GB2505629A - Segmented carbon-carbon exit cone assembly - Google Patents

Abstract

An exit cone (10) for solid propellant rocket motors or liquid propellant rocket engines is fabri­cated as discrete carbon-carbon segments (12) and subsequently assembled into a cone. Preferably, longitudinal and circumferential supporting stiff­eners (32,34,44) are formed integrally therewith. This segmented construction means that if one part of the cone is flawed or damaged, it is necessary only to replace that part rather than the whole one.

Description

SEGMENTED CARBON-CARBON EXIT CONE ASSEMBLY

The present invention relates to a segmented exit conà f or a rocket fabricated from discrete segments and a method for forming the segmented exit cone.

The exit cone portion of a nozzle is an essential I component of a rocket motor or engine. The exit cone provides some of the thrust and often directs the thrust for guidance of the rocket.

there is an ongoLng emphasis to reduce the weight, simplify the construction, lower the cost and increase io the dependability of solid propellant rocket motors.

The exit cone of solid propellant rocket motors or liquid propellant rocket engines continually presents a focal point for the improvement of the above-listed characteristics. Most prior art exit cones for s!lid propellant application have been made of materials such as carbon, silica or glass cloth, or fibers in a phenolic resin binder. Metals, while stronger than these materials, are too heavy and costly both in the manufacture and operation of the rocket motor or engine.

Carbon materials offer an extremely suitable choice f or the rocket nozzle exit cone material. At present the carbon rocket exit cones are manufactured in one piece but are limited as to size and variations in design. A major drawback in the present state of the art is the loss of an entire exit cone some of which can range up to 50 inches(127 cm) in diameter, if a single defect or flaw is found in the cone, the entire cone must be discarded with a total loss of all the time and materials it took to manufacture the now useless item.

An object of the present invention is to provide a light weight yet strong and temperature resistant rocket exit cone suitable for use in a highly oxidizing environment like that of the rocket exhaust products that contact the rocket nozzle during operation of the rocket.

Another object of the present invention is to pro-vide a rocket exit cone which can be manufactured with a reduction of waste in time and materials over presently available methods.

Yet another object of the present invention is to provide a rocket exit cone which substantially extends the maximum size exit cone that may be manufactured with present manufacturing equipment.

Still another object of the present invention is to provide a rocket exit cone that is easier and simpler to fabricate than presently available.

Yet another object of the present invention is to provide a rocket exit cone which greatly reduces the scrap costs attributed to presently available exit cones, since a defect in one segment does not cause a loss of the entire cone.

Another object of the present invention is to pro-vide an exit cone with more flexibility of design than presently available.

Still another object of the present invention is to provide a rocket motor nozzle exit cone that is made of lighter material than any metal presently used but with at least as good performance characteristics.

In accomplishing these and other objectives of the invention there is provided a segmented nozzle exit cone including a plurality of identical segments including connecting means which when attached to one another form an exit cone for a rocket engine or a rocket motor. Each segment includes a concave/convex skin or membrane which, with the correct number of identical segments, I it together to form a frustum-shaped member.

Each segment may include a plurality of longitudinal stiffeners as well as circumferential stiffeners, either of which may be integral with each segment.

These and other objects and features of the present invention will be better understood and appreciated from the following detailed description of a number of embodiments thereof, selected for purposes of illustra-tion and shown in the accompanying drawings.

Having summarized the invention, a detailed description follows with reference being made to the accompanying drawings which form part of the specifica-tion, of which: Figure 1 is a perspective view of an exit cone of the present invention formed by four identical 900 segments; Figure 2 is a perspective view of one of the identical segments forming the cone in Figure 1; Figure 3 is a perspective view of another embodi-ment of the segmented exit cone assembly; and Figure 4 is a detail illustrating connection and stiffening of the present invention for one embodiment.

An exit cone in the form of a frustum suitable for use with either a solid propellant rocket motor or liquid propellant rocket engine is illustrated in each * of Figures 1 and 3. In Figure 1 a plurality of identi-cal segments 12 are assembled to form an exit cone 10.

