GB1426378A - Power driver devices suitable for driving fasteners - Google Patents

Abstract

1426378 Fastener driving tools ILLINOIS TOOL WORKS Inc 14 Sept 1973 [22 Dec 1972] 43362/73 Heading B4C A device for driving fasteners comprises a drive piston 30 operable within a bore 14, an accumulator piston 26 biased downwardly by, for example, a charge of gas and subjected to hydraulic pressure of the power fluid within the bore 14, and a seat 54 which makes a seal with the drive piston when this is moved upwardly by, for example, hydraulic pressure supplied through a line 200 and which is provided with a through-passage 53 and a relief valve 101, the arrangement being such that when the power fluid is supplied through a line 202 to the bore 14 via a passage 208 and port 204 to compress the accumulator piston the relief valve opens at a predetermined pressure to permit the power fluid to break the seal between the drive piston and seat and act on the full area of the drive piston with the aid of the pressure stored in the accumulator. After a driving operation on the fastener 300 shown, the hydraulic oil pump is switched to pass low pressure oil through the line 200 and through passages in a shock-absorbing member 80 to cause a brake spool 60 to carry the drive piston 30 up to its cocked position in sealing contact with the seat 54. In this cocked position the next fastener in a collated strip is indexed by low pressure oil in the line 211 pressing a piston 218 of a carriage 224 to the left against the action of a spring 220. When the trigger 12 in the handle 116 is pulled to fire a fastener, the hydraulic oil pump is switched to pass high pressure oil through the line 202 to cause the return of the brake spool to its lower position and to cause the accumulator piston 26 to compress an initial charge of gas at, for example, 2000 p.s.i. to, for example, 4000 p.s.i. When the upper pressure is reached, the relief valve 101 in the seat opens and the high pressure oil passes to the surface 38 of the piston to separate the piston from the seat and permit the oil to act on the full area of the piston, the force being maintained by the pressure of the gas in the accumulator. The drive piston is cushioned as its head 36 enters the taper in the brake spool and the oil under the brake spool is dispersed through passages in the member 80. A ball valve 56 in the seat relieves trapped oil when the piston is brought into contact with the seat. In a second embodiment, Figs. 10 and 11 (not shown), the seat extends through the accumulator piston chamber and serves as a guide for the accumulator piston (26a) which is annular in shape. Also in this embodiment the piston is provided with a counterbore (131) to reduce weight. In an alternative construction of a brake spool, Fig. 9 (not shown), the tapered bore is stepped to modify the cushion action and passages 73 allow circulation of oil for cooling purposes when the brake spool is in its upper cocked position.