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Soldering

Soldering is a process of joining two metal pieces by means of a low temperature fusible alloy called solder applied in molten state. Solders are alloys of low melting point metals like lead, tin, cadmium and zinc. Of these tin-lead alloys are most common and are called soft-solders. A combination of 62% lead and 38% tin produces the lowest melting point and is called 60–40 solder. This corresponds to the eutectic composition of Pb–Sn series and has a fixed m.p. of 183°C. Increasing tin content produces better wetting and flow qualities. Hard solders are also available and have higher melting points. Before applying solder, the surfaces to be joined are cleaned and a flux like ammonium chloride is used. Then the solder is melted and spread upon one surface, while the other surface is applied to it under pressure. When the solder solidifies, the two pieces get joined. The process of soldering does not call for any joint preparation. A common example of soldering can be seen in joining electrical wires of P.C.B. circuits.

(H.N.Gupta, Manufacturing Processes 2nd Edition; Page:140)

Blow Moulding

This process has been used for making plastic bottles, toys, hollow dolls and

similar other items. The blow moulding begins with a heated tubular piece of plastic, which is called PARISON. The bottom opening of the parison gets pinch closed and sealed as the two piece mould closes. Air is then injected into the parison under pressure (0.7–10 kg/cm2) thereby forcing the plastic to acquire the shape of the mould. The mould is opened and the part formed inside the mould is removed after it has cooled sufficiently. The above process is similar to making articles of glass by blowing air into a mass of molten glass.

(H.N.Gupta, Manufacturing Processes 2nd Edition; Page:171)

Tail Stock

A tailstock is provided at the right hand end of the bed. It can slide along the guide ways provided on the bed and may be brought nearer to the headstock, if so desired. It can then

be clamped or fixed on the bed in that position. The tailstock has a spindle in the upper part of the tailstock, the axis of which coincides with the axis of the headstock spindle, both being at the same height above the bed. This spindle can be moved forwards or backwards by rotating a hand wheel. The front portion of tailstock spindle carries a ‘dead’ or ‘live’ centre. When a long work piece is held in the chuck at the headstock end, it is supported at the tailstock end by moving forward the tailstock spindle. Of course, there has to be a small conical hole in the centre of the work piece, in which the tailstock centre may be inserted to provide support. If the centre (being carried in its own bearings) rotates along with the work piece, it is called a live centre. However, if the tailstock centre remains stationary and work piece alone rotates, the centre is called ‘dead centre’ and the conical tip of centre has to be lubricated with grease to reduce the friction between the tailstock centre and the work piece.

(H.N.Gupta, Manufacturing Processes 2nd Edition; Page:93)

Metrology

Metrology or the science of measurement is a discipline that plays an important role in sustaining modern societies. It deals not only with the measurements that we make in day-to-day living, e.g. at the shop or the petrol station, but also in industry, science and technology. The technological advancement of the present-day world would not have been possible if not for the contribution made by metrologists all over the world to maintain accurate measurement systems. In the modern world metrology plays a vital role to protect the consumer and to ensure that manufactured products conform to prescribed dimensional and quality standards. In many countries the implementation of a metrological system is carried out under three distinct headings or services, namely scientific, industrial and legal metrology. Industrial metrology is mainly concerned with the measurement of length, mass, volume, temperature, pressure, voltage, current and a host of other physical and chemical parameters needed for industrial production and process control. The maintenance of accurate dimensional and other physical parameters of manufactured products to ensure that they conform to prescribed quality standards is another important function carried out by industrial metrology services. Industrial metrology thus plays a vital role in the economic and industrial development of a country. It is often said that the level of industrial development of a country can be judged by the status of its metrology.

(Basic Metrology for ISO 9000 Certification, G.M.S. de Silva; Page:7)