Similarly, in Figure 3, a plurality of identical seg-ments 13 are assembled to form an exit cone 11. Each segment in each cone is identical. The exit cone, in each case, is a frustum-shaped member of which each segment is a submember. Figures 1 and 3 illustrate 90° is and 45° segments, respectively. The scope of the pre-sent invention is not limited by the number of segments 12 or 13 in the respective cone assembly 10 or 11. The segments may take many forms and still accomplish the * objectives of the present invention. Therefore, it is clear that not every segment -embodiment can be dis-cussed. Flexibility of design is one of the objectives of the present invention, and it will be clear to those skilled in the art that variations of the embodiments discussed herein may be suitable for practicing the pre-sent invention.

Each segment 12, as shown in Figure 1, is identical and comprises a relatively thin membrane 14 having a S convex surface 16 and a concave surface 18. typical membrane thicknesses vary from.05 to.15 inches (0.127-0.381 cm.) with each segment in a cone assembly 10 having the same thickness. Segment thickness varies depending upon the performance characteristics that a particular exit cone will be required to meet. Each segment 12 is bounded by first and second longitudinal edges 20 and 22 and first and second curved edges 24 and 26. The longitudinal edges and curved edges do not meet at right angles, since curved edge 26 is longer than curved edge 24. Inspection of the drawings will show that this is a result of the frustum shape of the assembled exit cone 10. The first circular opening 28 defined by the assembled segments 12 is smaller than the second circular opening 30, also defined by the assembled segments 12. Again, this is a result of the final shape assumed by the assembled segments. Each segment 12 may taper, that is, become thinner, from the first curved edge 24 to the second curved edge 26.

In one embodiment of the present invention each segment 12 includes a first longitudinal stiffening ridge 32 that extends perpendicularly and radially away -7-.

from convex surface 16 along longitudinal edge 20.

Likewise, second longitudinal stiffening rib 34 extends perpendicularly and radially from convex surface 16 along second longitudinal edge 22. Both ribs 32 and 34 extend S from first curved edge 24 to second curved edge 26. In one embodiment adjacent segments may be fastened together by means of a plurality of fasteners 38 passing through a plurality of opposing holes 36 in the adjacent engaging ribs. The ribs 32 and 34 may contain a plura-lity of cooperating pins and holes for facilitating alignment of the segments when the latter are assembled into the frustum shape, since the segments are iden-F tical and the spacing of holes 36 is the same for each segment. Fastening means 38 may comprise threaded bolts 42 and nuts 40 or other suitable fastening means. The scope of the present invention is not intended to be limited by the means in which the segments are held together. For example, a suitable clamp means, not shown, may be used to clamp the segments together by means of the stiffening ribs. A number of other fastening means are discussed for purposes of illustra-tion only.

The design of a particular exit nozzle may require circumferential stiffening of the individual segments.

In one embodiment, illustrated in Figure 2, an integral circumferential stiffening rib 44 extends perpendicularly from convex surface 16. Rib 44 in the present embodi-ment extends from longitudinal rib 32 to longitudinal rib 34. When an exit nozzle 10 is assembled from segments 12 as just described, the nozzle will be structurally strengthened both longitudinally and cir- cumferentially. Although only one circumferential stif-fening rib 44 is illustrated in Figure 2, it will be clear to those skilled in the art that any reasonable number of circumferential stiffening ribs 44 could be provided. In the same manner additional longitudinal stiffening ribs or any variation thereof may be included on segment 12.

Other embodiments of the present invention are illustrated in Figures 3 and 4. Figure 3 illustrates an exit cone 11 comprising segments 13 which may or may not have stiff éning ribs or fastening means as previously described. Instead, after segments 13 are assembled in the desired cone 11, an overwrap 46 may be wound around the segments and then cured by forming a segmented cone of the present invention. In the presently described embodiment, overwrap 46 may comprise a carbon fiber material which is well known in the art.

