Abstract:
A suction device for a double-point coating system is used to remove excess powder ( 3′ ) from a double-coated fabric web ( 1 ). The suction device has a powder-suction element ( 4 ) to remove excess powder, a fabric-web-suction unit to align the fabric web and at least one beater roller ( 8, 9 ) to loosen excess powder. The fabric web suction unit has at least one suction roller ( 5, 6, 7 ) that can rotate to convey the fabric web ( 1 ) and support it. That way, the fabric webs can be transported tension-free, which largely prevents adhesion of individual dots of paste and clogging of the textile.

Description:
FIELD AND BACKGROUND 
     The present invention concerns a suction device for a double-point coating system. 
     In double-point coating, first a paste is applied to a fabric web in dots at even intervals and a powder is then sprinkled over it, by means of which the paste points or bumps and the areas in between them are at least partially covered with the powder. 
     However, the goal of double-point coating is to produce fabric webs that have, at least on one top side, individual nops or dots made of a paste and a powder sprinkled on them connected to the paste, so that the fabric web stays uncoated in the areas between the individual nops or dots. Therefore, suction devices are used that suck loose powder off the fabric web. 
     A proven suction device is known in which a fabric web is run under a powder-suction element which sucks off the loose powder. Two suction nozzles are arranged in the direction in which the fabric web moves, before and after the powder-suction element, that suck down the fabric web from underneath and thus provide tension on the fabric web. A beater roller is arranged in the direction of movement in front of the powder-suction element, said beater roller making a beating motion on the bottom of the fabric web, thus throwing the powder up before it is caught by the powder-suction element and sucked off for further use or disposal. 
     Although this double-point suction device yields satisfactory results, the arrangement of the paste/powder points has nonetheless often been shown to be uneven and, in serious cases, the powder even clogs the fabric. This is especially true in the case of elastic materials. The reason for this is that the fabric webs in the double-point suction device are subjected to tension, which stretches the fabric. 
     The problem of the present invention is to create a double-point suction device in which the fabric web is subjected to no tension or subjected only to slight tension. 
     BRIEF SUMMARY 
     This problem is solved by a double-point suction device with the features exemplified herein below. 
     By using rotating, actively driven suction rollers instead of fixed suction nozzles, the fabric web may be moved through the double-point suction device without tension. 
     In one preferred embodiment, a suction roller is arranged under a powder-suction element having a suction channel. Preferably, this suction roller has at least one blow nozzle in order to stir up the powder or keep it suspended. 
     Advantageously, at least one other suction roller is arranged in front of the powder-suction element, in relation to the direction of movement of the fabric web. To prevent the suction roller from sticking, there is a squeegee or at least one blow nozzle to remove powder deposits on the suction roller. The advantage of the blow nozzle is that it may be arranged inside the suction rollers in order that the suction holes in the roller may be cleaned by being blown out. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the subject of the invention is presented on the attached figures and explained in the description below. 
     FIG. 1 shows a schematic view of a suction device according to the invention for a double-point coating system; 
     FIG. 2 a  shows a cross section through the first suction roller according to the invention; 
     FIG. 2 b  shows a longitudinal section through the suction roller in FIG. 2 a;    
     FIG. 3 a  shows a cross section through a second suction roller according to the invention; 
     FIG. 3 b  shows a longitudinal section through the suction roller in FIG. 3 a.   
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a fabric web  1  which has been coated with dots by a coating system with a paste  2  and with powder  3  sprinkled over it, and is being conveyed through a double-point suction device according to the invention in order to remove the excess powder  3 ′ not connected to the paste  2 . The means used for this purpose are known and are therefore not shown or described here. 
     The double-point suction device according to the invention is designed as follows, wherein the individual elements are described in the direction of transport of the fabric web: 
     A control element  11 , for example a UV lamp, is arranged above the coated top of the fabric web  1 . Said control element  11  is followed by a powder-suction element  4  with a suction channel  40  and a set of controls  16 , and then an air-seal nozzle  10  and associated a valve  15 . 
