Note: Descriptions are shown in the official language in which they were submitted.
311
90-331
Ill~q~lOD AIID APPARaTlJ8 FOl~ T}B
COIITROL OF T}ll~ IIIIP--PI~
1 ~r~ I~ A PAPISR III~ING llaClIII~
The invention relates to a method usable in the press
section of a paper or paperboard making machine for regulating the
axial linear-load profile(s) in a press nip or nips, in which method
the axial temperature profile(s) of the outer mantle(s) of a press
roll or rolls is/are regulated and thereby the variation of the
diameter of the press roll in the axial direction is controlled on
the basis of thermal expansion, whereby distribution, in the
transverse direction of the machine, or the linear load in the press
nip or nips formed by the press roll or rolls is affected.
The invention further relates to a press section of a paper
machine, comprising at least two, most appropriately more than two,
press rolls, which rolls form a press nip; or nips with each other,
through which nips one or several press felts are passed.
To remove water out of a paper or paperboard web, press nips
are commonly used, which are formed between two opposite press rolls
and a press felt or felts running between these rolls. In a press
nip, the felt and the paper are compressed so that the water
contained in them fills the open space substantially completely.
Within the press zone, and possibly also to some extent thereafter,
the water that escapes from the web enters into the hollow faces of
the press rolls, which faces are made "hollow" by the provision of
such openings as grooves or bores therein. This construction results
in the moisture profile of the felt or felts entering into the press
nip hardly affecting the moisture profile of the paper or paperboard
departing from the nip. Thus, the press nip tends to equalize the
moisture profiles of the web and of the felt in accordance with the
~o l~
-
transverse distribution of the linear load in the nip.
The linear load profile in the transverse direction of the
paper making machine that exists in the press nip has a direct effect
on the corresponding moisture profile of the web compressed in the
nip, so that the higher the linear load in the nip, the higher
becomes the dry solids content of a paper web as it leaves the nip.
On the other hand, the linear load in the nip must be kept below a
certain limit in order that the compression process should take place
without destruction of the fiber structure of the web.
As is known from the prior art, attempts have been made to
affect the transverse distributions of linear loads in press nips by
means of variable-crown or adjustable-crown rolls (as stated
hereinafter, variable-crown rolls), in which, inside the roll mantle,
there are a number of hydraulically loaded glide shoes placed side by
side. By means of these variable-crown rolls, it is, however, not
possible to alter the distribution of the linear load in a press nip
very abruptly or at a very precise location in the nip. However, by
using rolls adequate in zones thereof, it is also possible to adjust
local faults in the distribution of linear load, which cannot be
accomplished by means of normal so-called floating variable-crown
rolls.
It is known from the prior art, in press rolls and calender
rolls, to employ inside temperature profiling of the roll mantle such
that the roll is divided into separate zones in the axial direction,
into which respective zones mediums of different temperatures are
passed, whereby the radius of the roll is altered based on thermal
expansion. In this way it is possible to change the linear load
profile in a press nip or calendering nip quite abruptly.
In the prior art, profiling devices placed outside
~,o IB~1
calendering rolls are also known, which are based either on hot-air
blowing or on inductive heating. With respect to such structures,
reference is made by way of example to the U.S. Patents 3,489,344 and
3,770,578.
It is a commonly recognized drawback of the prior-art roll
presses that the temperature profile of the roll mantle in the axial
direction is not even close to being uniform. The lateral areas in
the mantles of variable-crown press rolls are colder or hotter than
the middle area. The axial temperature gradient of a press-roll
mantle can be as high as about 20C/m. Temperature gradients of this
order, and even lower gradients, cause such abrupt changes in the
linear load profile of a roll nip that, generally, these changes
cannot be completely controlled by means of the prior-art
variable-crown rolls or by other means known in this prior art.
The temperature gradient of a roll mantle is dependent on
such factors as the reconditioning of the press felt, the effect of
air flows, the different physical and chemical properties of
respective rolls, such as the thermal energy generated by the end
bearings of a variable-crown roll, and the thermal energy introduced
by the web.
As stated previously, the temperature gradient of a roll
mantle is partly a result of the reconditioning of the press felt,
because the felt absorbers produce an uneven felt moisture profile
such that in its lateral areas the felt has a higher moisture content
than the middle area. This moisture profile of the press felt is
"copied" in the temperature profile of the roll in that, the higher
the moisture content in a certain area of the felt is, the colder
becomes the portion of the press roll that is in direct contact with
the felt in that certain area.
~l8~ll
In recent years, attempts have been made to develop various
rolls to substitute for rolls made of rock in paper making machines,
such as metal rolls, in connection with which the profiling problems
of the web have been further aggravated.
