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LESSON I, PA

ANINTRODUCTION TO METALS

1.1 SOURCE AND MANUFACTURING

Metals come from natural deposits of ore in the earths crust. Most ores are contaminated

with impurities that must be removed by mechanical and chemical means. Metal extracted

from the purified ore is known as primary or virgin metal, and metal that comes from scrap

is called secondary metal. Most mining of metal bearing ores is done by either open pit or

underground methods. The two methods of mining employed are known as selectivein

which small veins or beds of high grade ore are worked, and bulkin which large quantities

of low grade ore are mined to extract a high grade portion.

1.1.0.1 There are two types of ores, ferrous and nonferrous. The term ferrous comes

from the Latin wordferrum

meaning iron, and a ferrous metal is one that has a high iron

content. Nonferrous metals, such as copper and aluminum, are those that contain little or

no iron. There is approximately 20 times the tonnage of iron in the earths crust compared

to all other nonferrous products combined; therefore, it is the most important and widely

used metal.

1.1.0.2 Aluminum, because of its attractive appearance, light weight and strength, is the

next most widely used metal. Commercial aluminum ore, known as bauxite, is a residual

deposit formed at or near the earths surface.

1.1.0.3 Some of the chemical processes that occur during steel making are repeated

during the welding operation and an understanding of welding metallurgy can be gained by

imagining the welding arc as a miniature steel mill.

1.1.0.4 The largest percentage of commercially produced iron comes from the blast

furnace process. A typical blast furnace is a circular shaft approximately 90 to 100 feet in

height with an internal diameter of approximately 28 feet. The steel shell of the furnace is

lined with a refractory material, usually a hard, dense clay firebrick.

1.1.0.5 The iron blast furnace utilizes the chemical reaction between a solid fuel charge

and the resulting rising column of gas in the furnace. The three different materials used for

the charge are ore, flux and coke. The ore consists of iron oxide about four inches in

diameter. The flux is limestone that decomposes into calcium oxide and carbon dioxide.

The lime reacts with impurities in the ore and floats them to the surface in the form of a

slag. Coke, which is primarily carbon, is the ideal fuel for blast furnaces because it

produces carbon monoxide gas, the main agent for reducing iron ore into iron metal.

Lesson 1The Basics of Arc

Welding

Lesson 2Common Electric

Arc WeldingProcesses

Lesson 3Covered Electrodes

for WeldingMild Steels

Lesson 4Covered Electrodes

for Welding LowAlloy Steels

Lesson 5Welding Filler Metalsfor Stainless Steels

Lesson 6Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAW

Lesson 7Flux Cored Arc

Electrodes CarbonLow Alloy Steels

Lesson 8Hardsurfacing

Electrodes

Lesson 9Estimating &

Comparing WeldMetal Costs

Lesson 10Reliability of Welding

Filler Metals

Page 1 of 1Lesson 1 - Basics of Arc Welding

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