US1866310A - Metal coiling - Google Patents

Description

Patented July 5, 1932 UNITED STATES CLIFFORD A. KAISER, OF CHICAGO, ILLINOIS METAL COILING No Drawing.

The present invention relates to metal coiling and has particular reference to the coiling of metal strips, sheets and the like in such a manner asv to avoid defects such 'as coil breaks. l

- In the past it has been customary to process smelted metal to render the same suitable for coil.

manufacturing purposes by subjecting the metal in the form of bars, usually while hot, to processing in a hot mill. A hot mill unit consists essentially of one or two stands of rolls, a pair of furnace, one or more sheet furnaces and a squaring shear. The bars are heated in a pair furnace, passed back and forth through a stand of rolls, reheated in the sheet furnace when they are too cool for further working and are then finished by further passing back and forth through the rolls.

The sheets formed in this manner vary in width from about 12 to 36 inches and in length from about to feet) At the present time, this process is being superseded by the continuous method. In this method, hot bars of a much greater size arestarted at one end of'a series of from 2 to 10 or more mills and reduced in thickness progressively by. each mill until they have been rolled outinto long strips or strip sheets which may be one hundred feet or more in 7 length. In order to facilitate handling, these sheets are customarily formed into coils.

In rolling mills using the continuous proc Application filed September 24, 1931. Serial No. 564,981.

In the tight coiler method, the end of the strip is held between a set of jaws placed in a revolving drum. This drum pulls on the strip as it leaves the laststand of rolls, forming the strip into a coil approximately inches in inside diameter. This method of coiling results in essentially the same kind-of a coil as is produced by the loose coiler.

Some rolling mills place the coilers as close as practical to the last stand of mills and if the strip has been rolled hot it is generally thought that coiling while still hot permits the sheet to acquire .a certain mount of self annealing. Other mills do not coil the strip until the last portion of the strip has cleared the last hot mill stand, but no attempt is made to regulate the temperature of the metal during the coiling operation.

When such a coil is utilized for manufacturing purposes difliculty is encountered when the strip is being uncoiled. As the strip is uncoiled, it usually uncoils in a series of jerks,

and at each jerk a bend occurs across the strip from one side to the other. This bend is what is known in the trade as a coil-break, and thus far, practically all attempts at eliminating coil-breaks have been directed toward preventing the jerking motion as the strip is being uncoiled.

A primary object of the present invention is to coil metal in such a manner that difliculties met with in utilizing the coiled strips are avoided.

An'additional object is to produce a coil of metal which is not permanently deformed in the shape of a coil. I

Still another object is to produce a metal coil,v free from coil-breaks and other faults.

These and other objects will become apparent from the consideration of the following description. i

My invention is based upon the discovery that, intbe present method of coiling strips or sheets of metal, one surface of the strip or' sheet is reducedand the other surface i is increased in length when the strip is=coiled or uncoiled to such an extent that a series of failures occurs in the strip or sheet. If the strip is coiled hot, the failures occur when the strip is uncoiled, whereas, if coiled cold, the failures occur both while the strip is coiled and uncoiled. In accordance with my invention, these failures or coil-breaks are prevented by producing coils of a diameter z a constant,

regardless of the kind of stress developed,

whether 'tensile, compressive, or shearing, and regardless of the way the stress and deformation are produced, whether by axial, bending, or torsional loads. The numerical value of this constant ratio, however, is in general different for any one material when subjected to the different types of stress, and is also different for the different materials subjected to the same type of stress.

v The numerical value of the constant ratio of the unit-stress in a material to the accompanying unit-strain within the proportional limit is called the modulus of elasticity of the material, and the symbol E isj-g'enerally used to denote the modulus of-elasticity.

- For illustration, my invention will be described with particular reference to cold iron or steel, where the modulus-bf elasticity, or E, is approximately29,000,000 pounds per square inch, both for tension and compression, andv the proportional limit is about 29,000 pounds, depending on the composition and method of manufacture.

If a bar one square inch in cross section and 100 inches long is subjected to a stress, either tension or compression, it will be deformed. Applying a stress of 29,000 pounds, and solving the equation it is found that e equals 0.001 for a bar one inch long, or 0.1' for a bar 100 inches long.

Thus, if the stress be tension, the bar will be'elongated to 100.1 inches, or, if compres- "sion, the bar 'will be shortened to 99.9 inches. In either case when the stress isreleas'ed the bar will go back to its original length.

If a stress of more than 29,000 pounds is .applied to thebar, it will be distorted to morethan 0.1, and will not regain its original length when the stress is relieved.

make a cylinder having a neutral axis 30 inches in diameter. The inside surface of the coil, however, will be shorter than they neutral axis and the outside will be longer. The inside surface will be 1rX29.75O0=93.4;626 inches,

and the outside will be 1rX s0.2500=95.0334. inches.

ference of the neutral axis is, as before,

94.2480 inches and'the diameter is 30 inches. The inside diameter and circumference are, respectively, 29.9750 inches and 94.1695 inches, while the outside diameter and circumference are, respectively, 30.0250 inches and 94.3265 inches. The difference from the neutral axis in either case amounts to 0.07854 inch. From the equation it is seen that S=,24,200 lbs. per square inch. This is less than the proportional limit and the surface of the steel will not be permanently deformed. In accordance with my invention operation in this manner eliminates coil-breaks.

