Weld Overlay Repair of Sintering Machine Toothed Rollers and Grate Plates
Sintering machines are critical equipment in iron and steel production, where toothed rollers (gear rollers) and grate plates (bar grates) serve as the primary wear components responsible for conveying and compacting the sinter mix. These components operate under extreme conditions of thermal cycling, abrasive wear, and mechanical impact, leading to progressive material degradation and eventual failure. Weld overlay repair of these components represents a specialized, high-value technical capability that extends equipment service life, reduces downtime, and delivers significant cost savings compared to full replacement.
1. Definition and Principles
1.1 Component Description
Sintering machine toothed rollers are heavy-duty cylindrical rollers with machined teeth or grooves along their circumference, designed to grip and advance the sinter grate through the sintering bed. Grate plates (also referred to as bar grates or grate bars) are the perforated structural plates that form the moving surface of the sintering machine, supporting the sintering mixture while allowing air flow through the bed for combustion and solidification. Both components experience severe multi-modal degradation including abrasive wear from iron ore fines, thermal fatigue from contact with hot sinter cake (temperatures reaching 900–1200°C), and mechanical impact from material loading.
1.2 Weld Overlay Repair Principle
Weld overlay repair involves the deposition of specialized hardfacing alloys onto worn or damaged surfaces of toothed rollers and grate plates to restore dimensional integrity and provide enhanced resistance to the operating environment. The fundamental principle relies on creating a metallurgically sound bond between the base material (typically low-carbon steel or cast iron) and the overlay layer through controlled heat input, ensuring a dilution ratio that maintains the desired microstructure and hardness of the deposited alloy. The overlay material is selected to resist the specific wear mechanisms encountered in sintering operations, including:
- Abrasive wear: Caused by continuous sliding contact with iron ore fines and limestone particles
- Thermal shock and fatigue: Resulting from repeated heating and cooling cycles during sintering
- Impact wear: From material loading and mechanical forces during operation
- Corrosive wear: From molten slag and hot gas contact in the sintering bed
1.3 Metallurgical Mechanisms
The effectiveness of weld overlay repair depends on achieving proper microstructural characteristics in the overlay layer. Hardfacing alloys typically contain high concentrations of carbide-forming elements (Cr, Mo, V, W) that produce dispersed carbide particles providing hardness and wear resistance. The dilution zone between the base metal and overlay must be carefully controlled to prevent softening of the overlay or excessive hardness in the transition zone, which could lead to cracking. Post-weld heat treatment may be applied to relieve residual stresses and optimize the carbide distribution within the overlay layer.
2. Category and Business Positioning
2.1 Technology Classification
Weld overlay repair of sintering machine toothed rollers and grate plates falls within the MIG/TIG Weld Overlay technology route of Cladding Technology Shanxi Co., Ltd. This positions the capability within the company's core service offering of surface engineering solutions for heavy industry equipment. The technology bridges the gap between routine maintenance welding and specialized cladding fabrication, targeting components that require both dimensional restoration and surface property enhancement.
2.2 Business Value Proposition
- Cost reduction: Repair and overlay of worn components typically costs 30–60% less than purchasing new replacement parts, particularly for large-diameter toothed rollers where fabrication costs are substantial
- Downtime minimization: In-situ or rapid-turnaround repair programs reduce unplanned production stoppages in continuous sintering operations
- Performance enhancement: Overlay alloys can provide superior wear resistance compared to the original base material, extending service intervals beyond the original design life
- Sustainability: Component reuse through overlay repair reduces material consumption, energy use in new part fabrication, and industrial waste
2.3 Market Positioning
This capability addresses a critical pain point in the sintering segment of the iron and steel industry, where toothed rollers and grate plates are among the highest-frequency replacement items. The ability to deliver technically qualified overlay repair with documented WPS (Welding Procedure Specification) and PQR (Procedure Qualification Record) provides customers with a reliable, standards-compliant alternative to full component replacement.
