US3448023A - Belt type electro-chemical (or electrolytic) grinding machine - Google Patents

Description

June 3, 1969 R. M. BELL 3,448,023

BELT TYPE ELECTRO-CHBMICAL (0R ELECTROLYTIC) GRINDING MACHINE Filed Jan. 20, 1966 Sheet of :s

INVENTORL RAMSAY M BELL June 3, 1969 R. M. BELL 3,448,023

BELT TYPE ELECTRO-CHEMICAL (OR ELECTROLYTIC) GRINDING MACHINE Filed Jan. 20, 1966 Sheet 2 of s Q a h 7b 5 46 m 7 ie. 9

INVENTOR.

RAMSAY M. BELL Af/WP/VEVS June 3, 1969 M. L 3,448,023

BELT TYPE ELEGTROCHEMICAL (OR ELECTROLYTIC) GRINDING MACHINE Filed Jan. 20, 1966 Sheet 3 or s INVENTOR. RAMs/w lVl. BELL United States Patent U.S. Cl. 204143 10 Claims ABSTRACT OF THE DISCLOSURE An electro-chemical (formerly called electrolytic) grinding apparatus having a perforate, electrically conductive, abrasive belt supported on a pair of spaced pulleys with one of the pulleys being located such that a workpiece contacts the abrasive belt at a point whereby the one pulley constitutes a backing for the belt. A recess is provided in the one pulley and the one pulley is additionally provided with openings through the periphery thereof. An electrolyte is introduced into the recess of the one pulley and flows, impelled at least in part by centrifugal force, radially outwardly through the openings in the periphery of the one pulley and through the perforate abrasive belt against the workpiece. Means are provided for applying a unidirectional electrical potential difference between the workpiece and the abrasive belt.

This invention relates to electrolytic grinding and, more particularly, relates to an apparatus for carrying out belttype electrolytic grinding operations with the electrolyte being applied through a contact wheel.

While the broad principles of electrolytic grinding have been known for a number of years, and its commercial acceptance has been substantial in certain areas, there have been so many problems present in the application of these principles to specific problems and machines that the use of electrolytic grinding methods has been slow in achieving commercial acceptance in certain other areas in which its intrinsic advantages should make it highly desirable. More specifically, substantial progress has been made in the adaptation of electrolytic grinding principles to use with grinding wheels, particularly where face grinding has been involved for workpieces of small area, as exemplified by Keeleric Patent No. 2,826,540 when applied to the grinding of single point tools, and more recently progress has been made in the application of electrolytic grinding principles to belt-type grinding machines for larger work areas wherein the work is urged against a zone of the belt intermediate the pulleys and the belt is itself backed up by a suitable platen, as exemplified by my Patent No. 3,162,588 and assigned to the same assignee as the present application. However, the application of electrolytic grinding principles to contact wheel grinders, that is, belt-type grinders wherein the work is applied against that portion of the belt which is in contact with one of the pulleys, has not developed and a primary reason for such failure to develop has been the many problems incident to supplying the electrolyte simultaneously between the belt and the work while maintaining the belt in electrical connection with the proper terminal of an electrical source. Attempts have been made to supply electrolyte in the same manner as is utilized for face wheel grinding, that is, by discharging same between the grinding surface and the work, but this has proven inadequate.

Accordingly, the objects of this invention include the following:

(1) To provide an apparatus for applying electrolytic grinding principles to the contact wheel type of belt grinding.

(2) To provide an apparatus, as aforesaid, which will provide smooth and uniform grinding by electrolytic means and with a good uniformity of finish.

(3) To provide an apparatus, as aforesaid, which can operate at a sufficiently low voltage to avoid discomfort or danger on the part of the operator.

(4) To provide apparatus, as aforesaid, in which said flow of electrolyte will be substantially uniform across that portion of the belt normally contacted by the work.

(5) To provide an apparatus for introducing an electrolyte into the contact wheel, from whence it flows through the abrasive belt into the zone between the belt and the workpiece.

