WO2020254082A1

WO2020254082A1 - Machine and method for the discontinuous dyeing of spools of yarn

Info

Publication number: WO2020254082A1
Application number: PCT/EP2020/064753
Authority: WO
Inventors: Danilo Cagnazzi
Original assignee: Danilo Cagnazzi
Priority date: 2019-06-18
Filing date: 2020-05-27
Publication date: 2020-12-24
Also published as: CN113966420A; IT201900009276A1; EP3987103A1

Abstract

A machine and a method for the discontinuous dyeing of spools of yarn, which entails, within a closed tank (1) which contains the spools (2) of yarn to be processed immersed in a treatment bath, changing the quantity of bath held inside the spools of yarn a certain number of times per minute and conveniently mixing the remaining quantity of free bath inside the closed tank (1). A first pump (8) is substantially used to change the bath inside the spools and a second pump (20) is used to mix the free bath in the closed tank (1). Furthermore, an external heat exchanger (22) is installed on the circuit of the second pump (20) and is adapted to heat and/or cool the bath.

Description

MACHINE AND METHOD FOR THE DISCONTINUOUS DYEING OF SPOOLS OF YARN

The present invention relates to a machine and a method for the discontinuous dyeing of spools of yam, where the term "spool of yam" means any mass of yam or textile fiber, including the form of flock or carded or combed ribbon, not necessarily wound around an axis, such as spools, spindles, beams, cops, clews, skeins, tops, muffs.

In the sector of machines for the discontinuous dyeing of spools of yams, it is known to maintain the spools at least partially immersed in a dyeing bath, which is made to circulate unidirectionally, i.e. from inside the yam toward the outside, or bidirectionally, i.e. alternating from outside the yam into the yarn and vice versa, inverting the flow according to preset times.

Various examples of these machines are described in US3908409.

In particular, it is known to use a closed tank which contains both the spools to be dyed, mounted on corresponding rod-like supports, and the treatment bath.

Properly defined, the spools, which are cylindrical or fmstum- shaped, are typically constituted by yarn which is wound around a cylindrical, conveniently perforated tube, and have a weight that is typically comprised between 1 kg and 3 kg.

The closed tank is connected to a reversal device for reversing the circulation of the bath and a main centrifugal pump. A heating coil can be positioned inside the closed tank, and is struck by the flow of the treatment fluid in both directions, according to the condition in which the reversal device is currently in.

The principle of operation of dyeing machines for the discontinuous dyeing of spools is based on making the treatment bath contained in the closed tank pass through the spools bidirectionally.

The treatment bath is, in particular, pushed by the main pump through adapted hydraulic circuits and is forced to pass radially through the yam that is wound on the perforated tube.

The bath can be forced through from outside the yam toward the inside or vice versa, according to the condition of the reversal device.

The main pump needs to supply a flow rate that is sufficient to make all of the bath contained in the closed tank circulate through the spools in both the directions allowed by the reversal device.

Therefore the head of the pump must be sufficient to defeat the flow resistances generated by the tubes and by the wound yam as well.

Typically, it is good practice to make the entire quantity of bath contained in the closed tank circulate through the spools three times in one minute. This in order to ensure the homogeneity of the temperature of the dyeing bath and the same concentration of color on all the surfaces of the yams.

All this quantity of bath therefore needs to pass through the conduits, which are conveniently dimensioned, through the spools, through the coil and through the bath reversal device.

The flow resistance conditions generated by the spools is a function of:

- the type of yarn (polyester, cotton, nylon etc.),

- the density with which the yarn has been wound on the tubes (greater density results in greater flow resistance),

- the fact that the yarn can shrink as a result of the treatment it is subjected to (a typical behavior of polyester), thus increasing resistance to the passage of the bath during the process.

