Background Art Equipment for unwinding a metal strip from a coil is often referred to as decoilers by persons skilled in the art. For practical reasons, the term decoiler will be used in the following description.

A known decoiler marketed by the Dutch company "Brain"has a circular plate or table which is rotat- able about a vertical axis and which supports the coil horizontally. The coil-supporting table is supported by rollers which are in frictional contact with the lower side of the rotatable table. One of the rollers is driven and two rollers are freely rotatable. The table is driven by a hydrostatic speed variator acting on the drive roller via a coupling. The three rollers are equidistant- ly spaced from each other at the peripheral portion of the rotatable table. The axes of rotation of the rollers are perpendicular to the vertical axis of rotation of the coil table, and said axes of rotation of the rollers extend radially from said vertical axis.

The metal strip is guided from the coil to a strip- guiding unit, in which the strip is held between rollers.

The strip-guiding unit is attached to the upper end of an arm which is pivotally mounted on the base structure of the decoiler. The strip is fed from the strip-guiding

unit to a forming head of the tube former by means of a drive roller arrangement before the forming head.

The arm supporting the strip-guiding unit is movable towards and away from the coil-supporting table by said pivotal movement. In order to achieve appropriate guiding and tensioning of the strip, the pivotal movement of the arm is carefully adjusted. It is also important to con- trol the feeding rate of the strip and, of course, the rotational speed of the coil-supporting table.

When the production is stopped in the tube former, for instance for cutting a finished tube, the feeding of the strip into the forming head is stopped. After a short delay, the rotation of the coil table must be stopped, otherwise the slack of the strip between the coil table and the forming head will be too large. To avoid this, the arm supporting the strip-guiding unit is moved away from the coil table as soon as the production is stopped.

This movement of the arm takes up most of the slack of the strip and keeps an appropriate tension of the strip.

When the production is resumed, the rotation of the coil table must start quickly and the arm is moved towards the coil table in order to"catch"the slack of the strip.

This known decoiler has certain disadvantages.

Since the coil often has a weight of about 3,000 kg, the load is significant, and the three rotatable rollers under the coil table very often worn, especially the drive roller. For this reason, vibrations of the table often occur which jeopardise the unwinding and the feed- ing of the strip. This problem is particularly pronounced when the decoiler has been used a long time. The drive roller wheel is connected to the speed variator via a X coupling.

When a 3,000 kg coil is put on the coil table, the load on the driving motor and associated bearings is extremely high. Every time the production is stopped and started again, the motor must take care of the accelera- tion and the retardation of the coil table. Thus, the

rotational direction of the motor is frequently switched in operation. In practice, the motors of decoilers of this type must be replaced at rather short intervals.

Partly because of these motor problems but also due to the inherent inertia of the coil-supporting means, the period of time for acceleration and retardation of the strip feeding is quite long, in practice about 6 s. As the production is stopped and started very often in ope- ration, these time delays are disadvantageous.

Thus, there is a need of a new type of decoiler.

Summary of the Invention An object of the present invention is to provide an improved apparatus or decoiler for unwinding a strip from a coil, by means of which the above-mentioned problems are solved.

A special object of the invention is that it should be possible to use the improved apparatus for the manu- facture of different products, although the main object is to improve the manufacture of helically-wound lock- seam tubing.

These and other objects, which will appear from the following description, have now been achieved by means of an apparatus having the features of appended claim 1, preferred embodiments being defined in the subclaims.

In a preferred embodiment of the invention, there is provided an apparatus for unwinding a strip from a coil and feeding the strip to an assembly for processing the strip. The apparatus has a rotatable table for supporting the coil and a drive unit for rotating the coil-support- ing table. The drive unit has a driving gear which meshes with a toothed periphery of a gear ring mounted on the table and which is driven by a motor. Further, the appa- ratus has a device for guiding and tensioning the strip between the coil-supporting table and the processing assembly. This device includes a pivotable arm having a strip-guiding unit which is movable towards and away from the coil-supporting table by pivoting of the arm, and

means for controlling the movement of the arm and thereby the movement of the strip-guiding unit in accordance with the strip-feeding rate and the rotational speed of the coil-supporting table.

