Abstract:
In a method and apparatus for sizing a yarn sheet, the yarn sheet is passed over rollers through a wetting unit and a following roller nip that reduces the moisture content to a selected level. The wetted yarn sheet then passes through a sizing unit and over rollers forming a nip to reduce the sizing content to a desired level. The rollers of the wetting unit and the rollers of the sizing unit are in close proximity to minimize the reach of the yarn sheet there between and thereby minimize the heat loss in the yarn sheet. The reach is covered by a cover having a heater that extends over the yarn sheet reach to maintain the yarn sheet at a desired temperature as it enters the sizing unit. The temperature of the wetting agent bath in the wetting unit is 65°-95° C., with the temperature of the wetting agent being approximately 5°-10° C. higher than the temperature of the sizing agent bath. The temperature of the yarn sheet entering the sizing unit is maintained at a temperature no less than 10° C. of the sizing agent temperature. The nip of the wetting agent rollers reduces the moisture in the wetted yarn sheet to 25% to 50%.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of German patent application DE 199 14 285.8, filed Mar. 30, 1999, herein incorporated by reference 
     FIELD OF THE INVENTION 
     The invention relates to a method and apparatus for sizing a yarn sheet, wherein in a first step wetting agent, which is at a temperature of 65 to 95° C., is applied to the yarn sheet, which is then squeezed until it contains a selected residual moisture, and in a second step a sizing agent, which is at a temperature of 65 to 95° C., is applied to the yarn sheet, which is then squeezed until it contains a selected residual moisture. 
     BACKGROUND OF THE INVENTION 
     In preparation for weaving, a sizing is applied to warp yarn in the form of a yarn sheet. In the process, the yarn sheet is passed through a sizing bath, is squeezed thereafter and finally dried. 
     It is known from DE 42 37 962 to pass a warp yarn sheet through a water bath prior to the sizing bath, and to subsequently squeeze the yarn sheet following the water bath. The water bath is heated above room temperature and contains chemical additives. This pre-treatment results in the finishing being pre-loosened and partially washed out. It also improves the absorption capability of the warp yarns. 
     It is also known from DE 42 34 279 to apply sizing to a sheet of fine-capillary yarn of the micro-filament type, wherein the yarn is pre-wetted in a first step with a liquor which is diluted in comparison to the final concentration of the sizing liquor and is squeezed in a second step until it contains a first residual moisture, and immediately following the squeezing is treated with a sizing liquor at an end concentration, and subsequently is squeezed until it contains a second residual moisture. 
     The wetting agent is essentially water, containing little or no sizing. The wetting agent is heated to a temperature of close to approximately 90° C. A yarn of the micro- filament type can be produced by this method, which has a core relatively low in sizing or containing no sizing, as well as a sheath sufficiently stable for weaving and containing a relatively large amount of sizing agent. 
     For successful sizing it is necessary to maintain a defined sizing concentration and a defined sizing temperature in the sizing bath. With too high a sizing concentration, too much sizing is used up, which is undesirably expensive. On the other hand, too low a sizing concentration can lead to problems during subsequent weaving. A defined sizing temperature of, for example, 85° C., is required for setting a viscosity of the sizing bath which assures an even sizing application. 
     In connection with single-stage sizing without pre-wetting, Applicant knows to set the sizing concentration and the sizing temperature by supplying steam under ambient pressure and adding sizing liquor, hereinafter called sizing agent, to the sizing bath. This setting is performed in such a way that the sizing liquor removed with the yarn sheet and the water, which evaporates because of the high sizing temperature, are continuously replaced. 
     Applicant furthermore knows to provide the sizing unit with a double sheath heated by steam under ambient pressure. Because of this the amount of steam introduced directly into the sizing bath for heating can be reduced. 
     If the yarn sheet is pre-wetted in a first step, and sized in a second step, the yarn sheet is already provided with the wetting agent and slightly cooled when it reaches the sizing bath. The pre-wetted yarn sheet absorbs less sizing agent than a dry yarn sheet. When sizing after pre-wetting, more energy is needed for heating the yarn sheet provided with the wetting agent on the one hand, but on the other hand less sizing agent is needed. In the course of heating the sizing bath by supplying steam, a considerable dilution of the sizing concentration can occur at start-up, if no compensating steps are taken. If the sizing concentration is set in such a way that it attains its desired value after start-up, the yarn sheet is charged with too great an amount of sizing at start-up. In this case the initial amount lies above the desired amount of sizing by 15 to 20%, and the desired amount of sizing is only reached after the first 2000 to 3000 m of yarn sheet. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to further develop a method and apparatus for sizing a yarn sheet in such a way that the normal significant dilution of sizing concentration during start-up is minimized. 
