GB2152943A - Anti-punking mineral fibre product - Google Patents

Abstract

Use of a mineral fibre product which has been treated with an aqueous solution of a melamine formaldehyde precondensate etherified with an aliphatic alcohol containing 1 to 4 carbon atoms, for the heat insulation of super heated fluids at temperatures above 400 DEG C. This mineral fibre product exhibits no punking behaviour, which means that at these high temperatures it can be used especially for the heat insulation of pipes carrying heated fluids.

Description

SPECIFICATION Fibrous mineral anti-punking product The invention relates to the use of a mineral fibre product of special composition for the heat insulation of super heated fluids, in particular fluids of which the temperature is above 400 C.

It is well-known for mineral fibre products for heat insulation to be manufactured in that directly after they have been produced from a molten mass, mineral fibres are directly sprayed with a binder after which they are compressed the compressed web of mineral fibre being subsequently allowed to harden.

Such mineral fibre webs can then be used for heat insulation, particularly for the lagging of pipes through which heated fluids are pumped.

The normally used mineral fibre products which contain phenol formaldehyde condensates as a binder can however only be used up to specific elevated temperatures without suffering destruction due to oxidation which occurs with relative rapidity. As soon as this limit temperature is exceeded, there is a tremendous development of heat in the mineral fibre product and furthermore a discoloration of the mineral fibre product. Consequently, dark zones initially form on the relevant surfaces of the mineral fibre product and can be attributed to the oxidation of this zone. Further raising of the temperature then leads to a complete destruction of the binder in the mineral fibre product which can extend to the point where fibres melt and cavities form in the material.And so the strength of the mineral fibre product is lost, the result of this being that the bottom part of the mineral fibre product with which the pipe is lagged sags so that the heat insulating effect is entirely lost.

This behaviour during which the strength of the mineral fibre product is lost by oxidation of the binder is described in English literature as "punking". A definition of this term is indicated for example in U.S. Patents Nos. 32 23 668 and 42 94 879, in which mixtures of phenol formaldehyde resins with dicyanodiamide or urea formaldehyde resins as a binder are described. The mineral fibre products known from the last-mentioned Patent Specifications are however not entirely punking-free. Instead, temperature can be higher or the thickness of the mineral fibre product may be increased without however eliminating the undesired punking effect.

Furthermore, mineral fibre products have already been used which have been treated with melamine formaldehyde binders. Such mineral fibre products are known for example from DOS 1694364,2543035, DAS 1271 666, German Patent Specification 958,868, DOS 20 20 033, DAS 1694378 or U.S. Patent Specification No. 3846 225. It is true that these products exhibit a better fire resistance than mineral fibre products which have been hardened with phenol formaldehyde resins but so far they have not been used for the heat insulation of superheated fluids, because it has only been possible to use mineral fibre webs produced by an impregnation process using melamine formaldehyde resin, but these are unsuitable for heat insulation of superheated fluids.These mineral fibre webs have been wrapped around the pipes, but due to the differing temperatures, intermediate spaces regularly form between the individual layers so that no effective heat insulation is achieved.

Furthermore, such webs often sag so that between the webs on the one hand and the pipe on the other cavities are created which encourage heat convection, which is likewise undesirable from the point of view of heat insulation.

DAS 1271 666 indeed discloses a mineral fibre web which has been strengthened with melamine formaldehyde condensation products. The mineral fibre products described therein were however only used for conventional heat insulation, the intention being to overcome the disadvantages which arise with glass fibre fleeces produced with phenol resins, in other words the unfavourable combustibility, the dark colouring, the unpleasant smell of phenol and strength losses under the effect of atmospheric humidity.

However, this Patent Specification did not suggest that mineral fibre products so manufactured and hardened with melamine formaldehyde binders ought to be used for heat insulation at elevated temperatures.

The invention is based on the problem of providing a mineral fibre product which, at elevated temperatures, particularly at temperatures above 400% can be used without punking behaviour being observed.

