EP1227289A1

EP1227289A1 - Drying method for textile material or tanned hides, and relative device

Info

Publication number: EP1227289A1
Application number: EP02001864A
Authority: EP
Inventors: Roberto Franchetti; Bruno Scortegagna
Original assignee: Lafer SpA
Current assignee: Lafer SpA
Priority date: 2001-01-29
Filing date: 2002-01-28
Publication date: 2002-07-31
Also published as: ITUD20010016A1

Abstract

Drying method and device for textile material in the form of strip (11), or hides, wherein the strip (11) or hide is made to pass inside a closed chamber (12) inside which an environment is created in depression with respect to the atmospheric pressure. The strip (11) or hide passing through the depression chamber (12) is subjected to a heat treatment in order to take the water contained in the strip (11) to a temperature at least near to that of boiling. The heat treatment is associated with at least a mechanical treatment to remove the water and humidity present on the strip (11) or hide.

Description

FIELD OF THE INVENTION

The invention concerns a drying method for textile material, tanned hides or other similar or comparable material, and the device able to embody the method.
The invention is applied in the finishing of textile material such as cotton, wool, mix, synthetic, knitwear, elastics, and is employed mainly at outlet from wet treatments such as washing, vaporization, impregnation, dyeing, décatissage, calandering and suchlike.
The invention is also applied for drying hides emerging from a tanning treatment.

BACKGROUND OF THE INVENTION

In finishing operations for textile material, the fabric emerging from wet treatments must be subjected to at least a drying step so that it can be sent to subsequent operations. Drying must be performed in such a manner as to remove the maximum quantity of water and humidity from the textile material without ruining it or deteriorating it in any way, particularly the touch or appearance.
Usual drying methods provide to hit the textile material with a flow of hot air to make the water contained therein evaporate until the desired level of humidity is reached.
Drying machines such as are commonly used, known as rameuses, consist of chambers inside which the fabric is made to pass between an inlet and an outlet by chains or similar means. Rameuses can have one or two planes according to the path which the textile material has to follow to complete the drying operation.
Another drying system using heat treatment provides to transport the textile material into contact with heated cylinders according to a pre-defined path.
These heat drying systems, which include a conventional system using radio-frequency waves, have the disadvantage that they entail a very high energy consumption, which can be estimated as 1200÷1500 kcal to evaporate 1 kg of water.
In combination with or alternative to heat drying systems, mechanical drying systems may be provided. Among these, the state of the art includes the squeeze drying system, for example with cylinders arranged in a configuration like a foulard; this however has the disadvantage of leaving a residual water in the textile material of not less than 60% with respect to the weight of the fabric.
Among the mechanical systems, the state of the art also includes the centrifugal system; however, apart from leaving a residual water in the textile material of not less than 50% of the weight of the fabric, this system also has the disadvantage that it is discontinuous and therefore only allows very low production. Another method provides to pass the textile material to be dried in cooperation with one or more suction bars; in this case too, there is low drying efficiency together with high energy consumption.
An example of a conventional drying device for textile material is shown in the document GB-A-2.301.425. In this device, a wet fabric is guided inside an insulated processing chamber, which is at atmospheric pressure, inside which there are two cylinders, which can be heated or not. The fabric is made to advance inside a transit channel made around said two cylinders and delimited by a case associated at inlet and outlet with sealing means.
Before entering into contact with the first of said cylinders, the fabric is made to cooperate with two suction bars, the function of which is to remove water and humidity from the fabric. The suction bars are connected to a vacuum pump, which is associated with a separator, the function of which is to separate the water from the gases. The gases obtained in the separator, after being heated by the vacuum pump by means of compression, are returned to the processing chamber, coming into contact with the fabric. The hot gases absorb the humidity and water present on the fabric, substantially performing a pre-drying of the fabric, and then are sucked in by the suction bars.
The solution described in this state of the art document permits to improve the performance of the suction bars by exploiting part of the energy of the vacuum pump, which would otherwise be lost.
However, it is not completely satisfactory from the point of view of drying efficiency, since the fabric, during the whole drying process, never finds itself in a vacuum environment, but always substantially at atmospheric pressure; in fact, a vacuum is obtained only locally inside the suction bars and inside the pipes which connect the suction bars to the vacuum pump and the separator, but this does not permit to exploit the advantages which derive from drying the fabric in an environment under strong depression.
In particular, this solution does not exploit the reduction in the fabric's capacity to attract the water molecules which is obtained by subjecting the fabric to heating in an environment subject to a condition of strong depression with respect to atmospheric pressure.
At present therefore, there is a requirement for a method for the continuous drying of textile material or hides which will allow to obtain high level performance without entailing high energy consumption.
The present Applicants have devised and embodied this invention to overcome the shortcoming stated above, and to obtain further advantages.

