Technical field of the invention

The present invention relates to an apparatus and a method for shrinking knitted fabrics in a flat or tubular form.

Background

In the textile industry it is known that the weaving, bleaching, dyeing and finishing processes exert to the subjected fabrics continuous stresses which accumulate in their fibers and tend to persist over time mainly due to friction between the wires.

When a knitted fabric or a finished piece of clothing made with it is washed or is in conditions of high humidity, it may easily deform and / or shrink. Indeed, wires are not dimensionally stable, as they are made of fibers, for example natural fibers, which are deformable both in the longitudinal and in the transverse direction. Water and soap act as lubricants between the wires which, regaining a partial relative mobility, tend to shorten back to their original length. This results in a narrowing of the fabric up to a dimensional equilibrium of the fibers, which causes considerable problems during the various stages of processing of tissues and of the finished garments.

Various methods and systems are known which allow to obtain high dimensional stability of fabrics, thus minimizing the problems of shrinkage and deformation.

The patent US 4882819 discloses for example a shrinking device of fabrics comprising a shrinking station having a feeding cylinder and a counter-rotating retarding cylinder and arranged consecutively in a working direction. The retarding cylinder rotates at an angular speed lower than that of the feeding cylinder. Among the feeding cylinder and the retarding cylinder two opposing blade profiles are arranged that define a cavity of calibrated thickness passage in correspondence of which the tissue in contact with the feeding cylinder is deflected and passes in contact with the retarding cylinder. Since the retarding cylinder rotates at a lower speed than that of the feeding cylinder, in the transition zone defined by the profiles the fabric is forced to slow down, undergoing progressively, and throughout its width, to a shrinking in the forward direction. The fabric is arranged with warp yarns aligned in the forward direction, so that in the area of passage from the feeding cylinder to the retarding cylinder the shrinking takes place by making closer the weft threads. In order to facilitate the sliding of the fibers during the shrinking process, the fabric is previously subjected to a treatment with steam, which is supplied upstream of the feeding cylinder in a vaporizing station.

The US patent US 5016329 and the international publication WO 2008/052025 describes shrinking apparatuses similar to the stated above one.

The patents US3431608 and US3448499 disclose apparatuses for shrinking fabrics as defined in the preamble of claim 1, comprising a feeding cylinder, a retarding cylinder and means to blow air on the fabric.

The shrinking apparatuses known in the art have a considerable structural complexity which results in preparation and operating costs that are considered too high by persons skilled in the art.

It is also strongly felt the need to increase the shrinking of fabrics without resorting to the use of multiple machines in series.

Summary of the invention

The technical problem addressed and solved by the present invention is therefore that of providing a shrinking apparatus which allows to overcome the aforementioned drawbacks with reference to the prior art.

This problem is solved by a shrinking apparatus according to claim 1 and by a shrinking method according to claim 7.

Preferred features of the present invention are defined in the dependent claims. The shrinking apparatus according to the invention has a structure similar to that described in the above mentioned US patent US4882819 as regards to the use of a shrinking station comprising a feeding cylinder and a retarding cylinder arranged in succession and rotating at angular speeds one greater than the other. The shrinking apparatus according to the invention differs from that described in the US patent US4882819 in that the air is insufflated in countercurrent on the two faces of the fabric in transit in the cavity between the feeding cylinder and the retarding cylinder. The insufflation of air in countercurrent generates a braking action on the fabric that is added synergistically to that of the retarding cylinder, increasing the shrinking of the fabric.

The air may be heated and/or moistened in order to facilitate shrinking of the fabric. Thanks to this feature, the presence of a vaporizing station which precedes the shrinking station in the forward direction of the fabric is not strictly necessary, and this fact offers the advantage of a structural simplification of the shrinking apparatus.

According to a preferred embodiment of the invention, the shrinking station comprises a pair of parallel guide surfaces which are arranged in the feeding direction of the fabric and are made of a low friction coefficient material, such as for example PTFE. The guide surfaces have respective openings or seats through which the feeding cylinder and the retarding cylinder face each other, and are movable one in respect to each other transversely according to the thickness of the fabric F to be treated. This configuration allows to guide the fabric to be compacted from the feeding cylinder to the retarding cylinder without resorting to the use of blade profiles such as for example the shrinking apparatus described in the above US patent US4882819, and this fact offers the advantage of a considerable structural simplification.

Other advantages, features and methods of use of the present invention will be apparent from the following detailed description of some embodiments, presented by way of a non-limiting example.

Brief description of the drawings

Reference will be made to the figures of the attached drawings, in which:

Figure 1 is a side view showing schematically a shrinking apparatus according to the invention;

Figure 2 is a side view schematically showing a shrinking station of the apparatus of Figure 1;

Figure 3 is a detailed view showing schematically the path of a fabric between the feeding cylinder and the retarding cylinder of the shrinking station of the apparatus according to the invention. Referring to figure 1, a shrinking apparatus according to the invention is generally indicated by the reference number 100 and is shown schematically in a two-dimensional reference system in which a longitudinal direction L represents the forward direction along which a fabric F to be treated proceeds through it, and a vertical direction V, perpendicular to the longitudinal direction L, represents the direction along which the force of gravity acts.

The apparatus 100 comprises, according to the prior art, a loading station 110 from which a fabric F is fed from a container, a trolley or similar, to an inlet 111 where it is received through a set of rollers 112, 113 which have the function of tensioning it and stretching it in the direction of its height.

According to an embodiment of the invention, the loading station 110 may advantageously comprise a spreading assembly (not shown), such as for example that described in the European patent EP 1127184 B l in the name of the Applicant.