Surprisingly, it has now been found that mineral fibre products treated with an aqueous solution of a melamine formaldehyde condensate etherified with an aliphatic alcohol containing 1 to 4 carbon atoms can be used for the heat insulation of superheated fluids, particularly of fluids of which the temperature is above 400 C.

Therefore, among others, it is surprisingly possible for the mineral fibre products known from DAS 1271 666 and which have been treated from a completely etherified melamine formaldehyde precondensate, for heat insulation of such highly heated fluids.

It has been found that mineral fibre products used according to the invention exhibit no punking behaviour, i.e. that the binder contained in the mineral fibre product is not destroyed even when the product is used for lagging pipes containing liquids above 400 and as high as 500 C in temperature.

A more exact analysis of a mineral fibre product used in this way demonstrated that the binder in the mineral fibre product was vaporised in the immediate vicinity of the pipe and had become sublimated farther outwards, within the mineral fibre product. Consequently neither the form stability nor the insulating properties of the mineral fibre product according to the invention had become restricted, meaning that by virtue of this surprising behaviour a mineral fibre product was for the first time made available and could be used for heat insulation at temperatures above 400 C. This is not possible with the conventional mineral fibre products according to the state of the art, in other words those treated with other binders.

Furthermore, it is possible that the mineral fibre webs treated with melamine formaldehyde precondensates can be processed to produce pipe-shaped shells without premature hardening out being feared. To this extent, a not yet hardened web is wound onto a perforated core and processed to produce a tubular shell, hot air being passed in per se known manner through this perforated core until such time as complete condensation of the binder is achieved. Particularly with such pipe shells which are preferably used for heat insulation of pipes carrying heated media, it has surprisingly been established that the mineral fibre products treated with the melamine formaldehyde precondensates are punking-free, in other words rapid oxidation of the binder in the pipe shell, producing heat - as mentioned above - is entirely prevented.

Further details, advantages and embodiments are described hereinafter with reference to the accompanying drawings, in which.

Figure 1 shows a cross-section through a punking-free pipe shell; Figure 2 is a graphic representation of the gel time pattern of melamine resins, and Figure 3 a) is a graphic representation of a punking measurement of a mineral fibre panel according to the invention, and b) is a graphic representation of a punking measurement of a mineral fibre panel hardened with phenol resin.

The melamine formaldehyde precondensates to be used according to the invention exhibit the following formula:

in which R = H or -CH2 OR' and R' = H or low alcohol.

The melamine molecule is condensed with the formaldehyde in a ratio of : 1.5 to 1 : 4. preferably : 1.8 to 1 : 3 and in particular 1 : 2 to 1 : 2.5 on a molar basis. Consequently, in the case of the preferred embodiment, about half of group R is the group -CH2 OR', the balance of R having the significance of H.

This hydroxy methyl melamine (with a significance of R' = H) is however very readily reactive in an aqueous solution and by reason of the very short gel time explained in Figure lit is not suitable for spraying heated mineral fibres in a gravity shaft.

It has been established that the special etherification of these hydroxy methyl melamines according to the invention can prolong the gel time so that the melamine formaldehyde products used in this way, in the partially etherified form, can also be used for spraying mineral fibres in the gravity shaft.

According to the invention, therefore, the etherification ratio is advantageously at least 20 to 100 and is in particular around 40 to 65%. Consequently, in the preferred embodiment, 40 to 65% of the OH groups have been etherified with a low alkanol, while the remainder of the constituent remains non-etherified, i.e. R' has the significance of H.

Possible low alkyls are the methyl, ethyl, propyl or butyl group, the methyl group being preferred.

Consequently, methanol is used as an etherification medium preferably in the case of partially condensed melamine formaldehyde precondensates, a partially etherified methoxy methyl melamine being obtained.

The precondensates according to the invention form a clear liquid with easily viscous properties and have a pH value of about 9 to 10.

