EP2474665A1 - Drying cylinder for a tissue paper machine - Google Patents

Abstract

The drying cylinder has a hollow roll body (1) made of cast iron solidified gray with freely stored graphite. The graphite is provided as spherical graphite. A hard material layer (4) is applied on an outer extent surface (3) of the hollow roll body.

Description

The invention relates to a drying cylinder for a tissue paper machine, in particular a Yankee cylinder.

Drying cylinders for tissue paper machines, also called Yankee cylinders, usually have a hollow roll body, which is poured for usually gray-solidifying cast iron with lamellar graphite. Alternatively, the roll body can also be produced by welding steel sheet. During operation of the drying cylinder, the hollow cast iron body is usually subjected to a water vapor pressure of about 10 bar.

Such drying cylinders are used in the dewatering of fibrous materials (tissue material) from which, for example, paper or cellulose products such as absorbent and soft kitchen towels, toilet paper, baby diapers, crepe paper or the like is produced. In the manufacturing process, a so-called doctor blade abuts on the outer circumferential surface of the roll body, whereby the paper is stripped and crimped from the peripheral surface of the cylinder.

In this process, the doctor blade carries material from the peripheral surface, in particular from the edges of the roll body from. For this reason, drying cylinders must occasionally be sanded down. Frequent sanding can cause the jacket drum's jacket thickness to reach a limit officially set for pressure vessels. In this condition, the drying cylinder usually needs to be replaced. In order to increase the service life of the drying cylinder, a hard material layer may be provided on the outer peripheral surface of the roller body. A hard material layer is understood as meaning a layer of a hard material which has a greater hardness than the material of the roller body.

In the DE 690 07 828 T2 For example, a Yankee cylinder and a method for coating a Yankee cylinder are described. The cladding coating is applied directly to the surface of the shell, which is made of cast iron or steel. Alternatively, an intermediate layer of a martensitic stainless steel is first applied to the mantle surface of the Yankee cylinder, which is then again coated again.

From the DE 10 2004 057 480 A1 is a roller known for the production of tissue material. The roller has a metal core or metal body on which a relatively soft inner layer and a relatively hard outer layer are applied. Both the inner and outer layers are made of solid rubber.

The object of the invention is to provide a coated drying cylinder with improved dry properties for a tissue paper machine, which can be produced inexpensively and procedurally simple.

According to the invention, a drying cylinder for a tissue paper machine, in particular a Yankee cylinder, comprises a hollow roll body of gray cast iron (GJS) with freely embedded graphite, which is present at least substantially as spheroidal graphite, wherein on a outer peripheral surface of the roll body a hard material layer is applied. The cast structure of the roller body is advantageously also in its radially outer region predominantly, preferably at least substantially gray, so solidified solid. Gray solidified cast iron with free embedded graphite advantageously has a higher thermal conductivity than white solidified cast iron, whereby the dry properties of the drying cylinder can be improved. The drying process can thus be made more energy-efficient, that is cheaper and more environmentally friendly. Gray cast iron can also be better worked than white, in particular, including boring.

In particular, the roll body may have a diameter of at least 1.5 m and preferably at most 7 m, preferably at least 4 m and preferably at most 6 m. The roll body may have a length of at least 2 m and preferred not more than 9 m, preferably of at least 4 m and advantageously not more than 7 m. Furthermore, the roll body can have a shell thickness of at least 20 mm and preferably at most 150 mm, preferably at least 40 mm and in particular at most 100 mm. The roller body can form a pressure vessel, which can be acted upon by a pressure, in particular a water vapor pressure, of preferably up to 15 bar. The shell thickness of the roll body can be adapted to the water vapor pressure to be resisted in order to comply with legal requirements for pressure vessels.

In a preferred embodiment, at least one rib, in particular a circumferential rib may be arranged on an inner surface of the roller body. Such ribs provide greater heat transfer and at the same time for a stiffening of the roll body. Preferably, a plurality of ribs, in particular at the same distance from one another, are arranged on the inner surface of the roller body.

In a further embodiment, an inner cylinder, preferably coaxially, can be arranged as a so-called displacer within the roller body. By arranging an inner cylinder, the volume of the roller body to be acted upon with water vapor pressure is advantageously reduced.

