[0001] The invention relates generally to producing fiber webs. Particularly the invention
relates to a forming section according to the preamble of claim 1.
[0002] As known from the prior art in fiber web machines, especially in paper and board
machines, the fiber web is produced and treated in an assembly formed by a number
of apparatuses arranged consecutively in a process line. A typical production and
treatment line comprises a forming section comprising a head box and a forming unit
and a press section as well as a subsequent drying section and a reel-up. The production
and treatment line can further comprise other devices and sections for finishing the
fiber web, for example, a size press, a calender, a coating section. The production
and treatment line also comprises typically at least one winder for forming customer
rolls as well as a roll packaging apparatus. In this description and the following
claims by fiber webs are meant especially container-board or cartonboard webs.
[0003] The task of a forming unit is to remove water from fiber suspension fed by the head
box. When the web is manufactured of watery fiber stock, water in the stock is removed
on the forming section through a forming wire or forming wires for starting the formation
of the web. Fibers remain on the forming wire or between the forming wires moving
together. Depending on the grade of the web being manufactured, different types of
stocks are used. The volume for which water can be removed from different stocks for
achieving a web of good quality is a function of many factors, such as e.g. a function
of the desired basis weight of the web, the design speed of the machine, and the desired
level of fines, fibers and fill materials in the finished product. Many types of devices
are known on the forming unit such as foil strips, suction boxes, turning rolls, suction
rolls, and rolls provided with an open surface, which have been used in many different
arrangements and arrays when trying to optimize the volume, time and location of water
being removed when forming the web. The manufacturing a high-quality end-product of
desired grade is a function of the volume of dewatering, the dewatering method, the
duration of dewatering, and the location of dewatering. When it is desired to improve
the water removal capacity and to maintain or improve the quality of the end-product,
many times unforeseeable problems are created as the result of which either the water
removal volume has to be decreased for maintaining the desired quality or the desired
quality has to be sacrificed for achieving the greater water volume.
[0004] In patent application publication
EP 1096067 A2 is disclosed a former for a fiber web machine, which former is constructed as a gap
forming unit, in which stock suspension from the head bow is fed into a gap formed
between two wire loops, in between of which wire loops a forming gap is formed. The
gap forming unit comprises at least two, advantageously three rolls, which are at
least partly in contact with both wires.
[0005] In patent publication
US 4,925,531 is disclosed a twin-wire former for a paper machine having a lower wire and an upper
wire. The former has a twin-wire forming zone which has forming members and forming
zones situated in a specific sequence as follows. A downwardly curved forming zone
is conformed to a sector of a large-diameter forming roll mounted on a frame of a
lower wire unit, the magnitude of this sector being within the range of <90°. A second
forming roll then follows which is preferably provided with a hollow face and onto
which the wires arrive from the first forming roll. The twin-wire forming zone is
curved within a certain sector of less than 90° on the second forming roll so as to
become horizontal. A forming shoe is provided with a ribbed deck and fitted after
the second forming roll inside the lower wire loop, this forming shoe having a relatively
large curve radius after which the twin-wire forming zone ends and the web is arranged
to follow along with the lower wire.
[0006] In the twin-wire formers known form prior art there is typically combined a forming
roll with large wrap angle and a long pulsating forming shoe, which provides for good
water removal but has high energy consumption. During the in the beginning non-pulsating
water removal with the forming roll condenses the fiber web so much that there is
difficulties of achieving desired water removal without powerful and long lasting
pulsating water removal.
[0007] These types of forming sections are typically high; about 10 meters, and thus expensive.
The height of opening of the head box typically is at height level of about 8 meters,
due to the large wrap angle of the forming roll and the long forming shoe. The height
as such might not raise so many difficulties but this type of construction leads to
in high locations rotating, heavy rolls, which tend to create vibration and thus the
frame and support structures need to be dimensioned for heavy loads.
[0008] Especially when producing board webs problems occur due to low consistency of fiber
stock in the head box, which leads to increased need of water removal in the forming
unit, whereby in types of forming sections one disadvantage relating to optimizing
water removal and desired quality of the board web. Typically this has been tried
to solve by adding water removal devices of the forming unit, which naturally increases
costs and complicates the construction of the forming section.
[0009] In patent application publication
WO 2010046527 A1 is disclosed a forming section comprising two wire loops which form a twin-wire zone
which comprises a dewatering element performing initial dewatering and a dewatering
device following it. The dewatering device comprises a stationary support shaft on
which are supported support elements around which circles an im-permeable belt loop.
