Mechanical tools

Specify rivets The common types of rivets and state their uses Rivets are cylindercal rods having heads of various shapes. Theys are used for assembling the parts of a workpiece together. Specification of a rivet The rivet is specified by the shape of the head diameter, and the length. Shape of head The shape of the rivet head is to be selected according to the intended use of the workpiece to be riveted. Diameter The diameter is to be selected depending on the required strength Length Length is to be selected depending upon the thickness of the components to be riveted Types and uses Snap head It is the most commonly used form, and it gives a very strong joint. Pan head It is used where strength is the only consideration such as heavy structural work . Conical head It is generally used in light assembly where riveting is done by hand hammering. Countersunk head It is used where projection of the rivet head is to be avoided. Bifurcated rivet The shape of the head is shown in the figure...

The different bending tools The uses of twisting and scroll bending The prevention of defects in bending Bending✌👰 Bending is a method of chipless shaping by which the external grain structure is lengthened 👉while the internal grain structure is shortened. Types of bending Bending to curve Bending to an angle BENDING TOOLS Vice or anvil edge An angle bend may be hammering in a vice or over the edge of an anvil. Bending block Bending blocks with lever and pegs are very convenient to use in a smithy. These are massive blocks pierced with holes in which pegs can be inserted. The work to be bent is placed between a series of pegs, already inserted in the holes, and the work is bent with a lever. Tool inserted in a hardle hole Some of the bending tools, like ring, mandrel are inserted in the hole of the anvil for bending the workpieces Beak of the anvil Curving of the workpieces can also be carried out on the beak of the anvil Bending links Bending links with top fullers are used for smal...

  The types of metals used in sheet metsl work The uses of the different types of metals In sheet metal work, different types of metals sheets are used. The sheets are specified by standard gauge munbers. It is very essential to know the different uses and applications of these metal sheets. Black iron The cheapest sheet metal is black iron, which is rolled to the desired thickness. It has a bluish black appearance, and is often referred to as  uncoated sheet. Since it is uncoated, it corrodes rapidly. The use of this metal is limited to articles that are to be painted or enamelled such as tanks, pans, stoves, pipes etc Galvanised iron Zinc -coated iron is known as galvanised iron. This soft iron sheet is popularly known as GI sheet. The zinc coating resists rust, improves the appearance of the metal and permits it to be soldered with greater ease. Because it is coated with zinc, galvanised sheet iron withstands contact with water and exposure of weather. Articles such as pans...

.Name the fuels used in hand forging . qualities of a good forge fire . the correct method of placing stock in fire For heating metals to be forged, different types of fuels are used. Fuels are combustible materials capable of generating heat energy. Forge furnaces are fired with petroleum gas, producer gas, oil, coal and charcoal. For hand forging, the hearths are heated with soild fuels like coal or charcoal with low sulphur content. For heating tools steels charcoal is preferred as the fire burns more evenly when charcoal is used. Heating and metal stock For efficient heating, the way in which the fire is maintained is important. Thr fire which is maintained on the top surface will be thin and not suitable for heating the metal to carry out forging. The fire should come from deep in the hearth. The forge fire should be maintained clean i.e, free from ash, clinkers and dust. Clinkers is formed as the coke burns. This settles down at the bottom of the hearth and solidifies. Accumulati...

. function of a forge . the parts of a forge and state their functions . identify the forge tools and state their uses The forge supplies heat for raising the temparature of the metal to be forged. Parts of a forge and their uses Hearth The hearth is the main part where the heating of the metal takes place. It is prepared with refractory (fire) bricks and clay. Tuyers The forced air is sent through the tuyers to burn the fuel. The tuyer covered with refractory materials to avoid melting. The air also passes through a cooling tank. Cooling tank To keep the tuyer cool always, the cooling tank is filled with cold water. Air valve The air valve is used to regulate the supply of air to the hearth Blower The blower supplies air to the forge for burning the  coal or coke. The blowers are operated manually or by electric Power. The blower is fixed independently to each forge or it supplies ait to a number of forges which are controlled by independent air valves. Hood and chimney Smoke and...