     This object is attained by indirectly heating the sizing agent, preferably by a contact surface at a temperature of 100 to 160°. 
     It is important that energy is supplied indirectly for heating the sizing agent instead of steam which condenses to water in the sizing bath, thereby diluting the size concentration. Several possibilities of indirect heating of the sizing agent in the size box can be employed, such as one or several heating panels or heating coils arranged in the size box, which are heated by a heating medium, such as steam under pressure, or hot oil, or electricity. It is also important that a temperature of at least 100° C. be maintained at the contact surface by the heating medium, which is at a temperature of greater than 100° C. Temperatures between 120 and 140° C. are particularly advantageous. 
     Indirect heating of the sizing agent allows the setting of the sizing temperature without the supply of water. Only a defined amount of wetting agent, mainly water, is introduced into the sizing bath by the replacement of wetting agent with sizing agent in the yarn sheet. A defined amount of water evaporates from the sizing bath because of the high sizing temperature. In comparison with the amount of the evaporated water, only a small excess of the amount of water introduced by means of the yarn sheet leads to the dilution of the sizing bath during start-up. The lowering of the sizing concentration during start-up is less than 10%, for example, wherein the equilibrium of the sizing concentration will already be reached after a few hundred meters of the yarn sheet. It is possible to accept such slightly increased initial amounts of sizing agent, namely less than 10%, so that the sizing concentration can be set by adding sizing agent alone. Additional steps, such as the measurement of the sizing concentration and regulation of the sizing application on the basis of weight measurements described, for example, in DE 42 34 279, or by matching the sizing concentration by means of a concentration mixer, are no longer required. 
     A temperature of the wetting agent in the first step, for example 5 to 10° C. higher than the temperature of the sizing agent in the second step, i.e. the sizing temperature, reduces the temperature difference between the yarn sheet already provided with wetting agent and slightly cooled, and the sizing temperature. The yarn sheet provided with the wetting agent can be heated more rapidly, resulting in less energy being required for heating. 
     Preferably, cooling of the yarn sheet wetted in the first step until it is acted upon by the sizing agent in the second step is maximally limited to 10° C. Limiting the cooling can take place by the second step immediately following the first step. This can be made possible by a compact construction of the sizing device. The limitation of cooling can also be provided by insulating the yarn sheet by means of a cover and/or the supply of heat to the yarn sheet on the way from the wetting agent bath to the sizing bath. The limitation of cooling assures the low energy consumption in the second step. 
     In the preferred embodiment, in the first step after pre-wetting the yarn sheet, it is squeezed so it contains a residual moisture between 25 and 60%. The residual moisture corresponds to the weight of the water as a function of the weight of the yarn sheet. The residual moisture of the yarn sheet following sizing and squeezing in the second step is set, as described in DE C 42 34 279, to be the same, but in most cases higher. A comparatively low residual moisture of the yarn sheet after the first step prevents a strong dilution of the sizing bath, adds to a stable sizing concentration and has an advantageous effect on the energy consumption because of the small amount of wetting agent which needs to be heated. 
     In the apparatus of the present invention, which is suitable for carrying out the method of the present invention, the sizing unit has an indirect heater with a flat contact surface. 
     Depending on the amount of heat output required, the contact surface constitutes a portion of or the entire bottom of the sizing box, wherein the contact surface of the indirect heater is integrated into the bottom of the size box. This integration and the flatness of the contact surface assure the even heating of the sizing agent in the size box without the danger of sizing agent baking onto a transition edge or onto irregularities. A simple and compact structure of the size box, and therefore of the entire sizing device, is made possible by the integration of the contact surface into the bottom. 
     Preferably, the indirect heater has a heating plate designed as a steam pressure panel consisting, for example, of two plates which are connected with each other in places and, has a low structural height. Its surface can moreover easily be matched to the required heat output. 
