[0001] This invention relates to an apparatus for manufacturing corrugated board, and particularly
to the corrugating unit, which is an important component of this apparatus.
[0002] Notoriously, the corrugating unit of an apparatus for manufacturing corrugated board
forms the so-called "single-faced corrugated board", i.e. a corrugated paper having
glued thereon a plain board or liner. In order to form the single-faced corrugated
board, the corrugating unit comprises two cooperating corrugating cylinders, i.e.,
a so-called inlet cylinder and a so-called central cylinder, both having a corrugated
configuration and receiving therebetween the paper to be corrugated. The corrugated
paper passed between the pairs of corrugating cylinders is held in firm contact with
the corrugated configuration of the central corrugating cylinder, where the ridges
or tips of the corrugated paper are coated with glue by means of a glueing unit. Thereafter,
the corrugated paper, still engaged with the corrugated configuration of the central
corrugating cylinder and coated with glue on the ridges thereof, is bonded to the
liner and is passed, together with the latter, between the central corrugating cylinder
and a pressure cylinder, and then it is moved away from the central corrugating cylinder
and out of the corrugating unit.
[0003] The production of a satisfactory single-faced corrugated board having regular and
uniform characteristics, with complete bonding of the liner to the corrugated paper,
is a basic requirement to obtain a double face corrugated board having high mechanical
characteristics. For this purpose, the corrugated paper or medium must be held adhering
to the corrugated surface of the central corru= gating cylinder during the formation
of the corrugation until it is associated with the liner, and practically, therefore,
over a central corrugating cylinder sector defined between the area of contact with
the inlet corru= gating cylinder and the area of contact with the pressure cylinder.
[0004] The adherence engagement between the corrugated paper and the corrugated surface
of the central corrugating cylinder has been achieved heretofore by mechanical means
formed by comb-like finger members, which entailed, however, considerable operative
costs, high maintenance costs and poor quality of the single-faced corrugated board
(non-
-uniform corrugations, i.e. corrugations with flutes of different heights, unsatisfactory
glueing, distorted corrugations, and other inconveniences). Specifically, the finger
members create non-glued stripes on the single-faced corrugated board, with resulting
detriment to "the mechanical characteristics of the corrugated board.
[0005] As a consequence, corrugating units with no fingers, called suction corrugating units
(or fingerless units), have been developed wherein the close adherence contact between
the corrugated paper and the corrugated surface of the central corrugating cylinder
is effected pneumatically by suction effect, i.e. by means of depression below atmospheric
pressure. Suction is exerted either through peripheral suction holes, notches or channels
in the central corrugating cylinder, communicating with internal suction conduits
in the body of said cylinder, or through peripheral annular grooves formed in the
corru= gating cylinder and communicating either with discrete suction conduits or
with a vacuum chamber located outside of the central corrugating cylinder, that is
at the sector thereof opposite to that which is being engaged by the corrugated paper.
