US3459027A - Method for levelling sheet stock - Google Patents

Description

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R. G- BROWNST METHOD FOR LEVELLING SH EIN 3,459,027

EET STOCK Filed Sept. 28, 1967 \NCEPHON OF STRNN HRQDEBHNG mvsmon F4 wow 6. Bmwsrsm PERCENTAGE $TRNN STRESS-STRNN CURVE FOR M\\ D STEEL ATTORNEYS United States Patent 3,459,027 METHOD FOR LEVELLING SHEET STOCK Raymond G. Hrownstein, 300 Fountain Ave, Ellwood City, Pa. 16117 Filed Sept. 28, 1967, Ser. No. 671,265 Int. Cl. BZIb 1/38; B2111 1/02, 3/02 U.S. Cl. 72366 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the treatment of metal sheet stock in order to prepare it for further manufacturing operations.

Metal sheet stock to be used for stamping or drawing is rarely suitable for its ultimate use without further treatment. Metal plate after rolling, or metal strip after uncoiling, is passed through a leveller in order to flatten it preparatory to moving on to other operations. The leveller in use today normally has anywhere from nine to twenty-three staggered rollers which cause the material to pass through a series of reversing bends thereby producing a straight sheet. Since the material is not uniformly flat those areas that are flat are bent within the elastic limit, and the areas that are not flat are bent beyond the elastic limit. The commercially flat product results from this combination of bending and springing back repeated a sufficient number of times. The size of the rollers, number of rollers, and roller spacing are determined by the type and dimensions of the material being worked, which usually is no more than 1 /2 thick. When metal sheet stock is levelled on such an apparatus, plastic stress is set up in the outer one-third of the material from the neutral axis. In order to perform the required operations on a material being treated with this commonly used apparatus, the operator must make many adjustments, the most important of which is roller spacing. The required results in the product are achieved by passing the sheet stock through the apparatus several times, or passing it through several similar machines which represent a significant investment in terms of equipment and labor and which take up an undue amount of floor space.

When thin sheet stock is passed through such conventional apparatus, bridles must be located at the entry and exit ends of the apparatus to maintain proper tension in the material. This, of course, means that there is additional equipment which must be separately installed, thereby further increasing operating costs on such conventional apparatus.

Accordingly, it is an object of this invention to provide a method of straightening metal sheet stock which overcomes the aforementioned and other such disadvantages. It is a further object of this invention to provide a method of straightening metal sheet stock which is relatively fast and easy to perform.

An additional object of this invention is to provide a method of straightening metal sheet stock consistent with the foregoing objects which eliminates complicated equipment, is simple, and provides improved results in a single pass through the appropriate apparatus.

These and other objects of this invention will become apparent by reference to the following description and the drawings wherein:

FIGURE 1 is a diagrammatic side elevational view of an apparatus which can be utilized to perform the method of this invention;

FIGURE 2 is an end view of the apparatus of FIG- URE 1 with some portions omitted for clarity; and

FIGURE 3 is a stress-strain curve for mild steel to be treated in accordance with the present invention.

I have found that metal sheet stock, particularly steel, develops a so-called hinge when subjected to forces that produce a plastic stress. Such forces may be set up by compressing or bending the stock, or by a combination of compression and bending. Compressing the stock between rollers with a suitable load sets up a definite volume under plastic stress and elongates the fibers of the stock, in the plastic volume, in the direction of travel. This is best accomplished by using rollers of different sizes. The compression gives the fibers a certain flatness at the point of contact, or hinge. By bending or tensing the stock as it emerges from the rolls, to a particular degree, the fibers are oriented in a definite direction or plane of travel and all fibers follow in this same plane to produce flat stock.

The degree of compression, and the angle at which the stock is bent, are dependent on the stock material itself and are determined by the plastic limit of the material. The method of this invention is based upon this observation and upon the fact that the plastic stress applied to the sheet stock is in the full thickness of the same.

Metallic materials, and particularly steel, are characterized by the fact that plastic limit or the maximum plastic stress that can be applied is reached before strain hardening begins. The total plastic stress applied by compressing the material between the rollers and by bending the material as it emerges from the rollers must not exceed its plastic limit. Thus, it may be seen that the load applied to the rollers and the angle at which the material is bent will be regulated according to this characteristic of the material.

Turning now to FIGURE 1 of the drawings, the metal sheet stock 10, preferably formed of steel, is guided into the apparatus by the entry roll 12 and between the feed roll 14 and the pressure roll 16 with compression being applied at 18. Platic stress results at point 18 which is termed the hinge causing the crystals, or fibers of the stock 10 to elongate in the direction of travel. As the stock 10 emerges from between the feed roll and the pressure roll, the exit roll 20 bends the stock angularly downward and out of its feeding plane, the degree of bend being exaggerated in the drawing for purposes of illustration. As can be seen, the feed roll 14 is of greater diameter than the pressure roll 16, and in the preferred embodiment, the ratio of the diameters of the feed roll to the pressure roll is approximately 2:1. Ideally, a roll would bear on a flat surface to produce the desired plastic stress. Since such a construction would be impractical, the ideal situation must be approximated. This is done by using a diameter ratio as large as possible. Practical considerations such as cost, size, drive requirements etc., however, force a compromise, which is reflected in the 2:1 ratio as most practical for most applications, but not as a limiting ratio. The angle at which the stock is bent is regulated by the setting of the exit roll 20 which is adjusted by known means, as are the entry, feed and pressure rolls 12, 14 and 16.

