CA2052596A1

CA2052596A1 - Method and device in the drying section of a paper machine in the threading of the web

Info

Publication number: CA2052596A1
Application number: CA002052596A
Authority: CA
Inventors: Heikki Ilvespaa; Antti Kuhasalo; Jouko Yli-Kauppila
Original assignee: Valmet Paper Machinery Inc
Current assignee: Valmet Paper Machinery Inc
Priority date: 1990-10-01
Filing date: 1991-10-01
Publication date: 1992-04-02
Also published as: EP0479748A1; FI86900C; DE69119859D1; FI904841A; ATE138702T1; CA2052059A1; FI904841A0; EP0479748B1; FI86900B; CA2052059C; DE69119859T2

Abstract

(57) Abstract Method and device in a multi-cylinder dryer of a paper machine in the threading of the paper web, said threading taking place substantially without a system of threading ropes. The web is passed along a meandering path, in twin-wire draw, over drying cylinders (10A,10B) and, in single-wire draw, on a drying wire (11), over drying cylinders (10;10') and leading suction cylinders (20,20') or rolls (20,20').
The leader (S) is guided by means of air blowings (F1) extending across a substantial proportion or the whole of its width (L1), said air blowings (F1) being applied from the doctor beam (12) to the area (K) of the tip of its doctor blade (14) at a certain small angle (B) in relation to the plane of the doctor blade (14).

Description

~etho~ and d~c~ e ~g se~t~o~ of a ~aper mach~ae in the thr~ding of ~he we~

S 'rhe i~venP.on ~on~ems a metho~ in a mul~-cyli~e~ d~yer of a pa~ mac~e in the ehreadin~ of th~ papes Web7 said ~a~ing t~king pla~e subst~ntially wit~out a o,ystem o~ eading ~pes, in whit~h method dhe web is pass~d ~lon~ a ~ dgsing pa~, n twin-~ dr~w, ove~ g cylinders a~d, in single-wlre d~aw, on a drying w~e, over dryDg cylinders and leading suc~ion cylillders os ~o'~ls.
Ft rther, the invention concerns a devi~e for caIrying out the method.

As i~ ~own in pnor art, in the dryin~ s~on of a paper machi~e, s~calIe~ single-~vire d~aw or tu~ vnre draw is en~ployed. In ~uch a ~ase, for the thr~din~ o~ the 15 w~, as a rule, ~pe ~de mean~ are used, by who~e means ~he leader~ wl~ch ~as bee~ c~t out oi' a full-widt~ we~, is pa5sed over the c~ing ~ylinder~, whereupon th~
le~der is widened to a we~ of f~ ndth. The system of ~ ~ is quiæ a costly a~ld complicat~d ~evice, ~d ~is~bance occ~s ~ its aperatiOh. This is why ~tte~pts haYe b~ made eo a~ge the threading without a set of t~ueadin~ ropes.
20 Said mode~ of threadin~ without ~opes haYe been applied in pa~icul~r with sin~le-w~ dTa~v. ~ this respect, refe~e~ce is m~de t~ ~e pape~ by Sam P~aæolo, ~N~
draw drying" in ~il~. September 1990, pp. 225 228.

As is stat~d ln said pa~ ~ith single-w2~ d~aw, the threading invc~lv~ ~he d~wb~k~5 that tl2e lcader tends to follow & smoo~2 face o~ the d~ying ~linder ~ stead of the d~g ~ he w~e ~uns from ~he dry~g cylinder to the following leadin~ suc~n cyli~der o~ roll. ~o m~ke sure ~at the l~ade~ ~ollows exp~essly ~ wire, ~cording to ~aid p~er, ~angc~ents of ~ir ~ozzles have been employed, of whi~h n~zle asangenaen~ one ha~ been fi~ted befo~e each leading su,tion ~ylinder and 30 t~ou~h w~ich nox21e ~an~eme~ts ai~ 3e~ ~e blown to guidz the ~un o~ the leadOE.
~oy, at~empts aIe made to mabe sure ~at ~e leader rema~s on the ~, wi~e.
After ~e leader has ~clled ~e su~OJ~ ne on the l~d~ng c~nder, the le~der is trans~erred on the wi~e ont~ the ne~t drying cylinder.