Figure 4 illustrates an alternative stiffening and fastening means for the present invention. Two iden-tical segments 48 are shown in Figure 4. For each segment 48 there is shown an associated longitudinal stiffening rib 50, 52 and fasteners 54. The segment and cone assembly embodiment illustrated in Figure 4 includes at least one circumferential hoop 56 that circumferen-tially stiffens the exit nozzle and holds segments 48 together much like barrel hoops hold the staves of a barrel together. A plurality of opposing notches 58 in the adjacent and engaging ribs 50 and 52 allow for the passage of hoop 56 about the assembled cone. Figure 4 only illustrates a detail of this embodiment, and it should be clear to those skilled in the art that any number of circumferential hoops may be used. In addi-tion, the fastening and stiffening means discussed above are not intended to be mutually exclusive, and any corn-binátion of fastening and stiffening means may be used to roduce the desired exit cone and still be within the scope of the present invention.

In a preferred embodiment the segments 12, 13 and 48 are made of carbon-carbon materials, a composite material of bonded carbon-graphite fibers. The fibers are bonded together in a desired matrix such as random fibers, integrally woven fibers, graded fibers, or fabric. This is similar to a fiber resin composite well known in the art except that it is entirely carbon material.

Each of segmented cone assemblies fo Figures 1 and 3 comprises a plurality of identical segments which in a preferred embodiment are made form carbon-carbon material. Fabrication of the segments is done by con-ventional techniques; either matched die molding or ply lay up on a mold followed by a vacuum bag cure, that is curing of the resin impregnated carbon fabric.

Typically, a curing process involves the placement of a vacuum bag over the uncured carbon fabric laminate which had been laid up in a mold or form block. For about four hours the mold including the vacuum bag resides in an autoclave under approximately 250 in 300 pounds per square inch pressure at approximately 300°? to 325uF.

Following this step, cooling to 100°F. takes place under pressure within the autoclave after which the piece can be removed. The cured segment now hai the desired con-figuration and needs only to be removed from the mold prior to the final two steps which follow the curing process.

The use of an "inert" as possible material for the exit cone is desirable. This is necessary in view of the highly oxidizing and burning gases which tend to oxidize all the materials that the combustion gases con-tact. the next step after curing the segment is generally to carbonize the segment whereby the organic resin in the original material is reduced to carbon.

The oxygen and nitrogen, etc. that are present in the material are driven off by the heat of carbonization.

Carbonization temperatures may go to approximately 1000"c. When requiring a more ordered structure, the exit nozzle may be graphitized during which time the temperatures may exceed 2000'C. Either of these pro-cesses are known in the art.

Higher segment exit cone densities may be obtained S by a series of impregnations with a resin or coal tar pitch followed by a carbonization and graphitization.

At this point in the manufacturing process, the segment of the exit cone is complete to the extent that it has the desired shape icluding any integral stif-fening ribs. If it hasn't already been done in the molding process, the segment may now be modified to receive any external fastening means 38 or externally applied circumferential hoops or stiffeners 56. In the case of the exit cone of Figure 1, holes 36 may be drilled in the ribs 32 and 34. In the case of the exit cone of Figure 4, notches 58 and 60 would be milled at the appropriate location in ribs 50 and 52.

While specific embodiments have been shown and described, many variations are possible. The particular shape and dimensions of the segments or staves including the stiffener dimensions may be changed, as desired, to suit the design characteristics of the exit cone. The configuration and number of segments may vary although the embodiments described show from four to eight mdi-vidual segments assembled to form the exit cone of the present invention. The segment materials may vary although carbon materials are preferred. A fabric that is satisfactory for use with the present invention is WCA fabric that currently is being used for similar applications. Improved materials woven from PAN (Polyacrylonitrile) carbon fibers are also suitable.

Thus, in accordance with the present invention, there has been provided an improved exit cone that is fabricated as discrete carbon-carbon segments and sub-sequently assembled into a cone, with longitudinal and circumferential supporting stiffeners being formed integrally therewith. The improved exit cone is made by a semi-automated molding process and the current labor intensive hand lay up procedure. The exit cone is characterized by its light weight, résistance to high temperatures, and capability of withstanding high pressures and loads and also a high oxidizing environ-ment. The exit cone is further characterized by its freedom from serious constraints relative to allowable size, quality, and design flexibility. Design flexibi-lity is a result of the easier handling of the individual segments and availability of including in each segment aifferent means for connecting the segments both longitudinally and circumferentially. Quality control is improved because the smaller segments are easier to fabricate, and moreover, simplify non- -* destructive test procedures. Scrap costs are reduced because individual defective segments can be scraped instead of a completed cone.

