US2275095A - Method and means for leveling and hardening thin gauge metals - Google Patents

Description

March 3, 1942. H. v. THADEN 2,275,095

METHQD AND MEANS FOR LEVELING AND HARDENING THIN GAUGE METALS Filed July 5, 1939 3 Sheets-Sheet l FIG. 1.

. w e V [me/ 2w]? 5 Sheets-Sheet 2 liweizfars H. V. THADEN Filed July 5, 1939 March 3, 1942.

METHOD AND MEANS FOR LEVELINQ AND HARDENING THIN GAUGE METALS March 3, 1942. H. v. THADEN METHOD AND MEANS FOR LEVELING AND HARDENING THIN GAUGE METALS Filed July 5, 1959 3 Sheets-Sheet 5 1 Jfi 1760676507". #525527- Z maE/v,

Patented Mar. 3, 1942 METHOD AND MEANS FOR LEVELING AND HARDENING THIN GAUGE METALS Herbert V. Thaden,-Mount Lebanon, Pa. Application July 5, 1939, Serial No. 282,918

3 Claims.

This invention relates broadly to a method and means for leveling or flattening thin strip or sheet-like metals and simultaneously cold workhardening or tempering such material.

In cold leveling or flattening thin metal by conventional rolling mill practice, it has been observed that in the cold reduction of strip or sheet metals, undesirable buckles or dimples in the center of a sheet or scallops in the edges thereof, ora combination of these undesired occurrences frequently develop. Such phenomena is thought to be due to non-uniformity of the strains induced in the metal by compressive rolling forces imposed by the rolls' of the mill. It has been observed that even a minute change in the diameter of the rolls at some place locally or non-uniformly across the rolls, affects materially the contour or strains in the stri and manifests itself in the production of a buckled or wavy strip. The prime reason for such undesired occurrence is believed to be due to variation in the compressive rolling load caused by the altered or varying diameter of the rolls. A change in roll diameter can be attained and premeditated by contouring the rolls by machining a crown or hollow in them, or by thermal means effective to expand or contract portions of the rolls locally. The latter method is especially effective on small diameter rolls, such as used conventionally on modern mills. Changes in roll diameter, especially non-uniform changes, are particularly critical when rolling high tensile strength and thin,

gauge metals, such as stainless steel and the like, which are subject to extreme hardening by coldwork.

It is difficult to consistently control a uniform diameter and contour of roll and avoid an inequality of strains either across or lengthwise in a long strip. In. conventional practice, flatness in such cases is obtain-ed only by subjecting the strip to a. multiplicity of passes through the rolls so as to bring about a gradual equalization of stresses throughout the length and breadth of the strip. Such process requires a highly specialized operating technique.

Obviously, such prior. practice is uneconomical or costly because of the mill labor time consumed and because of the operating time required for expensive mill equipment. Furthermorain view of the fact that rolling stresses are inherently accompanied by reduction of thickness, it frequently happens that a strip which has been reduced to the desired gauge, but which requires further flattening, is produced only with an accompanying loss of gauge or too high a temper. Such undesired result frequently results in the rejection of an entire strip.

Furthermore, such multiplicity of passes of metal through the rolls adversely affects the residual ductility of the metal. It would appear that the fewer the passes for a given cold reduction from an annealed state to the required gauge and temper, the higher the residual ductility of the resultant rolled material. My present invention aims to obtain flatness with fewer passes through the rolls than heretofore possible.

With heavy gauge material, flatness can be obtained by stretcher leveling wherein sheets are gripped on opposite sides and subjected to a.

tensile stretching force of such magnitude that plastic flow takes place and a permanent setting in the metal results. In practice, while such procedure is effective, it involves certain difficulties and the use of expensive equipment and is not applicable to continuous processing of strip metal.

Another conventional methodused is roller leveling" in which a sheet or strip of metal is passed without back tension-through a number of rolls so positioned that the metal is alternately bentin one and then in the otherdirection. The degree of bend is such that a certain amount of plastic flow takes place when the sheet is bent over the top of the roll. This tends to equalize the residual stresses in the metal and to elongate the tight areas.