It is ~ dlawbaclc of the b}ow a~gement degcr~b~d ~bove that, if th~ lesder has ~~ed into connec~on with the blade o~ ~he doctor oper~ng a~t ~e dry~g S cylinder, the lea~er cannot be p~ssed forwards fI~m ~e bladç w~thout marluallyoperat~d all~iliary blowisl~s. In t~d~ng, there is, how~v~, a n~d to dra~? the Ieade~ fro~n the lower faces of se~re~al or ail of ~he dryin~ cylDIde~s ~y means of the doct4r blade dow~ into ~he broke processing system pla~ undeme~ h~ not been readily pos~ible in the p~r-art ro~-free web threadin~ arrangements.
~a On the other ha~nd, in a drying s~tion, i~ is ~nown in prior a~t to employ ai~^~low de~ices fitted irl connecti~ with doctor beams, ~ut these blow d~vices axe usually tlsOcI ~t)r air~onditioning of the d~n~ seetion, and ~ nozzles blow ~oss the en~e ~ansver~e wid~ of the w¢b, Also"n threadin~, blow devic~s ~ra~ng in 15 conn~c~o~ with a doe~r h~ve been ~ d, but ~ ave ~vol~ed a numb~r o~ drawb~c~ and ~ey a~0 not as such s~ ble for u~e in r~f~ ~adillg. In respect of said ~or-a~ d~vices, reference is ~de, by way of e~ample, to th~ FI
Pa~ts ~nd P~lblished Pagent ~pplica~ons Nos. $0,263, 54,g54, and 62,571 and to the FI Pa~ent Applicadons No~. 833590 ~d 8~460~. In some of said publi~dons, 2~ bl~w deYic~s piaced ahe~ ~he dry~g section a~e descnbed, by whose mea~s the 1eader is ~de~.

The p~ ipa} object of the p~ nt inl~ention is t~ p~de novel soludolls ~r the p~oblems discussed above so that sa~d d~awbac~s are 1asgely ~voide~.
In view of achievillg ~he objecti~ tated above and those ~at will come out la~, t~e me~h~d of the inve~ti~n is ~na~nly ~haracterized in tba~ in the method, the 1eader is guided by me~s of ai~ blowings e~cte~ across a substan~al prc~o~oll or ~e wh~1~ of iSs width, ~ id ~ b~ow~gc a~e ~pplîed f~om the doc~r ~ o the 30 area of the ~p of i ;s ~ blade ~t a ce~in ~m~ll angle ~n ~e1adon to she pla~ of the doct~ blade.

~5~5~r~

On the o~r hand~ the d~ce in ~ccor~ance ~fith the iJIv~n~on Is ~nly Cha~aGter-ized i~ that the blow d~ice is in~d in conne~on with ~ doctor ~s of the drying cyhnders, that ~e blow device compli~s a tra}~ erse nozzle pipe ~ ~
eq~i~ralen~ noz:z~e a~angan~ pla~d at the ~vel ~f the lea~e~ at the pro~im~q o~ the 5 end of the d~ct~r ~am a~ ~e dr~v~ng side of ~e mach}ne, sai~ n~zz}s p~po or equivalent ~vmpqi~ a num~er of no~le ~ngs phced side by ~d~ or an lent nazzle slot7 asld t~at ~e bl~w d~on of said nozzles is dire~t~ at ~
cc~tain small angle in l~lation ~o ~he pl~ne of the blade of said doeto~ in th~ area of the ~p of the blade ~perating aga~nst the face of ~e ds~ing cylinder.
1~
The invention can be appli~l both in drysn~ ~ylin~er groups provided with single-w~e d~aw and in cylindel g~oups provide~ with tw~n-wi~ d~w, ~ ne~essaIy, over the en~ g~h of ~he ~ryin~ section. In conaec~on wi~ ~gle-~ ~w, the imen~n is suitabl~ fo~ use ~t;h in normal ~roups and ~n inverted group~. Acco~ding 15 to ~he presen~y }~owled~e, the inv~n~on is most ~dvan~eously a~plicable in co~ne~tion with single~ e draw.