Having described the invention in detail those skilled in the art will appreciate that modifications S may be made of the invention without departing from its spirit. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments illustrated and described. Rather, it is intended that the scope of this invention be determined by the appended claims and their equivalents. S.

Claims (12)

1. CLAIMS1. An exit cone for a rocket comprising: A plurality of identical segments, each segment including a membrane of carbonized and S densified carbon-carbon composition, each segment having a first and a second longitud-inal edge, a first curved end edge and a second curved end edge, the second end edge being longer than the first end edge and shaped such that the plurality of segments, when joined together along longitudinal edges, define a f rust urn, a first circular opening defined by the plurality of first curved edges and a second circular opening defined by the plurality of second curved edges, the second circular opening being larger than the first circular opening, and means for attaching the segments together to form the frustum. S.
2. 2. An exit cone as set forth in claim 1 comprising: means for longitudinally stiffening each segment of the plurality of segments.
3. 3. An exit cone as set forth in claim 1 comprising: means for circumferentially stiffening each segment of the plurality of segments.
4. 4. An exit cone for a rocket comprising: A plurality of identical segments of carbonized and densified carbon-carbon composition, each segment including a relatively 1thin, shaped membrane having a convex surface and conOave surface, each membrane being bounded by a first longitudinal edge, a second longitudinal edge, a first curved edge, and a second curved edge longer than the first curved edge, whereby joining the plurality of segments at the longitudinal edges with the segments oriented so that the ends of the adjacent first curved edges meet and forms a cone having a first circular opening defined by the plurality of joined first curved edges and a second circular opening defined by the plurality of joined second curved edges,Hthe second circular opening being larger than the first circular opening, each segment including a first and a second integral longitudinal stiffening rib of the carbonized and densi-fied carbon-carbon composition, the first rib extending radially outwardly from the membrane convex surface and extending the axial length of the segment from the first curved edge to the second curved edge along the first longitudinal edge, the second rib extending radially outwardly from the membrane convex surface and extending the length of the segment from the first curved edge to the second curved edge along the second longitudinal edge, a plurality of bolts and associated nuts for fastening said segments together, each rib including a plurality of holes, with the holes in each of said ribs being similarly placed, for receiving a bolt whereby said plurality of bolts extending through aligned opposing holes in adjacent ribs of abutted segments are operative, in cooperation with said nuts, to fasten the segments together, and each segment including a plurality of integral, circumferential stiffening ribs of the carbonized and densified carbon-carbon composition, the circumferential Vi ribs extending radially outwardly from the membrane con-vex surface and extending between and perpendicular to the first and second longitudinal, stiffening ribs.
5. 5. An exit cone as set forth in claim 4 in which the carbon-carbon composition has a density of from 1.45 to 2.0 g/cc.
6. 6. An exit cone segment comprising: a relatively thin membrane of carbonized and densi-fied carbon-carbon composite, the membrane having a concave surface and, a com-plementary, opposite convex surface, the membrane being bounded by first longitudinal edge, a second longitudinal edge, a first curved edge, a second curved edge longer than the first curved edge, whereby the membrane defines a longitudinal section of a surface of frustum-shaped member, a first longitudinal stiffening rib of carbonized and densified carbon-carbon composition integral with the segment, the first rib extending radially outwardly from the convex surface, the first rib being co-extensive iith the segment adjacent a first longitudinal edge; a second longitudinal stiffening rib of carbonized and densified carbon-carbon composition integral with the segment; the second rib extending radially outwardly from S the convex surface, the second rib being co-extensive with the segment adjacent the second longitudinal edge; the first longitudinal rib defining a first plurality of holes, and the second longitudinal rib defining a second plurality of holes, whereby a plurality of longitudinal fasteners pass through to hold together a plurality of pairs of segments having abutting first and second longitudinal edges; a plurality of aircumferential stiffening ribs of carbonized and densified carbon-carbon composition integral with the segment, the plurality of circumferential ribs extending perpendicularly outwardly from the convex surface and extending between and perpendicular to the first and second longitudinal stiffening ribs.
