US2034425A - Method of pack rolling ferrous metals - Google Patents

Description

Patented Mar. 17, L936 METHOD OF PACK ROLLING mnmovs METALS Terrence W. Allsworth, Middletown, Ohio, as-

slgnor to The American Rolling Mill Company, Middletown, Ohio, a corporation of Ohio No Drawing. Application November 25, 1933, Serial No. 699,801

Claims.

I shall describe my invention in connection with, the rolling of iron and steel sheets in packs, and in connection with the preparation of metal pieces for pack rolling, in which fields my invention, while it is not limited thereto, has especial utility.

In the packi'olling of ferrous metals it has been known that for best results (a) sheets should have between them a separating substance of proper characteristics to prevent formation of stickers, i. e. the welding of the sheets together 1n the pack during the rolling operation, yet, at the same time (b) the sheets should be permitted to adhere together sufficiently -to form a properly set pack. While the term set pack may have slightly varying meanings under different circumstances, and while it may not necessarily imply that the sheets are so joined, as it were, adhesively one to the other as to produce a. pack which will roll as though it were a unitary piece of metal, yet it does imply, and for the purposes of this description I intend it to imply, the existence of ,such a physical relationship between the several sheets which go to make up the pack, as will permit efiicient pack rolling, and prevent flopping as the pack enters the pass of rolls.

It has been known that a proper coating of oxide on the sheets or pieces wouldprevent sticking.

while permitting setting of the pack. In the old Welsh method of rolling, where the conditions were proper, a suitable coating of oxide could be produced upon the pieces individually, since sheet bars were heated and rolled individually, as by being broken down and run over, in the first stage or part of the rolling operation, and prior to any matching for pack rolling. Specific problems have, however, arisen primarily in connection with newer methods of rolling utilizing the newer raw materials now available for the purpose. I refer to the products of the new continuous hot mills which produce strip sheets from slabs. These mills can furnish as the starting pieces of subsequent rolling operations, sheet or plate material of varying gauges, quite as cheaply as sheet bars per unit weight, but much thinner in gauge and of much greater area. Consequently, there have been developed numerous processes of rolling thin bar, rough plate or the like by hand or in automatic machinery, which processes have the advantage of starting withthinner raw material and frequently are able to arrive at thinner gauges with fewer heatings or parts. Thus starting with thin bar or the like, rolling processes have been developed which.call for the initial doubling of thin bar or pieces, or the formation of packs at the outset of the rolling operation and prior to the heating operation. As a consequence, the doubles or packs are heated and rolled priorto the formation upon the surfaces of each individual sheet or'layer, of a proper protective oxide. 5 Secondly, it has been found advisable when using such relatively thin materials to remove whatever scale remains from the hot continuous mill operation beforeany subsequent rolling, if smooth sheets are to be produced. Hence, the product of the continuous hot mill has been picked prior to subsequent rollings; and it will be obvious that the doubling of pickled pieces, or the formation of pickled pieces into packs before the heating step, is a further factor in preventing the formation of a proper oxide coating and in producing stickers. Thirdly, the newer methods of rolling have rendered advisable the use of modern quick furnaces, and particularly furnaces having neutral or reducing atmospheres which are not conducive to the formation of oxide. Fourthly, where thin material is being used, it is not advisable to attempt to develop oxide on its surfaces by the oxidation of the material itself and by means of heat unless this can be carefully regulated and carried on in a very even manner.

Faced with these problems, the art has endeavored to use various inert separators, but has encountered two primary difliculties: (a) unless the inert separators are applied very evenly, smooth, thin gauge sheets are not produced; (b) while inert separators if properly used may prevent sticking, they appear also to prevent the proper setting of the pack.

- My invention has for its primary object the provision of materials for rolling and a rolling process involvingthe production upon the surfaces of the metal pieces of a protective coating 'which not only acts as a separator, but also permits setting of the packs. My invention also has 49 for its object the provision of an oxide coating upon the. surfaces of sheets or pieces, the-oxide being primarily derived not from the body metal of the sheets, but from material superposed thereon in a controlled manner. My invention also has for its object the provision of a process of treating metal sheets or pieces to produce coatings thereon of the desired characteristics.

