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With some alloys, changes in the cast structure brought about by boat treatment may be essential to give

them the properties required. Example of such changes are the maileablising of white irons, the annealing of carbon steels, the quenching and tempering of alloy steels and solution treatment followed by quenching and ageing of some light alloys.. However, some white irons, steels and bfconzes

in the as-cast conditions have useful properties.

The design and application of a casting may neaessitate a heat treatment such a.s stabilising or stress re lie f. Subsequent iterations such as machining or surface finishing also may require heat treatment to improve machining and surface properties. With ingots for subsequent working, heat treatment may be necessary to improve the plasticity

of the Blloy and hence the deformation properties of the ingot.

Ara and J Z Z S welding

In repair by these processes the areas to bo welded

are to bo first correspondingly prepared. Those places are gouged pr scarfed upto the sound metal and then carefully

cleaned by grinding, filin g , or chipping. The prepared

edges must not have sharp angles, protuberance, depressions and so on ( fig .3 *l apd 3*2).

'Defect located in the casting one from another on a distance not more than 20 mm are gouged or drilled separt-

oly while the entire gouging of the defective place is used when defects .are located on a nesrbr distance. When the

depth of the defect is more than 4~5mm special hollows or flats with the angle of opening 70-80degress for arc wel­ ding and with the angle of opening 90-100 degress for

gae welding are chieeled out in the place of the defect

casting surface, are gouged and then drilled on the ends (Fig.3*4). The ends of an unthrough crack are drilled tp the depth 2-4mmf while ends of a through crack are drilled to the whole depth wdthja d r ill 6-10mm in diameter.

Broken Off parts of castings are restored by the wel* ding of missing parts out out from rejected castings or cast with the pattern*

place for weldingi(a)era-

Materials that can be welded by this process include most

of the foundry metals (except magnesium). Great cars

must be taken in choosing a welding rod for repair a given casting, often the most desirable welding rod is not the same composition as the base metal.

The electrode for metalware welding may be a bare wi±e, or it may be coated with various materials (Pig.3*6).

Metal-aro welding with coated electrodes accounts for per­ haps 80 per cent of a ll welding construction performed;

nearly a ll welding of steel castings is performed in this mahner. Coated electrodes produce denser, stronger, tough­

ain cellulose-type materials decomposing and protecting

the molten metal of the weld from the bad effects of exp­

Welding rod coatings often contain slag»forming ingradients (titanium oxide, calcium fluoride, and silicon dioxide), deoxidizing elements (ferromanganese and others), and alloying agents(ferromolybdenum, ferrochromium,etc.), in addition to arc stabilizers and cellulose.