FR3141459A1 - METHOD FOR MANUFACTURING E-GLASS FIBERS FROM A MIXTURE OF MINERAL MATERIALS COMPRISING A CALCIUM SILICATE - Google Patents

Abstract

Process for manufacturing E-glass fibers having a target composition, comprising the melting of a mixture of raw materials constituting a melt, said mixture of raw materials comprising a calcium silicate comprising, in weight percentage, more than 30% of SiO2 and more than 20% of CaO, preferably at least 25% of CaO, CaO and SiO2 together representing more than 60%, or even more than 70% or even more than 80% of the total weight of said silicate and in that said silicate is introduced into the mixture in the form of a powder whose median grain diameter is less than or equal to 400 micrometers.

Description

PROCESS FOR PRODUCING E-GLASS FIBERS FROM A MIXTURE OF MINERAL MATERIALS COMPRISING A CALCIUM SILICATE

The invention relates to the field of melting a mixture of raw materials, in particular for the production of glass fibres, in particular E-glass fibres. E-glass yarn is not only used in the textile industry but also for the reinforcement of composite elements.

Its excellent electrical insulation properties, even at low thickness, combined with its mechanical resistance and its behavior at different temperatures, were the basis of the first applications of E-glass wire.

E-glass fibre thus has a low thermal conductivity. The fibre can withstand temperatures of over 600°C and is incombustible. In addition, it has excellent chemical resistance. E-glass fibre products are resistant to oils, solvents and most chemical agents. In addition, they are rot-proof. E-glass yarn is also insensitive to variations in temperature and humidity and has a low coefficient of expansion.

E-glass fibre products are also particularly resistant to abrasion and vibration, and have excellent flexibility. Glass yarn has a higher specific strength (tensile strength/volumetric mass) than steel. This characteristic now makes it possible to develop glass yarns that will reinforce high-performance composites.

Typically, E-glass is obtained by melting a bath of raw material comprising silica, lime, kaolin, a source of boron such as borax or boric acid and possibly dolomite, the basic components being judiciously chosen to provide a glass composition producing fibres combining flexibility and robustness to mechanical traction as well as to heat, to chemical agents as well as to electrical potential. To obtain the best properties, it is essential to limit as much as possible the levels of MgO and alkali oxides Na ₂ O and K ₂ O or iron oxide Fe ₂ O ₃ in the composition of the E-glass finally obtained. Typically, to the silica, lime, alumina or the source of alumina, a boron oxide such as borax or boric acid or colemanite is added, while any alkali oxide is excluded to obtain E-glass. This composition is heated until it melts. It is considered that at 1400°C, the liquid is homogeneous, but it is only at 1500°C that the last bubbles and impurities disappear from the glass. Refined, the molten mass is normally perfectly transparent when it leaves the furnace. This mass passes through dies (platinum alloy plates pierced with hundreds of holes) to produce a glass thread. This thread is then sized, wound and then dried.

It is generally accepted that the choice of the raw materials mentioned above is necessary to obtain good quality glass, particularly after its fiberization. Among the properties considered essential, we can cite the homogeneity of the glass (in particular the homogeneity in CaO, an essential constituent of E glass). Good homogeneity of the glass in composition conditions the quality of the fiberization, and more particularly the rate of breakage of the fiber and therefore the yield of the manufacture of E glass fibers. In particular, the local concentration of CaO in the glass impacts its viscosity at the fiberization temperature, which can modify the diameter of the fiber and cause breakage during fiberization in the event of even minimal variations in the local concentration of CaO.

Energy consumption (energy required to melt the mixture of raw materials) is also an element to take into account.

To meet the above requirements, glass is usually prepared by melting in a furnace raw materials comprising silica and at least one alkaline earth (to give the glass resistance to hydrolysis) in the form of limestone (calcium carbonate). An alumina carrier (such as kaolin) and a boron carrier (e.g. borax or boric acid or colemanite), are the two other major elements in the composition of a current bath.

The originality of the present invention lies in the choice of raw materials. Indeed, it was discovered that it was possible to use silicates as raw materials in an E-glass manufacturing process to limit the energy consumption of its manufacturing process while maintaining good homogeneity of the final glass.