  The necessary of preheating high speed steel The hardening process of high speed steel High speed steels get their name from the fact that they may be operated as cutting tools at much higher speeds than is possible with plain carbon tool steels. Since the maximum hardness of high speed steels is  obtained on tempering at high temparatures, they can be operated as cutting tools in the same temparature range without loss of hardness. That is the rise in temaprature due to friction will not reduce the temper of the tool pointas it cuts into the steel. Tool steels are often annealed for softening before machining or forming, and also for obtaining grain refinement. An nealing Soak at 900° C for about four hours. Then cool slowly at not more than 20°C per hour to 600°C. It may then be cooled to room temparature in still air. Hardening Pre -heat to 850°C slowly to prevent cracking. Then heat rapidly to approximately 1250°C depending upon the alloy used. This rapid heating reduces...

. state the process of case hardening by gas nitriding . state the process of case hardening by nitriding in a salt bath In the nitriding process, the surface is enriched not with carbon, but with nitrogen. There are two systems in common use, gas nitriding and salt bath nitriding. Gas nitriding The gas nitriding process consists of heating the parts at 500°c in a constant circulation of ammonia gas for up to 100 hours. During the gas nitriding process, the parts are in an externally heated gas tight box, fitted with inlet and outlet bores for the ammonia gas which supplies the nitrogen. At the completion of the soaking the ammonia is still circulated untill the temparature of the steel has fallen to about 150°c, when the box is opened, and the cooling completed in air. Nitriding causes a film to be produced on the surface but this can be removed by a light buffing. Nitriding in salt bath Special nitriding baths are used for salt bath nitriding. This process is suitable for all alloyed...

. advantage and disadvantage of hot working metal . advantage and disadvantage of cold working of metal Working on metals This involves the manipulation of metals /materials when in the solid state Examples of working are forming, rolling, forging etc. Working processess can be classified Hot working Cold working  Hot working  Hot working is done at a suitable high temparature so that any damage to the grains is repaired. The temparature required varies from metal to metal. Examples of hot working Forging, rolling, extrusion et Advantage of hot working -hot working is relatively a low cost process -refinement of grain from cast structure is possible. -the scale givea some protection against corrosion during storage. After the process also the product will be in the fully annealed condition, suitable for further cold working. Disadvantage of hot working -poor surface finish is likely -dimensional inaccuracy is possible due to shrinkage on cooling -geometrical accuracy is possib...

. meaning of friction . advantage and disadvantage of friction . different types of friction . methods of reducing friction Friction is the force that offers resistance to relative motion between surfaces in contact. Friction opposes motion irrespective of the direction. When a book is made to slide on the surface of a table from left to right, the force of friction acts on the lower surface of the book towards the left. Advantages Friction plays an important role in our life. Walking would be impossible without friction between the foot and the ground. Unless there is friction, it would not be possible to lean a ladder against a wall, turn the pages of a hook, tie shoelaces etc. Because of friction -rolling motion is possible -sliding motion is possible -gripping effect is possible Disadvantage -reduction in efficiency of machines -wear and tear of all sliding surfaces in contact -unwanted heat generation Types of friction Different types of friction are as follows -Limiting friction ...

. effect of carbon on the mechanical properties of steel. Steel  can be defined as an alloy of carbon and iron, in which carbon is in a combained state. The carbon content is a very important factor to get the desired properties of steel. Carbon Carbon is a very important constituent of steel. The addition of carbon  at varying proportions modifies the characteristics of iron and makes it harder, stronger and of greater use in the engineering industry. Slight variations in the carbon content of steel leads to great differences in the properties of steel. Depending upon the properties they are put to different uses. At room temparature in the annealed condition plain carbon steel contains three main constituents. -ferrite -cementite -pearlite Ferrite is a very weak solid solution of carbon and iron with about 0.006% carbon. This is a very soft and ductile constituent. Pearlite contains alternate layers of ferrite and cementite. This laminated structure makes pearlite stronger. ...

. purpose of heat treatment . purpose of annealing . difference between the processess of annealing and normalising The properties of steel depend upon its composition and its structure. The properties of steel and its structure can be changed by heating it to a particular temparature and then, allowing it to cool at a definite rate. The process of heating and cooling for changing the structure of steel,and thus obtaining the required properties is called ' heat treatment of steel '. If steel is heated to a suitable temaprature, and then, slowly cooled, the steel will be soft, weak and ductile. If steel is heated to a suitable temaprature, and then, rapidly cooled (quenched) the steel will be hard and brittle. Classification of heat treatments The treatments that produce equilibrium conditions are annealing and normalising. Treatments that produce non-equilibrium conditions are hardening and tempering (usually done in conjunction with each other) Annealing In this process, stee...

