CA1131012A - Material treatment apparatus - Google Patents

Abstract

I.
ABSTRACT OF THE DISCLOSURE

An air cylinder for supporting a moving web of material during heat treatment, particularly during drying, of such web. The cylinder comprises a plurality of nozzles which axe arranged in a part-circular array around which the moving web passes the nozzles being of the Coanda type wherein the discharged gaseous medium flows over a transversely extended lip surface of the nozzle between the extended surface and. the adjacent surface of a web being treated and is caused to cling to such extended surface by the so-called Coanda effect, In order to support the moving web particularly stably in the radial direction relative to the cylinder, the nozzles are arranged in pairs, with the respective trans-versely extended surfaces of the two nozzles in each pair extending in opposite directions whereby air flowing over these two extended surfaces flows in opposite circumfer-ential directions to respective radially inwardly directed air outlets. Each air outlet commonly serves two nozzles, one from each of two adjacent pairs of nozzles, respect-ively.
A plurality of the part-circular arrays of Coanda nozzles can be disposed with adjacent arrays inserted in relation to each other so as to support the materiel web in a circuitous path around such arrays.

Description

113101~ 1 ~.

. D~9~RIP'~ION
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, ~ he present inventio~ relates to float treatment apparatu~ L or treating a flo~ting web of mat~rial and is particularl~ concerned with such apparatus for use in ~ dryin~ co~tinuously formed material webs, such a~ -:; paper~
For the past 150 years or so paper production ha~
i.nvolved ~he passa~e of a conti~uously formed wet paper 1~ w~b around rotatin~ cast iron, steam heated drying c~linders to drive at least some of the moisture ~rom the webc It has long bee~ realised that the use of these cvlinders results in many practical disadvantages. In order to achieve reasonable dryi~g efficiency they have to b~ of massiYe size~ o that corxespondly massive supportin~ framework, bearin~3 and driving gears ars ~ec~sary. The apparatus thus occupies considerable floor space. ~he use of such cylinders normally requires . th~ additional use of felts or other fabric webs to hold the p~per w~b in close contact with the cylinders 7 the : latter f~lts or fabrics requiring periodic9 expensive replaceme~t a~d an additional plurality of roller~ to e the~ around the cy1inders. The use of such c~ d.ers ~l~o requires the p,rovision of a relatively complic~ted and ex~ensi~e venti~ation ~ystem i.n order to maintain unifor~ air conditio~s around the cylinders to achieve even approximately uni~orm drging conditions. ~owever, in prRctice it has bee~ fou~ld to be impossible to obta$n ~? , truly uniform dryin~ u~ing the traditional cylinders~
~ ttemp~s have been ~a~.e to replace individual ca.st iron cylinders with air cyl nders (see for exa~ple US
3279 091) whlch co~prise a plurality of air nozzles arran~ed in a part c~lindrical array whereby a web supported by pressurized air from the nozzle~ assume~ a corresponding part cylindrical formation in passing therearound. Such air nozzles have comprised elongate slots exte~din~ i~ parallel lo~lgitudinal directions along ~he surface of hollo-~ part cylindrical hollow shells.
~ he main problem with sush air~cylinders ha~ been, howe~er9 that in order to maintain a workable air cushion for the moving web, impossibly fine tension control is required since a balance has to be continuously ~5 maintained betwee~ the rRdially outwardly acting forces on the web arising from the air jets impinging thereon and the radially inwardly acting forces arising as a result of the tansion i~ the web establi~hed by means of separatsly controlled input and output drive nips disposed upstream and downstrQam of the cylinder, respectively. Furthermore, such known air c~linders have been subject to unsolved problems resulting from the ~ariable r~te of web shrinkage which is often inc~rred.
It is an objective of the pre~ent invention to provide an air cylinder in which the pre~ious requirement for fine tension control is obviated and ;~hich ca~
operate efficiently in a multi-cylinder arrangement.
~ The present invention make~ use of so-called Coanda nozzles, the basic principle of which has been k~own in 3 the hrt ~or some time. A Coanda nozzle is one in which the discharged gaseous medium, normally air, flows over a laterall~ extended curve~ lip ~urface of the ~03zle between that extended surface and the adjacent surface of the web being treated$ the discharged gaseous medium 35 bein~ caused to cling to ~uch extended surface by the so called (~oanda effect. Provicled that dimensions and g~3~