SUMMARY OF THE INVENTION

The invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the main embodiment.
The purpose of the invention is to achieve a drying device for textile material or hides able to guarantee high performance, in terms of drying efficiency, in a structure which is simple to construct and to use, at the same time ensuring much lower energy consumption compared with conventional devices and reduced risks of deterioration of the touch and appearance of the material to be dried.
In order to obtain this purpose, the invention provides to use the effect deriving from performing at least a heat treatment made on the material, preferably over its entire width, in a closed chamber inside which an environment is created with a strong depression with respect to atmospheric pressure, and to perform on the material which is passing in said depressed environment and which has been subjected to said at least one heat treatment, at least a mechanical treatment to remove the water and humidity present in the material.
To be more exact, the invention provides to pass a fabric, or hide, to be dried inside a closed and insulated chamber associated with means able to create a desired condition of depression (vacuum), in order to exploit the action deriving from the heating of the fabric in a depressed environment in order to take the water and humidity contained in the fabric to boiling temperature.
The invention therefore allows to exploit the lower temperature at which the water boils, the weakening of the molecular links and the reduction in the external counter pressure which opposes the detachment of the water and humidity molecules from the surface of the fabric.
Inside this chamber, in a preferred solution, there is provided at least a mechanical squeezing step of the fabric to extract the water, brought substantially to boiling point by the combined action of heating and depression. In another solution, at least a suction step is provided in this chamber to remove the water brought substantially to boiling temperature.
According to a further solution, the invention provides to perform, inside this depressed chamber, both one or more squeezing steps and one or more suction steps.
Performing a squeezing operation, or a suction operation, or a combined squeezing/suction operation, in an environment kept in a strong depression with respect to atmospheric pressure and after the material has been subjected to heat treatment, allows to achieve a plurality of advantages in terms of drying efficiency.
In fact, it is well-known that in a liquid mass at rest, each molecule is stressed by a combination of forces of attraction by the other molecules, in equilibrium with each other. In correspondence with the surface separating liquid and air, this equilibrium generates a resulting tension, between the attraction of the inner molecules and those of the outside means; the molecules of the surface are attracted towards the inside of the liquid, forming a sort of taut skin which opposes the penetration of foreign bodies.
The surface tension of this skin opposes every action which tends to increase the contact surface. When this happens in an environment under strong depression, this surface tension is drastically reduced.
Moreover, in conditions of rest and at ambient temperature, the kinetic movement of the molecules of a liquid mass is very weak and the links between the molecules, and hence the force of cohesion between them, are very strong. On the contrary, when the liquid mass is heated, the movement of the molecules is very strong, able to encourage the expansion of the mass until it evaporates, and the links and the forces of cohesion between the molecules are very weak.
Therefore, when there is an environment kept under depression, and a heat treatment performed on the material to be dried, the result is that the surface tension of the liquid is extremely reduced and the resistance of the molecules to detachment is very low; in fact, unlike atmospheric pressure, the vacuum does not constitute a brake to the separation of the water molecules from the surface of the textile material. Moreover, the water boils at considerably lower temperatures, also because the forces of cohesion between the molecules are very weak.
By subjecting the fabric to squeezing and/or suction under these conditions, we therefore obtain a much more efficient and efficacious removal of the water, yet without ruining the fabric thanks to the much lower working temperatures; moreover, since the water boils at a lower temperature, for example at about 54°C for a pressure in the range of about 0.15 bar, we obtain a considerable saving in terms of energy consumption.
It is therefore possible to use this method with delicate fabrics too, and those particularly sensitive to heat, with lower risks of damaging and deteriorating them.
The value of depression at which the chamber through which the fabric passes and is treated has to be maintained does not constitute a critical parameter, although the lower said value is, the lower the value of the boiling temperature and hence the higher the drying performance.
Values in the range of 0.1÷0.2 bar of residual pressure are preferential at least in the case of squeezing alone. In the case of suction, values of 0.3÷0.5 bar of residual pressure are preferential; these slightly higher values derive from the fact that the performance is higher if the flow which passes through the fabric has a certain density.
With these values of residual pressure, the improvement in the removal of water and humidity with respect to traditional drying systems has values of between a minimum of 40% and a maximum of 80%, according to the type of fabrics treated.
The heat treatment on the material to be dried, in a preferential embodiment, is performed by making the material transit over heated cylinders located inside the closed chamber. In another embodiment, the heat treatment is performed by means of the focused emission of infra-red rays or microwaves using batteries and emitters arranged inside the closed chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

