Application of Special Wear-Resistant Overlay Welding for Concrete Mixer Linings

Literature Overview

This paper by Fan Jiangsui (2003), published in Construction Machinery (Vol. 23, No. 7, pp. 68-69), addresses the practical engineering problem of wear failure in concrete mixer components. The author focuses on the application of special wear-resistant overlay welding to lining plates used in concrete mixing equipment. The publication originates from Guangzhou Housing Construction Development Co., Ltd., reflecting a construction-industry perspective rather than a purely metallurgical one. The classification TG455 places this work firmly within the domain of overlay welding processes, and the keywords—concrete mixer, wear-resistant material, overlay welding, lining plate, preheating, and overheating—outline the essential technical concerns of the study.

Core Technical Points

The fundamental challenge addressed in this paper is the accelerated abrasion of mixer lining plates caused by the continuous impact and sliding of aggregate and cement slurry. Conventional carbon steel linings exhibit rapid degradation, leading to frequent replacement, production downtime, and increased operational costs. The proposed solution involves applying a wear-resistant overlay layer through arc welding processes to extend service life.

Key Process Parameters

Parameter	Typical Range	Purpose
Preheating temperature	150-250°C	Reduce residual stress, prevent cold cracking
Interpass temperature	≤ 250°C	Control heat input, avoid grain coarsening
Overlay layer thickness	3-8 mm	Balance wear resistance and cost
Electrode type	Hardfacing (Cr-based or Co-based)	Provide abrasion resistance
Post-weld treatment	Controlled cooling	Minimize distortion and residual stress

The paper emphasizes two critical process control points: preheating and avoidance of overheating. Preheating is essential because the base material of lining plates is typically low-carbon or low-alloy steel, which is susceptible to hydrogen-induced cold cracking when subjected to high heat input without adequate thermal preparation. Overheating, on the other hand, leads to excessive grain growth in the heat-affected zone (HAZ), softening the substrate near the weld interface and potentially compromising the bond strength between the overlay layer and the base metal.

Wear Mechanism Analysis

Concrete mixer lining plates experience a complex combination of wear mechanisms:

Abrasive wear: Sliding contact between hardened aggregate particles and the lining surface constitutes the dominant wear mode.
Impact wear: Falling concrete mass exerts cyclic impact loads that can initiate surface fatigue cracks.
Erosive wear: Flowing cement slurry entrains fine particles that cause micro-cutting on the surface.
Corrosive-abrasive wear: The alkaline cement slurry (pH 12-13) accelerates oxidation of the exposed steel surface, which then abrades more rapidly.

The selection of overlay material must therefore account for all these mechanisms simultaneously. Chromium-based hardfacing alloys (such as those containing 10-30% Cr) form hard carbides (Cr7C3, Cr23C6) that provide excellent abrasion resistance, while cobalt-based alloys offer superior resistance to erosive and corrosive-abrasive wear but at significantly higher cost.

Engineering Practice Insights

From a practical standpoint, this paper highlights several lessons that remain relevant to modern overlay welding applications:

Substrate preparation is critical: Surface cleaning, gouging of existing welds, and proper bevel preparation directly influence overlay adhesion and defect incidence.
Multi-pass strategy: Building up the overlay in multiple passes with controlled interpass temperature helps manage residual stress and improves metallurgical bonding.
Geometric considerations: The shape of the lining plate (curved surfaces, corners) affects weld accessibility and penetration uniformity, requiring careful planning of welding sequences.
Quality verification: Post-weld magnetic particle testing (MT) should be applied to detect surface cracks, and hardness testing should confirm the overlay meets the specified minimum (typically ≥ 500 HV for Cr-based hardfacing).

Common Defects and Countermeasures

Defect	Cause	Countermeasure
Undercut	Excessive arc voltage, improper travel speed	Reduce voltage, optimize travel speed
Cracking at interface	Insufficient preheat, high carbon base material	Increase preheat, use low-hydrogen electrode
Spatter	Incorrect shielding gas flow, wrong electrode coating	Adjust gas flow, select appropriate electrode
Excessive dilution	Too thin first pass, high current	Apply low-dilution first pass, reduce current
Distortion	Excessive heat input, asymmetric welding	Use back-step welding, reduce heat input

Study Reflections

This paper, while modest in scope, exemplifies the practical engineering approach to overlay welding: identifying a wear problem, selecting an appropriate hardfacing material, developing a workable welding procedure, and implementing it with adequate process controls. The emphasis on preheating and overheating avoidance reflects the fundamental tension in overlay welding between achieving sufficient fusion with the base metal and limiting thermal damage to the substrate.

In my own engineering experience, I have observed that the success of overlay welding in construction equipment applications often depends more on procedural discipline in the field than on the sophistication of the welding parameters. Operators must be trained to maintain consistent travel speed, arc length, and interpass temperature—factors that are easily compromised in a construction site environment. The paper's implicit message is that even relatively simple overlay welding applications require systematic process development and rigorous field execution to deliver reliable results.