US2871177A

US2871177A - Electrolytic grinding apparatus

Info

Publication number: US2871177A
Application number: US342372A
Authority: US
Inventors: D George E Comstock
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1953-03-16
Filing date: 1953-03-16
Publication date: 1959-01-27
Anticipated expiration: 1976-01-27
Also published as: GB770998A; FR1097716A

Description

G. E. COMSTOCK 3D ELECTROLYTIC GRINDING APPARATUS 2 Sheets-Sheet l INVENTOR. GEORGE E. C70M5T0UK,3R17.

ATTORNEY Jan. 27, 1959 Filed March 16, 1953 1959 G. E. cbMsTocK 3D 2,

ELECTROLYTIC GRINDING APPARATUS Filed March 16, 1953 2 Sheets-Sheet 2 j ---75 INVENTOR. W 84 GEDR'E'E E. CUM5TUUK,3RII.

722 C 52 BY 44%; 77am;- HG. 5 A

ATTORNEY ELECTROLYTIC GRINDING APPARATUS George E. Comstock 3d, Holden, Mass, assiguor to Norton Company, Worcester, Mass, a corporation of Massachusetts Application March 16, 1953, Serial No. 342,372

3 Claims. (Cl. 204-218) This invention relates to electrolytic grinding and more particularly to an electrolytic grinding system and apparatus.

. One of the objects of this invention is to provide an electrolytic grinding system and apparatus which can be easily installed in factories or plants already provided with circuits or sources of alternating current electrical energy and in which conversion of the latter to unidirectional electrical energy at the locus or electrolytic stock removal can be controllably effected by simple and relatively inexpensive apparatus or parts adapted for simple and eflicient coaction with or in response to electrical conditions at the locus of electrolytic stock removal, to achieve reliable and practical protective action under the varying conditions of practical use. Another object is to provide a system and apparatus of the just mentioned character that will be relatively free from the disadvantages of complications of circuits and control equipment and capable of functioning Without detrimental wastefulness of electrical energy. Another object is to provide a system and apparatus for electrolytic stock removal from a work-piece that will be easy to install, of good durability and low maintenance requirements, and well adapted for ease and facility of adjustment or setting where the latter are desired or necessary. Other objects will be in part obvious or in part pointed out hereinafter.

In the accompanying drawings, in which are shown illustratively the mechanical and electrical features of my invention and in which similar reference characters refer to several parts throughout the several views of the drawings,

Figure 1 is a front elevation, with certain parts shown or indicated diagrammatically, of the grinding machine;

Figure 2 is a fragmentary side elevation thereof;

Figure 3 is a fragmentary horizontal sectional view on an enlarged scale, showing certain mechanical and electrical features of one form of grinding wheel in relation to a work-holder and certain electrical features re lated thereto;

Figure 4 is a fragmentary or detached front elevation of a wheel-guard cover and associated electrolyte-distributing parts, as seen from the front in Figure 1 and from the left in Figure 3;

Figure 5 is a diagrammatic representation of the apparatus and the electrical energy conversion and control system, and

Figure 6 is a graph indicating a preferred form of voltage-current control characteristic.

As conducive to a clearer understanding of certain features of my invention it may here be noted that there are many advantages to be gained in stock removal by electrolytic grinding in which, by the coaction of an electrolyte and direct or unidirectional current, stock is removed from the work-piece by electrolytic decomposition of the work face, especially for machining hard cemented carbides (such as cobalt-bonded tungsten and/ or titanium carbide) whereby, when the rotating con- States Patent 0 Patented Jan. 27, 19 59 ductive element or face of the grinding wheel contains abrasive grain, the cutting action of the abrasive grain may be very materially supplemented. Most industrial plants or factories are equipped with or wired for alternating current energy, usually and illustratively threephase and of 60 cycles. One of the objects of my invention is to provide efficient and dependable electrolytic grinding apparatus and compact, simple, and coacting controllable energy supply system that needs only to be electrically connected to the existing alternating current supply lines and controllably furnish, at the locus of stock removal, the required unidirectional current or electrolytic action. As heretofore attempted to be practiced, so-called electrolytic grinding has encountered various difficulties or the systems or apparatus have inherent limitations or there arise phenomena detrimental to or destructive of the grinding Wheel, and these handicaps become all the more serious where, as is frequently the case, it is desirable to use diamond grinding wheels, which are costly. Another dominant aim of this invention is to avoid or alleviate such handicaps, shortcomings or risks by simple, compact, and relatively inexpensive apparatus, and to achieve materially greater overall efficiency, whether or not diamond or other abrasives are employed, by effecting dependable and automatic controls of the conversion of the alternating current energy to direct current energy in response to changes in harmful direction of the electrical conditions at the locus of electrolytic decomposition of the work-piece.

