Method and apparatus for cleaning a roller surface

Disclosed is a method and apparatus for cleaning a cylinder surface. The method is particularly suitable for use on flexographic printing cylinders where the automatic cleaning apparatus facilitates the cleaning of plate cylinders or on any type of cylinders. The method comprises detaching particles such as dust, fibers and other foreign objects deposited on the cylinder surface by means of pressurized fluid of air, liquid, ultrasound or other suitable media. After the particles have been detached, the cylinder surface is exposed to a vacuum unit whereby the detached particles and other material deriving from the cleaning medium are sucked off the surface of the cylinder. The advantage is that, in many cases, it will not be necessary to halt the printing process for cleaning the cylinder. The apparatus comprises a cleaning head or pipes capable of providing the pressurized fluid to the cylinder surface and removing any particles detached from the cylinder surface while the cylinder is in normal operation.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for automatic cleaning of a 
cylinder, especially a cylinder of a printing machine, in which the 
cylinder is provided with plates and used for printing on a print carrier 
made of e.g. paper, plastic film, or metal film, and in which the 
cylinders become smudged, during printing, with printing ink, particles 
detached from said print carrier such as dust or fibres, and other foreign 
objects, wherein an area of the cylinder surface is cleaned by exposing 
said area to a pressurized flow of fluid so that the foreign objects 
inside the area on the cylinder surface are detached, and wherein said 
area is exposed to a vacuum to remove said detached foreign objects and 
any other material originating from said flow of fluid. 
So-called flexographic printing on a print carrier of paper, plastic film 
or metal film uses a system consisting of a first cylinder, around which a 
web of the print carrier runs, a second cylinder performing the actual 
printing and being provided with plates for this purpose, and a third 
cylinder transmitting ink to the second cylinder. 
When the printing process has continued for a certain time, there will 
normally arise problems with the printing quality. This is because the 
second cylinder, the printing cylinder, has become smudged with dust, 
fibres or other particles from the web of paper, plastic film or metal 
film. When this occurs, it is necessary to halt the printing process, 
displace the cylinder from its bearing and then manually brush or wash 
impurities off the second cylinder. This is a serious inconvenience since 
it means that the stoppage periods may amount to as much as 30 per cent of 
the total time in which the machine is in use. This means that the 
operation time in which printing takes place may risk being reduced to 70 
per cent of the time in which the machine is in use. Out of those 30 per 
cent of time in which the machine is halted, up to 90 per cent is due to 
cleaning the printing cylinder. Furthermore, the waste of paper, plastic 
film or metal film is substantial because there is a certain running-in 
period after a stoppage and the web of paper or film being printed during 
this period does not have a sufficient quality and must be discarded. 
EP-0,369,565 describes a cleaner for automatic cleaning of a cylinder by 
pressing or otherwise discarding impurities from the surface of the 
cylinder. The cylinder cleaner comprises a brush extending along the total 
length of the cylinder or, in another embodiment, a bar for applying 
pressurized air or ultrasound. The cleaning takes place by rotating or 
displacing the brush along the entire length of the cylinder or by 
applying pressurized air or ultrasound along the entire length of the bar. 
This cleaner, however, has the great inconvenience that the efficiency of 
the cleaning is strongly reduced. Firstly, cleaning by using a brush 
quickly results in the brush being worn up together with the surface of 
the cylinder being worn. Secondly, cleaning by using pressurized air or 
ultrasound being applied to the total length of the cylinder has the 
effect that the efficiency of the cleaning is not the same over the total 
length of the cylinder. The pressurized air or the ultrasound is applied 
at one end of the bar and, therefore, the efficiency of the cleaning will 
be highest at the first end of the bar and lowest at a second end of the 
bar opposite the end at which the pressurized air or the ultrasound is 
applied. 
WO 94/12349, a document published after the priority of the present 
invention, describes an apparatus also for cleaning the surface of a 
cylinder. The apparatus comprises a jet nozzle being located inside a 
suction nozzle. The jet nozzle emits a single jet of liquid, and the 
liquid together with impuries detached from the surface of the cylinder 
are evacuated through the suction nozzle. The jet nozzle is arranged in 
the centre of the suction nozzle, and at the opening of the suction nozzle 
a means for supplying compressed air into the chamber of the suction 
nozzle is also provided. This apparatus has the inconvenience of using a 
jet of liquid for cleaning the surface of the cylinder. After cleaning, it 
will be necessary to wait until the surface is completely dry before 
further printing can take place. However, an even more serious 
inconvenience of the apparatus is that only one jet nozzle is provided. 