According to the invention, it was found by the applicant company that the particle size of the mineral raw materials should also be taken into account for the preparation of the initial mixture in order to limit the energy consumption of such an E-glass fiber manufacturing process and guarantee its mechanical properties.

Thus, according to a first aspect, for type E glasses, among the different oxides constituting the glass, calcium oxide is the one that most impacts the homogeneity of the glass. CaO is however necessary in the composition of E glass because it reinforces the hydrolytic resistance and helps to control the viscosity and the liquidus temperature of the molten bath of raw materials.

As previously noted, inhomogeneous molten glass can particularly have a negative impact during glass fiberization due to a possible increase in the frequency of fiber breakage at the fiber manufacturing die, even if the local variation in CaO composition is minimal.

In order to improve the homogeneity of the glass, it is known and common in the field to reduce as much as possible the particle size distribution (or PSD) of the raw materials and in particular the median diameter D50 of the raw material source of Ca in the final glass, i.e. usually limestone as described in the publication "Influence of limestone grain size on glass homogeneity, Glass Technology, Society of Glass Technology, 2010, 51 (3), pp.116".

However, by reducing the PSD of limestone (with a D ₅₀ of around 114 micrometers currently), the amount of respirable dust generated in the composition workshop increases, which requires additional means to prevent their inhalation by operators. The service life of the furnaces used for melting the mixture is also reduced, due to the increase in its residue content, accelerating the corrosion of the refractories.

Above all and primarily, working with finer limestone affects and significantly reduces the ability of the raw material mixture, introduced into the furnace in lump form, to absorb the heat from the melting means, typically burners, arranged within the furnace, the heat transferred from the flames to the raw material mixture depending greatly on the emissivity of said mixture. A lower emissivity of the raw materials therefore corresponds to a less efficient heat transfer.

As a result, while working with fine limestone would theoretically improve the chemical homogeneity of the glass, it does have major drawbacks, which are:

- increased energy consumption of the oven (less favorable energy transfer).

- the generation of dust in the production plant, causing hygiene and safety problems for personnel,

- the generation of a greater entrainment phenomenon in the furnace, which accelerates the corrosion of refractories.

There schematically illustrates a furnace 2 for melting raw materials. The raw materials are introduced as a mixture into the furnace 7 in the form of a compact lump 1. The lump 1 initially floats on the molten glass 6. The lower surface of the lump first melts due to the convection of the molten glass under the effect of electrical resistance 4 (electrical boosting) arranged in the lower part of the furnace. A bubbler 8 increases the convection of the glass and thus mechanically induces better homogeneity of the glass. The upper surface of the lump is also heated by radiation using a series of burners 3 positioned at the side walls of the furnace as shown schematically by the below. After melting of the lump, a foaming phenomenon 5 is observed due to the refining of the glass.

As previously indicated, it has been demonstrated by the experiments carried out by the applicant company that the efficiency of heating by the burners is linked to the emissivity of the raw materials used and in particular of the calcium source used. Thus, a raw material with low emissivity produces a thermal mirror on the surface of the tile, which reduces the melting kinetics and increases the energy consumption of the furnace to achieve the same degree of melting.

The object of the present invention is thus to propose a method for manufacturing E-glass fibers allowing a homogeneous distribution of calcium oxide in said final glass, while reducing the energy consumption necessary for said manufacturing.

The object of the present invention is thus to propose a method for manufacturing E glass allowing a homogeneous distribution of calcium oxide in said final glass, while reducing the energy consumption necessary for said manufacturing.

More specifically, the present invention relates to a method for manufacturing E-glass fibers having a target composition, comprising melting a mixture of raw materials constituting a melt bath, said target composition meeting the following criteria, in weight percentages:

SiO ₂ : between 45 and 60%, preferably between 50 and 60%

CaO: between 20 and 35%, preferably between 20 and 30%

Al ₂ O ₃ : between 10 and 20%, preferably between 12 and 18%

B ₂ O ₃ : between 3 and 10%, preferably between 4 and 8%

MgO: less than 2%, preferably between 0 and 1%

_K2O + _Na2O : less than 2%, preferably between 0 and 1%

Iron oxide: less than 1%, preferably less than 0.5%

other oxide(s): between 0 and 3% cumulative,

the remainder being made up of unavoidable impurities,

said method being characterized in that the mixture of raw materials comprises a calcium silicate comprising, in weight percentage, more than 30% of SiO ₂ and more than 20% of CaO, preferably at least 25% of CaO, CaO and SiO ₂ together representing more than 60%, or even more than 70% or even more than 80% of the total weight of said silicate and in that said calcium silicate is introduced into the mixture in the form of a powder whose median grain diameter D ₅₀ is less than or equal to 400 micrometers.

