TECHNICAL FIELD The present invention concerns a metal fibre- reinforced packing material including at least fibres of cellulose and metal. The invention also concerns a method for manufacturing of this packing material. BACKGROUND ARTS Earlier asbestos has been constituting as the prevailing material in packings, above all in packings, which are proposed to be used at high temperatures. In connection with that the risks for injuries from asbestos have been obvious it has been a endeavour to replace as- bestos with other materials with as well as without fib¬ res in these packings and also in other products.

It is earlier known to produce electrically con¬ ducting board and paper by mixing metal fibres in the pulp from which the board or the paper is produced by dewatering. It is also known to admix other fibres but cellulose fibres and metal fibres at manufacturing of such a board or such a paper. Further it is also known to replace cellulose fibres by e.g. fibres of plastic mate¬ rial in such applications. Electrically conducting board can be used for elektro-magnetic shielding in electroni¬ cal apparatuses and the similar. It is also known to ma¬ nufacture heating resistor elements of materials contai¬ ning metal fibres.

In all up to now known applications metal fibres are present in the shape of short fibres which are ran¬ domly oriented in a base material, e.g. a pulp containing cellulose fibres, fillers and the similar. A drawback with packings containing such metal fibres and which are proposed to be used at a high temperature, is that they can not be given a satisfactory strength but need a use of additional binding means upon which the packing mate¬ rial is secured.

DESCRIPTION OF THE INVENTION

The purpose with the present invention is to bring about a metal fibre reinforced packing material which do not show the drawbacks of the up to now known materials and a method for its manufacturing. The purpose has been achieved by a metal fibre reinforced board in¬ cluding at least fibres of cellulose and metal, at which the cellulose fibres preferably are proposed to bind eventual additional materials in the board and the metal fibres are proposed to constitute a bounded layer of me¬ tal fibres giving the desired strength to the board mate¬ rial e.g. at a use in packings for high temperature. Preferably the packing material includes at least one layer of metal fibres, which is situated bet- ween a first layer of cellulose fibres and a second layer of cellulose fibres, at which at least one layer of cel¬ lulose fibres contains a heat resistant material as kao¬ lin, kyanite or vermiculite. The packing material accor¬ ding to the invention is characterized in that the layers of cellulose fibres contain unbleached cellulose fibres, that fibres in the layers of cellulose fibres has a length less than 1 mm and that fibres in the layer of metal fibres is constituted by carbon steel with a carbon content of 0,08-0,12 % and with a fibre thickness of 8-80 ,um. Preferably the first and/or the second layer of cellulose fibres contains lignine. The layer of metal fibres also can be completely or partly penetrated by material from the first and the second layer of cellulose fibres and eventual binder which is brought between the layers of cellulose fibres. By this a resistent connec¬ tion of layers of cellulose fibres and layers of metal fibres is achieved.

The heat resistent materials as kaolin, kyanit or vermiculite being a part of at least one layer of cellulose fibres increase the capacity of the board to resist high temperatures. Owing to that the fibres in the layers of cellulose fibres have a length which is less

than 1 mm the board can be made satisfactory gas-tight.

The method according to the invention is charac¬ terized in that sheets containing cellulose fibres is made by dewatering of a pulp of cellulose fibres and heat resistant additional materials, that the sheets of cellu¬ lose fibres are provided with a binder on the sides which are proposed be facing each other in a complete packing and that at least one cloth (carpet) of steel fibres is brought between at least two sheets of cellulose fibres and that the sheets of cellulose fibres and the cloth of metal fibres are pressed together. The pressing of the sheets of cellulose fibres and the cloth of metal fibres is preferably carried out at an elevated temperature.

Thus it is possible by the invention to utilize fibres of carbon steel in a board which is produced from a pulp of cellulose fibres with a high water content. In the up to now known applications with admixing steel fi¬ bres in a board or a similar material it has been neces¬ sary to use stainless steel or other metals which are not affected of the water in the pulp from which the board is produced. By keeping the production of the layers of cel¬ lulose fibres from a pulp in water apart from the produc¬ tion of the layers of metal fibres it has been possible to use fibres of carbon steel. By applying the carbon steel fibres in a shape of a cloth (carpet) in the board the length of the fibres can be made very large and by that give god reinforcing properties. In order to in¬ crease the termal and the mechanical stability of the board it also can be to prefer to mix steel fibres with aluminium fibres. It is also possible to use aluminium fibres only in certain applications.

As an exemple of the heat resistance of the board at admixing different additional materials, a tem¬ perature resistance of 1300 C is achieved by admixing kyanit, 800°C by admixing vermiculite, which shall be compared with the heat resistans of resin of up to 500°C and cellulose of some above 100°C.

In examples of packing materials where particu¬ larly good results have been achieved the board according to the invention shows 1-4 layers of steel fibres with a carbon content of 0,08-0,12 % and a fibre thickness of 8-18 yum. The layers of steel fibres are surrounded on both sides of layers containing unbleached cellulose fibres and eventually lignine, which usually is washed from the boiled pulp at production of cellulose, but which in this case preferably can remain as it has proved to improve the properties of the packing material. The layers also contain softeners in the shape of latex mate¬ rials and also resins from the cellulose production as binders. The packing material is given a total thickness of 0,5-6 mm and has proved to stand a pressure of 65 bar at 265°C. At heating of the packing material, which normaly takes place in operation on the place where it is used, a vulcanization of the latex material takes place by the presence of sulphur in the other packing material. DESCRIPTION TO DRAWINGS The invention is described below as an embodi¬ ment according to the enclosed drawings.

Figure 1 shows three sheet-like parts constitu¬ ting layers for a board plate before pressing to a unit. Figure 2 shows five sheet-like parts for a board plate before pressing and cutting to a unit.

The three sheet-like parts, which shall be pres¬ sed to a unit according to figure 1 , show a first plate 1 and a second plate 2 containing cellulose fibres and de¬ sired fillers as e.g. kyanite and vermiculite. The plates are coated on the sides facing each other with a binder as e.g. resin. Between the plates of cellulose fibres a plate-shaped cloth 3 (carpet) of steel fibre is arranged, which, at pressing of the plates 1 , 2 of cellulose fib¬ res, will be penetrated of the binder and partly also of cellulose fibres and fillers in the plates 1 , 2 of cellu¬ lose fibres.

The example according to figure 2 shows five

joining sheet parts, of which a first, a second and a third plate 1, 2, 4 of cellulose fibres each also con¬ tains desired fillers, and of which a plate-like cloth 3 (carpet) is arranged between the first and the third plate 1 , 4 of cellulose fibres and between the third and the second plate 4, 2 of cellulose fibres. The first and the second plate 1 , 2 of cellulose fibres are coated with a binder as in the example according to figure 1 , while the third plate 4 of cellulose fibres is coated on both sides. Also in this example the cloths 3 (carpets) of steel fibres are penetrated of the binder, cellulose fibres and filler at pressing of the sheets into a unit.