TPT March 2013

Article

Comparison of production costs Plasma offers considerable energy savings compared to the traditional tube furnace. Ion bombardment on the material results in heating being directed to the material, with only minor radiation losses in the heating module. The energy efficiency – which is measured as heat induced in the material vs total power of plasma annealer during normal production – is for plasma annealer between 70% and 85%, subject to application. The energy efficiency of a traditional tube furnace is about half that value. Energy efficiency of a traditional tube annealer drops further in case of under- utilisation and when energy used during lengthy heating up is considered. Energy used for running multiple takeups and payoffs in a multi-line tube furnace also adds to the total cost of energy required to run the annealing plant. This should be taken into account when energy balance is compared for the two alternative annealing processes. Furthermore, the plasma annealer requires up to 80% smaller power connection, which can be a substantial additional cost saving. Replacing a traditional tube furnace with a plasma annealer brings substantial energy related saving. Energy savings will depend on specific application, production patterns, the type of furnace (electrical or gas fired furnace) and of course the price of energy to the producer. The actual energy savings are therefore specific to individual producers and cannot be quantified in general. Plasma annealing consumes noticeably less purging gas than the traditional tube furnace. On one hand this due to fewer lines in operation. On the other hand, further reduction in purging gas consumption comes from the gas being fed to the vacuum system at low pressure. Production that uses expensive purging gas such as hydrogen would record high gas savings by using plasma annealer as an alternative to the traditional tube furnace. The type of purging gas used in plasma annealing depends on application and surface requirements of the finished product. Nitrogen is commonly used in non-ferrous applications. Hydrogen, argon, helium or their mixture can be used on stainless steel applications that require good surface finish. Forming gas can also be used in ferrous applications.

The cooling section is located after the dwell module. A plasma annealer can be equipped with water cooling, gas cooling or a combined system depending on the type of material and surface requirements of the finished material. Plasma annealers are usually supplied with an inbuilt transport system to ensure appropriate speed and tension control of the material in production (see capstans in Figures 2 and 7). The inbuilt transport system is then integrated with the takeup and payoff as necessary. Every plasma annealer is equipped with PLC controls and touch screen HMI (Figure 6). The PLC controls allow computer assisted adjustments to all production parameters for all components of plasma annealer. Individual components of plasma annealer are visualised for user-friendly operation. The controls allow the operator to store production parameters for different products produced on the line. Plasma annealer for production of tubes can be equipped with an inline defect detection system, which records the location and indicates the size of any puncture in a tube wall. The drop in pressure the vacuum system is detected by the PLC and recorded in defect detection database. Plasma annealer vs traditional tube/strand furnace Slow annealing speeds in the traditional tube or strand furnace mean that the annealing of stainless steel or nickel alloys tubes has to be performed in multi-line configurations. Multi-line production requires considerable capital investments in transport systems, payoffs and takeups. Multi- line configuration takes extra floor space and requires more manpower for material manipulation. The material processed on a multi-line furnace also locks-in a significant amount of working capital. The production speed of a plasma annealer can be up to ten times the speed of the traditional tube furnace. This allows for a considerable reduction in the number of lines for the same annealing output. In some cases plasma annealing can run in-line with a drawing machine or a coating process, which can further simplify production and reduce material manipulation.

Figure 7: PlasmaANNEALER for SS tube

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March 2013