GB1605454A

GB1605454A - Cast double-base propellant

Info

Publication number: GB1605454A
Application number: GB2343475A
Authority: GB
Inventors: Robert Reid
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1975-05-29
Filing date: 1975-05-29
Publication date: 2008-02-27
Also published as: DE2623992B3

Description

\

J PATENT SPECIFICATION

Tf

I/) (21) Application No. 23434/75 (22) Filed 29/05/1975

O (23) Complete Specification filed 15/03/1976

(44) Complete Specification published: 27/02/2008

(51) International Classification7

C06B, 21/00 25/00 25/18 27/00 41/00 41/02

(52) Index at acceptance

C1D; D6A1G; D6A2C; D6A2D; D6A2E; D6B4

(72) Inventor(s) ROBERT REID

(ii) 1 605 454

(54) CAST DOUBLE-BASE PROPELLANT

(71) We Imperial Chemical Industries Limited, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:-

5 This invention relates to cast double-base propellants and more particularly to such propellants containing lead salts to modify their ballistic properties.

A cast double-base propellant is one containing nitro-cellulose plasticised or gelatinised with a liquid nitric ester, the usual ester being nitroglycerine, although others such as diethylene glycol dinitrate and metriol 10 trinitrate may be employed. The propellant charge is made by filling a single (based on nitrocellulose only) or double-base propellant casting powder into a casing, allowing a 'casting liquid' containing nitroglycerine and a liquid non-explosive plasticiser for nitro-cellulose to displace all the air in the casing, and curing at about 40-65°C for several days to allow the powder to swell to form a homogeneous rigid or rubbery mass. Alternatively, the charge may be made by filling a container with a preformed slurry of powder in casting 15 liquid with subsequent curing by heat.

Conventional propellants have a burning rate at a fixed ignition temperature given by the expression r = kpn where r is the burning rate, p is the pressure and k and n are constants. Normally the exponent n has a value of 0.5 to 0.8 but compositions have been developed incorporating lead salts as ballistic modifiers which have 20 the effect of reducing the exponent to zero or nearly so over a substantial range of useful working pressures. The graph pf the log r against log p contains a flat portion or plateau and these compositions are therefore termed 'platonised' and it is convenient to refer to the burning rate over the plateau range as the 'plateau burning rate'. These platonised propellants are particularly suited to gas producing and rocket charges where the desired characteristics are a plateau covering a wide pressure range and, especially for rocket 25 boost charges, a high plateau burning rate. These two requirements are not easily satisfied simultaneously and the composition is usually designed to achieve a compromise of burning rate and plateau characteristic at the desired working pressure. A particularly suitable burning rate is achieved when the ballistic modifier comprises a mixture of lead salicylate and lead P-resorcylate.

30 The effect of these salts are described in the United States Patent Specification No 3,088,858 and their effect in conjunction with copper salts are described in the United States Patent Specification No 3,138,499.

However, cast double-base charges in which the ballistic modifier consists of a mixture of lead P-resorcylate and lead salicylate normally show a downward drift in burning rate after storage, the drift being faster at 35 elevated temperature. Usually the burning rate decreases on storage to a minimum value about 5 to 15% lower than the rate immediately after curing.

2 1,605,454 2_

It is an object of this invention to provide cast double-base propellant charges platonised with a mixture of lead salicylate and lead P-resorcylate which maintain their plateau burning rates when the charges are stored at elevated temperature.

5 Under normal atmospheric conditions the equilibrium moisture content of the casting powders used is about 0.4 to 0.6% w/w and we have now found that the downward drift in burning rate is eliminated by drying the casting powder to a moisture content of less than 0.25% w/w. This effect is possibly due to the migration of these particular ballistic modifiers in the cast propellant being inhibited at low moisture contents.

10 In accordance with this invention a cast double-base propellant charge comprises as ballistic modifying agent a mixture of lead salicylate and lead P-resorcylate and is cast from a casting powder containing not more than 0.25% w/w of water. The ballistic modifying mixture conveniently comprises lead salicylate and lead P-resorcylate in a weight ratio from 1:4 to 4:1 and the propellant charge conveniently comprises 1 to 5% w/w of the mixture.

15

From a further aspect the invention consists in a method of preparing such a cast double-base propellant charge wherein a casting powder is dried to a moisture content of 0.25% w/w or less before mixing with a casting liquid.

20 In addition to the nitrocellulose, liquid nitric ester, non-explosive plasticiser and ballistic modifier, the propellant charge may include stabilisers, glazing agents and the like as are conventional in such charges. Metal powders such as aluminium may also be incorporated, if desired, to raise the heat of combustion (and consequently the specific impulse). Carbon black is also commonly added to increase the burning rate.

