EP0079992B1

EP0079992B1 - Apparatus for drying wet textile fabrics

Info

Publication number: EP0079992B1
Application number: EP19810305521
Authority: EP
Inventors: Vyankatesh Apte Vasant
Original assignee: PRIMATEX MACHINERY PRIVATE Ltd
Current assignee: PRIMATEX MACHINERY PRIVATE Ltd
Priority date: 1981-11-23
Filing date: 1981-11-23
Publication date: 1988-02-03
Also published as: DE3176638D1; EP0079992A1

Description

This invention relates to a stenter for drying wet textile fabrics.
In what follows, the word "stenter" includes a single layer stenter, a multi-layer stenter and a float-dryer, and the word "chamber" includes a plurality of chambers.
A stenter is a machine essentially comprising (i) a mechanism to feed continuously a wetted textile fabric into a chamber in which (ii) processes such as equalising, finishing or curing are carried out on the moving fabric while it is being simultaneously dried, and (iii) a mechanism for delivering from said chamber dried processed fabric.
Stenters in current use employ dry air as the evaporating medium in its chamber. Good results could be obtained if the drying medium is moistureless air but that is never possible because the drying operation on wetted fabric must produce vapour and the air in the chamber can never be completely dry. However, it has been ascertained that the optimum ratio of air to moisture in the medium circulating in the chamber should be 9:1 by weight. Since evaporation is a continuous process, the said ratio will be fluctuating and in course of time, it is bound to fall below the optimum. It then becomes necessary to exhaust some of the medium from the chamber. As a result of the partial exhausting of the medium, a slight vacuum is created resulting in the sucking in of fresh air from gaps in the entry and exit of the fabric into and from the chamber. The fresh air has to be raised to the temperature of 150°C. The temperature of the exhausted medium is around 130°C. There is thus a distinct loss and expenditure of heat energy.
It is an object of this invention to minimise the aforesaid loss and expenditure of heat energy. This is achieved by substituting for the hot air, super-heated steam at about 150°C which will save a considerable amount of heat energy. This change of medium does not involve injection of steam into the chamber because the evaporation of the moisture of the fabric itself will produce continuously the requisite quantity of steam but it has to be heated to a temperature of about 150°C in order to achieve an efficiency that is better than that air. Over and above the saving of heat energy, this change makes it possible:-

(a) to maintain uniform temperature,
(b) to obtain increased production,
(c) to improve the handling quality of the fabric, and
(d) to prevent yellowing of the fabric.

According to the present invention there is provided a stenter for drying wetted fabric by means of superheated steam, comprising a chamber, a carrier for moving the fabric through the chamber, one or more fans (2, 3) located in respective fan housing(s) for propelling super- heated steam along one or more tunnels, mutually-parallel elongate venturi openings in the or each tunnel through which steam from the tunnel(s) is discharged against the fabric in the chamber, a channel between adjacent venturi openings for collecting and removing steam reflected from the fabric, one or more exhaust outlets from the chamber and means for producing heated steam so that it has a temperature of 150°C as it is discharged against the fabric, the arrangement being such that the steam discharged against the fabric is derived solely from the moisture of the fabric.
U.S. Patent Specification No. 3015893 describes a stenter in which steam evaporated from a textile fabric is heated and recirculated so that it is in contact with further textile. This proposal has never, as far as we are aware, been used; the specification makes no disclosure of the critical temperature of 150°C generated from moisture evaporated during the drying process. The provision of external steam is wasteful of heat and the use of temperatures above or below 150°C lead to a lowering of efficiency in the use of fuel. Furthermore the U.S. Patent makes no disclosure of the arrangement of venturi openings required by the present invention.
The chamber design has to be modified because of the change of medium from hot air to superheated steam.
Stenters known hitherto have a chamber provided with longitudinally aligned heat radiators, each radiator being located in the vicinity of a linear plurality of suction fans, each fan being located in a circular fan-housing opening into a tapering rectangular tunnel with openings in its side facing the moving fabric. In these known stenters, the openings are a plurality of holes.
The stenter of the present invention, however, provides discharge of superheated steam by elongate venturi openings which preferably extend across the whole width of the fabric to direct a jet of superheated steam onto the moving fabric. Between adjacent venturi openings a channel is provided for the collecting and removing steam reflected from the surface preferably to a space in the vicinity of the means for producing heated steam, which is preferably a radiator.
The steam propelled down the tunnel may be guided into the venturi openings by means of mutually parallel slats positioned transverse to the venturi openings.
In known stenters, an exhaust is located in the top of the stenter chamber. This position of the exhaust is not desirable when the drying medium is superheated steam. Being lighter than air, the steam tends to rise to the top of the chamber leaving some air at the bottom. Furthermore, the medium in the chamber contains the vapour of oil or wax used in finishing the fabric, the condensation of which near the exhaust in the top of the chamber would produce droplets which might fall on the running fabric and damage it. Accordingly, it is preferred that in the stenter of the present invention one or more exhaust openings are provided in the bottom of the chamber. The bottom location of the exhaust openings ensure the complete removal of air from the chamber. With the change of medium in the chamber to super- heated steam, the possibility of the pressure inside the chamber exceeding the safety level cannot be ruled out. This invention accordingly optionally provides each of the exhaust openings with a damper adapted to operate only when the pressure inside the chamber exceeds the safety level. The damper may be actuated by a mechanism which is in turn actuated by a signal from a photoelectric cell which becomes activated only when the level in a manometer limb connected to the chamber goes down beyond the safety level.
How the invention may be carried out will now be described with reference to the accompanying drawings in which:

Figures 1 and 2 show schematically a single layer stenter in sectional elevation and plan;
Figures 3 and 4 show schematically a multi layer stenter in sectional elevation and plan;
Figures 5 and 6 show schematically a float-dryer in sectional elevation and plan;
Figure 7 is a section of the chamber Y taken along the line AB in Figures 2, 5 and 6;
Figure 8 is a similar view to Figure 7 showing a section of the chamber Y taken along the line CD in Figure 3;
Figures 9 and 10 illustrate respectively in perspective and plan a part of a tapering tunnel connected to the fan-housing; and
Figure 11 illustrates schematically the operation of the damper in the exhaust to the chamber.

