Mechinopedia For Mechanical Engineers

 When Bronze contains phosphorus, it is called phosphorus bronze. The composition of this metal varies according to weather it is to be forged and wrought or weather made into castings. A common type of  wrought phosphor bronze has copper 93.7, tin 6 , and phosphorus 0.3 per cent. Phosphorus increases the strength, ductility and soundness of castings. The alloy possesses good wearing quality and high elasticity. The metal is resistant to salt water corrosion. It is used for all average bearings in which wearing qualities are desired. Pump parts, linings and propellers are examples of cast manufacture. A variety of phosphor bronze suitable for casting contains 11 percent and 0.3 per cent phosphorus alloyed with copper. This is used for bearings which must carry heavy loads, worm wheels, gears, nuts for machine lead screws, springs and many other purposes. 

BRONZE :   Bronze is an alloy composed mainly of copper and tin. The useful range of composition in 5 to 25 per cent tin and 75 to 95 per cent copper.  The alloy is comparatively hard, resist surface wear and can be cast into shape or rolled into wire, rods and sheets very easily. In corrosion resistant properties bronzes are superior to brasses. It is used in hydraulic fittings, pump linings, in making utensils, bearings, bushes, sheets, rods, wires and many other stamped and drawn articles.    Some of the more common types of bronze and the special purposes for which they are used are given below :  a.) Phosphorus Bronze b.) Silicon Bronze c.) Manganese Bronze  d.) Gun Metal & Bell Metal 

 Babbitt metal is a tin base white metal and it contains 88 per cent tin, 8 per cent antimony and 4 per cent copper. It is soft material with low coefficient of friction and has little strength.   Babbitt metal makes a fine bearing and does not scour the shaft very easily when the lubricant fails. It is the most common bearing metal used with cast iron boxes when the bearings are subjected to high pressure and load. 

 Bearing metals may be classified into the following groups :  1. Copper Base Bearing metals containing copper, tin and lead.  2. Tin-base bearing metals containing tin, antimony and copper.  3. Lead - Base bearing metals containing lead, tin and antimony.  4. Cadmium - Base Bearing metals containing cadmium and nickel.  Those alloys in which tin, lead, and cadmium are predominating elements are designated as white-metal bearing alloys. They have the properties of high plasticity combined with the low hardness and comparatively low melting point, which facilitates the formation of  bearings by casting the metal directly in place and usually require no machining. The copper based alloys are harder and stronger than the white metals and are used for which are required to resist heavier pressures. Tin-base white metals are used where bearings are subjected to high pressure and load, whereas for light roads and pressure lead - base alloys are used. Of the lead base alloys , the alloys whic

Tin is Obtained from tin stone, and oxide by a refining process carried out in a reverberatory furnace. In India, Its sources are quite negligible. It is a brilliant white metal with a yellowish tinge. The melting point of tin is 232*C. Soft, malleable and ductile, It can be rolled into very thin sheets. Tin does not corrode in wet and dry climates, making it useful as a protective coating for Iron and Steel. It is also used for tinning copper wire before the latter is made into cables. 

LEAD : Lead is the heaviest of the common metals. It is extracted from lead ore called galena, which is a sulphide of a lead. India is having very little lead ores. Lead has a blueish - grey color and dull, metallic lustre, but this is lost on exposure to the air, the surface becoming a dull grey.  Lead is very soft, malleable and ductile metal and can be rolled easily. It is resistant to corrosion and many acids have no chemical action on it. Because of  this it is used for water - pipes, roof covering, the sheathing of  electric cables and for construction material of chemical plants. The melting point of lead is 327*C.  ALLOY OF LEAD : Lead Alloyed with tin forms solders and alloyed with other metals makes bearing white metals and type metal. Alloyed with small percentage of arsenic, lead is used to produce shots for munitions.  

COPPER : Copper is easily distinguished from all other metals on account of  its red color. It is not found in pure state under the earth. Copper is extracted for copper ores., the chief being copper pyrites. Copper ore is first ground and then smelted in a reverberatory or small blast furnace producing an impure alloy called matte. In the second step air is blown through the molten metal to remove Sulphur and Iron contamination to obtain blister copper in the converter. In the last stage further refinement is carried out to produce pure copper (99.9 per cent) using electrolysis. For pyrites (CuFeS2) and copper glance (Cu2S) , the roasting / smelting process liberates fumes of Sulphur and arsenic which are mandatory for the smelting unit. In India, copper ore is found at Ghatsila in Bihar. Copper is relatively soft and is very malleable, ductile and flexible, yet very tough and strong. A very efficient conductor of heat and electricity , being second only to silver, it is largely u

