GB2265695A

GB2265695A - Rocket motor

Info

Publication number: GB2265695A
Application number: GB8123590A
Authority: GB
Inventors: Roy William Atkins; Anthony James Kinloch
Original assignee: UK Secretary of State for Defence; Royal Ordnance PLC
Current assignee: BAE Systems Global Combat Systems Munitions Ltd; UK Secretary of State for Defence
Priority date: 1980-08-06
Filing date: 1981-08-03
Publication date: 1993-10-06
Anticipated expiration: 2001-08-03
Also published as: FR2685387A1; BE889839A; DE3130735C1; GB2265695B

Description

This invention relates to the manufacture of Rocket motors, particularly to rocket motors in which the propellant is of an odd shape or is of delicate construction.

When bonding propellants to rocket motor casings it has been the practice to use an uncured liquid rubber as an adhesive. The propellant is held under pressure against the motor by stuffing the remaining cavity with paper or by inflating an air bag within the cavity, typically curing times of 4 hours are experienced. Four problems may be encountered when using these techniques: Air bubbles may be trapped between the propellant and the motor casing, thereby causing the propellant to drop off in flight and undergo excessive burning; difficulty may be experienced in aligning the propellant and motor casing accurately; the propellant has no real green strength, that is uncured strength, and may be damaged easily; and if a delicate extruded type of propellant is used it may be damaged by exerting pressure in the conventional manner.

It is an object of the present invention to provide a rapid, high, quality method of rocket motore manufacture which does not cause damage to a delicate propellant configuration.

According to the present invention a rocket motor includes a cylindrical casing having a propellant liner attached by an interjacent adhesive layer, wherein the propellant liner has been applied to the casing in radially expandable form before setting the adhesive layer, and the liner was maintained in contact with the casing by centrifugal force until setting occurred. Advantageously the centrifugal force has been sufficient to expel substantially all of the air from between the casing and the liner. Desirably the propellant liner is mounted on paper.

The propellant liner may comprise sub-width strips as hereinafter defined.

Preferably the propellant liner comprises extruded propellant, and most preferably the propellant liner comprises hydroxy-terminated-polybutadiene.

The propellant may have a finned surface and a flat, paper mounted, surface.

Advantageously the propellant is mounted on the paper by means of a bonding agent which is a urethane or an epoxide or a cyanoacrylate or an acrylate or and acrylate ester.

The adhesive layer may comprise a heat cured adhesive. Desirably the heat cured adhesive is identical with the bonding agent.

Alternatively the adhesive layer may comprise an anaerobic adhesive.

According the present invention a method of rocket motor manufacture includes the steps of: inserting adhesive and a conformable propellant liner into a substantially cylindrical rocket motor casing, the adhesive being then interjacent the propellant liner and the rocket motor casing; then maintaining the adhesive layer in contact both with the propellant liner and the rocket motor casing by centrifugal force until setting thereof occurs.

Advantageously the centrifugal force chosen is sufficient to expel substantially all the air from between the casing and the liner.

The flat surface of the propellant may conveniently have the bonding agent coated on it and the bonding agent is desirably compatible with the propellant.

The bonding agent and the propellant may be cured simultaneously.

The centrifugal force may be accompanied by a heating action in an oven.

alternatively an anaerobic accelerator may be supplied to the exposed surface of the paper before insertion of the liner into the rocket motor casing.

The invention will now be described, by way of example only, with reference to the accompanying drawings of which: figure 1 shows a length of extruded propellant; figure 2 is a block schematic diagram of a rocket motor production technique using spinning to effect bonding of propellent to motor casing; figure 3 shows an apparatus for coating the inner surface of a rocket motor casing with an adhesive layer; and figure 4 is a cross-section of a rocket motor.

