The stenter machine as described herein includes any textile machine such as tenter, dryer and the like machine in which a fabric in stretched and/or unstretched condition is dried and/or stabilized by heating.

More particularly this invention relates to a stenter machine in which fabric is heated in the heating zone of the machine, by radiation, through hot plate (s) provided either below and/or above and below the fabric and heated by gas burner (s), without using any blowers, and heat of the exhaust gases is also utilized for direct heating of the fabric thereby reducing the length of the heating zone and drastically reducing the fuel cost and/or pollution, and high quality of stabilization of a fabric is achieved by providing fabric temperature sensor, measuring desired temperature of fabric at the exit end of the heating zone and signals of the said temperature sensor being utilized for controlling the fabric speed.

BACKGROUND ART: Polymer like the polyester are thermoplastic, they soften when heated and harden when cooled. During production, synthetic or blended fabric is subjected to various strains which cause shrinkage during wet processing or washing and this shrinkage is called relaxation shrinkage. In the fabrics made of synthetic/thermoplastic fibers the strains can be nullified by heat setting, i. e. by heating the fabric, while keeping it under dimensional control, to a temperature of about 30°C higher than the temperature used in wet processing or washing.

For achieving heat setting of the fabric it is heated to the required temperature of about 180°C to 210°C through out its cross-section. Such heat-setted fabric becomes dimensionally stable.

For achieving the above described heat setting of the fabric, stenter has been developed, in which jets or streams of hot air come into contact with the fabric.

Stenter has two main features, a high intensity convection heating system and provision for fabric width control. The latter is necessary because practically in all processing stages the fabric is subjected to longitudinal or warps wise tension to varying degrees and hence it

shrinks widthwise to varying extent at different sections along its length. Width control is effected in stenter with the help of a series of clips or pins mounted on a pair of endless chains. The clips or pins grip the selvedges of the wet fabric and adjust the fabric to the required width as it is dried in the stenter.

The heating section consists of a series of high velocity air jets. The air used is heated to temperature levels of the order of 180 ° C to 210° C, usually in heaters/radiators. Large quantities of the air are recirculated and reused to conserve heat. A certain amount of air is, however, removed continuously from the system, through one or more exhaust fans, to prevent build-up of excessive humidity.

The stenter which is presently in use in the textile industries mainly comprises a fabric feeding system, a heat-setting system and a fabric receiving system. The fabric feeding system consists of a set of rollers, which stretches the fabric widthwise and feeds it in to the heat setting system. The heat-setting system consists of a plurality of heating chambers and cooling chambers through which fabric passes in fully widthwise stretched condition with the help of a series of pins/clips mounted on a pair of endless chains which are moving in heat-setting system. Each of heating chamber is provided with a pair of air blowers attached to a pair of air ducts having perforations for producing air jets, a pair of heaters/radiators/gas burners for heating the air, a pair of air filters for removing fumes and loose fibers, to prevent them from entering the heaters/radiators/gas burners and blowers.

An exhaust fan and a damper is also provided in an exhaust/out-let of the heating chamber for occasionally discharging the air in to the atmosphere in order to control the humidity and air volume and pressure inside the heating chamber. Air heated by the heaters/radiators/gas burners is blown by the blowers in to the perforated ducts and the hot air jets/streams strike the moving fabric from its top and bottom sides. The hot air is recirculated in heating chamber continuously. After heating the fabric upto a required temperature of about 180° C to 210° C, in a number of heating chambers, the fabric passes in to the cooling chambers, where the cool air in the form of air jets/streams passes over the moving fabric from its top and bottom sides, there after the fabric is rolled or pleated in the fabric receiving system.

The main draw back of the existing stenter is that it is not thermal efficient and thereby is not economic. There is huge wastage of thermal/heat energy. The heat is wasted in initial heating of the air, inside the heating chamber The air as well as the fabric are heated by

convection i. e. , heaters/radiators which are generally thermic oil heaters or steam heaters are having heating media inside the tubes and air passes over the tubes, hence the heat transfer efficiency is very low. A lot of heat is wasted when the hot air is exhausted out of the heating chamber. Due to a large volume of hot air being circulated continuously in heating chamber, there is a heat loss through the chamber walls. Outside air enters the heating chamber through the fabric inlet/entry and similarly hot air leaks out of the heating chamber through the fabric exit, which also adversely affects the thermal efficiency of the stenter. Due to low thermal efficiency a large number of heating chambers are required which increase the size of the stenter and thereby wastage of materials, and electric power used for operating blowers and larger endless chains.

