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Praxair Technology, Inc. 1998. 70р. This training program describes the arc plasma characteristics and basic properties of shielding gases, as well as their applications in the welding and cutting processes most frequently used by industry today.
E-Book Content
SHIELDING GASES SELECTION MANUAL
TABLE
Chapter
OF
CONTENTS
Topic
Page
▲
Introduction
1
1
Properties of Electric Arcs and Cases
3
Basic Electrical Concepts
3
Physical Properties of Gases
8
2
3
4
Basic Gas Properties
10
Gas Tungsten Arc Welding (GTAW)
13
Process Description
13
Gas Flow Rate
14
Preflow and Postflow
15
Backup Shielding and Trailing Shields
15
Shielding Gases for GTAW
15
Plasma Arc Processes (PAW and PAC)
19
Plasma Arc Welding (PAW)
19
– Process Description
19
– Application of PAW
21
– Shielding Gases for PAW
22
Plasma Arc Cutting (PAC)
24
– Process Description
24
– Gas Flow Rates
27
– Shielding and Cutting Gases for PAC
27
Gas Metal Arc Welding (GMAW)
29
Process Description
29
Metal Transfer Modes in GMAW
30
Metal-Cored Electrodes
34
Shielding Gases for GMAW
35
TABLE
Chapter
5
6
7
8
a-z
OF
CONTENTS
Topic
Page
Flux-Cored Arc Welding (FCAW)
43
Process Description
43
Flux Effects
44
Metal Transfer
44
Shielding Gases for FCAW
45
The Economics of Gas Selection for GMAW
47
Labor and Overhead
47
Effect of Shielding Gas on Welding Speed
48
Effect of Shielding Gas on Duty Cycle and Cleanup
48
Consumable Costs
50
Total Cost of a Shielding Gas
51
Gas Supply
53
Gas Supply Systems
55
Cylinder Storage Systems
55
High Pressure Cylinders
56
Identification of Gases in Cylinders
56
Carbon Dioxide Supply
56
Gas Mixing
57
Pre-Blended Mixtures
57
Bulk Storage Systems
57
Inert Gas Distribution Systems
58
Precautions and Safe Practices
59
Welding and Cutting
59
Shielding Gases
62
Material Safety Data Sheets (MSDS)
63
Glossary
64
INTRODUCTION
▲ Shielding Gases Selection Manual
▲ During any arc welding process, oxygen and
Selection of the most economical shielding
other atmospheric gases can react with the
gas or blend must be based on a knowledge
molten metal, causing defects that weaken the
of the gases available, volume requirements,
weld. The primary function of a shielding gas
their applications, and the overall effect they
is to protect the molten weld metal from
have on the welding process. Praxair’s
atmospheric contamination and the resulting
Shielding Gas Selection Manual describes the
imperfections. In addition to its shielding
arc plasma characteristics and basic properties
function, each gas or gas blend has unique
of shielding gases, as well as their applica-
physical properties that can have a major
t