In stock removal by electrolytic decomposition at the work face, the conductive work-piece is made the anode, and at the work-wheel interface, where there may or may not be physical contact and where there may or may not be accompanying abrasive action, there is adequately supplied a suitable electrolyte, which also serves as a coolant, and it is desirable to use high current density since the rate of electrolytic decomposition at the work-piece face is proportional to current flow. Various conditions can occur or be brought into being at the work-wheel interface that will cause detrimental actions, such as arcing, which can also cause high or excessive rates of wheel Wear which, particularly where'diamond abrasives are embodied in the wheel, can prove prohibitively costly. It can be shown that a desirable characteristic of supply of direct current for the electrolytic circuit is one where the voltage across the work-wheel interface is maintained substantially constant up to the point where the electrolytic current flow approaches a critical value above which deleterious arcing occurs, followed by current-limiting action at a selectable current value less than the critical current, to relatively rapidly reduce the voltage across the work-Wheel interface to prevent the current from reaching or exceeding the critical value, and preferably capable of reducing the voltage to zero; the operational voltage characteristic may thus be said to be substantially rectangular. A further object of this invention is to effect conversion of alternating current electrical energy into direct current energy at the work-wheel interface with the energy conversion'controlled, in response to conditions at the work-wheel interface so that the just described characteristic of energy supply at the work-wheel inter- 7 conductive grinding wheel and for mounting or supporting, or even for resting thereon for manual movement (as in so-called oil-hand grinding), a work-piece, such as a cemented carbide tool or other piece of Work or object to be ground or machined, whereby to obtain relative movements between the grinding wheel'and the sup ported work. Many and various forms of mechanism are well known for cooperatively relating a grinding wheel and a Work-piece for relative movement'therebetween and providing for various relative adjustments and/or move- 1 ents between the grinding wheel spindle and work together with various manual or automatic controls for such adjustments and movements. For example, I may utilize a machine such as is shown in U. 3. Patent 2,101,787, in which a work-table, underlying an adjustably mounted and rotatively driven grinding wheel dle, is movable and reciprocable relative to the grinding wheel and is mounted on a cross slide for shifting it transversely, that is, forwardly or rearwardly of the machine, relative to the grinding wheel; in the machine of that patent the work-table can be reciprocated upon the transverse or cross slide by manual means or by fluid pressure mechanism as there described, while the cross slide may be manually or mechanically moved to advance the worktable and the work-piece supported by it in steps or at a rate according to the setting of the infeed mechanism or according to the manual actuation thereof, as by a hand wheel. Or, it may utilize a grinding machine, by way of further illustration, of the type or kind disclosed in Patent 2,381,034, the machine of that patent being particularly adapted to shaping tool bits, particularly bits or tools of the above-mentioned hard cemented carbides, and in that machine the operator manually shifts the holder or carrier that supports the work-piece or tool, relative to an adjustable table or support and relative to the flat side face of the grinding wheel, according to vari ous curvatures of surfaces or fiat surfaces, sometime with the aid of templates or with the aid of various adjustments of various angularitics, according to the specific character of surface shaping that the particular tool or tool bit requires. These two patented disclosures are i1- lustrative of'two of the many types of grinding machines to which my system and controls are applicable for effecting stock removal by electrolytic decomposition at the face of the Work-piece.

Accordingly, in the drawings, 1 have shown in Figures 1 and 2, a driving mounting for the rotating conductive element together with an illustrative work-piece and workholder or support, with a work-table for the latter depicted largely diagrammatically, particularly in so far as its adjustability and movement relative to the rotating grinding wheel are concerned, inasmuch as such adjustability and movement, and the mechanism for effecting them, may take any-suitable or known form, and many thereof are well known in the art.

Thus the apparatus may have a base or main frame 10 which, at its rear, supports a column or vertical standard 11 which, as indicated by the arrows thereon, is rotatively adjustable about a vertical axis and is also adjustable in up-and-down direction; the column ll) supports a Wheel head 12, in which is journaled a grinding wheel'spindle 13 which projects both forwardly and rearwardly of the wheel head, and at its rear end carries a pulley 14 which is driven by a belt l from a pulley 16 on the shaft of a motor 17, which is suitably carried by the top of the standard 11. I

The front end of the spindle 13 is appropriately constructed to have or is provided with means for mounting a grinding wheel thereon, as by providing it with a .tapered portion 21 (Figures 34), that is received into the tapered bore of a flanged sleeve 22, a nut 23 which is threaded onto the spindle l3 holdin the flanged sleeve 22 securely in place. he flanged sleeve 22 is suitably constructed to carry and have secured thereto a grinding wheel which is electrically conductive and which is illus- 34, manually operable, as by the handle 35.

tratively and preferably constructed, as is shown in Figures 3 and 4 and as is later to be described.

When the grinding wheel is so mounted at the front end of the spindle 13 it substantially overlies or overhangs a work-table 24, which is reversibly movable and reciprocable, as indicated by the double-headed arrow in Figure 1, being supported in suitable lengthwise extending ways provided in the cross slide diagrammatically indicated at 25, the latter being adjustable or movable, reversibl as indicated by the double-headed arrow in Figure 2, being suitably carried or supported, for that purpose, on suitable ways provided in the base 10.

The work-piece W, which for purposes of better illustrating certain features of my invention, may be considered to be a block of cemented carbide and suitable means are provided for releasably holding or clamping it to facilitate control of its movement relative to the operative face of the grinding wheel, and such means may comprise a heavy work-holding bar 27, which is provided with a suitable hole or recess 28 in which the work W is received and in which it is clamped securely, as by a clamping screw '23. In the electrolytic grinding circuit the work W is to serve'as the anode in the electrolytic cell and accordingly suitable provision is made for connecting the work W appropriately into the electrical circuit, and such means may comprise a suitably heavy connector screw 3% by which a conductor may be clamped, carried by and threaded into the work-holding bar 2'7, as is better indicated in Figures 3 and 4. The workholding bar 27 may in turn be carried by a vise, generally indicated at 3i; the vise may be of any suitable construction and may, for example, comprise a fixed vise jaw 32 and a movable vise jaw 33, between which the bar 27 may be releasably clamped and held, as by the screw The vise 31 can rest on the work-table 2:3, with which, when suitably secured thereto, it is movable according as the worktable 24 is moved or actuated the above-mentioned Patent 2,101,787, or relative to which the vise may be manually moved, as in the above-mentioned Patent 2,381,034, in either case to efiect the desired or controlled traversing movement or movements of the work W relative to the grinding wheel and to effect the desired feeding and the retracting movement or movements thereof relative to the wheel. As indicated in the drawings, I may provide suitable means such as bolts 36 for'clainping the vise 31 at any desired angularity to the work-table 21, where it is desired that the vise move with the table, the bolts being simply omitted when it is desired to manually shift or control the movements of the vise and workpiece W relative to the table. in Figures 1 and 2 the grinding wheel is generically indicated by the reference character CR, and by way of illustration but not by way of limitation it is constructed to present a conductive ring surface at its flat annular side face which, according to the rotational setting about its vertical axis, of the column 11 which supports the wheel head 12, may be given any desired angularity relative to the longitudinal path of movement of the movable work-table 24, according to the needs of any particular grinding job, but for greater simplicity of description the wheel head may be considered as set so that the plane of the operative annular side face of the wheel extends parallel to the line along which the work-table 24- is movable or reciproczible.

