ENGINE FRAMES

MARINESHELF publishes articles contributed by seafarers and other marine related sites solely for the benefit of seafarers .All copyright materials are owned by its respective authors or publishers.

Engine Frames.

These fit between the bedplate and cylinder block beam. They are sometimes referred to as the entablature. They serve the following functions.

a)      Support the cylinder blocks, turbo-chargers, camshaft and driving gear, scavenge belt etc.

b)      Provide a facing for the girders & absorb the guide forces.

c)      Develop an oil tight easing, for forced lubricating oil system, & support pipes & walkways.

‘A’ – Frames.

In old engines the frames were of cast iron and made hollow to reduce weight without reducing rigidity. The frames or columns were held in compression by tie-bolts. These frames were later fabricated from mild steel tube and plate with guides of cast iron bolted onto the frames. This type of arrangement uses individual frames at each transverse girder position of the bedplate with the longitudinal spaces between frames filled by plates bolted to the frames. The structure is strong and rigid in the transverse plane but relatively flexible longitudinally. This makes oil tight fixing of the side covers difficult unless very heavy covers or longitudinal stiffness are used. It also produces a weak structure if exposed to internal pressure from a crankcase explosion and will allow alignment of the cylinder blocks to the bedplate to vary in relation to ship movement.

The ‘A’-frame construction is now being abandoned in favor of longitudinal girder construction.

Improved methods of prefabrication which can be relied upon to produce large, distortion free units has allowed longitudinal girders to be manufactured so that the longitudinal stiffness of the structure can be increased without altering the transverse stiffness. This also contributes to the bedplate stiffness and reduces effects of hull hogging and sagging. ‘MAN’ engine manufactures claim that the bedplate only contributes 17% to the overall stiffness compared to 60% for the traditional ‘A’-frame construction.

In the ‘Sulzer’ engine the fabricated longitudinals form a sandwich by enclosing a cast iron centerpiece at each transverse girder spaces. The cast iron centerpiece forms the crosshead guides. The structure is bolted together.

In the ‘B&W’ engine the entablature retains the ‘A’ transverse section but both longitudinals and transverse components are fabricated into a box form. The guide faces are bolted to the transverse components. The entablature is formed in two pieces connected at the camshaft drive position at the middle of the engine.

In the ‘MAN’ engine, regular box shaped fabrications are used, again with longitudinal and transverse sections welded together to form a single unit. The layer sizes (more than 700 mm bore) have the box divided into 2 on the horizontal plane. The upper box has openings on the back into which the cast iron guide faces are bolted. In the ‘Doxford-J’ engine a continuous girder is fabricated for the guide side of the framework with the columns at each main bearing position welded to the longitudinal. The front of the engine is left more open to allow easy access to the running gear.

Apart from increased stiffness which reduces:

i)                    Misalignment,

ii)                  Bearing distortion,

iii)                Vibration,

The structure is more oil tight, as fewer joints are required & the structure ‘works’ less. It is also easier to build the engine & ensure equivalent alignment when the engine is reassembled in the ship.