Abstract:
A dryer is used for drying a web of material. The dryer includes a passage duct for the material web. Drying takes place within this passage duct which includes at least one straight section. The dryer is disposed on a printing group which includes vertical web guidance. The passage duct straight section is essentially horizontal and receives the web of material delivered to it by the printing group. The passage duct is comprised of at least two sections through which the web of material travels in opposite directions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This U.S. patent application is the U.S. national phase, under 35 USC 371, of PCT/DE2003/002296, filed Jul. 9, 2003; published as WO 2004/035313 A1 on Apr. 29, 2004, and claiming priority to DE 102 48 249.7, filed Oct. 16, 2002, the disclosures of which are expressly incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention is directed to a dryer for a web of material. The dryer has a transit channel for the web of material in which the drying takes place and which has at least one straight section. 
   BACKGROUND OF THE INVENTION 
   If a paper web is processed in a folding apparatus immediately after having been imprinted, without the printing ink having had sufficient time for drying, there is the danger that, because of the contact of the paper web with the rollers of the folding apparatus, ink may be smudged or may be transferred from one web to another web because of the contact between several webs of material being processed simultaneously in the folding apparatus. Modern printing presses attain such high web speeds that the length of time between the imprinting of a web section and its arrival at the folding apparatus is of a length of only a few fractions of a second. Sufficient drying of the ink is not possible during this length of time if it is not speeded up by the provision of technical aids. 
   Drying devices for drying a freshly imprinted web of material are shown, for example, in DE 41 33 555 A1 or DE 44 29 891 A1. 
   DE 41 33 555 A1 describes a rotogravure printing press with several printing rollers for use in multi-color printing. After passing over every individual printing roller, a web of material travels over a transport path whose direction is changed by several rollers, on which transport path drying devices are arranged. Here, the course of the transport path has been selected in such a way that the first change of direction effecting rollers, over which the web of material runs after having passed through a printing gap, touch the non-printed back of the web. Only after the web has passed through the drying devices, and there is no longer a danger of smudging the ink, by contact with the change of direction roller, change of direction rollers follow, which also touch the imprinted surface of the web. 
   In connection with printing presses, for use in imprinting both sides of a paper web, the construction described in DE 41 33 555 A1 cannot be used. Contact of the freshly imprinted web with a change of direction roller, or with any other arbitrary surface, is to be avoided so long as the printing ink has not dried completely. 
   DE 44 29 891 A1 therefore uses a longitudinally extending drying oven for drying a web which is imprinted on the front and back, and through which the printed web runs in a straight line. It would be desirable to be able to conduct the web vertically upward, in the same direction in which it leaves the printing group, through the drying oven in order to prevent, in this way, contact of the not yet completely dried printed web with a change of direction roller. However, such an arrangement would require a structural height of several meters. Therefore, it would be difficult to install such a machine in a work room. To avoid this, and to be able to install the drying oven horizontally, a change of direction roller between the outlet of the printing group and the inlet of the drying over has to be accepted. Although an arrangement with a horizontally oriented drying oven described in the above-mentioned publication does not require any additional external height of the work room for its installation, it does require a considerable base area, since a length of several meters of the drying oven is required to achieve a dwell time in the drying oven which is sufficient for drying the ink on the imprinted web of material Although a portion of this base area can be used for installing roll changers for the printing group underneath the drying oven, for reducing the space requirement of such a printing installation it is necessary to be able to reduce the length of the drying oven. This requirement for length reduction occurs, to a greater extent, as a function of the higher the web speeds are in the printing installation. To assure sufficient web drying, with increasing web speeds, it is necessary, in connection with the known construction, to increase the length of the drying oven proportionally to the web speed. 
   DE 298 19 202 U1 discloses a dryer in which a web of material is rerouted. This dryer uses turning stations on which air is blown. 
   DE 100 44 676 A1 and DE 40 33 642 A1 show devices for rerouting a web of material by the use of compressed air. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is directed to providing dryers for webs of material. 
   In accordance with the present invention this object is attained by the provision of a web dryer that has a transit channel through which the web of material passes. The transit channel has at least one straight section. The web dryer is arranged on a web printing group with vertical guidance of the web. The transit channel has at least one section in which the web is guided horizontally. A plurality of air outlet nozzles can be located in at least one of these sections. 
