Cemented carbide sealing rings are core components in mechanical sealing systems, widely used in pumps, valves, hydraulic equipment, chemical reactors, and other applications. Their primary function is to prevent fluid (liquid or gas) leakage through tight fitting. Since they operate long-term under complex working conditions such as high pressure, high-speed friction, and medium corrosion, the material performance of sealing rings directly determines the operational stability of equipment. Choosing the right material allows a sealing ring to work continuously for thousands of hours; choosing the wrong one may lead to frequent downtime due to rapid wear or corrosion failure, and even trigger safety accidents. Cemented carbide has become the mainstream choice for sealing rings due to its high hardness, wear resistance, and corrosion resistance. However, cemented carbides with different compositions vary significantly in their suitability for different working conditions. Starting from the operational requirements of sealing rings, this article details the key indicators for material selection, the applicable scenarios of common alloy grades, and practical selection steps, helping you accurately match the most suitable material for cemented carbide sealing rings.
1. First Clarify Requirements: Core Performance Requirements for Cemented Carbide Sealing Rings
Before selecting materials, it is necessary to clarify the working environment of the sealing ring, as different working conditions impose distinct requirements on the material’s hardness, toughness, corrosion resistance, and wear resistance. The following are four core operational factors that affect material selection:
1. Medium Type: Determines Corrosion Resistance
The medium in contact with the sealing ring (such as clean water, oil, acid-base solutions, high-temperature steam, etc.) directly dictates the required corrosion resistance:
- Neutral media (clean water, lubricating oil): Low corrosion resistance requirements, which can be met by ordinary cemented carbide.
- Corrosive media (acid-base solutions, seawater, chemical raw materials): The material must have chemical corrosion resistance to prevent the cobalt (Co) binder phase in the alloy from being corroded and dissolved.
- Particle-containing media (slurry, ore pulp, sand-containing sewage): In addition to corrosion resistance, high wear resistance is required to prevent the sealing surface from being worn by particle erosion.
2. Operating Temperature: Affects Strength Stability
Temperature changes can alter the mechanical properties of cemented carbide. In particular, the cobalt binder phase may soften at high temperatures:
- Low-temperature conditions (-50℃~100℃): Most cemented carbides can operate stably without special requirements.
- Medium-temperature conditions (100℃~300℃): The material must have a certain level of heat resistance to avoid hardness reduction caused by the softening of the cobalt phase.
- High-temperature conditions (300℃~600℃): Heat-resistant alloy elements (such as titanium and tantalum) need to be added to prevent oxidation or strength attenuation of the material at high temperatures.
3. Operating Pressure: Related to Impact and Compression Resistance
The higher the pressure, the greater the fitting pressure between the sealing ring and the mating part (such as a graphite ring or metal ring), which imposes higher requirements on the material’s compressive strength and toughness:
- Low-pressure conditions (≤1MPa, e.g., ordinary water pipe valves): Low toughness requirements for the material; cemented carbide with medium hardness is sufficient.
- Medium-pressure conditions (1MPa~10MPa, e.g., hydraulic systems): The material must balance hardness and toughness to avoid cracks under medium pressure.
- High-pressure conditions (>10MPa, e.g., high-pressure pumps, reactors): High-toughness cemented carbide must be selected to prevent the sealing ring from fracturing due to impact loads.
4. Relative Rotational Speed: Determines Wear Resistance Requirements
The higher the relative rotational speed between the sealing ring and the mating part, the more severe the heat generation and wear caused by friction:
- Low-speed conditions (≤500r/min, e.g., manual valves): Mild wear, requiring low wear resistance of the material.
- Medium-speed conditions (500r/min~3000r/min, e.g., ordinary centrifugal pumps): The material must have good wear resistance to reduce friction loss.
- High-speed conditions (>3000r/min, e.g., high-speed gear pumps): Materials with high hardness and low friction coefficient are required. Meanwhile, lubrication measures should be adopted to avoid overheating and wear.
