108 / 116
106
M
arch
/A
pril
2007
Advanced technologies for copper
tube production
By Dr G Voswinckel, Otto Junker GmbH, Germany
1. Introduction
Innovative equipment developments are required to address the
ever-increasing demands for high quality copper tubes. The main
requirements for the production process of these tubes are tighter
manufacturing tolerances and better process safety, together
with the reduction of energy and personnel costs. For the tube
production, alternative technologies have been developed for
different copper tube applications, eg for installation of tubing or
tubes for air conditioners and refrigeration (ACR).
Solid billets can be made by continuous casting, and then extruded
into tubes and brought up to their final dimensions by cold-rolling
or drawing. Alternatively, hollow bar can be instantly achieved
through continuous casting and rolled and drawn to the requisite
tube dimensions. Figure 1 shows an overview of these different
technologies.
›
Figure 1
:
Process technologies
Regardless of which technology is adopted for the production of
seamless copper tube, there are always thermal processes at the
start and end of the process chain. Copper melting and pouring
marks the start of the cycle, which is completed by heat treatment
of the net-shape tubes.
The melting and pouring steps at the start of the manufacturing
process irreversibly determine the material quality with regard
to analysis accuracy and purity, while recrystallization annealing
firmly sets the mechanical properties of the tube. This shows the
importance of the thermal processes.
The following text describes the advanced equipment solutions used
for these process steps today, ie for inductive melting and pouring
of the metal and the heat treatment of copper tubes in roller-hearth
furnaces.
2. Induction melting and pouring
The technical and economical advantages offered by induction
melting and pouring furnaces have made them more in demand.
Induction heating allows for an accurate temperature regime and
process control, low firing losses and precisely controllable bath
movement. In the past couple of decades induction furnaces have
become increasingly popular. As compared to fuel-fired furnaces,
their main advantages are:
• The direct heating of the load (no overheating)
• The exact temperature regime
• The precisely controllable bath movement resulting in low fire
losses
• Being friendly to the environment and working conditions
regarding heat, dust and noise
Last but not least, the induction furnace stands out because of
its extremely neutral metallurgical behaviour. Induction heating
enables an efficient and high-quality melting control and process
automation. These advantages have been extended further with
the transition from the traditional mains-frequency technology to the
digitally controlled medium-frequency technology.
The diverse technologies and design options for induction melting,
in conjunction with the basic process advantages of induction
furnace systems, ensure the availability of optimum solutions for
various process technology requirements.
2.1 Melting: coreless or channel-type furnace?
The two basic principles of induction furnace technology, ie melting
by a coreless or channel-type furnace, both constitute viable
alternatives in copper melting. Nevertheless, depending on the
technological requirements and process objective, one or the other
furnace type is preferable. In a channel-type unit, the inductor(s)
can be fitted to the bottom and/or to the sides of the furnace. This
gives virtually unlimited options in furnace vessel design, in addition
to outstanding compatibility with siphon solutions.
In
particular,
the
significant
energy
savings achieved by
channel-type furnaces
in copper melting
environments (almost
100kWh/t compared
to a coreless furnace),
have made them an
important competitor
in this field.
›
Figure 2
:
Channel-type furnace