1 Heat Treatment & Protective Coating

Report No: 01 Shop:Heat Treatment & Protective Coating

Title: Study & Observation the Heat Treatment & Protective Coating Shop.

Heat Treatment Shop: •

Heat Treatment

Heat treatment is a term used in the industry to describe a process whereby the physical properties of a metal may be charged by subjecting it to heat. There are two principal reasons for heat-treating steel: one is to harden it and the other is to soften it. Metals can be of two types: alloy steel/tool steel and mild steel. •

Alloy steel

Alloy steels are those which contain, in addition to carbon and iron, some alloying elements, such as chromium, vanadium, nickel, molybdenum or tungsten, which give them some particular characteristics not possessed by ordinary steel. Alloys are put into steels for the following reasons: to secure greater hardness, toughness or strength, to enable the steel to hold its size and shape during hardening, or to enable the steel to retain its hardness at high temperatures. Alloy steel is hardened directly in oil or air. •

Mild steel

Mild steel is hardened in oil, water or air after carburizing. Preparation for carburizing: 1) Charcoal – 58% 2) Barium carbonate – 15% 3) Sodium – 2% 4) Treacle – As required 5) Coal – 25% For heat treatment many types of gas and furnace are used. Functions-Carburizing is its function. Temperature of carburizing varies from 950 to 1000 0C), the temperature of hardening is from 150 to 550 0C, the temperature of annealing is 600 – 650 0C, and also normalizing is performed. Page-1

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Different types of machine and furnace-

1) Electric Super Heating Furnace -1 (Function: hardening) 2) Salt Bath Muffle Gas Fire Furnace (Liquid)-1 (Function: Carburizing and hardening) 3) Rock Well Hardness Tester Machine-3 (Function: Hardness measurement) 4) Heat Air Electrical Circulating Tempering Furnace -1 (Function: Tempering) 5) Grinding Wheel Machine-1 (Function: Testing the sparking of a material) •

Operations involved in the heat treatment of steel-

Normalizing, annealing, quenching, tempering, strain drawing, cyaniding, carburizing and nitriding. Normalizing- Normalizing is the uniform heating of steel above the usual hardening temperatures followed by cooling freely in air. Application: This treatment is used to put steel back in a normal condition after forging or after an improper heat treatment. Annealing- Annealing is accomplished by heating the steel slowly above the usual hardening temperature, keeping it at that heat for ½ to 2 hr followed by a slow cooling, preferably in a furnace. Application: This operation is for the purpose of softening a piece of work that is too hard to machine or because it is necessary to machine a job that has been hardened. Annealing is also done to relieve internal strains in a piece of steel that have been set up in it by extensive machining. Quenching- Quenching is the operation of cooling a heated piece of work rapidly by dipping it in water, brine or oil. Tempering- Tempering is a process whereby a certain degree of hardness is sacrificed, to reduce brittleness and to increase the toughness of a steel tool. Page-2

Carburizing Carburizing is another method of giving a hardened case to a piece of steel. The piece of work is placed in a metal box containing a mixture of bone, leather, charcoal, and other carburizing materials. The lid is scaled with fire clay and the box is placed in a furnace for some hours at a temperature of 1700 0F. The depth to which the carbon penetrates the steel depends upon the length of time the work is left in the furnace. After the steel is removed from the furnace and it is cooled to room temperature, it can be normalized by reheating at 1500 to 1560 0F and allowed to cool in air. It can then be hardened by inserting it into a furnace or a lead pot, heating it to the required temperature, and quenching it in the same manner as other high carbon steel, but only the part that absorbed carbon will become hard. The inside which did not absorb the carbon will remain soft. Nitriding Nitriding is a method of putting an extremely hard surface on a piece of steel. The process consists of exposing the steel to hot ammonia gas for some hours. The ammonia breaks down into nitrogen and hydrogen because of the heat, and the nitrogen reacts with the steel to form a nitrite case around the steel.

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Protecting Coating Shop: Electroplating The coating that is given on a particular type of any metallic substance with the help of electricity by submerging it in a solution made of various chemicals is called electroplating. For this, rectifier, diaramo and registance board is required, by which volt and ampire can be controlled. Purpose:- Usually it is seen that if any ferrous machine parts is kept within any types of coating, grease or oil, it can be damaged within a few days. Thus, brass, bronze etc. get affected. So, by giving electroplating not only the beauty of many valuable job is increased but also it remains intact for a long time. So, it is very necessary to give electroplating or any type of coating. Types of plating :1) Cu plating – Copper cyanide is used. 2) Zn plating – Zinc cyanide is used. 3) Ni plating - Nickel salt (nickel sulphate, nickel chloride and boric acid) Procedure It should be observed that if small rust is found then the job should be kept in acid solution (Na (HCl) + H2SO4 : H2O) for about 10-12 minutes, If it becomes necessary then the time can be increased. Hen the job should be cleaned with the help of crush wheel. If no rust is found then the job should not be kept in acid solution. For grinding on a job with deep scratch the grinding wheel with no. 90 emery shirize is used. But for light scratch the grinding wheel with no. 120 emery shirize should be sufficient. At the time of grinding, it should be observed that the shape of the job is not changed at all. Hen buffing is performed in a buffing machine. The buffing machine consists of motor and wheel. In a buffing wheel two chemicals are used – Hifire and Laster. Laster removes scratch and Hifer increases brightness of the job. The r.p.m. of the buffing machine is 2780. The degreasing is performed after applying chalk powder on it. After degreasing, it should be washed in pure water. Then it should be dipped in an acid solution (HCl : H 2O = 1:5) for only 2 seconds. Then it should be cleaned in water perfectly and Cu plating is performed

Page-4 in a Cu tank. This coating increases the life time of a job and any other coating especially Ni coating can form on it perfectly after Cu plating. But for Zn, hard crom plating is not necessary. Finally, it should be dipped in bright crom solution which is only applicable for Zn or Ni plating. Ni plating - Actually Ni plating is used for any fancy type of job. Hard Cr plating – This plating is very long lasting, but not glossy. Chemical filter machine There is a chemical filter machine in heat treatment and protective coating shop of BITAC. It is used for purifying the chemical solution (Zn solution, Ni solution, hard Cr solution, etc.) of different tanks.

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