(6) To provide an apparatus, as aforesaid, which will supply a sufficiently large flow of electrolyte through said belt to insure good ion flow between the belt and the work in the electrolytic grinding operation.

(7) To provide apparatus, as aforesaid, wherein the electrolyte is introduced into the interior of the contact wheel and is then caused to flow radially outwardly through the periphery of said wheel and thence through said belt.

(8) To provide apparatus, as aforesaid, in which the flow of electrolyte is confined generally to the portion of the belt contacted by the work.

(9) To provide apparatus, as aforesaid, for effecting a good electrical contact with the belt in order to establish an electrical potential of the desired value between said belt and the work.

(10) To provide apparatus, as aforesaid, which will not be excessively expensive to build and/or maintain in openating condition.

Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.

In the drawings:

FIGURE 1 is a somewhat schematic side view of a typical machine embodying the invention.

FIGURE 2 is a sectional view of the machine shown in FIGURE 1 taken on the line IIII of FIGURE 1.

FIGURE 3 is a partially sectional and partially end elevational view of the contact wheel or pulley.

FIGURE 4 is a section taken on the line IVIV of FIGURE 3.

FIGURE 5 is a section generally similar to FIGURE 4 showing a modification.

FIGURE 6 is a section taken on the line VI-V-I of FIGURE 5.

FIGURE 7 is an oblique, fragmentary view of one 2 form of the contact wheel showing the random arrangement of openings through the peripheral surface thereof.

FIGURE 8 is a section generally similar to that of FIGURE 4 and showing a still further modification, the section being further indicated by the line VIII-VIII in FIGURE 9.

FIGURE 9 is a sectional view taken on the line 1XIX of FIGURE 8.

FIGURE 10 is a view similar to FIGURE 7 and showing a modified form of the contact wheel in which the openings are arranged in axially aligned rows and each of said rows is depressed in a trough or groove.

FIGURES 11 and 12 are illustrative alternate sectional illustrations of the belt adaptable to the practice of the invention.

GENERAL DESCRIPTION In general, invention comprises (1) providing a perforate abrasive belt having an electrically conductive portion, (2) utilizing a hollow, perforate contact wheel for backing said belt with respect to the work, (3) introducing an electrolyte into the interior of said contact wheel and (4) imposing onto said electrolyte within the contact wheel sufficient pressure to cause it to flow radially outwardly at a substantial rate through both the periphery of said wheel and through said abrasive belt. The electrolyte may be introduced into the contact wheel either (1) under only sufiicient pressure to cause suitable flow thereof and the pressure primarily efiYecting its radially out-ward flow may be created, by centrifugal force or otherwise, after said electrolyte enters within the contact wheel or (2) the electrolyte may be subjected at the time of its entry into the contact wheel to a sufficient externally developed pressure to cause it to flow radially outwardly either independently of centrifugal force or only supplemented thereby.

The apparatus of the invention particularly constitutes various specific means for controlling said electrolyte, for creating pressure thereon if desired after it enters into the contact wheel and for confiningsaid electrolyte to a desired portion of the periphery of the contact Wheel. While in one form of the invention the entire interior of the contact wheel defines the electrolyte receiving zone, in other forms of the invention the electrolyte receiving zone is defined within the contact wheel by other means occupying only a portion of the space therewithin. Centrifugal force is in some cases utilized for effecting outward flow of electrolyte, external pressure is in another form of the invention applied to the electrolyte within the zone defined as above mentioned for assisting centrifugal force in urging the flow of electrolyte radially outwardly through the wheel and abrasive belt and in still another form of the invention means are provided within said zone itself for generating a pressure by which centrifugal force is assisted in urging the flow of electrolyte radially outwardly through the contact wheel and the abrasive belt.

DETAILED DESCRIPTION Referring now to the drawings in more detail, there is shown in FIGURES 1 and 2 a machine of generally conventional nature to which the apparatus of the invention has been applied. While it will be evident as the description proceeds that the invention may be applied to a considerable variety of such machines, it will be convenient for the purpose of disclosing the invention to utilize and refer to the machine shown in FIGURES 1 and 2 and, accordingly, such reference will be made.

