Monitoring of the Natural Ageing over 16 years of two Single Base Propellants Used in Car Safety Systems

摘要

A natural ageing of two gas generators (GG) used in seat belt restraint systems (preten-sioner) was initiated by TRW. The gas producing materials of the GGs are of type single base nitrocellulose propellants. The natural ageing was performed by an environmental test center near Miami, Florida, USA. The climate at this site is characterized with warm to hot and humid. The situation in a car was simulated by placing the seat belt systems in a box. The GGs were not exposed to direct sun light but the humidity could reach them. The storage started in October 1987 and ended in October 2003. Several times samples have been taken out and analysed with regard to GG performance and propellant stability. After 16 years of natural ageing the GG performance expressed as pressure-time curves is in the tolerance range which means that the GGs are still further usable. The results of the stability tests on the propellants lead to the assessment stable after this elevated environmental stress. A systematic change of the stability results was found and quantified. This allowed determining a further significant usetime for the GG of four to six years. A comparison is made with data from new type of propellants used in belt restraint systems.