This suction engagement of the corrugated paper or medium against the corrugated surface
of the central corrugating cylinder reduces the possibility of formation of irregular
corrugations, i.e. of high and low corrugations, and ensures, therefore, a more satisfactory
bonding (glueing) of the single-faced corrugated board, compared with that ensured
by the corrugating units equipped with comb members. The use of suction to effect
a close adherence to the corrugated paper against the surface' of the corrugating
cylinder, however, has some drawbacks. Specifically, the central corrugating cylinder
must be provided with peripheral suction holes, notches or channels communicating,
in some embodiments, with suction conduits formed in the body of said cylinder. The
construction of this type of suction corrugating cylinders is extremely complicated
and expensive. Moreover, the suction holding of the corrugated core board against
the surface of the central corrugating cylinder through peripheral holes, notches
or channels thereof, causes a non-uniform holding between said corrugated paper and
central corrugating cylinder until a condition of uniform pressure differential between
the board and cylinder is reached. Located between the vacuum pump and the corrugated
board are various elements, such as conduits, holes, notches, channels and the like,
which cause load losses, whereby said suction ensures a relatively poor adherence
of the corrugated board against the central corrugating cylinder, even under high
vacuum conditions. Therefore, the corrugated paper will not adhere thoroughly uniformly
and evenly against the surface of the central corrugating cylinder. This drawback
is emphasized in particular operative conditions, such as in case of very porous papers,
worn cylinders, during the acceleration and deceleration steps, and the like. In order
to eliminate these drawbacks, the suction corrugating units must be operated with
high vacuum values so as to take into account said strong losses, which, however,
causes the paper (especially if of poor substance) to be sucked and more or less drawn
into the peripheral suction holes, notches or channels of the central corru= gating
cylinder. This deformation of the corrugated core board or medium can cause the formation
of non-glued stripes in the single-faced corrugated board, and can also progressively
wear the sharp edges of suction peripheral holes, notches or channels of the central
corrugating cylinder. Moreover, in the suction corrugating units, impurities in the
ambient atmosphere and in papers cause obstructions and deposits in the suction system
and reduce the efficiency of said system with resulting further load losses, which
entails frequent and complicated cleaning and maintenance operations. Finally, in
case of suction corrugating'units, the width of the papers should pre= ferably be
the same as the length of the cylinders to avoid exposing peripheral suction holes,
notches or channels of the central corrugating cylinder, thus losing vacuum.
[0006] This invention aims to eliminate said drawbacks of the heretofore known corrugating
units, both of the suction fingerless type and of the finger type.
[0007] This object is achieved by the invention in that the adherence of the corrugated
paper or medium against the corrugated surface of the corrugating cylinder is caused
by an air cushion rather than by suction, i.e. it is caused by a slight air pressure,
just higher than atmospheric pressure, applied to the outside surface of the corrugated
paper or medium, on the side opposite to that which is being engaged with the corrugating
cylinder.
[0008] The air cushion applied to the outside surface of the corrugated wore board at the
central corrugating cylinder, contemplated an air cushion zone followed by a controlled
air decompression section, and is applied to the central corrugating cylinder active
side, i.e. the side of this cylinder where the corrugated paper or medium is coated
with glue and is then bonded to the liner.
[0009] The air cushion, according to the invention, preferably acts against the central
corrugating cylinder sector included between the nip of said central corrugating cylinder
and inlet corrugating cylinder and the region where the liner board is bonded to the
corrugated paper coated with glue.
[0010] Preferably, according to a further characteristic of the invention, the liner board
is approached and pre--associated to the corrugated paper, i.e. it is just approached
with slight contact with the corrugated paper by means of a suitable approaching roll,
located between the glueing unit and the pressure cylinder, and the air cushion presses
on the corrugated paper at the central corrugating cylinder sector included between
the nip of the central corrugating cylinder and inlet corrugating cylinder and the
region where the liner board is approached to the corrugated paper by means of said
approaching roll, while downstream of said region, to the region where the liner board
is bonded to the corrugated board, the single--faced corrugated paper being formed
is acted upon by the air cushion in a decompression ambient. A progressive and controlled
evacuation of the air entrapped between the corrugated core board and the liner board
is thus obtained.
[0011] According to the invention, to obtain a sati= sfactory and uniform engagement of
the corrugated board against the central corrugating cylinder by means of air cushion,
the invention provides means to maintain the interstice between the corrugated surface
of the central corrugating cylinder and the corrugated paper in communi= cation with
the atmosphere, thus permitting a controlled evacuation of the air seeped through
the board. Said means for communication with the atmosphere may be formed, for example,
by shallow annular grooves suitably spaced on the central corrugating cylinder.
