E-Book Overview
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