Rocket engine thrust chamber assembly

A thrust chamber assembly for liquid fueled rocket engines and the method of making it wherein a two-piece mandrel having the configuration of an assembly having a combustion chamber portion connected to a nozzle portion through a throat portion is wrapped with a silica tape saturated with a phenolic resin, the tape extending along the mandrel and covering the combustion chamber portion of the mandrel to the throat portion. The width of the tape is positioned at an angle of 30 to 50.degree. to the axis of the mandrel such that one edge of the tape contacts the mandrel while the other edge is spaced from the mandrel. The phenolic in the tape is cured and the end of the wrap is machined to provide a frustoconical surface extending at an angle of 15 to 30.degree. with respect to the axis of the mandrel for starting a second wrap on the mandrel to cover the throat portion. The remainder of the mandrel is wrapped with a third silica tape having its width positioned at a angle of 5 to 20.degree. from the axis of the mandrel. The resin in the third tape is cured and the assembly is machined to provide a smooth outer surface. The entire assembly is then wrapped with a tow of graphite fibers wetted with an epoxy resin and, after the epoxy resin is cured, the graphite is machined to final dimensions.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to thrust chamber assemblies for rocket engines.
 2. Prior Art
 It is known to use ablative liners for rocket engine combustion chambers.
 U.S. Pat. No. 4,458,595 discloses a solid rocket motor having a layer of
 silicone rubber and a second layer of an ablative lining placed between
 the motor casing and the propellant grain. The ablative lining layer
 contains chopped novoloid fibers 14 microns in diameter and having a
 nominal length of 1 millimeter interspersed throughout the polymeric
 composition.
 U.S. Pat. No. 5,352,312 discloses a rocket motor insulation made of a
 liquid crystal polymer such as a wholly aromatic polyester with fillers
 such as glass or carbon fibers.
 U.S. Pat. No. 3,973,397 discloses a rocket motor with an ablative lining
 made of a terpolymer of ethylene, propylene and a nonconjugated diene and
 inert fillers such as heavy metal halides, calcium hydroxide and magnesium
 hydroxide.
 SUMMARY OF THE INVENTION
 A thrust chamber assembly for liquid fueled rock engines and the method of
 making it wherein a two-piece mandrel having the configuration of an
 assembly having a combustion chamber portion connected to a nozzle portion
 through a throat portion is wrapped with a silica tape saturated with a
 phenolic resin, the tape extending along the mandrel and covering the
 combustion chamber portion of the mandrel to the throat portion. The width
 of the tape is positioned at an angle of 30 to 50.degree. to the axis of
 the mandrel such that one edge of the tape contacts the mandrel while the
 other edge is spaced from the mandrel. The phenolic in the tape is cured
 and the end of the wrap is machined to provide a frustoconical surface
 extending at an angle of 15 to 30.degree. with respect to the axis of the
 mandrel for starting a second wrap on the mandrel to cover the throat
 portion. The remainder of the mandrel is wrapped with a third silica tape
 having its width positioned at a angle of 5 to 20.degree. from the axis of
 the mandrel. The resin in the third tape is cured and the assembly is
 machined to provide a smooth outer surface. The entire assembly is then
 wrapped with a tow of graphite fibers wetted with an epoxy resin and,
 after the epoxy resin is cured, the graphite is machined to final
 dimensions.

DETAILED DESCRIPTION OF THE INVENTION
 Referring now in detail to the drawings, there is shown in FIGS. 1 and 4 a
 two-piece mandrel having a combustion chamber portion 12 connected to a
 nozzle portion 13 through a throat portion 14, these portions having the
 configuration of the inner surface of the thrust chamber assembly to be
 made by this process--a generally hourglass configuration. The mandrel is
 made in two pieces 19 and 20 (FIG. 4) such that it can be taken apart and
 withdrawn from the completed thrust chamber assembly.
 FIG. 2A shows the first step in the making of this thrust chamber assembly.
 A ring 24 extending around the end of the combustion chamber portion 12 of
 the mandrel is provided with a surface 25 which is inclined at an angle of
 30 to 50.degree., preferably 40 to 45.degree., with respect to the axis 26
 of the mandrel. The surface 25 provides a starting point for the wrapping
 of a first silica tape 30 saturated with a phenolic resin, such that the
 width of the tape is positioned at the same angle with respect to the axis
 26. The actual positioning of the tape is shown in FIGS. 2A-3. With the
 tape 30 wrapped in this manner one edge of the tape is in contact with the
 mandrel such that, when the combustion chamber portion is used as a
 combustion chamber the layers of the wrapped tape cannot delaminate.