Normally a maximum admissible differential pressure is imposed on the main centrifugal pump, for example 1.5 bar, in order to prevent the force generated by the bath in passing through the spool 5 from damaging the yam. Therefore, if the differential pressure tends to exceed the maximum permitted value, the inverter of the pump reduces the number of revolutions, so as to lower the flow rate and prevent the maximum admissible differential pressure from being exceeded. For this reason, the flow rate value of the pump is typically lower than expected, thus compromising the yield of the heat exchange and the capacity to render the bath contained in the closed tank uniform, i.e. compromising the very result of the process.

Therefore, the conventional solution described above has the following drawbacks:

- reduction of the efficiency of heat exchange (heat exchange coefficient as a function of the flow rate);

- reduction of the capacity to render the condition of the bath uniform inside the dyeing closed tank;

- reduction of the capacity to render the temperature uniform inside the closed tank;

- non-uniform distribution of the chemical products and of the dye, in particular a different concentration in the closed tank and therefore also from spool to spool and along the thickness of the yarn;

- non-stable condition of sending the bath to the tanks of chemical products, and, especially, conditions of introducing the products and dye into the circuit of the main pump which can vary as a function of the operating condition of the main pump;

- high power of the main pump.

The aim of the present invention is to provide a dyeing machine for dyeing spools of yarns and a corresponding dyeing method that are capable of improving the known art in one or more of the above mentioned aspects.

Within this aim, an object of the invention is to improve the distribution in the closed tank of the dye and/or of the chemical products with which to treat the yams.

Another object of the invention is to render the temperature uniform and increase the efficiency of heat exchange inside the closed tank.

Another object is to reduce the electricity consumed by the main pump during the process.

Another object of the invention is to render the machine capable of rendering the bath uniform independently of the differential pressure that is generated on the spools of yam.

Another object of the invention is reduce the dimensions of the hydraulic circuit of the main pump.

Furthermore, another object of the present invention is to overcome the drawbacks of the known art in an alternative manner to any existing solutions.

Another object of the invention is to provide a dyeing machine for dyeing spools of yams and a corresponding dyeing method that are highly reliable, easy to implement and of low cost.

This aim and these and other objects which will become better apparent hereinafter are achieved by a machine according to claim 1, optionally provided with one or more of the characteristics of the dependent claims.

The aim and objects of the invention are likewise achieved by a method according to claim 10.

The quantity of bath held inside the spools of yam is substantially changed a certain number of times per minute inside a closed tank which contains the spools of yam to be processed immersed in a treatment bath, and the remaining quantity of free bath is conveniently mixed inside the closed tank. Then a first pump is used to change the bath inside the spools and a second pump is used to mix the free bath in the closed tank. Furthermore, an external heat exchanger is installed on the circuit of the second pump and is adapted to heat and/or to cool the bath.

Further characteristics and advantages of the invention will become better apparent from the description of a preferred, but not exclusive, embodiment of the machine according to the invention, which is illustrated by way of non-limiting example in the accompanying drawings wherein: - Figure 1 schematically illustrates a dyeing machine for dyeing spools of yarns according to the prior art;

- Figure 2 shows the machine in Figure 1 in the condition in which the flow is reversed;

- Figure 3 schematically illustrates a dyeing machine for dyeing spools of yarns according to the invention;

- Figure 4 shows the machine in Figure 3 in the condition in which the flow is reversed.

With reference to the figures, a conventional dyeing machine for dyeing spools of yarn comprises a vertically-extending closed tank 101 which contains both the spools 102 to be dyed, mounted on corresponding rod-like supports 105, and the treatment bath 103.

In the figure a single spool 102 is shown, but typically a plurality of rod-like supports 105 are arranged in the closed tank 101, on each one of which a plurality of spools of yarn 102 are mounted, one above the other.

The rod-like supports 105 are mounted on a base plate 106 which distributes to the supports 105, or receives from them, the treatment fluid which is made to circulate by a main pump 108 by way of a circuit 109 and a reversal device 107 for reversing the circulation, in order to carry out the bidirectional change of the treatment bath.

A heating coil 104 can be positioned inside the closed tank, and is struck by the flow of the treatment fluid in both directions, according to the condition in which the reversal device is currently in.

