Cladding Repair Process for Crusher Hammer Heads in Cement Engineering

Literature Overview and Background

This study, conducted by Chen Jiabin and Yang Feng under the Xuzhou Science and Technology Plan Project (XM09B008, 2009), addresses the cladding repair of crusher hammer heads used in cement production lines at Xuzhou Zhonglian Cement Co., Ltd. Crusher hammer heads are critical wear components in impact crushers that process limestone and other raw materials in cement manufacturing. The operating environment is extremely abrasive, with continuous high-impact loading and material attrition causing rapid surface degradation. The original hammer heads, typically made of low-alloy steel, exhibit insufficient surface hardness and wear resistance, resulting in frequent replacement cycles and significant downtime costs. The research aims to develop a reliable weld-overlay repair process that restores and enhances the surface properties of these components, extending their service life and reducing maintenance costs.

Core Technical Approach and Process Parameters

The cladding process employed in this study is based on manual arc welding (SMAW) and/or submerged arc welding (SAW) overlay techniques, depending on the specific hammer head geometry and repair area. The base material of the hammer heads is typically Q345 or 45 steel, while the overlay material is selected to provide high hardness and abrasion resistance. The following table summarizes the key process parameters and material selections identified in the study.

Parameter	Specification
Base material	Q345 / 45 steel
Overlay material	Hardfacing alloy (Cr-C-Mo system)
Welding process	SMAW and/or SAW
Electrode type	H08CrMo or equivalent hardfacing electrode
Preheat temperature	150–250 °C
Interpass temperature	Below 250 °C
Post-weld treatment	Controlled cooling or tempering at 550–600 °C
Target surface hardness	HRC 50–60
Overlay thickness	6–12 mm

Process Sequence and Key Controls

The repair process follows a systematic sequence: surface preparation, preheating, multi-pass overlay welding, post-weld heat treatment, and dimensional verification. Surface preparation involves grinding away damaged material to expose sound base metal, followed by chamfering of the repair groove to ensure adequate fusion and dilution control. Preheating is critical to reduce thermal gradients and minimize the risk of cold cracking, particularly given the carbon content of the base material and the high dilution rate typical of hardfacing applications.

The multi-pass overlay strategy is designed to progressively refine the microstructure and ensure adequate bond strength. The first pass establishes the base-to-overlay transition, while subsequent passes build up the required thickness with controlled dilution. The final pass is executed with precise travel speed and arc voltage to achieve uniform bead profile and consistent hardness distribution across the repaired surface. Post-weld heat treatment is essential to relieve residual stresses and optimize the carbide distribution within the overlay layer, preventing microcracking during service.

Microstructural Analysis and Performance Evaluation

Metallographic examination of the cladded hammer head specimens reveals a gradient microstructure at the base-metal/overlay interface, progressing from martensite in the heat-affected zone through a mixed martensite-ferrite region to a hardfacing microstructure dominated by primary carbides embedded in a martensitic matrix. The carbide phase is predominantly M7C3 and M23C6 type chromium carbides, which provide excellent abrasion resistance. The transition zone typically exhibits a dilution rate of 15–25%, which is within acceptable limits for hardfacing applications where some base metal incorporation is tolerable.

Mechanical testing confirms that the overlay layer achieves a surface hardness of HRC 50–60, compared to the original base metal hardness of approximately HRC 25–30. This represents a doubling of surface hardness, directly translating to improved wear life. Bond strength tests demonstrate that the overlay-to-base interface meets or exceeds the requirements specified in relevant standards for weld-overlay repair applications. The overlay layer also exhibits satisfactory impact toughness, indicating that the hardfacing process does not introduce brittle fracture susceptibility that could compromise structural integrity under impact loading.

Engineering Practice and Defect Analysis

In practical field application, the most common defects encountered during hammer head cladding repair include overlay cracking, lack of fusion at the interface, and excessive porosity. The following table summarizes these defects with their root causes and countermeasures, analyzed using a FMEA approach.

Defect Type	Root Cause	Countermeasure
Overlay cracking	High residual stress, excessive carbon dilution	Reduce preheat, control interpass temperature, optimize post-weld tempering
Lack of fusion	Insufficient preheating, poor surface preparation	Increase preheat temperature, ensure clean oxide-free surface
Excessive porosity	Moisture in electrode coating, inadequate shielding	Bake electrodes, ensure proper gas shielding or flux coverage
Hardness non-uniformity	Inconsistent travel speed, arc voltage variation	Standardize welding parameters, operator training

Field trials at the cement plant demonstrated that the cladded hammer heads achieved a service life improvement of 2.5 to 3.5 times compared to uncladded replacement parts. This translates to significant economic savings in terms of reduced part consumption and decreased crusher downtime. The study also highlights the importance of proper fit-up and alignment of the hammer head on the crusher rotor, as geometric misalignment can lead to uneven wear and premature failure even with a high-quality overlay.

Study Insights and Reflections

This research exemplifies the practical engineering approach to wear part repair through weld overlay, balancing material selection, process control, and economic considerations. The choice of Cr-C-Mo hardfacing alloy is well-suited to the abrasive wear regime of cement crusher applications, where sliding and grinding wear dominate. The study's emphasis on post-weld heat treatment is particularly noteworthy, as many field repair operations neglect this step, leading to premature cracking and reduced service life. From a quality assurance perspective, the process could benefit from additional non-destructive testing, such as magnetic particle inspection for surface cracks and ultrasonic testing for internal defects, to ensure reliability before returning the hammer head to service.

The broader implications of this work extend to other abrasive wear components in cement and mining industries, where similar cladding strategies can be applied to chutes, hoppers, and grinding media. Future work should explore more advanced overlay techniques, such as plasma transferred arc cladding or laser cladding, which offer improved dilution control and finer microstructural features, potentially enabling even greater performance enhancement. The integration of thermally sprayed hardfacing coatings as a complementary surface treatment, applied over the weld overlay for additional protection, also warrants investigation.