JP2972339B2 - Rocket motor structure with porous binder core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Industrial applications]

The present invention relates to a method for manufacturing a solid propellant based rocket motor.

[0002]

[Prior art]

The ultimate goal of rocket motor design is to achieve a large propulsion impulse and a large impulse-to-weight ratio, while extending the time of impulse generation to produce the maximum range for a given payload. The propellant burns at a controlled rate in a predetermined geometric pattern and continues to burn until the propellant is completely burned, which can lead to premature explosion and destruction of the motor case. It is necessary to avoid certain excessive temperature rises. Propellant grains that achieve this most effectively have a rubbery viscosity that suppresses the formation of discontinuities such as cracks in the grain body and gaps between the grains and the case wall. Such discontinuities create an explosion hazard because they increase the surface area of the solid propellant exposed to the advancing combustion surface. Burning rate and efficiency are also affected by the proportions of oxidizer, binder, and fuel contained in the propellant grains, and the heterogeneity of the grain composition. Thus, overall, the composition, viscosity, and shape of the propellant grains, and the mechanical properties, and the manner in which the grains are bonded to the motor case, provide the desired safety, reliability, and favorable mechanical properties for a rocket motor. It is an important factor to achieve.

[0003]

[Problems to be solved by the invention]

A conventional method of manufacturing a composite case rocket motor begins with the manufacture of a motor case that covers a mandrel in the form of a propellant grain, which can be used for disposable structures made of gypsum or sand, or small-sized parts. Assemble a disassembled or removable assembly. Prior to forming the motor case, the mandrel is coated with an insulating material by winding a tape or using a pre-molded insulator. Once this process is performed, the motor case itself is formed by winding a filament made of graphite or polyethylene fibers pre-impregnated with an epoxy resin around an insulated mandrel. Thereafter, the wound filament is cured to form a hard shell. Then remove the mandrel from the hardened shell,
Instead, a liquid propellant material is poured and cured to a predetermined state using a suitably shaped core rod to form a central perforation in the grain to form a propellant grain. Unfortunately, mandrel extraction is a labor-intensive and costly process, and overlaps with many other steps and steps in the overall process, resulting in errors,
Creates opportunity to cause damage and loss.

[0004]

[Means for Solving the Problems]

The present invention is directed to these and other problems arising in the manufacture of conventional rocket motors. According to the present invention, a porous polyvinyl alcohol (PV) having perforated open passages in place of a mandrel for temporary use in a conventional method is provided.
A) Use a solid polymer core. Thereafter, the PVA is coated with an insulating material, and a case outer shell is formed over the PVA core. The motor is completed by filling the opening passage of the core with the liquid oxidant. The liquid oxidizer can penetrate the PVA, causing the PVA to swell and form a continuous solid mass of propellant having a rubbery viscosity. The PVA core is formed with an axial passage corresponding to the central bore of the completed motor, which passage is closed when a liquid oxidant is added and penetrates the PVA.

[0005] Replacing the prior art aluminum foam as a grain matrix with PVA offers several distinct advantages. For example, aluminum foam is rigid and retains rigidity even after other propellant components, such as oxidants and binders, have been filled into the voids. As a result, structural integrity is poor and the layer structure is prone to defects when the rocket motor is exposed to temperature cycling.

While the porous PVA core may be formed in a variety of ways, a preferred method is formed from a corrugated PVA sheet material with a flat or non-corrugated PVA sheet material interposed therein, and the final axial direction of the mandrel or rocket motor. It is affixed in layers over the perforated core that corresponds in shape to the passage. Although various liquid oxidants can be used, preferred oxidants are ammonium nitrate,
Either lower alkyl ammonium nitrate, lower alkyl hydroxyl ammonium nitrate, hydroxyl ammonium nitrate, hydrazinium nitrate, lithium nitrate, or any combination of two or more of these species.
Preference is given to combinations of these liquid oxidants which remain in the liquid phase even when the temperature is lowered to at least 30 ° C. In a more preferred embodiment, the fuel is included in the form of a metal, such as aluminum, in small (1-100 microns) particles. These metal particles may be included as a dispersion in a liquid oxidizing agent or as an additive incorporated into the PVA sheet material or applied to the surface.