According to preferred but non-limiting embodiments of the present invention, but which can of course be combined with each other:

• SiO₂: entre 30 et 60%, de préférence entre 40 et 55%,
• CaO : entre 25 et 55%, de préférence entre 35 et 50%,
• Fe₂O₃: entre 0 et 4%, par exemple entre 0,1 et 0,5%,
• Al₂O₃: entre 0 et 8%, par exemple entre 0,5 et 2%,
• CO₂: entre 0 et 20%, notamment entre 0 et 15%,
• moins de 5% d’autres oxydes, de préférence moins de 3% d’autres oxydes.

- said calcium silicate has the following composition, in weight percentages:

• SiO ₂ : between 30 and 60%, preferably between 40 and 55%,
• CaO: between 25 and 55%, preferably between 35 and 50%,
• Fe ₂ O ₃ : between 0 and 4%, for example between 0.1 and 0.5%,
• Al ₂ O ₃ : between 0 and 8%, for example between 0.5 and 2%,
• _CO2 : between 0 and 20%, particularly between 0 and 15%,
• less than 5% of other oxides, preferably less than 3% of other oxides.

- Said calcium silicate comprises, in weight percentage, at least 30% of SiO ₂ and at least 30% by weight of CaO, SiO ₂ and CaO together representing more than 75% and preferably more than 85% by weight of said calcium silicate.

- Said calcium silicate is introduced into the mixture in the form of a powder whose median grain diameter is between 10 micrometers and 400 micrometers, preferably between 20 micrometers and 350 micrometers, and very preferably between 30 micrometers and 300 micrometers.

- Said calcium silicate is introduced into the mixture in the form of a powder whose maximum diameter is less than 1500 micrometers, preferably less than 1250 micrometers and very preferably less than 1000 micrometers.

• ledit silicate de calcium,
• une source de silicium notamment choisie parmi la silice, le calcin de verre E ou des fibres minérales recyclées ou leur mélange,
• une source de bore de préférence choisie parmi le borax ou un oxyde de bore et de calcium, en particulier la colémanite, ou un oxyde de bore, de sodium et de calcium, en particulier l’ulexite et/ou la tincalconite et/ou la kernite,
• optionnellement une source d’aluminium tel que le kaolin, de l’alumine éventuellement hydratée ou la pyrophyllite,
• optionnellement du calcaire CaCO₃ou de l’hydroxyde de calcium Ca (OH)₂ou de la chaux vive CaO,
• optionnellement un laitier.
• Ledit mélange comprend en outre un silicate de calcium et d’aluminium comprenant, en pourcentage poids, plus de 30% de SiO₂, plus de 15% poids de CaO et plus de 20% d’Al₂O₃, SiO₂, CaO et Al₂O₃représentant ensemble plus de 70% et de préférence plus de 75% dudit silicate de calcium.
• Ledit silicate de calcium et d’aluminium répond à la composition suivante, en pourcentages poids :
• SiO₂: entre 40 et 60%, de préférence entre 45 et 55%,
• CaO : entre 10 et 30%, de préférence entre 12 et 20%,
• Al₂O₃: entre 25 et 35%,
• SiO₂, CaO et Al₂O₃représentant ensemble plus de 85%, de préférence encore plus de 90%, voire plus de 95%,
• Na2O : entre 0 et 4%,
• Fe₂O₃: entre 0 et 4%, par exemple entre 0,1 et 1%
• moins de 5% d’autres oxydes, de préférence moins de 3% d’autres oxydes.
• Ledit mélange comprend un oxyde de bore et de calcium comprenant, en pourcentage poids, plus de 30% de B₂O₃et plus de 20% poids de CaO.
• On utilise en outre du kaolin ou de la pyrophyllite comme source d’aluminium.
• Le mélange de matières premières contient moins de 12% poids de CO₂, de préférence moins de 10% de CO₂, de préférence encore moins de 5% de CO₂.
• On introduit en outre dans le bain de fusion du calcin de verre E ou des fibres minérales recyclées, en particulier de la laine de verre recyclée ou de la laine de roche recyclée.
• Le calcin de verre E recyclé ou de fibres minérales recyclées représente entre 10 et 50% du poids total du bain de fusion. Les fibres minérales recyclées présentent de préférence la composition suivante :

