US3162588A - Belt type electrolytic grinding machine - Google Patents

Description

Dec. 22, 1964 R. M. BELL 3,152,533

BELT TYPE ELECTROLYTIC GRINDING MACHINE Filed April 17. 1961 RAIVISAY M. BELL AT TO R NEYS United States Patent 3,162,588 BELT TYPE ELECTRGLYTEC GRINDING ll IAQHINE Ramsay M. Bell, Schoolcralt, Mich, assignor to Harnmond lsiiachinery Builders, Erica, Kalamazoo, h lich, a corporation of Michigan Filed Apr. 17, 196i, Ser. No. 194,201 1 Claim. ((Il. 294-441) This invention relates in general to an electrolytic grinding machine and, more particularly, to a type thereof having a perforated belt and platen through which electrolyte is moved with a minimum of obstruction so that satisfactory grinding can be performed with a minimum of electrical potential.

This application is a continuation-in-part of my application Serial No. 762,163, filed September 19, 1958, and entitled Belt-Type Electrolytic Grinding Machine, now abandoned.

The use and construction of belt-type grinders have long been familiar and many specific forms have been used. Likewise, the advantages and techniques involved in removing particles of electrically conductive materials by electrolytic erosion (often called electro-chemical decomposition) are also well established. However, insofar as I am aware, little or no success has been achieved in applying the principl s of electrolytic erosion to the belt-type grinding machine, even though it is well known that a belt-type grinder is capable of performing certain types of grinding operations in a much more efficient and convenient manner than other types of grinders, such as the disk grinder for example, particularly because the platen and belt can be formed to fit or otherwise suit cer* tain types of formed workpieces.

Among those obstacles which have apparently impeded the development of a belt-type eletrolytic grinding machine are the proper control and the adequate supply of electrolyte to the grinding zone. Previous attempts to effect acceptable electrolytic grinding operations with a belt grinder have required an electrical potential which is so high that it creates an uncomfortable sensation for the machine operator.

While pursuing this problem, it was found that in order to obtain reasonably satisfactory electrolytic erosion with a belttype grinder, the spacing betwen the anode (workpiece) and the cathode of the apparatus must be eX' tremely uniform and must be held to a very small value, normally under 0.005 inch and preferably about 0.001 of an inch. It was also found that the movement of electrolyte between the cathode and the anode must have a minimum of obstruction so that there is always an ample supply of electrolyte in the grinding zone. By meeting this conditions, it is possible and practicable to carry out an electrolytic erosion operation effectively and efiiciently with a voltage supply which is low enough to be acceptable to the operator.

Accordingly, a primary object of this invention has been the provision of an electrolytic grinding machine utilizing a belt-type abrasive element.

A further object of this inventionhas been the provision of a belt-type electrolytic grinder wherein a sufficiently continuous and adequate supply of electrolyte can be maintained in the zone between the anode and cathode of the grinding machine to effect a satisfactory grinding operation with a sufficiently low electrical potential that it will not produce uncomfortable sensations for the operator.

A further object of this invention has been the provision of a structure whereby the basic construction of a non-electrolytic grinding machine can in the manufacturing operation be modified to provide an electrolytic grind- 3,l2,58$ Patented Dec. 22, 1964 ing machine without materially changing such basic construction and without increasing the cost unreasonably by comparison with the cost of a conventional non-electrolytic, belt-type grinding machine.

A further object of this invention has been the provision of an electrolytic, belt-type grinding machine, as aforesaid, which is extremely easy to operate, which requires a minimum of maintenance, which is sturdy and reliable in construction and which performs accurately.

A further object of this invention has been the provision of a construction for a belt-type electrolytic grinder, as aforesaid, wherein the reach of the belt by which the grinding operation is performed can be caused to operate on non-linear surfaces of various shapes which may be convex and/or concave, such nonlinearity being either lengthwise or crosswise of the belt.

Other objects and purposes of the invention will become apparent to persons familiar with this type of equipment upon reading the following specification and examining the accompanying drawings, in which:

FIGURE 1 is a broken, front elevational view of that portion of a belt-type, electrolytic grinding machine embodying the invention.

FIGURE 2 is a broken, fragmentary side elevational view of said grinding machine.

PXGURE 3 is an enlarged sectional view taken along the line Ill-411 of FIGURE 1.

FIGURE 4 is a broken sectional view taken along the line IVlV of FIGURE 3.

FlGURE 5 is a sectional view taken along the line VV of FIGURE 2 and showing a modified platen construction.