Ideally, the aqueous solution has a solids content of 30 to 80 and preferably 50 to 75% and is miscible at will with cold water.

Furthermore, this solution can be used at least for half a year so long as it does not come in contact with proton donors such as acids or the ammonium salts of strong mineral acids, and is not heated. Such precondensates can either be produced at the factory stage from the corresponding starting product such as melamine formaldehyde and advantageously methanol or can be used as an already finished product.

Manufacture of the melamine formaldehyde precondensates according to the invention, which are etherified, takes place in per se known manner. For example, melamine is firstly heated in aqueous formaldehyde solution in the previously described molar ratios at temperatures of about 50 to 90"C and at a pH value of about 7.5 to 10. This reaction can last up to 30 minutes. Then the reaction solution obtained is preferably acidulated and afterwards etherified with the corresponding alkanol, advantageously in a heated state, in the previously described molar quantities.

Figure 2 compares the gel time behaviour of a partially etherified melamine formaldehyde resin A according to the invention with that of a non-etherified but otherwise identical resin B.

The gel time behaviour is thereby a measure of wrkability of the resin at specific temperatures, the gel time becoming increasingly shorter as the temperature rises, since the condensation velocity likewise rises.

In order to be able to work mineral fibres in the heated state, i.e. in a shaft, the gel time must amount to more than about 7 to 8 and be ideally 10 to 12 minutes, at around 115 C. As Figure 2 shows, the gel time for a non-etherified conventional resin B is considerably below this level, at about 3 to 4 minutes and is thus not feasible. Such a resin leads therefore to a mineral fibre product which is already completely hardened out when it leaves the shaft.

In contrast, the partially etherified resin A according to the invention, such as is supplied for example by Messrs. HOECHST AG under the designation T 3102, has a considerably prolonged gel time which does not fall notably until about 135 C. This resin is therefore particularly suitable for spraying mineral fibres which have been heated and which are falling through a shaft and whose temperature is normally less than 135 C.

Advantageously, shaft temperatures lie thereby in a range from 70 to 130on. Consequently, polycondensation of the binder according to the invention in the shaft does not occur since the reaction behaviour of the resins according to the invention is too sluggish.

Therefore, the fact that heated mineral fibres can be sprayed with an aqeuous binder solution on a basis of etherified melamine resins which loses its water content due to evaporation and in which the solids become deposited on the mineral fibres without cross-linking occurring, while non-etherified resins harden out immediately in the shaft is surprising. If the reaction is thereby so controlled that the residual moisture in the fibres sprayed therewith is negligible, then a mineral fibre product which is obtained in this way, i.e. loose and sprayed with the partially etherified melamine formaldehyde precondensate according to the invention, can be obtained at the shaft outlet and does not have to be further processed immediately.It is well known that conventional formaldehyde precondensates, particularly those which are phenol based, dry out very quickly once they have been sprayed onto heated fibres in a shaft and they must therefore be compressed in a train of procedural steps and passed through a hardening station.

According to the invention, although no such treatment has to be carried out, it is however preferable from the point of view of production engineering.

In order to spray the mineral fibres explained hereinafter, the water clear liquid containing the precondensate according to the invention and having the previously mentioned high solids constituent must be so diluted with water that the proportion of binder in the hardened mineral fibre product lies in a ratio of 2 to 10 and preferably 3 to 6% by weight. Consequently, an aqueous solution is used which has at least 5 and preferably 10 to 12% by weight of solids.

Ideally, this solution is mixed with per so known adhesive agents, for example based on reactive amino silanes. Under such circumstances, these adhesive agents will be used in a quantity of approximately 0.1 to 0.3 and preferably 0.2% by weight in relation to the solid resin.

Furthermore, such solutions may advantageously comprise a catalyst which accelerates the rate of reaction of the polycondensation. To this end, acid-splitting agents (proton donors), for example ammonium chloride, ammonium sulphate or ammonium phosphate, are used, their proportion again related to the solid resin being about 0.5 to 2% by weight.

