Manufacturing of Surfaced Alloy Seal Rings for Mechanical Seals

Literature Overview

This technical paper by Wang Min and Zeng Xingshao from Zigong Mechanical Seal Factory, Sichuan, published in Fluid Machinery (1995, Vol. 23, No. 5, pp. 36-38), describes the manufacturing process for alloy seal rings used in mechanical seals, with emphasis on the selection of base and overlay materials, determination of surfacing layer thickness and hardness, and control of surface defects. Mechanical seals are critical components in rotating equipment such as pumps, compressors, and agitators, where they prevent fluid leakage between the rotating shaft and the stationary housing.

Material Selection and Design Considerations

The performance of a mechanical seal is determined by the tribological pair—the combination of materials used for the rotating and stationary seal faces. The selection of materials must consider:

Chemical compatibility: Resistance to the sealed fluid (acid, base, solvent, slurry)
Thermal stability: Ability to withstand frictional heating at the seal interface
Wear resistance: Hardness and toughness balance for long service life
Thermal conductivity: Ability to dissipate frictional heat
Friction coefficient: Low friction to minimize heat generation and wear

Common base materials include carbon-graphite, silicon carbide, alumina, and tungsten carbide. Overlay materials include Stellite (Co-Cr-W), tungsten carbide-cobalt, and high-chromium iron alloys.

Typical Material Combinations

Base Material	Overlay Material	Application
Carbon-graphite	Stellite 6	General chemical service
Silicon carbide	Tungsten carbide-cobalt	High-pressure, high-temperature
Alumina	High-chromium iron	Slurry and abrasive service
Tungsten carbide	Stellite 6	Severe wear, high pressure

Surfacing Process Parameters

The surfacing of seal rings requires precise control to achieve the desired layer thickness, hardness, and surface quality. The following parameters are critical:

Parameter	Typical Value	Rationale
Surfacing method	TIG, plasma arc, or HVOF	TIG for precision, HVOF for thick layers
Layer thickness	0.5-2.0 mm	Depends on application and base material
Hardness	40-60 HRC	Balance of wear resistance and toughness
Surface roughness	Ra 0.2-0.8 μm	Smooth surface for low friction
Heat input	Low to moderate	Minimize distortion and base metal damage

Layer Thickness Determination

The surfacing layer thickness is determined by:

Wear allowance: The thickness must accommodate expected wear during the service life of the seal
Base material properties: The base must be strong enough to support the overlay without deformation
Thermal expansion mismatch: The overlay and base must have compatible thermal expansion coefficients to avoid cracking during thermal cycling
Manufacturing constraints: Excessive thickness may lead to distortion, cracking, or poor adhesion

Surface Defect Control

Surface defects in seal rings are critical because they can initiate fluid leakage, increase friction, and lead to premature seal failure. The following defects and their controls are discussed:

Defect	Cause	Control Measure
Cracks	Thermal stress, high hardness	Reduce heat input, temper after welding
Porosity	Gas entrapment, surface contamination	Improve shielding, clean surface
Inclusions	Flux contamination, poor technique	Use clean consumables, proper technique
Uneven thickness	Inconsistent travel speed, arc instability	Use automated equipment, monitor parameters
Poor adhesion	Surface contamination, insufficient fusion	Thorough cleaning, proper preheating

Quality Control and Inspection

The quality of surfaced seal rings is verified through:

Visual inspection: Check for surface defects, uniformity, and dimensional accuracy
Hardness testing: Verify overlay hardness at multiple locations
Dimensional measurement: Confirm inner diameter, outer diameter, and thickness
Surface roughness measurement: Ensure Ra within specified limits
Non-destructive testing: Magnetic particle testing for surface cracks, ultrasonic testing for subsurface defects

Engineering Practice and Study Insights

This paper provides a practical guide for the manufacturing of alloy seal rings, emphasizing the importance of material selection, process control, and quality verification. The key insight is that the performance of a mechanical seal depends not only on the design but also on the manufacturing quality of the seal faces. Even a small surface defect can lead to seal failure, making quality control critical.

For modern engineers, this paper highlights the continued relevance of traditional surfacing techniques in high-precision applications. While advanced manufacturing methods such as laser cladding and electron beam welding have been developed, the fundamental principles of material selection, layer thickness control, and defect prevention remain the same. The paper also underscores the importance of post-weld machining and surface finishing in achieving the required dimensional accuracy and surface quality for seal applications.