In FIGURES 1 and 2 there is shown, as one convenient form of work feeding means, a horizontally positioned feeding conveyor belt 1 arranged over pulleys 2 and 3, one of which will ordinarily be driven by any convenient means, not shown, and the other will be an idler. Said pulleys are supported upon frame structure generally indicated at 4 which may be of any convenient form. A platen 6 is arranged under the belt 1 for supporting said belt firmly with respect to the hereinafter described abrasive belt. The conveyor belt 1 is electrically conductive so that electrical potential can be applied to the workpieces supported thereon. Other work-feeding mechanisms such as a reciprocating feed table, or a succession of metal plates fixed to a conveyor belt, can be used instead of the belt 1.

Arranged above the conveyor belt 1 is a perforate abrasive belt 7 which is positioned around and supported by a pair of pulleys 8 and 9, one thereof being a driving pulley and the other being an idler. In the present instance, the lower pulley 8, which here is also the contact wheel, is driven by a motor 11 but in other instances the upper pulley may be the driven pulley. Adjustment mechanism 12 of any convenient type, which in this instance is air driven but which in some cases may be mechanical, is provided for adjusting the vertical position of the upper pulley with respect to the lower pulley whereby to adjust the tightness of the belt 7. A hood or casing 13 is placed over the belt 7 to confine the spray which would otherwise fly unrestrictedly from the belt.

The machine as thus far described is of conventional nature and is well known to the industry. Thus, no further description is necessary.

Turning now to further details of the machine thus far described in broad terms, which embody the apparatus phases of the invention and comprise specific means by which the invention may be practiced, attention is directed particularly toward the belt 7 and to the pulley by which said belt is held in controllable relationship with the work-supporting surface of the conveyor belt 1. In this instance, such pulley is the lower pulley 8. The respective sides of a suitable electrical D.C. source are then applied to the workpiece and to the belt for supplying electrical potential therebetween.

Referring first to the belt 7, the belt will be formed in any convenient manner so that it will have an electrically conductive layer and nonconductive abrasive grit protruding from the layer as illustrated somewhat schematically in FIGURES 11 and 12. Such a belt (FIGURE 11) is desirably comprised of a noncoductive flexible backing 33, such as a woven textile, having nonconductive abrasive grains 34 adhered thereto, as by an adhesive. Where it is conventient to apply electrical potential directly to the front surface of the belt, or along a grain-free side edge 36, a conductive layer 35 is applied only to the front surface of the backing, same being applied thereto in such a manner that the abrasive grains protrude through said conductive layer. Where, however, for mechanical or other design reasons it is preferred to apply the electrical potential to the back of the belt, then a conductive layer 37 (FIGURE 12) can be applied to the back surface of the backing and the two conductive layers can be connected by conductive connections 38 which extend through the textile layer. Other types of belts such as those made with a metal backing can be used or the grain may be adherently embedded into the conductive layer rather than being adhered to the backing. The abrasive grains may be of any desired kind, such as diamond bort, which are of appreciably less electrical conductivity than the electrolyte used. Such grains will hereinafter be referred to for convenience as nonconductive but it will be understood that this is a relative term and does not preclude a grit having same electrical conductivity providing only that it is of sufficiently less conductivity than that of the electrolyte as not appreciably to impair, or short, the flow of electrical current through the electrolyte. Many spectific belt designs will he obviously available and any thereof may be used Within the terms of the invention providing only they include a conductive layer as above indicated and carry nonconductive (as above defined) abrasive grains thereon. Especially satisfactory belt designs are disclosed in the application of Dyer et al., Ser. No. 392,741, filed Aug. 28, 1964, now US. Pat. 3,334,041 and Duke et al., Ser. No. 408,521, filed Nov. 3, 1964, now US. Pat. 3,377,264.

