US2475586A - Method of electropolishing the internal surface of a hollow valve - Google Patents

Description

9 K. M.BIV\RTL 'r 2,475,586

METHOD OF ELEGTR'OPOLISHI THE INTERNAL SURFACE OF HOLLOW VALVES -F'iled April 9, 1945 Patented July 12, 1949 METHOD OF ELECTROPOLISHING THE INTERNAL VALVE SURFACE OF A HOLLOW Kenneth M. Bartlett, Cleveland, Ohio, assignor to Thompson Products Inc., Cleveland, Ohio, a

corporation of Ohio Application April 9, 1943, Serial No. 482,378

1 Claim. 1

This invention relates to a method of electropolishing the internal surface of a hollow metal valve and to the hollow metal valve so produced.

Hollow metal valves have heretofore been made by forging operations. After the valve has been forged, it is customary to ream out the stem portion of the valve to provide a relative smooth internal wall, and then to polish the wall with abrasive paper. The result of these reaming and polishing operations has always been to leave an amorphous layer over the surface of the internal wall of the valve. Such an amorphous layer, which is sometimes called a Beilby layer, is inherently formed as a result of any mechanical workin of a metal surface. One disadvantage of such a layer is that it has a relatively low grade of heat transfer, so that it to some extent obstructs the passage of heat from the coolant, which may be metallic sodium, copper or the like, used in a hollow valve, to the wall of the valve and thence to the valve guide. It is, of course, very desirable to provide the highest efliciency of heat transfer in order that the head of the valve may be kept as cool as possible, to thereby prevent overheating of the valve.

I have now found that if the internal surface of a valve, or the like, is electropolished, a smooth, polished surface can be obtained that is entirely free from the objectionable amorphous layer produced by the mechanical working of the metal of the valve. The result is that a hollow valve having an electropolished interior surface permits a more eflicient transfer of heat from the coolant used in the valve to the stem portion of the valve, and thence to the external guides.

It is therefore an important object of this invention to provide a method for electropolishing internal metal surfaces to insure a more efficient rate of heat transfer through such surfaces.

It is a further important object of this invention to provide a method for the electropolishing of the internal surfaces of hollow metal valves to eliminate or minimize the deleterious effect of scratches, remaining after a final mechanical polishing or smoothing by the use of abrasive cloths, on the endurance strength of the valve by partially or whollyremoving such scratches.

It is a further important object of this invention to provide a hollow valve having an electropolished internal surface that is free from any amorphous layer and that is characterized by a high rate of heat transfer. a a

Other and further important objects of this invention will be apparent from the disclosures in the specification and the accompanying drawings.

On the drawings:

Figure 1 is an elevational view, partly in section, of an apparatus embodying the principles of my invention and suitable for carrying out a method of electropolishing the internal surface of a hollow valve; and

Figure 2 is an enlarged fragmentary, sectional view of the valve and attachment illustrated in Figure 1, with parts in elevation.

The reference numeral l0 indicates generally a support, having a base II and an upright rod I2 extending from said base. A valve, indicated generally by the reference numeral [3 is adapted to be supported from the stand It] by means of a clamping member l4, adjustably mounted along said rod [2 by means of a thumbscrew I5. Said clamping member I4 is provided at its free end with a ring [6 having an inner, annular lining ll of rubber, or other insulating material. The valve I3 is adapted to be inserted in said ring 16 at its stem end I8 to be frictionally supported therein.

As illustrated, the valve l3 comprises a mushroom shaped head portion l9 and an elongated stem portion 20. The head portion I9 is formed with a cavity of a shape in general conforming with the external contour of the head IS. The stem 20 is also formed with a cavity, indicated by the reference numeral 22, which extends for its full length and merges smoothly into the head cavity 2|. Ordinarily, the valve 13 as it comes to the electropolishing step about to be described will have been reamed to produce the stem cavity 22. It may also have been mechanically polished, as by use of an abrasive cloth. It is advantageous that some mechanical means have been used that will leave the wall of the stem cavity 22 in a fairly smooth condition, relatively free from tool marks, since in that case the electropolishing step has less Work to do and can be accomplished at a lower cost. Aside from this matter of cost, the electropolishing method about to be described could be used even where the internal surface of the stem of the valve is relatively rough, since in the electropolishing step the high points on the surface, or crests, are anodically dissolved away until, if the method is carried out for a sufiicient length of time, the surface is left perfectly smooth and with a mirror polish.

