AN INSULATING BODY BASED ON MINERAL WOOL, AND A METHOD FOR ITS MANUFACTURE

Abstract: Method for the manufacture of insulating bodies based on mineral wool. In the method, one side of a mineral wool body manufactured in a manner known per se is subjected to a vacuum and its opposite side is contacted with a clay slurry, e.g. bentonite slurry, whereupon the clay slurry is absorbed into the mineral wool, and finally the impregnated mineral wool body is dried at an elevated temperature. In an insulating body according to the invention, the fibers of mineral wool bonded with an organic bonding agent are oriented in a tubular body mainly against the radius and in a board-like piece mainly in parallel to the main planes of the board, the body contains clay material up to 40 percent by weight, its compressive strength with a compression of 5 % is at maximum 120 kN/m<2>, and its heat conductivity lambda 10 is 0.032-0.048 W/mK.

Description: An insulating body based on mineral wool, and a method for its manufacture The present invention relates to an insulating body based on mineral wool, and to a method for its manufacture. Insulating troughs made from various materials and, for example, mineral wool are used for the insulation of pipes, for example. Such troughs have usually been more or less soft, which means that the insulating material around the pipe cannot withstand being walked on; an insulation which can be walked on is a normal requirement in industrial plants. There have, however, been developed calcium silicate based, fiber reinforced insulating troughs having a good compressive strength. Such insulating troughs. are manufactured by mixing fibers with a calcium silicate slurry, whereafter the mix is cast in molds and cured in an autoclave. The compressive strength of the trough obtained is, as said, very good. Consequently, thinner than usual surface material, e.g. thin metal sheet, can be used around the trough. However, the disadvantages of the troughs include on the one hand an expensive manufacturing method and on the other hand the brittleness of the cured insulating material. The insulating trough fractures easily during handling. Also, the conductivity factor of the insulating trough is higher than that of mineral wool based insulants. Also known are so-called rockwool bricks, which have a high compressive strength. They are manufactured by mixing fluffed, rockwool with clay slurry and by taking up the thereby obtained mix onto a rotating drum by means of a vacuum, whereby it at the same time is pre-dried by suction to a moisture content of approx. 65 %. The layer is removed from the drum, pressed into the form of a board, cut to suitable dimensions, and dried in a furnace. The advantages of the method are that an insulating product having a high compressive strength is obtained and that an inexpensive mineral wool can also be used for raw material, and thus the method is economical. Its dis¬ advantages are that the conductivity factor of the product is considerably higher than that of a conventional mineral wool product, and that the product is heavy, i.e. its bulk 3 density is approx. 200-300 kg/m . The object of the present invention is therefore to provide a method for the manufacture of insulating bodies based on mineral wool, a method by which it is possible economical ly to manufacture insulating bodies having a better compressi strength than have conventional rockwool products,• and a lower conductivity factor than have the hard rockwool products described above, because the mineral wool fibers contained in the product are oriented in the best possible ■ manner considering the capacity of preventing the transfer of heat. This problem is solved according to the invention in such a way that one side of a mineral wool body made by a method known per se is subjected to a vacuum, and the opposite side is contacted with a clay slurry in order to saturate the mineral wool with clay slurry, whereafter the saturated mineral wool body is dried at an elevated temperature. When the method is applied to the manufacture of tubular insulating bodies, a tubular mineral wool body, made in a manner known per se, is placed around a perforated core and immersed in a clay slurry in a vessel, and the core is connected to a source of vacuum in order to cause clay slurry to be absorbed into the mineral wool body, whereaf er the impregnated mineral wool body is removed from the core and dried at an alevated temperature. When the method is applied to the manufacture of board¬ like insulating bodies, a mineral wool board, made" by a method known per se, is placed in a vessel provided with a perforated tray so as to be supported by the tray, the vessel is filled with