US3427698A - Rocket nozzle - Google Patents

Description

ROCKET NOzzLE l Filed Nov. 26. 196s FIGLI INVENTOR EDMUND' GUZEWICZ BY ATTORNEY United States .Patent ihce I3,427,698 Patented Feb. 18, 1969 3,427,698 ROCKET NOZZLE Edmund A. Guzewicz, Wallingford, Conn., assiguor to Chandler Evans Inc., West Hartford, Conn., a corporation of Delaware Continuation-impart of application Ser. No. 183,537, Mar. 29, 1962. This application Nov. 26, 1965, Ser. No. 513,651 U.S. Cl. 29-157 7 Claims Int. Cl. B21d 53/92; B64d 33/04 ABSTRACT OF THE DISCLOSURE The method of manufacturing a monolithic rocket chamber, throat and nozzle assembly comprising the successive steps of forming by plasma arc spraying on a rotating mandrel of selected shape rst a 'layer of pure tungsten, and then successive layers of a mixture of tungsten and zirconia to form a seamless monolithic structure, grinding the outer surface of the monolithic structure to conform to the inner surface of a steel shell, dissolving the mandrel without dissolving the tungsten to thereby form the chamber, throat and nozzle, and then clamping the monolithic structure in an encapsulating steel shell to lock all of the components of said monolithic structure in place.

This invention pertains to the jet nozzles of rocket motors, and more particularly has reference to the construction of such nozzles as monolithic structures of refractory materials which are highly resistant to elevated temperatures and the erosive and oxidizing effects of the gases that compose the propulsion jets.

This application is a continuation-impart of my copending application, Ser. No. 183,537, led Mar. 29, 1962.

For optimum rocket propulsion efficiency, rocket motors must operate at or near stoichiometric fuel/ oxidizer ratios which result in high temperatures, ranging from 5000 F. to 6500 F. To build rocket nozzles capable of withstanding these temperatures .and the erosive effect of high velocity jet gases is a basic problem `Whose solution has been long sought in the art.

Heretofore, prior art designs have generally lbeen of segmented construction, wvhere high-temperature resistant refractory inserts are retained in critical locations by ablative cooled composites. This type of construction leaves seams in the surface Where the segments meet and these seams are conductive to severe erosion from the high temperature and velocity of the jet gases. Also, ablative cooled composites char and change dimensionally, as well as have a tendency to reduce the enthalpy of the combustion gases, thus reducing the overall propusion efficiency.

My invention solves the temperature and erosion problem by utilizing refractory material (e.g., tungsten) Whose melting point is above that of the combustion temperature, and then using additional refractory material (e.g., zirconia) of low thermal diffusivity and conductance, to minimize the transient and steady-state temperature at the outside surface of the nozzle. This technique thus permits the use of a conventional steel casing with which 4to transmit the reaction thrust to the vehicle being propelled.

My invention comprises the use of a monolithic tungsten liner for the rocket chamber,throat and nozzle, with no segments or seams. The tungsten liner is externally overlaid by heat-insulating material having a low thermal conductivity so that a minimum of heat is transmitted from the jet gases, thus maintaining the highest possible enthalpy. The tungsten liner itself is approximately `87% of theoretical hulk density, and this p'orosity further increases the resistance to heat flow lfrom the propulsive gases.

`One of the unique lfeatures of my invention is that it permits a .geometric shape to be made out of pure tungsten metal, which has never been accomplished before. Tungsten is a member of a unique family of metals, possessing high room-temperature brittleness with a low hardness. It is extremely diflicult to machine this metal and the complete machining of the required nozzle shape from bar stock is practically impossible. Pressed and sintered powder metallurgy techniques also cannot be used because of the complicated die and iixturing required. I have discovered that relatively new advent of the plasma arc as a useful manufacturing tool permits the construction of jet nozzles out of these high melting point metals, according to my invention.

One object of my invention is to provide a method for making rocket nozzles as monolithic structure of the desired shape, having no segments or seams, and composed of (l) a basic layer of a refractory metal whose melting point is above the temperature (5000 F. to 6500 F.) of rocket jet gases, and (2) is overlaid by a covering layer of refractory material of low thermal diifusivity and conductance, which minimizes the transient and steady-state temperature at the outside sur-face of the nozzle.