[0012] With respect to suction corrugating units known heretofore, the unit according to
the invention has the advantage of using a central corrugating cylinder of conventional
type, that is without holes or internal ducts. Therefore, the manufacturing and maintenance
costs of these corrugating cylinders are greatly reduced, while avoiding the drawbacks
of both the corrugating units equipped with comb members, and the corrugating units
of the suction type with no comb members. Moreover, as in the corrugating unit according
to the invention the air cushion applied onto the corrugated core board is fed into
a zone which is followed by a successive controlled decompression section, partly
defined by said corrugated board, there will be, practically, no appreciable pressure
drop between the air cushion acting on the board and the air fed to, and present at,
the air cushion zone followed by a controlled decompression section, so that the entire
pressure differential between the air cushion in said zone and the ambient atmosphere
is exploited to maintain the corrugated paper adhering against the corrugated surface
of the central corrugating cylinder, with a negligible loss and in any operative contidion.
Under these operative conditions, a satisfactory and uniform corrugation of the paper
will be obtained, thus avoiding the formation of corrugations of different heights,
even with papers of poor substance and resistance, and achieving the production of
corrugated board having high mechanical characteristics Moreover, an optimum efficiency
of the heat exchange between the central corrugating cylinder and the corrugated paper,
with resulting energy saving in the operation of the corrugating unit. The improved
heat exchange efficiency also permits higher temperatures of the corrugated paper
and/or lower temperatures of the cylinders and/or higher rates of speed when operating
with boards of good substance and permits to operate, in this instance, even at the
setting temperature of the adhesive. Since in the corrugating unit according to the
invention the air cushion applied to the outside surface of the corrugated core board
is distributed uniformly over the entire length of the respective sector of the central
corrugating cylinder, for a same total bearing force there will be a smaller specific
pressure at the very narrow peripheral channels and, therefore, a negligible drawing
effect of corrugated paper into said channels, whereby a uniform and continuous glueing
will be obtained between the corrugated paper and the liner board at the ridges of
all corrugations and over the entire length of said ridges, even at the very narrow
peripheral channels. A further advantage of the corrugating unit according to the
invention is that the latter enables the production of single-faced corrugated board
of any reduced length with respect to the length of the corrugating cylinders, because
the air cushion applied to the outside surface of the corrugated core board grants
the constant adherence contact of said board against the corrugated surface of the
central corrugating cylinder, regardless of the width of papers. The annular air discharge
grooves formed in the central corrugating cylinder and designed to establish the communication
to atmosphere from the interstice between the corrugating cylinder and corrugated
paper, are very narrow and in small number. Therefore, even when operating with papers
of reduced length that expose some of the annular grooves of the central corrugating
cylinder, any leaks and flowrate drops at the means generating the air cushion are
negligible and do not affect the good adherence contact of the corrugated papers against
the corrugated surface of the central corrugating cylinder. In the corrugating unit
according to the invention, the correct operation of the unit and the good adhering
contact of the corrugated paper against the corrugating cylinder surface are not affected
by any impurity either in the ambient atmosphere or of the board material. Specifically,
any impurity of the board material is ejected into the atmosphere, whereby the corrugating
unit according to the invention is to be ragarded as self-cleaning, thus reducing
considerably the maintenance operation and shut-down drawbacks.
[0013] An embodiment of the corrugating unit according to the invention aill be described
hereinafter as a non--limiting example with reference to the accompanying drawings,
wherein:
Figure 1 is a diagrammatic cross-sectional view of a corrugating unit according to
the invention;
Figure 2 is a fragmentary longitudinal sectional view, on a larger scale, of the sealing
means at one end of a corrugating cylinder;
Figure 3 is a fragmentary longitudinal sectional view, on a larger scale, of the sealing
means at one end of an approaching roller and of an associated press roller.
[0014] With reference to the drawings, the corrugating unit of an apparatus for manufacturing
corrugated board comprises an inlet corrugating cylinder 1, a central corrugating
cylinder 2 and a press cylinder 3, all rotating as indicated by the arrows. The peripheral
surfaces of the two corrugating cylinders 1 and 2 have a corrugated configuration,
and these cylinders 1 and 2 are in mesh similarly to gear wheels.
