Mechanical Engineering

9 September 2016

Plain carbon steel is essentially an alloy of iron and carbon which also contains manganese and a variety of residual elements. These residual elements were either present within the raw materials used in the production process e. g. iron ore and scrap steel additions, or they were added in the production process for a specific purpose, e. g. deoxidization by means of silicon or aluminium. Hence they are called residual elements to distinguish them from alloying elements that are deliberately added according to specified minimum amounts.

The term “cleanliness” refers to the amounts of various phases such as oxides, sulphides and silicates that can be present in steel. The smaller the amount of these phases, the cleaner the steel. For many years steels have been produced by casting the molten steel into moulds and allowing it to solidify into ingots which were then processed by rolling etc. steel produced by ingots is subdivided into four categories according to the deoxidization process used. These categories are rimmed, capped, semi-killed and killed steel.

Mechanical Engineering Essay Example

When un-deoxidized steel is cast into an ingot, carbon monoxide is evolved during solidification because the solubility of oxygen decreases as the temperature decreases. 1b) Steels that contain specified amounts of alloying elements, other than carbon and the commonly accepted amounts of manganese, copper, silicon, sulphur and phosphorus are known as alloy steels. Alloying elements are added to change mechanical or physical properties. Alloy steels are melted together in an electric furnace. This step usually involves 8 to 12 hours of intense heat.

Next, the mixture is cast into one of several shapes including blooms, billets and slabs. After various forming steps, the steel is heat treated and then cleaned and polished to give it the desired finish. The semi-finished steel goes through forming operations, beginning with hot rolling, in which the steel is heated and passed through huge rolls. After the steel is formed, most types must go through an annealing step. Annealing is a heat treatment in which the steel is heated and cooled under controlled conditions to relieve internal stresses and soften the metal.

Some steels are heat treated for higher strength. However, heat treatment requires careful control, for even small changes from the recommended temperature, time, or cooling rate can seriously affect the properties. 1c) Plain carbon steel is used in many industries such as in the construction of roads, railways, infrastructures, appliances, and buildings. Carbon steel is used to erect a strong and lasting frame to most modern buildings, steel beams (girders), joists and studs are engineered to create the skeleton of a building.

Steel is also used in a variety of construction materials, such as pipes, tubing, plates, bolts, nails, screws and equipment like tools, bulldozers, cranes etc. 1d) In the construction industry, gears, pipes, beams, w shape beams , boilers, pressure valves and other things are fabricated from alloy steels. By coupling additional elements to the carbon and iron based building metal you can strengthen it to withstand quite a bit more. Alloy steels can be non-magnetic, high-quality, and corrosion-proof.

Furthermore they can be used in highly demanding applications such as commercial steel buildings, turbine blades in jet engines, spacecrafts and nuclear reactors. Stainless steel is the most widely known alloy steel. What distinguishes stainless steel from carbon steels is that it contains a minimum of 10% chromium. As a consequence, stainless steel building metal is resistant to staining, and is rust proof, which makes it perfect for cooking utensils, cutlery, jewelry as well as aircraft parts, architectural components, and surgical implements. 2)

In the production of aluminium, first the ore is mixed with a hot concentrated solution of sodium hydroxide. The NaOH will dissolve the oxides of aluminium and silicon but not other impurities such as iron oxides, which remains insoluble. The insoluble materials are removed by filtration. The solution which now contains the oxides of aluminium and silicon are next treated by bubbling carbon dioxide gas through the solution. Carbon dioxide forms a weak acid solution of carbonic acid which neutralizes the sodium hydroxide from the first treatment.

This neutralization selectively precipitates the aluminium oxide, but leaves the silicates in solution. Again filtration is used for the separation. After this stage the purified aluminium oxide is heated to evaporate the water. The molten mixture is then electrolysed with a very large current and the aluminium ions are reduced to form aluminium metal The physical properties of aluminium make it a perfect material for construction. Its light weight means that the load on the bearing structure is less, and its strength makes it suitable for a great variety of solutions.

