US3418686A - Apparatus for forming rocket propellant grains - Google Patents

Description

Dec. 31 1968 R. G. GUENTER 3,418,686

APPARATUS FOR FORMING ROCKET PROPELLANT- GRAINS ori inal Filed July 16, 1965 INVENTOR/ 2126mm 6. Guam fer W 544,! ATTORNEW- 3,418,686 APPARATUS FOR FORMING ROCKET PROPELLANT GRAINS Richard G. Guenter, Wilmington, Del., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Original application July 16, 1965, Ser. No. 472,742, now Patent No. 3,390,210, dated June 25, 1968. Divided and this application Jan. 23, 1967, Ser. No. 622,379

3 Uaims. (Cl. 18-12) ABSTRACT OF THE DISCLOSURE A large grain propellant forming device having reduced, outwardly tapered and unreduced or die segments. A disc shaped axially moveable ram is positioned in the reduced segment, and is utilized to extrude the propellant through a multiplicity of orifices positioned adjacent the outwardly tapered segment. The movement of the extruded material is opposed or retarded by a disc shaped consolidation ram positioned in the die segment which slides loosely on a stake. The retarding of the movement of the material results in a product having a large propellant grain while at the same time relieving the stresses and strains generated by the extrusion.

This is a division of application Ser. No. 472,742, filed July 16, 1965, now Patent No. 3,390,210.

This invention relates to an apparatus for the extrusion of solid rocket propellants.

The product of this invention has various uses, but may be employed to particular advantage for purposes requiring large and complex shapes, as for example, for the propellant charge in a jet propulsion rocket motor.

Whereas solid propellant charges, of formulation designated composite and double-base, can and are made by processes termed casting, by far the greatest quantity have been produced by the solventless extrusion of double-base formulation, and the majority of the installed manufacturing facilities in this country and elsewhere is of the latter type. This process comprises the mixing of the ingredients, usually in a water suspension, followed by removal of the excess water such as by centrifuging and hot air drying, then subsequent colloiding of the material on heated revolving rolls to form leathery sheets of propellant 0.1 in. thick. These sheets are convolute wound into rolls, and in this form inserted into a press, from which the propellant is forced, under high pressure, through a forming die. This die has a diminishing cross-sectional area, or approach section, followed by a length of uniform cross-section and, if the final product so requires, has one or more pins or stakes, that produce suitable perforations axially through the extruded product. Issuing from the press therefore, is a consolidated propellant strand of uniform cross-section but considerably smaller than before extrusion. The step of extrusion introduces stresses which must be relieved by high temperature annealing in order to fully stabilize the strain created. Also, the dynamic formation reflects the presence of irreducible batch to batch variation in the chemical and physical variations of ingredients, variations in all previous processing stages, and variations in the extrusion conditions, to a degree that the cross-section dimensions of the extruded grains vary sufiiciently as to require subsequent machining to avoid excessive variation of ballistic properties among a quantity of rockets loaded with propellant charges made by the solventless extrusion process.

In the consolidation of the roll charge into a homogeneous strand, it is well understood by the industry that the individual strips comprising the roll are welded nited States Patent 0 3,418,686 Patented Dec. 31, 1968 ice together in the approach section of die by pressure and dynamic flow, coupled with a continuing reduction in cross-sectional area in the approach section of the die. The minimum percentage reduction in cross-sectional area necessary for consolidation varies with propellant composition and extrustion temperature, but is generally conceded to be about 300%. Thus a standard press, having a basket 16 in. in diameter, can produce as a solid strand product not larger than 9 in. in diameter. Thus, the solventless extrustion process can produce only a small diameter product, only an axially symmetrical product, only a product having undesired internal stresses and a product that requires machining to eliminate variations in cross-sectional dimensions.

It is therefore, the object of this inventon to eliminate the above restrictions by enlarging the die so that it contains the entire finished charge an accomplishing the consolidation of the charge through the combination of a multiplicity of small orifices located at the entrance to the die and a retarding force that is asserted immediately downstream of said orifices.

In the drawing:

FIGURE 1 of the drawing is a diagrammatical illustration of the apparatus employed in carrying out the process of this invention;

FIGURE 2 is an enlarged cross-section of the stake,

taken on the 22 line of FIGURE 1.

