Method of manufacturing a rocket combustion chamber

The present invention is directed particularly to an improved method using owder metallurgy for the manufacture of the grooved cooling wall of a liquid-propellant rocket combustion chamber. The surface of an inner cylinder constituting the cooling wall is formed with cooling grooves, and these grooves are densely filled up with a filler such as paraffin wax. Thereafter, metal powder which will provide an outer cylinder is compression-molded to a predetermined thickness around the inner cylinder. This metal powder is the same material as the material of the inner cylinder. After the paraffin wax which is the filler is evaporated and removed, the compression-molded metal powder body is sintered in a furnace. During this sintering heat treatment, the inner and outer cylinders are rigidly joined together by the sintering reaction between the atoms of the inner cylinder and the atoms of the metal powder.

TECHNICAL FIELD 
This invention relates to a method of manufacturing the grooved cooling 
wall of a combustion chamber, particularly a liquid-propellant rocket 
combustion chamber. 
BACKGROUND ART 
In recent years, cooling of the combustion chamber has become the most 
important task as the combustion pressure of a liquid-propellant rocket 
engine has increased. 
Heretofore, a combustion chamber has been manufactured by bundling several 
hundred tubes as shown in FIG. 1B of the accompanying drawings which is an 
enlarged view of the interior of the dotted circle of FIG. 1A. However, 
such a tube structure is inferior in cooling performance and cannot be 
adopted in a high combustion pressure engine for large heat load. 
For this reason, a combustion chamber having a grooved cooling wall as 
shown in FIG. 2 of the accompanying drawings has been developed. This 
grooved cooling wall has a dual merit that the area of the inner surface 1 
of the combustion chamber which is in contact with hot combustion gases is 
small as compared with the tube structure of FIG. 1B while, on the other 
hand, the area of cooling passages 2, namely, the cooling area, is large, 
and thus it is a very advantageous structure for an engine of high 
combustion pressure. 
However, the manufacture of such grooved rocket combustion chamber has 
suffered from numerous problems. That is, in the method of manufacture 
according to the prior art, grooves 5 extending axially on the combustion 
chamber as shown in FIG. 3B of the accompanying drawings are formed in an 
inner cylinder 4 made of copper or a copper alloy as a metal of good heat 
conductivity as shown in FIG. 3A of the accompanying drawings, by machine 
work. Subsequently, an outer cylinder 6 is attached to the outer side of 
the grooved portion in a manner as shown in FIG. 3C of the accompanying 
drawings and in that case, the inner cylinder 4 and the outer cylinder 6 
must be rigidly joined together without the cooling grooves 5 being 
adversely affected. 
The brazing method and the electroforming (electrolytic deposition) method 
are known as such joining method. However, in the brazing method, the 
brazing material flows into the cooling grooves 5 to vary the 
cross-sectional area of the grooves, and this makes it difficult to obtain 
a predetermined cooling effect and may in most cases lead to the burning 
of the engine. Also, it is nearly impossible to accomplish brazing 
uniformly over the entire engine. 
On the other hand, the electroforming method is a method of forming an 
outer cylinder 6 outside the inner cylinder 4 by electroplating and, for 
instance, used in the manufacture of an engine for a space shuttle. 
However, the outer cylinder formed by this method readily permits internal 
stress to be created therein and thus is weak in strength. To suppress 
such internal stress, it is necessary to delay the electrolysis reaction 
and a reaction time as long as several hundred to several thousand hours 
is required for making an outer cylinder of a predetermined thickness. 
Moreover, the outer cylinder 6 thus manufactured is made of Ni and is 
therefore poor in ductility, and it is known that the stress created in 
the engine concentrates in the inner cylinder 4 of Cu, thereby reducing 
the life of the engine. 
SUMMARY OF THE INVENTION 
The present invention has as its object to provide a method of 
manufacturing an outer cylinder which does not have the above-noted 
disadvantages by covering the inner cylinder of a cooling wall with a 
rigid outer cylinder. 
Such object of the present invention is achieved by a method of 
manufacturing the cooling wall of a combustion chamber which comprises the 
steps of making an inner cylinder formed with grooves in the surface 
thereof, filling up the grooves of the inner cylinder with a filler, 
compression-molding metallurgy powder of outer cylinder material to a 
predetermined thickness around the inner cylinder having its grooves 
filled up with the filler, and sintering the compression-molded powder to 
thereby form an outer cylinder joined with the inner cylinder.