[0015] The paper 4 to be corrugated is fed to the inlet corrugating cylinder 1 in the direction
indicated by the arrow and is passed around said cylinder and between the inlet corrugating
cylinder 1 and central corrugating cylinder 2 and is thus corrugated. The corrugated
paper will remain on the central corrugating cylinder 2 until it has just passed the
pressure cylinder 3, as will be described hereinafter. At the sector of the central
corrugating cylinder 2, included between the inlet corru= gating cylinder 1 and pressure
cylinder 3, a glueing unit 5 is provided comprising a glue-containing tank 6 and a
glueing roller 7 dipping into the tank 6 and cooperating with the central corrugating
cylinder 2 to apply the glue, withdrawn from the tank 6, to the ridges of the corru=
gations of the corrugated paper. The glueing roller 7 cooperates with a metering roller
8 provided with a doctor blade 9.
[0016] Located between the glueing roller 7 and pressure roller 3 is an approaching roller
10 cooperating with the central corrugating cylinder 2 and a pressure roller 11. The
liner board 12 is fed to the approaching roller 10 after passing around the pre-heating
cylinders 13 and between the approaching roller 10 and associated pressure roller
11. The approaching roller 10 places the liner 12 on the glue-coated ridges of the
corrugated paper 4 supported on the central corrugating cylinder 2, without exerting
any bonding pressure, that is with only a slight contact, thus effecting a mere pre-bonding
between the corrugated paper 4 and the liner board 12.
[0017] The corrugated paper 4 and liner board 12 slightly contacted thereon by the approaching
roller 10 are then passed, thus associated and pre-bonded with each other, between
the central corrugating cylinder 2 and the pressure cylinder 3, where they are definitively
glued and bonded. The single-faced corrugated board 14 thus obtained then moves away
from the central corrugating cylinder 2 and moves forward as indicated by the arrow
towards other units, to be submitted to further operations.
[0018] At the sector of the central corrugating cylinder 2, which is included between the
inlet corrugating cylinder 1 and the approaching roller 10, the corrugated paper is
kept closely and uniformly adhering to the shaped (corru= gated) surface of the central
corrugating cylinder 2 by means of an air cushion applied to the outside surface of
said corrugated paper, i.e. to the surface thereof facing away from the corrugating
cylinder 2. For this purpose, on the side of the central corrugating cylinder 2 wrapped
by the corrugated paper, an air cushion zone 15 is provided which is followed by a
controlled air decompression section, wherein the desired amount of air is fed and
kept under control by means of blowers, air pumps, compressors or any other source
of compressed air (not shown). Included in this air cushion zone 15 followed by a
controlled air decompression section, is also the glueing unit 5.
[0019] In the illustrated embodiment, the air cushion zone 15 followed by the controlled
air decompression section is located between two side walls 115 and is defined by
a front wall 215 and a bottom wall 315, and on the upper side and the opposite side
from the front wall 215, by a roller 16 and the inlet corrugating cylinder 1, central
corrugating cylinder 2, approaching roller 7 and associated pressure roller 11. The
roller 16 is coated with anti-adherence rubber resisting to high temperature and is
pressed against the inlet corrugating cylinder 1, while the airtight closure between
the roller.16 and front wall 215 of the air cushion zone 15 followed by a controlled
air decompression section, is ensured by a doctor blade 17. The airtightness between
the two metallic corrugating cylinders 1 and 2 is ensured by the meshing engagement
of these two cylinders and interposed corrugated paper. The closure between the central
corrugating cylinder 2 and approaching roller 10 is ensured by the pre-association
or approaching engagement of the corrugated paper and liner. The closure between the
approaching roller 10 and respective pressure roller 11 is ensured by the engagement
between these two rollers with the interposed liner board 12. The approaching roller
10 is also covered with an anti--adherence rubber coating resisting to high temperatures.
The pressure roller 11 is made of metal, and the closure between this roller 11 and
the back wall 315 of the air cushion zone 15 follwed by a decompression section is
ensured by a doctor blade 18.