 Silica tape is commercially available. The tape is woven from fiberglass
 fibers and then treated with nitric acid. The nitric acid leaches out the
 sodium and lithium to leave a silica fabric The fabric is cut on the bias,
 at 45.degree., to form strips (not shown) having a width generally the
 same as the that desired for the tapes. The ends of the strips are then
 sewed together to form long lengths of the tape. When a tape of his type
 is used, the inner edge of the tape is free to compress and the outer edge
 is free to stretch. This allows the tape to be wound as described herein.
 The tape is saturated with a phenolic resin prior to being wrapped. The
 angles described herein are the angles between a line formed by the
 intersection of the tape with a plane in which the axis of the assembly is
 lying.
 The first tape is wrapped from the combustion chamber portion to the throat
 portion 14 and terminates in an end 31. The phenolic resin in the wrapped
 silica tape is cured and the end 31 of the wrap is machined to a line 34
 (FIG. 2A) to provide a starting point for the wrapping of the second
 silica tape 35. This machining provides a frustoconical surface (line 34))
 which is the starting point for wrapping the second tape 35, the width of
 this surface being positioned at an angle of 15 to 30.degree., preferably
 15 to 25.degree., to the axis 26 of the mandrel. The second tape 35 is
 wrapped on the throat portion 14 of the mandrel at this angle until the
 end of the throat portion 14 is reached.
 The resin in the second tape is then cured and the end of the second
 portion is machined to a line 37 (FIG. 2C) to give a starting surface for
 the third wrap of silica tape 41 (FIG. 2D). This third wrap 41 is
 positioned at an angle of 5 to 15.degree., preferably 8 to 12.degree., to
 the axis of the mandrel and is carried to the end of the nozzle portion
 12. The third wrap is then cured and the first wrap is cut off along line
 45 of FIG. 3 and then the assembly is machined to provide a smooth outer
 surface and to provide a surface 42.
 FIG. 1 shows the last wrapping step. A tow 47 of graphite filaments is
 wetted with an epoxy resin and then wrapped as shown in FIG. 1, the
 mandrel being mounted on a shaft 48 (FIGS. 1 and 4) which is driven slowly
 by a motor 49. One end of the mandrel is fitted with a dome 52 carrying a
 row of pins 53 extending around the dome. The purpose of the pins 53 is to
 hold the filaments making up the tow 47 in place as the tow is wrapped
 around the dome.
 The other end of the mandrel is fitted with a pair of concentric rings 57
 and 58 positioned as shown in FIG. 1, the rings being supported by posts
 61 and 62, respectively. The rings 57 and 58 carry a plurality of pins 65
 and 66, respectively. The purpose of the pins 65 and 66 is to hold the
 filaments in the tow 47 in alignment as the tow is wound over the rings
 for the next pass over the mandrel. From FIG. 1 it can be seen that when
 the mandrel is completely covered by the tow 47, the wrapped tow will
 exhibit a diamond pattern.
 After the graphite tow wrapping is completed, the epoxy resin is cured and
 the graphite layer is severed along lines 70 and 71. The outer surface of
 the graphite layer is then machined to a smooth surface. The two piece
 mandrel is then removed from the thrust chamber assembly and an injector
 (not shown) is attached to the upper end of the thrust chamber assembly.
 Such an injector is disclosed and claimed in application Ser. No;
 09/168,341, filed: Oct. 5, 1998 in the names of Charles A. Cornelius, et
 al. for LOW COST INJECTOR ASSEMBLY.
 Prior to use of the use of the thrust chamber assembly, a pair of
 attachment rings 74 and 75 (FIG. 5) are bonded to the assembly. These
 attachment rings are using for supporting other equipment (not shown)
 which cooperates with the assembly and gimbals the entire assembly for
 steering a rocket (not shown) on which the assembly is mounted
 In operation, the injector (not shown) injects streams of kerosene and
 liquid oxygen into the combustion chamber where the kerosene is burned to
 provide thrust for the engine. A char layer forms on the silica phenolic
 tape layer, providing insulation for the assembly. The angle at which the
 silica layers are wrapped prevents the tape layers from delaminating.