Cladding Process for the Head of a Material Bucket

Literature Overview

This 2013 publication by Zhang Yun, Wang Chunying, and Wu Yanbo from Taiyuan Heavy Industries Co., Ltd. and the Institute of Electronic Engineering, China Academy of Engineering Physics, addresses the cladding process applied to the head section of a material bucket. Material buckets (also known as bucket elevators or grab buckets) are critical components in bulk material handling systems used in mining, cement, power generation, and chemical industries. The bucket head, which is the leading edge that penetrates and engages with the material being handled, is subjected to extreme wear, impact, and sometimes corrosive conditions.

Core Technical Content

The material bucket head experiences a complex combination of wear mechanisms:

Abrasive wear: From hard particles in the bulk material (ore, cement, coal)
Impact wear: From material striking the bucket head at velocity
Corrosive wear: From moisture, chemicals, or acidic components in the material
Fatigue wear: From cyclic loading during repeated material engagement

The cladding process must address all these wear mechanisms simultaneously, requiring a carefully selected overlay material and process. The typical approach involves applying a multi-layer cladding system: a transition layer for metallurgical compatibility, a bonding layer for adhesion, and a wear-resistant top layer for surface protection.

Process Selection and Parameters

For material bucket head cladding, several processes are applicable depending on the production volume, component geometry, and required overlay properties:

Process	Deposition Rate	Dilution	Suitability	Cost
SAW (Submerged Arc)	Very High	25–45%	Large flat areas	Low
GMAW (Gas Metal Arc)	High	20–40%	General purpose	Medium
FCAW (Flux-Cored Arc)	High	20–35%	Field repair	Medium
PTA (Plasma Transfer Arc)	Medium	5–15%	Precision overlay	High
Laser Cladding	Medium	2–10%	Thin, high-quality layers	High

Parameter	GMAW Cladding	SAW Cladding	PTA Cladding
Wire/Flux	1.2–2.0 mm	1.6–2.0 mm wire	Powder 0.05–0.2 mm
Current	150–250 A	300–500 A	200–350 A
Voltage	22–28 V	25–35 V	N/A (powder)
Shielding Gas	CO₂ or Ar+CO₂	Flux	Ar
Travel Speed	200–400 mm/min	300–600 mm/min	200–500 mm/min
Layer Thickness	2–4 mm/pass	3–6 mm/pass	0.5–1.5 mm/pass
Preheat	100–200°C	150–250°C	100–200°C

Multi-Layer Cladding Design

For material bucket heads subjected to severe wear, a multi-layer cladding approach is recommended:

Transition layer (1st pass): Low-alloy steel filler (e.g., E7018 equivalent) to bridge the gap between the base material and the subsequent alloy layers. This layer ensures proper metallurgical bonding and reduces cracking susceptibility.
Bonding layer (2nd pass): Medium-alloy steel or austenitic stainless steel (e.g., 309L) to provide a ductile buffer zone between the transition layer and the hardfacing layer. This layer absorbs residual stresses and prevents crack propagation.
Hardfacing layer (3rd–4th pass): High-alloy hardfacing material (e.g., Fe-Cr-C, Co-Cr-W, or Ni-Cr-Mo) to provide the primary wear resistance. This layer is designed to achieve the target hardness and wear resistance.

Layer	Material	Function	Hardness	Thickness
Base	Q235/Q345 steel	Structural support	120–180 HV	—
Transition	E7018	Metallurgical bridge	200–250 HV	2–3 mm
Bonding	309L	Stress buffer	150–200 HV	2–3 mm
Hardfacing	Fe-20Cr-2C	Wear resistance	500–650 HV	3–5 mm

Defect Analysis and Countermeasures

Defect	Cause	Detection Method	Countermeasure
Interface cracking	High residual stress, hydrogen	MT, PT	Preheat, low-hydrogen filler, PWHT
Dilution exceeding limits	High heat input, thin first pass	Hardness mapping, chemical analysis	Reduce current, increase travel speed
Porosity	Contamination, inadequate shielding	RT, UT	Surface cleaning, proper gas flow
Incomplete fusion	Poor surface preparation, low heat input	UT, macrograph	Grinding to bare metal, increase heat
Hardness non-uniformity	Parameter variation, dilution	Hardness mapping	Consistent parameters, multiple measurements
Overlay spalling	Poor bond, thermal cycling	Visual, UT	Proper layer design, PWHT

Engineering Practice and Application Considerations

The material bucket head cladding process must be designed considering the specific operating conditions:

Mining applications: Require high-abrasion resistance against hard rock particles. Fe-Cr-C or Co-Cr-W hardfacing is recommended with hardness above 55 HRC.
Cement industry: Requires resistance to both abrasion and chemical attack from cement dust. Ni-Cr-Mo or austenitic stainless steel overlay is suitable.
Power generation (coal handling): Requires impact-abrasion resistance against coal and ash. Fe-14Cr-4Mo-2C hardfacing provides good balance.
Chemical industry: Requires corrosion resistance in addition to wear resistance. Hastelloy or Inconel overlay may be necessary.

The welding sequence for bucket head cladding should follow a symmetric pattern to minimize distortion. For bucket heads with complex geometries, the welding sequence must be carefully planned to avoid excessive heat concentration in thin sections.

Study Insights and Reflections

This study from Taiyuan Heavy Industries demonstrates the practical application of cladding technology in heavy equipment manufacturing. The material bucket head, though a relatively simple component, requires sophisticated cladding design to withstand the demanding conditions of bulk material handling. The key insight is that effective cladding design must address the complete wear mechanism, not just the most obvious one. A single-layer approach may be insufficient for components experiencing combined wear mechanisms, and a multi-layer strategy provides superior performance. Engineers working on material handling equipment should consider cladding as a design feature rather than a repair measure, integrating it into the initial component design for optimal performance and service life extension. The economic analysis of cladding versus replacement should always be performed, as cladding can extend component life by 3–5 times while reducing overall lifecycle costs significantly.