US3362202A

US3362202A - Strip tensioning apparatus

Info

Publication number: US3362202A
Application number: US466899A
Authority: US
Inventors: Gay Pierre Andre
Original assignee: Compagnie des Ateliers et Forges de la Loire SA
Current assignee: Compagnie des Ateliers et Forges de la Loire SA
Priority date: 1964-07-03
Filing date: 1965-06-25
Publication date: 1968-01-09
Anticipated expiration: 1985-01-09
Also published as: FR1426137A; DE1527944A1; DE1527944C3; DE1527944B2; BE666342A; GB1113667A

Description

Jan. 9, 1968 P. A. GAY 3,362,202

' STRIP TENSIONING APPARATUS Filed June 25, 1965 5 Sheets-Sheet 1 11 j 56.2 r I Z? 1 [2. I m 5 4 8 e2 -C/ 5 4 3 2 m m 172 m m J 1 5: 5/ A/ 5 6 a! a a,

Jan. 9, 1968 J P. A. GAY 3,362,202

' STR-IP TENSIONING APPARATUS Filed June 25, 1965 I I 3 Sheets-Sheet 2 11 g 17 l8 19" W P. A. GAY

Jan. 9, 1968 3 Sheets-Sheet 3 Filed June 25, 1965 J Hill! W JY 2 T T z/ r W v A h 2 a1 ,v I. I|.|| a 0 Z k United States Patent ABSTRACT OF THE DISCLOSURE An apparatus designed to place metallic strips under continuous tension formed by rollers separated into two sets. One of said sets driving while the other brakes the strip passing between the rollers. Each of the rollers of the sets for braking and driving with the exception of one of the rollers of the braking set and one of the rollers of the driving set begin provided with a slip coupling to permit a slipping under a regulatable predetermined cou pling, for example a powder-magnetic type coupling.

In sheet metal working plants it is often required to subject sheet and strip material to elongation and tension. This may be necessary for various purposes, such as planishing the sheet, or performing any of various operations on the sheet while in a state of tension, including inter alia alternate flexing of the tensioned sheet for simultaneously planishing and cold-working it, light rolling of the tensioned sheet in a skinpass roll mill, and the like.

Strip-tensioning apparatus as used for the above purposes generally comprises two sets of rollers rotatable on parallel, e.g. horizontal, axes. The rollers in both sets are so disposed that a strip to be tensioned can be passed over a sinuous path around the rollers of a first set in frictional engagement with opposite surface arcs of said rollers, and then in similar fashion around the rollers of the other set. The rollers of one set, the one situated foremost along the direction of strip travel, are driven to feed the strip in that direction, while the rollers of the other, rearmost, set are driven in corresponding directions but at slightly lower velocities, or are braked, so as to impose a retarding force on the strip. In this manner the strip can be placed under substantial elastic tension in the region between the two sets of rollers.

In any strip-tensioning process, the important factor generally is the degree of elongation imparted to the strip rather than the tension force developed therein. It is the degree of elongation percent, rather than the tension, that is directly related to the basic mechanical characteristic of the strip material, including elastic limit and tensile yield point. It is, consequently, important that during a strip tensioning process means be available for accuracy controlling the actual degree of elongation of the strip. Strip-tensioning machines of the prior art have been deficient in this respect. As will be later shown in detail, su h conventional machines are so constructed that they must be operated to determine a certain value of tension, not elongation, in the sheet, or alternatively, it operated to impose a prescribed degree of elongation, they inevitably result in considerable slippage between the strip and the roller surfaces, causing damage to the surface condition of the sheet to a degree that is intolerable in many applications.

Objects of the present invention include the provision of improved sheetand strip-tensioning apparatus and improved drive and control systems therefor, possessing some or all of the following advantages:

The actual elongation in the strip imparted during the tensioning process is controllable to within close tolerances, in a simple and reliable manner.

Strip elongation can be maintained at any accurately prescribed value over a broad range without subjecting the strip to substantially any slippage against the roller surfaces.

The full capacity of the power plant is at all times utilized for maximum efiiciency and economy of the process.

The process is readily controllable through manual and/ or automatic means in order to vary the elongation and tension imparted to the strip while retaining optimal slipfree operation.