pressures are suitably chosen, the web of material will float stably on the noæzle at a small distance from the extended surface. The present invention is, however, not concerned with the theory of operation of such nozzles which has been well documented elsewhere (see for example IJnited Kingdom 1,302,091) but with the use of such nozzles in an arrangement which provides an advantageous operating performance.
The invention provides a float treatment apparatus for drying a paper with gas comprising (a) a plurality of separate but adjacent nozzle arrays, each nozzle array comprising a plurality of nozzle pairs disposed in generally U-shaped curved arcs that have a curvature approximating at least half of a circle, adjacent nozzle arrays being ~-shaped in opposite directions and being arranged and positioned with respect to each other so that a paper web passing thereover will move in a serpentine path that takes it around a more than 180 circum-ferential portion of an array, (b) each nozzle pair in each array being of the Coanda-type and having lip surfaces extending in opposite directions from the point where gas exits through each nozzle pair, whereby the gas exiting from each nozzle pair flows in opposite circumferential directions, and (c) a plurality of gas outlets, each outlet being located between the outer lip edges of adjacent nozzle pairs said outlets extending radially inward~
ly and being adapted to receive the streams of gas flowing toward each other over the lip surfaces of adjacent nozzle pairs.
The use of Coanda nozzles in this manner has the result that, rather than being merely loosely supported in the radial direction as in the case of the known air cylinders, the moving web is positively held to the contour of the cylinder by virtue of the air flow pattern achieved. As a result, very wide variations in tension in the web can be accepted from substantially zero to ~3 IL~

approaching web breakage whereby the mechanical running problems encountered with the known arrangements are eliminated.
Since drying of the web by means of a uniformly distributecl film of hot air can now be achieved, advantages are obtained in that:
(a) Drying is absolutely uniform.
(b) The moist air can be exhausted from the cylinder by means of a standard exhaust duct so that only the moisture leaving the sheet from its bac~ side remote from the nozzles may need a simple canopy to remove it.
(c) One is no longer restricted to steam heating; forms of heating other than steam can enable much higher temperatures to be used and hence much higher evaporation rates to be obtained.
(d) No fabrics are required to guide the web around the cylinder and the vapour escapes from both sides of the sheet, resulting again in higher evaporation rates.
The arrangement with each gas outlet serving two nozzles has been found to result in a particularly efficient air flow pattern over the cylinder which holds the moving web stably in the radial and longitudinal directions relative to the cylinder whi]e enabling the web to be drawn in a substantially frictionless manner around the cylinder.
Obviously, for drying purposes, the air supplied by the nozzles is pre-heated, for example by gas burners.
The invention is described further hereinafter, by way of example, with reference to the accompanying drawings in which:-Figure 1 is a diagrammatic vertical section through one embodiment of a float treatment apparatus constructed in accordance with the present invention;
Figure 2 is a diagrammatic illustration of a plurality of part cylin-drical arrays in accordance with the invention arranged for transporting a material web;

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~5--Fig~ 3 is a diagr~mmatic section through one of a pluralitg o~ nozzle units which together make up part oX the cylinder of Figo 1;
Fig. 4 i~ a partial plan view of a portion of the nozzle unit of Fig, 3;
~ig. 5 is a partial view showing fur~her portions of th~ ~ozzle unit of Figc3; and ~ig. 6 is a section o~ -the li~e Vl-VI of ~i~. 1, to a reduced scale~
The c~linder 10 G~ Fig~ 1 compri~es a pl~ralit~
thirteen in this instance, of individual nozzle units 12 disposed in a part circular array~ the noz~le units 12 ea~,h being constructed as she~n i~ more detaii in Fig. ~ he radially inner ends of the no~zzle units 12 communicate with a c~lindrical central chamber 14 con~ected ~ia pipewor~ 16 (s~e Fig~ 6) to a heated pressure medi~n supply (not sho~) which would normally be hot air, the air exiting from the .radially outer ends of the ~ozzle units being such as to be capable of suppvrtin~
~a~d guiding around the cylinder a travellin~ web 18, as show~ in ~ig. 1.
With refere~ce to ~ig5. 3, 4 and 5, each ~ozzle unit 12 comprises a nozzle bo~ 20 commu2icating - at it~ radially inner end wit~ the ckamber 14 by way of a radially extendi~g pipe 22. The box 20 i~
~ormed by a pair of lo~gitudinal side walls 24,26 ~ormed from sheet metal~ a base wall 2~ havlng a pluralit~ o~ c~lindrical openin~s which receive the pipe~ 22 (s~e ~ig. 6)~ closed end walls 30,32 and a top ~.rall defined principally by a pair of profiled ~heet ~etal member~ 34,3~. B~ virtue of its connection to the inner cJlindrical chamber 14, each box define~ a pressure ch~n~er ~7 which xeceiv~s hea~ed , ~ .