These characteristics and advantages of the invention will become clear from the following description of the preferential form of embodiment, given as a non-restrictive example, with reference to the attached drawings wherein:
Fig. 1a shows a first embodiment of a drying device according to the invention;
Fig. 1b shows the detail I of Fig. 1a;
Fig. 1c shows a detail of a variant of the invention;
Fig. 2 shows another embodiment of a drying device according to the invention.

DETAILED DESCRIPTION OF SOME PREFERENTIAL EMBODIMENTS

With reference to the attached Figures, the number 10 denotes generally a continuous drying device for textile material in the form of a strip 11, or hides, arriving from wet treatments.
In the following description we shall refer generically to strip 11, but the invention can also be applied in the same way, with the due adaptations, to hides to be dried.
In the embodiment shown in Fig. 1a, a strip 11 to be dried is made to pass inside a closed chamber 12, in this case with a circular section, including sealing means with rollers 13a at inlet and sealing means with rollers 13b at outlet. The strip 11 can reach the chamber 12 cold or preheated.
Inside the chamber 12 the strip 11 is made to pass in contact, in this case, with three cylinders 14, respectively 14a, 14b and 14c, of which at least the first 14a is heated to a temperature preferably in the range of 140÷150°C. It is obvious that the number of cylinders 14 as in Fig. 1 is only indicative, and can vary from one to any desired value.
The chamber 12 is associated with a vacuum assembly 15 able to create therein an environment under strong depression with respect to atmospheric pressure, with a desired residual pressure with a value advantageously, but not restrictively, in the range of 0.1÷0.5 bar.
The vacuum assembly 15 is connected to the chamber 12 by means of an extractor conduit 16 and a condenser 17 of the evaporation fumes including an inlet 18a and an outlet 18b for cooling water.
The condenser 17 has a discharge 19 connected to an assembly 20 which sends the condensation to subsequent treatments and for possible re-use.
Inside the chamber 12, and in cooperation with the first heated cylinder 14a, there is a squeezer roller 21, advantageously lined with rubber, suitable to exert on the strip 11 passing through an adjustable pressure, from about 10 kg up to 100 kg per linear centimetre.
The functioning of the device as shown in Fig. 1a provides that the strip 11 to be dried is introduced inside the closed chamber 12 inside which a vacuum environment is created, and made to pass in contact with the heated cylinder 14a. To condition the path of the strip 11 around the cylinders 14a, 14b and 14c there are guide rollers 22.
For the segment A-B in contact with the hot surface of the first cylinder 14a, the strip 11 is progressively taken to a temperature equal to the temperature of boiling in the depression conditions created inside the chamber 12, for example between 45 and 80°C.
In such conditions, the strip 11 is subjected to mechanical squeezing by the squeezer roller 21, exploiting the loosening of the links between the molecules of boiling water and the fibres of the fabric, and the reduction in the external counter pressure; these factors allow to obtain a much higher removal of water and humidity than occurs in conditions of environmental pressure.
To be more exact, the contact under pressure of the squeezer roller 21 and the heated cylinder 14a forms (Fig. 1b) a pressure segment 25, with a width "1" of several centimetres, due to the deformation of the rubber. The strip 11 enters the pressure segment 25 between the roller 21 and the cylinder 14a at a temperature, for example, in the range of 45÷80°C, and is subjected to squeezing; the cylinder 14a, heated to a temperature in the range of 140÷150°C, superheats the water contained in the fabric in the pressure segment 25, therefore with the difference between the temperature of the cylinder 14a and that of the strip 11 being very great.
