Page 82 - Introduction to Marine Engineering

Steam turbines and gearing 69

From L P turbine Primary Prom H P Primary
'I wheel turbine 'pinion

Secondary
pinion

Drive to
propeller
Figure 3.14 Double reduction system of gearing

Flexible coupling

A flexible coupling is always fitted between the turbine rotor and the
gearbox pinion. It permits slight rotor and pinion misalignment as well
as allowing for axial movement of the rotor due to expansion. Various
designs of flexible coupling are in use using teeth, flexible discs,
membranes, etc.
The membrane-type flexible coupling shown in Figure 3.15 is made
up of a torque tube, membranes and adaptor plates. The torque tube fits
between the turbine rotor and the gearbox pinion. The adaptor plates
are spigoted and dowelled onto the turbine and pinion flanges and the
membrane plates are bolted between the torque tube and the adaptor
plates. The flexing of the membrane plates enables axial and transverse
movement to take place. The torque tube enters the adaptor plate with a
clearance which will provide an emergency centring should the
membranes fail. The bolts in their clearance holes would provide the
continuing drive until the shaft could be stopped.

Turning gear

The turning gear on a turbine installation is a reversible electric motor
driving a gearwheel which meshes into the high-pressure turbine
primary pinion. It is used for gearwheel and turbine rotation during
maintenance or when warming-through prior to manoeuvring.