FIXATION DEVICE

Abstract: Fixation device for permeable web materials, such as felts and wires for paper machines, where air at controlled temperature and pressure is pressed through the web from jets in at least one pressure chamber (12) on one side of the web, to at least one corresponding suction chamber (15) on the other side of the web, the device thereby comprising an upper structure (9) and a lower structure (10) between which the web is running during operation where a pressure chamber (16) with a corresponding suction chamber (13) being arranged in front of, and a pressure chamber (14) with a corresponding suction chamber (11) being arranged behind, at least one middle pressure chamber (12) with a corresponding suction chamber (15), each pressure chamber (12, 14, 16) being provided with two jets arranged in an acute angle to the web and towards each other, with one front jet (17, 19, 21) and one rear jet (18, 20, 22), thereby establishing and maintaining an overpressure between the jets and the web, jets arranged in opposed pressure chambers and adjacent each other thereby directing air passed each other in such a way that air from one pressure chamber substantially is prevented in penetrating into the adjacent suction chamber, and the upper and lower structures (9, 10) being provided with ducts (30, 31) for an air flow having a controlled temperature, thereby avoiding deformations of the upper structure (9) due to temperature influences from the heated air in the fixation process.

Description: Fixation Device The present invention is related to a fixation device for felts and wires for paper maschines, according to the preamble of the claims. Felts and wires for paper maschines today are produced in widths up to 10 meter and constructed to withstand large strains of different types, such as high moisture content, large temperature, large pressure, tension forces in the longi- tudinal direction and influence from chemicals. The felts and the wires, shaped as endless bands, are running at very hight speeds in the paper maschines, in extreme cases up to 2000 meter per minute. It therefore is substantial that they are homogeneous both in the longitudinal as well as in the tranversal direction to ensure operation without problems. One of the processes involved in the production of all types of felts and wires today is the heat treatment at a temperature substantially higher than the highest temperature by which the products are used in the paper maschines. This heat treatment, the fixation, provides the felts and the wires with thermical stabile properties and desired stretching pro¬ perties. Additionally the felts and the wires also are treated with chemical solutions hardening at spesified temperatures. To provide the felts and the wires with the desired properties it is important that the same maximum temperatures is achieved across the whole width during the fixation process. Furthermore it is desired to achieve the same temperature throughout the thickness of the felt and the wire, in other words in the upper and lower surfaces as well as in the middle. During fixation the felt and the wires, as endless bands, are stretch between two parallel rolls of which at least one is driven in such a way that the felts can be moved through the fixation zone which is arranged parallelly to and between the axis of the rolls. A normal heating method in the fixation process is blowing heated air against both sides at the felt. As stated above, it is very important, and necessary, to maintain the . same air temperature across the whole width of the felt or the wire. It is, however, not sufficient that only the tempera¬ ture of the blown air is the same across the width as pressure differences may occur in the fixation zone due to small differ- 5 ences in the hight air velocity which is necessary to achieve a good heat transfer to the felt. Surrounding air very easily will be drawn into the process by induction, which means that the enviromental air is drawn into the fixation zone itself and here mixed with the air having controlled temperature. ■° The main pharameters influencing the result of the fixation process are the temperature aware penetrating the felt, the amount of air penetrating, the velocity of the air through the felt and strongly influencing the afore-mentioned, the distance between the jets and the felt is of major import- is ance, e.g. the distance must be uniform along the entire length of the jets. Influencing the distance between the jets and the felt during operation is the behaviour of the upper struc¬ ture due to the heat influence, which across a length of 10 meter or even more, can lead to a not acceptable distance 0 difference between the middle of the structure and the ends. Any leakage of surrounding air into the fixation zone will lead to a temperature reduction, and especially local reductions thereby increasing the danger of undesired tempera¬ ture variations across the surface of the felt. Such air leak- 5 age is reduced to a certain extent by the use of sealings at apertures where the felt and the wire is transfered into or out of the heating zone, but a complete elimination so far has been difficult to achieve in practical work. By the fixation device according to the present invention, however, 0 this problem in the fixation process is