The treatment bath is pushed by the main pump 108 through the circuit 109, the plate 106 and the rod-like supports 105 and is forced to pass radially through the yarn, from outside the spools 102 toward the inside (in a first configuration of the reversal device 107, shown in Figure 1) and from inside the spools 102 toward the outside (in a second configuration of the reversal device 107, shown in Figure 2).

If the quantity of bath contained in the closed tank 101 is 3800 liters, then the flow rate required of the main pump 108 is 11400 1/min and that is to say 684 mVh in order to be capable of changing the bath 103 three times a minute. Normally, the hydraulic head required to enable this quantity of bath to overcome the flow resistances along the circuit is 15 mew (meters of column of water) at the duty point. Therefore, the characteristic required of the main pump is 684 mVh at 15 mew.

A dyeing machine 100 for discontinuous dyeing according to an embodiment of the invention is illustrated in Figures 3 and 4.

The machine 100 comprises a closed tank 1 which is adapted to be filled at least partly with a treatment fluid so as to form a treatment bath 3 inside the closed tank 1. The treatment bath is formed by a treatment fluid which can consist of water or of a mixture of water mixed with a dye and/or with an auxiliary chemical product (for washing, soaping, scouring and/or bleaching).

The closed tank 1 , which is usually cylindrical and closed at the ends, can be vertically extended as in the case shown, i.e. with the central axis of the cylinder substantially perpendicular to the ground on which the closed tank 1 rests.

In an alternative embodiment, not shown, the closed tank can instead be horizontally extended, i.e. with the central axis of its cylindrical body lying substantially parallel to the ground on which the closed tank rests.

The closed tank 1 internally comprises at least one vertically-extended spool-supporting rod 5, of a known type and consisting, preferably, of a rectilinear manifold which is mounted, at a bottom end thereof, on a distribution chamber 6 inside the closed tank 1 with which the rod 5 is in fluid communication.

At least one spool of yarn 2, and preferably a stack of spools of yarn 2, is mounted on each spool-supporting rod 5, and the rod 5 is mounted together with the distribution chamber 6 inside the closed tank 1 so as to keep, during use, the spools 2 at least partially immersed in the treatment bath 3.

In the invention described in this application, the term "spool of yarn" 2 means any mass of yam or textile fiber (including in the form of flock or of carded or combed ribbon) wound or not around an axis, such as for example a spool, a spindle, a beam, a cop, a clew, a skein, a top, a muff.

Each spool-supporting rod 5 enables the treatment fluid to pass transversely through the spools mounted upon it. In particular, the spool supporting rod 5 is in practice a straight tube which is perforated substantially over all of its lateral surface, in order to radially direct the stream of treatment fluid that axially passes through it.

The distribution chamber 6 on the other hand can substantially be an internally-hollow cylinder, with its axis parallel to the axis of the spool supporting rod 5, and provided on its surface with an opening connected to a respective spool- supporting rod 5 and, below, with a single opening for the passage of the treatment fluid.

In the preferred embodiments of the invention, the closed tank 1 comprises a plurality of spool-supporting rods 5, which are mounted inside the closed tank 1, vertically parallel to each other on a same distribution chamber 6, or mounted in groups on separate and laterally adjacent distribution chambers 6, which are also contained inside the closed tank 1. A plurality of spools of yarn 2 is fitted onto each one of these spool- supporting rods 5, and are therefore stacked on each other along the respective rod 5.

The machine 100 further comprises recirculation means which are hydraulically connected to the closed tank 1 for moving the treatment fluid between the inside and the outside of the closed tank 1.

In particular, the machine 100 circulates the entire treatment bath 3 contained in the closed tank 1, through the spools 2, at least three times a minute, in consideration of two requirements.