According to a preferred embodiment of the inven- tion, the control means comprises a potentiometer which is mechanically connected to the arm and whose output voltage signal is proportional to the position of the arm. The output voltage signal controls the rotational speed of the coil-supporting member and thereby the feeding of the strip to the processing assembly.

It is also preferred that said potentiometer has a first end position corresponding to a first end position of the arm remotest from the coil-supporting member, and a second position corresponding to a second end position of the arm closest to the coil-supporting member. The output voltage signal of the potentiometer has values within a range limited by the end positions of the poten- tiometer.

Preferably, the control means further comprises a frequency converter for converting the output voltage signal from the potentiometer to a frequency signal which controls the rotational speed of the motor driving the rotatable coil-supporting member by the gear mesh.

The invention confers several advantages. The inven- tive decoiler is mechanically improved by the new drive arrangement. The former rolling wheels are avoided, and thanks to the gear drive at the periphery of the gear ring, a very reliable rotation of the coil-supporting member is achieved. Further, the load on the motor is lower since the gear mesh at the periphery of the gear ring provides a torque with respect to the vertical axis of rotation of the coil-supporting member.

The inventive decoiler is also improved in terms of controlling the unwinding and feeding of the strip.

Thanks to the new control means acting on the pivotable arm which supports the strip-guiding unit, the delays for

acceleration and retardation can be significantly reduc- ed. In practical tests, the acceleration time has been 1.0 s and the retardation time has been 0.8 s at standard strip-feeding rates of about 60 m/min.

Brief Description of the Drawings The invention will now be described by means of a presently preferred embodiment, reference being had to the accompanying schematic drawings which, however, are non-limiting for the invention.

Fig. 1 is a side view of a decoiler according to an embodiment of the invention.

Fig. 2 is a plan view of the decoiler.

Fig. 3 is a view III-III in Fig. 2 on a larger scale.

Fig. 4 is a view IV-IV in Fig. 2 on a larger scale, and Fig. 5 is a diagram illustrating components of con- trol means associated with the decoiler.

Detailed Description of the Preferred Embodiment Figs 1-2 show an apparatus 1 for unwinding a strip <BR> <BR> <BR> <BR> 2 from a coil 3. The strip is fed to an assembly 4 for processing the strip 2. In this example, the apparatus is a so-called decoiler 1, and the strip is a metal strip 2 which is fed to said processing assembly, which in the example is a machine 4 (tube former) for manufacturing helically-wound lock-seam tubing 5 from a forming head 6 known per se. The strip 2 is fed in the direction of the arrows, and the tube former 4 has a feeding unit 7 which in known a manner is equipped with drive rollers (not shown) for feeding the strip 2 into the forming head 6.

The strip-feeding unit 7 is driven by a motor 8.

The coil 3 is supported by a rotatable member in the shape of a circular, horizontal table 10 having a verti- cal axis of rotation C1. The annular coil 3 is placed around a central part 9 extending vertically from the coil-supporting table 10. In Fig. 2, the coil 3 is par-

tially cut away for illustrating a drive unit for rotat- ing the coil-supporting table 10.

This drive unit comprises a gear ring 11 which is non-rotatably mounted on the lower side of the table 10, see also Fig. 4. The axis of rotation of the gear ring 11 coincides with the axis of rotation Cl of the rotatable table 10. The gear ring 11 meshes with and is driven by a driving gear 12 driven by a motor 13 mounted on a base structure 14 of the decoiler 1 under the table 10. As can be seen in Fig. 4, the driving gear 12 has a vertical axis of rotation C2 which is spaced from and parallel with the axis of rotation C1 of the gear ring 11 and of the rotatable table 10. Thus, the gear mesh 15 between the driving gear 12 and the gear ring 11 is spaced from said axis of rotation C1 since the gear mesh 15 is on the periphery of the gear ring 11. Thus, the gear mesh 15 creates a torque with respect to the main axis of rota- tion Cl, which results in an improved rotation of the table 10 causing a lower load on the motor 13 of the drive unit than in known decoilers.

Thanks to this new gear arrangement 11,12, the rotatable table 10 can be driven very smoothly without vibrations and wear problems encountered in known decoilers. Especially, the table 10 can be stopped and started faster than in known decoilers in intermittent operation of the tube former 4, which is frequently stop- ped.

