Специальность «Эксплуатация судовых энергетических установок»
МЕТОДИЧЕСКИЕ УКАЗАНИЯ II КУРС
I. Контрольная работа № 2
II. Практика устной речи:
1. MATERIAL FORMING
2. MACHINING
3. SHIPBOARD MAINTENANCE OF MACHINERY
4. WORKSHOPS
III. Чтение и устный перевод текстов:
1. WELDING
2. INDUCTION BRAZING AND SOLDERING
3. THREADS
4. GEARS
Практика устной речи
MATERIAL FORMING
In the production of engineering equipment various different processesare used to produce the assortment of component parts. These formingor shaping processes can be grouped as follows:
1. Casting.
2. Forging.
3. Extruding.
4. Sintering.
5. Machining.
Casting is the use of molten metal poured into a mould of the desiredshape. A wooden pattern, slightly larger in dimensions than the desireditem, to allow for shrinkage, may be used to form a mould in sand. Entryand exit holes, the gate and riser, are provided for the metal in the sandmould. Alternatively a permanent metal mould or 'die' may be made intwo parts and used to make large quantities of the item. This method iscalled 'die casting'. The molten metal may be poured into the dies orforced in under pressure.
Forging involves shaping the metal when it is hot but not molten. Inthe manufacturing process of forging a pair of die blocks have the hotmetal forced into them. This is usually achieved by placing the metal onthe lower half die and forcing the top half down by a hydraulic press.
Extrusion involves the shaping of metal, usually into a rod or tube cross section, by forcing a block of material through appropriately shaped dies. Most metals must be heated before extrusion in order to reduce the extruding pressure required.
Sintering is the production of shaped parts from metal powder. A suitable metal powder mixture is placed in a die, compressed and heated to a temperature about two thirds of the material melting point. This heating process results in the powder compacting into a metal in the required shape.
Machining of one type or another is usually carried out on all metal items. This may involve planing flat surfaces, drilling holes, grinding rough edges, etc. Various equipment, such as milling machines, drilling machines, grinders, lathes, etc., will be used. Many of these machines are automatic or semi-automatic in operation and can perform a number of different operations in sequence.
MACHINING
Any one of a group of operations that change the shape, surface finish, or mechanical properties of a material by the application of special tools and equipment. Machining almost always is a process where a cutting tool removes material to effect the desired change in the workpiece.
Typically, powered machinery is required to operate the cutting tools. Although various machining operations may appear to be very different, most are very similar: they make chips. These chips vary in size from the long continuous ribbons produced on a lathe to the microfine sludge produced by lapping or grinding. These chips are formed by shearing away the workpiece material by the action of a cutting tool. Cylindrical holes can be produced in a workpiece by drilling, milling, reaming, turning, and electric discharge machining (EDM). Rectangular (or nonround) holes and slots may be produced by broaching, milling, grinding, and nibbling; and cylinders may be produced on lathes and grinders.
Special geometries, such as threads and gears, are produced with special tooling and equipment utilizing the same turning and grinding mentioned above. Polishing, lapping, and buffing are variants of grinding where a very small amount of stock is removed from the workpiece to produce a high-quality surface. In almost every case, machining accuracy, economics, and production rates are controlled by the careful evaluation and selection of tooling and equipment. Speed of cut, depth of cut, cutting-tool material selection, and machinetool selection have a tremendous impact on machining. In general, the more rigid and vibration-free a machining tool is, the better it will perform.
SHIPBOARD MAINTENANCE OF MACHINERY
Maintenance problems have recently become more serious, particularly because of the over-complicated designs, delivery delays of spares and unmanned engine room working.
Too much of complication in machinery has made repair more difficult worldwide.
The most efficient and cost effective method of repair is the fitting of proper maker’s replacement parts in-situ by the ships’ engineers but this requires that the correct spare parts are always on the ship at the right time.
There are many thousands of different parts for the main and auxiliary diesels and hundreds more for each auxiliary machine. It soon becomes impossible to predict, even by computer, which part is going to be required next, so as to ensure its availability on board.
When an urgent request from a ship for spares is received, the problem of availability at the makers’ works arises. Delivery times range from days to months. So delivery by air has become commonplace.
When spares become available all that is necessary is an aircraft to deliver them. This may take only a few hours – always assuming the ship’s next destination is known.
Larger parts require special charter flights which take extra time to organize and the cost of transport can amount to many times the value of the part concerned.
WORKSHOPS
In addition tospecial portable tools, much improved workshop machinery is now provided, to enable a wider spectrum of repair work to be undertaken on board. A medium size universal lathe with all attachments is the first essential thing in the workshop.
A large vertical drill and a universal shaping machine can also save many hours of hard manual work and achieve greater accuracy. Special valve grinding equipment can also be very useful on board.
A welding plant is essential preferably portable, to enable it to be taken on deck for work on the ship, as well as for use in the workshop. Welding work must however be approached with caution and only be done by persons who have received proper instruction. Its use should be limited to simple or emergency work, unless welding seems can be checked and tested for safety, especially if used for lifting gear or on boilers or pressure vessels.
So important and valuable can a well-equipped engineers’ workshop prove that consideration is now being given to making it an extension of the engine control room to be soundproof and air-conditioned and, at the same time, be handy to the monitoring and control center.