[0020] To reduce air escape from the air cushion zone 15 followed by a controlled decompression
section, at the ends of the various cylinders and rollers 1,2,7,8,10,11,16, any suitable
radially and/or axially acting means may be provided, designed to accommodate any
thermal expansion of said cylinders, rollers and/or respective shafts. Figures 2 and
3 show two embodiments of axially-acting sealing means provided at an end of the inlet
corrugating cylinder 1 (Figure 1) and of the approaching and pressure rollers (Figure
3). In the embodiment of Figure 2, compressed against the end face of the corrugating
cylinder 1, around the shaft 101 of said cylinder 1, is an annular seal 19 carried
by a sealing ring 20 axially slidable within a cylindrical extension 122 of a ring
member 22 fixed to the side wall 23. The sealing ring 20 is axially urged by springs
24 toward the end of the corrugating cylinder 1 and is guided by bolts or stems 25
fixed to said ring 20 and slidably passing through holes in the ring member 22 and
side wall 23. A seal 21 is provided between the slidable ring 20 and the fixed cylindrical
extension 122.
[0021] In a similar manner, as shown in Figure 3, sealing rings 20 are axially urged against
the end faces of the approaching roller 10 and pressure roller 11, either with or
without interposed annular front seals. The sealing rings 20 are slidably arranged
each in a cylindrical extension 122 of a ring member 22 fixed to the side wall 23
around a bearing 26 supporting the shaft of the respective cylinder, as shown for
the shaft 110 of the approaching cylinder 10. Again, the slidable rings 20 are axially
urged by springs 24 against the ends of the respective rollers 10, 11, i.e. they resiliently
yield axially and are fixed to bolts or stems 25 slidably guided through holes in
the ring member 22. Seals 21 are interposed between the slidable rings 20 and respective
cylindrical extensions 122.
[0022] To permit the access to the corrugating cylinders 1, 2 and to the pressure cylinder
3, the two side walls 115 and the front wall 215 and bottom wall 315 of the air cushion
zone followed by a controlled decompression section 15, may be arranged on a carriage
27, while the glueing roller 7, metering roller 8, sealing roller 16, approaching
roller 10 and respective pressure roller 11 may be supported by the side walls 115
or remain in a pre-set position on the main body of the corrugating unit. The carriage
27 is slidable on rails 28 arranged transversely of the corrugating cylinders 1 and
2 and pressure cylinder 3, whereby it may be moved away from these cylinders 1,2,3
together with the rollers 7,8,10,11,16. The leaking of air between the side walls
115 of the carriage-supported assembly 15 and the fixed walls of the apparatus may
be easily reduced by means familiar with those skilled in the art.
[0023] Between the approaching roller 10 and pressure cylinder 3, that is between the zone
of pre-engagement of the corrugated paper with the liner and the zone of definitive
glueing and bonding thereof, the single-faced corrugated board being formed passes
through a decompression section 29 communicating with the atmosphere. In this section
29, the adherence of the corrugated paper against the corrugated surface of the central
corrugating cylinder 1 is ensured by the liner board which is placed over said corrugated
paper. Therefore, in the decompression section 29, any air enclosed and entrapped
within the corrugations of the corrugated board upon said pre-engagement step at the
approaching roller 10 is ejected and its pressure is reduced quickly and continuously
to atmospheric pressure. Therefore, at the sector of the central corrugating cylinder
2, corresponding to the decompression section 29, a progressive and uniform approach
will be effected between the corrugated paper and liner board, which will be already
associated with each other at the nip between the central corrugating cylinder 2 and
pressure cylinder 3, and the latter then causes the final bonding thereof.
[0024] The central corrugating cylinder 2 is provided with shallow annular grooves 102 to
establish the communi= cation between the atmosphere and the interstice between the
surface of the central corrugating cylinder 2 and the corrugated board adhering against
said surface, and to permit the continuous evacuation of the air existing between
the central corrugating cylinder 2 and the corrugated board and of the air seeping
through said board at the air cushion zone 15. The amount of air seeping through the
corrugated board and evacuated to the atmosphere, anyway, is relatively small, whereby
said annular grooves 102 may be very narrow and in small number.
