US3777532A

US3777532A - Method of and apparatus for extending and reducing thickness of a metallic band

Info

Publication number: US3777532A
Application number: US00269775A
Authority: US
Inventors: O Noe
Original assignee: BERG und WALZWERK MASCHINEN
Current assignee: BERG und WALZWERK MASCHINEN
Priority date: 1971-07-09
Filing date: 1972-07-07
Publication date: 1973-12-11
Anticipated expiration: 1990-12-11
Also published as: JPS5010827B1; DE2134405A1; GB1379265A; FR2154402B1; BE783776A; IT962562B; DE2134405B2; AT314453B; FR2154402A1

Abstract

A metallic band is subjected to a longitudinal tension equal to at most 80 percent of its mean tensile strength as it is passed through a plurality of bending units. In the units the band is bent back and forth through increasingly smaller radii of curvature causing lowering of the band''s elastic limit at the bend and plastic flow and elongation thereat. The band engages each roll over an arc preferably greater than 5* and the diameter D of each roll or of each set of roll is calculated according to the formula:

Description

United States Patent [1 1 Noe [ Dec. 11, 1973 METHOD or AND APPARATUS FOR EXTENDING AND REDUCING THICKNESS or A METALLIC EAND [75] Inventor: Oskar No,Mulheim/Rhur, Germany [73] Assignee: Firma BWG Bergwerk-und Walzwerk-Maschinenbau Gmbli, Duisburg, Germany 221 Filed: July 7,1972

[21] Appl. No.: 269,775

[30] Foreign Application Priority Data July 7, 1971 Germany P 21 34 405.8

52 Us. Cl. 72/205, 72/160 [51] Int. Cl B21b 39/08 [58] Field of Search 72/205, 160, 162, 72/165 [56] References Cited UNlTED STATES PATENTS 2,060,400 11/1936 Niemann 72/160 X 3,605,470 9/1971 Polakowski 72/163 Primary Examiner--Milton S. Mehr Attorney-Karl F. Ross [57] ABSTRACT A metallic band is subjected to a longitudinal tension equal to at most 80 percent of its mean tensile strength as it is passed through a plurality of bending units. in the units the band is bent back and forth through increasingly smaller radii of curvature causing lowering of the bands elastic limit at the bend and plastic flow and elongation thereat. The band engages each roll over an are preferably greater than 5 and the diameter D of each roll or of each set of roll is calculated according to the formula:

D l/( 1), wherein h is the thickness of the band in cm, E is the modulus of elasticity of the band in kg/cm, K is a constant between 25 and 50, and kp is the mean tensile strength of the band in kg/cm. The strip engages each roller over an arc which is greater than 5, while the imaginary contact with this roller is greater than 25.

11 Claims, 5 Drawing Figures ZMENTEB SEC 11 1975 3771.532 sum was PATENTED DEC 3 1 I975 3.711.532 SHET 2 BF 5 PATENTEI] DEC 1 1 1975 SHEET 3 BF 5 FMENTEUDECH I975 3777.532 SHEET NF 5 METHOD OFAND APPARATUS FOREXTEND ING AND REDUCING THICKNESS OF A METALLIC BAND FIELD or THE INVENTION Thepresentinvention relates'toa method of elongating and reducing the cross-section *ofa metallic band and, more particularly, to'a "method of andapparatus for cold-treating a sheet-metal strip to make it longer and thinner.

BACKGROUND OF THE INVENTION A sheet-metal band or strip is customarily made thinner and longer by the process of cold-rolling wherein pair immediately upstreamhThe work done by the rolls is consumed approximately one-half for plastic deformation of the band, and one-half in the production of useless heat of compression which must be conducted away from the work to prevent the temperature rise thereof beyond an optimal maximum. Thus such a system is highly wasteful of energy.

