Walking Beam Reheat Furnace

Overview

A walking beam reheat furnace heats steel slabs to rolling temperature, around 1,200 degrees C, just before a hot rolling mill. Its name comes from how it moves the stock: instead of dragging slabs along the hearth or pushing them in a packed line, it carries them on beams that walk. The beams lift the slabs, step them forward, set them down on fixed supports, then return empty underneath to repeat the cycle. Because each slab is lifted clear and spaced apart, hot gas reaches all four sides and the underside is heated almost as well as the top, which gives a more even slab than older pusher or rotary-hearth furnaces. The Furnace Shell forms the chamber, the Walking Beam Mechanism does the walking, the Burner System supplies the heat, the Skid Cooling System keeps the supports from melting, and the Furnace Control tracks every slab and holds each zone on temperature.

Shell and lining

The furnace is a long lined tunnel. A Steel Structure of columns and buckstays carries the suspended Furnace Roof and the Refractory Lining hot face, with Fibre Module ceramic fibre behind it to cut shell heat loss and lower stored heat for faster startups. At the cold end a Charge Door admits slabs and at the hot end a Discharge Door lets them out, each a Door Panel raised by a Door Cylinder. Lining quality sets fuel use and the maximum temperature the furnace can hold.

The walking beam mechanism

The Walking Beam Mechanism is what defines the furnace. Slabs rest on rows of Fixed Beam beams. Between them run Moving Beam beams carried on a Lift Frame and a Traverse Frame. A cycle has four motions: Lift Cylinder cylinders raise the moving beams to lift the slabs off the fixed beams, Traverse Cylinder cylinders advance them one pitch, the lift lowers them back onto the fixed beams further along, and the traverse returns the empty beams. This rectangular path, guided by Linear Guide Rail rails, walks every slab forward by one step without sliding it, so the underside is never scuffed and the slabs keep their spacing.

Burners and heating zones

The Burner System is split into zones along the length: a cool preheat zone near the charge end, a hot heating zone in the middle, and a soaking zone at the discharge end where the slab core catches up to its surface. Roof Burner burners fire down on the slab tops and Side Burner burners fire along their length, each through a Burner Nozzle anchored on a Burner Tile. Fuel arrives through the Gas Train with its Gas Safety Valve block valves and Gas Regulator, a Zone Valve sets firing rate per zone, and a Flame Rod proves each flame. Splitting the furnace into zones lets a slab heat slowly at first to avoid cracking, then quickly, then soak to an even temperature throughout.

Skid cooling and heat recovery

The beams and supports inside run red-hot, so they are water-cooled. The Skid Cooling System circulates water through Skid Pipe rails wrapped in Skid Insulation to limit heat loss, driven by Cooling Pump pumps and cooled in a Cooling Tower. The trade-off is the skid mark, a cooler stripe where each slab touches the cooled rail, which the soaking zone and beam spacing are designed to even out. Waste heat is recovered by the Recuperator: its Recuperator Core preheats the air that the Air Blower feeds to the burners, with a Bypass Damper guarding it from over-temperature gas.

Handling, exhaust, and control

The Charge and Discharge unit moves the stock in and out. A Charge Roller Table table feeds cold slabs to the Charging Machine, and at the hot end an Extractor lifts each finished slab onto the Discharge Roller Table table bound for the mill, past Pyrometer sensors that confirm temperature. Flue gas leaves through the Flue System: a Flue Duct routes it past the recuperator to the Stack, and a Pressure Damper holds the chamber slightly positive so cold air cannot leak in.

Coordinating all of this is the Furnace Control. A Furnace PLC runs firing and beam motion, while a Level-2 Server holds a thermal model that predicts each slab core temperature as it travels, so the furnace can vary firing to deliver slabs at the exact temperature the mill needs even when the line slows or stops. A Zone Controller per zone trims each Zone Thermocouple to setpoint, the Flame Safety System system supervises the burners, and operators work from the Operator HMI. Because reheating is one of the largest energy users in a steel plant and uneven slabs cause rolling defects, the value of the walking beam design is in even heating with controlled energy use, which is why it is the standard reheat furnace ahead of modern hot strip and plate mills.