Besides very low thermal efficiency of the existing stenter it is observed that heat-setting of the fabric is not uniform through out the cross section of fabric, as the fabric is heated by the hot air jets and thus the portions of the fabric between the air jets are less heated in comparison with the portions of the fabric where the hot air jets strike directly.

In the conventional stenter air media used, is heated by using either coal, oil or gas fired boilers, which generates pollution. Further when air is exhausted out from the heating chambers it carries with it oil particles and fibres, which also cause pollution.

Stenter using infrared electric heating are also known in prior art in which a number of electric heating panels are provided in the heating zone. This infrared electric heating stenter could not be commercially used, as it is very costly and expensive in terms of operational cost, electricity is also not readily available in many places or there is a heavy electric power cut or breakdown. Further drawback of this stenter is that, in this stenter speed of the fabric is kept constant and temperature is controlled by controlling the various heating panels, hence the productivity remains low.

The main object of this invention is to over come the above described draw backs of the existing stenters and to provide a gas heated stenter which is very economic, pollution free and in which there is no need of air circulation and in which heating of fabric takes place by radiation, through gas heating, there by completely eliminating the use of pollution generating fuel and at the same time dispensing with the filters, hot air blowers, perforated air ducts, exhaust fan and damper along with the typical heating chambers which are essentially used in the existing stenters.

A further objects of the present invention is to provide a gas heated stenter in which the fabric is heated to the desired temperature, uniformly through out its width/cross section, thereby resulting into better heat seating or better finishing of the fabric.

A further object of the present invention is to provide a gas heated stenter, which requires very less maintenance, as there is no hot air blower, air duct, air filter damper and exhaust fan and thus reducing break down time resulting into higher productivity.

A further object of this invention is to provide a gas heated stenter which is very easy to transport, easy to assemble and install, as there are comparatively less number of parts, and which requires simpler and cheaper frame work and foundation.

A further object of this invention is to provide a gas heated stenter in which temperature is kept constant as desired for heat setting of a fabric and speed is controlled by using a sensor at the exit end of the fabric resulting into higher productivity for the same length and energy consumption of the stenter.

DISCLOSURE OF INVENTION This invention provides a stenter machine for heat processing of, fabric comprising of a fabric feeding system, a heat processing zone, a cooling system and a fabric delivery system, the said heat processing zone, comprises a chamber having fabric inlet, fabric exit and an exhaust, a set of fabric guiding rollers, a pair of tracks mounted on track stands with means for moving the fabric, in fully widthwise stretched form, through the chamber, a first gas burner provided at fabric inlet end and a second gas burner provided at the fabric exit end, each of the said burners being connected to a heating box which consists of a highly heat conducting material such as copper plate at the top side and mild steel plate, covered by heat insulation material, at other sides.

A stenter machine wherein the said copper plate at the top side of the heating box is provided with steps or wavy formations, to increase the surface area of hot plate, for more absorption and transmission to fabric.

A stenter machine wherein each of the said heating box is tapered away from the said gas burner for continuously reducing its volume and keeping the temperature constant.

A stenter machine wherein direct fabric temperature monitoring means is provided at the fabric exit end to maintain a desired temperature of the fabric and controlling/varying the fabric speed, for perfect fabric stabilization with high productivity.

A stenter machine wherein the exhaust gas from the heat processing zone/chamber is directly impacting the incoming fabric, for heating the fabric and utilizing the waste heat in exhaust.

A stenter machine wherein first burner at the fabric inlet end side is used for drying the wet fabric and the second burner at the fabric exit end side is used for heat setting of the fabric.

A stenter machine wherein, for heat processing of dry fabric, the first gas burner at the fabric inlet side is not used and only the second burner at the fabric exit end side is used for heat setting of fabric.

A stenter machine wherein the hot plate is provided either below and/or above the fabric.

BRIEF DESCRIPTION OF DRAWINGS : FIG. 1-Shows in perspective view the stenter machine, according to an embodiment of this invention.