3. Technical Purpose and Value
3.1 Primary Technical Objectives
- Dimensional restoration: Rebuild worn tooth profiles and grate plate surfaces to original or improved geometry, ensuring proper material handling and sinter bed integrity
- Wear resistance enhancement: Deposit hardfacing alloys with hardness typically in the range of HRC 50–65, providing 2–5 times the service life of the original material
- Thermal fatigue resistance: Select overlay alloys with appropriate thermal conductivity and thermal expansion coefficients to minimize cracking during thermal cycling
- Mechanical integrity: Ensure sound weld bonds with no defects that could propagate under operational loading
3.2 Quantitative Value Metrics
| Parameter | Original Component | After Overlay Repair | Improvement |
|---|---|---|---|
| Surface Hardness | HRC 25–35 (base steel) | HRC 50–65 (overlay) | 1.5–2.0× increase |
| Service Life (abrasive wear) | Baseline | 3–5× baseline | 200–400% extension |
| Replacement Frequency | Every 6–12 months | Every 24–48 months | 50–75% reduction |
| Cost per Service Cycle | 100% (new part) | 35–60% (repair) | 40–65% savings |
| Production Downtime | Full roller/grate change | On-site or rapid repair | 60–80% reduction |
4. Key Process and Implementation Points
4.1 Surface Preparation
Proper surface preparation is the foundation of successful weld overlay repair. The following steps are mandatory:
- Inspection and assessment: Measure remaining wall thickness, assess base material condition, identify cracks or structural defects using magnetic particle inspection (MPI) or ultrasonic testing (UT)
- Mechanical preparation: Grind away loose oxide scale, rust, and severely worn material to expose sound base metal; create a weldable edge profile at the transition between worn and intact areas
- Thermal conditioning: Preheat the component according to the base material's carbon equivalent and thickness to prevent cold cracking; typical preheat temperatures range from 150–300°C for low-carbon steel components
- Cleanliness verification: Ensure the weld zone is free of oil, grease, moisture, and other contaminants that could cause porosity or hydrogen-induced cracking
4.2 Weld Overlay Process Parameters
The following table summarizes typical parameters for MIG and TIG weld overlay of hardfacing alloys on toothed rollers and grate plates:
| Parameter | TIG Overlay (GTAW) | MIG Overlay (GMAW) | Notes |
|---|---|---|---|
| Welding Current | 80–180 A | 150–350 A | Dependent on wire diameter and layer thickness |
| Welding Voltage | 14–22 V | 22–32 V | Short-circuiting transfer for MIG |
| Travel Speed | 50–120 mm/min | 150–400 mm/min | Controlled for consistent bead profile |
| Shielding Gas | Ar 100% or Ar + 2% O₂ | Ar + 5–10% CO₂ | Argon for TIG; mixed gas for MIG |
| Wire Diameter | 1.6–3.2 mm | 1.2–2.4 mm | Hardfacing wire per ASTM A5 |
| Interpass Temperature | ≤ 250°C | ≤ 300°C | Prevent grain coarsening and cracking |
| Preheat Temperature | 150–250°C | 200–300°C | Based on carbon equivalent of base |
| Number of Layers | 2–5 layers | 2–4 layers | Multi-pass for dimensional build-up |
| Post-Weld Treatment | Controlled cooling or PWHT | Controlled cooling or PWHT | Relieve residual stress |
4.3 Overlay Material Selection
The selection of hardfacing alloy is critical and must be matched to the specific wear mechanism and operating conditions:
| Alloy Type | Typical Composition | Hardness (HRC) | Primary Application | Standards Reference |
|---|---|---|---|---|
| High-Carbon Chromium | Cr 20–30%, C 2.5–4.5% | 55–62 | Severe abrasive wear, toothed rollers | ASTM A5 Class 3 |
| Medium-Carbon Chromium | Cr 10–20%, C 1.5–2.5% | 50–58 | Moderate abrasive wear, grate plates | ASTM A5 Class 2 |
| Stellite (Co-Cr) | Cr 24–30%, Co balance, Mo 5–8% | 42–50 | High-temperature wear, thermal cycling | ASTM A5 Class 7 |
| Iron-Based with Mo-W | Cr 6–10%, Mo 8–12%, W 5–8% | 50–58 | Impact + abrasive combination wear | ASTM A5 Class 1 |
| Transition Layer (309L) | Cr 23–25%, Ni 12–14% | 25–32 | Dilution control, stress relief buffer | GB/T 10044, AWS A5.4 |
4.4 Multi-Layer Overlay Strategy
For toothed rollers and grate plates, a multi-layer overlay strategy is typically employed to balance dilution control, hardness, and cost:
- Layer 1 – Transition/Binder Layer: Deposit a low-dilution-sensitive alloy (e.g., 309L stainless steel or austenitic filler) to reduce the dilution effect from the base metal and create a metallurgically compatible interface. This layer typically has lower hardness but excellent ductility to absorb thermal stresses.