Should the pH value of this solution alter, then it should ideally be adjusted with ammonia to a value of about 9 to 10 in order not to increase the reaction velocity.

Adjusted in this way, a binder solution containing the etherified melamine formaldehyde precondensate is added to the mineral fibres which fall through the shaft which extends from the fibre production unit to the mineral fibre web production line.

The mineral fibres are manufactured in per se known manner, the conventional mineral starting products, for example silicate rocks, glass batch or metallurgical slags are used, which are melted in glass tank furnaces or cupolas.

The mineral fibres themselves are manufactured in per se known manner by the centrifugal process, jet process or jet drawing process. The fibres produced, while still hot, fall through the shaft or a so-called "collecting chamber" and - as previously stated, sprayed with the aqueous binder solution. During spraying, the water contained in the binder solution is evaporated. Evaporation itself is carried out according to the purpose to which the sprayed fibres are to be put, depending substantially upon the amount of heat available and required to evaporate the water.

Following on from the spraying with binder, if the mineral fibres are to be further processed, i.e.

compacted as then hardened by being heated, then the sprayed mineral fibres must still retain a certain residual moisture as otherwise with the etherified melamine formaldehyde precondensate according to the invention, polycondensation will not produce the desired gluing together of individual fibres. The residual moisture in the mineral fibres should advantageously be 1 to 10 and in particular 3 to 5% by weight in relation to the mineral fibres.

If the mineral fibres which comprise the etherified melamine formaldehyde precondensate according to the invention are substantially dry, in other words no longer capable of reacting, then the capacity for polycondensation can be restored if the mineral fibres are sprayed with water in the aforementioned quantities. In consequence, a mineral fibre while heated can be sprayed with an aqueous solution of binder without the substantially dry binder hardening subsequent to the spraying and evaporation of the water.

What is particularly surprising however is the fact that - as mentioned above - the capacity for polycondensation can be revived by simple spraying of water onto the mineral fibres which comprise the binder. Thus, a crude felt can be kept in stock and for manufacturing specific parts it can be fed into the production process once it has been sprayed with water. Furthermore, such a product can be used for making sandwich parts composed of different webs of mineral fibre material, i.e. mineral fibre webs webs which have, for instance, been treated with the binder according to the invention and a different binder such as phenol formaldehyde precondensate.In such a case, the phenol resin impregnated mineral fibre web is produced on-line, while the mineral fibre product provided with a partially etherified melamine formaldehyde resin according to the invention is for example taken from stock and sprayed with water on the production line. This stage would then be followed by the normal production stages of compacting the mineral fibres and subsequent hardening of these compacted fibres.

The mineral fibre products manufactured according to the invention are, after being sprayed in the shaft, subjected to a compression treatment, during which the loose fibres are compacted into a mineral fibre web.

Compression thereby follows a factor of 1: 4to 1 : 6 and the mineral fibre products obtained therefore, and according to the invention, ideally exhibit a crude density of 10 to 200 and in particular of 80 to 120 kgicu.m.

In per se known manner, compression already occurs in the gravity shaft and subsequently on a perforated conveyor belt, currents of air of normal magnitude being drawn by vacuum through the crude felt.

The compression treatment in a compacting station is followed by a hardening treatment in a conventional hardening station, throughflow hardening furnaces normally being used in which ideally both compression and also heating of the binder-treatment fibre web can be conducted.

As Figure 2 shows, at the start of polycondensation, at least a temperature of about 135 C is necessary.

Ideally, the temperature in the hardening station is in a range from 180 to 250 C.

Upon hardening, firstly the water still present in the fibre is evaporated, polycondensation being initiated at the same time and in the aforedescribed preferred temperature range, it will be carried out in a relatively short time.

