| 摘要 |
<p>1279307 Shearing; hold downs HITACHI Ltd 11 Sept 1969 [13 Sept 1968 (2)] 45008/69 Heading B3W A vertically-operating shear comprises a housing 1 having a transverse through opening through which a knife assembly, consisting of upper and lower knives 6 and 8 and their respective holders 5 and 7, is inserted in or removed from the shear as a unit, the sides of the opening guiding the unit during a knife change operation and during shearing, balance cylinder devices 20, 21, 22 and a hold-down 40 remaining mounted on the housing during the knife changing operation. The knife holder 5 is moved downwardly to shear sheet metal by a crank 3, the connecting rod 4 engaging in a bearing 12 in the holder 5. The knife holder is returned by means of the cylinder devices 20-22. Each cylinder 27 is slidably mounted in bearings 23, 24 on the housing and urged upwardly by springs 25 and a piston-rod 28 is also urged upwardly by means of fluid fed to the lower end of cylinder 27 during shearing operations. The cylinder devices also act as damping means. The hold down 40 is slidably mounted on a frame 41 which is pivoted at 42 to the housing 1 and during downward movement bears against stops 48 on the upper knife holder until the hold down contacts the workpiece. Hydraulic cylinder means (44- 46), Figs. 1 and 6 (not shown) are actuated continuously during shearing to maintain the hold down in workpiece-engaging position. Thrust applied longitudinally of the upper holder 5 due to variations in the workpiece thickness is borne by plates (55), Fig. 4, adjustable horizontally by hydraulic piston and cylinder units (59) on the housing 1 and engaged in a recess (56) in the holder 5. To change the knife assembly, the hold down 40 is prevented from vertical movement relative to the frame 41 by means of a lock (49) (Fig. 1) and the crank is notched to its lower dead centre position in which the holder 5 is not in contact with the hold down frame 41 which is pivoted by an hydraulic cylinder 43 out of the opening 11. The supply of fluid to cylinders 27 is cut off, discharge valves are opened gradually and the holder 5 moves down under its own weight below its lowest shearing position until it engages stops 100 on the lower knife holder 7. The rods 28 continue to move leaving a clearance Y2 between them and the holder 5. The cylinders 27 are urged upwardly by springs 25, leaving a clearance Y1. The thrust plates (55) are moved out of engagement with the holder 5 and a connecting rod (60), Fig. 4, of a quick change device is engaged with the lower knife holder 7. A piston-rod 65 connected to a slide 62 connected to rod 60 is actuated by cylinder 65 to withdraw the knife assembly. The springs 25 may be replaced by an hydraulic cylinder unit (26), Fig. 8 (not shown).</p> |
