Submerged Arc Automatic Hardfacing of Port Machinery Hopper Liners

Literature Overview

This paper by Huang Wanjun and Wan Guowei from Shanghai Maritime University (published in Journal of Shanghai Maritime University, 2002, Vol. 23, No. 4, pp. 9-11) presents a practical engineering solution for extending the service life of belt conveyor hopper liners in port machinery through submerged arc automatic hardfacing. Port hopper liners are subjected to severe abrasive wear from bulk materials such as coal, ore, and grain, and their replacement represents a significant maintenance cost for port operators. The authors developed a dot-pattern submerged arc hardfacing process that improves both production efficiency and wear resistance.

Application Context

Port machinery hopper liners serve as wear plates in the transfer points of bulk material handling systems. The wear conditions are characterized by:

Material: Abrasive bulk materials (coal, iron ore, bauxite, grain)
Impact energy: Materials drop from heights of 2-5 meters
Sliding angle: Typically 30-60 degrees from horizontal
Environment: Outdoor, often humid or marine atmosphere
Service life requirement: 12-24 months before replacement

The base material of hopper liners is typically Q235 or Q345 carbon steel, which provides adequate structural strength but poor wear resistance. Without hardfacing protection, liners may wear through in as little as 3-6 months under severe conditions.

Process Development

Dot-Pattern Hardfacing Geometry

The authors selected a dot-pattern (circular spot) hardfacing arrangement rather than continuous strip hardfacing. The advantages of this approach include:

Feature	Dot Pattern	Continuous Strip
Residual stress	Lower (isolated spots)	Higher (continuous constraint)
Distortion	Minimal	Significant warping
Production speed	Faster (no overlap required)	Slower
Material usage	Lower (less overlap)	Higher
Wear resistance	Adequate with proper spacing	Higher surface coverage
Repair capability	Individual spot repair possible	Difficult to repair locally

Process Parameters

Parameter	Value	Notes
Welding process	Submerged arc (SAW)	Single-wire, single-shield
Wire diameter	φ2.0-2.4 mm	Standard hardfacing wire
Current	250-350 A	DCEN preferred
Voltage	25-30 V	Stable arc, good penetration
Welding speed	500-800 mm/min	High speed for productivity
Flux coverage	Adequate	Prevents oxidation
Spot diameter	15-25 mm	Optimized for impact resistance
Spot spacing	20-30 mm	Ensures adequate coverage
Preheat	100-150°C	Reduce cracking tendency

Hardfacing Wire Composition

The hardfacing wire is typically a high-carbon, high-alloy composition designed for abrasive wear resistance:

Element	Content (%)	Function
C	2.5-4.0	Carbide formation
Cr	15-25	M₇C₃ carbides, hardening
Mo	2-5	MC carbides, hot hardness
Mn	1.0-2.0	Solid solution strengthening
Si	0.5-1.5	Deoxidation, grain refinement
Fe	Balance	Base metal

Microstructural Characteristics

The dot-pattern hardfacing deposits exhibit a microstructure consisting of:

Matrix: Martensite with retained austenite (5-15%)
Carbides: M₇C₃ (Cr carbides) and MC (Mo carbides) in a eutectic arrangement
Hardness: 55-62 HRC in as-welded condition
Wear resistance: 3-5 times that of base steel (measured by pin-on-disk test)

The retained austenite in the microstructure provides a beneficial transformation toughening effect: under impact loading, the austenite transforms to martensite, absorbing energy and preventing crack propagation. This is particularly important for hopper liners that experience impact from falling materials.

Performance Results

The authors report that the dot-pattern hardfacing process achieves:

Service life extension: From 3-6 months to 18-24 months (3-4 times improvement)
Production efficiency: 30-40% faster than continuous strip hardfacing
Material savings: 20-30% less hardfacing wire consumed
Distortion: Negligible warping of hopper structure

Engineering Practice Considerations

Several practical aspects deserve emphasis for engineers implementing this process:

Surface preparation: The hopper surface must be cleaned to remove rust, paint, and mill scale. Shot blasting to Sa 2.5 grade is recommended.
Edge preparation: A shallow groove (V-groove, 2-3 mm deep) is cut at each spot location to ensure adequate fusion.
Sequencing: Spots should be welded in a pattern that minimizes cumulative distortion (alternating sides, working from center outward).
Inspection: Each spot should be inspected for cracks using magnetic particle testing before proceeding to the next spot.
Post-weld treatment: Light hammering of the hot deposit can reduce residual stress and improve toughness.

Study Insights and Implications

This paper represents a practical engineering optimization that balances wear resistance, production efficiency, and cost. The selection of dot-pattern hardfacing over continuous strip hardfacing demonstrates a thoughtful approach to the trade-offs inherent in surface engineering: while continuous coverage provides slightly higher wear resistance, the dot pattern offers superior productivity, lower distortion, and easier field repair.

The submerged arc process is particularly well-suited to this application because of its high deposition rate, consistent quality, and automation capability. The automatic wire feed and constant travel speed ensure uniform deposit properties across all spots, which is critical for predictable service life.

From a cost-benefit perspective, the investment in hardfacing equipment and consumables is easily justified by the extended service life and reduced downtime. For a large port handling millions of tons of bulk material annually, even a modest improvement in liner life translates to significant cost savings.

The methodology presented here is directly transferable to other abrasive wear applications in bulk material handling, mining, and cement industries, where similar hopper and chute configurations are employed.