In carrying out an electrolytic grinding operation, it is well known that an adequate supply of electrolyte must be provided between the Work and the abrasive medium inasmuch as the electrical erosion of the workpiece is dependent upon the flow of ions between the work and the belt. This is fully discussed in the prior art, for example, the Keeleric patent above mentioned. However, in experimenting with contact wheel electrolytic grinding, it has been found that the supply of electrolyte is not effective when applied to the surface of the belt in a manner analogous to the application of electrolyte to the surface of a face grinding wheel in said Keeleric patent. Accordingly, the present invention contemplates introduction of said electrolyte into the interior of the contact wheel or pulley against which the work is held and said electrolyte is then caused to flow radially outwardly from said pulley through the belt arranged thereon and into the space between said abrasive belt and the workpiece.

This is accomplished by introducing electrolyte into the interior of the lower pulley 8 and causing it to flow radially outwardly through both the peripheral surface of the pulley and through also at least the portion of the belt facing the workpiece, whereby the electrolyte contacts the work.

In FIGURES 3 and 4 there is shown one means for accomplishing this operation. The pulley 8 is here arranged on a shaft 16 which shaft is driven by suitable means, as belts, from the motor 11 and is supported by a suitable bearing 15 in the upright member 10, said bearing being fully insulated electrically from said upright member 10. The pulley 8 is keyed to the shaft 16 in any convenient manner, such as by the key 17. The pulley 8 is provided with a series of peripheral perforations 19 which can be arranged in a variety of patterns. For example, the perforations 19 may be in a random arrangement (FIGURE 7), may be in rows (FIGURES 4, 5 and 8) or may communicate with longitudinally aligned grooves 21 (FIGURE 10) in the periphery of the pulley in order to provide continuous communication between said openings and thereby a continuous supply of electrolyte across the width of the belt.

The shaft 16 has a central passageway 22 communicating with the interior of said pulley 8 through the radial passageway 23 and communicating at its other end with a manifold 24 into which fluid, such as an electrolyte, is received from the conduit 26. Electrolyte is supplied to said conduit 26 from any convenient source, not shown.

A slip ring 18 and brush 20 may be provided to supply electrical potential to the pulley and belt.

The pulley 8 is held firmly onto the shaft 16 by any convenient means, such as by the nut 27 urging said pulley against the shoulder 28.

The shield 29 is preferably provided closely adjacent the pulley 8 at its upper side and extending around as much as possible of the portion of the periphery of said pulley which is not contacted by the belt. A bracket 31 extending from an appropriate point on member 10 holds said shield 29 in place.

A suitable collecting structure, such as a trough 32, is disposed for receiving the electrolyte from whence it flows to and through suitable recycling means such as a return tank T, suitable filtering means F if desired and a pump P, and thence back to the conduit 26.

OPERATION In the operation of the apparatus shown, a suitable electrolyte is supplied to the conduit 26 and flows from said conduit through the passageways '22 and 23 to the interior 48. When said pulley is rotating rapidly, suflicient centrifugal force is developed with respect to said electrolyte that it will be urged radially outwardly through the penings 19, thence through the interstices of the belt 7 into the region between said belt and a workpiece on the conveyor belt 1. Electrical potential of suitable value, usually between about and volts DC, is applied from any convenient source 33 to the belt 7 and to the platen 6.

With the supply of electrolyte to the interior of the lower pulley 8 established, and electrical potential applied between the platen 6 and the belt 7, the feeding conveyor 1 may be started and workpieces W supplied thereto. As the workpieces enter into the zone directly under the low point of the belt 7 so that they are contacted by the abrasive grains on saidbelt, they will also be acted upon by electro-chemical current carried between said workpiece and said belt through the electrolyte and the desired electro-chemical erosion will take place. The specific mechanics of the electrical erosion are already well known to the industry, are sufliciently published in Keeleric Patent No. 2,826,540 and need no detailed description.

The hood 29 prevents electrolyte from being thrown upwardly through the periphery of the pulley 8 in a manner which could cause undesirable splashing around the machine. However, said hood may be omitted insofar as the basic operation of the apparatus is concerned without detracting from the broader aspects of the invention.

