Zhuojin Pipe Fitting Co., LtdZD Series Surface Overlay Materials for Roller Mills
Literature Overview
This paper by Xu Jian, published in "New Century Cement Herald" in 2005, describes the ZD series of surface overlay welding materials developed by the Zhengzhou Machinery Research Institute. The ZD series, comprising ZD1, ZD2, ZD3, and ZD310, represents a comprehensive system of flux-cored wires and stick electrodes specifically designed for roller mill surface overlay applications. The materials are available in both submerged arc welding (SAW) and CO2 gas shielded metal arc welding (GMAW) consumable formats, and the system is designed to create a hardness gradient on the roller surface through the strategic combination of transition layers, buffer layers, hard surface layers, and wear-resistant pattern layers.
Material System Description
The ZD series is notable for its systematic approach to overlay welding, which recognizes that a single material cannot optimally address all the challenges of roller surface protection. Instead, the system provides multiple material grades that are designed to be used in combination to create a layered structure with graded hardness and toughness properties. The materials are available in the following configurations:
| Material Type | Format | Diameter | Application Layer |
|---|---|---|---|
| ZD Series SAW Wire | Submerged Arc | 4.0 mm, 3.2 mm | Transition, Buffer, Surface, Pattern |
| ZD Series GMAW Wire | CO2 Shielded | 1.6 mm | Transition, Buffer, Surface, Pattern |
| ZD Series Stick Electrodes | Manual Arc | Various | Transition, Buffer, Surface, Pattern |
The four-layer concept is particularly important for understanding the design philosophy of this material system:
- Transition Layer: Applied directly to the base steel to ensure metallurgical compatibility and prevent cracking at the weld interface. This layer typically has lower carbon and alloy content to reduce hardenability and improve weldability.
- Buffer Layer: Serves as an intermediate layer that gradually increases the hardness from the transition layer to the surface layer. This layer helps to accommodate the difference in thermal expansion between the base metal and the hard surface layer.
- Hard Surface Layer: Provides the primary wear resistance through high hardness, typically achieved through high carbon and alloy content that promotes the formation of hard carbides.
- Wear-Resistant Pattern Layer: Applied as the final layer to create a surface profile that enhances material retention and reduces slippage between the roller and the material being ground.
Process Considerations
The availability of both SAW and GMAW consumables provides flexibility in the welding process selection. SAW is preferred for initial build-up passes due to its high deposition rate and good penetration, while GMAW is often used for finishing passes and for applying the pattern layer due to its better controllability and ease of use. The choice between SAW and GMAW depends on the specific application, the thickness of the overlay required, and the availability of equipment.
The welding parameters must be carefully controlled to ensure proper fusion between layers and to prevent defects such as cracking, porosity, and lack of fusion. The interpass temperature should be maintained within the recommended range to prevent excessive grain growth and to minimize residual stress. Preheating of the base metal is typically required, particularly for thick rollers or in cold ambient conditions, to reduce the risk of cold cracking.
Engineering Practice and Material Selection
The selection of the appropriate ZD material combination depends on several factors, including the hardness of the material being ground, the operating pressure, the feed rate, and the desired roller surface profile. For grinding soft materials such as limestone, a lower hardness surface layer may be sufficient, while grinding hard materials such as flint or bauxite requires a higher hardness surface layer with enhanced impact resistance.
The concept of creating a hardness gradient through material combination is a sophisticated approach that addresses the fundamental challenge of balancing hardness and toughness in overlay applications. A uniformly hard surface would be brittle and prone to spalling, while a uniformly tough surface would wear rapidly. The graded approach provides the best of both worlds, with a tough foundation that resists cracking and a hard surface that resists wear.
Study Insights
The ZD series material system represents a mature approach to roller mill overlay welding that has been refined through extensive field experience. The systematic design of the material system, with clearly defined roles for each layer, provides engineers with a practical framework for selecting and applying overlay materials. The availability of multiple consumable formats ensures that the system can be adapted to different welding setups and production requirements.
One important consideration that this paper highlights is the need for rational material matching. The combination of transition, buffer, surface, and pattern layers must be carefully selected and applied in the correct sequence to achieve the desired performance. Using the wrong combination or applying the layers in the wrong order can result in poor performance, premature failure, or excessive cost.
The practical value of this material system lies in its proven track record in cement grinding applications, where it has been used to extend roller life and reduce maintenance costs. Engineers working in related industries, such as mining, power generation, and mineral processing, should consider the applicability of this approach to their own equipment maintenance challenges.