Another object of my invention is to provide a method for making monolithic rocket nozzles which comprise a basic layer of metal (e.g., tungsten), and successive overlying layers of a mixture consisting of a progressively decreasing percentage of said metal with a corresponding-ly increasing percentage of a refractive material of low thermal dilusivity and conductance (e.g., zirconia), so that the outermost layer of the nozzle consists of pure zirconia.

Another object of my invention is to provide a method of making monolithic rocket nozzles in which the brittle refractory component materials are locked in place by an encapsuling steel sleeve or shell.

A further object of my invention is to provide as articles of manufacture rocket nozzles of monolithic construction consisting of a plurality of layers of a mixture of a metal and a refractory material in which the metal varies from 100 percent (with the refractory material from zero), in the innermost layer, to zero percent metal (with 100 percent refractory material) in the outermost layer; said nozzles being inca'psuled in a steel shell which locks the brittle component materials in place.

With these and other objects in view of which may be incident to my improvements, my invention consists in the combination and arrangements of elements shown in the accompanying drawing in which FIG. 1 is a longitudinal section of a rocket nozzle made according to my invention, and FIG. 2 is a cross-section on the line 2--2 of FIG. 1. In the drawing, the reference numeral 1 denotes an innermost layer or liner of pure tungsten, which is immediately overlaid by a layer 2, consisting of a mixture of about tungsten and 20% zirconia. Layer 2 is in turn overlaid by a layer 3, consisting of a mixture of about 20% tungsten and 80% zirconia. Finally, overlying layer 3 is an outermost layer 4 of pure zirconia, which fills all the space between layer 3 and steel shell 5, and serves to thermally insulate said shell from heat radiating from the combustion chamber in liner 1. Shell 5 comprises a cylindrical sleeve 6 of stainless steel, having at its open end an internal flange 7, which ts snugly over an outwardly-extending, integral flange 8 on liner 1.

The inner end of sleeve 6 has an outwardly-extended flange 9, which is clamped, by a plurality of adjustable screw bolts 10, to a mating flange 11 of a stainless steel end cap 12, so that when sleeve 6 and cap 12 are assembled, as shown in -FIG. 1, they form an outer shell which closely contacts the entire outer surface of layer 4, and incapsules the brittle, refractory elements 2, 3 and 4 and securely locks them in place.

Before assembling, the outer surface of the nozzle is finished ground to fit the inner surfaces of sleeve 6 and cap 12.

Liner 1 and cap 12 are each provided with a plurality of holes for the reception of a liquid fuel injector 13 and an oxidizer injector 14.

Liner 1 and overlying layers 2, 3 and 4 are formed Aby first plasma spraying pure tungsten powder onto a removable metal mandrel which is then removed. Due to the difference in expansion of tunsten and zirconia gradated layers of composites are then sprayed over the tungsten. `Layer 2 of 20% zirconia and 80% tungsten is the first insulation layer applied. This layer is then followed up by additional layers 3 and 4 of progressively less tungsten content, until the final layer 4 is of pure zirconia.

The mandrel on which the tungsten is plasma sprayed is made of a soft metal, such as brass or aluminum, which is readily dissolved in either an acid (for brass) or a strong alkali (for alumnium). The mandrel is machined precisely to the desired contour, and is then mounted in a suitable chuck or jaw, and rotated at a uniform speed depending on the following factors:

(a) Maximum diameter of mandrel. (b) Rate of powder deposit.

(c) Type of coatings to be applied. (d) Desired density.

I have found that a mandrel surface speed (at its greatest diameter) of 35 to 40"/min., and at a deposition rate of approximately 4 lbs. of tungsten powder per hour, produce a tungsten coating of approximately 87% density. A greater surface speed will result in a lower density coating.

