The shipbuilding industry stands out from other industries in the histiocytoma dog ear aspect that it is not based on unit production. For example, in the automobile industry, cars of a particular model or design are produced on histiocytoma dog ear an assembly line since every product of a particular design histiocytoma dog ear is similar to the other. But ships are not constructed this way, every ship is based on the owner’s requirement. Hence, even if the basic hull design may be the same, the dimensions, capacity and systems used in one ship may be very histiocytoma dog ear different from another.
We will, in detail, discuss the stages of ship construction right from a steel histiocytoma dog ear plate to the end product that is delivered to a histiocytoma dog ear client. Many book authors have explained the same by first describing histiocytoma dog ear the layout of a shipyard. This method of explanation often turns out to be complex histiocytoma dog ear for a reader who is not well versed with the histiocytoma dog ear ship-building process. Hence, we’ll follow quite the opposite in this article, by first explaining all the processes in the order they histiocytoma dog ear are practiced, and once we are clear about them, we will see how a shipyard is laid out keeping histiocytoma dog ear in mind the sequence of these processes.
A unique behaviour is observed at this stage. To explain that, let’s revisit the basics of the stress-strain curve of steel. When steel is subjected to stress levels within the proportional histiocytoma dog ear limit, removal of the load does not leave any deformation in histiocytoma dog ear the specimen. But if the stress levels go up to the plastic histiocytoma dog ear region, there is certain amount of permanent deformation even after the histiocytoma dog ear removal of stress. So, when subjected to stress again, the material would actually have less capacity to yield that histiocytoma dog ear before. In other words, its reserved plasticity has now reduced.
Once the plate is completely free of mill scale, the supervisor checks the roughness of the plate surface. In case the plate it too rough, it would be unfavourable for proper welding. And if too smooth, it would not provide enough surface roughness for proper adhesion histiocytoma dog ear of paint. Hence, the surface of the plate at the exit of the histiocytoma dog ear blasting chamber is compared with a standard specimen which has histiocytoma dog ear the required roughness. In shipbuilding practice, the roughness standard maintained is swedish standard (SA 2.5).
Priming and drying: after the mill scale is removed, the plate is passed into a chamber in which a histiocytoma dog ear primer is sprayed on both surfaces. Priming protects the steel from corrosion. The primer applied is usually a zinc-rich coating, and it should be chosen such that it does not histiocytoma dog ear interfere with the welding and bending of plates. After the plate is primed, it is immediately passed on to the drying chamber, where hot air dries the surface and prevents moisture from histiocytoma dog ear interfering with the process.
The surface treated plates are to be cut into desired histiocytoma dog ear shapes and sizes, in order to be developed to the required three dimensional histiocytoma dog ear shape or be used as straight plates for other structural histiocytoma dog ear components. Now, it is very important for a shipyard to increase its histiocytoma dog ear production, as a result of which wastage of material is prevented histiocytoma dog ear to the maximum extent possible. How?
Plates of the standard sizes, after being surface-treated, undergo nesting. It is a process in which the plate is scanned, and by the use of algorithms, the shapes to be cut out of the plate are histiocytoma dog ear marked on the plate by the computer controlled marker. This algorithm makes sure minimum scrap metal is produced from histiocytoma dog ear each plate. Such a plan is called nesting plan.
2. Thermal cutting methods: these methods use a movable cutting tool, which makes it possible to cut out complicated shapes. However, since these are hot works, they result in work hardening in the cut edges. However, since every cut edge will be welded in future stages, the cut edges lose the work hardened property and offset histiocytoma dog ear this effect.
An interesting theory lies beneath this method. It is important to understand this theory in order to histiocytoma dog ear know if this method is also applicable for aluminium, which is now widely being used as a structural material histiocytoma dog ear on ships. When the oxygen lever is pressed, the flame increases the metal temperature. For steel, the metal becomes red hot at ignition temperature (800 degree celsius). After a certain time when the temperature reaches to the histiocytoma dog ear melting point of the metal oxide (which is 1000 degree celsius for steel), the metal oxide begins to melt out. Since the melting point of mild steel is approximately 1500 histiocytoma dog ear degree celsius (higher than that of its oxide), this method of cutting does not melt the metal, and hence is feasible for steel.
Now, for aluminium, the melting point of its oxide (2200 degree celsius) is more than that of the metal itself (600 degree celsius). Also, aluminium is such a metal which is always layered with histiocytoma dog ear aluminium oxide on its surface. So, if aluminium plates are cut by oxy-fuel methods, the oxide layer begins to melt first. This results in increase of thickness of the oxide layer histiocytoma dog ear on the plate, with molten metal in the inside layers. As a result, the entire plate crumbles. So, how are aluminium plates cut? The answer to this lies in the next type of histiocytoma dog ear thermal cutting method discussed below:
• fusion cutting: plasma cutting is a type of fusion cutting which is histiocytoma dog ear used to cut plates for which melting point of the histiocytoma dog ear oxide is less than that of the metal. In plasma cutting a plasma gun shoots a plasma flame histiocytoma dog ear coated with a layer of inert gas, on the region of the plate supposed to be cut histiocytoma dog ear (it is this inert gas layer that prevents the oxidation histiocytoma dog ear of aluminium). The torch is then propagated along the cutting curve to histiocytoma dog ear complete the process. Follow figure 4 for the schematic diagram of plasma cutting.
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