Mechanical tools

. 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. ...

. 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...