5 The present invention refers in general to a dyeing plant of threads and, in particular, to an oxidation apparatus applicable to continuous dyeing plants, in plane and with indigo dye, of warp threads for denim fabrics. The oxidation apparatus is

10 configured to oxidise the threads passed through the dyeing plant after each single dyeing and with variable and recoverable capacity.

Denim is the most produced fabric in the world, since it is used to make jeans. As known, indeed, jeans

15 are trousers of practically universal use and availability .

Denim is produced by weaving a chain of warp threads, already dyed with indigo, with an unbleached weft thread. Both the threads are made of cotton. The

20 warp chains are dyed, continuously, with indigo. Indigo is a dye having very special characteristics, which requires a special method of application. This dye, having relatively small molecules, has very little affinity with cellulose fibre, such as cotton, and for

25 the application thereof it needs not only to be reduced in alkaline solution, but also to be subjected to a plurality of impregnations separated by dehydration and subsequent oxidation with air. In practice, a medium or dark colour tone is obtained only by subjecting the

30 thread to a first dye in a suitable tank, immediately followed by many overdyes in successive tanks.

The plants that carry out this particular dyeing should be built respecting certain base parameters, relative to the immersion and oxidation times of the thread. This is to allow the thread to have optimal absorption of the dyeing bath and, after squeezing, a complete oxidation before entering the next tank, so as to be able to "rise", i.e. darken its colour tone. In practice, however, every manufacturer of dyeing plants applies different parameters from its competitors and therefore these parameters are highly variable. Moreover, very often users require specific parameters to adapt the obtainable results to their particular requirements .

In a generic dyeing plant the number of dyeing tanks varies from 6 to 8, the immersion time of the thread in the dyeing bath varies from about 8 seconds to about 20 seconds, whereas the time for the oxidation of the thread itself, after squeezing, varies from about 60 seconds to about 80 seconds. This means that the thread must remain exposed to air for about 60-80 seconds before being reimmersed in the next dyeing tank. This time of exposure to air is repeated for all of the tanks of the dyeing plant.

The average dyeing speed can be considered variable from 25 to 40 metres per minute. Consequently, for every dyeing tank, the amount of thread immersed in the respective dyeing bath is on average equal to about 4-11 metres, whereas the amount of thread exposed to air between one dyeing tank and the next ranges from about 30 to 40 metres.

Thus, taking a standard plant with eight dyeing tanks as an example, the thread passed through just the dyeing tanks and the relative groups of oxidation cylinders can reach a substantial length. The maximum length of the thread, in this case, is equal to 408 metres based on the following formula: [(11 metres x 8 tanks = 88 metres) + (40 metres x 8 oxidation apparatuses = 320 metres) ] . This amount of thread, with the addition of smaller amounts due to the passing of the other parts of the dyeing plant (pre-treatment and final washing tanks of the thread, sizer to which the dyeing plant is connected, etc.), in reality reaches a total of about 500/600 metres, which contributes to making the plant itself more difficult to control.

A big drawback encountered in conventional dyeing plants is caused by the large amount of thread that is lost at each change of batch. In this operating condition, indeed, the entire aforementioned amount of thread, which constitutes the tail end of the batch of thread, the dyeing of which is finished and which remains in the plant after it has stopped, must be considered lost, since it is not evenly dyed. Similarly, the same amount of thread that constitutes the start of the new bath and that, connected to the tail end thread, replaces it in passing the dyeing plant (carried out at low speed for technical and safety requirements), is also not evenly dyed and must thus be eliminated.

It should be specified that a reduction of the aforementioned amount of thread is already possible in very few plants that have the new dyeing technology in an inert environment, which allows the reduction of the number of dyeing tanks. This dyeing technology in an inert environment is described in documents EP 1771617 Bl and EP 1971713 Bl to the same Applicant. A reduction of the aforementioned amount of thread is also possible in the few plants that have oxidation intensifiers, like for example the one described in document EP 0533286 Bl again to the same Applicant.