FIGURE 6 is a sectional view taken along the line VI-VI of FIGURE 5 and rotated degrees clockwise.

FIGURE 7 is a fragmentary top view of a modified grinding machine embodying the invention.

For convenience in description, the terms upper, lower and derivatives thereof will have reference to the grinding machine as appearing in FIGURES l and 2, unless otherwise stated to the contrary. The terms inner, outer" and derivatives thereof will have reference to the geometric center of said grinding machine and parts associated therewith. The terms front and rear will have reference, respectively, to the left and right sides of the said machine as appearing in FIGURE 2.

The term perforate or derivatives thereof shall be used to describe objects having a multiplicity of openings therethrougn, regardless of whether such openings are formed by a perforating operation or other type of fcrming operation and the number and size of such openings being sufficient to permit the electrolyte to flow therethrough at the required rate.

General Description The ob ects of the invention, including those set forth above, have been met by providing a grinding machine having a pair of spaced and axially parallel rollers around which an endless belt extends, one reach of said belt being, in the embodiment here illustrated and described, disposed in a substantially vertical plane and having a belt supporting platen adjacent its inner side and a work supporting table adjacent its outer side. Said belt is in the illustrated embodiment fabricated from an electrically conductive material but is in any case a material through which an electrolyte can pass with a minimum of obstruction. Said belt is of uniform thickness throughout its length and has an abrasive coating on its outer surface which is electrically nonconductive and is of substantially uniform thickness. The platen has a perforated region which is located substantially opposite and extends slightly above the work as it faces the platen. 'l he perforate porner.

. 2) on'its front surface which lies closely adjacent to'and tion of said platen defines one side of an electrolyte chamber which is defined on the remaining sides by the walls of a casing secured to said platen. A device for creating an electrical potential is connected between the. work supporting table and the platen, which are otherwise electrically' insulated from each other. The platen and/or the belt supported thereon serve as a cathode and the workpiece supported upon the table serves as the anode.

Mechanism including a collecting basinand a pump are provided for receiving the electrolyte as it moves away from the grinding zone and returning such electrolyte under pressure to the electrolyte chamber so that it will pass again through the openings and back into said grinding zone.

Detailed Construction The belt-type electrolytic grinding machine (FIG- URES 1 and 2) is herein selected to illustrate the invention and may have a basic construction similar to the belt-type grinder disclosed in patent application Serial -No. 738,869, filed May 29, 1958, entitled Machine Tool,

and assigned to the assignee of this application, now Patout No. 2,900,766. More specifically, the grinding machine 10 is comprised of a central housing 11 supported upon the upper portion. of a pedestal 12 which also supports a driving motor 13 below said housing. An upper pulley 16 is vertically adjustably supported upon the housing 11 and a lower pulley 17 is supported upon the shaft 18 of the motor 13 for rotation thereby. The pulleys 16 and 17, which are axially parallel and arranged so thatthe lower pulley 17 is directly under the upper pulley 16, are encircled by an endless belt 19 of uniform thickness.

Said belt 19 (FIGURE 3) is in the illustrated embodiment fabricated from an electrically conductive material, such as a strip of woven fabric of copper or aluminum. Other materials of non-electrically conductive character, such as fabric, will in certain instances be satisfactory. From whichever material the belt 19 is made, it will have a plurality'of closely spaced openings 21 through which an electrolyte can easily pass. These openings should be arranged to cover 'the entire surface of the workpiece substantially uniformly with electrolyte, but any random or geometric pattern capable of doing this is acceptable. The

' openings will normally extend over the entire area of the belt, but should at least cover a band along said belt as wide as, or slightly wider than, the width of the workpiece. The openings should be arranged to cover an area somewhat wider than the workpiece if it is desired to reciprocate the workpiece crosswise of the belt during the grinding process. The flow of electrolyte through the belt is primarily controlled by the openings provided, as hereinafter described, in the platen behind the belt so that, for commercially acceptable purposes, it is normally preferable to provide openings over the entire surface of the belt. The outer surface 22 of the belt19 has a coating of electrically nonconductive abrasive material, such as aluminum oxide, silicon carbide or diamond bort, which may be afiixed to said belt in any conventional manner. Itis important that the particles comprising the coating extend from the outer surface of the belt not more than approximately 0.005 inch, preferably about 0.001 inch, and thatthey do so in a highly uniform man- As a still further alternate, a belt has been satisfactorily made from non-conductive, flexible, material, as fabric, suitably perforated and provided with (a)- electrically conductive paint on the rearward (against the platen) side and extending through the openings, and (b) suitable bonding-material and abrasive non-conductive grit onits frontward (adjacent the work). side.