The first requirement is to change the bath contained inside the yam of the spools 2. In fact, any treatment that it is desired to be carried out on the yam must take place with a continuous administration of treatment fluid, i.e. of water and dye and/or water and chemical products. This operation to change the bath contained in the yam, in substance, makes it possible to bring the chemical products and/or the dye inside the yarn so as to enable a transformation of the yarn (deriving from an operation like scouring, bleaching, coloring, soaping, washing). This transformation in general is a chemical/physical process that occurs in successive steps, for example whitening with hydrogen peroxide and/or soda, washing, coloring with suitable dyes as a function of the composition of the fiber, passage from an acid fluid to a basic fluid or vice versa in order to make chemical reactions happen, and the like. All these transformations are made possible by the change of bath that takes place in the yarn.

The second requirement for changing the entire bath at least three times a minute is to render uniform or homogenize the bath 3 contained in the closed tank 1. Every time that, in order to make a transformation happen, chemical products and/or dyes are added, or the state of the temperature is changed inside the closed tank 1 , transients are introduced which change the state locally in portions of bath and therefore, in order to prevent the changes in state from happening unevenly, which would produce different shades of the color in the various layers of the wound yarn and/or from spool to spool in the same batch, such transients need to be rendered uniform.

In the present invention, the two operations to change the treatment bath 3 and homogenize it are assigned to two different pumps.

In particular, considering that the portion of the treatment bath 3 that is retained by absorption by the yam of the spools 2 contained in the bath is known in advance, and the remaining, second portion of the treatment bath 3 is therefore also known, it is possible to use a first pump 8 which is adapted to only change the bath and which has a flow rate that is such as to change only the aforementioned first portion of the treatment bath 3 contained in the yam a preset number of times per unit of time, for example at least three times a minute.

The first pump 8, for example of the centrifugal type, is associated with a first hydraulic circuit 9 which optionally comprises flow reversal means 7 and which passes through the spool- supporting rods 5 and, if present, the distribution chamber 6.

In the change operation performed by the first pump 8, the direction of the flow can be reversed at least once by way of the flow reversal means 7, which are conventional. The flow reversal means 7 can comprise a flow diverter which is actuated by a controlled actuator (as in the case shown in the figures) or they can be incorporated in the first pump, in which case it is a reversible pump.

The flow rate of the first pump, preferably, is comprised between 1 and 3 times the overall weight of the yam multiplied by the preset number of times, per unit of time, the first portion of the treatment bath 3 is changed. This factor comprised between 1 and 3 takes account not only of the treatment fluid that remains retained in the spools 2, but also of flow losses owing to leaks or seepage between the cores of the spools (tubes) stacked on each other and also of the fluid that is in the first hydraulic circuit 9 associated with the first pump 8, including the gaps between the spools 2.

For example, if the total quantity of treatment bath 3 contained in the closed tank 1 is 3800 liters, as in the example of the prior art described above, and if the total load of spools 2 is 600 kg, then it can be estimated that the quantity of bath 3 absorbed by the spools and the quantity circulating in the circuit of the main or first pump is 2.85 x 600 kg = 1710 liters, which means that the first portion of the treatment bath 3 is about 45% of the total bath 3 while the second portion of the treatment bath 3 is the remaining 55% approximately.

In order to make 1710 liters pass through the spools 2 three times a minute, the flow rate of the first pump 8 must be 5130 liters/min, i.e. approximately 310 nrVh, which is less than half the flow rate of the main pump 108 of the example of the prior art.

For mixing the second portion of treatment bath 3, there is a second pump 20 which is associated with a second hydraulic circuit 21 which passes through from outside the closed tank 1.

The flow rate of the second pump 20 is such as to make the second portion of the treatment bath 3 exit from the closed tank 1 and return into it, so as to mix the second portion of the treatment bath, i.e. the portion that is not retained by the spools 2 and by the first hydraulic circuit 8. Returning to the previous example, in order to mix the remaining 2090 liters of the treatment bath 3, the flow rate of the second pump 20 is approximately 120 m³/h.

In this manner, the portion of bath that was not moved by the first pump 8 is mixed, thus more effectively and constantly rendering uniform the bath contained in the closed tank 1 outside of the spools 2.