A suitable wheel guard 33 is provided, being secured to the wheel head by suitable brackets 39 being provided with a hinged front cover 4% so that access to the wheel spindle 13 may be gained for mounting or demounting the grinding wheel; the wheel guard with its cover 40 may be shaped substantially as shown in Figures 1, 2, 3 and 4, being cut away as shown to expose a suitable portion of the front face of the wheel where the conductive ring surface is operative and so that the work W may be presented thereto, and to expose a complementary back portion of the wheel for purposes-about to be described.

Suitable means are provided to supply a suitable electrolyte to the region of contact or of juxtaposition between the grinding Wheel CR and the work W; such means may comprise a broad-mouthed nozzle N, which is preferably adjustably positionable, as by a suitable length of deformable metal tubing 41, which is connected to and supported by a rigid pipe 42 secured to the wheel guard as indicated (see also Figures 3 and 4). Accordingly, deformable tube 41 may be manually bent and set to give the nozzle N the desired location, the mouth of the nozzle being appropriately dimensioned to discharge the liquid electrolyte at and throughout the entire width of the conductive ring surface of the wheel CR, where the work-piece W is presented to the latter.

In Figure l I have shown a tank 44 containing liquid electrolyte 45; the latter can be a solution of sodium chloride in water, preferably reasonably concentrated; for example, when the tank is full of pure water, a surplus of common salt may be added thereto so as to leave a vquantity of undissolved salt which simply rests on the bottom of the tank. Other salts can be used, but for keeping corrosion at a minimum the very corrosive salts, .such as calcium chloride, magnesium chloride and sodium chloride are preferably avoided. Salt, such as sal ammoniac (ammonium chloride) can be used. The carbonates, such as sodium carbonate and potassium carbonate, can be used and in some cases may be preferred, as they are somewhat less corrosive than sodium chloride.

Mounted on the cover plate 46 of the tank 44 is an electric motor 47 which drives a pump 48, the input end of which is connected by a pipe 49 to the inside of the tank 44, with the open end of the pipe being preferably near the bottom of the tank. The output end of the pump 48 is connected by suitable piping 50, and a suitable length of flexible hose to a valve 52 on the end of the pipe 42 which is secured to the hinged wheel guard cover 40. An arrangement such as just described may be used to supply the work-wheel interface adequately with electrolyte; from that location the electrolyte copiously runs out of the bottom of the wheel guard and it and any drippings thereof are eventually collected by a large pan 53 which is built around the top edge of the work-table 24, and as shown in Figure 2, a spout 54 carried by the work-table and movable therewith discharges the pancollected liquid into a stationary pan 55 that is suitably supported by the base of the machine and which extends throughout the full length of maximum travel of the spout 54 as the latter moves with the work-table. A return pipe 56 extends from the pan 55 to the tank 44.

The wheel CR may be of any suitable construction and may have one or more conductive faces, which I arrange to coact in effecting, in the electrical energy conversion and supply system, control or modification of the alternating current energy to provide direct current energy of the earlier above described characteristic of substantially constant voltage across the work-wheel interface followed by current limiting action with diminished voltage so that critical current values are not reached or exceeded and preferably so that the D. C. voltage across the workwheel interface is rapidly reduced, giving the system a substantially reactangular operating characteristic, as above noted.

Referring now to Figures 3 and 4, the single-conductive-faced wheel is there generally indicated by the reference character 60, and in order also to gain certain advantages in achieving electrical insulation or isolation, the wheel 6% comprises a strong rigid backing B of any suitable cured plastic or the like, such as Bakelite resin; at its center it has molded into it a hole (Figure 3) so that it can be received onto the flanged sleeve 22. As better appears from Figure 3, the backing B has an outer rim-like or annular portion which is of greater thickness than the central portion which is received onto the flanged sleeve 22 and which is clamped between the flange and the spanner nut 61; this outer portion of greater thickness presents an annular side face, being the left side face as viewed in Figure 3 and being the front face as viewed in Figure 4, and at that face and preferably coaxially therewith the wheel 60 carries a conductive abrasive ring CR which presents, in the illustrative construction, an annular conductive face with which the work-piece W and the electrolyte can coact. This ring CR may be secured to the backing B in any suitable manner, but preferably the ring is constructed so that it is embedded in the nonconductive material of the backing B and preferably it is assembled to the backing itself when the latter is initially molded out of the uncured resinous material which is,

during the molding process, made to flow about the faces of the ring except its operative face and to become interlocked therewith upon curing of the resinous or other plastic, as under heat and pressure; for better interlocking the ring CR may be of a conformation that provides a continuous annular dovetail D (Figure 3), which can be integrally formed at the back of the ring.