The drive system is simple and economical, requiring only a single prime mover to power all the rollers of both sets, and the entire system is reversible.

Other objects and advantages will appear. An exemplary embodiment of the invention will now be described for purposes of illustration but not of limitation with referrence to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic view in elevation illustrating the principel of a strip-tensioning process;

FIG. 2 is a simplified plan view showing an improved strip-tensioning apparatus according to the invention;

FIG. 3 diagrammatically shows a set of rollers of the apparatus and serves to indicate certain quantities involved in the determination of the torque settings to be used in the slip couplings employed in the invention;

FIG. 4 is a circuit diagram of a control circuit usable in controlling the apparatus of the invention; and

FIG. 5 is a diagrammatic view, partly in plan and partly in circuit schematic form, illustrating one form of automatic control usable in the apparatus of the invention.

In the diagrammatic view of FIG. 1 the general operating principle of any strip-tensioning apparatus is illustrated. Such apparatus basically includes two spaced sets of rollers a a and b b so disposed that a strip 1 can be fed over a sinuous path in frictional engagement with mutually opposed surface portions of successive rollers in each set. Assuming the direction of strip travel is to be leftward as indicated by arrows, then the rollers of the foremost group b b are all rotated to impart this direction of feed to the strip. It will be clear that for this purpose the upper rollers b b and 11., should be rotated counterclockwise and the lower rollers b and [2 clockwise.

The rollers of the rearmost group a -a are operated to impose a retarding force to the strip 1. For this purpose, generally speaking, the rollers a a may be driven in the same directions as the corresponding rollers in the set b b but at slightly slower speeds to impart the desired retarding force, or said rollers ti -a may have braking torques applied thereto with generally similar results.

Under these conditions, it will be evident that the strip 1 will be subjected to tension and consequent elongation in the straight lap of its path of travel between rollers a and b Any desired strip-working machine may be interposed in this section, such as a rolling mill, an alternate bending device, or any other machine serving to work the strip while in its tensioned and elongated condition.

In the past, two broad classes of power drive systems have been available for powering the rollers of such strip-tensioning apparatus. In a first class, the rollers in each of the two sets il -L1 and b b may be geared together for rotation at corresponding angular speeds, and the two sets may be driven from a common motor or separate motors at the requisite differential speeds, with the group b rollers being driven in the same directions as but slightly slower than the group a rollers to impart the desired retarding force to the strip.

Such systems are advantageously simple, and they have a further important advantage in that they make it possible accurately and reliably to control the actual degree of elongation sustained by the strip between the two sets of driving and retarding rollers. The elongation is proportional to the speed differential between the two sets of rollers, and since the rollers are positively driven the speed difference is well determined and accurately controllable. However, such a drive system has had a very serious drawback in that slippage necessarily occurs between the strip and at least some of the rollers in each set.

The reason for this slippage is that the tension present in the strip is not uniform throughout the apparatus, but varies from a minimum at a point ahead of the foremost retarding roller a to a maximum between the output retarding roller (1 and input driving roller b and then back to a minimum value beyond the output roller b of the driving set. The tension increases in increments as the strip moves past each of the retarding rollers a, and decreases again in increments as the strip moves past each of the driving rollers b. Due to these incremental variations in strip tension, as imparted by each successive roller, it is evident that the strip must slip relative to the roller surface by the amount required to take up the difference in tension across the roller. Such slippage seriously damages the surface condition of the strip.

In an attempt to overcome this difficulty, a minor variation of the conventional drive system just described has involved imparting incrementally varying diameters to the successive rollers in each set, the diameters being increased from a to 6 and then decreased from 12 to b so as to cause corresponding incremental variations in the peripheral velocity of the rollers for taking up the aforementioned incremental variations in tension and thereby prevent slippage. Such a known arrangement, however, is capable at best of preventing slippage for one specific set of operating conditions, i.e. for one type of strip material (which determines the friction coefficient) one size of strip (determining the area of frictional contact), and one type of processing applied to the tensioned strip (determining the maximum tension of the strip). The arrangement therefore does not really solve the stated problem.