In the treatment of relatively thick and soft material, such operation is very effective. However, where the gauge is reduced and the stiffness or temper of the material is increased, the ability to cause plastic flow in the metal by bending over practical sized, small diameter, rollers of wide width, becomes impractical and in the case of metals su'ch as full hard, stainless steel in thin gauges of .025" and under, it has been demonstrated that the roller leveler is incapable of removing the buckles or other deformations or to flatten a strip.

It is one of the underlying features of the present invention to provide a novel method and means for effectively flattening such thin gauge high tensile strength material, such a stainless steel or the like, which cannot be satisfactorily processed by any of the hereinbefore mentioned methods or devices heretofore known to'those skilled in the art. The present invention will be fully understood from the following description of the method as carried out by the use of the novel combination of apparatus shown somewhat conventionally in the accompanying drawings.

In the drawings- Figure 1 is a diagrammatic elevation of suitable apparatus for carrying out the method;

Fig. 2 is an enlarged view of a portion of the apparatus shown in Fig. 1, effective for alternately bending the strip under treatment in opposite directions;

Fig. 3 is a detailed longitudinal. section illustrative of operating mechanism for varying the relationship between the toothed elements of the apparatus;

Fig. 4 is an elevation of the apparatus shown in Fig. 3;

Fig. 5 is a View illustrating an alternative mechanism for sequentially imparting reverse bends to all portions of the material as it is fed through the apparatus;

Fig. 6 is a side elevation of the apparatus shown in Fig. 5;

Fig. '7 is a plan view of Fig. 6; and

Fig. 8 is a diagrammatic view illustrating a modified arrangement of apparatus.

In accordance with the present invention, sheet or strip material S to be flattened and at the same time cold-worked or tempered is fed in the direction of the arrow A shown on the drawings. A pair of coacting rolls I8 and I2 are driven from any suitable source of power. These rolls are efiective to cause every portion of the sheet to traverse an undulating or zigzag pass. In so doing, the sheet is caused to alternately contact the apexes of teeth I4 and IE carried by the lower head I8 and upper head 20, respectively. The teeth of the two series thus mounted may be said to define an undulating or zigzag active pass for the material. The heads I8 and 20 are movable relatively to one another by suitable means hereinafter described so as to permit of a variation in the magnitude of reverse bending or cold-working of the sheet as it traverses the staggered sets of teeth. Preferably, a back tension is applied to the sheet or strip, suitable means indicated conventionally at 22 and 24 serving to exert a force or sol-called back tension in the direction of the arrow B which is contrary to the direction of pull or forward feed exerted by the rolls I and I2. The amount of such back tension can be varied by suitable adjustments of the rolls 22 and 24. Further back tension variation can be secured by varying the relative positions of the heads I8 and 28. While the back tension in most cases is exerted by a separate tensioning device. it is possible to secure the required tension effect by the multiplicity of teeth which define the zigzag or undulating path of the pass. In short, the necessary tension in the strip, being reversely bent by the staggered teeth, may be secured by the drag of the staggered .teeth themselves or equivalents thereof.

Means are provided for varying the relative positions of such heads I8 and 20, as shown in Fig. 3, wherein said members are slidable between guides I8a. and 200.. A suitable mechanical screw adjustment or hydraulic cylinder, such as I8b with a piston I80, is provided for moving the head I8. Similarly, for the member 28 there is a mechanical screw or hydraulic cylinder 28b within which is mounted a piston 20c. Respective links I8d and 28d couple the pistons with the heads I8 and 28. Suitable means (not shown) are provided for locking the pistons and the related members I8 and 28 in desired positions of adjustment. Each set of cylinders I8b-2Ilb will be interconnected hydraulically by suitable piping. Cylinders I8b and 20b are closed by suitable detachable heads I86 and 286 screwed in the respective ends thereof, these heads being provided with hydraulic pipe connections I8 and 20 Instead of using the hydraulic adjustment of the heads I8 and 28 which carry the alternate bending teeth, I may employ the mechanism shown in Figs. to 7 inclusive. In this alternative arrangement, the tooth-carrying heads I8zr and x are provided with laterally extending arms 26 and 28, which are pivoted at 30' to a suitable fixed bearing block 32. The head 20a: in this modification carries an extension lug 34 which rides freely within a slot 36 of a yoke 38 having legs 40 and 42 and a bridge portion 44. The legs 48 and 42 of the yoke support a pin 48 which also extends through the extended end 48 formed on the head I8.