clay slurry up to a point above the mineral wool board, and a vacuum is created under the tray in order to cause the clay slurry to be absorbed into the mineral wool board, whereafter the iπpregnated mineral wool board is removed from the vessel and dried at an elevated temperature. In each case, the clay slurry sucked through the mineral wool piece can be recycled into the vessel. The insulating body according to the invention is characterized in that a mineral wool body which is bonded by an organic bonding agent and in which the fibers are oriented in a tubular body mainly perpendicularly to the radius and in a board-like product primarily in parallel to the main planes of the board, contains clay material up to 40 percent by weight, its compressive strength 2 with a compression of 5 % is at maximum 120 kN/m , and its heat conductivity λ,_ is 0.032-0.048 W/mK. In the accompanying drawing, Figure 1 depicts schematical- ly the manufacture of an insulating trough by the method according to the invention, and Figure 2 depicts in a corresponding manner the manufacture of a board-like insulating body. O FI In the drawing, 1 indicates a vessel in which a per- - forated core 2 can be placed; the core is connected by means of conduit 3 to a pump 4 which creates a vacuum. ■ A tubular piece 6 shaped from mineral wool in a manner known per se is placed around the core 2, clay slurry 7 is introduced into the vessel 1, and the pump 4 is started, whereupon clay slurry is absorbed into the mineral wool body in a very short time. When a vacuum of approx. 0.5 bar is used, the impregnation, time is about 10 s. From the pump 4 the clay slurry can be returned to the vessel 1 via a pipe 5. After the inpregnation the mineral wool body is removed from the core and dried in a furnace at an elevated temperature, which can adva tageously be approx. 200 C. In the embodiment depicted in Figure 2, the vessel 8 is provided with a perforated tray 9. That part of the vessel 8 which is below the tray 9 is * connected by conduit 10 to a pump 11 which creates a vacuum. A board-like mineral wool body 13 made in a manner known per se is placed on top of the tray 9, clay slurry 14 is fed into the vessel up to a point above the board 13, and the pump 11 is started, whereby clay slurry is absorbed into the board 13. In this case also, the clay slurry can be returned from the pump 11 via a conduit 12 into that part of the vessel 8 which is above the tray 9. After the iπpregnatin the mineral wool board 13 is removed and dried in a furnace in the manner described above. Depending on the dimensions of the tubular mineral wool body to be manufactured, cores of the corresponding size must, of course, be used. One clay material suitable for use in the method according to the invention is bentonite.1_he concentration of the slurry OMFI being absorbed, i.e. its bentonite content, or the amount of the slurry can be used for affecting the bentonite content of the completed product, which for its part has a direct effect on the compressive strength of the product. However, the viscosity of the slurry sets a limit on the bentonite content, since viscosity for its part sets a limit on the absorption of the slurry into mineral wool. If the viscosity is too high, a sediment of bentonite is formed on the surface of the mineral wool, and this layer prevents further absorption of slurry into the mineral wool, and furthermore, the body of mineral wool may collapse owing to the vacuum prevailing inside or below it. After the preparation of the slurry the viscosity of the bentonite slurry rises to close to its maximum value in approx. 10 hours. However, the increase in viscosity can be prevented by agitating the slurry continuously. An increased viscosity can also be caused to fall to its initial value by agitation. For this reason it is advan.ageo to stir the bentonite slurry in the vessel, and this is illustrated in Figures 1 and 2 by a schematically shown propeller 15. Taking the above viewpoints into consideration, the bentonite content of the slurry to be used may be at maximum 10 percent by weight, in which case the water content may be respectively approx. 