US1907020A - Sheet metal producing process - Google Patents

Description

May 2, 1933, J. B. TYTUS 1,907,020

SHEET METAL PRODUCING PROCESS Filed Jan. 18 1929 INVENTOR.

ATTORNEYfi,

Patented May 2, 1933 UNITED; STATES PATENT OFFICE JOHN B. 'IY'IUS, OF mDLETOWN, OHIO, ASSIGNOR TO THE AMERICAN ROLLING 1! COMPANY, O I MIDDLETOWI T, OHIO, IA CORPORATION OF OHIO SHEET METAL PRODUCING PROCESS Application illei i January 18, 1929. Serial No. 333,264.

My invention is of importance in-processes of producing sheet metal which involve a cold rolling operation which is of substantial character and, is relied upon at least 1n part to bring the metal to gauge. One way of making sheet iron or steel comprises hotrolling to gauge, pickling and finishing 1n any way desired. But for many uses a cold rolled product is to be preferred. To make it, it is usual to practice a preliminary hotrolling, as of a sheet bar to a thick sheet, or a slab to a wide strip, pickle, and then cold roll to gauge with a substantial r'eduction. An annealing normally follows the cold rolling. The process may be carried out discontinuously'or in the so called continuous manner.

My invention comprises a new procedure in the manufacture of'iron and steel sheets, andparticularly a new sequence of process steps in a process involving heavy cold rolling. While its usefulness is not restricted thereto, it has the effect of facilitating the operation of continuous processes of producing sheet metal; but more primarily it is directed to the production of new sheets having properties hitherto unattainable.

In order that my invention may be understood, it is necessary to point out some of the problems involved in the continuous or discontinuous processing of sheet metal which are solved by my invention. As an example of a continuous process in present use (and discontinuous processes are likely to present the same difiiculties, as will presently be outlined, i'neven an enhanced measure) sheet metal or iron may be made by hot rolling a slab to form astrip, pickling, cold rolling the strip ,to gauge, boX annealing the coldrolled strip in coils, and'skin passing, if

desired. As a substitute for box annealing.

or as an extra step in the process, a continuous annealing may be used. The strip may be sheared into sheet length before the boX annealing, and annealed in packs. Continuous annealing may comprise passing strip or stitched sheets through a furnace of horizontal type maintained at a suitable temperature for annealing, and of such length, taken together with the speed of travel of the material therethrough, as will allow the t1me interval for the heat treatment.

proper The first difliculty arises in the lack of uni- ,of individual pieces passing through the train of rolls, and the resultant strips formed from these pieces will exhibit more or less strains according to the temperature. The variations are likely to be greater in discontinuous than in continuous operations. They will inevitably occur unless the rolling be done with the stock always well above the A3 point at the end of the rolling operation. Thus hot rolled strip or sheet will not be entirely uniform in physical characteristics.

Such non-uniformity in physical characteristics as results from this cause will obviously persist through the subsequent cold-rolling operation. Nor, as will hereinafter be pointed out, can it beeliminated by any method hitherto suggested at any stage in the process which does not involve operating difliculties. It cannot, specifically, be eliminated by annealing treatments. These are heat treatments of time and temperature variables; they are carried out below the A3 point of the metal involved.

It is common practice in the manufacture of cold rolled products at times to give intermediate annealings. Upon recoiling such annealed stock it-is strained beyond its elastic limit in many places, these strained areas being known as cross breaks or coiler breaks. In diflicult drawing operations those cross breaks again become evident as Welts across the drawn pieces, even though the sheet process has proceeded with additional cold-rolling and box annealing. Ob-

. and uniform grain, are practically free from tions of time, temperature, atmosphere and the like, and since continuous annealing operations are limited by the apparatus employed and the commercial considerations of speed of travel, further difiiculties arise. Box annealing is thus far the most carefully controlled type of annealing and gives best results. It has already been pointed out why it is unsuitable for intervening annealings in a cold rollingiprocess of continuous character. Hence such intervening heat treatments as have been necessary have usually been of the continuous type and box annealing is preferably carried on with the strip cut apart in sheets and placed in the boxes in packs. But while in box annealing the general conditions of time, temperature and atmosphere may be most carefully controlled, there is a limit upon the temperatures practicable, and further, there is a lack of uniformity in the heat treatment in any given box, because it is not possible to heat all parts of coils or packs to the same temperature under identical conditions.

