METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 2
j.
Aluminum Bronzes.
The surface is quickly covered with a heavy
scum that tends to mix with the molten metal and is difficult to
remove. Welding of these bronzes is extremely difficult.
k.
Brasses and Bronzes.
True brass contains zinc which gives off
white fumes when melted, while bronzes contain tin that increases
fluidity. Some bronzes contain zinc and will fume, but not as much
as brass.
l.
Copper. Because of the heat-conducting properties of copper, a
larger flame is required to produce fusion than for other metals.
Copper melts suddenly and solidifies instantly.
Copper alloys,
containing small amounts of other metals, melt quicker and solidify
slower.
m.
Lead. Lead melts at a very low temperature and the molten metal
becomes covered with a thin, dull slag.
n.
Magnesium. Magnesium oxidizes rapidly when heated in the air to
its melting point; because of this and as a safety precaution, this
metal is melted in an atmosphere free from oxygen.
When heated in
the open air, it produces an oxide film which is highly refractory
and insoluble in the liquid metal.
o.
Monel Metal. Monel flows clearly without any sparkle.
A heavy
black scale forms on cooling.
p.
White Metal Die Castings.
The melting points are low and the
metal will boil under the torch.
7.
a.
General.
The quality of hardness is a complex one which
detailed study has shown to be a combination of a number of physical
properties. It is most often defined in terms of the method used for
its measurement and usually means the resistance of a substance to
indentation. Hardness may also be defined in terms of resistance to
scratching and, thus, is related to wear resistance.
The word
"hardness" is sometimes used to refer to the stiffness or temper of
wrought products because the indentation hardness of a metal is
closely related to its tensile strength. The cutting characteristic
of metal, when used as a tool, is sometimes called its hardness, but
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