~aRY OF THB INVENTIO~
An object of the present invention is to provide a novel
method and apparatus through which the drawbacks discussed above can
be substantially avoided.
More specifically, it is a further principal object of the
present invention to provide such a method and apparatus for
regulation of the linear load profile in a roll nip which have the
advantages of simple construction and operation and by whose means it
is possible to produce sufficiently abrupt changes of required
magnitude in the axial temperature profile of a roll and, by the
effect of thermal expansion, also in the linear load profile in a
press nip formed by the same roll.
With a view to achieving the objectives stated above and
those that will be apparent from the description hereinafter, the
method of the invention comprises the temperature profile of the
outer mantle(s) of the press roll or rolls being regulated by a press
felt or felts running through the press nip or nips formed by the
press roll and thereby applying a heating/cooling effect whose
profile in the axial direction of the roll is regulated, and/or by
directing a plurality of water jets onto the outer mantle(s) of the
press roll or rolls, the jets' quantity distribution and/or
temperature distribution being regulated so as to obtain a desired
distribution in the nip-pressure profile.
A first embodiment of the equipment of the invention
comprises, in the proximity of the press felt, before the felt enters
1 o l8~l 1
the press nip, a profiling heating device extending substantially
over its entire width is fitted, such as a radiator device, a jet
pipe, or a corresponding temperature profiling system, which
comprises a series of jet nozzles, through which a heating effect of
regulated quantity profile and/or temperature profile can be applied
to the felt placed in the proximity of the nozzles.
A second embodiment of the equipment of the invention
comprises, in connection with one or several of said press-roll
mantles, a jet pipe being fitted through which a set of water jets of
regulated quantity and/or temperature profile is applied directly
onto said roll face.
In the method in accordance with the invention, when the
press roll is profiled by the intermediate of a felt running over the
roll, in addition to, or instead of, a set of water jets, it is also
possible to employ other heating/cooling media, such as air, or known
radiation heating methods, such as heating by various electromagnetic
types of radiation, such as microwave and/or infrared radiation. If
air blowing is applied, in some places in the press section
difficulties may occur because such large quantities of air are
required that they cause disturbance in the running of the felts or
the web. When sets of water jets are employed, the necessary amounts
of heat can be transferred by means of relatively small amounts of
water, which may be just of an order of 10-20 g/s/meter of felt
width. When sets of water jets and, in a corresponding manner, air
are employed, in the press roll profiling it is also possible to make
use of cooling methods whose use is not possible when radiation
heating is employed.
The invention can also be practiced by making use of
temperature profiling applied directly to the roll face, but, when
9_o
G
used alone, this is not the most advantageous embodiment of the
invention. In temperature profiling applied directly tot he
press-roll mantle, within the scope of the present invention, a set
of water jets is used, whose quantity and/or temperature distribution
is regulated.
BRIFF DF8~11.10~ OF TH~ DRA~ING~
In the following, the invention will be described in detail
with reference to some exemplifying embodiments of the invention
illustrated in the Figures in the accompanying drawing, the invention
not being confined to the details of the embodiments.
Figure l is a schematical side view, and partially a block
diagram illustration, of a compact press in which a regulation method
and apparatus in accordance with the invention is applied.
Figure 2 shows the embodiment of the regulation method and
apparatus shown in Fig. l in a plane transverse to the paper making
machine.
Figure 3 illustrates typical surface temperature profiles of
the center roll and of a variable-crown roll in the press shown in
Fig. l without a regulation method in accordance with the invention.
Figure 4 illustrates typical moisture profiles of a press
felt before and after passing through a press nip before introduction
of the method of the invention.
Figure 5 illustrates a typical temperature profile of a
variable-crown roll as shown in Fig. 6 without a regulation method or
apparatus in accordance with the invention.
Figure 7 shows a press roll in accordance with Fig. 6 as
provided with a temperature profiling device acting directly upon the
cylindrical mantle of the roll.
~ l8~(1
D~D~K11 ~1O~ OF T~E lA~KK~ E~BODI~eNT8
The arrangement of rolls shown in Fig. 1 is known in the
prior art. This compact press section is marketed by the Applicant
under the trade mark SYM-PRESS II ~. The press shown in fig. 1
comprises three subsequent press nips Nl, N2, N3, wherein the
first nip Nl is formed between a hollow lower roll 13 which has a
hollow face 13' and a suction roll 11. The first nip Nl is a
two-felt nip, and through the nip the upper felt 10 and the lower
felt 14 run, the latter being guided by the guide rolls 15. The
upper felt 10 also acts as a pick-up felt and carries the web W on
its lower face into the first nip Nl and transfers the web W from
it further over the suction zone lla of the suction roll 11 into the
second nip N2. The second nip N2 is formed between the suction
roll 11 and center roll 16 which has a smooth face 16'. In
connection with the center roll 16, the third nip N3 is formed
together with the press roll 17, which has a hollow face 17'. The
felt 18 in the third nip N3 is guided by the guide rolls 19.