ALUMINUM : Aluminum is a white metal produced by electrical processes from the oxide ( alumina ) , which is prepared from a clayey mineral called bauxite. In India they are chiefly available in Bihar, Madhya Pradesh, Karnataka, Maharashtra and Tamil Nadu. It is silvery - white in color and extensively used where a light non corrosive metal is desired as in aircraft and automobile components where the saving of weight is an advantage. In its pure state the metal would be weak and soft for most purposes, but when mixed with small amounts of other metals it becomes hard and rigid. So it may be blanked, formed, drawn, turned, cast, forged, and die-cast. Its good electrical conductivity is an important property and aluminum is used for over head cables. The high resistance to corrosion and its non-toxicity make it a useful metal for cooking utensils ; under ordinary conditions, water and air have practically no effect on it. Since pure aluminum is more corrosion resistant than any alloy of

Non - Ferrous metals are those which do not contain Iron as base. Their melting points are generally lower than that of ferrous metals. Non ferrous metals suffers generally from hot - shortness, poses low strength at high temperature, and their shrinkage is generally more than that of ferrous metals. Non ferrous metals are used for the following reasons : 1. Resistance to corrosion  2. Special electrical and magnetic properties  3. Softness and facility of cold working. 4. Fusibility and ease of casting. 5. Good formability. 6. low density. 7. Attractive Colour. The principal non ferrous metals used in engineering purposes are : Aluminum, Copper, lead, tin , zinc , nickel , etc. and their alloys. 

Cutting alloys are used on tools that operate at very high cutting speeds with high temperatures up to 1000*C to 1100*C developing on the cutting edges. Since they cannot be machined by ordinary methods, they are applied to cutting tools either by means of hard - facing techniques (as a weld deposit or tips brazed to the tool shank or body).  As to the method by which they are produced, cutting alloys are classified as cemented carbides and cast cutting alloys (Stellites). Cemented Carbides : They are made up of powdery mixture of tungsten and titanium carbides and metallic cobalt which is first compacted and then sintered, thus employing the well-known powder metallurgy process. In their finished form cemented carbides consist of extremely fine grains of tungsten and titanium carbides with a cobalt binder. These alloys are extremely hard with Rockwell hardness number up to 85 and even higher and they retain this hardness at temperatures up to 1000*C. The one most widely used grade of

  There are four general types of  High Speed Steel ,   1. 18-4-1 High Speed Steel :   This Steel, containing 18 per cent tungsten , 4 per cent chromium, and 1 per cent vanadium with about 0.75 per cent carbon is considered to be one of the best of all-purpose tool steels. This steel is extensively used for lathe, planer and shaper tools, drills and milling cutters. 2. Cobalt High Speed Steel :  This is known as super high speed steel. Normally cobalt is added from 5 to 8 per cent to increase better hot hardness and wear resistance than 18-4-1 type. One analysis of cobalt high speed steel contains 20 per cent tungsten, 4 per cent chromium, 2 per cent vanadium and 12 per cent cobalt. 3. Vanadium High Speed Steel :  This steel contains 0.70 per cent carbon and more than 1 per cent vanadium. High Vanadium with carbon high speed steel is superior to 18:4:1 type for difficult - to - machine materials. This has excellent abrasive resistance. 4. Molybdenum High-Speed Steel : This Steel contai

  MARTENSITIC STAINLESS STEEL : This group often termed plain chromium types of stainless steel , which contain 10 to 14 per cent chromium and with the old exception , have no other major alloying element. These steels are all harden-able by heat treatment. FERRITE STAINLESS STEEL : This group contains mainly 14 to 18 or 23 to 30 percent chromium again with no other major alloying element. They cannot be hardened by heat treatment. Stainless Steels have great strength and toughness and extremely good resistance to corrosion and heat. The heat resisting properties are increased by the addition of about 3 percent of silicon. They find wide application in the brewery, diary and chemical industries , in making cutlery, all types of surgical and dental instruments, household appliances  such as kitchen utensils, sinks, saucepans, and many others. Considerable amounts of these steels are used for components in power stations, particularly in the field of nuclear power-production because of t

 Austenitic Stainless Steel are probably the most important under this group is that containing 15 to 20 percent chromium and 7 to 10 per cent nickel. A steel containing 18 per cent chromium and 8 per cent nickel is very widely used and is commonly referred to as 18/8 stainless steels. Such a steel may be readily cold - worked so that the hardness and tensile strength are markedly increased and wire may be produced by cold working. Owing to the high ductility , The steel lends itself readily to manipulate and fabrication, and is used extensively for the production of pressings. The steel is readily weldable after welding, it is susceptible to corrosive attack in an arc adjacent to the weld. Additions of molybdenum are made to certain grades to increase their corrosion resistance, whilst others have titanium or niobium added to stabilize the carbon. They cannot be hardened by heat treatment. Austenite in these steels is stable at all service temperatures. Austenite stainless steels are

