Note: Descriptions are shown in the official language in which they were submitted.
CA 02546444 2006-05-12
EQUIPMENT AND METHOD FOR CUTTING OF WEB AND FOR CLEANING OF
FABRIC IN A WEB-FORMING MACHINE
The present invention concerns equipment for cutting a web and for cleaning a
fabric in a web-forming machine, where the web-forming machine comprises a
fabric for supporting and transporting the web formed on the machine, and
where
the equipment comprises:
- a high-pressure unit and nozzle equipment connected to it for forming a high-
pressure water jet,
- support elements for making the nozzle equipment move in the cross direction
of
the web-forming machine,
- water collection devices, which are located essentially at the location of
the nozzle
equipment but on the other side of the fabric from the nozzle equipment, which
is
located on the same side of the fabric as the web, for both cutting the web
against an unsupported fabric and for cleaning the fabric.
The invention also concerns a method for cutting a web and for cleaning a
fabric in
a web-forming machine.
In a web-forming machine, the web is cut for example in order to trim the
edges of
the web or to separate a threading tail from the web. The web is still moist
at the
beginning of web formation, so that air jets can be used for cutting. However,
as the
web dries, its strength increases. Water cutting is hence used often, with the
web
cut against a fabric using a water jet. The fabric becomes dirty during
cutting, which
is why separate cleaning equipment needs to be used. In known solutions, the
cleaning equipment is placed on the upper cycle of the fabric at a point where
there
is no web.
The known solutions contain several drawbacks. Separate cleaning equipment is
expensive, and it needs to be placed in a difficult environment in the upper
part of
the hood of the web-forming machine. The suction roll located close to the
cutting
point also becomes clogged, which causes runnability problems. Moreover,
separate equipment is needed for cutting and cleaning, which means that for
example double high-pressure pumps and support beams are needed.
Many of the said drawbacks can be avoided by using equipment presented in
Finnish patent application 20040791. In the said equipment, a single nozzle
arm
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contains two sets of nozzles connected to a single pressure water source. The
first
nozzles cut the web and the second nozzles clean the fabric. Water collection
chutes are also located at location of the water jets. This solution avoids
double
equipment, because the same pressure water source can be used for both cutting
the web and for cleaning the fabric. Furthermore, only one support beam is
needed.
The nozzles can also be placed at the lower part of the hood, which
facilitates
maintenance and reduces the need to protect the equipment. The collection
chutes
also remove cutting waste from the web-forming machine.
Despite the improvements achieved, the said equipment still contains some
drawbacks. The equipment contains several nozzles which require maintenance.
Furthermore, double water pipes with their own valves are needed in the
equipment
for different purposes. Two collection chutes are also needed, which is a
problem in
view of the confined location. The collection chutes have an open structure,
so that
water can spread to the environment despite the collection chutes.
The object of the present invention is to accomplish new type of equipment for
cutting a web and for cleaning a fabric in a web-forming machine, where the
equipment is simpler and more efficient than before. The characteristic
features of
the equipment according to the invention will be more fully understood from
the
enclosed patent claim 1. Another object of the present invention is to
accomplish a
new type of method for cutting a web and for cleaning a fabric in a web-
forming
machine, where the method can be applied easily in conjunction with different
types
of machines. The characteristic features of the method according to the
invention
will be more fully understood from the enclosed patent claim 7. The equipment
and
method according to the invention can be used for efficiently cleaning
problematic
locations in particular. Despite this, the cutting of the web fulfils the
requirements
set. In the method according to the invention, the equipment is used in a new
and
surprising way. Furthermore, the structure of the equipment is simple and
contains
but few components despite versatile functions. It is also easy to control the
equipment. Moreover, cutting waste and water can be removed precisely and
efficiently using water collection devices according to the invention.
In the following, the invention is described in more detail with reference to
the
accompanying drawings describing some applications of the invention, where:
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FIG. 1 shows the principle of the equipment according to the invention on the
dryer section of a web-forming machine;
FIG. 2 shows the equipment according to the invention seen from the side;
FIG. 3 shows a part of the equipment according to the invention seen from the
machine direction;
FIG. 4a shows the principle of a function of the equipment according to the
invention in the cleaning of a fabric;
FIG. 4b shows the principle of an alternative function of the equipment
according to the invention in the cleaning of a fabric;
FIG. 4c shows the principle of another alternative function of the equipment
according to the invention in the cleaning of a fabric.