[0025] Of course, the invention is not limited to the embodiment here shown and described,
but broad changes and modifications may be made thereto, especially of constructional
nature and within the scope of technical and operational equivalents, without departing
from the basic principle set forth above and claimed hereinafter.
1) A corrugating unit for an apparatus for manufacturing corrugated board, comprising
two cooperating corrugating cylinders, namely an inlet cylinder and a central cylinder,
both having a corrugated configuration, the paper to be corrugated being passed therebetween
and the corrugated paper coming out from the pair of corru= gating cylinders being
kept in engagement with the corrugated configuration of the central corrugating cylinder,
where the tips or ridges of the corrugated paper receive glue by means of a glueing
unit, whereafter the corrugated paper or medium is associated with a liner and is
passed together with it between the central corrugating cylinder and a pressure cylinder
cooperating therewith, characterized in that the contact of the corrugated paper with
the corrugated surface of the corrugating cylinder is determined by an air cushion
applied to the outside face of the corrugated paper, i.e. to the face thereof opposite
to that which is being engaged with the central corrugating cylinder.
2) A corrugating unit according to claim 1, characterized in that said air cushion
applied to the outside face of the corrugated paper on at least the sector of the
central corrugating cylinder included between the contact zone of said central corrugating
cylinder with the inlet corrugating cylinder and the area where the liner is placed
on the glue-coated corrugated paper.
3) A corrugating unit according to claim 1, characterized in that said liner is applied
to the corru= gated paper and pre-bonded thereto, i.e. it is merely approached with
a slight contact to the corrugated paper, by means of a suitable approaching roller
arranged between the glueing unit and the pressure cylinder, and the air cushion is
applied to the corrugated paper at the central corrugating cylinder sector included
between the contact zone of the central corrugating cylinder with the inlet corrugating
cylinder and the area where the liner is approached to the corrugated paper by means
of the approaching roller, while downstream of said zone to the area where the corrugated
paper is bonded to the liner, i.e. at the central corrugating cylinder sector included
between the approaching roller and pressure cylinder, the single-faced corrugated
board being formed is processed at atmospheric pressure in a decompression ambient
(zone).
4) A corrugating unit according to claim 1, characterized in that on the side of the
central corru= gating cylinder with which the corrugated paper is in contact, there
is provided an air cushion zone followed by a controlled decompression section extending
from at least the contact area of the central corrugating cylinder and inlet corrugating
cylinder to the area of pre-bonding' of the corrugated board and liner by means of
an approaching roller, and said air cushion zone is connected to means for continuously
feeding into into said zone air at a pressure slightly higher than atmospheric pressure.
5) A corrugating unit according to claim 4, characterized in that the air cushion
zone followed by a controlled decompression section is situated within a structure
enclosing the glueing unit and connected to the inlet corrugating cylinder by means
of a roller and doctor blade, and to the approaching roller by means of pressure roller
and a doctor blade.
6) A corrugating unit according to claim 5, characterized in that the structure enclosing
the air cushion zone followed by a controlled decompression section may be moved away
from the inlet and central corrugating cylinders and from the pressure cylinder, preferably
but not necessarily together with the sealing roller, approaching roller and respective
pressure roller.
7) A corrugating unit according to claim 1, characterized by means for maintaining
the communication from the interstice between the corrugated surface of the central
corrugating cylinder and corrugated paper to the atmosphere with continuous evacuation
of the paper dust and consequent cleaning effect.
8) A corrugating unit according to claim 1, characterized by the fact that the system
fro holding the corrugated paper by means of an air cushion generates an optimum plasticization
(conditioning) of the paper to be corrugated due to the formation of condensate generated
by the contact of the ambient air with the heated surfaces of the corrugating and
press cylinders having at their interior superheated steam at 14/16 Ate (180°C).