A~o~ g tc~ the in~ , when the blow pipes with ~eir noz~ e pla~ed ressly in connection with the doctor beams, al~ ad tageous a~d solid "base" is 20 o~tained for the blow d~ so~t ha~g to ma~e use of sepa~ate support cotls~:ruc~ions. Pit~ of such construc~ons ~n t.he nar~ow gaps b~ween ~e cy~inde~s . iS diffict~lt. 'rhw, the co~Stn~c~on of ~e auxiliary de~rices for threadill~ iS ~plified a~d ~e ma~ntena~ce and opera~orl of said d~ices ~ecome e~sie~.

Ac~o~g to ~e imen~d~n, whe~ the ai~ ~ets are dir~ted e~cpressly at ~he 2~ of the~p of the doc~F blade ~t a ~uitable small angle~m rel~don to the plarle of the ~ el the blow~gs ~ e deflected along the cylind~r f~ ~at p~ bl~e so that ~he e~f~ct of the bl~win~ e~tends into ~he op~ nip. In this way ~e blowings ob0in a suf~ient sup$ort asld Pans~er eff~ on ~e leader. C~ course, in ~he ~0 blowin~ sufflc~en~y high ener~y rnllst be uged ~ prov~de a reli~le ~ans~er and pport ~fe~

In ~e follo~, the ;nven~ qll be described in detail with ~eference t~ ~ome p~rred exempli~ em~odimems of th~ ~ven~on ill~s~ted in the ISguros :i~ the aceompan~g ~rawing, th~ inv~n~on b~ing no~ suppos~d to be confir~ e de~ils C~f ~id embodimelns.
s Figu~ 1 shows a d$~ing se~ion of a papes ~n~ch~ne which is provid~ wi~ sinF.~le~w~ draw and in which the method and the de~ice of the inv~n~on are a~

Figu~e 2 illustrates paramete~ th~t are of signi~cance in the loca~on and di~ension-~0 in~ of the method a~d the de~nce in accoldance with the in~entio~.

Figu~e 3 is a s~de Yiew of ~ first embodiment of etluiplnent o~ ~he inYention.

~ igure 4 sllows ~ same d~vice as F}g. 3, se~n in the dire~on IV~.
1~
Figure S shows a device ~ll accor~ce with the invention as applied in an ~nverted ~ylinde~ ~roup pr~vided ~n~ sirlgle-w~e dr~w.

Figure ~ sh~ws ~ application of the inven~on in a gap b~ ylillder grollps in 20 which ~ on is transfe~ed from s~le~ e d~w ~o ~ ~ draw as well ~n a cy~inde~ group wi~h twin-~ d~aw.

3~igure 7 shows an a~ of the inven~ion in cylin~er group~ w~ t~rin-w~
~w and in ~e gaps between 3u~h ~ylinde~ glOUpS~
Fi~ s a sche~a~ic illustla~on of a cylindet group with singl~ ~raw, ~ whi~h, e uppe~ row, ther~ a~ heated d~g cylindels 10 and, ~n t~e l~r row, l~g cylinders 20 wi~ perforat~d and ~rooved outer man~e. Fig. 5 s~ows a ~ondin~ oup, whe~ein the d~ying cy~inde~s lO' a~e placed ul ~e 30 l~wer ro~v ~nd, co~es~n~ly7 the l~ading suc~on cylinders ~)' in th~ uppe~ ~w.

As is sh~wn in ~:ig, 1, the d~ying w~e 11 of the sin le-wire d~aw ru~s me~ndenng 5~3~

