DESCRIPTION

Technical field

This invention relates to a method and a device for the treatment of fabrics, and in particular, for drying and finishing the fabrics, with hot or cold air.

Prior art

Fabrics, be they woven, knitted, or non-woven (felts and the like) are frequently treated using machinery in which the fabric is subjected to a heat treatment with hot air in order to dry it and/or thermally fix the constituent fibres, or to a treatment with cold air in order to cool it after a heat treatment.

More specifically, machines designed for continuous treatment with hot air basically comprise a horizontal tunnel which the fabric is made to travel through so that it meets air heated in various ways and brought into contact therewith.

In some cases, the fabric is fed by means of conveyor belts, as for example in free dryers, or by means of gripper or pin chains, as for example in stenters.

Documents DE-4228454 and EP-0933607 describe air systems used typically in stenters, whereas documents US-3812599 and CA-2323723 describe similar air systems used in dryers in which the fabric is fed by conveyor belts.

Document ES-413182, on the other hand, describes the air system of a free dryer where the fabric feed means are outside the treatment tunnel.

In all the machines mentioned above, the treatment tunnel is provided with hot air supply points alternated with extraction points, which means that the hot air is projected in a direction substantially at right angles to the fabric, remains in contact therewith for a very brief stretch and is immediately moved away by the suction system which recirculates it and/or expels it to the outside.

In other cases, the fabric is fed by means of pneumatic systems.

For example, in continuous tumblers, the fabric is moved in both directions inside a duct with a narrow, elongate cross section into which air is blown at a pressure and volume flow rate such as to carry the fabric in one direction and then in the other direction, alternately. For this purpose, the feed duct is provided with openings which are directed in substantially opposite directions in order to reverse the motion of the fabric.

This occurs, for example, in GB-2158472, which describes an apparatus substantially comprising two non-airtight chambers for accumulating the fabric and feeding it in/out. The chambers are located at the ends of a duct having the shape of an upturned U, into which the air is supplied through slots located along the vertical stretches of the duct. In the apparatus, the fabric is reciprocated through the duct exclusively by the air supplied into the duct and the air thus always flows in the direction in which the fabric moves. The air fed in also causes cooler air to be sucked in from the chamber upstream. In the apparatus described in GB-2158472, as in any continuous tumbler, the length of the treatment duct is limited by the need to be able to feed the fabric from one end to the other without obstructions.

Fabric treatment with cold air is, generally speaking, carried out using devices similar to those used with hot air. Tunnels which blow cold air onto the surface of the fabric are normally preset at the final stage of stenters and, often, of the free dryers mentioned above.

For the purposes of this invention, it should be noted that, generally speaking, the textile machines which treat the fabric in open-width form need to stretch and centre the fabric at the points where the fabric is fed into and out of the machine and, in some cases, also at intermediate points in the machine.

This type of operation is usually performed by mechanical means, which always operate directly in contact with the fabric and always with the fabric positioned vertically.

Mechanical means of this kind are, for example: rollers with left- and right-hand projecting helical blades for stretching and pivot rollers for centring.

These devices produce friction and a high stretching effect which are relatively detrimental to many types of fabrics, especially knitted fabrics. At present, however, there are practically no valid alternatives to devices which operate by direct mechanical action.

Although the drying, thermal fixing and similar treatments performed by the machines mentioned are relatively adequate, the need is felt for a device which is more efficient, more productive, much less cumbersome, much more economical and suitable for use both as a stand-alone machine and as an addition to a machine of existing type, also incorporating the capability of centring and stretching the fabric being treated.

Disclosure of the invention

The main aim of this invention is to provide a method and a device for the treatment of fabrics with hot or cold air, and which allow obtaining high performance levels in terms of efficacy of treatment and, in particular, in terms of drying or cooling.

A further aim of the invention is to provide a method and device for treating fabric with air and which cause the fabric to be stretched and centred without using mechanical means acting on the surface of the fabric.

The above aims are achieved by a device and a method according to the accompanying claims.

Further aims and advantages of the invention, as well as its technical features, will become more apparent from the following detailed description of non-limiting example embodiments of it.

Brief description of the drawings

In the drawings:

- Figures 1-3 schematically illustrate a preferred embodiment of a device according to the invention for treating fabrics with air;

- Figure 4 shows a partial schematic view of a first variant embodiment of the device; - Figure 5 schematically illustrates a second variant embodiment of the device;

- Figures 6-9 illustrate four examples of machines equipped with the device according to the invention.

