FI61738C - FOERFARANDE VID TILLVERKNING AV STENVALS FOER PAPPERSMASKIN - Google Patents

Description

61738

Method for making a paper machine design Förfarande vid tillverkning av stenvals för pappersmaskin

The invention relates to a method for reducing or eliminating deflections occurring in connection with the operation of a paper machine design, in particular a press roll.

5 Natural stone, especially gray granite, has long been used as a raw material for paper machine rolls. Since sufficiently large defect-free granite bodies for the large rolls of a paper machine are not readily available, efforts have been made to find materials to replace granite which, however, have not replaced or displaced the use of stone due to some excellent properties of the stone. Granite is generally considered to be the best material for hard-surfaced press rolls, e.g. because the granite roll can be refurbished and renewed without changing its surface properties.

15 An example of the size of the design is the largest granite roll in the world to date, supplied by the applicant, with a diameter of 1600 mm and a casing surface length of 9250 mm.

The different constituents of the rock roll aggregate may be unevenly distributed 20, as a result of which its coefficients of thermal expansion at different points in the material may be different. For this reason, the behavior of the roll at varying temperatures cannot always be predicted quite accurately by calculation.

In practice, a significant disadvantage of the designs is the fact that the perfectly straight and pre-polished designs are deflected, which are very detrimental when the design acts as a press roll, e.g. as a smooth surface of the applicant's "Sym-Press" press (trademark) , in connection with which at least two press nips are formed. The deflections cause an uneven distribution of the nip pressure 30, which is reflected in the uneven moisture profile of the press-treated web.

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The present invention provides a simple and effective method for preventing said deflections from occurring. To this end, the method of the invention is mainly characterized in that the cylindrical shell of the embodiment is ground to its final shape at substantially the same temperature as where the embodiment will operate in a paper machine.

In the following, the invention will be described in detail with reference to the figures of the accompanying drawing.

10

Figure 1 shows an example of an embodiment in which the invention is applied.

Figure 2 shows graphically the deflection of a granite roll as a function of surface heat-15 space.

In the following, the structure of a stone will first be described as a background of the invention. The structure and manufacturing method of the roll shown in Figure 1 are described in more detail in the applicant's FI patent No. 57,989.

20

The embodiment shown in Figure 1 comprises a uniform sheath 10 of natural stone, e.g. gray granite, which is a one-piece granite cylinder with a relatively large hole 14 drilled in the middle. The diameter of the hole 14 is e.g. about 50% of the diameter of the granite sheath 10. 25

A shaft tube 13 is placed in the hole of the granite sheath 10, inside which shaft shafts 12a and 12b of the design are attached to both ends, the ends of which have bearing parts 11a and 11b. The shaft tube 13 extends outside the granite sheath 10 so that annular end flanges 15a and 15b can be placed on it, between which the granite sheath 10 is pressed.

In order to center the granite shell 10 with respect to the center line C-C of the roll axis, grooves 35 are machined in the edges of the hole 14 of the granite shell 10, in which centering rings 16 are arranged, the inner parts of which correspond to the outer surface of the shaft tube 13.

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Among other things, in order to find out the background of the invention, the deflections of the design were studied at room temperature and colder when the roll was outside the paper machine. In this case, the temperature was found to have a clear effect on the deflection of the roll. Measurements were continued with the same design installed in 5 locations on the paper machine. In the first deflection measurement, the surface temperature of the roll was about + 20 ° C, which corresponded quite closely to the ambient temperature. After the paper machine was started, the deflection and surface temperature were measured every 12 h during the first two days. Thereafter, the measurement interval was reduced by 24 h and measurements were performed for 10 weeks. In the last check measurement, the surface temperature of the roll had stabilized at about + 53 ° C and the deflection was about 0.25 mm measured from the center of the roll.

The results of the measurements discussed above are shown graphically in Figure 2, to which the previously measured values have also been added. Based on all measured values, a linear regression line has been calculated for the deflection-temperature dependence, the equation of which is y - 0,00659 x - 0,0848 ± 0,0356 (1) 20 for the roll under study where y is the deflection at the center of the roll in millimeters and x is the roll surface temperature ° C.

All measured values and the regression line calculated from them are shown in Fig. 2. Curve 1 shows the stage in which the design cools out, curve 2 shows the stage in which the design heats up in room air and curve 3 shows the situation in which the design is placed in a paper machine. The dotted line shows the regression line of Equation (1).

30 The correlation coefficient r is 0.967168 and the explanation percentage is 93.5. Considering the difference between the surface temperature and the average temperature of the roll due to the heat capacity of the roll, the deflection of the roll can be considered to be practically completely temperature-dependent and linear over the temperature range studied.

As is known, the finishing of the outer surface of the design is carried out in a grinding machine in which the roller rotates on its own axis. The outer surface is ground using either abrasive stone or diamond grinding into a cylinder with a surface roughness of the order of 1.6. The roll is then balanced.

In the method according to the present invention, the design, in particular the granite roll, in the roll grinder is heated, e.g. by water jets, to the temperature at which the roll will operate in the paper machine, e.g. in its press section. The grinding of the roll to its final shape is carried out according to the invention in this same thermal state corresponding to the operating temperature of the roll. In this way, the shape defects due to the uneven thermal expansion of the aggregate of the roll are compensated so that when the roll thus ground is placed in the press section of the paper machine, there are no deflections due to temperature changes.

15 The normal operating temperature of the stone roll in the press section of the paper machine is approx. 35, .. 40 ° C. If, in connection with the press section, the so-called the steam box, the structure of which is described in more detail in e.g. U.S. Patent No. 4,163,688, has an operating temperature of about 50.55 ° C.

20 In practice, it has been found that the operating temperature of the design in the middle of the paper machine is slightly higher than in the vicinity of the ends of the design. In this case, the method of the present invention can also be carried out by grinding the bead so that its center portion is heated to a temperature corresponding to the operating temperature of the center portion and the areas near the ends are heated to a temperature corresponding to the operating temperature of these regions. Such a temperature profile mimicking the operating temperature of the roll can be achieved, for example, by using water jet devices, from which temperature-controlled water is fed to certain points in the design.

An alternative way of heating the design during grinding to the temperature referred to in the invention is to provide a hot water pool with temperature-controlled water 35 in connection with the grinding roll, in connection with which the roll rotates.

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The method according to the invention can, of course, be used both in making new designs and in renovating old rolls.

The following are claims within the scope of which the various details of the invention may vary within the scope of the inventive idea.

Claims (7)

61738 A method for reducing or eliminating deflections during the operation of a paper machine design, in particular a press roll, characterized in that the cylindrical shell (10) of the design is ground to its final shape at substantially the same temperature as the design will operate in the paper machine. Method according to Claim 1, characterized in that the cylindrical shell (10) of the design is ground to its final shape at a temperature of about 35 to 40 ° C. A method according to claim 1, characterized in that such designs, which act as a roll of a paper machine press in connection with which a steam box is used, are ground 13 to their final shape at a temperature of about 50 to 55 ° C. A method according to claim 1, 2 or 3, characterized in that the grinding of the cylindrical shell (10) of the design into its final shape is performed in the axial direction of the design at different temperatures, which different temperatures substantially correspond to the operating temperatures of the respective points in the paper machine. Method according to Claim 1, 2, 3 or 4, characterized in that the heating of the grinding design to said temperature 25 is carried out using water jet devices. Method according to Claim 1, 2, 3 or 4, characterized in that the heating of the design to said temperature level is carried out using a water basin with temperature-controlled water, in connection with which the grinding design rotates.