US2250398A - Method and apparatus for making coated metal - Google Patents

Description

July 22, 1941.

M. SCHON METHOD AND APPARATUS FOR IAKING COATED METAL Filed June 28, 1937 mbm/ Patented July 22, 1941 TES I einen METHD AND APPARATUS FOR MAKING CUATED :METAL Matthew Schon, Baltimore, Md., assigner to Crown Cork & Seal Company, Inc., Baltimore, Md., a corporation of New York Application `lune 28, 1937, Serial No. 150,858

d Claims.

This invention is an improved method and apparatus for treating metal particularly strip metal, such as hot rolled band or strip steel, either for the manufacture of so-called Bright finished sheet for use, as such, in the fabrication of metallic articles or for application of a coating, such as tin.

Heretofore, in the manufacture of Bright finished sheet, for example, it has been the practice to subject the same to at least two pickling bath treatments for removing oxide coating and foreign matter, one preceding a cold rolling operation and another following annealing.

An object of the invention is to provide;` a method and apparatus for cold rolling `and annealing metal, which eliminates conventional pickling. This latter has long presented difficulties but no suitable plant practice has been lhere` tofore advanced. Among the objections to pickling are the difficulties ofremoving all ofthe acid, blistering and brittleness, due to occluded hydrogen, difficulty inl controlling the acid solutions with resultant burning of the metal` due to overpickling, high initial expense of apparatus installation, cost of upkeep, rapiddepreciation of equipment Aand metal loss which averages 2%.

Numerous attempts have been made to overcome the foregoing and other objections to the treatment of the metal by baths of acid, such as sulphuric acid, but until the present invention there has been no successful commercial operation in which pickling has lbeen altogether eliminated.

In carrying out 4the invention, the metal is cleaned as by an abrading treatment is followed by cold rolling and then by annealing in a nonoxidizing atmosphere. With this procedure, not only is the initial pickling step avoided, but the usual white pickle following annealing is unnec essary, and the metal may be cut to sheet form or coiled, as desired, although it is preferred to subject the same to a, skin pass following the annealing.

It has been found that sheet metal produced by such procedure, and in the absence of pickling baths, has a high resistance to oxidation and rust, and is unusually suitable for coating, for example with tin, and such coatings may be made considerably thinner than customarily found necessary where pickling treatments are used. `For example, in accordance with the present invention, a substantial reduction in the amount of tin per base box ispossible, and satisfactory coatings are obtained with the use of 1.1 lbs. of tin per .base box as compared to previous procedure requiring at least 11/2 lbs. per base box.

Moreover, instead of a metal loss of approximately 2%, it has been found practicable, under the method of the present invention, to reduce the loss to less than 1/2 of 1%. By a simple control of the force, character (grain size and kind, e. g. cast iron or steel shot) and volume of the abrading streams in each unit, as well as the time of treatment therein, the loss of metal is negligible as compared to the loss resulting from pickling baths of acid which attack the base I metal ,beneath the oxide lm which it removes.

sheet to form Vtin plate or other coated metal.

In this connection, the invention may be practicedupon various metals, and is not limited to steel strip or bands, and the coating metal may be other than tin. The invention is particularly useful in the making of Bright finished sheet or tin plate, but, as will be appreciated, it is not restricted to the manufacture of these articles.

From an examination of the flow sheet, it will ,be observed that the customary pickle used preliminary to the cold rolling operation is eliminated, as Well as the conventional White pickle rey sorted to following the annealing step. These pickling treatments are unnecessary, and the objections and difficulties incident thereto are avoided by abrasively removing the oxide simultaneously from opposite sides of a moving strip which is thereafter subjected to the usual cold rolling operation, and then annealed in a furnace under conditions which will prevent formation of oxide lm.

To illustrate the invention, and to describe a' preferred embodiment, S indicates a coil of hot rolled strip or band steel which is supplied in the usual manner from the mill, preferably in the form of coils weighing approximately three tons. Such strips or bands have a surface coating of oxide which normally is removed by a so-called continuous pickler.