The dewatering device further comprises a curvilinear dewatering zone over which the
wires travel supported by the belt loop. The degree of curvature of the curve of the
curvilinear dewatering zone increases in the travel direction of the belt such that
increasing dewatering pressure is applied to stock suspension travelling between the
wires on the curvilinear dewatering zone. said at least one curvilinear dewatering
zone of said at least one dewatering device, consists of two partial curves such that
the radius of curvature of a first partial curve is greater than the radius of curvature
of a second partial curve following the first partial curve in the travel direction
of the web.
[0010] An object of the invention is to create a forming section, in which the disadvantages
and problems of prior art are eliminated or at least minimized.
[0011] In particular an object of the invention is to provide a new type of forming section
in which height of the forming section can be decreased.
[0012] In order to achieve the above mentioned objects the forming section according to
the invention is mainly characterized by the features of the characterizing clause
of claim 1. Advantageous embodiments and features are disclosed in the dependent claims.
[0013] According to the invention the forming section comprises a twin-wire forming unit
formed between a lower wire and an upper wire, in which first water removal means
of the twin-wire forming unit is a forming roll with a wrap angle, wherein in the
twin-wire forming unit following the forming roll is a sleeve roll and run between
the forming roll and the sleeve roll is free of vacuumed dewatering i.e. between the
forming roll and the sleeve roll no vacuumed dewatering is located.
[0014] According to an advantageous feature of the invention the sleeve roll comprises a
stationary support shaft, an belt loop, which is led to circle around the stationary
support shaft, that the sleeve roll further comprises at least one curvilinear dewatering
zone consisting of two partial curves such that the radius of curvature of a first
partial curve is greater than the radius of curvature of a second partial curve following
the first partial curve in the travel direction of belt loop.
[0015] According to an advantageous feature of the invention the sleeve roll comprises a
support elements supported at a distance from each other on the stationary support
shaft, the belt loop to circle around the stationary support shaft is supported by
the support elements and the belt loop is impermeable.
[0016] According to an advantageous feature of the invention distance between the forming
roll and the sleeve roll is 0,2 - 2 meters, advantageously 0,3 - 1,5 meters, which
distance is measured between the point, in which lower and upper wires wrap angle
ends on the forming roll and the point in which lower and upper wires are in the contact
on the sleeve roll i.e. the point in which the contact of the lower and upper wires
begins on the sleeve roll.
[0017] According to an advantageous feature of the invention the forming unit comprises
first a one wire part followed by the twin-wire part and advantageously the one wire
part is substantially horizontal or inclined. According to an advantageous feature
the one wire part comprises a forming shoe with a deck and suction openings in the
deck.
[0018] According to an advantageous feature of the invention at a distance from the sleeve
roll the twin-wire forming unit ends as run of the upper wire turns away from the
lower wire and end part of the forming unit is formed as one wire part.
[0019] According to an advantageous feature of the invention the overall height of the forming
section is less than 8 meters.
[0020] According to an advantageous feature of the invention the highest point of the sleeve
roll is on a higher vertical position than the lowest point of the forming roll.
[0021] By the forming section according to the invention many advantages are achieved. The
overall height of the forming section can be decreased even 2 - 3 meters and thus
also the frame and support structures can be dimensioned for smaller loads. The overall
height of the forming section is less than 8 meters. The properties, especially strength
properties of the fiber web are improved as the amount of pulsating water removal
is minimized. Further there is less contacting water removal means in the forming
section, thus the life time of wires is increased as well as the power consumption
is decreased. Also good strength properties of the fiber web are achieved as there
is no vacuumed, pulsating dewatering between the forming roll and sleeve roll. Further
savings in investment and use costs are achieved. Short distance from the forming
roll to the sleeve roll enables manufacturing of packaging board grades with high
quality, efficiency and capacity.
[0022] In the following the invention is explained in detail with reference to the accompanying
drawing to which the invention is not to be narrowly limited.
In figure 1 is shown schematically an advantageous example of a forming section according
to the invention.
In figure 2 is shown schematically an advantageous example of a forming section according
to the invention.
In figures 3A - 3B is shown very schematically a forming shoe and a sleeve roll.
[0023] During the course of the following description like numbers and signs will be used
to identify like elements according to the different views which illustrate the invention
and its advantageous examples. In the figures some repetitive reference signs have
been omitted for clarity reasons.
