Note: Descriptions are shown in the official language in which they were submitted.
~138175
me invention c~ncPrn~ a drying apparatus of the kind set
forth in the cl~;fying portion of claim 1.
In conventional rotary intaglio printing m~ch;n~s the
printing ~P~h~n;~ which a web of paper passes through at high
speed are arranged horizontally in side-by-side relat;on~h;p.
Disposed above each printing m~h~n;~n is a downwardly open, box-
like dryer housing into which the web of paper issuing from the
printing mechanism passes. In the dryer housing the web of paper is
guided over a distance which is as long as poss;hle, by means of
guide and direction-ch~ng;ng rollers, which are referred to as guide
sp;n~ , before the web of paper passes from above to the next
printing m~ch~n;~n in order to be printed upon therein with a
further ink.
In order to carry out the drying operation, provided in each
of the dryer h~ ;ng~ are so-called ;mr;n~mPnt jet noæ~le
arrangements which are disposed in respective pairs on mutually
opposite sides of the web of paper. Each of those impingement jet
nozzle arrangements ;ncl~ s a plll~l ;ty of n~le pipes which are
parallel to each other and which are arranged in sncc~s;~n in the
direction of movement of the web of paper, in such a way that they
extend transversely to the direction of movement, substantially over
the entire width of the web of paper. Each of the ~O~1P pipes has
a plurality of air discharge n~les with which the noæ~le pipe
faces the respective side of the web of paper at a small sp~c;ng
th~l~Ll~ll. A spec; f;~ fan is pr~vided for each impingement jet
nozzle arrangement, the fan sucking air out of the interior of the
dryer housing and feeding it to the no~lp pipes, the air issuing in
a jet through the no~æle openings of the no~le pipes and ;m~;ng;ng
on the respective side of the web of paper. As that air is heated,
it results in drying of the ink ~pl;e~ in the preceding printing
~P~h~n;~, that is to say the solvent in the ink, for ~x~mrle
2138175
tolu~e, is caused to diffuse extensively out of the Arpl;cAtion of
ink and the paper. As a result the air which is circulated in the
dryer housing by the fan has an increased content of solvent
vapours. In order to ~L~v~nL the cnnc~rlLLaLion of solvent vapours
from rising above an ~m;~s;hle value (generally 50% of the lower
~xplos;~n limit), air must be continuously sucked away out of the
dryer housing and fed to a solvent separation installation.
The solvent separation installation operates all the better,
the greater the degree to which the air sllrpl;~ thereto is charged
with solvent vapours. The optimum procedure therefore would involve
going as closely as poss~hl~ to the above-mentioned ~mi~s;hle limit
value. That is not possihle in practice however bec~ e another
purpose of sucking air out of the dryer h~l~;ng is to generate a
reduced pressure which is intended as far as po~s;hl e to ~l~v~nL
solvent vapours from being blown out of the dryer h~ ;ng into the
area imnediately surrounding it. Rec~ e of the great width of the
openings which the dryer housing has, in par~; C~ r towards the
printing m~h~n;~m which is disposed therebeneath, for the last-
mentioned purpose air must be sucked out of the dryer housing to
such a great degree that the optimum level of solvent conc~llLLaLion
is far from being attained. None~hel~, it is not poss;hle totally
to prevent solvent vapours from issuing into the area surrounding
the dryer housings and printing m~h~ni~m~, so that the entire
printing mA~h; ne must be covered over with a downwardly open hood
from which ~i r iS further sucked so that the solvent vapours which
~cclT~ te in the hood are also fed to the separation installation.
m e level of solvent concellLLaLion in the air which is sucked out of
the ~h;n~ hood is even lower and thus more disadvantageous, than
in the air which is taken from the dryer housings.
A high level of energy ~xp~;ture is required for operation
of the known dryer apparatuses, and the object of the present
-
~ 2138175
invention is to reduce that energy Pxr4n~; ture without in that
respect adversely affecting the dryer ~ff;~;~ncy.
To attain that ob~ect, the invention provides the features
which are set forth in claim 1.
