US3414501A - Method and apparatus for shaping, sharpening and polishing razor blades - Google Patents

Description

Dec. 3, 1968 J. B. KRUGER 3,414,501

METHOD AND APPARATUS FOR SHAPING, SHARPENING AND POLISHING RAZOR BLADES Filed Dec. 21, 1964 5 Sheets-Sheet 1 METHOD AND APPARATUS FOR SHAPING, SHARPENING Dec. 3, 1968 J. B. KRUGER 3,414,501

AND POLISHING RAZOR BLADES 5 Sheets-Sheet 2 Filed Dec. 21, 1964 Dec. 3, 1968 J.B.KRUGER METHOD AND APPARATUS FOR SHAPING, SHARPENING AND POLISHING RAZOR BLADES Filed Dec. 21, 1964 5 Sheets-Sheet 3 Dec. 3, 1968 J KRUGER 3,414,501

METHOD AND A R US FOR SHA G, ARPENING P SHING RAZ B ES Filed Dec. 21, 1964 5 Sheets-Sheet 4 J. B. KRUGER Dec. 3, 1968 METHOD AND APPARATUS FOR SHAPING, SHARPENING AND POLISHING RAZOR BLADES 5 Sheets-Sheet 5 Filed Dec. '21, 1964 mum ii R m? i mm :3 Q mm United States" Patent 3,414,501 METHOD AND APPARATUS FOR SHAPING, SHARPENING AND POLISHING RAZOR BLADES James B. Kruger, Staunton, Va., assignor to Philip Morris Incorporated, New York, N.Y., a corporation of Virginia Filed Dec. 21, 1964, Ser. No. 419,836 6 Claims. (Cl. 204206) ABSTRACT OF THE DISCLOSURE An apparatus and method for electrolytically shaping a cutting edge on a continuous length of razor blade stock in which the blade stock is advanced edgewise through an electrolytic machining chamber spacedly adjacent working faces of cathode electrodes in the machining chamber to effect electrolytic removal of metal from the stock in correspondence with the shape of the cathode electrode working faces, the continuous length of razor blade stock being rendered anodic in the electrolytic circuit by advancing it through a liquid contactor bath connected with the positive terminal of a DC power source preliminary to its entry into the machining chamber, the cathode electrodes each being provided with slotted electrolyte feed passages outletting at the working faces for delivering fresh electrolyte to the gap between the working faces and the edge surface being formed on the stock.

This invention relates to a method and apparatus for producing cutting blades and refers more particularly to a method and apparatus for electrolytically shaping, sharpening and polishing razor blades in a continuous strip and in a continuous operation.

Prior art production of razor blades generally involves feeding a continuous strip of blade stock through a series of abrasive grinding wheels, polishing wheels and like tools, which sharpen and finish the strip, the strip thereafter being severed into individual blades. One of the disadvantages inherent in these prior art methods is that the grinding wheels generate considerable heat at the cutting edge of the blades which in some cases may change the metallurgical character of the material, whereby blade strength is diminished and the life of the cutting edge materially lessened. An additional disadvantage involves the minute defects left in the surface finish of the cutting edges by the finishing wheels. These surface defects give rise to excessive friction along the sides of the blades where they contact the material being cut (whisker hairs for example) and thus impair the efiiciency of cutting action. Another problem engendered by prior art methods is the physical limitations imposed in moving shaping tools, grinders and related equipment of complex shape and size at the high speeds required for large scale production of razor blades and like devices. While it has been known in the prior art to shape and sharpen tools, needles etc. by means of electrolytic reduction, it has not been proposed to shape, sharpen and finish a continuous strip of razor blades by means of electrolytic machining and polishing in a continuous operation. Nor has it been proposed to utilize the flexibility of the electrolytic technique to generate cutting edges which heretofore were impossible to attain through use of conventional grinding techniques.

It is, therefore, a primary object of the present invention to provide a method of electrolytically shaping, sharpening and polishing razor blades.