However, industrial history tells of the difficulties and reluctance following the introduction of new technologies. Dyeing plants under nitrogen, therefore, by conformity, uniformity of production, technological inertia, particular market conditions, fashion, etc., have also only been manufactured in a few units.

Oxidation intensifiers, on the other hand, have had much greater success, but the number of dyeing plants that are equipped with them represents a negligible part of all operating dyeing plants and also newly produced ones, which mostly still adopt the classic groups of air cylinders as oxidation apparatuses. Oxidation intensifiers have allowed a reduction, not significant but partial, of the amount of thread exposed to air. This reduction of the amount of thread exposed to air is in any case obtained with the application of mechanical apparatuses that require not only a certain economic investment, but also a continuous energy cost and constant cleaning operations of the filters, as well as the necessary maintenance.

Further prior art documents include document US 6355073 Bl, which however does not illustrate an oxidation apparatus with variable and recoverable capacity, but rather a module for continuously dyeing warp chains with indigo and other dyes, commercially called "Reactor". Document JP 3706689 B2 illustrates a device for the continuous application of a product on bands of fabric or threads. In practice, a pump feeds the product to a collector, which deposits such a product on a deflector which, in an alternate manner, transfers such a product on the bands. Document DE 4342313 Al illustrates an indigo dyeing module in an inert environment. Document CN 103938387 A finally concerns a conventional continuous indigo dyeing machine, in cords, with a vaporizer placed at the exit of the dyeing section.

In light of the above, there is clearly a need to be able to drastically reduce the amount of thread exposed to air in oxidation apparatuses, which is the cause of the relative deterioration both during the end of batch operations, i.e. before the stopping of the dyeing plant necessary for the introduction of the new batch of thread, and during the starting operations of the new batch of thread, i.e. when the plant is started up at low speed. This possibility, in the above operations, would lead to a substantial economic saving, prudently quantifiable in the recovery of at least 400/500 metres of warp chain, and moreover it would also give a worthwhile contribution to environmental protection and sustainability .

The purpose of the present invention is therefore to make a dyeing plant of threads, in particular an oxidation apparatus applicable to continuous indigo dyeing plants, which is capable of overcoming the aforementioned drawbacks of the prior art in an extremely simple, cost-effective and particularly rational and functional manner.

In detail, a purpose of the present invention is to make an oxidation apparatus for continuous indigo dyeing plants that makes it possible to drastically reduce, both at the end of each batch of thread, i.e. before the stopping of the plant for the introduction of the new batch of thread, and at the start of a new batch of thread, the amount of thread exposed to oxidation in air.

In this way there would be the advantage, secondary but not of little importance, of having the possibility, without having to change the pass as standard oxidation apparatuses require, of varying the amount of thread chain exposed to air by oxidation, bringing it to the minimum necessary according to the requirements of the dyeing process, the count of the thread, the work speed, etc., to facilitate the control of the plant. A further advantage consists of the possibility of using the oxidation apparatus, suitably complete with the necessary actuator devices, to carry out the adjustment function of the synchrony between one dyeing group and the next, replacing the classic dandy roll, to keep the tension of the thread constant.

This and other purposes according to the present invention are accomplished by making a dyeing plant of threads, in particular an oxidation apparatus applicable to continuous indigo dyeing plants, as outlined in claim 1.

Further characteristics of the invention are highlighted by the dependent claims, which are an integral part of the present description.

The characteristics and advantages of an oxidation apparatus for continuous indigo dyeing plants according to the present invention will become clearer from the following description, given as an example and not for limiting purposes, referring to the attached schematic drawings, in which:

figure 1 is a side elevational view of a generic continuous indigo dyeing plant, provided with a plurality of dyeing/squeezing groups, on which it is possible to mount an oxidation apparatus having variable and recoverable capacity according to the present invention;

figure 2 is a schematic view of a part of a generic dyeing plant, provided with three dyeing/squeezing groups, between which an oxidation apparatus having fixed capacity according to the prior art is arranged;

figure 3 is a schematic view of a part of a generic dyeing plant, provided with three dyeing/squeezing groups, between which an oxidation apparatus having variable and recoverable capacity according to the present invention is arranged, shown in the position of maximum capacity;

figure 4 is a schematic view of a part of a generic dyeing plant, provided with three dyeing/squeezing groups, between which an oxidation apparatus having variable and recoverable capacity according to the present invention is arranged, shown in the position of minimum capacity;

figure 5 is a perspective view of a particular embodiment of the oxidation apparatus having variable and recoverable capacity according to the present invention, shown in the position of maximum capacity; and

figure 6 is a perspective view of the oxidation apparatus having variable and recoverable capacity of figure 5, shown in the position of minimum capacity.

