Reeds Vol 8 General Engineering Knowledge for Marine Engineers. Year: Language: english. Author: Paul Anthony Russell. Genre. Review of Vector Calculus. Chapter 5 gives an overview for the problem of solving partial Figure_Equation 2 Level reed's general engineering. Reeds-8 General Engineering Knowledge for Marine Engineers. - Ebook download as PDF File .pdf), Text File .txt) or read book online.
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Reeds Vol 8 General Engineering Knowledge for Marine Engineers (Reeds for Marine Engineers (Reeds Marine Engineering and Technology Series) pdf. 4 days ago Knowledge for Marine Engineers marine engineering textbook listing Reeds naval architecture for marine engineers pdf naval architecture. This eighth volume of Reed's Marine Engineering Series preparesstudents for the Department of Transport Certificates of Competency inGeneral.
X-rays produced in a Coolidge tube give quick results and a clear negative. Radioactive material e. Cobalt 60 which emits y-rays does not give a picture as rapidly as the X-rays, however, to compensate for its slowness, it is a compact and simple system. With ultrasonics we do not have the limitations of metal thickness to consider as we have with radiographic testing, high frequency sound waves reflect from internal interfaces of good MATERIALS metal and defects, these reflected sound waves are then displayed onto the screen of a cathode ray oscilloscope.
Size and position of a defect can be ascertained, it can also be used for checking material thicknesses e. A pqrtable, battery operated, hand held, cylindrical detector with cable to a set of headphones can be used to detect leakages e.
A recent application of ultrasonics is testing condensers. A generator placed inside the condenser 'floods' it with ultrasound.
By using a head set and probe, tube leakage can be homed in on. Where a pinhole exists sound 'leaks' through and where a tube is thinned it vibrates like a diaphragm transmitting the sound through the tube wall.
When iron is heated up to its melting point two similar arrests occur wherein there is heat absorption. The temperatures at which these arrests occur are called 'critical points' and these are of great importance. At these critical points considerable changes of internal structure takes place and therefore different physical properties are available if these structures could be trapped. With steels, these changes in the internal structure of the iron at the critical points affect also the carbon which is present in the form of iron carbide.
At the upper critical temperature range to C in the solid state the range is due to the variable carbon content the iron structure formed has the ability to dissolve the iron carbide into solution forming a new structure.
If at this stage the steel is suddenly quenched in water the iron carbide will remain in solution in the iron, but the iron's structure will have reverted to its original form. This completely new structure which has been brought about by heating and then rapidly cooling the steel is called 'Martensite', a hard needle like structure consisting of iron supersaturated with carbon, and is basically responsible for hardening steels.
If a steel of approximately 0. In this condition the steel would be fully hardened i. Choosing a temperature lower than the above but not lower than C lower critical and then quenching, will produce a partly hardened steel having a Brine11 numeral between 2, to 6, Hardening material in this way produces internal stresses and also makes the material brittle.
To relieve the stresses and restore ductility without loss of hardness or toughness, the material is tempered. Tempering consists of heating the material to about C, retaining this temperature for a duration of time this depends upon the mass and the degree of toughness required and then quenching or cooling in air.
The combination of hardening and tempering is greatly employed with steels and alloy steels, a wide range of properties is available thereby.
Components such as drills, chisels, punches, saws, reamers and other tools are invariably subjected to the above process. Straight carbon steels whose carbon content is below 0.
The reason could be attributed to the smaller quantity of Martensite which would be produced.
What actually happens is that the work forces cause dislocations to be set up in the crystal latticework i. Case Hardening This is sometimes referred to as 'pack carburising'.
The steel component to be case hardened is packed in a box which may be made of fire clay, cast iron, or a heat resisting nickel-iron alloy.
Carbon rich material such as charred leather, charcoal, crushed bone and horn or other material containing carbon is the packing medium, which would encompass the component.
The box is then placed in a furnace and raised in temperature to above C. The surface of the component will then absorb carbon forming an extremely hard case. Depth of case depends upon two main factors, the length of time and the carbonaceous material employed.
Actual case depth with this process may vary between 0. Gudgeon pins and other bearing pins are examples of components which may be case hardened. They would possess a hard outer case with good wearing resistance and a relatively soft inner core which retains the ductility and toughness necessary for such components. Nitriding In this process the steel component is placed in a gas tight container through which ammonia gas NH3 is circulated.
Nitrides are then formed in the material, at, and close to the surface, which increases the surface hardness to a marked degree. A nitride is an element combined with nitrogen, usually nitride promoting elements are present in the steel such as aluminium, chromium, vanadium or molybdenum. Actual depth of hard case is not so great with this process as compared to case hardening, viz 0.
