Surfacing Repair of Crane Machinery Components

Literature Overview

This paper by Wan Weiguo from the Technical Center of Maanshan Iron and Steel Co., Ltd., published in Crane and Transport Machinery (2005, Vol. 11, pp. 59-61), provides a practical guide to the surfacing repair of crane machinery parts using manual arc surfacing (SMAW). The paper addresses local wear, machining defects, and dimensional deviations in crane components, presenting a systematic approach to repair that combines proper consumable selection, technique, and post-weld machining. The work reflects the practical engineering philosophy common in Chinese heavy industry: maximizing equipment utilization through effective repair rather than premature replacement.

Failure Modes in Crane Machinery Components

Crane machinery components experience diverse degradation mechanisms that necessitate surfacing repair:

Contact wear at bearing surfaces, pin holes, and contact pads
Adhesive wear in sliding interfaces such as hoist wheels and slewing rings
Abrasive wear from sand, scale, or other particulate contamination
Machining defects including oversize bores, undersized shafts, and surface damage from improper machining
Corrosion at unprotected surfaces exposed to outdoor environments

These failure modes create specific requirements for repair surfacing that differ significantly from new part fabrication.

Surfacing Repair Process Parameters

The paper emphasizes manual arc surfacing (SMAW) as the primary repair method, which is appropriate given the field conditions typical of crane maintenance operations. Key process parameters for effective surfacing repair include:

Parameter	Recommended Value	Purpose
Electrode type	Hardfacing (high Cr-C or Cr-Cr)	Match wear resistance requirements
Preheat temperature	100-250°C depending on base material	Reduce residual stress and hydrogen cracking risk
Interpass temperature	Below 250°C	Control dilution and microstructure
Current density	15-25 A/mm²	Ensure adequate penetration without excessive dilution
Surfacing layer thickness	3-5 mm (minimum)	Provide adequate wear-resistant layer after machining
Number of passes	2-3 layers	Achieve uniform composition and minimize dilution
Post-weld machining allowance	1.5-3 mm	Achieve final dimensions and surface finish

Consumable Selection Strategy

The selection of surfacing consumables must be guided by the specific wear mechanism and service conditions of the repaired component:

For sliding wear surfaces: High chromium (12-25% Cr) martensitic hardfacing electrodes provide good resistance to adhesive and sliding wear. The hard carbide network (Cr₇C₃) dispersed in a tempered martensite matrix offers excellent sliding wear resistance.
For abrasive wear surfaces: Cr-Cr compound electrodes (such as Cr12MoV-type hardfacing) produce a microstructure of hard Cr₇C₃ and Cr₂₃C₆ carbides in a martensitic matrix, providing superior resistance to abrasive wear from hard particles.
For components requiring toughness: Medium-carbon low-alloy surfacing electrodes with 0.4-0.6% C provide a balance between wear resistance and impact toughness, suitable for components subject to impact loading.

Machining Considerations After Surfacing

A critical aspect emphasized in this paper is the machining process following surfacing repair. Hardfacing deposits, particularly high-chromium martensitic types, present significant challenges for machining:

Tool selection: Carbide tools with proper rake angles are essential. For Cr-Cr hardfacing materials, CBN (cubic boron nitride) tools may be required for high-production operations.
Cutting parameters: Reduced cutting speeds (20-40 m/min for carbide tools) and appropriate feed rates are necessary to avoid tool chipping.
Coolant application: Flood cooling with water-soluble cutting fluid is recommended to manage heat generation during machining of hardfacing deposits.
Dimensional control: The residual stress from surfacing welding can cause dimensional instability during machining, requiring careful machining sequence planning and possibly stress-relief annealing before final machining.

Quality Control and Inspection

Post-repair quality control should follow a systematic approach:

Visual inspection: Check for surface cracks, porosity, and undercut along weld toes.
Hardness testing: Verify that the surfacing layer hardness meets specification (typically 50-60 HRC for hardfacing applications).
Dimensional verification: Confirm that machined dimensions meet the original equipment manufacturer (OEM) tolerances.
Load testing: For safety-critical crane components, a proof load test at 1.25 times rated capacity is recommended before returning the component to service.

Engineering Practice and Lessons Learned

The paper's emphasis on practical repair methodology reflects an important engineering principle: the cost-effectiveness of repair versus replacement must be evaluated on a case-by-case basis. For crane machinery operating in steel mills and industrial facilities, where component replacement requires extended downtime and high procurement costs, surfacing repair offers a technically viable and economically attractive alternative. However, engineers must recognize that surfacing repair is not universally applicable. Components with extensive fatigue damage, severe corrosion, or geometric distortion beyond repair limits should be replaced rather than repaired. A proper engineering assessment using principles similar to FMEA (Failure Mode and Effects Analysis) should be conducted before deciding on the repair approach.