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pressure medil~ (air) from the chc~n~er 14~ the box discharging the pressure medium through a pair of nozzle slots 38.
~ he oute.r lips of the siots 38, i.e. the lips remote from one another, are defined by rounded surfaces 40 on the profiled sheet metal members 34,36. ~he i~ner lips axe defined by lateral edges 42 of a medial plate ~ which is ~upported in position between the outer lips b~
~Q means of a box sectioned tube 46 to which the plate 4~ is rigldl~ attached, for example by a pluralit~
of rivets 48 (Fig~ 4). ~he box sectioned tube is itself mounted b~ means of longitudinally pro~ecting pegs 50 at its two ends which are received in suitable ~uides (not shown) in a main framework of the cylinder. ~ransver~ely orientated spacer plates 52 are disposed at i~tervals along the plate 44~ each ~pacer 52 ha~i~g proaections 54 which engage in respective slots 56 i~ the plate 44 whereby to maintain ~he width of the slots 38 at a predetermi~ed constant width over their whole :le~gth. It will be appreciated that the aforegoi~g assembl~ permits æimple disassembly to e~able access to the interiors o~ the boxes 20 for cleani~g purposes.
he rounded sur~ace~ 40 blend with the substant-iall~ flat outer sur~aces 58 of the profiled plate~
34,36~ The sur~aces 58 are arranged to stand proud of a flat outer surface 60 of the medial plate 44 a~d the rou~ded surface~ 40 are likewise substantially proud of the flat surface 60. ~he pressure in the chamber 37, the width of the nozzle slots 38 and the radius of the rounded surfaces 40 are so chosen that gaseous medium disch~r~ed Xrom the nozzle slot~
~8 tends to follow the rounded surface3 40 and flow over the outer surfaces 58 i~ accordance with the - -.~ -.

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_7-Ceanda e~fe~k~ as shown by ~rows in Fig~ he spent ~aseous medium flows awa~ into exhaust ch~mbers ~2, located hetween adjacen~ nozzle t~.ti-ts 1~ b~
way of slot8 or apertures 64 ~ormed between the 5 adaacent profiled sheet meta.l members ~4~35 of adaacent nozzle units. ~he spent gaseous medit~m pas~es to a commo~ chamber 66 at the bottom of the cylindcr which communicates with discharge pipewor~ 58 (Fig. 6 ~he theory o~ the manner in ~rhich the web 18 is supported will not be ~iven ina~much as the in~entio~ is not concerned with the theory but with the construction of the apparatus. Su~fice it to say that, due to the Coanda effect, the discharged gaseous material lea~i~g the nozzles 38 is caused to cling to the contour of the outer ~urface~ of the members 34,36 whereby the web 18 i8 supported relatively 3tably above each nozzle unit a~ a short distance above the sur~aces 58.
~0 Due to the arrangeme~t of the nozzle tmits to for~t a partial c~Jlinder shown in Fi~;~ 1, the web 18 is continually supported on a cushion of pressure mediv~ in passing over the c~ er so th~t it is maintained at a substantially constant distance from the cylinder at all times. Furthermore~ the ho~ pres~ure medium applied to the underside of the web serves to dry the ~eb whereb~ the air c~linder acts as a float drier. If de~ired, drying can be assistea by the provision o~ a~ outer convected air drier of convention~l construction which can mounted around the c~linder opposite the outer side of the web. Such a drier could be in th~ form of an air cap ox accelerator hood whereby to increase the evaporation rate from the web.
The aroregoing c~linder can be used in place of conventional rotating cast iI~On cy~.inders used 7 for ., , , ~, . , , .~ .

