Patent GB-632596-A (GB)
Title: Improvements in and relating to pneumatic vibrator machines
IPC: G01N3/36
Filed: 1947-05-29
Abstract: 632,596. Fatigue testing of materials. BRITISH THOMSON-HOUSTON CO., Ltd. May 29, 1947, No. 14271. Convention date, May 29, 1946. [Class 106 (ii)] [Also in Group XXIII] A device or machine wherein a tool or specimen is vibrated by pneumatic means, comprises a resiliently mounted armature part or specimen, preferably having a pair of pistons thereon, co-operating with a pair of cylinders, to which compressed gas is supplied from a common manifold, the outlet ports of the cylinders being closely adjacent to and facing the pistons, and the pistons being adapted to open and close the cylinder ports as they vibrate between the ports. As shown, the invention is applied to a machine for fatigue testing a metal specimen 2, such as a gas turbine bucket, which is welded &c. at its lower end to a clamp bolt within an electric &c. furnace 4, and has secured thereon at its upper end a pair of opposed piston elements 6, 6a facing two adjustable extensions 14, 15 of cylinders 13, 13a respectively. The cylinders are carried in ball seat means 16, 17 in pedestals which allow axial transverse adjustment of the cylinders. Compressed air for both cylinders is supplied from a conduit 18, 18a, including a stop valve 19 and a branch leading to a pressuremeasuring manometer 20, which communicates with a manifold 23 in which are two cylinders 24, 25 slidably mounted therein and adjustable by screw means 27. These cylinders are connected, respectively, to pipes 21, 22 leading to the cylinders 13, 13a. The adjustment of the cylinders 24, 25 relatively to the manifold 23 enables the apparatus to be adjusted such that the time of travel of sound in air from one piston 6 to the other piston 6a, through the manifold 23, is equal to one half cycle of the natural period of vibration of the test specimen 2. This synchronous relationship is stated to diminish noise and reinforce the pulse pressure of the compressed air at each piston and so increase the efficiency of the whole machine. The pistons 6, 6a, which do not contact the cylinders, are shaped as shown, whereby escaping air is directed away from the specimen and furnace in a path approximately the reverse of its initial direction. The amplitude of vibration of the specimen is indicated or recorded: For this purpose, a permanent magnet 29 secured to the free end of the specimen is adapted to vary the flux in a magnetic circuit 30, 31 incorporating a frequency meter 32 or a recorder. The total number of vibrations may be counted by a counter 33 driven from a synchronous motor energized by the pick-up coil 31. When the specimen breaks, there is a slight rise in pressure in the conduit 18a, and, if the manometer 20 is of the mercury type, the rise in the column of mercury may be arranged to complete an electrical circuit 34 to operate a relay valve 35 to cut off the air supply to the conduit 18a. In a modification, wherein a specimen is tested by torsional vibrations, the specimen is clamped at its lower end and carries at its upper end a circular head having diametrically opposite pistons arranged tangentially to the head and facing in opposite directions to co-operate with adjustable extensions of two compressed air cylinders. Another pair of pistons and cylinders could be used. A further form is described (see Group XXIII) for vibrating a tool, wherein the tool is carried in a chuck on an armature vibrating between a pair of opposed compressed air cylinders.