The housing 11 has a relatively fiat platen 26 (FIGURE is parallel with the inner surface 27 of the frontreach 28' of the belt 19, which reach preferably moves down wardly. Said platen 26, which may be generally similar to the platen shown in Patent No. 2,562,229, has a plurality of closely spaced, relatively small openings .29 located in the portion of said platen opposite the grinding position of the workpiece. Said openings cover an area slightly wider than the surface of the workpiece engaged by the belt. This area must be somewhat wider if crosswise reciprocation of the workpiece is desired. In a: vertical direction the area of openings 29 commences at, or slightly above, the lower edge of the workpiece and extends somewhat above the upper edge of the workpiece. The extent of the openings above the upper edge of the workpiece will depend somewhat. on the freeness ,(rateat which an aqueous liquid can pass through the belt under moderate pressure) of the belt. In any event the area of openings -will be sufiicient to enable the electrolyte to' pass through the belt and furnish an adequate supply of electrolyte to all portions, including the upper portion, of the workpiece. The openings are of relatively small size in order to effect amore complete and uniform distribution 'of electrolyte being discharged against, and

through, the belt. 7

The platen 26, will preferably be made of any suitable electrically conductive material, but it should be of suffi cient wear resistent properties that it will not be unreasonably abraded by the belt. Tungsten carbide is preferable although for a relatively light service other types of wear resisting materials or platings can be utilized. If the platen 26 is itself not made of electrically conductive material, then other electrode means will be provided to establish one side of an electrical potential through electrolyte being expelled through the platenand belt in the region of the workpiece 47, such as by making the casing 31 of electrically conductive material, by providing an electrically conductive terminal within a non-electrically conductive casing 31 or other convenient means for providing. an electrode in contact with the electrolyte within the casing 31. a

The exact pattern of openings 29 in the area of the platen. occupied by-said openings may be readily varied as required to fit a given workpiece either by replacing the platen 26 as needed or by providing the openings in a suitable insert 26a removable from the platen.

As shown in FIGURES 3 and 4, a casing 31 of shallow depth is secured to the rear side of the platen 26 by means, such as the bolts 32, and combines with the perforate region of the platen 26 to define a small electrolyte chamber 33, which communicates with the openings 29. The chamber -33 is connected by a conduit 34 to a pump 37, which may be of the positive displacement type. Said pump 37 has its inlet 38 connected to a low point in a collecting basin 39 which is disposed beneath and surrounds the lower pulley 17, as well as the lower portion. of the belt 19. The basin 39 extends upwardly and forwardly a suflicient distance to catch the electrolyte which is moved downwardly from the grinding zone by gravity and/or the downward movement of the front reach 28.

A work support table- 42 is preferably adjustably supported upon the pedestal 12 bymeans suchas the arm 43 so that its rear edge 44 is close to but spaced from the front or outer surface 22 of the front reach 28; The worktable 42 is electrically conductive and is connected to one side ofla source 45 of uni-directional electrical energy of either steady or pulsing value and preferably Operation With the grinding machine assembled as shown in FIGURES 1 and 2, it is made ready for use by connecting the source '45 of electrical energy between the table 42 and advanced toward the outer surface 22 of 13 and pump 3'7. A workpiece 47 is placed upon the table 42 and advanced toward the outer surface 2 2 of the front reach 28 of the belt :19 until it is just touching said front reach 28. The pump 37 causes the electrolyte to flow from the chamber 33 through the openings 29 and 21 toward and against the workpiece 47 and fresh electrolyte is constantly supplied thereto partly by direct flow through the belt adjacent the workpiece and partly through the belt above the workpiece from which location it is carried into the grinding zone by the motion of the belt. From the grinding zone the electrolyte partly drops from gravity and partly moves with the belt 19 downwardly into the collecting basin 39.

The pump 37 receives the electrolyte collected by the basin 39 and moves it upwardly through the conduit 34 back into the chamber 33 under sufiicient pressure that such electrolyte will again flow through the openings 29 in the platen 26 and thence through the openings '21 in the belt 19. The electrolyte thus passing through the belt -19 permits the flow :of current between the workpiece and the platen whereby small particles of such workpiece are set free in a known manner by electrolytic erosion or electrochemical decomposition so that they can be wiped downwardly by the abrasive coating on the belt 19. it has been found that 80 or 90 percent, and sometimes more, of the metal removal from the workpiece 47 is effected by the electrolytic erosion and the remaining proportion of metal, and/or products of decomposition otherwise remaining on the work surface, appears to be removed by mechanical action of the abrasive grits constituting the coating. Thus, the primary function of the abrasive coating is :to insulate the belt '19 from direct electrical contact with the workpiece 47 and a secondary function appears to be to wipe off the decomposition products of the electrical action.