[0024] In figure 1 is shown an example of a forming section, which is a twin-wire forming
unit type forming section and begins with a twin-wire part. The forming section comprises
a head box 30, from which the stock suspension M is fed to the forming unit formed
as a twin-wire forming unit comprising a lower wire 10 and an upper wire 20, each
comprising rolls 12, 22 for guiding and driving the wire as an endless loop. The stock
suspension M is first fed into a gap formed between the lower wire 10 and the upper
wire 20. The first water removal means is a forming roll 13 with a wrap angle 13V,
which forming roll 13 is located inside the loop formed by the lower wire 10. The
wrap angle 13V is advantageously 40-110 degrees for ensuring required water removal
capacity. The forming roll 13 is advantageously a suction roll. The forming roll 13
is followed support foils 26 that support the lower wire 10 but do not participate
in active dewatering, only remove water from the bottom surface of the wire 10 and
support the run of the wires 10, 20 between the forming roll 13 and the sleeve roll
50. The support foils 26 do not deviate the run of the wires 10,20 and thus no dewatering
pressure is effected to the fiber web between the wires 10, 20.The support foils 26
are followed by a sleeve roll 50, which is located inside the loop formed by the upper
wire 20. The distance L between the forming roll 13 and the sleeve roll 50 is only
about 0,2 - 2 meters. The distance is measured between the point in which lower and
upper wires 10, 20 wrap angle 13V ends on the forming roll 13 and between the point
in which lower and upper wires 10, 20 are in the contact on the sleeve roll 50 i.e.
the point in which the contact of the lower and upper wires 10, 20 begins on the sleeve
roll 50. According to the invention, there is no need to use suction boxes between
the forming roll 13 and the sleeve roll 50. The support foils 26 can be also situated
after the sleeve roll 50 for removing water from the surface of the wire 10. After
the sleeve roll 50 the fiber web is further guided between the upper and the lower
wire 20, 10 and at a distance towards the pick-up roll 31 transferring the fiber web
to a press section the run of the upper wire 20 turns upwards away from the lower
wire 10 and the end part of the forming unit is formed as a one wire part. Inside
the loop formed by the lower wire 10 further water removal means 16 are located as
shown in the example of the figure. The further water removal means 16 may comprise
forming shoes and/or suction devices. For ensuring the low height of the forming section,
the highest point of sleeve roll 50 is on the higher vertical position than the lowest
point of the forming roll 13.
[0025] In figure 2 is shown an example of a forming section begins with a short one wire
part followed by a twin-wire part. The forming section comprises a head box 30, from
which the stock suspension M is fed to the forming unit formed as a twin-wire forming
unit comprising a lower wire 10 and an upper wire 20, each comprising rolls 12, 22
for guiding and driving the wire as an endless loop. The stock suspension M is first
fed onto the lower wire 10 and onto the area of a forming shoe 17 and thereafter the
stock on the lower wire is guided into a gap formed between the lower wire 10 and
the upper wire 20 forming the twin-wire part of the forming unit. The beginning of
the forming unit with a short, substantially horizontal or inclined one-wire section
comprising a forming shoe 17 removing water by suction provides for exact control
of the head box flow, so that water is sucked through the lower wire 10 but stock
suspension is not bouncing on the wire 10 as there is no pulsating water removal.
The first water removal means in the twin-wire part is a forming roll 13 with a wrap
angle 13V, which forming roll 13 is located inside the loop formed by the lower wire
10. Wrap angle 13V is advantageously 40-110 degrees for ensuring required water removal
capacity. The forming roll 13 is advantageously a suction roll. The forming roll 13
is followed support foils 26 that support the lower wire 10 but do not participate
in active dewatering, only remove water from the bottom surface of the wire 10 and
support the run of the wires 10, 20 between the forming roll 13 and the sleeve roll
50. The support foils 26 do not deviate the run of the wires 10, 20 and thus no dewatering
pressure is effected to the fiber web between the wires 10, 20. The distance L between
the forming roll 13 and the sleeve roll 50 is only about 0,2 - 2 meters. The distance
is measured between the point in which lower and upper wires 10, 20 wrap angle 13V
ends on the forming roll 13 and between the point in which lower and upper wires 10,
20 are in the contact on the sleeve roll 50 i.e. the point in which the contact of
the lower and upper wires 10, 20 begins on the sleeve roll 50. According to the invention,
there is no need to use suction boxes between the forming roll 13 and the sleeve roll
50. After the sleeve roll 50 the fiber web is further guided between the upper and
the lower wire 20, 10 and at a distance towards the pick-up roll 31 transferring the
fiber web to a press section the run of the upper wire 20 turns upwards away from
the lower wire 10 and the end part of the forming unit is formed as a one wire part.