In addition the rolls are extremely expensive and require frequent replacementand/or refinishing because, under the enormous compressive forces to which they are subjected, they tend to "wear rapidly. It is common practice to back up the working rolls which define the working gap with large-diameter support rolls. The working rolls often must be replaced daily in a large cold-rolling installation, and the support rolls every few weeks. Thus the rolling string is often out of service and the output of the mill is limited.

Customary rolling installations are controlled by highly expensive devices which regulate the working gaps and circulate the various coolants, keeping these coolants, which are necessarily sprayed on the workpiece in the gaps, clean and cool. In tandem strings with four ormore roll sets the power consumption is often in the neighborhood of 15,000 to 20,000 kilowatts, with very heavy-duty transformer switching and rectifi cation stations necessary. The cost of'the electrical control and power installations may thus approach the cost of the mechanical parts of the system.

It is also known to stretch a sheet-metal band by passing back and forth between a pair of drums. This method has never met with commercial success since the operation is inherently discontinuous, thereby not for plastic deformation of a strip in a typical straightening operation. In this method the band to be straightened is passed under tension through'successive setsof rollers each of which bends it inadirection oppositeto the bend direction of the preceding pair. However each bend is through a larger radius of curvature than the previous one so that by the time the band passes through the entire group of bending rollers it'is straight.

Such a method is perfectly efficient for straightening a bent band but has little effect on either the length, width, or thickness of the band.

Y OBJECTS or THE INVENTION lt'is therefore an object of the present invention to provide an improved method of reducing the thickness of a band.

"Another object is the provision of'a method of and apparatus for elongating a band while reducingits thickness.

Yetanother'object is to provide an installation which issimple'and inexpensive tomake and operate.

SUMMARY OFTHE INVENTION l'attain these objectsaccorc'ling to the'presentinvention in al'engthening system wherein the band is bent backand "forth through eversmaller radii of curvature while it'is'longitudinally tensionedwith a force below its elastic limit or mean tensile strength. The latter is "defined as the tensile force which, in the absence of bending or other working is sufficient by itself to permane'ntly stretch the strip.

Ithas' been foundfthat such bending reduces the elastic limitlocally, at the bend, to permit plastic flow and elongation in this region without any necessity of compressing or squeezing the band. The bending rollers are staggered alongthe path of the band, exerting no compressive force on the band, so that they are not subject to the considerableforces present ina rolling opera- I tionJTherefOre the heat buildupan'd wear in general is reduced to a fraction of what it is in a'cold-rolling mill while 3 of freedom for working are obtained as opposedto the 1 of freedom (transverse force) of the rolling mill.

According to another feature of this invention, each bending roll is situated so with respect to the rolls immediately upstream and downstream that a pair of imaginaryplanes both crossing the workpiece path and tangentto the middle roller and each tangent to a respective flanking roller define an arc B of at least 25 on the middle roller between their contact lines thereon. At the same time, however, the band only engages an are 'a slightly larger than 5 on the this middle roll. Were the strip perfectly elastic and of zero thickness it would lie along thearc a, but its inherent rigidity makesthisiinpossible. This arc a is increased for increased stretching of the band, and decreased if less stretching is desired. In reality the arc a and the arc B areinterdependent so that they increase and decrease together according to a function which is primarily deter'rnined by the rigidity of the strip. In addition, the strip tension is a factor which determines the angular size of these arcs; the greater the longitudinal tension in the band, the greater these arcs will be. It should be noted that the actual contact angle [3 here is much smaller than the theoretical contact angle a. In addition, theoretical contact arc or is actually defined by two planes as described above which are, however, parallelto planes tangent to the'upstream and downstream rollers, and spaced from these planes by a distaiice equal to the workpiece thickness.

The diameter of each roll is calculated with the formula:

D (h E)/(K k5) wherein D is the rolls diameter, h is the band thickness in cm, E is the modulus of elasticity in kg/cm k is the mean tensile strength in kg/cm, and K is a constant from 25 to 50. According to another feature of the invention a longitudinal tension is exerted on the band which is of the order of 80 percent at most of the band mean tensile strength.

