TPT March 2007

With level-wound coils, however, the set temperature cannot be attained inside the coil, as is apparent in the charts. This results in grain size and hardness variations. With the Otto Junker high-convection technology the temperature of the furnace chamber at the end of the annealing cycle is almost identical with the outside and inside coil temperature. This means extremely uniform annealing quality. 3.2 Equipment options Following are three typical designs presented from the multitude of roller hearth system configurations.

› Figure 13 : Longitudinal view of the furnace

› Figure 15 : High convection roller hearth furnace

A high-convection multi-tier roller hearth furnace is used for bright annealing of level wound coils (LWC and pancakes), with a vacuum lock chamber.

of operation the vacuum chamber is not in use. The furnace is then sealed only by the curtains that are lowered in position in the entry and exit lock chambers when this mode of operation is used. For continuous operation of the line all drive sets, in this case thirteen, are equipped with servo motors enabling them to be run together at a slow speed. A high-convection roller hearth furnace is used for bright annealing of level-wound coils, pancakes and straight copper tubes up to 6m long. As you will see from figure 15 this furnace is similar to that of the first example. However, this furnace line has entry and exit vacuum chambers about 6m long. This line can anneal up to 5t/h of copper tube, either straight, pancakes or level-wound coils, with vacuum lock chambers. 3.3 Innovations The Otto Junker Copper Tube Purging (CTP) system with connection to one end of the tube coils This system produces clean, high-quality copper tubes by expelling the lubricant vapours from the tube bore as they form during heat- up in the furnace. This reduces the carbon and lubricant deposits on the inside surface of the heat-treated tube.

The equipment is made up of the following units:

• Loading table • Entry vacuum lock chamber • Entry vestibule • High-convection furnace – indirectly gas-fired or indirectly electrically heated • High-convection cooling zone • Exit vacuum lock chamber • Unloading table • Tray return track with cross conveyor, stacker and destacker • Electrical equipment control and temperature control by PLC • Visualisation and data logging by PC A multi-purpose single-tier high-convection roller hearth furnace is used for the bright annealing of level-wound coils, pancakes and straight copper tubes up to 2.5m long. It has vacuum lock chambers and is up to 6m long in continuous operation. Figure 14 shows a multi-purpose high-convection roller hearth furnace for the bright annealing of level-wound coils, pancakes and straight copper tubes with a throughput capacity of about 2t/h. Design is similar to the furnace just described, with vacuum chamber, furnace and cooling zone and indexing conveyor system. A special feature of this furnace, in addition to the vacuum chamber, is entry and exit lock chambers with curtains for sealing the furnace ends. The curtains are used for annealing of straight tubes exceeding the length of the vacuum chamber. In this mode

€ Figure 14 :

Multi-purpose high-convection roller hearth furnace

€ Figure 16 :

The Otto Junker copper tube purging system

110

M arch /A pril 2007