EP1198429A1

EP1198429A1 - Production of mineral fibres

Info

Publication number: EP1198429A1
Application number: EP00940276A
Authority: EP
Inventors: Vermund Rust Christensen; Soeren Lund Jensen; Jens Ranloev
Original assignee: Rockwool International AS
Current assignee: Rockwool AS
Priority date: 1999-05-28
Filing date: 2000-05-26
Publication date: 2002-04-24
Also published as: AU5526200A; WO2000073233A1

Abstract

Man-made vitreous fibres having a composition comprising 16 to 23 % alumina and 4 to 8 % alkali oxides are produced from a charge which comprises molded briquettes comprising at least 5 wt.% of a material selected from (a) alkali feldspar, nepheline, leucite and sodalite (mineral concentrates), (b) syenite nepheline syenite, phonolite, alkali basalt and other natural rocks containing at least 40 % alkali feldspar and (c) front screen glass waste and mixtures thereof.

Description

PRODUCTION OF MINERAL FIBRES

This invention relates to processes for the production of man-made vitreous fibres (MMVF) which are durable in use but which can be shown to be biologically advantageous, and to novel briquettes suitable for use in such processes.

It is known to produce MMVF by providing a charge of mineral material having an appropriate composition, melting this charge in a furnace and fiberising the melt, for instance by a cascade spinning process.

The charge can be melted in various types of furnace. One known furnace type is the shaft furnace (for instance a cupola furnace) , in which combustion air is blown into the furnace through the charge, which includes fossil fuel to provide energy for melting. In order to achieve a uniform heating and melting profile, it is important that the air flow through the stack is not disrupted. Therefore in such a process it is important that the charge forms a self-supporting stack which has considerable strength even at the high temperatures (eg above 1,000°C) which prevail in the furnace. The stack should also be sufficiently permeable that melt may drain to the bottom of the stack. In such a system, raw materials are often charged as coarse lumps, for instance of rock or slag, or are formed into molded briquettes of particulate material. The use of briquettes allows the inclusion of fine particulate material which may not be suitable for direct addition to the furnace. Such briquettes are usually molded in the presence of a binding agent such as cement or molasses . In recent years the requirement for biologically soluble fibres has been addressed by modifying the chemical composition of the fibres, for instance the amount of alumina Al₂0₃. In 096/14454 and W096/14274 we described that advantageous biological solubility properties were obtained with medium to high amounts of alumina, with values of 14 or 16% upwards being exemplified in 096/14274 and amounts of 18% upwards being described and exemplified in W096/14454.

Although several of the fibres specifically disclosed in W096/14454 and 096/14274 have proved to be very interesting and valuable as fibres which are soluble in biological media, there remains a desire to achieve an improved combination of biological solubility, especially when determined by in vivo tests, and ease and efficiency of manufacture . The ease of manufacture problems arise because the compositions that provide the required analyses of MMVF are preferably fiberised using a cascade rotor process, for instance as described in O92/06047. In a cascade rotor process, the molten composition (mineral melt) is poured on to the first rotor in a set of substantially horizontally mounted rotors, and the melt is thrown from that rotor on to a second rotor in the set, from which it is thrown as fibres. Some melt is usually thrown off the second rotor onto a third rotor in the set, from which melt is thrown as fibres, and in preferred processes melt is also thrown off the third rotor onto a fourth rotor, from which it is thrown as fibres.

There is a desire to provide fibres which have improved biosolubility, but which can still be made by methods which are generally conventional and cost effective .

Other workers in the field have attempted to develop improved fibres. In O97/30002 it is proposed to make fibres containing 35 to 45% Si0₂, 18 to 25% Al₂0₃, 0 to 3% iron oxide and 0 to 3% total alkali. In the only example, the fibre contains 40% Si0₂, 0.4% alkali and 1.7% iron. These fibres also contain phosphorus .