Such an arrangement functions at high or low throughput speeds so that it may be combined with galvanizing equipment or any other continuous operations. It is also possible to stop the band and start it up again with no noticeable effect on the finished product. Advantageously the band after such stretching is immediately subjected to a straightening operation, and even to a cold-rolling operation to eliminate any minor irregularities in thickness.

Since a relatively small amount of the energy exerted is transformed into heat in comparison to the amount working to stretch the band, the device is highly efficient. No complicated cooling arrangement need be provided, neither need any complicated devices to regulate the positioning of the rolls be connected to the apparatus.

The rolls can, according to another feature of this invention, be of constantly decreasing diameter in the direction of workpiece travel. Alternately they can be arranged in groups of four or more rollers all of the same size, with the downstream group smaller. The roll size can even decrease in each group, with the furthest downstream roll of one group being slightly larger than the furthest upstream roll of the next group downstream. In any case it has been found advantageous according to yet another feature of the present invention to provide auxiliary drive or advancing means between each two groups to ensure good advance of the band.

DESCRIPTION OF THE DRAWING The above and other objects, features, and advantages will become apparent from the following description, reference being made to the accompanying draw- SPECIFIC DESCRIPTION As shown in FIG. 1 a steel band 18 is unwound from a braked drum 1 and eventually wound up on a driven drum 2, passing in a transport direction 29 through the apparatus. A shear 3 and a welding device 4 are provided immediately downstream of the drum 1 in order to cut off the end of this band 18 and attach the leading edge of another such band thereto. Another such shear 5 is provided immediately upstream of the takeup drum 2. Two gripping and driving arrangements 6 and 7 are provided at the upstream and downstream ends, respectively, of the apparatus, and are equipped with respective drive motors 6a and 7a which drive the upstream device 6 slower than the downstream one, the speed differential being sufficient to stress the band 18 in direction 29 to at most 80 percent of its mean tensile strength. My copending application Ser. No. 139,575, filed May 3, 1971 and my U.S. Pat. No. 3,559,431 describe drives suitable for use with this invention.

Between the drives 6 and 7 the band I8 runs through six different groups 8fof rolls 9 14 respectively. The rolls 9 are of greater diameter than the rolls It) and so on with the rolls 14 being the smallest. Large driven rolls 15a 15e separate the bending units 8a 8f from one another. The furthest downstream bending unit 8f is followed by a pair of straighteners 16a and 16b of conventional type flanking a conventional cold-rolling unit 17 serving to eliminate any minor imperfections in the band 18.

FIGS. 3 and 4 show the bending units 8a 8c in greater detail, with the unit 8b shown in its entirety. The rolls 10 of this unit comprise three

upper rolls

10a, 10a" and IOa, and two lower rolls lllb and 10b". The roll 10a is larger than the roll 10b, with the roll 10a being the smallest. In addition the roll Mia is smaller than the immediately preceding roll 9a and the roll I0a' is larger than the following roll Ila.

All of the upper rolls 10a Itla' are supported on rollers on flanges formed on a vertically displaceable framework 25 and the lower rollers 10b and 10b" are supported on rollers 10d carried on flanges formed on the frame 30 of the device. A pair of hydraulic cylinders 26 can vertically displace the upstream end of the framework 25 and another pair of double-acting cylinders 27 support the downstream end. Since rolls 10b and 10b" are rotatable about respective axes lying in a common horizontal plane, and the rotation axes of the rolls 10a 10a are coplanar and parallel to the framework support 25, tilting of the support 25 by the

cylinders

26 and 27 to the horizontal will change the gapping of the rolls of the bending bending unit 8b. Advantageously the leading end of the beam 25 is depressed by the cylinder 26 less than the trailing end to ensure a tighter bend at this trailing end. Also when a new workpiece 18 is to be threaded through the apparatus the beams 25 are fully raised.

