APPARATUS FOR HEAT TREATMENT OF MATERIAL, PARTICULARLY INFRA-RED RADIATION OF A CONTINUOUS PAPER WEB IN A PAPER MACHINE

Abstract: Apparatus (1) for treatment of a continuous paper web (18) in a paper machine by means of infra-red radiation, comprising, in parallel relation to the paper web, infra-red heaters (17), which are separated from the paper web by protection panes (12), a cooling air system being provided to cool infra-red heaters and protection panes. The protection panes (12) are arranged by way of a series of separate panes overlapping each other and forming ventilation gaps (27), which are directed substantially in parallel relation to the web in the same direction or in two opposite directions (Figs. 1 and 2).

Description: Apparatus for heat treatment of material, particularly infra-red radiation of a continuous paper web in a paper machine. The present invention relates to an apparatus for heat treatment of material, particularly infra-red radiation of a continuous pa¬ per web in a paper machine and is more closely defined in the pre amble of claim 1. It is previously known to expose e.g. a continuous paper web in a paper machine to infra-red radiation for drying the web wholly or partially. Hereby, the infra-red radiation creates a great heat p tential, which entails the need for cooling the radiation and pro tection of the paper web against smear spots and other polution, the risk of fire and unequal drying. For achieving such a protec¬ tion, supply and/or exhaust air currents are used, which affect t radiation and the paper web. Thesa currents are provided to bring about guaranteed cooling, but without minimizing the efficiency o the drying process and without adversely affecting the path of th web, respectively. These demands have, so far, not been met by pr viously known techniques. Such apparates do often comprise a s.c. counter reflector provide to throw back part of the heat radiation having passed through th paper against same. It is desirable, for making the drying proces more efficient, to arrange the counter reflector as close to the paper web as is possible. Hitherto, the counter reflector had, ho ever, to be arranged at relatively large distan e to the paper we for various reasons, which brought about decreased efficiency. Th same applies to the reflector itself with the radiation source which, mainly because of security reasons, had to be arranged at relatively large distance from the paper web in previously kno n apparates, which rendered a clearly worse degree of efficiency. O major importance in this connection is, however, the guidance of the web, which so far, for certain combinations of paper weight, structure, moisture contents, free length in the direction of the web etc, has been adversely affected by reflectors arranged too closely nearby, because of negative affects of the cooling air currents on the web. Further drawbacks of known techniques are great waste of power , difficulties to perform maintenance and service, maintaining an equal degree of efficiency and need for frequent service. The object of the invention is to provide an improved apparatus of the kind as Initially defined, which avoids the said drawbac A superior purpose of the invention is to provide a basis for u the components comprised by the apparatus as efficiently as pos le, to. increase the level of efficiency substantially and to pr vide, in spite of these advantages, the same or even increased curity. A further object of the invention is to improve techniq in this field in various other respects. These objects are achieved according to the invention in that a apparatus of the kind as initially defined substantially is cha terized by the features of the characterzing clause of claim 1. Thanks to these features, it is possible to arrange the radiato with the reflector very close to e.g. a paper web, namely, acco ding to obtained test results, at 20 mm distance between protec glaε panes and a paper web, which is to compare with app. 50 mir. according to previously known technique. In such a way, a much extensive drying is, of course, obtained and the level of effic cy may be increased further by arranging even the counter refle closer to the web. In spite of these features, it is possible t ensure an advantageous web guiding, which is not or only neglig affected by e.g. air currents. Said features do also safeguard, that the apparatus is, as far as possible, kept free from dirt. The lack of substantial free air currents brings about a degree purity which is unknown so far, and which considerably increas both efficiency and safety. Furthermore, the concept of overlapping protective panes offers advantage, that tolerances and ther ical expansion won't affect tightness of the assembled glas surface. Further