US3667270A - Method for smoothing rolls for cold rolling or finishing cold rolling of bright metal sheet or the like - Google Patents

Abstract

A considerable reduction of the polishing of rolls of a rolling mill for cold-rolling metals is obtained by periodically passing a blue annealed steel sheet through the rolls of the rolling mill while these exert a pressure on the sheet. The blue annealed sheet so used exerts a polishing action on the rolls, avoiding need for taking the rolls out of the stands to be polished. One blue annealed sheet can be used several times for this purpose.

Description

United States Patent Deurloo 51 June. 6, 1972 METHOD FOR SMOOTHING ROLLS FOR COLD ROLLING OR FINISHING COLD ROLLING OF BRIGHT NIETAL Appl. No.: 819,528

Foreign Application Priority Data May 1, 1968 Netherlands ..6806l54 U.S. Cl ..72/236, 72/236, 72/365,

29/90 Int. Cl ..B21b 27/00 Field of Search ..72/236; 29/90, 90.5

[56] References Cited UNITED STATES PATENTS 1,072,195 9/1913 Townsend ..72/236 1,525,173 2/1925 Ernst 2,024,007 12/1935 McColloch et al. 1,945,935 2/1934 Fischer Primary Examiner-Milton S. Mehr Attorney-Hall & Houghton [57] ABSTRACT A considerable reduction of the polishing of rolls of a rolling mill for cold-rolling metals is obtained by periodically passing a blue annealed steel sheet through the rolls of the rolling mill while these exert a pressure on the sheet. The blue annealed sheet so used exerts a polishing action on the rolls, avoiding need for taking the rolls out of the stands to be polished. One blue annealed sheet can be used several times for this purpose.

3 Claims, No Drawings METHOD FOR SMOOTHING ROLLS FOR COLD ROLLING OR FINISHING COLD ROLLING OF BRIGHT METAL SHEET OR THE LIKE The present invention relates to a method for smoothing rolls for cold rolling or finishing cold rolling of bright metal sheet or other metal sheet without particular coating or intentional oxide layers, and to a method for cold rolling or finishing cold rolling of such sheet. Metal sheet, for instance obtained by hot rolling, cold rolling, annealing and finishing cold rolling as is usual for steel sheet, will, in the last step of cold finishing rolling obtain a surface, of which the roughness is essentially determined by the roughness of the rolls of the rolling mill. This roughness is of great importance in view of the purpose for which the sheets have to be used and the appearance of the sheet. In order to express this roughness CLA-values are used in micro-inch, or the roughness is expressed in Ra-values in y. according to German Standard DIN 4762. These values give the mean heights of the elevations and depressions in the surface. In general a distinction is drawn between coarse, mean, fine, semi-smooth and smooth material, the CLA-value for smooth material being at most about 3 micro-inch and for semi-smooth material being at most 20 micro-inch.

In the usual rolling plants a material is obtained which is semi-smooth or somewhat coarser than semi-smooth and if the final product to be obtained has to be smoother it is necessary to give the sheet an after-treatment in special devices, often in specialized plants and in such after-treatment polished rolls are used.

The present invention aims at obtaining a semi-smooth or smooth sheet metal in a more simple and less expensive manner than available up to now.

To attain this purpose according to the invention a blue annealed steel sheet is passed between the rolls while they exert a rolling pressure on the sheet.

Surprisingly, applicant has discovered that by doing this the operating rolls for the cold-rolling or cold finishing rolling are polished considerably. Thus it is possible to use the rolls during a much longer period than before and thus in a simple and cheap manner smoother metal sheets are obtained.

A blue annealed steel sheet is a steel sheet with a blued (darkened) surface which is caused by the formation thereon of a thin oxide layer bonded intimately to the steel.

It is possible to obtain such an oxide layer by bringing water vapor or oxygen into contact with the steel sheet in a predetermined temperature region during annealing in a bell type annealing furnace, or to apply a continuous annealing method in a certain oxidizing atmosphere. In the book of H. Silman:Chemische und Galvanische Uebeizuge, 1952, page 166, the fact has been noted that steel at certain temperatures in an oxidizing atmosphere shows annealing colors, which remain present after cooling and are due to the formation of an oxide layer.

For certain applications of the steel sheet such as stove tubes and baking tins such an annealing color is deemed desirable. This is so because the steel sheet should be resistant against brown or "red porous oxidation, because an esthetic appearance is required, because a good oxide layer gives a good adhesion of grease, oils and cleaning substances and sometimes also because the reflection characteristics and the electrically insulating characteristics are of importance.

When oxidizing the steel sheet in contact with air such annealing colors will usually occur in the temperature range of between 220 and 360 C. For the lower temperatures more yellow colors are generated and for the higher temperatures greyer colors. For temperatures about in the middle of the said temperature range, usually at 300 C, a blue color is obtained. As usually this blue color is desired and as this color is obtained in about the middle of said temperature range, it is usual in practice to speak of blue annealing for all annealing treatments in which such colors are obtained, even if the color obtained is not exactly the blue color as obtained at 300 C.

Usually the blue annealing takes place in a continuous annealing furnace, through which the steel to be treated is fed as a continuous long strip. In such furnaces it is possible to control the temperature and the atmosphere exactly at any point of the furnace and it is possible to correct the color obtained during the annealing as it is possible to check the color of the sheet where this leaves the furnace.

It is also possible to realize the blue annealing in an open coil annealing device, provided care is taken that the atmosphere is of oxidizing nature only and exclusively within the given temperature range.