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exa~qple, in paper machines and for drJing textiles and indeed for heating or coolin~ any web material, Wh~n used i~ place of known flat float drying apparatus, it will be appreciated that considerable floor ~pace can be saved by the cylindrical ~ature ~f the present arrangement. Fig~ 2 illustrates one possible arrangement which maximises the length of web which can be treated while minirnising floor space utlisation wherei.n the web 18 is passed 10 around a pluralit~ of cylinders 10, alternate ones of which are inverted whereby the web extends ~ubstantially tangentially between adjacent cylinders~
Additional ad~an~ages of the presen-t construction over.the known cast iron c~linders used for web drying, e.g. in paper machines7 are as follows.
The web can ~hrink freely in the longitudina7 direction and all that is required is a constant te~3ion means to relate the ~peecl of addi'ional rolls~ e.gO ~ wrap rolls 9 contact; rolls or calender rolls ? to the speed of the web.
~he or each cyli~der can be supplied w.ith hot air heat;ed directly b~ gas Ol' any other appropriate heati~ medium) provlding temperatures of up to say 600~.
?5 No fabric~ or ~elts are required to support the web in its passage over the or each cylinder 10.
Mai~tainance problems can be expected to be reduced due to the few number of movin~ parts.
Lessbre~ka~e9 in the web during its passage 3 thr~ugh tke drier can be expected due to the web being co~pletel~ f~ee to shrink in the lon~itudinal directio~.
With the arran~ement as illustrated in ~ig. 2, for exa~ple, the draw~ between adjacent cylinders can be muc~ shorter th.an usual and the web can be 3~ ~ 2 _9_ ub~tantially wbo~ly enclosed between t~e cylinder~.
~hese factors assist when wor~in, with ~er~ high speed~ light~7ei~ht web~
B~sides use i~ connection with paper dr~i~g, the present cylinders can also be u5ed ~or heatl~g or coolin~ plastics webs or films or dryin~ ~a};-tiles.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A float treatment apparatus for drying a paper with gas comprising, (a) a plurality of separate but adjacent nozzle arrays, each nozzle array comprising a plurality of nozzle pairs disposed in generally U-shaped curved arcs that have a curvature approximating at least half of a circle, adjacent nozzle arrays being U-shaped in opposite directions and being arranged and positioned with respect to each other so that a paper web passing there-over will move in a serpentine path that takes it around a more than 180°
circumferential portion of an array, (b) each nozzle pair in each array being of the Coanda-type and having lip surfaces extending in opposite directions from the point where gas exits through each nozzle pair, whereby the gas exiting from each nozzle pair flows in opposite circumferential directions, and (c) a plurality of gas outlets, each outlet being located between the outer lip edges of adjacent nozzle pairs said outlets extending radially inwardly and being adapted to receive the streams of gas flowing toward each other over the lip surfaces of adjacent nozzle pairs.

2. A float treatment apparatus according to claim 1 wherein each nozzle pair is connected to a separate nozzle box which feeds gas to that nozzle pair and the nozzle boxes are in turn coupled to a common distribution chamber dis-posed radially inwardly of the nozzle boxes and which is connected to pressur-ized air supply via an air inlet duct.

3. A float treatment apparatus according to claim 1 wherein each nozzle pair is formed by a pair of uniformly circumferentially spaced profiled sheet members, which define said oppositely extending lip surfaces of the nozzles, and a medial plate each of whose two lateral side edges is uniformly spaced from a respective one of the profiled sheet members whereby to define a uniform slot therebetween.

4. A float treatment apparatus according to claim 3 including a plurality of radially directed spacer plates disposed at intervals along the length of the medial plate to maintain uniform said slots between the medial plate and the adjacent profiled sheet members.

5. A float treatment apparatus according to claim 5 including a support-ing beam to which the medial plate is rigidly attached and which is removably mounted in an associated nozzle box to enable easy access to the nozzle box interior for cleaning purposes.