Note: Descriptions are shown in the official language in which they were submitted.
r ~ CA 02229214 1998-02-10
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E, ~ T~S a~ ~ [38800/477]
T~ TF~AN~LAT~ON
~OLLER
The invention relates to a roller of the type corresponding to the preamble of
Claim 1.
Such rollers are used in many different ways for treating the webs in question,
particularly for glazing and satin-fini~hin~ paper. In this case, a roller with an
5 elastically resilient coating works together with a heated counter-roller that has a
smoothly polished roller circumference made of steel, as presented in DE 30 20 669
Al, for example. The elastically resilient coating can be comprised of plastic with a
radial thickness of about 10 mm to 30 mm. In earlier times, in particular, the
elastically resilient rollers were structured as so-called paper rollers, ring-shaped disks
10 of paper being lined up one behind the other on the roller body, and compressed
between end disks made of steel, under high axial pressure, to form a compact surface.
The paper rollers are buffed, so that they have a precise cylindrical circumference
surface. The paper covering has properties which are particularly advantageous for the
process of glazing or satin-fini~hin~ paper. In the calender or in the glazing unit, the
15 paper rollers are generally used alternating with hard rollers with a steel surface, which
are heated if necessary. Predomin~ntly, therefore, a soft roller and a hard roller are
paired together in the roller nip of a calender or a glazing unit.
The actual glazing effect occurs on the side of the heated "hard" roller, while
hardly any change in the paper is found on the side of the "soft" roller. The soft roller
20 is used to ensure a certain resilience in the roller nip. The incoming paper web has an
int~rn~l structure with thicker and harder spots. If such a paper web were to be glazed
between two hard rollers, a so-called grease effect could occur in the paper, with the
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harder spots being forcibly made level and therefore demonstrating a certain g~ cinesc
and, under some circumstances, even a dark discoloration. These effects come about
due to overly high pressure at the denser spots of the paper, which are avoided by the
interaction of a hard roller with a soft roller.
In order to achieve the necessary overall effect on the paper web, it is alreadyknown from DE 32 01 635 C2 to have two pairs of rollers act on the paper web, one
immediately after the other, where the contact of the soft roller can take place from the
same side of the paper web if the aim is to protect the soft coverings which are subject
to the milling work, and the desired effect is to be achieved in two steps, or from
different sides if the paper is to be given the desired surface improvement on both sides
at the same time.
In the known devices for creating glaze and shine, the soft roller actually hardly
participates at all in the desired effect, but rather only has the function of protecting the
paper web. This has the result that in many cases, several roller nips are necessary in
order to achieve the desired effect.
The invention is based on the task of structuring a roller of the type indicated,
in such a way that it can be included to a greater extent in the treatment process of the
web, particularly the paper web.
This task is accomplished by means of a roller of the type corresponding to the
preamble of Claim 1.
With regard to elastic resilience, it is possible to ensure that the conditions are
similar to those for a roller provided with a plastic coating, for example of harder
polyurethane, by means of a suitable selection of the soft metal. In the presentconnection, the term "soft metal" is intended to mean metals whose modulus of
elasticity amounts to several times the modulus of elasticity of the usual plastic
coatings, but which still possess sufficient resilience and elastic memory to be able to
exercise the function of reducing pressure stress peaks in a substrate such as paper,
when used as a roller coating, if this paper is being glazed bet~veen a roller coated with
"soft metal" and a hard roller.
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The decisive point of the soft metal coating, however, is that a roller with a
metal coating is far superior to a roller with a plastic coating with regard to heat
conductivity. Such a roller can therefore influence the amount of heat transferred
between the web and the roller in a completely different way than a roller provided
5 with a plastic coating, or a paper roller.
This property is particularly effective if the roller is heated from the inside and
heat is to be transferred to the web surface through the coating. This works to a much
greater extent in the case of a metal coating than in the case of a plastic or paper
coating.
In accordance with Claim 2, possible soft metals are those with a melting point
of more than 200 ~C and a lrnodulus of elasticity of less than 80,000 N/mm2,
particularly less than 20,000 N/mm2 (Claim 3).
The 200 ~C limit is determined by the maximum surface temperatures of
rollers for treating paper, plastics, and the like which occur at present. The upper limit
15 for the modulus of elasticity ensures that the elastic resilience is still present to a
sufficient degree and is comparable in its function to a coating of plastic or paper.