Another object is .to provide a method of shaping, sharpening and polishing razor blades which eliminates 3,414,501 Patented Dec. 3, 1968 "Ice heretofore essential but undesirable mechanical sharpening operations, as for example grinding.

Another object is to provide a method and apparatus for shaping, sharpening and polishing a continuous strip of razor blades in a continuous operation.

Another object is to eliminate the use of costly equipment such as grinding and polishing wheels in the production of razor blades.

A further object is to provide a method of shaping, sharpening and polishing razor blades which reduces production costs and increases production rates measurably beyond those heretofore possible.

A still further object is to provide a method of producing razor blades which permits a wide latitude in design of blade geometry overcoming prior art limitations wherein the blade geometry was generally that marked by a series of arcs generated by a grinding wheel.

Another object is to provide a method of producing razor blades which permits cutting edges of various shapes to be formed such as straight, concave, convex and combinations thereof.

Another object is to provide a method and apparatus for electrolytically shaping, sharpening and polishing razor blades which is applicable to use on materials from very hard steels to materials which are relatively soft such as aluminum.

Other objects of the present invention will become apparent during the course of the following specification.

In achieving the aforementioned objectives of the present invention a continuous strip of razor blade stock which has been connected to the positive side of a DC current source is fed through an electrolytic machining chamber comprising one or more cathode electrodes having working faces which are specially shaped at least in the final stages to correspond with the shape of the blade edge desired. The strip passes through the electrolytic machining chamber in close spaced relation with the cathode electrodes, the gap therebetween being filled with a suitable electrolyte, the electrolyte being fed onto the strip through orifices formed in the cathode electrodes. Since the cathode electrodes are connected with the nega tive side of the DC current source, an electrolytic flow ensues between the strip, electrolyte and cathodes resulting in the removal of material from the strip, the metal removed being carried off in the electrolyte. As the strip passes through the electrolytic machining chamber, the cutting edge is shaped and sharpened according to the constantly changing shape of the cathode working faces. When the strip exits from the electrolytic machining chamber, it is directed through an electrolytic polishing chamber wherein it is subjected to an electrolytic action in the same manner but to a considerably lesser degree than that occurring in the electrolytic machining chamher.

The invention Will appear more clearly from the following detailed description when taken in conjunction with the acompanying drawings showing by way of example a preferred embodiment of the inventive concept.

In the drawings:

FIG. 1 illustrates diagrammatically, apparatus for shaping, sharpening and polishing razor blades in a continuous strip in accordance with the principles of the present invention;

FIG. 2 is a perspective view of one of the cathode electrodes which may be utilized in the electrolytic machining and polishing chambers;

FIG. 3 is a front elevational view of the cathode electrode shown in FIG. 2;

FIG. 4 is a front elevational view of an insulating spacer used in the electrolytic machining and polishing chambers;

FIG. 5 is a side fragmentary elevational view showing the alternating arrangement of cathode electrodes and insulating spacers in the electrolytic machining and polishing chambers;

FIG. 6 is a longitudinal sectional view of the construction shown in FIG. 5, the view being taken on a vertical plane passing through the center of the cathode electrodes and insulating spacers;

FIG. 6a is a front elevation, partly in section, illustrating the form of casing which may be used for enclosing the electrolytic machining and polishing chambers, and the piping for supplying and removing electrolyte, the height/width ratio of the blade strip being greatly exaggerated for purposes of clarity;

FIG. 7 is a fragmentary perspective view showing a portion only of the composite cathode electrode and insulating spacer construction in the electrolytic machining chamber, and the manner in which its contour gradually changes to effect the shaping and sharpening of the strip of razor blade stock, the electrolyte orifices and outlet passages in the cathode electrodes and insulating spacers not being shown in detail;

FIG. 8 is a perspective view of a longitudinal half-section of another embodiment of cathode electrode wherein the cathode is of single piece construction;

FIG. 9 illustrates diagrammatically the progressive shaping of the blade edge on the strip at various stages of its advance through the electrolytic machining chamber;

