How to Use a Paste Reduction Melting Furnace: A Comprehensive Guide

Think of this as your pre-flight checklist. You wouldn’t hop on a plane without checking the engines, right? Same here—skipping prep steps is a recipe for delays, damage, or worse.

• Safety Gear: This is non-negotiable. You’ll need heat-resistant gloves (the kind that can handle 500°C+), a face shield (not just goggles—sparks fly!), a flame-resistant apron, and steel-toed boots. Oh, and a respirator with a lead-specific filter—lead fumes are no joke.
• Lead Paste: Your “fuel” for the furnace. This should be pre-processed: dried, filtered, and free of debris. Most facilities use a filter press equipment to squeeze out excess moisture and collect clean, dry paste. Aim for a consistency like wet sand—too wet, and it’ll clump; too dry, and it’ll dust everywhere.
• Reduction Agent: Usually carbon (coke or charcoal) or sulfur. This chemical reaction is what turns lead oxide into lead metal. Check your furnace manual for the right ratio—too little, and the reduction won’t complete; too much, and you’ll waste material.
• Tools: A long-handled shovel for feeding paste, a temperature probe (infrared or thermocouple), a ladle for sampling molten lead, and a brush for cleaning spills. Keep a fire extinguisher (Class D, for metal fires) nearby—water makes lead fires worse!
• Equipment Check: Inspect the furnace inside and out. Look for cracks in the refractory lining (the heat-resistant material inside), loose wiring, and blocked vents. The air pollution control system? That’s part of the furnace setup too. Make sure your air pollution control system equipment is running—this could be a scrubber, baghouse, or cyclone to catch fumes and dust. If it’s offline, shut down the operation until it’s fixed.环保局 (environmental protection bureau) inspectors love surprise visits, and a working APC system keeps you compliant.

Heating a furnace from cold to 1,000°C takes time—rushing this step can crack the refractory lining. Here’s how to do it right:

1. Power On: Flip the main switch, then turn on the control panel. The display should light up—if not, check the circuit breaker. Some furnaces have a “preheat” mode; use that first to warm up the elements slowly (think of it like preheating an oven before baking).
2. Set Target Temperature: Most lead paste reduction happens between 900°C and 1,050°C. Enter this into the control panel. Pro tip: Start 100°C lower than your target, then ramp up by 50°C every 15 minutes. Slow and steady wins the race here.
3. Monitor the Lining: Use your infrared thermometer to check the external temperature of the furnace shell. If one spot is significantly hotter than others, there might be a thin spot in the refractory—shut down and inspect before proceeding.
4. Check Gas/Air Flow (If Applicable): If your furnace uses natural gas or propane, verify the gas pressure and air-to-fuel ratio. Too much air, and you’ll waste heat; too little, and you’ll get incomplete combustion (hello, carbon monoxide).

Now that the furnace is up to temp, it’s time to add the lead paste. This isn’t a dump-and-go process—how you feed the paste affects how well it reduces and how much lead you recover.

1. Start Small: Begin with a small batch—about 10% of the furnace’s capacity. This lets you test the temperature stability. If the temp drops more than 50°C after feeding, wait for it to recover before adding more.
2. Mix Paste and Reduction Agent: In a separate container, blend the lead paste with your reduction agent (e.g., 5% coke by weight). Mix thoroughly—imagine making cookie dough; you don’t want clumps of coke hiding in the paste.
3. Feed Evenly: Use a shovel to sprinkle the mixture into the furnace’s charging port. Avoid dumping it all at once—this creates hot spots and can cause splashing. Aim for a steady, thin stream, like shaking salt onto food.
4. Watch the Flame: A healthy reduction reaction will produce a blue or clear flame. If you see thick black smoke, that means unburned carbon—adjust the air flow or slow down feeding. White smoke? That might be lead oxide fumes—check your APC system to make sure it’s capturing them.

How often should you feed? It depends on your furnace size, but a good rule is to add paste every 15–30 minutes. For example, a furnace that holds 500kg might take 2–3 hours to fill with paste, fed in 50kg increments.

Once the furnace is loaded, the real work begins: the reduction reaction. Lead oxide (PbO) reacts with carbon (C) to form lead (Pb) and carbon dioxide (CO₂). This takes time—usually 2–4 hours, depending on the furnace size and temperature.

What should you do during this phase? Monitor, monitor, monitor.

• Check Temperature Every 30 Minutes: Use your probe to measure the melt temperature. It should stay between 950°C and 1,050°C. If it drops, adjust the heat input; if it spikes, check for overfeeding.
• Sample the Melt: Every hour, use a metal ladle to scoop a small amount of molten lead. Let it cool, then break it open. The lead should be shiny and free of gray or black spots (those are unreacted oxide). If you see spots, add a bit more reduction agent and stir gently with a graphite rod.
• Inspect the Slag: Slag is the byproduct—mostly impurities and unreacted material. It floats on top of the molten lead. A good slag is thick and glassy; if it’s runny, there might be too much silica (from battery separators). Skim off slag periodically to prevent it from mixing back into the lead.

After 2–4 hours (or when your sample looks pure), it’s time to “tap” the furnace—i.e., drain the molten lead into molds. This is the moment you’ve been waiting for!

1. Prepare Molds: Line up metal molds (usually iron or steel) on a flat, heat-resistant surface. Coat them with a release agent (like graphite powder) so the lead doesn’t stick. Make sure the molds are clean—grease or dirt will burn into the lead, ruining it.
2. Open the Tap Hole: Use a steel rod to gently tap the clay or refractory plug covering the tap hole. Start slow—you don’t want a sudden gush of lead. Once the hole is open, molten lead will flow out; guide it into the first mold using a ladle or a metal chute.
3. Fill Molds to the Top: Leave a small gap at the top (about 1cm) to account for shrinkage as the lead cools. If a mold overflows, use a dry rag (never wet!) to wipe up spills—molten lead solidifies quickly, so act fast.
4. Close the Tap Hole: When the furnace is empty (or you’ve tapped enough lead), plug the tap hole with fresh refractory clay. Smooth it with a wet hand (wear gloves!) to seal it tightly.

Once the lead ingots cool (this takes 30–60 minutes), they’re ready to be transported to a refinery for further purification—or, if your facility has a lead refinery machine equipment , you can process them on-site!