However, non-uniformity persists through all of these aiihealing treatments whether continiious or box. Broadly, it is not possible to .produce metal of absolute uniformity so far as strains are concrned aris ing from. previous working, excepting the metal be heated above the A3 point, or into the lower part of the gamma range. This cannot be done in ofdinary box annealing. In other words in commercial practice, it is at practicable to attempt to normalize in a x. But it is practicable to normalize otherwise, and it is commercially advantageous to normalize continuously. By process, most briefly stated, comprises a substantial cold-rolling followed by a normalizing treatment. So far as I am aware, this is broadly new; and

' th' li ti I d t t t m is app ca on eslre 0 secure i en is a cold-rolling to gauge, and is to be disprotection uponits broader aspects.

, By this proces I am able to make sheets of great uniformity as between individual pieces. My sheets are characterized by a fine non-uniformity of physical properties in the piece, and show no evidence of directional properties. They are practically free from any tendency to cross breaks,. They have the further advantage that they may be produced continuously and rapidly with the attendant commercial savings. My Sl IBBtS are a new product, and it is to be pointed out that they differ from a hot rolled and normalized product as will be shown. and further that the process of this application may be carried further, as by an additional'annealing step to the formation of still other products. In an application of even date 'herewith,and1 bearing Serial Number 333,263 I have described and claimed a process involving cold-rolling, normalizing, and annealing.

The objects of 'm invention set forth above, and others w ich will be set forth hereinafter or will be obvious from what follows, I accomplish by that certain process of which -I shall now describe a referred embodiment, reference being ha to the drawing accompanying these specifications,

The preferred embodiment which I shall 6 describe is a continuous process for the formation of sheets from wide strips, which in turn are rolled from slabs. Its analogy to other processes in which my invention will find equal usefulness will be readily understood by one skilled in the art.

A slab 1, which may be cold, is heated to ,a temperature for hot-rolling in a billet 1 heating furnace 2, usually of the pusher type.

The hot slab may then be passed through a universal mill 3 with edging passes, and then through a tandem of four four-high mills .4, etc etc. It is now in the form of a hotrolled strip which is coiled on a coiler 5 into the coil 6.

The coil 6, at the start of the next step, is placed in an uncoiler 7. As additional coils are processed the ends thereof may be connect-ed together by a traveling spot welder 8 or otherwise, so that to all intents and purposes a continuous traveling strip of metal is formed for further processing. This strip, which I have indicated as 9, passes through a continuous pickling tank 10, which may be equipped with a scrubber and drying furnace indicated broadly at '11, and is then, after having been sheared apart into strips again by a shear 12, recoiled into a coil 611 by a coiler 13.

When ready for the next step the coil 6a isuncoiled in an uncoiler 14. The next step tinguished from a mere skin passing, or rolling for leveling or the like. It is such a cold rolling as results in a substantial reduction of the metal, and is relied upon to produce substantially the required finished gauge. It may be accomplished by a tandem of four or more four-high cold rolls, indicated at 15, 15a etc. The operation is usually finished by a recoiling into coils on a recoiler 16.

Next, an uncoiler 17 straightens out the coil 66, and again a traveling spot welder. 18, a' stitcher, orother suitable device connects the strips serially for continuous proc essing. The band of metal is conducted through a heat treating furnace 19 which will be preferably fitted with a cooling duct 20. A normalizing process is carried on in this furnace, and I desire it to be understood that by this term I mean such a heat treatment as will bring the metal above-the A3 point, or-into the lower part of the gamma ran e and then quickly cool it, as distinguis ed from a mere annealing. By doing.

malizing of steel or iron of any given,car-

bon content, the necessary temperature may quickly be determined from the well known iron-carbon equilibrium diagram for the critical range.

My new sheet has thus been hot-rolled,

cold rolled, and normalized. As one result.

\ of this the strains which have been put into it both as the effect of the hot and the cold rolling are completely relieved. l have already l pointed out that my product ischaracterized by uniformity in'bulk and in the piece, by lack of directional properties, and by lack of cross breaks. It is also necessary to point out that it differs from and is superior to ordinary hot rolled and normalized steel in a number of respects. First it has a superior uniformity of grain size and structure. The reasons for this and the other points of difierence in my product are matters of physical structure upon which I do not wish to be bound by theory. AI long series of tests has demonstrated the differences.

' Possibly due to grain size inheritance, or-

some other reason, the grains in my product tare more uniform in size and shape throughout thegntire cross-section of the sheet than they are in the older hot-rolled and normalized sheet steel. When heavily coldworked is-heated to the upper part of the alpha range it recrystallizes with a fine grain, and the more the cold work, the finer the grain. Then when this fine grained iron is converted to gamma iron" by a further increase of temperature, it is possible that the newly formed gamma grains are more uniform than when formed from much coarser alpha grains as would be the case in normalizing hot-worked steel.- In turn then, the

new alpha grains formed by cooling comparatively quickly through the Ar? point would be small and more uniform. I a; Secondly, in regular hot mill practice it is not unusual to encounter irregularities in a thickness due to the uneven flow of the metal in the hot mill caused by an improper amount of center in the stock or improper shape of the rolls. This condition will show up as welts or ridges across deeply drawn forms,.

and will cause rejections. My improved sheet does not have this defect, which is known as" mill choke.

