Grate bars (also called furnace bars or grid bars) are critical components in sintering machines, incinerators, boilers and other high-temperature equipment, requiring properties such as heat resistance, wear resistance and corrosion resistance. The manufacturing process primarily involves material selection, casting/forging, heat treatment, machining and surface treatment. Below is the typical production workflow:

1. Material Selection

Grate bars are typically made from high-alloy heat-resistant steel or special stainless steel. Common materials include:

• Heat-resistant cast steel: ZG40Cr25Ni20 (HK40), ZG35Cr24Ni7SiN (resistant above 1100°C)
• Stainless steel: 310S (0Cr25Ni20), 309S
• High-chromium cast iron: Cr28, Cr30 (for high-wear environments)
• Nickel-based alloys: Inconel 600/625 (for extreme high-temperature corrosion)

Selection criteria: Based on operating temperature (800-1300°C), oxidation/sulfidation levels, and mechanical loads (compression/impact resistance).

2. Key Manufacturing Processes

(1) Casting Process

Used for complex shapes or mass production:

• Sand casting: Cost-effective for small batches
• Investment casting: High dimensional accuracy, smooth surfaces
• Centrifugal casting: For tubular/symmetric structures (dense microstructure)

Process flow:

Raw material melting (electric/medium frequency furnace) → Pouring → Cooling → Demolding → Sand removal → Gate cutting → Initial inspection

(2) Forging Process

For grate bars requiring high mechanical properties:

• Open die forging: Simple shapes
• Closed die forging: High precision for mass production

Process flow:

Blank preparation → Heating (~1200°C) → Forging → Slow cooling → Rough machining

(3) Heat Treatment

• Annealing: Stress relief, improved machinability
• Quenching & Tempering: Enhanced hardness/wear resistance (e.g., HRC50+ for high-Cr iron)
• Solution treatment: For austenitic stainless steels (e.g., 310S)

(4) Machining

• Turning/milling: For mounting holes/sealing surfaces
• Drilling: Ventilation/fastening holes
• Grinding: Surface finishing (Ra≤3.2μm)

(5) Surface Treatment

• Shot blasting: Improved fatigue resistance
• Aluminizing/chromizing: Enhanced oxidation resistance
• Hardfacing: Wear-resistant coatings (Stellite/tungsten carbide)

3. Quality Control

• Chemical analysis (spectrometry): Verifying alloy composition
• Mechanical testing: Hardness (HB/HRC), tensile strength (≥500MPa), impact toughness
• NDT: X-ray (internal defects), magnetic particle inspection (surface flaws)
• High-temperature simulation: Testing oxidation rate/deformation

4. Application-Specific Processes

5. Industry Trends

• Composite materials: Ceramic-reinforced metal matrix composites (MMCs)
• 3D printing: Complex geometry integration, reduced welding defects
• Smart casting: CAE-optimized pouring systems for lower rejection rates
•