Important exemplary embodiments for soft metals to be used according to the
invention are those such as lead and/or m~gnesium and/or alllminllm (Claim 4). Lead
has a melting point of 327 ~C and a modulus of elasticity of about 17,500 N/mm2,20 magnesium has a melting point of about 650 ~C and a modulus of elasticity of about
29,000 N/mm2, alllminnm has a melting point of approximately 660 ~C and a modulus
of elasticity of about 77,000 N/mm2.
For an optimum adjustment of the mechanical properties of the coating, pure
metal will not be used in most cases, but rather a suitable lead and/or magnesium
25 and/or alllminllm alloy will be used (Claim 5).
Possible lead alloys are, for example, materials such as hard lead, diecasting
alloys with a lead base, and bearing metal with a lead base.
It is also possible to use an alloy which contains lead and/or magnesium, in
which lead and/or magnesium and/or aluminum are not the base material, but rather
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only an additive to an alloy structured in some other way (Claim 6).
The thickness of the soft metal coating can correspond approximately to the
thickness of a conventional plastic coating, and amount to 5 mm to 20 mrn (Claim 7),
particularly 10 mm to 15 mm (Claim 8).
For producing the lead coating on the cylindrical roller body, all suitable
known methods can be used. For example, in accordance with Claim 9, the coating
can be applied to the roller body in the melted, fluid state, for example by way of lead
dipping, or by means of processes similar to application welding, or by spraying.
In accordance with Claim 10, however, the coating can also be applied to the
10 roller body in the forrn of molded parts, which are soldered to the roller body and, if
necessary, to each other.
One possibility, for example, is winding on strip-shaped extruded profile
material made of the soft metal, in the manner of DE 25 45 146 Al, DE 27 22 023 Al,
or DE 27 26 812 Al. However, rings which correspond to the diameter ofthe roller15 body can also be put on and soldered to the latter and to each other, at their faces.
Finally, it is also possible to bend plates in accordance with the circumference of the
roller body and to affix them there.
The roller provided with the coating of soft metal is subsequently turned and
buffed, so that it obtains a clean, sealed cylindrical surface.
To improve the elastic properties of the soft metal, the latter can be dispersion-
hardened (Claim 11).
An ~ltern~tive possibility consists of using amorphously solidified soft metal,
which is obtained by leaving a soft metal melt on a very cold counter-surface, for
example a cooled drum, or spraying it on (VDI-Nachrichten (1985), Issue 22 datedMay 31, 1985, page 6). The undercooled metal layers, i.e. the flat metal layers which
solidified before reaching a crystalline arrangement, can be joined together to form
thicker units which result in the coating.
An important further development is the subject matter of Claim 13. The
porous structure results in advantageous elastic resilience for the treatment purpose,
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because of the reduced bealing cross-section, in spite of the metallic material, i.e.
material with good heat conductivity. The existing forces are concentrated on the
material framework present between the pores, and result in higher deformations there,
in accordance with the higher stresses at a specific force.
The porous structure can be produced by means of a sintering process (Claim
14). A possible embodiment is ~interin~ together small hollow spheres of the soft
metal at their outside circurnference (Claim 15), which makes it possible to lower the
total modulus of elasticity of the coating below the value of the compact metal. In
order to make this particularly effective, small hollow spheres with a relatively low
10 wall thickness according to Claim 16 are recommencle-l Alnmim-m is of particular
significance for the small hollow spheres.
The porous structure can also be brought about by foaming up a metal melt
(claim 17) (VDI-Nachric*ten (1995), No. 37 dated September 15, 1995, page 24),
which results in a metal sponge.
However, a coating of a soft metal in the form of micro-honeycombs (Claim
18) is also included in the concept of the porous structure, these can be obtained by
corresponding deformation of metal foils and are known from catalyst technology. It
is practical if the micro-honeycombs, which have a hexagonal cross-section, for
exarnple, stand radial to the roller with their axis.
In the porous material, the remS~ining cross-sections and therefore the heat
conductivity are reduced as compared with a solid m~tf~ri~l In order to balance this
out, it can be recommenclecl that the pores are at least partially filled with a heat-
conductive material different from the m~teri~l ofthe coating (Claim 19).
In most instances, the rollers in question work at elevated temperatures in the
25 range of up to about 200 ~C. They cool down to ambient temperature during thebreaks in operation. In order not to have severe heat stresses occur in connection with
these temperature differences, which could cause the coating to come loose from the
cylindrical roller body over time, the development according to Claim 20 is
recommen(le~l, where an alllmimlm material is suited as the carrier material for the
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possible soft metals (claim 21).
The webs exert a significant wear effect on the processing surface of the roller,
particularly if they consist of paper and contain mineral components. The unprotected
soft metal surface would not withstand this effect for long.