FIG. 2 is essentially identical to FIG. with the same reference numerals being used for identical structure whenever applicable.

After leaving the welding unit 4 the band 18 passes between two sets of tensioning rollers 19 flanking a straightener 20. Thereafter the band passes through a storage area 21 and into a pickling bath 22, whence it passes through the drive 6, the bending units 8a 8f, the straighteners 16a and 16b, the rolling apparatus 17 and the drive 7 to another storage area 23. A galvanizing station 31 is provided immediately downstream of the storage area 23 followed by another pair of tensioning rollers 24, the shear 5, and the takeup spool 2.

In this embodiment, however, all of the rolls 9 are of the same diameter, as are the rolls 110, and so on. A decrease in the bending radius in the transport direction is obtained exclusively by tilting the plane of the axes of the upper rolls relative to that of the lower rolls with the

cylinders

26 and 27.

FIG. 5 shows how the band passes through three rolls 9. Were the band 18 perfectly elastic it would assume the position shown by dashed lines 28, engaging the middle roll over an arc a of 65. However, the inherent stiffness of the band 18 causes it to assume a sinusoidal path between two rolls so that it only engages the roll over an arc B of about 30. In straighteners a much smaller contact are is used.

The are B should exceed 5 and are a should be greater than 25. Since are a is substantially equal to that are defined with reference to the middle rollers rotation axis by a pair of planes tangent to it and to the neighboring rolls, it can be seen that adjustment can be achieved either by displacing the rolls toward each other in the transport direction ,or raising or lowering every other roller relative to its neighbors. This latter method is the most efficient and practical solution.

In the apparatus according to the present invention the band is made longer, narrower, and thinner as it passes through the several bending units. In the first bending unit the thickness may be decreased by around 70 percent while the width is reduced by 30 percent without exceeding the brittle-fracture point. In the fol lowing units, however, the relative reduction is of a lesser degree since the tensile strength is increased and the reduced thickness, even with increasingly tighter bends, is less susceptible to flow during bending. Starting with a steel band of between 1 and 5 mm in thickness a device as shown in FIGS. 1 5 can reduce its thickness depending on the setting of the rolls from to 100 percent. The thicker bands are passed through all five bending units; thinner ones need only pass through the last three or four. Similarly, if the desired thickness is obtained, the last several bending units may not be used.

SPECIFIC EXAMPLE The diameter D (in centimeters) is calculated according to the following formula:

D (h E)/(K k wherein it is the thickness of the band in centimeters, E is the modulus of elasticity in kg/cm, k is the mean tensile strength in kg/cm and K is a constant between 25 and 50.

Employing a K equal to 35 with a steel band 3 mm thick having a mean tensile strength of 2,500 kg/cm a roller diameter of 72 mm is used. Since this will reduce the thickness of the band, the other rollers are calculated on the basis of reduction obtained. In the arrangement of FIG. 2 a steel band of 3 mm thickness is longitudinally stressed at 2,000 kg/cm and passed between the six rolling units whose rolls are dimensioned 80, 65, 50, 40, 30, and mm in diameter.

I claim: 1. A method of stretching a metallic band comprising the steps of:

continuously advancing said band longitudinally along a transport path; longitudinally tensioning said band as it advances between two longitudinally spaced locations along said path with a tension force below the mean ten sile strength of the band in an unbent state; locally bending the advancing tensioned band between said locations through a first radius of curvature sufficient to locally lower the mean tensile strength of said band at the bend below the tension force thereby elongating the bent portion; and locally bending the advancing tensioned band at a location downstream of the first bending thereof through a second radius of curvature smaller than said first radius to locally lower the mean tensile strength of said band again and to permit local plastic elongation of said band.

2. The method defined in claim I wherein said band is bent without compression being exerted thereon at the headings.

3. The method defined in claim 1, further comprising the steps of cold-rolling and straightening the band after elongation thereof.

