Building Marine Machinery

The engines that drive modern steamships or motorships must, despite their enormous size, be built with the accuracy and precision which characterize the most intricate and minute mechanisms

THE POURING OF MOLTEN METAL is among the most spectacular sights in a foundry for casting components of marine machinery. Molten iron is shown above being poured into a mould for a marine engine cylinder. After the pouring it takes many days for a casting to cool. When it is cool the casting is removed and prepared for machining.

TO the average man the most impressive feature of a marine engine is its size. Herein lies one of the most difficult problems faced by the builders of ships’ machinery. In the production, handling and machining of enormous castings and forgings the skill of the marine engineer is put to exacting tests. In addition the machinery that drives a ship or renders her innumerable services at sea must be within certain limits of weight and must be absolutely reliable.

The materials used must be of the best quality, ensured by repeated tests, and workmanship has to admit of no errors. The utmost precision must prevail in fashioning every component part.

It is on this high degree of accuracy that the safety of thousands of lives is dependent at sea. not only at the height of great storms, but also in fair weather when failure of steering gear or propeller shaft may spell disaster.

The dimension difficulty has been met by the builder of marine engines with the characteristic courage that dominates all who build ships or brave the seas in them. The erecting shop in which the modern marine engine first takes shape is of enormous size. It has to be, for in it are erected the complete sets of engines that will eventually be packed inside the hull of, perhaps, a mammoth liner. And even within the confined space of a liner’s hull there is room for a fair-sized street of houses, so that the area of flooring that must be set aside for building the ship’s machinery can readily be visualized.

The machine shops adjoining the slipways of a shipbuilder’s yard are vast halls covering acres of ground. The shops are interlaced with railway lines for the supply of materials and the removal of a ship’s engines, either as complete sets or piecemeal, for subsequent re-erection in the hull of the vessel in the fitting-out basin. Along the walls of the shops there run gantries carrying powerful overhead travelling cranes, operated electrically, that serve the machines or erecting beds below.

A marine engineering works is divided into a number of different departments, separate from one another, but all working in co-operation to produce the enormous engines required by the modern ship. These may be the steam reciprocating engines usually associated with the cargo vessel, the turbines of a liner or warship, or the huge oil engines of a motorship.

It may assist if we consider first the building of engines for a large twin-screw cargo steamer. Often two sets of triple- or quadruple-expansion engines are installed in a vessel of this type.

In the drawing office all the blueprints are prepared for use in the various shops. Here are prepared the designs for every part of the vast complication that is presented by a reciprocating marine engine. Here, too, is worked out the system of “packing” that ultimately will fill the ship’s machinery spaces with her power plant.

When the designers and draughtsmen have settled all points of detail the construction can begin. Work on the engines for one ship is carried out simultaneously in all departments so that there shall be no delay in the final erection of the engine.

The largest components of a marine reciprocating engine are the bed-plate, on which the whole structure is built up, the standards, and the cylinders that are ultimately bolted to the tops of the standards. These components are cast usually in high-grade iron, but sometimes in steel. It is in the design of these huge castings for marine use that the great skill of the engineer is exhibited. The castings, despite their great size, must be as light as possible consistent with maximum strength. Large flat surfaces, such as steam chest covers and condenser inspection doors, are provided with ribs, cast in the solid metal, to impart strength where pressure is encountered either internally or externally.

Special precautions, too, must be taken to ensure that the casting shall not crack in cooling or become distorted . It is partly for this reason that all thin portions of the casting are curved or “faired” into the thicker portions No sharp interior corners are permitted.

The mixing and testing of the various grades of iron used in marine castings are matters of great importance, especially where cylinders are concerned. A marine engine cylinder is subject to shock from the sudden admission and expulsion of steam, at high temperatures and to the wear of the piston.

Huge Cylinder Castings

Cast iron is often regarded as an exceedingly “solid” material. It is, however, capable of being stretched, and under hydraulic pressure water can be forced through it. A marine high-pressure steam cylinder is subject to great tension and must be of material and proportions that will not permit of any appreciable stretch, which would have the effect of enlarging the diameter and permitting the leakage of steam past the piston.

Large castings in iron follow the same general practice, modified as required to suit the work in hand. The first process is the making of the patterns, generally of wood, that are used in the preparation of the sand mould to receive the molten metal. The patterns are made a little larger than the castings, to allow for the shrinkage of the metal on cooling. The casting is done on the floor of the foundry, where the patterns are lowered into pits and buried in large quantities of special moulding sand, a dark, earthy material that takes the impression of the surface against which it is rammed. The lower part of the pattern is impressed in the sand and the upper part is dealt with in a large open box, also containing sand, which is lowered over the pit or lower box.

Next are prepared “cores” of sand which are placed within the mould to prevent the flow of metal in the spaces they occupy and so form the bores and steam passage-ways of cylinders or any necessary recesses in other components. The moulds are then dried ready for the pouring of the molten metal. Marine engine cylinders may be any size up to 10 feet in internal diameter by 6 feet stroke. The magnitude of this foundry work will thus be appreciated.

