Vibration (c.103-104)

Vibration is caused by lack of balance in the rotating parts of machinery. It has always been a source of trouble, due not only to the fact that the excessive wear on the bearings caused by vibration affects the accuracy and life of the machinery, but also to the fact that the exact point of “unbalance” has been difficult to locate and difficult to correct.

If in building up speed a turbine starts to vibrate, slow down immediately. If the vibration ceases at a lower speed, run at that speed for several moments. Then, again attempt to build up the speed. If no further vibration is noted, it may be assumed that the trouble was probably due to unequal

heating of the rotor or to an accumulation of water in the turbine. If the vibration does not cease at a lower speed steps should immediately be taken to locate and remedy the trouble.

When the turbine begins to vibrate and rumbling is heard coming from it, the trouble is due to water or other foreign matter in the turbine. If after slowing down or correcting faulty boiler operation the trouble is not eliminated, the turbine must, except in case of emergency, be shut down. If a sharp metallic sound is heard after the rumbling noise, it may be assumed that part of the blading has been damaged; the turbine must be shut down and not used until the cause of the trouble has been found.

Accurate alignment is essential to smooth operation. Flex­ible couplings should be aligned as accurately as possible because although they will absorb the shock caused by eccen­tric loading, impulses will be transmitted to the shafts and will cause vibration.

Mechanical power transmission means are often the cause of vibration. Gears which are inaccurately cut, worn, or are not meshing properly will set up disturbing forces. If they fall in step with a resonant frequency of the machine, severe vibration will result.

The origin of vibration may be at the bearings. Any con­dition that causes metallic contact between the shaft and the bearing will lead to vibration. The bearing may be unaligned бг pinched in the housing, or may be loose in the housing.

Words to be Learnt

foreignmatterинородный предмет faulty['fo:lti] неправильный excessiveчрезмерный wearизнос exactточный pointзд.место toceaseпрекращаться to attempt пытаться rumbling стук emergency аварийный to damage повреждать accurate alignment точная центровка

essential важный smooth operation плавная работа to absorb поглощать shock удар eccentric loading эксцентричная нагрузка tomeshвходить в зацепление tosetupпроизводить frequency частота severe vibration резкая вибрация disturbing forces возмущающие усилия to pinch зажимать (в корпусе) tolooseослаблять

Notes

lack of balance отсутствие баланса

a source of trouble источник неполадок

causedbyvibrationвызванный вибрацией

tobuildupspeedповышать скорость, доводить до заданного числа оборотов

torunatthatspeedработать на такой скорости

it may be assumed можно допустить

the trouble is due to неполадки происходят из-за

steps should be taken следует предпринять шаги

to remedy the trouble исправить повреждение

incaseofemergencyв случае чрезвычайной необходимости

mechanicalpowertransmissionmeansмеханические средства передачи мощности

tofallinstepwithсовпадать, попасть в такт с