These and other objects of my invention which will be set forth hereinafter or will be apparent 50 to one skilled in the art upon reading these specifications, I accomplish by that certain procedure of which I shall now describe a preferred embodiment of the character aforesaid.

While I have hereinabove referred to the rolling of the product of the modern continuous hot mill as setting forth a set of circumstances in which my invention has especial utility, it will be understood that this forms no limitation thereon. My

invention has utility under any circumstances in which it is desired to produce upon the surfaces of metal pieces, coatings of oxide the characteristics herein referred to, and quite irrespective of the origin of the said metal pieces. My invention is of particular utility in connection with the treatment of break-downs which may be defined as material suitable for formation into packs and pack rollings, which material will be uniform enough and of sufficiently light gauge to permit of a finishing rolling operation without any further heating. It will be obvious that breakdowns can be formed in a number of ways. In the continuous mill as is well known, slabs previously formed by rolling from ingots are continuously rolled in a train of tandem hot mills to form rough plate stock, which is then sheared apart into rough plates or break-downs. A continuous mill break-down is therefore material which has been produced on a continuous mill, which can be formed into packs for rolling and which will be uniform enough and of suificiently light gauge to permit of a finishing rolling operation without any further heat.

In the practice of my invention I preferably coat my sheets or pieces in a controlled manner with a salt of the body metal which, under the conditions of the subsequent heat treatment, will decompose or be converted into an oxide. While a number of salts or compounds of iron will serve the purpose, yet it is important to choose one which (a) is easily and uniformly applied; (b) may be uniformly converted to the oxide; may be converted to the oxide under modern furnace conditions, and more particularly under neutral or reducing atmospheres; and (d) may be converted to the oxide under temperatures normally employed for fitting the metal pieces for hot rolling. Under some circumstances it is advantageous to employ a salt which bears a certain relationship to the pickling operation, where employed. Of the several salts which I might use, I prefer to employ ferrous sulphate or copperas. This may, if desired, be derived from a pickling bath; but this is not necessary, and it is frequently preferable to apply the ferrous sulphate as an operation distinct from pickling. Nor is the application of ferrous sulphate to already pickled sheets or pieces a necessary limitation upon my process. I may however, use other salts or compounds such as either the ferric or ferrous nitrate of iron, preferably coating the sheets with a solution of nitrate of iron containing free acid, but not exceeding one-half of one percent, or chloride of iron, etc.

I prefer to apply the ferrous sulphate or other compound either from a solution or suspension thereof. It is possible to employ a pickling bath containing considerable ferrous sulphate either added thereto or derived from the iron pieces in previous pickling operations, and without washing the sheets or pieces after the pickling operation, to permit them to dry so that they become coated with the ferrous "sulphate. Where this is done, however, care must be taken to cause the liquid to dry evenly on the surfaces of the sheets or pieces without collecting unevenly thereon. This maybe done by moving the pieces during the drying operation. Moreover, it is preferable not to have too great a quantity of free acid present unless the sheets are to be rolled immediately,

since the free acid would continue its attack upon the iron and produce pits.

These considerations render advisable the use of a separate step for the application of the salt to the surfaces of the sheets or pieces; and in my preferred procedure I immerse the pieces in a separate tank containing a solution and/or suspension of ferrous sulphate. When this is separate treatment does not require the maintenance of any relatively large content of ferrous sulphate in the pickling tank, but leaves me free to carry on the pickling itself under optimum conditions. If a pickling precedes my coating treatment, it is not necessary to wash or neutralize sheets between the two steps, although this may be done if desired.