FIG. is a perspective view of another form of cath ode electrode which may be utilized in the electrolytic machining and polishing chambers to direct flow of elec trolyte away from the final shaped and sharpened blade edge;

FIG. 11 is a perspective view of the insulating spacers used in conjunction with the cathode electrode shown in FIG. 10;

FIG. 12 is a front elevational view of the composite arrangement of cathode electrode and insulating spacer of FIGS. 10 and 11 showing the path of electrolyte flow therethrough; and

FIG. 13 is a schematic wiring diagram illustrating the manner in which the cathode electrode and strip of razor blade stock are connected with the DC source of current, and the means by which the current input is controlled at various points in the electrolytic machining and polishing chambers.

Throughout the specification like reference numerals are used to indicate like parts.

Referring now in detail to FIG. 1, a continuous strip 1 of razor blade stock is fed over billy roll 2 into the mercury bath 3 of a mercury chamber 4 which is connected as at S with the positive terminal of a direct current output from the circuit generally indicated at 6, the strip which is of conductive material thus becoming an anode. Of course, any other liquid contactor employing a suitable electrolyte may be employed for the latter purpose in place of the mercury bath. The razor blade stock may be a continuous band approximately .010" thick in the case of single edge injector type blade stock or it may be a band used for manufacturing double edge blades in which case it may be approximately .004" thick and be provided with spaced central, longitudinally directed slots which are common to double edged blades for locating the blades in the razor type with which they are used. The strip advances around idler roll 7 in the mercury chamber 4 exiting therefrom onto another billy roll 8 and through a mercury scrub chamber 9 wherein mercury residue is removed in known manner from the strip, mercury vapor from the bath 3 and scrub chamber 9 being exhausted by means of exhaust pipes 10 and trap 11. The strip then passes through feed rolls 12 and onto turning rolls 13 which change its orientation from a horizontal to a vertical plane preparatory to its advance into the electrolytic machining chamber 14.

The electrolytic machining chamber 14 shown in FIG- URES 2 and 3 comprises a plurality of cathode electrodes 15 interspaced with insulating spacers 16 (FIG. 4), this alternating or segmental arrangement being best seen in FIG. 6. The cathode electrodes may further be arranged in groups 17, 18 and 19, each group being connected respectively with an associated bus bar 17', 18' and 19. The bus bars 1719 are each connected as at 20 with the negative terminal of the direct current output of circuit 6 in the manner to be described later in detail.

Each cathode electrode 15 and insulating spacer 16 is provided with an upper slotted opening 21 and a pair of lower symmetrically arranged openings 22 and 23 (FIGS. 3 and 4) so that the composite construction is provided with an electrolyte feed plenum 24 comprised of the aligned openings 21, and return flow plenums 25 and 26 comprised of the aligned openings 22 and 23, respectively, (FIG. 6a). Referring again to FIG. 1, electrolyte 27 (FIG. 3) is fed to electrolytic machining chamber by means of pump 28, the electrolyte passing through filtration tank 29, electrolyte analyzer 30 wherein it is analyzed for conductivity, pollution, etc. and thence by pipe 31 to plenum 24 (FIG. 6a). Return flow from plenums 25 and 26 to pump 28 may be made by means of pipe 32 as shown in FIG. 60. As seen in FIGS. 2 and 3, the front face of each cathode electrode 15 is provided with a downwardly tapering sluice 33 which directs electrolyte flow across the upper surfaces of the blade strip 1, the electrolyte thereafter flowing to return plenums 25 and 26 by means of slots 34 in the rear face of the cathode electrode, the electrolyte flow path being generally indicated by the arrows in FIG. 6.