FIG. 2. -Shows sectional elevation of the heating system/zone (heat processing zone) of the stenter machine.

FIG. 3. -Shows plan view of the heating zone of stenter machine.

BEST MODE FOR CARRYING OUT THE INVENTION : Referring to the Fig. 1, the stenter machine mainly comprises a mangle 1, a fabric feeding system 2, a heating system or heat processing zone 3, a cooling system 4, and a fabric delivery system 5. The mangle and the fabric feeding system consists of a set of rollers which stretches the fabric 6 widthwise and feed it into the heating system/zone through which fabric passes in fully widthwise stretched condition, with the help of a series of pins/clips mounted on a pair of a endless chains which are kept moving in the heat processing zone. After heat setting in heat processing zone fabric passes into the cooling system and thereafter the fabric is rolled or pleated in the fabric delivery system. All these systems/parts being well known are not described and illustrated in details for brevity sake.

Inventive features of this invention lie in heating system, which is described in details, hereinafter and illustrated in the Figs. 2 and 3. Now referring to the Figs. 2 & 3, the heat processing zone 3 is provided with a gas burner 7 at the fabric feeding/inlet end side, for dyeing the wet fabric and a gas burner 8 is provided at the fabric delivery/exit end side, for heat setting of the fabric. Each of the burners 7 and 8 is connected to a heating box formed

of a copper plate9, at its top side and a mild steel (M. S. ) plate 10, at its bottom side and other sides. M. S. plate 10 is covered by heat insulation 11 for preventing or minimizing heat energy losses. The copper plate 9 which remains towards the moving fabric may preferably provided with step formations or wavy formations for increasing the heating surface area for better utilization of heat energy generated by gas burners. Further the heating box attached to each of the burners is made tapered away from the burner, for continuously reducing its volume, in order to achieve uniform heating. A plurality of rollers 12 are provided in the heat processing zone for guiding the movement of fabric 6 in the heat processing zone and tracks 13, mounted on track stands 14 are provided for moving the fabric in fully widthwise stretched condition.

The heat processing zone 3 is confined by the walls 15 and an exhaust system 16 is provided in the topside wall of the heat processing zone. The exhaust heat from the exhaust system 16 may also be utilized to directly heat the fabric before entering into the heat processing zone 3.

For heat setting of the wet fabric, gas burner 7, at the fabric feed/inlet end is used for drying the fabric and the second burner 8, at the fabric, delivery/exit end is used for heat setting of dry fabric at predetermined desired temperature, depending upon the type/quality of fabric.

For heat setting of dry fabric first burner 7 is not used and only the second burner 8 is used for heat setting.

For increasing the productivity of the stenter machine the number of burners in the heat processing zone can be increased but in the way zone length will also be increased thereby needing more floor area for installing the stenter machine.

Direct fabric temperature monitoring means, such as fabric temperature sensor is provided at the fabric exit end for sensing the temperature of processed fabric. According to this invention, temperature is kept constant, as desired, for heat setting of the particular fabric being processed, and the speed of fabric moving through the heat processing zone is regulated/varied, by sensing the temperature of fabric at the exit end, thereby higher productivity is achieved for the same length and the same thermal energy consumption, in comparison with prior art stenter where speed is kept constant and temperature is controlled as desired, by regulating the heating system.

As seen in Fig. 2, hot plate 9 is provided below the fabric for heating the moving fabric 6 from below only, but as an alternative, fabric can be heated from any side or both the sides by providing the hot plate 9 below and/or above the fabric.

INDUSTRIAL APPLICABILITY : The stenter machine is having industrial applications for heat setting of fabric, stabilization of fabric and the like hot processing of fabric.

The advantages of this invention are less thermal energy requirement, heat transmission is faster, productivity of the machine is high, exhaust gas from the heating zone is directly impacting the incoming fabric thereby fully utilizing the heat energy and also reducing the heating zone length, fuel cost is drastically reduced, pollution is minimized and high quality of fabric stabilization is achieved, by directly monitoring the fabric temperature at exist end and by keeping the desired temperature at constant level and varying the speed of fabric and the maintenance cost is also very low as there is on blower, damper, air jet, etc.

The above description and illustrations in Figs. 1, 2, & 3 are given just to understand the invention rather than to limit its scope.