As indicated above, it is essential to the satisfctory operation of this type of machine that the distance between the outermost conductive surface of said belt '19 and the workpiece 47 be held to a very small value such as not over 0.005 inch and preferably 0.001 inch, and that the flow of electrolyte from the chamber 33 to the adjacent side of the workpiece 47 receives a minimum of obstruction. Otherwise, the potential required to effect the erosion or decomposition will create an undesirable sensation in the person handling the workpiece 47. With a good electrolyte, which may be any of many known kinds, the potential provided by the source 45 can be maintained at less than -10 volts if the thickness of the belt 19 and the thickness of the abrasive coating on said belt are accurate and uniform and within the dimensional limits set forth above.

Platens and associated structure embodying the invention may be contoured in a wide variety of specific shapes to handle work of difierent shapes. For example, as shown in FIGURES 5 and 6, a platen 51 having a concave front surface 52 may be provided between the main belt supporting rollers, such as those shown at 16 and 17 in FIGURE 1. The front reach 56 of the grinding belt 57 (FIGURE 6), which my be substantially identical in construction with the belt 19, may be urged against the front surface 52 of said platen 51 by the workpiece 53 which is supported upon the table 59. Means, such as the roller shown in broken lines at 60 in FIGURE 6, may be rotatably mounted upon the table 59 for assisting in holding the belt 57 against the platen 5'1.

6 The portion of the platen 5 1 opposite the workpiece has a plurality of openings 61 (FIGURE 6) which communicate between the openings '62 in the belt 57 and the chamber 63 behind the central portion of said platen 51. Accordingly, by using the alternate platen structure 5'1 it is possible to produce convex surfaces by means of a belt-ty-pe, electrolytic grinder.

FIGURE 7 illustrates a further alternate platen 66 having a convex outer surface 67 around which the belt 68 extends. A pair of idler rollers 69 and 70 may be used if desired to assist in holding the belt in place with respect to the platen. A guide wheel 72, which is coaxial with, and of a slightly larger radius than, said convex surface 67, may also if desired be provided adjacent to the platen 66 and between said rollers 69 and '70. The alternate platen has an electrolyte chamber in the central portion thereof which communicates with the inlet conduit 71 and with openings through the outer surface of the platen 66 in substantially the same manner as set forth with respect to the structure shown in FIG- URE 3. Accordingly, a machine having the alternate platen 66 can be used for providing concave surface in a workpiece by the electr c-chemical decomposition process.

While in each of the embodiments shown the belt is in a vertical position, and in at least the embodiments of FIGURES 1 to 6, inclusive some reliance is placed upon gravity to return the electrolyte to the low pressure side of the pump provided for circulating S81E16, it will be recognized that the apparatus of the invention may be readily modified to operate in any other desired position according to the purposes to be served and reference herein to particular positions will be understood as used only in connection with the particular embodiment here chosen to illustrate the invention and not as limiting.

Although particular preferred embodiments of the invention have been disclosed above in detail for illustrative purposes it will be understood that variations or modifications of such disclosure, which lie within the scope of the appended claim, are fully contemplated.

What is claimed is: A method. of electrolytically grinding a workpiece using an endless, perforate abrasive belt having nonconductive abrasive grit thereon, said belt being backed by a perforated platen, which comprises:

placing a worlcpiece in touching relationship with the grit on the abrasive belt :which is continuously moved unidirectionally past said workpiece so that the Workpiece is spaced a small distance from the belt proper;

continuously circulating an electrolyte through said perforated platen and said belt and against said workpiece, the electrolyte being supplied through the region of the belt contacted by the workpiece and in the region of the belt above the workpiece so that all portions being ground of the workpiece, including the upper portion, are bathed by the electrolyte; and

continuously applying a unidirectional electrical potential difference between the workpiece as the anode and the electrolyte as it passes through said belt.

References Cited in the file of this patent UNITED STATES PATENTS 2,526,423 Rudorff Oct. 17, 1950 2,562,229 Bell July 31, 1951 2,722,787 Hallewe'll et al. Nov. 8, 1955 2,997,437 Whitaker Aug. 22, 1961 3,004,910 Keeleric Oct. 17, 1961 3,060,114 Sanders Oct. 23, 1962 3,099,904 Bell Aug. 6, 1963

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