   The advantages which can be gained by use of the dryer for a web of material, in accordance with the present invention, consist, in particular, in that the dryer can be constructed in a very compact manner and requires no change of direction rollers which come into contact with the webs of material before they are completely dried. This is accomplished because, instead of change of direction rollers, curved change of direction surfaces, which are equipped with air outlet openings, are employed in the transit channel of the dryer. By creating air cushions, by the use of the air exiting between the change of direction surfaces and the web of material looped around them, an extremely low-friction guidance of the web of material is made possible. Also, contact of the web of material with a surface, which could lead to smudging of the ink, is prevented. For providing a uniform air cushion between the change of direction surface and the web of material, it is desirable that the change of direction surface has a radius of curvature which is minimal at an vertex line of the change of direction surface and which increases towards each of the edges of the change of direction surface. In particular, such a change of direction surface can have a hyperbolic cross section, particularly in connection with change of direction angles of 90°, or a semi-elliptical cross section. 
   Air outlet openings are preferably arranged along the vertex line of the change of direction surface. 
   By the provision of a plurality of such change of direction surfaces, it is possible to conduct a web of material, which is to be dried in a compact volume, over a great length. Accordingly, long dwell times of the web in the dryer can be achieved, even at high web speeds. For intensifying the drying effect, the dryer preferably has heat sources, such as, for example, in the form of heat radiators, arranged in the transit channel. 
   The drying effect can also be intensified by increasing air movement. For this reason, air outlet nozzles, which are directed onto the web of material, have therefore been provided in the at least one straight section of the transit channel. A heating device in a supply line of the nozzles, for use in heating the air exiting through these nozzles, can be advantageously assigned to these air outlet nozzles. In particular, the heating device can be a burner. 
   In a dryer, in whose transit channel a plurality of sections, provided with air outlet nozzles have been arranged, a heating device is preferably provided in the air supply line of the nozzles of at least one of the sections which is located upstream, in the running direction of the web of material, while such a heating device is lacking in the air supply line of the nozzles of at least one section which is located downstream, in the running direction of the web of material. While the web of material is heated in this way in the upstream-located section of the dryer for the web of material and drying of the web of material is thus intensified, the downstream-located section of the dryer makes possible a rapid cooling of the web of material. 
   A pressure pump can be arranged in a supply line for the nozzles and is operable for driving the air flow through the nozzles. However, instead of this, or in addition it is also possible to provide a suction pump for use in generating a negative pressure in the transit channel. Such negative pressure makes drying easier by lowering the boiling temperature of the ink components which are to evaporate. Moreover, it can be used for driving an air flow through the nozzles. 
   To achieve a large web length, along with a compact construction, the transit channel preferably has at least two sections through which at least two sections the web of material moves in opposite directions. In this case, a first section preferably extends from an inlet of the dryer over a first distance in a first direction. A second section, which follows the first section via a change of direction surface, extends over a second distance which is greater than the first distance and which extends in the opposite direction. Therefore, the dryer extends from the dryer inlet in two opposite directions, which structure simplifies the mounting of the dryer on a printing group, even if the dryer extends in the first direction, or in the second, opposite direction, beyond the printing group. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention are represented in the drawings and will be explained in greater detail in what follows. 
     Shown are in: 
       FIGS. 1 and 2 , schematic sectional views of a change of direction surface for accomplishing the contactless change of direction of a web of material, in 
       FIG. 3 , a basic view of a dryer, and in 
       FIGS. 4 to 7 , several preferred embodiments of a dryer in accordance with the present invention and mounted on a printing group. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A schematic, cross-sectional view through a change of direction surface  01 , which is also called an air saddle  01  in what follows, and which is used for changing the direction of travel of a material web  07 , for example a paper web  07 , over an angle of 180° is represented in  FIG. 1 . The air saddle  01  has a housing  02 , typically in the shape of an ellipse which has been halved along its short diameter, and which housing  02  extends in the transverse direction of the web  07  of material, in the direction perpendicular in relation to the drawing plane of  FIG. 1 . The housing  02  can be made of sheet steel, a rigid plastic plate or the like. The cross section of the housing  02  is symmetrical with respect to a plane A which intersects the housing  02  along a vertex line  03 . The housing  02  is provided with a plurality of air outlet openings  04  spaced along the vertex line  03 , which air outlet openings  04  communicate with a compressed air duct  06  extending in the interior of the housing  02  in the longitudinal direction of the latter. Compressed air exiting the air outlet openings  04  is distributed between the housing  02  and a web  07  of material looped around the housing  02 . In this way, an air cushion is formed and which maintains the web  07  of material at a distance from the surface of the housing  02 . The amount of excess pressure between the housing  02  and the web  07  of material, which is required for maintaining an air cushion of a thickness of typically 0.3 to 0.5 mm, is a function of the tension in the web  07  of material. It is therefore possible to provide pressure sensors on the surface of the housing  02  around which the web  07  of material is looped, and also in the compressed air duct  06 . By the use of the values measured by these pressure sensors, the web tension is controlled. If necessary, an emergency stop of a press containing the change of direction surface on air saddle  01  can be initiated if the detected pressure indicates a web tear or another error. 
