JP4656946B2 - Heated cylinder - Google Patents

Description

  The present invention provides a paper, paperboard, thin paper or other fiber web in a machine for producing and / or finishing a fiber web having a cylinder shell that is heated at least partially from the inside and / or partially within the cylinder shell. It relates to a heated cylinder for drying.

  In these heated cylinders, a temperature gradient towards the cylinder surface is established during operation as a result of the release of heat to the fibrous web. Tensile stress is created on the cylinder surface because of the more thermally induced expansion of the inner area of the heated cylinder.

  The thermal energy that can be transferred from the inside to the outside per unit surface is limited so that these thermal tensile stresses do not exceed the allowable strength value.

  The object of the present invention is therefore to minimize these tensile stresses in a heated cylinder without reducing the movable thermal energy.

  According to the invention, the object is that the cylinder shell comprises at least two shell layers, the material of the outer shell layer being higher than the material of the inner shell layer, with a higher thermal expansion coefficient and average operating temperature at an installation temperature below the average operating temperature Is achieved by having a lower coefficient of thermal expansion at installation temperatures above and / or that the layer thickness of the outermost shell layer is less than the layer thickness of the inner shell layer.

  For cylinder shells with only two shell layers, the average operating temperature is defined as the temperature within the contact area of the shell layer, and for more than two shell layers, during normal operation of the cylinder drying the fiber web Is defined as the average of the inner and outer surfaces of the cylinder shell.

  The result is minimization of stresses in the heated cylinder under the temperature distribution that occurs during cylinder operation.

  In the case of the outermost shell layer, there are also restrictions on material selection from an economic point of view, since there are specific requirements, especially regarding hardness. As a result, if the outer shell layer must be made of a material having a relatively low thermal conductivity, its thin, yet proper thickness, will reliably transfer heat towards the fibrous web.

  However, due to the loading of the inner shell layer, a minimum limit is imposed on the thickness of the outermost shell layer.

  Therefore, additionally or alternatively, stress can be reduced by appropriately selecting the material for the coefficient of thermal expansion, elastic modulus, thermal conductivity, thickness relationship, material quantity distribution and connection between shell layers. It may also be advantageous to reduce.

  When the installation temperature is less than the average operating temperature, the outermost shell layer is surely expanded to a greater extent than the inside when heated.

  In other cases, for example during welding of the shell layer, the installation temperature exceeds the average operating temperature. In this case, it should be taken into account that low stress annealing, which is preferably followed, cannot completely eliminate the stress between the shell layers. Generally, in this case, each outer shell layer should be kept from shrinking more than the inside when it cools after installation. In this case, the minimum value of stress must be reached in the temperature distribution that occurs during operation of the cylinder.

  This means that each inner shell layer will expand less than before and / or the outer shell layer located above it will expand more than ever. Preventing expansion in one layer inevitably leads to increased expansion in adjacent layers. By considering the higher temperature in each inner shell layer, the material combinations and thickness relationships can even be chosen so that the same degree of expansion is established in the inner and outer shell layers, respectively.

  For example, heating is performed by steam from the inside, or by a heating medium guided to the inside through a channel or between shell layers.

  To simplify the structure, the cylinder shell includes two shell layers. However, to improve stress dissipation, the cylinder shell can also include more than two, preferably more than four shell layers. In this case, the outer and inner shell layers are also arranged in the cylinder shell. What is important for the names “inside” or “outside” is simply the question of which shell layer is placed on top of the other.

  In particular, to avoid friction and damage during rotation of the heated cylinder, the shell layer must be fixed at least against relative rotation. This can be done by welding, screwing or other adhesive bonds.

  Furthermore, it is advantageous that the material of the outermost shell layer has a higher thermal conductivity than one of the inner shell layers, preferably all materials. This reduces the temperature gradient in the outer shell layer, and hence the tensile stress in the outer shell layer.

  It is also advantageous for reducing the tensile stress if the material of the outermost shell layer has a lower elastic modulus than the material of the preferred inner shell layer.

  The advantages with regard to thermal conductivity and weight are in particular when at least the intermediate and / or outermost shell layer is made of aluminum.

  Due to the high requirements regarding wear and smoothness of the cylinder shell, the outermost shell layer must be made of a hard material, for example a hard material in the range of 170-220 HB hardness.

  It may be advantageous if the inner shell layer is configured as a load bearing layer so that in the best way the requirements concerning the coefficient of thermal expansion, thermal conductivity and hardness in the outermost layer can be met.

  Such a heated cylinder can be used in particular as a drying cylinder in a drying section for drying and as a press roll in a pressing section for dewatering the fiber web.

  The invention is explained in more detail in the following text using exemplary embodiments. In the accompanying drawings, the figures show a schematic cross section across a drying cylinder.

  The drying cylinder has a metal cylinder shell, and the inside 2 of the heated cylinder is heated with steam. The heat energy introduced by the steam is transmitted to the outside through the cylinder shell and is used for heating and drying the fiber web 1 wound around the drying cylinder.

  In this case, the fiber web 1 is usually pressed against the circumferential surface of the drying cylinder by a dryer cloth.

  This heat transfer results in a temperature gradient toward the outer shell surface and thus also in the outer region. In order to reduce these tensile stresses, the cylinder shell includes two shell layers 3, 4 of different materials.

  The outer shell layer 4 is made of a material having a higher thermal expansion coefficient than the material of the inner shell layer 3. As a result, the outer shell layer 4 expands much more than before despite the low temperature of this layer, leading to a reduction in tensile stress.

  This dissipation of stress is further promoted by the fact that the thermal conductivity of the outer shell layer 4 is higher than that of the inner shell layer 3 and the elastic modulus is lower than that of the inner shell layer 3.

  The shell layers 3, 4 are implemented as tubes joined together by screwing.

Figure 3 shows a schematic cross section across a drying cylinder.

Claims (8)

For heating paper, paperboard, thin paper or other fiber webs in a machine for producing and / or finishing fiber webs having a cylinder shell heated at least partly from the inside and / or partly in the cylinder shell A heated cylinder of
The cylinder shell includes at least two shell layers (3, 4), and the material of the outer shell layer (4) has a higher coefficient of thermal expansion at an initial temperature below the average operating temperature than the material of the inner shell layer (3). together with, has a lower thermal expansion coefficient at the initial temperature above the average operating temperature, or the outermost shell layer (4) is characterized in that it is made of a hard material ranging 170~220HB hardness Heated cylinder.     The heated cylinder according to claim 1, characterized in that the cylinder shell has at least two shell layers (3, 4).     2. A heated cylinder according to claim 1, characterized in that the cylinder shell has three or more, preferably four or more shell layers (3, 4).     A heated cylinder according to any one of the preceding claims, characterized in that the shell layer (3, 4) is fixed at least against relative rotation.     5. The material according to claim 1, wherein the material of the outermost layer (4) has a higher thermal conductivity than one of the inner shell layers (3), preferably all materials. The heated cylinder as described.     The material of the outermost layer (4) has a lower modulus of elasticity than one of the inner shell layers (3), preferably all materials. Of heated cylinders.     A heated cylinder according to any one of the preceding claims, characterized in that at least the middle and / or the outermost shell layer (4) is made of aluminum.     A heated cylinder according to any one of the preceding claims, characterized in that the inner shell layer (3) is configured as a load bearing layer.

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