The other class of conventional power drive system referred to above has consisted in connecting each of the driving rollers b b to an individual drive motor, and each of the retarding rollers (1 to an individual braking generator or equivalent braking device. This of course makes it possible to proportion the driving and retarding torques applied to the individual rollers in such a way as to eliminate slippage completely. However, another serious difficulty is introduced. Since in such a system it is the torque, rather than the velocity, of each roller that is positively determined by the system, the apparatus when thus driven will operate to impart a determined tension to the strip rather than a determined elongation. In view of the practicably unavoidable variations in the thickness and other characteristics of the strip material, it then becomes difficult or impossible to impart the precise desired value of elongation to the strip, which elongation values are of course in all cases very small. As stated above, the important factor to be considered when working a sheet or strip under tension, is the precise value of its elongation.

The invention completely eliminates the above deficiencies of prior art strip-tensioning apparatus by providing an improved drive and control system for the rollers, as will now be described with reference to FIG. 2.

This figure shows in plan view the set of retarding rollers (l -a and the set of driving rollers b b Mounted on the shafts c of the retarding rollers a -a respectively in a manner later described, are meshing gears al -d and mounted on the shafts of the driving rollers 12 -12 are meshing gears e -e As here shown all the gears are substantially identical. Preferably however gear d has a pitch diameter slightly smaller than that of gears d d and gear e has a pitch diameter slightly larger than that of gears b -b As a result, it will be noted that roller a imparts substantially no additional increment of tension to the strip and roller [1 imparts substantially no decrement of tension.

The input gear c of the driving roller set is driven through bevel gearing fi-g from the output shaft of a motor h. The motor output shaft is connected with the input gear of a differential gearing i, shown as a conventional bevel-gear epicyclic train, and the output of this differential, by way of a further bevel gearing g f drives the gear d associated with the output roller of the retarding set.

To adjust the velocity differential between the input and output of the differential 1', means are provided for controlling the rate of rotation of the spider of the differential, and as shown a worm gear k secured on the spider meshes with a worm j, which may be driven from any suitable means such as conventional speed variator .not shown.

In the drive shaft 0 of each of the rollers of both sets other than the output retarding roller a and input driving roller b a torque-limiting coupling device In is interposed. The devices in may be any suitable type of torque limiter or slip clutch capable of automatic disengagement when the torque through it exceeds a prescribed, adjustable, value. Preferably slip couplings m are of the powdermagnetic type disclosed in French Patents 973,367 and 988,971, wherein the limiting torque is substantially proportional to the energizing current applied to a winding of the coupling.

In the operation of this apparatus, it will be obvious that with the motor h revolving in an appropriate direction (in the present instance clockwise as looking leftward from the outer end of the motor shaft), all of the rollers of the driving set b b will be rotated through gearing g -f in the requisite directions to feed the strip 1 leftward as indicated with reference to FIG. 1. If differential spider i is held stationary then it can easily be seen that the rollers of the retarding set a a are also driven in the same directions as the corresponding driving rollers (l -(l and at the same speeds as they.

If now the differential spider i is rotated in a suitable direction at a slow rate by way of its control input j, then the forward angular velocity of the retarding rollers a a will be decreased by a corresponding small amount, and said rollers will exert the desired retarding force upon the strip. It may be noted in this connection sheet the disclosed embodiment is reversible. In that strips can be fed there-through in either direction, and either of the two sets of rollers can be made to act as the driving set, or as the retarding set, merely by reversing the sense of rotation of the differential input j.

The elongation undergone by the strip in the straight lap between rollers a and [1 is proportional to the difference between the peripheral velocities of said two rollers. Hence, any desired degree of elongation can be accurately imparted to the strip by suitably controlling the angular velocity imparted to differential spider i.

At the same time, the system makes it possible to impart the desired elongation to the strip without subjecting the strip to relative slippage over any of the rollers of either set, ti -a or [l -b For this purpose, the slip clutches m are preset so that each clutch will disengage for a particular, determinable value of the torque transmitted through it.