In service situations where steels must resist high temperatures,. corrosion, shock, etc. special alloy steels are invaluable. The most important groups of special alloy steels are described in the following discussions, MAGNET STEELS : High Cobalt Steel, when correctly heat treated, are frequently used in the making of permanent magnets for magnetos, loud speakers and other electrical machines and instruments. Steels having compositions 15 to 40 percent cobalt 0.4 to 10 per cent tungsten possess improved magnetic properties. HEAT RESISTING STEELS : Heat Resisting steels are those which are particularly suitable for working at high temperatures. Such Steels must resist the influences which lead to the failure of ordinary steels when put to work under high temperature. A steel containing chromium, nickel and tungsten, with the carbon content suitably controlled (developed for the stainless series) provides a useful combination of non-scaling and strength - retaining properties together

 They may be divided into several groups as  1) Stainless Steels  2.) Scale and Heat Resisting Steels. 3.) Wear Resisting Steels. 4.) Magnet Steels. 5.) Steels with Special thermal Properties such as creep resisting steels, etc.  Check this page for detailed description on Special Alloy Steels  

They are employed in tool manufacture in cases when the tool life provide by carbon steels is insufficient.  The tool industry is supplied with : 1. Low alloy steels which retain high hardness at temperatures up to 250*C. 2. Medium and high alloy steels, e.g., high speed steels which retain high hardness at temperatures up to 620*C. They acquire high cutting properties only after suitable heat treatment. Alloy tool steels are smelted in open-hearth and electric furnaces and belong to high quality classes. 

They are divided into three groups : low alloy (up to 5 per cent alloying elements) , medium alloy ( over 5 per cent) and high alloy ( more than 10 per cent).  IS : 7598 - 1974  Alloy structural steels are widely employed in engineering industry for parts that are subject to both static and dynamic loads in operation. They have more favorable set of mechanical properties than carbon steels especially for articles of large cross-section. The alloying elements strengthen the ferrite , which is the chief constituent in the structure of these steels; increase the hardenability , refine the grain size ; and increase the resistance to softening on heating to moderate temperatures. The principal alloying elements in structural steels are chromium, nickel, and manganese. Tungsten, molybdenum, vanadium, and titanium are not usually employed as independent additions, They are added in conjunction with chromium, nickel and manganese. 

 Alloy steel may be classified according to their chemical composition, structural class and purpose. Classification according to chemical composition :  In this aspect alloy steels are divided into three-component steels , containing one alloying element in addition to iron and carbon : four component steels, containing two alloying elements, etc. Classification according to structural class :  On the basis of the structure obtained when specimens of small cross-section are cooled in air and they are classified as : a) pearlite b) martensitic  c) austenitic  d) ferritic  e) carbidic  Classification according to purpose : As to the uses for which their properties fit them alloy steels can be classified : a) Structural steels. b) Tool steels . c) Steels with special physical properties. 

  Alloy steel may be defined as steels to which elements other than carbon are added in sufficient amounts to produce improvements in properties. The most common alloying elements added to steel are chromium, nickel, manganese, silicon, vanadium, molybdenum, tungsten, phosphorus, copper, titanium, zirconium, cobalt, columbium, and aluminum. Each of these elements confers certain qualities upon the steels to which it is added. They may be used separately or in combination to produce desired characteristics in the steel. Like carbon, a number of alloying elements are soluble to produce alloys with improved strength, ductility, and toughness. Also carbon besides forming an intermetallic compound with iron, combines with many alloying elements and form alloy carbides. These alloy carbides as well as iron-alloy carbides are usually hard and lack in toughness. Some alloying elements are added to prevent or restrict grain growth. Aluminum is considered the most effective in this respect. Othe

 In order to select the alloy steel that is best suited for given design, the effects of primary alloying elements must be taken into account. They are :  Nickel provides toughness, corrosion resistance, and deep hardening. Chromium improves corrosion resistance, toughness and hardenability. Manganese deoxidizes , contributes to strength and hardness, decreases the critical cooling rate. Silicon deoxidizes promotes resistance to high temperature oxidation, raises the critical temperature for heat treatment, increases the susceptibility of steel to decarburization and graphitization. Molybdenum promotes hardenability , increases tensile and creep strength at high temperature. Vanadium deoxidizes and promotes fine-grained structure. Copper increases resistance to corrosion and acts as strengthening agent. Aluminum deoxidizes, promotes fine-grained structure, and aids nitriding. Boron increases hardenability.