Title:
LAMINATED STATIC CHARGE SUPPRESSOR AND METHOD OF MAKING SAME
United States Patent 3652897
Abstract:
A laminated static charge suppressing bus which is composed of a strip of insulating material to which a conducting strip and a plurality of ionizing elements are mounted. The conducting strip is mounted on one side of the insulating strip and the plurality of ionizing elements are mounted serially along the other side of the insulating strip directly opposite the conducting strip. The ionizing elements are capacitively coupled to the conducting strip and contain pointed emitting tips extending beyond the edge of the insulating strip. When the ionizing elements are excited, the emitting tips establish a corona discharge in gas around the tips for removing static charges from paper, plastic webs and sheetlike textile materials.
US Patent References:
Neutralizing bar
Rostal - March 1928 - 1663466
Neutralizing apparatus and manufacture of same
Chapman - January 1946 - 2392808
Electrical bus bar with non-adhering plastic inserts
Erdle - August 1966 - 3264403
METHOD OF MAKING LAMINATED BUS BAR ASSEMBLY
Stopp - September 1969 - 3466745
Neutralizing bar
Rostal - March 1928 - 1663466
Neutralizing apparatus and manufacture of same
Chapman - January 1946 - 2392808
Electrical bus bar with non-adhering plastic inserts
Erdle - August 1966 - 3264403
METHOD OF MAKING LAMINATED BUS BAR ASSEMBLY
Stopp - September 1969 - 3466745
Inventors:
Iosue, Michael F. (Danielson, CT)
Sanders, Robert E. (Saybrook, CT)
Sanders, Robert E. (Saybrook, CT)
Application Number:
05/070781
Publication Date:
03/28/1972
Filing Date:
09/09/1970
View Patent Images:
Export Citation:
Assignee:
Rogers Corporation (Rogers, CT)
Primary Class:
International Classes:
H05F3/04; H05F3/00; H05F3/00; H01T19/04
Field of Search:
317/2F,4 174/2B
Primary Examiner:
Hix L. T.
Claims:
What is claimed is
1. A laminated static charge suppressing bus comprising:
2. The laminated suppressing bus of claim 1 wherein:
3. The laminated suppressing bus of claim 1 wherein:
4. The laminated suppressing bus of claim 1 wherein:
5. The laminated suppressing bus of claim 4 wherein the plates have a rectangular configuration with one side corresponding dimensionally to the width of the continuous conductive strip.
6. The laminated suppressing bus of claim 4 wherein:
7. The laminated suppressing bus of claim 1 wherein:
8. The laminated suppressing bus of claim 1 further including:
9. The laminated suppressing bus of claim 8 including still further:
10. The laminated structure of claim 1 wherein:
1. A laminated static charge suppressing bus comprising:
2. The laminated suppressing bus of claim 1 wherein:
3. The laminated suppressing bus of claim 1 wherein:
4. The laminated suppressing bus of claim 1 wherein:
5. The laminated suppressing bus of claim 4 wherein the plates have a rectangular configuration with one side corresponding dimensionally to the width of the continuous conductive strip.
6. The laminated suppressing bus of claim 4 wherein:
7. The laminated suppressing bus of claim 1 wherein:
8. The laminated suppressing bus of claim 1 further including:
9. The laminated suppressing bus of claim 8 including still further:
10. The laminated structure of claim 1 wherein:
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of static suppressors and is more particularly directed to static suppressors used in manufacturing paper, plastic webs and other sheetlike textiles.
2. Description of the Prior Art
In many manufacturing processes, a web of material is translated over rollers or through wiping elements and in these processes, the web may acquire a charge of static electricity. For many operations, it is desirable to have a charge-free web or sheet to facilitate handling of the material and to obviate any possibility of a static discharge occurring between the web and other structures. Furthermore, it may be necessary to deliver the finished web material in a charge-free form. In any of the above cases, the removal of a static charge may be accomplished by passing the web in close proximity to a charge suppressing device.
There are already a number of charge suppressing devices available and in use. One such device is composed of a high voltage cable having a plurality of pointed emitter pins projecting laterally along one side of the conductor. A high voltage conductor within the cable is coupled capacitively through insulation to each of the emitter pins. The cable is mounted in a grounded, cylindrical, metallic shell having a longitudinal slot. The emitter pins project from the cable through the longitudinal slot to a region adjacent the web as the web is transported past the pins. By exciting the high voltage conductor with suitable AC power, the pointed ends of the emitter pins ionize air in the immediate vicinity of the pins in a corona discharge. The ionized air serves as a conductive path and allows static charges to be drained from the web through the metallic shell to ground. Thusly, all static charge is removed from the web.