. micarta, or hard metal.

A jack screw 50 is threaded throughlthe bridge portion 44 of the yoke and carries a crank arm 52 and a crank handle 54. As thus constructed, it will be understood that by turning the jack screw 50 in the appropriate direction, the heads I82: and 20x can be caused to either approach or recede from one another so as to thus vary the magnitude of the bend effected between adjacent teeth as the sheet is propelled therebetween.

When the heads I: and 20.70 are moved in a slightly arcuate path, the respective lengths of arms 26 and 28 and the clearance between the arms 48 and 42 of the yoke is such that satisfactory adjustments for all practical purposes can be readily obtained.

In the modification illustrated in Fig. 8, the alternate bending of different portions of the sheet in its traverse through the apparatus is effected in a slightly different manner. In this figure, there are spaced rolling mills indicated generally at RI and R2, the former consisting of two coacting rolls 56 and 58 and' the latter two similar rolls 60 and 62. The respective speeds of these rolls are such that a suitable back tension will be applied to the portion of the sheet between the two mills and in its traverse from one mill to the other the sheet will pass first over the apex of a tooth-like plate 64 and thus be bent in one direction, and will then pass under the apex of a tooth-like plate 66, whereupon it will be bent in the reverse direction.

The teeth I4I6 of the apparatus shown in Figs. 1 to 7, inclusive, are preferably formed of non-galling material such as compressed wood, During the traverse of the sheet of strip through the apparatus, the same is preferably flooded with oil or other lubricant, such as known types of oil and water emulsions, which also function as coolants.

As the sheet of strip traverses the undulating or zigzag pass, which it is compelled to follow by virtue of the staggered arrangement of the spaced teeth, all progressing portions of the strip will be alternately bent to a degree where the fibres exceed their elastic limit, first, in compression and then in tension, or vice versa. In this way, a permanent set or plastic flow of the metal takes place. The effect of this cold-working is to equalize residual stresses in the metal sheet or strip, which results in an eventual flattening of the end product resulting from practice of the method.

While the material is being thus flattened, it is simultaneously cold-Worked so as to impart the desired hardness or temper thereto. This is all vanci'ng portions of the sheet in opposite directions, such sharp bends being of a radius much smaller than could be attained in practice by the use of rolls.

It is found that by the method described, areas of local high stress or tightness in the material passing between the teeth are appreciably elongated during the period of plastic flow which takes place as the metal is subjected to a combined stress of tension (due to back tension) and bending moment as the'strip is deflected over the apex of each tooth. The method of flattening is applicable to any width of strip and is intended to effectively control the amount of stretching at any given place across a passing strip.

In the apparatus described in Figures 3 and 4, the relative position of the teeth (closer or farther apart) can be varied locally by manipulation of the hydraulic pistons shown, or equivalent mechanical means. Thus; oppositely positioned pistons can be simultaneousely compressed, causing a closer positioning of the upper and lower set of teeth in the localized area adjacent the plane of the pistons, thereby producing a greater stretching of the strip or sheet in such area. Any combination of tooth pressures can be readily secured by means described, and thus it will be apparent that local stretching or an ironing effect can be obtained to any desired degree transversely across the sheet or strip or along the length of the moving sheet or strip.

The teeth may be contoured transversely to compensate for local unevenness or for any tendency of the sheet or strip to be thicker or thinner near any predetermined zone in its transverse width. The transverse contouring of the teeth may be accomplished by crowning the strip contacting faces thereof or by exerting pressure by the hydraulic cylinders described, or by the jack screws or the like described, at one or more points along the transverse dimension of the sheet. In other words, by varying the pressure on a substantially straight tooth at different points along a line transversely of the path of travel of the sheet, the material of the tooth may be deflected at local points transversely of the sheet so as to secure the desired compensating effect.

