CLADDING TECHNOLOGY SHANXI CO., LTDHardfacing Repair of Sintering Machine Toothed Rollers and Grid Plates
Literature Overview
This 2006 study by Yu Guangming, Zhong Yi, and Duan Liren from Wuhan Iron and Steel Group Corporation addresses the practical engineering problem of restoring worn sintering machine components through weld overlay hardfacing. Sintering machines in iron and steel production operate under severe abrasive and corrosive conditions, with toothed rollers and grid plates experiencing rapid material loss from friction, impact, and high-temperature oxidation. The study presents a systematic approach to selecting appropriate hardfacing alloys and welding processes to extend the service life of these critical components.
Technical Background and Failure Mechanisms
The sintering machine operates at temperatures ranging from 200°C to 900°C, depending on the position of the component within the sintering bed. The toothed rollers and grid plates are subjected to a combination of:
| Failure Mode | Mechanism | Typical Location |
|---|---|---|
| Abrasive wear | Contact with sinter cake and ore particles | Roller teeth, grid plate surface |
| Oxidative wear | High-temperature oxidation of exposed metal | Grid plate upper surface |
| Impact wear | Falling ore particles at high velocity | Grid plate edges |
| Thermal fatigue | Repeated heating and cooling cycles | Roller body near teeth |
| Corrosive wear | Sulfur and chlorine in sintering atmosphere | Interdental regions |
The base material of these components is typically low-carbon steel or low-alloy steel, which is insufficient for the operating conditions. Without protective overlay, the service life of toothed rollers may be as short as 200–400 hours, resulting in frequent downtime for replacement.
Hardfacing Process and Material Selection
The study evaluates several hardfacing approaches, including submerged arc welding (SAW), gas metal arc welding (GMAW), and plasma transferred arc (PTA) welding, with the following material options:
- High-carbon martensitic alloys: Such as Cr13-type or Cr20-type steels, providing hardness in the range of 50–55 HRC. These are suitable for moderate wear conditions but may crack under thermal cycling.
- High-chromium cast irons: Such as Co-Cr or Fe-Cr-C alloys, offering hardness of 60–65 HRC and excellent abrasion resistance. These materials are preferred for grid plates exposed to severe abrasive wear.
- Nickel-based alloys: Such as Stellite-type alloys, providing superior corrosion resistance and moderate abrasion resistance. These are used in regions exposed to corrosive atmospheres.
The process parameters for the selected hardfacing operation typically include:
| Parameter | Recommended Value |
|---|---|
| Welding current (SAW) | 400–600 A |
| Arc voltage | 25–35 V |
| Travel speed | 100–200 mm/min |
| Overlay thickness | 2–4 mm per pass |
| Total overlay thickness | 6–12 mm |
| Number of passes | 2–4 |
Quality Control and Defect Prevention
The study emphasizes the importance of quality control during the hardfacing repair process. Common defects include:
- Cracking: Caused by high carbon equivalent of the overlay material or inadequate preheating. Countermeasures include preheating the base to 200–300°C and using low-hydrogen flux.
- Porosity: Resulting from inadequate flux coverage or contamination of the base surface. Countermeasures include thorough surface preparation and maintaining proper flux coverage.
- Undercut: Occurring at the edges of the weld bead, reducing the effective overlay thickness. Countermeasures include adjusting the travel speed and arc length.
- Delamination: Caused by poor wetting or contamination at the interface. Countermeasures include mechanical preparation of the base surface to a matte finish.
The hardness profile of the overlay layer is verified by surface hardness testing, typically using a Rockwell C hardness tester. The bond strength is assessed through macrograph examination and, in critical applications, through peel testing or ultrasonic bond testing.
Engineering Practice and Cost-Benefit Analysis
The economic justification for hardfacing repair versus replacement is a key consideration. The study demonstrates that a properly executed hardfacing repair can extend the service life of a toothed roller from approximately 300 hours to over 1500 hours, representing a fivefold improvement. The cost of hardfacing repair is typically 10–20% of the cost of a new roller, making it a highly economical maintenance strategy. However, the quality of the repair depends critically on the skill of the welder and the consistency of the process parameters.
Summary
This literature provides a practical and well-documented approach to hardfacing repair of sintering machine components, demonstrating that the selection of appropriate overlay material, welding process, and quality control measures can significantly extend component life and reduce maintenance costs. The study serves as a valuable reference for engineers dealing with abrasive wear problems in bulk material handling equipment across various industries.