2. Core Indicators: Key Parameters of Cemented Carbide Sealing Ring Materials
The performance of cemented carbide is determined by three key factors: tungsten carbide (WC) grain size, cobalt (Co) content, and additives. Understanding the impact of these parameters is essential for accurate material selection:
1. Tungsten Carbide (WC) Grain Size: Influences Hardness and Wear Resistance
WC serves as the "framework" of cemented carbide, and its grain size directly affects the material’s hardness and wear resistance:
- Fine-grain WC (1~3μm): High hardness (HRA 90~92) and excellent wear resistance, but relatively low toughness. It is suitable for medium-to-high speed, low-impact sealing scenarios (such as clean water pumps).
- Medium-grain WC (3~5μm): Moderate hardness (HRA 88~90) and balanced toughness. It is suitable for most general-purpose working conditions (such as hydraulic systems and ordinary valves).
- Coarse-grain WC (5~8μm): Lower hardness (HRA 85~88) but better toughness. It is suitable for high-pressure, impactful working conditions containing particles (such as ore pulp pumps and slurry valves).
2. Cobalt (Co) Content: Balances Toughness and Corrosion Resistance
Co acts as the "adhesive" that binds WC particles together. Its content affects the material’s toughness and corrosion resistance:
- Low Co content (6%~8%): High material hardness and good wear resistance, but poor toughness and average corrosion resistance. It is suitable for low-pressure, impact-free dry conditions (such as gas sealing).
- Medium Co content (8%~12%): Balanced toughness and wear resistance, with moderate corrosion resistance. It is the preferred choice for general-purpose sealing rings (such as lubricating oil and clean water media).
- High Co content (12%~15%): Excellent toughness, capable of withstanding high-pressure impacts, but slightly reduced wear resistance and corrosion resistance. It is suitable for high-pressure working conditions with slight particles (such as high-pressure hydraulic systems).
3. Additives: Targeted Improvement of Special Properties
To adapt to complex working conditions, small amounts of special elements (such as titanium, tantalum, nickel, etc.) are often added to cemented carbide, which can be selected as needed:
- Adding titanium carbide (TiC) or tantalum carbide (TaC): Improves high-temperature stability and corrosion resistance, suitable for high-temperature environments above 300℃ or weakly corrosive media (such as steam pipelines and dilute acid solutions).
- Replacing part of Co with nickel (Ni): Significantly enhances corrosion resistance, suitable for strongly acidic and alkaline media (such as chemical reactors and seawater treatment equipment).
- Adding vanadium carbide (VC): Refines grains and improves the material’s wear resistance and impact resistance, suitable for high-speed working conditions containing particles (such as slag pumps).
3. Practical Recommendations: Material Selection for Cemented Carbide Sealing Rings Under Different Working Conditions
Based on the above parameters and operational requirements, the following material recommendations for common scenarios are provided for direct reference:
| Working Condition Type | Typical Application Scenarios | Recommended Material Grade | Core Advantages |
|---|---|---|---|
| General neutral media (low pressure, low speed) | Ordinary water pipe valves, lubricating oil pumps | YG8 (medium-grain WC + 8% Co) | High cost-effectiveness, balanced toughness and wear resistance |
| Medium pressure and medium speed (clean water/hydraulic oil) | Centrifugal pumps, hydraulic system seals | YG10 (medium-grain WC + 10% Co) | Better toughness and impact resistance, suitable for medium pressure |
| High pressure with particles (ore pulp/slurry) | Ore pulp pumps, slurry valves | YG15 (coarse-grain WC + 15% Co) | High toughness, resistant to particle impact and wear |
| High-temperature conditions (300℃~600℃) | Steam pipelines, high-temperature reactors | YT15 (contains TiC, 8% Co) | High-temperature resistant and oxidation resistant, suitable for high-temperature steam media |
| Weakly corrosive media (dilute acid and alkali) | Chemical centrifugal pumps, seawater treatment equipment | YG8N (Ni replaces part of Co) | Better corrosion resistance than ordinary YG series, suitable for weak acid and alkali |
| Strongly corrosive media (concentrated acid and alkali) | Acid-base storage tank valves, chemical reactors | YN6 (high Ni content) | Resistant to strong corrosion, preventing Co from being corroded and dissolved |
| High-speed sealing (>3000r/min) | High-speed gear pumps, precision hydraulic equipment | YG6X (fine-grain WC + 6% Co + TaC) | High hardness and low friction, wear-resistant and suitable for high-speed friction |
4. Selection Steps: Four Steps to Choose Cemented Carbide Sealing Ring Materials
Faced with diverse working conditions and material grades, you can screen step by step as follows to avoid blind selection:
- Clarify core operating parameters: Record the working medium (whether corrosive or particle-containing), temperature range, pressure value, and relative rotational speed of the sealing ring to form an "operating condition list" (example: medium is clean water, temperature is 80℃, pressure is 5MPa, rotational speed is 1500r/min).
