SE512374C2 - Thermal insulation device and insulating element for the jacket of a thermal roller - Google Patents

Abstract

PURPOSE: To enhance heat insulating capacity by forming a wall surrounding a hot oil passage into double wall structure, and sealing a cavity between double walls in a vacuum or gas filled state in a heat insulating assembly or element for a hot roll bearing end and a contactless surface area. CONSTITUTION: A heat insulating assembly 15 for reducing heat conduction from at least one heating medium channel 4 extending into a roll shell 1, to a contactless area of the shell 1, and an element 10 for reducing heat conduction from oil channels 6, 7 in a roll shaft 3 to a bearing 5, comprise a first wall 11 disposed concentrically with the center axis of the channels 4, 6, 7 to surround the channels 4, 6, 7, and a second wall 12 concentrically disposed around the first wall 11, and a cavity between these walls 11, 12 is sealed in a vacuum or gas filled state.

Description

15 20 25 30 35 512 574 2 bores in the roll shell. The circulation of the oil in the roll shell is arranged so that the oil first passes to the opposite end of the roll and then returns along a parallel bore to the end where it was introduced into the shell. The return of the oil is controlled via the end flange and a second bore in the roller shaft back for heating.

The surface of the thermal roller is heated to a fairly high temperature in order to apply an intense heat effect to the rapidly moving web during the short time interval that the web experiences in the nip. When oil is used for heating the roll, the roll surface temperature can be higher than 200 ° C. The temperature of the heating oil introduced into the roll can be as high as 280-300 ° C, which obviously results in an extremely serious heat load on the bearing. Depending on the high loads placed on the roller bearings, the roller shaft must be provided with large bearings, and in fact the inner diameter of the bearings in modern equipment is about 0.5 m, with the outer diameter of about 1 m. the heating caused by the heat flow from the hot oil passing through the roller shaft.

The length of the thermal roll and the soft roll is slightly larger than the width of the web being smoothed, whereby non-contact surfaces with the web are present at the ends of the rollers. When an extremely high heat flow per unit area is transferred from the thermal roll to the web, while at the ends of the roll the heat can leave the roll surface only by radiation and convective losses, the surface temperature of the end non-contact areas rises to a higher value than the roll surface portion contacting the web . Such a temperature difference causes serious disadvantages.

The higher temperature at the roll ends obviously results in greater thermal expansion at the roll end regions. The outer edge of the roll shell consequently curves outwards from the center axis of the roll, and the bending moment created by the thermal expansion correspondingly presses the area adjacent to the curving area radially inwards towards the center axis. This sunken area coincides exactly with the edge of the web. Since the roll diameter in this shrunk area is smaller than the roll diameter at the roll center, the thickness of the web will be greater at the bank edge than at the center of the web.

Consequently, the thickness profile of the web will not be uniform in the cross-machine direction, leading to printing problems and thus spoiling the quality of the web.

In addition, a thick edge on the web causes difficulties in winding, because the wound roll is not homogeneously dense and narrower roll slots from the ends of the machine roll become conical. An additional problem is created by the risk of the thermal roll shell contacting the soft roll surface, whereby the polymer coating on the soft roll is thermally destroyed.

If the thermal expansion of the roll end areas is too large, the radially expanded end area of the roll may extend so far towards the center of the roll that it reaches the bank edge, thereby drawing the smaller diameter area of the roll closer to the roll center so that the web profile becomes wavy. When soft calenders are used for smoothing large quantities of low-weight paper, the thickness of the web can be extremely small, and even very small variations in the roll diameter and cross-machine contour profile will cause very large relative variations in the paper web cross-machine profile. For these reasons, deformations in the shape of the thermal roller must be kept as small as possible.

Reduction of heat conduction to the non-contacting end area of a thermal roller has been achieved by means of bushings or coatings of materials with low thermal conductivity. Coatings used have included zirconia, and thermally insulating bushings have been made of polytetrafluoroethylene (PTFE). Obviously, thermally insulating bushings and coatings can be made of many different materials, such as ceramic and polymeric thermally insulating simple and they can be lightweight materials. The production of such bushings and covers is relatively arranged around heating oil channels. However, thermal insulations of solids may not provide sufficient thermal insulation; For example, PTFE has a thermal conductivity that is ten times the thermal conductivity of the air. Since the thermal insulation must tolerate a temperature as high as 300 ° C during a simultaneous mechanical load, conventional thermal insulation materials cannot be used unless the roller shaft is designed with a complicated structure.

FI patent 72 S80 describes a heated roller, in which hot oil is circulated in a cavity which exists between a cylindrical outer jacket on the roller and an inner jacket which is concentrically enclosed by the outer jacket. The heating medium is led to the heating cavity via holes taken up towards the end of the inner jacket. In this roll embodiment, excessive heating of the roll end region has been attempted to be prevented by enclosing the entire end of the inner jacket with a thermally insulating ring, consisting for example of a solid material such as polytetrafluoroethylene, or made in the form of a hollow, filled metal ring with either a sealed structure or a structure provided with openings, whereby a heat transfer medium can be circulated in the ring. Such a thermal insulation device is suitable only for use in connection with the roller described in the publication, in addition it has a relatively complicated structure which is difficult to manufacture.

