Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to an apparatus used
in a paper machine for improving the surface smoothness and gloss
of the paper or cardboard, which apparatus comprises one or
several smoothing means, the operation of which is mainly based
on a rubbing action directed to the surface of the web to be
smoothed.
Conventionally, the surface smoothness and gloss of
paper are achieved in a paper machine by a calender treatment
subsequent to the drying process. Without such treatment, the
surface of the paper web remains more or less uneven and rough.
This unevenness is due to the paper manufacturing process. At
its forming phase in the web end of the paper machine the paper
is in contact on one or both sides wire and felt fabrics so that
these cause in the paper web surface the so-called marking, that
is a pattern consistent with the structure of the fabrics in
question. In part, the unevenness and roughness of the paper
result from shrinkage and crumpling of the paper during the
drying process.
The calender treatment may be accomplished either with
a machine calender, placed in the paper machine between the drying
cylinder section and the reeling attachment, or with a separate
so-ca~led super-calender, which belongs to the paper after-
treatment equipment. The smoothing and burnishing action both
in the machine calender and in the super-calender is based on
compression and deformation work exerted on the paper web in
the nip defined by the rolls. There is no difference of velocity
between the calender rolls and the web in the said nips. The
eff~ct produced by the machine calender and the super-calender
is apparent not only as increased smoothness and gloss of the
paper but also as a considerable reduction in thickness of the
paper and equalization of its thickness variations, which is a
consequence of the pressure exerted on the web in the nip.
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A friction calender was widely used for one-sided
burnishing of cardboard and of certain so-called high gloss
special papers. The usual friction calender comprises two rolls,
one of them an elastic paper roll and the other a glossy chill-
cast roll. The latter is rotated at a peripheral velocity
2 to 4 times that of the paper roll. The paper web or cardboard
passes through the nip defined by the opposing rolls. In the nip
the chilled roll, which has a speed higher than that of the
web, causes a burnishing action on the surface of the web which
is turned towards this chilled roll. If it is required to burnish
the web on both sides, it has to be run twice through a pair of
calender rolls. It is also possible to install two calenders one
after the other, one of them for the top side and the other for the
underside of the web to be burnished.
There have been other proposals for smoothing papers
webs, such as, for example, in German patents nos. 527,130 and
597,449.
Calender treatment is necessary in particular for
writing and printing paper. In the case of writing paper and of
paper on which mainly text is going to be printed, a machine
calender treatment may suffice. For accurate reproduction of
illustrations or multicolour printing, the paper is required
to possess high surface smoothness and frequently also gloss at
the same time. In such cases a paper smoothing and burnishing
treatment effected with a separate so-called super-calender is
necessary.
~ n object of the prescnt invcntion is to providc a
simple apparatus easily incorporable in the normal operation and
construction of a paper machine for improving the gloss and
smoothness of the web.
Another object of the invention is to provide an
apparatus which makes the use of a separate super-calender
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dispensable.
A further object of the invention is to provide an
apparatus for improving the gloss of the cardboard while simul-
taneously preserving, to such an extend as possible, the
stiffness of the cardboard in the paper machine direction.
These objects are achieved with an apparatus comprising
one or several smoothing means, which apparatus is characterized
in that each of the smoothing means is placed against at least one
drying cylinder of the paper machine and extends over the whole
breadth of the web to be smoothed in a direction parallel to the
axis of said cylinder and in that each of the smoothing means
comprises a supporting beam carried by the frame of the paper
machine and a smoothing member extending along the supporting
beam. The smoothing member consists of hard metal or ceramic
microporous material is urged by force means associated to the
supporting beam, against the web to be smoothed passing on the
drying cylinder of the paper machine.
Usually the smoothing member is a non-rotating member
having a shoe-like cross-section. To prevent it getting hot and
wear locally, it must be slowly reciprocating around its axis.
This reciprocating smoothing shoe-like may be replaced
in certain instances which is carried on the supporting beam so
as to be rotatable.
In this case, no external means need to be connected
to the axis of this roll member to rotate it. On the contrary,
the rotation movement, which is caused by contact of the member
against the paper surface, is braked by suitable (regulatable)
means so that the peripheral velocity of the roll is appreciably
lower than that of the web to be smoothed and the desired friction
effect is achieved.
