Why Are Cemented Carbide Sealing Rings Indispensable in Pumps and Valves? A Comprehensive Guide

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In rotating equipment such as pumps, compressors, and reactors, an inconspicuous yet critical component—the mechanical sealing ring—plays a vital role in preventing liquid or gas leakage. Its failure can lead to anything from unscheduled downtime to serious safety incidents.

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Cemented carbide (tungsten carbide) is one of the primary materials used in manufacturing these sealing rings. Below is a clear explanation from the perspectives of material properties and manufacturing processes.

I. Key Performance Characteristics of Cemented Carbide Sealing Rings

1. High Hardness

Cemented carbide offers significantly higher hardness than ordinary steel. For example, grade YG6 has a hardness of approximately 89.5 HRA, enabling effective resistance against wear caused by hard particles in the medium.

2. High Compressive Strength

The compressive strength of cemented carbide can exceed 4000 MPa, giving it a load‑bearing capacity several times that of conventional structural steel.

3. Good Flatness

According to Chinese standard JB/T 4127.1‑1999, the flatness of the sealing end face shall not exceed 0.0009 mm (approximately three optical bands). For more demanding applications, flatness can be controlled within 0.0006 mm.

4. Low Surface Roughness

The same standard specifies that the surface roughness (Ra) of the hard material sealing end face should not exceed 0.2 µm. Mirror‑grade finishing can further reduce friction.

5. Corrosion Resistance

Conventional tungsten‑cobalt (YG) alloys are not suitable for highly corrosive media. In contrast, nickel‑based (YN) alloys exhibit good corrosion resistance in acidic, alkaline, and seawater environments.

II. Common Grades and Typical Applications

YG6 (approx. 6 % Co) – Density: 14.6–15.0 g/cm³, hardness: ≥ 89.5 HRA. Suitable for general abrasive conditions such as clean water and oil.

YG8 (approx. 8 % Co) – Slightly higher toughness than YG6, suitable for moderate impact conditions.

YN8 (approx. 8 % Ni) – Density: 14.6–14.8 g/cm³, hardness: approx. 90.5 HRA. Good corrosion resistance, suitable for chemical and marine environments.

III. How Is the Accuracy of the Sealing Surface Inspected?

1. Flatness Inspection – Optical Band Method

Per JB/T 7369‑2011, an optical flat is used together with a monochromatic light source to observe interference fringes (optical bands). One optical band corresponds to approximately 0.00029 mm of flatness. Three or fewer optical bands are considered acceptable, while two optical bands indicate higher precision.

2. Roughness Inspection

The Ra value is measured with a roughness tester. Mirror‑grade surfaces can achieve Ra values below 0.05 µm.

3. Dimensional Inspection

Critical dimensions such as diameter and thickness are verified using pneumatic gauges or coordinate measuring machines (CMM). Tolerances are typically specified as h8 or H8.

IV. Summary

Thanks to their high hardness, excellent flatness, low surface roughness, and material selection tailored to different operating conditions, cemented carbide sealing rings have become indispensable components in mechanical seals.

(Disclaimer: The data cited in this article are derived from publicly available national standards and general industry information. They do not constitute a performance guarantee for any specific product. Actual technical requirements shall be subject to the drawings and contracts mutually agreed upon by both parties.)