JPH04300384A - Drying roll having heating surface with uniform temperature distribution - Google Patents

Abstract

PURPOSE:To obtain the subject drying roll having uniform temperature distribution on the heating face and useful for the heating and drying, etc., of paper pulp, film, food, etc., by forming a specific coating layer on the heating face of the outer circumference of a roll. CONSTITUTION:The objective roll is produced by forming a coating layer 2 on the heating face 1 of the outer circumference of a roll. The thermal conductivity of the coating layer in X direction (corresponding to the axial and circumferential directions of the roll) is 1.5-20 times as large as the thermal conductivity in Y direction (corresponding to the radial direction of the roll). The coating layer is a metallic and/or ceramic particle layer 4a,4b composed of flat metal particles 3,3a having an oxide layer on the particle surface.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION This invention relates to a roll used for drying wet paper web in a paper manufacturing process, and particularly to a proposal regarding the structure of a coating layer on the heat transfer surface of the roll. The drying roll of this invention can be used not only for paper pulp but also for fibers,
Suitable for fields that require heat transfer processing such as heating, drying, cooling, and freezing of films, polymer membranes, foods, pharmaceuticals, and industrial raw materials.

0002

2. Description of the Related Art In general, paper manufacturing processes involve paper pulp fibers containing a large amount of water, and therefore drying processes are provided throughout the manufacturing process. Further, in the drying process, steel drying rolls whose heat source is exclusively heated steam are often used. However, when used as a drying roll for a long period of time, as a result of repeated adhesion and evaporation of moisture, the roll surface gradually corrodes, and the smoothness of the roll surface is affected by the formation of iron rust and local peeling and falling off of iron rust. drying conditions, and it becomes impossible to maintain uniform drying conditions. In particular, in the case of a long drying roll, the difference in surface temperature between the central part and both ends in the axial direction becomes large, and the degree of drying of the paper passing through the roll becomes non-uniform. In addition, cast iron rolls
In addition to the above-mentioned surface changes, during casting, phenomena such as segregation of free graphite or irregularities in crystal grain size and crystal growth direction occur due to uneven cooling rate of the molten metal in the roll axis direction. As a result, the roll base material itself becomes a structure having different thermal conductivity. Furthermore, the inside of the roll is corroded by the heating steam and drain, and the formation of an iron rust layer with high heat transfer resistance and local peeling occur discontinuously, making the temperature distribution on the roll surface even more uneven. Due to the above-mentioned phenomena, long-term use of drying rolls causes uneven drying of the passing paper due to the roughening of the roll surface and the adhesion of paper waste to the rough surface, which ultimately reduces productivity and paper quality. Problems such as deterioration occur.

[0003]Currently, as a countermeasure to the above-mentioned problem, measures such as periodically mechanically polishing the surface of the drying roll or applying hard chrome plating are taken. however,
The former requires frequent suspension of operations, resulting in a significant drop in productivity.Although the latter can be expected to extend its life to some extent, under operating conditions of 250°C or higher, the coating layer of this type of roll usually deteriorates. The chrome plating layer used softens,
In addition to being easily scratched, there are problems such as a large amount of time and money being spent on operations such as removing and transporting large drying rolls each time electroplating is performed, and installing them after plating.

0004

SUMMARY OF THE INVENTION An object of the present invention is to provide a drying roll that does not cause uneven drying, that is, can maintain a constant temperature on its heat transfer surface.

[0005]

[Means for Solving the Problems] This invention provides a heat transfer surface of the outer circumferential portion of the roll with x
This is a drying roll having a heat transfer surface with an even temperature distribution formed by forming a coating layer whose thermal conductivity in the direction is higher than the thermal conductivity in the y direction corresponding to the radial direction of the roll.

In practice, it is also advantageous for the thermal conductivity in the x-direction to be 1.5 to 20 times the thermal conductivity in the y-direction.

The drying roll according to the present invention is characterized in that a coating layer having so-called anisotropy, in which the thermal conductivity in the x direction and the thermal conductivity in the y direction are different, is formed on the heat transfer surface. This coating layer will be explained in detail below.

Now, the coating layer formed on the heat transfer surface of the drying roll is made of a material that has higher heat resistance, corrosion resistance, and wear resistance than the roll material, that is, a protective oxide film that is electrochemically more noble than iron. It can be appropriately selected from metals (including alloys), cermets, ceramics, etc. that form the . In order to impart anisotropic thermal conductivity, it is preferable to utilize differences in thermal conductivity caused by the morphology of particles constituting the coating layer or to mix good thermal conductors and poor thermal conductors. . In other words, in the case of good conductor particles, in the x direction of the coating layer, the grain boundaries that act as a barrier to heat transfer are minimized to improve heat conduction, and in the y direction, conversely, the grain boundaries Increase layers to reduce thermal conductivity. The presence of a poor conductor of heat in the x direction is particularly effective. In addition, the coating layer can be formed by electroplating, electroless plating, PVD method, CVD method, or a combination thereof.
Thermal spray methods are most advantageously suited.