Particularly advantageously, the as yet not hardened mineral fibre products according to the invention are processed to produce a tubular shell shown, for example, in Figure 1.

This Figure 1 shows a tubular shell 10 consisting of mineral fibre product manufactured according to the invention and containing as binder the etherified melamine formaldehyde resin in a polycondensed form.

The tubular shell 10 thereby enclosed a pipe 12 in which hot fluids are conveyed. Since these fluids may be at temperatures above 400 C, the mineral fibres must be punking-free, i.e. the mineral fibre insulating material solidified with binder and used for heat insulating purposes may not have its structure destroyed in the effect of heat causing oxidation of the binder.

This anti-punking behaviour of the tubular shells manufactured according to the invention is described hereinafter and is shown in Figure 3.

The tubular shell is produced in per se known manner, for example in accordance with the method disclosed in DOS 252 0462. With this method of manufacture, the as yet non-hardened mineral fibre web is wound onto a heated rotating spindle after which the resultant shell body is conveyed into a heated room where the free passage of hot gases over its entire surface area is made possible to ensure an even polymerisation.

As already stated hereinabove, a tubular shell produced in this way and consisting of the mineral fibre product according to the invention can be used for the heat insulation of pipes conveying a fluid which is at a high temperature.

As Figure 3 shows, a mineral fibre panel manufactured according to the invention is punking-free whereas a mineral fibre panel treated with conventional phenol resin based binder suffers destruction after about 5 hrs.

In the case of the experiment shown in Figure 3, a mineral fibre panel having a crude density of 80 kg/cu.m and a thickness of 30 cm was used. This mineral fibre panel has a binder content of 4% by weight but the binder is different.

Punking measurement is carried out in that the mineral fibre panel is placed on a hot plate, the temperature of which is maintained constant at the test temperature, for example around 500 C. At a distance of 20 mm (in the case of the phenol resin bonded mineral fibre panel according to Figure 3b) or 40 mm (for the melamine resin bonded mineral fibre panel according to Figure 3a), temperature sensors are introduced into the mineral fibre panel. The temperature measured is then plotted as a function of the test duration. When the mineral fibre panel is placed on the heated hot plate, measurement commences and the results are shown in Figure 3.

Figure 3a shows a number of graphs identified by reference numerals 1 to 9. Graph 1 represents the temperature ofthe hot plate while graphs 2to 8 showthetemperature in the mineral fibre panel as a function of the distance from the hot plate - as explained hereinabove. Graph denotes the surface temperature of the mineral fibre panel.

Figure 3b on the other hand has the gaps between the individual temperature sensors - as likewise described hereinabove - smaller, the graph 1 again identifying the temperature of the hot plate while the graphs 2 to 17 represent in each case the temperature between the relevant measurement points. Once again graph 18 indicates the surface temperature of the mineral fibre panel.

A comparison of Figures 3a and 3b reveals that at the start of measurement, therefore after about 2 to 5 hours, Figure 3b shows a sharp rise, attaining in the end peak values of some 860 C, in other words 360 C above the hot plate temperature. The exothermal reaction which occurs during this process is attributable to the punking, in other words the oxidation of the binder.

In contrast, there is no such temperature rise in a melamine resin bonded mineral fibre panel according to Figure 3a. Therefore, in contrast to the mienral fibre panel bonded with phenol resin, this panel is suitable for use on pipes and other appliances which are subject to a high temperature e.g. 400 to 550 C.

The gel time shown in Figure 2 indicates when and at what temperature the resin changes from the liquid to the gel-like state. The time lapse between the commencement of the test and the moment at which the resin changes to the gel state is generally referred to as the "gel time".

This gel time is measured as follows: The resin is further condensed at a given temperature in a glass vessel. The resultant variations in viscosity in the resin sample tested are determined by the power absorbed by a stirring probe. When a preselected limit viscosity is reached, the gel point, measurement is ended and the time from the commencement of gelling to the end of the test is automatically stopped.

