US 3559435 A
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Description (OCR text may contain errors)
Feb. 2, 1971 GERBER 3,559,435
LIQUID BRIDGE WIRE Filed Sept. 25, 1968 3 Sheets-Sheet 1 III! --I|||| X I ig-iii if; 1} 5m \4 ii 3 ft": 6 I :1 I ""ll "'"ln J J? m 11m ||||H TANK ELECTRIC STORAGE UNIT INVENTOR HOWA RD L. GERBER ATT'Y.
H. L. GERBER LIQUID BRIDGE WIRE Feb. 2, 19711 Filed Sept. 25. 1968 3 Sheets-Sheet 2 tr/ V//// INVENTOR HOWARD L. GERBER BY 4 z a m 2,, W71 H. L. GERBER 3,559,435
LIQUID BRIDGE WIRE Filed Sept. 25, 1968 I5 Sheets-Sheet 5 INVENTOR HOWARD L. GERBER United States ABSTRACT OF THE DISCLOSURE An electrohydraulic system having two electrodes spaced in water and a very small conduit through one electrode to direct a thin stream of conductive liquid from that electrode to another electrode so that any discharge across the electrode follows the path provided by the conductive liquid.
My invention relates to an electrohydraulic spark discharge system and particularly to an electrohydraulic spark discharge system which has a liquid bridge wire of highly conductive liquid.
Electrohydraulic forming systems of the prior art have used in many cases two electrodes having only a space therebetween and in other cases have used a conductive bridge wire across the space to form a conductive pathway for the heavy current which passes between the electrodes to form a spark discharge. The bridge wire system is subject to the disability that each time the system is fired the bridge wire must be replaced. This system is very slow to operate.
Firing an electric current across two electrodes produces a non-uniform path for the electric discharge. Because of the nonuniform path the pattern of strength generated by firings is variable. Further, the breakdown potential necessary to start discharge across this path varies. Discharge through an insulating liquid requires large electric fields and a resultant short gap with short gap tolerances. This gives rise to a high rate of erosion of electrodes and a greater susceptibility to variable gap spacing. Performance from test to test may vary greatly because of the shortness of the gap between the electrodes and erosion caused by repeated firing, the percentage variance of the gap causes differences of impulse and differences of potential necessary to break down the gap. Because of these facts a varying amount of residual energy is available for forming.
By using an electrically conductive preferential pathway and controlling the diameter and the type of flow in the pathway I can control the magnitude and direction of the pressure wave using a minimum of electrical energy to establish a highly conductive plasma in a particular configuration. Generally, for best efiiciency the pathway is of small diameter with maximum energy density.
The breakdown in this process is not an avalanche, as in the case of dielectric breakdown, but a plasma that grows until a critical size is achieved. After this critical size is achieved an avalanche of electrons proceeds and rapid breakdown occurs, During the time of the plasma growth the flowing conductor and conductor pathway determines the discharge path. After the critical size is reached, the discharge is determined mainly by the elecatent 3,559,435 Patented Feb. 2, 1971 "ice tric fields and photo-ionization. The fact that the plasma growth follows the conductive solution is a primary advantage of this conductive system. The breakdown is controlled by directing the fiow of the conductive fluid. If nonsymmetrical forming is required, the flow can be appropriately directed as indicated elsewhere in the disclosure; If repetitive forming is contemplated as in can forming the saving of electricity and fluid are appreciable. No energy is lost as in breaking down an insulating liquid because a conductive pathway is provided.
It is an object of this invention to provide an electrohydraulic spark discharge system having high efficiency and a low energy requirement for breakdown.
It is a further object of this invention to provide an electrohydraulic system in which the arc discharge can be repeated at a rapid rate with uniform results.
It is a final object of my invention to provide an electrically conductive pathway of small diameter and maximum energy density.
In brief, my invention is a can shaped pressure chamber having a thin expansible outer membrane forming the outer shell of the chamber. The chambers filled with water and two electrodes project into the chamber. A thin stream of highly conductive liquid is pumped through a small hole in one electrode and impinges against the other electrode. When a high potential is placed across the electrodes, current preferentially follows the highly conductive stream giving a discharge of uniform strength and shape from one electronic discharge to the next electronic discharge.
Other objects and advantages of the present improved method and apparatus will become apparent during the following discussion of the drawing, wherein:
FIG. 1 is a right-side elevational view partly broken away and partly in section showing an electrohydraulic forming apparatus of my invention.