The apparatus 100 may also include according to the prior art a vaporizing station 120, set downstream the loading station 110 in the longitudinal direction L, in which steam is dispensed on the opposite faces of the fabric F in transit. The vaporizing station 120 may for example comprise a pair of boxes 121, 122 each provided with one or more delivery openings facing the feeding path of the fabric F. As is known, the steam has the function of moistening and lubricating the textile fibers favoring their relaxation before the subsequent compacting phase.

Downstream the vaporization station in the longitudinal direction L there is a shrinking station 130.

The shrinking station 130 comprises, according to the prior art, a feeding cylinder 131 having the function of driving the fabric F to be treated at a nominal speed, which may be set through a control system (not shown) of the apparatus 100, and a retarding cylinder 132 appropriately spaced from the feeding cylinder 131 in the longitudinal direction L, driven by the control system at an angular speed lower than that of the feeding cylinder 131. Both the feeding cylinder 131 and the retarding cylinder 132 are provided with a roughened, textured mantle or covered with a material with a high friction coefficient, suitable to prevent slipping of the fabric F to be shrunk. As is known, this configuration is such that in the cavity or area of passage from the feeding cylinder 131 to the retarding cylinder 132, the fabric F slows down, making closer its weft threads, i.e. its shrinking in the longitudinal direction L. The feeding cylinder 131 and the retarding cylinder 132 may, for example, be counter-rotating, as in the illustrated embodiment, intended to come into contact with opposite faces of the fabric F to be compacted.

The feeding cylinder 131 and the retarding cylinder 132 may be advantageously equipped with heating elements, for example electric resistors, or they may be heated from inside by insufflating steam or diatermic oil, thus contributing to the relaxation of fibers of the fabric F according to the teachings of the prior art.

According to the invention, the shrinking station 130 comprises blowing means in fluid communication with a cavity C or area of passage of the fabric F between the feeding cylinder 131 and the retarding cylinder 132. The blowing means, for example one or more fans (not shown), are connected to the cavity of passage of the fabric through one or more channels that terminate in the vicinity of the feeding cylinder 131 and of the retarding cylinder 132, for example therebetween or downstream the latter with respect to the longitudinal direction L. The air is insufflated in countercurrent with respect to the forward direction of advancement of the fabric F.

The insufflation of air in countercurrent air generates a braking action on the fabric F, which is synergistically summed with that of the retarding cylinder 132 increasing the shrinking of the fabric F. It is thus possible to obtain about 30% degree of shrinking or higher than a degree of 15-25% typically obtainable with shrinking apparatuses known in the art, such as those described in the US patent US4882819.

Air may be heated and/or moistened in order to facilitate shrinking of fabrics. Thanks to this feature, the presence of the vaporizing station 120 is not strictly necessary, which offers the advantage of a structural simplification of the shrinking apparatus.

With reference to Figures 2 and 3, according to a preferred embodiment of the invention, the shrinking station 130 comprises a pair of guide surfaces 133, 134, parallel to each other, which develop in the longitudinal direction L and are polished and/or made of a low friction coefficient material, such as PTFE. The guide surfaces 133, 134 have respective openings or seats through which face the feeding cylinder 131 and the retarding cylinder 132.

The gap between the fabric F is therefore defined by the guide surfaces 133, 134.

The guide surfaces 133, 134 are movable relative to each other in the vertical direction V, for example by means of respective linear actuators or equivalent means. The distance between the guide surfaces 133, 134 is set through the automatic control system of the apparatus 100 according to the thickness of the fabric F to be treated, and is for example variable between 0 and 3 mm, thus allowing the transit of the fabric F spread with a minimum gap.

The channels for supplying countercurrent air are advantageously obtained or reported in the guide surfaces 133, 134. In the illustrated embodiment the channels are for example two, indicated respectively by the reference numbers 135, 136, and are obtained for example downstream the retarding cylinder 132 in the longitudinal direction L each in one of the guide surfaces 133, 134, thus allowing air to act on both sides of the fabric F. The arrows in Figure 3 schematically show a condition of operation of the shrinking station 130.

The angle of incidence of the channels 135, 136 is for example 45°, but it will be understood that this angle is not a limiting feature of the invention.

This embodiment of the invention allows the transit of the fabric F to be compacted from the feeding cylinder 131 to the retarding cylinder 132 without recurring to the use of guide profiles such as for example the shrinking apparatus described in the above-mentioned US patent US4882819, which offers the advantage of a considerable structural simplification and consequent reduction of costs for realizing the apparatus 100.

The use of a low friction coefficient material for the guide surfaces 133, 134 also favors the mobility of the weft yarns of the fabric F, effectively contributing to its shrinking process.

It will be understood, however, that the insufflation of air in countercurrent in the cavity C through which the fabric F passes is also applicable in the case of use of guide profiles, i.e. the idea underlying the invention may also be used for the modernization of existing shrinking apparatuses. Pressure, flow rate, temperature, humidity degree of air supply are parameters that may be set through the control system of the apparatus 100. For example, the supply pressure may be between 1 bar and 5 bar, the temperature may be comprised between 20°C and 250°C depending on the characteristics of the fabric F, while the moisture content may vary from 5% up to 60% always in function of the characteristics of the fabric F.

The fabric F exiting from the shrinking station 130 is received in a collection station (not shown), where it is rolled up or folded according to subsequent processing or simply prepared for storage. For example, the collection station may be a folding device of the type described in the Italian patent application 102017000082267 in the name of the Applicant.

The present invention has been described up to now with reference to its preferred embodiments. It will be understood that there may be other embodiments linked to the same inventive core, all comprised in the scope of protection defined in the claims set out below.