Billet Heating Furnace

Overview

A billet heating furnace brings metal billets up to the temperature where they can be forged or extruded. Aluminium is heated to roughly 450 degrees C and steel to well over 1,100 degrees C, the point where the metal is soft enough to flow under a press but still solid. The furnace is a long lined chamber fired by gas burners and divided into zones so a billet is warmed gradually as it travels from the cold charge end to the hot discharge end. The Furnace Shell holds the heat, the Burner System supplies it, the Billet Conveyor moves the billets through, and the Recuperator recovers waste heat to raise efficiency. The Charge and Discharge feeds and unloads billets and the Furnace Control keeps every zone on temperature while proving each flame safe.

Shell and lining

The chamber is built like a vacuum flask for heat. A welded Steel Casing carries a hot face of Refractory Lining rated above furnace temperature, behind which a layer of Backup Insulation ceramic fibre cuts the heat that reaches the shell. Billets ride on Hearth Skid skid rails inside. Each end has a lined Furnace Door whose Door Panel is raised by a Door Lift Cylinder and sealed by a Door Seal to limit the cold-air leakage that would waste fuel and chill the load. Good lining is the single biggest factor in fuel use, so it is maintained closely.

Burners and gas supply

Heat comes from the Burner System, a set of Burner units grouped into temperature zones. Each burner mixes fuel and air at its Burner Nozzle, anchors the flame on a refractory Burner Tile, and swirls air through an Air Register for clean, complete burning. Fuel reaches them through the Gas Train: a Gas Filter cleans it, a Gas Regulator holds pressure steady, and a pair of Gas Safety Valve block valves cut fuel instantly on any trip. Every burner has an Ignitor to light it and a Flame Rod to prove the flame, while a Zone Valve trims firing rate per zone so the billet heats on a controlled curve rather than all at once.

Conveying the billets

The Billet Conveyor steps billets through the furnace using a walking-beam motion. A pair of Walking Beam beams, driven by Beam Cylinder cylinders and the Beam Drive, lift the billets off the fixed Skid Rail rails, carry them forward one pitch, and set them down again. The beams then return empty under the billets to repeat the cycle. Walking-beam conveying spaces the billets so flame and hot gas reach all sides, which heats them more evenly than dragging them along a hearth and avoids the scratching a pusher furnace can cause.

Heat recovery and air supply

Flue gas leaves the chamber still very hot, so the Recuperator captures that heat before it is wasted. In its Recuperator Core, held inside the Recuperator Shell, outgoing flue gas warms the incoming combustion air without the two streams mixing, and a Bypass Damper damper protects the core from over-temperature gas. The Combustion Air System system then delivers that preheated air: an Air Blower with its Blower Impeller pushes it through Air Ducting ducting, and Air Damper dampers set the flow so each burner runs at the right air-to-fuel ratio. Preheating the air this way can cut fuel use by a quarter or more, because the burner spends less energy heating cold air.

Exhaust, handling, and control

Spent gas exits through the Flue System. A Flue Duct routes it past the recuperator and out the Exhaust Stack, while a Pressure Damper holds the chamber at a slight positive pressure so cold air cannot leak in around the doors, and a Flue Thermocouple watches efficiency. Billets are moved by the Charge and Discharge unit: a Charge Pusher drives each cold billet in through its Pusher Cylinder, and at the far end the Discharge Table carries the hot billet out, sometimes through a Hot Log Shear that crops it to length, past a Exit Pyrometer that confirms it reached temperature.

The whole furnace runs under the Furnace Control. A Furnace PLC coordinates firing and conveying, a Zone Controller per zone trims each Zone Thermocouple to its setpoint, and the Flame Safety System system supervises every burner so unburned gas can never accumulate. Operators set recipes at the Operator HMI. Because under-heating gives a hard, hard-to-form billet and over-heating ruins the metal structure, the value of the furnace is in holding a tight, even temperature across the load, which is why it sits directly ahead of every forging press and extrusion press in a hot-working plant.