Skip to main content

Jominy Or End Quenching Test

 The Simplest and most reliable of these methods is the Jominy or end quench test. The standard Jominy specimen consists of a cylindrical rod 100 mm long and 25 mm in diameter. In making a test, the specimen is first heated to a suitable  austenitic temperature and held there long enough to uniform austenitic structure. It is then placed in a jig and a stream of water is allowed to strike one end of the specimen. The experimental arrangement is shown in the image. 




The advantage of the Jominy test is that in a single specimen one is able to obtain a range of cooling rates varying from a very rapid water quench at one end to slow air quench at the other end. Following the complete transformation of the austenite in the bar, two shallow flat surfaces are ground on opposite sides of the bar and Rockwell hardness values are taken at 1.5 mm Intervals along the bar. The results of the test are expressed by the hardenability number lc, in which l is the distance from the quenched end to the point with a semi-martensite structure, and c is the hardness value. The measured hardness values may also be plotted against the distance to obtain a hardenability curve. A typical example is shown in the image where it can be seen that the hardness is greatest where the cooling is most rapid - near the quench end. 

After plotting such a curve, a horizontal line may be drawn at the corresponding hardness of the semi - martensite zone for the given steel. The intersection this line with the curve will indicate the length of the hardened zone ( distance from the quenched end ). 


Labels:

Comments

Post a Comment

Popular posts from this blog

SIMPLE CARBURETOR - CONSTRUCTION AND WORKING

CONSTRUCTION OF SIMPLE CARBURETOR :  The main Components of Simple Carburetor are : Float Chamber, float, nozzle, venturi, throttle valve, inlet valve, and metering jet . In the float chamber, a constant level of petrol is maintained by the float and a needle valve.  The float chamber is ventilated to atmosphere.  This is used to maintain atmospheric pressure inside the chamber. The float which is normally a metallic hollow cylinder rises and closes the inlet valve as the fuel level in the float chamber increases to certain level. The mixing chamber contains venturi, nozzle and throttle valve. The venturi tube is fitted with the inlet  manifold. This tube has a narrow opening called venturi. A nozzle is provided just below the centre of this venturi. The nozzle keeps the same level of petrol as that of the level in the float chamber. The mixing chamber has two butterfly valves.  One is to allow air into the mixing chamber known as choke valve. The other is to al...
Post a Comment
Read more

MELTING FURNACES FOR FERROUS METALS : CUPOLA AND ITS WORKING

Various types of melting furnaces are used in different foundry shops, depending upon the quantity of metal to be melted at a time, and the nature of work that is carried out in the shop.  The primary objective in cupola is to produce iron of desired composition, temperature and properties at the required rate in the most economical manner. Besides, this furnace has many distinct advantages over the other types, e.g., simplicity of operation, continuity of production, and increased output coupled with a high degree of efficiency.  Description Of a Cupola : The Cupola Furnace consists of a vertical, cylindrical steel sheet, 6 to 12 mm thick, and lined inside with acid refractory bricks or acid tamping clay. The refractory bricks or the tamping clay used consist of  silicon oxide acid (SiO2) and alumina (Al2O3). The lining is generally thicker in the lower where the temperatures encountered are higher than in the upper region. The shell is mounted either on a brick work fo...
Post a Comment
Read more

Advantages And Disadvantages Of Air Refrigeration System :

 Advantages Of  Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of  Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content. 
Post a Comment
Read more