US2570748A - Wire drawing apparatus - Google Patents

Description

Patented Get. 0, 1951 WIRE DRAWING APPARATUS Fillmore Franklin Bain and Olney Broun, Baltimore, Md., assignors, by mesne assignments, to Armco Steel Corporation, a corporation of Ohio No Drawing. Application July'9, 1945,

Serial No. 604,088 1 1 Claim. (01. 29- -155.42

Our invention concerns the production of stainless steel and similar wire having uniform composition and characterized by its high luster and freedom from surface defects and the like. More particularly, it is directed to the ready manufacture of large-diameter wire of this general type.

An object of our invention is to produce a stainless steel or similar wire, particularly largediameter wire of this general type, which while characterized by its uniform composition throughout its extent, its substantial freedom from clevage lines, and from all occlusions, pits, scams or scale, its high tensile strength and sturdiness while in use and by its high surface luster, nevertheless is quickly and rapidly produced with a minimum of operational steps and manufacturing costs and requiring but little skilled supervision and attendance during production.

Another object is to provide a method of manufacturing a wire product of the general type described in the foregoing which method is rapid, certain, reliable, inexpensive, requires a minimum of operational steps and which may be readily supervised and carried into effect.

Other objects will in part be obvious and in part pointed out hereinafter during the course of the following description.

Our invention accordingly resides in the several operational steps and in the relation of each of the same with one or more of the others, as well as in the product resulting therefrom, the scope of the application of all of which is more fully set forth in the claims at the end of this specification.

To facilitate a more ready and thorough understanding of the present invention, it may be noted at this point that as the use of stainless steel has come more and more into prominence in widely diversified industrial, commercial and household fields, particularly ornamentation, the need has increased correspondingly for a stainless steel wire of high surface finish, particularly adapted for fabrication of what may conveniently be termed quality products. Illustrative of this general type are refrigerator shelves, ornamental grids of various types, restaurant cooking utensils, cake rests and the like. The foregoing listing is by no means exhaustive, but is simply typical of the widespread application to which stainless steel wire' can be put.

Moreover, a wire which, metallurgically speaking, is of uniform cross-section is highly desired and in fact is almost imperative in precision work of all sorts. The same uniform quality is essential where substantial tensile loads are carried.

Heretofore, substantial difliculty has been encountered in producing stainless steel wire which completely satisfies these many requirements. Particularly is this true of comparatively largediameter wire. Expensive and time-consuming centerless grinding has heretofore been required, especially in the production of wire of large diameter. Heavy cold reductions have been required when manufacturing small-diameter wire, say of 0.200 inch diameter or less. In conventional wire drawing, the surface of the wire in the larger size is left with pits and scams. While these may disappear in substantial measure during the heavy cold reduction heretofore referred to and employed in drawing the 'wire to small diameter, they remain in the larger sizes and are not removed by velectropolishing. Thus, heavy cold reductions have heretofore been required to achieve a fine lustrous surface. Even when this technique is resorted to, however, it is satisfactory only in the case of small diameter wire.

Very occasionally in the past it has been found that some appreciable extent of the large diameter wire is substantially without blemish. This represents an unpredictable chance specimen,

however, produced from a piece of wire carefully selected from the batch because it chances to be comparatively free from surface defects. Such metal stock, limited in quantity and of good quality, therefore sells at a premium. The art recognized asubstantial demand for large-size wire which combined the multiple advantageous features of uniform high quality, plentiful supply and low price.

A thorough understanding of these difficulties encountered in the practice of the prior art is of substantial advantage in appreciating the solution established with the present invention. Accordingly, it may be noted that the difiiculties under consideration in large measure stemmed from and comprised the result of the preliminary hot rolling processing of the metal billet. At the same time such defects as are caused by annealing, pickling and the like may likewise be relieved by the practice of our invention.

The common practice in producing stainless steel wire is to roll this wire hot from billet stock, this hot-rolling operation being conducted until the wire has been reduced to what may be termed a relatively large diameter, say about onehalf to three-eighths inches. Heretofore smaller diameter wires are produced from these larger stock sizes through a succession of annealing and cold-drawing operations until the finished sizes are achieved. That is, the wire is cold-drawn through a series of passes until it becomes extremely hard, whereupon it is annealed and colddrawing resumed. Varied reasons justify terminating the hot-rolling operation at relatively large diameter. Chief among them may be noted, however, that the hot-rolled wire is subject to a number of defects which most economically can be removed by cold-drawing or cold-rolling.

These defects, observable upon the surface of the metal, are attributable to many causes. Illustratively they may be occasioned by slivers,

imbedded scale, pits resulting from the picklingertheless the production of high luster smooth wire is not always easily achieved. Particularly is this true of the larger sizes where the number of cold-drawing passes is limited by a combination of dimensional and economical reasons.