With reference in particular to figure 1, a generic continuous dyeing plant for threads is shown, wholly indicated with reference numeral 10. In particular, the plant 10 is a plant configured to operate according to the open width dyeing system.

The plant 10 comprises a plurality of dyeing/squeezing groups 12 arranged in line, each of which is provided with a respective impregnation or dyeing tank 14A, 14B, 14C in which a warp thread 100, which advances from left to right with reference to the representation of the plant of figure 1, is immersed in a dyeing bath containing a dyeing substance. The dyeing bath can, for example, consist of an alkaline solution of indigo dye.

As shown in figures 2-4, the warp thread 100 arrives in each tank 14A, 14B, 14C passing over a respective guide roller 16 and then immerses in the tank 14A, 14B, 14C itself winding onto a plurality of return rollers 18. At the exit of each tank 14A, 14B, 14C the warp thread 100 undergoes a squeezing passing between a pair of squeezing cylinders 40 that constitute the so-called squeezing padder.

The oxidation of the warp thread 100 is carried out in the area of the dyeing plant 10 arranged between the pair of squeezing cylinders 40 at the exit of a first tank 14A and the guide roller 16 associated with the next tank 14B. The oxidation of the warp thread 100 is thus carried out by a suitable oxidation apparatus 20 that comprises a plurality of return rollers 22A, 22B configured to arrange the warp thread 100, which is in continuous movement, on a plurality of vertical planes parallel to one another (see figures 2-4), so as to increase the surface thereof exposed to air.

Conventional oxidation apparatuses 20, for example like the one shown in figure 2, consist of a support frame 24 on which the return rollers 22A, 22B are rotatably mounted. The support frame 24 is normally placed downstream of the dyeing/squeezing groups 12 and consists of a laterally, downwardly and upwardly open structure to allow the oxidation of the dyeing substance by means of the contact of the dyed warp thread 100 with the maximum possible amount of air. The support frame 24 thus comprises at least one upper strut 26 and at least one lower strut 28 on which a plurality of upper return rollers 22A and a plurality of lower return rollers 22B are respectively mounted. The distance between the upper strut 26 and the lower strut 28 and, therefore, between the upper return rollers 22A and the lower return rollers 22B is fixed. Consequently, the conventional oxidation apparatus 20 has a fixed capacity or, in other words, the amount of thread 100 exposed to air between two contiguous tanks 14A, 14B, 14C is constant.

The oxidation apparatus 20 according to the present invention, schematically illustrated in figures 3 and 4, also comprises a support frame 24 placed downstream of the dyeing/squeezing groups 12 and consisting of a laterally, downwardly and upwardly open structure to allow the oxidation of the dyeing substance by means of the contact of the dyed warp thread 100 with the maximum possible amount of air. The support frame 24 again consists of at least one upper strut 26 and at least one lower strut 28. On the upper strut 26 a plurality of upper return rollers 22A are mounted, whereas at least one part of the lower return rollers 22B is rotatably mounted on at least one respective movable support device 30A, 30B, 30C. In detail, each support device 30A, 30B, 30C is movable in the vertical direction between a first operating position (figure 3), in which such a movable support device 30A, 30B, 30C is arranged close to the lower strut 28 of the support frame 24 to keep the lower return rollers 22B at a maximum predefined distance from the corresponding upper return rollers 22A, and a second operating position (figure 4), in which such a movable support device 30A, 30B, 30C is arranged close to the upper strut 26 of the support frame 24 to keep the lower return rollers 22B at a minimum predefined distance from the corresponding upper return rollers 22A.

