GB656447A - Improvements in and relating to pneumatic vibrating machines employed in fatigue testing materials - Google Patents

Abstract

656,447. Fatigue testing of materials. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 13, 1949, No. 988. Convention date, Jan. 21., 1948. [Class 106 (ii)] A pneumatic vibrator of the type described in Specification 632,596, is provided with means for maintaining the amplitude of vibration constant. A reed 1 to be tested supports a piston 2 driven by compressed air from nozzles 3, and a triangular portion 5 arranged to obstruct an air port 4 in its centre position, and to uncover progressively the port 4 on either side of its centre position. Associated with the air supply to the vibrating reed is a control valve 13 actuated by a spring-compensated diaphragm 11 in a chamber 8. The diaphragm 11 divides the chamber 8 into two compartments 9, 10. Air is supplied via a constant pressure regulator 6 to the lower compartment 10 and then through a valve 14 to the nozzles 3. A further supply of air is taken via a branch valve 7 to the upper compartment 9 and the regulating air port 4. In operation, increased amplitude of vibration beyond the normal amplitude results in the port 4 being uncovered for longer periods of time causing a slight drop in the pressure in compartment 9, causing the diaphragm to move upwards, closing slightly the valve 13 and reducing the air supply to the nozzles 3. Reduced amplitude of vibration results in the port 4 being covered for longer periods and causes an increased pressure in compartment 9, causing the diaphragm 11 to move downwards opening the valve 13 to increase the air supply to nozzles 3. In a modification shown in Fig. 4, regenerative control is applied for a more sensitive control by connecting the branch valve 7 into the air conduit after the chamber 10 instead of ahead of it as previously shown. In operation, decreasing vibrational amplitude increases the pressure at port 4 and in the upper compartment 9 as before and movement of the diaphragm and valve 13 to increase the pressure in compartment 10 and the nozzles 3 also applies a further increase to compartment 9 via the valve 7, thus providing regeneration to compensate amplitude errors more quickly. A regenerative decrease of pressure in chamber 9 is similarly caused by increased vibrational amplitude. In this modification, the constant pressure regulating valve 61 may be dispensed with.