- The raw material mix includes:

• said calcium silicate,
• a source of silicon chosen in particular from silica, E-glass cullet or recycled mineral fibers or their mixture,
• a source of boron preferably selected from borax or an oxide of boron and calcium, in particular colemanite, or an oxide of boron, sodium and calcium, in particular ulexite and/or tincalconite and/or kernite,
• optionally a source of aluminum such as kaolin, possibly hydrated alumina or pyrophyllite,
• optionally limestone CaCO ₃ or calcium hydroxide Ca (OH) ₂ or quicklime CaO,
• optionally a milkman.
• Said mixture further comprises a calcium and aluminium silicate comprising, in weight percentage, more than 30% of SiO ₂ , more than 15% by weight of CaO and more than 20% of Al ₂ O ₃ , SiO ₂ , CaO and Al ₂ O ₃ together representing more than 70% and preferably more than 75% of said calcium silicate.
• Said calcium and aluminum silicate has the following composition, in weight percentages:
• SiO ₂ : between 40 and 60%, preferably between 45 and 55%,
• CaO: between 10 and 30%, preferably between 12 and 20%,
• Al ₂ O ₃ : between 25 and 35%,
• SiO ₂ , CaO and Al ₂ O ₃ together representing more than 85%, preferably more than 90%, or even more than 95%,
• Na2O: between 0 and 4%,
• Fe ₂ O ₃ : between 0 and 4%, for example between 0.1 and 1%
• less than 5% of other oxides, preferably less than 3% of other oxides.
• Said mixture comprises a boron and calcium oxide comprising, in weight percentage, more than 30% of B ₂ O ₃ and more than 20% by weight of CaO.
• Kaolin or pyrophyllite is also used as a source of aluminum.
• The raw material mixture contains less than 12% by weight of _CO2 , preferably less than 10% of _CO2 , more preferably less than 5% of _CO2 .
• In addition, E-glass cullet or recycled mineral fibres, in particular recycled glass wool or recycled rock wool, are introduced into the melting bath.
• Recycled E-glass or recycled mineral fibre cullet represents between 10 and 50% of the total weight of the melt. Recycled mineral fibres preferably have the following composition:

SiO ₂ : between 30 and 50%, preferably between 35 and 45%

_Na2O : between 0 and 10%, preferably between 0.4 and 7%

CaO: between 10 and 35%, preferably between 12 and 25%

MgO: between 1 and 15%, preferably between 5 and 13%

CaO+MgO: between 11 and 40% cumulative,

Al ₂ O ₃ : between 10 and 27%,

_K2O : between 0 and 2%, preferably between 0 and 1%

Iron oxide: between 0.1 and 3%,

other oxide(s): between 0 and 5% cumulative, preferably less than 3%,

the remainder being made up of unavoidable impurities.

The invention also relates to the mixture of raw materials described above.

In particular, the invention also relates to the mixture of raw materials for the manufacture of E-glass fibers described above, and comprising in particular a calcium silicate comprising, in weight percentage, more than 30% of SiO ₂ and more than 10% of CaO, preferably more than 15% of CaO, CaO and SiO ₂ together representing more than 60%, or even more than 70% or even more than 80% of the total weight of said silicate, said calcium silicate having a median grain diameter less than or equal to 400 micrometers.

Such a mixture of raw materials preferably comprising:

- a source of silicon chosen in particular from silica, E-glass cullet or recycled mineral fibers or their mixture,

- a source of boron preferably chosen from borax or an oxide of boron and calcium, in particular colemanite, or an oxide of boron, sodium and calcium, in particular ulexite and/or tincalconite and/or kernite,

- at least one source of calcium chosen from said calcium silicate,

- optionally a source of aluminum such as kaolin, possibly hydrated alumina or pyrophyllite,

- optionally limestone CaCO3 or calcium hydroxide Ca(OH)2 or quicklime CaO.