(A reference to pointed emitting tips or pins is to be interpreted throughout the specification and claims to include tapered pins or pins having small diameter, rounded end surfaces suitable for generating the corona discharge.)
While the prior art static suppressors are adequate as far as their operating capabilities are concerned, the cost of manufacturing the prior art suppressors, particularly a coaxial suppressor, is substantial. A selected, uniform capacitive coupling between the high voltage conductor and the emitter pins must be insured and contributes to the manufacturing costs. It is, accordingly, desirable to have a static suppressor bus which can be manufactured more cheaply than the prior art busses, and without substantial difficulties in controlling the uniformity of the capacitive coupling in the bus.
SUMMARY OF THE INVENTION
In accordance with the present invention, a laminated static charge suppressing bus is formed principally of a base strip of insulating material, a high voltage conductor and a plurality of ionizing elements or emitters. The high voltage conductor is also in the form of a strip and is secured to one side of the insulating base strip. The plurality of ionizing elements take the form of small capacitor plates from which pointed emitters project and are mounted to the other side of the base strip. The ionizing elements are positioned directly opposite the high voltage conductor for optimum capacitive coupling. Also, the ionizing elements are positioned serially along the bus with the pointed emitters projecting slightly beyond the edge of the base strip. A layer of insulation is applied to the exposed surfaces of the high voltage conductor and the ionizing elements.
Since the novel static charge suppressing bus has a laminated construction, it may be readily manufactured by building up the bus from the base strip in a sequence of simple operations. The high voltage conductor is applied to one side of the base strip and the ionizing elements are applied to the opposite side of the strip. To facilitate the handling and positioning of the plurality of ionizing elements, the elements are stamped from a single strip of material and bridging portions are retained between adjacent elements so that all of the elements are interconnected. In this fashion the plurality of elements may be handled as a single strip while the elements are mounted. The interconnections between elements can be removed after the elements are in position. The base strip of insulating material and the external layers of insulation may initially be an uncured epoxy fiberglass so that the finished laminated structure can be held together in a molded form by the cured epoxy.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel laminated static charge suppressing bus and its method of construction will be described and better understood by reference to the following drawings in which the same elements bear the same reference numerals throughout the several figures.
FIG. 1 is a cross-sectional view of a prior art coaxial static suppressing bus mounted within a grounded metal shield for removing static charge from a film.
FIG. 2 is a side view of the laminated static charge suppressing bus of the present invention with portions of the different laminates removed.
FIG. 3 is a cross-sectional view of the laminated bus as viewed along the section line 3--3 in FIG. 2.
FIG. 4 is a side view of two interconnected ionizing elements as the elements appear at an intermediate stage of manufacture.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
To more clearly understand the operation and function of the laminated static suppressor bus of the present invention, reference is first made to the prior art static suppressors shown in FIG. 1 in a working environment. The laminated static suppressor of the present invention is intended to replace the prior art coaxial suppressors in the same environment.
FIG. 1 shows a web or film F being transported in the direction indicated by the arrow over the coaxial static suppressor, generally designated 10, shown in cross section. The film F may be any type of film such as paper, plastic and other sheetlike textile materials which are likely to acquire a static charge during manufacturing or other processing. The film F may acquire such charge by frictional contact with other structures such as rollers, slides and brushes. Static charge acquired by the film F may interfere with subsequent handling of the film due repulsion or attraction caused by the static charge. The charge itself may interfere with the application of coatings or the "wetting" of the film by liquids in a given manufacturing process. The static suppressor might be employed as the last step of a manufacturing process so that the film can be delivered as a finished item without residual static charges. The suppressor may simply remove static charges before they reach a level which could create a damaging or, possibly, catastrophic discharge between the film and surrounding structure.
The prior art coaxial suppressor 10 is composed basically of a central high voltage conductor 12 and a plurality of ionizing pins 14 with pointed emitting tips 16. The pins 14 are distributed serially along one side of the suppressor and project radially through an outer layer 18 of insulation. Each pin 14 is press-fitted at its inner end in a corresponding ring 20. Both the pins 14 and the rings 20 are metallic elements and are, therefore, electrically conductive. The ring 20 is positioned coaxially with respect to the high voltage conductor 12 and is separated from the conductor 12 by means of an inner layer 22 of insulation. The radial thickness of the layer 22 is selected so that the capacitive coupling between conductor 12 and ring 20 establishes a high voltage at the pointed emitting tips 16 of pins 14 and produces a corona discharge in the vicinity of the tips. The thickness of the layer 22 must be sufficient to prevent direct discharges between conductor 12 and layer 22 and, therefore, varies according to the dielectric constant of the insulating material.
