COLD-ROLLING.Cold-rolling usually refers to
the working of metal at room temperature. In this
operation, the materials that have been hot-rolled to
approximate sizes are pickled to remove any scale, after
which they are passed through chilled finished rolls.
This action gives a smooth surface and also brings the
pieces to accurate dimensions. The principal forms of
cold-rolled stocks are sheets, bars, and rods.
COLD-DRAWING.Cold-drawing is used in
making seamless tubing, wire, streamline tie rods, and
other forms of stock. Wire is made from hot-rolled rods
of various diameters. These rods are pickled in acid to
remove scale, dipped in lime water, and then dried in a
steam room, where they remain until ready for drawing.
The lime coating adhering to the metal serves as a
lubricant during the drawing operation. Figure 1-23
shows the drawing of rod, tubing, and wire.
The size of the rod used for drawing depends upon
the diameter wanted in the finished wire. To reduce the
rod to the desired wire size, it is drawn cold through a
die. One end of the rod is filed or hammered to a point
and slipped through the die opening, where it is gripped
by the jaws of the draw, then pulled through the die. This
series of operations is done by a mechanism known as
the drawbench, as shown in figure 1-23.
To reduce the rod gradually to the desired size, it is
necessary to draw the wire through successively smaller
dies. Because each of these drawings reduces the
ductility of the wire, it must be annealed from time to
time before further drawings can be accomplished.
Although cold-working reduces the ductility, it
increases the tensile strength of the wire enormously.
In making seamless steel aircraft tubing, the tubing
is cold-drawn through a ring-shaped die with a mandrel
or metal bar inside the tubing to support it while the
drawing operations are being performed. This forces the
metal to flow between the die and the mandrel and
affords a means of controlling the wall thickness and the
inside and outside diameters.
and other favorable properties, can be economically
extruded to more intricate shapes and larger sizes than
is practicable with many other metals. Extruded shapes
are produced in very simple as well as extremely
A cylinder of aluminum, for instance, is heated to
750°F to 850°F, and is then forced through the opening
of a die by a hydraulic ram. Many structural parts, such
as stringers, are formed by the extrusion process.
ALLOYING OF METALS
A substance that possesses metallic properties and
is composed of two or more chemical elements, of
which at least one is a metal, is called an alloy. The
metal present in the alloy in the largest proportion is
called the base metal. All other metals and/or
elements added to the alloy are called alloying
elements. The metals are dissolved in each other while
molten, and they do not separate into layers when the
solution solidifies. Practically all the metals used in
aircraft are made up of a number of alloying elements.
Alloying elements, either in small or in large
amounts, may result in a marked change in the properties
of the base metal. For example, pure aluminum is a
relatively soft and weak metal, but by adding small
amounts of other elements such as copper, manganese,
magnesium, and zinc, its strength can be increased many
times. Aluminum containing such other elements
purposely added during manufacture is called an
In addition to increasing the strength, alloying may
change the heat-resistant qualities of a metal, its
corrosion resistance, electrical conductivity, or
magnetic properties. It may cause an increase or
decrease in the degree to which hardening occurs after
cold-working. Alloying may also make possible an
increase or decrease in strength and hardness by heat
treatment. Alloys are of great importance to the aircraft
industry in providing materials with properties that pure
metals alone do not possess.
FERROUS AIRCRAFT METALS
The extrusion process involves the forcing of metal
through an opening in a die, thus causing the metal to
take the shape of the die opening. Some metals such as
lead, tin, and aluminum may be extruded cold; but
generally, metals are heated before the operation is
The principal advantage of the extrusion process is
in its flexibility. Aluminum, because of its workability
A wide variety of materials is required in the repair
of aircraft. This is a result of the varying needs with
respect to strength, weight, durability, and resistance to
deterioration of specific structures or parts. In addition,
the particular shape or form of the material plays an
important role. In selecting materials for aircraft repair,
these factors, plus many others, are considered in
relation to their mechanical and physical properties.