25 The preferred cast double-base propellant composition has a moisture content of not more than 0.25% w/w and comprises as basic ingredients from about 35 to 55% by weight of nitro-cellulose, from about 30 to 50% by weight of nitroglycerine or other liquid nitric ester, from about 5 to 12% by weight of a non-explosive plasticiser, from about 1 to 5% by weight of the ballistic modifying agent and from about 1 to 3% by weight of stabiliser. The preferred stabiliser comprises 2-nitrodiphenyl-amine or N-methyl-p-nitro aniline and the

30 preferred non-explosive plasticiser comprises triacetin or dibutyl phthalate.

The invention is further illustrated by the following Examples wherein all parts and percentages are by weight.

35 Examples 1 and 3 are propellant charges prepared from casting powders which had not been specially dried and are not in accordance with the invention but are included for comparison. The Examples were cast double-base propellant charges having the composition and calculated heats of explosion as shown in Table 1 and prepared by the following procedure.

40 In the preparation of the casting powder all the ingredients of the casting powder shown in Table 1, together with a sufficient quantity of a solvent for nitrocellulose, were mixed in an incorporator mixer to form a homogeneous rubbery dough. The dough was extruded into cords and the cords cut on a rotary cutting machine to produce granules. The solvent was removed from the resulting powder granules by hot stoving and the finished powder was glazed by tumbling with graphite in a rotating pan glazer. After discharge from

45 the stove and during the glazing process, the casting powders of Examples 1 and 3 attained equilibrium moisture contents of about 0.53 and 0.56% respectively under normal atmospheric conditions. The casting powders of Examples 2 and 4 were dried to reduce the moisture contents to 0.18 and 0.20% respectively and were subsequently stored under anhydrous conditions in dry sealed containers until cast.

50 In the casting operation the casting powder was filled into a cellulose acetate beaker in a casing and a casting liquid as shown in Table 1, which had been evacuated under high vacuum for about 2 hours to remove water and volatile impurities, was added to displace the air in the beaker.

3

1,605,454

3

The moisture content of the casting liquid was less than 0.1% w/w after the evacuation procedure.

The charge was cured at elevated temperature under nitrogen at a pressure of 25 psi for 4 days to allow the powder to swell to form a homogenous rigid or rubbery mass.

5

The curing temperature was 43°C for Examples 1 and 2 and 65°C for Examples 3 and 4, having a higher nitrocellulose content.

The final propellant compositions shown in Table 1 were calculated from the measured powder to liquid 10 (weight to weight) ratios of the cast propellant charges.

The heats of explosion (expressed in Table 1 as Kilojoules/Kilogram) were calculated in the conventional manner. The ballistic data quoted in the Examples and illustrated in the accompanying graphs was obtained by burning a 122mm x 61mm x 20mm slab of propellant in a motor at an ignition temperature of 20°C and 15 obtaining the pressure v time curve. This method of ballistic proof is well known in the art.

Example 1

The cast double-base propellant charge of this Example was prepared from a casting powder which had 20 attained an equilibrium water content of 0.53% by weight. The charge had the following burning rates when fresh and after storage at 50°C. It will be noted that there was a significant downward drift in the plateau burning rate after storage.

25

30

35

The rate of burning v pressure curves at 50°C are also shown graphically in Fig. 1. The plateau burning rate reached a minimum value after 2 to 5 weeks and showed no significant change on further storage at 50°C.

40 Example 2

This Example had the same composition as Example 1 but the casting powder was dried on trays at 50°C for 24 hours and maintained in anhydrous conditions until cast. The moisture content of the casting powder was 0.18%.

45

The charge had the following burning rates when fresh and after storage at 50°C.

Pressure (bar)

80

100

120

140

160 ;

180

Burning Rate mm/sec

Fresh (after cure)

21.42

23.02

23.08

22.95

22.51

22.12

After storage at 50°C

2 weeks

18.24

19.73

20.47

21.10

21.52

21.28

5 weeks

16.76

18.08

19.31

19.88

20.02

20.11

24 weeks

16.72

18.12

19.28

19.75

20.05

20.06

50

4

1.605.454

4

Pressure (bar)

80

100

120

140

160

180

Burning Rate mm/sec

5

Fresh (after cure)

21.47

23.05

23.08

22.91

22.47

22.16

After storage at 50°C

10

12 weeks

21.49

23.02

23.06

22.87

22.49

22.24

It will be noted that the burning rate did not reduce on storage at 50°C and the plateau characteristics were essentially the same as those of Example 1 (fresh after cure) and shown graphically in Fig. 1.

15 Example 3

The cast double-base propellant of this Example was prepared with a lower energy casting powder than Examples 1 and 2. The equilibrium moisture content of the casting powder was 0.56%.

20 The charge had the following burning rates when fresh and after storage at 50°C. It will be noted that there was again a significant downward drift in the plateau burning rate after storage.