In the construction shown, the electrolyte feed is preferably maintained as a closed system, with the cathode electrodes, insulating spacers and bus bars comprising the electrolytic machining chamber being enclosed in a casing 35 (FIG. 6a) which may be insulated from the bus bars and cathode electrodes in conventional manner (not shown). During the electrolytic machining of strip 1, a

'certain amount of hydrogen gas may be generated and is conveniently removed from the electrolytic machining chamber by means of burn-off pipe 36 (FIG. 1). To compensate for loss of electrolyte due to leakage, dilution etc., an electrolyte make-up feed tank 37 is provided, it being controlled automatically in known manner by a signal received from electrolyte analyzer 30.

It will be readily understood that the strip 1 enters the electrolytic machining chamber as a rectangle and during its passage therein has the shape of its upper edge portion changed to that of the desired blade cutting edge shape. For example, the cutting edge may comprise the two straight sides of an isosceles triangle with the included angle being of a very small measure, as for example, between 18 to 24. On the other hand, the cutting edge may comprise two intersecting convex surfaces with the included angle, once again, being very small. It is thus necessary that the geometry of the cathode electrodes 15 be of a constantly changing character from entry to exit of the electrolytic machining chamber. In other words, the cathode electrode 15 shown in FIGS. 2 and 3 has a triangularly slotted segment 38 through which the strip 1 passes in very close proximity therewith (0.0" to .010") since this particularly so shaped segment, as seen in FIG. 3, is utilized at a location well toward the end of the electrolytic machining chamber at which point the shaping of the triangular cutting edge 39 (FIG. 6a) is almost completed. The cathode electrodes near the entry to the electrolytic machining chamber will not, however, have such a radically angled segment. In fact they will present a segment with relatively flat surfaces or working faces 40 which lie opposed to the upper corners of the edge of the blade strip for the purpose of starting metal removal at the corners as seen in step a, FIG. 9, the removed metal being carried off in solution in the electrolyte 27. As the blade strip advances in the electrolytic machining chamber, the cathode electrode shapes undergo a smooth but constant transition presenting segments whose side surfaces or working faces 40 change from relatively fiat to more acutely inclined, following generally the transition illustrated in steps a to e, FIG. 9.

As a further understanding of the foregoing, reference is made to FIG. 7 wherein the shaping of blade strip 1 from generally rectangular cross section to one having a triangular cutting edge 39 is clearly seen. The arrangement of a one-half portion only of all the cathode electrodes and insulating spacers comprising the electrolytic machining chamber is generally denoted by reference numeral 41 in FIG. 7. It will be seen that from entry to exit of the electrolytic machining chamber, the cathode electrodes and insulating spacers have segments which not only change from flat to acute angular, but segments in which the height from base to apex is constantly changing. If the blade cutting edge 39 is to be triangular as shown, the apices of the triangular shaped segments in the cathode electrodes will lie on and along the slightly, downwardly curving line 42. In a like manner, the lower extremity of the sides or working faces of the segments will lie upon a line that curves inwardly and downwardly as along the line 43. For the sake of clarity in the drawing, feed plenum 24 and return plenums 25 and 2 6 are not shown in FIG. 7 in detail other than is shown with respect to the constructional details of the endmost cathode electrode 15. It will be apparent that the cathode electrode geometry may be varied within the scope of this invention according to the shape of the cutting edge to be formed on the blade strip. For example, a cutting edge comprised of convex intersecting surfaces will require that the cathode electrodes segments undergo a transition from initially flat to arcuate surfaces or working faces.

It is further apparent that the electrolytic machining chamber will include a large number of cathode electrodes. It will be readily apparent that the problem of feeding a rectangular shaped strip into the electrolytic machining chamber and shaping it therein with a specific shape of blade cutting edge, involves precision to the highest degree in design and fabrication of the cathode electrodes. Not only must the cathode electrodes be provided with the necessary and constantly changing contoured surfaces or working faces to gradually shape the strip, but they must define a smoothly transitioning path that maintains the gap between the wonking faces and the moving strip within the limits required for effective electrolytic erosion. If the gap is too large, electrolyte discontinuity may occur and metal removal will cease.