- Layer 2 – Intermediate Layer: Apply a medium-carbon hardfacing alloy that provides a hardness gradient between the transition layer and the final wear surface. This layer also helps control residual stress distribution.
- Layer 3 – Final Wear Layer: Deposit the high-hardness, high-carbon hardfacing alloy that provides the primary wear resistance. Multiple passes may be used to achieve the required overlay thickness (typically 3–8 mm for toothed rollers and 2–5 mm for grate plates).
- Post-Weld Heat Treatment: Apply controlled cooling or low-temperature stress relief (500–650°C) to reduce residual stresses without compromising the hardness of the overlay. For cobalt-based alloys, avoid temperatures exceeding 600°C to prevent carbide coarsening.
4.5 Geometric Considerations for Toothed Rollers
Toothed rollers present unique challenges due to their complex geometry:
- Tooth profile restoration: The overlay must be deposited in a manner that maintains or improves the original tooth geometry (typically trapezoidal or V-profile), ensuring proper engagement with the grate drive mechanism
- Root stress concentration: The tooth roots are critical stress concentration zones; overlay deposition at roots requires careful heat input control to prevent cracking
- Circumferential uniformity: Overlay thickness must be uniform around the roller circumference to prevent imbalance during rotation; post-weld machining may be required to achieve final geometry
- Roller runout: Post-repair roller must meet runout tolerances (typically ≤ 0.1 mm TIR) to prevent vibration and accelerated wear
4.6 Grate Plate Overlay Considerations
- Perforation integrity: Overlay around perforation holes must not obstruct airflow; careful bead placement is required to maintain slot geometry
- Edge reinforcement: The leading edges and contact surfaces of grate plates experience the most severe wear and require maximum overlay thickness
- Warping control: Flat grate plates are susceptible to thermal distortion during overlay; sequential welding patterns and back-up fixtures are essential
- Plate-to-plate compatibility: When overlaying individual grate plates, ensure dimensional compatibility with adjacent un-repaired plates to maintain proper mesh engagement
5. Applicable Standards and Acceptance Criteria
5.1 Welding Procedure and Qualification Standards
- GB/T 19866 – Welding procedure specification for steel
- NB/T 47014 – Qualification of welding procedures for pressure equipment (referenced for procedure qualification methodology)
- ASME Section IX – Qualification rules for welding, brazing, and fusing
- GB/T 985 – Welding symbols and marking methods
- ISO 15614-1 – Qualification of welding procedures for metallic materials – Arc welding
5.2 Weld Overlay Specific Standards
- GB/T 19866.1 – Weld overlaying – Part 1: General requirements
- ASTM A5/A5M – Standard specification for low-alloy depositing electrodes and bare rods for shielded metal arc welding
- ASTM A397 – Standard specification for electrode assemblies for shielded metal arc welding
- ISO 18275 – Welding – Weld overlaying – General recommendations
- NACE MR0175 – Sulfide-resistant materials (where applicable for environmental considerations)
5.3 Non-Destructive Testing Standards
- GB/T 11345 – Ultrasonic testing of welds in steel
- GB/T 26952 – Magnetic particle testing of welds
- GB/T 3323 – Radiographic testing of welds
- ASME Section V – Non-destructive examination
- ISO 17637 – Ultrasonic testing of welds – General recommendations
5.4 Acceptance Criteria
| Inspection Item | Method | Acceptance Criteria | Standard Reference |
|---|---|---|---|
| Surface Defects (cracks, porosity) | Visual Inspection (VT) | No cracks; porosity ≤ 2 per 100 mm length, each ≤ 1 mm | GB/T 3323, ISO 17637 |
| Subsurface Cracks | Magnetic Particle Inspection (MT) | No linear indications; round indications ≤ 3 mm | GB/T 26952, ISO 17640 |
| Internal Defects | Ultrasonic Testing (UT) | No indications above reference level; dilution zone soundness verified | GB/T 11345, ISO 17637 |
| Overlay Hardness | Rockwell C Hardness Test | Meets specified HRC range for selected alloy (±3 HRC) | GB/T 230.1, ASTM E18 |
