DE3423468A1 - METHOD FOR FASTENING THE FORBIDDEN DRIVER SET OF A SOLID FUEL ENGINE - Google Patents

Description

9559 patent department

Method for attaching the front burner propellant of a solid rocket engine

The invention relates to a method for fastening an end burner propellant charge to the combustion chamber wall a solid rocket engine, with a layer of hardened between the propellant charge and the combustion chamber wall Plastic is provided.

Such a method is known from the documents of the German utility model 6 600 205. The one with a The propellant charged with the insulation layer is transported into the combustion chamber with the formation of an annular gap between the insulation layer and combustion chamber wall, whereupon the annular gap is foamed with the plastic compound. Through this the attachment of the propellant should be guaranteed even with strong temperature fluctuations.

In the case of a forehead burner propellant, according to this utility model In addition to the insulation layer, however, a reduction in the size of the plastic foam layer required the combustion surface and thus a corresponding reduction in fuel throughput. To the For example, with a propellant charge diameter of 330 mm, an additional plastic foam layer with a Thickness of 3 mm reduces the burning surface and thus the fuel throughput by approx. 4%.

The invention, as it is characterized in the claims, is based on the object, even with large ones Temperature fluctuations ensure reliable attachment of the front burner propellant increasing the fuel throughput by reducing the thickness of the insulation layer without to impair the insulation effect of the insulation layer.

9559 patent department

The invention is based on the surprising finding that the thermal diffusivity of a plastic foam layer noticeably diminished when it is compressed.

This determination was made with the test arrangement shown in the drawing. In it each show schematic:

FIG. 1 shows a cross section through several plastic foam sheets arranged one above the other;

Figure 2a

and FIG. 2b is a top view of measuring elements arranged between two plastic plates;

FIG. 3 shows a longitudinal section through a solid rocket engine; and

FIG. 4 shows a detailed view of FIG. 3 in an enlarged reproduction.

According to Figure 1, six plastic foam sheets were A to F arranged one above the other. The foam sheets A to F consist of a commercially available polyurethane foam (type MH 25-65 from Elastogran Kunststoff-Technik GmbH, Lernförde) and each have a thickness of 6 mm.

The foam plates A to F are arranged between a ^{metal plate 1 heated to 200 °} C. and a metal plate 2 which is at room temperature. Furthermore, a resistor element 3 is arranged between the heated plates 1 and the foam plate A and a resistor element 4 between the foam plates E and F, as can be seen from FIGS. 2a and 2b, a resistor element 5 and two spaced apart

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arranged thermocouples 6 and 7 between the foam sheets A and B as well as two spaced apart thermocouples 8 and 9 between the foam sheets B and C.

The thermal diffusivity was calculated on the basis of the values measured with the measuring elements 3 to 8 at the following compressive stresses between the metal plates 1 and 2: 0; 7.5; 15 and 2 0 bar.

The thermal diffusivity was calculated according to U. Grigull and H. Sandner

Springer Verlag, 1979, page 62 ff.
Fourier equation:

The thermal diffusivity values given in the table below were obtained.

Compressive stress (bar)

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temperature
conductivity
(m ² / s) * X 10 ~ ⁶ Plate thickness
(mm)
(Compression) U, 0938 X 10 " ⁶ 6th 0.0761 X ΙΟ " ⁶ 4.75 0.0716 X ΙΟ " ⁶ 3.06 0.0567 2.88

7.5 15 20

^ Measured 480 seconds after the compressive stress has been reached.

It can be seen that the thermal diffusivity at a pressure tension of 7.5 bar by approx. 18.9%, at 15 bar by approx. 23.7% and at 20 bar by approx. 39.5% compared to the uncompressed plastic foam (0 bar) decreases.

In the experimental arrangement shown in FIG. 1, the foam sheets A to F can laterally when pressed together emigrate. To a corresponding compression

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of the plastic foam in a closed room, so in the combustion chamber of a solid rocket engine obtained, a significantly higher compressive stress is required. For example, for the same compression, which is achieved with a polyurethane foam with the open arrangement according to FIG. 1 with a compressive stress of 10 bar a pressure tension of approx. 40 bar is required in a closed space or a combustion chamber.