     It is possible to obtain a compact structure of the sizing apparatus by use of a common housing for the wetting unit and the sizing unit, which is divided into a wetting agent box and a size box by a separating wall. 
     A compact structure is also obtained by the size box being arranged directly downstream of the wetting agent box and with its bottom at the approximate height of the last roller of the wetting unit. In this case the first roller of the sizing unit is located closely downstream of and slightly above the last roller of the wetting unit. The length of the reach of the yarn sheet between the wetting unit and the sizing unit is reduced by this compact construction. The minimal length of the reach prevents excessive cooling of the yarn sheet. Therefore, only a comparatively small supply of energy from the indirect heater is required for heating the sizing agent. This permits a comparatively small heating panel, for example, which can be advantageously accommodated in the sizing agent bath. 
     A cover over the yarn sheet reach and preferably a heater in the cover, are further features which present excessive cooling of the yarn sheet on its way from the wetting unit to the sizing unit. 
     The preferred embodiment of the invention is illustrated in the accompanying drawings and diversified in detail thereafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of a yarn sizing range incorporating the apparatus for sizing a yarn sheet according to the preferred embodiment of the present innovation; 
     FIG. 2 is an enlarged diagrammatic view of the yarn sizing apparatus included in FIG. 1; and 
     FIG. 3 is an enlargement of a portion of the bottom of the size box of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A range for sizing a yarn sheet  1  represented in FIG. 1 has a feeding section  2 , a sizing apparatus  3 , a dryer  4  with drying cylinders  5  and a take-up apparatus  6  with a take-up beam  7 . The feeding section  2 , the dryer  4 , in whose housing the sizing device  3  is located, and the take-up device  6  are arranged one behind the other in the conveying direction of the yarn sheet  1 . The sizing device  3  has a reversing roller  8 , a wetting unit  9  and a sizing unit  10 . It is shown in greater detail in FIG.  2 . The reversing roller  8 , embodied as a measuring and draw-off roller for the feeding section  2 , for example, is located in the lower area, or underneath in front of a wetting agent box  11 . 
     Besides the wetting agent box  11 , the wetting unit  9  has three rollers  12 ,  13  and  14  mounted above the wetting agent box  11 . The wetting agent box  11  extends transversely in respect to the conveying direction of the yarn sheet  1  over the entire width of the rollers  12 ,  13  and  14 , which are of the same width. The diameters of the second roller  13  and the third roller  14  are of the same size, the diameter of the first roller  12  is about half of these diameters. The second roller  13  and the third roller  14  are arranged one above the other, and the first roller  12  is arranged in the upper area in front of the second roller  13 . In this case the second roller  13  projects into the wetting agent bath in the box  11  as far as below a minimum marker of a level indicator  15 . As indicated by an arrow  16 , the first roller  12  is provided with pressure means, for example a compressed air cylinder, by means of which it can be pressed against the second roller  13 . In this way a first squeeze nip  17  is formed between the first roller  12  and the second roller  13 , and a trough  18  is formed above the squeeze nip  17 . A wetting agent feed device  19  terminates in this trough  18  to provide wetting agent therein. The second roller  13  is connected with a driving mechanism, as indicated by an arrow  20 . As indicated by an arrow  21 , the third roller  14  is provided with pressure means, which are threaded rods, by means of which it can be moved toward the second roller and pressed against it. Thus, a second squeeze nip  22  is formed between the second roller  13  and the third roller  14 . In this way the rollers  12 ,  13 ,  14  form a draw-in unit for the sizing unit  10 . 
     A size box  23  of the sizing unit  10  is arranged closely downstream of the wetting agent box  11  above the level of the wetting agent box  11 , and its bottom  24  lies at the height of the aforementioned third roller  14 . 
     Besides the size box  23 , the sizing unit  10  has three rollers  25 ,  26  and  27 , arranged in the area of the size box  23 . In the same way as the wetting agent box  11 , the size box  23  extends transversely in respect to the conveying direction of the yarn sheet  1  over the entire width of the rollers  25 ,  26  and  27 , which are of the same width. 