The coaxial bus 10 is mounted transversely to the film F within a grounded, metallic sleeve 24 by brackets (not shown). Pins 14 project radially through a longitudinal slot 26 extending along one side of sleeve 24. The plurality of pins 14 and associated rings 20 are positioned serially along the coaxial bus 10. Each set of a pin and ring is electrically isolated from the other sets. The separation between the pins and the number of pins is selected so that static charge across the entire surface of film F is removed.
In operation, the high voltage conductor 12 is excited by an AC power source, for example a source providing 800-15,000 volts at 60 c.p.s. The capacitive coupling of conductor 12 through layer 22 to a ring 20 and pins 14 raises the voltage at the emitting tips to a value which ionizes the air locally around the tips 16 of pins 14. The ionized air forms a conductive path between the film F and the grounded sleeve 24 so that static charges can be removed from the film F as it translates in close proximity to the emitting tips 16. The static charge is safely drawn off the film through the ionized gas and sleeve 24 before the charge interferes with or injures the film.
While the prior art coaxial static suppressor busses operate in essentially the same fashion as the laminated suppressor of the present invention, the coaxial construction is considerably more costly and utilizes more space while performing the same function. The positioning of several pins with rings at stations serially along the coaxial conductor and the formation of the coaxial package require a more sophisticated manufacturing process than that permitted by a laminated construction. The laminated structure, taking a planar form, is well suited to designing and controlling capacitive coupling between the high voltage conductor and emitters and occupies considerably less space while performing the same static suppressing function within a discharging envelope such as sleeve 24 in FIG. 1.
Accordingly, the novel laminated static charge suppressing bus, generally designated 30, is shown in FIG. 2 with portions of the several laminates removed to expose the internal construction. The complete laminated structure is shown in cross-section in FIG. 3.
The intermediate layer of the laminated structure is a strip 32 of insulating material which forms a base of limited stiffness upon which the other laminates are built. The base strip 32 may be an epoxy fiberglass having a thickness primarily established to provide insulation between the high voltage conductor 34 and the plurality of ionizing tip plates 36. The spanwise stiffness of the laminate structure is controlled principally by the thickness of the base strip 32 and the conductor 34. Interposed between the base strip 32 and the high voltage conductor 34 is another layer 38 of epoxy fiberglass which is used in conjunction with the external layer of fiberglass 40 to mount the high voltage conductor 34 to the base strip 32. The layer 38 is optional or may simply be a part of the base strip 32. The conductor 34 is a strip of highly conductive material, such as brass or copper, and extends continuously along one side of strip 32. Dimensionally, the conductor 34 has a width which is less than that of strip 32 to provide an apron along the one edge of strip 32 for mounting the laminated bus in close proximity to a film as the coaxial bus 10 is shown in FIG. 1. The laminated construction is completed by a second insulating layer 42 which covers the exposed surfaces of the tip plates 36.
The tip plates 36 have a planar configuration with the emitters 44 projecting from one side of the rectangular body portion of the plate 36. The projecting ends 46 of emitters 44 are pointed for ionizing gas in the same manner as the pointed tips 16 of pins 14 in the prior art suppressor 10 shown in FIG. 1. Plate 36 is positioned and oriented on the one side of base strip 32 so that the plate is directly opposite the high voltage conductor 34. The width of the conductor 34 and the parallel dimension of the plate are substantially equal, therefore, a structure resembling a conventional flat capacitor is formed between conductor 34 and each of the plates 36. The thickness of base strip 32 and the additional layer 38 determine the capacitance between plate 36 and conductor 34. The significant considerations in this regard are the separation between the plates and conductor and the dielectric constant of the intervening material since these principal factors determine the breakdown voltage between the conductor 34 and plates 36. The voltages required to generate a corona ring around the emitter tips 46 must be comparatively high, in the vicinity of 800-15,000 volts; therefore, the thickness of the base strip 32 and other intervening layers must be selected to insure adequate electrical isolation without discharges which could lead to catastrophic failure of the suppressing bus.