~ contaGt with the ~r~ng cylinde~s 10 and ~he leading cylinde~ 20 so that, on t}~e d~yin~ çyli~de~s 10, ~h~ we~ to be dri~d ente~s in~ direcs cont~ the h~sted smooth faces of the cyLi~de~ sd, on ~he 1~adiQ~ cylinders 20~ t~e we~ ~s pla~
at th~ side of the ~utside curv~: on the outer face of ~e ~ 11, wh~e it ss ~ by negati~e ~ressur~ ~s3g from the in~ri~ of th~ cylinder ~0 ~rough the pe~
and grwves ~not ~hown) in i~ e. On th~ Iuns o~ the ~ 11 and the we~ ~n whi~ th~y run togeth~ ~ e d~ing cylinde~s 10 ~a ~e 1~din~ cylin~rs ~07 at the ~ide o~ the wire 11, a bl~w box 1~ is p~vided7 fo~ example a d~ce ma~3~ted 'oy the appli~ant w~h the ~ade n~c "UNO ~UN BLC)W BO~", by ~eans o~ which fo~mation of a dekiInen~ally high negative pressure ~n the pressur~zed nip N+ ispre~ted and a suitable nega~ve pressure is ma~ined at the side of the wire 11, which rlega~ pressure ~7Ua~tees that the web remains on ~e fa~ ~f the wsre 11 on said s~ght runs.

As is shown in Fig. 1, doctors oper~te ag~st ~Lhe ~ lower se~or of ~e cylinders ~û, w~ich ~oct~3 co~pn~e a d~tor bea~ a doc~or blade ~4, whi~h i~
a~ched to sa~d beam by means of a holder 13 and doctors and kee~s the smooth f~es of the cyli~e~s 10 clea~ verted cyl~nder grou~ wn in Fig. 5, ~responding doctors are fitte~ a~ove ~e ~ylinders 10' a~ainst ~e5ir ~r~ ~tors.
2~) 3~ ac~o~danc~ wi~ ~ present ~vention, ~e doc~rs 12,13,14 ~ p~ovided wi~h blow devices~ by whose means blowin~s F~ a~e dir~t~ a~ainst t~l8 ~p portis of the do~ bl~des 14, fom whi~h the ~lowings bounce and are "re1ected" in the di~c-~n ~ ~oward~ the ~g nip ~-. By nleanS of the blow~g~ Pl and F2, such ~
s~ua~on is pI~ven~ ~aI the leade~ S we~e de~ched fro~ ~e d~ny w~e 11 a~d f~llowed the ~ylinder lU f~ce.

ig. 1, the end of the le~der S is denoted with th~ reference S," wbich r~en~
the siblation in whi~h the end S~, is trans~er~ed on ehe suc~on se~tor of ~e le~ding suction cyli~de~ 20 to the ne7ct ~ylinder lQ. Figs. 2, 3 and 4 show ~n embodimen~ of ice in more de~ail. Accoqding to Figs. 3 ~nd 4, an ai~ dis~bution pipe 2~ has been ~ttached to ~e sid~ of ~he doctor beam 12, one end of said pipe ~ being a $

close~ e~d Z~, whereas th~ other e~ ~ommu~icates with the blow-~ supply duet 24.The blow pipe 22 is provi~ w~ a nu~ber of nozzle hole~ ~3 a~ss the wi~th L~o Ihe blow pipe is ~hed to 1ts place by means of flan~s 25 and 2~.

5 Out of the nozzle holes 23, air 3e~ F, are blown, which a~e directed p~ ly ~ ~he ~t K ~ig. 3~ at the pr~ximi~ of the tip of ~e doctor b3~de 1~. ~hu~, ~n th~
inveq~on~ the blo~ings. F, ar~ not direeted in the direc~on of the plall~ o~ ~e blade 14, but at a small an~le B toward~ the blade.

10 By mean~ of suitable ch~ce of the a~gle ~, the a~ jets F~ can be di~e~ at the area of the dp of the doctor blade 14 so th~t the ~ir jets bounce and ~e "re~lect~ m the pla~e of the do~o~ bl~le ~nd ale deflected in a dire~n pa~lel to the outer f~ce o~ thc cylinder 10, being dire~d in the direction F~ at the opel~ing nip N~. ~ this ~ay~ a gufficiently high ~sfe~ ~nd sup~ effect is p~oduc~d fo¢ ~e blowings Fl, ~5 said effec~ being a~plied to the lea~e~. Of course, the ene~y of the blowin~s E7~ must be hi~h enou~h to achie~e ~i~ obiect~ves.