With respect to that aspect of the invention which contemplates the cold work-hardening and cold tempering of thin metals, it is to be noted that conventional methods of making high tensile strip metal by cold working by the utilization of the compressive force of a set of rolls induces a non-uniformity and undesired directionality of the stresses in the metal. This undesirable phenomena is known to those skilled in the art as the Bauschinger Effect and manifests itself as a difference in compressive yield strength of the metal when determined transversely to the direction of rolling, compared with longitudinally of the direction of rolling. In general, the compressive yield strength transverse to thedirection of rolling is higher than the tensile yield strength either transversely or longitudinally and the compressive yield strength longitudinally is less than 1 ferred to hereinabove.

the tensile yield strength either transversely or longitudinally.

It is believed that the reason for this nonuniformity resides in the fact that conventional method of cold rolling through a set of rolls induces a definite or pref-erred orientation of the grains in the direction of rolling,-the grains being deformed into long stringers characterized by the presence of residual and unequalized strains, and the grains are more readily compressed longitudinal to the rolling direction thantransverse to such direction. This results in a lower compressive modulus and compressive yield strength longitudinally to the strip.

One of the chief characteristics of the invention herein disclosed and claimed relates to the method and means for overcoming th objectionable features of conventional practice just re- In short, the present invention overcomes a problem which has been unsolved by those skilled in the art. By the practice of my invention, the metal is cold-worked in such a way that the grains are deformed in a more uniform equi-axed grain structure as distinguished from the orientation or elongated axed structure induced by conventional rolling methods and mills.

According to the present invention in contrast to prior practices, the metal in passing over the apex of each tooth is subjected to a bending moment and an accompanying plastic flow of the material. Such bending of the metal over each tooth involves a compressive stress on the inside of the bend and a tensile stress on the outside of the bend. By virtue of such alternating bending stresses, the metal on opposite sides of the neutral axis of the strip is alternately compressed and tensioned beyond the elastic limit of the material. This alternate compressing and tensioning constitutes a cold working of the metal which effectively hardens or tempers the same without materially reducing the gauge or materially elongating the strip as is-done. by conventional rolling methods.

While I have described quite precisely certain detailed steps of the method and certain specific apparatus for carrying out the method, it is to be understood that various modifications may be made by those skilled in the art without departure from the spirt and scope of the invention as defined in the appended claims.

I claim:

1. The improved method herein described of processing solid thin gauge ferrous metal sheets or strip material which consists in sequentially bending all portions of the material over fixed sharply curved teeth first in one direction, then in the opposite direction to thus simultaneously apply a tension and a compressive stress to the fibers at spaced portions of the material, the shape of the undulations formed in the material and the sharpness of the bends at spaced points being such as to stress the material beyond the yield strength thereof and to 'work harden said material and deform the grains so that they attain an equi-axed grain structure as distinguished from the normal elongated axed structure eifected by conventional rolling practice.

2. An apparatus for flattening strip or sheet material consisting of upper and lower sets of pointed teeth of triangular cross sectional contour with rounded apexes of extremely sharp radius that is of the order of one-eighth inch or less defining an active pass of uniform undulating shape from end to end, means for advancing I thereof whereby the material is work hardened and the grains are deformed so that they attain an equi-axed grain structure as distinguished from the normal elongated axed structure effected by conventional rolling practice.

3. An apparatus of the character described for flattening and cold working strip or sheet material comprising opposed sets of spaced teethof equal height defining an active pass with peaks and valleys of uniform height from end to end, 7

supporting means for the respective sets of teeth, means for varying the relative positions of said supporting means so as to thus vary the altitude between said peaks and valleys, means for pulling the material through the active pass defined by said, teeth, and means acting in a direction contrary to that of the pulling means for exerting a back tension on the material as it traverses the active pass, the sharpness of the teeth being such that when the material is bent thereover in an undulating path of particular altitude it is stressed beyond the yield strength thereof whereby the material is work hardened and the grains are deformed so that they attain an equi-axed grain structure as distinguished from the normal elongated axed structure effected by conventional rolling practice.

HERBERT V. THADEN.

Images