Apparatus for igniting a propellant charge in a tool

Abstract

A tool for driving a nail or other fastener is actuated by a caseless propellant charge formed of combustible material that is transported into a combustion chamber on a strip. The propellant charge is ignited by striking a sensitizer portion of the charge at an oblique angle. The ignition member intermixes the sensitizer material with an oxidizer layer of the surface of the propellant charge, resulting in combustion of the charge. When ignited, the propellant charge is compressingly interposed between an orifice plate and a movable portion of the combustion chamber. The orifice plate includes a pedestal with an annular compression surface that separates the surface of the ignition area from the remaining surfaces of the charge, insuring that ignition gases are forced through the charge. An annular C-shaped ring is interposed between the orifice plate and the movable portion of the combustion chamber. When the charge is ignited, the resulting gas pressure resiliently expands the annular C-shaped ring and urges opposite axial ends of the C-shaped ring into sealing relationship between the relatively movable components of the combustion chamber. Combustion gases are communicated through orifices in the orifice plate to a cylinder where the gases force movement of a driver, which driver strikes and drives a fastener such a nail. The driver is reciprocally movable within the cylinder and is returned to its precombustion position by a gas spring return cylinder. The gas return cylinder in mechanically interconnected to the driver and contains a sealed gaseous fluid that is independent of and segregated from fluids in the combustion chamber. An assembly for deaccelerating the driver includes a series of spaced and aligned progressively sized metal cup members of progressively increasing mass, contact surface area and interface angles.