Showing papers on "Critical speed published in 1978"

Optimum Bearing and Support Damping for Unbalance Response and Stability of Rotating Machinery

Abstract: This paper presents a rapid approximate method for calculating the optimum bearing or support damping for multimass flexible rotors to minimize unbalance response and to maximize stability in the vicinity of the rotor first critical speed. A multimass rotor is represented by an equivalent single-mass model for purposes of the analysis. The optimum bearing damping is expressed as a function of the bearing stiffness and rotor modal stiffness at the rigid bearing critical speed. Stability limits for aerodynamic cross coupling and viscous internal rotor friction damping are also presented. Comparison of the optimum damping obtained by this approximate method with that obtained by full scale linearized transfer matrix methods for several rotor-bearing configurations shows good agreement. The method has the advantage of being quickly and easily applied and can reduce analysis time by eliminating a time consuming search for the approximate optimum damping using more exact methods.

Tool Wear in Cutting Carbon-fiber-reinforced Plastics : The Effect of Physical Properties of Tool Materials

Abstract: A turning (facing) test on glass-fiber-reinforced-plastics was performed with several tool materials, e.g., sintered carbides, cermets and ceramics, and the wear patterns and wear land growth rate were analyzed to clarify the relationship between physical (mechanical) properties and flank wear of cutting tools. The main results are obtained as follows: (1) When cutting speed is increased, the rate of wear on the nose in every tool material starts to increase remarkably at a certain speed, i.e., a critical speed. (2) Thermal conductivity coefficient versus critical speed curve is approximately linear when plotted on log-log coordinates. The higher the thermal conductivity coefficient of tool material, the higher the critical speed becomes. There also seems to exist an influence of the compressive strength and thermal expansion coefficient of tool materials on its performance in high speed cutting of GFRP.

Turbine acceleration governing system

Abstract: A turbine speed control system comprising a pair of concurrently operable electronic microprocessor-based controllers which are coupled together by a data link to functionally cooperate in controlling turbine acceleration primarily during start-up operations in accordance with a set of predetermined measured and calculated turbine conditions One controller is operative to control the speed of the turbine at selected accelerations from turning gear to a predetermined speed value This same controller monitors a plurality of temperature differences from preselected regions of the turbine and inhibits turbine acceleration in accordance with an out-of-limit temperature condition associated therewith In addition, the one controller is further operative to selectively override the turbine speed hold initiated by an out-of-limit temperature condition, the override permitting the one controller to proceed with controlling the speed of the turbine at a desired acceleration The other controller is selectively operative to govern the turbine acceleration as controlled by the one controller based on calculated present and anticipated rotor stresses which are derived concurrently with the speed control operations of the one controller A turbine speed hold may be initiated by either a detected differential temperature out-of-limit condition or a detected calculated rotor stress limit condition In either case, the one controller is further operative to detect if the speed hold occurs in one of a number of predetermined critical speed zones and to adjust the turbine speed outside of the zone in which the speed hold occurs

Shaft vibration damper

Abstract: An apparatus (120) for intermittent support of a rotatable shaft (22) comprises an axial collar (120) substantially coaxial with the shaft (22) and fixed thereabout for rubbing contact with the shaft (22) only after the shaft deflects a predetermined amount from its rotational axis (140) to alter the bending mode of the shaft (22) thereby increasing the first order critical speed of the shaft (22) to a level above the maximum speed at which the shaft (22) may be driven to prevent excessive vibration and consequent damage to the shaft (22), associated end couplings (35,56) and housing (78,84,92).

Control system and method

Abstract: Disclosed are apparatus and methods for controlling parameters of fluid-driven systems. A control unit of the invention compares an input control signal to a tachometer signal from a fluid-driven turbine to produce a flow signal for controlling the turbine speed. The speeds of turbines in series are linked by the tachometer signal of the first turbine acting as the control signal for the following turbines. A critical speed interval is identified in relation to a range of values of the control signal. As the speed of a turbine is increased or decreased, its control unit holds the turbine speed at the limit of the critical speed interval, then rapidly accelerates the turbine through the interval to avoid prolonged operation at the turbine's critical speed. The individual critical speeds of separate turbines in series may be accommodated by critical speed intervals defined in separate control units for each of the turbines. Multiple critical speeds for a given turbine may also be provided for by defining multiple critical speed intervals within the corresponding control unit.

Motor speed control circuit

Abstract: A motor speed control circuit for use in a washing machine includes a timer which in normal operation accelerates the motor from a wash speed to a distribution speed before a fast acceleration to the spin dry speed. The control circuit includes speed measurement means for maintaining the motor at spin speed in the event of a power interruption during a spin cycle provided the drum speed remains above a given critical speed when the power returns. If not, a redistribution cycle takes place before the motor is accelerated to its spin speed.

The Stability of an Asymmetric Rotor in Damped Supports

Abstract: A general-purpose method of evaluating the stability of an asymmetric flexible rotor, mounted in symmetric damped bearings, is defined. This method evaluates the complex eigenvalues of the rotor system by solving the equations of motion in a rotating coordinate frame. The application of this method to a rotor mounted in tilting-pad bearings is demonstrated. The observed behavior of a number of different rotor configurations is compared with corresponding predictions of stability. For the configurations predicted to be unstable, a distinct and unnegotiable threshold of instability is encountered. The sharpness of this threshold is emphasized by careful balancing at speeds fractionally below the threshold. In a final configuration predicted to be marginally stable, lightly damped resonant behavior, negotiable by balancing, is encountered in the region of the first critical speed.

Vibration of Casing of High Speed Rotating Machine

Abstract: 著者らが先に提案した縮小インピーダンス合成法を用いて, 機械構造物の振動を計算するプログラムを作成した.これをシリンダブロックの二つの部分に適用して計算したところ, 固有振動数は打撃試験の結果と約1割の誤差範囲で一致し, 一方固有モードはボログラム振動試験結果とよく一致した.この結果, 本プログラムは回転機械のケーシングの振動特性を設計段階で予知するのに十分有用であることが判明した.

Self-excited speed operated control switch - has permanent magnet generator with threshold circuit and display unit for speed exceeding critical speed

Abstract: The switch is operated by the speed of a shaft rotation above and below a critical value. It has a multi-pole sub-divided permanent magnet, a.c. generator (11) connected to the driving shaft (19). It generates an initial a.c. signal with an amplitude corresponding to the shaft speed. A threshold circuit (12) has a data input connected to the above a.c. generator and generates an operating signal when the initial a.c. signal indicates a speed exceeding a critical value. A local current source (20) is supplied by the a.c. generator, and generated a d.c. voltage constant over a wide frequency speed range. It is the only energy supply for the threshold circuit. A display device (13, 18) is activated by the operating signal, and displays the shaft over-speed.

Problem of Rotor Passing through Critical Speed with Gyroscopic Effect : Analysis by Asymptotic Method and Experiments

Abstract: The nonstationary vibration of a rotor with a gyroscopic effect in passing through its critical speed is studied by using the asymptotic method. In particular, the influence of a gyroscopic effect in passing through a critical speed is studied in detail on two cases, i.e., one of a constant acceleration and the other considering the interaction between the driving source and the vibration system. The effect of an internal damping on the stability is also studied. The experiments support the analysis.