Wire Technology

Process Engineering and Metallurgy

Roger N. Wright

• Publisher: Butterworth-Heinemann
• Year: 2016
• eBook ISBN: 9780128026786
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Wire Technology: Process Engineering and Metallurgy, Second Edition, covers new developments in high-speed equipment and the drawing of ultra-high strength steels, along with new computer-based design and analysis software and techniques, including Finite Element Analysis. In addition, the author shares his design and risk prediction calculations, as well as several new case studies. New and extended sections cover measurement and instrumentation, die temperature and cooling, multiwire drawing, and high strength steel wire. Coverage of process economics has been greatly enhanced, including an exploration of product yields and cost analysis, as has the coverage of sustainability aspects such as energy use and recycling. As with the first edition, questions and problems are included at the end of each chapter to reinforce key concepts. - Written by an internationally-recognized specialist in wire drawing with extensive academic and industry experience - Provides real-world examples, problems, and case studies that allow engineers to easily apply the theory to their workplace, thus improving productivity and process efficiency - Covers both ferrous and non-ferrous metals in one volume

Chapter 1

The General Idea

Abstract

The concept of drawing addressed in this book involves pulling a wire, rod, or bar workpiece (to be generally referred to as “wire”) through a die to decrease cross-sectional area and increase length. The combination of the pulling force and the pressure force from the die allows the wire to be plastically thinned and stretched without the wire breaking downstream from the die. In addition to the die, held in a die block, a basic drawing operation involves a payoff to deliver the wire and a take-up to accumulate the drawn wire. Also necessary is a system for applying lubricant to the wire before it enters the die.

A drawing operation must have a method for pointing the wire. Pointing involves reducing the “front” end diameter of the wire sufficiently to allow it to be initially passed through the die and gripped en route to initial winding onto the take-up.

Keywords

Drawing; Wire/rod/bar; Die; Lubricant; Pulling force; Pressure force; Reduction; Pointing

Contents

1.1 Concepts 1

1.1.1 Drawing 1

1.1.2 Wire, Rod, and Bar 1

1.1.3 Materials 2

1.2 How Does Drawing Work? 2

1.2.1 Why Not Simply Stretch the Wire, Rod, or Bar? 2

1.2.2 A Simple Explanation of the Drawing Process 3

1.2.3 Comparison to Other Processes 4

1.2.4 Overall Process Hardware 5

1.3 Questions and Problems 6

1.1 Concepts

1.1.1 Drawing

The concept of drawing addressed in this book involves pulling wire, rod, or bar through a die or converging channel to decrease cross-sectional area and increase length. In the majority of cases, the cross section is circular, although noncircular cross sections may be drawn and/or created by drawing. In comparison to rolling, drawing offers much better dimensional control, lower capital equipment cost, and extension to small cross sections. In comparison to extrusion, drawing offers continuous processing, lower capital equipment cost, and extension to small cross sections.

1.1.2 Wire, Rod, and Bar

In general, the analyses of wire, rod, and bar drawing are similar, and we may use the term workpiece, or simply the term “wire,” when there is no distinction to be drawn. However, there are major practical and commercial issues to be addressed among these terms. Bar drawing usually involves stock that is too large in cross section to be coiled and hence must be drawn straight. Round bar stock may be 1-10 cm in diameter or even larger. Prior to drawing, bar stock may have been cast, rolled, extruded, or swaged (rotary cold forged). Rod drawing involves stock that may be coiled, and hence may be delivered to the die from a coil, and taken up as a coil, on a block or capstan. Round rod stock will often have a 0.3-1-cm diameter and will often have been cast and/or rolled prior to drawing. Wire drawing involves stock that can be easily coiled and subjected to sequential or tandem drawing operations with as many as a dozen or more draws occurring with a given drawing machine. Each drawing operation or “pass” will involve delivery of the wire to the die from a coil on a capstan, passage through the die, and take-up on a capstan that pulls the wire through the die. Fine wire drawing typically refers to round wire with a diameter of less than 0.1 mm, and ultra-fine wire drawing typically refers to round wire as fine as 0.01 mm in diameter.

1.1.3 Materials

Essentially any reasonably deformable material can be drawn, and the general analysis is the same regardless of the wire, rod, or bar material. The individual technologies for the major commercial materials, however, involve many nuances. The drawing technologies are often divided into ferrous (steel) and nonferrous and electrical (usually copper and aluminum), although there is specialty production and research and development interest in such high-value-added products as thermocouple wire, precious metal wire, biomedical wire, wire for high temperature service, superconducting wire, and so on.

Apart from the material drawn, drawing technology depends substantially on the materials used for dies (“carbide,” diamond, tool steel) and on the materials or formulations used for lubricants and coatings.

1.2 How Does Drawing Work?

1.2.1 Why Not Simply Stretch the Wire, Rod, or Bar?

It can be argued, at least in principle, that some of the objectives of drawing could be achieved by simply stretching the wire with a pulling force. The cross section could be reduced and elongation accomplished, but dies would not be needed and the friction and metal flow issues presented by the die could be avoided.

The principal problem with just stretching the wire with a pulling force is the necking phenomenon. Basically, after a certain amount of uniform stretching, all further elongation will be concentrated at a single location (a neck), which will rapidly thin and break. This occurs because the decrease in cross-sectional area eventually weakens the wire more than any strengthening that occurs by work hardening. Heavily drawn wire will have little or no work-hardening capability and will neck almost at once if subjected to simple stretching. Although some complex “dieless” drawing systems have been invented, simple stretching has only limited application because of its vulnerability to necking.

1.2.2 A Simple Explanation of the Drawing Process

In the drawing process, a pulling force and a pressure force, from the die, combine to cause the wire to extend and reduce in cross-sectional area, while passing through the die, as schematically illustrated in Figure 1.1. Because of this combined effect, the pulling force or drawing force can be less than the force that would cause the wire to stretch, neck, and break downstream from the die. On the other hand, if a reduction too large in cross-sectional area is attempted at the die, the drawing force may break the wire. In commercial practice, engineered pulling loads are rarely above 60% of the as-drawn strength, and the area reduction in a single drawing pass is rarely above 30% or 35% and is often much lower. A particularly common reduction in nonferrous drawing is the American Wire Gage (AWG) number or about 20.7%. Many drawing passes are needed to achieve large overall reducti...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface
• About the Author
• Chapter 1: The General Idea
• Chapter 2: A Brief History of Technology
• Chapter 3: Twentieth Century Equipment Concepts
• Chapter 4: Basic Engineering Variables Pertinent to Drawing
• Chapter 5: Basic Drawing Mechanics
• Chapter 6: Drawing Temperature
• Chapter 7: Drawing Speed
• Chapter 8: Friction, Lubrication, and Surface Quality
• Chapter 9: Drawing Die and Pass Schedule Design
• Chapter 10: Shaped Dies and Roller Dies
• Chapter 11: Mechanical Properties of Wire and Related Testing
• Chapter 12: Drawability and Breaks
• Chapter 13: Relevant Aspects of Copper and Copper Alloy Metallurgy
• Chapter 14: Relevant Aspects of Carbon and Low-Alloy Steel Metallurgy
• Chapter 15: Other Metallurgical Systems for Wire Technology
• Chapter 16: Wire Coatings
• Chapter 17: Redraw Rod Production
• Chapter 18: Wire Forming
• Chapter 19: Physical Properties
• Chapter 20: Current and Near-Term Developments
• References
• List of Symbols
• Selected Formulae
• Index