Surfacing Repair of PYZ-2200 Cone Crusher

Literature Overview

This paper by Li Shuwen from Chuxiong Mining and Metallurgy Co., Ltd.选矿厂, published in Mining Machinery in 2003, documents a practical engineering solution for the surfacing repair of a PYZ-2200 cone crusher base seat. The case study addresses a critical wear problem where the bearing seat bore had developed excessive clearance due to progressive wear, threatening the continuous operation of a key production unit.

Problem Description

The PYZ-2200 medium cone crusher is classified as a department-controlled critical equipment in the mining operation. The failure mode identified was progressive enlargement of the clearance between the base seat 150-hole and the spherical bearing housing 1500 bearing seat. The wear manifested primarily in the drive shaft direction and at 90° to the drive shaft at four points, with maximum clearance reaching 5 mm.

The root cause analysis identified a self-accelerating wear mechanism:

Initial clearance enlargement allowed oscillatory motion between the bearing housing and base seat during operation.
This oscillation produced reciprocating sliding friction at the contact surfaces.
The friction accelerated material removal from both surfaces, further enlarging the clearance.
The progressive clearance increase amplified vibration and noise, creating a feedback loop that accelerated equipment degradation.

Repair Methodology

The repair employed manual metal arc welding (SMAW) with specialized surfacing electrodes to rebuild the worn bearing seat bore:

Repair Parameter	Specification	Rationale
Surfacing electrode type	Hardfacing electrode (Cr-based)	Provides wear resistance and build-up capability
Electrode diameter	4.0 mm	Adequate for thick deposit build-up
Welding current	140-180 A	Sufficient penetration for multi-layer build-up
Layer thickness per pass	3-5 mm	Maximizes build-up efficiency
Total layers	3-5	Achieves required dimensional recovery
Preheat temperature	200-250°C	Reduces cracking tendency in thick section
Interpass temperature	250-300°C	Controls cooling rate and residual stress
Post-repair machining	Bore to original dimensions	Restores bearing fit tolerance

FMEA Analysis of the Failure

Applying a Failure Mode and Effects Analysis (FMEA) framework to this case:

Failure Mode	Cause	Effect	Severity	Occurrence	Detection	RPN
Bearing seat clearance enlargement	Wear from oscillatory motion	Vibration, noise, eventual seizure	9	7	4	252
Surface cracking during repair	High residual stress, rapid cooling	Loss of repair integrity	8	5	3	120
Dimensional inaccuracy	Inadequate machining after surfacing	Bearing fit problems	7	4	2	56

Engineering Practice Lessons

This case study provides several valuable lessons for equipment repair engineers:

Early detection is critical: The 5 mm clearance represents a late-stage failure. Vibration monitoring and periodic clearance measurement should be implemented to detect progressive wear at earlier stages (e.g., when clearance exceeds 0.5 mm).
Root cause treatment: Simply rebuilding the bore without addressing the oscillatory motion mechanism will lead to repeat failure. The repair must include measures to prevent the original wear mechanism (e.g., improved bearing alignment, anti-vibration mounting).
Material selection for thick deposits: When building up thick sections (exceeding 15 mm total), the risk of cracking increases significantly. The choice of electrode with good ductility and low hydrogen content is essential.
Sequential repair strategy: The repair should proceed in stages—initial build-up with a ductile transition layer, followed by wear-resistant surfacing layers, and finally precision machining to restore dimensional accuracy.

Process Optimization Recommendations

Based on the case study, the following process improvements are recommended for similar repairs:

Implement a step-wise welding sequence starting from the most severely worn areas, working outward to maintain dimensional control.
Use alternating weld directions to balance residual stresses and minimize distortion.
Apply a post-weld stress-relief treatment (600-650°C for 2 hours) before final machining.
Consider using a low-dilution surfacing process (such as the coupled arc hot-wire GTAW described in Topic 1) for the final wear-resistant layer to ensure maximum hardness in the service surface.

Study Insights and Implications

This practical case study underscores the importance of integrating metallurgical knowledge with mechanical engineering in equipment repair. The surfacing repair of the cone crusher base seat demonstrates that even severe wear damage can be effectively addressed through proper welding methodology. However, the long-term success of such repairs depends on addressing the underlying mechanical causes of wear, not merely on the quality of the deposited material. For mining equipment maintenance, this approach offers a viable alternative to complete component replacement, significantly reducing downtime and repair costs.