In the use of a separate coating step I prefer to employ a hot solution of ferrous sulphate maintained very near the boiling point. concentration of ferrous sulphate may vary considerably, and I have attained good results using from five to twenty-five per cent by weight of the iron salt. Concentrations between eight and fifteen per cent seem to give optimum results most consistently; but none of the figures hereinabove given appear to be limiting. The acid concentration of the ferrous sulphate solution is preferably kept below one per cent by weight although, as I have hereinabove indicated, higher concentrations of acid may be employed if the pieces are immediately heated for rolling.

In an exemplary procedure in accordance with my invention, the product of the continuous hot mill may be pickled in the usual manner. Then the pieces are dipped into a tank containing the hot ferrous sulphate solution hereinabove described, and, when withdrawn therefrom, are dried very rapidly. They will be found to have upon their surfaces a thin, uniform coating of crystallized ferrous sulphate. By pieces I mean, of course, such lengths as may be found suitable for any given rolling operation. Such lengths may vary from relatively short pieces suitable for pack formation to strip sheets themselves, or even to continuous bands of metal.

After the coating as aforesaid, packs may be formed of the pieces, the pieces may be doubled, or matched and doubled, or bands of metal may be superposed to form pack-like structures. These structures are then passed to a furnace which may be and preferably will be of the modern quick-acting type having a reducing atmosphere, although this again is not limiting. When the structures are heated for rolling the ferrous sulphate upon their surfaces undergoes a change of state, which I believe comprises first, a loss of the water of hydration, and second, as the heat in the structure increases, a decomposition to form ferric oxide and the oxides of sulphur, which latter materials, of course, pass off in the form of gas. In the presence of reducing atmospheres in the heating furnaces, the ferric oxide is partly reduced to ferrous oxide in most cases, the mixture of ferric and ferrous oxides (ordinarily termed magnetic oxide) forming a thin uniform coating over the surfaces of the pieces. Under The differing conditions the various oxides appear to be somewhat differently formed, and I do not desire my invention to be limited to any particular oxides or mixture of oxides, nor to any theory of the nature of the decomposition which takes place. A thin uniform coating of oxide permits the pack to set uniformly and solidly between the rolls of the mill, after which the pack can be elongated to the desired length. Uniformity of coating as hereinabove set forth is of great importance, since the packs may have a tendency to roll apart or break open in areas having had too heavy a coating, or in the case of adjacent areas having no coating to weld together forming stickers.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A process of preparing ferrous metal breakdowns for pack rolling, which comprises the steps of dipping said metal pieces into a liquid containing a compound of the metal of said pieces adapted to be converted into an oxide of said metal, drying said pieces so as to form a uniform coating of said compound upon the surfaces thereof, and converting said compound into an oxide.

2. A process of preparing ferrous metal pieces for hot rolling which comprises dipping said pieces into a liquid containing ferrous sulphate, said liquid being maintained at a temperature high enough to promote rapid drying of said pieces when removed therefrom, removing and drying said pieces, forming said pieces into plural layered units for rolling, heating said units, and rolling said units.

3. A process of preparing ferrous metal pieces for hot rolling which comprises dipping said pieces into a liquid containing ferrous sulphate, said liquid being maintained at a temperature high enough to promote rapid drying of said pieces when removed therefrom, removing and drying said pieces, forming said pieces into plural layered units for rolling, heating said units rapidly under non-oxidizing conditions, and rolling said units.

4. A process of preparing ferrous metal pieces for pack rolling which comprises dipping said metal pieces into a solution containing between five to twenty-five per cent by weight of ferrous sulphate, said solution being maintained near the boiling point thereof, withdrawing said pieces and rapidly drying them so as to form upon their surfaces a coating of ferrous sulphate, and subsequently converting said ferrous sulphate to the oxide form under the influence of heat.

5. A process of preparing ferrous metal pieces for hot rolling which comprises coating said pieces with a liquid containing ferrous sulphate, said liquid being maintained at a temperature high enough to promote rapid drying of said pieces in air, drying said pieces, forming said pieces into plural layered units forrolling, heat ing said units, and rolling said units.

TERRENCE W. ALISWOR-TH.