Furnace with multiple electric induction heating sections particularly for use in galvanizing line

A method for heating ferrous workpieces, said method including the steps of:

• feeding discrete ferrous workpieces in an end-to-end relation to form a continuous supply of ferrous workpieces, some of said ferrous workpieces having heating rates differing from workpiece to workpiece for heating to a predetermined desired furnace discharge temperature;
• continuously heating said ferrous workpieces in sequential first, second, third and fourth furnace sections;
• controlling said second furnace and said fourth furnace section to heat said ferrous workpieces at discrete and substantially constant heating rates;
• rapidly adjusting a heating rate by said first furnace section according to said differing required heating rates to continually discharge said continuous supply of ferrous workpieces from said second heating furnace at a predetermined required discharge temperature;
• and
• rapidly adjusting a heating rate by said third furnace section according to said differing required heating rates to continually discharge said continuous supply of ferrous workpieces from said fourth heating furnace at a predetermined required discharge temperature.

A method for supplying heated ferrous workpieces for galvanizing, said method including the steps of:

• providing sequential first, second, third and fourth furnace sections having separate furnace controls for heating lengths of elongated ferrous workpieces passed in succession in an end to end relation in each furnace section, said first and third furnace sections each having at least one inductor coil pair for heating said ferrous workpieces;
• controlling each of said second and fourth furnace sections to provide substantially constant furnace operating temperatures for heating a length of said ferrous workpieces when resident therein;
• controlling current applied to the electrical inductor coil pair of said first furnace section to provide a substantially constant exit temperature for said ferrous workpieces at the exit of said second furnace section;
• controlling current applied to the electrical inductor coil pair of said third furnace section to provide a substantially constant exit temperature for said ferrous workpieces at the exit of said fourth furnace section, the control of the current applied to the electrical inductor coil pair of said third furnace section being variable from an in phase relation for the applied current to the coil pair at temperatures above the Curie temperature and an out of phase relation for applied current to the coil pair at temperatures below the Curie temperature to heat said ferrous workpieces independently of the Curie temperature;
• and
• cooling the ferrous workpieces discharged from said fourth furnace section to a predetermined temperature for the application of galvanizing.

A method for annealing ferrous workpieces for galvanizing, said method including the steps of:

• providing sequential first, second, third and fourth furnace sections having separate furnace controls for heating lengths of elongated ferrous workpieces passed in succession in an end to end relation in each furnace section, said first and third furnace sections each having at least one inductor coil pair for heating said ferrous workpieces;
• controlling each of said second and fourth furnace sections to provide substantially constant furnace operating temperatures for heating a length of said ferrous workpieces when resident therein;
• controlling current applied to the electrical inductor coil pair of said first furnace section to provide a substantially constant exit temperature for said ferrous workpieces at the exit of said second furnace section;
• controlling current applied to the electrical inductor coil pair of said third furnace section to provide a substantially constant exit temperature for heating said ferrous workpieces to a temperature sufficient to effect annealing of the workpieces after heating by said fourth furnace section, the control of the current applied to the electrical inductor coil pair of said third furnace section being variable from an in phase relation for the applied current to the coil pair at temperatures above the Curie temperature and an out of phase relation for applied current to the coil pair at temperatures below the Curie temperature to heat said ferrous workpieces independently of the Curie temperature;
• controlling said fourth furnace section to provide substantially constant furnace operating temperature for annealing said ferrous workpieces at a predetermined temperature;
• and
• cooling the ferrous workpieces discharged from said fourth furnace section for application of galvanizing metal.

A furnace for heating ferrous metal workpieces, said furnace including the combination of:

• a plurality of pairs of sequential furnace sections for heating ferrous workpieces arranged in an end to end relation to form a continuous supply of workpieces, some of said workpieces requiring heating rates differing from workpiece to workpiece for heating to a desired furnace discharge temperature, each pair of furnace sections including:
• a first adjustable furnace controller to control a first of the sequentially occurring pair of furnace sections for heating a preselected one of said workpieces at a heating rate different from a heating rate for another said workpieces forming said continuous supply of workpieces for discharge at correspondingly different workpiece temperatures;
• and
• a second furnace heating control a second of the sequentially occurring pair of furnace sections for maintaining a furnace operating temperature sufficiently constant to further heat said workpieces to a predetermined required temperature for discharge therefrom.