Raw Material Processing: Advances in Spheroidize Annealing of Wire Rod Using 100% Hydrogen0 pages

Raw Material Processing: ttttt
t Advances in Spheroidize Annealing ttt

of Wire Rod Using 100% Hydrogen

by:
Christopher J. Messina
Vice President, Sales & Projects
RAD-CON Inc.
13001 Athens Ave., Ste. 300
Cleveland, OH 44107  USA
www.RAD-CON.com

Over the past decade, advances made in the area of hydrogen
bell-type furnace convection design and atmosphere control
have been merged into a spheroidize annealing system for
cold-heading quality wire that is delivering new levels of quality
consistency and productivity, while reducing running costs.

Less Equipment (a Lot Less) & Higher Quality

One hydrogen bell-type annealing base can do the
spheroidizing of three conventional/nitrogen multi-stack
(20 ton) bases, or eight single-stack (7 ton) bases—and
produce consistently at a higher quality level and a lower
per-ton running cost.

Bells Have Been a Mainstay

For decades, the bell-type furnace (seen in Figure 1) has
been a standard for the heat treatment process of spheroidize
annealing medium-carbon alloy steels for cold-heading quality (CHQ), which is a key step in preparing wire rod for the
fastener manufacturing process. The advantages include a
well controlled convection system leading to product uniformity—of critical importance to the spheroidize annealing
cycle. A sealed inner cover along with a protective atmosphere
of nitrogen inhibits decarburization. The nature of the bell
furnace concept results in efficient use of the furnace chamber
space, resulting in lower atmosphere and fuel consumption.
The furnace can be configured for a single-stack of coils, or
for multiple-stacks under one inner cover.

on the nature of the sealing system, and other process factors,
sometimes an additive gas is employed.

Hydrogen—An Established ttt
Standard in Bell Annealing

For the bell annealing of cold-rolled strip steel, hydrogen
has become the standard protective atmosphere, starting back
in the 1980s. The benefits of hydrogen to this process are welldocumented including shorter cycle times, improved surface
properties, larger charges—all resulting in lower overall operating costs and a smaller facility footprint. The safety systems
from established manufacturers have been well-developed
and have stood the test of time. Today, virtually all new bell
furnaces for steel strip worldwide are hydrogen type.

Using Hydrogen to tttt
Spheroidize Anneal Wire Rod

Very Short Cycle Times. The modern bell-type hydrogen
annealing system shortens the cycle in every segment including oxide reduction, soaking, spheroidizing and cooling.
Closed-loop atmosphere control (e.g., patented RAD-CON
AC/APEx™) uses the hydrogen to minimize the oxide reduction step, in contrast to long dew point holds in conventional
equipment. The soaking is shortened as the convection system drives heat into the charge much faster. Spheroidizing is
shortened due to the tight temperature uniformity throughout
the charge. And removal of the heat from the charge is also
accelerated (see Table 1).
Table 1. Typical Performance Difference.

Fig. 1 — Bell-type batch annealing furnace.

Early bell furnace designs, and conventional ones today,
use nitrogen as the protective atmosphere for annealing wire
rod. The inert nitrogen gas displaces and dilutes O2, CO2, and
H2O to levels that minimize the decarburization of the wire
rod surface—the bane of fastener manufacturing. Depending
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Fastener Technology International/February 2011

Unprecedented Convection. The convection flow of
today’s hydrogen annealing equipment is more than five times
the flow of the advanced systems of the 1980s, and 10 times
some of the conventional nitrogen annealers in use today
throughout the world (see Figure 2). The higher convection
flow along with the properties of hydrogen itself, substantially
increases the rate at which heat is delivered to the charge.
This convection also maintains tight uniformity through
the critical spheroidizing segment. With the temperature differential throughout the charge stabilized at ±5°C (9°F) or
better, the time the furnace must spend in the spheroidizing
segment is vastly reduced. When the uniformity is not so
tight as in the case of a less sophisticated furnace, additional
furnace time must be expended as each part of the disparate
charge passes through the spheroidizing window at differ-