PRIOR ART A general method in the manufacturing of a fire proof door comprises the cutting of panels made of gypsum or silicate into appropriate dimensions, whereby also openings are made for possible locks or the like. The panels are laid in place and may be fixed against the respective door sheet by an adhesive. An insulation material, e. g. mineral wool, may be applied to the gypsum panels for instance by adhesively securing, whereafter the door leaf is assem- bled. Each gypsum panel that covers a door sheet is about 6-12 mm thick and contains about 18-20 percent by weight tightly bound water.

The German patent publication DE 36 03 705 (WOLFGANG ARHEILIGER) relates to a fire protection door with panels and spacers of asbestos-free silicate fibre (also called fibre calcium silicate) with a water content of not more than 10%. The spacers are arranged in pairs in such a way that spaces are formed between these and the panels. The spaces contain air or are filled with some other heat resistant and insulating material.

The German patent publication DE 38 07 833 (PAUL SCHMITZ GMBH) relates to a sound-insulated steel door containing damping panels on the inside of the door sheets. The panels are of fibre silicate material and have also a fire

protecting effect. Mineral wool is applied in the door as a filling material.

There also exist, as depicted in the European patent application EP 0 741 003 (GRUNZWEIG+HARTMANN AG), fire protecting viscous silicate masses sandwiched between two glass-fibre textures, which masses are dried at a tempera- ture of 130° Celsius. These fire protecting elements are prefabricated and are then appropriately cut to dimensions adapted for an application and mounted.

The problems of these known fire protection doors and elements are that it is relatively time-consuming to cut the fire protecting panels and adhesively secure them and thereafter to secure the insulation.

Besides, they are not flexible to the extent that if an extra strong fire protection is desired locally, this is difficult to achieve. The door leaves also become rela- tively heavy.

Furthermore, the silicate masses need a relatively long hardening or drying time. The panels are intermediate stored in this respect at least a few days.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method in the manufacturing of a door arrangement, parti- cularly a door leaf, a door frame or a dressing of a door, with fire protection function that is effective and flexible.

Another object of the invention is to provide a fire protecting door arrangement of relatively low weight and to a low cost.

These and other objects are accomplished according to one aspect of the invention by a method according to which a

first and a second door sheet, each door sheet having a first and a second surface, are provided. A fire protect- ing mainly homogeneous silicate suspension with hardener is applied to at least the first surface of the first door sheet. The silicate suspension ought to comprise a sili- cate of an alkali metal and a filler, preferably manu- factured according to a method where the filler is treated with an acid in a slurry, whereafter this is mixed with an aqueous solution containing a alkali metal silicate. The method is further described in the European patent appli- cation EP 0 507 368 (THORS KEMISKE FABRIKKER A/S). A fill- ing complement material, such as for instance the insula- tion material mineral wool, is applied to said silicate suspension, whereafter the door leaf is assembled, i. e. the first and second door sheets are mounted with the first surface of the respective door sheet facing each other. Finally, the fire protecting mainly homogeneous silicate suspension is allowed to harden and give off part of its loosely bound water.

The fire protecting mainly homogeneous silicate suspension is preferably applied in a relatively large amount, parti- cularly at least 1-2 kg per square meter door sheet. In this respect it is possible to apply the silicate suspen- sion in a varying amount over the surface to locally vary the fire protecting capability of the door leaf. The sili- cate suspension may also be applied to the first surface of the second door sheet. Conventional glue may be applied to further increase the adhesion in the door leaf.

A problem of such an inventive door leaf, particularly in environments with large temperature gradients, may be that the silicate suspension gives off so large amounts of water that the door leaf leaks out water. It is therefore preferable to locate an absorbent means in the door leaf for absorption of the water that is given off from the fire protecting mainly homogeneous silicate suspension.