It will be realized that as earlier indicated the tension present in the strip 1 at different points of its path through the apparatus is not uniform. This tension is at a minimum, say t ahead of the input roller a of the retarding set, then increases in increments as the strip moves past each successive retarding roller, from t to t (across roller al then from t to 1 (across roller a and so on up to a maximum value t just 'beyond the roller a No additional tension is imparted across the output roller a This maximum tension 1 is maintained in the straight lap of the strips path and across the input roller b of the driving set. Thereafter the tension again decreases in increments, from L, to t;, (across roller b and so on until it is restored to a value which generally is substantially the initial value t beyond the output driving roller 11 In view of these incremental variations in strip tension along its path, it is apparent that if the rollers in each group were positively driven through their positively intermeshing gears, various amounts of slippage would inevitably have to occur between the strip and the various rollers of each set in order to take up the differences in tension. The need for strip slippage is avoided through the provision of the slip couplings m of the invention, each clutch yielding as required to take up the difference in strip tension produced across the associated roller.

In accordance with a feature of the invention, the torque values for which the various slip couplings m are set to yield, are predetermined in each case so as to result in the minimum amount of slippage required to take up the difference in tension, and thereby utilize the drive capacity of motor h to a maximum degree.

For this purpose, the said preset yield torque of each slip coupling m is made somewhat less, by a safety coefiicient somewhat less than unity, than the theoretical value of the torque required to be applied to the particular roller under consideration in order to generate the corresponding incremental variation in the tension of the strip as the strip moves past said roller. This may be clarified as follows.

Considering FIG. 3, the five rollers I to V there shown may be considered as constituting, for example, the retarding rollers a a If the initial tension of the strip ahead of the input roller is t and designating by t t t t the successive tension values in the strip as measured immediately beyond the rollers :1 a a in, then the theoretical values of the retarding torques which the rollers would have to apply in order to produce the incremental tension variations are In these expressions C C C C are the torques applied by the retarding rollers and R is the common roller radius.

From the mechanics of friction, it is known that each of the tension values t t t I is related to the preceding tension value by the following equations where f is the friction coefiicient of the strip on the roller surface, the alphas are the winding angles of the strip around the rollers (see FIG. 3), and e is the base of natural logarithms.

From the above Equations 1 and 2, and introducing the above-mentioned safety coefficient 1, the following set of expressions can be written for the yield torques to be preset in the respective slip couplings of each set:

It is to be noted that the initial tension t can, if desired, be expressed in terms of the final tension L; by applying the relations (2).

Knowing the geometry of the system and the characteristic friction coetficient of the strip material being processed, the above torque values C C C C can easily be calculated in each particular instance, and the slip couplings of each roller set a and b can then be preset in accordance with the calculated values to provide optimal operation, wherein: (a) a prescribed degree of elongation can be accurately imparted to the strip by controlling the rate of rotation of the differential spider i, (b) the strip will be free of any damaging slippage during its contact with any of the rollers, and (c) the power input of the system is utilized with maximum efiiciency.

As earlier noted, conveniently the slip couplings used are of the type wherein the yield torque is proportional to the energizing current applied to the coupling. In such cases all the slip couplings of each set are advantageously controlled through a common current control circuit such as the one shown in FIG. 4. In this

circuit

13, 14, 15, 16 represent the energizing windings of the four slip couplings m, connected in series with related variable resistors or potentiometers 17, 18, 19, 20. The four series combinations are connected in parallel across a pair of energizing lines connected by way of a general adjustment potentiometer 12 with a constant current source 11. It will be evident that with this circuit arrangement the resistors 1720 can be individually adjusted in accordance with the torque values as computed from Equations 3, whereby the desired operation will be obtained. According to a further aspect of the invention, means are provided for automatically varying the values of the energizing current for the slip couplings m of each set in accordance with the tension applied to the strip, while maintaining said current values at all times proportional to the optimal yield torque values as determined by Equations 3.

The usefulness of this aspect of the invention arises from the fact that the effective final tension of the strip in the section thereof between the retarding rollers a and driving rollers b may vary, as when said strip is for example subjected to rolling bending or other operations in its said intermediate section. The precise value of said final tension (t and hence that of the initial tension (t may be difficult to determine, and may vary during a given process. The embodiment of the invention now to be described maintains the correct values for the yield torques of the slip couplings, as defined above, regardless of such variations in tension.

