First Use of Slab Induction Heating
McLouth Steel's decision to cast unusually thick slabs (12 inch) led them to reheat the slabs inductively. The whole setup was difficult to undertake, as well as uneconomical to use. The giant heaters resembled upside-down toasters, and made a loud buzzing sound when in operation.
The nature of the induction heating process is such that heat input to the slab is not restricted to the surface, but actually penetrates into the slab. The depth of penetration is determined by the frequency of the electrical power supply and the metallurgical makeup of the steel.
Although induction heating was well established as an effective and economical process fulfilling many types of heating requirements, it had never been seriously considered for heating anything like the 12" thick by 60" wide by 26' long, 30 ton slabs McLouth wanted to produce. The fact that they wanted over 600 tons of steel heated per hour did nothing to help the situation.
Several induction heating companies were contacted to determine if they would be interested in a project of this magnitude. Just one company expressed interest. Ajax Magnethermic from Warren, Ohio. Ajax informed McLouth that they had a new coil design which would be capable of doing the job. After discussions, McLouth entered into a shared cost, joint development venture with the company to design, build, and test a prototype coil system.
Early in 1965, several small 12" thick slabs of rimmed steel were repetitively heated in a prototype 1,000 kW rectangular coil. The tests proved that cold 12" thick slabs could be heated to rolling temperature in less than one hour.
The next year, McLouth ordered 21 heaters (including three spares) as part of a $105 million program expected to be completed by the summer of 1968. The program expanded the hot metal facilities with a four strand caster and the new induction heaters. Production capacity at the plant was raised from 1,800,000 tons a year to 2,400,000.
A full size computer system was installed to automatically switch heaters on or off as required to rebalance the phase loading and to remove the threat of a 120 KV line outage. Detroit Edison permitted McLouth a maximum phase imbalance of 43 MW's. The computer shut off heaters if a limit was reached and provided printouts of hourly demands, alarms, engineering logs, as well as maintenance logs.
Overall, the system was a novel idea, but really only worked on paper. Auto transformer failures were frequent, as were bus connection failures. When all 18 heaters were running at full capacity, McLouth Steel was Michigan's second largest consumer of electricity (first was the city of Detroit). The environmental impact was very low due to a closed water cooling system and heaters being shut off during non-operating hours.
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