avoided in such a way that leakage air from the environment is not effecting the conditions in the fixation zone. This advantage is achieved by the fixation device according to the invention as defined by the features stated 5 in the characterizing clauses of the claims. In the drawing Fig. 1 discloses schematically a verti¬ cal section in longitudinal direction of the felt,. of a fixat¬ ion device according to the invention, and Fig. 2 and 3 dis- close diagrams with the temperature of the felt in the longi¬ tudinal direction, of the upper surface of the felt, respectiv¬ ely in the middle of the felt. Fig. 1 discloses the principal structure of a fixation device according to the invention, comprising an upper struc¬ ture 9 and a lower structure 10 extending across the total width of the felt or the wire 27, perpendicularly to direction of movement of the felt. The felt as such creates an endless band, whereas only a short segment is disclosed in the Figure. The upper structure 9 comprises a middle pressure chamber 12 supplied with pressurized air through a slit 28 in a duct 29, arranged in such a way that the air conditions as to temperature and pressure in the lower end of the pressure chamber 12 and especially across the full length of jets 5 and 17 arranged in the chamber, are substantially uniform. The upper structure 9 is arranged in a distance from the lower structure 10, whereby the felt or the wire 27 is transfered between the structures. A middle suction chamber being arranged in the lower structure 10 is adapted to receive the pressurized air from the middle pressure chamber 12 in the upper structure after the air having passed through the felt 27. From the suction chamber 15 the air is brought to the devices adapted for conditioning of the air before reen- trance into the pressure chamber 12, when using a closed cir- cuit system. In the lower structure 10, one pressure chamber is arranged on each side of the middle suction chamber 15, a front pressure chamber 16 and a rear pressure chamber 16. The pressure chambers 14 and 16 are supplied with pressurized air principally in the same manner as the pressure chamber 12, in such a way that the pressure conditions in the upper parts of the pressure chambers 14 and 16 being substantially uniform when entering first and second jets 19 and 22 in the pressure chamber 14 and first and second jets 21 and 20 in the pressure chamber 16. Front and rear suction chambers 13 and 11 are arranged in the upper structure 9 opposed to the lower pressure chambers on each side of the middle pressure chamber 12. From the sue- tion chambers 11 and 13 the air is guided to devices for rein- troduction into the pressure chambers 14 and 16, separately or independently when using a closed circuit system. The front jet 17 in the middle pressure chamber 12 is arranged on the inside, e.g., towards the middle of the fixation device as such, of the second jet 20 in the lower pressure chamber 16 in such a way that substantially all air from the jet 17 pressed through the felt and into the middle suction chamber 15 whereas the air from the jet 20 in the lower pressure chamber 16 passed into the front suction chamber 13. All jets of the pressure chambers are arranged substan¬ tially in the front or rear part of the chambers and directed in an acute angle in relation to each other and to the web in such a way that the air from the jets is building up an overpressure between the jets and the felt and pressed through the felt into the opposed suction chamber. In this way the jets 20 and 21 of the front pressure chamber 16 in the lower structure are directing the air into the opposed suction cham- ber 13 in the upper structure, the jets 17 and 18 in the middle pressure chamber 12 are directing the air into the opposed middle suction chamber 15 and the jets 19 and 22 of the rear pressure chamber 14 are directing the air into the opposed suction chamber 11 in the upper structure 9. For furthermore to avoid the air coming from the rear jet 20 of the front pressure chamber 16 and from the front jet 19 of the rear pressure chamber 14 in penetrating through the felt into the middle suction chamber 15, a bar 23 is exten¬ ding across the entire length of the structure arranged in front of the jet 17 thereby substantially closing the gap between the felt and the structure without touching the felt to thereby avoid destruction of the felt surface. The air from the jet 20 thereby is guided on the outside of the bar 23, respectively the air from the. jet 19 being guided on the outside of a bar 26 arranged behind the jet 18. Corresponding¬ ly, by means of a bar 24 inside the jet 20, and a bar 25 inside the jet 19, air from jets 17 and 18 is guided on the inside of the bars 24 and 25, thereby additionally contributing to avoid air from the front and rear pressure chambers to be brought into the middle air system. The bars 23-26 have such a form and are such arranged that they do not or just even touch the felt and substantially close the distance between the felt and the upper, respectively the lower structure 9 and 10. During operation the environmental air necessarily is sucked in together with the felt 27 through the apertures between upper and lower structurees 9 and 10, at both their front and rear portions. This environmental air will be taken up by the