6 MODIFICATION In the form of the invention shown in FIGURES 3 and 4, the force impelling the electrolyte radially outwardly is wholly centrifugal force if the lower pulley 8 is not filled with electrolyte or such centrifugal force may be supplemented by a pump pressure if the lower pulley is so filled. In either case, such force is effective through out the entire periphery of the lower pulley "8, excepting as same would be stopped by the shield 29. In FIGURES 5 and 6 of the drawings, there is shown an example of one means by which a centrifugally impelled electrolyte is substantially confined within a relatively narrow zone of the periphery of said pulley and is, accordingly, confined more closely to the area of the workpiece. This will provide a more efficient use of the electrolyte and much less splashing of same around the interior of the machine. The embodiment of FIGURES 5 and 6 represents primarily a refinement of the invention to obtain a more precise control over the flow of electrolyte.

As shown in FIGURES 5 and 6, there is provided an open end pulley 8a corresponding functionally to the pulley 8 of FIGURES 'l to 4, inclusive. Said pulley 8a is provided preferably with openings 19a, which are arranged in any desired pattern as above described and correspond functionally to the openings 19 of the pulley 8. Pulley 8a, however, is mounted on a shaft 41 by a hub 42 and held by suitable fastening means indicated generally at 43. Said shaft 41 is supported by suitable means, not shown, but which may be similar to the means holding shaft 16 in FIGURE 4, and is driven by the motor 11.

Extending into the open end of said pulley 8a is a bracket 44 supported as convenient from the frame of the machine and on which is supported an angle iron 46 on which is mounted a squeegee 47. The squeegee 47 is caused to bear against the internal surface 48 of the pulley 8a, either by its own resilience or, if desired, by a leaf spring 49, sufliciently firmly to minimize the passage of electrolyte between said squeegee and said internal surface 48. For this purpose, it is desirable, although not essential, that the squeegee be made of a resilient material, such as rubber, synthetic rubber, plastic or other elastomer, suitably resistant to chemical attack by the electrolyte.

A conduit 51 extends into the pulley and along the inner surface 48 thereof in front of the squeegee 47 whereby the fluid can be flowed into the interior of the pulley close to the periphery thereof.

It will be apparent that a second squeegee (not shown) may, if desired, be provided to contact the interior surface of the pulley on the opposite side of the conduit 51 from the squeegee 47 so that the flow of the fluid will be further restricted.

Referring now to FIGURES 8 and 9, there is shown a still further form of the invention wherein means are provided within the lower pulley by which pressure is generated and applied directly to the internal surface of said pulley. Here, there is provided a pulley 8b occupying the same position as the pulley 8 in the form of the invention shown in FIGURES 1 to 4, inclusive, and mounted for rotation upon 'a shaft 41 which is driven by the motor .11 and received within a hub 42 for supporting the pulley 8b. Thus far, the pulley 8b and its means of support and rotation is the same as that above described in connection with FIGURES 5 and 6. In this instance, however, the bracket 44 supports a pump structure 66 which consists of a pump housing 67 in which are contained a pair of pump gears 68 and 69. A manifold 74 is connected to the lower portion of said pump housing and defines a chamber 73 therewithin which is -in communication with a lower portion of the inside surface 48 of the pulley 8b. The circumferential ends of the chamber 73 are closed by any convenient means, here rollers 76 and 77, preferably resilient and the ends of said chamber 73 are closed by the end plates 78 and 79 which bear both 7 against the ends of said rollers and against the inside surface 48 of the pulley 8b. The discharge openings of said pump are connected to the chamber 73.

The pump gears 68 and 69 may be driven from any convenient source, which may be the shaft 41. The shaft 81 from the gear 68 has a noncircular portion 82 which is received into a similar noncircular opening 83 in the end of the shaft 41.

With this arrangement, electrolyte is introduced through the conduit 71 into the pump structure 66. Suitable pressure is created thereon by said pump and the fluid is .then discharged directly into the chamber 73. From said chamber it passes through the openings 19b in said pulley 8b in the region thereof adjacent at a given moment the chamber 73 and thence through the portion of the belt adjacent thereto and into the region between said belt and a workpiece.

