US2602538A - Deformation of metals - Google Patents

Description

y 3, .1952 c. w. BIMBA ETAL 2,602,538

DEIFORMATION 0F METALS Filed March 18, 1948 fled EPOZd/b fiw p WJM M k 3:3

Patented July 8, 1952 DEFOPL-MATION OF METALS Charles W. Bimba and Fred Brown, Chicago, IlL,

assignors to La Salle Steel Company, Hammond, Ind acorporation of Delaware Application March 18, 1948, Serial No. 17,926

3 Claims. ((31. 205-2) v This invention relates to the deformation of metals and, in particular, refers to cold reduction by means of dies. In this specification the term die is used in a generic sense to indicate fixed dies, movable dies (rolls) etc. i

In the cold deformation of metals two ofthe major desiderata with regard to the reduced product are accurate dimensions and highly finished surfacesi Dimensional accuracy is a function of the wear resistance of the die. and of course, many attempts have been made in the past to decrease the rate of attrition of the dies andthus increase their life or lengthen the period during which they produce satisfactory dimensions. To this end new die materials have been developed, the carbides at the present having thelongest life. Certain improvements have also been made in the-methods of lubricating the die surface as the reduced stock passes across it under heavy pressure. Probably the most effective of these comprises the combined use of the usual liquid lubricants and the so-called dry lubricants, these usually being in the form of a phosphate or sulphate coating on the surface of the metal being cold reduced. However, it is common knowledge that even when .the most effective lubricants are used with the best materials that the die life is still very short.- It is, therefore, an object of our invention to very substantially. decrease the rate of attrition and increase'the life of cold reduction apparatus.

The surface finish of the cold reduced metal is also, to some extent, a function of the wear resistance of the dies. Initially these have smooth surfaces and are therefore capable of producing smooth, highly finished surfaces. Due

to wear, however, they soon become pitted and scored and transmit these surface defects to the metal passing threthrough. When the stock "difliculties which are encountered in producing highly finished surfaces by means of conventional methods, it is an object of our invention to provide a process and apparatus which will produce a finished surface of quality heretofore unobtainable by cold deformation apparatus for any commercially reasonable length of time. i

, In order to accomplish the first object of our invention, i. e., to reduce wear, we employ the principle that under uniform conditions of pressure and lubrication and for continuous operation, the wear of a die is substantially proportional to the rateat which materialis passed over its surface. In our invention we greatly decrease the rate at which material is passed over the die surface but we do this without adversely affecting the output or rate of production of the die. We accomplish this by inserting a movable strip or sheet of thin material (or what we call a shim) between the surface and the stock being reduced. With this arrangement the wear of the die is proportional to the rate at which the shim passes across its surface. This rate can be controlled as desired. There is, 0f course a relative movement between the shim and the stock passing through the reduction apparatus which causes attrition of the shim. This however, is spread out over a considerable length of shim so that rate of wear of any cross section is extremely small. Obviously, this phase of our invention is applicable to either hot or cold deformation processes.

As stated above, the second major object of our invention is to produce cold deformed stock having highly finished surfaces. We have found that we can do this and at the same time reduce the wear which occurs on the faying surfaces of the contacting shim and the die. We achieve this result by using a shim having a suitable surface coating, such as a phosphate coating, which serves to lubricate the joint between the shim and the die and to polish or lightly abrade the surface of the stock. The quality of the finished surface may be varied by means of the relative movement between the shim and the stock. As the ratio of the speed of the stock to the speed of the shim increases, so do the luster and the mirror-like qualities of the finished surface.

' In order to describe more specifically our invention and additional objects and features thereof, we willnow refer to the accompanying drawing which is a diagrammatic representation of cold deformation apparatus embodying the invention.

As hereinbefore stated, the term die is used generically in this specification so that while the die sections 1 and 3 of the drawing represent in particular a cross section on a plane through the tapered aperture 5 of a fixed die 1, they may be considered as a set of rolls or any other apparatus wherein controlled deformation of the metal occurs as a result of pressure and relative motion.

In the particular embodiment selected for the P rpose of illustrating the principles of this invention, the aperture 5 is rectangularas is the reduced section of the bar A being drawn through the die by means of grip 9.

pare the shims from material having a greater yield strength, and hence greater resistance to plastic deformation, than that of the bar stock A. The energy available for deformation is therefore absorbed by the bar A and the shims l and I! are not deformed by their passage through the aperture 5.