As above indicated, it is sometimes desirable that the rotating conductive element in electrolytic grinding contain abrasive grains and the wheels 60 may be constructed also in a manner to facilitate embodiment of abrasive grains when and where desired. For the grinding of hard cemented carbides, such as those illustratively mentioned above, suitably bonded diamond grains, as of bort, are usually employed because silicon carbide abrasive grains are hardly as effective on cemented carbides, while alumina grains grind them hardly at all. While, in the illustrative embodiments of my invention I prefer to use diamond abrasive grains, grains of other materials, including silicon carbide and aluminum oxide, may be employed, and as is later made clear, in electrolytic grinding, stock removal may be effected solely by electrolytic decomposition of the metal at the work-face without any material abrasive action by any of the grains in the rotating conductive ring or face. Where grains are employed, in order that the ring CR be conductive, the abrasive grains are metal-bonded, and particularly where diamond grains are employed it is preferred that they be embodied in only a relatively small depth in relation to the over-all thickness of the ring itself and accordingly, as is clear from Figure 3, the ring CR comprises an outer abrasive or grain-containing portion 62 of small thickness or depth, and an inner and usually thicker and heavier portion 63 that need not contain any grains and is of metal throughout, serving as a strong rigid support or backing for the thinner diamond-bearing portion 62. Where a dovetail element D is employed, it forms a part of the metal backing portion 63, as shown in Figure 3, and may be integrally formed or molded therewith 0 turned or machined to the desired shape.

In making the conductive abrasive ring CR any suitable or known methods or techniques may be employed and need not be described in detail here. For that matter, the patented art describes how, with the use of powdered metal, to make up a unitary integral abrasive ring or annulus having an outer diamond-bearing abrasive portion and an inner support portion wholly of metal. I might note, however, that a usual method of manufacture comprises placing in a suitably shaped mold, to the desired depth, powdered metal that is to correspond to the non-abrasive backing portion and, after leveling or smoothing off, placing thereover a suitable depth of a mixture of diamond particles and powdered metal, to correspond with the abrasive portion and, after leveling or smoothing off, subjecting the contents of the mold to substantial pressure and then sintering the pressed piece,

usually in a protective atmosphere such as hydrogen. By appropriately shaping the mold parts the backing portion 63 may be conformed to have a projecting dovetail part or ring, such as the dovetails D of Figure 3, or, as above noted, and since the backing portion 63 contains no abrasive grains, the dovetails D need not be formed by 7 molding but can be turned or machined to the desired shape after pressing and sintering are completed.

Any suitable metal bond appropriate for bonding the abrasive grains and for giving the rings suitable electrical conductivity may be used. In the abrasive-containing portion of each ring, such as the portions 62 of Figure 3, the concentration of abrasive grains should, of course, not be so great as to detrimentally afiect electrical con ductivity. For finely divided diamond as the abrasive grain, a concentration thereof in the abrasive portion on the order of or less by volume is suitable. Of the many and various metals that are usable for metalbonding the diamond grains, I prefer to employ a mixture of copper and tin powders in the proportion of about 82% copper and 18% tin, making for both excellent electrical conductivity and good bonding of the grains, and

this same mixture of copper and tin is employed in making up the non-abrasive backings, such as the portions 63 of Figure 3, and I set out the just mentioned mixture of copper and tin as an illustration. The wheel 6% is driven in clockwise direction as viewed in Figures 1 and 3, at a suitable speed to give its conductive ring-face suitable surface speed for appropriate abrasive action, and suitable means are provided to electrically connect its conductive ring CR into the electrical circuit so that the conductive ring is the cathode, for electrolytic decomposition at the face of the work-piece W; such means conveniently comprises a slip ring constructed and coaxially mounted for rotation with the grinding wheel spindle l3, and a suitable coacting mounting for supporting a brush that bears against the slip ring. in Figure 3 l have shown such a slip ring at S and it is preferably carried by the non-conductive backing B of the grinding wheel 6%, preferably on the back face of the latter, whereby it is also protected, by centrifugal action, against access thereto of electrolyte which the nozzle N (Figure 4) discharges onto the front face, where the conductive ring CR is operative. Conveniently, the slip ring is mounted at the back face of the insulating back B in juxtaposition to the conductive ring CR (Figure 3), and it may be secured in position and electrically connected to the conductive ring CR in any suitable manner.

For example, it may be mounted in position after the back B has been molded and cured with the ring R interlocked, Eat the front face, with the cured molded insulating material, and then secured in position by a suitable number of equi-angularly spaced tension tiemernbers 65, which extend through suitable holes in the back B "and are anchored, as by threading, at their inner ends to the conductive ring CR in which tapped holes are provided in the backing portion 63 thereof; the outer ends or" these tie rnen'ibers, which preferably take the form of long screws preferably made of copper or of a copper tin alloy, extend into suitable countersunk holes in the slip ring S thus to clamp the latter securely and concentrically in position at the back face of the wheel back B and at thc same time forming multiple electrical connections of high-current-carrying capacity between the slip ring and the conductive ring CR The screws may be headed, in which case the heads me countersunk into the sliprings, or the screws may be headless, in which case tnose portions that extend. into the countersunk holes in the slip rings may be rad ally expanded by pressure or by pe .ing to fill up the tapered holes in the slip ring, the taper being appropriately proportioned to the cold-flow characteristics of the metal of the screw shank to facilitate cold-flow expansion thereof as just mentioned. The faces of the slip rings may then be machined, as by turning in a lathe, or by grinding, to be sure that they fall in a plane at right angles to the axis of the grinding wheel and to be sure that the ends of the screws es are flush with the faces of their respective slip rings, thus to insure smooth coaction with the brushes of the circuits in which the parts are to coact.