     On the bottom of the fabric web and some distance in front of the powder-suction element, there is a first rotating beater roller  8  having a square cross section in this example. Said beater roller  8  is followed by a first suction roller  5  in the form of a perforated roller and a second beater roller  9 , also having a square cross section. All known means that make a beating motion on the fabric web can be used for the beater rollers. Other shapes are possible for the cross section of the beater roller. 
     A second suction roller  6  is arranged under the powder-suction element  4  having a height that can be adjusted. Preferably, the suction roller  6  is arranged higher than the first suction roller  5 , in order that the fabric web runs through without lifting. Next, that is after the powder-suction element, there is a third suction roller  7 , which is preferably arranged approximately at the same height as the first suction roller  5  and at the same distance from the second suction roller  6 . 
     Preferably, all of the suction rollers  5 ,  6 ,  7  are composed of perforated template rollers in whose hollow spaces there is a partial vacuum. However, other rotating rollers that achieve an even suction effect may also be used. The suction effect is governed by means of controls  13 ,  14 . 
     Preferably, all suction rollers  5 ,  6 ,  7  have the same diameter, wherein at least the second suction roller  6  arranged under the powder-suction element  4  may have its height adjusted. Since the suction rollers  5 ,  6 ,  7  are mounted in order that they may rotate, they turn with the fabric web  1  and they move the fabric web on them forward. Preferably, the topmost point of the surface of each of the suction rollers  5 ,  6 ,  7  lifts over the main plane of dispersion of the fabric web  1 , wherein the first and third suction rollers  5 ,  7 , also referred to as conveyor rollers, only lift the fabric web  1  slightly, for example on the order of the coating thickness. However, the second suction roller  6 , also referred to as the supporting roller, lifts the fabric web  1  in a sinus shape. 
     The fabric web  1  being sucked is first run over the first beater roller  8 , which makes a beating motion on the bottom of the fabric web  1 , thus loosening the powder. The fabric web  1  then runs over the first suction roller  6 , wherein the fabric web  1  is preferably lifted slightly. The second beater roller  9  loosens the excess powder permanently from the fabric web  1  and whirls it upward. By means of the second suction roller  6 , the fabric web  1  is lifted in the direction of the powder-suction element  4 , which sucks the excess powder  3 ′ off through the suction channel  40 . The control element  11  enables verification of whether the powder  3 ′ not attached has actually been whirled up. The air-seal nozzle  10 , also controlled by a valve  15 , forms a barrier due to the air streaming out that prevents the stirred up powder from being able to pass the powder-suction element  4  and from being deposited again on the fabric web  1 . The fabric web  1 , which has passed the powder-suction element  4 , is now run over the third suction roller  7  and is run to the next station for further processing. 
     FIGS. 2 a  and  2   b  show one special form of embodiment of a first suction roller  5  or conveyor roller, which is arranged in the direction of movement of the fabric web  1  in front of the powder-suction element  4 . Said roller has a hollow roller tube  50  having suction holes distributed over its surface being preferably made of metal. The suction holes are preferably a fine screen of holes with a size of approximately 1000 μm and 11 mesh (holes per inch of length). The roller tube  50  is mounted on both ends by known means and may rotate around its central axis by means of drive means that are also known and are not shown here. 
     This roller tube  50  has a suction channel  51 , preferably made of metal, that runs through it and is mounted in the roller tube  50 . The suction channel  51  preferably projects on both sides out of the roller tube  50 , and it is connected to an outer connecting tube  52 , here shown with a round cross section, and is closed on its second end. The suction channel  51  preferably has a square cross section, wherein one side surface runs at least approximately parallel to the plane of the fabric web  1 , and its diagonal in the area near the first end corresponds almost approximately to the diameter of the roller tube  50 . The suction channel  51  becomes narrower toward the second end, wherein the top side facing the fabric web  1  runs at least approximately horizontal, and its width remains basically unchanged as well. On its second end, a supporting element  55  projecting downward is arranged, which is used to support the suction channel  51  on another blow tube  56  described below or another fixed element. The suction channel  51  is thus held in its position on one hand by the connecting tube  52  and on the other by the supporting element  55 , wherein the roller tube  50  may rotate around the suction channel  51  whose position is stable. 