- Determine key performance requirements: Prioritize requirements based on the list. For example, prioritize corrosion resistance for corrosive media, toughness for high-pressure conditions, and wear resistance for high-speed conditions.
- Match material parameters: Screen materials according to priorities—choose Ni-based alloys for corrosion resistance, high Co content for high pressure, and fine-grain WC for high speed.
- Conduct small-batch test verification: For critical equipment, first purchase a small number of samples for installation testing (observe wear and leakage after 100~200 hours of operation). Only purchase in large quantities after confirming no issues.
5. Common Misconceptions: Avoid "Taken-for-Granted" Mistakes in Material Selection
In practical selection, many people fall into misunderstandings due to empiricism, leading to premature failure of sealing rings. The following problems need to be avoided:
Misconception 1: "The Higher the Hardness, the Better—Fine-Grain Alloys Are Always Reliable"
Fact: Fine-grain alloys have high hardness but poor toughness, and are prone to fracturing under high-pressure or particle-containing working conditions. A factory selected fine-grain YG6 alloy for the sealing rings of ore pulp pumps to improve wear resistance. However, due to particle impact in the ore pulp, cracks appeared in less than 100 hours. After switching to coarse-grain YG15, the service life was extended to 800 hours.
Misconception 2: "High-Cost YN Series Must Be Chosen for Corrosion Resistance"
Fact: The YN series (with high Ni content) has strong corrosion resistance but a high price. For weakly corrosive media (such as tap water and dilute salt water), YG8N (with Ni replacing part of Co) is completely sufficient. A water treatment plant used YN6 sealing rings for tap water treatment. The cost was three times higher than that of YG8N, but the actual service life difference was only 5%, resulting in unnecessary waste.
Misconception 3: "Ignore the Material of Mating Parts and Only Focus on the Sealing Ring Itself"
Fact: The wear of the sealing ring is closely related to the mating parts (such as graphite and ceramics). For example, when cemented carbide is paired with graphite, wear mainly results from the "grinding" of graphite by cemented carbide, so medium-hardness alloys can be selected. When paired with ceramics, the two materials have similar hardness, so fine-grain alloys with higher wear resistance must be selected; otherwise, the sealing ring is easily worn by ceramics.
6. Conclusion: The Core of Material Selection Lies in "Working Condition Adaptation"
The key to selecting materials for cemented carbide sealing rings is not to pursue "maximum hardness" or "the most expensive grade", but to accurately match material performance with working condition requirements—prioritize toughness for high-pressure conditions, corrosion resistance for corrosive media, and wear resistance for high-speed scenarios. For professionals in the tungsten carbide industry, when recommending materials, it is necessary to first inquire about the customer’s detailed working condition parameters (medium, temperature, pressure, rotational speed), and then provide customized suggestions based on alloy characteristics, rather than simply recommending general-purpose grades.
If the sealing rings of your equipment frequently suffer from problems such as rapid wear and corrosion failure, or if you need customized cemented carbide materials for special working conditions (such as high temperature, high pressure, and strong corrosion), feel free to communicate with us. We can provide material sample testing and working condition analysis services to help you find the optimal solution.