As is better shown in Figure 3, the wheel head 12 has secured to it, as by cap-screws as shown, a bracket 66 which extends in a radial direction relative to the grinding wheel es and which is constructed in any suitable way to insulatingly support a brush 67 which is springpressee to the left to bear against the face of the rotating slip ring S Suitable means are provided, such as a connector screw 68, for electrically connecting the springpressed brush 67 into the energy-supply-and-control circuit.

in Pi" 5 the conductive element CR of the grinding wheel 6t) and the work W presented to it are diagrammatically shown, together with the slip ring S and brush 67, the latter and the work W being electrically connected by conductors 6? and 7% respectively into the energy-sit ly-and-control system for coaction therewith in responsively controlling or affecting the conversion of alternating current energy derived from the power circuit "Ii- 72 to unidirectional current energy of the desired and respective voltage and current characteristics as dictated by conditions at the interface or electrolytic cell of the work W and rotating conductive part CR The A. C. power circuit '7l72 rrray be of any of the types usually found in factories or industrial plants and it may be single-phase or multi-phase; for greater facility of description and by way of illustration and not by way of limitation the circuit fl- 72 is shown as single-phase, deriving its energy from. a suitable source of A. C. single-phase energy indicated at '73, and the circuit 71-72 may be of any usual voltage.

From the A. C. power circuit '71-'72 l energize a circuit comprising a capacitance and a reactance arranged in series and, depending upon their relative respective capacitive reactance and inductance reactance, they have the characteristics of a circuit capable of being placed in resonance; the capacitive reactance takes the form of any suitable condenser or capacitor, diagrammatically indicated at C, and the inductive reactance takes the form of an inductive winding related to a saturable core and preferably comprises two serially connected windings L -L about the respective outer legs '74, '75 of a shell-type of core '76 provided with two core windows, as indicated, so as also to have a center leg 77, about which extends a winding '78, which is unidirectionally energized, as is later described, for certain control of the flux in the core 76, thus to vary or control the inductive reactance X of the windings in relation to the capacitive reactance X of the capacitor C and in relation to tne resonance characteristic of the series circuit comprising these two reactances as energized at fixed frequency from the substantially constant voltage power circuit 7 1-7 3.

in the just stated series circuit comprising capacitor C and the iron core inductive windings 1. -1), an alternating potential exists across the capacitor C and also across the terminals of the serially connected windings L and from one of them, preferably the inductive windings, l derive energy for conversion into direct current for supply to the work-wheel interface for electrolytic decomposition at the face of the work W; this 1 preferably do by employing a full-wave rectifier bridge R3, to the D. C. output terminals of which the workwheel interface and also the flux-control winding 78 on the middle leg 7'7 of the core 76 are connected in series, and to the A. C. input terminals of which rectifier bridge RB supplied alto sting current energy derived'as above noted, preferably from the terminals of the inductive windings le -13, preferably by a suitable step-down transformer, which may be of any suitable form, such as an autotransfor ier with adjustable output voltage tap but which prefc cly is in the form of an insulating stepdown transformer, as shown in Figure 5 at TR. l'his transformer has a core 3i), with a primary winding 81 connected by conductors 82, $3 to the respective terminals El i, lid of the serially connected inductive windings Is -L the winding 81 being suitably insulated from the core 80 and from the secondary winding 86 by insulation, not shown, thus to isolate the secondary winding and its output circuit from the relatively high potentials that can become effective in the primary winding 81 because of its connection, in shunt relation, to the inductive reactance L L that is in series with the capacitor C. The secondary winding 86 is connected through a variable tap as shown, by

conductors

87, 88 to the input terminals of the rectifier bridge RB, and full-wave rectified and hence unidirectional current is supplied to the work-wheel interface, with the work W anodic, in the circuit that extends from one output terminal to the rectifier RB, conductor 70, work W, conductive Wheel element CR slip ring S, brush 67, conductor 65 through a variable tap to one side of winding 78 on the middle leg 77 of the core 76 and, from the other terminal of winding 78, by conductor 89 to the other output terminal of the rectifier bridge RB.

Inductive windings L L are so wound and connected that their respective fluxes are additive in the outside rectangular loop of the core 76 and are opposed to each other in the middle leg 77 of the core 76 so that with the two windings of equal numbers of turns and energized by the same current values their respective fluxes cancel out in the middle leg 77 and hence no A. C. voltages are induced in the D. C. winding 78 on the middle leg 77. Accordingly, with the core 76 made of iron or steel of suitable permeability and suitably proportioned, the unidirectional flux produced by the D. C. winding 78 can, according to its energination and number of effective turns, the latter being adjustable by the tap 90, shift the operating point of the inductive windings L L up and down on the magnetic permeability curve of the core 76; in that manner I achieve a range of shift along such a portion of the magnetic permeability curve of the core that the inductive reactance of the windings L L varies substantially inversely as the D. C. current flowing through the saturation control winding 78 on the middle core leg 77.