The decoiler 1 of the invention further comprises a device for guiding and tensioning the strip between the coil-supporting table 10 and the tube former 4 (see Fig. 1). This device includes a pivotable arm 20, which at its upper end has a strip-guiding unit 21 known per se, including guide rollers 22 between which the strip 2 is engaged. The lower end of the arm 20 is pivotably mounted on the base structure 14 by means of a bolt 23 shown in Fig. 3. For moving the arm 20 towards and away from the coil-supporting table 10, the arm 20 is pivoted

about said pivot bolt 23 as is shown by a double arrow A.

This movement is accomplished by a link mechanism 24 con- necting the lower end portion of the arm 20 with a shaft 25 of a rotational potentiometer 26 to be further de- scribed below. For damping the movements of the arm 20, there is a gas spring 27 known per se, connecting the arm 20 with the base structure 14 of the decoiler 1. Further, there is an adjustable stopper 28 for limiting the move- ment of the arm 20 in the direction away from the coil- supporting table 10.

The potentiometer 26 controls the movement of the arm 20 and thereby the movement of the strip-guiding unit 21 in accordance with the feeding rate of the feeding unit 7 of the tube former 4 as well as the rotational speed of the coil-supporting table 10. As described above, the potentiometer 26 is mechanically connected to the arm 20, which means that the output voltage signal of the potentiometer 26 is proportional to the position of the arm 20. Further, the output voltage signal of the potentiometer 26 is proportional to the rotational speed of the coil table 10.

As is schematically shown in Fig. 5, the potentio- meter 26 is of the rotational type having two end posi- tions 29 and 30 corresponding to the end positions of the arm 20. The limited rotation of the potentiometer 26 between these end positions 29,30 is preferably about 45° corresponding to a 45° angular range of movement of the arm 20. The output voltage signal of the potentio- meter 26 can vary within the range limited by the end positions 29,30 of the potentiometer 26. The output vol- tage signal from the potentiometer 26 is fed to a fre- quency converter 31 which converts the output voltage signal to a frequency signal which controls the rota- tional speed of the motor 13 which drives the rotatable coil-supporting table 10 schematically shown in Fig. 5.

The output voltage signal of the potentiometer 26 has

values within a range limited by the end positions of the arm 20.

In operation, the decoiler 1 of this embodiment functions as follows.

When the tube-forming production is started by acti- vating the feeding unit 7 feeding the strip 2 to the forming head 6, the arm 20 is moved towards the coil-sup- porting table 10 for taking up slack of the strip 2 and for maintaining an appropriate tension of the strip 2.

Then the link mechanism 24 rotates the shaft 25 of the potentiometer 26 in clockwise direction with respect to Fig. 3 (double arrow B), whereby a proportional output voltage signal is fed from the potentiometer 26 via the frequency converter 31 to the motor 13, which activates the rotation of the coil-supporting table 10 by the gear arrangement 11,12. On the other hand, when the tube- forming production is stopped, the arm 20 is moved in a direction away from the coil table 10, whereby the link mechanism 24 rotates the shaft 25 of the potentiometer 26 in counter-clockwise direction, thereby deactivating the motor 13 through a corresponding feeding of signals in accordance with the description above.

Practical tests have shown that the delay for acce- leration and retardation as described above can be sub- stantially reduced by means of the decoiler 1 of the invention. At a standard strip-feeding rate of about 60 m/min, the acceleration time is about 1.0 s and the retardation time is about 0.8 s. This is much less than in known decoilers available on the market.

A further advantage is that the load on the drive motor 13 is much lower than in known decoilers.

Preferably, the arm 20 is slidably mounted on the base structure 14, as is schematically shown in Fig. 2 (arrow D). Since the arm 20 is displaceable in a direc- tion substantially perpendicular to the feeding direc- tion of the strip 2 into the tube former 4, it is easy to

adjust the decoiler 1 in accordance with different widths of the strip 2 and different diameters of the coil 3.

Finally it should be pointed out that the invention is by no means restricted to the embodiments described above, and several modifications are feasible within the scope of the appended claims. For instance, it should be mentioned that other control means can be used for con- trolling the movement of the arm and the signals for con- trolling the feeding rates and rotational speeds used in the decoiler.