Various metals and alloys may be employed in 39 and a rheostat 40.-

as Hastelloy steel; non-ferrous nickel-chromium alloys such as Brightray; and cobalt, chromiumand tungsten alloys such as Stellite. It should be understood, of course, that .theinvention herein described is not limited to the use of these particular alloys. It should' 'further be understood that the hollow valve'to which the method of my invention is applied may be either forged, cast or otherwise formed.

As illustrated in Figure 1, a reservoir 23 for holding a supply of an electrolyte 2d is mounted above the valve l3 from the ring stand in, by means of a clamping member 25-. Said reservoir 23, as illustrated, comprises a funnel having a stop cock 26 for controlling the rate of flow of the electrolyte.

The reservoir 23 is connected by means of a flexible hose 2i to a tubular electrode 28 that extends into the hollow valve l3 for the: full length of the stem portion 20. The electrode 28 may'suitably be supported by a clamping member 29, adjustable upon the ring stand W. A spacer 30 of insulating material is mounted in the stem end it) of the cavity 22 for spacing said electrode 28 equidistantly from the wall of the cavity 22. A second spacer 3i serves to center the lower end of said electrode 28. Both of the spacers 3t and 31 areprovided with openings therethrough, such as the openings 32 and 33 respectively, which serve for the upward flow of the electrolyte that is introduced by the hollow electrode 1 25 into the head cavity 2 i.

An electrical circuit, comprising lead wires 34 and 35, connected to a suitable source of electrical energy (not shown), is arranged to include the valve I3 and the electrode 28. For this purpose, the lead wire34, connected to the positive side of a source of direct current electricity, is connected to the'valve l3 by means of a band connector 36, and theneg-ative wire 35 is connected to the electrode 28 by means of a screw tightened clamping band-31; A switch 38 is provided in the lead wire 34, as are also an armneter A voltmeter 4| is connected in parallel with the inner circuit through the electrolyte in the valve [3 by means of a wire t2 extending across the lead- wires 34 and 35. As will be evident fromthis description, the valve l3 itself forms the anode of the circuit that includes the electrolyte within said valve, While the electrode 28 forms the cathode of the circuit.

Any suitable electropolishingelectrolyte may be used in the method-of my invention. Among the electropolishingelectrolytes that are known to those familiar with the art may be mentioned sulphuric and phosphoric acids, and [mixtures of the two. As a result of'considerable research, concentrated orthophosphoric acid at a-temperature between about 50 and 150 F. has been found to give the most satisfactory results in the electro-polishing of theinternal stem surface of a hollow valve made of a chromium-containing steel, or one of alloys referred to above. Preferably, a 75% aqueous solution-of phosphoric acid, containing 75% of orthophosphoric acid by weight of the solution, and heated-to about 100 F, is-emp1oyed= When-the cor-iditionsof operation hereinafter described are followed, a mirrorlike, polished surface, free from any armorphous layer, is produced by the use of 75% orthophosphoric acid. Other electrolytes, however, may be used satisfactorily, provided that they are adapted to. electropolish the particular metal or alloy of which the valve l3 ismade.

In operation, the electrolyte 24 from the reservoir 23 is allowed to flow through the stop cook 25 into the hollow'valve l3 at a suitable rate which is controlled by proper adjustment of the stop cock 26,. The electrolyte flows down through the hollow electrode 2.8 into the head cavity 2i of the valve and, afterfilling the valve, overflows through the opening 32 in the upper spacer 30, and runs down over the surface of the valve I3 into an overflow basin 43. After the valve I3 has filled up with electrolyte, the rate of flow may be adjusted to about 2 cc. per minute.

As soon as the valve l3 has been filled with the electrolyte,- thecircuit comprising the lead wires 3% and 35 is energized by closing the switch 38. A direct current capable of'delivering'an operating voltage of around 4 to 5 volts has been found suitable.- The rheostat is adjusted to give'a reading on the ammeter 39. of around-2.5 to 3.5-

amperes. Onthe basis ofthe internal surface of the 'valveundergoing electropolishing, this will ordinarily give about 0.5:ampere per square inch anode current density. If the anode current density is much greater or much less than-this, the rheostat 40. should" be adjusted to bringit within the limits mentioned.