Due to this effect the cleaning process will take a large amount of time 
because the single and relatively small jet of liquid has to be displaced 
along the entire length of the roller in order to clean the whole surface 
of the roller. This displacement, therefore, has to take place very slowly 
in order to ensure cleaning of the whole surface. 
JP 63-4947 describes af further apparatus for cleaning the surface of a 
roller in a typographic rotary press. This apparatus comprises a jet 
nozzle for supplying a jet of pressurized air, contrary to liquid, and 
also a vacuum duct for evacuating the impurities detached from the surface 
of the roller. Like in the previous publications, the jet nozzle is 
located inside in the vacuum duct. Although using pressurized air, this 
apparatus also has the great inconvenience of having only one jet nozzle 
for supplying the pressurized air. Like before, the jet nozzle has to be 
displaced along the length of the roller very slowly in order to ensure 
that the whole surface of the roller is cleaned. Therefore, the cleaning 
process when using the apparatus described in that publication will also 
take a very large mount of time. 
Thus, it is the object of the present invention to provide a method which 
may be carded out automatically, and in which the above-mentioned 
inconveniences, such as unsuitable, cleaning media and very long time for 
carrying out the cleaning process, are avoided. 
This object is achieved by a method characterized in that the cylinder 
surface is constituted by adjacent areas lengthwise and crosswise on the 
cylinder surface provided by such area extending over a minor part of the 
circumference of said cylinder and a minor part of the length of said 
cylinder, and that said adjacent areas of said cylinder surface are 
cleaned successively, wherein the pressurized fluid is provided by mixing 
pressurized air and a liquid in a mixing chamber, and that the so-formed 
mixture is led to the print plate through nozzles being connected with the 
mixing chamber. 
In addition, apparatuses for use by the method will be disclosed. 
By the method according to the present invention it is now possible, during 
operation, to clean a cylinder, particularly a flexographic printing 
cylinder. In this manner one avoids the substantial time waste previously 
associated with cleaning the cylinder. Reducing the time waste, one also 
reduces the waste of material accordingly as cleaning is accomplished 
during ordinary operational conditions. If cylinder cleaning is carried 
out before it is so smudged as to deteriorate the printing quality, there 
will be neither material nor time waste during cleaning. 
By using several nozzles or a slot, the area around the length of the 
cylinder is extended as compared to using only one nozzle. Thereby the 
amount of time used for cleaning the surface is strongly reduced. A larger 
area, although still just a small area of the surface, is cleaned and 
accordingly, an orifice with a cleaning can be displaced along the length 
of the roller at a much higher speed. As mentioned before, it is very 
important to reduce the amount of time used during the cleaning process. 
The method is advantageous in that cleaning is performed automatically and 
preferably while the printing process is running. 
As pressurized air containing the admixed liquid is used for detaching the 
particles from the printing cylinder it is possible to obtain a secure and 
effective cleaning even if ink and dust stick very hard to the printing 
cylinder. This will not be possible with the liquid jets nor with the air 
jets. Surprisingly, and in contradiction to the expectation for the 
skilled in this art it has shown that is is possible to use such mixture 
in a cleaning process while the printing process is running. It has shown 
that the cleaning will not harm the quality of the printing even though it 
is not a dry cleaning as explained in the JP 63-4947. It is believed that 
the reason for the effective cleaning is that a mist is produced, which 
mist is led to the printing cylinder. Such mist may be sucked away very 
effective in comparison with a liquid even if rather limited level of 
vakuum is used. 
For various reasons, however, it may be advantageous to use other media, 
e.g. depending on the ink used for printing, the material being printed 
on, the kind of particles to detach from the cylinder, or the speed at 
which the printing process is operating. Among other options for cleaning 
media besides a mixture of pressurized air and liquids, there could be 
mentioned a media influenced by an ultrasound field, and likewise various 
kinds of solid matter particles may be added to the fluid media 
constituting a fluidized medium. 
Having become detached from the cylinder surface, the particles will 
normally have to be removed from the surface. This is accomplished in 
that, after the particles have been detached from the surface, the 
cylinder is exposed to a vacuum sucking the particles off the surface. Any 
other material originating from the cleaning process, e.g. solid matter 
particles which have been used in the cleaning process, may be sucked off 
at the same time. It will also be possible to load the particles that are 
to be detached, or have become detached, with static electricity and 
subsequently to use an electric voltage field to remove the particles from 
the cylinder surface. 
