammatically shown in  FIG. 9 . The cell  24  is supported on rails  37  secured in the cabinet chamber  23  to enable the cell to be readily removed from the cabinet. A control knob  38  controls certain electrical circuitry of the unit and an indicator light informs an operator that high voltage power supply is energized and implies the electronic cell is properly functioning. If the indicator light goes out or blinks, this signals an operator that the cell has a short circuit or similar failure requiring service. A post filter  83   a  is positioned above the cell plates or fins and entraps droplets and particles that might remain to assure clean air entering the room. 
   The foregoing description is of a typical electrostatic precipitator cell. One major problem with commercial electrostatic precipitators is the tracking of conductive fluids from the electrical contacts to ground. Typically, dielectric material is used to mount and insulate the conductive portion of the contact from ground. 
   Referring now to  FIGS. 3 and 4 , it will be seen that one embodiment of the novel electrical power contact assembly  40  is there shown. The contact assembly  40  includes a rectangular support member  41  formed of a dielectric material such as fiberglass reinforced thermoset polyester resin or phenolic resin. The support member  41  has a pair of vertically spaced apart rectangular openings  43  in one side portion thereof. Each opening accommodates a portion of an electric contact member  44 . 
   Each contact member  44 , which is formed of a spring like conductive material (preferably stainless steel), includes flat, elongate mounting strips  45  which are secured to the support member by fastening elements  46  such as the rivets shown. Each contact member  44  includes a central element  47  spaced from the mounting strips  45  and including a generally v-shaped contact portion  48  projecting through an opening  42 . Each contact member  44  has a pair of male socket elements  49  each of which is bent at right angles to and integral with a mounted strip  45 . One male socket element  49  of each contact member  44  is engaged by a female socket element  50  that is connected to a source of high voltage electrical current. Although the voltage to the contact member may vary, depending on the application, the voltage may be of the order of up to 4,700 volts. 
   The contact assembly  40  also includes an identical electric contact member  51  positioned on the other side portion of the support member  41  adjacent the opening  43 . The contact member  51  includes a pair of mounting strips  52 , secured by rivets or fastening elements  53  to the support member. A central element  54  having a v-shaped contact portion  55  projects through the opening  43 . The mounting strips  52  are also provided with male socket elements  56  which are engaged by a female socket element  50   a  connected to a source of high voltage current. In some applications, the voltage may be as high as 9,600 volts. 
   The electrical contact assembly  40  is mounted on the inner side wall  57  spaced inwardly from the adjacent outer side wall  16  of the cabinet  15 . In the embodiment shown, the contact assembly  40  is secured to the inner side wall  57  by nut and bolt assemblies  58 . Dielectric plastic standoff sleeves (preferably nylon)  59  surrounds the bolts of the nut and bolt assembly and serves to space the contact assembly from the inner wall  57 . The air gap  59   a  defined between the contact assembly and inner side wall  57  isolates the contact assembly to ground. It will be noted that the inner wall  57  has a rectangular shaped opening  60  therein which is only slightly smaller than the mounting member  41  of the contact assembly. This opening  60  spaces the electrical contact members from any surface or edge of the inner wall  57 . The air gap  59   a , dielectric stand off elements  59 , and opening  60  substantially eliminates tracking to ground by liquid. The support member  41  also has a vertical opening  41   a  in the mid portion thereof which extends between the contact member  51  and the contact members  44 . The opening or slot  41   a  has a width dimension large enough to prevent high voltage sparking from the contact member  51  to the contact members  44 . 
   Referring again to  FIG. 3 , it will be seen that a rectangular shaped contact element  61  is mounted on a rectangular shaped mounting element  62  which is formed of a dielectric material. The mounting element  62  is secured to the adjacent side rails  27 ,  28  of the precipitator cell by rivets  63  or other suitable fastening means. When the precipitator cell is moved into the cabinet, it will be seen ( FIGS. 3 and 4 ) that the v-shaped contact portions  48  of the contact elements  44  will engage the contact member  61 . The springy characteristic of the v-shaped portions assures good contact with the contact element  61 . Referring now to  FIG. 5 , it will be seen that the contact element  61  is provided with an inner conductive strip  65  having a bent portion  66  which projects through an opening  67  in the mounting element  62 . A rivet  63  secures the contact element  61  and its associated conductive strip  65  to the mounting element  62 . The contact elements  61  and  65  may be formed of any yieldable conductive material, preferably phosphor bronze material. The bent portion therefore has a spring-like characteristic to assure effective contact with a plurality of the power fins  30 . It will also be noted that the top rail  27  of the precipitator cell  24  has a plurality of slots  27   a  therein in which the power fins and ground fins project to assure proper positioning and spacing of the fins. 