Other phosphorus-containing fibres are described in O99/08970 in which the amount of Si0₂ is 38 to 47%, A1₂0₃ 16 to 20%, alkali 0 to 6% and iron 3 to 10%. In each of the examples the amount of Si0₂ is 42% or more and the amount of alkali is 3% or less. In WO97/29057 the amount of Si0₂ is 30 to 51%, Al₂0₃ 11.5 to 25% and alkali 10 to 19%. A somewhat similar definition is given in DE-U-29709025 but the highest exemplified amount of Al₂0₃ is 15%. In WO98/15503 various fibres having more than 18% alumina are exemplified. The amount of alkali is low and the highest amount exemplified is 2.3%. O83/01947 is not concerned with providing fibres having advantageous biological solubility properties. Instead it is concerned with providing fibres which are suitable for strengthening cement and concrete products and which must thus have high resistance to chemical attack by the alkali in the cement mixtures. A composition is exemplified in which the amount of alumina is 17.6%. There is no suggestion to use briquetted raw materials to form the fibres and the publication simply discloses grinding of raw materials such as slate and limestone and admixing and melting them in a furnace.

It would be desirable to provide processes for producing fibres with advantageous biological solubility and in which good processing characteristics are obtained. To this end, we wish to produce fibres which comprise amounts of alumina (Al₂0₃) of from 16 to 23%, preferably 19 to 23%, and alkali (Na₂0 and K₂0) of from 4 to 8%. The defined amounts of alkali in particular are unusual for fibres of the high alumina type.

In order to produce such fibres it is necessary to provide starting materials having sufficiently high content of alkali oxides. However, the standard materials for providing alkali content, namely calcined sodium and potassium carbonate (soda ash and potash) , although in theory they would be beneficial because they can provide high levels of the relevant oxides, are, we have found, inappropriate in practice for production of stone wool fibres. These materials tend to disintegrate rapidly in the furnace when added as supplied. This is a particular problem when the melt is being produced in a shaft furnace such as a cupola furnace. As discussed above, in such a furnace it is important that the charge forms a self- supporting stack. Materials which disintegrate rapidly in the furnace cannot provide support in the stack and can lead to disruption of the air-flow.

Consequently, we have attempted to incorporate such materials into molded briquettes, with the intention of incorporating high levels of alkali into the fibres without collapse of the charge. However, we have also found that the presence of these materials in briquettes can cause problems with the briquettes themselves. In particular, when cement is used as che binding agent, soda ash and potash tend to inhibit successful curing of the cement, and can also hinder curing when the curing agent is molasses. Furthermore, these materials tend in any case to evaporate rapidly from the furnace and use of the raw material is thus inefficient.

Conventional waste glass cullet (eg from window panes) is another potential candidate for providing alkali content but tends to melt too rapidly even in briquettes and thus is also inappropriate in a shaft furnace.

DT2536122A is a general disclosure concerning a method for the addition of basalt and other raw materials to furnaces for production of melts for various purposes, including production of mineral wool. Basalt is formed into briquettes and various other materials may also be included, including nepheline syenite and phonolite amongst a wide range of other materials. A briquette is exemplified which comprises 45 parts phonolite but these briquettes are clearly intended for use in a glass oven and not a shaft furnace.

This publication does not disclose any fibre compositions. In particular, it does not disclose fibres of the type discussed above containing high levels of alumina and relatively high levels of alkali. Nor does it address the difficulties, discussed above, in providing such fibres from materials such as soda ash and potash, especially in a shaft furnace. In particular, the publication appears to equate soda ash, potash, nepheline syenite and phonolite. It mentions a range of binders, including molasses and cement, but does not address the specific problems we have found arise when materials such as soda ash and potash are used together with cement or molasses binder.

Consequently, we have investigated alternative raw materials for such a process and have found that a selected group of materials are particularly appropriate for providing fibres with high levels of alkali oxides but can also be incorporated into briquettes without difficulty and, despite their often relatively high content of alkali metal, can be used efficiently in the furnace without excessive evaporation.