The spacing ofthe anode'from the cathode is In 3 the apparatus illus-- trated, the cathode electrode 28 may suitably be relatively important.

acopper tube having an outsidediameter of oneeighth ofan'inchandaninside diameter of onesixteenth of an inch. With the usual diameters of the stem-caVity-IZZ', this williresult in an anodecathode spacing of. between one-eighth of an.

inch and three-eighthsrof an inch. These are, in general, the minimum andmaximum anodecathode spacings, for; optimum electropolishing results. The cathode electrode 28 need not be made of copper, but maybe. made of stainless steel, Monel metal or other suitable metal or alloy.

The ratio of anode to cathode area should not vary. for best-results very greatly from the ratio of 3.5. to 1.0. This ratioof anode to cathode area rather takes careof itself if :the anode-cathode spacing is properly controlled as aboveindicated.

It is important, of course, that the cathode 28 thestem cavity 22 has received a smooth, mirror like polish, or whatever degree of polish is desired; With the conditions of electropolish-ing such as those above described, the entire electropolishing operation requires in the neighborhood of forty minutes: At-the -end'of this period,- the current is shut off ahd thevalve l3 removed from-- its-clamping bracket I14,- em ptied-=of the electrolyte' and thoroughly washeda The internalsur-' face-of the-stem cavity 22 will be" found to have takenone smooth, mirror-like polish and will be entirely free from any amorphous layer.

The electrolyte solution;-' may, ofcourse, be re-used; asbyreturning the exce'ssof electrolyte from the overflow receptacle backtothe res-- ervoir 23. Upon continued use, the dissolved solids contents of the electrolyte increases due to the anodic dissolution of metal from the surface of the stem cavity 22, until finally the electrolyte is no longer effective. This point is reached when about 0.17 gram of chromium are present for each cc. of the electrolyte. The electrolyte may then be regenerated, or a new electrolyte used.

In my copending application, filed of even date herewith, I have described a method and an apparatus for descaling the wall of the valve head cavity, such as the cavity 2| of the valve l3. The descaling of the head cavity, as described in this copending application for patent, would ordinarily be carried out before electropolishing the inner surface of the stem portion of the valve. If desired, apparatus such as shown in my copending application might be used for the electropolishing of the walls of the head cavity 21, using the operating conditions hereinabove set forth for the electropolishing of the stem portion of the valve. In the method as above described, however, very little, if any, electropolishing of the walls of the head cavity takes place, because the cathode electrode 28 is relatively farther away from the walls of the head cavity 2| than it is from the wall of the stem cavity 22 and hence an insufficient amount of current passes through the walls of the head cavity to effect polishing. The lower end of the cathode electrode 28 may, of course, be inserted into the stem cavity 22 for only such distance as electropolishing of the stem portion may be desired to be carried, or, by using the electrode extension of my copending application, the walls of the head cavity 2| may be electropolished, as well as descaled.

It will, of course, be understood that various ,details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claim.

What I claim is:

The method of electropolishing the inner surface of the stem of a hollow valve which comprises positioning a hollow electrode in said stem, flowing an electropolishing electrolyte through said hollow electrode into said valve while permitting the excess of said electrolyte to overflow from said valve, making said inner stem surface the anode and said electrode the cathode, and while continuing said electrolyte flow passing an electric current from said anode through said electrolyte to said electrode of sufiicient current density and for a suflicient period of time to effect a polishing of said inner stem surface and to render said inner stem surface free from any amorphous layer.

KENNETH M. BARTLETT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 883,756 Steiner Apr. 7, 1908 1,501,862 Midgeley July 15, 1924 1,850,426 Tyrrell Mar. 22, 1932 2,070,102 Weslake Feb. 9, 1937 2,332,569 Greenslade et al. Oct. 26, 1943 2,347,040 Faust Apr. 18, 1944 2,373,459 Colwell Apr. 10, 1945 FOREIGN PATENTS Number Country Date 335,003 Great Britain Sept. 18, 1930 577,030 France May 26, 1924 OTHER REFERENCES Proceedings of The American Electroplaters Society, 1941, pages 20 through 27, and 104 through 112.

The Metal Industry, Jan. 29, 1943, pages 69, 70.

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