In figure 1 a strip of extruded hydroxy-terminated polybutadiene propellant of width 2, has fins 1, which give a high surface area to weight ratio, and a flat base 2. In figure 2 four sub-width strips of propellant 10 of the form shown in figure 1 are laid fin side downwards in a coater 11 which includes a support to reduce the likelihood of damage to, and give support to, the fins. the sub-width means that the propellant width 3 is an approximate fraction of the circumference of the rocket motor. The flat base of each strip is then coated with approximately 4g of an adhesive 12 which is 100 part of hydroxy-terminated polybutadiene, hereinafter referred to a HTPB, and 16 parts diphenylmethane-diisccyanate, hereinafter referred to a MDI.The four strips of coated propellant are then passed to a backing machine 13 where they are laid side by side flat base downwards on a piece of brown paper 14. The assembly so created is then passed to an oven 15 where it is cured at 60"C for 40 minutes. By the use of an adhesive that is similar to the propellant bind, compatibility causes no problems and the adhesive and propellant are curable in a single operation.

The reason that four strips each of about a quarter of the desired width are used, rather than a single strip of the desired width, is that the total weight of propellant used in a rocket motor needs to be closely controlled. The required quality is more easily achieved by using a plurality of strips which can be selected from over and under specification batches of extruded propellant than by using a single strip of propellant.

Mounting the strips on the brown paper serves to join them together and also controls the burning surface byinhibiting contact with air. Coating the adhesive 12 onto the back of the strips rather than the paper further prevents air from coming into contact with the flat surface of the propellant, this is expecially relevant is the back of the propellant is uneven and therefore aids quality assurance. The curing period also allows penetration of the adhesive into the paper to occur in order to facilitate future bonding and to inhibit burning of the paper when in use. It is undesirable for either the flat surface of the propellant or the paper to ignite in use as this may cause the propellant to detach from its position in the rocket motor and considerably impair the propulsion of the rocket.A peel test performed on a sample of propellant mounted on paper and cured gave cohesive failure in the propellant at 0.25Nmm -l width.

A rocket motor casing 16 is mounted on a coating machine 17 which coats the inner surface of the rocket motor casing with an adhesive 18. the coating machine 17 is shown in Figure 3 and has an adhesive dispenser 30 which is both axially and radially displaceable relative to the rocket motor casing 16. By utilising an appropriate combination of axial and radial displacement the inside of the rocket motor casing may be coated with an even layer of adhesive from the dispenser 30 in a substantially helical path. The adhesive 18 is the same adhesive as that used to bond the propellant strips to the brown paper. The rocket motor case may be steel, aluminium or a fibre reinforced plastic.

The paper backed propellant is rolled into a cylinder and inserted into the adhesive coated rocket motor case at 19.

The rocket motor casing and the propellant is then mounted in a machine 30 which imparts an axial rotation of about 1400 rpm, to the rocket motor casing for about 2 to 5 minutes. The pressure due to the rotation causes air to be excluded from between the paper and the adhesive coated rocket motor casing and brings the paper and adhesive into close contact with one another. The rocket motor casing is then rotated at a reduced rate of about 100 to 500 rpm for 40 minutes at a temperature of 60"C in an oven 21 in order to cure the bond before the rocket motor is removed at 22.

In a modification of the method, alternative adhesives may be used to bond the propellant strips to the paper backing for example: 100 parts HTPB to 11 parts isophorane di-isocyanate, hereinafter referred to as IPDI to 0.2 parts dibutyltindilaurate; and 100 part HTPB to 8 parts MDI to 5 parts IPDI; and also other di-isocyanate and triisocyanate mixtures.

In a further modification of the method shown by the broken lines in figure 2, the adhesive 18 is a single component anaerobic adhesive which only hardens when air is excluded. A suitable adhesive is based upon a dimethacrylate ester. An accelerator 23 is applied to the exposed surface of the paper backing in an applicator 24. The accelerator enables the anaerobic adhesive to harden more rapidly when it contacts the accelerator.