An object of the invention is to create such a thermal insulation device which provides superior thermal insulation, compared with the prior art, and which is insensitive to stresses imposed by its operating environment.

The invention is based on the adaptation of such a bushing-shaped thermal insulation element around the oil ducts of the thermal roller jacket that it contains a gas-tight cavity.

According to the most advantageous embodiment of the invention, the cavity of the thermally insulating element is evacuated to a high vacuum.

More specifically, the device according to the invention has the features in the characterizing part of claim 1. Furthermore, the thermally insulating element according to the invention has the features according to the characterizing part of claim 5.

The invention provides significant advantages.

The embodiment according to the invention has an extremely high thermal insulation capacity. While the highest insulating ability is achieved with a bushing whose insulating cavity is evacuated to a vacuum, a bushing filled with air, suitably inert gas such as nitrogen or other gas, offers better insulating ability than any solid insulating material. The evacuated bushing according to the invention can easily be produced with the aid of electron beam welding equipment, as the gas-tight welded bushing will automatically maintain a vacuum equal to that prevailing in the vacuum chamber of the welding equipment during welding. Correspondingly, a gas-filled bushing can be produced in an inert gas atmosphere using, for example, laser welding.

The material of the bushing can be the same structural steel used in other parts of the thermal roller, and the bushing can be designed with sufficient strength to make it less susceptible to damage during installation or use. When the bushing is hermetically sealed, its thermal insulation capacity will not deteriorate during use. If the roll consists of the same material as the roll shell, the coefficients of thermal expansion of all roll parts will be the same and consequently no stresses caused by different thermal expansion will occur between them.

The invention is described in more detail in the following with reference to the accompanying drawings.

Fig. 1 is a side view in half section of a thermal roll end suitable for feeding a heating medium to the roll and comprising a thermal insulation device according to the invention.

Fig. 2 is a cross-sectional end view of the sheath of the thermal roll in Fig. 1. Fig. 3 is a detailed cross-sectional side view of a thermal insulation element according to the invention for a roll shaft.

Fig. 4 is a detailed cross-sectional side view of another thermal insulation element according to the invention for an oil channel at the roll shell.

This application describes a thermal insulating device for the sheath of a thermal roller based on the use of the insulating element according to Fig. 4. Another thermal insulating device for the shaft of a thermal roller based on the use of the insulating element according to Fig. 3 is described in a parallel application, submitted by the present applicant. As is clear from Fig. 1, a thermal roller is advantageously adapted for combination use in both devices.

A thermal roller comprises a body with a jacket 1 and two end pieces 2, 3. Conventionally, a heating medium, which is typically oil, is led to the roller and away from the roller via only one end of the roller. The construction shown in Fig. 1 represents such a supply end of the roller with oil circulating means. The jacket 1 of the thermal roller is a thick-walled hollow cylinder, the circumference of which is provided with oil channels 4. The end piece comprises an end flange 2 and a shaft 3. The roller is mounted in bearings by the shafts 3 of the end pieces being supported by the bearings 5. is provided with a supply channel 6 for heating oil, through which channel the oil is conveyed to radial channels 8 received in the end flange 2. The heating oil is conveyed via these radial channels to longitudinal channels 4 in the jacket 1, in which channels the oil is led to the opposite end of the jacket 1 and directed there for return via the parallel channels 4. At the supply end of the roller, the heating oil is collected again via radially drilled channels 9 and led to a return channel 7, which is arranged in the center of the shaft coaxially surrounding the oil supply channel 6 and thus serves to moving the oil away from the end of the shaft 3 to a reheating circuit. Oil circulation in the roller can be arranged in different ways, so that in! 10 15 20 25 30 35 5'l2 5274 7 the forward flow and return channels of the oil in the roll shell can alternate next to each other, each forward flow channel being led back via two return channels, or with other configurations. Similarly, the supply of heating oil via the shaft 3 and in the end flange 2 can be designed in different ways. Since the present invention is not related to the construction of the oil supply duct system, the various alternatives will not be described in more detail here. However, the construction of the roller used in connection with the invention must be such that the heating oil or similar medium is circulated in separate channels 4 in the jacket 1 of the roller.

A thermal insulating element 15, which extends from the end edge of the roll shell 1 to the oil channel 4 towards the roll center so far that it reaches slightly below the edge of the web 16, is arranged around the ends of the oil channels 4 in the shell 1. The edge of the paper web 16 divides the surface of the roll shell the machine transverse direction in two parts, namely the non-contacting end area and the contacting center area, on which the web runs. The insulating element 15 comprises an inner cylindrical bushing 11 which serves as the outer wall of the heating oil duct 4, and an outer bushing 12, which together with the end parts 13 of the insulating element delimits a hermetically sealed cavity 14. The end parts 13 are connected to the ends of the bushings 11 and 12 by electron beam welding in a vacuum chamber. The sealed cavity of the insulating element 15 then becomes at a vacuum equal to the operating vacuum of the vacuum chamber of the welding equipment, which vacuum is typically in the order of 10 Pa (1x10 4 bar). a relatively high vacuum, which provides a good thermal insulation capacity to This vacuum is, as will be appreciated, a space sealed to withstand this vacuum.