DETAILED DESCRIPTION OF THE EMBODIMENT 
An embodiment of the present invention will hereinafter be described with 
respect to a case where both of inner and outer cylinders are made of 
copper. 
As shown in FIG. 4, the inner cylinder 11 is made into a predetermined 
shape by machine work. The grooves 12 of this inner cylinder 11 are filled 
up with molten paraffin wax 14 so that no hole is created therein. Then, 
with the wax 14 solidified, a compression pressure of the order of 1 
ton/cm.sup.2 is applied to the wax 14 as by a hydrostatic pressure to 
thereby make the wax denser. If the wax 14 precipitates due to this 
compression, further wax may be added to make the top 15 of the groove 
partition walls and the surface of the wax 14 flush with each other. If 
this process is incomplete, there will occur a phenomenon that during 
formation of the outer cylinder 13 to be described, the outer cylinder 13 
becomes curved into the grooves 12 due to the precipitation of the wax 14 
and therefore, the above-described operation may be repeated as required 
and it may be confirmed that precipitation of the wax 14 is not caused by 
the hydrostatic pressure. 
Subsequently, the top 15 of the groove partition walls of the inner 
cylinder 11 is surface-treated as by sand paper to thereby enhance the 
sintering property thereof with respect to the outer cylinder. 
The inner cylinder 11 subjected to the abovedescribed treatment is placed 
into a mold having a pressure bag 16 disposed therewithin, and as shown in 
FIG. 5, the gap between the inner cylinder 11 and the pressure bag 16 is 
filled up with copper powder 17 which is the same material as the inner 
cylinder 11. The copper powder 17 may be electrolytic copper powder of 
150-400 mesh. 
A copper powder layer 17 is then compression-formed as by a hydrostatic 
pressure method. The compression pressure may be of the order of 1 
ton/cm.sup.2. 
This compression-molded body is installed in an electric furnace and 
sintered in an atmosphere of hydrogen gas or rare gas or in vacuum to 
prevent oxidation of the copper powder. At first, the furnace temperature 
is kept at 400.degree. to 500.degree. C. and the paraffin wax 14 filling 
the grooves 12 is removed. If the paraffin wax remains, the sintering 
reaction thereafter will be marred and therefore, the paraffin wax must be 
removed completely. After it is confirmed visually or by means of an 
instrument that the paraffin wax has completely evaporated, the furnace 
temperature is increased to about 900.degree. C. and maintained at this 
temperature for about two to three hours. The furnace temperature and the 
time during which the furnace temperature is maintained are more or less 
variable by the particle diameter of the copper powder used, the 
compression-molding pressure, etc. and therefore, optimum values thereof 
must be predetermined by a preparatory test. Due to this heat treatment, 
the sintering reaction not only of the copper powder but also between the 
copper atoms of the inner cylinder 11 and the atoms of the copper powder 
progresses, whereby a tough outer cylinder 13 integral with the inner 
cylinder 11 is formed. 
Finally, the sintered layer formed more or less thickly is finished into a 
predetermined thickness by machining, whereby the outer cylinder 13 is 
completed. 
Partly cross-sectional views of the completed combustion chamber are shown 
in FIGS. 6A and 6B. 
In the above-described process, powder of ceramics such as alumina or 
magnesia or other metal powder may be mixed with the paraffin wax filling 
up the grooves 12. Such mixed wax is great in density and the compressing 
operation for preventing the precipitation of the wax surface by the 
hydrostatic pressure may be much less frequently effected than in the case 
where only paraffin wax is used. However, the added powder stilI remains 
in the grooves after the sintering of the outer cylinder and it must be 
physically or chemically removed by washing or chemical treatment. 
According to the present invention, as described above, the outer cylinder 
is manufactured by using a material of the same quality as the inner 
cylinder and by powder (dust) metallurgy, and this leads to the following 
advantages: 
(1) The cooling grooves are filled up with a filler during the 
compression-molding of metallurgy powder and therefore, there is no flow 
into the grooves as in the case of brazing and predetermined cooling 
material flow passages are obtained; 
(2) The metallurgy powder is uniformly pressed against the inner cylinder 
as by a hydrostatic pressure and the inner and outer cylinders of the same 
material are rigidly joined together, and this completely eliminates the 
possibility of partial exfoliation occuring; 
(3) Since an electrochemical method is not resorted to for the formation of 
the outer cylinder, no internal stress occurs and the working time is much 
shortened; and 
(4) Since the inner and outer cylinders are formed of materials of the same 
quality, the stress created in the rocket combustion chamber does not 
concentrate in the inner cylinder and this is suitable for a reusable type 
rocket engine.