The propellant is rolled into a cylinder and inserted into the anaerobic adhesive coated rocket motor casing at 19. The rocket motor casing and the propellant is then mounted in the machine 20 which imparts and axial rotation of about 1400 rpm to the rocket motor casing and also causes the anaerobic adhesive to contact the accelerator in the absence of air and to harden. The rocket motor is then removed at 25, no further curing being necessary.

Figure 4 is a cross-section of a rocket motor manufactured according to the above method. Four segments of finned extrudate are mounted on brown paper 41 which is bonded to a cylindrical rocket motor casing 42 by an interjacent layer of adhesive 43.

Claims

1. A rocket motor including a cylindrical casing having a propellant liner attached by an interjacent adhesive layer, wherein the propellant liner has been applied to the casing in radially expandable form before setting the adhesive layer, and the liner maintained in contact with the casing by centrifugal force until setting occurred.

2. A rocket motor as claimed in Claim 1 wherein the centrifugal force has been sufficient to expel substantially all of the air from between the casing and the liner.

3. A rocket motor as claimed in Claim 1 or Claim 2 wherein the propellant liner is mounted on paper.

4. A rocket motor as claimed in Claim 3 wherein the propellant liner comprises subwidth strips as hereinbefore defined.

5. A rocket motor as claimed in any one of the preceding claims in which the propellant liner comprises extruded propellant.

6. a rocket motor as claimed in any one of the preceding claims in which the propellant liner comprises Hydroxy terminated polybutadiene.

7. A rocket meter as claimed in any one of Claims 3-6 wherein the propellant has a finned surface and a flat, paper mounted, surface.

8. A rocket motor as claimed in any one of Claims 3-7 wherein the propellant is mounted on the paper by means of a bonding agent which is a urethane or an epoxide or a cyanoacrylate or an acrylate or an acrylate ester.

9. A rocket motor as claimed in any one of the preceding claims in which the adhesive layer comprises a heat cured adhesive.

10. A rocket motor as claimed in Claim 9 wherein the heat cured adhesive is identical with the bonding agent.

11. A rocket motor as claimed in any one of Claims 2-8 wherein the adhesive layer comprises an anaerobic adhesive.

12. A rocket motor substantially as hereinbefore described with reference to the accompanying drawings.

13. A method of rocket motor manufacture including the steps of: inserting adhesive and a radially expandable propellant liner into a substantially cylindrical rocket motor casing, the adhesive being then interjacent the propellant liner and the rocket motor casing; then maintaining the adhesive layer in contact both with the propellant liner and the rocket motor casing by centrifugal force until setting thereof occurs.

14. A method as claimed in Claim 13 wherein the centrifugal force chosen is sufficient to expel substantially all the air from between the casing and the liner.

15. A method for manufacturing a rocket motor as claimed in any one of claims 7-12 wherein the flat surface of the propellant has the bonding agent coated on it.

16. A method as claimed in Claim 15 wherein the bonding agent is compatible with the propellant.

17. A method as claimed in Claim 15 or Claim 16 wherein the bonding agent and the propellant are cured simultaneously.

18. A method of manufacturing a rocket motor as claimed in Claim 9 or Claim 10 wherein the centrifugal force is accompanied by a heating action in an oven.

19. A method of manufacture of a rocket motor as claimed in Claim 11 wherein an anaerobic accelerator is applied to the exposed surface of the paper before insertion of the liner into the rocket motor casing.

20. A method of manufacture of a rocket motor substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A rocket motor including a cylindrical casing having a propellant liner attached by an interjacent adhesive layer, wherein the propellant liner has been applied to the casing, in such a form as to be conformable to the contour of said casing, before setting the adhesive layer, and the liner has been maintained in contact with the casing by centrifugal force until setting occurred.

13. A method of rocket motor manufacture including the steps of: inserting into a substantially cylindrical rocket motor casing adhesive and a propellant liner conformable to the contour of said casing, the adhesive being then interjacent the propellant liner and the rocket motor casing; then maintaining the adhesive lay in contact both with the propellant liner and the rocket motor casing be centrifugal force until setting thereof occurrs.