MOULDS IN THE DARK SAND that comprises the foundry floor. The moulder is resting his left hand on a pattern and is pointing to the pattern’s impression with his other hand. Behind him is a bottle-shaped core that is placed in the mould to produce a hollow casting. In the centre is the upper moulding box for the mould in front of it, and on the right is a pattern with the mould, for a four-way flanged pipe joint.

The metal is melted in cupolas fired by solid fuel, oil or gas, and is run off into huge ladles for the final pouring. When the casting has cooled (a matter of several days) it is taken from the mould, cores are removed, and all surfaces are cleaned to get rid of the sand. Now follows the machining, a process that varies in the different marine engineering works. One widely adopted method is to use a machine tool known as a boring mill. This machine comprises a horizontal turn-table fitted with slots for bolts that hold the casting to it securely.

The turn-table may be as much as 20 feet in diameter and is revolved by an electric motor. On either side of the turn-table are two heavy standards that support a massive over-bridge carrying a slide and tool holder. The tool holder can be moved up, down or sideways, and as the turn-table with its casting revolves, a high-speed steel tool is brought into action against the surface to be machined.

The cylinders of a large steam reciprocating marine engine cannot be removed readily from the ship when they have become worn. To overcome this difficulty the bores are fitted with removable liners. These cylinder liners are of special cast iron, or of steel, and they can be replaced when worn by the action of the piston.

Marine pistons are of cast iron or, in the largest and fastest running engines, of steel, and are approximately cone-shaped. Just as the engines of a ship may be said to constitute her “heart”, so can the piston be described as the heart of the engine. Its rapid movement and reversal of direction call for the lightest possible construction, but it must be of adequate strength to withstand the high temperature and the series of shocks that are part of its working life.

A particularly important feature of piston construction lies in the method of its casting. The design must allow for the cooling of the metal without cracking. In the early days of cast marine engine pistons it was a fairly common occurrence to have a sudden engine breakdown at sea.

“Junk-Rings” for Pistons

When a cylinder cover was removed the piston would be found grouped artistically round a bare piston rod — in a hundred pieces. The piston had become faulty during the cooling of the casting, with consequent failure at an inopportune moment.

Failure of this kind is now rare, especially where the casting has been done in steel. Piston castings are carefully machined in a lathe or vertical mill, a tapered hole is bored in the central boss for the piston rod, and a groove is turned in the working face for the piston rings. In a marine cylinder the piston rings perform the same function as their smaller counterparts in the motor-car. They keep the working “gas” on the right side of the piston and thus prevent leakage.

The piston rings are of close-grained cast iron and are retained in the groove by a “junk-ring”. The name “junk” is a survival from the days when pistons were rendered steam-tight by a groove packed with rope or “junk”. Later the top flange of the groove was replaced by a removable ring, called the junk-ring, which permitted renewal of the rope packing without withdrawing the piston from the cylinder. Modern pistons are rendered steam-tight with highly efficient patent packing, and not rope or junk, but the term junk-ring still survives.

A MASSIVE CASTING IN A PLANO-MILLER. The bed of this machine slides, as in a planing machine. The cutting tools, however are of the revolving type and remove the surplus metal as in a milling machine. The casting is part of the bed-plate for a large diesel engine.

The columns that support the cylinders are usually of cast iron or cast steel. Or they may be made of wrought steel, with a flange at top and bottom for bolting to the cylinder and the engine foundation respectively. The design of these columns calls for great care. They are subject not only to the push-and-pull stresses of the pistons and connecting rods when working, but the rolling and pitching of the ship also have a tendency to snap them off “at the roots” in the same way that a heavily topped tree will be uprooted in a gale. This comparison is not inapt, because, during the war of 1914-18, in a British merchant ship hit by a torpedo in the engine-room, a set of large triple-expansion engines was blown over sideways — torn from its foundations.

Apart from the columns, there is another part of the engines that has to withstand stresses additional to the mechanical strains of their working. This is the bed-plate or foundation. A ship is not a rigid thing — she lives and fights the seas with the movements of her hull , but this bending and “giving” must not be transmitted to the machinery. Great care must therefore be exercised in the design of the foundations that carry the engines, so that they form a rigid unit.

Again cast iron or cast steel is used, and the casting is machined in a huge planing machine which prepares the seatings for the columns, main bearings and other parts of the engines. A planing machine comprises a rectangular table provided with X slots for bolting down the work. This table is driven backwards and forwards on a bed-plate by an electric motor. On either side of the bedplate are columns supporting an over-bridge and tool slide similar to that of the boring mill, and as the work passes to and fro the surface to be machined is brought into contact with the cutting tool.

Cylinder and valve chest covers are cast and machined in a similar manner to pistons. Light steel castings are used for the crossheads that join the piston rods to their connecting rods and take the side thrust of the piston’s working stroke.

Components such as connecting and eccentric rods and the main crankshaft are forged from billets of solid steel. The giant of the forge is the mighty steam hammer that, can deliver a blow of enormous power or can accurately crack an eggshell with equal facility.