     In another embodiment, not shown here, instead of the supporting element  55  there is a rounded slot, which is arranged on the bottom of the suction channel  51  and which interlocks, but slides on the inside of the roller tube  50 . 
     The top of the suction channel  51  pointing toward the fabric web  1  has a suction hole  54 , which extends at least approximately over the entire length of the roller tube  50  and which runs at least approximately parallel to the tangent t of the highest point of the roller tube  50 . Either the suction channel  51  is designed to be slotted for this purpose, has a recess or the top has a screen having holes in it. This suction hole is surrounded on both sides along its entire length by labyrinth-like plates  53 , which are arranged on top of the suction channel  51  and make contact with the inside of the roller tube  50  and loop over this inside with springs. Preferably these plates  53  are made of metal. In the suction space  54  formed by the plates  53 , a partial vacuum is produced. A fabric web  1 , which is moved over the suction rollers  5 , is sucked over the screen of the roller tube  1 , wherein the rotational movement of the suction roller  5  moves the fabric web  1  forward without tension. 
     A blow tube  56  is also arranged inside the roller tube  50  and has a stable position. It is in the direction of rotation of the suction roller  5  after the suction space  54 . In this example, it is arranged under the suction channel  51 . This blow tube  56  is connected to a connecting tube  57  on the first end and closed on the second end. It is mounted with known means which are arranged inside and/or outside the roller tube  50 . The blow tube  56  has blow holes at least approximately over its entire length, facing the roller tube  50 . Air streaming out is blown by the screen of the roller tube  50  and therefore removes any powder that may be stuck to the roller. The blow tube  56  thus acts as a means of cleaning. Instead of the blow tube  56 , other cleaning means may be used, for example a squeegee that works on the outside of the roller tube  50 . 
     The third suction roller  7  or conveyor roller which follows the powder-suction element  4 , is in one preferred embodiment basically identical to the first suction roller  5  described above. However, it has no blow nozzles, since it does not become covered much with loose powder. 
     FIGS. 3 a  and  3   b  show a second suction roller  6  or supporting roller. It is also basically identical to the second suction roller  5  described above. The roller tube in FIGS. 3 a  and  3   b  is marked with the reference number  60 , the suction channel  61 , the accompanying connecting pipe  62 , the plates  63 , the suction hole  64  and the supporting element  65 . There is also in turn a blow element in the form of a blow tube  66 , which is now used not to clean, but to loosen excess powder  3 ′. It is therefore not connected to the suction space but is arranged in front of it or, as shown here, preferably in it. In the example shown here, the blow tube  66  has an oval cross section, and its connecting pipe  57  has a round cross-section. These cross section shapes are not essential, however. The blow tube  66  in turn has blow holes, which point toward the roller tube  60 . In the case of the second suction roller  7 , the blow holes or nozzles preferably point perpendicularly upward or toward the powder-suction element. Air is blown through the blow holes and the screen of the roller tube  50  through the fabric web  1 . In this way, excess powder that is not attached is kept suspended longer and powder still lying on the fabric web  1  is whirled up high. Loose excess powder  3 ′ can thus be grasped better by the powder-suction element  4  and sucked off the fabric web  1 . If the supporting roller  6  is raised, so that the fabric web is lifted as it passes over that roller, the intermediate spaces between the individual paste bumps are opened and the powder blown from the back loosens more easily. 
     The supporting and conveyor rollers described above may be used individually. However, to optimize the efficiency of the suction device, they are used in combination.