The absorbent means is drying during a very long period of

time. Alternatively, or as a complement, the door leaf may be held at a higher temperature during assembly. A pre- ferable temperature is hereby about 50-70° Celsius. The temperature should be high enough to yield a fast evapora- tion but at the same time low enough to prevent the tight- ly bound water (that constitutes the real fire protection) to vanish. It is also possible to blow, particularly with compressed air, through the door leaf and hereby remove further water.

According a second aspect of the invention the above described method is utilized in a corresponding way in the manufacturing of a door frame and a dressing of a door with fire protecting properties.

The advantages of the present invention comprise a simpler and cheaper manufacturing process and flexibility in placement of the fire protecting material.

Yet another advantage of the invention is that the mainly homogeneous silicate suspension is non-polluting and allows for a non-polluting manufacturing process. It serves also as a sound-absorbing material.

Still another advantage is that the door leaf is lighter (about 10-20 kg lighter for a door with a 60 minutes classed fire protection), which implies another, more advantageous, dimensioning of hinges and cheaper trans- ports. The weight of the door leaf is certainly affected by the choice of thickness of the sheet metal and amount of applied silicate suspension.

Further advantages of the invention will be apparent from the specification below.

SHORT DESCRIPTION OF THE DRAWINGS The invention is described closer below with reference to Figures 1-3, which are shown only to illustrate the inven-

tion and shall therefore in no way limit the same.

Figure 1 shows a fire protecting door leaf in two views according to the present invention.

Figure 2 shows a cross-section of said inventive door leaf along the line A-A in Figure 1.

Figure 3 shows part of said cross-section in larger scale.

PREFERRED EMBODIMENTS In the following description, with purposes of explanation and not limitation, specific details are set forth such as particular applications, techniques etc to give clear understanding of the invention. It shall though be clear to the man skilled in the art that the invention may be performed in other ways.

In Figure 1 an inventive door leaf is shown comprising door sheets 1 made of steel sheet. They may be bent along the sides so that they more easily may be assembled to the finished door leaf.

A silicate mass or a silicate suspension 2 is mixed with a hardener (accelerator) and is applied to the door sheets 1 through an orifice in relatively large amount, particular- ly about 10 times more than with conventional gluing, which implies about 1-6 kg for a door leaf in a standard size (about 1-3 kg/m2). Applied amount is related to the fire protection desired and the other parameters of the door. The silicate suspension, which is also referred to as a silicate-based binder, and comprises alkali metal silicate and filler, is object to a separate patent appli- cation, see EP 0 507 368, which publication is hereby included as a reference. The binder is further described below in this description. The hardener or accelerator, that may contain about 30-60% esters, is applied preferab- ly in small amounts, particularly about 2-5% of the amount

of silicate suspension. To achieve a satisfactory fire protection a two-component mass is probably necessary.

Examples of products comprising such a silicate suspension and hardener are Thorsil 7104 Tm and Thorsil K67-PTM manu- factured by EKA CHEMICALS.

The applying is performed in flowing form so that parts of or the complete surface is covered by a couple of milli- meters thick layer of silicate suspension. This applying is very flexible and if a better fire protection is desired locally, a thicker layer of suspension is applied there.

A filling material 3 is then applied, which preferably is constituted by an insulation material such as mineral wool, a spacer or the like, whereafter the door sheets 1 are mounted together to form a door leaf. In this respect the door sheets are screwed or welded together. They may alternatively be mounted on a frame of, for instance, bent or rolled steel sheet. The door sheets may also be inte- gral with each other from the beginning, i. e. constitute part of solely one sheet.

In this respect cutting out, mounting and gluing of the panels that are described in known art may be despensed with. Fire protection and adhesion may now be obtained at the same time by the same material.

A fire proof door made of wood may be manufactured accord- ing to the invention in a corresponding way. The door sheets are manufactured in wood or in some laminate mate- rial and the filling material may be constituted preferab- ly of fibreboard.

A traditional water glass consists of about 35% of a mixture of Na2O and Si02, commonly in the relationship 1: 3,4, and the rest is water. This implies that such a water glass may give off all its water at room tempera-

ture. In practice there remains a lesser part tightly bound water, about 5%, that vanishes first at higher temperatures.