Those integers according to the invention are based on the
realisation that the drying effect which is produced by the
impingemRnt jets decreases greatly with an increasing degree of
drying, as a gel layer is formed on the surface of the ink, and that
gel layer permits scarcely any solvent to came out of deeper layers
of the ink, to the surface U~eL~or, even when each portion of the
web of paper has a prolonged rPs;~nce time in the dryer and even
when a higher approach flow speed is enployed. m e aLL~I~L~ made
hitherto to achieve an improved thorough drying effect by higher and
higher fan outputs and longer and longer distances over which the
web of paper moves in the dryer housing, have U ~L~Lol~ resulted in
an increase in ~xrPn~; ture, which is greatly over-~Lv~olLional in
c~l,~clison with the effect achieved.
In part;~ r it follows from the foregoing r~ tion,
that the air jets which æ e blown from one of the two impingement
jet n~zle arrang~,~nLs against the side of the paper web which is
"dry", that is to say not freshly printed upon, make virtually no
contribution to the drying effect. Accordingly, they essentially
only serve to support the paper web against the pressure of the air
jets which are blown against the "wet" side of the web of paper.
As tests c æ ried out in a practical context have shown, a
support action of that kind, which is afforded by means of the guide
surface provided in accordance with the invention, is possible in a
completely satisfactory manner, in p æ ticul OE when very high speeds
of movement of the paper web are involved. m at is surprising
30 ; n~of~r as it could initially be assumed that the high speed at
which the web of paper moves would cause a venturi effect between
`~ 213817S
the flat surface of the web of paper and the flat surface region of
the guide surface, which venturi effect results in a suction action
between those mutually p æ allel surfaces. In actual fact however,
because of its rollghness, on each of its sides the web of paper
entrains with it a layer of air which can be several centil~Lles
thick when measured perp~n~ 1~ 11 Arly to the direction of movement,
when high speeds are involved. By virtue of the fact that a
"funnel" which tapers in a downstream direction and which is fonmed
by the web of paper and the curved surface portion provides that the
above-mentioned layer of air is entrained and pressed into the
downstream-disposed air gap of uniform width, a sufficiently high
pressure occurs in that air gap that it reliably prevents contact
between the web of paper and the guide surface. In order to ensure
that there is a sufficiently increased pressure when the web of
paper is moving at lower speeds, for ~Am~le when the printing
n~h;n~ is being started up or when it is being slowed down, the
apparatus may preferably have a device for injecting blowing air
into the air gap between the web of paper and the guide surface.
The amount of air which is required for that purpose is con~ rably
less than the amount of air which was circulated by the secon~
i~;ng~m~nt jet ~oz~le arrAng~TPnt that was previously c~n~ red
n~cesSAry, and the associated fan.
Thel~fol~, by virtue of the arrAn~ nt according to the
invention, without a reduction in the drying effect it is poss;bl~
to omit one of a respective pair of ;mr;n~TPnt jet noz~le
arrangements and the associated fan, so that a 50% reduction in fan
output is achieved. In the case of a l~Laly intaglio printing
machine which ;ncl~ 5 eight printing m~hAn;~m~ for double-sided 4-
ink printing, that results in an immense saving of energy.
In conventional rotary intaglio printing mA~h;n~s, it is
`-- 2138175
n~cPssAry to arrange a respective so-called ste_m lance downstream
of each of the drying apparatuses. That is a pipe which exLends
transversely to the direction of movement of the web of paper and
which has a plurality of n~zzl e openings through which steam or
water vapour flows onto the web of paper in order to moisten it.
That colle~ Ls a shrinkage process that the web of paper suffers in
the conventional dryers and which would otherwise have an adverse
effect on register accuracy.
A par~ lAr advantage of the drying apparatus according to
the invention is that the above-mentioned steam lance can be
integrated into the apparatus. Preferably it is arranged
;mn~;~tely downstream of the device for injecting air into the air
gap fonmed between the web of paper and the guide surface, so that
the steam or water vapour also flows into th_t air gap. By virtue
of that co~f;~lration, unlike the state of the art in which the
major part of the water vapour or steam does not penetrate into the
web of paper, it is poss;hle to achieve very intensive moistening of
the web of paper, whereby heat energy is addi~;~nAlly saved.