The intake inlet of the second pump 20 is hydraulically connected to the bottom end of the closed tank 1 , so as to withdraw the treatment bath that is located below the region of the spools 2, while the outflow of the second pump 20 is hydraulically connected with a heat exchanger 22 outside the closed tank 1 which is adapted to heat or to cool the treatment bath on the basis of a predefined program for treating the yam, which is programmed in the control system of the machine 100.

Inside the closed tank 1 , in particular in the bottom region below the spool-supporting rods 5 and the distribution chamber 6, there is a diffuser 4 which is hydraulically connected downstream of the heat exchanger 22 along the second hydraulic circuit 21 and which consists, preferably, of a substantially annular manifold (i.e. a tubular conduit which is provided with a plurality of through holes on its lateral surface and which is substantially circular if the closed tank 1 has a vertical axis or quadrangular if the closed tank has a horizontal axis). The positioning of the diffuser 4 is on the bottom of the closed tank 1 and is adapted to make it block the flow of the first portion of treatment fluid in both of the possible directions of flow imposed by the flow reversal means 7. In this manner, the first portion of the treatment bath is subjected to a heat exchange following contact with the diffuser 4 and, in particular, it is heated if the heat exchanger 22 is used to heat the second portion of the treatment bath which passes through the second hydraulic circuit 21.

The annular manifold that constitutes the diffuser 4 preferably occupies space in a horizontal direction substantially corresponding to the horizontal extension of the base of the interspace that is left between the outermost spools 2 and the vertical inner lateral surface of the closed tank 1, thus allowing the flow of the first portion of bath which enters or exits radially with respect to the spools and which passes through this interspace to go on to strike the diffuser 4.

Finally, the machine 100 can comprise at least one tank 120 of a dye and/or at least one tank 121 of an auxiliary chemical product, for example a product for washing, scouring or bleaching the yam. In the example shown, the tanks 120 and 121 introduce their content proximate to the intake inlet of the first pump 8.

In an alternative embodiment, not shown, the tanks 120 and 121 introduce their content proximate to the intake inlet of the second pump 20, or directly into closed tank 1.

There can also be a tank for preparing the bath 3, which can be used during a step of continuous washing of the yarns. Such tank can coincide with one of the tanks 120 and 121, as in the embodiment shown in the figures.

Operation of the invention is evident from the description of the machine 100.

In any case, it entails first of all inserting the spools 2 of yarn into the closed tank 1, in particular fitting them onto the spool- supporting rods 5 which are mounted on the distribution chamber 6 and inserting the assembly into the closed tank 1. The insertion of the assembly constituted by the distribution chamber 6, the rods 5 and the spools 2 occurs, in the case shown, from above, i.e. by removing the rounded upper cover of the closed tank 1 and lowering the structure with the spools 2 from above.

Then the closed tank 1 is at least partly filled with the treatment fluid used in the first step of the cycle envisaged for the specific yam used. The filling is such that all the spools 2 are at least partially immersed in the treatment bath 3.

At this point, during the first step of the above mentioned cycle, the control system of the machine 100 repeats, at least three times a minute, the steps of movement (Figure 3) and reversal (Figure 4).

In the movement step, a pumping is carried out with the first pump 8 which moves the first portion of the treatment bath 3 along the first hydraulic circuit 9, which is substantially equal to the known portion of the bath 3 that is known to be retained by the specific yam to be treated on the spools 2, optionally increased by a factor comprised between 1 and 3 on the basis of the configuration of the first circuit 9. In the case shown in Figure 3, in this first step the volume of treatment fluid, under the action of the first pump 8, is sucked in by the distribution chamber 6 and therefore by the spool-supporting rods 5, after moving back up along the interspace between the spools 2 and the inner lateral surface of the closed tank and after having passed radially through the spools 2 from the outside toward the respective rods 5. The flow thus enters the reversal means 7 in order to then be fed anew to the closed tank by the first pump 8 from the bottom end of the closed tank toward the diffuser 4, modifying the temperature of the flow as a result of contact with the diffuser 4 and of mixing with the flow exiting from the diffuser 4, moving back up again in the aforementioned interspace.