Giant of the Forge

The modern steam hammer, with its extremely accurate action, makes light work of the largest and most intricate crankshaft, whether for the steamer or for the great oil engines of a motor ship. Connecting rods and other components that are made by forging also come under the steam hammer in the initial stages of their manufacture, and their working surfaces are machined later.

Crankshafts for steam or oil engines are turned, after the preliminary forging, in huge lathes that machine the bearing journals and crank-pins to a high degree of accuracy. The components of marine oil engines are built by methods similar to those adopted for reciprocating steam engines, although the designs differ widely. When all the components have been finished in the various departments in the works they are taken to the erecting shop for the building of the engine which, on completion, is subjected to numerous tests. It is then taken to pieces, partly or wholly, for re-erection in the ship’s hull in the fitting-out basin.

There is one auxiliary that is absolutely essential to the economical working of the marine steam engine, whether reciprocating or turbine. This is the condenser. Its construction has many points of interest, and although condensers show considerable variety in their size, shape and design, all have certain features in common. The body of the condenser may be a casting or a number of castings bolted together, or it may be built up of plates riveted together.

THE BORING MILL, with its enormous turn-table, makes light work of marine engine cylinders. Mounted on the turn-table is a cylinder of a diesel engine, and the engineer is “setting up” the work in readiness for the machining operations.

The plates into which the tubes are fitted are of brass or a similar non-corrosive alloy, and the tubes are secured by ferrules and packing that renders them steam-tight on one side and water-tight on the other. In early condensers, before the adoption of screwed ferrules to secure the tubes m the end plates, the ferrules were made of soft wood such as pine or lime. The wood was dry and well seasoned, and the ferrules were nearly an eighth of an inch larger in diameter than the holes in the tube plate. The ferrules were traced in a special press to compress the wood and enable them to be pushed over the tube ends and inserted in the holes in the tube plate. Soon after fitting, the ferrules absorbed moisture and swelled, thus providing exceedingly tight joints that lasted for years. Modern conditions, however, demand the screwed and packed ferrules that are now in general use.

We have seen how the foundry, the forge machine and erecting shops all pool their efforts in the building of a reciprocating marine engine, whether steam or diesel. The methods adopted vary but little in either type of power unit.

The steam turbine, however, the action of which has been fully described in the chapter “Steam Turbine Engines”, calls for special comment on the method of its construction. A set of turbines usually comprises three separate cylinders or casings enclosing rotors for high, intermediate and low pressures respectively. The complicated castings for the upper and lower halves of the casings are made in a fashion similar to those of a marine engine cylinder. The high- and intermediate pressure casings are cast in steel, and the low-pressure casings in iron.

After they have been cast, the upper and lower casings are accurately machined. The grooves that will provide clearance for the moving blades, and those for the reception of fixed blades are bored out, and all flat jointing surfaces and seatings are planed. Turbine half-casings are often cast in two or more sections, and the abutting flanges are faced off and provided with a number of holes for the fixing bolts. Large numbers of holes are also drilled in the horizontal flanges for the bolts that hold the two halves of the casing together. Every turbine of the set is bolted at one end to the gear-case, and at the other to a pedestal attached to the main foundations.

Perfectly Balanced Rotors

Turbine rotors are forged from solid steel billets and then turned, with their hundreds of grooves, in huge lathes. The blades are usually formed out of solid bars by milling machines, in which the surplus metal is removed by revolving cutters. The blades may be of stainless steel, monel metal (an alloy of nickel and copper, with small quantities of iron and manganese) or of phosphor bronze. The greatest care is taken in fitting the blades, and the rotors are perfectly balanced so that, despite their size, they can be spun as easily as a child’s top. The modern turbine gear-case is a massive iron casting containing the rotor pinions and the large helical gear wheels with which they mesh. Main gear-wheels usually consist of a cast iron central portion attached to a forged steel shaft, and the rims on which the helical teeth are cut are of forged steel. The cutting of teeth on one of these main gear-wheels takes several weeks in an automatic “hobbing” machine, equipped with revolving cutters.

Modern marine boilers have features in their construction that are noteworthy. The marine boiler comprises a number of drums joined together by banks of tubes in a casing lined with firebrick. The steel tubes are made by forcing a solid white-hot bar of steel over a pointed “former” of the required diameter. The tubes are expanded by a special appliance into holes drilled in the drums. The modern method of building drums for water tube boilers is to roll them from a solid billet of white-hot steel. When cool the drums are machined all over and the holes are drilled for the tubes and boiler fittings. Scotch boiler shells are made from rolled steel plates riveted together.

All boilers are tested by hydraulic pressure before they are put in steam, and a large factor of safety is insisted on by the Board of Trade before a boiler is passed for service.

IN COURSE OF CONSTRUCTION in the works of the North Eastern Marine Engineering Co., Ltd., at Wallsend-on-Tyne, is a huge diesel engine. The great eight-throw crankshaft in the foreground is ready to take its place on the four-section bed-plate surmounted by the nine massive standards towering above the floor of the erecting shop

You can read more on “Building a Liner”, “Motor Engines” and

“The Queen Mary’s Engines” on this website.