Overlay Welding Repair Process Research for Crusher Hammers

Literature Overview

The paper by Chen Jiabin and Yang Feng from Xuzhou Zhonglian Cement Co., Ltd. and Xuzhou Institute of Technology, published in Cement Engineering (2011, No. 3, pp. 47–48), investigates overlay welding repair processes for crusher hammers used in cement production. The research was supported by the Xuzhou City Science and Technology Program (XM09B008). Crusher hammers are identified as critical consumable components that operate under extreme conditions of high impact, high stress, and severe abrasive wear.

Operating Conditions and Failure Modes

Crusher hammers experience a unique combination of loading conditions that make them among the most severely stressed components in cement production:

Condition	Description	Impact on Hammer
High-speed rotation	Centrifugal force at operating speed	Dynamic loading, fatigue
Material collision	Impact with falling rock/ore	High impact stress, chipping
Abrasive wear	Contact with hard mineral particles	Progressive material loss
Thermal cycling	Friction heating and cooling	Thermal stress, microcracking

The paper identifies two primary failure modes:

Abrasive wear: Progressive material loss from the hammer face and edges, reducing crushing efficiency and requiring replacement.
Fracture/breakage: Catastrophic failure of the hammer, often initiated by stress concentration at worn edges or pre-existing defects. This causes unplanned shutdowns and production losses.

Overlay Welding Repair Process

The overlay welding repair process for crusher hammers involves several critical steps:

Surface Preparation

The worn hammer surface must be prepared by grinding to remove:

Cracked and spalled surface layers
Oxide scale and contamination
Residual stress from prior welding or heat treatment

The preparation depth is typically 2–5 mm, depending on the extent of surface damage. Insufficient preparation leads to poor bond strength and early repair failure.

Welding Process Selection

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

Process	Advantage	Limitation
SAW (Submerged Arc Welding)	High deposition rate, deep penetration	Limited to flat/positionable work
FCAW (Flux-Cored Arc Welding)	Good all-position capability	Moderate deposition rate
GMAW (Gas Metal Arc Welding)	Good visual control, versatile	Lower deposition rate
TIG (GTAW)	High quality, low dilution	Very low deposition rate

For hammer repair, SAW or FCAW is typically preferred due to the need for high deposition rates to restore hammer geometry efficiently.

Overlay Alloy Selection

The overlay alloy must provide:

High hardness (HV 500–800) for wear resistance
Adequate toughness to resist impact fracture
Good bond strength with the base metal (typically medium-carbon steel or high-manganese steel)

Common overlay alloy systems include:

High-chromium white iron (Cr 12–28%)
High-manganese austenitic alloy (Mn 12–18%)
Carbide composite alloys (WC, Cr7C3, TiC)
Nickel-based alloy 6 (for corrosion-resistant applications)

Heat Treatment

Post-weld heat treatment is often required to:

Relieve residual stresses (600–650°C for 2–4 hours)
Transform martensite to tempered martensite (if applicable)
Improve the toughness of the overlay layer

Defect Analysis and Countermeasures

Based on the paper's discussion and general engineering experience, common defects in hammer overlay welding include:

Defect	Cause	Countermeasure
Cold cracking	Hydrogen diffusion, high carbon base metal	Preheat 200–300°C, low-hydrogen consumables
Hot cracking	Low-melting-point inclusions, high sulfur/phosphorus	Control consumable chemistry, proper filler selection
Poor bond	Surface contamination, insufficient penetration	Thorough surface prep, adequate root penetration
Overlay spallation	High residual stress, poor toughness	Stress relief, multi-pass welding, alloy selection
Excessive dilution	High heat input, thin overlay passes	Low heat input, multiple thin passes

Engineering Practice Case

In cement plant operations, crusher hammer repair is typically performed during scheduled maintenance shutdowns. The repair process follows a PDCA cycle:

Plan: Assess hammer condition, determine repair extent, select overlay alloy and process parameters.
Do: Perform surface preparation, overlay welding, and post-weld heat treatment.
Check: Inspect weld quality (visual, MT/PT), measure hardness, verify dimensional accuracy.
Act: Adjust process parameters for subsequent repairs based on observed service performance.

The economic benefit of repair versus replacement is substantial. A single crusher hammer may cost USD 2,000–5,000 to replace, while overlay welding repair costs USD 200–500 per hammer, with the repaired hammer achieving 60–80% of the service life of a new hammer.

Study Insights

This paper underscores the importance of overlay welding as a maintenance technology for high-wear components in cement production. The key insight is that hammer repair is not merely about adding material—it is about restoring functional performance under severe impact and abrasive conditions. The selection of overlay alloy, process parameters, and post-weld treatment must be tailored to the specific operating conditions of the crusher. Engineers should not apply a one-size-fits-all approach; instead, they should analyze the failure mode of each hammer and select the repair strategy accordingly.