Surfacing Technology for Left and Right Turntables of EBZ125 TBM

Literature Overview

This paper by Liu Weibin, Zhang Yawen, and Lei Zhenhua from Shaanxi Construction Machinery Co., Ltd. Heavy Copper Equipment Research Institute, published in Mining Machinery in 2009, describes the surfacing technology applied to the left and right turntables of the EBZ125 roadheader (tunnel boring machine). The EBZ125 is a specialized machine for coal and semi-coal-rock tunnel excavation, where the turntables are critical components subjected to severe abrasive wear from non-metallic cutting materials.

Equipment Background and Wear Analysis

The EBZ125 roadheader operates in coal and semi-coal-rock tunnel environments where the cutting materials include:

Coal (abrasive due to embedded quartz and pyrite)
Soft rock (containing hard mineral inclusions)
Semi-coal-rock (mixed abrasive severity)

The left and right turntables serve as the drive interfaces that rotate the collected material through the conveyor system. The primary wear mechanism is abrasive wear from non-metallic materials, supplemented by adhesive wear from metal-to-metal contact at high loads.

Wear Parameter	Typical Value	Impact
Material hardness (Mohs)	3-7 (coal to semi-rock)	Determines abrasive severity
Contact pressure	50-150 MPa	Drives subsurface damage
Sliding velocity	0.5-2.0 m/s	Affects wear rate
Ambient temperature	25-45°C	Influences material properties
Contaminant content	5-15% (abrasive particles)	Accelerates three-body abrasion

Surfacing Process Design

The surfacing technology for the EBZ125 turntables was designed to provide a multi-layer protection strategy:

Layer	Material	Thickness	Hardness	Function
Transition layer	Low-carbon steel (E5015/E5016)	2-3 mm	200-250 HV	Stress buffering, crack arrest
Intermediate layer	Medium-Cr alloy (E6015-D1)	2-3 mm	350-400 HV	Toughness support
Surface layer	Cr-based hardfacing	2-4 mm	600-800 HV	Primary wear resistance

The multi-layer approach addresses the fundamental challenge of surfacing repair: achieving high surface hardness without compromising the toughness of the base material. The transition layer prevents crack propagation from the brittle hardfacing surface into the ductile base metal.

Process Parameters

Parameter	Value	Control Objective
Welding method	SMAW (manual arc)	Flexibility for curved surfaces
Electrode type (transition)	E5015 (low hydrogen)	Crack-free transition
Electrode type (surface)	Cr-based hardfacing	Maximum surface hardness
Welding current (transition)	120-150 A	Controlled penetration
Welding current (surface)	100-130 A	Reduced dilution for hardfacing
Travel speed	100-200 mm/min	Uniform bead profile
Bead overlap	50-60%	Ensures complete coverage
Preheat temperature	150-200°C	Hydrogen crack prevention
Interpass temperature	<200°C	Controls HAZ grain growth

Quality Control and Verification

Following the PDCA (Plan-Do-Check-Act) methodology, the surfacing quality was verified through:

Visual inspection (VT): Checking for surface defects, undercutting, porosity, and incomplete fusion.
Magnetic particle testing (MT): Detecting surface and near-surface cracks in the surfacing layer and HAZ.
Hardness testing: Verifying surface hardness meets specifications (≥600 HV for the hardfacing layer).
Microstructural examination: Confirming proper carbide distribution and absence of brittle phases.
Service performance monitoring: Tracking wear rate during operational use to validate the repair effectiveness.

Engineering Practice Case Study

The implementation of this surfacing technology on the EBZ125 turntables yielded the following results:

Pre-repair condition: Turntables showed 3-5 mm of wear after 200-300 hours of operation, requiring frequent regrinding or replacement.
Post-surfacing condition: The surfaced turntables maintained acceptable surface condition for 800-1200 hours of operation, representing a 3-4× improvement in service life.
Economic benefit: The cost of surfacing repair was approximately 15-20% of the cost of complete turntable replacement, providing significant economic advantage.
Downtime reduction: Extended service life between maintenance intervals reduced unplanned downtime by approximately 60%.

Key Technical Challenges and Solutions

Challenge	Root Cause	Solution
Cracking in hardfacing layer	High residual stress, rapid cooling	Preheating, low-hydrogen electrode, controlled cooling
Excessive dilution	High heat input, long arc	Short arc length, lower current, multiple thin passes
Surface porosity	Inadequate shielding, contamination	Clean surface preparation, consistent arc length
Dimensional accuracy	Welding distortion	Symmetric welding sequence, fixture support
Layer delamination	Poor metallurgical bonding	Proper transition layer, adequate penetration

Study Insights and Implications

This practical application demonstrates the effectiveness of multi-layer surfacing technology for extending the service life of critical mining equipment components. The EBZ125 turntable repair case illustrates several important principles:

Material selection must match the wear mechanism: For non-metallic abrasive wear, Cr-based hardfacing with fine carbide distribution provides optimal performance.
Multi-layer design is essential for thick repairs: The transition-intermediate-surface layer sequence provides the necessary gradient in mechanical properties from the base metal to the wear surface.
Process control is as important as material selection: Consistent welding parameters, proper preheating, and quality verification are critical to achieving reliable repair results.
Economic analysis must include downtime costs: The total cost of ownership—including production losses from frequent replacements—often favors surfacing repair over component replacement.

For mining equipment maintenance engineers, this case study provides a replicable methodology for addressing abrasive wear on rotating components. The systematic approach—combining wear analysis, material selection, process design, quality control, and performance verification—can be adapted to similar applications in other mining and construction equipment.