.   structural changes of plain carbon steel while heating . the structural changes of plain carbon steel in normal cooling Distinguish between the lower and upper critical temparature during heating and cooling. Heating While heating uniformly a piece of plain carbon steel in a furnace, the temparature will increase uniformly and it will be halted or will fall slightly for a short time although the heat is supplied to the steel. At this point, the heat, is being used to  cause a rearrangement of the iron atoms which, in turn,, causes the formation of a solid solution called austenite. The temparature at which austenite is formed is called the lower critical point (heating ) and is at 723°c. If the steel contains less than 0.83% carbon there will be some ferrite present after the above change also. And if it contains more than 0.83% carbon, there will be some cementite present after this change. If the heating is further continued, the ferrite or cementite present will be grad...

. The different methods of identifying ferrous metals and alloys . state how non ferrous metals and alloys are identified A fitter has to handle different types of metals in his  work. A knowledge about how to recognise and differentiate the commonly used metals will help him in many ways. Ferrous metals and alloys can be identified by Their appearance (colour, texture etc,) Their weight (light or heavy ) The sound Cold hammering The spark test (grinding ) Apart from the above tests steel bars are also identified by the code colours painted on them. Different colours are marked, based on the different composition of materials and grade. Colours charts are available to determine the different metals. Most non ferrous metals and alloys can be identified by their colour. copper colour is distinctive red colour Aluminum colour is  dull  white Lead colour is bluish grey colour Tin colour is silvery white, with a slightly yellowish tinge Brass colour is distinctive yellow colou...

The principle of the L. D converter Name the raw materials used for the charge in L.D process👍 L. D. Process The name L.D. is derived from the initials of two towns,LINZ & DONAWITZ in Austria where this process was first used. The L. D. is converter or the basic oxygen converter is designed to produce high quality steel in a relatively shorter time. The basic raw material used in the process are the molten pig iron from the blast furnace and the steel strap. Fluxing agents are used for reacting with impurities and form a slag on the top of the molten metal. In this process of 👍producing steel, a jet of pure oxygen is blown through a lance which is water cooled.The lance is brought near the molten metal and oxygen is blown at high pressure on the molten metal bath. This leads to the oxidation of carbon and other impurities causing violent agitation which allows all the molten metal to come in contact with the oxygen stream. When the blowing is over,the converter is tipped to remov...

.The different manufacturing processes of steel . manufacturing process of steel by the bessemer process . distinguish between acid process and basic process Manufacturing processes The different manufacturing processes of steel -Bessemer process -L. D process -Electric process -Open hearth process Bessemer process Sir Henry Bessemer, a British engineer invented this process of converting molten pig-iron to steel  using a large pear shaped container. This is called the Bessemer converter. It is a method of producing steel by blasting compressed air through molten iron and burning out the excess carbon and other impurities. This does not use any source of heat other than obtained from the oxidising process used to remove carbon and other impurities. The three stages of this process are -the preliminary stage (The slag formation ) -the boil stage (The brilliant flame blowing period) -the finishing stage (The reddish smoke period ) The molten pig iare from the blast furnace is poured ...

  Colouring of metals . methods of colouring by heat .different methods of colouring metals . method of blackening /black oil finishing of metal surfaces Machined or filled ferrous metal  surfaces can be colored by the following methods. Heating and cooling Application of chemicals Colouring by heating Attractive colours can be given to metals by  heating. In this process, the metal surface to be treated is thoroughly polished. The metal is then placed in a heat treatment oven or flame heated. During the heating of the metal, watch the colours as they appear. When the desired colour is seen, remove and quench suddenly in water or oil. Rub gently with steel wool. Black oil finish For blackening the surface of a ferrous metal, first clean the surface thoroughly, and apply a coating of thick lubricating oil. Then heat the metal to 150° to 175° c for about 5 to 8 minutes. This will give a black and rust preventing coating on ferrous metal surfaces. Chemical colouring Polished...

. different angles formed at the cutting edge of tools . the important of clearance and rake angles in metal cutting Metal cutting Knowledge about the principal for metal cutting relating to the various tool angles will assist in carrying out of metal cutting work efficiently. Workpiece are shaped and brought to the required dimension by the use of cutting tools. While cutting materials the following four important elements interact. Cutting tool Tools holding or grinding device Work holding devices, and work Although the metal cutting process involves the combination of the above four elements, everything begins with a cutting tool and its impact at the time of contacting the workpiece. The common metal cutting processes are carried out either by the  use of a single point or multi point cutting tools. Cutting edge are taken as the factors for determining the tool life, surface finish, and the force required for cutting. The important angles of the cutting edge are Clearance angle...