Since there will be a certain amount of wear of the shim surfaces adjacent to the neck of the aperture 5 weiprovide means for moving the shim relative to the die I .in order to maintain dimensional identity among the drawn bars. This means may be of any desired structure but we prefer to use conventional reelers or coilers such as are used widely in the rolling of thin gauge material. The upper shim I5 is therefore unwound from the coil [9 and wound on to the coil 2| at a predetermined rate. The lower shim I1 is unwound from coil 23 and wound on coil 25 at a predetermined rate. One satisfactory alternate construction for moving the shims would be to arrange them in the form of endless belts, however, we prefer to use coilers because greater lengths of shims can be employed and the apparatus occupies a minimum of space.

Passage of the shims through the die 1, even at low rates of speed, creates appreciable frictional forces in the joint between the die faces II and I3 and the outer sides of the shims be cause of the high pressures involved. Though our invention is not so limited, we find it advantageous to reduce the coeficient of friction and thus these frictional forces by means of the so-called dry or solid lubricant coatings which we apply to the outer surfaces of the shims l5 and I1. Any of the coatings which will reduce wear under such conditions may be applied to the shims. We have found that when the shim .is made of steel that the non-metallic coatings,

such as the oxide coatings and especially the phosphate -coatings, are excellent forthis 'purpose. Phosphate coatings are usually applied by means of processes well known to the art as parkerizing and bonderizing. Coatings applied by these and similar processes are particularly effective in combating wear when used in conjunction with the usual liquid lubricants such as heavy oil.

It will now be realized that we have achieved the first object of our invention, which is to have found that we can improve the production 1 of highly finished bars, which is the second principal object of our invention.

As indicated abovewe consider it desirable, in order to maintain accuracy of finished dimensions, to use shims having a greater resistance to plastic deformation than the bar A. In more common terms; the shims are harder than the 'bar A and, under the extreme pressure of de- "formation, will cause flow of the surface layers of the bar A'so that it will have surfaces Ofap-wu.

proximately the same quality as :the contacting shim surfaces. Since the character of the shim 4 will be only negligible wear thereof because of shim movement as discussed above, our arrangement makes it possible to produce bars, having high quality surfaces, for very long periods of time, these periods being limited only by the length and rate of movement of theshims.

The largest and most important field of application of deformation apparatus embodying our invention is in the processing of ferrous metals, steel in particular. In drawing steel bars it is, of course, necessary to use steel shims in order to obtain harder materials. We have found, however, that in this case it is not, in general, enough that the shim be harder than the bar. Under extreme pressure these elements of similar material may become momentarily welded together at irregularly spaced points of contact and the subsequent rupture of these welds results in severe wear and-very poor surface quality. These results, it is presumed, would occur. regardless of what specific materials were employed so long as the contacting surfaces tended to fuse together to form a consolidating weld-type joint. To avoid this, as well as to take advantage of superior physical properties, we therefore prefer to use a steel shim when-processing non-ferrous metals, though a scheme similar to that to be presently described for processingsteel stock may be used if it is necessary to have the shim and stock of similar material. 7

The art has been faced before with this problem of excessive wear due to the welding of steel bars to steel dies. It .has solved it by coating the bars with suitable materials such as sulphates and phosphates. When this is done, as it is .in the'precessing of a large percentage of steel-stock, the finished surface is not bright and metallic. On the contrary, it is dark due to the fact that the phosphate or other coating particles have been worked into the surfaces of the steel to blacken it and adversely affect its mirror-like qualities.

In our invention instead of coating the bar A as taught by the art, we coat the inner surfaces of the shims l5 and H. The first requirement of this coating is that it be of a materialwhich will prevent the weld-type of wear just referred to. This requirement usually necessitates that the coating be of a material other than steel, preferably non-metallic, and that it be bonded gto the shim surface with sufficient adhesion to enableit to perform its lubricating function and to prevent its being engrained in the surfaces of the steel bars being deformed. The second requirement is that the coating be capable of polishing or lightly burnishing the surfaces of the steel bars-A. Actually, it has been our experience that coatings either satisfy both or none of these requirements. 7 3

As a practical commercial matter, 'it is too eX- pensive to coat the outer surfaces of the shims A. Hence, in our preferred embodim'ent, we [coat both surfacesof each shim with the same material which is preferably a phosphate applied by some 'suitableprocess such as bonderizing or parkerizing. When we do this we obtain all the benefits that the art has known by coatingthe bar, Aand in addition, we producesurfaces on the bars which are smoother andwhlch.