     The diameters of the second sizing unit roller  26  and the third sizing unit roller  27  are equal, the diameter of the first sizing unit roller  25  is approximately two-thirds of those diameters. The three rollers  25 ,  26 ,  27  are arranged one behind the other, wherein the second and the third rollers  26 ,  27  are at the same height and extend into the sizing agent bath in the size box  23  as far as below a minimum marker of a level indicator  28 . The first roller  25  is arranged in the upper area of the second roller  26 . In this case it can extend slightly above the second roller  26 . As indicated by an arrow  29 , the first roller  25  is provided with pressure means, for example a compressed air cylinder, by means of which it can be pressed against the second roller  26 . Because of this, a first squeeze nip  30  is formed between the first roller  25  and the second roller  26 , and a trough  31  above it. A sizing agent feed device  32  terminates in this trough  31  to provide sizing therein. The second roller  26  is connected with a driving mechanism, as indicated by an arrow  33 . As indicated by an arrow  34 , the third roller  27  is provided with pressure means, by means of which it can be moved toward the second roller  26  and pressed against it. Thus, a second squeeze nip  35  is formed between the second roller  26  and the third roller  27 . 
     The size box  23  has an overflow wall  37 , which extends parallel in front of a rear wall  36  and is of a height corresponding to the maximum filling level of the bath. 
     The size box  23  has an indirect heater with a heating panel  38 , namely a steam pressure panel, which has been inserted into the bottom  24  of the size box  23 . The heating panel  38  has an upper plate  39  and a lower plate  40 , which are connected with each other at defined places. Channels, for example in a serpentine pattern, for the heating medium are formed by these connections between the plates  39  and  40 . Further spot-shaped connections for stabilizing the heating panel  38  can be provided. 
     It is important that a contact surface  41  of the upper panel  39  of the heating panel  38 , which is oriented toward the interior of the sizing agent bath  23 , is level and closes off the bottom  24  by means of an inner surface  42  (see FIG.  3 ). A steam feed line  43 , with a valve  45  which is provided with a control  44 , leads to the heating panel  38  embodied as a steam pressure panel. A discharge line with a condenser  47  for discharging the heating medium, namely the steam, is connected to the heating panel  38 . 
     Instead of being designed as a steam pressure panel, the heating panel  38  can be designed as a hot oil panel or as an electrically heatable panel. In place of two plates  39 ,  40 , which constitute conduits for the heating medium, it is for example possible to provide heating coils or heating tubes, which are connected with each other, for the heating medium underneath the bottom  24  or in another panel. It is important that the indirect heater has a flat contact surface  41 . As in this example, the contact surface  41  can constitute a portion of the bottom  24  and ends flush with the inner surface  42  of the bottom  24 . But it can also extend over the entire bottom  24  of the size box  23 . 
     The sizing apparatus  3  has a compact structure provided by the arrangement of the wetting agent box  11  and of the rollers  12 ,  13 ,  14  of the wetting unit upstream of the size box  23 , wherein the rollers  13 ,  14  of the wetting unit  9  are arranged one above the other, and the size box  23  above the wetting agent box  11 . Because of this arrangement the length of the reach  48 , over which the yarn sheet  1  is conducted from the last roller  14  of the wetting agent box  11  to the first roller  25  of the size box, is reduced. The reach  48  extends between a departure point  49  of the yarn sheet  1  at the surface of the last roller  14  of the wetting unit  9  and an arrival point  50  of the yarn sheet at the surface of the first roller  25  of the sizing unit  10 , i.e. between the contact points  49  and  50  of a tangent line drawn on the surface of the rollers  14  and  25 . The size of the reach is in the order of 1 m, preferably 250 to 750 mm. 
     A cover  51  with a heater  52  can be provided above the reach  48 . The wetting unit  9  and the sizing unit  10  can have a common housing  53 . 
     In the course of operation, the yarn sheet  1  is pulled off the feeding section  2 , is conducted through the sizing apparatus  3  and over the drying cylinder  5  of the dryer  4  to the take-up apparatus  6 . It is wound onto a take-up beam  7  in the take-up apparatus  6 . 
     In a first step, the yarn sheet in the sizing device  3  is acted upon by the wetting agent bath in the wetting unit  9 , preferably water at a temperature between 65 and 95° C., and is squeezed to contain a residual moisture of 25 to 60%. The temperature of the wetting agent is set to be approximately 5° C. higher, for example, than that of the sizing agent. The residual moisture of the yarn sheet  1  when it leaves the wetting unit  9  is determined as a function of the wetting capability of the yarn sheet  1  and the wetting agent temperature. 