For this purpose, in the embodiment now to be described with reference to FIG. 5, the torque applied to the rigidly mounted roller of either (or each) set, i.e. the output roller a of the retarding set or/ and the input roller b of the driving set, is measured directly on the roller shaft, as by means of a strain-gauge or other suitable torque-measuring device. The resulting torque signal which is a measure of the final tension present in the strip beyond roller 12;, or ahead of roller b is applied as a control signal to vary the energizing currents to the slip couplings, without altering the proportionality relationships therebetween.

In the specific example of such an arrangement shown in FIG. 5, the left-hand shaft 0 represents either of the rigidly coupled shafts in FIG. 2, e.g. the shaft carrying the output retarding roller a A torque-measuring device is illustrated as an assembly of four strain-gauges n bonded to a surface of the shaft between the roller and drive gear, and arranged in a balanced bridge circuit having its one (or input) diagonal connected by way of slip-rings O with a voltage source shown as including a DC source u and potentiometer p. The other (output) diagonal of the strain-gauge bridge circuit is connected to sliprings 0 for providing an output voltage signal proportional to the torsional strain of the shaft as sensed by the strain gauges.

The output signal is applied to a first differential amplifier 11 which has one of its inputs connected to one of the sliprings 0 directly, and its other input connected to the other slipring 0 by way of a voltage source a" and potentiometer p", for conventional balancing purposes.

Connected with the output of amplifier n are four potentiometers in parallel, p 7 1 2 only 2 being shown in the drawing. These four potentiometers are respectively associated with the energizing windings of the four slip couplings In.

One of said slip couplings is shown at m in FIG. 5 mounted on its related shaft (cg. one of shafts u n, in FIG. 2), and only the connection of this slip coupling with its potentiometer will be described, it being understood that similar circuits are provided in respect to the other three slip couplings and related otentiometers.

Potentiometer 17 has its resistance terminal remote from the terminal connected to amplifier n grounded, and has its adjustable tap connected to one input of a further difierential amplifier q The output of amplifier q is connected to one input of a suitable firing circuit 1, having its other input grounded. The firing circuit 1 has a pair of outputs connected with the control electrodes of respective controlled rectifier diodes r. The diodes r have terminals of similar denomination connected to the ends of the secondary winding of a supply transformer, whose primary is connected across an A-C supply. The other terminals of controlled diodes r are connected in common to a slipring O, which is connected with one end of the energizing winding, not shown, of slip coupling m. The other end of said energizing winding is connected through another slipring O to ground.

A midtap of the secondary of the supply transformer is connected through a shunt resistor s to ground, and is also connected to the second input of differential amplifier q to provide a stabilizing feedback connection.

In the operation of this circuit, a voltage signal from the strain gauge device, representative of the torque of the rigid shaft of roller (1 and hence the final tension in the strip, is applied, after amplification in 12 to all four potentiometers p 12 11 p, in parallel. A portion of this voltage signal, as determined by the setting of each said potentiometer, is applied through amplifier 1 to firing circuit t. The firing circuit operates to control the rectifier diodes in proportion with the voltage applied to its input, and the rectifiers apply unidirectional current of accurately regulated intensity from the supply transformer to the control winding of slip coupling in.

It will be understood that the circuit just described is but one convenient means of applying precisely regulated current to all four slip clutches m, proportional to the torque strain sensed in the shaft of the rigid roller a or b while maintaining at all times between the currents applied to the respective slip clutches the accurately predetermined relations given by Equations 3 above. These relations as will be understood, are predetermined by the settings of the potentiometers p 2 p and 12 The strip tensioning apparatus of the invention, as herein disclosed, has many important advantages over similar apparatus equipped with drive means of the prior art. Accurately controlled elongations can be imparted to strips with a degree of precision which was not heretofore achievable without at the same time subjecting the strips to objectionable slippage and surface shear. Controlling the roller drive so as to maintain strip elongation, rather than strip tension, constant, as made possible by the invention, makes it feasible and safe to planish metal sheets by subjecting them to elongations just short of the yield point of the metal, in cases where the elastic limit and yield point are quite close to each other, as in certain light alloys. Accurate control of the elongation is also important in skin-pass operations since the cold working involved in such processes depends directly on the amount of elongation rather than tension imparted.