The laminated bus 30 can be mounted in a number of ways. As shown in FIG. 2, a plurality of apertures 50 are distributed along the apron at the upper edge of base strip 32. The apertures 50 also extend through layers 38, 40 and 42 of insulation so that mounting screws 52 may be inserted through the bus and associated mounting brackets. If the mounting apertures 50 are close to conductor 34, the conductor may include a cutout 54 in the contiguous conductor section to provide adequate electrical isolation.
At one end, conductor 34 is joined with a connector 56 for connecting the bus 30 to a suitable source of AC power. The connector may be either crimped, clamped or soldered to the connector 44 to provide a low resistance, low capacitance junction for the high voltage AC power.
One of the significant advantages of the laminated suppressor structure is the lower cost of construction due principally to the fact that a more simplified assembly procedure can be followed. Basically, each of the elements are individual laminates which need only to be sandwiched in a unified structure. In manufacturing the coaxial constructions of the prior art, the locating and assembling of the various components is more difficult and must be more accurately controlled to preserve product quality. It is appropriate, however, to examine preferred methods by which the laminated suppressing bars of the present invention are manufactured.
Initially the base strip 32 of epoxy fiberglass is placed in side-by-side relationship with the strip 34 of conductive material with the aid of the fiberglass insulating layers 38 and 40. The epoxy fiberglass of both strip 32 and layers 38 and 40 can be easily molded and formed against conductor 34 when the epoxy is in the uncured stage, commonly known as the B stage. The conductive strip 34 is positioned generally intermediate the lateral edges of the base strip 32 with a sufficient apron at one side of strip 32 to accommodate the mounting apertures 50. The apertures may be formed during the molding of the fiberglass with the conductor 34 since the cutouts 54 in the conductor must correspond with the apertures. Of course, it is feasible to insulate the mounting screws 52 from the conductive strip 34 in mounting holes lying wholly within conductor 34 where an ample conductor cross section is provided.
The next step in the manufacturing process for suppressing bar 30 is the mounting of the plurality of tip plates 36 to the side of the base strip 32 opposite the conductor 34. As will be understood from the above description of the operation of the suppressor bus 30, tip plates 36 must be located at selected stations along base strip 32 and in positions on the base strip 32 which are directly opposite the conductor 34 to provide the most efficient capacitive coupling between strip 34 and the plates 36. Furthermore, the precise positioning of plates 36 is also demanded by the fact that the pointed emitting tips 46 of each plate 36 must be located in substantially the same plane so that the separations between the several emitting tips and a film to be discharged are equal when bus 30 is mounted in close proximity to a film. It will be immediately recognized that the individual positioning of several plates with the emitters 44 precisely located could be a time-consuming and difficult step of the manufacturing process. Accordingly, the tip plates 36 with the integral emitters 44 are formed from a single strip of conductive material, such as stainless steel, by stamping all plates simultaneously with bridging portions interconnecting the plates. As seen from FIG. 4 where the plates are shown at reduced scale, the bridging portions 60 extend between the emitters 44 of adjacent plates. A die for stamping such plates can be readily constructed and is capable of producing a plurality of interconnected plates rapidly. Of course, it may be equally desirable to employ a chemical etching process to form the interconnected plates.
The mounting of the plurality of plates interconnected through the emitters 44 can be readily accomplished by locating the interconnected plates on the base strip 32 in a position directly opposite conductor 34. Separation and orientation of the plates are kept uniform by the bridging portions 60.
Once the plates have been properly located, the external layer 42 of epoxy fiberglass is overlaid on the exposed surfaces of the plates. The entire laminated structure is then placed in a pressurized mold and cured by applying heat and pressure for a prescribed period of time to set the epoxy resin in the fiberglass. It is advantageous to maintain the interconnecting portions 60 between the several plates 36 during the curing process so that the alignment and positioning of the plates is not disturbed before the epoxy is set.
The removal of the bridging portions 60 after curing is accomplished by cutting the emitters along the dotted line indicated in FIG. 4 to form the pointed tips 46 seen in FIG. 2. A separate cutting die may be employed to cut the pointed emitters or the emitters may be partially severed from the bridging portions 60 during the initial stamping of the plates to weaken the union of the emitters and bridging portions at the dotted lines in FIG. 4. The severance can then be completed after the fiberglass has cured. Since the interconnecting portions 60 preserve the spacing and orientation of the plates 36 during the curing process, positioning of the plates will be uniform. Also, the amount by which emitters 44 project beyond the upper edge of base strip 32 as seen in FIG. 2 is insured of greater uniformity.