The mixture of raw materials according to the invention is intended to be heated to a temperature and under conditions allowing its fusion to obtain a glass corresponding to said target composition.

As demonstrated in the examples which follow, it was thus possible to obtain E-glass fibers without defects, and whose homogeneity is improved, from the mixture according to the invention as will be shown in the examples which follow.

To produce the glass, the Si carrier is very preferably introduced into the mixture of raw materials in the form of sand. The calcium is provided in the form of said calcium silicate and possibly a calcium and aluminum silicate. The Al carrier can advantageously be introduced into the mixture of raw materials in the form of kaolin or advantageously in the form of a calcium and aluminum silicate, identical or different from the previous one. Each raw material is introduced into the mixture of raw materials in such a quantity that the molar percentage of its cation (such as Si, Ca, Al, B, etc.) relative to the sum of the moles of all the cations is the same as in the final glass. The raw materials of the mixture are chosen to lead to a glass whose target composition falls within the framework (the percentage ranges in the different oxides) described above.

The mixture of raw materials is heated until a molten glass is obtained, generally in a furnace. The temperature and duration of heating vary depending on the quality of the glass required, in particular the degree of tolerance for unmelted particles (called "unmelted") and bubbles. Generally, the maximum heating temperature of the molten glass is between 1400 and 1700°C. For the transformation of the mixture of raw materials into glass, glass melting techniques well known to those skilled in the art can be used. This transformation can be carried out in any type of furnace such as an electric electrode furnace, an overhead burner furnace such as a transverse burner furnace or a loop furnace, or a submerged burner furnace.

For heating and melting into glass, the mixture of raw materials, if necessary moistened, may be introduced into a furnace in a powdered state, which implies that each raw material it contains is in a powdered state. For heating and melting into glass, the mixture of raw materials, if necessary moistened, may be introduced into a furnace in a compositional state comprising cullet and the mixture of raw materials, the latter being if necessary powdered.

In the context of the present invention, it is possible to dispense with the use of a system for shaping (i.e. forming) the mixture of raw materials by mechanical pressure, in particular using molds leading to calibrated agglomerates (briquettes, balls, granules, pellets, etc.), such as hoop compactors. Thus, before introduction into a furnace, the mixture of raw materials may not be shaped by mechanical pressure. It is also not necessary to use a technique for granulating the raw material according to which the material is rotated (in particular in a rotating drum type tank) generally in the presence of a binder so as to lead to granules (pellets in English).

Unless otherwise indicated, all particle size values (median diameter D50, maximum diameter D _max ) in the present description and the claims are given by mass and are obtained by conventional sieving techniques, in particular for the calcium silicate according to the invention.

The invention will be better understood by reading the examples which follow, intended to illustrate its advantages, without of course the invention being considered as limited to these, in any of the aspects described.

Examples

According to this series of examples, different mixtures of raw materials are prepared in order to compare a mixture as currently used for the manufacture of E glass to obtain the final composition, which has approximately the following formulation in weight percentage of oxides:

Elements Weight Percentage% SiO ₂ 54 CaO 24 MgO <1 Al ₂ O ₃ 14 B ₂ O ₃ 6 Na ₂ O <1 K ₂ O <0.3 Na ₂ O + K ₂ O <1 Fe ₂ O ₃ <0.5

Example 1 (prior art)

According to a first example, a composition of the E-glass synthesis corresponding to the previous formulation is synthesized.

Table 2 below gives the proportions of the different raw materials (in weight percentage) and the final composition of the glass theoretically obtained from this mixture:

SiO ₂ Al ₂ O ₃ CaO MgO B ₂ O ₃ Na ₂ O K ₂ O Fe ₂ O _{3 CO2} TiO ₂ SO ₃ Matter Kg/ton of glass D50
(μm) Weight percentage Sand 365 14* 99.2 0.37 0.1 0.02 0.01 0.06 Borax 27 NM 48.5 21.9 Colemanite 138 69 4.7 0.1 28.1 1.9 39.9 0.07 0.03 0.03 0.27 Kaolin 372 10* 45.9 37.7 0.21 0.19 0.54 0.02 Na-sulfate 4 NM 43.4 0.02 56.1 Limestone 361 114 0.2 0.04 55.6 0.46 0.01 0.02 43.1 0.01 Final glass composition
(% weight) 54.0 14.2 24.0 0.4 6.1 0.6 0.06 0.2 0.04

NM: not measured *: laser measurement

The particle size of the various raw materials is obtained by sieving, with the exception of kaolin and sand, the particle size of which is measured by laser.