According to the invention we provide a process of producing MMV fibres which have a composition comprising

(by weight of oxides) 16 to 23% (preferably 19 to 23%) Al₂0₃ and 4 to 8% Na₂0 plus K₂0 comprising providing in a furnace a charge of mineral material, melting the mineral material to form a mineral melt and fiberising the mineral melt, wherein the charge comprises molded briquettes which comprise at least 5 wt.% of a mineral material selected from the group consisting of (a) mineral concentrates selected from alkali feldspar, nepheline, leucite and sodalite, (b) natural rocks selected from syenite, nepheline syenite, phonolite and alkali basalt and those natural rocks containing at least 40% alkali feldspar (eg pegmatite and granite rich in alkali feldspar) and (c) front screen glass waste (i.e. waste glass from the front screens of tubes used for televisions, monitors etc) and mixtures thereof.

Definitions of the mineral materials may be found in "An Introduction to the Rock-forming Minerals", Deer, Howie and Zussman (Longman, 1983), which defines (a) mineral concentrates in particular and "Igneous and Metamorphic Petrology", Best (Freeman, 1982), which defines (b) natural rocks in particular.

Preferred mineral concentrates (a) have content of alkali (Na₂0 + K₂0) of from 8 to 30 wt.%, more preferably 10 to 26 wt.%, in particular from 12 to 24 wt.%. Preferred alkali feldspars comprise up to 12% Na₂0 and up to 12% K₂0, in particular 1 to 12% Na₂0 and 1 to 12% K₂0. Preferred nephelines contain 14 to 18% Na₂0 and 0 to 3% K₂0. Preferred leucites comprise 3 to 6% Na₂0 and 18 to 22% K₂0. Preferred sodalites comprise 10 to 25% Na₂0 and 0 to 5% K₂0.

Preferred alkali feldspar rich rocks contain at least 50%, more preferably 60%, alkali feldspar. Preferred rocks include those which have Na₂0 content of from 3 to 5 wt.% and K₂0 content of 3 to 5 wt . % . They may be for instance pegmatites (eg zoned pegmatites or simple or complex pegmatites) or alkali-feldspar rich granite. Preferred nepheline syenites have content of 7 to 9% Na₂0 and 5 to 7% K₂0. Syenites having content of 4 to 7% Na₂0 and 4 to 7% K₂0 are particularly useful. Preferred phonolites comprise 6 to 9% Na₂0 and 5 to 7% K₂0. Preferred alkali basalts comprise 3 to 6% Na₂0 and 2 to 5% K₂0.

A further, although less preferred, raw material is (c) waste front screen glass. This is waste glass from the front screen of tubes used for televisions, monitors etc. We find that this type of glass is particularly beneficial in the invention in comparison with, say, standard glass cullet from window panes and even in comparison with the glass which forms the remainder of a tube. The front screen glass contains a combination of minerals which are particularly suitable for providing the properties required in the invention. It often contains for instance medium levels of barium (e.g. 0.3 to 15, often 1 to 12%) and strontium (e.g. 0.5 to 12.5, often 1 to 10%), which can provide advantages in stone wool fibres . It generally contains lower levels of alkaline earth metals such as calcium and magnesium than other types of waste glass cullet. Preferred levels of alkali are from 10 to 17 wt.%, preferably from 14 to 16 wt.%.

In this specification, alkali content of raw materials is measured by weight of oxides . Preferably the raw material has a content of alumina also, in particular at least 15 wt.%, preferably at least 19 wt.%, more preferably at least 24 wt.%. Suitable materials which contain alumina include phonolite, nepheline syenite and syenite. Preferably the content of silica in the raw material is not more than 65 wt.%, preferably not more than 55 wt.%. Front screen glass waste is particularly suitable for providing low silica content and its content of silica is often below 65%, preferably below 62%. This is to be compared with standard glass cullet which may have content of silica of 70% or greater.