In this brief segment, therefore, we have a rapid increase in the temperature and superheated steam is formed with respect to the boiling temperature which, in such conditions of depression, is in the range of 45÷80°C. At outlet from the pressure segment 25 the steam expands at very high speed, taking with it a high quantity of water without finding an external counter pressure.
Then, the strip 11 is wound on the possibly heated cylinders 14b and 14c to complete the drying action and in particular to remove the residual humidity before it is discharged.
The water removed from the strip 11 collects on the bottom of the chamber 12 and is removed therefrom, for example by means of discharge holes connected with pump-type extraction means.
It is clear that the solution shown in Fig. 1a serves only as an example, since the device 10 can be equipped with a single heated cylinder 14a and a single squeezer roller 21, with a single cylinder 14a and several squeezer rollers 21, or substantially with every combination of heated cylinders and squeezer rollers compatible with the overall size of the device and in particular of the chamber 12.
Moreover, according to a variant which is not shown here, the cylinder 14 is not heated, and the heat treatment on the strip 11 is performed by means of emitters of infra-red rays or microwaves suitably arranged at least upstream of the squeezer roller 21.
The variant shown in Fig. 1c comprises, in the interspace between the cylinders 14a and 14b, a suction bar 26, arranged facing the free segment of the strip 11 between the two cylinders and in a position extremely close thereto. It has a length preferably at least equal to the width of the strip 11 being treated.
The function of the suction bar 26 is to remove the residual humidity of the strip 11 after it has passed through the squeezer roller 21, if present; otherwise the suction bar 26 constitutes the main element of mechanical removal of humidity and water in the event that there is no squeezer roller 21. The efficiency of the suction bar 26 is also encouraged, in a similar manner as seen above, by the environmental conditions of strong depression to which the strip 11 is subjected throughout its travel from its entry into the chamber 12 until the position of said suction bar 26, and by the heating to which the strip 11 is subjected before it is sent towards said suction bar 26.
The suction bar 26 has a longitudinal suction slit 27 facing towards the strip 11 being treated, and is connected by means of a tube 28 to a ventilation/suction system 29 connected in turn to the extractor conduit 16 by means of a tube 30.
The system 29 determines the passage of a flow of gas (air, water vapor, CO₂, etc.) through the strip 11, with a speed which depends on the entity of the depression generated by the system 29 itself. The flow determines the mechanical removal of substantially boiling water and humidity from the strip 11 during its passage in the free interspace between the two cylinders 14a and 14b.
There may be several ventilation/suction systems 29 included, for example installed at the two sides of the suction bar 26, or the suction bar 26 can be directly connected to the extractor conduit 16. The longitudinal suction slit 27 can advantageously have a herring bone configuration, or other geometry suitable to optimize the suction action. There may also be included two or more suction bars 26 arranged along the path of the strip 11 inside the chamber 12.