Thirdly, when the surface of the old type of hot rolled and normalized steel shows i1 regularities, due .to rough. rolls or other causes, and the material is normalized in this condition, the portions which hre hi h,

upon being subsequently cold rolled receive more cold work than the lower portiohs. Thus they become harder, and they remain so even through a subsequent box annealing. When such metal is drawn, the harder spots stand up in relief and give rise to the defect I known as open surface or orange peel in the drawn article. My new sheet is free from this defect. In it a normalizing has been practiced subsequent to all hotand coldwork to gauge. So far as I am aware, continuous furnaces have not hitherto been used for heat treating operations ab vethe A3 point, i. e. for normalizing cold reduced material when the cold reduction has been of theorder of 20% 01 35 higher. Ordinary annealing is a function of time and temperature as well as other conditions, and as has already been ointedout the control of all of these condi ions is difiicult in continuous operation. No such difi- Q culty; however, attends continuous normalizs ing, and it is only necessary to raise the furnace temperature to such a point as to cause the sheet withcertainty to reach the A3 point, i

#to accomplish this endHL'lhe' time of the E treatment is unimportant providing the temperature is attained, the change occurring at that temperature; and indeed it is a thing which may be controlled by yisual examination, if desired. 'The sheet or strip is normalized when the dark spots disappear. Normalizing implies a comparatively quick cooling, and the ontinu'ous'furnace and its equipment are Well adapte for this.

. After the normalizing the strip is conducted through a pickler 2 1. Scrubbers and drying furnace, indicated ,at22, may again be used, and the strip is sheared. by a shear 23 into sheets 24. They may be left in this condition, or finished as may be desired, possibly by skin passing through cold rolls. For some uses the pickling step last described may be omitted; again, my process as described may serve as the foundation for subsequent treatment by annealing or otherwise". Such a process is described and claimed in my copending case'hereinabove referred to. The instrumentalities in my process, which I have indicated diagrammatically in the drawing are all well known and require no description. Nor is my process restricted to instrumentalities of a particular type or the operation thereof as described. Thus, -as an Example, instead of carrying my process through with strip, I may use sheets which will preferably 'be connected together by stitching for the continuous parts thereof. Or again, each step of'my process may, if desired, and at some sacrifice of economy, 12"

Ill

be carried on discontinuously. Various heating said manta least to 1650 deg1;eesmodifications may be practiced without de- F. and quickly coohng it, pickling, she'armg parting from the spirit 'of' my invention, or said metal to the desired length, and skin varying that sequence of process steps with passin which my invention is concerned. Having thus described my process, what I claim as new and desire to secur'e by Letters Patent 1s: p

1. The process of producmg sheet metal fwhich comprises cold-rolling the metal to gauge. and afterwards heating the metal at least to the A3 point, and quicklycooling it.

2. That process of producing sheet. metal which-comprises forming metal into shet' gauge by hot and cold rolling and"afterwards subjecting said metal-to a normalizing treatment, whereby strains due to working are completely removed. J i 3. That process of producing sheet metal which comprises cold-rolling ;the metal to gauge and afterwards normalizing it.

4. Thatprocess of continuously producing sheet metal which comprises cold rolling to gauge, normalizing and pickling in the,

order named.

5. That process of producing sheet metal the order named.

6. That process of producing sheet metal which comprises hot rolling slabs to form strips, interconnecting said strips and pickling them, shearing into strips, cold-rolling said strips to gauge, interconnecting said strips and continuously normalizing and pickling them.

7; That process of producing sheet metal which comprises hot rolling slabs to form' strips, interconnecting said strips and pickling them, shearing into strips, cold-rolling said strips to gauge, interconnecting said strips and continuously normalizing and which comprises hot-rolling, pickling, cold- 7 p 11. That process of producing iron or steel pickling them, shearing them into sheets and skin-passing said sheets. 8. That process of producing sheet metal rolling to gauge, normalizing, and pickling in the order named.

9. That process of producing sheet metal which comprises hot-rolling, pickling, coldrolling to gauge, normalizing, pickling,

shearing to sheets and skin passing, in the ;order named. i '10 That process of producing iron or steel sheets of a'carbon content less than .25 which comprises cold-rolling metal of said. character to gauge, and afterwards heating lowed by a rapid cooling.

sheets of a carbon content less than .25 which comprises hot rolling metal of said character,

pickling, cold-rolling said metal. togauge,

said metal at least to 1650 degrees F. fol-:

Images