It will be understood from the above that the novel laminated static charge suppressor can be constructed with accuracy and rapidity without compromising quality. The assembly of the several components of the suppressor 30 can be performed by conventional procedures and is not imbuded with many of the difficulties of the prior art. In addition, the finished laminated suppressor bus occupies considerably less space while performing the same function as the prior art coaxial suppressor busses.
It will be understood by those skilled in the art that numerous modifications and substitutions can be made in the structure and the manufacture of the novel laminated suppressor bus without departing from the spirit of the invention. For example, while an epoxy fiberglass has been described as the base material forming the insulation between conductor 34 and plates 36, other fiber-reinforced or plastic materials used as substrates for electrical components can be utilized with equally satisfactory results. The materials from which the conductors 34 and plates 36 are formed may also be changed so long as the electrical characteristics of the materials are preserved. It is also obvious that the order in which the strips 32, 34 and the interconnected plates 36 are assembled prior to curing may be interchanged. In certain cases it may be desirable to remove the interconnecting strips 60 immediately after the plurality of plates 36 have been positioned so that the bridging portions 60 do not interfere with the molding apparatus. The external insulating layers 40 and 42 need not be formed of the same insulating material as that interposed between conductor 34 and plates 36. In some cases, the external insulation may be eliminated entirely. Accordingly, while the novel laminated suppressor bus has been disclosed in a preferred embodiment, numerous changes to the specific structure are possible without losing the essential benefits of the laminated construction. The laminated bus and its method of manufacture have, accordingly, been described by way of illustration rather than limitation.
1. Field of the Invention
This invention relates to the field of static suppressors and is more particularly directed to static suppressors used in manufacturing paper, plastic webs and other sheetlike textiles.
2. Description of the Prior Art
In many manufacturing processes, a web of material is translated over rollers or through wiping elements and in these processes, the web may acquire a charge of static electricity. For many operations, it is desirable to have a charge-free web or sheet to facilitate handling of the material and to obviate any possibility of a static discharge occurring between the web and other structures. Furthermore, it may be necessary to deliver the finished web material in a charge-free form. In any of the above cases, the removal of a static charge may be accomplished by passing the web in close proximity to a charge suppressing device.
There are already a number of charge suppressing devices available and in use. One such device is composed of a high voltage cable having a plurality of pointed emitter pins projecting laterally along one side of the conductor. A high voltage conductor within the cable is coupled capacitively through insulation to each of the emitter pins. The cable is mounted in a grounded, cylindrical, metallic shell having a longitudinal slot. The emitter pins project from the cable through the longitudinal slot to a region adjacent the web as the web is transported past the pins. By exciting the high voltage conductor with suitable AC power, the pointed ends of the emitter pins ionize air in the immediate vicinity of the pins in a corona discharge. The ionized air serves as a conductive path and allows static charges to be drained from the web through the metallic shell to ground. Thusly, all static charge is removed from the web.
(A reference to pointed emitting tips or pins is to be interpreted throughout the specification and claims to include tapered pins or pins having small diameter, rounded end surfaces suitable for generating the corona discharge.)
While the prior art static suppressors are adequate as far as their operating capabilities are concerned, the cost of manufacturing the prior art suppressors, particularly a coaxial suppressor, is substantial. A selected, uniform capacitive coupling between the high voltage conductor and the emitter pins must be insured and contributes to the manufacturing costs. It is, accordingly, desirable to have a static suppressor bus which can be manufactured more cheaply than the prior art busses, and without substantial difficulties in controlling the uniformity of the capacitive coupling in the bus.
SUMMARY OF THE INVENTION
In accordance with the present invention, a laminated static charge suppressing bus is formed principally of a base strip of insulating material, a high voltage conductor and a plurality of ionizing elements or emitters. The high voltage conductor is also in the form of a strip and is secured to one side of the insulating base strip. The plurality of ionizing elements take the form of small capacitor plates from which pointed emitters project and are mounted to the other side of the base strip. The ionizing elements are positioned directly opposite the high voltage conductor for optimum capacitive coupling. Also, the ionizing elements are positioned serially along the bus with the pointed emitters projecting slightly beyond the edge of the base strip. A layer of insulation is applied to the exposed surfaces of the high voltage conductor and the ionizing elements.