In other words, the oxidation apparatus 20 according to the present invention is provided with a plurality of movable support devices 30A, 30B, 30C that operate from movable platforms for at least one part of the lower return rollers 22B. Each movable platform 30A, 30B, 30C, suitably guided and tensioned, can rise and fall inside the support frame 24 of the oxidation apparatus 20, thus making it possible to vary the capacity of use of the oxidation apparatus 20 itself and drastically reduce, in the change of batch step of the warp thread 100 (stopping/restarting of the dyeing plant 10), the amount of thread 100 contained in the dyeing plant 10 to avoided discarding it.

With reference to the particular embodiment of figures 5 and 6, each movable support device 30A, 30B, 30C of the oxidation apparatus 20 according to the present invention can be moved vertically along a plurality of linear guide uprights 32, integral at the bottom to a pair of lower struts 28, parallel to one another, of the support frame 24 and integral at the top to a pair of upper struts 26, parallel to one another and to the lower struts 28, of such a support frame 24. In other words, the upper struts 26 and the lower struts 28 of the support frame 24, together with the linear guide uprights 32 of each movable support device 30A, 30B, 30C, constitute the perimeter of a parallelepiped-shaped cage that supports the upper return rollers 22A and the lower return rollers 22B.

Each movable support device 30A, 30B, 30C of the oxidation apparatus 20 can also be provided with upper struts 26 separate from the corresponding upper struts 26 of the movable support devices 30A, 30B, 30C contiguous to it, so as to make the entire oxidation apparatus 20 modular. In other words, the linear guide uprights 32 of each movable support device 30A, 30B, 30C can be made integral to the lower struts 28 by means of reversible fixing means 46, like for example bolts .

Each movable support device 30A, 30B, 30C of the oxidation apparatus 20 can be provided with at least one movement means 34, operatively associated with the support frame 24 of the oxidation apparatus 20 and with the electronic control unit 50 of the dyeing plant 10. Alternatively, a single movement means 34 or a plurality of movement means 34 can be provided, operatively associated on one side with the support frame 24 of the oxidation apparatus 20 and on the other side, by means of corresponding movement transmission means (not shown but consisting for example of belts, chains or transmission shafts), with a plurality of movable support devices 30A, 30B, 30C that are separate from one another.

Each movement means 34 can without distinction be of the pneumatic, hydraulic, electric or mechanical type, or it can consist of a combination of such systems. In the embodiment shown in figures 5 and 6, the movement means 34 is of the pneumatic type and consists of a pneumatic actuator cylinder 36, integral to a fixed portion of the support frame 24, the stem 38 of which is integral to a respective movable support device 30A, 30B, 30C by means of the interposition of a guide rod 42.

The oxidation apparatus 20 according to the present invention makes it possible to vary the amount of thread 100 exposed to air for oxidation with a process that has the following steps. During the indigo dyeing process, all of the movable support devices 30A, 30B, 30C of the dyeing plant 10 are normally placed at the bottom, in other words in their first operating position of figure 3, on the respective support frame 24. The warp thread 100, in a per se known way, is tensioned according to requirements by weights, by one or more pneumatic pistons or other. In this first operating position of the movable support devices 30A, 30B, 30C there is the maximum amount of thread 100 exposed to air for oxidation.

By means of a position transducer 48 it is also possible to place one or more movable support devices 30A, 30B, 30C at a predefined intermediate height between the lower struts 28 and the upper struts 26 of the support frame 24. This intermediate height can be set and/or modified automatically and/or manually to increase or reduce the amount of thread 100 passed through the dyeing plant 10, adapting it to possible production requirements.

At the end of each batch of thread intended for dyeing, the warp thread 100 that feeds the dyeing plant 10 is practically all passed through, with the exception of the few metres of reserve that are necessary to tie it to that of the new batch of thread. In this operating condition all of the traction motors of the warp thread 100 from the driving calandar up to the squeezing cylinders 40 of the first dyeing tank 14A stop, leaving in operation all of the remaining motors of the part of dyeing plant 10 placed downstream of such a first dyeing tank 14A.