[0007] By applying the present invention, the manufacture of a rocket motor is considerably facilitated, and a reduction in cost and an improvement in reliability are achieved. According to the present invention, a dangerous operation such as removal of the perforated core and mixing of the propellant is eliminated, so that a safer processing step is obtained. Another safety advantage is that, according to the present invention, a non-dangerous rocket motor (i.e., a motor prior to the addition of the oxidizer) is transported to the launch site where the liquid rocket is injected into the oxidizer reservoir. By adding a liquid oxidant in a manner, the motor can be easily ready for launch.

[0008] One of the unique advantages of the present invention in a preferred embodiment in which the core is formed from a corrugated sheet of PVA, is a propellant grain whose composition can change radially to achieve a controlled burn rate change. It can be produced. Controlling the combustion rate in this manner can improve system performance because a relatively high propellant charge can be used to obtain a neutral pressure curve with a sharp tail-off. As a result, more efficient use of propellant is possible, propellant waste is very low, and the motor can be designed for optimal operating pressure rather than peak pressure that is significantly higher than average operating pressure. The burn rate control may also reduce or eliminate the need for special corework to reduce premature exposure of the insulation on the front of the motor case and the dome of the protective wall. A method of changing the burning speed in the radial direction by applying the present invention will be described later.

The present invention can also be applied to facilitate the manufacture of small tactical rockets. As with rocket motors, small tactical rockets are formed from preformed PVA foam or other porous foam of PVA, and then filled with liquid oxidizer. This manufacturing process offers advantages in terms of cost, reliability and safety, as well as those in rocket motors. For small motor dimensions, there is a trade-off between cost and performance, and as with most tactical rocket motors, the availability of prefabricated metal containers, similar to rocket motor cases. Often there. The invention can also be used to advantage by inserting a preformed porous PVA structure into a prefabricated case. The porous PVA structure may be fully or partially inserted to facilitate manufacture. Thereafter, the processing of the propellant grains is completed by simply injecting a liquid oxidant into the PVA structure.

[0010] Other objects and advantages of the present invention will become apparent from the following description.

The ability of polyvinyl alcohol to absorb liquid oxidizing agents, especially liquid nitrating and oxidizing agents, and its ability to swell and form a rubbery mass are characteristics of this binder suitable for use in the present invention. Other polymeric binders exhibiting similar effects can also be used.

For use in the present invention, the PVA is in the form of a hard but porous mandrel having the same shape as the final propellant grain of the rocket motor. Thus, the mandrel is generally cylindrical with an open axial passage corresponding to the central bore of the propellant grain. The mandrel is
Further, it is porous, i.e., porous, with grooves or interconnected pores or passages filled with a liquid or liquid slurry containing the remaining components that make up the desired propellant.

[0013] PVA is processed in various ways into a rigid, porous body that is integral. In one example, a block of foamed PVA is machined to a desired shape and size. In another example, a solution or prepolymer is cast with a blowing agent, such as ammonium bicarbonate, or other similarly acting blowing agents to form a PVA.
Is molded. In a third example, a porous or perforated PVA
PVA around the core mandrel, using a sheet material of notched or notched or varying in height along the surface
Is formed so that voids or passages are formed when the sheet material is deposited in layers. Other examples will be apparent to those skilled in the art.

A particularly effective technique for forming a mandrel is PV
Using a thin sheet material of A, a corrugated sheet and a flat sheet are alternately laminated to form a multilayer. The flat sheet layer maintains the grooves of the corrugated sheet layer that are open to form a passage to be filled with the liquid oxidant, allowing the oxidant to flow freely between the layers. For both corrugated and flat sheets, holes may be further provided on the surface of each sheet to facilitate radial liquid flow from one layer to the next.

The porosity, ie, the ratio of the volume of the void inside the groove and hole to the total volume of the mandrel, excluding the hollow axial core, determines the volume ratio of binder to oxidant in the propellant composition. Is metal fuel included, or is that kind of fuel
The porosity will determine the ratio of binder to fuel or fuel to oxidant, depending on whether they are originally incorporated into PVA, liquid oxidizer, or both. The choice of the optimal or most appropriate porosity for any particular propellant grain depends on the final properties of the grain and the rocket motor, and others are not important in the present invention. But,
For most applications, approximately 30% to approximately 90%, preferably approximately 50%
Best results are obtained with a porosity of from about 80% to about 80%, most preferably around 67%. In addition, the porosity between one layer and the next layer can be varied to create a radial change, such as a radial gradient. Radial change in porosity is one of several means of controlling the burn rate.

