3218
.pdfWith 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
(Fig.3.3). |
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X - Form gouging (ffcom both |
sides) |
o f edges |
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made |
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in places accessible for welding from two sides of the |
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wall i f its |
thickness |
is more |
than 15mm(Fig. 3*3*b |
and &)* |
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Craoks, |
ends of |
which do |
not |
go out |
of lim its |
of |
the |
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*
Fig. 3.1. Preparing a defective |
Pig,3.2. A scheme of |
place for weldingi(a)era-
Fig*3*3* Dressing |
a defecting* |
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Fig*3•4•Preparation |
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place for welding* |
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o f a orack before |
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a) |
one-sided |
V-shaped |
fla ty |
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welding* |
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b) |
two-sided |
X-shaped |
fla t, |
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when the wall |
thickness is |
less |
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than 20mm, |
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more than 20mm* |
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o) the same for wall thickness |
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Foundry Department |
"Casting defects |
and |
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Dr.V. Bastrakov |
measures of |
their |
prevention" |
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Oiroction , |
, Direction |
Coaled metal |
of travel ‘ |
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•f travel |
electrode |
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A-C orD -C power
kWeW deposit
VworK
Pig*3*5Carbon-aro welding |
Pig*3*6. Shielded |
arc welding |
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with coated electrode* |
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direction |
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r oftravel |
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Weldino rod |
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Feed |
.automatic |
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feed |
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Carbon |
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tube |
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electrode |
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finished weld |
Welding |
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(slap removed) |
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rod |
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J 9 * " |
Granulated flax |
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Pig*3*7* |
Submerged melt |
ilding Fig*3*6Electro-4olag |
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welding |
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Pig*3*9* Inert-gas-shilded |
Pig*3*10. Gas welding |
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aro welding |
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Foundary Department |
"Casting |
defects |
and |
Dr*V. BastraJkov |
measures |
of their |
prevention" |
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
er , |
tougherf |
and more ductile welds than can be produced |
with |
uncoated |
rods. |
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Coatings |
fu lf ill a uariety of functions. They cont |
ain cellulose-type materials decomposing and protecting
the molten metal of the weld from the bad effects of exp
osure |
to air and stabilizers |
promoting better innization |
in the |
arc and causing it to |
be more stable (titanium |
oxide |
and potassium compounds). |
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.