In FIGURE 2, the apparatus is shown in an end view incorporating an adjusting means, generally designated by the numeral 24, at each end of pressure roll 16. The adjusting means 24 includes a pressure transmitting member 26 into which the end of the roll 16 is journaled. Adjusting screw 28 threadedly engages cross-beam portion 30 of the main supporting frame generally designated 32 and is secured by lock nut 34. Adjusting screw 28 raises or lowers spring seat 36, thereby applying pressure to spring 38 which bears on pressure transmitting member 26.

By properly adjusting the screws 28, the spring seats 36 can be selectively raised or lowered and the pressure placed on the roll 16 by springs 38 easily adjusted. Suitable means (not shown) are provided for Opening rolls 14 and 16 for easy material entry without disturbing the pressure setting.

While a preferred embodiment is described for loading the adjusting means 24 it is clear that any suitable means such as fluid cylinders or torque devices could be substituted for the spring loaded adjusting means. Whatever means is used must insure uniform roll force across the face of the pressure roll.

This method may be used with stock of any thickness t and is only limited in this respect by practical consideration since there is not theoretical maximum thickness of material which may be straightened. When using this method with thin metal sheet stock, it is necessary to utilize entry and exit bridles to maintain sufficient tension in the material. The bridles may be mounted, unlike prior art equipment and methods, in the same housing as the entry, pressure, feed, and exit rolls and are preferably located as close to the entry and exit rolls respectively as possible.

A specific embodiment of this invention, not to be considered unduly limiting, is described in the following example:

Example A semi-circular mild steel bar 2" wide and /2 thick was passed once through a leveller with 3" diameter entry and exit rolls, a 4" diameter pressure roll and an 8" diameter feed roll. The rolls were 9" long.

By reference to FIGURE 3 it can be seen that the plastic range for the mild steel ranges from about 0.1 to about 1.5% strain, therefore the allowable plastic forces applied to this material must not exceed 1.5%.

The load applied to the pressure roller, and thence to the steel bar as it passed through the rolls, was calculated using the following formula:

where:

S =Maximum compressive stress=33,000 p.s.i. P=Load applied per linear inch E=Modulus of elasticity=30 l0 d=Diameter of pressure roll=4 inches M (.59l) E :417 pounds per linear inch and for 2 inch width P=834 pounds The entry roll was set for a horizontal feed and the pressure roll was set to apply a force of 834 pounds on the 2 inch wide bar. The exit roll was set to provide a bend in the bar at the hinge corresponding to /z% additional fiber elongation. The total strain was Within 1 /2 The levelled bar, when measured on a flat guage surface, was perfectly fiat.

The apparatus used for this example could level a bar up to about 3" in thickness, being limited only by the size of the particular machine.

It will be readily understood that the method of this invention need not be limited to any particular material but is applicable to all types of steel, aluminum and any other metal which requires levelling at any stage of its manufacture. The amount of compressive force and the degree of bending are dependent on the material being levelled and can be easily determined by reference to standard data.

It is apparent that the method of this invention has been described in accordance with the foregoing objects.

What is claimed is:

1. A method of straightening metal sheet stock comprising the steps of feeding the stock between a pair of parallel straightening rollers which apply pressure to the stock thereby setting up plastic stress in the stock and elongating the fibers in the stock in the direction of travel of the stock, and then diverting the stock as it leaves the rollers at an angle with respect to the plane of the stock as it passes the rollers to apply additional plastic stress to the stock and to orient the elongate fibers in the stock in the direction of travel, the total plastic stress applied to the stock being in the full thickness of the stock and within the plastic limit of the stock.

2. The method of claim 1, wherein one of the pair of rollers is greater in diameter than the other.

3. The method of claim 2, wherein one of the pair of rollers is twice the diameter of the other.

4. The method of claim 2, wherein the stock is diverted in a direction away from the smaller of the two rollers.

5. The method of claim 1, wherein the stock is passed horizontally through the pair of parallel straightening rollers and then diverted downwardly as it passes the rollers.

6. The method of claim 5, wherein the parallel straightening rollers consist of an upper pressure roller and a lower feed roller, said feed roller having twice the diameter of said pressure roller.

7. The method of claim 5, wherein the stock is diverted by means of an exit roller.

8. The method of claim 1, wherein the stock comprises steel and the total plastic stress is within 1 /2 percent strain.

9. The method of claim 1, wherein the stock is up to about 3 inches in thickness.

10. A method for straightening metal sheet stock comprising the steps of horizontally passing the stock between a pair of parallel straightening rollers which apply pressure to the stock thereby setting up plastic stress in the stock and elongating the fibers in the stock in the direction of travel of the stock, said parallel straightening rollers consisting of an upper pressure roller and a lower feed roller, said feed roller having twice the diameter of said pressure roller; and then diverting the stock downwardly as it passes said parallel straightening rollers by means of an exit roller, thereby applying additional plastic stress to the stock and orienting the elongate fibers in the stock in the direction of travel of the stock, the total plastic stress applied to the stock being in the full thickness of the stock and within the plastic limit of the stock.

References Cited UNITED STATES PATENTS 874,692 12/1907 Lindstrand 72l60 X 2,190,986 2/1940 Hudson 72l60 X 2,301,681 11/1942 Cameron 72l60 3,094,442 6/1963 Perry 148-l2 MILTON S. MEHR, Primary Examiner US. Cl. X.R.

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