In a mandrel formed of alternating layers of corrugated and flat sheets, the width (ie, diameter), or height, of the grooves in the corrugated layer, or the thickness of the corrugated sheet, flat sheet, or both, can be varied. The porosity by varying the ratio of the groove diameter to the sheet thickness of the corrugated sheet, using multiple layers of corrugated sheet, flat sheet or both, or other techniques readily apparent to those skilled in the art. Can change. The sheet thickness itself is variable. However, in general, approximately 0.003 cm to 0.2
Best results are obtained with a sheet thickness in the range of cm, preferably about 0.01 cm to 0.05 cm.

A convenient method of forming an alternating layer between a corrugated layer and a flat layer is
Winding or wrapping a stretched sheet or web of PVA onto a core winding rod. According to this technique, a corrugated layer and a flat layer are laminated to form a composite web first, and then wound over a core mandrel until the desired thickness is obtained. The composite is constructed, for example, from one corrugated web and one flat web, or one flat web on each side of one corrugated web.

The corrugated web may be formed by passing the flat web through a pair of counter-rotating fluting rollers.
Further, if it is desired to perforate one or more webs, the objective can be achieved by passing the webs through a pair of perforating rollers that rotate counter to each other. All such roller pairs may be arranged in a continuous processing line that terminates in a core winding rod.

Since a rocket motor usually has a dome-shaped end, the PVA mandrel according to the present invention can also be formed with a dome-shaped end. If web wrapping techniques are used, the dome-shaped end may be formed by cutting the web or composite web along both edges using a movable cutter prior to reaching the core winding rod. The dome is formed by the distance between the cutters determining the width of the web wound on the core winding rod and adjusting the width to decrease as the winding progresses. Conventional cutting tools such as discs or blades can be used and the spacing between the cutters and the speed at which the spacing is reduced can be manually or automatically and / or.
Or controlled by a programmed device to obtain the desired dome curvature at the end.

To facilitate the formation of corrugations in the flat web of PVA, a PVA having a water content sufficient to provide flexibility to the web may be used. The appropriate or optimal water content for a web having a particular thickness, density, or PVA type is readily determined by routine experimentation. However, in most cases, about 2% by weight or more, preferably about 5% by weight to about
20% by weight, more preferably about 5% to 15% by weight
The required flexibility is obtained at a water content level of. Once the corrugations are formed, the water content may be reduced to retain the corrugations and provide adequate stiffness when wound on the core take-up rod to provide structural integrity of the roll. Once the winding is complete and the mandrel is completely formed, the water content is further reduced to make the mandrel sufficiently rigid and strong, and the filament is wound and conformed to the case. Dehydration may be performed by conventional techniques such as drying gas steam, especially hot dry air.

In conventional rocket motor manufacture, an insulating liner is inserted between the propellant grains and the outer shell of the motor case. Since the conventional manufacturing process uses a disposable or removable mandrel, the mandrel is insulated prior to winding the filament to form a shell. The process of the present invention may also include this type of insulation treatment, and directly after the PVA has been fully fabricated.
Can be placed over the mandrel.

As in conventional constructions, the insulator performs the insulating function of protecting the shell, but by providing the propellant grains with radially varying burning rates as described above, the need for the insulator is eliminated. Are reduced or eliminated.

The insulation may be formed of materials conventionally used for this purpose, and generally an elastomer is used. In a manner similar to that used on removable or disposable mandrels, such as wrapping, dipping or spraying in liquid form, and subsequent curing, which are generally performed at ambient temperature, and in various other ways. This material may be coated.

Once the insulation has been applied and cured, the outer shell of the motor case is covered in a conventional manner. Generally, this is accomplished by impregnating with an epoxy resin and performing a filament winding process with carbon or polyethylene fibers to wrap the insulating coating grains. Thereafter, the resin is cured, typically at a low cure temperature using a heat radiation lamp or other conventional heating method. At an appropriate point in the manufacturing process prior to the filament winding process, a nozzle is added to the PVA core and the winding is further extended to cover the nozzle.