Pressure (bar)

80

100

120

140

160

180

25

Burning Rate mm/sec

Fresh (after cure)

19.62

20.60

21.44

21.91

21.89

21.78

30

After storage at 50°C

3 weeks

18.76

19.93

20.38

20.77

20.92

20.93

12 weeks

18.02

19.06

19.73

20.05

20.11

20.10

18 weeks

17.96

19.02

19.70

20.01

20.13

20.10

35

The rate of burning v pressure curves at 20°C are also shown graphically in Fig. 2. The plateau burning rate reached a minimum value after 3 to 12 weeks and showed no significant change on further storage at 50°C.

40 Example 4

This Example had the same composition as Example 3 but the casting powder was dried on trays at 50°C for 24 hours and maintained in anhydrous conditions until cast. The moisture content of the casting powder was 0.20%.

45

50

1.605.454

Pressure (bar)

80

100

120

140

160

180

Burning Rate mm/sec

5

Fresh (after cure)

19.57

20.58

21.40

21.85

21.84

21.71

After storage at 50°C

10

12 weeks

19.59

20.54

21.40

21.82

21.81

21.75

It will be noted that the burning rate did not reduce on stroage at 50°C. The plateau characteristics were essentially the same as those of Example 3 (fresh after cure) and shown graphically in Fig. 2.

15

Table 1 - Compositions

Casting Powder (Parts)

Component

Example 1

Example 2

Example 3

Example 4'

Nitrocellulose (12.6%N) Nitroglycerine N-methyl-p-nitro aniline 2-nitro diphenylamine Aluminium powder Carbon black Lead salicylate Lead P-resorcylate Graphite glaze Water content (weight%)

60.0 33.0 1.0

7.5

0.3

3.0

4.0

0.05

0.53

60.0 33.0 1.0

7.5 0.3 3.0 4.0 0.05 0.18

75.0 17.0

2.0

0.3 3.0 3.0 0.05 0.56

75.0 17.0

2.0

0.3 3.0 3.0 0.05 0.20

Casting Liquid (Per Cent)

Nitroglycerine Triacetin

2-nitro diphenylamine

76.0 23.0. 1.0

76.0 23.0 1.0

Cast Propellant (Per Cent)

Nitrocellulose (12.6%N) Nitroglycerine N-methyl-p-nitro aniline 2-nitro diphenylamine Aluminium powder Carbon black Lead salicylate Lead P-resorcylate Triacetin Graphite glaze

37.10

45.25

0.61

0.33

4.64

0.19

1.86

2.47

7.52

0.03

37.28

45.12

0.61

0.32

4.66

0.19

1.87

2.47

7.45

0.03

50.75 35.90

1.68

0.20 2.03 2.03 7.38 0.03

50.67 35.96

1.67

0.20 2.03 2.03 7.41 0.03

Powder/liquid ratio (w/w)

67.3/32.7

67.6/32.4

67.9/32.1

67.8/32.2

Heats of Explosion (KJ/Kg)

Calculated heat of explosion

4560

4564

4052

4053

20

25

30

35

40

45

50

Claims

6

1,605,454

6

WHAT WE CLAIM IS:

1 A cast double-base propellant charge comprising as ballistic modifying agent a mixture of lead salicylate and lead P-resorcylate, the charge being cast from a casting powder containing not more than

5 0.25% w/w of water.

2 A propellant charge as claimed in Claim 1 wherein the ballistic modifying mixture comprises lead salicylate and lead P-resorcylate in a weight ratio from 1:4 to 4:1.

10 3 A propellant charge as claimed in Claim 1 or Claim 2 comprising 1 to 5% w/w of ballistic modifying agent.

4 A propellant charge as claimed in any one of Claims 1 to 3 wherein the moisture content is not more than 0.25% w/w, comprising from 35 to 55% w/w of nitrocellulose, from 30 to 50% w/w of liquid

15 nitric ester, from 5 to 12% w/w of non-explosive plasticiser, from 1 to 5% w/w of ballistic modifying agent and from 1 to 3% w/w of stabiliser.

5 A propellant charge as claimed in Claim 4 wherein the stabiliser comprises 2-nitrodiphenylamine or N-methyl-p-nitro aniline.

20

6 A propellant charge as claimed in Claim 4 or Claim 5 wherein the non-explosive plasticiser comprises triacetin or dibutyl phthalate.

7 A cast double-base propellant charge substantially as described herein with particular reference to 25 Example 2 or Example 4.

8 A method of preparing the propellant charge claimed in any one of Claims 1 to 7 wherein a casting powder is dried to a moisture content of 0.25% w/w or less before mixing with a casting liquid.

30 9 A method of preparing a cast double-base propellant charge substantially as described herein with particular reference to Example 2 or Example 4.

35 BAE SYSTEMS PLC, Group IP Department, Lancaster House, PO Box 87, Farnborough Aerospace Centre, Farnborough, Hampshire, GUI4 6YU.