In order to ensure that the cylinder with the plates is cleaned both on and 
between the plates, the cleaning medium should preferably be directed in 
an inclined angle in relation to the tangent of the cylinder surface. This 
will ensure that particles depositing on the sides of the plates are 
removed as well. Thus, the inclined flow will attack both the cylinder 
surface and the cylinder sides in an inclined angle, not parallel or 
perpendicular. The method is further advantageous in that no damage is 
done to the plates during the cleaning process. 
As mentioned, the method is suitable for cleaning printing cylinders in 
flexography which printing process uses cylinders with printing plates. 
However, the method may be used for many types of rollers and cylinders, 
not just printing cylinders. 
Apparatuses for use by the method according to the present invention may be 
designed in many different ways. Two types of apparatuses are disclosed 
according to the present invention. One apparatus comprises mobile 
cleaning members in the shape of a cleaning head being slid over the 
cylinder surface whereby successive cleaning of the surface takes place. 
The other apparatus comprises fixed cleaning members provided with an 
internal device likewise conducting a successive surface cleaning. It is a 
common feature that an antechamber is provided for effecting a mixing of 
liquid and a pressurized air.

FIG. 1 illustrates part of a machine for flexographic printing, which 
machine is provided with an apparatus according to the invention. The 
machine comprises a cylinder 1 with plates 2. The cylinder 1 rotates 
around a shaft 3. The apparatus comprises a boom 4 on which a cleaning 
head 5 is conveyed. Conveyance is effected by means of a band 6 driven by 
a motor 7 such as a pneumatic motor, a hydraulic motor or other type of 
motor. The motor 7 is located at one end 8 of the boom 4, and the band 6 
is led over a pulley 9 in the other end 10 of said boom. The cleaning head 
5 is fixed to the hand 6 by means of a slide 11 which is movable relative 
to the boom 4. The cleaning head 5 is mounted on said slide, and the 
cleaning head is provided with three tubes 12, 13, 14 connected thereto. 
The thin tubes 11, 12 are used for conveying compressed air from an 
external pressure source, and liquid is fed to the cleaning head 5 through 
an antechamber or mixing chamber 15 wherein mixing of compressed air and 
liquid takes place. The thick tube 14 is used, during exposure of the 
cylinder surface 16 to a vacuum from an external vacuum source, to remove 
loosened particles and other material from the cylinder surface. 
In order to secure sufficient cleaning of the cylinder surface 16, the 
cleaning head 5 is provided with small nozzles through which the 
compressed air and the liquid, possibly containing fluidized particles of 
solid matter, are conveyed to the surface. The direction of cylinder 
rotation r will preferably be oriented in such a manner that the surface 
areas to be cleaned are led towards the cleaning head front 17, which is 
opposite the side of the cleaning head 5 mounted on the slide 11. By this 
arrangement cleaning is effected by means of a combination of one or more 
of the elements air, liquid and solid matter particles, immediately 
succeeded by the application of a vacuum to the cylinder surface. The 
whole cylinder is cleaned as the cleaning head 5 is moved back and forth 
along the boom 4 while the cylinder 1 is rotating. 
FIG. 2 illustrates a cross-section through a cleaning head 5. The cleaning 
head 5 comprises two chambers 20, 21, the first chamber 20 of which is 
connected to the antechamber 15 (see FIG. 1), and the second chamber 21 is 
connected to the thick tube for vacuum application. The underside 22 of 
the cleaning head 5 constitutes a segment of a circle and when mounted it 
is immediately adjacent the cylinder surface. An orifice 23 of the first 
chamber is inclined in relation to the periphery of the cleaning head 
underside 22. This ensures improved cleaning of the cylinder surface 16. 
In preferred embodiments, the orifice 23 of the first chamber will be 
provided with screens which are provided with nozzles or slots, which may 
have different sizes and different directions (see FIGS. 3A-3C and 3D-3F). 
For mounting of the screens, the cleaning head is provided with a recess 
24 before the orifice 23 of the fast chamber 20. The second chamber 21 is 
provided with an orifice 25 having an extension that ensures that all 
material from the cylinder surface 16 will be removed. 