4. The method defined in claim 1 wherein said band is longitudinally tensioned at at most of its mean tensile strength.

5. The method defined in claim 1 wherein said band is bent over rolls spaced one after the other along the transport path, said method further comprising the step of situating said rolls such that said band engages each roll over an actual contact arc greater than 5.

6. An apparatus for stretching a metallic band comprising:

means for continuously advancing the band longitudinally along a transport path;

means at an upstream end and at a downstream end of said path for longitudinally tensioning said band with a tension force below the mean tensile strength of said band;

a first bending roll along said path of a predetermined diameter;

means for locally bending said band around said first roll to conform same thereto;

a second bending roll along said path downstream of said first roll and of a diameter smaller than the diameter of said first roll; and

means for locally bending said band around said first roll to conform same thereto. I

7. The apparatus defined in claim 6 wherein each of said means for locally bending said band includes a pair of guide rolls flanking the respective bending roll.

8. The apparatus defined in claim 6 wherein each bending roll has a diameter D dimensioned according to the formula:

wherein h is the thickness in cm of the band fed to the respective guide roll, E is the modulus of elasticity of the band in kg/cm k is the mean tensile strength of the band in kglcm and K is a constant between 25 and 50.

9. The apparatus defined in claim 6 wherein each of said bending rolls engages said band over an arc of more than 5.

10. The apparatus defined in claim 9 wherein a pair of imaginary planes passing through said band and each tangent to a respective guide roll and both tangent along respective angularly offset tangent lines to the respective bending roll define between their tangent lines an arc of more than 25 on said blending roll.

11. The apparatus defined in claim 10, further comprising means for displacing said bending rolls transverse to said transport path for adjustment of said arcs. a: =1:

Claims

1. A method of stretching a metallic band comprising the steps of: continuously advancing said band longitudinally along a transport path; longitudinally tensioning said band as it advances between two longitudinally spaced locations along said path with a tension force below the mean tensile strength of the band in an unbent state; locally bending the advancing tensioned band between said locations through a first radius of curvature sufficient to locally lower the mean tensile strength of said band at the bend below the tension force thereby elongating the bent portion; and locally bending the advancing tensioned band at a location downstream of the first bending thereof through a second radius of curvature smaller than said first radius to locally lower the mean tensile strength of said band again and to permit local plastic elongation of said band.

2. The method defined in claim 1 wherein said band is bent without compression being exerted thereon at the bendings.

4. The method defined in claim 1 wherein said band is longitudinally tensioned at 80% at most of its mean tensile strength.

5. The method defined in claim 1 wherein said band is bent over rolls spaced one after the other along the transport path, said method further comprising the step of situating said rolls such that said band engages each roll over an actual contact arc greater than 5*.

6. An apparatus for stretching a metallic band comprising: means for continuously advancing the band longitudinally along a transport path; means at an upstream end and at a downstream end of said path for longitudinally tensioning said band with a tension force below the mean tensile strength of said band; a first bending roll along said path of a predetermined diameter; means for locally bending said band around said first roll to conform same thereto; a second bending roll along said path downstream of said first roll and of a diameter smaller than the diameter of said first roll; and means for locally bending said band around said first roll to conform same thereto.

8. The apparatus defined in claim 6 wherein each bending roll has a diameter D dimensIoned according to the formula: D (h . E)/(K . kF) wherein h is the thickness in cm of the band fed to the respective guide roll, E is the modulus of elasticity of the band in kg/cm2, kF is the mean tensile strength of the band in kg/cm2, and K is a constant between 25 and 50.

9. The apparatus defined in claim 6 wherein each of said bending rolls engages said band over an arc of more than 5*.

10. The apparatus defined in claim 9 wherein a pair of imaginary planes passing through said band and each tangent to a respective guide roll and both tangent along respective angularly offset tangent lines to the respective bending roll define between their tangent lines an arc of more than 25* on said bending roll.

11. The apparatus defined in claim 10, further comprising means for displacing said bending rolls transverse to said transport path for adjustment of said arcs.