It should be mentioned that polyurethane foam for the invention This process is particularly well suited thanks to its high volume compressibility.

example
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In a cylinder block having an inner diameter of 33 6 then, the inside of which a polyurethane foam with a layer thickness of 3 mm is lined, a preheated to 80 ⁰ C fuel mass is filled, consisting of 25 wt .-% ammonium perchlorate, 25 wt .-% Polybutadiene binder, 40% by weight boron powder, 8.5% by weight aluminum powder and 1.5% by weight hardener. The fuel mass filled in is allowed to harden under a pressure of 40 bar at a temperature of 80 ^° C. for 12 hours.

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As a result, the polyurethane foam is pretensioned to approx. 40%. The adhesion between the polyurethane foam and the cured propellant is so excellent that at first strength tests the propellant tore inside,

^ O but not the adhesive surface between the polyurethane foam and the propellant. Also, no gap between the propellant charge and the cylinder block forms at temperature between +60 and -40 ⁰ C. The propellant charge is free to shrink mm in this temperature range by approximately 14.4.

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Due to the excellent adhesion of the propellant to the

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Polyurethane foam can therefore dispense with any bonding agent layer between the polyurethane foam and the propellant. Furthermore, according to the above statements, at this pressure (40 bar) with a reduction in thermal conductivity (approx. 20 to 40%), compression of the polyurethane foam layer by 1.2 mm is achieved. Overall, with a propellant charge with a diameter of 330 mm + 2.4 mm in diameter and a length of 1500 mm with a propellant density of 1.72 g / cm ^3, a fuel gain of 3.2 kilograms is achieved, since only a density of 1.67 g / cm ^{3 can be} achieved.

According to Figure 3, a layer 11 is made between the combustion chamber wall 10 and the propellant charge 12 of the rocket engine foamed plastic provided, e.g. B. from polybutadiene, Polyurethane or silicone. During pressing, a load 13 is exerted on the propellant charge 12, e.g. B. from 40 bar, whereby the foam layer 11 is biased, d. H. its layer thickness is reduced by 40%, for example.

According to FIG. 4, which shows the detail X according to FIG. 3 in an enlarged reproduction, the layer thickness of the foam is reduced from a to b by the prestressing with the load 13. Since the fuel is poured in at a temperature of approximately + 80 ^° C., the layer thickness of the foam 11 is reduced to c due to the thermal expansion of the propellant charge 12.

In use temperature range of the rocket engine zwisehen -40 ⁰ C and +60 ⁰ C, the layer thickness changes of the foam 11 between d and e, where even at -40 ⁰ C still remaining prestress against the non-prestressed foam (a) is present.

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Due to the temperature change between the pouring in of the fuel (+ 80 ⁰ C) and the lowest operating temperature of -40 ⁰ C, the propellant charge 12 continues to shrink in the axial direction, namely from f to g. However, the foam 11 can slide on the combustion chamber wall 10 since, according to the invention, a binder is not provided between the foam layer 11 and the combustion chamber wall 10. Tensions in the foam 11 are thus prevented. Nevertheless, a gap between the combustion chamber wall 10 and the foam 11 is excluded by the aforementioned pretensioning of the foam material 11 and thus sufficient holding force of the foam 11 on the combustion chamber wall is achieved, as well as preventing an increase in the ignition volume.

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Claims (3)

10 claims /1.J Method for attaching a front burner propellant ^ - ^ on the combustion chamber wall of a solid rocket engine, a layer of foamed plastic is provided between the propellant charge and the combustion chamber wall, characterized in that the combustion chamber wall CO) is covered with a layer (11) of hardened foamed plastic is lined, whereupon the fuel mass in the Combustion chamber given and pressurization and let the temperature rise cure. 2. The method according to claim 1, characterized in that a pressure in the hardening of the fuel mass Combustion chamber of at least 10 bar is used. 25th 3. The method according to claim 1 or 2, characterized in that that polyurethane is used as a foamed plastic. 35