An improved method for decatizing in an autoclave

Abstract: There is described herein an improved method for decatizing in an autoclave (4) wherein steam is led into the jacket (3) surrounding said autoclave, at a pressure level increasing up to a stationary level within the autoclave. That is obtained by means of an automatically and adjustably controlled throttling valve (1) at the steam inlet to the jacket, said valve being for instance driven by means of a microprocessor routine, and having an autoclave inlet valve (2) associated therewith. In case the outer jacket is missing there might possibly be provided only an automatically controlled autoclave inlet valve performing also as a throttling valve, in order to have a gradually increasing inlet pressure.

Description: This invention concerns an improved method for steam decatizing fabrics in an autoclave. As it is already known, for decatizing fabrics in an autoclave, the steam to be used, coming from a high pressure supply line,normally flows through a throttle valve which reduces the steam pressure to the values required by the decatizing treatment, usually 2×10⁵ Pa (about 2 atmospheres or about 29 psi). The autoclave is usually provided with an outer jacket which is flooded with said steam and has the double function of heating the actual autoclave in order to avoid condensation, and of equalizing the temperature of steam before the latter enters the autoclave. When starting the decatizing operation, steam is withdrawn from the outer jacket and introduced inside the autoclave by opening a valve thereof connected with some sensors (thermometers, pressure gauges, and so on..), in order to introduce steam in the autoclave until desired levels of pressure and/or temperature are reached. It is also known that in the autoclave decatizing machines, as they have been used until now, the autoclave inlet pressure remains constant for the whole duration of the decatizing cycle, since constant set levels are used both for the throttling valve and for the inlet valve. Of course, still during the decatizing cycle, the pressure inside said autoclave is variable due to the filling by the steam coming in, at least until a stationary value is reached. In this way though, out of phase actions take place during the injection of steam coming from the jacket. The latter, coming into contact with the roll of fabric subjects it to a squeezing action which remains strong until all the steam has passed through said roll. In fact, while the autoclave chamber is flooded with steam, the central portion thereof is connected with the environment, for instance through a vent, possibly connected with a vacuum pump, provided at the core of said roll, which enables the air initially contained therein to be vented out, being displaced by said steam pressure. When all the air, and thereby the oxygen contained therein, have come out, the vent is closed and the autoclave may be pressurized. However, during the transient, while steam floods the chamber surrounding the roll and the internal vent is open, the fabric is subjected to a high force in that the steam coming in has a high pressure already, for instance in the range of 1,2 × 10⁵ Pa (about 1,2 atmospheres or about 17 psi). The pressure difference between the incoming levels and the vent connected to the environment is made possible by the resistance opposed by the fabric roll, acting as a large filter. Therefore, it should be apparent that, if predetermined pressure levels are desired inside tha autoclave (for instance a final pressure of 1,5 x 105 Pa (about 1,5 atmospheres - about 21.5 psi) the throttle valve will have to be already set initially at said level, as a matter of fact preferably at a slightly higher level because of the unavoidable pressure losses. Of course, the higher the pressure, the stronger the squeezing action on the roll. To summarize, it will be stated that usually a conventional decatizing system is provided with valves which cannot be controlled (a steam pressure throttling valve set at a high level and an autoclave steam inlet valve, of the on/off type). For example DE-A-3147861 relates to a decatizing method and apparatus providing a special cylinder with pipes parallel to the longitudinal axis and directly in conctact with the inner perforated surface thereof. To solve the problem of steam condensation with production of water, which is dangerous to the decatizing treatment, the cylinder is pre-heated by means of steam flowing through the said pipes. No particular low of feeding steam is provided. It is further known that the above-mentioned fabric roll squeezing effect, at the start of the decatizing cycle, causes a different decatizing action on the fabric layers located either on the outside or on the inside of the roll, when taking into account that decatizing is due to a combination of two different actions like mechanical squeezing and the steam temperature. Therefore, the result is that the fabric portion wound around the outside of the roll and subjected to a stronger squeezing and to a higher temperature is treated differently from the portion of the fabric wound inside the roll, whereby also the final results on the fabric quality will be different. Therefore it is an object of the present invention to provide a decatizing method that can overcome the above-mentioned problems of feeding steam in the transient period and of different decatizing action in the outer and inner fabric layers in a roll. This is obtained with a method according to the characterizing features of claim 1 which provide for feeding the autoclave with a gradually increasing steam pressure. In such a way, the steam pressure acting on the roll will be lower than with the method known in the art, in that at any moment the inlet pressure will be lower than if the throttle valve were set at a fixed pressure level, which would unavoidably be the maximum to be reached inside the autovclave, or even higher. Accordingly, the throttling valve, which is initially set at very low pressure levels, increases its set level as the autoclave internal pressure is increasing. In other words, it may then