Tilting Rotary Melting Furnace

Overview

A tilting rotary melting furnace is a horizontal refractory-lined barrel that rotates about its axis while a burner fires into one end. It is the workhorse of secondary non-ferrous melting, used to recover aluminium, lead, zinc and copper alloys from scrap, dross, swarf and skimmings that a static furnace would handle poorly. The rotation constantly tumbles the charge so every piece passes through the hottest zone, and it folds salt flux through the melt to strip oxides and trapped metal off dirty feedstock. Because the whole furnace tilts, the same machine charges through its front mouth, melts with the drum horizontal, and pours by rotating the Tilting Cradle forward.

The design centres on a few heavy subsystems. The Rotating Drum and Lining holds and tumbles the charge. The Oxy-Fuel Burner supplies the heat. The Rotation Drive turns the drum, the Tilting Cradle swings it for charging and tapping, and the Fume Extraction System captures the dust and gases that secondary metal melting produces in quantity.

How a rotary furnace melts

Scrap and salt flux are loaded through the Charge and Pour Door into the lined drum. The Oxy-Fuel Burner fires down the axis of the drum and heats the lining and the charge. As the drum slowly rotates at one to four revolutions per minute, the lining picks up heat on the upswing and gives it back to the cold metal on the downswing, so the refractory acts as a rotating heat store. This regenerative tumbling is far more efficient at heating loose, low-density scrap than radiating onto a static bath. Salt flux melts into a molten cover that wets the oxide skins, coalesces small droplets and floats the dross clear, which is why rotary furnaces achieve recovery rates of 90 to 98 percent on aluminium scrap that a reverberatory furnace would lose to oxidation.

Drum and lining

The Drum Shell is a welded steel cylinder carrying a monolithic Drum Refractory Lining of high-alumina or magnesia refractory. Two machined Riding Ring bands around the shell run on four hardened Support Roller units that carry the full weight of drum, lining and melt. A pair of Thrust Roller units bears against a riding ring face to stop the drum walking along its axis as it tilts. The lining sees both thermal shock from each charge and chemical attack from molten salt, so it is the main consumable and is patched or replaced on a regular campaign cycle.

Burner and combustion

The Burner Nozzle mixes fuel gas and oxygen and injects a high-temperature flame through a refractory Burner Quarl set in the drum end wall. Oxy-fuel firing replaces combustion air with near-pure oxygen, which removes the nitrogen that would otherwise carry heat out the stack, so flame temperature and fuel efficiency both rise and exhaust volume falls sharply. A Flame Scanner proves the flame and a spark Burner Igniter lights it under control of the burner management system. The Fuel and Oxygen Skid regulates and meters both fuel and oxygen, with a Ratio Control Valve holding the correct fuel to oxygen proportion across the firing range and a Safety Shutoff Valve pair isolating fuel on any trip.

Rotation and tilting

The Rotation Drive uses a variable-speed Drive Motor through a Helical Gearbox to a Drive Pinion that meshes with the Girth Gear ringing the drum. A Rotation VFD sets speed: slow for gentle melting, faster to wash flux through the bath, and reverse-creep for controlled pouring. The entire rotating assembly sits in a Tilt Cradle that tilts on two Tilt Pivot Bearing bearings, driven by two Tilt Cylinder units from the Hydraulic Power Pack. Tilting back opens the mouth for charging, tilting forward up to 110 degrees pours metal through the Pour Spout and then drains the salt slag separately.

Fume extraction and emissions

Secondary metal melting releases dust, salt fume and combustion products, so the Fume Extraction System is integral rather than optional. A swing Fume Hood sits over the drum mouth and an induced-draught Induced-Draught Fan pulls the gas stream through a Cyclone Separator for coarse dust, a Gas Quench Cooler to drop gas temperature, and a fabric Baghouse Filter that brings outlet particulate below 10 milligrams per cubic metre. Captured salt-bearing dust is collected for treatment or disposal under hazardous waste rules.

Operation and applications

A melting campaign runs as a batch cycle: charge, close the door, fire and rotate until molten, hold to homogenise alloy and flux, then tilt and tap metal and slag in turn. The Control Panel sequences the burner, rotation and tilt and logs temperatures from the drum and exhaust thermocouples. These furnaces dominate the aluminium recycling industry, lead-acid battery smelting, brass and bronze recovery and zinc reclamation, wherever the feedstock is dirty, mixed or low grade and high metal recovery from each charge is the economic driver.