FIG. 1 presents the principle of the equipment according to the invention in a
web-
forming machine. Paper and board machines are the most common web-forming
machines. In FIG. 1, the dryer section comprises seven consecutive cylinder
groups
and 10', each with several drying cylinders 11 and vacuum rolls 12.
Furthermore,
each cylinder group 10 and 10' comprises a dryer fabric as the fabric 13, with
the
fabric 13 running as an endless loop via drying cylinders 11 and vacuum rolls
12.
The fabric supports and transports the web formed on the web-forming machine.
For example when starting tail threading, the web is run down into the pulper
15
before the dryer section. After successful tail threading, the web is spread
to full
width and run down to another pulper 16. When tail threading is continued, the
tail is
cut from the web using equipment located in the last cylinder group. The
equipment
can also be used for trim cutting the edge of the web.
On the dryer section, most fabrics are also provided with equipment for
cleaning the
fabric. Fabric washers of known type supply washing water to the fabric, and
the
washing water is then removed with the material that has come off the fabric.
However, the last cylinder group is an exception here, because the equipment
is
intended for cutting the web and for cleaning the fabric in the web-forming
machine.
The overhead fabric washer is hence not needed in the last cylinder group 10'
(FIG.
1 ). The basic components of the equipment include a high-pressure unit 17,
the
principle of which is presented in FIG. 1. In practice, the high-pressure unit
comprises a high-pressure pump, which is connected to nozzle equipment for
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forming a high-pressure water jet. The structure of the equipment is presented
in
more detail in conjunction with FIGS 2 and 3.
The equipment also comprises support elements 18 for making the nozzle
equipment 19 move in the cross direction of the web-forming machine. Here, the
support elements 18 comprise a support beam 20, onto which a carriage 21 with
its
nozzle equipment 19 is supported by means of guideways (FIG. 2). The support
beam also comprises elements for moving the carriage at the desired speed and
connections for supplying high-pressure water from the high-pressure unit to
the
nozzle equipment. Furthermore, the equipment comprises water collection
devices
22, which are located essentially at the location of the nozzle equipment 19,
but on
a different side of the fabric 13 from the nozzle equipment 19. The structure
of the
water collection devices will be described in more detail below. In practice,
the
nozzle equipment 19 is located on the same side of the fabric 13 as the web
14. The
web 14 is hence cut against an unsupported fabric 13. In other words, the
water jet
23' can penetrate the fabric. The nozzle equipment 19 also cleans the fabric
13.
Unlike in known solutions, the nozzle equipment 19 according to the invention
comprises one or more needle nozzles 23 in order to cut the web 14 and to
clean
the fabric 13 using a single water jet 23'. In other words, the fabric is
cleaned using
the same water jet that cuts the web, without changing the pressure or other
settings of the equipment. The structure of the equipment is hence simple and
its
operation and control are uncomplicated. Due to the location of the equipment,
cutting and cleaning are separate functions which exclude one another. In
practice,
cleaning is only possible when there is no web on the fabric. Such a situation
occurs
for example during a web break. At least part of the width of the fabric can
also be
cleaned during tail threading.
In conjunction with the cleaning of the fabric, the needle nozzles are in
practice
located essentially at a point in the cross direction of the web-forming
machine
which corresponds to the location of the water jet during the cutting of the
web. In
other words, the water jet cleans the fabric in the cross direction of the web-
forming
machine essentially at a point where the web is cut. This is in particular the
case in
conjunction with edge trimming, where a narrow area of the fabric becomes
especially dirty. The cutting point may change occasionally, in which case the
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CA 02546444 2006-05-12
cleaning point is also changed. Problems caused by the fouling of the fabric
can
hence be avoided. The preferred nozzle size of the needle nozzle is 0.05 - 0.4
mm.
Correspondingly, the pressure applied is 60 - 800 bar, preferably 200 - 400
bar. This
provides a sufficiently efficient water jet for both cutting and cleaning.
Because a
single nozzle and pressure is used, the size and shape of the water jet is
always
almost identical irrespective of whether the water jet is used for cutting or
cleaning.
However, the needle nozzle is positioned and directed in accordance with the
primary purpose of the water jet, i.e. cutting.
FIG. 2 shows a support beam 20 and a carriage 21 fitted on it. The carriage 21
comprises a nozzle arm 24, on which the nozzle equipment 19 is located. FIG. 2
also shows the water jet 23', which penetrates the fabric 13. On the opposite
side of
the fabric, there are water collection devices 22, which are only composed of
a
single collection chute 25. According to the invention, the collection chute
25 has a
cross-sectional shape of a letter C, and the collection chute 25 is placed so
that it
opens towards the water jet 23'. The water can hence be collected in a
controlled
manner without the creation of adverse mist. Furthermore, the ends of the
collection
chute 25, which is located in the cross-direction of the web-forming machine,
are
lower in elevation than the middle point of the collection chute 25 (FIGS 4a -
c).