The measuring apparatus used is a gel time meter of the type DiA-RVN made by Messrs. Bachofer of Reutlingen, which has a stirring probe for a viscosity range of about 50 to 70,000 mPa ~ s. This meter is adjusted to a specific temperature which is maintained constant throughout the duration of the test.

A measured viscosity curve normally shows first of all a portion of constant viscosity which is attributable to evaporation of the residual solvent. This area is then followed by one with a constant rise in viscosity which ends at 100% deflection, in other words a viscosity of 70,000 mPa 'Sand above. The commencement of the rise to the end of the measurement is thereby established as the gel time.

The measured gel time values are plotted as a function of the measurement temperature in Figure 2 and thus show the anticipated pattern of condensation of the relevant resin as a function of the selected temperature.

What must be regarded as particularly surprising in Figure 2 is the fact that the partially etherified melamine formaldehyde precondensate used according to the invention has at 135 C and below a virtually infinite gel time, i.e. it is no longer capable of polycondensation at temperatures below this level. On the other hand, however, this property increases very rapidly above this critical temperature. Thus, the precondensate according to the invention can be used for polycondensation at temperatures as low as 160 C and above.

Starting point of the invention was the development of mineral fibre shells which were to be used at elevated temperatures for heat insulating purposes. It was intended that the mineral fibre shells should enclose pipes conducting fluids at 400 C and above.

For this purpose, it was necessary to develop mineral fibre shells in which the normally organic binder was not completely destroyed by auto-ignition. Therefore it was necessary to create a mineral fibre product which would be punking-free in the range of temperatures of 400 C and above.

To this end, the following experiments were undertaken. Mineral fibres were in conventional manner reacted with equal quantities of the undermentioned binders.

a) 40 parts by weight phenol resin 30 parts by weight urea and 30 parts by weight dicyanodiamide formaldehyde A pipe shell produced in this way has a punking resistance up to a maximum of 350 C, and is completely destroyed at temperatures above this.

b) 55 parts by weight phenol resin 45 parts by weight urea and 10 parts by weight boric acid.

Shells produced with this binder have only an inadequate mechanical strength and thus cannot be used.

c) Phenol resin or urea-modified phenol resin and aqueous solutions of colloidal silica gel or potassium or sodium silicate neutralised with acid aluminium salts, phosphates or borates.

The workability of the binders was very difficult due to the instability of the solutions. The mechanical strength values of the mineral fibre products were about 50% lower than with the normal phenol resin binding, with the result that they were not suitable for the manufacture of pipe shells.

d) Urea modified phenol resin with colloidal aluminium oxide.

Also a mineral fibre product which is so produced has poor mechanical strength and cannot therefore be used for producing pipe shells.

Set out below is a comparison of the combustion values of binders used for mineral fibres and also of additives: Joulesigr Phenol resin without urea 28,000 Phenol resin with approx. 25% urea 23,800 Phenol resin with urea and dicyanodiamide - 1:1:1 21,000 Partially etherified melamine formaldehyde precondensate according to the invention 19,400 Urea resin 17,400 Urea 10,500 Dicyanodiamide 16,200 Starch 15,100 The foregoing summary shows that the combustion values of the melamine resin according to the invention and of the conventionally used binders consisting of phenol resin and modified with urea are relatively close to one another.

By virtue of this combustion value situation, it was not anticipated that the melamine ether formaldehyde resin according to the invention would exhibit a basically different behaviour under greatly increased temperatures than the other aforementioned binders.

In fact, according to the invention, it was surprisingly established that the etherified melamine formaldehyde condensate exhibits an entirely different decomposition process during the punking test.

Whereas, namely, phenol resin on hardened mineral fibres burns away completely from the fibres at a temperature loading, the melamine ether resin sublimates in the temperature range above 350 to 400 C out of the mineral fibre insulating material and condenses as a white deposit in the outer cooler fibre layers.

