Hard-
Surfacing,
Building
Fusion
Welding
Carbon
Welding
Non-Ferrous
Metals
Heating
& Heat
Treating
Braze
Welding
Welding
Cast Iron
Welding
Ferrous
Metals
Brazing
&
Soldering
Equipment
Set-Up
Operation
Equipment
For
OXY-Acet
Structure
of
Steel
Mechanical
Properties
of Metals
Oxygen
&
Acetylene
OXY-Acet
Flame
Physical
Properties
of Metals
How Steels
Are
Classified
Expansion
&
Contraction
Prep
For
Welding
OXY-Acet
Welding
& Cutting
Safety
Practices
Manual
Cutting
Oxygen
Cutting By
Machine
Appendices
Testing
&
Inspecting
2
This chapter will cover what are termed
the physical properties of metal. Chapter 8 will be devoted to the
mechanical properties of metals, with
emphasis on steel. The physical properties of a material are properties not
related to the ability of the material
to withstand external mechanical forces, such as pushing, pulling, twisting,
bending, etc. These properties include
density, melting point, specific heat, heat of fusion, thermal conductivity,
thermal expansion, electrical conductivity,
and corrosion resistance. Density.
The measure of unit mass; in everyday terms, the weight
of a unit volume. Density is variously expressed as
grams per cubic centimeter (g/cm3), kilograms
per cubic meter (kg/m3), pounds per cubic
inch (lb./in.3), pounds
per cubic foot (lb./ft.3).
For comparative purposes, density is often expressed as specific
gravity, the ratio of the density
of the material to the density of water. The specific gravity of aluminum is 2.70
– in other words, it is nearly three
times as heavy as water. Iron has a specific gravity of 7.86; for gold, the value
is 19.3. Melting
Point. Every pure metal has
a specific melting point. If you apply heat to a solid specimen, its temperature
will rise until it reaches that melting
point. It will then start to melt, and it will remain at the melting point
temperature, even though the heating
is continued, until the specimen is completely melted. Then, and only then,
will the temperature of the liquid
metal start to rise once more. The amount of heat required to melt a unit mass
of metal includes
the heat required to raise that mass to its melting point, and the additional
quantity of heat required to
accomplish complete melting once the melting point has been reached.
Melting Point of Alloys.
Most alloys do not melt completely at a specific temperature.
Melting starts when the material
has reached a certain temperature, but is not completed until a somewhat higher
temperature has been reached.
This is a fact of great significance in the welding of steel; we’ll get into
this more deeply in Chapter 10, and
when we get to talk about the practice of welding. Specific
Heat. The amount of heat required to
raise a unit mass of solid metal one degree in temperature is
termed specific
heat. The lighter the metal, the greater the specific heat. In other words,
it takes more heat to raise the
temperature of one kilogram of aluminum one degree than it takes to raise the
temperature of one kilogram of iron
one degree.