FIG. 2 shows an embodiment of the electrohydraulic chamber of my invention wherein one electrode is concentrically mounted about another.
FIG. 3 shows a schematic diagram of the synchronous electrical and hydraulic firing system.
FIG. 4 shows an embodiment of my invention with one electrode mounted above another.
FIG. 5 shows the embodiment of my invention with one electrode mounted above another and swirling water about the conductive path.
FIG. 6 shows a detailed view of the electrohydraulic chamber, can body and stylizing die of FIG. 1.
Electrohydraulic forming devices are used in various applications and my arrangement can be used in various applications but is shown here in FIG. 1 as a device for forming or stylizing a can. One type of forming apparatus 1 for a tubular material is shown here. A control panel may be provided at the front of the apparatus to control the various steps of the forming operation. An energy storage unit 2 is shown to store large amounts of electricity in capacitors. A bank of capacitors may be in the storage unit, and power cables conduct the energy from the capacitors to the electrodes of the die assembly.
The die assembly 3 illustrated is used for forming a can to give a stylized exterior around the peripheral circumference of the can. The die assembly 3 has a pair of vertical split die halves 4 carried in a pair of die holders 5 which are adapted for a snug fit. Inserts 6 are provided in the die holders so that they may fit the die halves being used in the particular application. The split die holders 5 are mounted on the frame of the apparatus for horizontal movement between a closed forming position and an open or unloading position wherein the die halves are spaced apart from each other in a horizontal direction. The arrangement in FIG. 1 is shown only for purposes of illustration.
The embodiment of my invention in FIG. 2 shows a channel 7 centrally located in the primary electrode 8 and mounted in the center of the electrode holding stations. A durable elastomeric boot 9 is mounted about the electrodes and sealed to form a chamber. A conductive solution or electrolyte is pumped down through the center channel 7 of the inner electrode 10 around the outer electrode 11 and back up into the exit conduit 12. Ordinary tap water or distilled water, as may be de sired, is pumped into the forming element through conduit 13 down into the bottom 14 of the chamber where it passes back toward the electrode station 8 and passes out of the chamber along with the conductive solution. In this way there is little or no contamination of the water. All channels and ports are shown oversized for ease of illustration.
If a valve 15 is inserted in the conduit 16 which feeds the conductive solution through the center electrode 8 (FIGS. 2, 4 and 5), the conductive solution may be used as a trigger for allowing the storage capacitor 2 to discharge electricity from one electrode to the other electrode. If the arrangement of the parts in the can chamber is such as to allow the conductive solution to function as a trigger then the circuit arrangement shown in FIG. 3 may be used. The tank valve and trigger '17 are synchronized so that shortly after the conductive solution forms a conductive bridge between the electrodes the electric current is triggered and released to pass current from one electrode through the conductive bridge and to the other electrode. The conductive solution is exploded and generates force which may be used to electrohydraulically form a workpiece into a die cavity as shown in FIG. 1. By
intermittent flowing of the conductive solution a savings of solution is effected. However, the conductive solution may be run continuously if so desired.
As an alternative embodiment the electrodes may be mounted one above the other and concentric to a common axis as show-11in FIG. 4. In this embodiment the conductive solution is passed into the chamber through a channel 18 along the axis of the upper electrode 19 and passes out of the chamber through a channel in the lower electrode 20. Located radially from the channel are ports 21 for admitting water or some other nonconductive pressure transmitting liquid such as benzene or acetone. This water flows through the chamber in the same direction as the conductive solution. The conductive solution and 'water may exit together as waste (FIG. 4) or may exit separately as shown in FIG. 2.
In FIGS. 2 and 4 the internal edges 22 of the electrodes are shown in the rounded condition they assume after repeated arcings between the electrodes have caused erosion of the electrodes along their inner edge near the conductive solution. The electron current in the embodiment shown is from the lower cathode to the upper anode 19. The upper electrode is more easily replaced and wears more rapidly due to electron impact. In order to reduce erosion due to heat vaporization materials such as tungsten copper, tungsten silver, tungsten and stainless steel may be used in the upper and lower electrodes.
The upper and lower electrode arrangement appears more attractive since the arc is directed vertically from one electrode to the other. In this arrangement the force of the pressure or shock wave is primarily radial (cylin drical wave) and transmits maximum force against a can side to alter its shape. In the upper and lower electrode arrangement the conductive solution and the water move at about the same speed so that there is very little mixing between them.