suction chambers 11 and 13 together with air from the suction chambers 11 and 13 and therefore will not influence the heat treatment of the felt or the wire. As disclosed in Fig. 1, the upper structure 9 is provi- ded with a sport structure having closed channels 30 in the upper portion and corresponding closed channels 31 in the lower portion. The upper structure naturally also can be provi¬ ded with further channels for the same purpose. The channels 30, 31 are used for air flow having a controlled temperature thereby securing that the upper structure 9 is not being defor¬ med by influence of the heat from the fixation operation. This feature is essential especially for upper structures 9 having a relatively small hight and bridging a rather long distance across the felt. The air through the channels 30 and 31 may be taken from one of the pressure chambers or from an oxiliarly device. By providing a separate circuit for the air between the middle chambers and a further circuit for the air in the outer chambers, possibly separate circuits even for the two outer chambers, a uniform treatment of the felt is ensured during fixation and thereby a homogeneous felt. Control of such circuits may be computerized by a computer device. Tests have been performed with measurement of the temperature in the internal parts of the felt and on the sur- face of the felt at measuring points 1-8 as disclosed in Fig. 1. The measured values from those tests are disclosed in dia¬ grams Fig. 2 and 3. Nominal temperature of the air was 150°C and the resting time of the felt in the treatment zone was approximately 2 minutes and 15 secunds. The weight of the 2 felt used was 1,03 kilo per m and the permeability of the felt was 40 meter per minute at 250 Pa. As disclosed in the diagrams 2 and 3, a very homogen- eous temperature curve was achieved between the measuring points 4 and 6 and the temperature curves in this area approxi¬ mately are the same on the upper surface of the felt as in the middle of the felt.

Claims: P a t e n t C l a i m s 1. Fixation device for permeable web materials, such as felts and wires for paper maschines, where air at control- led temperature and pressure is pressed through the web from jets in at least one pressure chamber (12) on one side of the web, to at least one corresponding suction chamber (15) on the other side of the web, the device thereby comprising an upper structure (9) and a lower structure (10) between which the web is running during operation, CHARACTERIZED IN a pressure chamber (16) with a corresponding suction cham¬ ber (13) being arranged in front of, and a pressure chamber (14) with a corresponding suction chamber (11) being arranged behind, at least one middle pressure chamber (12) with a corresponding suction chamber (15), each pressure chamber (12, 14, 16) being provided with two jets arranged in an. accute angle to the web and towards each other, with one front jet (17, 19, 21) and one rear jet (18, 20, 22), thereby establishing and maintaining an overpressure between the jets and the web, jets arranged in opposed pressure chambers and adjacent each other thereby directing air passed each other in such a way that air from one pressure chamber sub¬ stantially is prevented in penetrating into the adjacent suction chamber, and the upper and lower structures (9, 10) being provided with ducts (30, 31) for an air flow having a controlled temperature, thereby avoiding deformations of the upper structure (9) due to temperature influences from the heated air in the fixation process. 2. Device according to claim 1, CHARACTERIZED IN sealing devices (23-26) extending across the length of the chambers at least between the web and the middle pressure chamber and between the web and the middle suction chamber, arranged between the jets of the pressure chambers and adjac ent suction chambers, thereby preventing air from the front or rear pressure and suction chambers in penetrating into the air system of the middle pressure and suction chamber. 3. Device according to claim 1-2, CHARACTERIZED IN the pressure and temperature of the air _from one pressure chamber to a corresponding suction chamber being independently controlable concerning pressure and temperature for the air, from the air flow in other pressure chambers- and sunction chambers. 4. Device according to claim 1-3, CHARACTERIZED IN a duct (29) being provided in each pressure chamber along the entire length of the chamber, having an outlet (28) for air arranged opposed to the jets in the chamber, in such a way that the air at the input of the jets have uniform temperature and pressure along th entire length of the jets. 5. Device according to claim 1, CHARACTERIZED IN the upper structure (9) being provided with at least upper and lower ducts (30, 31) for air having controlled tempera¬ ture, thereby avoiding thermal deformations due to the influ- ence of the air transfer between the chambers. 6. Device according to claim 3, CHARACTERIZED IN the parameters for the air transfered from the individual pressure chambers to the respective suction chambers, as well as the moving speed of the felt, being controlled by a central computer unit.

Inventors: GUNDERSON HARALD, GUNDERSON, HARALD
Applicants: ALFSEN & GUNDERSON
Application year: 1987
Main classification: D21F1
IPC codes: D06B5, D06C7, D21F1, D21F7