y ~ i~sel~ o~, ~e docso~ beams 12 a~e a~tached by th~ ends, by means of a~le joumal5 16, Ln s:onnection ~ith the~r p~wting and lo~din~ meaa5 ~not show~.
2~
ig. 4, ~e ~id~ O~ der S ~s denot~ wi~ ~e reference L,. Th~ nsion I~ of ~e ~lowing5 p~ Lhe ~verse direction is of ~e same o~der ~wid~ L~ as the width L, of the l~de~ S. ~* f~om the blo~gs F, ~s guide~ ~tong t~e face of th~
~linde~ 1~ in ~he di~c~n of the a~sow F~ ~to :he ~ nip ~-. In this wa~, it . ~ i~ a~hi~ved hy mean~ of the blowings Fl,F. tha~ the ~ies S is p~d again~t th~
wlre 11, in which pos~ n the suction effec~ of the blow box 15 l~ s th~ lead~r S.

When the leade~ Inust ~e made to fall ~own ont~ the b~oke process~g n~eans (not m) at a cer~ cylinder 10, the blowing3 F~ of the doctor p}a~ ~elow said ~0 cy~inde~ 10 are closed, whereby ~he ~eade~ S is c~ied by na~ ~o ~e doctol b~ad~
14, which detaches it f~ta the ~ylinder 10, and the le~el ~alls do~n ~nto the brok~
conYeyor pta~ed und~ea~, whic3~ conveyor ca~es the brok~ into the pulpe~. When ., . : .

the leade~ S h~s to be p~ ~ om said cy~ ~ 10, ~e blo~lnng~ F, at thi5 ~ylinder 10 are conLrolled to m~ce them operati~re, whereby, owing to the dil~onof the blovl/ings ~" ~ey detach ehe le~cler from the doctc)r blade 14 ~nd guid~ ~e lea~er S onto the suppo~t o~ the wire 1~ pl~d facing i~, which w~e c~es the 5 leadel S o~r~ the Suc~oll zone of ~e le~din~ suc~n cylin~ 0 onto ~e ne~t cylinder 10.

Fig. 2 illust~ates parameters significant in ~e din~ensionin~ and align~lent of the device in ~ccord~nce with th~ invention. In the following, so~e typical prefelTed 10 ranges of v~ous para~e~s ~ill be giYen~ the in~en~on being not confined to s~id rarlges. Ythell the diameter of the upper cylinders is of an or~er of ~800 mm, the angle ~ is typically A = 35~. ..45. The pe~pendicula~ distance of the doctor blade 14 f~om ~e ad~acen~ wire 11 i~ S = 160...200 mm, ~d the dist~nce of ~e no~zle holes~m the ~p of the doctor ~la:ie is L 5~ 200 mm, and the angle C ~ 0~. The angle lS ~ o~ the dire~on of ehe jets F, is, as a rule, in ~e rsnge of B = 5~ 45, p~eferably ~ the .~g~ af B ~ 10...3~. When the width L, of the leade~ is ab~ut 200 mn~, the w~d~ 1~ of the blowîngs in ~he llansv~e di~ect~on is typica~ly about 2~...350 mm=

The ~egy of the blowin~ F, and P2 must be sufflci~ttly high to praiuce ~e desiled 20 ~ects. 1 his is why th~ air pres~u~e p used in the blow pipe æ must be ~et at a suf~iently high level. As a rule~ said p~eSsu~e p is ir.t the ~ e of p ~ ~0...3~0 kPa. Said pressure r~ge is used a t~ )usly in connec~on with the dime~sion~g o~ the n~zl~ holes 23 to be described later. In the in~ ion, the ~low ~dth is~
howe~rer, not equally critical as the an~le ~ o~ ~e dir~ n of ~e blo~ Fl.
~ .
As the blaw pipe 22, it is poss~ble to use a per~ora~ed pipe, ~n which the diamete~ of ~e nozz;le holes is ~pical~y 3...4 mm asld ~he sp~ing 30...50 mm. The ~low wi~thL~ may be nas~owe~ than th~ width L, of the leader, but, as ~ ~ule, the ~a~w w~d~ 1,2 shauld p~efe~ably not ~e v~ry ~uch la~ han the width l.t of the leader. For ~0 e~nple, wi~ blowin~s F, extendin~ across a width of ~bout 300 mm it is possi~le ~o g~ide a lead~r S eY~n as wide ~s about 600 ~rn, but, as a rule, ~e w~d~ p~opor-s ca~ot ~e ~e~sed~