The unidirectional current flow in the D. C. winding 78, in the D. C. circuit above described, is the same as that which flows across the work-Wheel interface,

and changing conditions at that interface can affect E =wheel-work voltage, referred to the A. C. primary 81 of the output transformer TR. I,,,=wheel-work current, referred to the A. C. primary 81 of the output transformer TR. E =power line voltage, that is, across line 7172. X =capacitive reactance of capacitor C X =inductive reactance of windings L and L k=proportionality constant in the relaiton As above indicated, various conditions can occur or arise at the work-wheel interface to vary or change the current flow thereacross as electrolytic decomposition of the work W proceeds, even to the extent of causing a current flow so high as to cause destructive arcing; for a given type of grinding operation it is, therefore, desirable that work-wheel interface conditions that call for excessive current promptly initiate current-limiting actiofi and that, until such conditions arise, it is desirable that the voltage impressed across the work-wheel interface be maintained more or less constant, permitting current flow to be variable or self-adjusting in magnitude until a selected maximum safe flow of current is reached, after which current-limiting action is initiated. In the above described system, with the inductive reactance L -L and the capacitor C connected across the supply circuit 7172, were the inductive reactance and the capacitive reactance to become equal at any point in the just stated operating range of current flow across the work-wheel interface, that is, from zero current up to the selected maximum safe current, resonance would occur and the voltage across the circuit 8283 and hence the voltage E would be extremely high, the condition of resonance causing a curve or characteristic of voltage that is steep, on the order of the broken-line curves or characteristics indicated at Y and Z in Figure 6. On the other hand, if appropriate values and constants, in the above equation, are selected so that the condition of resonancewould occur at a load current outside of the desired operating current range, then the effect within the desired operating current range is to give the voltage an approximately fiat or slightly rising characteristic up to the point where, with increasing current, the reactance drop across the capacitor C becomes effective rapidly to reduce the load voltage, as indicated in the full-line curve A of Figure 6.

The three characteristics indicated in Figure 6 are curves of voltage E plotted against current I for various resonance points in order to illustrate the functioning of the system, utilizing various values for the constant k; E was taken as 10 units; I maximum, 10 units; and X 1 unit. When the constant k is made unity, the characteristic curve Z results, and, starting at the left, the voltage rises at a steep slope, and reaches a peak (broken off and not shown) of very high value, within the current operating range from zero to 10 units. When the constant k is given a value of 9, a characteristic like the curve Y results and the voltage, starting at the left, rises less rapidly but still at substantial slope, reaching a peak (broken off and not shown) that is also of high value, within the desired operating current range of from zero to 10 units; from the peak value, in curve Y, the voltage will be seen to drop very rapidly, to zero. 'acteristic shown at A in Figure 6 results and the voltage, starting at the left, rises only slightly, indicating that, were the curve to continue as a true resonance curve, other factors permitting it, resonance and high-peak value of voltage would occur materially to the right of the peakvalue of curve Y land hence would be beyond the selected maximum current value of the selected operating current range, but as the voltage curve A approaches the upper current limit of the selected current range, as the current increases, there occurs, as is later explained, such progressive reduction in the inductive reactance X of the inductive windings L L that, in relation thereto, the increasing reactance drop across the capacitor C becomes effective rapidly to reduce the effective voltage across the inductive windings L L and hence across the work-wheel interface, as is indicated by the rapid steep-slope and almost vertical drop of the full-line voltage curve A as the current value approaches and reaches the selected maximum value of 10 units. The resultant characteristic A will thus be seen to be substantially rectangular. Under the conditions just explained as to Figure 6, the constant k is numerically equal to the D. C. current in amperes required to energize D. C.

winding '78 at the condition of resonance of the series Giving the constant k a value of 20, the charll to varying conditions at the work-wheel interface. Through its flux, winding 78 afi'iects the coactions between the series-connected inductor L L and capacitor C and this it does as dictated, increment by increment, by changes in interface conditions; it directly affects relative reactance values thereof and, in relation to current flow, relative reactance voltage drops are affected. So long as a selected current value, illustratively about 9 units in Figure 6, is not exceeded even though interface current varies, relative reactance values voltage drops prevail to hold the effective voltage 3 across the interface more or less constant, as along the portion a-b of curve A. In practice, that voltage can be about 10 volts; it can be set to a different level where a different maximum safe current value is selected according to the type of grinding job and other factors, as will now be understood. Should the interface call for current beyond the value at point 12, where the characteristic would otherwise tend toward continued rise of voltage to seek or approach a condition of. resonance away beyond (to the right in Figure 6) the selected maximum current of 10 units, the coactions continue to affect relative reactance values and utilize the higher current values sought by the interface; the inductive reactance of winding L -L is lessened, by the flux of winding 7'8, in relation to the capacitive reactance of capacitor C so that the reactance drop across the latter, increasing with increased current, rapidly reduces the voltage across winding L L from which is derived, by rectification, the D. C. voltage acros the interface. Thus small successive in crements of increase in current, as the latter approaches the upper limit of 10 units, rapidly reduce the interface voltage, as in Curve A, explained above in connection with Figure 6. As shown in Figure 6, the voltage drops very rapidly, almost vertically, from about the point I) on.