7. 7. An exit cone according to claim 1, substantially as herein described with reference to Fig. 1, Fig. 2, Fig. 3 or Fig 4 of the accompanyiny drawings.Amendments to the claims have been filed as followsCCLAIMSl An exit cone for a rocket comprising: -A plurality of replaceable segments, each segment including a membrane of carbonized and densified carbon-carbon composition, having a convex and a concave surface, first and second longitudinal edges, a first curved end edge and a second curved end edge, the second end edge being longer than the first end edge and shaped such that the plurality of segments, when joined together along longi-tudinal edges, define a cone frustum, with a first circular opening defined by the plurality of first curved edges and a second circular opening defined by the plurality of second curved edges, the second circular opening being larger than the first circular opening, wherein to secure the segments together to form a cone frustum, longitudinal ribs are provided which extend at least partially along the length of the first and second longitudinal edges of each of the segments from the first curved edge to the second curved edge, each said rib extending radially out-wardly from the convex surface of the respective membrane and being attached thereto and means for detachably securing the ribs of adjacent segments together to form the frustum, whereby an individual segment may be removed and replaced.2. An exit cone as claimed in claim 1 wherein the segments are identical.3. An exit cone as claimed in claim 1 or claim 2 further comprising means for c-ircumferentially stiffening each segment of the plurality of segments.4. An exit cone as claimed in claim 3 wherein the circumferential stiffening means comprises one or more integral, circumferential stiffening ribs of the carbonized-Cand densified carbon-carbon composition, the circUmferential ribs extending radially outwardly from the convex surface of the membrane and extending between and perpendicular to the first and second longitudinal ribs.5. An exit cone as claimed in any preceding. claim wherein the longitudinal stiffening ribs are made of the carbonized and densified carbon-carbon composition, and are formed integrally with their respective cone segments.6. An exit cone as claimed in any preceding claim wherein the means for securing the ribs together comprises a plurality of fasteners for fastening said segments together, each longitudinal rib including a plurality of holes, with the holes in each of said ribs being similarly placed for receiving a fastener through each pair of aligned opposing holes in adjacent ribs of abutted segments to fasten the segments together.7. An exit cone as claimed in claim 6, wherein the fasten-ers comprise nuts and bolts.
8. 8. An exit cone as claimed in any preceding claim wherein the longitudinal ribs are coextensive with the respective longitudinal edges along which they run.
9. 9. An exit cone as claimed in any preceding claim in which the carbon-carbon composition has a density of from 1.45 to 2.00 g/cc.
10. 10. A replaceable segment for a rocket exit cone comprising: a relatively thin membrane of carbonized and densified carbon-carbon composite, having a concave surface and a complementary, opposite convex surface and being bounded by a...first longitudinal edge, a second loPgitudinal edge,' a first curved edge and a second curved edge longer than the first curved edge, whereby the membrane defines' a longitudinal section of a surface of frustum-shaped member, S first and second longitudinal stiffening ribs of carbonized and densified carbon-carbon composition integral with the segment, extending radially outwardly from the convex surface and co-extensive with the segment adjacent respective first and second longitudinal edges; means includinga first and a second plurality of h?les defined by the first and second longitudinal ribs respectively for passage of a plurality of longitudinal fasteners therethrough and through corresponding holes of corresponding segments to hold together detachably a plurality of pairs of segments having abutting first and second longitudinal edges whereby the segment may be replaced by another segment; and a plurality of circumferential stiffening ribs of carbonized and densified carbon-carbon composition integral with the segment, the circumferential ribs extending perpendicularly out-wardly from the convex surface and extending between and perpendicular to the first and second longitudinal stiffening ribs.
11. 11. An exit cone according to claim 1, substantiallyas herein described with reference to Fig. 1, Fig.2 or'Fig.3 of the accompanying drawings.
12. 12. An exit cone segment according to claim 10 substantially as herein described with reference to Fig.2 e.rg.3 of the accompanying drawings.