Alternatively, insulated grains can be placed inside the motor case shell preformed by cartridge loading. In a typical technique, insulated grains are inserted into the open end of a preformed motor case. Once the grains are located, an end cap containing the motor nozzle is secured over the open end to close the motor and complete the case. This method is useful for small tactical missiles and can be fully adopted as a mass production technology.

The product at this stage is a porous binder solid that is encased in a rocket motor and lacks an oxidizing agent primarily to complete the propellant grain composition. Thereafter, a liquid oxidant is added, but the central perforation through the porous binder is closed so that the liquid oxidant penetrates only the binder. The addition of the liquid oxidant may be performed at the time of use, so that the binder contained in the case can be stored and transported without the oxidant and without any risk of explosion. Also, the addition of an oxidant to bring the motor into a ready-to-use state is a relatively simple process.

Various liquid oxidants can be used in the present invention. These include various inorganic oxidants well known to those skilled in the art, especially ammonium perchlorate, lower alkyl ammonium perchlorates, lower alkyl hydroxyl ammonium perchlorates,
Perchlorates such as hydroxylammonium perchlorate, hydrazinium perchlorate, and lithium perchlorate and ammonium nitrate, lower alkylammonium nitrate,
Nitrate salts such as lower alkylhydroxylammonium nitrate, hydroxylammonium nitrate, hydrazinium nitrate, and lithium nitrate are included. These substances are
It is liquefied in various ways, including in combination with solvents or other materials that lower the melting point.

However, it is preferred to use inorganic nitrates in combinations that exhibit eutectic action and produce a complete liquid mixture at temperatures near ambient temperature. These combinations include the following. (Ii) ammonium or lower alkyl ammonium nitrate and hydroxyl ammonium nitrate; (ii) hydrazinium nitrate and hydroxyl ammonium nitrate; (iii) ammonium or lower alkyl ammonium nitrate, hydrazinium nitrate and hydroxyl ammonium nitrate; (iv) ammonium or lower alkyl Ammonium nitrate, hydrazinium nitrate and lithium nitrate; and (v) lower alkylhydroammonium nitrate and hydroxylammonium nitrate

The composition ratio used for preparing each combination is such that the melting point is approximately 30%.
° C, preferably about 25 ° C, and most preferably about 10 ° C, to a lower level to ensure that the mixture is in a homogeneous liquid state throughout the temperature range that may be encountered during storage, transport, handling and processing. Try to keep. Such a ratio can be readily determined by routine experimentation that can be adequately performed by the laboratory technician's expertise.

Of the combinations listed above, those relating to ammonium or lower alkyl ammonium nitrate and hydroxyl ammonium nitrate are preferred. Examples of lower alkyl ammonium nitrates include methyl ammonium nitrate, dimethyl ammonium nitrate, ethyl ammonium nitrate, diethyl ammonium nitrate, propyl ammonium nitrate and ethylenediamine dinitrate. Although the properties vary, the best result is that ammonium or lower alkyl ammonium nitrate is approximately 3% by weight of the combination.
To about 30% by weight, preferably about 5% to about 15% by weight, usually obtained.

The closing or closing of the axial passage (central perforation) during the addition of the oxidizing agent can be achieved by leaving the core winding rod covered with the initially formed layer of PVA intact, once the oxidizing agent has been added to the binder. After the permeation and solidification of the compounding agent, the rod is removed in the next stage. However, the preferred method replaces the rod with an inflatable bag. Under pressure, the bag fills all passages and maintains the pressure while the liquid oxidant is added and allowed to solidify. Thereafter, the bag is shrunk and removed.

In an upright motor case, the liquid oxidant is injected from the top or sucked upward from the bottom. To promote complete penetration of the binder into all gaps, grooves and pores, addition from the bottom is preferred.

In a preferred embodiment of the present invention, a metal fuel is included in the propellant component to form the final propellant grain. Examples of metal fuels include aluminum, zirconium, boron, bismuth and magnesium. Aluminum is preferred. Metal fuels are most conveniently incorporated in powders of 5 to 60 microns. The relative amount of metal fuel to total propellant grains is variable, but is generally in the range of about 10% to about 40% by weight of the grains. If the metal fuel is initially incorporated into the PVA, the proportion in the mixture lacking the oxidant will generally be in the range of about 40% to about 70% by weight.