Fur~h~r~nre, the heat content of the steam contrihutes to
i~ v~d diffusion of the solvent out of the paper and the layer of
ink ~rpl;~ thereto. If in addition, as is ~leL~ldbly the case, the
housing of the drying apparatus according to the invention is of
such a configuration that it is completely closed, with the
exception of two narrow gaps through which the web of paper passes
into and out of it, the air circulating in the dryer hollc; ng is
enriched with moisture so that the web of paper shrinks to a lesser
degree, from the outset.
A further advantage of the almost almost clns~ housing
configuration is that the air circulating in the holl~;ng can be
enriched with solvent to a s~b~L~ILially greater degree, without
solvent vapours issuing from the dryer ho~l~;ng. Th~L~Lole, the air
`~ 2138175
which is sucked out of the dryer housing can achieve levels of
solvent concenLL~Lion close to the value, which is admitted by law,
of 5C~ of the lower PXplos;on limit, whereby the level of ~ff;~;~ncy
of the solvent adsorption installation is c~n~ rably improved. In
S addition, there is no need for air to be sucked out of the ~h;ne
hocd.
In rotary intaglio printing ~h;nes which have a final
drying section in which the r~T~;n;ng solvent content in the finally
printed prcduct is furthernPl1~cP~, it is advantageous for the air
which is prcduced in that final drying section and which has a high
heat content but which is only relatively slightly charged with
solvent vapours to be fed to the drying apparatus according to the
invention in order here to make use of a part of the heat produced
in the final drying section and further to enrich the air with
solvent before the air is fed to the separation installation.
To sum up it is to be ~m~h~c;~e~ that the features according
to the invention can not only considerably reduce the electrical
power required for operation of the drying apparatus but they can
also substantially reduce the distance that the web of paper must
cover in passing through the drying apparatus, in order to permit
further processing without the risk of smudging of the ink. In
actual fact the drying section hec~T~s so short that the web of
paper can pass through the drying a~kaLaL~s in a straight line
between the entry and exit openings, and the drying a~LdL~s does
not require any guide sp; n~ 1 ~S whatsoever. Accordingly a drying
apparatus of that kind is of optimum suitability for installation in
a rotary intaglio printing m~h;~e in which the printing mechanisms
are arranged one above the other in a tower-like construction and
the web of paper is guided in each of the towers only by the plate
cylinders and i~"~lession cylinders of the printing mP~h~n; ~, but
is otherwise contact-free, as is described in prior European patent
`-- ~138175
Arpl;~Ation No 93 117 070.8.
These and further advantages are set forth in the ~rp~n~Ant
claims.
The invention is described hereinafter by means of an
~mho~;m~nt with reference to the drawing in which the single Figure
is a highly diayL~,..~Lic, partly sectional side view of a drying
apparatus according to the invention.
The drying apparatus 1 ;ncl ~ a substantially closed
housing 2. Disposed in the part of the holl~ing which is at the left
in the Figure is a fan (not shown) which sucks air out of the
interior of the housing and blows it by way of a plurality of no~le
pipes 4 in the direction of the arrows L onto a web of paper 6 which
passes through the dryer housing 2 downwardly in the direction
indicated by the arrows P. It is ~-51 ~n~A in that respect that
disposed ;~ne~;Ately above the drying apparatus 1 is the printing
~ h~n;~m of a rotary intaglio printing m~h;n~, the web of paper
having been printed with ink on the side that is on the left in the
Figure, in the printing ~hAn;~.
In order to ensure an adequate drying effect, a plurality of
mutually parallel noz~le pipes 4 æ e so arranged that they are
disposed in SUCC~55; ~n in the direction of movement of the web of
paper 6, in opposite relat;~n~h;p to the freshly printed side of the
web of paper 6. In that configuration the no~le pipes 4, each of
which has a plurality of air disch æ ge no~ .5, extend LL~I~v~l~ely
to the direction of movement of the web of paper 6, a~Luximately
over the entire width of the web of paper. m e connecting conduits
by way of which the air coming from the fan is fed to the n~
pipes 4 cannot be seen in the sectional view in the Figure.
