Abstract:
An electrically self-grounding connector for joining end portions of fluid flow conduit sections, and two processes for fabricating the connector. A connector formed according to one process includes an inner layer formed by electrically conductive, contiguous carbon ribbons, an outer layer of chopped carbon fibers, and a layer of surfacing veil between the inner and outer layers. A connector formed according to the other process substitutes a layer of carbon cloth for the carbon ribbons. In both connectors, electrically conductive carbon forming the inner and outer surfaces acts to dissipate and neutralize electrostatic charges generated by triboelectric processes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of application Ser. No. 09/882,683 filed Jun. 18, 2001 and published as Ser. No. 2002/0017333 A1, entitled “Electrostatic Charge Neutralizing Fume Duct With Continuous Carbon Fiber,” now pending. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to gas and fluid flow conduits such as ductwork, and more particularly to a self-grounding connector for joining end portions of conduit sections. The connector includes carbon fibers which dissipate and neutralize built-up electrostatic charges resulting from triboelectric processes as vapors, gases or liquids flow through a conduit.  
           [0004]    2. Description of the Related Art  
           [0005]    Published application Ser. No. 2002/0017333 A1 (“&#39;333”), which is incorporated in its entirety herein by reference, discloses a self-grounding dual-wall duct for transporting corrosive vapors and gases, and a process for fabricating such ducts and pipe. The duct has a laminated inner wall whose innermost layer incorporates continuous, helically-wound carbon filament ribbons which dissipate and neutralize built-up electrostatic charges resulting from vapor or gas flow. The &#39;333 reference further discloses a joint assembly providing high electrical conductivity, and thereby self-grounding, across the joint. The assembly includes a self-grounding collar for joining two dual-laminate duct sections. The collar has a laminate construction including two relatively thin inner layers of carbon filament ribbon impregnated with an epoxy or any other type of chemically resistant vinyl ester resin-and-curing agent admixture, and a relatively thick outer layer of glass filament ribbon impregnated with the admixture. The assembly further includes a sealant having chopped carbonized carbon fibers. The filament layers provide self-grounding of the collar inner surface, and the fibers provide self-grounding of the collar outer surface.  
           [0006]    Pat. No. 6,315,004 (“&#39;004”) to R. L. Wellman et al., which is incorporated in its entirety herein by reference, discloses a laminated inner wall of a dual-wall fume duct for transporting corrosive vapors and gases, and a process for fabricating the wall. The innermost layer of the wall is made of a cured epoxy or any other type of chemically resistant vinyl ester resin incorporating chopped carbonized carbon fibers.  
         OBJECTS OF THE INVENTION  
         [0007]    It is a primary object of the present invention to provide an improved connector impermeable to hazardous gases, vapors and fluids, and which dissipates and neutralizes electrostatic charge build-up on its inner and outer surfaces.  
           [0008]    Another object of the invention is to provide a self-grounding connector fabricated using a substantially automated production process amenable to standardization and high quality control.  
           [0009]    Yet another object of the invention is to provide a simplified production process using fewer types and lesser amounts of fabrication materials per unit connector.  
           [0010]    Other objects of the invention will become evident when the following description is considered with the accompanying drawing figures. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and description.  
         SUMMARY OF THE INVENTION  
         [0011]    These and other objects are achieved by the present invention which in a first aspect provides a self-grounding connector for joining end portions of fluid flow conduit sections. The connector includes a hollow resinous body incorporating a highly electrically conductive material which dissipates and self-grounds electrostatic charge accumulating on the inner and outer surfaces. In a first embodiment carbon fiber filaments ground the inner surface, and chopped carbon fibers ground the outer surface. In a second embodiment carbon cloth grounds the inner surface, and chopped carbon fibers ground the outer surface.  
           [0012]    In another aspect the invention provides a process for making a self-grounding connector for joining end portions of fluid flow conduit sections. The steps include: (a) covering a mandrel with a non-sticking material; (b) forming over the material a layer using a conductive material and a fluidic admixture; (c) forming over the layer a second layer using a second conductive material and the admixture; and (d) removing the formed layers from the mandrel to form the connector.  