The stopping of all of the traction motors of the warp thread 100 that are placed upstream of the first dyeing tank 14A, as well as of the traction motors of the warp thread 100 that belong to the first dyeing tank 14A itself, forces the dyeing plant 10 to be fed with the warp thread 100 passed through the portion of oxidation apparatus 20 placed immediately downstream of the first dyeing tank 14A. Consequently, the first movable support device 30A arranged between the first dyeing tank 14A and the second dyeing tank 14B is lifted proportionally to the decrease in the amount of thread 100 passed through the aforementioned portion of oxidation apparatus 20 placed immediately downstream of the first dyeing tank 14A.

The lifting of the first movable support device 30A continues until the respective second operating position of figure 4 is reached, in other words until the maximum limit of the upper end-stroke with reference to the upper struts 26 of the support frame 24 is reached. The electronic control unit 50 of the dyeing plant 10 is operatively connected to at least one sensor 52 provided on each movable support device 30A, 30B, 30C. Consequently, once it has been identified through the sensor 52 that the maximum limit of the upper end-stroke has been reached by the first movable support device 30A, the electronic control unit 50 stops the actuation motors of the squeezing cylinders 40 of the second dyeing tank 14B.

The operations described above will be repeated for the second movable support device 30B arranged between the second dyeing tank 14B and the third dyeing tank 14C as well as, in an identical and sequential manner, for all of the next dyeing tanks. The emptying of the end portion of the oxidation apparatus 20, in other words of the last movable support device, will stop all of the remaining motors of the dyeing plant 10 still operating, i.e. those of the washing tanks 44 placed downstream of all of the dyeing/squeezing groups 12.

It has thus been seen that the oxidation apparatus

20 applicable to the continuous indigo dyeing plants according to the present invention achieves the purposes highlighted earlier. The clear advantage of being able to recover two times, and thus of being able to use, conservatively, at least 80% of the amount of thread 100 passed through the oxidation apparatus 20, which in dyeing plants equipped with conventional oxidation apparatuses is discarded, is added to with the advantage of a substantial reduction of the time necessary for the change of batch operation.

The fact that the amount of thread 100 contained in the dyeing section is reduced to the minimum, by positioning the movable platforms that constitute the movable support devices 30A, 30B, 30C of the return rollers 22A, 22B of the oxidation apparatus 20 at the maximum upper limit, drastically reduces the time needed for passing the joining knots of the two batches of thread 100 and of the combs that adjust the width thereof, during the change of batch operations, which must be carried out at reduced speed for technical and safety reasons.

Moreover, the same advantages described above and referring to the end of dyeing operations are also obtained in the subsequent starting operations of the new batch of thread 100. These operations are carried out in the opposite direction, i.e. introducing into the dyeing plant 10, at low speed, the new batch of thread 100 with all of the movable support devices 30A, 30B, 30C passed through with the minimum amount of thread 100, in other words in the second operating position of figure 4. Thereafter, the total capacity of the oxidation apparatus 20 is restored by moving the movable support devices 30A, 30B, 30C downwards in sequence, starting from that of the first dyeing tank 14A up to that of the last dyeing tank, to then proceed with the dyeing operations of the thread 100 in a conventional manner. In this case, the electronic control unit of the dyeing plant 10 is configured to identify that the maximum limit of the lower end-stroke (with reference to the lower struts 28 of the support frame 24) has been reached by the various movable support devices 30A, 30B, 30C, so as to start in sequence the actuation motors of the dyeing/squeezing groups 12.

The oxidation apparatus 20 having variable and recoverable capacity according to the present invention can be inserted in any conventional indigo dyeing plant. In the same dyeing plant 10, a variable number of movable support devices 30A, 30B, 30C can also be provided according to requirements.

The oxidation apparatus applicable to the continuous indigo dyeing plants of the present invention thus conceived can in any case undergo numerous modifications and variants, all of which are covered by the same inventive concept; moreover, all of the details can be replaced by technically equivalent elements. In practice, the materials used, as well as the shapes and sizes, can be whatever according to the technical requirements.

The scope of protection of the invention is therefore defined by the attached claims.