Preferably, at least one spacer element can be provided between an inner surface of the roller body and an outer surface of the inner cylinder. Advantageously, a plurality of spacers are provided as axial ribs between the inner surface of the roll body and the outer surface of the inner cylinder, whereby both the heat transfer and the rigidity of the roll body can be improved.

bestimmt werden, wobei die Prozentangaben Gewichtsprozent sind.Advantageously, the roll body is produced by casting against silicon carbide bricks, preferably in a casting of silicon carbide bricks. In the casting process, the cooling rate of the cast body can be adjusted so that the melt solidifies gray even in the peripheral edge zone of the roll body. In particular, the gray-solidified cast iron of the roll body can have a saturation degree S _c of at least 0.8 and at most 1.1, preferably of at least 0.96 and at most 1.003. The saturation level can with $${\mathrm{S}}_{\mathrm{c}}\mathrm{=}\mathrm{\%}\mathrm{C}\mathrm{/}\left(\mathrm{4}\mathrm{.}\mathrm{26}\mathrm{-}\mathrm{1}\mathrm{/}\mathrm{3}\mathrm{*}\left(\mathrm{\%}\mathrm{Si}\mathrm{+}\mathrm{\%}\mathrm{P}\right)\right)$$

are determined, wherein the percentages are weight percent.

In preferred embodiments, the graphite spheres of spheroidal graphite have an average diameter of at least 0.01 mm and at most 0.1 mm, preferably of at least 0.02 and at most 0.04 mm. The precipitation of the graphite in the form of only such small graphite balls is advantageous for the mechanical strength and can be achieved in the casting process by adding seed elements. By a targeted adjustment of the cooling rate, the size of the graphite balls can be controlled.

Spheroidal Graphite Cast Iron (GJS) has higher strength and higher elongation than cast iron with lamellar graphite (GJL). For this reason, the safety factor for spheroidal graphite cast iron (GJS) is lower, so that lower shell thickness of the roll body can be implemented. Lower jacket thicknesses in turn lead to a lower mass moment of inertia of the drying cylinder, resulting in a more favorable energy balance. Advantageously, the proportion of spheroidal graphite on freely stored graphite at least 80 wt.%, Preferably at least 90 wt.%, Amount.

The hard material layer may have a thickness of at least 0.01 mm and preferably at most 1 mm, preferably at least 0.1 mm and in particular at most 0.5 mm. In particular, the hard material layer may comprise a ceramic material, preferably tungsten carbide, or nickel or chromium. The word "or" is understood in the usual logical sense and therefore as an "inclusive or", thus includes both the meaning of "either ... or" as well as the meaning of "and", as far as the respective concrete context exclusively opens only a limited meaning. Accordingly, the hard material layer may comprise a ceramic material, nickel or chromium as a single compound or more of these materials in combination.

In a preferred embodiment, the hard material layer can be applied by means of flame spraying or plasma spraying. Flame or plasma spraying are procedural suitable surface treatments with which articles of different geometry and dimensions can be coated. Especially for a very large-sized roll body, these coating methods have been found to be advantageous. Alternatively or additionally, to form the hard material layer, hard material can be deposited galvanically, electrolytically or autocatalytically on the outer peripheral surface of the roller body.

The hollow roll body is made by casting cast iron. For the mold, silicon carbide bricks or other cooling materials may be used. The casting parameters, such. Thickness of the mold, mold material, inoculant, as well as the cooling rate are adjusted so that the cast iron solidifies as a gray cast iron with spherical spheroidal graphite (GJS). In this way, the advantages listed above regarding the improved drying properties of the drying cylinder are achieved. The invention therefore also relates to a method for producing a drying cylinder in which a hollow roll body is cast from a cast iron, wherein the cast iron solidifies as gray cast iron with spheroidal graphite (GJS), and a hard material layer is applied to the outer peripheral surface of the roll body.

Advantageous features are further disclosed in the subclaims and their combinations.

Fig. 1

einen Walzenkörper eines Trockenzylinders für eine Tissue-Papiermaschine in einem Querschnitt,

Fig. 2

den Querschnitt A-A der Fig. 1,

The invention will be explained below with reference to a preferred embodiment. The features disclosed in the exemplary embodiment advantageously each individually and in each combination of features form the subject matter of the claims and also the embodiments explained above. Show it:

Fig. 1

a roller body of a drying cylinder for a tissue paper machine in a cross section,

Fig. 2

the cross section AA of Fig. 1 .

In the Fig. 1 a hollow roll body 1 of a drying cylinder for a tissue paper machine is shown in a cross section. The roller body 1 has a diameter of preferably at least 4 m and at most 6 m and a length of preferably at least 4 m and at most 7 m. The shell thickness of the roll body is preferably at least 40 mm and at most 100 mm.

