Introduction to pouring molten metal

Molten Metal

As methods of joining materials pouring molten metal improved through the ages, so did the environment and mode of living for humans. Materials, tools, and machinery improved as civilization developed.

Fastening together the parts of work implements began when an individual
attached a stick to a stone to make a spear or axe. Egyptians used stones to
create temples and pyramids that were fastened together with a gypsum mor
tar. Some walls that still exist depict a space-oriented fi gure that was as ap
propriate then as now— an ibis-headed god named Thoth who protected the
moon and was believed to cruise space in a vessel.

Other types of adhesives were used to join wood and stone in ancient
times. However, it was a long time before the ancients discovered a method
for joining metals. Workers in the Bronze and Iron Ages began to solve the
problems of forming, casting, and alloying metals. Welding metal surfaces
was a problem that long puzzled metalworkers of that period. Early metal
joining methods included forming a sand mold on top of a piece of metal
and casting the desired shape directly on the base metal, so that the two
parts fused together form a single piece of metal,  

Another early
metal-joining method was to place two pieces of metal close together and

 

pour molten metal between them. When the edges of the base metal melted,
the flow of metal was dammed using sand, and the molten metal was allowed
to harden, 
The Industrial Revolution, from 1750 to 1850, introduced a method of
joining pieces of iron together known as forge welding or hammer welding.
This process involved the use of a forge to heat the metal to a soft, plastic
temperature. The ends of the iron pieces were then placed together and hammered until fusion took place.

Forge welding

Forge welding remained the primary welding method until Elihu Thomson, in
1886, developed the resistance welding process. This process produces a weld
at the faying surfaces of a joint by the heat obtained from the resistance to the
flow of welding current through the workpieces from electrodes that serve to
concentrate the welding current and pressure in the weld area. This process provided a more reliable and faster way of joining metal than did previous methods.
As techniques were further developed, riveting was replaced in the United
States and Europe by fusion welding, which melts together filler metal and
base metal, or base metal only, to produce a weld. At that time the welding
process was considered to be vital to military security: Welding repairs to
ships damaged during World War I were carried out in great secrecy. Even
today some aspects of welding are closely guarded secrets.

 

WELDING DEFINED

A weld is defined by the American Welding Society (AWS) as “a localized coalescence (the fusion or growing together of the grain structure of
the materials being welded) of metals or nonmetals produced either by
heating the materials to the required welding temperatures, with or without the application of pressure, or by the application of pressure alone,
and with or without the use of filler materials.” Welding is defined as “a
joining process that produces coalescence of materials by heating them
to the welding temperature, with or without the application of pressure
or by the application of pressure alone, and with or without the use of
filler metal.” In less technical language, a weld is made when separate
pieces of material are joined to form one piece by heating them to a temperature high enough to cause softening or melting and flow together.
Pressure may or may not be used to force the pieces together. In some
cases, pressure alone may be sufficient to force the separate pieces of
material to combine and form one piece. Filler material is added when
needed to form a completed weld in the joint. It is important to note
that the word material is used because today welds can be made from a
growing list of materials, including plastic, glass, and ceramics.

USES OF WELDING

Modern welding techniques are employed in the construction of numerous products. Ships, buildings, bridges, and recreational rides are fabricated using welding processes, to produce the machines that are used to manufacture new products.

Welding has made it possible for airplane manufacturers to meet the
design demands of strength-to-weight ratios for both commercial and
military aircraft.