Preferred mineral concentrates (a) are alkali feldspar and nepheline. Preferred natural rocks (b) are nepheline syenite, alkali basalt and syenite, especially alkali basalt and syenite.

In the invention the charge must comprise briquettes comprising at least 5 wt.% of one or a mixture of these materials. Preferably at least 20 wt.% of the charge, more preferably at least 40%, comprises such briquettes. The amount may be up to for instance 85 or 90%, but is generally not more than 70%.

In most cases it is beneficial to include other components of the charge as coarse lumps. Of the materials above, alkali basalt may be added as coarse lumps in addition to that which is added in the briquettes.

In the charge as a whole the total amount of the essential raw materials defined above is preferably at least 5%, more preferably at least 10 or 20%. Generally it is not more than 70%, preferably not more than 50% or 40%. It is preferred in the invention that the furnace is a shaft furnace, in particular a cupola furnace, since the invention is particularly beneficial in such a process. However, the invention can be applied in other types of furnaces, such as electric and tank furnaces.

The process requires the use of briquettes to form part of the charge. These include at least 5 wt.% (based on the briquette) of the defined material. Preferably they include at least 10% or 12%, preferably at least 15 or 20% and more preferably at least 25% of materials selected from the defined group. The briquettes may contain up to 80%, preferably not more than 70%, and in practice generally not more than 50%, of such materials.

The amount of any one of the defined materials can be up to the levels above but preferably is not more than 50%, more preferably not more than 40% and in particular not more than 30%. Preferably all briquettes contain at least 5 wt . % of the defined materials, although more than one type of briquette (ie composition of the briquettes) may be used. If briquettes which contain less than 5% of these defined materials are used these preferably constitute less than 50%, more preferably less than 30%, of the briquettes in the charge .

The briquettes may be made in known manner by molding a mix of the desired particulate materials (including the defined alkali-containing material) and a binder into the desired briquette shape and curing the binder.

The binder may be a hydraulic binder, that is one which is activated by water, for instance cement such as Portland cement. Other hydraulic binders can be used as partial or complete replacements for the cement and examples include lime, blast furnace slag powder (JP-A- 51075711) and certain other slags and even cement kiln dust and ground MMVF shot (US 4,662,941 and US 4,724,295). Alternative binders include clay. The briquettes may also be formed with an organic binder such as molasses, for instance as described in W095/34514. Such briquettes are described herein as formstones . The invention is particularly beneficial when the binder is cement, because standard alkali-containing materials such as soda ash and potash give problems in combination with cement . The invention can also be beneficial when the binder is molasses, which can also give problems in combination with soda ash and potash.

In the process the fibres produced comprise 19 to 23% Al₂0₃, preferably 20 to 22%. They also comprise 4 to 8% Na₂0+K₂0, preferably 4.2 to 7%.

The fibres are generally of the type known as stone fibres and thus preferably contain 20 to 35% CaO+MgO, more preferably 25 to 30%.

Preferably the fibres comprise 34 to 39% Si0₂, more preferably 35 to 38%.

It is also preferred that they contain 0 to 3% Ti0₂, more preferably not more than 2%, in particular 0.5 to 2%.

The amount of iron is preferably from 3 to 10%, more preferably from 4 to 9%. Throughout this specification, the amount of iron is quoted as FeO .

P₂0₅ may be present, preferably in an amount of from 0 to 2%, more preferably 0 to 1%, especially 0.1 to 0.8%. Other elements may be present in amounts up to 5%, more preferably up to 2%. The invention is particularly suitable for the production of novel fibres which we have described in our copending application number ... (reference PRL04240WO claiming priority from British Patent Applications 9915043.5 and 9912564.3). These fibres are particularly beneficial for efficient fiberisation. The combination of ease and cost of manufacture and solubility properties is optimised, in particular in comparison with those exemplified in W096/14454 and W096/14274. In particular, the process can be used to provide novel MMV fibres having a composition which includes, by weight of oxides,