Fig. S show3 ~ u~ of ~e blowin~s ~ an invelrted cylinder ~oup provide~ wi~h single~ e d~aw, where~ t~e cl~n~, cylirders 10' are pla~ed in the lowe~ ro~
the leadi~l~ suctio~ inders ~0' ~n the upper row. ~hc ~pera~oll of t~e bl~ P, 5 an~ F~ ~s similar to ~at describe~ above. Of ~ours~, ~rom the upp~r face of the cylirlder lt~ q leade~ cannot be docto~d onto the bIoke conv~yor.

Ac~ ing to Fig. 5, in ~nnec~ion with the docto~ beams 12, additional blowings P`3 and F4 are provided, by whos~ means the leader S is held vn the leadsng cyli~de~ ~0' .
10 McneoYer, between the ~eadin~ cy~indeIs 2~', it is possib~e to employ addi~onal blow pipes 17, from which blowings Fs are dire~ted a,,ainst ~e le~d~ S so a~ to ~uide the lead~r over ~e suc~on zone~ of the ~eading cylinde~s 20' onto the following drying ;;yli~der 10'.

~S Fig. 6 shvws ~ adon of the inYe~don i~ a g~0~3? gap formed ~ ve~rl a g~up w~th s~ngl~w~e d~w and a ~oup with twin-wire dIaw. ~rhe we~ is t~ansf~ from the dryin~ wire 11 o~ group with s~ngle-~e d~aw ~y means of a ~uc~ion box 32 a~e$ a guide ~oll 33~ as a f~ee draw Wp onto the lawe~ wire 11~ of the ~roup with ~ draw. In the group ~th twin-wiTe d~aw, in the way ~ io~
20 there ~e two ~ws of steam-hea~gd drying cylinders 10..~ ~nd lOB, one row ~bove l~e ot~ s well as an u~per w~re I lA ~nd a lowe~ 7 which aIe guided by gu~de r~ls 31A;31B. ~ nnec~ion w~th ~he d~y~ng wire~ llA aDd 11~ at he p~umity o~ the~r guide r~lls 31A;31B, blow boxes 32 ale pl~, by wh~se sne~ns ~e support c~n~ct betwce~ the web and the u~re is p~moted.
~cco~ding eO ~i~. 6t ~he doctor ~eams 12 a~ provided wit}l blow pipes ~2, from which ~e blowin~s F, in a~cosdance with ~he imention a~e direceed at the area of th~
~p of ~he doctor bla~e 14. Accord~ng t~ Fi~. 6, irl connectio~n wi*~ the d~to~ b~
12 of the fir~ l~we~ dryin~ cy~der 10~, a second blowing ~3 is al50 ~mploy~d, 30 ~hi~h is ~li~ct~d towards the pat~ of runnin~ oî the le~de2 S, ~he ~lowin~s F, are not necessari}y ~lways n~ded in an area o~ ~e ~aYv, or ~e ~low~ng5 Pt may ~g Yely ~ea3cO On th~ co~tr~y, the blssv~ngs F3 ~r~ ~en rno~e h~sl~. Isl a g~up with twill-~ draW7 the we~o has free ~lraws W,t and the le~i~r S also run~ ng ~es~me route when it is pa*æ~ ~ugh the graup with twin-wire ~aw, be~g aided by means nf the method and the de~e of the mve~on.

S Fig. 7 shows tw~ su~equent ~ups wi~l twiQ-wLre draw. The w~ is ~ansf~ed as a ~ee d~aw Wp ~om 0118 ~0~ the ot~er and onto th~ 1013 in tter g~oup b~ewe~ the g~ e rol~s 31A and 31B. Bod~l ~f ~ u~ twin-wi~ d~aw ~re pravided wi~h doctor ~eams 1~, at which bl~w pip~$ 2~ ~n a~rd~
w~th the ~Yention a~e pl~ced at s~ le loc~tions, from ~hich blow pipes blowin~,s10 F, and/o~ F3 in accordas~oe witl~ inYenti~n are applied to produ~e ~e effe~s d~d above.

