Patent GB-263504-A (GB)
Title: Process of and apparatus for balancing rotating bodies
IPC: G01M1/04
Filed: 1925-07-02
Abstract: 263,504. Marks, E. C. R., (Precision Balancing Machine Co.). July 2, 1925. Testing balance of rotary apparatus. - The amount of unbalance is ascertainable from a measure of the maximum amplitude of oscillation of the support, by mounting the support so that it is free to oscillate with negligible damping resistance to oscillation, and causing the period of critical relationship between speed and oscillation to be passed through at a slow and repeatable rate. The method depends for success upon the empirical fact that when damping has been reduced to a minimum, the maximum amplitude of vibration which occurs as the rotating body passes through the critical speed is proportional to the correction necessary to place the body in dynamic balance. The apparatus comprises a frame 1 carried on two supports 2 by means of aligned knife-edges 7. The fly-wheel or like to be balanced is supported on a shaft 5 mounted in antifriction bearings 6 in the frame 1, the knifeedges being in a plane at right angles to the axis of the shaft which plane is not the medium plane of the fly-wheel. A long arm 8 is secured to the frame a pointer 9 at the end of which moves over a scale 10. A spring 14 is secured to the arm and tu the foundation 13. A carefully balanced duplicate of the wheel 4 is drilled with holes 17 each at the same radial distance from the axis, and the wheel is mounted in the apparatus with the edge 18 in alignment with the plane of the knife edges 7. The pointer 9 will remain still when the wheel is rocked and the zero of the scale is brought opposite the pointer. An arbitrary weight is then inserted in any hole 17 in the plane 19. The wheel is now rotated faster than the natural period of the frame and is allowed to drift freely through the critical speed, the maximum amplitude as indexed by the pointer being noted. This divided into the weight added gives the correction necessary per scale unit for the particular class of body being balanced. The apparatus may be so arranged that the speed of rotation is constant and the natural period of oscillation of the frame varied. The wheel to be balanced is next substituted for the standard. The corrective weight calculated from the maximum amplitude of vibration is then placed at a point in the circle 20 scribed on the wheel and in the plane 19. From a further observation of the maximum amplitude and the last one the necessary angular movement of the weight may be calculated or obtained by reference to a prepared chart. A further rotation serves to check this for direction and the correction is then placed or marked on the body. The next step consists in repeating the test with the edge 19 of the wheel in the plane of the knife edges and marking the correction on the plane 18. When it is not convenient to place the edge 19 into line with the knife edges, the correction in the plane 19 must be fixed and the plane 18 moved out of alignment whilst determining the correction in the plane 18. When nothing definite about the body is known, two planes of the body are selected for correction and the body rotated as before with one plane in the plane of the knife edges. Some definite correction is made at successive definite points in a definite circle of the plane and a curve plotted with angles as abscissµ and maximum amplitudes in ordinates. From this curve the phase and amount of the out of balance is determined.