Embodiments of the invention

With reference to Figures 1-3, a device 1 for treating a fabric T with air comprises: - an airtight chamber 10 provided with at least one opening 12 (12a, 12b) for the supply of forced air;

- at least two ducts 14,16 for the treatment of the fabric, said ducts being at least partially located inside the airtight chamber and at least partially outside it so that each of them has one respective mouth 14a, 16a in communication with the exterior of the airtight chamber for the infeed/outfeed of the fabric T; - fabric transferring means 22 located between the mouths 14b, 16b of the ducts 14, 16 inside the airtight chamber 10.

As shown in the example of Figure 1 the method for the treatment of a fabric T implemented by this invention comprises the following steps:

- forced feeding of air into the airtight chamber 10 and outflow of the air from the chamber through the two ducts 14,16,

- feeding the fabric into the mouth of one of the two ducts, outside the airtight chamber 10 (the mouth 16a of the duct 16 in the example shown in Figure 1),

- moving the fabric inside the duct (16) in the direction opposite to the direction of the air flowing along the same duct (16),

- feeding the fabric out of the duct mouth located inside the airtight chamber (the mouth 16b in the example),

- transferring the fabric by means of a roller 22, either idle or motorized, to the mouth of the other duct (thus, in the example, the mouth 14b of the duct 14),

- moving the fabric inside the second duct (14) in the same direction as the air flowing along the selfsame duct (14),

- feeding the fabric out of the mouth (14a) of the second duct (14) located outside the airtight chamber.

Obviously, the fabric may travel along the two ducts continuously in the direction opposite to that shown in Figure 1 (that is, it may be fed into the other duct 14 through the opening 14a outside the airtight chamber, be made to travel along the duct 14 in the direction opposite to that of the air flow, be fed out through the opening 14b thereof located inside the airtight chamber, be transferred by the roller 12 to the mouth 16b of the duct 16, be made to travel along that duct in the same direction as the air flow and be fed to the outside through the mouth 16a) or - as in the example described below - alternately in both directions.

The air used for treatment, coming for example from a fan 24 equipped with a heat exchanger 26, is made to flow into the airtight chamber 10 through the opening 12 and, since there are no other ways out, is forced into both of the ducts 14,16 through which the fabric T passes, and reaches the mouths 14a, 16a located outside the airtight chamber. In the preferred embodiment illustrated, the two ducts 14,16 are rectilinear, substantially vertically oriented, mutually parallel and protruding from the bottom of the airtight chamber 10. To supply the air into the airtight chamber 10, one or preferably at least two lateral openings (12a,12b; see Figures 2-3) are provided.

In the embodiment of the device schematically illustrated in Figure 4, the air is supplied into the airtight chamber 10 through at least one bottom opening 12c.

A cover or door, not illustrated in the drawings, may be provided to give access to the airtight chamber for the purposes of inspection and drawing-in of the fabric.

The cross sections of the ducts are such as to allow the fabric to move through the ducts easily while at the same time letting a quantity of air sufficient for treatment to also flow through parallel to the fabric itself.

In particular when they are intended for treating a fabric in open-width form, the ducts 14,16 have a transversal cross section which is preferably rectangular with long sides much longer (at least ten times longer) than the short sides, whereas when they are intended for a fabric in rope form, the ducts are preferably square or circular in cross section.

The ducts must be long enough to allow the air to act on a sufficiently large surface of the fabric. For this purpose, in the case of fabric in open-width form, the length of the ducts is advantageously greater than half the size of the long side of the cross section. In the case of fabrics in rope form the ducts are advantageously at least five times as long as the diameter of the circle which circumscribes their transversal cross section.

The ducts may differ in size so that the one downstream is longer and/or different in cross section from the one upstream, thus providing a resultant force for moving the fabric which assists or substitutes the force applied by the transfer roller between the two ducts in the pair.

In a device according to the invention, the air flows generated travel through the treatment ducts simultaneously, one in a direction which is the same as the fabric feed direction and the other in a direction which is opposite to the feed direction, and at speeds - determined substantially by the reduced cross section size of the ducts - which are high enough to produce an intense heat exchange with the fabric. It has been found that the combination of the strong heat exchange with the continuous renewal of the air layer which is in contact with the fabric and which, owing to the high speed, penetrates the fabric in depth, produces an extraordinarily good drying, heating or cooling effect. At the same time, the creation inside the two treatment ducts of laminar air flows with streamlines substantially parallel to the fabric feed direction produces a marked stretching and centring effect on the fabric.

This is obtained with air flows which are considerably smaller than those required by continuous tumblers in the prior art, where the ducts are mainly horizontal and the air flows must be strong enough to also support the fabric.

This effect may, even by itself, justify the use of the device of this invention in applications where traditional stretching and centring actions applied by mechanical means produce undesirable tension and friction on the fabric. In particular, when treating tubular knitted fabric, the device also prevents twisting.