FIGS. 3A, 3B and 3C illustrate different embodiments of screens 30. FIG. 3A 
shows a screen 30 provided with several small holes 31 the longitudinal 
axis 1.sub.A of which is directed (FIG. 3D) in a 90.degree. angle 
.alpha..sub.A in relation to the plane p.sub.A of the screen. By this 
arrangement the cleaning jet is oriented in the same direction compared to 
the cylinder surface as the inclined direction of the orifice 23 of the 
first chamber 20. The screen is further provided with bolt holes 32 so 
that the screen may be affixed to the cleaning head 5. FIG. 3B shows a 
second screen provided with a slot 33 instead of holes. The slot is also 
inclined (FIG. 3E) in a 90.degree. angle .alpha..sub.B in relation to the 
plane p.sub.B of the screen. FIG. 3C shows an additional semen, likewise 
provided with a slot 34. However, the slot 34 of this embodiment is 
directed (FIG. 3F) in a 75.degree. angle .alpha..sub.c in relation to the 
plane p.sub.c of the screen. By this arrangement the direction of the jet 
conveyed through the slot 34 will be deflected and have a direction 
towards the cylinder surface 16 differing from that of the orifice 23 of 
the first chamber 20. As will become apparent, it is possible by means of 
different types of screens to change the flow pattern and flow direction 
of the cleaning fluid conveyed onto the cylinder surface. 
FIG. 4 illustrates part of a machine provided with a second embodiment of 
an apparatus according to the invention for use by the method according to 
tho invention. Like the machine illustrated in FIG. 1, said machine is a 
machine for flexographic printing. Thus, the machine comprises a cylinder 
1 provided with plates 2, said cylinder being supported by a shaft 3. 
Positioned alongside the cylinder is a pipe member 40. The pipe member 40 
comprises two pipes, a nozzle pipe 41 and a suction pipe 42, respectively, 
and a jacket 43. The pipes 41, 42 are supported in both ends, a first end 
44 and a second end 45, respectively. The second end 45 of either pipe is 
open and connected with compressed air and liquid pipes 46, 47 and, 
respectively, a suction pipe 48 for the application of a vacuum from an 
external vacuum source to the suction pipe 42. 
FIG. 5 shows that the first end 44 of either pipe 41, 42 is closed and that 
the pipes are interconnected by means of a gear comprising two gear wheels 
49, 50 so that the pipes are rotatable around the longitudinal axes at a 
given mutual speed of rotation. A motor 51, such as a pneumatic motor, a 
hydraulic motor or other type of motor, is connected to the suction pipe 
42. The motor drives the suction pipe 42, which drives the nozzle pipe 41 
via the gear transmission with the latter. The motor 51 and the gear are 
sheltered by a box 52. The figure illustrates the first end 44 of the pipe 
member 40 seen from a side 56 facing the cylinder. On this side, the 
jacket 43 of the pipe member 40 is provided with nozzles 53 and a slot 54. 
The nozzles 53 are in connection with the outside surface of the nozzle 
pipe 41, whereas the slot 54 is in connection with the outside surface of 
the suction pipe 42. 
FIG. 6 illustrates the nozzle pipe 41 or, alternatively, the suction pipe 
42. A preferred embodiment of either one of the nozzle pipe and the 
suction pipe is provided with a slot 55 spiraling along the length of 
either pipe. The slot 55 extends in such a manner that the spiral 
completes exactly one turn over the extension of the slot from one end of 
either pipe to the other. In an alternative embodiment, one or both of the 
pipes are just provided with a rectilinear slot. The function of the two 
pipes will be described below. 
FIG. 7 is a cross-section illustrating the position of the nozzle pipe 41 
and the suction pipe 42 relative to each other inside the pipe member 40. 
Besides the two pipes 41, 42 the pipe member comprises, as mentioned, a 
jacket 43 enclosing the two pipes which are thus positioned in two 
cavities in the jacket. As an alternative to the jacket, the nozzle and 
suction pipes may be enclosed in the hollow space formed by the inside of 
additional pipes having an inside diameter corresponding to the outside 
diameter of the nozzle pipe and the suction pipe, respectively. In that 
case, these additional pipes would be provided with nozzles 53 and a slot 
54 corresponding to the ones provided in the jacket. 
The nozzles 53 and the slot 54 in the jacket 43 extend from one side 56 of 
the pipe member 40, facing the cylinder 1, to the nozzle pipe 41 and the 
suction pipe 42, respectively. In use, the nozzle pipe 41 will be 
connected to a source of compressed air and possibly also a source of 
liquid which may contain fluidized particles of solid matter. As an 
alternative to the compressed air source, the nozzle pipe 41 may be 
connected to an ultrasound source which effects a cleaning of the cylinder 
surface 16 by means of the liquid. 