Because of the foregoing, it has heretofore been the common practice of manufacturers to -.fill orders requiring superior finish with centerless-ground material. This is undesirable. Centerless-ground wire is more expensive, the operation of straightening before centerless-grinding is undertaken adding appreciably to this expense. Moreover, it is not always desirable to fill orders with straightened wire. Many customers, to illustrate, prefer stock in coils for further processing or for shaping on machines which are equipped to handle coiled wire.

Our invention accordingly includes as an important object thereof the provision of a simple and economical method for removing or avoiding in substantial measure the various defects, disadvantages and deficiencies of the prior art as hereinbefore recited, and at the same time permitting the production of stainless steel wire hav ing smooth finish and high luster, uniform construction throughout its cross-section and of uniform analysis throughout its length, all of which can be achieved both in large and small diameter wire with but a comparatively few passes through the reducing dies.

Briefly, our invention may be envisioned as comprising the steps of passing the wire to be processed through one or more revolving dies, and then electropolishing the drawn wire in any of the standard electropolishing solutions. The wire thus produced, even large diameter sizes, is characterized by its substantial freedom from the pits and seams heretofore present in wire produced in conventional manner. In one typical instance, a die of the type generally employed in drawing stainless steel wire is carefully centered in a revolving chuck. The wire to be drawn is led through the die and is then wound around a take-01f drum. Both the drum and chuck are motor-powered.

Nearly equally satisfactory results are achieved by passing the wire through revolving rolls. Wire passed through certain types of straightening machines using revolving rolls, and then electropolished, presents surface finishes approximating those achieved by revolving dies.

We have devoted considerable time to a determination of the optimum rates of die speed and of wire drawing. Our careful research in this respect has failed to establish any optimum rotational speeds for the dies or rolls. Our investigations lead to the conclusion that no such listing is practical. The speed at which the wire may be drawn through the die may vary greatly. This is also true of the speed at which the die re- .volves. The determining factor in all cases for this considerable variation is the grade of the steel used coupled with the condition thereof. That is to say, one determining factor is the quantity of imbedded slivers, scale, seams and the like. In general, our experimental work indicates that any rate, both of draw and of rotational speed, is satisfactory below that which gives rise to excessive generation of frictional heat. Similarly, the variable rate of wire drawing is dictated by a combination of the factors constituted by the nature of the steel, its condition, the temperatures resulting from the drawing operation and the like.

In the foregoing discussion attention has been directed to the use of revolving dies as distinguished from fixed dies. It has been developed that the dies may be either plate-like in nature with the die aperture centered therein, the die then rotating about its center, or the wire stock may be passed through cooperating rolls, the outer periphery of which contacts with the wire, the rolls in this instance thus properly being defined as revolving relative to the wire. In either instance, it is properly said that the wire stock passes across an adjacent rotating surface. It is by no means essential that the number of dies be limited to one. Moreover, in those instances where a plurality of dies are resorted to, and this is usually the case for expediency, it is by no means necessary that all reductions employed in producing finished wire be accomplished through the use of revolving dies. Quite on the contrary, it is entirely convenient, and is quite often the practice, to use the revolving dies in conjunction with fixed dies. Furthermore, it is entirely possible, with observed satisfactory results when a combination of revolving and fixed dies is resorted to, to employ the revolving die early in the drawing operation. It is likewise entirely feasible to employ the revolving die for the finishing pass, just before the electropolishing. We have observed from a practical standpoint, however, that optimum results appear when the revolving die is used in the finishing pass, or preferably in all of the passes.

As suggested hereinbefore, the total reduction achieved will vary with the steel used, its metallurgical condition, its initial dimensions, and the required dimension of the end product.

As to the electropolishing technique forming the last phase of our invention, this may be carried out according to any standard technique heretofore satisfactorily employed with stainless steel. Among these may be listed those according to the United States Letters Patent to Ostrofsky, Nos. 2,331,721 and 2,335,354; the pending applications for United States Letters Patent of Clingan, Serial No. 319,056, filed February 15, 1940, now abandoned, Serial No. 319,057, filed February 15, 1940, now abandoned, and Serial No. 378,576, filed February 12, 1941, now Patent No. 2,379,066, issued June 26, 1945, as well as in the pending applications for United States Letters Patent of Feild, Serial No. 460,296, filed September 30, 1942, now Patent No. 2,442,591, issued June 1, 1948, and Serial No. 484,777, filed April 27, 1943, now abandoned. These are simply illustrative of a large number of such techniques. Since the electropolishing technique itself does not per se form part of our invention, it is unnecessary to recite this latter in greater detail at this point, and it is omitted for clarity.

To crystallize the general rule relative to the practice of our invention as set forth in the foregoing, it will be most helpful at this point to narrate a typical specific illustration of a technique embodying such invention. Illustratively, a billet of the 17% chromium grade of stainless steel was hot-rolled until it was reduced to a diameter of 0.395 inch. The steel was thereupon annealed at approximately 1400 F. from approximately 4 to 6 hours. It was then air-cooled to soften the metal before cold-drawing. Following air-cooling, it was pickled in a sodium hydride pickling bath, and then rinsed in water. It was thereupon dipped quickly in a 10-15% solution of hot nitric acid, this being followed by a further water rinse.