In the step of reversing the flow of the first portion of the treatment fluid, the reversal means 7 are switched (Figure 4) so as to invert the flow of the first portion of treatment fluid inside the closed tank with respect to the previous step (Figure 3), while the operation of the first pump 8 remains unchanged with respect to the previous step. The volume of treatment fluid, under the action of the first pump 8, enters from the bottom end of the closed tank 1, rises in the distribution chamber 6 and along the spool- supporting rods 5, passes radially through the spools 2 to the outside of them, descends along the interspace between the spools 2 and the inner lateral surface of the closed tank 1, flows over the diffuser 4 and enters the reversal means 7 in order to then be fed anew to the distribution chamber 6.

During the repetitions of the above two steps of movement and of reversal, the remaining, second portion of the treatment bath 3 is made to recirculate along the second hydraulic circuit 21 through the second pump 20.

The passage through the heat exchanger 22 entails a thermal conditioning of the volume of fluid of the second circuit 21, for example a heating thereof, so that the flow exiting to the diffuser 4 changes the temperature of the flow that passes through the interspace between the spools 2 and the inner lateral surface of the closed tank 1 around them.

Once the step of treatment with a first fluid is finished, the control system of the machine 100 can carry out other steps such as the introduction of dyes or chemical products originating from the tanks 120 or 121 or the draining of the treatment bath.

Returning to the numeric example of a treatment bath of 3800 liters and an overall weight of spools 2 of 600 kg, it has been seen that the flow rate of the first pump 8 can be approximately 310 mVh and the flow rate of the second pump 20 can be approximately 120 mVh.

Assuming 15 mew of hydraulic head for the first pump 8 and 9-10 mew for the second pump 20, we get a power of 22 kW for the first pump 8 and 5.5 kW for the second pump 12, for a total of 27.5 kW against the 45 kW of the main pump 108 of the prior art (at 684 mVh flow rate and 15 mew of head). The saving of electricity that can be achieved by virtue of the present invention is therefore evident (38.88% in the specific case).

In addition to the saving of electricity consumed during the process, it can be seen that the invention achieves the intended aim and objects.

A flow rate is made to pass through the spools which is less than half of the flow rate that needs to pass with the machines of the prior art. This makes it possible to be more delicate in the process, in addition to being able to work with a lower differential pressure. Making a greater quantity of bath pass through the same spools necessarily implies applying a greater differential pressure, therefore with a greater physical stress on the yarn.

All of the hydraulic circuit of the first pump 8 is consequently smaller, in terms of dimensions, than that of the main pump 108 of the prior art. Therefore there are smaller dimensions of the flow diverter 7, smaller pipe diameters, smaller diameters of the heat exchanger 22 and a smaller quantity of needless bath in the pipes.

The heat exchanger of the invention operates under conditions of constant heat exchange efficiency, in particular not as a function of the differential pressure of the first pump 8.

The mixing of the treatment bath always occurs in the same way and is not influenced by the differential pressure that is generated on the spools. There is also, therefore, a better uniformity of the entire system.

The tanks of dyes or auxiliary chemical products, in the same way, both for transferring the bath of the closed tank to the tanks and for introducing the chemical products or dyes from the tanks into the closed tank, are provided under conditions of constant operation from step to step and between different batches.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements. In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to the requirements and to the state of the art.

The disclosures in Italian Patent Application No. 102019000009276 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A dyeing machine (100) for dyeing spools (2) of yam, which comprises a closed tank (1) which is adapted to be filled at least partly with a treatment fluid so as to form a treatment bath (3), and recirculation means (8, 20) which are connected to said closed tank (1) in order to move the treatment fluid between the inside and the outside of said closed tank (1), said closed tank (1) comprising internally at least one spool supporting rod (5) on which it is possible to fit at least one spool of yarn (2), so that a first portion of said treatment bath (3) is retained by absorption by the yam of said at least one spool (2) and a remaining second portion of said treatment path remains outside said at least one spool (2),

said spool- supporting rod (5) being adapted to allow at least said first portion of the treatment bath to pass transversely through said at least one spool (2),

characterized in that said recirculation means comprise:

