What is cold - working in Manufacturing ?

The working of metals at temperatures below their re-crystallization temperature is defined as cold-working. Sometimes this working temperature is well above room conditions as in cold finishing of hot-rolled products. Most of the cold-working processes, however, are performed at room temperature.

When materials is cold - worked the resulting change in material shape brings about marked changes in the grain structure. The effect of the cold-working on the structure of steel is to distort or elongate the grain in the direction of the flow of metal. Much greater pressures are needed for cold-working than for hot-working. The metal, being in a more rigid state, is not permanently deformed until stress exceeding the elastic limit is passed. Severe stress, known as residual stress is, therefore, set up inside the metal during cold-working. This effect of cold - working is reduced or minimized by heating the metal into the re-crystallization or annealing range, and finally the metal is brought to its original condition. This sequence of repeated cold working and annealing is frequently called the cold work anneal cycle.

It is customary to produce cold-worked products like strip and wire in different tempers, depending upon the degree of cold reduction following the last anneal. The cold-worked condition is described as the annealed (soft) temper, quarter-hard, half-hard, three-quarter hard, full-hard, and spring temper. Each temper condition, indicates a different percentage of cold reduction following the annealing treatment.

Cold-working is employed chiefly as a finishing operation, following the shaping of the metal by hot-working. It also controls the mechanical properties of steel in a large measure. It increases the tensile strength, yield strength and hardness of steel, but lowers its ductility. The increase in hardness resulting from cold-working is described as work-hardening.

In general, cold-working produces the following effects :

1. Internal stresses are set up which remain in the metal unless they are removed by proper heat - treatment.

2. A distortion of the grain structure is created.

3. Strength and hardness of the metal are increased but ductility is decreased.

4. Smooth surface finish is produced.

5. Accurate dimensions of parts can be maintained.

The principal methods of cold-working are as follows :

1. Rolling

2. Forging

3. Drawing

4. Bending

5. Spinning

6. Extruding

7. Squeezing

8. Peening

9. Sizing, coining, hobbing.

Comments

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...

TOP POLLUTION RECORDED IN WORLD

CHERNOBYL NUCLEAR DISASTER (NUCLEAR POLLUTION) : In April 26,1986, the melt down of the Chernobyl nuclear reactor , in Russia, has leaked out the radioactive rays and radioactive materials. Effects : 1. In this Pollution nearly 2000 persons have been killed by the accident. 2. People suffered due to the illness such as, degeneration of the cells, severe bleeding, anemia, skin cancer. 3. Animals, Plants are also affected by nuclear radiation. MINAMATA EPIDEMIC (1953) : MARINE POLLUTION ( CASE STUDY ) Minamata is a small coastal village in Japan. The Chisso Chemical Company , which produces vinyl polymer plastics used organomercurial compound. The industry released its effluent into Minamata sea. The effluent containing mercury ions is converted into methyl mercury, which is highly toxic. The marine organisms like phytoplankton and zoo-planktons easily absorb the toxic methyl mercury compound. These organisms are consumed by small fishes and these are in ...

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...

Mechinopedia For Mechanical Engineers

Search This Blog