Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coating or impregnation provides heat or fire protection
Reexamination Certificate
1998-04-14
2001-07-24
Cole, Elizabeth M. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coating or impregnation provides heat or fire protection
C442S180000, C428S920000, C428S921000
Reexamination Certificate
active
06265330
ABSTRACT:
TECHNICAL FIELD
The present invention relates to non-asbestos insulation materials particularly for use in rocket motor casings.
BACKGROUND ART
Solid fuel rockets are in widespread use due to the many advantages of working with solid propellants as opposed to liquid or gaseous fuels. Typically, solid fuel rocket motors provide the solid propellant within one or more annular metal rings, which are flexible to allow for temperature-induced expansion and contraction. Between the outermost annular ring and the exterior wall of the rocket motor a layer of insulation is provided, which is adhesively bonded to the inner surface of the external casing.
Previous insulation materials have been composed of a range of asbestos and non-asbestos-type materials. Representative of asbestos containing materials are the asbestos-filled phenolic resins (U.S. Pat. No. 3,243,956), neoprene or nitrile rubber having a solid additive such as asbestos, impregnated therein (U.S. Pat. No. 3,269,113), and a reaction product of tung oil with a phenolic resin, which contains a filler such as powdered asbestos (U.S. Pat. No. 3,990,369).
Due to the environmental and health concerns associated with the use of asbestos, various non-asbestos approaches to rocket motor insulation have been proposed in recent years. One approach employs two layers of material, the outermost layer being a sleeve composed of fiber glass impregnated with a high temperature resin, such as a phenolic resin, adjacent to which is provided a sheath composed of a high temperature rubber, such as Buna-N rubber (U.S. Pat. No. 3,928,965).
Also, a three component insulation wall assembly has been proposed, which contains a fire barrier layer, a middle thermal insulation layer, and an outer layer that provides structural stability. The fire barrier layer contains an ablative composite material within an ablative matrix material, such as a ceramic within a phenolic resin. The thermal insulation layer is made of a non-metallic honeycomb core material (U.S. Pat. No. 4,495,764).
Another approach is to employ an insulating adhesive to join the solid propellant to the rocket motor casing. A proposed material for use in this approach employs an epoxy resin, a chopped aramid (Kevlar) fiber pulp, and a microfine silicon dioxide filler (U.S. Statutory Invention Registration H1140). Relatedly, is an elastomeric insulating material comprising a crosslinked elastomeric polymer in which is dispersed a char-forming organic fiber, such as polyaramid pulp, and an inorganic particulate such as silica (U.S. Pat. No. 4,501,841). Hydrated alumina is mentioned as being an additive that can be used to enhance the flame-retardant properties of the insulation. U.S. Pat. No. 4,507,165 mentions that the polyaramid fibers can be replaced with cotton flock.
In yet another approach, a rocket motor insulation material is composed of a wound layer of insulation arranged about an inner solid propellant. The insulation layer contains a thermoplastic elastomer binder and is provided within an outer cylindrical casing formed of a composite material, such as graphite fibers and a thermoplastic elastomer binder. Representative of the thermoplastic elastomer binder is a polybutadiene/polystyrene block copolymer or fiberglass-reinforced polysulfone. A representative formulation for the insulation material contains thermoplastic elastomer binder at 57% by weight, alumina trihydrate at 13% by weight, other polybenzimidazole fibers at 16%-17% by weight, and lesser amounts of zinc borate and silene 732D. This particular arrangement of casing, insulation, and propellant, each of which contains thermoplastic elastomer binder, is reported to be effective in simultaneously fusing these layers to create a unitary motor structure (U.S. Pat. No. 5,388,399).
It is desired to develop a non-asbestos insulation material for use in rocket motors that is relatively simple to manufacture, has a low rate of char formation, and has improved resin curing properties. This object is met by the present invention.
SUMMARY OF THE INVENTION
The present invention is for a rocket motor insulation material that comprises a glass fabric and a resin composition, which resin composition contains alumina trihydrate. Asbestos is not a component of the material.
Preferably, an insulation material of the invention comprises glass fabric in about 35%-75% by weight and the resin composition in about 25%-65% by weight. It is preferred that the aforementioned resin composition comprises a phenolic resin and a Buna-N rubber, which is an acrylonitrile-butadiene-acrylic acid terpolymer. Preferably, the resin composition contains the phenolic resin in about 30%-60% by weight, the Buna-N rubber in about 1-30% by weight, and alumina trihydrate in about 5%-40% by weight.
An insulation material of the present invention is manufactured by combining a phenolic resin with a Buna-N rubber in an organic solvent, such as acetone. It is preferred that the alumina trihydrate also be added to this combination. The resulting mixture is then applied to a glass fabric in a ratio of about 40 parts resin mixture to 60 parts glass fabric. Upon drying of the fabric to remove solvent, the impregnated fabric can be wound on a spool. The insulation material can then be installed into a metal rocket casing and filled with a solid propellant.
The invention will now be described in more detail with reference to certain examples.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a rocket motor insulation material that is free of asbestos. The insulation material comprises a glass fabric, i.e., fiberglass, a resin binder component, and a fire retardant. The insulation material is prepared by combining the resin binder with the fire retardant in a suitable solvent. This mixture is then applied to the glass fabric, which is then dried to remove solvent.
A preferred glass weave fabric for use in the present invention is 1610 glass fabric available from Clark Schwabel, 2200 South Murray Ave., Anderson, S.C. 29622. This material provides an inert and flexible matrix for support of the fire retardant and resin binder. Other suitable glass fabrics include knit, mat and braid form with plain, leno, satin and basket styles. A common characteristic of these glass fabrics is the use of E-glass, although S-glass can also be used.
A glass fabric of the present invention preferably has areal weight in the range of about 1.4 to 53.0 oz./yd
2
, particularly about 2.3 oz./yd
2
. The glass fabric has a tensile strength of about 30 pound per lineal inch (pli), preferably in the range of about 20 to 50 pli.
A resin binder component of the present insulation material comprises a phenolic resin and a Buna-N rubber. The phenolic resin provides a good adherence of the binder to the glass fabric, while the Buna-N rubber provides a high temperature resistance. Representative of the phenolic resin is SC-1008, available from Borden Chemical Company, 6210 Camp Ground Rd., Louisville, Ky. 40216. Other suitable phenolic resins include Ironsides 91LD, Ashland Chemical 9201. The Buna-N rubber is an acrylonitrile-butadiene-acrylic acid terpolymer, such as is available from H.B. Fuller, 2400 Energy Park Dr., St. Paul, Minn. 55108. The phenolic resin and Buna-N rubber are conveniently dissolved in an organic solvent. Preferred organic solvents include acetone, and other low molecular ketones.
A phenolic resin for use of the present invention can be characterized in many respects, the most important of which for purposes of the present invention include percent solids, pK, and specific gravity. A preferred phenolic resin has solids present in an amount of about 30 to 60% by weight, preferably 63%. The pK for a preferred phenolic resin is in the range of about 4 to 10, particularly 8.2. A preferred specific gravity range is about 0.8 to 1.4 g/cc particularly about 1.1 g/cc.
The Buna-N rubber component of the resin binder of the present invention is primarily characterized in terms of percent solids. Preferably, the Buna-N rubber is provided in solution with an organic solvent i
Davidson Thomas F.
Pennington William L.
Skolnik Edward G.
Atlantic Research Corporation
Cole Elizabeth M.
Nixon & Vanderhye P.C.
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