It is therefore recommen~led that the coating in turn have a thin coating of a
wear-resistant material (Claim 22), e.g. hard materials (Claim 23).
Possible hard m~tPri~l~ are, for example, carbide m~t~ri~lc such as tnn~t~n
carbide, chrome carbide, and ~il~iulll carbide, or oxide materials such as Al203,
AlTiO3, liL~~ l oxide, chrome oxide, and the like. Processes are known to enable10 application of such coatings on substrates, in a thin layer, without using particularly
high temperatures. Such coatings are used successfully, for example, for cuttingmaterials.
In the massive form, the m~teri~l~ mentioned are very brittle. In a thin layer,
however, they are very elastic and are able to follow the deformations of the soft metal
15 nntlernP~th them without breaking or splintering. Since this elasticity depends on the
thinne.~ of the layer and the accompanying freedom of the structure from defects, a
thickness of the coating layer of less than 50 My is recommenclc~l, in accordance with
Claim 24, in many cases even one of less than 10 My (Claim 25).
The point of dt;~al lu.~ of the invention and its significant case of application is
20 paper-gl~7ing The invention is also embodied in a gla7ing unit for treating paper, in
accordance with Claim 26.
Here, the known "soft" roller with a plastic coating, as in DE 30 20 669 A1 and
DE 32 01 635 C2, for example, is replaced with a roller with a coating of a soft metal,
which allows significantly greater heat transport from the interior of the heated roller
25 to the back of the paper web which lies opposite the heated steel roller. In this way, a
treatment effect is also brought about on this back of the paper web, and the "soft"
roller is included in the treatment function. In some cases, this will make it possible to
avoid double arrangements of roller pairs to achieve a sufficient one-sided or double-
sided effect, and to achieve sufficient gla_ing for some types of paper in only one roller
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nip.
The tre~tment effect can be inten~ified if two rollers of the type according to
the invention work against one heated steel roller (claim 27).
The drawing shows an exemplary embodiment of the invention.
Fig. 1 shows a detail of the border region of the roller, indicated in Fig. 2 with
I, where the coating is cut open in a plane passing through the axis;
Fig. 2 shows a view of a roller pair, the top roller being structured according to
Fig. 1.
The roller indicated as a whole with 10 in Fig. 1 comprises a cylindrical rollerbody 1. This roller body 1 can be a solid roller with or without internal channels for
hc~ting However, roller body 1 can also be a hollow roller of a deflection-controlled
roller, which is hydraulically supported from the inside and which can be heated from
the inside by means of the hydraulic fluid which serves to support it, or by means of an
additional heat carrier fluid.
Fig. 1 shows only a detail of a region of cylindrical roller body 1, close to the
surface. In practice, roller body 1 can have a diameter from 500 to 1000 mm.
Roller body 1 carries a coating 2 with a uniform thickness over the entire
surface, which is comprised, in the exemplary embodiment, of a lead alloy which is
soldered at border surface 3 to the outer surface of cylindrical roller body 1, as
indicated by heavier line 6. Soldering is only possible if coating 2 was previously
present as a molded part. If coating 2 is applied in the melted, fluid state, 6 refers to
the connection surface with cylindrical roller body 1.
In the exemplary embodiment shown, thickness 7 of coating 2, i.e. its radial
çxr~n~e, is 12 mm.
On its outside circumference, coating 2 possesses a thin coating 4 of tlmp~ten
carbide, outside 5 of which forms the processing surface of the roller and is intçn(le~l to
reduce the wear effect on the soft lead alloy of coating 2. The thickness of coating 4 is
shown in exaggerated manner in Fig. 1. In fact, it is only on the order of about 10 My.
Fig. 2 shows a case of use of roller 10, in the form of a two-roller glazing unit
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100 with rollers 10 and 20, which together form a roller nip 8, through which a paper
web 9 is passed.
Top roller 10 can be deflection-controlled and heated, and possesses a coating 2of a lead alloy with a wear-resistant coating 4, as shown in Fig. 1. Bottom roller 20 is
5 a roller which can be heated, with a polished circumference made of chilled cast iron.
While there was hardly any participation of the soft roller in the glazing process
in the known roller pairs in glazing units, in which one roller had a coating made of
plastic, because of its poor heat conductivity, coating 2, if it consists of a lead alloy,
conducts the heat from the interior of heated roller 10 to the surface of the paper web
10 practically in the same manner as is the case for hard roller 20 with the steel surface.
In this way, the total amount of heat transferred to the paper web is significantly
increased, on the one hand, and in particular, an effect on the back of paper web 9,
which lies opposite roller 20, also takes place, resulting in increased smoothness there,
also.
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