Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms
Reexamination Certificate
2000-07-25
2004-03-02
Hoffmann, John (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
C065S482000, C065S121000, C065S134600, C065S134800, C501S030000, C501S036000
Reexamination Certificate
active
06698245
ABSTRACT:
This invention relates to methods of making man-made vitreous fibres (MMVF) and in particular to the manufacture of rock fibres.
MMV fibres are made by melting mineral solids and thereby forming a mineral melt, and then fiberising the melt by, usually, a centrifugal fiberising process.
Rock fibres (by which we include stone and slag fibres) are usually made from cheaper raw materials (often including waste materials) and by more economic processes than are used for glass fibres. Because many glass fibres are required to have particular properties that justify the cost and inconvenience of handling fluoride-containing or other difficult raw materials, it is economic to include such raw materials in the melt. Thus the associated cost of, for instance, effluent control processes may be fully justified by the improved strength or other physical properties of the glass fibres that are obtained. However rock fibres generally do not need to have such onerous physical properties and achieve their main objective of providing good insulation if it is possible to form them to an appropriate small fibre diameter, adequate length and minimum shot formation.
It is therefore not only possible but also desirable to utilise some recycled waste material as part of the charge for forming the rock melt from which rock fibres are made. These waste materials include waste MMV fibres but also include numerous other wastes such as fly ash.
Despite the widespread use of wastes in the manufacture of rock fibres, in practice the wastes which are used are never wastes that contain environmentally significant amounts of toxic materials. This is because there is no perceived benefit in using a toxic waste in preference to a non-toxic waste, and because the use of a toxic waste would necessarily require modified procedures, such as the provision of rigorous effluent treatment systems. Accordingly the numerous references in the literature to the manufacture of rock fibres using wastes such as fly ash have always related to the use of non-toxic fly ash, in contrast to the special forms of fly ash which can contain significant amounts of toxic material, for instance at least 1% fluoride. similarly, the halide content of some virgin rock can be variable. Thus some grades of apatite have low halide content but others are more toxic because they have high halide content, and so have to be treated as toxic wastes.
One particular description of a process using industrial wastes is in U.S. Pat. No. 5,364,447. This describes a complex method of treating the wastes and forming fibres from melt which is produced in one part of the process. There is no detailed description of what charge should be used for forming the melt but it appears that the charge will be formed entirely of hazardous waste materials.
Similarly, another complex process for dealing with hazardous material is described in U.S. Pat. No. 5,134,944 but again this does not appreciate the possibility of actually being able to obtain significant benefit in the fibre forming process by the use of small amounts of particular wastes.
Accordingly, deliberate and controlled amounts of fluoride-containing raw materials have been used in glass fibre production in order to promote the properties required for some particular uses of glass fibres but variable wastes generally have not been used (because of the variable impact on the properties of the glass fibres), whilst wastes have been used for rock fibres but fluoride-containing and other toxic wastes have been considered undesirable because there is no justification for providing the necessary modifications in procedures, for instance in effluent treatment.
We have now realised that the efficiency of rock fibre production (especially as regards the amount of shot which is formed) is improved by the use of a high halogen waste and that, contrary to conventional thinking, it is in fact very desirable to make rock fibres from a charge which contains a high halogen mineral waste.
In the invention rock fibres are made by a process comprising forming a pool of rock melt by melting mineral solids and forming fibres from the melt, and in this process 80 to 98% by weight of the mineral solids are low-halogen mineral materials that each contain less than 0.5% by weight halogen and 2 to 20% by weight of the mineral solids are high halogen mineral waste containing at least 1% by weight halogen.
We use the term “rock fibres” to distinguish the products from glass fibres. In the following discussion of compositions, all amounts are expressed in terms of the weight of oxide.
Glass fibres traditionally contain relatively low total amounts of alkaline earth metal and iron (calcium, magnesium and iron), generally below 12%. However the rock fibres of the invention contain more than 15%, and usually more than 20%, calcium, magnesium and iron (total of all three oxides). Glass fibres are generally substantially free of iron, but the rock fibres made in the invention generally contain at least 1%, and often at least 3% and frequently 5 to 12% or more iron measured as FeO.
Glass fibres traditionally contain a high content of alkali metal (sodium oxide plus potassium oxide), usually above 12%, but the rock fibres made in the invention preferably contain below 10% alkali metal.
The rock fibres generally contain silica in an amount which is from 30 to 70%. Various other oxides, including especially alumina, are also often present.
The invention is of particular value in the production of fibres which can be shown to be soluble in physiological saline. Some such fibres contain a relatively low amount of aluminium, for instance not more than 4%, optionally together with 1 to 5% phosphorus and 1 to 5% boron (all measured as oxides, by weight). Typical of these low aluminium fibres are the disclosures in, for instance, EP-A-459,897 and in WO92/09536, WO93/22251 and WO96/00196. Reference should be made to each of these.
However the invention is of particular value when applied to the production of fibres which have higher aluminium contents, for instance at least 15% and usually at least 17% and most usually at least 18% Al
2
O
3
, e.g., up to 30, 35 or 40% Al
2
O
3
.
The invention is particularly suitable for making high aluminium fibres because many wastes containing more than 30 or 40% aluminium (as Al
2
O
3
) also contain significant amounts of fluoride or other halide. Suitable high aluminium, biologically soluble, fibres which can advantageously be made in the present invention are described in WO96/14454 and WO96/14274. Others are described in WO97/29057, DE-U-2,970,027 and WO97/30002. Reference should be made to each of these. In general the fibres and the melt from which they are formed have an analysis (measured as % by weight of oxides) within the various ranges defined by the following normal and preferred lower and upper limits:
SiO
2
at least 30, 32, 35 or 37; not more than 51, 48, 45 or 43
Al
2
O
3
at least 14, 15, 16 or 18; not more than 35, 30, 26 or 23
CaO at least 8 or 10; not more than 30, 25 or 20
MgO at least 2 or 5; not more than 25, 20 or 15
FeO (including Fe
2
O
3
) at least 2 or 5; not more than 15, 12 or 10
FeO+MgO at least 10, 12, 15; not more than 30, 25, 20
Na
2
O+K
2
O zero or at least 1; not more than 10
CaO+Na
2
O+K
2
O at least 10, 15; not more than 30, 25
TiO
2
zero or at least 1; not more than 6, 4, 2
TiO
2
+FeO at least 4, 6; not more than 18, 12
B
2
O
3
zero or at least 1; not more than 5, 3
P
2
O
5
zero or at least 1; not more than 8, 5
Others zero or at least 1; not more than 8, 5
The fibres preferably have a sintering temperature above 800° C., more preferably above 1000° C.
The melt preferably has a viscosity at fibre forming temperature of 5 to 100 poise, preferably 10 to 70 poise at 1400° C.
The fibres preferably have an adequate solubility in lung fluids as shown by in vivo tests or in vitro tests, typically conducted in physiological saline buffered to about pH 4.5. Suitable solubilities are described in WO96/14454. Usually the rate of dissolution is at least 10 or
Christensen Vermund Rust
Jensen Soren Lund
Ranlov Jens
Dickstein Shapiro Morin & Oshinsky LLP.
Hoffmann John
Rockwool International A/S
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