Patent GB-746987-A (GB)
Title: Micro hardness tester
IPC: G01N3/42
Filed: 1954-03-29
Abstract: 746,987. Hardness testing apparatus. ZEISSSTIFTUNG, C., [trading as ZEISS, C., [Firm of]]. March 29, 1954 [April 15, 1953], No. 9039/54. Class 106 (2). A micro-hardness tester comprising a micioscope objective 1, an indenter 6 guided in the direction of the microscope axis A-A<SP>1</SP> and spring means 3, 4 or weights for producing a test load, has driving means for moving the indenter along the axis comprising a hollow elastic body in which a pressure fluid acts. The diamond 6 is fitted in a border zone of the front lens 1<SP>1</SP> of the objective 1 mounted in an inner tube 2 suspended in an outer tube 5 by cup springs 3, 4. The outer tube 5 is vertically splined in a horizontal slide 7 mounted by parallel springs 8, 9 on a base 10 and movable between eccentric stops 13, 14 finely adjustable so that alternatively the objective axis A-A<SP>1</SP> and diamond axis B-B<SP>1</SP> is located in the microscope axis. The pre-stress of the cup springs 3, 4 with the inner tube 2 in its lowest position relative to the outer tube 5 may be adjusted by moving the tube 5 vertically by turning a drum 15. A common hydraulic or pneumatic drive is provided for the horizontal movement of the slide 7 and vertical movement of the tube 2. Compressed air is introduced through a nipple 20 to elastic bellows 21, mounted between a fixed bracket 22 and the slide 7 and expansion of the bellows moves the slide 7 against the action of a spring 23 to the position shown against the stop 14, but before sufficient pressure builds up to overcome the spring 23 compressed air passes through a tube 24 to a folded rubber siphon membrane 25 inflating it to move the tube 2 to its lowest position determined by feet 2<SP>1</SP> engaging the wheel 18. The springs 3, 4 are now pre-stressed and the objective is in the optical axis of the microscope so that the sample can be viewed and the part to be tested can be brought into the optical axis. The compressed air is gradually released, the slide 7 moves under the force of spring 23 to engage the stop 13 bringing the diamond axis into line with the microscope axis, the membrane 25 collapses and releases the prestress of the springs 3, 4 so that the tube 2 rises and the diamond 6 comes into contact with the selected part of the sample and penetrates under the test load. After the impression has been made, air is admitted again, the diamond is retracted, the springs 3, 4 pre-stressed and the slide 7 moved to enable observation of the impression, after which the next test is initiated. To ensure that the membrane 25 always functions before the bellows 21 the drum 15 is arranged to adjust the spring 23 appropriately simultaneously with adjustments of the prestressing of the springs 3, 4. An optical load indicator comprises a half-silvered mirror 29 and, in the path of rays reflected thereby, an objective 30 and load scale 31. In the observing position shown, as only the central part of the objective 1 is illuminated any light reflected by the mirror 29 falls on the wall of the tube 2 and fails to illuminate the objective 30 so that the image of the sample is not disturbed by an image of the scale 31. In the load position a reciprocating diaphragm 32 automatically cuts off the beam from the objective 1 which would have produced an image of the sample to interfere with the image of the load scale.