| Dilution Ratio | Chemical Analysis (base/overlay interface) | ≤ 30% dilution in first overlay layer | ASTM E1019, GB/T 223 |
| Overlay Thickness | Dimensional Measurement | Uniform thickness within ±0.5 mm of specified value | Project specification |
| Geometric Tolerance | Machining and measurement | Roller runout ≤ 0.1 mm TIR; tooth profile within 0.2 mm | Customer drawing, ISO 286 |
6. Common Risks and Controls
6.1 Technical Risks
| Risk | Cause | Consequence | Control Measures |
|---|---|---|---|
| Hydrogen-induced cracking | Moisture in base or filler; excessive heat input; rapid cooling | Delayed cracks in overlay or HAZ; component failure | Preheat to specified temperature; use low-hydrogen filler; controlled cooling; bake filler wire |
| Excessive dilution | Too much base metal melted into overlay; single-layer approach | Reduced hardness and wear resistance of overlay | Multi-layer strategy with transition layer; control heat input; maintain low interpass temperature |
| Overlay cracking | High carbon/martensitic overlay on thick sections; thermal stress | Cracked overlay surface; premature wear failure | Post-weld stress relief; use ductile transition layer; optimize cooling rate |
| Thermal distortion | Uncontrolled heat input; asymmetric welding sequence | Roller runout; grate plate warping; dimensional non-conformance | Back-up fixtures; balanced welding sequence; preheat and post-heat; post-weld machining |
| Porosity | Surface contamination; insufficient shielding gas; wet filler | Reduced overlay integrity; stress concentration at pores | Thorough surface cleaning; adequate gas flow; use dry filler materials |
| Base material cracking | High carbon equivalent base; insufficient preheat | Structural failure of component | Pre-weld inspection for existing cracks; adequate preheat; limit heat input |
6.2 Quality Assurance Controls
- WPS/PQR development: Develop and qualify a welding procedure specification for each component type and overlay alloy combination before production welding begins
- Welder qualification: Ensure all welders performing overlay work are qualified per the applicable standard for the specific process, position, and material combination
- In-process inspection: Conduct visual inspection between layers; verify interpass temperatures; monitor bead profile and dilution indicators
- Final NDT: Perform complete NDT (VT + MT + UT as applicable) on all overlay welds before delivery
- Hardness verification: Test overlay hardness at multiple locations to confirm uniform deposition and correct alloy composition
- Documentation: Maintain complete traceability records including material certificates, WPS/PQR references, welder IDs, inspection reports, and test results
7. Application Across Company Technology Routes
7.1 TIG/MIG Weld Overlay Route (Primary Application)
This is the primary technology route for sintering machine toothed roller and grate plate repair. The TIG/MIG overlay capability provides:
- On-site repair capability: TIG equipment is portable and suitable for in-situ repair of large rollers without removal from the sintering machine
- High deposition rate: MIG overlay allows rapid rebuild of severely worn components with minimal downtime
- Material versatility: Wide range of hardfacing alloys available in both wire (MIG) and rod (TIG) forms
- Dimensional precision: Post-weld machining to achieve exact tooth profiles and plate geometries
7.2 Hydraulic Explosive Bonding Route
While hydraulic explosive bonding is not directly applicable to repair of existing worn components, the technology contributes to this application area through:
- New component fabrication: Manufacture of wear-resistant clad plates (e.g., 16Mn + high-carbon steel or 16Mn + Stellite) for grate plate assemblies, providing superior wear resistance from the outset
- Replacement component supply: When overlay repair is not feasible due to excessive wear or structural damage, supply of new clad grate plates or roller segments with inherent wear-resistant surfaces
- Technology integration: Combine overlay repair of critical areas with clad plate replacement for non-critical areas in a comprehensive maintenance strategy
