Patent GB-607579-A (GB)
Title: Improvements in or relating to devices for testing the hardness of metals
IPC: G01N3/42
Filed: 1946-02-08
Abstract: 607,579. Testing hardness of materials. STOKES, C., BACKHOUSE, H., BOOTH, C. H., MENSFORTH, T., and STAVES, K. Feb. 8, 1946, No. 4060. [Class 106 (ii)] In hardness-testing apparatus of the kind in which an impression is made by an indentor through the medium of a spring under load, such as described in Specifications 280,292, [Class 106 (ii)], and 464,005, the spring is arranged to have increasing stiffness as the amount of the applied load is increased. A microscope combined with a screen of the type described in Specification 368,038, [Group XX], but having improved features, is incorporated for measuring the indentations. As shown, the apparatus comprises a base 1 supporting a rotatable pillar on which is a vertically adjustable bracket 3 having arms 4, 5 (not shown) carrying, respectively, the indenting-mechanism and the microscope 6. The arm 4 has a portion 9, Fig. 4, supporting a nut 14 engaging a screw-threaded spindle 13, the nut being rotatable through worm-gearing by rotating a hand wheel 16 to raise or lower the spindle. A central frame 22 in a portion 10 of the arm 4 connects the spindle 13 to a bearing 23 in which an indentor rod 12 is guided, the latter being secured at its upper end by a clamp 26 to two flat springs 27, 28. Rollers 29, 30 on the frame 22 are adapted to engage the outer ends of the spring 27, and subsequently on further descent of the frame 22, rollers 31, 32 engage the spring 28. A single spring whose free length is governed by its deflection may be employed. The indentor rod 12 carries a diamond 24 which, on contacting a specimen, arrests the movement of the rod, and the relative movement between the frame 22 and rod 12 actuates a load-indicating and a loadarresting means. A vertically adjustable pallet 36 on the rod 12 is adapted to engage one arm of a bell-crank lever 35 pivoted on the frame 22, the other end of this lever engaging a plate 44 carrying a rack 42 mounted on a pin 43 for horizontal movement. A load-indicator 39 movable over a dial 38 is mounted on a spring-controlled shaft 40 having a pinion 41 engaging the rack 42. The pallet 36 has screw-threaded engagement with an extension of the rod 12 and can be rotated for vertical adjustment by a friction wheel which is mated with the pallet on lowering a shaft having an operating knob outside the casing 10. The load-arresting means comprises a ratchet-wheel 62, mounted on the shaft 15 which supports the hand-wheel 16, engageable by a pair of pawls operated by the plate 44 engaging a spring-tensioned arm 55 on a vertical shaft 56. When the pawls move within the orbit of the teeth on the wheel 62 they are caught up to lock the latter and so prevent further rotation of the hand-wheel 16. The hand-wheel 16 operates on the shaft 15 through a slip-clutch. The springs 27, 28 may be pre-loaded to save time during testing by means comprising a sleeve 73 having screw-thread engagement with a sleeve 71 screwed into the bearing 23, the sleeve 73 engaging a collar 69 on the indentor rod 12. The sleeve 71 provides a further adjustment for the rod 12. The upright pillar carrying the bracket 3 is lockable in indenting position. This pillar is screw-threaded at the lower end to engage a nut adapted to rise against a boss when the pillar is moved to indenting position. The specimen is supported on a compound slide 96, each slide being operated by a calibrated hand-wheel. The microscope arrangement is mounted on a bracket 92 supported for limited vertical adjustment by two pairs of leaf springs 93, 94 on the main bracket 3. An image of the form of indenting-tool may be thrown on to the screen for comparison with a master outline on a slide arranged behind the screen. The optical arrangement is such that the ratio distance of objective lens to field lens divided by the distance of field lens to eyepiece lens is between 2.5 and 2.75.