. instead ;of vbei-ng dark, are metallic. I

In principle, our coated shims function to is very attractive.

polish the bar surfaces in much the same way as a dull abrasive belt. Hence, the quality of the finished surface is to some degree affected by the relative motion between the shims and the bar A. As pointed out above, however, surface quality is not the only factor to be considered in determining the rate of movement of the shim since this rate also affects the wear of the apparatus and the life of the shims. We have found that the governing consideration regarding the minimum rate of speed of the shim is the rate of removal of the coating. The rate at which the coating is removed is, in the terms of the apparatus, largely a direct function of the pressures or drafts involved. In cold reducing a 0.219" x 4.40" bar to 0.200 we found'that less than one-half inch of bonderized coating was removed during the passage of ten feet of bar through the apparatus. Thus a minimum speed I ratio of about one to two hundred and forty had to be maintained. The shim and bar may move in the same direction or in opposite directions and at various relative speeds. When the shim travels at the same rate in the same direction as the bar, a satiny finish is produced which When there is appreciable relative motion between the bar and the shim,

as when they travel in opposite directions or at widely different speeds in the same direction, the bar surfaces are highly polished and lustrous. In the intermediate ranges of relative motion, various degrees of luster are obtained.

At no speeds are the objectionable dark surfaces, such as are produced by conventional processes, obtained.

A number of advantages associated with the practice of our invention, as compared with conventional methods of deforming metals, have now become clearly apparent. First of these is a large reduction in expenditure for dies. This results from negligible wear on the die faces which makes it possible to use inexpensive die materials. Another advantage associated with cold deformation processes results from the superior finish of stock deformed by apparatus embodying our invention. In the past grinding, burnishing and other polishing and finishing methods were employed as a'step after cold deforming to improve the surface finish. These were done at considerable expense and are, of course, unnecessary when stock is processed in accordance with our invention.

Those who are well acquainted with the steel art will realize another important but less obvious advantage of our invention which concerns a long sought improvement in the quality of the finished product. This is that it is now practical to eliminate surface and sub-surface pits from the finished product. These pits result from the hot rolling, rusting and from the action of the pickling acids on the surface of the steel beneath the hot-rolled scale being removed in the pickling bath. In order to remove them a light surface removal operation is required after pickling, such as sanding. When these pits are not removed they are worked into the body of the stock during subsequent deformation. Referring specifically to the conventional drawing of bars, this sanding operation represents a step backwards in the processing cycle. This is due to the fact that the pickling operation, usually in a bath of sulphuric acid, coats the bar stock with a sulphate which is necessary for successful drawing of thebar. This coating is, of course, removed by sanding so that it is necessary to apply another coating to the stock before drawing by conventional methods. When this is done, however, the coating together with the lime and oil used in drawing bars, is worked into the bar surface to make it dark and unattractive as mentioned hereinbefore. In our invention, however, the bar can be pickled and then sandblasted, or subjected to a similar surface removal operation, and then drawn, there being no necessity to coat the bar since we use coated shims. As a matter of fact, the slightly roughened surface imparted to the bar by sanding seems to absorb oil and facilitate the drawing operation. Thus our invention makes it possible to produce a superior finished stock having no pits and at no additional cost as compared with stock produced by the usual methods.

As stated hereinbefore, the invention may be applied to various types of hot or cold deformation processes and apparatus and we therefore do not wish to be limited to the specific details of our invention which have been set forth above.

We claim:

1. The method of deforming metal stock by means of a die, which comprises passing the stock through the die at one speed, and simultaneously passing a plurality of thin elongated shims through the die between the die and the stock at a different and slower speed, said elongated shims being sufficiently wide to separate all working surfaces of the die from the sto ck, thereby to reduce the wear of the working surfaces of the die.

2. The method of deforming metal stock by means of a die, which comprises coating with a solid lubricant the opposed surfaces of each of a plurality of thin elongated shims, passing the stock through the die at one rate, and simultaneously passing the lubricant coated shims through the die between the die and the stock at a different and slower rate, said elongated shims being sufiiciently wide to separate all Working surfaces of the die from the stock, thereby to reduce the wear of the working surfaces of the die.

-3. The method of deforming metal stock by means of a die, which comprises coating the opposed surfaces of each of a plurality of thin elongated shims with a solid lubricant, passing the stock through the die, and simultaneously passing the lubricant coated shims through the die between the die and the stock at different points around the stock, said elongated shims being sufficiently wide to separate all working surfaces of the die from the stock, and the rate of movement of said shims through the die being substantially less than the rate of movement of the stock through the die but less than the rate at which the solid lubricant coatings are removed from the shims.

CHARLES W. BIMBA. FRED BROWN.

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

UNITED STATES PATENTS Number Name Date 1,384,448 Gilbert July 12, 1921 2,116,954 Singer May 10, 1938

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