           [0013]    In yet another aspect the invention provides a first process for making a self-grounding connector for joining end portions of fluid flow conduit sections. The process steps include: (a) forming a fluidic admixture of a settable chemically resistant resin and a curing agent; (b) coating a non-sticking sheeting covering a mandrel with a layer of the admixture; (c) helically winding around the sheeting a band formed by contiguous, continuous electrically conductive ribbons having continuous carbon filaments impregnated with the admixture, thereby forming a ribbon-layer embedded in the admixture layer; (d) coating the ribbon-layer with a second admixture layer; (e) helically winding a layer of surfacing veil wetted out with the admixture; (f) coating the veil with a third admixture layer; (g) depositing chopped carbon fibers to cover the veil; (h) integrating the fibers and admixture to form a layer of wetted out fibers terminating in a smooth outer surface; and (i) orthogonally winding a second band having at least one ribbon impregnated with the admixture, thereby forming a circumferential bead.  
           [0014]    In still another aspect the invention provides a second process for making a self-grounding connector for joining end portions of fluid flow conduit sections. The process steps include: (a) forming a fluidic admixture of a settable chemically resistant resin and a curing agent; (b) coating a non-sticking sheeting covering a mandrel with a first layer of the admixture; (c) helically winding around the sheeting a layer of carbon cloth wetted out with the admixture; (d) curing the admixture layer and wetted out cloth; (e) covering the cloth with a layer of putty; (f) helically winding into the putty a layer of surfacing veil; (g) curing the putty; (h) coating the veil with a second layer of the admixture; (i) depositing chopped carbon fibers to cover the veil; (j) integrating the fibers and admixture to form a layer of wetted out fibers terminating in a smooth outer surface; and (k) orthogonally winding a second band having at least one ribbon impregnated with the admixture, thereby forming a circumferential bead.  
           [0015]    A more complete understanding of the present invention and other objects, aspects and advantages thereof will be gained from a consideration of the following description of the preferred embodiments read in conjunction with the accompanying drawings provided herein. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a perspective view of a self-grounding connector according to the invention, including a circumferential bead.  
         [0017]    [0017]FIG. 2A is a schematic cross-sectional view of the FIG. 1 connector fabricated according to a first process embodiment.  
         [0018]    [0018]FIG. 2B is a schematic cross-sectional view of the FIG. 1 connector fabricated according to a second process embodiment.  
         [0019]    [0019]FIG. 3 schematically shows a first step in making a FIG. 2A or FIG. 2B connector wherein a thin coating of an admixture of a settable chemically resistant resin and a curing agent therefor is rolled onto a non-sticking sheeting covering a rotating mandrel.  
         [0020]    [0020]FIG. 4 schematically shows a second step in making the FIG. 2A connector wherein continuous, contiguous carbon fiber-filament ribbons, after transiting a bath containing the FIG. 3 admixture, are helically wound around the sheeting until its surface is totally covered with a single ribbon-layer, as hereinafter defined.  
         [0021]    [0021]FIG. 5 schematically shows a second step in making the FIG. 2B connector wherein a layer of carbon cloth wetted out with the FIG. 3 admixture is helically wound around the FIG. 3 sheeting.  
         [0022]    [0022]FIG. 6A schematically shows a third step in making the FIG. 2A connector wherein a second thin coating of the FIG. 3 admixture is applied to the outer surface formed by the FIG. 4 contiguous ribbons and trapped air is rolled out with a roller.  
         [0023]    [0023]FIG. 6B shows a third step in making the FIG. 2B connector wherein a thin coating of putty is applied to the outer surface of the FIG. 5 carbon cloth after it has cured.  
         [0024]    [0024]FIG. 7A schematically shows a fourth step in making the FIG. 2A connector wherein a layer of surfacing veil, wetted out with the FIG. 3 admixture, is helically wound into the FIG. 6A admixture coating.  
         [0025]    [0025]FIG. 7B shows a fourth step in making the FIG. 2B connector wherein a layer of surfacing veil is helically wound into the still-soft FIG. 6B putty, which is then cured.  
         [0026]    [0026]FIG. 8 shows a fifth step in making the FIG. 2A or FIG. 2B connector wherein, respectively, a third or second, thin coating of the FIG. 3 admixture is applied to the veil outer surface.  
         [0027]    [0027]FIG. 9 schematically shows a sixth step in making the FIG. 2A or FIG. 2B connector wherein a layer of chopped carbonized carbon fibers is deposited onto and into the layer of FIG. 3 admixture covering the FIG. 8 veil outer surface.  
         [0028]    [0028]FIG. 10 schematically shows a seventh step in making the FIG. 2A or FIG. 2B connector wherein a roller is used to smooth out the FIG. 9 fibers.  
