Patent Publication Number: US-3876499-A

Title: Web forming between two wires having a curved path of travel

Description:
United States Patent 1191 Vesanto 1 Apr. 8, 1975 [75] Inventor: Arto Antero Vesanto, Vuksenniska,  
 Finland [73] Assignee: Enso-Gutzeit Osakeyhtio, Helsinki,  
 Finland 221 Filed: Jan. 25, 1971 211 Appl. No.: 109,499  
 [30] Foreign Application Priority Data Primary E.\&#39;aminerS. Leon Bashore Assistant Examiner-Richard V. Fisher Attorney, Agem, or F irmBrooks Haidt &amp; Haffner [57] ABSTRACT Paper, cardboard and the like fibrous material is formed between two wires defining a wedge-shaped space between them. In order to obtain effective removal of water throughout the whole forming section draining elements are so positioned that the wires after first touching at a breast table at the beginning of the forming zone are guided at similar speeds along a broken or curved line formed through the points at which the draining elements support the wires. The radius of curvature of line of travel of the wires decreases continuously towards the point where the fibre web has been formed, whereafter the fibre web is guided over suction boxes into a press section. Preferably the length of the broken or curved line is such that so much water escapes from the fibre suspension when travelling this distance that the dry-substance content of the formed fibre web is at least 1.5 7:. The draining elements may be doctors which scrape water from the lower surface of the wires.  
 8 Claims, 2 Drawing Figures /NVENTORI 6% A TTORNE).  
 WEB FORMING BETWEEN TWO WIRES HAVING A CURVED PATH OF TRAVEL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of manufacturing of webs of papers, cardboards and the like fibrous material and particularly to the removal of water from such web during the formation phase in which a fibre suspension is conducted from a head box into a wedgeshaped space formed between two wires whereafter water is removed through both wires.  
 2. Description of the Prior Art In the most commonly used methods the fibre pulp, which contains approx. 0. l 5l.0 7r of dry substance, is poured from the head box on endless moving wire material, supported by rolls and/or water-removal lists, from which screen the water is removed partly by gravity, partly through rolls or through a vacuum created by suitably formed lists. After&#39; the web has attained a sufficient dry-substance content, when so much water has escaped that the fibres cannot anymore be considered to float in water suspension, the fibre pulp is supported as a web and further dried by means of suction boxes supporting the wire material and equipped with lids having holes and openings and operating at low pressure. Further, such equipment is known in which the web is formed from a head box or other pulp distribution part on a rolling cylinder covered with wire material, from which cylinder the water is removed by gravity or vacuum.  
  In recent years, several methods have been developed where the web is formed between two wire materials moving at the same speed and in the gap formed by them, the fibre pulp is fed from the head box and the water escapes through both wire materials.  
  Two main objects have led the development in this direction. Firstly, the speed of the paper plants (the wore paper is used here in wide significance regardless of surface weight and fibre material) has increased considerably. Heretofore, in the plants representing the oldest type where the pulp is poured from the head box on a wire material, there have been many difficulties principally because the upper surface of the web is free. One problem has been splashing caused by different factors, which splashing is apt to impair the evenness of the web. The other reason for forming the web between two wire materials, is the possibility to remove water either simultaneously or alternatingly in both directions whereby the formation distance required, that is, the distance through which the fibres must travel to raise the percentage of dry material in the web to about 1.5 to 2.0% is reduced substantially. Since the material travels at very high speeds in modern plants (900 to 1,200 meters per minute), and also because water removal in the production of some kinds of paper is slowed down by the required grinding and repulping processes. the quick removal of water is of considerable importance. All known web formation methods have, however, one weakness, and the method and apparatus for web formation are directed to overcoming this problem. I  
  As known, the water escapes in the early stages of the process fairly easily and becomes more difficult to remove when the dry-substance content increases. In almost all known methods the water removal is based&#39;on utilization of the evenly acting force in the early stages of web formation, either on gravity or centrifugal force and on force acting at intervals, using varying] low pressure brought about in&#39;various manners. In one known method, web formation takes place between two vertically moving wire materials whereat the water escape takes place primarily through doctors attached to the equipment; the doctors press the wire material alternatingly from both sides. In this method gravity evidently does not cause water escape from the paper web itself.  