Accordingly, so long as conditions at the work-wheel interface, though varying, are such that current flow thereacross is within the range (1-15 of curve A of Figure 6, the changeable or variable current across the interface so affects, through the D. C. winding 78, the inductive reactance in relation to the capacitive reactance that the voltage across the interface remains more or less constant, and changes in pressure or area of contact (actual or apparent) between the work W and the conductive wheel element CR inherent in many grinding operations, can thus freely take place up to a point Where such a change calls for a current flow of a magnitude that can cause damage to the wheel, as by arcir that point or arcing magnitude of current would be, the curve A of Figure 6, a value somewhat in excess of the 10 units there shown at point on the curve, and hence being to the right of p int c, in order to provide a suitable margin or factor of safety; such condition arising, the current seeks to increase, oftentimes very rapidly, the current value thus moving toward the right along curve A to reach point I), after which cont" med small increments of current increase are effective rapidly to reduce the voltage along the portion b-c of the curve and thus preventing current flow in excess of the selected upper and safe limit of current of 1-0 units. A detrimental or wheel-damaging magnitude, that is, in excess of the illustrative units, of current flow can thus not take place and damage to the wheel is thereby prevented. In some types of grinding, as in off-hand grinding or as in tool grinding by way of a machine as in Patent 2,381,034, pressures and areas of contact between the work W and the conductive wheel element CR are oftentimes rapidly and abruptly altered, but whatever the instantaneous work-wheel condition, be it a light contact or small area of contact, or intense pressure or large area of contact (by way of illustration), the particular instantaneous condition dictates, to achieve good capacity of stock removal and dependable safely against damage of the wheel, whether the electrolytically-acting current flow takes place under more or less constant voltage (portion ab of curve A) with freedom of current variation as needed (from zero current at point a to about 9 current units at point b), or takes place under more or less constant and limited current (represented by the almost vertical portion bc of the curve, being from 9 current units to 10 current units) accompanied by selfadapting changes in magnitude of voltage (up or down the curve portion b-c) It will thus be seen that there has been provided in this invention an electrolytic grinding system in which the several objects above noted, together with many thoroughly practical advantages are successfully achieved; it is compact, highly eflicient and well adapted for ease and facility of installation in existing industrial plants or factories equipped with usual power circuits or sources of alternating current energy.

As many possible embodiments may be made of the mechanical features of the above invention, and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

i claim:

1. in electrolytic grinding apparatus, in combination, means for supplying alternating current energy, rotatable conductive means having an operative face for coaction with a work-piece, means for supporting a work-piece in operative juxtaposition to said face of said rotatable conductive means with means for supplying liquid electrolyte to the interface between the work-piece and said conductive means, said rotatable conductive means and said work-supporting means having means associating them for effecting relative movement between the fac of said rotatable conductive means and the work-piece whereby interface current-demanding conditions there- -between may vary, such as changes in area or pressure of actual or apparent contact there'cetween, as relative movement between the work-piece and the face of said conductive means takes place for the purpose of shaping the work-piece by electrolyti stock-removal, a rectifier bridge having a unidirectional current output circuit in which is included said interface with the work-piece positive and said rotatable conductive means negative for electrolytic decomposition at the face of said work-piece for shaping the latter, a capacitor and an iron-cored inductive winding connected in series and energized from said means for supplying alternatins current energy and having a control winding on the core of said inductive winding, said control winding being connected in said output circuit for unidirectional current energization thereof that varies as said conditions at said interface change, and means for energizing the input of said rectifier bridge by alternating potential derived from said inductive winding, said capacitor and inductive winding having respective values of capacitive reactance and inductive reactance, with the latter affected by core flux produced by said variable unidirectional current energization of said control winding, to provide a D. C. voltage-current characteristic across said interface of substantially constant voltage throughout changing current across the interface below a select d maximum current value such as a current value that causes arc-over at the interface and of relatively rapidly decreaQng voltage with limitation of current as the latter tends to exceed said selected value.

2. In electrolytic grinding apparatus, in combination, means for supplying alternating current energy, rotatable conductive means having an operative face for ccacticn with a work-piece, means for supporting a work-piece in operative juxtaposition to said face of said rotatable conductive means with means for supplying liquid electrolyte to the interface between the work-piece and said conductive means, said rotatable conductive means and said work-supporting means having means associating them for eifecting relative movement between the face of said rotatable conductive means and the work-piece whereby interface current-demanding conditions there between may vary, such as changes in area or pressure of actual or apparent contact therebetween, as relative movement between the work-piece and the face of said conductive means takes place for the purpose of shaping the Work-piece by electrolytic stock-removal, a rectifier bridge having a unidirectional current output circuit in which is included said interface with the work-piece positive and said rotatable conductive means negative for electrolytic decomposition at the face of said Work-p'ece for shaping the latter, a capacitor and an iron-cored inductive Winding connected in series and energized from said meansfor supplying alternating current energy and having a control winding on the core'of said inductive Winding, said control winding being connected in said output circuit for unidirecitonal current energizau'on thereof that varies as said conditions at said interface change, and means for energizing the input of said rectifier bridge by alternating potential derived from said inductive winding, said capacitor and inductive winding having respective values of capacitive reactance and inductive reactance, with the latter varying substantially inversely with the aforesaid varying unidirectional current energization of said control winding, to provide the over-all circuit with a pseudo-resonance characteristic which, at said interface, has a portion that is of substantially constant voltage throughout variations in interface current below a selected maximum current value such as a current value that causes arc-over at said interface whereby changing conditions at the latter determine the magnitude of current thereacross up to said selected value and a portion of rapidly diminishing voltage as changing interface conditions seek to cause current increases beyond said selected value.

