FIBROUS STRUCTURE OF FORGINGS : GRAIN-FLOW

In forging, metal flows similar to the flow of sand-cement mortar while being squeezed. Forging causes the grain flow and randomly dispersed small inclusions and segregations found in cast metal to become elongated in same direction as the metal is caused to flow. If a forged part is cut in a plane aligned with the direction and the surface is ground smooth and then immersed in an acid solution the exposed metal will appear to naked eye to have a fiber-like structure. These fibers are non-metallic inclusions or segregated phases that are elongated or "flowed" in the direction of working. Grain-flow, fiber structure, flow lines and forging fibers are terms used to describe this effect. The grain-flow of forged part resembles in many ways the grain of wood. Like wood, the strength and toughness of this metal is greatest in the direction of the fiber. In the directions at right angles to these fibers , the strength is normally no greater than that found in dense, sound casting.

If, on forging, the grain-flow is in a direction parallel to the principal grain-flow it is said to flow in its correct fiber direction, and if otherwise, it is said to flow in its incorrect fiber direction.

The effect of these flow-lines is to produce marked directional properties in steel. For static load, the directions of these flow-lines are not so important, but these are important on parts where shock and fatigue are encountered, The ductility and resistance to impact of the metal as less in a direction at right angles to the flow-lines than parallel with them. Special care is, therefore, taken in the making of forgings for gears, crankshafts or other highly stressed parts to have the metal flow in the most favorable direction in all portions of the forgings. It is common practice for purchasers of forgings to specify the desired directions for - the fiber-flow lines to meet the stresses expected under actual service conditions.

Comments

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...

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...

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The objec...

Mechinopedia For Mechanical Engineers

Live chat

Search This Blog