The preservation of the stiffness of the cardboard
in the machine direction, which was mentioned as an object
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of the invention, is ~ossible because the burnishing of the
cardboard takes place on one or several drying cylinders with
the aid of smoothing means according to the invention. It is
thus understood that the cardboard web is not forced to lap
rolls of comparatively small diameter as are calender rolls
which could cause loss of part of its stiffness.
The invention and the advantages gainable thereby
will be better understood with reference to the following non
restrictive description of several embodiments, taken in connec-
tion with the attached drawing, wherein:
Fig. l shows two embodiments of apparatuses according
to the invention and their mechanical operation principle,
mounted on a conventional machine calender;
Fig. 2 shows an embodiment of the apparatus according
to the invention wherein the smoothing member is a rotating
smoothing roll;
Fig. 3 shows an apparatus according to the invention,
applied in connection with a drying cylinder in a paper machine;and
Fig. 4 shows a schematic axial section of another
embodiment of the apparatus according to the invention provided
with means for oscillating the su?porting beam of the smoothing
member and the smoothing member in axial direction.
Fig. 1 shows a conventional machine calender having
a frame (not depicted) either of the so-called open or closed
type. Drying rolls 10, 11, 12, 13, 14 and 15 are provided with
a very hard and wear-resistant surfacing. As top and bottom rolls
lO, 15 in the calender, rolls which are compensated as regards
their deflection may be used. In special cases the intermediate
rolls 11, 12, 13 and 14 may also be deflection-compensated. The
web to be smoothed, 20, passes through the calender in serpentine
manner, a~ shown in dotted line.
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Fig. 1 also shows in association with the machine
calender, four smoothing means, one in a,ssociation with each
intermediate roll 11, 12, 13 and 14. The smoothing means
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comprises a supporting beam 30, which is e.g. a box-type beam.
The supporting beams 30 are affixed to the frame structure at
their ends by means of axle pins 31. Each supporting beam is urged,
most appropriately with adjustable force means against each roll
and the web to be smoothed, 20, passing over it.
The supporting beams 30 extend over the whole breadth
of the web 20, and their longitudinal axes are parallel to the
axes of the rolls 10 to 15. On the side of the supporting beams
30 adjacent to the rolls 11 to 14 a smoothing member 32 or 33 is
affixed, which is of a material chosen from the group consisting
of hard metals and ceramic substances such as silicium carbide,
aluminium oxide, etc., which are commercially commonly available
and which all have the characteristic feature, among others, of
a microporous surface, by which a suitable smoothing and burnish-
ing effect is obtained. For different paper grades, materials
with different porosities can be chosen. In the example represented
in Fig. 1, the web 20 passes so that it is subjected to the
effect of the smoothing member 32, 33 on both sides alternatively.
Fig. 1 shows, only in connection with the topmost
smoothing means 30, the force means by which the smoothing
member 33 is urged against the outer surface of the web 20
passing over the roll 14. This force means comprise an arm 24,
to the lower end of which the supporting beam 30 is attached by
its ends by a axle pin 31. The upper end of the arm 24 is mounted
with a pivot 22 to the frame of the paper machine. The piston
rod 21 of a power cylinder 19 is connected to the arm 24. By
the power cylinder 19 the smoothing means 32 is urged against
the web 20. The final result of the smoothing operation can be
affected by pressure adjustment of the power cylinders 19.
The smoothing member 32 or 33 is urged against the
moving web 20, so that friction is produced, which increases the
surface smoothness and gloss of the surface of the web 20. It is
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possible to use as smoothing member a rotating smoothing roll 33
or a reciprocating smoothing member having a shoe-type cross-
section 32.
Referring to Fig. 2, the smoothing member consists of a
rotating roll 33 of hard metal or ceramic material, which prefera-
bly has a comparatively small diameter and is supported by the
supporting beam 30 e.g. by means of roller bearings (not shown).