         [0029]    [0029]FIG. 11 schematically shows an eighth step in making the FIG. 2A or FIG. 2B connector wherein continuous, contiguous carbon fiber-filament ribbons, after transiting a bath containing FIG. 3 admixture, are orthogonally wound around the FIG. 10 surface to form a circumferential bead.  
         [0030]    [0030]FIG. 12 schematically shows how several FIG. 2A or FIG. 2B connectors are successively made by forming a plurality of FIG. 10 beads spaced along the mandrel. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    I. Introduction  
         [0032]    While the present invention is open to various modifications and alternative constructions, the preferred embodiment shown in the drawings will be described herein in detail. It is to be understood, however, there is no intention to limit the invention to the particular forms disclosed. On the contrary, it is intended that the invention cover all modifications, equivalences and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.  
         [0033]    II. Connector with Carbon Fiber-Filament Inner Wall  
         [0034]    [0034]FIGS. 3, 4,  6 A,  7 A,  8 ,  9 ,  10  and  11  show sequential steps in fabricating a self-grounding connector  20 A according to a first embodiment of the invention, as shown in FIGS. 1 and 2A. Referring to FIG. 3, in a first step a sheeting  22  made of a non-sticking material and covering a slowly rotating, generally circular mandrel  24  is evenly coated using a fiberglass applicator roller  26  with a thin layer  28  of a liquid admixture  30  of a settable chemically resistant resin, either halogenated or unhalogenated, and a curing agent therefor. Preferably these are, respectively, an epoxy vinyl ester impregnating resin and benzoyl peroxide. Preferably, the sheeting is a polyester film such as MYLAR®. Other materials which can be used include: (a) fluoropolymer films such as HALAR® ethylene trichlorofluoroethylene copolymer and KYNAR® (poly)vinylidene fluoride; (b) polyolefin films such as polypropylene film; (c) other polyester films; and (d) metallic foils such as wax coated aluminum foil. Alternatively, a cardboard tube is interposed between the mandrel and sheeting to further facilitate removal of the finished cylindrical product from the mandrel. Layer  28  has an interior surface  28 S contiguous to the sheeting  22  and an exterior surface  28 E. Layer  28  is 2 to 3 mils in thickness and is dispensed from a suitable dispensing device  32 . The benzoyl peroxide, which is 1 to 5 percent-by-weight relative to the weight of the resin, cures the liquid resin to a solid at ambient temperature. About 0.3 pound of resin per square foot of mandrel surface area is used. Preferably, the resin is type 510A-40 DERAKANE® manufactured by the Dow Chemical Company of Channahon, Ill.  
         [0035]    Mandrel  24  is clamped generally horizontally between a rotating chuck and a tailstock spindle of a filament winding machine, and rotates at a selectable constant rate. As detailed in the &#39;333 published application, a two-axis machine is used to apply a matrix of carbon fibers and resin under controlled tension to the mandrel in a predetermined geometrical pattern. As shown schematically in FIG. 4, in a second step a plurality of continuous carbon fiber-filament ribbons is helically wound onto the mandrel after passage through a bath  34  containing the admixture  30 . In a preferred embodiment eight ribbons, each about 0.250-inch in width and about 0.010-inch in thickness, after unwinding from contiguous spools S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8  and exiting bath  34 , are aligned edge-to-edge by a payout eye  36  to form a two-inch wide band  38 . The band is wound helically onto surface  28 E at an angle of about 72° with respect to the mandrel&#39;s longitudinal axis to form a diamond-shaped pattern. As the eye moves back and forth along the mandrel, interstices in the pattern are filled in to form a single continuous ribbon-layer  40  (see FIG. 6A). Ribbon-layer  40  is embedded in admixture layer  28  so that interior surface  28 S is integrated with a smooth continuous surface  40 S (see FIG. 2A) of resin-impregnated carbon fiber-filaments which preferably is about 63 percent carbon and 37 percent admixture, by weight, within a feasible range of about 50 to 70 percent carbon and about 30 to 50 percent admixture. Typically, the thickness of ribbon-layer 40 is about 25 mils, but can be between 15 and 35 mils. Alternatively, a lesser or greater number of ribbons may be used to provide a narrower or wider bandwidth. Preferably, the ribbon used is PANEX® 33-48K continuous carbon fiber which has a filament count of 45,700 and a yield of 450 ft/lb, manufactured from polyacrylonitrile (PAN) precursor by Zoltek Corporation of St. Louis, Mo.  
