Detailed Discussion on Cladding Repair of Cement Industry Grinding Equipment Accessories

Literature Overview and Context

The study by Huang Zhiquan, Yang Wei, and Li Junwei, published in 2014 in the New Century Cement Guide, provides a detailed technical discussion on the cladding repair of cement industry grinding equipment accessories. This work builds upon earlier research by the Zhengzhou Mechanical Research Institute team and addresses the practical challenges encountered in maintaining grinding equipment such as ball mills, rod mills, vertical mills, and roller presses. The study focuses on specific component types and the technical details that determine repair success or failure.

Core Technical Points

Classification of Grinding Equipment Components by Wear Type

The study categorizes grinding equipment accessories into distinct wear categories, each requiring a tailored cladding approach:

Component Type	Wear Mechanism	Overlay Material	Welding Process
Mill liner plates	Abrasion + impact	High-carbon martensitic steel (C 1.5–2.5%)	SAW or FCAW
Trunnion bearing surfaces	Sliding + fretting	Medium-alloy steel with B or Mo	GMAW or SAW
Grinding ring	Sliding abrasion	High-chromium cast iron or martensitic steel	SAW
Ball mill discharge grate	Abrasion + corrosion	Stainless steel or duplex alloy	GMAW
Roller press roll surface	Abrasion + impact	High-carbon steel with carbide particles	SAW or plasma arc
Feed chute and hopper	Abrasion	Chromium carbide composite	SAW or FCAW

Detailed Process Parameters for Critical Components

The study provides granular process details for the most commonly repaired components:

Mill Liner Plate Cladding:

Parameter	Specification
Substrate material	Q235 or Q345 carbon steel
Overlay material	High-carbon steel wire (C 2.0%, Cr 8%, Mo 2%)
Preheat temperature	150–200°C
Interpass temperature	< 250°C
Number of passes	2–3 layers
Total overlay thickness	8–15 mm
Final hardness	50–58 HRC
PWHT	Stress relief at 550–600°C for 2 hours

Trunnion Bearing Surface Repair:

Parameter	Specification
Substrate material	45 steel or 40Cr
Overlay material	Medium-alloy steel with boron or molybdenum
Preheat temperature	200–250°C
Welding process	GMAW with low-hydrogen flux-cored wire
Overlay thickness	3–5 mm
Final machining	CNC turning to original dimensions
Final hardness	30–38 HRC (matching original bearing surface)

Common Defects and Root Cause Analysis

The study provides a comprehensive defect analysis using a systematic approach:

Defect	Visual/NDT Signature	Root Cause	Countermeasure
Cracking at weld/HAZ boundary	MT indication, linear	High Ceq substrate, insufficient preheat	Increase preheat to 250°C, use low-hydrogen filler
Porosity in overlay	UT or RT indication, round	Flux moisture, surface contamination	Dry flux at 300°C for 2h, grind surface to bare metal
Lack of fusion	UT indication, planar	Insufficient current, poor flux coverage	Increase current by 10–15%, ensure proper flux depth
Excessive dilution	Hardness gradient, poor wear resistance	Low travel speed, deep penetration	Increase travel speed, use smaller wire diameter
Distortion	Dimensional deviation	Asymmetric thermal input	Symmetric welding sequence, use backing plates
Spalling of overlay	Visual, delamination	Poor bond strength, high residual stress	Improve preheat, perform PWHT, optimize interpass temp

Quality Control and Inspection Protocol

The study emphasizes a rigorous quality control protocol aligned with industry standards:

Pre-weld inspection: Visual examination of substrate, dimensional verification, surface preparation confirmation (grind to bare metal, Ra 6.3–12.5 μm).
In-process monitoring: Welding parameter logging, interpass temperature measurement, visual inspection of each pass.
Post-weld inspection: 100% MT of all welds, UT of critical welds, hardness survey across overlay cross-section (minimum 3 points per cross-section).
Post-PWHT verification: Hardness re-survey, dimensional check, visual inspection for cracking.
Final acceptance: Dimensional verification per drawing tolerances, surface roughness check, functional fit test.

Engineering Practice Integration

The detailed technical discussion in this study is directly applicable to maintenance engineers and welders working in cement plant maintenance departments. The following practical recommendations emerge:

Standardize welding procedures: Each component type should have a qualified welding procedure specification (WPS) documented per NB/T 47014 or equivalent standards.
Train and certify welders: Only welders qualified on the specific process and material combination should perform cladding repairs.
Implement a repair tracking system: Document each repair with component ID, date, process parameters, inspection results, and service life data.
Plan preventive maintenance: Schedule cladding repairs based on wear rate data rather than waiting for component failure.

Study Insights and Reflections

This study represents a mature and comprehensive treatment of cladding repair technology for cement grinding equipment. The systematic approach to defect analysis and the detailed process parameters provide a valuable reference for field engineers. The emphasis on quality control protocols is particularly important, as inadequate inspection is a leading cause of premature repair failure in industrial settings. The work by the Zhengzhou Mechanical Research Institute team demonstrates the value of sustained research and development in a specific industrial sector, building upon earlier findings to create an increasingly sophisticated body of practical knowledge. For engineers new to this field, this study serves as an excellent starting point for understanding the technical requirements and quality expectations of industrial cladding repair.