     In the sizing unit  10  the yarn sheet  1  is acted upon by the sizing agent bath in the size box  23  at a temperature between 65 and 95° C. in a second step, and is squeezed to contain a residual moisture of 80 to 160%. 
     The yarn sheet  1  is twice charged with wetting agent and subsequently twice squeezed. To this end, the yarn sheet  1  is guided from below over the reversing roller  8  around the top of the first roller  12  of the wetting unit  9  into the trough  18 , which is filled with wetting agent and is acted upon by the wetting agent. The yarn sheet  1  is squeezed for the first time in the first squeeze nip  17  underneath the wedge  18 . Thereafter the yarn sheet  1  is conducted around the bottom of the second roller  13 , and therefore through the wetting agent bath in the wetting agent box  11  and the wetting agent again acts on it. Then the yarn sheet  1  is further conducted around the top of the second roller  13  through the second squeeze nip  22 , where it is squeezed to contain the predetermined residual moisture. The squeezing force in the second squeeze nip  22  is customarily greater, for example ten times greater, than in the first squeeze nip  17 . 
     The yarn sheet  1 , which had been twice wetted and squeezed, i.e. is provided with wetting agent and heated to the wetting agent temperature, is conducted around the third roller  14  and over the reach  48  to the top of the first roller  25  of the sizing unit  10 . Cooling of the yarn sheet  1  as it travels in the reach is limited maximally to 5 to 10° C. The limitation of cooling in most cases is assured by the short length of the reach  48 . It is possible in addition to maintain the yarn sheet  1  at a temperature close to the wetting agent temperature by means of a thermally insulating cover  51  over the reach  48 , which can be provided with a heater  52 , if desired. 
     In the second step the yarn sheet  1  is acted upon by the sizing agent in the size bath in the size box  23  and subsequently squeezed twice. To this end, the yarn sheet  1  is conducted around the top of the first roller  25  into the trough  31 , which has been filled with sizing agent through the sizing agent feed device  32 , and is acted upon by the sizing agent. The yarn sheet  1  is squeezed for the first time in the squeeze nip  30  underneath the wedge  31 . Thereafter, the yarn sheet  1  is conducted around the underside of the second roller  26 , and thus through the sizing agent bath in the size box  23 , where sizing agent acts on it again. Subsequently the yarn sheet  1  is conducted through the second squeeze nip  35 , where it is squeezed to the predetermined residual moisture, to the dryer  4 . 
     The sizing agent acting on the yarn sheet  1  in the second step is heated to a temperature between 100 and 160° C. via the contact surface  41  of the indirect heater in the size box  23 . For this purpose, the heating panel  38  is designed as a steam pressure panel supplied with superheated steam, i.e. saturated steam under increased pressure. 
     The yarn sheet  1  is conducted through the sizing device  3  at a feed speed of 60 to 200 m/min and more. 
     EXAMPLE 
     Modified starch is added as the sizing agent and water as the wetting agent, if needed with other additives, to a yarn sheet  1  of cotton with a mass of 100 g/m 2  per unit area. The wetting agent temperature is set at 85° C., the residual moisture after wetting (first step) at 40%, the sizing agent temperature at 80° C. and the residual moisture after sizing (second step) at 140%. The heating panel  38 , designed as a steam pressure panel, is heated with superheated steam at a temperature of 142° C. and at a pressure of 3 bar. In this case the temperature of the contact surface is approximately 140° C. The feed speed is 120 m/min. During start- up, a dilution of the sizing agent concentration occurs in the first 200 to 600 m, in this case the first 400 m, of the yarn sheet  1 . In this case the initial amount of the sizing agent applied to the yarn sheet  1  is higher by 6 to 10%, in this case 8%, than the desired amount. A control or regulation of the applied amount of sizing by elaborate measuring and regulating techniques is not required. 
     Because of the two-stage method it is possible to save 50% of sizing agent with the same weaving efficiency or, with an improvement of the weaving efficiency by 3%, approximately 20% of the sizing agent can be saved. 
     It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.