Applicant has found that when applying the invention a smooth surface is obtained in the sense as indicated above, which means that the sheet after rolling has a roughness of 6 to 7 micro-inch or even of 3-micro-inch for the metal sheets which are cold rolled after a blue annealed sheet is passed through the rolling mill.

Applicant has further found that when rolling steel sheet after passing through the rolling mill a blue annealed sheet of for instance seven tenths of a millimeter thickness and a length of 1,500 meters but at least a length of 750 meters, it is possible to roll a total length of cold rolled bright steel sheet of 12,000 meters but at most 15,000 meters with the rolls thus treated while obtaining a roughness of the bright sheet of at most 6 micro-inch. Thereafter it is again necessary to pass a blue annealed sheet through the rolling mill in order to smooth the rolls and thus to maintain the required smoothness of the bright steel sheet rolled thereafter in the same mill. It is, however, possible to use the same blue annealed sheet several times, even up to 10 times for this smoothening purpose. It is moreover possible to make this blue annealed sheet useful for the same purpose again even after it has been used 10 times for roll smoothing by blue annealing it again.

The invention also opens important possibilities if it is desired after rolling a narrower sheet or strip during some time to switch over to the rolling of a sheet or strip with a greater width. Usually it is in such cases often necessary to give the rolls a supplementary grinding and polishing treatment because the rolls show more wear in the center than nearer to the ends. The present invention has disclosed that in many cases, by passing a blue annealed sheet through the mill according to the invention, such an additional treatment of the rolls is no longer necessary.

This invention moreover relates to a method for cold rolling or cold finishing rolling of bright metal sheet, in which, in order to obtain a smooth or semi-smooth surface of the metal sheet a blue annealed steel sheet is passed between the rolls while they exert a rolling pressure on the sheet before cold rolling or cold finishing rolling of the said metal sheet.

It is known that it is in certain cases possible to cold roll metal sheet after it has been hot rolled without applying thereafter a cold finishing rolling such as is often used after an annealing treatment. For such cases it is possible to apply the present invention for said cold rolling. If, however, after cold rolling an annealing treatment is applied, usually as a pretreatment for the cold finishing rolling, it is usually not desired to apply the invention during the cold rolling, because in that case the rolled sheet will become so smooth that the windings of the sheet coil, coiled at the end of the cold rolling, adhere to one another and thus when uncoiled show defects in their surfaces. However, if annealing takes place in a manner which does not involve this danger, for instance continuously in a tunnel furnace without coiling of smooth sheet, the present invention may also be applied for the first or main cold rolling.

If desired, a bright steel sheet which has been rejected for certain purposes and which finally will be used for packaging or other purposes for which it does not have to have a high quality, may be blue annealed and used for practicing this invention and thereafter as a packaging material.

This invention may be applied for the cold rolling not only of bright steel sheet, but also for other metal sheets, for instance when cold rolling brass, and in each instance, of course, the method for smoothing the rolls comprises the step of passing a blue annealed steel sheet between the rolls of the mill while such rolls are exerting thereon a sufficient pressure to effect smoothing of the roll surfaces, as aforesaid.

I claim:

1. A method for smoothing rolls of a rolling mill for cold rolling or finishing cold rolling of metal sheet, said method comprising the step of passing a blue armealed steel sheet between the rolls of the mill while such rolls are exerting thereon a sufficient pressure to effect smoothing of the roll surfaces.

2. A method of operating a rolling mill for cold rolling or finishing cold rolling of bright steel sheet or the like, said method comprising the step of passing a blue annealed steel sheet through the rolls of the rolling mill while such rolls are exerting a sufiicient pressure to effect smoothing of the roll surfaces by said blue annealed steel sheet, and then passing through the so smoothed rolls the bright steel sheet to be cold rolled thereby.

3. A method of operating a rolling mill for cold rolling or finishing cold rolling of metal sheet, in which first a narrower sheet and thereafter a sheet of greater width are rolled, said method comprising the step of treating the surfaces of the rolls for rolling the sheet of greater width by passing blue annealed steel sheet through the rolls after said rolls have been used for. rolling the narrower sheet and while the rolls are exerting a sufiicient pressure to effect smoothing of the roll surfaces by the blue annealed steel sheet, and then rolling the sheet of greater width with the so treated rolls.

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Claims (3)

1. A method for smoothing rolls of a rolling mill for cold rolling or finishing cold rolling of metal sheet, said method comprising the step of passing a blue annealed steel sheet between the rolls of the mill while such rolls are exerting thereon a sufficient pressure to effect smoothing of the roll surfaces.

2. A method of operating a rolling mill for cold rolling or finishing cold rolling of bright steel sheet or the like, said method comprising the step of passing a blue annealed steel sheet through the rolls of the rolling mill while such rolls are exerting a sufficient pressure to effect smoothing of the roll surfaces by said blue annealed steel sheet, and then passing through the so smoothed rolls the bright steel sheet to be cold rolled thereby.

3. A method of operating a rolling mill for cold rolling or finishing cold rolling of metal sheet, in which first a narrower sheet and thereafter a sheet of greater width are rolled, said method comprising the step of treating the surfaces of the rolls for rolling the sheet of greater width by passing blue annealed steel sheet through the rolls after said rolls have been used for rolling the narrower sheet and while the rolls are exerting a sufficient pressure to effect smoothing of the roll surfaces by the blue annealed steel sheet, and then rolling the sheet of greater width with the so treated rolls.