The incorporation of the metal powder may be by dispersing the powder in a liquid oxidizer prior to adding the oxidizer to the binder contained in the case, or by dispersing the powder in the binder as it is formed on the mandrel. This is achieved by incorporating In embodiments of the present invention where the mandrel is formed by laminating PVA sheets over a core rod or by winding a continuous web, metal powder can be incorporated into the PVA prior to forming the sheet or web. Alternatively, a metal powder may be applied to the surface of the sheet or web before lamination or winding over the core rod. This can be done in a variety of ways that will be apparent to those skilled in the art. One example is the dispersion of the powder in a PVA solution, which coats the sheet or web with a thin film formed therefrom.

In embodiments where the metal powder is applied or incorporated into the PVA prior to wrapping the sheet or web around the core rod, the ratio of the metal fuel is varied to achieve a radial gradient in the final propellant grain. As an alternative to the above porosity change,
This gradient can be used as a means of changing the radial burning rate.

Other means of changing the burning rate include changing the chemical composition of the sequentially laminated PVA. This includes altering the molecular weight, incorporating copolymers or derivatives with similar but different fuel velocities, or incorporating additives or both that increase or decrease the burn rate. . Accelerators and decelerators of various burning rates are well known in the art. Examples include iron oxide and navy blue.

[0037]

【Example】

One example of a manufacturing process according to the present invention is shown in FIGS. Two webs 11, 12 of PVA conveyed by a pair of perforating rollers 13, 14, 15, 16 rotating counter to each other are shown respectively,
One of the two webs 11 is further conveyed by a pair of grooving rollers 17 and 18 that rotate in opposite directions to form a corrugation. The non-corrugated web 12 passes over rollers 19, which apply adhesive to the webs and pull the two webs together to form a composite web 20. At a point downstream of the pair of grooving rollers, a heat source 21 directly heats the corrugated web to reduce the water content.

Thereafter, the composite web 20 passes through the cutters 22 and 23 movably installed on the track 24, and the interval between the cutters 22 and 23 changes according to the amount of progress of the composite web 20 to change the dome-shaped end. To form Further, the composite web proceeds to a core mandrel 24, which wraps the mandrel to shape the PVA structure 25 into the final shape of the motor grains.

Once the integration of the PVA surrounding core mandrel 24 is completed, an insulating material 26 is sprayed on the surface to cover the PVA, as shown in this figure, and then cured. Next, the installation of the nozzle 27 and the epoxy impregnated fiber filament
Case winding by 28 is performed. Then
The epoxy cures and the core mandrel 24 is removed.
Thereafter, the PVA contained in the case is transported to a use or launch site where the remaining steps are performed.

At the point of use or launch, an inflatable bladder 29 is located inside the central passage previously occupied by the core mandrel 24 to provide high pressure air.
Inflate the bag at 30 and completely block the aisle. PV with vacuum pump 32
The liquid oxidant 31 is pumped through A, and the liquid oxidant 31 is filled in any internal space in the motor case that is not closed by the inflatable bag 29. Next, the PVA and the oxidizing agent are cured, ie, the oxidizing agent is infiltrated into the PVA to form a solid rubber mass. After this, shrink the bag and remove it,
The motor is ready to fire.

The process shown was applied using 6 mil thick polyvinyl alcohol (PVA) with a molecular weight of about 200,000 daltons. The laminate of thin films was mechanically grooved to make a sheet with 1/32 inch grooves; approximately 37 mils separated between the center lines of the grooves. A grooved PVA made of the same material and a non-grooved sheet of the same dimensions were made and dried overnight at 135 ° F. (57 ° C.) to remove most of the moisture. 6 mil grooved and flat sheet
A propellant is prepared by inserting a binder made by laminating alternating sheets of PVA thin film to an appropriate thickness into a mold of the desired volume containing an amount of oxidizing agent calculated as a required amount based on the known binder weight did. The amount of the binder used was selected in order based on the known volume of the mold to be used.

The liquid oxidant was filled into the holes of the grooved PVA. After immersing the top in the mold to limit the sample, the sample was
(57 ° C.) to give the desired minimum smoke propellant. The following table compares the properties of two propellants prepared using the corrugated binder method and propellants of the same composition prepared by standard mixing techniques using powdered PVA.