Since the novel static charge suppressing bus has a laminated construction, it may be readily manufactured by building up the bus from the base strip in a sequence of simple operations. The high voltage conductor is applied to one side of the base strip and the ionizing elements are applied to the opposite side of the strip. To facilitate the handling and positioning of the plurality of ionizing elements, the elements are stamped from a single strip of material and bridging portions are retained between adjacent elements so that all of the elements are interconnected. In this fashion the plurality of elements may be handled as a single strip while the elements are mounted. The interconnections between elements can be removed after the elements are in position. The base strip of insulating material and the external layers of insulation may initially be an uncured epoxy fiberglass so that the finished laminated structure can be held together in a molded form by the cured epoxy.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel laminated static charge suppressing bus and its method of construction will be described and better understood by reference to the following drawings in which the same elements bear the same reference numerals throughout the several figures.
FIG. 1 is a cross-sectional view of a prior art coaxial static suppressing bus mounted within a grounded metal shield for removing static charge from a film.
FIG. 2 is a side view of the laminated static charge suppressing bus of the present invention with portions of the different laminates removed.
FIG. 3 is a cross-sectional view of the laminated bus as viewed along the section line 3--3 in FIG. 2.
FIG. 4 is a side view of two interconnected ionizing elements as the elements appear at an intermediate stage of manufacture.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
To more clearly understand the operation and function of the laminated static suppressor bus of the present invention, reference is first made to the prior art static suppressors shown in FIG. 1 in a working environment. The laminated static suppressor of the present invention is intended to replace the prior art coaxial suppressors in the same environment.
FIG. 1 shows a web or film F being transported in the direction indicated by the arrow over the coaxial static suppressor, generally designated 10, shown in cross section. The film F may be any type of film such as paper, plastic and other sheetlike textile materials which are likely to acquire a static charge during manufacturing or other processing. The film F may acquire such charge by frictional contact with other structures such as rollers, slides and brushes. Static charge acquired by the film F may interfere with subsequent handling of the film due repulsion or attraction caused by the static charge. The charge itself may interfere with the application of coatings or the "wetting" of the film by liquids in a given manufacturing process. The static suppressor might be employed as the last step of a manufacturing process so that the film can be delivered as a finished item without residual static charges. The suppressor may simply remove static charges before they reach a level which could create a damaging or, possibly, catastrophic discharge between the film and surrounding structure.
The prior art coaxial suppressor 10 is composed basically of a central high voltage conductor 12 and a plurality of ionizing pins 14 with pointed emitting tips 16. The pins 14 are distributed serially along one side of the suppressor and project radially through an outer layer 18 of insulation. Each pin 14 is press-fitted at its inner end in a corresponding ring 20. Both the pins 14 and the rings 20 are metallic elements and are, therefore, electrically conductive. The ring 20 is positioned coaxially with respect to the high voltage conductor 12 and is separated from the conductor 12 by means of an inner layer 22 of insulation. The radial thickness of the layer 22 is selected so that the capacitive coupling between conductor 12 and ring 20 establishes a high voltage at the pointed emitting tips 16 of pins 14 and produces a corona discharge in the vicinity of the tips. The thickness of the layer 22 must be sufficient to prevent direct discharges between conductor 12 and layer 22 and, therefore, varies according to the dielectric constant of the insulating material.
The coaxial bus 10 is mounted transversely to the film F within a grounded, metallic sleeve 24 by brackets (not shown). Pins 14 project radially through a longitudinal slot 26 extending along one side of sleeve 24. The plurality of pins 14 and associated rings 20 are positioned serially along the coaxial bus 10. Each set of a pin and ring is electrically isolated from the other sets. The separation between the pins and the number of pins is selected so that static charge across the entire surface of film F is removed.
In operation, the high voltage conductor 12 is excited by an AC power source, for example a source providing 800-15,000 volts at 60 c.p.s. The capacitive coupling of conductor 12 through layer 22 to a ring 20 and pins 14 raises the voltage at the emitting tips to a value which ionizes the air locally around the tips 16 of pins 14. The ionized air forms a conductive path between the film F and the grounded sleeve 24 so that static charges can be removed from the film F as it translates in close proximity to the emitting tips 16. The static charge is safely drawn off the film through the ionized gas and sleeve 24 before the charge interferes with or injures the film.