In the drawing, the strip or band S is passed from the uncoiler A through a conventional stitcher B by means of pinch rolls C and, then, the oxide film upon the strip is removed by subjecting the strip to cleaning units such as the wheel-abrader units D. The strip is thereafter passed successively through a shearing apparatus F for shearing the strip into lengths vto provide suitable transferable coils, then through the customary scrubber and dryer G, through an oiler H Thereafter, the coils in which the strip has al thickness of about .062 to .100 inch are uncoiled .at J and passed through a conventional cold rolling mill K to reduce the thickness to substantially any guage desired and recoiled as shown at L. 'Ihe c'oils are then passed from the uncoiler M through a welder N and the sheared ends thereof are welded together to form a continuous strip. From the welder N, the continuous strip is passed through a suitable electrolytic cleaner to a recoiling device P.

At the recoller P, the welds are cut out so that the strip will be formed into suitable transferable coils. These coils are uncoiled at Q, and the lengths are welded together at R. to form a continuous strip which is continuously travelled through a bright annealing furnace or other furnace T and annealed in an inert atmosphere. For-the usual type of hot rolled band or strip treated in accordance with this invention, as just described, the annealing furnace will preferably have a temperature of between 1100 F. and 1250 F. and the atmosphere may consist of hydrogen. carbon monoxide, or nitrogen. A preferable atmosphere is one consisting of 6 1/2% carbon dioxide, 13.2% carbon monoxide, '7.4 to 11% hydrogen, and .02% or less of oxygen. By continuously travelling the strip through the annealing furnace at the temperature described, and in an inert atmosphere, no opportunity for oxide to form on the surfaces is permitted and the bright hard-polished surfaces of the strip are not only preserved, .but they are actually improved. The strip is cooled in the annealing step to a temperature at which oxidation is inhibited, e. g., below 250 F. After the annealing operation, the strip is recoiled as shown at U and may be given a suitable skin pass as shown at V.

Heretofore, following the annealing treatment, it has been customary to clean the sheet by means of a white pickle. 'Ihe annealing operation in the present method is conducted under conditions to prevent oxidation; it therefore improves the surfaces of the sheet and a cleaning or pickling treatment is not required.

The steel strip or so-called Bright finished sheet produced in accordance with the method thus far described is useful for many purposes. For example, in the manufacture of tin plate, or other metal coated plate, the strip is uncoiled as shown at W. subjected to a conventional flying shear X, and severed into sheets or stripe Y of suitable length and width for tinning.`

It is to be understood, of course, that the metal strip or Bright nished sheet may be continuously passed through a tinning apparatus.

Where the strips or sheets Y are to be coated with a metal, for example, tin, conventional coating practice is resorted to and the strips are iirst held in the usual water bosh Ti from which they are passed through the tinning machine T2 for producing tin plate T3.

As heretofore explained, a thinner coating of tin may be utilized without impairing the eiliciency of the tin plate and affording a very substantial saving.

I claim:

1. 'I'he process of of bright annealed strip steel which comprises cold-rolling a continuous length of strip steel, thereafter annealing the strip steel under conditions to produce a bright anneal while preserving the bright hard polished surfaces of the strip, and thereafter coiling the strip from the annealing furnace. f

2. The process of preparing continuous lengths of bright annealed strip steel which comprises reducing the gauge of the metal by cold-rolling a continuous length of strip steel, annealing the strip steel under conditions to produce a bright lanneal while preserving the bright hard polished f surfaces of the strip, and thereafter coiling the strip from the annealing furnace.

3. The process of preparing continuous lengths of bright annealed strip steel which comprises reducing the gauge of the metal by cold-rolling a continuous length of strip steel, annealing the strip steel under conditions to produce a bright anneal while preserving the bright hard polished surfaces of the strip, giving the strip a skin pass, and then continuously tinning the uncut strip.

4. The process of preparing continuous lengths of bright annealed strip steel which comprises reducing the gauge of the metal by cold-rolling a continuous length of strip steel, coiling the cold-rolled steel, annealing the strip steel under conditions to produce a bright anneal while preserving the bright hard polished surfaces of the strip, coiling the strip from the annealing furnace. giving the strip a skin pass, coiling the strip and then continuously tinning the uncut strip.

MATTEW SCHON.

preparing continuous lengths

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