The measurements are carried out on approximately 100 g of representative sample (precision of 10 ^-2 g). The test sample is placed on the upper sieve of the column (Standard NF X 11501). The column is stirred for 5 minutes in a ROTAP sieving machine (Retsch AS200 TAP). The residue from the first sieve containing the grains is weighed (precision of 10 ^-2 g). The residue from each sieve is added, using the same procedure, to those from the previous sieves, and the cumulative mass is recorded each time.

The results are expressed as a cumulative % relative to the final total mass MF.

X1% = M1 x 100 / MF

X1 = % of cumulative rejection on sieve 1

M1 = mass of cumulative rejects on sieve 1

MF = final product mass.

This calculation will be carried out for each nominal sieve opening.

The D50 is calculated from an interpolation of the upper and lower particle sizes closest to 50%.

In particular, D ₅₀ is classically determined by the following equation:

D ₅₀ = [T<50%] + (50% - [X<50%]) × ([T<50%] - [T>50%]) / ([X<50%] - [X>50 %])

With :

T<50% = Sieve opening less than 50% of rejection

T>50% = Sieve opening greater than 50% of rejection

X<50% =% of cumulative refusal on T<50%

X>50% =% of cumulative refusal on T>50%

The particle size of sand and kaolin is measured using a Malvern Instruments Mastersizer 300 ® laser particle size analyzer according to ISO13320:2009, in isopropanol as dispersant.

We can thus deduce the particle size distribution as reported in tables 2 to 4.

Example 2:

In this example, the mixture of raw materials is this time as described in Table 3 below. The materials are the same as in Example 1. In this initial mixture, unlike Example 1, a mineral material consisting of a calcium silicate according to the invention whose median diameter D ₅₀ is 107 micrometers is introduced as a reagent to replace the limestone.

This material is introduced in a mixture with the other constituents in proportions adjusted accordingly to obtain a glass with a composition very close to that of reference example 1.

SiO ₂ Al ₂ O ₃ CaO MgO B ₂ O ₃ Na ₂ O K ₂ O Fe ₂ O _{3 CO2} SO ₃ Matter Kg/ton of glass Weight percentage Sand 134 99.2 0.37 0.1 0.02 0.01 0.06 Borax 27 48.5 21.9 Colemanite 138 4.7 0.1 28.1 1.9 39.9 0.07 0.03 0.03 0.27 Kaolin 370 45.9 37.7 0.21 0.19 0.54 0.02 Na-sulfate 4.3 43.4 0.02 56.1 Calcium silicate 446 51.6 0.3 44.7 0.7 0.1 0.3 Final glass composition
(% weight) 54.0 14.2 24.0 0.4 6.1 0.6 0.06 0.2 0.04

Example 3:

In this example, the same raw materials were used as in example 2, but as an exception, a calcium silicate with a larger particle size was used, i.e. D ₅₀ equal to 826 micrometers.

Table 4 below shows the granulometric characteristics determined using the method previously described for the different sources of calcium used as raw material in the previous examples:

Limestone “Fine” calcium silicate “Large” calcium silicate Example 1 2 3 D ₅₀ (µm) 114 107 826 Max grain size (µm) 250 800 4000 Number of grains
<100 µm (%) 30 42 <5

The following measurements are taken:

1°) The emissivity of the calcium sources used is measured from the reflectance spectra using the law of conservation of energy for opaque materials: absorbance α(λ, T) + reflectance ρ(λ, T) = 1. By applying Kirchhoff's law, the spectral emittance can be expressed in terms of total reflectance,

ε(λ, T) = α(λ, T)

with :
,

where B _T is the spectral irradiance of the black body at a temperature T of 2000°C, corresponding to the temperature of the air-gas flame of the burner.

Room temperature hemispherical reflectance measurements are performed with a 150 mm integrating sphere mounted on a Lambda spectrophotometer between 300 and 2500 nm, using a Spectralon plate as a reflectance reference.

For easy handling, the samples are pressed by applying a force of 0.4 tonnes/ ^cm2 and wetted with 10% water prior to measurement.