The combination of compressed air, liquid and possibly ultrasound conveyed 
to the nozzle pipe 41 will, during rotation of the latter, be conveyed out 
though the nozzles 53 in the jacket 43 every time the slot in the nozzle 
pipe 41 (see FIG. 6) is aligned with the nozzles of the jacket. This way 
of effecting a step-by-step application of cleaning medium to the cylinder 
surface reduces the risk of excessive pressure reduction occurring over 
the extension of the pipe. Since only a minor part of the total extension 
of the screw-shaped slot in the nozzle pipe 41 overlaps the nozzles 53 in 
the jacket 43, a uniform pressure will build up in the entire pipe. The 
cleaning medium is conveyed out through this part of the screw-shaped slot 
and on through the nozzles 53, and due to the uniform pressure in the 
pipe, the cleaning effect of the cleaning medium will be equal throughout 
the extension of the jacket 43. Contrarily, if the cleaning medium were 
conveyed out through all nozzles 53 at the same time, a pressure reduction 
would soon arise along the nozzle pipe, the lowest pressure occurring 
opposite the end where the pressure is conveyed to the pipe. The nozzle 
pipe 41 of the present invention is thus subject to constant feeding of 
cleaning medium but the medium is only conveyed to a small area of the 
cylinder surface corresponding to the location along the extension of the 
nozzles 53 where the slot of the nozzle pipe overlaps the nozzles. During 
the rotation of the nozzle pipe, alternating parts of the slot will 
successively overlap the nozzles. 
After the cleaning medium has loosened particles from the cylinder surface 
16, these particles and any material deriving from the cleaning medium 
have to be removed from the cylinder. This is accomplished with the use of 
the suction pipe 42. Its function is structured in such a manner that 
cleaning is only effected on minor areas of the cylinder surface, said 
areas being exposed successively to a vacuum whereby the whole surface of 
the Cylinder is cleaned. The suction pipe 42 is in a constant vacuum from 
an external vacuum source. The area of the .cylinder surface being exposed 
to the vacuum will be the area positioned adjacent the location where part 
of the screw-shaped slot 55 in the suction pipe 42 overlaps the 
rectilinear slot in the jacket 43. This will only be a minor part of the 
total extension of the slot 54 in the jacket, and thus a strong suction 
capacity is obtained at this location. Contrarily, if the vacuum had been 
applied to the whole slot 54 in the jacket at the same time, the suction 
capacity would be very limited and the suction capacity in the end of the 
pipe opposite where the suction tube 47 is connected would be reduced. The 
suction pipe 42 of the present embodiment is thus able to suck off 
particles successively from adjacent areas of the cylinder surface due to 
the fact that the overlap of the screw-shaped slot 55 in the suction pipe 
42 and the rectilinear slot 54 in the jacket 43 is transposed along the 
pipe member 40 during the rotation of the suction pipe. 
The slot 54 in the jacket 43 of a preferred embodiment is designed so as to 
extend over a shorter distance than the slot 55 in the suction pipe 42. By 
this arrangement it is possible in a simple manner, without the use of 
valves, to cut off the vacuum from the suction pipe. If the suction pipe 
42 is rotated to such an extent that the screw-shaped slot 55 in the pipe 
is moved away from the situation where the slot 55 is aligned with the 
slot 54 in the jacket 43, there will no longer be any connection between 
the inside of the suction pipe and the outside of the jacket, and the 
vacuum will be cut off. Likewise, the nozzles 53 in the jacket 43 extend 
over a shorter distance than the slot in the nozzle pipe 41. In the same 
manner as described above, it will thus be possible to turn off the flow 
of fluid from the nozzle pipe. In a preferred embodiment the mutual 
gearing between the nozzle pipe and the suction pipe is designed in such a 
manner that the flow of fluid from the nozzle pipe and the vacuum from the 
suction pipe are turned off simultaneously. 
The figures show specific embodiments of apparatuses according to the 
invention for use by the method. However, the illustrated apparatuses 
should not be seen as a complete presentation of conceivable embodiments. 
Thus, other apparatus designs and other apparatus parts, which are all 
covered by the method and the apparatuses according to the invention, may 
be deduced. Besides, the method according to the invention may be used for 
other types of cylinders than cylinders provided with plates; and rollers 
and cylinders in machines other than printing machines may be cleaned by 
means of the method according to the invention.