         [0036]    Referring to FIG. 6A, in a third step ribbon-layer  40  is evenly coated with a thin layer  42  of admixture  30 , and a fiberglass “deairing” roller  44  is used to roll out air trapped in the ribbon-layer. Layer  42  typically is 2-3 mils in thickness.  
         [0037]    Referring to FIG. 7A, in a fourth step a layer  50  of surfacing veil having an outer surface  50 S, about 10 mils in thickness and wetted out with the admixture  30 , is helically wound over layer  42 . Typically, the veil width is about 4 inches. Preferably, glass “C”-veil is used. C-veil is glass fiber tissue of randomly dispersed glass fibers bonded into a sheet by a polyester resin. The fibers are produced from “C” glass, a chemically resistant glass highly resistant to attack by both acid and alkaline environments. C-veil is available commercially from Owens Corning Corp.  
         [0038]    Referring to FIG. 8, in a fifth step surface  50 S is evenly coated with a thin layer  46  of liquid admixture  30 . Preferably, the thickness of layer  46  is about 10 mils. Referring to FIG. 9, in a sixth step a multiplicity of quarter-inch length chopped carbon fibers  52  are evenly applied onto and into layer  46  as the mandrel rotates. The fibers are manufactured by heating, oxidizing and carbonizing PAN fibers. Preferably, the fibers are PANEX® 33-CF, manufactured by Zoltek Corporation, which have a diameter of 0.283 mil, a density of 0.065 lb/in 3 , and an electrical resistivity of 0.00068 ohm-inch. Preferably, the fibers  52  are sprayed on using a chop-gun  54  such as manufactured by Venus-Gusmer Inc. of Kent, Wash. Alternatively, the fibers may be applied by hand. Referring to FIG. 10, in a seventh step a deairing roller  56  is used to break down any clumps of fibers and blend the fibers with admixture  30 , resulting in a homogeneous layer  58  of fibers and admixture having a thickness of about 10 mils and a generally smooth outer surface  58 S.  
         [0039]    Referring to FIG. 11, in an eighth step a plurality of continuous carbon fiber-filament ribbons, aligned edge-to-edge by a stationary payout eye  60  to form a band  64  of a preselected width, are orthogonally wound around surface  58 S after passage through a bath  62  containing admixture  30 . Sufficient ribbon-layers are formed to create a circumferential bead  66  having a height in a range from 0.187- to 0.250-inch. FIG. 11 schematically shows four ribbons unwinding from contiguous spools R 1 , R 2 , R 3 , R 4 . The number of spools and the ribbon width used in a particular manufacturing run depend on the bead width desired. FIG. 12 schematically shows that after a bead is completed the payout eye is moved a preselected distance along the mandrel and another bead is formed. After curing the resultant carbon-glass-carbon cylindrical tube at ambient temperature and sliding it off the mandrel, a plurality of beaded connectors C 1 , C 2 , C 3 , . . . are produced by successively sawing off transverse segments each having a bead equidistant between its ends. Alternatively, sawing may be done with the tube still on the mandrel.  
         [0040]    Paragraph 0041 and FIG. 9 of the &#39;333 application disclose a collar used in a joint assembly to connect the end portions of two fume duct sections. The same technique is employed in using the self-grounding connectors of the present invention to connect the end portions of two conduit sections.  
         [0041]    III. Connector with Carbon Cloth Inner Wall  
         [0042]    [0042]FIGS. 3, 5,  6 B,  7 B,  8 ,  9 ,  10  and  11  show sequential steps in fabricating a self-grounding connector  20 B according to a second embodiment of the invention, as shown in FIGS. 1 and 2B. The first, fifth, sixth, seventh and eighth steps are identical, respectively, to the first, fifth, sixth, seventh and eighth steps used in fabricating connector  20 A. So only the second, third and fourth steps are described below.  
         [0043]    Referring to FIG. 5, in a second step a single layer  70  of carbon cloth having an interior surface  70 S and an exterior surface  70 E, wetted out with the admixture  30 , is wound helically onto layer  28 , and then allowed to cure at ambient temperature. The cured resin fills the interstices of the porous cloth to form an impermeable barrier. Preferably, the cloth is carbon “boat” cloth about 10 mils in thickness, available commercially from Zoltek Corporation.  