The tungsten powder is heated to a plastic state in the plasma jet and as the particles are directed on to the previously roughened surface of the mandrel, the individual metal particles strike the mandrel with a relatively high velocity. There is a slight increase of temperature at the surface of the particles, due to the conversion of their velocity energy to heat upon impact. This rise in temperature causes some local melting on the part of the mandrel, and some fusion bonding between the deposited particles and the mandrel takes place. Thus, the bond between the coating and mandrel is both mechanical and fusion. The mechanical bond results from the plastic particles interlocking in the roughened surface of the mandrel.

This relative tight bond causes no difficulty since the mandrel is then removed by dissolving it out with a suitable mandrel solvent, such as an acid or strong alkali, depending upon whether the mandrel is made of either brass or aluminum, repsectively.

The remaining oxide-metal and pure oxide (zirconia) coatings are applied essentially in the same manner. Intentional roughening of the surface of the deposited coat is not required, prior to applying the next metaloxide or pure oxide coat. Due to the nature of the coating process, as described above, whereby the particles are only plastic but not fused, the coat (as deposited) is suficiently rough to constitute a satisfactory mechanical bond for the remaining coats.

I have found that no change in the depositing variables was necessary up to the final pure zirconia coat. The oxide and metal particles are both ejected from the plasma jet in a plastic state, although due to the higher fusion or melting point of tungsten, the oxide particles are in a state of more plasticity. However, the zirconia possesses a heat capacity of approximately four times that of tungsten, which property tends to off-set its lower melting point.

For the final pure zirconia coat, I found it necessary to adjust the powder material flow so that approximately 1-2 pounds of oxide was deposited per hour.

The complete nozzle is then finished ground to fit the interior surface of the two-piece stainless steel shell 5. Holes are put into the nozzle chamber for the liquid fuel and oxidizer injectors 13 and 14.

F'IG. l clearly shows the encapsuling feature, whereby the brittle refractory materials of tungsten and zirconia are securely locked in place by the overall steel shell.

The number and shape of the coating composition of thermal insultion of layers 2, 3 and 4 vary in accordance with the combustion chamber temperature and outside envelope configuration. In most instances, two different proportions of tungsten and stabilized zirconia, as in layers 2 and 3, between the pure tungsten liner 1 and outer pure zirconia layer 4 are found adequate. The purpose of these inter-layers 2 and 3 is to avoid marked thermal expansions between the tungsten and stabilized zirconia which differ by considerable magnitude. Grading of the composition of the coating layers reduces the sheer stresses at the interfaces of any two layers, caused by the different thermal expansions of these materials.

The tungsten and stabilized zirconia generally consist of powdered grain particles of -100 to +325 mesh size. A mixture, consisting of approximately 75% tungsten and 25% zirconia by volume, is fed into a plasma spray gun, such as that disclosed in Patent 2,922,869. Due to the difference in the mass of the two powders, some of the lighter zirconia particles are blown aside in the plasma depositing process and are not recovered. I have found that with this mixture ratio a coating will be deposited consisting of approximately tungsten and 20% zirconia. This particular coating 2 is the one that is applied directly on the pure tungsten liner 1.

The next coating 3 will consist of a deposited coat of approximately 80% stabilized zirconia and 20% tungsten. The mixture, however, as fed into the plasma gun will run about 5% richer in the lighter zirconia material. This coat is then followed up with a final coating of pure stabilized zirconia.

It is to be particularly noted that the particles of tungsten and zirconia are not melted during the coating process, but are heated to a plastic state, hence there is no fusion or alloying of the metal (tungsten) and zirconia. The coatings (except the innermost coating in contact with the mandrel) are bonded together by mechanical and metallurgical bonds, owing to the plastic state of the deposited particles during the coating process. The bond between the innermost coating and the mandrel differs somewhat from the bonds between the other coatings, owing to local melting of the mandrel metal and some fusion bonding between the particles of the mandrel and the tungsten coating.

The density of the tungsten liner coating 4(87%) is the natural end result of the following factors in applicants coating process:

(a) Particle size of the tungsten powderto 125 mesh size.

(b) Temperature of particles at time of deposit, i.e near, but below the melting point of tungsten.