Various modifications may be introduced into the embodiment shown and described without exceeding the scope of the invention. Thus, while the differential gearing shown provides a preferred means for imparting the desired differential angular velocities to the positively driven rollers of the respective sets, other positive drive means capable of driving said rollers at the desired speeds may be used. Also, the yieldingly driven rollers, rather than all being geared with one another and with the positively driven rollers, may be connected with the source of mechanical power through other forms of drive transmission, provided these include the yielding connections or slip-couplings which form an essential feature of this invention.

While it is essential according to the invention that there is a roller in each set which is positively driven, in order to produce an accurately determinable elongation in the strip corresponding to the difference in the drive velocities of said positively driven rollers, it is not essential that said positively driven rollers constitute the output roller of the retarding set and the input roller of the driving set.

What is claimed is:

1. Strip tensioning apparatus comprising:

two sets of rotatable rollers arranged to have a strip fed over a sinuous path in frictional engagement with the roller surface of first one then the other set;

positive drive means connected for rotating a roller in each set at accurately determinable different speeds so as to feed said strip past said sets while imposing a prescribed elongation to the strip as determined by the difference in said speeds; and

other drive means connected for rotating the remaining rollers said other drive means including yielding connections, whereby said remaining rollers will participate in feeding and tensioning the strip in a Substantially slip-free manner.

2. Strip tensioning apparatus comprising:

two sets of rotatable rollers arranged to have a strip fed over a sinuous path in frictional engagement with the rollers of first one then the other set; a source of mechanical power; a positive drive connection from the power source to a roller of one of the sets;

differential gearing having an input connected to be positively driven from the power source and having an output connected for positively driving a roller of the other set, and having another input rotatable to impart a selectable speed differential to the speeds of said positively driven rollers; and

drive means connected for rotating the remaining rollers from the power source, and including yielding connections whereby said remaining rollers will participate in feeding and tensioning the strip in a substantially slip-free manner.

3. The apparatus defined in claim 2, including a gear fixedly connected with each of said positively-driven rollers, and further gears connected by way of said yielding connections with each of the remaining rollers, said further gears being in meshing relationship with one another and with the respectively associated first-mentioned gears.

4. Strip tensioning apparatus comprising:

two sets of rotatable rollers arranged to have a strip fed over a sinuous path in frictional engagement with the rollers of first one then the other set;

a source of mechanical power;

positive drive means connected to the power source for rotating a roller in each set at determinable different speeds so as to feed the strip past said sets while imposing a prescribed elongation to the strip as determined by the difference in said speeds; other drive means connected to the power source for rotating the remaining rollers of both sets; and

slip coupling means interposed in said other drive means connected to each said remaining roller, including means for individually setting the maximum value of transmitted torque in each of said slip coupling means.

5. The apparatus defined in claim 4, including means for simultaneously varying said maximum transmitted 9 torque values in all of said slip coupling means while maintaining said values proportional to preset quantities. 6. The apparatus defined in claim 4, including means sensing the tension in a strip, means connected with the 10 8. The apparatus defined in claim 1, wherein said positively driven rollers comprise an output roller of said first set and an input roller of said second set.

9. The apparatus defined in claim 1, wherein each of sensing means and with each of said slip coupling means 5 said positively driven rollers is slightly smaller in difor simultaneously varying said maximum transmitted torque value in all of said slip coupling means in proportion to the sensed strip tension, and means for maintaining the said values proportional to preset quantities.

7. The apparatus defined in claim 4, including means sensing the torque developed in one of said positivelydriven rollers, means connected with said sensing means and with each of the slip coupling means for simultaneously varying said maximum transmitted torque value in all of said slip coupling means in proportion to the sensed torque, and means for maintaining said values proportional to preset quantities.

ameter than the diameter of the remaining rollers of the related set.

References Cited UNITED STATES PATENTS 1,943,005 1/1934 Coryell 72205 2,287,380 6/1942 Klein et a1. 72-205 2,526,296 10/1950 Stone 72205 15 RICHARD J. HERBST, Primary Examiner.

R. D. GREFE, Assistant Examiner.