[0009]

[Operation] In the drying roll according to the present invention, in order to impart anisotropy to the thermal conductivity of the coating layer formed on the heat transfer surface, first, the heat transfer characteristics between the particles constituting the coating layer and their grain boundaries are took advantage of the difference between In other words, it goes without saying that heat conduction depends on the inherent thermal conductivity of the particle material, but focusing on the fact that aggregate particles are more strongly influenced by grain boundaries, In order to improve thermal conductivity, the number of grain boundaries per unit area was reduced, while in the y direction, the number of grain boundaries was increased. When such a coating layer is formed on the surface of the roll, the heat receiving area is large in the x direction, and the thermal barrier effect due to grain boundaries can be almost ignored, but heat conduction in the y direction of the coating layer is affected by the grain boundaries. Since there are a large number of , heat conduction is delayed compared to the x direction. As a result, although some heat loss occurs, this phenomenon actually appears as an effect of equalizing the temperature distribution on the surface of the coating layer.

FIG. 1 shows a cross section of a coating layer obtained by thermal spraying and having the above characteristics. In the figure, 1 is a heat transfer surface of a steel roll that is internally heated by water vapor, and particles 3 forming a coating layer 2 formed on this heat transfer surface 1.
are flat, so among the particles 3, the particles 3a that are in direct contact with the heat transfer surface 1 receive heat exclusively from the heat transfer surface 1, and the heat distribution in the particle layer 4a of these particles 3a is The heat distribution is almost the same as that of surface 1. However, since there are many grain boundaries 5 formed by flat grains, these act as a barrier to heat conduction and the thermal conductivity decreases in the grain layer 4b located above the grain layer 4b. Therefore, heat transfer surface 1
Even if the temperature distribution on the surface is non-uniform, the temperature distribution on the surface of the coating layer becomes uniform because the proportion of heat particularly from the high temperature portion of the heat transfer surface 1 being transmitted in the x direction in the coating layer increases.

FIG. 2 also shows that Al2O3, Cr2O3, ZrO2, Cr
Ceramic particles such as 3C2 or NbC are present. That is, 21 in the figure is the heat transfer surface 1
Metal particles 22 constitute the coating layer 2 formed on the metal particles 21 and 23 are ceramic particles formed on the metal particles 21.
is a grain boundary. In this way, by layering ceramic particles with lower thermal conductivity than metals, it is possible to further increase the anisotropy of thermal conductivity, and by adjusting the amount, the anisotropy ratio, that is, x The thermal conductivity ratio in direction/y direction can be controlled.

Further, FIG. 3 shows a cross section of a coating layer according to the present invention formed by electroplating or electroless plating. For example, Al2O in Ni plating solution
When electricity is applied while suspending the fine particles of No. 3, metal Ni 31 is eutectoid with the Al2O3 particles 32 on the surface of the heat transfer surface 1, and the resulting coating layer has anisotropy in thermal conductivity. In addition, in the electroless plating method, A is added to the plating solution.
After suspending the 12O3 fine particles, a coating layer having the same structure as the coating layer shown in the figure can be obtained by processing the entire liquid while stirring it.

[0013] When applied to a drying roll in a general paper manufacturing process, the x direction/y direction in the coating layer is
It is preferable that the thermal conductivity ratio in the direction is about 1/1.5 to 1/20. This is because if it is less than 1/1.5, the effect of uniformizing the temperature distribution on the heat transfer surface is poor, whereas if it is more than 1/20, although it is possible to achieve uniform heat distribution on the heat transfer surface, the economic efficiency decreases due to the loss of thermal energy. This is because problems arise.

Furthermore, in order to form an anisotropic coating layer by a thermal spraying method, when the particles constituting the coating layer are metallic, the particles are flattened and an oxide film or a reaction layer ( For example, a nitride layer) must form and act as a barrier to heat transfer. Therefore, electricity (including plasma), propane, flammable gas such as acetylene, etc. can be used as the thermal spraying heat source, but it is important to form the coating in an atmospheric environment. are not compatible due to the lack of oxide formation on their particle surfaces. However, when spraying Ti in a nitrogen gas atmosphere, TiN is generated on the surface of the Ti particles.
This acts as a barrier to heat transfer and can exhibit anisotropy.

[0015] However, even when spraying in the atmosphere, the thermal conductivity varies depending on the type and thickness of the oxide film of the metal particles constituting the coating layer. and granularity etc. must be selected,
It is difficult to apply conventional thermal spraying methods as they are. Therefore, in practice, the thermal conductivity of the formed coating layer in the x direction and the y direction may be measured, and if the ratio of the two is in the range of 1.5 to 20, it may be determined that the method is applicable.