         [0044]    Referring to FIG. 6B, in a third step a thin layer  72  of putty  73  is dispensed from a dispensing device  74  onto surface  70 E. Preferably, the thickness of layer  72  is about 10 mils. Preferably, the putty is an admixture including vinyl ester resin and benzoyl peroxide curing agent, chopped carbon fibers in a percentage-by-weight of 1 to 20 percent, and fumed silica in a percentage-by-weight of 3 to 10 percent. Alternatively, the putty is an admixture including epoxy resin and amine curing agent, chopped carbon fibers in a percentage-by-weight of 1 to 20 percent, and fumed silica in a percentage-by-weight of 3 to 10 percent.  
         [0045]    Referring to FIG. 7B, in a fourth step a layer  76  of surfacing veil having an outer surface  76 S is wound into the still-soft putty. Preferably, the veil is glass C-veil about 10 mils in thickness. Before proceeding to the fifth step wherein surface  76 S is evenly coated with a thin layer of liquid admixture  30 , the putty is allowed to cure.  
         [0046]    IV. Resistivity Test Results  
         [0047]    A. Test Method  
         [0048]    Volume and surface resistivity tests according to ASTM D 4496-87 were performed on specimens cut from a connector having fabricated according to the first process embodiment of the present invention. The connector was approximately 6 -inches in diameter by 3.5-inches wide by 0.070-inch thick. The tests were performed by Delsen Testing Laboratories, Inc. of Glendale, Calif. Five specimens, each approximately 3.5-inches by 1-inch, were cut out from the axial direction of the connector. The specimens were cleaned with isopropyl alcohol and distilled water and dried at room ambient conditions. A four-point measurement technique was used to determine the resistance of the specimens. Two ends of each specimen were painted with conductive silver paint and served as current electrodes. Two conductive silver paint lines were applied across the width of the inner surface of each specimen and served as potential electrodes. While DC current was applied to the specimen through the two outer electrodes, the potential drop between the two inner electrodes was measured.  
         [0049]    Resistance was calculated as follows:  
         
       R=V/I  
     
         [0050]    where R=resistance (ohms); V=potential drop (volts); I=applied currrent (amperes).  
         [0051]    Volume and surface resistivity were calculated as follows:  
         ρ V =((2.54 ×t×W )/ L )× R    
         ρ S =( W/L )× R    
         [0052]    where  
         [0053]    ρ V =volume resistivity (ohm-cm)  
         [0054]    ρ S =surface resistivity (ohms/square)  
         [0055]    R=resistance (ohms)  
         [0056]    t=specimen thickness (inches)  
         [0057]    L=distance between potential electrodes (inches)  
         [0058]    W=specimen width (inches)  
         [0059]    B. Test Results  
         [0060]    All tests were performed at 73° F. temperature and 35% relative humidity. Table 1 shows the resistances measured on each of the five specimens, and the calculated volume and surface resistivities. In all cases the measured resistance was extremely low.  
                                                                                         TABLE 1                           VOLUME AND SURFACE RESISTIVITY                TEST METHOD:   ASTM D 4496-87 (Reapproved 1998)           ELECTRODE TYPE:   Conductive silver paint           TEST CONDITIONS:   Tested at 73° F. and 35% R.H.                                    DISTANCE                               BETWEEN           SPECIMEN   SPECIMEN   POTENTIAL       VOLUME   SURFACE       CURRENT   WIDTH   THICKNESS   ELECTRODE   RESISTANCE   RESISTIVITY   RESISTIVITY       DIRECTION   inches   inches   inches   ohms   ohm-cm   ohms/square                    Specimen No. 1                               Forward   1.00   0.070   1.98   10.72   0.96   5.4       Reverse   1.00   0.070   1.98   10.73   0.96   5.4       Specimen No. 2       Forward   1.01   0.070   1.97   9.46   0.86   4.9       Reverse   1.01   0.070   1.97   9.47   0.86   4.9       Specimen No. 3       Forward   0.99   0.070   1.98   9.46   0.84   4.7       Reverse   0.99   0.070   1.98   9.46   0.84   4.7       Specimen No. 4       Forward   1.01   0.070   1.97   6.79   0.62   3.5       Reverse   1.01   0.070   1.97   6.79   0.62   3.5       Specimen No. 5       Forward   1.01   0.070   1.97   9.30   0.85   4.8       Reverse   1.01   0.070   1.97   9.30   0.85   4.8