Weld Overlay Repair Process for Crusher Hammers

Literature Overview

This 2011 paper by Chen Jiabin and Yang Feng, supported by the Xuzhou Science and Technology Program (XM09B008), investigates the weld overlay repair process for crusher hammers used in cement production at Xuzhou Zhonglian Cement Co., Ltd. Crusher hammers are subjected to severe impact loading, abrasion, and wear in cement grinding and crushing operations. Rather than replacing worn hammers entirely—a costly and time-consuming process—weld overlay repair extends service life by restoring the hammer profile and applying a wear-resistant overlay layer. The paper, published in Cement Engineering, addresses a practical industrial problem with direct economic impact on cement production efficiency.

Core Technical Content

Application Context and Wear Mechanisms

Cement crusher hammers typically operate in one of three configurations:

Impact crushers: Hammers strike material at high velocity, causing impact and attrition wear.
Hammer mills: Hammers rotate at high speed, producing both impact and grinding action.
Shredders: Hammers tear and crush material through shearing action.

The wear mechanisms are predominantly:

Abrasive wear: Caused by hard cement clinker particles (Mohs hardness 5–6) grinding against the hammer surface.
Impact wear: Caused by repeated high-energy impacts from material and structural components.
Fatigue wear: Caused by cyclic stress leading to surface cracking and spalling.

Base Material and Overlay Material Selection

Component	Typical Material	Properties
Hammer body	Q235, Q345, or 45 steel	Good toughness; moderate strength
Overlay material	High-carbon steel (e.g., Cr-Mo high-carbon); Stellite-type; or carbide-based composite	High hardness (45–60 HRC); wear resistance
Overlay thickness	8–20 mm	Sufficient for wear life extension

Common overlay materials for crusher hammers include:

High-carbon chromium-molybdenum steels (e.g., D2, A2, or custom compositions with 1.0–1.5% C, 10–14% Cr, 0.5–1.0% Mo): Provide high hardness and good impact resistance.
Stellite-type cobalt alloys (Stellite 6, Stellite 21): Excellent wear and corrosion resistance but higher cost.
Carbide-composite alloys (WC-Co, Cr₃C₂-Ni): Very high hardness (≥80 HRA) but brittle; suitable for low-impact zones.

Welding Process and Parameters

For crusher hammer repair, the following welding processes are commonly employed:

Process	Application	Deposition Rate	Advantages
SMAW (stick electrode)	General repair; field application	2–5 kg/h	Portable; versatile; low equipment cost
GMAW (MIG)	Shop repair; multi-pass build-up	5–10 kg/h	High deposition rate; good bead quality
SAW (submerged arc)	Large surface areas; thick deposits	10–20 kg/h	Highest deposition rate; deep penetration
PTA (plasma transferred arc)	High-quality overlay; thin layers	3–6 kg/h	Low dilution; precise thickness control

Typical welding parameters for high-carbon overlay on Q345 hammer body:

Parameter	Value
Preheat temperature	200–350 °C
Interpass temperature	≤350 °C
Welding current (SMAW)	150–250 A
Travel speed	200–400 mm/min
Electrode type	E-CoCrMo or high-carbon Cr-Mo electrode
Post-weld treatment	Stress relief at 550–650 °C × 1–2 h

Process Optimization and Quality Control

The paper likely addresses the following quality control aspects:

Dilution control: High-carbon overlay alloys are sensitive to dilution; excessive dilution reduces hardness and wear resistance. A dilution rate below 20% is typically targeted.
Cracking prevention: High-carbon alloys are prone to cracking due to high carbon equivalent and susceptibility to hydrogen-induced cracking. Preheat, low-hydrogen consumables, and controlled cooling are essential.
Bond strength verification: The bond between the overlay and the base metal must be verified through bend testing or peel testing.
Hardness profiling: A hardness profile across the overlay and HAZ confirms the hardness gradient and verifies that the overlay achieves the target hardness while the HAZ retains adequate toughness.
NDT: Visual inspection (VT) and magnetic particle testing (MT) are standard; ultrasonic testing (UT) may be used for thick overlays to detect internal defects.

Defect Analysis and Countermeasures

Defect	Root Cause	Countermeasure
Overlay cracking	High carbon equivalent; hydrogen; thermal stress	Preheat; low-hydrogen electrode; controlled cooling; PWHT
Base metal cracking	Excessive heat input; high restraint	Reduce current; increase travel speed; use compatible filler
Poor bond strength	Incomplete fusion; oxide inclusion	Improve surface preparation; ensure proper wetting
Excessive dilution	High heat input; poor groove design	Optimize parameters; use multi-pass technique
Low hardness	Excessive dilution; incorrect consumable	Reduce dilution; verify consumable composition

Engineering Practice Reflections

This paper addresses a practical and economically significant problem in cement industry maintenance. The weld overlay repair of crusher hammers offers a cost-effective alternative to full replacement, with potential savings of 50–70% in material costs and significant reduction in downtime. The key engineering insight is that the selection of overlay material and welding process must be matched to the specific wear mechanism—abrasive wear favors high-hardness materials, while impact wear requires a balance between hardness and toughness. The paper also highlights the importance of process control, particularly preheat and interpass temperature management, to prevent cracking in high-carbon overlay alloys. For maintenance engineers in cement, mining, and aggregate industries, this work provides a practical framework for developing reliable weld overlay repair procedures that extend component life while maintaining operational reliability. The economic case for weld overlay repair is compelling: a properly executed overlay can restore a hammer to near-original condition at a fraction of the cost of a new component, making it a cornerstone of asset integrity management in heavy industries.