   The contact elements  44  when connected to a source of electrical current supply current to the power fins  30 . A rectangular shaped electrical contact element  68  having inturned flanges  69  is provided and is secured to an elongate channel shaped bus bar  70  by nut and bolt assemblies  71 . The nut and bolt assemblies are provided with conductive standoffs or spacer  72  ( FIG. 6 ) which position the contact member  68  such that its outer surface is disposed in the same plane as the outer surface of the contact member  61 . It will be seen that when the precipitator cell  24  is slid into the cabinet, the contact elements  61  and  68  will be engaged by the v-shaped portion contact of elements  44  and  51 . The curved surfaces defined by the inturned flanges  69  assures smooth interaction of the v-shaped portion  55  with the contact element  68  during the insertion of the cell into the cabinet. It is pointed out that the vertical spacing between the contact members  44  enables the v-shaped portions  48  to avoid engagement with the contact  68 . The contact members  48  and  55  simultaneously engage the contact elements  61  and  68  respectively. 
   Referring now to  FIGS. 6 and 7 , it will be seen that the bus bar  70  includes a web portion  73   a  integral with flanges  73 . Both ends of the bus bar are positioned within and supported by ceramic cups  74  having small extensions  75  which projects through openings  25   a  in the front and rear walls of the precipitator cell frame. 
   Referring again to  FIGS. 6 and 7 , it will be seen that an elongate conductive strip  77  is mounted against the web  73   a  of the bus bar  70  and extends substantially throughout the length of the bus bar. The strip  77  is also flexible. The conductive strip  77  has a plurality of spaced apart fingers  78  extending downwardly therefrom through openings  81  in the lower flange  73  of the bus bar  70 . The fingers  78  include angularly extending terminal portions  79  each having a hook  80  formed at its lower end. The strip  77  also has upwardly projecting fingers  78   a  integral therewith which engage the web and upper flange with frictional engagement. 
   Each ionizer wire  32  is provided with a loop  82  at its end for engaging a hook  80  of a finger  78 . When electrical current is transmitted through the contact element  51  of the contact assembly, this current will be transmitted to ionizer wires. It is pointed out that a much higher voltage is transmitted to the ionizer grid than the power fins. 
   During operation of the electrical precipitator unit, air entrained coolant and particles will be moved through the inlet opening in the unit and machine tool and a substantial amount of coolant and particles will be removed when passing through the mist impingers  83 . Air entrained coolant and particles will then pass upwardly through the ionizer grid and will be ionized and become charged. These charge carrying coolant and metal particles will collect and agglomerate on the ground plates ( FIG. 9 ) and flow downwardly by action of gravity and drip from the ground plates. The ionized particles will be driven towards the ground fins by the charged fins. High voltage up to about 4,700 volts DC is required for the charged fins to repel the ionized particles against the adjacent ground fins. The high voltage required to ionize the particles passing the ionizer wires is up to 9,600 volts DC. Referring to  FIG. 9  it will be seen that while drops agglomerate on the lower edge portions of the ground plates, the enlarged drops will not be able to extend across to the adjacent power fin. Therefore, this attendant problem of shorting to ground is minimized if not avoided altogether. 
   The ionized charged particles are moved by the electromagnetic force generated by the charged fins towards the ground fins where particles (liquid, metallic, etc.) collect. In commercial prior art units ( FIG. 8 ), the charged fins extend below the ground fins. The purpose of this design was to start the ionized particles moving towards the ground plates of the collector as the particles moved upwardly from the ionizer. However, this arrangement created the problem of the globules extending across and contacting the charged fins. 
   In the embodiment shown, electrical contact members for supplying current to both the ionizer grid and the power fins of the precipitator cell are components of the same assembly. This is the preferred embodiment even though separate assemblies for the ionizer grid and the power fins can be provided. The dielectric standoffs, the isolating air gap and the enlarged opening  60  in the inner wall are of crucial importance in minimizing tracking to ground by liquid. The electrical contact members  44  are electrically insulated from the electrical contact member  51  for the ionizer grid. The slot  41   a  in support member  41  minimizes, if not eliminates, the tendency of a high voltage spark jumping across to the contact member  44  when the support member becomes moist. 
   It is pointed out that in the embodiment shown a unit having a single precipitator cell is disclosed, larger units having several electrostatic precipitator cells are also subject to the same problem of shorting to ground by liquid tracking. Therefore, each cell in a multi cell unit will be provided with its electrical contact assembly having standoffs to provide the important isolating air gaps. 
   It will be seen that by providing the precipitator cells with shorter power fins relative to the collector ground fins and by providing air gap defining standoffs for the electrical contact assembly, applicant has provided a precipitator cell(s) which substantially avoids tracking to ground by liquids.