Si0₂ 34.0 to 40.0%, preferably 34.0 to 39.0%, more preferably 35.0 to 38.0% A1₂0₃ 19.0 to 23.0%, preferably 20.0 to 22.0%

CaO + MgO 20.0 to 35.0%, preferably 25.0 to 30.0%

Ti0₂ 0 to 3%, preferably 0 to 2%

Na₂0 + K₂0 4.0 to 8.0%, preferably 4.2 to 7.0% FeO 3.0 to 10.0%, preferably 4.0 to 9.0%

P₂0₅ 0 to 2%, preferably 0 to 1%

Other elements 0 to 5%, preferably 0 to 2%.

It should be understood that any of the preferred lower or upper limits may be used in combination with any of the essential or preferred upper or lower limits for each element, and that any combination of the essential and preferred amounts for the different elements may be made.

The amount of Si0₂ is preferably at least 35.0% and is preferably not more than 38.0%. It is particularly preferred that the amount of Si0₂ should be at least 35.0% but preferably not more than 37.0%. The amount of A1₂0₃ is usually at least 20.0% and is preferably not more than 22.0%. Values of from 20.0 to 21.5% are particularly preferred, especially when the amount of Si0₂ is at least 35% and/or not more than 37%.

The amount of Na₂0 plus K₂0 is preferably at least 4.2% and is preferably not more than 7.0%. It is preferably at least 4.3% but preferably not more than 6.0%.

The amount of iron is preferably at least 4.0% but is usually not more than 9.0%. Preferably it is at least 5.0% but preferably not more than 8.0%.

Throughout this specification, the amount of iron is quoted as FeO.

The amount of Si0₂ + Al₂0₃ is generally below 62.0% and preferably it is below 60.5%. In particular, best results are generally obtained when it is from 55.0 to 59.0%, and in particular when it is from 56.0% to 58.0%.

The amount of Si0₂ + Al₂0₃ + 2R₂0 (where R is sodium plus potassium) is preferably in the range 63.0% to 75.0%. Generally it is at least 64.0, preferably at least 64.5% and often it is at least 65.0%. Generally it is not more than 70.0% and preferably it is not more than 69.0%. It is meaningful to define these fibres partly by reference to Si0₂ 4- Al₂0₃ and/or partly by reference to Si0₂ + Al₂0₃ + 2R₂0 because the selection of the relative amounts of Si0₂, Al₂0₃ and alkali is dictated by the inter- relationship which we have established these components have on biosolubility and on viscosity. We have found that reducing Si0₂ increases biosolubility but that if the amount of Si0₂ is lower than 34%, and generally if it is lower than 35%, it is difficult to select amounts of alkali and alumina that will allow the easy formation of a melt having suitable flow properties. If the amount of alumina is higher than around 23%, or preferably if it is more than about 22%, it becomes difficult to provide, using convenient raw materials, a melt in which all the alumina and other materials will rapidly dissolve in a cupola or other furnace to give a melt having satisfactory flow properties .

Achieving the required melt properties is facilitated by increasing the amount of alkali above the amounts generally used in, for instance, W096/14454. A higher amount of alkali facilitates in these compositions an increased melt viscosity and at the same time acts as a fluxing agent thus improving the melting of the high- alumina raw materials in the furnace . However if the amount of alkali is increased too much the fire resistance of the fibres is adversely* influenced. When selecting the amount of alkali, the amount which is required for any particular effect is, on a weight basis, approximately twice the amount of alumina which is required, and so selecting within the defined preferred ranges of, for instance, Si0₂ + A1₂0₃ + 2R₂0 gives a meaningful indication of the balance that is required for each of these components to achieve the desired combination of properties . The amount of CaO is usually larger than the amount of MgO but this is not essential and valuable fibres can be made when the amount of MgO is 1.1 to 2 times, or more, the amount of CaO . Generally, however, the amount of CaO is 1.5 to 2.2 times the amount of MgO. Preferred amounts of CaO are generally in the range 15.0 to 22.0% and preferred amounts of MgO are generally in the range 6.0% to 14.0%. If the amount of iron is too low the physical properties of the fibres, especially when heated, are likely to be adversely influenced. For instance the fibres will shrink and will not have good sintering properties. However if the amount is too high, as mentioned above, this makes the process of melting unsatisfactory when using a cupola or shaft furnace .