7.3 Explosion Welding Route
Explosion welding contributes to the sintering machine repair ecosystem through:
- Heavy-duty cladding: For components requiring thick wear-resistant layers (≥ 5 mm) that are impractical to achieve by weld overlay alone, explosion welding produces metallurgically bonded clad plates suitable for grate plate fabrication
- Specialized alloy combinations: Create clad substrates with specific wear/thermal property combinations (e.g., nickel-aluminum bronze backing with cobalt-chromium surface) that exceed what is achievable by welding alone
- Large-format production: Produce large clad plates in single operations, suitable for grate plate sections that require uniform, thick overlay across large flat surfaces
8. Qualification Building and Customer Value
8.1 Qualification Development
The research and development of weld overlay repair for sintering machine components contributes to the company's qualification portfolio through:
- WPS library expansion: Development of qualified welding procedures for specific base materials (Q235, 16Mn, HT250 cast iron, etc.) and overlay alloys used in sintering applications
- Technical expertise documentation: Systematic documentation of process parameters, material selections, and inspection protocols establishes institutional knowledge and repeatable quality
- Industry-specific credentials: Successful repair projects in the sintering segment build a track record that differentiates the company from general welding service providers
- Standards compliance: Demonstration of conformance to GB/T, ASTM, ASME, and ISO standards provides customers with assurance of technical rigor
8.2 Customer Value Delivery
- Production continuity: Rapid turnaround repair programs (typically 24–72 hours for standard components) minimize unplanned downtime in continuous sintering operations
- Total cost of ownership reduction: Extended component life and reduced replacement frequency deliver measurable savings on annual maintenance budgets
- Technical consulting: The research-driven approach enables the company to provide customers with wear analysis, material selection recommendations, and preventive maintenance planning
- Performance guarantee: Documented WPS/PQR and NDT results provide objective evidence of repair quality, supporting warranty commitments and customer confidence
8.3 Continuous Improvement Pathway
- Field data collection: Track service life of repaired components under actual operating conditions to refine material and process selections
- Microstructural analysis: Conduct post-service metallurgical examination to understand failure mechanisms and optimize future repairs
- Process automation: Evaluate robotic MIG overlay for repeatable, high-quality deposition on standard grate plate geometries
- Advanced material development: Investigate new overlay alloys (e.g., ceramic-reinforced composites, amorphous alloys) for next-generation wear resistance
- Condition monitoring integration: Develop predictive maintenance protocols using wear rate monitoring to schedule overlay repairs proactively
9. Conclusion
Weld overlay repair of sintering machine toothed rollers and grate plates represents a technically demanding yet high-value capability within the Cladding Technology Shanxi Co., Ltd. portfolio. The successful execution of this technology requires deep understanding of wear mechanisms in sintering operations, metallurgical expertise in alloy selection and dilution control, precise process parameter management, and rigorous quality assurance. By combining research-driven process development with standards-based qualification, the company delivers reliable, cost-effective solutions that extend equipment life, reduce operational costs, and support the sustainability goals of the iron and steel industry. The integration of this capability with the company's broader technology routes—hydraulic explosive bonding for new clad component fabrication and explosion welding for heavy-duty cladding—creates a comprehensive surface engineering service offering that addresses the full lifecycle needs of sintering machine maintenance and optimization.