Inside the loop formed by the lower wire 10 further water removal means 16 are located
as shown in the example of the figure. The further water removal means 16 may comprise
forming shoes and/or suction devices. This kind of forming section is especially good
for forming higher basis weight webs, because forming shoe 17 reduces the web layer
thickness around 20 - 40% and web doesn't tend to extrude between the wires on the
forming roll 13 area.
[0026] The forming sections of the examples of figures 1 and 2 comprise a twin-wire forming
unit with a sleeve roll, in which the twin-wire forming unit is formed between the
lower wire 10 and the upper wire 20. Due to the location of the sleeve roll following
next the first forming roll 13 at a distance L of 0,2 - 2 meters, advantageously 0,3
- 1,5 meters, also the location height of the upper wire 20 can lowered and thus further
the location of the head box and the forming unit can be lowered.
[0027] In figure 3A is schematically shown a forming shoe 17, in which the deck 18 comprises
suction openings 19, through which a suction effect is created to remove water from
the stock suspension and the formation of the stock suspension is improved. Advantageously
deck 18 design does not cause pulsations to the web in the beginning forming shoe
17. The openings 19 are formed between foils, which foils have width of 5-15 mm located
at a distance between 5-15 mm between each other and advantageously the forming shoe
17 is connected to a suction device.
[0028] In figure 3B is schematically shown a sleeve roll 50 with decreasing radius, which
comprises a stationary support shaft 51 on which support elements 52 are supported
at a distance from each other, an impermeable belt loop 53 which is led to circle
around the stationary support shaft 51 supported by the support elements 52. The sleeve
roll 50 further comprises at least one curvilinear dewatering zone K via which the
wires 10, 20 are led to travel supported by the belt loop 53. The degree of curvature
of the curve of the curvilinear dewatering zone K increases in the travel direction
of the belt 53 such that increasing dewatering pressure is applied to the stock suspension
travelling between the wires 10, 20 on said at least one curvilinear dewatering zone
K. Radius of curvature of the curvilinear dewatering zone K consists of two partial
curves such that the radius of curvature K1 of a first partial curve is greater than
the radius of curvature K2 of a second partial curve following the first partial curve
K1 in the travel direction of belt loop 53. Radius of curvature of the curvilinear
dewatering zone K can be contain several curves such that the radius of curvatures
decreases in the running direction of the wires.
[0029] Above only some advantageous examples of the inventions has been described to which
examples the invention is not to be narrowly limited and many modifications and alterations
are possible within the invention.
1. Forming section comprising a twin-wire forming unit formed between a lower wire (10)
and an upper wire (20), in which first water removal means of the twin-wire forming
unit is a forming roll (13) with a wrap angle (13V), characterized in that in the twin-wire forming unit following the forming roll (13) is a sleeve roll (50)
and that run between the forming roll (13) and the sleeve roll (50) is free of vacuumed
dewatering i.e. between the forming roll (13) and the sleeve roll (50) no vacuumed
dewatering is located.
2. Forming section according to claim 1, characterized in that the sleeve roll (50) comprises a stationary support shaft (51), an belt loop (53),
which is led to circle around the stationary support shaft (51), that the sleeve roll
(50) further comprises at least one curvilinear dewatering zone (K) consisting of
two partial curves such that the radius of curvature (K1) of a first partial curve
is greater than the radius of curvature (K2) of a second partial curve following the
first partial curve (K1) in the travel direction of belt loop (53).
3. Forming section according to claim 1 or 2, characterized in that the sleeve roll (50) comprises support elements (52) supported at a distance from
each other on the stationary support shaft (51), that the belt loop (53)led to circle
around the stationary support shaft (51) is supported by the support elements (52),
and that the belt loop (53) is impermeable.
4. Forming section according to any of claims 1-3, characterized in that distance (L) between the forming roll (13) and the sleeve roll (50) is 0,2 - 2 meters,
advantageously 0,3 - 1,5 meters.
5. Forming section according to any of claims 1-4, characterized in that the forming unit comprises first a one wire part followed the twin-wire part.
6. Forming section according to claim 5, characterized in that the one wire part is substantially horizontal or inclined.
7. Forming section according to any of claims 5 or 6, characterized in that the one wire part comprises a forming shoe (17) with a deck (18) and openings (19)
in the deck (18).
8. Forming section according to any of claims 1-7, characterized in that at a distance from the sleeve roll (50) the twin-wire forming unit ends as run of
the upper wire (20) turns away from the lower wire (10) and end part of the forming
unit is formed as one wire part.
9. Forming section according to claim 4, characterized in that the overall height of the forming section is less than 8 meters.
10. Forming section according to claim 4, characterized in that the highest point of the sleeve roll (50) is on a higher vertical position than the
lowest point of the forming roll (13).