While the prior art coaxial static suppressor busses operate in essentially the same fashion as the laminated suppressor of the present invention, the coaxial construction is considerably more costly and utilizes more space while performing the same function. The positioning of several pins with rings at stations serially along the coaxial conductor and the formation of the coaxial package require a more sophisticated manufacturing process than that permitted by a laminated construction. The laminated structure, taking a planar form, is well suited to designing and controlling capacitive coupling between the high voltage conductor and emitters and occupies considerably less space while performing the same static suppressing function within a discharging envelope such as sleeve 24 in FIG. 1.
Accordingly, the novel laminated static charge suppressing bus, generally designated 30, is shown in FIG. 2 with portions of the several laminates removed to expose the internal construction. The complete laminated structure is shown in cross-section in FIG. 3.
The intermediate layer of the laminated structure is a strip 32 of insulating material which forms a base of limited stiffness upon which the other laminates are built. The base strip 32 may be an epoxy fiberglass having a thickness primarily established to provide insulation between the high voltage conductor 34 and the plurality of ionizing tip plates 36. The spanwise stiffness of the laminate structure is controlled principally by the thickness of the base strip 32 and the conductor 34. Interposed between the base strip 32 and the high voltage conductor 34 is another layer 38 of epoxy fiberglass which is used in conjunction with the external layer of fiberglass 40 to mount the high voltage conductor 34 to the base strip 32. The layer 38 is optional or may simply be a part of the base strip 32. The conductor 34 is a strip of highly conductive material, such as brass or copper, and extends continuously along one side of strip 32. Dimensionally, the conductor 34 has a width which is less than that of strip 32 to provide an apron along the one edge of strip 32 for mounting the laminated bus in close proximity to a film as the coaxial bus 10 is shown in FIG. 1. The laminated construction is completed by a second insulating layer 42 which covers the exposed surfaces of the tip plates 36.
The tip plates 36 have a planar configuration with the emitters 44 projecting from one side of the rectangular body portion of the plate 36. The projecting ends 46 of emitters 44 are pointed for ionizing gas in the same manner as the pointed tips 16 of pins 14 in the prior art suppressor 10 shown in FIG. 1. Plate 36 is positioned and oriented on the one side of base strip 32 so that the plate is directly opposite the high voltage conductor 34. The width of the conductor 34 and the parallel dimension of the plate are substantially equal, therefore, a structure resembling a conventional flat capacitor is formed between conductor 34 and each of the plates 36. The thickness of base strip 32 and the additional layer 38 determine the capacitance between plate 36 and conductor 34. The significant considerations in this regard are the separation between the plates and conductor and the dielectric constant of the intervening material since these principal factors determine the breakdown voltage between the conductor 34 and plates 36. The voltages required to generate a corona ring around the emitter tips 46 must be comparatively high, in the vicinity of 800-15,000 volts; therefore, the thickness of the base strip 32 and other intervening layers must be selected to insure adequate electrical isolation without discharges which could lead to catastrophic failure of the suppressing bus.
The laminated bus 30 can be mounted in a number of ways. As shown in FIG. 2, a plurality of apertures 50 are distributed along the apron at the upper edge of base strip 32. The apertures 50 also extend through layers 38, 40 and 42 of insulation so that mounting screws 52 may be inserted through the bus and associated mounting brackets. If the mounting apertures 50 are close to conductor 34, the conductor may include a cutout 54 in the contiguous conductor section to provide adequate electrical isolation.
At one end, conductor 34 is joined with a connector 56 for connecting the bus 30 to a suitable source of AC power. The connector may be either crimped, clamped or soldered to the connector 44 to provide a low resistance, low capacitance junction for the high voltage AC power.
One of the significant advantages of the laminated suppressor structure is the lower cost of construction due principally to the fact that a more simplified assembly procedure can be followed. Basically, each of the elements are individual laminates which need only to be sandwiched in a unified structure. In manufacturing the coaxial constructions of the prior art, the locating and assembling of the various components is more difficult and must be more accurately controlled to preserve product quality. It is appropriate, however, to examine preferred methods by which the laminated suppressing bars of the present invention are manufactured.
Initially the base strip 32 of epoxy fiberglass is placed in side-by-side relationship with the strip 34 of conductive material with the aid of the fiberglass insulating layers 38 and 40. The epoxy fiberglass of both strip 32 and layers 38 and 40 can be easily molded and formed against conductor 34 when the epoxy is in the uncured stage, commonly known as the B stage. The conductive strip 34 is positioned generally intermediate the lateral edges of the base strip 32 with a sufficient apron at one side of strip 32 to accommodate the mounting apertures 50. The apertures may be formed during the molding of the fiberglass with the conductor 34 since the cutouts 54 in the conductor must correspond with the apertures. Of course, it is feasible to insulate the mounting screws 52 from the conductive strip 34 in mounting holes lying wholly within conductor 34 where an ample conductor cross section is provided.
