Method for making a propellant having a relatively low burn rate exponent and high gas yield for use in a vehicle inflator

• US 6,315,930 B1
• Filed: 09/24/1999
• Issued: 11/13/2001
• Est. Priority Date: 09/24/1999
• Status: Expired due to Fees

• Current Assignee: Autoliv ASP Incorporated (Autoliv Incorporated)
• Original Assignee: Autoliv ASP Incorporated (Autoliv Incorporated)
• Inventors: Hamilton, Brian K.
• Primary Examiner(s): Silbaugh, Jan H.
• Assistant Examiner(s): Poe, Michael I.
• Application Number:
  US09/406,023
• Time in Patent Office: 781 Days
• Field of Search: 214/3.1, 214/3.2, 214/3.3, 149/19.7, 149/46, 149/60
• US Class Current: 264/3.1
• CPC Class Codes: C06B 21/0075 by extrusion
• CPC Class Codes: C06B 31/30 with vegetable matter; with resin; with rubber
• CPC Class Codes: C06D 5/06 by reaction of two or more solids

Abstract

A method for making a propellant composition that results in a desirable gas output when combusted. The propellant can be part of an inflator used in a vehicle for inflating an air bag. The propellant has a relatively low burn rate exponent of no greater than about 0.7. The propellant is substantially dense, with the propellant having a density that is at least 85% of theoretical density. In making the propellant, its density can be reduced using a roller mill that flattens the propellant to a controlled thickness. The propellant preferably includes phase-stabilized ammonium nitrate and fibrous cellulose.

Claims

1. A method for making propellant for use in an inflator located in a vehicle, comprising:

providing phase-stabilized ammonium nitrate by integrating potassium nitrate with ammonium nitrate such that said ammonium nitrate and said potassium nitrate are fused together;

mixing said phase-stabilized ammonium nitrate with at least fibrous cellulose to form a mixture, wherein said fibrous cellulose is between 6% and 12% by weight of said mixture of said phase-stabilized ammonium nitrate and said at least fibrous cellulose;

forming a thin, continuous length of propellant having a first density from said mixture of said phase-stabilized ammonium nitrate and said at least fibrous cellulose; and

working said thin, continuous length of propellant to provide said thin, continuous length of propellant with a second density greater than said first density.

2. A method, as claimed in claim 1, further including:

cutting said thin, continuous length of said propellant into a number of propellant pieces.

3. A method, as claimed in claim 1, wherein:

said second density is at least 85% of theoretical density.

4. A method, as claimed in claim 1, wherein:

said second density is a predetermined density related to a burning rate of said propellant.

5. A method, as claimed in claim 1, wherein:

said working step includes causing said propellant to have a thickness in a range of about 0.4 mm-6 mm and a burning rate in a range of about 5 mm/sec-100 mm/sec at about 5000 psi.

6. A method, as claimed in claim 1, wherein:

said propellant is a substantially uniform mixture in which, for each selected cross-section of said substantially uniform mixture, any 1,000-micron portion of said selected cross-section has the same composition as any other 1,000-micron portion of said selected cross-section.

7. A method, as claimed in claim 1, wherein:

said forming step includes extruding said mixture of said phase-stabilized ammonium nitrate and said at least fibrous cellulose.

8. A method, as claimed in claim 1, further including:

grinding said phase-stabilized ammonium nitrate before said mixing step.

9. A method, as claimed in claim 1, wherein:

said phase-stabilized ammonium nitrate further includes at least one of the following;

potassium fluoride, magnesium carbonate, copper/nickel amine complexes, potassium dinitramide, ammonium polyphosphates and cesium nitrate.

10. A method, as claimed in claim 1, wherein:

said phase-stabilized ammonium nitrate includes a copper material.

11. A method, as claimed in claim 1, wherein:

said working step includes continuously flattening said propellant using a roller mill having at least a first press element that is in contact with said propellant.

12. A method, as claimed in claim 11, wherein:

said roller mill includes a second press element over which said propellant moves and said working step includes controlling said second density to a predetermined density by a force applied to one of said first and second press elements.

13. A method for making a propellant for use in an inflator located in a vehicle, comprising:

providing phase-stabilized ammonium nitrate by integrating potassium nitrate with ammonium nitrate such that said ammonium nitrate and said potassium nitrate are fused together;

forming a propellant having a first density that includes at least said phase-stabilized ammonium nitrate mixed with fibrous cellulose having amounts by weight as follows;

(a) ammonium nitrate 76.65%±

5%;

(b) potassium nitrate 9.35%±

3%;

(c) fibrous cellulose 9.00%±

3%; and

working said propellant to provide said propellant with a second density that is at least about 85% of theoretical density.

14. A method, as claimed in claim 13, wherein:

said first density is less than 80% of theoretical, density.

15. A method, as claimed in claim 13, wherein:

said working step includes flattening said propellant using a roller mill having at least a first press element.

16. A method, as claimed in claim 13, wherein:

said propellant has a burn rate exponent no greater than 0.7.

17. A method for making a propellant for use in an inflator located in a vehicle, comprising:

providing phase-stabilized ammonium nitrate by integrating potassium nitrate with ammonium nitrate such that said ammonium nitrate and said potassium nitrate are fused together;

forming a propellant having a first density that includes at least said phase-stabilized ammonium nitrate mixed with fibrous cellulose, said propellant being a substantially uniform mixture in which, for each selected cross-section of said substantially uniform mixture, any 1000-micron portion of said selected cross-section has the same composition as any other 1000-micron portion of said selected cross-section; and

working said propellant to provide said propellant with a second density that is at least about 85% of theoretical density, with a thickness in a range of about 0.4 mm-6 mm and with a burning rate in a range of about 5 mm/sec-100 mm/sec at about 5000 psi.

18. A method, as claimed in claim 17, wherein:

said working step includes flattening said propellant using a roller mill having at least a first press element.

19. A method, as claimed in claim 17, wherein:

said propellant has a burn rate exponent no greater than 0.7.

20. A method, as claimed in claim 17, wherein:

said phase-stabilized ammonium nitrate further includes at least one of the following;

potassium fluoride, magnesium carbonate, copper/nickel amine complexes, potassium dinitramide, ammonium polyphosphates and cesium nitrate.

21. A method, as claimed in claim 17, wherein:

said phase-stabilized ammonium nitrate includes a copper material.