  Jerking water removal caused by rollers, by profiled doctors bringing about vacuums, by so called wet suction boxes, or by other corresponding devices that cause momentary maximums for water escape, has to be carefully controlled so that there is no partial breaking in the fibre web about to be formed, since such breaking has a harmful effect on the utilization properties of the web. This is rather important especially in the early stages of the web formation. The aim of this invention is to improve the web formation by combining properly the use of several water removal techniques with a continuous or almost continuous increase in centrifugal force to enhance the drying effect at the several stages. By means of the present invention, when the process progresses and the water removal becomes more difficult, the force improving the water removal can be properly increased.  
  As evident from the above, there exist known methods in which centrifugal force is used for water removal. However, prior art techniques have employed either evenly acting centrifugal force whereat the radius of curvature remains constant, or else discontinuous processes in which the wire materials and the web between them are led over a bending roller which is followed by a straight oralmost straight section which has the length of several diameters of this roller and which is often followed by another bending roller.  
 SUMMARY OF THE INVENTION This invention provides a method and apparatus for forming a paper, cardboard or other fibrous web which meets the requirements of effective removal of water even at relatively high web speeds.  
  From a head box the fibre suspension is conducted into a wedgelike space formed between two wires whereafter water is removed through both wires. The first Contact point of the wires is at a breast table following the breast rollers.  
  The improvement comprises guiding the wires, after the first point of contact, along a broken or curved line formed by the points at which the wires in mutual engagement, are in contact with the surfaces of draining means. The radius of curvature of the contact line decreases as the line approaches the point at which so much water has been removed that a fibre web is formed, whereafter the fibre web is guided over suction boxes into a press section.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an apparatus according to the invention and FIG. 2 shows, also schematically, a slightly different arrangement.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1. The pulp is fed from the suitably constructed head box 1 or from some other pulp distribution part between two wire materials shown as wires 2 and 24. The wires form, when going over the rollers 3 and 4, a gap that can be regulated because either of or both rollers 3 and 4 are constructed so that they are movable in relationto each other. Further, it is expedient to construct the head box so that it can be moved to some degree, whereat the point at which the material sprayed from the headbox on to the wires can be regulated if necessary. The wires join each other at the properly built breast table 5. The breast table is made suitably concave on its outer surface. After this, both wires travel at the same speed over suitable controls and supports 6, 7, 8 so that the radius of curvature of the travel is suitably decreased in a continuous or almost continuous manner and thus are increasing centrifugal force is directed on the pulp between the wires removing water from it. As the centrifugal force is proportional to the square of speed and inversely proportional to the radius of curvature this has as result that when the speed increases a water-removing-force growing as the square of the speed is projected on the pulp web and on the other hand as the radius of curvature decreases the effeet is rectilinear. Both are important, when one is attempting to produce forces acting in the right direction to decrease the time required for water removal and to increase the speed of the plant, since the force required to remove water increases as the dry substance content of the web increases.  
  By utilizing suitably selected supports, such as discharging lists and rolls, water can also be removed in opposite direction. The term list refers to structures known in the are, which aerodynamically create waterremoving suction as the web moves past them. Further, as required, the water removal can also be affected by using as required different stretching of wires whereat the increased stretching brings about increased pressure on the pulp between them.  
  Conveniently combining all these different methods, the equipment can be constructed in accordance with the quality properties of the paper to be manufactured and operating speed and the effects of these factors on water removal and quality while the process is under way. The water removed by the increased pressure force caused by the centrifugal force and the joining of wires on the breast table, is collected in trough and from here it is conducted further, outside the wires through outlet 21, which is, as needed, on the service and operating sides of the plant or only on one side. In order to prevent the splashing caused by turning rollers 8 and 9, and penetration back into the gap formed by them, these rollers can advantageously be equipped with a suitable splash doctor 25, which conducts the water into the collecting trough 20. The water removed by water-removing-parts 5, 6 and 7 located on the other side of the wires, is collected into suitably formed troughs 22 and 26, and is removed outside the wires either from the front or the back or both sides via 23 and 27, e.g., conducting it into the aforementioned trough 20. It may also be mentioned that these water removal parts are as such known constructions and their grouping, size and number can be selected to correspond to all purposes. However, of course, each breast roller is in any case always first followed by a so called breast table 5. The roller 8 causes the water to be pressed on top of the upper wire, from here it is removed with a doctor, e.g., in a known manner combining the kinetic energy of water and a slight vacuum in the doctor which consists of a nozzle and a low pressure chamber, through which the water escapes.  