     FIG. 2  shows a sectional view, analogous to the one shown in  FIG. 1 , through an air saddle  01  with a change of direction angle of 90°. The functional principle of operation of this air saddle  01  of  FIG. 2  is the same as with the air saddle  01  in  FIG. 1 . Air, which exits through the compressed air duct  06  and through the spaced air outlet openings  04 , which are arranged along a vertex line  03  of the housing  02 , is distributed between the surface of the housing  02  and a web  07  of material looped around the housing  02  and, in this way, creates an air cushion which allows a substantially friction-free conveyance of the web of material  07 . 
   In a structure, which is different from the preferred embodiments shown in  FIGS. 1  and  2 , half an air saddle could also have an asymmetric cross section. In such a case, the vertex line  03  of the housing  02  is defined as that line on the surface of the housing  02  which contacts an imaginary plane that extends perpendicularly with relation to a sum F Σ  of the tensile force vectors F V , F R  acting on the web  07  of material upstream and downstream of the change of direction surface  01 . The amount of air put through the change of direction surface  01  required for building up an air cushion is reduced. 
     FIG. 3  shows a basic view of a dryer equipped with air saddles  11 ,  12 ,  13  in accordance with  FIG. 1  or  2 . The direction of a web  07  of material to be dried is changed by 90° at a circumferential face  11 , for example at an air saddle  11 , such as, for example, an inlet air saddle  11 . The changed web direction then extends straight through a transit channel  08 , for example through a first gap  08  between two plates  14 , which are provided with air outlet nozzles. The web direction then loops around a circumferential face  12 , such as an air saddle  12 , and, for example, a 180° air saddle  12 , and passes through a second gap  08  to a circumferential face  13 , which may be, for example, an air saddle  13 , such as, for example, an outlet air saddle  13 , and leaves the dryer from outlet air saddle  13  extending in a horizontal direction. Each of the plates  14 , which are provided with air outlet openings, delimits chambers  16  which, like the compressed air ducts  08  of the air saddles  11 ,  12 ,  13 , are connected with a pressure pump. Two pressure pumps  17 ,  18  are represented in  FIG. 3 , one of which supplies the air saddles  11 ,  12 ,  13 , and the other of which supplies the chambers  16 . It is necessary to supply the air saddles  11 ,  12 ,  13  with a higher pressure than that which is supplied to the chambers  16 . It would, of course, also be possible, in principle, to supply the air saddles  11 ,  12 ,  13  and the chambers  16  by the use of a common pressure pump and, in the course of this, to make use of flow resistance in the supply lines leading from the pressure pump to the air saddles  11 ,  12 ,  13 , or to the chambers  16  in order to provide the air saddles  11 ,  12 ,  13  with a higher excess pressure than is provided to the chambers. 
     FIG. 4  shows a first preferred embodiment of a dryer  22  mounted on a printing group  21  in accordance with the present invention. A transit channel of an imprinted web  07  of material, which web of material is coming vertically, from below, out of the printing group  21 , is comprised of an air saddle  11 , such as, for example, a 90° air saddle  11 , and with a horizontally oriented gap  08  between plates  14 , which are provided with air outlet nozzles, that are not specifically shown in  FIG. 4 . Except for the nozzles and for an inlet slit and an outlet slit for the web  07  of material, the plates  14  constitute a substantially sealed housing, with which a suction pump  26  is connected for use in generating a negative pressure in the gap  08 . The negative pressure causes the inflow of fresh air into the gap  08  via fresh air supply lines  27 , which are here constituted by spaces between the plates  14  and an outer housing  28  of the dryer  22 . In the first preferred embodiment depicted in  FIG. 4 , fresh air flows substantially over an outlet  24  of the dryer  22 , out of which the web  07  of material is conducted. The fresh air can be pre-heated by a heating device, which is not specifically represented in  FIG. 4 . The web  07  of material exiting the outlet  24  loops around a cooling roller  29  and finally reaches the folding apparatus  31 . 
   A second preferred embodiment of the present invention is represented in  FIG. 5 . The printing group  21  is the same as in the first embodiment depicted in  FIG. 4 . It comprises two component groups  32 ,  33  containing plate cylinders, each of which plate cylinders in one of the two component groups  32 ,  33  imprints the same side of the web  07  of material and which component groups  32 ,  33  can be moved apart in a frame  34  for allowing access to the plate cylinders. 
   The outer housing  28  of the dryer  22  extends over the entire width of the frame  34 . The inlet  23  for the web  07  of material lies approximately in the center of the underside of the housing  28 . A 90° air saddle  11  arranged on the underside of housing  28 , at the web inlet  23 , guides the web  07  of material coming from the printing group  21  into a first horizontal straight section  36  of the transit channel of the dryer  22  which first section  36  extends, starting at the web inlet  23 , in a first direction leading away from the folding apparatus  31 . At a 180° air saddle  12 , the first section  36  makes a transition into a second horizontal straight section  37 , which guides the web  07  of material in the second direction, opposite to the first direction, to a web outlet  24  that is adjoining the folding apparatus  31 . From web outlet  24 , the web  07  of material runs over a cooling roller  29  to the folding apparatus  31 . 