As a result of selecting the amounts within the narrowly defined ranges we have provided fibres which do give an improved balance of ease of manufacture, physical and mechanical properties in use and, especially, in vivo solubility.

There is a probability that the required standards of biosolubility will continue to increase. In particular, one method for determining biosolubility is by intra- tracheal tests, e.g. as described by Muhle et al in BIA- Report 2/98 : Fasern - Tests zur Abschatzung der Biobestandigkeit und vum Verstaubungsverhalten (Fibres - Tests for estimating the biopersistence and dust conditions) . The result of such a test is the elimination half-time, T₅₀ of WHO-fibres, i.e. the time until half of the WHO-fibres injected in the rat lung have been eliminated.

Present standards are usually all satisfied if the fibres have a T₅₀ of less than or equal to 65 days but it would be desirable to be able to produce fibres having a half-life considerably less than this, preferably below 50 days and most preferably 40 days or less. In particular, it would be desirable to able to produce fibres which have a half-life in the range of, for instance, not more than 30 days and preferably not more than 25 days.

These preferred fibres can have very satisfactory T₅₀ and in particular can provide the desired T₅₀ values above. Instead of or in addition to defining the biosolubility by in vivo tests, the fibres can also be characterised by having a high dissolution rate in buffered Gamble's solution of pH 4.5, for instance when tested by the in vitro flow through test described by Knudsen et al "New type of stonewool (HT fibres) with a high dissolution rate at pH = 4.5 (Glastechnische Berichte, Glass Science and Technology 69 (1996) ) . The fibres also have a moderately increased dissolution rate at pH 7.5. Additionally, the fibres have good resistance to atmospheric humidity and so can be used for insulation purposes where they will be exposed to atmospheric conditions. They also have good resistance to degradation by aqueous nutrients and other aqueous liquids which would be encountered when the fibres are used as products which serve as horticultural growth substrates .

In a second aspect of the invention, we also provide a novel process for producing these inventive fibres disclosed in our earlier unpublished application. In this process we provide these fibres by providing a charge of mineral material, melting the mineral material in a furnace to form a mineral melt and fiberising the melt. The charge comprises briquettes comprising at least 5% of a mineral material comprising from 1 to 30% Na₂0, from 0 to 25% K₂0 and from 3 to 50% Na₂0 + K₂0.

Preferably the mineral material is selected from those discussed above as essential in connection with the first aspect of the invention. Other preferred aspects of this process are as discussed in connection with the first aspect of the invention.

The invention also provides, in a third aspect, novel briquettes. These novel briquettes have a content, measured as oxides, of at least 2% Na₂0 and at least 5% alkali (Na₂0 + K₂0) and at least 25% Al₂0₃. Na₂0 + K₂0 is preferably at least 7%, more preferably at least 8 or 10%. Na₂0 is preferably at least 3%, more preferably at least 5%. A1₂0₃ is preferably at least 30%. Na₂0 is preferably not more than 30%, more preferably not more than 25 or 20%. Al₂0₃ is preferably not more than 50%, more preferably not more than 40%. The novel briquettes may have K₂0 content at least 2%, preferably at least 5%, 7% or 10%. Generally K₂0 content is not more than 15%.

These briquettes may be used in a process of producing MMV fibres.

The front screen glass waste may be used in the aspects of the invention discussed above. We also find that it is generally useful for the production of stone wool fibres. Thus in a fourth aspect of the invention we provide a process of producing stone wool fibres having a composition comprising at least 10% alkaline earth metal oxides comprising providing a charge of mineral material, melting the mineral material to form a mineral melt and fiberising the mineral melt, in which the charge comprises moulded briquettes which comprise at least 5 wt . % of front screen glass waste. In such a process, preferred features of the aspects of the invention discussed above may be applied, as appropriate.