[0043]

The foregoing description has been presented primarily for purposes of illustration. The operating conditions, materials, and operating conditions of the system disclosed herein without departing from the spirit and scope of the invention.
It will be apparent to those skilled in the art that the processing steps and other parameters can be changed to the dish or substituted in various ways.

[Brief description of the drawings]

FIG. 1 is a diagram showing a process up to the manufacture of a PVA structure in a process of one embodiment of the present invention used for manufacturing a rocket motor.

FIG. 2 is a flowchart showing a subsequent process performed on a manufactured PVA structure.

[Explanation of Signs] 11, 12 PVA web 13, 14, 15, 16 Perforating roller 17, 18 Grooving roller 20 Composite web 22, 23 Cutter 24 Core mandrel 25 PVA structure 26 Insulation material 27 Nozzle 28 Epoxy impregnated fiber filament 29 Inflatable bag 30 High pressure air 31 Liquid oxidizer 32 Vacuum pump

Continuation of the front page (72) Inventor Clark George M. United States 40300 Orange Vale, California, Keats Circle 6006 (56) References JP-A-1-297397 (JP, A) JP-A-57-47789 (JP, A) Special Table Heisei 3-500665 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02K 9/32-9/34 F42B 3/093 F42B 3/02 C06D 5/00 F42B 1 / 036 F42B 1/032 F42B 3/08

Claims (10)

(57) [Claims] 1. A method for manufacturing a solid propellant-based rocket motor, comprising: (a) solid porous polyvinyl in the form of propellant grains of a solid propellant-based rocket motor having an axial path. Forming a body of alcohol; (b) accommodating said body of solid porous polyvinyl alcohol in a solid inert shell; (c) closing said axial passage to remove said solid porous polyvinyl alcohol. Filling the void volume of the body with a liquid oxidant; and (d) allowing the liquid oxidant to penetrate into the polyvinyl alcohol, thereby forming a solid continuous mass. how to. 2. The method of claim 1, wherein said body of solid porous polyvinyl alcohol has about 50% to about 80% voids. 3. The method according to claim 1, wherein the liquid oxidizing agent is (i) ammonium or lower alkyl ammonium nitrate and hydroxyl ammonium nitrate; (ii) hydrazinium nitrate and hydroxyl ammonium nitrate; (iii) ammonium or (Iv) ammonium or lower alkyl ammonium nitrate, hydrazinium nitrate and lithium nitrate, and (v) lower alkyl hydroxyl ammonium nitrate and hydroxyl ammonium nitrate. A method wherein the component ratios in each of the compositions are selected such that the lowest temperature at which the composition is completely in the liquid phase is in the range of about 30 ° C. or less. 4. The method of claim 1, further comprising the step of incorporating metal fuel particles into said solid continuous mass. 5. The method according to claim 1, wherein prior to step (b), the outer surface of the cylindrical body of porous polyvinyl alcohol is coated with an elastomeric material so that all openings in the outer surface are closed. A method further comprising the step of sealing. 6. The method of claim 1, wherein: (i) wrapping a strip of a fiber matrix impregnated with a resin around the cylindrical body; and (ii) curing the resin. b) The method comprising the steps. 7. The method of claim 1, wherein step (a) comprises combining a corrugated sheet of polyvinyl alcohol and at least one non-corrugated sheet of polyvinyl alcohol into a composite sheet, wherein the composite sheet comprises a mandrel. Wrapping around to form a cylindrical body of porous polyvinyl alcohol having an axial passage defined by the mandrel. 8. The method of claim 7, wherein said polyvinyl alcohol in said corrugated and non-corrugated sheets has a water content of at least about 2% by weight, and said method has sufficient water content. The method further comprising increasing the stiffness of the polyvinyl alcohol between steps (a) and (b) by reducing the amount to a reasonable amount. 9. The method of claim 7, wherein in step (a) the composite sheet is formed and the composite sheet is wrapped around the mandrel and the solid continuous mass formed in step (d). Having a variable burning rate that decreases radially through the cross section of the liquid oxidant impregnated polyvinyl alcohol. 10. The method of claim 7, wherein the thickness of the polyvinyl alcohol on both the corrugated and non-corrugated sheets is between about 0.01 cm and 0.05 cm.