3. In apparatus for electric stock removal to shape a work-piece, in combination, means for supplying alternating current energy, conductive electrode means and means for supporting a conductive work-piece in operative juxtaposition thereto, said conductive electrode means and said work-supporting means having means associating them for effecting relative movement between the face of said conductive electrode means and the work-piece whereby current-demanding conditions therebetween may vary, such as changes in relative areas of juxtaposition or in pressure of actual or apparent contact therebetween, as relative movement between the' 1d workpiece and the face of said conductive electrode means takes place for the purpose of shaping the Workpiece by stock removal by electronic flow therefrom, a capacitor providing a capacitive reactance and an ironcored inductive winding providing an inductive reactance, said capacitor and inductive winding being in a seres circuit connected to be energized from said means supplyiug alternating current energy, said reactances providing, when energized, respective reactance voltage drops thereacross, and means for energizing said interface by unidirectional current for eflecting stock-removal from the work-piece face by electronic current flow between the latter and said electrode means comprising rectifying means, means for deriving an alternating potential from the reactance voltage drop across one of said reactances and for connecting the derived potential in circuit with said rectifying means and said interface with the workpiece positive and said conductive electrode means negative and including a control Winding on the core of said inductive Winding whereby the latter produces a flux in said iron core in response to changes in current across said interface, said capacitor and said inductive Winding having respective values of capacitive reactance and inductive reactance, with the latter varying substantially inversely with the unidirectional current energization of said control winding, to provide the over-all circuit with a pseudo-resonance characteristic at the frequency of said alternating current energy, with substantially constant 7 D. C. voltage across the interface throughout direct-current changes across the interface as dictated by conditions at the latter up to a selected maximum current value and with current limitation at said value and diminishing D. C. voltage across the interface for interface conditions demanding current in excess of said value.

References Cited in the file of this patent UNITED STATES PATENTS Saretzky Mar. 16, 1948 OTHER REFERENCES Report No. MAB-IS-M of the National Research Council, Jan. 18, 1952, pages Appendix VI-2 to VI-9 and Figs. 1 to 4.

Keeleric: Electrolytic Grinding, Steel, vol. 130, No. 3, Mar. 17, 1952, page 84.

Claims

1. IN ELECTROLYTIC GRINDING APPARATUS, IN COMBINATION, MEANS FOR SUPPLYING ALTERNATING CURRENT ENERGY, ROTATABLE CONDUCTIVE MEANS HAVING AN OPERATIVE FACE FOR COACTION WITH A WORK-PIECE, MEANS FOR SUPPORTING A WORK-PIECE IN OPERATIVE JUXTAPOSITION TO SAID FACE OF SAID ROTATABLE CONDUCTIVE MEANS WITH MEANS FOR SUPPLYING LIQUID ELECTROLYTE TO THE INTERFACE BETWEEN THE WORK-PIECE AND SAID CONDUCTIVE MEANS, SAID ROTATABLE CONDUCTIVE MEANS AND SAID WORK-SUPPORTING MEANS HAVING MEANS ASSOCIATING THEM FOR EFFECTING RELATIVE MOVEMENT BETWEEN THE FACE OF SAID ROTATABLE CONDUCTIVE MEANS AND THE WORK-PIECE WHEREBY INTERFACE CURRENT-DEMANDING CONDITIONS THEREBETWEEN MAY VARY, SUCH AS CHANGES IN AREA OR PRESSURE OF ACTUAL OR APPARENT CONTACT THEREBETWEEN, AS RELATIVE MOVEMENT BETWEEN THE WORK-PIECE AND THE FACE OF SAID CONDUCTIVE MEANS TAKES PLACE FOR THE PURPOSE OF SHAPING THE WORK-PIECE BY ELECTROLYTIC STOCK-REMOVAL, A RECTIFIER BRIDGE HAVING A UNIDIRECTIONAL CURRENT OUTPUT CIRCUIT IN WHICH IS INCLUDED SAID INTERFACE WITH WORK-PIECE POSITIVE AND SAID ROTATABLE CONDUCTIVE MEANS NEGATIVE FOR ELECTROLYTIC DECOMPOSITION AT THE FACE OF SAID WORK-PIECE FOR SHAPING THE LATTER, A CAPACITOR AND AN IRON-CORED IN DUCTIVE WINDING CONNECTED IN SERIES AND ENERGIZED FROM SAID MEANS FOR SUPPLYING ALTERNATING CURRENT ENERGY AND HAVING A CONTROL WINDING ON THE CORE OF SAID INDUCTIVE WINDING, SAID CONTROL WINDING BEING CONNECTED IN SAID OUTPUT CIRCUIT FOR UNIDIRECTIONAL CURRENT ENERGIZATION THEREOF THAT VARIES AS SAID CONDITIONS AT SAID INTERFACE CHANGE, AND MEANS FOR ENERGIZING THE INPUT OF SAID RECTIFIER BRIDGE BY ALTERNATING POTENTIAL DERIVED FROM SAID INDUCTIVE WINDING, SAID CAPACITOR AND INDUCTIVE WINDING HAVING RESPECTIVE VALUES OF CAPACITIVE REACTANCE AND INDUCTIVE REACTANCE, WITH THE LATTER AFFECTED BY CORE FLUX PRODUCED BY SAID VARIABLE UNINDERECTIONAL CURRENT ENERGIZATION OF SAID CONTROL WINDING, TO PROVIDE A D. C. VOLTAGE-CURRENT CHARACTERISTIC ACROSS SAID INTERFACE OF SUBSTANTIALLY CONSTANT VOLTAGE THROUGHOUT CHANGING CURRENT ACROSS THE INTERFACE BELOW A SELECTED MAXIMUM CURRENT VALUE SUCH AS A CURRENT VALUE THAT CAUSES ARE-OVER AT THE INTERFACE AND OF RELATIVE RAPIDLY DECREASING VOLTAGE WITH LIMITATION OF CURRENT AS THE LATTER TENDS TO EXCEED SAID SELECTED VALUE.