Consequently, total oxidation reaction of the binder in the region of the intensely heated zone is suppressed and thus complete decomposition of the binder present in the mineral fibre product is avoided. In the last analysis, therefore, the moulded boxy produced from a mineral fibre product which is so hardened will not be destroyed and can therefore be successfully used for the heat insulation of superheated fluids. Thus the mineral fibre products according to the invention can be successfully used in the form of pipe shells for heat insulation in heating power stations and in the heat insulation of pipes in which superheated steam circulates at temperatures of 400 to 500 C.

The thickness of the pipe shell depends on the temperature of the fluid conveyed through the pipe.

Similarly, too, the raw density is dependent both upon the thickness and also on the temperature of the fluid.

It has been established that for a crude density of about 100 kg/cu.m, the pipe shell should ideally have a thickness of at least about 200 mm, if the fluid is at a temperature of some 400 C. This thickness can advantageously be increased to about 300 mm if the fluid temperature is some 500 C.

By reason of this relatively considerable thickness, it is according to the invention advantageous to use a plurality of pipe shells one over another so that their individual thicknesses add together to produce the total thickness. To this end, the pipe shells are matched to one another in their outer and inner diameters so that they can without difficulty be assembled together in a form-locking fashion.

Claims (13)

1. A method of insulation, whereby as insulating material there is used a mineral fibre product which has been treated with an aqueous solution of a melamine formaldehyde precondensate etherfied with an aliphatic alcohol containing 1 to 4 carbon atoms.

2. A method according to claim 1, for insulating a fluid at a temperature above 400 C.

3. A method according to claim 2, wherein said fluid is flowing in a pipe.

4. A method according to any preceding claim, characterised in that the etherification degree of the precondensate amounts to 20 to 100%.

5. A method according to claim 4, wherein the degree of etherification amounts to 40 to 65%.

6. A method according to any preceding claim, wherein the aliphatic alcohol is methanol.

7. A method according to any claim, wherein the precondensate is sprayed onto the mineral fibres in the form of an aqueous solution containing at least 5% by weight of solids.

8. A method according to claim 7, wherein the aqueous solution has a solids content of 10 to 12% by weight.

9. A method according to claim 7, wherein the aqueous solution contains an adhesive agent andlor acid-splitting agent.

10. A method, according to claim 1, wherein the mineral fibre product has an apparent density of 80 to 120 kgicu.m.

11. A method according to claim 1, wherein the polycondensation of the etherified melamine formaldehyde precondensate has been carried out at a temperature from 180 to 250 C.

12. A method according to claim 1, wherein the mineral fibre product is in the form of a pipe shell or of a moulding.

13. An insulating material comprising a mineral fibre product which has been treated with an aqueous solution of a melamine formaldehyde precondensate etherified with an aliphatic alcohol containing 1 to 4 carbon atoms, wherein the etherification degree of the precondensate amounts to 20 to 100%.

13. A method according to claim 12, wherein a plurality of pipe shells or mouldings are superimposed to a total thickness of at least 20 cm.

14. An insulating material comprising a mineral fibre product which has been treated with a aqueous solution of a melamine formaldehyde precondensate etherified with an aliphatic alcohol containing 1 to 4 carbon atoms.

15. An insulating material according to claim 14, in the form of a pipe covering shell or moulding.

Amendments to the claims have been filed, and have the following effect: (a) Claims 1 & 4 above have been deleted or textually amended.

(b) New or textually amended claims have been filed as follows: (c) Claims 5 to 13 & 15 above have been re-numbered as 4to 12 & 14 and their appendancies corrected.

1. A method of insulation, whereby as insulating material there is used a mineral fibre product which has been treated with an aqueous solution of a melamine formaldehyde precondensate etherfied with an aliphatic alcohol containing 1 to 4 carbon atoms, wherein the etherification degree of precondensate amounts to 20 to 100%.