Water hence runs by gravity to the ends of the collection chute 25, from where
the
water is taken further to waste water treatment. Moreover, at least part of
the length
of the collection chute 25 is provided with washing showers, which are shown
in
FIG. 2. The washing showers 26 can be arranged by means of a washing pipe 27
placed at the upper edge of the collection chute 25, with the washing pipe 27
having
suitable holes 28 for washing water (FIG. 3). Here, the washing pipe extends
over
the entire length of the collection chute. Correspondingly, the collection
chute
extends over the entire width of the web-forming machine. FIG. 3 also shows a
first
connection 29 for supplying washing water into the washing pipe 27 and a
second
connection 30 for discharging washing water from the collection chute 25. The
collection chute 25 is supported by its ends by means of a support structure
35 and
at the middle to an existing suction box 31. In new web-forming machines, the
collection chute can be integrated as part of the suction box or other nearby
structure.
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For reasons of clarity, FIG. 3 shows the carriage 21 detached. The nozzle arm
24
fastened to the carriage 21 contains nozzle equipment 19, which comprises here
one high-pressure needle nozzle 23. There is also a disc 32 around the needle
nozzle 23 in order to avoid damage if the fabric hits the nozzle equipment.
Due to
the novel way of operation, only a single pressure water line 33 is needed by
the
equipment. The travel direction of the carriage 21 is indicated by the two-
head arrow
in FIG. 3.
In addition to the equipment, the present invention concerns a method for
cutting a
web and for cleaning a fabric in a web-forming machine. In the method, a high-
pressure water jet is formed, and the water jet is moved in the cross
direction of the
web-forming machine. The web is cut with the water jet, and the fabric is also
cleaned with the water jet. At the same time, water is collected on the
opposite side
of the fabric essentially at the location of the water jet. According to the
invention,
the water jet is formed by means of one or more needle nozzles. In addition to
cutting the web, the fabric is cleaned with the same single water jet. In
practice, the
fabric is cleaned with the water jet when the fabric has no web, for example
during a
web break. A separate break washer is hence not needed.
During a web break, the fabric can be cleaned across its entire width. Due to
the
narrow water jet, there is in practice enough time to clean only a part of the
fabric
especially during short breaks. In these cases, the principle described above
is
applied, i.e. an area where the web has been cut earlier is cleaned. The
efficient but
narrow water jet can hence be directed correctly. In the third function, the
fabric is
cleaned simultaneously at two locations, preferably independently of each
other. For
this purpose, the nozzle equipment 19 includes at least two needle nozzles 23
installed in two separate nozzle units 34, which are functionally separate
from each
other (FIGS 4a - c). The web can hence be cut or the fabric can be cleaned at
two
locations simultaneously. A sufficient cleaning efficiency is achieved in
particular.
FIGS 4a - c present various cleaning methods. In FIG. 4a, a single nozzle unit
34
cleans the fabric 13 essentially across its entire width. In FIG. 4b, the
fabric 13 is
only cleaned over a narrow area at which the web has been cut earlier. FIG. 4c
shows the use of two independent nozzle units 34 for cleaning. The left-hand
side
nozzle unit 34 cleans the left side of the fabric 13 while the right-hand side
nozzle
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unit 34 cleans a narrow area on the right-hand side edge of the fabric 13. In
practice, the functions can be combined and varied as necessary.
In the cleaning of the fabric in particular, the needle nozzle is moved in the
cross
direction of the web-forming machine at a speed according to the invention,
which is
0.3 - 3 per mil of the travel speed of the fabric. For example, if the
carriage is moved
one millimeter per second during a web break of 15 minutes, a cleaned area of
almost one meter in width is achieved when the travel speed of the fabric is
1,800
meters per minute. By moving the carriage just a little faster than this and
especially
by using two independent nozzle units, the entire width of the fabric can be
cleaned
even during a short break. The equipment is preferably placed so that cleaning
is
started automatically during breaks.
The equipment according to the invention can be placed easily in conjunction
with
the fabric. The control of the equipment is also easy despite versatile
functions.
Unnecessary equipment and components can be avoided when using the method,
and sufficient cleaning efficiency is still achieved. Furthermore, water
consumption
is reduced, and water can be removed from the web-forming machine in a
controlled
manner.