(c) The rate of deposit of the particles, i.e., mandrel rotation speed, so that (at its greatest diameter) its surface speed is 35" to 40 per minute.

(d) The metal particles striking the mandrel with a relatively high velocity as compared to the surface speed of the mandrel.

While I use a plasma spray gun and direct its ame over the surface to be coated, and I inject the particles of the coating materials into the fiame, as disclosed in Patent 2,922,869, I do not follow the teaching of that patent, insofar as concerns the melting of the Vdeposited particles during the coating process. On the contrary, l adjust the electric arc and rate of gas flow, so as to obtain a maximum particle temperature below the melting points of the deposited particles, whereby the melting of the particles is avoided. Because of the much lower melting point of the mandrel metal, there is some local melting of the mandrel during the coating process, which causes some local fusion bonding of the contacting deposited particles with the mandrel metal. However, such fusion bonds are removed by the acid or alkali used to dissolve the mandrel.

While I have cited tungsten and zirconia as examples of the materials used in forming my improved rocket nozzle, it is to be understood that these particular materials are cited by way of example, and not as specic limitations of the scope of my invention, since other similar materials, such as those pertaining to Group IV of the periodic table of chemical elements, may be used in lieu of tungsten and zirconia.

It is also to be understood, that the proportions given for the materials forming the layers overlying the liner, are those preferred to attain the best results, but that these proportions may be varied somewhat to produce layers having different degrees of porosity and heat resistance. The preferred proportions given in the above example have been found to produce the most desirable degree of porosity and the highest heat resistance in the finished liner.

While I have shown and described the preferred embodiment of my invention, I desire it to be understood that the invention is not limited to the construction details disclosed by way of illustration, as these may be changed and modified by those skilled in the art without departing from the spirit of my invention nor exceeding the scope of the appended claims.

I claim:

1. The method of forming a monolithic chamber, throat and nozzle assembly for rocket motors which comprises the steps of plasma spray depositing upon a rotating mandrel of slectively soluble metal of selected shape a coat of pure tungsten, which forms the inner liner of said nozzle assembly, and then plasma spray depositing upon the outer surface of said liner at least one coat of selected thickness and shape consisting of a mixture of plastic tungsten and zirconia which forms `at heat insulator to minimize the escape of heat from the jet gases passing through the nozzles, the component coats of pure tungsten and a mixture of tungsten and zirconia forming an integral monolithic structure having no joints or seams, then grinding the outer surface of said integral monolithic structure to conform to the inner surface of an encapsulating shell, then removing said mandrel by dissolving it in a solvent in which tungsten does not dissolve to thereby provide a chamber, throat and nozzle of selected form.

2. The method of claim 1, including the additional step of incapsulating said monolithic structure in an adjustable steel shell which contacts the entire outer surface of said structure and securely locks its components in place.

3. The method of claim 2 wherein said coat of pure tungsten has a porosity corresponding to approximately 87% of its theoretical bulk density.

4. The method of claim 3, wherein the outermost coat consists of pure zirconia.

5. The method of claim 4, wherein rst formed coat consists of pure tungsten, and a second formed coat comprises a mixture of approximately percent tungsten and 20 percent zirconia.

6. The method of claim 5, including the additional step of forming over said second formed coat, a third formed coat, comprising a mixture of approximately 20 percent tungsten and 80 percent zirconia.

7. The method of claim 6, including the additional step of forming over said third formed coat, a fourth coat comprising percent zirconia.

References Cited UNITED STATES PATENTS 2,706,382 4/1955 Logan et al Z39-265.11 2,836,884 6/1958 Graham 29-423 2,956,399 10/ 1960 Beighley.

2,997,413 8/1961 Wagner 117-1052 X 3,016,311 1/1962 Stackhouse 117-1052 X 3,075,066 1/1963 Yenni et al. 29-200 OTHER REFERENCES Davis: How to Deposit Metallic and Nonmetallic Coatings With the Plasma Arc Torch, Metal Progress, March 1963, pp. 10S-148.

JOHN F. CAMPBELL, Primaly Examiner.

I. L. CLINE, Assistant Examiner.

U.S. Cl. X.R.

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