Figures 5 and 9 show a variant embodiment of the device, where a plurality of pairs of ducts 140,150 160,170 lead into a single airtight collector enclosure 100 and a suitable plurality of rollers 160 perform all the necessary fabric transfers, thus multiplying the fabric drying or cooling capacity.

The ducts are preferably oriented vertically and parallel to each other but, where necessary, they may also be divergent and/or have non-uniform cross sections. Also, they may be partly inside and partly outside the airtight enclosure 100, or they may be completely inside or completely outside the enclosure.

The system used in a device according to the invention differs substantially from those used in prior art drying tunnels, where the fabric comes into contact with the air for an extremely limited time and at a very limited speed because the continuous alternation of air inlet and outlet points along the tunnel allow the air to come into contact with the fabric for a very short length.

The invention also differs from the system used in prior art continuous tumblers because in the prior art, the air basically has a fabric transporting and impacting function, which makes it necessary to adopt aerodynamic solutions which cause the air to flow in the treatment duct in one direction and then in the other alternately and at very high supply pressures.

Moreover, in tumblers the hot air in the treatment duct flows at a high speed in the same direction as the direction the fabric is moving in at the same moment which, as mentioned above, causes very cold air to be also sucked in, thus considerably lowering the average temperature inside the duct. The quantity of air sucked in together with the fabric is quantitatively of the same order of magnitude as the hot air supplied by the process fan but at a temperature and humidity close, if not equal, to those of the extracted air channelled to the exhaust flue. In this invention, the air, starting from the collector enclosure, flows in one duct in the same direction as the fabric and, in the other duct, in the opposite direction to the fabric, without sucking more air in from the place where the fabric is fed in and fed out, but simply flowing totally therein. That means the air pressure and volume flow rate requirements are much more limited and, consequently, the power of the process fans are accordingly reduced.

The fabric treatment ducts, being vertical, facilitate the passage of the fabric through them and avoid the obstructions which easily occur in horizontal ducts and, consequently, their cross sections can be much more reduced in size. Consequently, under equal conditions of speed of the air in contact with the fabric, the volume flow rate required of the fan is also reduced, which in turn means a lower electrical and thermal power requirement.

Further, while offering the same drying capability, the device of the invention is typically extremely compact and considerably smaller in size than hot air textile dryers of any kind.

For example, a device according to the invention equipped with two treatment ducts, each three metres long, occupies just a little over three metres in height and a few decimetres in length (in the horizontal direction of fabric feed). A traditional drying tunnel, to have the same fabric surface area exposed to the air, would have to be at least six metres in length and, in height, just a little under the three metres of the above mentioned device given as an example of the invention.

Further, a device with four ducts, according to the invention, is just a few decimetres longer, whereas an equivalent traditional drying tunnel would be no less than twelve metres in length.

Moreover, the above is true even without considering the fact that under the same conditions of fabric surface area exposed to the air, a device according to the invention offers a considerably higher evaporation capacity.

It is easy to imagine the immense drying capabilities that can be achieved by constructing a device with a larger number of ducts and/or with longer ducts than those stated above by way of example.

Thanks to its versatility, this device can easily be used to construct a continuous or discontinuous machine which may be either a stand-alone machine or an in-line part of an existing machine.

Figure 6 shows a device according to the invention with two treatment ducts, used to move the fabric rapidly and alternately from one to the other of two piles while the fabric is fed in and withdrawn at a slower production speed.

Figure 7 shows the application of the device to an in-line machine with infeed pile. The machine following it may be a textile dryer or any kind, and more specifically, a continuous tumbler, a free dryer or a stenter.

Figure 8 shows a discontinuous machine equipped with a device according to the invention and with a vibrating tank with two sections 28a,28b on top of one another for drying to obtain dimensional restorability and stability of a knitted fabric.

Figure 9 shows a drying machine equipped with a device having two pairs of ducts 140,150 160, 170 for the treatment of the fabric. The hot air from the fan 24 is supplied into the airtight chamber 100 and into the ducts and flows out into a containment chamber 30 from which it is extracted by an exhaust fan 32.

Generally speaking a device according to the invention may be advantageously used as: - a stand-alone machine for the continuous or discontinuous drying of woven, knitted or non-woven fabrics, in open-width or rope form;

- a pre-drying section upstream of a free dryer, a stenter or a continuous tumbler;

- a single or multiple drying module of a continuous or discontinuous machine for the treatment of knitted fabrics, in open-width or rope form, with dimensional restorability effect (comprising, for example, single or multiple vibrating tanks/platforms); - a cooling section downstream of a dryer, a stenter or a continuous tumbler;

- a stretching and centring module for incoming fabric in open- width or rope form;

- an unwinding, stretching and centring module for tubular knitted fabric.