characteristics of and advantages wi h the invention ar vealed by the following specification with reference to the acc nying drawings which, schematically, illustrate a preferred, tn not limiting example. Fig. 1 is a cross-sectional view of an apparatus according to inventio . Fig. 2 is a sectional view according to line A ./. A in Fig. 1 il¬ lustrating conditions at relatively low pressure, Fig. 3 is a view corresponding to Fig. 2 at relatively high pressure Fig. A is a partial view of the embodiment according to Fig. 2 or an embodiment between Fig. 2 and 3, Fig. 5 is a view corresponding Fig. 4 of a modified embodiment, Fig.s 6 and 7 are a side elevational view and a top plan view, respe tively, of a preferred embodiment of a pane holder. In Fig. 1, 1 designates a preferred embodiment of an apparatus accor ding to the invention in its entirety. The apparatus comprises e.g. an elongated exterior housing 2 provided in one end wall 3 with an inlet 4, side walls 5 and a top side 6 with an outlet 7. Lowermost, the exterior housing shows an opening 5 occupying substantially the underside and laterally limited by narrow flanges 9, which preferab¬ ly are provided at a border 10 extending all-around the side walls 5 and the end walls 3 and permitting easy and complete access to the interior of the exterior housing. From below, pane holders 11 are attached to the flanges 9 and carry panes 12, which in principle cover the opening δ. Appearance and function of the pane holders will be more closely described in con ¬ nection with Fig. 2 - 5. Between the end walls 3, there extends an interior housing 13 with top side 1 *4 , side walls 15 and a lower opening 16, which is occupied by infra-red heaters 17 with reflectors (not shown) inserted into the interior housing and facing a paper web IS, which is guided out¬ side of the panes 12 and parallel to these. The web runs to the left or to the right in Fig. 1. The side walls 15 of the interior housing are arranged at distance from the side walls 5 of the exterior housing in order to provide exhaust air passages 19, which connect lower supp y air zo e Z _ between said heaters 17 and the inside of the panes 11 to an upper merging passage 21 between the top sices ό and 1-.. which rtersi r par- sage extends into said out let 7 to lead away the exhaust air. The supply air and the exhaust a;r are h :.- guided _. : a c l os ed systc:... Herein, the supply air is preferably filtered before entering t apparatus according to the invention. The exhaust air may wholl or partly be used in e.g. heat exchangers or other- energy using devices. The exhaust air is supplied in a pure state and does n require filtering, accordingly. The housings are suitably made stainless steel. On the reverse side of the paper web, there is preferably provi a counter reflector 22, which is previously known per se and ha the objective to throw back the major part of the radiation whi has penetrated the paper web and in this way heat up the latter even on that side which is turned away from the heaters 17. Tha to the invention, even the counter reflector can be arranged re tively" close to the paper w τ eb, e.g. 20 mm from same, while that distance previously was app. 50 mm. As revealed by Fig. 1, the supply air is distributed from the i or inlets 4 around and/or through the heaters 17 and through th supply air zone 20, which thus becomes a cooling zone, tow τ ards sides 5. The pressure of the supply air may easily be adjusted that the inlet 4 is connected to a fan 23 generating excess pre sure and/or in that the outlet 7 is connected to a fan 24 gene ting a vacuum. Possibly, a fan for the exhaust air is unnecess thanks to the invention. According to another, substantial feature of the invention, th panes 12 are arranged in series throughout the length of the e rior housing, i.e. at right angle in relation to the sheet pla of Fig. 1. The panes bridge the entire distance between the ju aposed pane holders 11 in one piece and have thus a length of 250 - 600 mm, preferably app. 350 mm. The width is preferably 100 - 300 mm only, suitably app. 150 mm. This width shows up i Fig.s 2 and 3, which also reveal another important feature of invention, namely that the longside regions 25, lc cf the pane overlap each other. The overlap is such, that gaps 27 are form w τ hich either all of them point in the same direction or,for in stance, commencing at the center of the apparatus, point in op site directions. The pane holders 11 are shown schematically only in Fig.s 2 and 3. They may be provided in a continuous way for receiving any number of panes or e.g. a pane each. They are furnished with a groove 29 for receiving the pane or panes. This groove may be so wide, that an overlap is possible within the groove, i.e. the