The cathode electrode 15 and its companion insulating spacer 16 illustrated in FIGS. 10 to 12 are intended for use at the terminal portions of electrolytic machining chamber 14 and in the electrolytic polishing chamber 44 to be described later in the specification. Instead of having a centrally disposed sluice for delivering electrolyte onto the strip 1, cathode electrode has in its front face a pair of inwardly angled channels 45 and 46 which direct the electrolyte feed (as shown by the arrows, FIGS. 10 and 12) away from the upper surfaces of the faces of cutting edge 39 generated in the earlier stages of strip movement and in particular, where it is desired to minimize impingement of fresh electrolyte against the final edge of the moving strip. Return feed of the electrolyte is made through appropriate slots in the insulating spacer Referring again to FIG. 1, the blade strip 1 leaves the electrolytic machining chamber with the cutting edge 39 generally shaped and sharpened as shown in step e, FIG. 9. It then passes through turning rolls 47 which orient the strip to a horizontal plane for feeding into feed rolls 48 from whence it is led out into a strip loop as at 49' for providing speed control of the strip through the apparat-us. The strip speed may be controlled in a known manner by a photoelectric detection device and other conventional means (not shown). The strip then passes through feed rolls 48' and onto turning rolls 50 which reorient the strip vertically for its entry into electrolytic polishing chamber 44.

Electrolytic polishing chamber 44 is constructed similarly to electrolytic machining chamber 14 and comprises a plurality of alternately arranged cathode electrodes (preferably the type shown in FIG. 10 although the actual geometry of the cathode electrodes will be that commensurate with the intended polishing operation and shape of blade cutting edge) and insulating spacers, the cathode electrodes being arranged in groups 51 and 52, the groups being connected with bus bars 51' and 52' respectively, the bus bars being connected as at 53 'with the negative terminal of the direct current output of circuit 6. Electrolytic polishing chamber 44 is supplied with electrolyte 27 in the same manner as electrolytic machining chamber v14, having a pump 54, filtration tank 55, electrolyte analyzer 56, make-up feed tank 57 and hydrogen burn-01f pipe 58.

The blade strip 1 is subjected to a polishing action within the electrolytic polishing chamber which removes only minute quantities of metal therefrom in relation to that removed in the electrolytic machining chamber. For this reason, the conductivity and the character of the electrolyte will be considerably different that than maintained in the electrolytic machining chamber.

It is also possible within the scope of the present invention to subject the blade strip 1 to a shaping and sharpening in the electrolytic machining chamber 14 and thereafter honing the keen cutting edge by known honing procedure rather than utilizing an electrolytic polishing chamber.

Upon leaving the electrolytic polishing chamber, the now shaped, sharpened and polished razor blade strip 1 is oriented to a horizontal plane by turning rolls 59 and fed by feed rolls 60 into a neutralizing and drying chamber 61. The neutralizing and drying chamber removes and/or renders neutral any electrolyte residue remaining on the strip.

Upon leaving the neutralizing and drying chamber, the blade strip passes through the jaws 62 of a blade breaker which severs the strip into individual razor blades 63.

The particular means of controlling the current in the electrolytic machining and polishing chambers is illustrated in FIGS. 1 and 13. As seen in FIG. 1, the electric circuit 6 includes a separate magnetic amplifier 64, DC rectifier 65 and saturable reactance coil 66 associated with each of the cathode electrode groups 17, 18, 19, 51 and 52 connected electrically therewith through their respective bus bars. Referring in detail to FIG. 13, one leg 67 of the AC input is wound around one side of each saturable reactance coil 66 as at 68. The input to the saturable reactance coil is by means of winding 69 connected to one leg 70 of the magnetic amplifier 64. The other leg 71 of the magnetic amplifier receives its power from the winding 72 connected across the AC power main. The center stator 73 of magnetic amplifier 64 is connected as shown by means of winding 74 with a shunt 75 which is in series with the associated electrode group 19 in the electrolytic machining or polishing chambers, and the negative terminal of DC rectifier 65. The positive terminal of the DC rectifier is connected by line 76 to mercury chamber 4. The DC current flow is thus from the rectifier to the mercury chamber, through mercury bath 3 to strip 1, from strip 1 through the thin layer of electrolyte 27 to the cathode electrode 15, through shunt 75 and back to the rectifier. As the strip 1 advances through the electrolytic machining and polishing chambers, the DC current will change at various points. This results from a change in the conductance of the electrolyte due to its contamination with the metal removed from the strip, and an increased resistance across the gap between the cathode electrodes and moving strip 1. Since it is preferable that the current density remain fairly constant (approximately 300 amperes per square inch) throughout the electrolytic machining and polishing chambers, the changes in the DC current will be manifested in shunt 75 and communicated to magnetic amplifier 64 which in turn controls the output of saturable reactance coil 66 and hence the AC voltage input to rectifier 65 thereby compensating for the DC current changes. It should be apparent that the functioning and purpose of each saturable reactance coil, magnetic amplifier and DC rectifier are the same for their associated cathode electrode groups.