  Having bent themselves after roller 9 most conveniently into horizontal direction, both wires and the web (which has now gained a dry-substance content of at least 1.5 go over the suction boxes. These are of known construction and in them water is further drained from the web by utilizing low pressure. When the dry-substance content has attained a suitable value (approx. 10 l4 the upper wire isseparated from the web. This is most conveniently done by placing a known bending roller covered with soft rubber, roll 12 on top of the suction box, hereat. The suction box 10 under the roller 12 keeps the web in contact with the lower wire at the point of departure of the upper wire. After this, water can again be drained through the lower wire with a suitable number of known suction boxes or with other known water-removal parts, after which the web supported by the lower wire is led over known suction roller 17 and after it, it is transferred in known manner on transfer felt 19 to the press section.  
  On the return side of the wires are placed a required number of wire-directing-rollers 16 and 14, drive rollers l8, tightening rollers 13 and 18 as well as wireguiding-rollers 15. They are all of known constuction. For the transport of wires the suitable and necessary ones of these rollers are provided with drive. In the construction of all rollers and supports and bracing parts of the wires attention should be paid to the fact that they do not bend to a detrimental degree because of tightening of wires and other forces affecting them. Further particularly concerning the construction of the supports and water-removalparts inside the curve formed by the common travel of the wires it has to be taken into consideration that they ar built so that they do not bend too much or start to shake disturbingly from the travel of the wires or from the escape of water.  
  As constructions for bending rollers 3, 4, 8 and 9 of the wires, appropriate known rollers can be used. For instance 3, 8 and 9 can be of the kind that the water can penetrate into the roller construction and then escape from the roller from there after the pressure section by means of centrifugal force. Roller 4 can be an ordinary roller with solid surface. In come cases it may even be advantageous to use known suction roller construction at rollers 8 and 9.  
 The adaptation shown in FIG. 2 differs from the adaptation in FIG. 1 in that that roller 9 has been left out.  
 and the wires travel horizontally after roller 8. Of  
 course nothing prevents, if it seems appropriate for one.  
 reason or other, directing of the wires after roller 8 either obliquely upward or downward to the suction roller.  
 What is claimed is:  
 v l. A method of forming a paper, cardboard or like fibre web, which comprises the steps of discharging a liquid suspension of fibres from a head box into a V- shaped gap between two endless wire screens passing over respective breast rollers to a breast table disposed at one side of said endless wire screens, said breast table having a convex surface supporting said endless wire screens in parallel with one another with the web to be formed disposed therebetween, draining water from said web by liquid draining means disposed beyond said breast table on the same side of said endless wire screens as said breast table, and supporting said endless wire screens on said liquid draining means with the points of contact of said liquid draining means with said endless wire screens defining for said endless wire screens a curved path of travel the radius of curvature of which decreases continuously for smoothly increasing dewatering centrifugal force along said path of travel towards the outlet end of a dewatering forming section formed by said endless wire screens and said liquid draining means, and drying said web at a web drying section beyond said web forming section.  
  2. A method as claimed in claim 1, which includes draining said liquid by means of discharging lists and tube rollers.  
  3. A method as claimed in claim 1, including draining said liquid by means of suction rollers at said outlet end.  
  4. A method as claimed in claim 1, including draining said liquid by means at said outlet end of rollers from which liquid is removed by centrifugal force.  
  5. An apparatus for forming a paper, cardboard or like fibre web, which comprises:  
 a. a first breast roller;  
 b. a first endless wire screen extending over said first breast roller;  
 c. a second breast roller;  
 (1. a second endless wire screen extending over said second breast roller and forming with said first endless wire screen a V-shaped gap;  
 e. a head box for discharging fibre suspension into said V-shaped gap;  
 f. a breast table disposed at one side of said first and second endless wire screens beyond said breast rollers;  
 g. said breast table having a convex surface for supporting said first and second endless wire screens in parallel with one another with the web to be formed therebetween;  
 h. liquid draining means disposed beyond said breast table on the same side of said first and second endless wire screens as said breast table;  
 i. said liquid draining means supporting said first and second endless wire screens with the points of contact of said liquid draining means with one of said first and second endless wire screens defining for said first and second endless wire screens a curved path of travel the radius of curvature of which decreases continuously towards the outlet end of a dewatering forming section formed by said first and second endless wire screens and said liquid draining means for smoothly increasing dewatering centrifugal force along said path of travel; and  
 j. a web drying section disposed beyond said web forming section.  
  6. Apparatus as claimed in claim 5, wherein said liquid draining means comprise liquid discharging lists and tube rollers.  
  7. Apparatus as claimed in claim 5, wherein said liquid draining means comprise suction rollers at said outlet end.  
  8. Apparatus as claimed in claim 5, wherein said liquid draining means comprise, at said outlet end, rollers from which liquid is removed by centrifugal force.