Its resistance to corrosion gives it special advantages: aluminium is perfect for regions with severe weather conditions. Finally, its fluidity gives freedom to architects and designers. Aluminium extruded, rolled and cast products are commonly used for window frames and other glazed structures ranging from shop fronts to large roof superstructures for shopping centres and stadiums, for roofing, siding and curtain walling as well as for cast door handles, catches for windows, staircases, heating and air-conditioning systems, power lines and the list goes on. 3)

Plastics are produced using a process called polymerization, where many thousands of monomers are joined together to form a polymer chain. Monomers are made of atoms like chlorine, nitrogen, oxygen, hydrogen and sulphur. Monomers are easily extracted from abundant organic. There are two main types of plastics, thermosetting plastics and thermoplastics. Both are produced by pouring liquid monomers into a mould where they undergo polymerization. Thermosetting plastics are permanent once moulded, they do not deform under heat. Thermoplastics will melt under heat can be reformed repeatedly.

The polymerization process increases the molecular weight of the constituent molecules, turning liquid monomers into solid polymers. (Increase of molecular weight causes the substance to undergo a phase change). During the moulding process, the monomer soup is superheated and condensed under many atmospheres worth of pressure. This causes polymerization to occur and ensures that the plastic is solid and uniform, lacking any internal air bubbles. Specialist plastic and rubber fabrications are used in a wide variety of industries including, civil engineering, medical, aerospace, military, atomic energy, marine and automotive.

Many products are used to contain aggressive chemicals which could be hazardous if not properly controlled. Furthermore the uses and advantages of plastics and rubbers are endless throughout the industries, some examples of these are, sealing, jointing and finishing products, containing applications, bio-degradable applications, hoses, wheels, profiles and consumables. 4a) Welding is a fabrication process that joins materials, usually metals or thermoplastics by causing coalescence.

This is often done by heating the work pieces and adding a material to form a pool of molten material that cools to become a strong joint, but sometimes pressure is used in conjunction with heat or by itself to produce the weld. This is in contrast with soldering and brazing, which involves melting a lower-melting point material between the work pieces to form a bond between them. Many different energy sources can be used for welding, including a gas flame (oxy-acetylene), an electric arc, a laser, an electron beam, friction and ultrasound.

While often an industrial process, welding can be done in man different environments including open air and under water. Welding is generally the simplest, fastest, and most cost-effective method, at least in the case of structural metals. Welding doesn’t require parts to fit exactly. Methods like bolts or screws require some type of flange or overlap of parts, so with welding, weight and material savings can be realized. A high quality weld can often be stronger than the parts to be joined, though this should not be depended on. 4b) Welding, without the proper precautions, can be a dangerous and unhealthy practice.

However, with the use of new technology and proper protection, the risks of injury and death associated with welding can be greatly reduced. Because many common welding procedures involve an open electric arc or flame, the risk of burns is significant. To prevent them, welders wear protective clothing in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat and flames. Additionally, the brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes the inflammation of the cornea and can burn the retinas of the eyes.

Goggles and helmets with dark face plates are worn to prevent this exposure, and in recent years, new helmet models have been produced that feature a face plate that self-darkens upon exposure to high amounts of UV light. To protect bystanders, transparent welding curtains often surround the welding area. These curtains, made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.

Welders are also often exposed to dangerous gases and particulate matter. Processes like flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides. The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, many processes produce various gases, most commonly carbon dioxide and ozone, and fumes that can prove dangerous if ventilation is inadequate.

Furthermore, because the use of compressed gases and flames in many welding processes pose an explosion and fire risk, some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace. 4d) Pipe Cutters A tubing or pipe cutter is a hand tool specifically designed to cut pipe. It works by clamping onto a portion of the pipe and cutting through it using a small, round blade. As the tool is rotated it tightens, causing the blade to slowly dig into the pipe, eventually sawing all the way through.

Tubing and pipe cutters are easy to use and provide a straight cut and edge to weld. Pipe Clamps For clamping pipelines on the outside whilst welding is taking place on straight sections, pipeline flanges or bends. Various types of external pipe clamps are suited to different applications. Chain clamps are extremely versatile for holding pipes up to 54″ suitable for elbows, tees, flanges, end caps and most other pipe fittings. Ratchet Line-up cage clamps are very strong and accurate, but are also lightweight with either ‘standard’ flat cross bars or ‘no tack’ arched cross bars.

External Hydraulic (no tack) Line-up cage clamps lines up pipe for welding to enable the maximum weld to be made without moving the clamp and comes with hand toggle or powerful hydraulic for accurate alignment. JA Type Mechanical Pipe Clamps allow efficient preparation of welding, whilst allowing easy handling but at the same time optimized working security, ensuring safety and peace of mind. 5a) Stress is the internal resistance, or counterforce, of a material to the distorting effects of an external force or load.

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