After the third nip N3, the web W is detached from the
smooth face 16' of the center roll 16 and transferred, e.g., onto a
drying wire (not shown). The center roll 16 is, e.g., a roll made of
rock or a roll with a metal body. In a position facing the suction
zone lla of the suction roll 11, a steam box 12 is fitted, by whose
means the temperature level in the web W is raised, and thereby the
draining of water in the second and third nips N2, N3 is
intensified. The press roll construction described above is known in
the prior art, and it is described in this connection just to
facilitate an understanding of the background of the invention and as
a basis for an exemplifying embodiment of the invention.
As is shown in Fig. 1, to practice the present invention,
inside the loop of the press felt 10, a jet pipe 21 is fitted, which
is divided into sections 211...21N in the transverse direction in
the manner shown in Fig. 2, the number of these sections being,
consequently, N. The various sections in the jet pipe 21 are
provided with nozzles 27, and each section communicates, via a pipe
261...26N of its own, with a flow supply and regulation unit 20.
By means of the unit 20, it is possible to control the flow-quantity
profile F1...FN and/or the temperature profile Tl...TN of the
water passing through each nozzle 27. Through the series of nozzles
21, a series of water jets is applied to the inner face of the felt
10 before it reaches the nip Nl, the temperature profile
Tl...TN and/or the flow-quantity profile Fl...FN of this
series of water jets being adjustable in accordance with the
invention. In this way, it is possible to control the moisture
profile and the temperature profile of the felt 10 entering into the
nip Nl such that the axial temperature profile and, thereby, the
diameter profile of the mantle 11' of the roll 11 in direct contact
with the felt 10 can be made such that, both in the nip Nl and in
the nip N2, the transverse distribution of linear load that is
desired is produced. In the invention, generally, the present value
is a uniform temperature profile of the press roll mantle, whereby
the final adjustment of the nip pressure profile in the nip Nl can
be carried out in a precise manner, e.g., by using an
adjustable-crown roll such as the lower roll 13 in the nip N1, the
regulating capacity of this lower roll, in such a case, facilitating
this final adjustment.
Also, as shown in Fig. 1, a jet pipe 22 corresponding to the
jet pipe 21 described above is also fitted inside the loop of the
lower felt 14 in the first nip N1, and a set of water jets of
~ C) f ~
adjustable quantity and/or temperature profile can be fed through the
series of nozzles 27 in the nozzle pipe 22 onto the inner face of the
felt 14, and by means of this regulation it is possible to act upon
the temperature profile of the mantle 13' of the roll 13 and, thus,
also upon the linear load profile in the nip Nl in the manner
described hereinbefore.
Moreover, in Fig. 1, a third jet pipe 23 is fitted inside
the loop of the felt 18, which jet pipe 23 operates in the same
manner as the jet pipes 21 and 22 and regulates the temperature
profile of the mantle 17' of the press roll 17 in the third nip N3
and, thereby, the distribution of the linear load in the nip N3.
It should be emphasized in this connection that, even though
hereinbefore and hereinafter the invention is described with
reference to temperature profiling produced by means of a set of
water jets only, instead of water it is also possible to use other
heating/cooling media, such as air. In addition to, or instead of,
temperature profiling of a press felt taking place by means of a
medium or a plurality of media, it is also possible to use various
modes of radiation heating, such as microwave and/or infrared
heating, by means of which an electrically controlled transverse
temperature profiling of a felt can be facilitated. However,
generally, water is the most advantageous heat-transfer medium,
because only a relatively small amount of water is required and, when
water is used, in roll profile regulation it is also possible to make
use of cooling. If, in the invention, temperature profiling applied
directly to the press roll mantle is employed alone or, as is
preferable, together with profiling of a felt, set of water jets is
used in the profiling applied directly to the roll mantle.
In Fig. 1, such an alternative embodiment of the invention
~of ~
- (
is illustrated in accordance with which the jet pipes 24 and 25
operate through whose sets of nozzles 27 sets of water jets F of
adjustable quantity and/or temperature profiles can be fed directly
onto the respective mantles 13';17' of the rolls 13;17, and thereby
it is possible, alone or together with the jet pipes 21, 22 and/or
23, to control the axial temperature profile of the rolls 13, 17 and
the distributions of nip pressures.
Generally, all of the jet pipes 21, 22, 23, 24, 25 shown in
Fig. 1 are not needed at the same time, and according to a preferred
embodiment of the invention, just the jet pipes 21, 23 spraying onto
the felt 10 common to the first and the second nips Nl, N2 and
onto the felt 18 of the third nip N3 are used.