In all aspects of the invention the fibres may be made in known manner. Generally they are made by a centrifugal fibre forming process. For instance the fibres may be formed by a spinning cup process in which they are thrown outwardly through perforations in a spinning cup, or melt may be thrown off a rotating disc and fibre formation may be promoted by blasting jets of gas through the melt. The invention is particularly beneficial when a cascade spinner is used and fibre formation is conducted by pouring the melt onto the first rotor in a cascade spinner. Preferably the melt is poured onto the first of a set of two, three or four rotors, each of which rotates about a substantially horizontal axis, whereby melt on the first rotor is primarily thrown onto the second (lower) rotor although some may be thrown off the first rotor as fibres, and melt on the second rotor is thrown off as fibres although some may be thrown towards the third (lower) rotor and so forth. The MMV fibres may be used for any of the purposes for which MMVF products are known. These include fire insulation and protection, thermal insulation, noise reduction and regulation, construction, horticultural media, and reinforcement of other products such as plastics and as_. a filler. The materials may be in the form of bonded batts (which may be flat or curved) or the materials may be comminuted into a granulate. Bonded batts include materials such as slab and pipe sections. The invention includes the use of a melt composition to provide fibres having the defined composition and which are biosoluble, in particular as indicated by T₅₀ of not more than 40 days, preferably not more than 30 days and most preferably not more than 25 days. The process of the invention can be used to make fibres which are shown to be biodegradable, for instance as given above, and wherein the fibres have the preferred analysis given above, especially when the fibres are the fibres of a bonded product, for instance which is used as thermal insulation, fire insulation or protection or noise regulation protection, or as horticultural growth medium, or wherein the fibres are used in free form as reinforcement or as a filler.

The invention also includes a method of making man- made vitreous fibre products comprising forming one or more mineral melts and forming fibres from the or each melt wherein the melt viscosity and biosolubility of fibres are determined (for instance by any of the methods described in W096/14274 or by the T₅₀ method described above) and a composition is selected which has a suitable viscosity (generally 10 to 40, preferably 10 to 30 poise, at 1400°C) and an appropriate biosolubility and fibres are made from the selected composition, and bonded or unbonded products are made from the fibres. The selected fibres may be provided in any of the forms conventional for man-made vitreous fibres. Thus they may be provided as loose unbonded fibres, for instance being used as free fibres for reinforcement of cement, plastics or other products or as a filler as an unbonded insulation. More usually the fibres are provided with a bonding agent, generally as a result of forming the fibres and collecting them in conventional manner in the presence of a bonding agent. The resultant product is consolidated as a slab, sheet or other shaped article. Bonded products may take the form of slabs, sheets, tubes or other shaped articles that are to serve as thermal insulation, fire insulation and protection or noise reduction and regulation, or in appropriate shapes as horticultural growing media .

The following are examples of the invention. Examples In the following examples, eleven different briquette compositions are used and nine different charges are produced which are melted in a conventional cupola furnace and the melt is used to produce nine different fibre compositions in known manner using a cascade spinner. The five briquettes used for the first four charges have the components shown in Table 1. The oxide compositions of the briquettes are shown in Table 2. Charges including these briquettes and other components are shown in Table 3. The compositions of the resulting charges (and fibres formed from them) are shown in Table 4. In the charge and fibre compositions below (although not in briquette compositions) all Fe is expressed as FeO.

Table 1

Briquette Components

Table 2

Briquette Composition

Table 3

Charge Components

Table 4

Charge and Fibre Compositions

r- o

Two further charges are created in similar fashion as follows. The briquette components are shown in Table 5. The oxide compositions of the briquettes are shown in Table 6. Charges including these briquettes and other components are shown in Table 7. The compositions of the resulting charges (and fibres formed from them) are shown in Table 8. Table 5 Briquette Components

Table 6

Briquette Compositions

Table 7

Charge Components

Table 8

Charge Compositions

4=^*.