Arranged on the side of the web of paper 6 which is opposite
to the no~l e pipes 4 is a hollow bcdy 8 which is of an aerofoil
configuration in cross-section and is so disposed that a flat
` -- 2138175
surface region 9 of its outside surface extends parallel to the web
of paper 6 and at a small sp~c;ng LlleL~rl~ll. p~L~n~ rly to the
plane of the Figure, the hollow body 8 is also of an extent which
~L~imately corL~ J~ to the width of the web of paper 6,
transversely to the direction of movement.
At its upper end the flat surface region 9 goes into a
curved surface region lO whose generatrices, perp~n~;~ll~rly to the
plane of the drawing, extend p æ allel to the web of paper 6, but
which in the illustrated sectional view is curved away from the web
of paper in such a way that the air gap 11 which is forT~ between
the web of paper 6 and the surface regions 9, lO increases in width
towards the entry end of the web of paper.
In that way, air is entrained into the air gap 11 by the
forward movement of the web of paper 6 in the direction of the
arrows P, in an amount which is sufficiently large that an air
cllch;Qn is formed between the web of paper 6 and the guide surface
formed by the surface regions 9, lO; at the air cll~h;on, the web of
paper 6 can be supported against the pressure ~xelLed by the air
flows L of the no~le pipes 4, without coming into direct contact
with the guide surface 9, lO. Paper te æ s and scratches in the ink
which can also already be ~rpl;e~ to the side of the paper web 6,
that is towards the guide surface 9, lO, æ e L~1~L~Y effectively
prevented.
As the housing 2 is ~Ler~L~bly in the form of an almost
closed unit which has only a very n æ row entry op~n; ng or slot 14
for the web of paper 6 at its upper end and an e~l~lly n æ row exit
opening or slot 15 at its lower end, it may be advantageous, for the
purposes of st~h;l;cing the air ~lch;on which is bu;lt up in the air
gap 11, to feed c~,~Lessed air in the region of the upper end of the
air gap, as is ; n~ ted by the arrows D. In that Le~e~L the
interior of the hollow body 8 can be used as a c~,~L~ssed air
` -- 2138175
conduit space. m e amount of blowing air that is required per unit
of time is substantially less than the amount of air which is blown
against the web of paper 6 by the oppo~tely disposed impingement
jet no~l e arr~ng~m~nt formed by the n~z~le pipes 4. m e energy
~x~n~;ture required for producing and feeding that blowing air is
therefore n~gl ;g;hly low, in c~"~dlison with the fan output of the
impingement jet nozzle arrangement.
Disposed below the row of c~"~lessed air no~ s is a steam
lance 18 formed by a pipe which extends transversely to the
direction of movement of the web of paper 6 and over the entire
width thereof and which has a plurality of nozzle openings which
make it possible for water vapour or steam which is supplied through
the pipe to be blown onto the web of paper in the direction of the
arrow W. m at moistening of the web of paper is nec~s~ry to
prevent the web of paper from shrinking due to ~x L~ion of water
which otherwise occurs in the dryer, whereby register accuracy would
be adversely affected. m at arrangement of the steam lance not only
penmits a reduction in size of the overall printing m~h; ne but it
also has the advantage that the steam being ~ h~rged can be
brought into very intensive contact with the web of paper. That
reduces the amount of steam required, and that contributes to a
saving on energy. In addition the th~rm~1 content of the steam is
used in the dryer to accelerate diffusion of the solvent out of the
ink. It is Ulel~roLe also poss;hl~ to save on drying energy.
The conduits which serve to discharge air charged with
solvent vapours from the housing 2 and to feed that air to an
adsorption and separation installation are not shown in the Figure,
like optional conduits through which preheated air which pos~;hly
~l~eady also contains small amounts of solvent can be fed to the
housing 2, for ~x~mpl~ fr~m a final drying section of the printing
machine.
` ~13817~
Essential aspects which can be clearly seen from the Figure
are the short length of the drying section and the fact that the web
of paper 6 passes through the dryer housing 2 in a completely
contact-free manner, and the drying apparatus thel~f~le ~n~s
without guide 5pin~les.