2°) The mixtures of the above examples are melted in a typical glass melting furnace based on flame technology shown schematically in the below.

Measurement of the energy consumed in the furnace for the melting of the mixtures:

During the various fusion tests corresponding to the examples above, the gas consumption is adjusted in order to maintain a similar profile temperature inside the furnace and at all points in it. From this, we deduce a gas consumption and therefore energy consumption necessary to reach the same heating point.

3°) Homogeneity in CaO in the final glass:

A sample is melted in a cylindrical platinum crucible from the same mixture of raw materials as described above. The sample is heated in air at 1410°C for 4 hours. The cooled glass is then cored and cut to obtain a slide comprising the cross section of the cylinder. This slide was polished, carbon metallized and analyzed using an electron microprobe at 15kV. The analysis consisted of determining the mass percentage of CaO over the entire height of the slide (or of the melted sample) on 50 measurement points, the measurement step was 200 microns.

It is thus possible on this basis to calculate the mean of the CaO concentration and the standard deviation. A criterion of homogeneity of CaO in the glass is provided by the ratio standard deviation divided by the mean concentration (σ _CaO /[CaO]). The smaller this value, the better the homogeneity of the CaO concentration in the final glass.

The results obtained are reported in Table 5 below:

Example 1 2 3 Source of calcium Limestone “Fine” calcium silicate “Large” calcium silicate Emissivity 0.20 0.27 0 .44 Glass homogeneity
(σ _CaO /[CaO]) (%) >5 <2 >ex.1 Energy consumed by the first burner in the oven Reference < Reference NM

Example 2 according to the invention, in which a calcium source consisting of a calcium silicate of suitable particle size according to the invention is used as raw material for said melt, allows an energy adjustment on the first burner 1 (the closest to the charging, i.e. the entry of the raw materials into the furnace) in the sense of a reduction in energy expenditure. Also, in the sense previously described, the homogeneity of the glass, in particular in calcium oxide, appears improved in the case of example 2 according to the invention, compared with the reference.

Claims (16)

A method of manufacturing E-glass fibers having a target composition, comprising melting a mixture of raw materials constituting a melt bath, said target composition meeting the following criteria, in weight percentages:
SiO ₂ : between 45 and 60%, preferably between 50 and 60%
CaO: between 20 and 35%, preferably between 20 and 30%
Al ₂ O ₃ : between 10 and 20%, preferably between 12 and 18%
B ₂ O ₃ : between 3 and 10%, preferably between 4 and 8%
MgO: less than 2%, preferably between 0 and 1%
_K2O + _Na2O : less than 2%, preferably between 0 and 1%
Iron oxide: less than 1%, preferably less than 0.5%
other oxide(s): between 0 and 3% cumulative,
the remainder being made up of unavoidable impurities,
said method being characterized in that the mixture of raw materials comprises a calcium silicate comprising, in weight percentage, more than 30% of SiO ₂ and more than 20% of CaO, preferably at least 25% of CaO, CaO and SiO ₂ together representing more than 60%, or even more than 70% or even more than 80% of the total weight of said silicate and in that said calcium silicate is introduced into the mixture in the form of a powder whose median grain diameter D ₅₀ is less than or equal to 400 micrometers. The method of claim 1, wherein said calcium silicate has the following composition, in weight percentages:

• SiO ₂ : between 30 and 60%, preferably between 40 and 55%,
• CaO: between 25 and 55%, preferably between 35 and 50%,
• Fe ₂ O ₃ : between 0 and 4%, for example between 0.1 and 0.5%,
• Al ₂ O ₃ : between 0 and 8%, for example between 0.5 and 2%,
• _CO2 : between 0 and 20%, particularly between 0 and 15%,
• less than 5% of other oxides, preferably less than 3% of other oxides.