groove is at least twice as wide as the thickness of the panes. It is also pos sible to provide several grooves 29, one for each pane, and/or ma the grooves and/or the pane holders be oblique in a way as illus¬ trated by the grooves 29 in Fig. 6. Furthermore, within or outsid of the grooves and at their lower end there may be stop means 30, which limit insertion of the panes in this direction. According to a special embodiment of the invention, these stop means may be pro vided to form or prolong or limit or affect, respectively, wholly or partly said gaps 27. A preferred embodiment is shown in Fig.s 6 and 7, where the holders form, in the direction of inclination, a lower projection 31, n which there is provided to rest an upper projection 32 arranged at the opposite side of the holders. The front edge of the lower projection 31 and the matching edge of the upper projection 32 may preferably be oblique for easier fitting in. The edges of the panes entering the grooves 29 may be furnished with some kind of lining, packing or the like (not shown}, which may have a certain elasticity for desirable adjustment or regulatio of the width of the gaps 27. In principle, at low pressure drop vi the gaps 27, the panes attain a position according to Fig. 2, wher supply air leaks through the gaps 27 in a controlled way. The flow points in the same direction and somewhat away from the panes and soewhat towards the paper web, which may be advantageous in certai cases. Mostly, a control according to Fig. 3 or closely to Fig.s 3 , 4 or 5 may, howver, to be preferred. Herein, most a relatively large pressure drop prevails via the gaps 27, which decrease in width simultaneously due to this pressure drop, as the superposed pane area 25 is pushed down towards the underlying area 26 of th*.. adjacent pane by the pressure. In this way. an automatic εelf-ac- just ent is alwayr- achieved, which cannot be affected even by wear and tear as time goes by. Kithin the gap itseli. a. lower pressure- arises, thanks to which the pane areas superimposing each other are so to Swea suck . towar s each other. Tb*Ou h the very narrcv; remaining gap, high velocity air currents 35 are pushed out in parallel relation to that side of the panes which faces the pap web, which pane sides simultaneously are kept clean and cooled thanks to these currents, which benefit,due to velocity and sub stantial momemtum, from the s.c. coanda effect, i.e. that an ai current is sucked towards a confinement by the arising vacuum. The volume of these air currents is however, so little, that t guidance of the web is not adversely affected in any way. An ad tage in this connection is also, that the partial currents assi each other by a combined sucking and pushing effect. The power a partial stre?.m may therefore not be chosen in such a way, tha the stream or current easily and quickly Ccin leave the region b ween panes and paper web, wnich likelv could give rise to turbu ces entailing interferences in the guiding of the w τ eb. Very fav rable is the laminar flow of air between panes and paper web. A high pressure drop, the flow τ direction is, as has been said, su stantially parallel to the panes, which may be further improved narrow and possibly long gaps, which are achievable by choosing longer overlap zones. At low pressure drop, it may be favourabl to direct the air currents slightly more towards the paper web better breaking up a steam layer surrounding the w τ eb. This flo pattern may accordingly be controlled,among other means,by cont of the pressure drop. Naturally, there may be provided special means for increasing/decreasing the width of the gaps, e.g. by of s.c. pivot points 36, around which the panes may turn or be turned simultaneously increasing or decreasing the gap w τ idth. ther means may be shaping the pane edges within the overlap zo e.g. by bevelling and/or curving which, to a certain degree, m have the effect of diffusing and/or increasing velocity. The p edges may also, in these areas, be ground in a special way to in combination, a ceratin desired jet design and thus render a increased length of throw respectively velocity at a certain d ference of pressure. Even in this way, the length of the gaps be controlled. Thanks to the invention, panes and infra-red heaters may readi be for instance exchanged, which is a favourable spin-off effe of the invention, which is to be compared with removing a large pane with many points of attachment, large weight and other dis¬ comfort . It will be appreciated, that the panes may be arranged alternate ly at different levels which, admittedly, will result in pairs o air currents pointing in opposite directions, which currents may, however, be designed differently or is it possible to obstruct o gap formation.