The roll 33 is rotated by friction of the web 20, and
is braked, preferably with an adjustable torque means. Therefore,
the peripheral velocity (Vl) of the roll 33 is substantially smal-
ler than the velocity (V2) of the web 20 passing on the roll 33,
(vl~c V2 ) .
The adjustable torque means may comprise a D.C. brake
51 with controllable speed. The brake 51 is connected to the roll
33 via chains 52 and 53, or equivalent. The roll 16 shown in
figure 2 is a roll of the paper machine to be specified later on.
It is advantageous in some instances if the supporting
beam 30 performs a slow reciprocating motion, that is, oscillates
about its axis 31-31. This movement is achieved by means of hydrau-
lic action means 23. The reciprocating motion is advantageousespecially in association with shoe-like smoothing members 32,
because it allows the whole outer surface of the smoothing
member 32 to be efficiently utilized and caused to wear uniformly,
and to keep the temperature of the smoothing member 32 from
rising locally to excessive calues. To this end, the outer surface
of the smoothing member 32 is curved so that the centre of its
radius of curvature R lies on the axis 31-~1.
The supporting beams 30 of the smoothing members 32,
33 may also reciproque axially as illustrated in Fig. 4. The
supporting beam 30 is at one end joined with a pivot 26 and a
lever arm 29 to a lever arm 28. The other end of the supporting
beam 30 is acted on e.g. by a hydraulic means 27, which produces
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a reciprocating motion of the supporting beam 30 in the direc-
tion of the arrow B. The supporting beam 30 is carried by
appropriate guides to enable its reciprocating motion.
The roll 17 shown in Fig. 4, which has journal pins
18, is a drying cylinder.
In order to achieve a continuous surface extending
over the whole breadth of the paper machine or of the web to be
manufactured therewith, it the smoothing members32 and 33
are advantageous assembled of a series of elements 32a, 32b and
32c side by side as shown in Fig. 4.
Fig. 3 shows a smoothing apparatus according to the
invention in association with the last two drying cylinders 35
in the drying section of a paper machine. It should be remembered
that the conventional drying section comprises drying cylinders
in two superimposed rows, alternatively interstitial to each
other. The web 20 travels part of its path between the surface
of the heatable drying cylinders 35 and the drying felt, in a
manner shown in itself in prior art. The guiding rolls for the
drying felt 36 have the reference numeral 37 and the web guiding
roll, the reference numeral 39. The rolls 33 serving as smoothing
member have been positioned to press against the web 20 on the
last drying cylinders 35 of the drying section. However, the
smoothing members may in principle be mounted in connection with
any drying cylinder 35, or they may be mounted on one or even on
more than two drying cylinders. The higher the moisture content of
the web 20, the easier is it to influence its surface smoothness.
On the other hand a remarkably wet web tolerated only little
friction, and therefore in connection with a wet web 20 only a
rotating smoothing roll 33 of Fig. 2 has to be employed as
smoothing member. In the embodiment example of Fig.3 the web 20
will be smoothed on both sides.
In the embodiment of the invention presented in Figs.
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3 the supporting beam 30 of the smoothing member 32, 33 can be
oscillated with means as shown in Figs. 2 and 4. In this regard
it should be noted that the force means shown in Figs. 2 and 4
the said means have been shown in a highly schematic way and in
actual practice they may even greatly differ from those shown in
the figures.
It is advantageous if the surface of the smoothing
member 32, 33 treating the topside of the web 20 has a micro-
structure finer than that of the surface of the smoothing member
32, 33 treating the wire side.
The smoothing and burnishing effect of the ceramic
material used according to the invention in the smoothing members
is in part at least based on the fine porosity of the material.
In the manufacturing of different paper and cardboard
grades the porosity of the smoothing member is chosen in accordance
with the particular type of paper and its quality. Moreover,
the number and placement of the smoothing members can be varied
to obtain in each case exactly such surface characteristics of the
paper or cardboard as are desired, and these characteristics
may further be influenced by adjusting the contact pressure between
the web 20 and the smoothing member 32, 33 and by selection of
the differential velocity (v2-vl) between the web 20 and the
surface of the smoothing member 33. It is thus understood that
there are several factors which can be varied in order to affect
the smoothness and gloss of the paper or cardboard that is
being produced.
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