Manufacturing of Clad Alloy Seal Rings for Mechanical Seals

Literature Overview

This 1995 publication by Wang Min and Zeng Xingshao from Sichuan Zigong Mechanical Seal Component Factory addresses the manufacturing of clad alloy seal rings for mechanical seals. Mechanical seals are critical components in pumps, compressors, and agitators that prevent leakage of process fluids. The seal faces must exhibit excellent wear resistance, low friction, and corrosion resistance under demanding operating conditions including high pressure, temperature, and chemically aggressive media. Cladding technology provides an economical means of achieving the required surface properties on mechanically robust substrates.

Technical Background

Mechanical Seal Face Requirements

Property	Requirement	Typical Value
Hardness	High and uniform	40–60 HRC for metal faces
Friction coefficient	Low	0.01–0.10
Thermal conductivity	High	>30 W/m·K
Corrosion resistance	Excellent in process fluid	<0.1 mm/y
Thermal shock resistance	High	>50 cycles without cracking
Flatness	Very high	<0.5 μm
Surface roughness	Very fine	Ra 0.05–0.2 μm

Material Selection for Seal Faces

The seal face material must be matched to the process fluid and operating conditions:

Service Condition	Seal Face Material	Cladding Approach
Water and mild chemicals	Carbon steel + Stellite 6	SAW or GTAW overlay
Acids and alkalis	Stainless steel + tungsten carbide	GTAW or laser cladding
High temperature (>300°C)	Alloy steel + cobalt alloy	PTA or GTAW
High pressure (>10 MPa)	Alloy steel + SiC composite	Specialized cladding
Corrosive + abrasive	Nickel alloy + ceramic	Multi-layer cladding

Manufacturing Process

Substrate Preparation

The seal ring substrate, typically made from 40Cr, 17-4PH stainless steel, or similar alloy, must be machined to close dimensional tolerances prior to cladding. The cladding surface should be ground to Ra 1.6 μm to ensure good fusion and minimize porosity. Surface contamination must be thoroughly removed using acetone or similar solvent.

Cladding Process Selection

The choice of cladding process depends on the seal ring geometry, required overlay thickness, and material combination:

Process	Overlay Thickness	Dilution	Application
GTAW (TIG)	0.5–3.0 mm	10–25%	Precision seal rings, small diameters
SAW (Submerged Arc)	1.0–5.0 mm	15–30%	Larger seal rings, thicker overlays
PTA (Plasma Transferred Arc)	0.3–2.0 mm	5–15%	Thin precision overlays, high dilution control
Laser cladding	0.1–1.0 mm	<5%	Ultra-thin overlays, minimal HAZ
Electroslag welding (ESW)	3.0–10.0 mm	20–35%	Thick overlays on large components

GTAW Cladding Process Details

For precision mechanical seal rings, GTAW is the most commonly employed cladding process due to its excellent heat input control and ability to produce smooth, uniform overlays. The process parameters for typical seal ring cladding are:

Parameter	Value	Notes
Current	80–180 A	DCEN for tungsten electrode
Arc voltage	10–14 V	Depends on electrode and gap
Travel speed	40–100 mm/min	Controls bead width and overlap
Tungsten electrode	2.0–3.2 mm CeLa₂O₂	Stable arc, low contamination
Shielding gas	100% Ar or Ar + 2% H₂	Reduces oxide inclusion
Gas flow	8–15 L/min	Adequate protection
Filler wire	1.6–2.4 mm alloy	Matched to overlay composition
Preheat	100–200°C	Reduces cracking tendency

Multi-Pass Deposition and Build-Up

For seal rings requiring overlay thickness greater than 1 mm, multi-pass deposition is necessary. The first pass establishes the bond with the substrate, while subsequent passes build thickness. The final pass must be carefully controlled to achieve the required surface finish and geometry. A typical multi-pass sequence includes:

First pass: Low current (80–120 A), high travel speed (80–100 mm/min) to minimize dilution and establish bond
Build-up passes: Moderate current (120–160 A), moderate speed (50–70 mm/min) to increase thickness
Final pass: Optimized for surface quality, may use slightly higher current for better wetting

Post-Cladding Machining

The clad seal ring must undergo precision machining to achieve the required dimensional tolerances and surface finish. The machining sequence typically includes:

Rough turning to remove excess overlay material
Semi-finishing to establish near-final dimensions
Final grinding to achieve flatness and surface finish specifications
Lapping or polishing for ultra-fine surface finish (Ra < 0.05 μm)

The machinability of the overlay material significantly affects the machining process. Stellite alloys and tungsten carbide composites require diamond or cubic boron nitride (CBN) cutting tools, while cobalt alloys can be machined with carbide tools at reduced speeds.

Quality Control and Testing

Inspection Requirements

Inspection	Method	Acceptance Criteria
Visual inspection	VT	No cracks, porosity, undercut
Penetrant testing	PT	No surface cracks or indications
Hardness	HV or HRC	Within specified range ±10%
Flatness	Optical flatness tester	<0.5 μm for critical seals
Surface roughness	Profilometer	Ra 0.05–0.2 μm
Chemical composition	Spark OES or wet chemistry	Within specified composition range
Bond strength	Peel test or shear test	>200 MPa for critical applications

Performance Testing

Clad seal rings must undergo performance testing to verify their suitability for the intended application:

Friction coefficient testing: Measured using a tribometer under simulated operating conditions
Wear testing: Pin-on-disk or block-on-ring testing against the mating seal material
Corrosion testing: Immersion testing in the process fluid for 720 hours minimum
Thermal cycling testing: 50–100 cycles between ambient and maximum operating temperature

Engineering Practice Integration

The manufacturing of clad alloy seal rings for mechanical seals requires careful coordination between the cladding process, machining operations, and quality control. The tight tolerances and surface finish requirements of mechanical seals demand that the cladding process produce a uniform, defect-free overlay that can be machined to the required specifications. Any porosity, lack of fusion, or compositional variation in the overlay can lead to premature seal failure in service.

The literature highlights the importance of process qualification and consistent parameter control in seal ring manufacturing. A WPS (Welding Procedure Specification) must be qualified per relevant standards (ASME IX, NB/T 47014, or ISO 15614) for each material combination and geometry. Operator skill and experience are critical factors in achieving consistent quality, particularly for the final pass that determines surface quality.

Key Reflections

This 1995 publication addresses a specific and technically demanding application of cladding technology in the mechanical seal industry. The fundamental challenges identified—dilution control, surface quality, dimensional accuracy, and metallurgical soundness—remain relevant today. Modern manufacturing has adopted additional technologies such as laser cladding and cold spray for seal ring overlay, offering even lower dilution and reduced heat input. However, the GTAW-based processes described in this work remain widely used for their cost-effectiveness and proven reliability.

The work also underscores the interdisciplinary nature of seal ring manufacturing, requiring expertise in welding metallurgy, machining, materials science, and tribology. Engineers involved in mechanical seal design and procurement should understand the capabilities and limitations of cladding processes to make informed material and manufacturing decisions.

This publication serves as a valuable reference for engineers involved in surface engineering and precision component manufacturing, demonstrating the practical application of cladding technology to a high-value, critical component.