TPT March 2007

Advanced technologies for copper tube production By Dr G Voswinckel, Otto Junker GmbH, Germany

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.

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.

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

106

M arch /A pril 2007