In general, the DC voltage in the circuit may vary between 10 and volts, with the DC current being approximately 175 amperes for a strip speed of approximately feet/minute. The gap between the strip and cathode electrode working faces is preferably maintained between 0.0" and .010, and the total cathode electrode length in each chamber is approximately 7.15 inches for a strip speed of 40 feet/minute.

A number of electrolytes have been found suitable for use in the present invention including 20% NaCl and NaClNaNO solutions.

In general, it is advantageous to use a high strip speed as rapid strip movement irons out surface defects and promotes better finish. This is believed to result from the fact that rapid movement of the strip serves to distribute the deleterious effects (backwash, under-cutting, contamination, etc.) of improper electrolyte over a long length. In other words by moving the strip rapidly past the electrodes, defects in electrolyte or electrode conditions at any given point do not have a chance to materially effect the cutting edge being formed. This is a distinct improvement over other prior art electrolytic machining methods wherein generally the workpiece is fixed relative to a moving electrode and transient cycle faults are reproduced in the workpiece.

FIGURE 8 illustrates a different embodiment of cathode electrode which may be used in the electrolytic machining and polishing chambers in place of the plurality of cathode electrodes 15 and insulating spacers 16 illustrated in FIGURES 2 to 4. In the embodiment of FIG- URE 8 only one-half of the cathode electrode 80 is shown. The cathode electrode 80 comprises an elongated blocklike body which is provided at its top center with a well 81 which is threaded internally as at 82 to provide connecting an electrolyte feed hose (not shown) to the cathode and the well 81 is in communication with longitudinal manifold passages 83 and 84 which are closed at the ends by means of plugs 85 and 86 respectively. Down flow passages 87 extend downwardly from the well and manifold passages as shown to direct electrolyte feed down onto the blade strip (not shown) advancing through the cathode in close spaced relation to the working faces 88 thereof, the working faces having the same smooth constantly changing contour as previously described. The top of the cathode electrode 80 is provided with a terminal 89 for connecting the negative output lead 90 of the direct current circuitry. It is seen that the bus bar connectors previously described are unnecessary when using this form of cathode electrode. The current control circuitry used in conjunction with cathode electrode 80 is otherwise the same as that shown in FIGURE 13.

It will be seen from the above description that the present invention offers a number of important advances in the production of razor blades. It eliminates the need for heavy, expensive equipment which shape and sharpen blades :by purely mechanical operations. It permits blades to be shaped and sharpened from a continuous strip in a continuous operation. Furthermore, it permits the shaping and sharpening of blades with improved cutting edges and with cutting edges of shapes distinctly different from those produced by prior art methods and apparatus. It is also applicable to producing blades of material heretofore considered too soft for machine grinding such as aluminum, and materials previously considered too hard for machine grinding such as tungsten carbide. Since it utilizes the principle of electrolytic reduction, blade production may be increased two to six fold beyond the capacity of known mechanical grinding methods. The latter is attributable to the fact that in mechanical grinding, the line speed cannot exceed a given ratio with respect to surface grinding speed or else the strip would have the effect of dragging across the wheels. No such limitation is imposed upon strip speed when employing the method of the present invention. Increased speed is achieved by increasing the total electrode length and for current density.