88-90 percent by weight. In addition, the slurry may contain a bonding agent such as phenol formaldehyde, its amount being preferably at maximum 2 percent by weight, an anti-foaming agent, the amount of which is preferably at maximum 1 percent by weight, and an agent such as boric acid, which increases the strength of the final product, the amount of this agent being preferably at maximum 0.5 percent by weight. The amounts given for the additives correspond to. the presented maximum limit for the bentonite content, and they vary in proportion to the bentonite content. The slurry. is prepared in such a way that water is added to boric acid, thereafter the bentonite is mixed with the water and, for example, after half an hour's stirring the anti-foaming agent is added, and.finally the bonding agent is added. Since a mineral wool body made in advance is used in the method according to the invention, the fibers serve as a good supporting structure for the product, and the orientation of the fibers is more advantageous in terms of heat conductivit .than it is in previously known products made from a mix. The continuous fiber network which serves as a frame is also a significant improve¬ ment in terms of the bending strength of the product, as compared with-a product made from a mix. The bulk density of the mineral wool piece used in the method according to the invention may vary within a rather wide range, for example 70-180 kg/m . The addition of clay to the mineral wool increases not only the compressive strength of the product but also its resistance to heat. The organic bonding agent used in conventional mineral wool insulants burns off at a temperature as low as approx. 250 °C, but a product made by the method according to the invention resists temperatures up to 800 °C at least. Insulating troughs were made in the manner described above using bentonite slurry for the .impregnation. The bentonite content and viscosity of the bentonite slurry used, the density of the mineral wool used as raw material, and the bentonite content, compressive strength, heat conductivity and density of the obtained final product are given in the table below. Table Bentonite slurry Mineral Final product bentonite viscos¬ wool bentonite compres¬ heat dens content ity density content sive conduc¬ strength tivity % by % by F 5 % λlO weight cP kg/m weight kN/m W/mK kg/m 2 2 143 9.3 26 0.0371 157 4 4 154 22 . 73 0.0439 196 7 45 147 32 103 0.0451 216 9 55 152 35 113 0.0480 208 7 45 115 32 14 0.0413 168

Claims: Claims 1. A method for the manufacture of insulating bodies based on mineral wool, c h a r a c t e r i z e d i n that one side of a mineral wool- body, .made in a manner known per se, is subjected to a vacuum-.and its opposite side is contacted with a clay slurry in order to iπpregnate the mineral wool with the. clay. slurry, whereafter the impregnated mineral wool body is dried at * an elevated temperature. 2. A method according to Claim 1 for the manufacture of tubular insulating pieces , c h a r a c t e r i z e d i n that a tubular mineral wool body, made in a manner known per se, is placed around a perforated core and immersed in clay slurry in. a vessel, and the core is connected to a source of.vacuum in order to cause the clay slurry to be absorbed into the mineral wool body, whereafter the ___rapregnated mineral wool body js removed from the core and dried at an elevated temperature. 3. A method according to Claim 1 for the manufacture of a board-like insulating body, c h a r a c t e r i z e d i n that a mineral wool board, made in a manner known per se, is placed in a vessel having a perforated tray so as to be supported by this tray in such a manner that it mainly covers the entire tray, the vessel is filled with clay slurry so as to cover the mineral wool board, and a vacuum is created under the tray in order to cause the clay slurry to be absorbed into the mineral wool board, whereafter the impregnated mineral wool board is removed and dried at an elevated temperature. 4. A method according to Claim 2 or 3, c h a r a c t e r i z e d i n that the clay slurry sucked through the mineral wool body is returned to the vessel. 5. A method according to any of the above claims, c h a r a c t e r i z e d i n that the clay slurry is stirred during the impregnation. 6. •. A method according to any of the above claims, .c h a r a c t e r i z e d i n that the clay material used is bentonite. 7. A tubular or board-like insulating body based on mineral wool, c h a r a c t e r i z e d i n that a mineral wool body which is bonded by means of an organic bonding agent and in which the fibers are oriented in a tubular body mainly perpendicularly to the radius and in a board-like product mainly in parallel to the main planes of the board contains clay material up to 40 percent by weight, its compressive strength with a 2 compression of 5 % is up. o 120 kN/m . and its heat conductivity. λ 1Q is 0.032-0.048 W/mK. 8. An insulating body according to Claim 7, c h a r a c t e r i z e d i n that the clay material is bentonite. OMFI

Inventors: JAEMSEN HANNU HELMER, TUOMISALO VAEINOE AKUSTI, JAEMSEN, HANNU, HELMER, TUOMISALO, VAEINOE, AKUSTI
Applicants: PARTEK AB, OY PARTEK AB
Application year: 1982
Main classification: F16L59
IPC codes: B28B19, C04B41