To optimize the performance of the suction bar or bars 26, it is preferable that the residual pressure maintained inside the chamber 12 has a value in the range of 0.3÷0.5 bar, so that the flow of gas passing through the strip 11 with the boiling water has a certain density.
In the embodiment shown in Fig. 2, wherein the same numbers used in Fig. 1a refer to equal or equivalent components, the vacuum chamber 12 is created in the space defined by four cylinders, 114a, 114b, 114c and 114d, which can be heated up to 140÷150°C.
The cylinders 114b and 114d preferably have a steel surface, while the cylinders 114a and 114c are preferably lined with rubber. These rubber-lined cylinders 114a and 114c can be pressed against the surface of the steel cylinders 114b and 114d to perform a double function: to seal the vacuum chamber 12 with respect to the outside and to squeeze the strip 11 with an adjustable pressure from about 10 kg up to 100 kg per linear centimetre at inlet and at outlet of the chamber 12.
At the ends of the cylinders a sealing device 31 is provided, suitable to insulate the inner environment of the chamber 12 with respect to the outside. The sealing device 31 can be of the type described in the European patent application EP-A-943.719, in the name of one Applicant of this application, or another suitable type.
The cylinders 114a-114d can also be arranged inside a closed chamber 23 defined by a box-like structure 24 able to create a thermally insulated environment with respect to the outside.
The strip 11 is introduced inside the chamber 12 after a first squeezing caused by the passage firstly between the cylinders 114a and 114d and then between the cylinders 114a and 114b; it is subjected to heating through contact with the surface of the cylinders; finally it is subjected to another squeezing at outlet from the chamber 12 due to its passage between the cylinders 114c and 114d.
It should be noted that the strip 11 is always heated by the cylinders to a temperature higher than boiling temperature in the pressure conditions present inside the chamber 12.
According to another variant which is not shown here, the strip 11 is wound for a segment outside the chamber 12 on the surface of the heated cylinder 114d to pre-heat it and thus to encourage the subsequent heating, by means of which the water on the strip 11 is brought to boiling point.
In this case too, using an environment inside which a condition of vacuum is substantially created allows to lower considerably the boiling temperature of the water, reduces the force of the molecular links and the external counter pressure which opposes the detachment of the molecules of water and humidity from the fabric.
All this allows to achieve both a considerable energy saving and also fewer risks of damaging the fabric thanks to the reduction of the working temperatures.
The embodiment shown in Fig. 2, with from 2 to 4 cylinders, is particularly suitable for drying hides after tanning; the short distance between the squeezing points of the cylinders enables an easy drawing in of the hides, which normally have a limited length.
The chamber 12 is associated with pump means, similar to those shown in Fig. 1a, to discharge the water extracted from the textile strip 11.
It is obvious that modifications and/or additions may be made to the method and device described heretofore, without departing from the spirit and scope of the invention. It is also obvious that, although the invention has been described with reference to specific examples, a skilled person shall certainly be able to achieve many other equivalent embodiments, all of which shall come within the field and scope of this invention.