In the drawing, the press basket 10 is filled with sheets of propellant 11 which are extruded through partition 12 having a multiplicity of orifices 12a by the extrustion ram 13 which is powered through a shaft 14. The extruded material passes into a guide chamber 15 of greater diameter and/or greater cross-sectional area. The movement of the extruded material is opposed or retarded by a consolidation ram 16 which maintains a friction tight fit at the perimeter and slides loosely on a tapered stake 17 held in a centered position in the die 18 by a cap 19. The ram 16 supplies the initial retarding force necessary to push the extruded material against the expanding walls 20, so that instead of making a propellant grain smaller than the press basket as is the usual custom, is the means that permits a much larger grain to be formed in the die. This retarding force also performs the additional function of retaining the expanded material in the guide chamber long enough to relieve the strains in the material caused by extrustion. The ram 16 supplies the retarding force when starting the operation, however once the ram is moved to the end of the die 18 and removed, the retarding force is supplied by the friction in the guide chamber 15 of the solid mass of 21 against the walls 20. This friction continues to supply the retarding force necessary in succeeding operations and this force continues to perform the dual function of consolidating the extruded material so that it is possible to make a considerably larger grain than the receptacle from which the material is extruded and at the same time while performing the consolidation function retaining the expanded material a sufiicient period to relieve stresses and strains built up by the extrustion. When the die 18 is filled With material, the die which contains a heating means (not shown) anneals the grain and the stake 17 is withdrawn by means of the cap 19. The stake 17 is tapered in a direction opposite to the flow of material and has longitudinal projections 22 tapered in direction opposite to the stake and tapered axially towards the center which govern the interior shape of the grain and which may be varied by changing the shape of the stake so that many geometrical configurations may be left in the interior of the grain depending upon the burning characteristics desired for any particular grain. Thereafter the cured grain may be removed from the die and the process continues without the ram 16 used in the initial operation by reason of the friction generated, by the movement of the mass 21 of the extruded material against the expanding Walls 20 of the guide chamber 15, supplying the retarding force necessary to produce a better and much larger grain.

The retarding force so essential to the operation of this invention was observed in the normal operation of extruding small diameter grains and appeared to occur possibly one in a million extrusions and changes were made to prevent a recurrence of this occasional action. This observation revealed that the product occasionally touched and adhered to a nonfunctional, larger diameter metal sleeve and that the mass enlarged to fill the larger sleeve even though no back pressure was exerted. Thus, it is concluded that the powder to metal friction alone accomplishes the enlargement.

In the adaptation of this concept in actual practice, tests were found to be completely satisfactory, however, the first few inches of the product were not consolidated and had to be cut-off. Therefore, to avoid waste on the initial run, a plywood disk or ram was utilized and sized so that it was a friction fit with the inside diameter of the mold and a very loose fit around the tapered stake, with a clearance of one to two inches, which further demonstrates that substantial back pressure is not required. The ram Was not used after the initial extrusion, the first charge being cut free from the press basket in the area facing the ram 16 leaving a heel of consolidated extruded powder that acts as the consolidation ram for each succeeding extrusion.

One of the advantages of this process is that the pressure in the mold is extremely low and the mold need be only sufficiently rigid to insure desired dimensional tolerances. Therefore equipment of nominal capital investment may be used to replace expensive equipment limited to a product of small diameter, for example nine to ten inches and at the same time produce a much larger more desirable product that may be axially unsymmetrical or con tain other desired geometrical configurations within the grain.

What is claimed is:

1. An apparatus for forming a large grain propellant, comprising a cylindrical press basket open at both ends containing sheets of propellant, a partition placed inside one end of the press basket containing a multiplicity of extrustion orifices, said partition so placed as to provide a portion of the press basket of same cross-sectional area for movement of extruded material immediately after passage through said orifices, an extrustion ram in the other end of the press basket for forcing the propellant through said orifices and the remainder of the press basket, a guide chamber with expanding walls to provide a larger cross-section than the press basket, 2. consolidation ram formed by the extruded material within the guide chamber made operational by the friction of the extruded material against the expanding Walls, a die of greater cross-sectional area than the press basket connected to the guide chamber, a stake tapered in a direction opposite to the flow of material, having longitudinal projections tapered in a direction opposite to the stake, said longitudinal projections tapered radially towards the center and said stake attached to a cap for the purpose of centering the stake in the die for the production of a rocket propellant charge larger in cross-sectional area than the press basket and containing interior configurations regulated by the shape of the stake.

2. An apparatus for forming a large grain propellant comprising:

a cylindrical press basket containing sheets of propellant having a multiplicity of small orifices at one end for extrusion of propellant,

means for extruding propellant from said press basket orifices to consolidate the material,

a guide chamber attached to extrusion end of the press basket having walls tapering outwardly to force an increase in the cross section of the ex truded material,

said tapered walls producing a retarding force by reason of the friction between the walls and the moving extruded material and a die attached to the widest portion of the guide chamber to receive the extruded material and form a propellant grain of substantially larger cross section than the press basket by reason of the delay caused by the retarding force in the guide chamber.

3. An apparatus for forming a large grain propellant comprising means for extruding propellant material from a press basket through a multiplicity of small orifices for consolidation of extruded material, a guide chamber having outwardly tapered metal walls for receiving the extruded material, a die having non-tapered walls connecting with said outwardly tapered walls, a consolidation means positioned in said die chamber to provide an initial retarding force which directs the extruded material against the outwardly tapered walls thereby forming a better and larger propellant grain, while at the same time relieving the stresses and strains generated by the extru- References Cited UNITED STATES PATENTS 2,332,829 10/1943 Parsons et al. 18-12 2,926,386 3/ 1960 Hutchinson 2643 2,952,876 9/ 1960 Miles.

3,155,749 11/1964 Rossen et al. 264-3 3,252,369 5/1966 Bartley et al. 264-3 CARL D. QUARFORTH, Primary Examiner.

M. I. MCGREAL, Assistant Examiner.

US. Cl. XJR. 18-3 0; 264-3

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