X, Y and Z indicate respectively in each of the Figures 1 to 6 the fabric feeding mechanism, the chamber and the fabric delivering mechanism. This invention is concerned with only the chamber Y in each of the illustrated machines, the same numerals being used to indicate identical parts performing identical functions in all the figures of the drawings.
Referring to Figure 7, 1 indicates the fabric sheet passing through the chamber Y. In the Figures 1 to 6, 1a indicates the wet fabric entering the chamber Y 1b the dry processed fabric delivered from the chamber Y and 9 indicates the vertical section of the walls of the chamber Y along the sectional line AB. The chamber has an exhaust opening 8 at its bottom. The fabric 1 is partially dry after its passage from the entry to the line AB. It is being further dried by superheated steam which is made to circulate in the chamber Y by means of fans 2 and 3 located inside the fan-housings 4.1 and 5.1 and the truncated tunnels 4.2 and 5.2 respectively. The tunnels have the openings 10 facing the fabric 1. The vapour produced by the evaporation of the moisture in the fabric 1 and the steam reflected from the fabric 1 proceed to the space surrounding the radiators 6 and 7 located in the chamber Y near its walls 9.1 and 9.2 respectively. The fans 2 and 3 are located below and above the radiators 7 and 6 respectively. The arrows in Figure 7 show the direction of the circulation of the medium.
Figure 8 is a duplication of Figure 7 with this difference that the fabric 1 is moving in the opposite directions in the upper and lower halves of the figure.
Referring to Figures 9 and 10, 10 indicates the linear venturi openings in the tunnel 4.2 or 5.2 with the channel 11 between them. Immediately below the channel 11 are a series of parallel pendant slats 12.
Referring to Figure 11, a manometer 13 is connected to the chamber Y. The arrows 14 indicate the position of a photoelectric cell. A signal from the photoelectric cell actuates the motorized drive 15 of the damper 16 in the exhaust opening 8.
The wetted fabric 1a is fed into the chamber Y where it is dried by superheated steam produced by the heating elements or radiators 6 and 7. The superheated steam is sucked in by the fans 2 and 3 through the opening in the fan housings 4.1 and 5.1 and pushed into the tunnels 4.2 and 5.2 from where the superheated steam is jet-discharged against the fabric 1 (a stage between 1a and 16) and is reflected along with vapour along the channel 11 towards the radiators 6 and 7 where it is heated to the requisite temperature and goes through the same cycle as described. The steam entering the tunnels 4.2 and 5.2 is pushed into the gaps between the pendant slats 12 and therefrom into the venturi openings 10 from where the steam is discharged in a linear jet against the fabric 1. In practice, there is a plurality of fans 2 (or 3) linearly disposed and corresponding tunnels 4.2 and 5.2 respectively. It is however possible for one fan to feed two or three tunnels by the requisite arrangement of fan-discharge ducts. Such an arrangement will increase space between the fans making increased suction possible.

Claims

1. A stenter for drying wetted fabric (1) by means of superheated steam, comprising a chamber (Y), a carrier for moving the fabric through the chamber (Y), one or more fans (2, 3) located in respective fan housing(s) (4.1, 5.1) for propelling superheated steam along one or more tunnels (4.2, 5.2), mutually-parallel elongate venturi openings (10) in the or each tunnel (4.2, 5.2) through which steam from the tunnel(s) is discharged against the fabric (1) in the chamber (Y), a channel (11) between adjacent venturi openings for collecting and removing steam reflected from the fabric, one or more exhaust outlets (8) from the chamber (Y) and means (6, 7) for producing heated steam so that it has a temperature of 150°C as it is discharged against the fabric (1), the arrangement being such that the steam discharged against the fabric (1) is derived solely from the moisture of the fabric (1).

2. A stenter as claimed in claim 1, characterised in that there are a plurality of mutually parallel slats (12) positioned to guide steam from the associated tunnel (4.2, 5.2) towards the venturi openings (10).

3. A stenter as claimed in claim 1 or in claim 2, characterised in that each of the exhaust outlets (8) is in the bottom of the chamber (Y).

4. A stenter as claimed in claim 3, characterised in that each exhaust outlet (8) is provided with a damper (16) which is adapted to be normally closed but to be opened when the pressure in the chamber exceeds a predetermined level.

5. A stenter as claimed in claim 4, characterised in that each damper (16) is connected to a motorised drive (15) the operation of which is triggerable by a pressure sensitive device (13, 14).

6. A stenter as claimed in any one of claims 1 to 5, characterised in that one fan (2, 3) is adapted to feed a plurality of tunnels (4.2, 5.2) by an arrangement of fan discharge ducts.