As is shown in Fig. 1, in connection with, or in the
proximity of, the respective mantles 11', 13', 17; of the rolls 11,
13, 17, a device for measurement of the axial temperature profile is
placed, which device, according to Fig. 1 comprises a series of
detectors or a traversing detector 29, which gives a measurement
message to a calculating apparatus 20 which can be a computer,
through a conductor or conductors 31. The unit 20 is preset or
programmed to output predetermined, preferably uniform temperature
profiles of the mantles of the rolls 11, 13, 17.
In connection with the control system in accordance with the
invention, if desirable, it is also possible to include apparatus for
the measurement of the moisture profile of the web W departing out of
the press. In Figs. 1 and 2, such an apparatus is illustrated
schematically by a block 30 and by a related series of detectors 33
for measurement of the moisture profile or a traversing moisture
detector. Such a system of moisture-profile measurement, which is
not always necessary, may be helpful when the set values of the
~c3 l8~1
control system are being formed so that a moisture profile, usually
desired to be as uniform as possible, is produced for the web W
departing from the press.
Fig. 3 illustrates the typical surface-temperature profiles
of press rolls without a regulation method in accordance with the
invention. The profile P1 represents a typical temperature profile
of the outer face 16' of a centre roll 16 similar to that shown in
Fig. 1 over the entire length L of the roll mantle. Both at the
service side of the roll 11 within the length 11 and at the
operation side of the roll, within the length 12, there is quite a
steep temperature gradient. The profile P2 is a typical
temperature profile of the mantle 13' of a variable-crown lower roll
13 in a press similar to that shown in Fig. 1. The profile P2
shows that the temperature of the roll mantle is about 10 degrees
higher at the operation side than at the service side. By means of
the present invention, generally, a uniform temperature profile of
the roll mantle is aimed at, such a profile being, in Fig. 3,
represented by the dashed line as the profile PO.
Fig. 4 illustrates typical moisture profiles of a press
similar to that shown in Fig. 1 without the effect produced by the
method of the invention. In Fig. 4, the profile P4 represents the
moisture profile H of the press felt 10 before it reaches the nip
N1, and the profile P3 represents a corresponding moisture
profile of the felt lo after it leaves the nip N1. It is noted
that the moisture content in the lateral areas of the felt 10
entering into the nip N1 is higher than its moisture content in the
middle area, and that in the lateral areas of the roll 11 the
moisture profile is lowered in the nip N1 by a considerably greater
amount than in the middle area. This lowering of the moisture
$ 1 1
profile is denoted by ~H in Fig 4.
In the invention, if desirable, instead of, or, preferably,
in addition to, the profiling taking place by the intermediate of a
felt or felts, it is possible to use a set of water jets applied
directly onto the mantle of a press roll, the distribution of these
water jets being regulated in the axial direction of the roll with
respect to their temperature and/or with respect to their quantity.
This embodiment is illustrated by Figs. 5, 6 and 7. Fig. 5
illustrates the temperature profile To of the mantle 13' of a
variable-crown roll 13A as shown in Fig. 6 over the length L of the
roll mantle. As is shown in Fig. 5, in the variable-crown roll 13A,
at the proximity of its ends, in the areas 11 and 12, there are
considerable temperature gradients, so that in the proximity of the
roll ends the temperature is higher than in the middle area of the
roll 13A, because the lateral areas of the variable-crown roll 13A
tend to be heated by the effect of warming up of the bearings (not
shown) of the mantle. This anomaly of the temperature profile To
and other anomalies relating to the linear-load pressure profile
within the press nips can be controlled and regulated in accordance
with the invention by or through the set of nozzles 27 in the nozzle
pipe 24 spraying water jets of adjustable temperature profile
T1...T 4 and/or quantity profile F1...F4 directly onto the
face 13' of roll 13. The effect of the regulation may be, e.g., such
that colder water is sprayed to the lateral areas 11 and 12 of
the roll 13, whereby the water, when penetrating into the hollow face
13 of the mantle, cools the lateral areas efficiently, and the
temperature profile To shown in Fig. 5 consequently becomes
substantially horizontal.
~o ~e~l1
-
In temperature profiling applied directly to the press roll
mantle, sets of water jets are used, because by means of water,
especially in a hollow face of a press roll, efficient exchange of
heat is achieved. Also, the amount of water that is needed is
relatively small and, when water is used, it is also possible to use
cooling in the profiling.
Details of the present invention may easily vary within the
scope of the inventive concepts set forth above, which have been
presented by way of example only. Therefore, the preceding
description of the present invention is merely exemplary, and is not
intended to limit the scope thereof in any way.