A method according to any preceding claim, wherein said calcium silicate comprises, in weight percentage, at least 30% SiO ₂ and at least 30% CaO, SiO ₂ and CaO together representing more than 75% and preferably more than 85% by weight of said calcium silicate. Method according to one of the preceding claims, in which said calcium silicate is introduced into the mixture in the form of a powder whose median grain diameter is between 10 micrometers and 400 micrometers, preferably between 20 micrometers and 350 micrometers, and very preferably between 30 micrometers and 300 micrometers. Method according to one of the preceding claims, in which said calcium silicate is introduced into the mixture in the form of a powder whose maximum diameter is less than 1500 micrometers, preferably less than 1250 micrometers and very preferably less than 1000 micrometers. Method according to one of the preceding claims in which the mixture of raw materials comprises:

• said calcium silicate,
• a source of silicon chosen in particular from silica, E-glass cullet or recycled mineral fibers or their mixture,
• a source of boron preferably selected from borax or an oxide of boron and calcium, in particular colemanite, or an oxide of boron, sodium and calcium, in particular ulexite and/or tincalconite and/or kernite,
• optionally a source of aluminum such as kaolin, possibly hydrated alumina or pyrophyllite,
• optionally limestone CaCO₃ or calcium hydroxide Ca(OH)₂or quicklime CaO,
• optionally a slag.

A method according to any preceding claim, wherein said mixture further comprises a calcium aluminium silicate comprising, in weight percentage, more than 30% SiO ₂ , more than 15% CaO and more than 20% Al ₂ O ₃ , SiO ₂ , CaO and Al ₂ O ₃ together representing more than 70% and preferably more than 75% of said calcium silicate. Process according to the preceding claim in which said calcium and aluminum silicate corresponds to the following composition, in weight percentages:

• SiO ₂ : between 40 and 60%, preferably between 45 and 55%,
• CaO: between 10 and 30%, preferably between 12 and 20%,
• Al ₂ O ₃ : between 25 and 35%,
• SiO ₂ , CaO and Al ₂ O ₃ together representing more than 85%, preferably more than 90%, or even more than 95%,
• Na2O: between 0 and 4%,
• Fe ₂ O ₃ : between 0 and 4%, for example between 0.1 and 1%
• less than 5% of other oxides, preferably less than 3% of other oxides.

A method according to any preceding claim, wherein said mixture comprises a boron and calcium oxide comprising, in weight percentage, more than 30% B ₂ O ₃ and more than 20% CaO. Process according to one of the preceding claims, in which kaolin or pyrophyllite is additionally used as the source of aluminium. Process according to one of the preceding claims, in which the mixture of raw materials contains less than 12% by weight of CO ₂ , preferably less than 10% of CO ₂ , more preferably less than 5% of CO ₂ . Method according to one of the preceding claims, in which E-glass cullet or recycled mineral fibres, in particular recycled glass wool or recycled rock wool, are additionally introduced into the molten bath. Method according to the preceding claim, in which the recycled E-glass or recycled mineral fibre cullet represents between 10 and 50% of the total weight of the fusion bath. Method according to one of claims 6, 12 or 13 in which the recycled mineral fibers have the following composition:
SiO ₂ : between 30 and 50%, preferably between 35 and 45%
_Na2O : between 0 and 10%, preferably between 0.4 and 7%
CaO: between 10 and 35%, preferably between 12 and 25%
MgO: between 1 and 15%, preferably between 5 and 13%
CaO+MgO: between 11 and 40% cumulative,
Al ₂ O ₃ : between 10 and 27%,
_K2O : between 0 and 2%, preferably between 0 and 1%
Iron oxide: between 0.1 and 3%,
other oxide(s): between 0 and 5% cumulative, preferably less than 3%,
the remainder being made up of unavoidable impurities. Mixture of raw materials for the manufacture of E-glass fibers comprising a calcium silicate comprising, in weight percentage, more than 30% SiO ₂ and more than 10% CaO, preferably more than 15% CaO, CaO and SiO ₂ together representing more than 60%, or even more than 70% or even more than 80% of the total weight of said silicate, said calcium silicate having a median grain diameter less than or equal to 400 micrometers. Mixture of raw materials according to the preceding claim, comprising:
- a source of silicon chosen in particular from silica, E-glass cullet or recycled mineral fibers or their mixture,
- a source of boron preferably chosen from borax or an oxide of boron and calcium, in particular colemanite, or an oxide of boron, sodium and calcium, in particular ulexite and/or tincalconite and/or kernite,
- at least one source of calcium chosen from said calcium silicate,
- optionally a source of aluminum such as kaolin, possibly hydrated alumina or pyrophyllite,
- optionally limestone CaCO3 or calcium hydroxide Ca(OH)2 or quicklime CaO.