Three further charges are created in similar fashion as follows. The briquette components are shown in Table 9. The oxide compositions of the briquettes are shown in Table 10 charges including these briquettes and other components are shown in Table 11. The compositions of the resulting charges (and fibres formed from them) are shown in Table 12.

Table 9 Briquette Components

Table 10

Briquette Compositions

Table 11

Charge Components

Table 12

Charge and Fibre Compositions

00

Claims

1. A process of producing man-made vitreous fibres having a composition comprising 16 to 23% alumina and 4 to 8% alkali oxides comprising providing a charge of mineral material, melting the mineral material to form a mineral melt and fiberising the mineral melt, in which the charge comprises molded briquettes which comprise at least 5 wt . % of a mineral material selected from the group consisting of (a) mineral concentrates selected from alkali feldspar, nepheline, leucite and sodalite, (b) natural rocks selected from syenite, nepheline syenite, phonolite and alkali basalt and those natural rocks containing at least 40% alkali feldspar and (c) front screen glass waste and mixtures thereof.

2. A process according to claim 1 in which the fibres have a composition comprising 19 to 23% alumina.

3. A process according to claim 1 or claim 2 in which the mineral material comprises alkali feldspar, nepheline, leucite, sodalite, syenite, nepheline syenite or natural rock containing at least 40% alkali feldspar.

4. A process according to any preceding claim in which at least 35, preferably at least 40, wt.% of the charge comprises the defined briquettes .

5. A process according to any preceding claim in which the fibres have a composition which includes, by weight of oxides,

Si0₂ 34 to 40%

A1₂0₃ 16 to 23% CaO + MgO 20 to 35%

Ti0₂ 0 to 3%

Na₂0 + K₂0 4 to 8%

FeO 3 to 10%

P₂0₅ 0 to 2% Other elements 0 to 5%.

6. A process according to claim 5 in which the fibres have a composition which includes, by weight of oxides, 34 to 39% Si0₂ and 19 to 23% Al₂0₃.

7. A process according to any preceding claim in which the furnace is a shaft furnace, preferably a cupola furnace .

8. A process according to any preceding claim in which the briquettes comprise from 10 to 50%, preferably 10 to 40%, of the mineral material.

9. A process according to any preceding claim in which the briquettes comprise cement binder.

10. A process according to any of claims 1 to 8 in which the briquettes comprise molasses binder.

11. A process according to any preceding claim in which the mineral melt is fiberised using a cascade spinner.

12. A process of producing MMVF fibres having a composition which includes, by weight of oxides,

Si0₂ 34 to 40% A1₂0₃ 16 to 23% CaO + MgO 20 to 35% Ti0₂ 0 to 3% Na₂0 + K₂0 4 to 8% FeO 3 to 10% P₂0₅ 0 to 2% Other elements 0 to 5%, the process comprising providing a charge of mineral material, melting the mineral material in a furnace to form a mineral melt and fiberising the mineral melt, wherein the charge comprises molded briquettes which contain at least 5 wt . % of a mineral material comprising from 1 to 30% Na₂0, from 0 to 25% K₂0 and from 3 to 40% Na₂0+K₂0.

13. A process according to claim 12 in which the fibres have a composition which includes, by weight of oxides, 34 to 39% Si0₂ and 19 to 23% A1₂0₃.

14. A briquette having a composition, by weight of oxides, which includes at least 2 wt.% of Na₂0, at least 5 wt . % Na₂0 + K₂0 and at least 25 wt.% Al₂0₃.

15. A process for the production of stone wool fibres having a composition comprising at least 10 wt.% alkaline earth oxides comprising providing a charge of mineral material, melting the mineral material to form a mineral melt and fiberising the mineral melt, in which the charge comprises moulded briquettes which comprise at least 5 wt . % front screen glass waste.