Oxy-Acetylene Welding and Cutting | Page 5

a fairly good
electrical conductor, being better than iron or steel. It is nearly three
times as heavy as steel and its tensile strength is 25,000 pounds per
square inch.
ALLOYS
An alloy is formed by the union of a metal with some other material,
either metal or non-metallic, this union being composed of two or more
elements and usually brought about by heating the substances together
until they melt and unite. Metals are alloyed with materials which have

been found to give to the metal certain characteristics which are desired
according to the use the metal will be put to.
The alloys of metals are, almost without exception, more important
from an industrial standpoint than the metals themselves. There are
innumerable possible combinations, the most useful of which are here
classed under the head of the principal metal entering into their
composition.
_Steel._--Steel may be alloyed with almost any of the metals or
elements, the combinations that have proven valuable numbering more
than a score. The principal ones are given in alphabetical order, as
follows:
Aluminum is added to steel in very small amounts for the purpose of
preventing blow holes in castings.
Boron increases the density and toughness of the metal.
Bronze, added by alloying copper, tin and iron, is used for gun metal.
Carbon has already been considered under the head of steel in the
section devoted to the metals. Carbon, while increasing the strength and
hardness, decreases the ease of forging and bending and decreases the
magnetism and electrical conductivity. High carbon steel can be welded
only with difficulty. When the percentage of carbon is low, the steel is
called "low carbon" or "mild" steel. This is used for rods and shafts,
and called "machine" steel. When the carbon percentage is high, the
steel is called "high carbon" steel, and it is used in the shop as tool steel.
One-tenth per cent of carbon gives steel a tensile strength of 50,000 to
65,000 pounds per square inch; two-tenths per cent gives from 60,000
to 80,000; four-tenths per cent gives 70,000 to 100,000, and six-tenths
per cent gives 90,000 to 120,000.
Chromium forms chrome steel, and with the further addition of nickel
is called chrome nickel steel. This increases the hardness to a high
degree and adds strength without much decrease in ductility. Chrome
steels are used for high-speed cutting tools, armor plate, files, springs,

safes, dies, etc.
Manganese has been mentioned under Steel. Its alloy is much used for
high-speed cutting tools, the steel hardening when cooled in the air and
being called self-hardening.
Molybdenum is used to increase the hardness to a high degree and
makes the steel suitable for high-speed cutting and gives it
self-hardening properties.
Nickel, with which is often combined chromium, increases the strength,
springiness and toughness and helps to prevent corrosion.
Silicon has already been described. It suits the metal for use in
high-speed tools.
Silver added to steel has many of the properties of nickel.
Tungsten increases the hardness without making the steel brittle. This
makes the steel well suited for gas engine valves as it resists corrosion
and pitting. Chromium and manganese are often used in combination
with tungsten when high-speed cutting tools are made.
Vanadium as an alloy increases the elastic limit, making the steel
stronger, tougher and harder. It also makes the steel able to stand much
bending and vibration.
_Copper._--The principal copper alloys include brass, bronze, german
silver and gun metal.
Brass is composed of approximately one-third zinc and two-thirds
copper. It is used for bearings and bushings where the speeds are slow
and the loads rather heavy for the bearing size. It also finds use in
washers, collars and forms of brackets where the metal should be
non-magnetic, also for many highly finished parts.
Brass is about one-third as good an electrical conductor as copper, is
slightly heavier than steel and has a tensile strength of 15,000 pounds

when cast and about 75,000 to 100,000 pounds when drawn into wire.
Bronze is composed of copper and tin in various proportions, according
to the use to which it is to be put. There will always be from six-tenths
to nine-tenths of copper in the mixture. Bronze is used for bearings,
bushings, thrust washers, brackets and gear wheels. It is heavier than
steel, about 1/15 as good an electrical conductor as pure copper and has
a tensile strength of 30,000 to 60,000 pounds.
Aluminum bronze, composed of copper, zinc and aluminum has high
tensile strength combined with ductility and is used for parts requiring
this combination.
Bearing bronze is a variable material, its composition and proportion
depending on the maker and the use for which it is designed. It usually
contains from 75 to 85 per cent of copper combined with one or more
elements, such as tin, zinc, antimony