The thermal insulation capacity of such a vacuum level is almost equal to that prevailing in evacuated bottles used in laboratories and is better than the vacuum level in vacuum bottles intended for storage of food and drink.

The thermal insulation element 15 extends from the edge of the roll shell 1 in the direction of the roll center only slightly below the edge of the web 16. Thus, it provides a moderate thermal insulation against the heat flow from the oil pipe to the non-contacting area of the jacket 1, but has no detrimental effect on the good heat conduction from the jacket 1 to the web 16. The required length of the thermally insulating element 15 and the length of its part as extends below the web is dependent on the design of the roller and the amount of heat applied. Obviously, the thermally insulating elements are mounted on both ends of all channels accommodated in the roll shell.

Fig. 1 also shows an insulating element suitable for use in the shaft 3 of the roller and with a construction which is described in more detail in a parallel application submitted by the present applicant.

In addition to what has been mentioned above, the present invention may have other embodiments. The insulating element is particularly advantageously manufactured by means of electron beam welding, whereby the interior of the element automatically remains at a vacuum level with a high thermal insulating ability. In order to make the insulating capacity of the evacuated insulating element significantly better than that contained in a gas-filled insulating element, the vacuum inside the element should be less than 1 kPa and preferably less than 100 Pa. Depending on the manufacturing advantages as above, the vacuum inside the insulating elements can obviously be easily made to be equal to the operating vacuum in the vacuum chamber of the welding equipment. A relatively good thermal insulation capacity is also achieved with a gas-filled insulation element. Such a gas-filled element can be produced by, for example, laser welding in an inert gas atmosphere, whereby the interior of the element remains filled with inert gas. The filling gas can be an inert gas, such as carbon dioxide, nitrogen or a noble gas. However, the inventive idea is not limited to any product manufactured by any specific manufacturing method.

Since the thermal insulation element is intended for use in connection with drilled oil channels, its shape is preferably cylindrical. However, any other shape can be used, and in fact a partially tapered shape can be used to lock the element to the inner surface of the drilled channel. The insulating element can be mounted for enclosing the oil channels in the jacket in a releasable manner, or alternatively the insulating element can be fixed as an integral part of the oil channel, for example by means of welding joints.

Claims (7)

10 15 20 25 30 35 512 574 10 PATENT REQUIREMENTS Device for reducing heat conduction to the non-contacting area of the jacket (1) of a thermal roller from heating medium channels (4) in the jacket (1), which device comprises at least one longitudinal channel (4) arranged to run in the roll shell (1) to the end for conducting a heating medium in the roll shell (1), characterized by - a first wall (11) surrounding the longitudinal channel (4) by being located concentrically with the center axis of the channel (4) , and - a second wall (12) located at a greater distance concentric with the center axis of the channel (4) so as to define, together with the first wall (11), a cavity (14) which is hermetically sealed and surrounds the longitudinal channel (4) and wherein the absolute pressure is less than 1 kPa and preferably less than 100 Pa. Device according to claim 1 for a thermal roller having a central area of the surface of the jacket (1), which area is intended to press with contact a web (16) to be finished, and at the ends of the roller there is a non-contacting end area which is defined by the edge of the web (16), characterized in that the cavity (14) delimited by the first wall (11) and the second wall (12) extends from the edge of the roll shell (1) to at least the edge of said contacting center area, ie the edge of the track (16). Device according to one of the preceding claims, characterized in that the cavity (14) delimited by the first wall (11) and by the second wall (12) has the shape of a cylindrical hollow shell. Device according to any one of the preceding claims, characterized in that the first wall (11) is arranged to form the inner wall of the heating medium channel 41 41 10 15 20 25 30 5 512 374 11 and the second wall (12) is formed by the inner wall of a duct bore included in the roll shell (1). Thermal insulating element (10) for insulating a heating medium duct (4) running in the jacket (1) of a thermal roller, characterized by - a first closed enclosing surface (11), - a second closed enclosing surface (12), which is arranged at a distance from the first enclosing surface (11), and - elements (13) suitable for connecting the first enclosing surface (11) and the second enclosing surface (12) to each other so that together they define a hermetically sealed cavity (14), wherein the absolute pressure is less than 1 kPa and preferably less than 100 Pa. Thermal insulating element according to claim 5, characterized in that the cavity (14) delimited by the enclosing surfaces (11, 12) is an element with rotational symmetry with respect to its longitudinal axis. 7. A thermal insulation element according to claim 5 or 6, characterized in that the absolute pressure in the hermetically sealed cavity (14) is approximately 10 Pa.