In the mainly homogeneous silicate suspension utilized in the present invention the portion tightly bound water is approximately 20-25% and the portion free water is of the same size. The rest is dry substance. Tightly bound water means water that vanishes at a higher temperature, parti- cularly at about 100-110°C, and loosely bound (or free) water means water that vanishes during the time at room temperature. The fact that the tightly bound water, which constitutes the main part of the fire protection, vanishes at a temperature of about 70-150°C or around, is essential for its fire protecting capability.

The silicate suspension may be manufactured according to the following. A filler is treated with an acid in a slurry, whereafter the slurry is mixed with an aqueous solution of an alkali metal silicate to a mainly homoge- neous suspension. The acid is preferably an aqueous soluble organic acid. The filler, that ought to be rela- tively stable in an acid environment and mainly stable in an alkali metal silicate solution, may be constituted of particles of kaolin, feldspar, pearlite, titanium dioxide, aluminium trihydrate, muscovite, talc or the like with a preferable diameter less than about 100 ßm. Preferably, the filler is applied in an amount corresponding to 4-80 percent by weight of the alkali metal silicate. The alkali metal silicate is a mixture of M20, where M is sodium, potassium or a mixture thereof, and Si02 in a relationship of 1 to about 2-4.

The suspension manufactured in this manner is constituted by a substantially stable mass that does not stratify. It is highly viscous (about 20000 centipois) and has a rela- tively good adhesion capability on certain kinds of sheet material, for instance zincified sheet material.

The silicate suspension described is not as sensitive to moisture as a traditional water glass and it does not give off as much water.

The silicate suspension is not commonly applied to the upbent edges of the sheets, but it may so be done. Conven- tional adhesive may also be applied to further increase the adhesion capability. The fire protection agent may furthermore be applied in a door frame and a dressing of a door, see below.

The loosely bound or free water vanishes commonly during a period of about two years in a mounted door leaf (much faster if the silicate suspension is lying exposed). A further fire protection the two first years may hereby be achieved. However, this implies also problems because of the fact that such large amounts as 1.5-2 kg water vanish.

Two solutions to this are proposed.

The first solution comprises that an absorber means 4 is applied in a door leaf and this absorbs the amount of water given off from the silicate suspension, so that the door leaf does not leak. The absorber means, which pre- ferably is applied in thin light layers, may absorb up to 100-200 times its own weight and dries over very long time.

The other solution comprises removing of the water (as far as possible) during manufacturing of the door leaf. This is performed by holding the door leaf during mounting at a temperature of 50-70° Celsius, whereby partly the mass hardens faster, partly the free water evaporates.

By blowing through the insulation by compressed air, large amounts of water may be removed. During experiments half of the water, i. e. 6 dl, has been blown away in about 15 min. The door leaf should, however, not be heated so the

first tightly bound water starts to vanish-the fire protection capability of the door leaf is thus reduced.

Tests in both model scale and full scale have shown that a door leaf according to the present invention pass the so- called EI-fire protection requirements with large margin as regards both temperature rise and integrity. It has also been shown that not more than 25% of the weight of the silicate suspension can vanish at normal room tempera- ture and humidity. Laboratory-aged test elements exhibit very good fire protection properties.

In the present invention the term door leaf is considered to include also gates and shutters. The door leaf may be a square-edge door or a rabbeted door leaf. Furthermore, the invention is applicable on other parts comprised in a door arrangement. For instance the silicate mass may be applied to a door frame, to its door frame side and/or to its door frame head. The frame may be a single or a double chamfer frame or a special door frame. Furthermore, the silicate suspension may be applied to a dressing of a door.

The present invention, as hereby described, solves the problems associated with known art by utilizing the prin- ciple of using a liquid material, particularly a silicate suspension, for direct application to door sheets, to door frames and to door dressings, for fire protection function or fire protection function and adhesion function. It is obviously not limited to the embodiments described above and shown on the drawings, but may be modified within a scope of the appended claims.