The roller body 1 is a cast body of gray cast iron (GJS) with freely embedded graphite, which is present at least substantially as spheroidal graphite. The schematic detail view shown next to the cross section of the roller body 1 illustrates that the hollow roller body consists of gray-solidified cast iron with finely distributed graphite balls 6.

On the outer circumferential surface 3 of the roller body 1, a hard material layer 4 is applied, which has a thickness of preferably at least 0.1 mm and preferably at most 0.5 mm. The hard material layer 4 is advantageously applied by means of flame spraying or plasma spraying of ceramic material. Alternatively or additionally, the hard material layer 4 may comprise galvanically, electrolytically or autocatalytically deposited nickel or chromium or their compounds.

The cavity of the roller body 1 can be subjected to a water vapor pressure of at least 2 bar, preferably at least 10 bar. The hollow roller body 1 thus forms a pressure vessel.

Like from the Fig. 2 it can be seen, circumferential ribs 7 are arranged on an inner surface 5 of the roller body 1 for improving the heat transfer and rigidity of the roller body 1. The circumferential ribs 7 are preferably machined in one piece from the material of the roller body 1. Preferably, the circumferential ribs 7 are arranged at the same distance from each other.

In an embodiment not shown here, an inner cylinder can be arranged coaxially as a displacer within the roller body 1. By means of the inner cylinder, the water vapor pressure to be acted upon volume of the roller body 1 can be reduced. Between the inner surface 5 of the roller body 1 and the outer surface of the inner cylinder, a plurality of axially arranged spacer elements may be provided. The Distance elements can advantageously improve both the heat transfer and the rigidity of the roll body 1.

Claims (15)

Drying cylinder for a tissue paper machine, in particular Yankee cylinder, with a hollow roller body (1) made of gray cast iron (GJS) with freely embedded graphite, which is present at least substantially as spheroidal graphite, wherein on an outer peripheral surface (3) of the roller body (3) 1) a hard material layer (4) is applied. Drying cylinder according to claim 1, characterized in that the roll body (1) has a diameter of at least 1.5 m and at most 7 m, preferably of at least 4 m and at most 6 m. Drying cylinder according to claim 1 or 2, characterized in that the roller body (1) has a length of at least 2 m and at most 9 m, preferably of at least 4 m and not more than 7 m. Drying cylinder according to one of claims 1 to 3, characterized in that the roller body (1) has a jacket thickness of at least 20 mm and at most 150 mm, preferably of at least 40 mm and at most 100 mm. Drying cylinder according to one of the preceding claims, characterized in that the hard material layer (4) has a thickness of at least 0.01 mm and at most 1 mm, preferably of at least 0.1 mm and at most 0.5 mm. Drying cylinder according to one of the preceding claims, characterized in that on an inner surface (5) of the roller body (1) at least one rib (7), in particular a circumferential rib, is arranged. Drying cylinder according to one of the preceding claims, characterized in that an inner cylinder, preferably coaxially, is arranged within the roller body (1). Drying cylinder according to claim 7, characterized in that between an inner surface (5) of the roller body (1) and an outer surface of the inner cylinder is provided at least one spacer element. Drying cylinder according to one of the preceding claims, characterized in that the roller body (1) forms a pressure vessel, which can be acted upon by a pressure, in particular a water vapor pressure, of preferably up to 15 bar. Drying cylinder according to one of the preceding claims, characterized in that the gray-solidified cast iron of the roll body (1) has a degree of saturation (S _c ) of at least 0.8 and at most 1.1, preferably from at least 0.96 and at most 1.003. Drying cylinder according to one of the preceding claims, characterized in that the graphite balls (6) of the spheroidal graphite have an average diameter of at least 0.01 mm and at most 0.1 mm, preferably of at least 0.02 mm and at most 0.04 mm. Drying cylinder according to one of the preceding claims, characterized in that the proportion of spheroidal graphite in the freely intercalated graphite at least 80 wt .-%, preferably at least 90 wt .-%, is. Drying cylinder according to one of the preceding claims, characterized in that the hard material layer (4) comprises a ceramic material, preferably tungsten carbide, or nickel or chromium or their compounds. Drying cylinder according to one of the preceding claims, characterized in that the hard material layer (4) is applied by means of flame spraying or plasma spraying. Drying cylinder according to one of the preceding claims, characterized in that for forming the hard material layer (4) hard material on the outer peripheral surface (3) of the roller body (1) is galvanically, electrolytically or autocatalytically deposited.

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