   In relation to a plane  43 , which plane  43  is determined by the vertically extending web  07  of material, the first horizontal straight section  36  is arranged on only one side of the plane  43 , wherein the second section  37  is arranged on both sides of the plane  43 . The second section  37  is at least twice as long as the first section  36 . 
   The two sections  36 ,  37  of the transit channel, as seen in  FIG. 3 , are each bordered by guide plates  38 , which conduct a fresh air flow, which fresh air enters the housing  28  of the dryer  22  at the web outlet  24  and which fresh air flow is driven by a pump, not represented, closely adjacent to the web  07  of material. The fresh air flow, which can also be pre-heated, moves at high speed along the web  07  of material and, in this way, provides effective drying of the printed web  07 . In the embodiment represented in  FIG. 3 , an air outlet  42  is located on the end of the dryer housing  28  opposite to the web outlet  24 . A lower one of the two guides plates  38  bordering the second section  37  is interrupted at the level of the web inlet  23 , so that the air flow can be split and a part of this air flow can reach the air outlet  42  along the first section  36 . It would, of course, also be possible to provide the air outlet  42  at the inlet  23  for the web  07  of material in order to force the air to flow in this way through the transit channel  08  along its entire length. 
   In a variation of this second preferred embodiment, the air supply to the first and second straight sections  36 ,  37  is provided, as in the first embodiment in accordance with  FIG. 4 , via air chambers  39 , which are separated from the transit channel by the guide plates  38 , and by nozzles which are formed in the guide plates  38 . 
   The third embodiment of the present invention, as seen in  FIG. 6 , differs from the second embodiment shown in  FIG. 5  in that the guide plates  38  in the first section  36  of the transit channel  08  and in the first half of the second section  37 , which is remote from the folding apparatus  31 , have been replaced by heat radiators  41 , such as, for example, by electrically operated heating rods. A pump, which is not specifically represented, drives a fresh air flow, which flows through the dryer housing  28  of the dryer  22  from the web outlet  24  to an air outlet  42  that is formed on an oppositely located end face of the dryer housing  28 . With this third embodiment the inflowing fresh air need not be pre-heated. To the contrary, it is used for cooling the web  07  of material in the right half of the second section  37  in a counter-flow, so that a cooling roller  29 , situated between the dryer  22  and the folding apparatus  31 , as used in the first and second embodiments, can be omitted in this third embodiment. 
   A fourth embodiment of the present invention, for a high drying output, is represented in  FIG. 7 . As previously shown in  FIG. 3 , with this fourth embodiment the sections of the transit channel  08 , which sections are identified by  36 . 1  to  36 . 5 , are surrounded by chambers  16 . 1  to  16 . 5 , whose wall plates facing the sections  36 . 1  to  36 . 5  of the transit channel  08  are supplied with air outlet nozzles. A total of five transit channel sections  36 . 1  to  36 . 5  has been provided. The chambers  16 . 1 ,  16 . 2 ,  16 . 3  of the three sections  36 . 1 ,  36 . 2 ,  36 . 3  which, with respect to the transport direction of the web  07  of material, are located upstream in the dryer  22  are provided with heated gases from a burner. The chambers  16 . 4 ,  16 . 5  of the two downstream located sections  36 . 4 ,  36 . 5  are provided with unheated fresh air in order to pre-cool the web  07  of material prior to its reaching a group of cooling rollers  29 . The output of such a dryer  22  is sufficient for heatset drying. 
   The fact that the dryer  22 , in accordance with the present invention, can be mounted on an existing printing group  21 , without increasing the space requirements of the printing group  21  or the required distance of this printing group  21  from other presses of the latter, renders the dryer  22  of the present invention particularly well suited for retrofitting already installed printing presses. In this way, the possibility is provided to also imprint higher quality paper having reduced absorption ability compared to customary newsprint, and in particular, paper with a coated surface, on such presses. The field of application of such printing presses is thus increased, so that they can also be used during the day, at a time during which no newspaper are typically to be printed. Because of this increased utilization, the efficiency of such a printing press can be considerably increased. 
   While preferred embodiments of a dryer for a web of material, in accordance with the present invention, have been set forth fully and completely hereinabove, it will be apparent to one of skill in the art that various changes in, for example, the specific structure of the press components, the type of pressure pumps used, and the like could be made without departing from the true spirit and scope of the present invention which is accordingly to be limited only by the following claims.