The shaping 23 of the upper and lower ends of the electrohydraulic compartment is designed to promote an even application of force to the sides of the can. As an optimum the length of the wave path is adjusted so that reflected waves interfere and there is a simple cancellation of all impulses except the initial shock Wave.
In FIG. 5 the electrodes are located one above the other each having a conduit solution entrance. The principal difference between the embodiment of FIG. 5 and that of FIG. 4 is that the water is given a tangential swirl by conduit 24 in the embodiment of FIG. 5. The tangentially swirling water plus any conductive solution which has been diffused into the tangentially swirling water is removed at a lower point and carried oif as shown at a water exit port. The conductive solution passes to the lower electrode port 25'where it is drawn oif'a'nd passed" up through one or more of the pillars 26 to a conductive solution exit port 27.
These elements of the electrohydraulic structure fit into a rubber boot 28 thus forming a chamber 29. The electrohydraulic chamber 29, can body 30 and stylizing die 4- are all mounted upon a can forming machine as shown in FIG. 1.
Greater detail of the electrohydraulic chamber 29, can body 30 and stylizing die 4 is shown in FIG. 6. A lifter plate 31 is underneath the entire structure and its contour is such that it fits exactly the bottom of the can being formed. Surrounding the electrohydraulic chamber 29 and the can body 30 is a stylizing die 6. The interior of this die is contoured to be the complement of the desired finish of the can. Very clearly the interior of the die can be used for reshaping, reforming, fine detail embossing or changing the can body shape. This forming chamber is usually made of split dies so that the die may be readily removed from the can after the can has been formed. The formed can is stronger and has greater volume than the unformed can.
Considering the elements of the electrohydraulic chamber and proceeding from the outside, the first element of the electrohydraulic chamber is the rubber membrane or boot 9 which surrounds and forms the outer element of the chamber. When an electrohydraulic arc is formed the boot is pressed outward from within and pressed against the can to push the can into the interstices of the forming die 6. The electrodes 32, 33 and their supporting structures 34, 35 are held a certain distance apart by support pillars 36 which extend from the upper electrode support structure 34 to the lower support structure 35. These pillars 36 may be hollow so that returning electrolyte and returning water may be passed through them. The supporting structures about the upper and lower electrodes are formed in the shape of a reflector so that impulses which come from the are between the electrodes are refiected to the area of the rubber boot 9 located near the top and bottom of the can which is to be stylized. In this way the pressure against the side of the can is more equalized throughout than would be the case without the reflectors. If the hydraulic length of wave travel between the point of generation and the point of impact is one quarter of a wave length than the second and subsequent waves interfere to give a net result of one wave only impinging on the boot and without reverberations.
Between the electrode and the upper supporting structure is an electrode insulator, which may be made of a rubberized material. The electrodes are located so that the are produced between them is central in the chamber to give a constant and nearly even impact against the sides of the chamber each time the arc fires.
The pressure transmitting liquid may be water but if maximum pressure transmission is desired a sorbitol or methylene chloride solution or benzene or acetone may be used. Concentrated solutions of sorbitol or methylene chloride produce a minimum of fifty percent (50%) more deformation than is produced by using water as the pressure transmitting liquid.
It is understood that the liquid in the chamber may be under pressure prior to the discharge of the electrohydraulic are as set forth in the application titled, Apparatus for Hydraulic-Electrohydraulic Forming of Tubular Elements, by Donald J. Roth and assigned to the same assignee as the present invention.
An advantage to the method and apparatus of the present invention is that a lighter weight can is possible because of walls which are strengthened by stylizing.
Another advantage is that the use of an electrolyte passing through water permits interior pressure to be exerted upon the chamber walls while the electrolyte is being jetted through the water.
A further advantage is that by circulating the solution and water in the same direction loss of conductive solution by mixing is held to a minimum.
Another advantage is that each pressure wave is of similar shape and strength to impart a similar result to a series of cans.
Another advantage is that higher efficiencies result because of the restriction of electric breakdown to a smaller volume with high energy density and less energy lost in breakdown.
Another advantage is that larger gaps and gap tolerances can be used with a liquid electrolyte because the current flow is restricted in cross section.
The final advantage is that savings of conductive fluid and electricity are effected where high speed operation with many arcings per minute is desired.
