CLADDING TECHNOLOGY SHANXI CO., LTDManual Cladding Hardening Treatment of Wall and Floor Tile Molds
Literature Overview
This 1994 paper by Wu Jun and Wu Jingshu from Wuhan Institute of Technology, published in Welding Technology, addresses a practical manufacturing challenge in the ceramics and building materials industry: the wear resistance improvement of tile molds through manual arc cladding. Wall and floor tile molds are subjected to repeated compression and friction from green (unfired) ceramic bodies, leading to progressive wear that degrades product dimensional accuracy and surface quality. The study investigated the application of manual metal arc welding (MMA) overlay as a cost-effective hardening solution.
Application Context and Requirements
Tile molds operate under conditions that differ significantly from conventional wear applications:
| Condition | Characteristic | Design Implication |
|---|---|---|
| Contact pressure | 50-150 MPa (intermittent) | Need for compressive residual stress |
| Sliding distance | 2-10 mm per cycle | High cycle count, low sliding per cycle |
| Abrasive content | Ceramic particles in green body | High hardness requirement |
| Temperature | Room temperature to 200°C | Moderate thermal requirement |
| Environment | Wet (slip-cast) or dry (press) | Corrosion consideration |
| Mold life target | 50,000-200,000 cycles | High durability requirement |
| Surface flatness | ±0.02 mm | Minimal distortion tolerance |
The manual welding approach was selected based on economic considerations: tile mold manufacturers typically operate with limited capital investment and require repair capability without expensive automated equipment. The challenge was to achieve acceptable overlay quality and uniformity through operator skill rather than process automation.
Welding Process and Alloy Selection
The authors evaluated several filler metal systems for manual arc cladding of tile molds, which were typically fabricated from carbon steel (Q235 or 20# steel) or low-carbon alloy steel.
Filler Metal Evaluation
| Filler Metal | Composition (wt%) | Hardness (HRC) | Crack Resistance | Cost Factor |
|---|---|---|---|---|
| D107 (cast iron type) | C 3.5-4.5, Cr 1.0-2.0 | 50-58 | Excellent | Low |
| D207 (high Cr iron) | C 2.5-3.5, Cr 26-30 | 55-62 | Moderate | Low |
| D407 (high Cr high C) | C 3.0-4.0, Cr 20-25 | 58-65 | Poor | Low |
| Custom Fe-Cr-C | C 1.5-2.0, Cr 15-20 | 48-55 | Good | Moderate |
| Ni-Cr alloy | Ni 55-60, Cr 25-30 | 38-42 | Excellent | High |
The authors recommended D107 (a cast iron-type electrode) as the primary choice for most tile mold applications. The high carbon content (3.5-4.5%) produced a hard ledeburite microstructure with dispersed cementite (Fe3C) particles, providing excellent abrasion resistance. The graphite flakes inherent in the microstructure acted as crack arrestors, providing inherent resistance to overlay cracking even without preheating.
Recommended Welding Parameters
- Electrode diameter: 3.2 mm for general areas, 2.5 mm for tight corners
- Current: 90-120 A (DC, electrode positive for D107)
- Arc length: 2-3 mm (short arc for dense deposition)
- Travel speed: 80-120 mm/min
- Stringer bead width: 6-8 mm
- Overlap between passes: 1/3 to 1/2 bead width
- Number of passes: 2 for 1.5-2.5 mm total thickness
- Preheating: 100-150°C for thick sections (>25 mm)
Microstructural Analysis and Performance
Metallographic examination of the D107 overlay revealed a complex microstructure consisting of a pearlite-ferrite matrix with dispersed ledeburite (Fe3C + graphite) particles. The carbide particles, measuring 5-20 micrometers in size, provided the primary wear resistance mechanism. The graphite flakes, while reducing hardness slightly, contributed significantly to the overlay's resistance to cracking by accommodating plastic deformation.
The dilution effect was found to be significant in the first pass (approximately 30-40% base metal dilution), reducing the effective carbon content and consequently the hardness of the first layer to approximately 45-48 HRC. The second pass, applied over the first, achieved the target hardness of 52-55 HRC with minimal additional dilution. This two-pass approach was identified as essential for achieving adequate hardness while maintaining crack resistance.
Performance Comparison
| Condition | Before Cladding | After D107 Cladding | Improvement Factor |
|---|---|---|---|
| Surface hardness | 180-220 HV | 550-650 HV | 3x |
| Mold life (cycles) | 30,000-50,000 | 120,000-200,000 | 3-4x |
| Surface flatness deviation | ±0.02 mm | ±0.03 mm | Acceptable |
| Cost per 1000 cycles | Baseline | 25-30% of baseline | 70-75% reduction |
Study Insights and Reflections
This paper exemplifies the principle that the most appropriate technology is not necessarily the most advanced, but rather the one that best matches the application requirements with available resources. The selection of a cast iron-type electrode for tile mold cladding demonstrates practical engineering judgment: the inherent crack resistance of the graphite-containing microstructure eliminates the need for expensive preheating and post-weld heat treatment, while providing adequate wear resistance at minimal cost.
The study's emphasis on operator technique for achieving uniform manual weld overlay quality is particularly relevant. In an era of increasing automation, this reminds us that skilled manual welding remains essential for complex geometries, repair work, and small-batch production. The key to successful manual cladding lies not in exotic filler metals but in disciplined technique: consistent arc length, controlled travel speed, and proper bead overlap.