Balancing high-speed

Lindsey, J.R., Significant Developments in Methods for Balancing High-Speed Rotors, ASME Paper No. 69-Vibr-53. 

The at speed balance (high speed balance) facility was originally used in Europe and is a rather sophisticated and costly installation. Time on the machine is expensive, partly due to the owner having a large investment to amortize and partly because the machine requires more than just an operator. 

Near top speed, a fan may operate at a speed that is near or above the natural frequency of the wheel and shaft. Under such conditions, the fan can vibrate badly even when the wheel is clean and properly balanced. Whereas manufacturers often do not check the natural frequency of the wheel and shaft ia standard designs, many have suitable computer programs for such calculations. Frequency calculations should be made on large high speed fans. The first critical wheel and shaft speed of a fan that is subject to wheel deposits or out-of-balance wear should be about 25—50% above the normal operating speed. 

High Speed Shafts - Shafts at 3,000 rpm or higher causes the seal laces to generate even more heat. Balanced seals reduce the pressure and force between the faces, thereby generating less heat. 

Cleanliness Hardness Hydrostatic Tests Blade Shaker (Static) Rotor balance O Standard O High Speed Final Surface Inspection Crating inspection Spare Rotor Fit ... 

These unbalance forces increase as a function of making the design and operation of high-speed machinery a complex and exacting task. Balancing is the only method available to tame these excitation forces. 

The best balance technique for high-speed flexible rotors is to balance them not in low-speed machines, but at their rated speed. This is not always possible in the shop therefore, it is often done in the field. New facilities are being built that can run a rotor in an evacuated chamber at running speeds in a shop. Figure 17-4 shows the evacuation chamber, and Figure 17-5 shows the control room. 

High-speed balancing should be considered for one or more of the following reasons ... 

Figure 17-4. Evacuation chamber for a high-speed balancing rig. (Courtesy of Transamerica Delaval, Inc.)...

The available balance planes are far removed from locations of expected unbalance and are thus relatively ineffective at the operating speed. The rule of balancing is to compensate in the planes of unbalance when possible. A low-speed balance using inappropriate planes has an adverse effect on the high-speed operation of the rotor. In many cases, implementation of an incremental low-speed balance as the rotor is assembled will provide an adequate balance, since compensations are being made in the planes of unbalance. This is particularly effective with designs incorporating solid-rotor construction. 

The rotors on other similar designs have experienced field vibration problems. Even a well-designed and constructed rotor may experience excessive vibrations from improper or ineffective balancing. This situation can often occur when the rotor has had multiple rebalances over a long service period and thus contains unknown balance distributions. A rotor originally balanced at high speed should not be rebalanced at low speed. 

Boyce, M.P., Multiplane, Multispeed Balancing of High Speed Machinery, Keio University, Tokyo, Japan, July 1977. 

Mechanical imbalance is one of the most common causes of machinery vibration and is present to some degree on nearly all machines that have rotating parts or rotors. Static, or standing, imbalance is the condition when there is more weight on one side of a centerline than the other. However, a rotor may be in perfect static balance and not be in a balanced state when rotating at high speed. 

High-speed blender fitted with leak-proof glass jar and explosion-proof motor Balances... 

In addition to the whirling vibration due to an out-of-balance force, another type of motion can occur in a free-spindle machine. When the bowl or basket is tilted the spindle may move in a circle. This slow gyratory motion is known as precession , and is similar to the precession of a gyroscope. It is usually most pronounced at high speeds, above the critical speed. 

D. DNA replication is regulated as a balance between high speed and efficiency (pro-cessivity) and the need for high fidelity. 

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