Final Report Summary - ALUHEAT (High Efficiency Aluminium Billet Induction Heater)
The 'High Efficiency Aluminium Billet Induction Heater' (ALUHEAT) aimed to develop new technologies based on new materials and novel electromagnetic design. The technology was based on the ability of superconductors to carry direct currents (DC) loss-free and the aim of ALUHEAT was to show how this ability can be combined with novel electromagnetic concepts to fully utilise the potential of the superconductor materials.
Work performed and end results
1. Life cycle analyses
Initially evaluating work of different concepts for billet heating was performed considering both environmental and economical aspects. Environmental life cycle assessments (LCA) of the process of heating aluminium billets show that the new superconducting DC induction heater gives a lower environmental impact than both conventional gas burners and ac induction heaters.
2 Superconductor development
MgB2 superconducting wire manufacturing
Amongst the advantages of MgB2 with respect to other superconductors is the very high flexibility in the selection of the wire configuration, that can be quite drastically adjusted between the flat tape shape to the round/square geometry. For our new induction heater demonstrator, the flat tape shape has been selected, because it maximises the flexibility and handling properties of the conductor, although this partly occurs at the expenses of the transport critical current density.
A reproducible process to manufacture this conductor in very long lengths has been studied and optimised. A regular production of this conductor in unit length of 1.7 km has been established. Because of the specific requirements of ALUHEAT in terms of required conductor (32 lengths of 550-600 meters each), 11 lengths of 1.7 km have been produced for this purpose.
For superconducting wire test and delivery, each length of MgB2 superconducting tape produced for ALUHEAT has been obtained by a highly reproducible route, and individually tested at both ends of the conductor by critical current measurements as a function of temperature and magnetic field.
The fluctuations of the critical current from batch to batch are limited to +/- 10%, which is acceptable for the specific application. In order to test the homogeneity of an entire length of 550 m, the only option has been to directly measure the quench critical current of an individual double pancake. For such purpose, a dedicated measuring system has been operated on a double pancake manufactured at Sintef and shipped to Columbus.
Quench currents of the double pancake wound at Sintef as a function of temperature and peak magnetic field on the winding. Comparing these results with the short sample critical current results, it appears that there is no major degradation of the superconductor due to the winding procedure.
The objective of producing a large amount (greater than 18 km) of MgB2 based superconducting tapes has been achieved. ALUHEAT has become so far the largest device ever developed using MgB2 superconducting material. The homogeneity of the produced material has been verified both by sampling the conductors at their ends, as well as by testing an entire double pancake, both leading to successful results.
3. Cooling technology
The cryosystem includes components such as thermal interface, radiation shield, superinsulation structure, mechanical support, current leads, vacuum vessel and cryocooleers. A stability analysis of the coil was performed. It was simulated that a safe quench can be performed. With the use of a dump resistor the coil can be cooled down faster to the operation temperature after a fault situation.
4. Current source
The overall layout of the DC power supply
The current rating has been upgraded to 300 A in order to be able to handle a superconductor with greater current carrying ability than previously expected. Moreover, a number of features for coil protection during a quench are included.
5. Mechanical design
The entire system consists of the following components:
- machine-bed with axial pressure unit
- turning spindle unit
- opposed spindle unit
- protection tunnel
- workpiece transfer
- workpiece magazine
- machine frame - cryostat storage
- main drive
- cooling unit.
The manufacturing of the mechanical system was not finalised within the project period.
6. Superconducting coil winding
The winding of the superconducting coils are performed in three steps:
- insulating the tape
- winding of double pan-cakes (coils consisting of two layers)
- assembly of the double pan-cakes to two coils.
Post project results
After the project certain activities have continued. One important such activity is the step 3 in the winding process of the coil. Another is testing of the coil. Specifically, the 16 double pan-cakes were stacked on top of each other. Stycast 2850 was used to fix the double pan-cakes to each other and to the cooling interface. The double pan-cakes were then connected in series by soldering the conductor end of one pan-cake to the end of the next. Good joints between the double pan-cakes are crucial to avoid heating.
Tests were performed in advance to secure a reliable soldering technique. A modified soldering iron which applied both heat and pressure to the joint was used. A high enough pressure was essential to squeeze out all the excessive soldering tin at the soldering temperature of 250 300 degrees Celsius. The soldering tin was regular Sn50Pb49Cu1 and this tin was applied to both contact surfaces before melting them together. Voltage taps were soldered to each end of the pan-cakes for measurements of the voltages over the joints and over the pan-cakes.