- a first pump (8), which is associated with a first hydraulic circuit (9) which passes through said at least one spool-supporting rod (5), said first pump (8) having a flow rate that is such as to change said first portion of the treatment bath contained in the yam a preset number of times per unit of time,

- a second pump (20), which is associated with a second hydraulic circuit (21) which passes through the outside of said closed tank (1) and has a flow rate that is such as to make said second portion of the treatment bath exit from the closed tank (1) and return it into the closed tank (1), so as to mix said treatment bath (3).

2. The dyeing machine according to claim 1, wherein said flow rate of the first pump (8) is comprised between 1 and 3 times the total weight of the yam of said at least one spool (2) multiplied by said preset number per unit of time.

3. The dyeing machine according to claim 1 or 2, characterized in that said second hydraulic circuit (21) comprises a heat exchanger (22) which is external to the closed tank (1) and is adapted to heat or cool said treatment bath (3) on the basis of a predefined program for the treatment of said yam which can be executed by the machine (100).

4. The machine according to one or more of the preceding claims, wherein said second hydraulic circuit (21) comprises a diffuser (4) which is arranged inside said closed tank (1).

5. The machine according to claims 3 and 4, wherein said diffuser (4) is a substantially annular manifold which is connected downstream of said heat exchanger (22) and is arranged below said at least one spool-supporting rod (5) and in a bottom region of said closed tank (1), so that it is stmck by a flow of the first portion of the treatment bath.

6. The machine according to one or more of the preceding claims, wherein said spool- supporting rod (5) consists of a rectilinear manifold and is associated, at a bottom end thereof, with a distribution chamber (6) which is hydraulically connected to said first pump (8) and/or to said flow reversal means (7).

7. The machine according to claim 5 or 6, characterized in that said at least one spool-supporting rod (5) is arranged inside said closed tank so as to leave an interspace between said at least one spool (2) and an inner lateral surface of said closed tank (1), said substantially annular manifold (4) preferably having a horizontal space occupation that substantially corresponds to the horizontal extension of said interspace.

8. The machine according to one or more of claims 3-7, wherein said second pump (20) is connected upstream of said heat exchanger along said second hydraulic circuit (21), at least one tank of a dye or of an auxiliary chemical product (120, 121) being in fluid communication with said closed tank (1).

9. The machine according to one or more of the preceding claims, characterized in that said first hydraulic circuit comprises flow reversal means (7), which are adapted to reverse at least once the direction of the flow of said first portion of the treatment bath inside said closed tank (1).

10. A method for the discontinuous dyeing of spools of yam in dyeing machines, which comprises the steps of:

- inserting at least one spool of yarn (2) into an closed tank (1);

- filling at least partially said closed tank (1) with a treatment fluid so as to form a treatment bath (3) in which said at least one spool of yarn (2) is kept at least partly immersed;

characterized in that it comprises a step of pumping, along a first hydraulic circuit (9), a first portion of the treatment bath (3) which is substantially equal to the portion absorbed by the yam of said at least one spool (2), a preset number of times per unit of time, preferably at least three times a minute;

and in that it comprises, during said pumping, a step of recirculation, along a second hydraulic circuit, of a remaining second portion of said treatment bath (3).

11. The method according to claim 10, wherein said step of recirculation comprises a step of heating or cooling said second portion of the treatment bath (3) outside said closed tank (1).

12. The method according to claim 11, wherein said step of recirculation comprises a step of diffusion of said second portion of the treatment bath, which is thermally conditioned as a result of said step of heating or cooling, in an interspace between said at least one spool (2) and an inner surface of said closed tank (1), said interspace also being passed through by said first portion of the treatment bath.

13. The method according to one or more claims 10-12, characterized in that it comprises, during said step of pumping, a step of reversing at least once the flow of said first portion of the treatment bath along said first hydraulic circuit.