Plastic and nonmetallic article shaping or treating: processes – Carbonizing to form article
Reexamination Certificate
1998-02-09
2001-07-03
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Carbonizing to form article
C264S137000, C264S234000, C264S257000, C264S301000, C264S322000, C442S136000, C442S180000, C210S507000, C210S509000, C210S510100
Reexamination Certificate
active
06254810
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermoformed mineral composition that can be used for coating, protecting and rigidifying a fabric made of heat-resistant fibers, such as a fabric made of glass fibers or silica fibers.
The invention also relates to a method for coating, protecting and rigidifying a fabric made of heat resistant fibers with the above mentioned composition.
The invention further relates to the fabric which is obtained by the above method and is provided with a protecting and rigidifying coating. Such a fabric is particularly useful for the manufacture of filters for the casting of the molten metals, especially aluminum.
BRIEF DESCRIPTION OF THE PRIOR ART
It has already been suggested to apply a protective coating onto a fabric made of fibers. This method is commonly used in the metallurgical industry for protecting the filters that are made of glass fiber fabrics and are used during the casting of a liquid metal, such as aluminum.
U.S. Pat. No. 5,124,040 issued in 1992 in the name of Jay R. HITCHINGS discloses a process for making a refractory filter for the casting of liquid ferrous and non-ferrous metal. In this process, a carbon-based resin is 25 deposited on the surface of a fabric made of glass fibers. The deposition is preferably achieved by dipping the fabric into the resin which is preferably a phenolformaldehyde resin. The dipped fabric is then heated at a temperature of about 300° C. for a period of three to five minutes. This heating or “curing” forms a coating made of “char”, which protects the fabric. It is worth mentioning that, on page 3, lines 45 to 50 of this patent, cellulose, phenolics and sugar are described as being “excellent examples of polymers which form strong, porous chars”.
An example of carbon-based resins that is commonly used as a coating for the manufacture of a refractory filter is the phenolic resin of the type sold by BAKELITE under the trademark RÜTAPHEN®.
According to a classification established by Leo H. BAEKELAND, the condensation of phenolic resins of the BAKELITE type is achieved in three steps.
The first step or “initial condensation” is called “A-stage” or resol. The resin obtained after this initial condensation comprises mainly an alcohol phenol or methylol. The resin at this stage is still in a thermoplastic state and soluble into organic solvents.
The second step is called “B-stage” or resitol. This stage corresponds to a condensation degree where the molecular weight has increased to such a level that the fluidity is decreased. Very few reticulations have occurred yet. The obtained resin, when it is hot, is soft and fusible. However, when it is cold, the resin is hard and brittle.
The third step is called “C-stage” or resite. This step is the final polymerization step. Most of the reticulations are completed and the resin becomes insoluble and non-fusible.
In practice, the fabric made of a glass fibers and impregnated with a phenolic resin can be processed to the intermediary B-stage. Subsequently, it can be processed to the final C-stage when it is processed by thermosetting.
It is also known in the industry to use coatings that are of the mineral type instead of the organic type, for the protection of fabrics made of glass fibers. By way of example of such a coating, reference can be made to U.S. Pat. No. 2,995,453 issued in 1961 to Richard B. NOBEL et al, which discloses the use of a coating made of colloidal silica.
The colloidal silicas that can be used for this purpose, are for example, those sold by DuPONT NEMOURS under the trademark LUDOX®.
It is further known in the industry to use coatings that include an organic part and a mineral part, for the protection of filters made of fabrics made of glass fibers. In this connection, reference can be made to U.S. Pat. No. 4,631,224 of 1986 in the name of Stephen GEORGE et al, which discloses the use a coating consisting of an aqueous suspension containing, on the one hand, colloidal silica, aluminium phosphate and aluminium chlorhydrate and, on the other hand, a phenolic or urea-formaldehyde resin.
SUMMARY OF THE INVENTION
It has now been discovered that one may obtain an excellent protective coating for a fabric made of heat-resistant fibers, in particular a fabric made of glass fibers like those used for the manufacture of filters in the metallurgical industry, when use is made, as a starting material, of a composition comprising an organic part made of sugar and a mineral part comprising colloidal silica and wollastonite. This composition allows thermoformed of the fabric and gives to the same a very strong protection and a rigidity. This is particularly interesting when the fabric is used for making a filter like those used in the metallurgy industry during the casting of a liquid metal, especially liquid aluminum.
Thus, a first object of the present invention is to provide a composition for coating, protecting and rigidifying a fabric made of heat-resistant fibers, this composition consisting of an aqueous suspension of wollastonite, colloidal silica and sugar having a sufficient viscosity to cover the fibers of the fabric while avoiding obturating the free spaces between these fibers.
Preferably, the composition is formulated in such a manner that
the suspension contains from 30 to 50% by weight of solids;
the colloidal silica and wollastonite are present in a weight ratio of colloidal silica to wollastonite ranging from 0.5 to 1.2; and
the sugar amounts to at least 25% by weight of the suspension and is present in a weight ratio of sugar to wollastonite+colloidal silica+sugar ranging from 0.55 to 1.0.
A second object of the invention is to provide a method for coating, protecting and rigidifying a fabric made of heat-resistant fibers, comprising the steps of:
a) preparing an aqueous suspension of wollastonite, colloidal silica sugar and water and having a sufficient viscosity to cover the fibers of the fabric while avoiding obturating the free spaces between said fibers, this suspension having a mineral part and an organic part;
b) depositing the suspension prepared in step a) onto the fabric in order to impregnate the fibers of said fabric, and then eliminating any excess of said suspension to avoid obturating in the free spaces between the fibers of the fabric;
c) drying the fabric obtained in step b) at a temperature ranging from 130 to 160° C.;
d) giving a requested form to the dried fabric obtained in step c) by submitting said fabric to a thermoformed treatment at a softening temperature ranging from 160 to 200° C.; and
e) subjecting the thermoset fabric obtained in step d) to a thermal treatment at a temperature above 200° C. and up to 400° C. in order to convert the organic part of the suspension into polymeric carbon and/or to fully eliminate this organic part.
A third object of the invention is to provide a fabric made of heat-resistant fibers and comprising a protective and rigidifying coating, such a fabric being obtained by the method disclosed hereinabove.
The invention and its advantages will be better understood upon reading the following non-restrictive detailed description thereof.
DETAILED DESCRIPTION OF THE INVENTION
As explained hereinabove, the invention is essentially concerned with the coating, protection and rigidification of a fabric made of heat-resistant fibers. Preferably, the fabric is made of glass fibers. However, the invention could also be used with any other kind of fabric, depending on the intended use of this fabric.
The first step (a) to be carried out in order to obtain the requested coating consists in preparing the composition intended to be applied to the fibers of the fabric. This composition consists of an aqueous suspension of wollastonite, colloidal silica and sugar having a sufficient viscosity to cover the fibers of the fabric while avoiding obturating the free spaces between these fibers.
As it can be understood, the suspension has, due to its formulation, a mineral part and an organic part.
The respective amounts of the ingredients that are present in the suspension are se
Delvaux Pierre
Desrosiers Luc
Gouin Marcel
Rouleau Michel
Cerminco Inc.
Foley & Lardner
Lee Edmund H.
Silbaugh Jan H.
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