An essential difference from case hardening is the more gradual change-over from hardened to unhardened part, thus reducing the risk of exfoliation.
Flame Hardening This process is used for increasing the surface hardness of cast irons, steels, alloy cast irons and alloy steels. With the increase in surface hardness there is a high improvement in wear resistance. To flame harden a component e. A water spray closely following the oxy-acetylene torch quenches the material thereby inducing hardness.
Care in operation of this process is essential, overheating must be prevented. Induction Hardening This is a method of surface hardening steels by the use of electrical energy. Hysteresis loss is heat energy loss caused by the steel molecules behaving like tiny magnets which are reluctant to change their direction or position with each alteration of electrical supply thus creating molecular friction.
Eddy currents are secondary electrical currents caused by the presence of nearby primary current. The resistance of the steel molecules to the passage of eddy currents generates heat.
Important points regarding induction hardening are: 1. Defects that can occur in castings are: 1. Shrinkage cavities. Blowholes caused by ineffective venting and dissolved gases in steels which have not been killed i.
Sand casting is slow and expensive and would only be used if the metal and casting shape are unsuitable for other techniques. Time of application of electrical power, governs depth to which heat will penetrate. Reduces time of surface hardening to seconds-i. Rapid heating and cooling produces a fine grained martensitic structure. Due to speed of operation no grain growth occurs or surface decarburization. No sharp division between case and core.
Die Casting Used mainly for aluminium and zinc base alloys. The molten metal is either poured in under gravity or high pressure-hence gravity and pressure die casting. This process gives a finegrained uniform structure and the mould can be used over again, whereas for sand casting it has to be removed. This process is employed to soften tool steels in order that they may be easily drawn and machined.
After shaping, the material is heated for hardening and the globules or spheres of cementite will be dissolved. Refining of the material prior to spheroidising may be resorted to in order to produce smaller globules. To ensure a sound casting the risers have to be carefully positioned to give good ventilation. Centrifugal action throws the molten metal radially out onto the inner surface of the mould to produce a uniform close-grained-due to chilling effect of mould-non-porous cylinder.
Such a casting process can be used for piston rings, the rings being cut from the machined cast cylinder, or for producing cast iron pipes. Forging This is the working and shaping of hot metal by mechanical or hand processes with tools called swages. During the process the coarse, as cast, structure of the metal is broken down to form a finer-grained structure with the impurities distributed into a fibrous form.
Items that are forged include connecting rods, crankshafts, upset ends of shafts and boiler stays, etc. Cold Working The pulling of metal through dies to form wires and tubes, cold rolling of plate, expansion of tubes in boilers and heat exchangers, caulking of plates, etc. In steels it increases strength and hardness but reduces ductility. As a graphitiser it is useful in cast irons, tending to prevent the formation of white cast iron and form instead graphitic cast iron.
The quantity of silicon in an iron or steel may vary between 0. Sulphur Reduces strength and increases brittleness. It can cause 'hot shortness', that is, liable to crack when hot. Normally the sulphur content in a finished iron or steel does not exceed 0. Phosphorus This also causes brittleness and reduction of strength but it increases fluidity and reduces shrinkage which are important factors when casting steels and irons.
It can produce 'cold shortness', that is, liable to crack when cold worked. Normally the'phosphorus content does not exceed 0. A low to medium carbon steel with 3 to 3. Nickel forms a finer grained material. Chromium Increases grain size, induces hardness, improves resistance to erosion and corrosion. This element is frequently combined with nickel to produce stainless steels and irons which are used for such items as turbine blades, pump rods and valves. Molybdenum Used to increase strength, especially employed for increasing strength at high temperatures which is one reason why it is used for superheater tubes, turbine rotors, etc.
Nickel-Chrome steels. Vanadium Increases strength and fatigue resistance. Used in conjunction with molybdenum for boiler tube materials. Manganese This element which is found in most commercial irons and steels is used as an alloying agent to produce steels with improved mechanical properties. Manganese is partly dissolved in the iron and partly combines with the cementite. Providing the manganese content is high enough, martensite, with its attendant hardness and brittleness will be formed in the steel even if the steel is slow cooled.
For this reason the manganese content will not normally exceed 1. Manganese and silicon are also employed as alloying agents, these have been previously dealt with.
It is also used a s t h e basis for many alloys and as an alloying agent. If copper is cold worked its strength and brittleness will increase, but, some restoration of ductility can be achieved by annealing. Hence, in this way, a wide range of physical properties are available.