GB638134A - Improvements in or relating to testing apparatus - Google Patents

Abstract

638,134. Testing physical qualities of materials. FIRESTONE TIRE & RUBBER CO.' Dec. 21, 1945, No. 34708. Convention date, Dec. 28, 1944. [Class 106 (ii)] Testing apparatus for fatigue testing rubber composition comprises at least one stationary pair of co-operating work-holding jaws and one movable pair of co-operating work-holding jaws in an opposed relation to the stationary pair of jaws, said movable jaws being mounted upon a rotatable plate adapted to be rocked about a fixed pivot pin, and a plate-actuating rod pivotally connected to said rotatable plate. Several vulcanized rubber test samples 45, Fig. 5, are tested simultaneously in the apparatus shown, each sample being in the form of a rectangular block having a transverse groove. The specimens are held in pairs in stationary and moving jaw structures 14 and 16 respectively, pins 49 on the lower jaws being received in recesses in the specimens which are clamped between serrated lower jaws and fulcrumed clamps 53 engaged by screws 55 in bosses 54, the clamping jaws applying a definite degree of compression to the specimen when the screws 55 are screwed down to the maximum extent. Six stationary jaw structures 14, facing alternate directions, are secured to a pair of angle irons 13, Fig. 4, supported by two brackets 12 mounted on a base 10. Depending from each of the corresponding moving jaw structures 16 are two integral plates 17 which are pivotally mounted on one of two shafts 18, mounted in blocks welded to the angle irons 13, and which have a series of apertures 21 in any pair of which a connecting rod 23 may be pivotally secured, the connecting rods being pivotally and eccentrically mounted on a crank shaft 24. Spacing members are placed between the eccentrics which are arranged at different angular positions on the shaft to prevent excessive vibration. The shaft 24 is journalled in the brackets 12 and in a central bracket and carries a flywheel 30 at each end, one flywheel carrying a slide-bolt 58 that may be engaged in one of a series of apertures 59 formed in the end bearing of the shaft to enable a specimen to be clamped in position when opposing jaw structures are in closest proximity. A sheet metal housing, having slots for the connecting rods 23, covers the shaft 24 between the brackets 12 and hot air blowers 67, controlled by a thermostat, are provided to heat the specimens. The whole apparatus is enclosed by a roller-mounted heat-insulating casing 61. To prevent any permanent set while the specimens are being heated, the shaft 24 is rotated slowly through an over-running clutch by means of an electric motor (not shown) driving through a speed reducing device and for the test itself the shaft is driven directly by a second electric motor (not shown). Thus, the specimens, under compression at the initial position, are repeatedly tensioned by oscillation of the moving jaws and the rate of growth of cracks in the grooves of the specimens or the time for cracks to appear or for the specimens to break may be observed. In a modification, Fig. 7, for testing two samples only, the stationary jaw structures 74 are secured to a plate 73 and the moving jaw structures 80 are mounted on a rocker 77 having a slotted portion 78 on either side of the plate 73 engaged by an adjustable pivot pin 76. An adjustable connecting rod 82 connects the rocker 77 to a bar 84 which is adjustable, to provide different degrees of eccentricity, in a groove in a disc 86 driven by an electric motor. By suitably adjusting the pivot pin 76, a shearing strain may be imparted to the samples. Slightly modified forms of the work-holding jaws are also described.