A most important feature of the present invention is that the cathode electrodes do not wear out as contrasted with the expense of periodically replacing grinding wheels, stropping devices and similar equipment in purely mechanical grinding methods. Another important feature of the invention is that the use of a large number of individual cathode electrodes and insulating spacers in the electrolytic machining and polishing chambers gives rise to a pulsing generated by the discontinuous nature of the electrode field patterns encountered by the strip moving through these chambers. This pulsing contributes to reducing the problems of hydrogen build-up and electrolyte contamination so manifest in prior art electrolytic processes.

While there are above disclosed but some embodiments of the method and apparatus of the present invention it is possible to produce still other embodiments without departing from the scope of the inventive concept herein disclosed.

What is claimed is:

1. In apparatus for electrolytically shaping a tapered cutting edge on a relatively flat continuous, strip of razor blade stock rendered anodic in an electrolytic circuit which includes:

an electrolytic machining chamber comprising a plurality of transversely arranged, upright, longitudinally spaced cathode electrodes, and insulating spacers located between succeeding cathode electrodes, with each of said electrodes having a central slotted segment presenting shaped working faces past which the strip is spacedly advanced to efiFect metal removal from said strip to an electrolyte in contact with said strip and said cathode electrodes, with the shapes of said working faces gradually changing from a contour at the entry end of the machining chamber corresponding essentially with the edge shape of the strip to a shape at the exit end of the machining chamber corresponding to the shape of the cutting edge to be formed, the improvement wherein said working faces comprise a pair of surfaces arranged symmetrically on each side of the longitudinal axis of said machining chamber and inclined with respect thereto, and

each of said cathode electrodes and insulating spacers have first openings therein which align one with the others and constitute an electrolyte feed plenum within said machining chamber,

each cathode electrode and insulating spacer further having second and third openings therein, the second and third openings of the respective cathode electrodes and insulating spacers aligning one with the others and constituting electrolyte return plenums in said machining chamber,

said cathode electrodes having at least one feed channel formed therein outletting at said working faces for communicating the space between said working faces and the edge surface of said strip with said feed plenum.

2. The apparatus of claim 1 wherein the working faces of said electrodes are flat surfaces only slightly inclined with the horizontal and in juxtaposition to the upper corners of the blade strip at the entry end of said machining chamber, said flat surfaces becoming more acutely inclined with the horizontal and ultimately intersecting one with the other in the direction of the exit end of said chamber.

3. The apparatus of claim 1 wherein the feed channels in said cathode electrodes comprise sluices extending vertically centrally in each cathode electrode and connecting the first openings in the respective electrodes with the working faces thereof for impinging electrolyte against the tip end of the cutting edge being formed.

4. The apparatus i-f claim 3 wherein said cathode electrodes are provided with return channels which communicate the working faces of the respective electrodes with the second and third openings therein.

5. The apparatus of claim 1 wherein the feed channels in said cathode electrodes comprise separate channels associated with each working face of the respective cathode electrodes and arranged symmetrically if the central axis of said machining chamber, said feed channels connecting the first openings in the respective electrodes with the working faces thereof at locations juxtaposed with the sides of the cutting edge being formed.

6. The apparatus of claim 5 wherein the space between said working faces and the edge surface of said strip is connected with said return plenums by means of return channels formed in said insulating spacers.

References Cited UNITED STATES PATENTS 1,942,025 I/ 1934 Frost 20428 2,667,456 1/1954 Young 204140 3,271,291 9/1966 Crawford et a1 204224 3,305,470 2/ 1967 Williams et a1. 204211 3,324,021 6/1967 Haggerty 204224 3,324,022 6/1967 Keeleric 204224 OTHER REFERENCES 1,005,458 9/ 1965 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner.

W. VAN SISE, Assistant Examiner.

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