If a strip be coiled while hot (above 1,000 F. for steel) the aforementioned equationmay or may not apply. When a strip is coiled hot,

only .09248 the physical and metallurgical characteristies are such that the individual grains of which. the metal is composed orient themselves in the new coiled formation while cooling and, when the coil is cool, any change in the form of the coil is met with the same amount of' resistance as the cold, flat strip exerts when being coiled and, when stressed beyond the proportional limit, coil-breaks occur. Thus, a coil 30 inches in diameter and .250 inch thick will be stressed beyond the proportional limit when it is being straightened and the coil .025 inch thick will not. In any case where a flat strip. of metal is desired upon uncoiling, and coil-breaks are to be eliminated, I have found that it is necessary to coil the metal While cool as well as to form a coil having an inside diameter greater than the diameter of coils produced heretofore.

I have further discovered that there is a definite relationship between the gauge of U the metaltobe coiled or uncoiled and the permissible diameter of the coil in order to prevent failure of the surface of either side of the sheet. I

The increase in length of the outside of any coil, or the decrease in length of the inside from the length of the neutral axis which does not change is where D is the outside or inside diameter of the coil, D is thediameter of the. neutral axis, and T is the thickness of the'metal in inches. In order to keep within the. proportional limit, the increase in length of the outside of the coil over that of the neutral axis must notbe more than .001 inch per inch of length.

N e E or e 29000000 .001 inch The increase in length of the outside=1r '1, and that must not I 'be greater than .001 X 1r D and solving for D .we find D =l,000 T, or in the case of steel, the diameter of the coil equals the thickness of the coil multiplied. by 1,000.

' As a general case, for any elastic material that is formed into a coil. in accordance with my invention the difference in legth between the outside or inside surface of the coiled strip and the neutral axis should be equal to or less than the unit deformation multiplied by the length of the coil, or e 1r D Since i Thickness Diameter pf metal of circle 7, in inches in inches The aforementioned figures apply to ordinary hot-rolled steel after it has been cooled and wh n it has a proportional limit of 29,000

N lbs. 1 01 square inch. They will be altered souu'what on cold-rolled material having a surface of the strip be stressed beyond the elastic limit, and that the strip be coiled at a temperature below that at which there is a rearrangement of the grains composing the metal due to the temperature. Consequently, the loose coiler method of forming metal strips into coils is unsuitable for use in accordance with my invention, since the loose coiler method causes a deformation of the metal beyond its elastic limit whereby the metal retains its coiled shape.

The utility of my invention is well demonstrated in the manufacture of sheets for materials or products such as metal furniture and the like where it is essential that the sheets have a certain degree of flatness. At the present time it is possible to obtain flat sheets from coiled strips only after subjecting the sheets to expensive further processing. In the old sheet mill process, after a sheet attained the required surface and degree of hardness, it was placed in a stretcher leveling machine and stretched beyond the elastic limit. The uniformity of the internal stresses within the sheet enabled the machine to stretch it uniformly over the entire sheet and, as a result, the sheet was stretched fiat, or sufliciently so for the purpose for which it was intended. After a sheet that has been made from a coiled strip has attained the required prerequisites as to surface finish and hardness, it too is'stretcher-leveled. Few of the latter sheets pass inspection at the first stretcherillJ leveling and, therefore, they require additional processing. This additional processing usually consists of most or all of the following: annealing, pickling, roller-leveling, cold-rolling, and additional stretcher-leveling, thereby adding greatly to thecost of the finished product. Elimination of the aforementioned steps by operation in accordance with my invention means a material saving of time, labor and money.

Ordinarily, after a strip has been coldrolled it is coiled either on a loose-coiler or tight-coiler as in hot-rolling. In this coiling,-

the strip is again stretched beyond theclastic limit on one side and compressed beyond the elastic limit on the other. As before, this introduces an internal stress within the strip 7 and when the strip is cut into sheets and the sheets placed in a stretcher leveler to be stretched flat, the internal. stress within the sheet is not overcome by the external stretching force, thereby preventing the sheet from being made flat. In order to prevent this internal stress, it is necessary that the strip be coiled in such a manner and to such a diam eter that, at no time will any portion of the strip be stressedbeyond the elastic limit. v

- The various modifications of my invention which are not included in the foregoing illustrative and explanatory description are in tended to be included in the appended claims.

I claim:

1. A method of treating metal which comprises heating the metal to a comparatively high temperature, rolling the heated metal into the form of a sheet, cooling the sheet to a temperature below that at which the grain structure is changed due to the temperature, and forming the cooled sheet into a coil having a diameter sufliciently large that the metal of the coil will not be stressed beyond its elastic limit when being coiled r uncoiled, said diameter being at least equal to the thickness of the sheet multiplied by 1,000.

2. A method of treating metal, which comprises forming the same into a sheet, and

,forming the sheet into a coil having a diameter sufficiently large that the metal of the coil will not be stressed beyond its elastic limit when being coiled or, uncoiled, said diameter being at least as large as that derived from the formula where D is the inside diameter of the coil, E is the modulus of elasticity of the metal, S is a unit stress ins'ufiicient to reach or. exceed the elastic limit of the metal, and T is the thickness of the metal sheet.

v 3. A method of treating metal, which comprises heating the metal to a relatively high temperature, rolling the heated metal into sheet form, cooling the sheet to a tempera- I ture below that at which the grain structure of the metal changes due to the temperature, and forming the cooled sheet into a coil having a diameter at least as large as that derived from the formula D gs,

where D is the inside diameter of the coil,.E

is the modulus of elasticity of the metal, S is I a unit stress insuflicientto reach or exceed the elastic limit of the metal and T is the thickness of the metal sheet, whereby said sheet does not acquire coil breaks when-being coiled. or uncoiled. V

In testimony whereof I have hereunto subscribed my name.

- CLIFFORD A. KAISER-.-