The next step in the manufacturing process for suppressing bar 30 is the mounting of the plurality of tip plates 36 to the side of the base strip 32 opposite the conductor 34. As will be understood from the above description of the operation of the suppressor bus 30, tip plates 36 must be located at selected stations along base strip 32 and in positions on the base strip 32 which are directly opposite the conductor 34 to provide the most efficient capacitive coupling between strip 34 and the plates 36. Furthermore, the precise positioning of plates 36 is also demanded by the fact that the pointed emitting tips 46 of each plate 36 must be located in substantially the same plane so that the separations between the several emitting tips and a film to be discharged are equal when bus 30 is mounted in close proximity to a film. It will be immediately recognized that the individual positioning of several plates with the emitters 44 precisely located could be a time-consuming and difficult step of the manufacturing process. Accordingly, the tip plates 36 with the integral emitters 44 are formed from a single strip of conductive material, such as stainless steel, by stamping all plates simultaneously with bridging portions interconnecting the plates. As seen from FIG. 4 where the plates are shown at reduced scale, the bridging portions 60 extend between the emitters 44 of adjacent plates. A die for stamping such plates can be readily constructed and is capable of producing a plurality of interconnected plates rapidly. Of course, it may be equally desirable to employ a chemical etching process to form the interconnected plates.
The mounting of the plurality of plates interconnected through the emitters 44 can be readily accomplished by locating the interconnected plates on the base strip 32 in a position directly opposite conductor 34. Separation and orientation of the plates are kept uniform by the bridging portions 60.
Once the plates have been properly located, the external layer 42 of epoxy fiberglass is overlaid on the exposed surfaces of the plates. The entire laminated structure is then placed in a pressurized mold and cured by applying heat and pressure for a prescribed period of time to set the epoxy resin in the fiberglass. It is advantageous to maintain the interconnecting portions 60 between the several plates 36 during the curing process so that the alignment and positioning of the plates is not disturbed before the epoxy is set.
The removal of the bridging portions 60 after curing is accomplished by cutting the emitters along the dotted line indicated in FIG. 4 to form the pointed tips 46 seen in FIG. 2. A separate cutting die may be employed to cut the pointed emitters or the emitters may be partially severed from the bridging portions 60 during the initial stamping of the plates to weaken the union of the emitters and bridging portions at the dotted lines in FIG. 4. The severance can then be completed after the fiberglass has cured. Since the interconnecting portions 60 preserve the spacing and orientation of the plates 36 during the curing process, positioning of the plates will be uniform. Also, the amount by which emitters 44 project beyond the upper edge of base strip 32 as seen in FIG. 2 is insured of greater uniformity.
It will be understood from the above that the novel laminated static charge suppressor can be constructed with accuracy and rapidity without compromising quality. The assembly of the several components of the suppressor 30 can be performed by conventional procedures and is not imbuded with many of the difficulties of the prior art. In addition, the finished laminated suppressor bus occupies considerably less space while performing the same function as the prior art coaxial suppressor busses.
It will be understood by those skilled in the art that numerous modifications and substitutions can be made in the structure and the manufacture of the novel laminated suppressor bus without departing from the spirit of the invention. For example, while an epoxy fiberglass has been described as the base material forming the insulation between conductor 34 and plates 36, other fiber-reinforced or plastic materials used as substrates for electrical components can be utilized with equally satisfactory results. The materials from which the conductors 34 and plates 36 are formed may also be changed so long as the electrical characteristics of the materials are preserved. It is also obvious that the order in which the strips 32, 34 and the interconnected plates 36 are assembled prior to curing may be interchanged. In certain cases it may be desirable to remove the interconnecting strips 60 immediately after the plurality of plates 36 have been positioned so that the bridging portions 60 do not interfere with the molding apparatus. The external insulating layers 40 and 42 need not be formed of the same insulating material as that interposed between conductor 34 and plates 36. In some cases, the external insulation may be eliminated entirely. Accordingly, while the novel laminated suppressor bus has been disclosed in a preferred embodiment, numerous changes to the specific structure are possible without losing the essential benefits of the laminated construction. The laminated bus and its method of manufacture have, accordingly, been described by way of illustration rather than limitation.