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...

. n ame four different types of surface hardening process . the purpose of case hardening . the purpose of carburising . the process of gas carburising Most of the components must have a hard, wear resisting surface supported by a tough, shock resisting core for better service condition and longer life. This combination of different properties can be obtained in single piece of steel by surface hardening. Types of surface hardening Case hardening Nitriding Flame hardening Induction hardening Surface hardening processes can be classified as -processes in which the whole component is heated, Eg. Case hardening and nitriding -processes in which only the surface of the component is heated Eg. Flame hardening and induction hardening Case hardening Parts to be hardened by this process are made from a steel with a carbon content of 0.15% so that they will not respond to direct hardening. The steel is subjected to treatment in which the carbon content of the surface layer is increased to about...

. 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 ...

. the principle of hardening . the effect of the carbon content in hardening . the process of hardening . the tempering of steel . the purpose of temaparing Introduction If a piece of steel is heated to a sufficiently high temparature, all the carbon will be dissolved in the solid iron to form the solid solution, austenite of the steel. When it is slowly cooled, the change in the arrangement of the iron atoms will cause a solid solution can only contain up to 0.006% carbon, and so the excess carbon will be forced to leave the solid solution, and produce cementite. This will, with ferrite, form a laminated structure called pearlite. The principle of hardening If steel is cooled rapidly (quenched ) the excess carbon will not have sufficient time to leave the solid solution with the  result that it will be trapped in the iron, and so cause an internal distortion. This internal distortion is the cause for the increase in the hardness of steel with a corresponding reduction in its stren...

. 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. ...