At the conclusion of this preliminary pickling treatment, this comparatively large diameter wire displayed a frosty exterior. It was rough to the touch and gathered lint when a cloth was stroked across its surface, this indicating the presence of minute slivers. Thereupon this wire was leaded and passed through a fixed die, reducing the diameter to 0.325 inch. It was thereupon cold-drawn through another fixed die to a diameter of 0.270 inch. A 10% cold nitric acid bath was then employed to strip off the lead jacket. The metal of the wire having become extremely hard as a result of the cold-working, the wire at this point was amiealed and pickled again, as described in the foregoing. The same characteristic frosty appearance resulted, although to a lesser degree'. Throughout the area of the entire surface numerous small pits and seams were visible to the eye, these being somewhat elongated in appearance.

In this stage of the processing we divided the coil into two parts. One of these we coated with lime while the other we left uncoated. The leading tip of both coils were pointed, and the wire run through a die revolving at approximately 900 R. P. M. with a rate of draw approximating 100 feet per minute. A light grease was applied to the uncoated wire just before entering the die to serve as a lubricant. The diameter of the wire, following passage through this die, was 0.250 inch, this comprising the finished dimension. The two coils were thereupon cleaned and.

electropolished in a citric-sulfuric acid solution, following the practice of the Ostrofsky United States Patent No. 2,334,354, page 1, column 2, lines 13 to 17, for a period of approximately seven minutes at an approximate current density of 0.5 to 0.75 ampere per square inch.

In marked contrast to the results theretofore obtained involving heavy cold reduction through fixed dies, the wire now displayed a smooth lustrous finish and exhibited only a few scattered lines and marks, practically invisible to the naked eye and perceptible comfortably only through a microscope. We found the uncoated wire to possess a finish slightly superior to that of the lime-coated wire. In each case, however, we observed the finish to be markedly superior to any theretofore obtainable other than through the use of the expensive and tedious centerless grinding method.

This new stainless steel wire both in large diameter (by which is meant, both here and wherever reference is made to large diameter in the claim, a diameter in excess of 0.200 inch) and small diameter (by whichis meant less than 0.200 inch in diameter) sizes displays high luster with the substantial absence of defects resulting from slivers, imbedded scale, pits resulting from pickling, seams, lines or other irregularities. The absolutely smooth surface is indicative of the uniform composition of the metal through average cross-sections taken at various points along the length of the wire. The treatment is rapid, efiicient, certain and requires but little replenishment either of physical parts or chemical compositions, and these only at infrequent intervals. Required attendance and supervision is minimized. Results are certain and accurate. For the first time finished wires for quality products are available in both large and small diameter sizes at a cost which is sufiiciently low effectively to meet the competition of wires of other compositions. All these and many other practical advantages attend upon the practice of our invention.

Many modes of the practice of our invention will readily occur, to those skilled in the art, once the broad aspects thereof are disclosed. As well, many modifications of the mode of realization hereinbefore set forth will likewise occur to those skilled in this practice. Accordingly, we intend that the foregoing disclosure be construed merely as illustrative and not by way of limitation.

We claim:

The method of producing stainless steel wire of high surface luster and substantially free of seams, slivers, lines and the like, comprising working stainless steel to the rough wire-size desired, coating the wire with non-metallic coating, cold-drawing the same through a die at the rate of about or more feet per minute while rotating the die during drawing at a rotational speed of approximately 900 or more R. P. M., removing the coating, and thereafter electropolishing the cold-drawn wire thus formed.

FILLMORE F. BAJN. OLNEY BROUN.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 491,668 Steel Feb. 14, 1893 603,836 Algeo, Jr. May 10, 1898 738,932 ODonnell Sept. 15, 1903 1,137,920 Sleeper June 4, 1915 1,520,905 Lauren Dec. 30, 1924 1,751,094 'Matteson Mar. 18, 1930 1,945,877 Bonte Feb. 6, 1934 2,065,166 Winwood Dec. 22, 1936 2,108,603 Mason Feb. 15, 1938 2,178,674 Simons Nov. 7, 1939 2,217,602 Smith Oct. 8, 1940 2,226,400 Gaines, 3rd Dec. 24, 1940.

2,239,580 Statz Apr. 22, 1941 2,250,610 Simons July 29, 1941 2,335,354 Ostrofsky Nov. 30, 1943 2,379,066 Clingan June 26, 1945 2,412,058 Pfeil Dec. 3, 1946 2,442,592 Field June 1, 1948 FOREIGN PATENTS Number Country Date 7,961 Great Britain Apr. 19, 1893 274,244 Great Britain July 21, 1927 OTHER REFERENCES Stainless Steel, by 'I'hum, pub. by Amer..Society of Metals, Jan. 1935, Cleveland, Ohio.

Making and Shaping and Treating of Steel, by Carnegie Illinois Steel Corp., Pittsburgh, Pa., 5th ed., pp. 1065-1155.