The remainder of the operation, particularly the electrolyte phases of the grinding, are the same as above described in connection with FIGURES =1 to 4, inclusive.

While three different means for introducing electrolyte have been utilized in the foregoing description for illustrating three broad aproaches to the apparatus of the invention, such employment of specific apparatus for illustrative purposes will be recognized as solely for illustrative purposes and will not be construed to limit the invention excepting as the claims hereinafter appended require by their express terms.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Electro-chemical grinding apparatus of the abrasive belt type, the combination comprising:

a perforate, electrically conductive, abrasive belt having nonconductive abrasive grains thereon;

a pair of spaced pulleys supporting and driving said abrasive belt, one of said pulleys being located in such a position that a workpiece can contact said abrasive belt at such a point thereon that said one pulley constitutes a backing for said belt;

means defining a recess within said one pulley and means defining openings from said recess through the periphery of said one pulley;

means for introducing electrolyte into said recess whereby said electrolyte will flow, impelled at least in part by centrifugal force, radially outwardly through the openings in the periphery of said one pulley and through said perforate abrasive belt against said workpiece at the point of contact thereof with said abrasive belt;

means for concentrating said electrolyte in a region substantially adjacent the point of contact between said workpiece and said abrasive belt; and

means for applying a unidirectional electrical potential difference between said workpiece and said abrasive belt.

2. An apparatus according to claim 1, wherein the means for concentrating the electrolyte is positioned within said one pulley and concentrates said electrolyte in a region within said pulley substantially adjacent said point of contact.

3. An apparatus according to claim 1, wherein said means for concentrating said electrolyte includes mechanical means for confining said electrolyte within a region substantially adjacent said point of contact.

4. An apparatus according to claim 3, wherein said mechanical means is positioned within said one pulley and confines said electrolyte within a circumferential region within said one pulley adjacent said point of contact, said circumferential region extending through an angle substantially less than 360 degrees.

5. An apparatus according to claim 3, wherein said mechanical means includes a shield substantially covering the upper half of said one pulley for maintaining the electrolyte discharged upwardly through the periphery of said one pulley substantially within the region adjacent said point of contact.

6. An apparatus according to claim 3, wherein said mechanical means includes a pair of circumferentially spaced, rotatable rollers disposed within said recess and defining said region therebetween, said rollers having resilient surfaces contacting the internal wall of said one pulley for confining the electrolyte in the region between said rollers.

7. An apparatus according to claim 3, wherein said mechanical means includes squeegee means mounted within said recess and extending into contact with the internal wall of said one pulley whereby the electrolyte will be prevented from moving with the internal wall of said one pulley as it rotates so that the electrolyte will flow out of said recess substantially adjacent said point of contact.

8. An apparatus according to claim 7, wherein said means for introducing electrolyte into said recess includes a discharge conduit positioned within said recess substantially adjacent the internal wall of said one pulley, said discharge conduit being positioned closely adjacent to but circumferentially spaced from said squeegee means, said discharge conduit and said squeegee means defining a space therebetween substantially adjacent said point of contact.

9. An apparatus according to claim 1, wherein said means for concentrating said electrolyte includes pantition means cooperating with the periphery of said one pulley for defining a confined space within said one pulley, said confined space being in substantial radial alignment with the point of contact of said workpiece against said abrasive belt, and wherein said means introduces said electrolyte into said confined space.

10. An apparatus according to claim 1, further including pump means within said one pulley for subjecting electrolyte within said one pulley to a substantial booster pressure and urging same under said pressure radially outwardly against the periphery of said one pulley, whereby said electrolyte will flow radially outwardly impelled in part by centrifugal force and in part by said booster pressure through the periphery of said one pulley and through the perforate abrasive belt against said workpiece.

References Cited UNITED STATES PATENTS 2,680,938 6/1954 Peterson 51266 2,997,437 8/1961 Whitaker 204-224 3,162,588 12/1964 Bell 204--141 3,238,114 3/1966 Halverstadt et al. 204-224 ROBERT K. MIHALEK, Primazy Examiner.

US. Cl. X.R.

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