In ~e ~oll~u~ng, the pat~t claims will be give~, and the ~ous details of the in~ention may show ~ariation within the scope o~ the inventiYe i~ea defi~ed in said lS claims and dif~e~ f~v~n wha~ ~as been stated above for t4ç sa~e of e~ample ~ly.

Claims

1. Method in a multi-cylinder dryer of a paper machine in the threading of the paper web, said threading taking place substantially without a system of threading ropes, in which method the web is passed along a meandering path, in twin-wire draw, over drying cylinders (10A,10B) and, in single-wire draw, on a drying wire (11), over drying cylinders (10;10') and leading suction cylinders (20,20') or rolls (20,20') c h a r a c t e r i z e d in that in the method, the leader (S) is guided by means of air blowings (F1) extending across a substantial proportion or the whole of its width (L1), that said air blowings (F1) are applied from the doctor beam (12) to the area (K) of the tip of its doctor blade (14) at a certain small angle (B) in relation to the plane of the doctor blade (14).

2. Method as claimed in claim 1, c h a r a c t e r i z e d in that, by means of said blowings (F1), the leader (S) is both detached from the doctor blade (14) and trans-ferred onto the drying wire (11) to be carried further, and it is ensured that the leader (S) remains on the drying wire (11).

3. Method as claimed in claim 1 or 2, c h a r a c t e r i z e d in that in the method the blowings (F1) applied from the nozzles of the nozzle pipe (22) placed in connec-tion with said doctor beam (12) to the area of the tip of the doctor blade (14) are deflected into blowings (F2) substantially parallel to the mantle of the drying cylinder (10) and are guided into the opening nip (N-) defined by the drying cylinder and the drying wire (11).

4. Method as claimed in any of the claims 1 to 3, c h a r a c t e r i z e d in that said angle of the direction of the blowings (F1) is in the range of B = 5°...45°, preferably in the range of B = 10°...30°.

5. Method as claimed in any of the claims 1 to 4, c h a r a c t e r i z e d in that said blowings (F1) are applied to the area of the tip (K) of the doctor blade (14) from a distance of L?250 mm at a pressure of p = 50...350 kPa when the diameters of the nozzle holes (23) of the blowings (F1) are of an order of 3...4 mm.

6. Blow device intended for carrying out the method as claimed in any of the claims 1 to 5, c h a r a c t e r i z e d in that the blow device in integrated in connection with the doctor beams (12) of the drying cylinders (10;10';10A,10B), that the blow device comprises a transverse nozzle pipe (22) or an equivalent nozzle arrangement placed at the level of the leader (S) at the proximity of the end of the doctor beam (12) at the driving side of the machine, said nozzle pipe (22) or equivalent nozzle ing a number of nozzle openings (23) placed side by side or an equivalent nozzle slot, and that the blow direction of said nozzles is directed at a certain small angle (B) in relation to the plane of the blade (14) of said doctor in the area (K) of the tip of the blade operating against the face of the drying cylinder.

7. Device as claimed in claim 6, c h a r a c t e r i z e d in that said nozzle pipe (22) and its nozzle openings (23) extend in the transverse direction substantially across the entire width (L1) of the leader.

8. Device as claimed in claim 6 or 7, c h a r a c t e r i z e d in that said nozzle pipe (22) is fitted in such a way that its nozzles are placed at a distance of about 100...300 mm, preferably about 200 mm, from the tip of the doctor blade (14).

9. Device as claimed in any of the claims 6 to 8, c h a r a c t e r i z e d in that, in connection with the doctor beam (12), there are additional nozzles, from which additional air jets (F3,F4) are directed at the leader (S) by-passing the doctor beam when the leader is placed on support of the drying wire (11) or as a free draw.

10. Device as claimed in any of the claims 6 to 9, characterized in that the blow device is fitted in connection with a doctor beam (12) at which the perpen-dicular distance (S) of the doctor blade from the by-passing drying wire (11) or from a corresponding free draw (W) of the web is 150...500 mm while the distance (L) of the nozzle holes (23) from the tip of the doctor blade (14) is L ? 250 mm.