Although FIGS. 1 to 3 show coating structures using metals and ceramics, the present invention can be applied even if cermet particles (mixtures of metals and ceramics, composites, etc.) are used. Of course, a covering layer can be formed.

[0017]

[Example] Example 1 Diameter 600mm, length 1400mm and wall thickness 20mm
On the surface of a steel roll of mm, by plasma spraying method,
A coating layer having the following composition was formed, heated steam at 180°C was introduced into the roll, and this state was maintained for 5 hours. Thereafter, the temperature of the roll surface was measured using an infrared temperature measuring device, and the temperature difference between the center and both ends in the axial direction of the roll was investigated to evaluate the uniformity of the temperature distribution of the coating layer. In addition, while the heated steam is flowing, the steel roll is rotated 2 to 3 times per minute, and a glass wool insulation material is pasted on the side surface of the roll to form a coating layer on the main heat dissipation part of the steel roll. and the rotating shaft of the roll.

(1) Ni(80)-Mo(20),
Coating layer thickness: 200 μm (However, the numbers in parentheses indicate wt%; the same applies below) (2) Ni(90)-Cu(10),
Coating layer thickness: 200 μm (3) Fe(87)-Cr
(13), coating layer thickness: 200 μm (4) Ni (9
5)-Al(5)/Al2O3(100), coating layer thickness: 100μm/100μm (5)Ni(80)-Cr(20)/Cr2O3(1
00), coating layer thickness: 100μm/100μm (6) Ni(80)-Cr(20)/Cr3C2(7
5)-Ni(20)-Cr(5), coating layer thickness: 10
0μm/100μm

[0019] Also, for comparison, electrolytic Ni plating coating,
Rolls coated with electrolytic Cr plating and untreated rolls were tested under the same conditions.

Table 1 shows the results of an investigation on the surface temperature distribution of the roll thus obtained.

As is clear from the table, comparative example (No.
7, 8, 9), a maximum temperature difference of 6 to 10°C is observed between the center and both ends of the roll, whereas in the roll according to the present invention, the difference is only 1 to 3°C,
It can be seen that a heat transfer surface with an even temperature distribution is formed. Furthermore, when each roll was used as a drying roll in an actual paper manufacturing process, it was found that the roll according to the present invention had superior corrosion resistance and abrasion resistance compared to conventional steel rolls, and there was no discoloration of passing paper due to the occurrence of red rust. Good paper quality was maintained.

Example 2 Using a steel roll with the same dimensions and shape as in Example 1, Al2 was added to Ni by electroplating and electroless plating.
A coating layer in which O3 fine particles were dispersed was formed to a thickness of 50 μm, heated steam at 150° C. was passed through the roll, and the temperature distribution on the roll surface was investigated. Table 2 shows the results.

As is clear from the same table, in this example as well, the coating in which Al2O3 fine particles were dispersed in the coating and had anisotropy in thermal conductivity exhibited excellent thermal uniformity with little difference in temperature distribution. .

[0024]

[Effects of the Invention] As explained above, by providing the coating layer formed on the heat transfer surface with different thermal conductivities in the x direction and the y direction, the temperature distribution on the roll heat transfer surface is made uniform. can be done. Therefore, when applied to the drying process of paper manufacturing, wet paper passing through the heat transfer surface of the roll has a uniform degree of dryness, improving paper quality and productivity, and can achieve effective use of heat. Furthermore, since many of the substances that cause anisotropy are generally hard, they can withstand abrasion caused by contact with wet paper, extending their lifespan and greatly contributing to improved productivity.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the cross-sectional structure of a coating layer formed by a thermal spraying method.

FIG. 2 is a schematic diagram showing a cross-sectional structure of a coating layer made of metal and ceramic particles formed by thermal spraying.

FIG. 3 is a schematic diagram showing a cross-sectional structure of a coating layer formed by electroplating and electroless plating.

[Explanation of symbols]

1 Heat transfer surface 2 Coating layer 3, 3a particle 4a, 4b particle layer 5 Grain boundaries 21 Metal particles 22 Ceramic particles 23 Grain boundary 31 Metal Ni 32 Al2O3 particles

Claims (5)

[Claims] [Claim 1] A coating layer is formed on the heat transfer surface of the outer circumference of the roll, the thermal conductivity of which is higher in the x direction, which corresponds to the axial and circumferential directions of the roll, than the thermal conductivity in the y direction, which corresponds to the radial direction of the roll. A drying roll with a heat transfer surface with even temperature distribution. 2. The drying roll according to claim 1, wherein the thermal conductivity in the x direction is 1.5 to 20 times the thermal conductivity in the y direction. 3. The drying roll according to claim 1, wherein the coating layer is made of metal. 4. The coating layer is made of flat metal particles,
4. The drying roll according to claim 3, wherein the metal particles have an oxide on their surfaces. 5. The drying roll according to claim 1, wherein the coating layer is made of metal and/or ceramics.