The foregoing is a description of the illustrative embodiment of the invention and it is applicants intention in the appended claims to cover all forms which fall within the scope of the invention.
What is claimed is:
1. An electrohydraulic device for forming tubular workpieces adapted to be inserted into a forming die comprismg:
a chamber of elastomeric material,
a first electrically nonconductive liquid in said chamber for transmitting a pressure wave,
electrodes mounted in said chamber and adapted for connection to an external power source,
means for establishing an ionized liquid preferential conductive pathway of small diameter between said electrodes.
2. An electrohydraulic device for forming tubular workpieces as set forth in claim 1 wherein said external power source comprises:
electrical energy storage means, and
means for conducting said first liquid into and out of said chamber.
3. An electrohydraulic device for forming tubular workpieces and adapted to be inserted into a forming die comprising:
a first electrode having a channel therethrough for passage of a fluid, a second electrode spaced from said first electrode, a chamber of elastomeric material mounted about said electrodes and having a nonconductive fluid therein,
means for forcing an electrolytic fluid through said channel and toward said second electrode to form a preferential conductive pathway between said electrodes,
means for providing a shielding current of fluid between said nonconductive fluid and said electrolytic fluid to avoid mutual contamination, and for flowing a nonconductive pressure transmitting fluid into said chamber,
means for conducting the overflow of said chamber out of said chamber, and
means for connecting energy storage means across said electrodes whereby an arc is formed when said preferential conductive pathway is established.
4. An electrohydraulic device as set forth in claim 3 further comprising:
mounting means in the top of said chamber for holding said first and second electrodes,
said first electrode being generally tubular in shape,
said second electrode being generally tubular and larger in diameter than said first electrode and mounted so that its lateral surfaces generally surround the lateral surfaces of said first electrode, and
an insulator secured between said first and second electrodes substantially filling the space between said first and second electrodes.
5. An electrohydraulic device as set forth in claim 4 in which said shielding current means comprises:
a body mounted in the bottom of said chamber and having means for directing a shielding current about said electrodes whereby said conductive fluid and said nonconductivefluid are kept separate.
6. An electrohydraulic device as set forth in claim 3 having,
first mounting means for closing the top of said chamber and supporting said first electrode and an insulator,
insulator means fastened between said first electrode and said mounting means for electrically insulating the first electrode from said mounting means,
said second electrode being generally tubular in shape to form a channel therethrough and of about the same size as said first electrode where said electrolytic fluid is jetted from said first electrode to said second electrode and evacuated from said chamber through said second electrode.
7. An electrohydraulic device as set forth in claim 6 in which said shielding current means comprises:
an annular channel formed between said mounting means and said insulator means,
conduit means formed in said mounting means and connecting said annular channel to the exterior of said device.
8. An electrohydraulic device as set forth in claim 7 in which said overflow conducting means comprises:
a second mounting means for holding said second electrode from said first mounting support means for spacing said second mounting means from said first mounting means,
second conduit means in said mounting means and said support means for conducting the electrolytic liquid from said channel in said second electrode and conducting the fluid overflow through ports in the second mounting means to ports at the exterior of said first mounting means.
9. An electrohydraulic device as set forth in claim 6 in which said shielding current means comprises:
conduit means in said first mounting means for injecting a nonconductive fluid into said chamber at a bias whereby a spirally swirling shielding current is set up in said chamber.
10. An electrohydraulic device as set forth in claim 9 in which said overflow conducting means comprises:
a curved conduit extending from adjacent said second electrode to outside said chamber whereby said nonconductive fluid is evacuated from said chamber.
11. An electrohydraulic device as set forth in claim 10 in which:
third conduit means is connected to said second electrode channel for evacuating said electrolytic fluid from said chamber.
12. A method of pressure wave generation comprising the steps of:
jetting an electrolyte solution from one electrode to another through a nonconductive liquid to form a conductive bridge,
flowing a sheet of nonconductive liquid in a plane generally adjacent to and surrounding said conductive bridge to form a shield between said nonconductive liquid and said conductive bridge,
7 applying an electric potential across said electrodes whereby an arc is formed to generate a pressure wave.
References Cited UNITED STATES PATENTS 3,200,626 8/1965 Callender 72-56 3,222,902 12/1965 Brejcha et a1 72-56 8 2/ 1966 Inoue 72-56 5/1966 Grove, Jr., et a1. 72-56 7/1969 Balcar et a1. 72-56 US. Cl. X.R.