Claims: CLAIMS 1. Apparatuε (1) for heat treatment of material, particularly infra-red radiation of a continuous paper web (18) in a paper machine, comprising a number of infra-red heaters (17) arranged in parallel relation to the paper web or the like and separated from the paper web by protection glass (12), a cooling air system being provided to cool infra-red heaters and protection glass, c h a r a c t e r i z e d i n t h a t the protection glass (12) is provided as a series of separate panes overlapping each other and forming ventilation gaps (27), which are directed sub- stantially in parallel relation to the web in the same direction or in two opposite directions. 2. Apparatus according to claim 1, c h a r a c t e r i z e d i t h a t it comprises a preferably elongated exterior housing (2; with an inlet (4) in one of the end walls (3) and with side walls (5) and a top side (6) with outlet (7) as well as lowermost an opening (8) occupying substatially the entire underside and late¬ rally confined by flanges (9) which, preferably", are arranged at a border (10) surrounding the side walls (5) and the end walls ( 3 3. Apparatus according to claim 2, c h a r a c t e r i z e - 'i t h a t between the end walls (3) there extends an interior hou sing (13) having a top sice (14), side walls (15) and a lower op ning (16), which is covered by infra-red heaterε (17) with refle tors inεerted into εaid interior housing and facing a web or the like (18), which is guided outside the panes, preferably in para lel relation to the latter, a n d t h a t the side walls (15! of the interior housing are arranged at distance from the sice walls (5) of the exterior housing to form exhaust air passages (19), which interconnect a lower supply air zone (20) between sa heaters (17) and the inside of the panes (12) with an upper erg passage (21) between the top sides (6) and (14), which merging passage connects to the outlet (7) for leading away the exhaus a 4. Apparatus according to claims 1 - 3, c h a r a c t e r z e in that to the flan.ee? ( 9 ) are, from below, attached pan holders (11) carrying the panes (12) which, in principle, cover the opening (8), a n d t h a t on the reverse side of said m terial in relation to the housings, there is provided a counter reflector (22) which, preferably, is located relatively close t said material, e.g. 20 - 30 mm from same. 5. Apparatus according to claims 1 - 4, c h a r a c t e r i z i n t h a tthe supply air is provided to flow from the inlet ( and preferably through the heaters (17) and through the supply zone (20) in order to design the latter as cooling zone, and to wards both sides (5), a n d t h a t the pressure of the sup air zone (20) is controllable by the inlet (4) being connected a fan (23) generating excess presεure and/or by the outlet (7) ing connected to a fan (24) generating a vacuum. 6. Apparatus according to claim 1, c h a r a c t e r i z e d t h a t the panes (12) are arranged in series along the length the exterior housing, t h a t the panes bridge the entire dis tance between opposite pane holders (11) in one piece, a n d t h a t the pane holders (11), preferably, are designed throug going to hold any number of panes in combination or one pane ea alternately. 7. Apparatus according to claim 6, c h a r a c t e r i z e d i t h a t the pane holders are equipped with a groove (29) to re ceive the pane or panes, respectively, which groove has such a width, that the overlap takes place within the groove, i.e. the groove is, at least, twice as wide as the thickness of the pane o r t h a t there are several grooves (29), one for each pane a n d / o r t h a t the grooves respectively the pane holders are arranged oblique. 8. Apparatus according to claim 7, c h a r a c t e r i z e d i t h a t, within or outside of the grooves, at their end positio most closely to said material, there are provided step means ( 3 which limit insertion of the panes in this direction, a n d t h a t these stop means, preferably, are provided to form, to prolong or to limit or to affect, entirely or partly, said gaps (27). 9. Apparatus according to claim 7, c h a. r a c t e r i z e d i n h a t the pane holders form, in the direction of inclination, a lower projection (31), on which is provided to rest an upper projection (32) arranged at the opposite side of the pane holders a n d t h a t the front edge (33) of the lower projection (31) and the matching edge of the upper projection (32), preferably, are oblique for better fitting in. 10. Apparatus according to claim 7, c h a r a c t e r i z e d i h a t the edges of the panes entering the grooves (29), prefe¬ rably, are furnished with a lining, packing or the like which, pr ferably, show τ s a certain elasticity for desrible adjust ant or re gulation of the width of the gaps (27), supply air being provided to leak through the gaps (27) in a controllable way with the flo in the same direction and directed slightly away from the panes and slightly towards said material, a n d / o r t h a t there i provided to prevail a relatively large pressure drop via the gaps (27), the width of which is provided to diminish due to said pres sure drop.

Inventors: HAMRIN KARL-ARVID, HAMRIN, KARL-ARVID
Applicants: INFRAROEDTEKNIK AB
Application year: 1988
Main classification: D21F5
IPC codes: D21F5, F26B3, F26B13