Claims

Drying method for textile material in the form of strip (11), or hides, wherein said strip (11) or hide is made to pass inside a closed chamber (12) inside which an environment is created in depression with respect to the atmospheric pressure, characterized in that it provides to subject said strip (11) or hide passing through said depression chamber (12) to at least a heat treatment in order to take the water contained in said strip (11) to a temperature at least near to that of boiling, said heat treatment being associated with at least a mechanical treatment to remove the water and humidity present on the strip (11) or hide.
Method as in claim 1, characterized in that said mechanical removal method comprises at least a squeezing step to remove the water taken to a temperature at least near to that of boiling.
Method as in claim 1 or 2, characterized in that said mechanical removal treatment comprises at least a suction step to remove the water taken to a temperature at least near to that of boiling.
Method as in any claim hereinbefore, characterized in that the depression inside said chamber (12) is taken to values of between about 0.1 bar and about 0.5 bar, and the heating of the strip (11) or hide is performed in such a manner as to take said strip (11) or hide to a temperature of about 45-80 °C.
Method as in claim 4, characterized in that the depression inside said chamber (12) is taken to a value of around 0.15 bar, and the heating of the strip (11) or hide is performed in such a manner as to take said strip (11) or hide to a temperature of around 54 °C.
Method as in claims 2 and 4, characterized in that the heat treatment of the strip (11) or hide is performed through contact with the surface of at least a heated cylinder (14a; 114a-114d), and in that said squeezing step provides to squeeze the strip (11) or hide while it is passing between said at least a heated cylinder (14a; 114a-114d) and at least a squeezer roller (21) or a mating cylinder (114a, 114c).
Method as in claims 2 and 4, characterized in that the heat treatment of the strip (11) or hide is performed by means of focused emissions of infra-red rays or microwaves.
Method as in any claim hereinbefore, characterized in that it provides to pre-heat said strip (11) or hide before it is introduced inside the depression chamber (12).
Drying device for textile material in the form of strip (11), or hides, comprising a closed chamber (12) through which said strip (11) or hide passes, means (15, 16, 17) able to create a depression inside said chamber (12) and means (14a; 114a-114d) able to heat said strip (11) or hide passing inside said chamber (12), characterized in that, inside said closed chamber (12) kept under depression, it comprises means able to perform at least a mechanical treatment to remove the water and humidity present on the strip (11) or hide, cooperating with said means (14a; 114a-114d) able to heat said strip (11) or hide.
Device as in claim 9, characterized in that said means able to perform a mechanical treatment to remove the water and humidity comprise at least a squeezing roller/cylinder (21; 114a, 114c) cooperating with at least one of said means (14a; 114b, 114d) able to heat the strip (11) or hide and able to act on said strip (11) or hide when the temperature of the water present therein has reached a value substantially near the boiling temperature.
Device as in claim 9 or 10, characterized in that said means able to perform a mechanical treatment to remove the water and humidity comprise at least a suction device (26) able to act on said strip (11) or hide when the temperature of the water present therein has been taken to a value substantially near the boiling temperature.
Device as in claim 9, characterized in that said means able to heat the strip (11) or hide comprise at least a heated cylinder (14a; 114a-114d) arranged at least partly inside said chamber (12) and on whose surface said strip (11) or hide at least partly winds.
Device as in claim 9, characterized in that said means able to heat the strip (11) or hide comprise at least means able to emit infra-red rays or microwaves towards said strip (11).
Device as in any claim from 9 to 13 inclusive, characterized in that it comprises sealing means (13a, 13b; 114a, 114c) arranged at inlet and outlet of the chamber (12).
Device as in claim 14, characterized in that a partial function of said sealing means (13a, 13b; 114a, 114c) is the mechanical squeezing of the strip (11) or hide.
Device as in any claim from 9 to 15 inclusive, characterized in that said means (15, 16, 17) are arranged in such a manner as to create inside said chamber (12) a depression in the range of 0.1÷0.5 bar, and said heating means (14a; 114a-114d) are configured so as to heat the strip (11) or hide to a temperature in the range of 45÷80 °C.
Device as in claim 9, characterized in that said chamber (12) is defined by an outer structure including an inlet and an outlet for the strip (11) or hide, said inlet and outlet being defined by respective sealing means (13a, 13b), inside which outer structure there are cylinders (14a, 14b, 14c), at least one of which is heated, in contact with which said strip or hide is made to pass.
Device as in claim 10, characterized in that said squeezer roller (21) is able to exert a pressure on said strip (11) or hide which can be adjusted from about 10 kg up to 100 kg per linear centimetre.
Device as in claim 9, characterized in that said closed chamber (12) is defined by cylinders (114a-114d) whose surfaces are arranged in reciprocal contact, at least two cylinders (114a, 114c) being included with the surface lined with rubber and able to be pressed against the relative cylinders (114b, 114d) with an adjustable pressure from about 10 kg up to 100 kg per linear centimetre so as to exert a sealing function at inlet and outlet of said chamber (12) and to exert a mechanical action to squeeze the water and humidity from said strip (11) or hide.