be said that the autoclave pressure level tracks the throttle valve set level, which in turn increases as the autoclave internal pressure increases. In such a way, during the whole filling cycle, there is never a large difference between the inlet steam pressure and the actual autoclave inner pressure. It should be noted that, if the jacket surrounding the autoclave was not provided, with the steam coming directly from the line, there would be a single autoclave inlet valve, having both functions of inlet and throttling valve, and this valve would have to be controlled at progressively increasing pressure levels, in the fashion mentioned above. These and other objects, advantages and features of the improved decatizing method of this invention will become apparent from the following detailed description, referring to the only attached drawing, which shows schematically how the subject method may be applied on an embodiment of a jacketd autoclave. Referring now to the drawing, steam coming from high pressure supply line 1a enters jacket 3 surrounding the autoclave 4, flowing through a throttling valve 1 wherein the pressure is reduced and brought down to the desired levels. According to this invention, valve 1, instead of being set at a constant pressure level during the whole decatizing cycle, is set at variable pressure level, being automatically controlled in any known way, for instance by means of a microprocessor routine, by a timer, by a pressure gauge and so on, whereby the steam exit pressure is gradually increasing with time. When opening autoclave inlet valve 2, the steam flowing into the autoclave will initially have a lower level, and the pressure on roll 6 will be relatively low in that, during said initial step of the decatizing cycle, the pressure will certainly be lower than the level which would correspond to valve 1 being set at a fixed pressure, as known in the art. The fabric roll 6 outer layers will then be subjected to a low level squeezing action, while the air present inside the roll, which damages the decatizing process due to the presence of oxygen therein, is led out through an inner vent 5, comprised for instance of the same perforated core of roll 6, connected to the outside along a passage through a vent. While the pressure within autoclave 4 increases due to the resistance opposed by the roll which acts as a filter between the steam entering through valve 2, and vent 5, also the inlet pressure increases due to the way valve 1 is controlled, while valve 2 may be a simple on/off through valve. Still according to what is known in the art, if for example it is desired to obtain a stationary level of 1,5 × 10⁵ Pa (about 1,5 atmospheres or 21.5 psi) of the inner pressure in autocalve 4, for the decatizing cycle, the pressure at valve 1 will have to be set at approximately 2 × 10⁵ Pa (about 2 atmospheres or about 29 psi). Therefore, when valve 2 is opened, chamber 4 is immediately impacted by steam having said high level of pressure and associated temperature, whereby the outer layers of roll 6 are subjected to a strong squeezing. If instead it is desired to perform the decatizing treatment still at 1,5 × 10⁵ Pa (about 1,5 atmospheres or about 21.5 psi) with the method of this invention, valve 1 may be controlled starting for instance from a pressure level of only 5 × 10⁴ Pa (about 0,5 atmospheres or about 7 psi), which is gradually increased to gradually reach eventually the desired level of 1,5 × 10⁵ Pa (about 1,5 atmospheres or about 21.5 psi). In this way thesqueezing values will be drastically reduced in that in the starting unbalanced pressure period inside the autoclave, the pressure fabric roll 6 is subjected to is substantially lower. Therefore, the decatizing treatment non-uniformities on the roll are done away with and reduced, and the associated finishing action on the fabric lump comprising roll 6 is substantially more uniform going from the outer fabric layers to those wound more internally. It should be noted that steam might also come directly from line la, without flowing through jacket 3, there being only provided a valve 1 which leads steam directly inside the autoclave. In such a case valve 1 performs also as inlet valve 2, but it is still substantially a throttling valve controlled at gradually increasing pressure levels, as mentioned before, according to this invention. It should be understood that, if in autoclaves there were no flow inversion problems (from the outside to the inside, or from the inside towards the outside) there would be no need for two valves, but a single one would be enough. Since the manufacturing processes include both direction for introducing steam, it is apparent that two valves are required. It should also be apparent that what has been described above holds true also when leading steam in from the inside towards the outside of the roll, in that to a steam intake through the foraminous cylinder there corresponds a venting of air in the autoclave chamber surrounding the roll. It should be understood that the subject of this invention is also extended to an autoclave wherein, through associated actuating and control apparatus, such as valves and so on, the method of this invention is carried out.

Claims: An improved method for decatizing fabric wound on rolls in an autoclave (4), wherein an air outlet vent (5), a supply line (1a) and a controlled inlet valve (1) is provided, characterized in that the pressure of steam supplied to the autoclave (4) from the supply line (1a) is variable through the automatically controlled inlet valve (1) and gradually increasing as the autoclave inner pressure increases, until a maximum desired level is reached which is equal to or higher than the stationary level within said autoclave, wherein the steam is led into the autoclave (4) through an inlet valve (2) in communication with a jacket (3) surrounding said autoclave (4) and in turn supplied with steam through said controllable valve (1).

Inventors: ALBERTO PIETRO, ALBERTO, PIETRO
Applicants: ALBERTO PIETRO, ALBERTO, PIETRO
Application year: 1991
Main classification: D06B5
IPC codes: D06B5, D06B3, D06B23, D06B19