Project information
The project website is http://www.aluheatproject.com
Work performed and end results
1. Life cycle analyses
Initially evaluating work of different concepts for billet heating was performed considering both environmental and economical aspects. Environmental life cycle assessments (LCA) of the process of heating aluminium billets show that the new superconducting DC induction heater gives a lower environmental impact than both conventional gas burners and ac induction heaters.
2 Superconductor development
MgB2 superconducting wire manufacturing
Amongst the advantages of MgB2 with respect to other superconductors is the very high flexibility in the selection of the wire configuration, that can be quite drastically adjusted between the flat tape shape to the round/square geometry. For our new induction heater demonstrator, the flat tape shape has been selected, because it maximises the flexibility and handling properties of the conductor, although this partly occurs at the expenses of the transport critical current density.
A reproducible process to manufacture this conductor in very long lengths has been studied and optimised. A regular production of this conductor in unit length of 1.7 km has been established. Because of the specific requirements of ALUHEAT in terms of required conductor (32 lengths of 550-600 meters each), 11 lengths of 1.7 km have been produced for this purpose.
For superconducting wire test and delivery, each length of MgB2 superconducting tape produced for ALUHEAT has been obtained by a highly reproducible route, and individually tested at both ends of the conductor by critical current measurements as a function of temperature and magnetic field.
The fluctuations of the critical current from batch to batch are limited to +/- 10%, which is acceptable for the specific application. In order to test the homogeneity of an entire length of 550 m, the only option has been to directly measure the quench critical current of an individual double pancake. For such purpose, a dedicated measuring system has been operated on a double pancake manufactured at Sintef and shipped to Columbus.
Quench currents of the double pancake wound at Sintef as a function of temperature and peak magnetic field on the winding. Comparing these results with the short sample critical current results, it appears that there is no major degradation of the superconductor due to the winding procedure.
The objective of producing a large amount (greater than 18 km) of MgB2 based superconducting tapes has been achieved. ALUHEAT has become so far the largest device ever developed using MgB2 superconducting material. The homogeneity of the produced material has been verified both by sampling the conductors at their ends, as well as by testing an entire double pancake, both leading to successful results.
3. Cooling technology
The cryosystem includes components such as thermal interface, radiation shield, superinsulation structure, mechanical support, current leads, vacuum vessel and cryocooleers. A stability analysis of the coil was performed. It was simulated that a safe quench can be performed. With the use of a dump resistor the coil can be cooled down faster to the operation temperature after a fault situation.
4. Current source
The overall layout of the DC power supply
The current rating has been upgraded to 300 A in order to be able to handle a superconductor with greater current carrying ability than previously expected. Moreover, a number of features for coil protection during a quench are included.
5. Mechanical design
The entire system consists of the following components:
- machine-bed with axial pressure unit
- turning spindle unit
- opposed spindle unit
- protection tunnel
- workpiece transfer
- workpiece magazine
- machine frame - cryostat storage
- main drive
- cooling unit.
The manufacturing of the mechanical system was not finalised within the project period.
6. Superconducting coil winding
The winding of the superconducting coils are performed in three steps:
- insulating the tape
- winding of double pan-cakes (coils consisting of two layers)
- assembly of the double pan-cakes to two coils.
Post project results
After the project certain activities have continued. One important such activity is the step 3 in the winding process of the coil. Another is testing of the coil. Specifically, the 16 double pan-cakes were stacked on top of each other. Stycast 2850 was used to fix the double pan-cakes to each other and to the cooling interface. The double pan-cakes were then connected in series by soldering the conductor end of one pan-cake to the end of the next. Good joints between the double pan-cakes are crucial to avoid heating.
Tests were performed in advance to secure a reliable soldering technique. A modified soldering iron which applied both heat and pressure to the joint was used. A high enough pressure was essential to squeeze out all the excessive soldering tin at the soldering temperature of 250 300 degrees Celsius. The soldering tin was regular Sn50Pb49Cu1 and this tin was applied to both contact surfaces before melting them together. Voltage taps were soldered to each end of the pan-cakes for measurements of the voltages over the joints and over the pan-cakes.
Project information
The project website is http://www.aluheatproject.com
