How Tungsten Carbide Seal Rings Are Made: Powder to Grinding and Lapping
A precision tungsten carbide seal ring may look like a relatively simple component: a hard circular ring with a flat sealing face. Its manufacturing route, however, is very different from machining the same geometry from conventional steel.
Cemented Tungsten Carbide is produced through powder metallurgy. WC powder is combined with a metallic binder system, compacted into a green body, densified by sintering, and only then finished to its final dimensions using processes such as diamond grinding and lapping.
What makes seal rings particularly demanding is that the final component must satisfy two very different requirements at the same time: the bulk material must have a controlled microstructure, while the sealing face must have precise geometry and surface condition.
Grinding can correct size. Lapping can refine a sealing face. Neither process can turn a poorly sintered carbide blank into a structurally reliable seal ring.
Select the Carbide Composition Before Preparing the Powder
The manufacturing process starts with the material specification, not with pressing.
Most conventional seal-ring grades consist primarily of tungsten carbide grains combined with a metallic binder. Cobalt-bonded WC-Co and nickel-bonded WC-Ni are common material directions.
The binder type and percentage, WC grain size, and any approved additives influence hardness, fracture resistance, corrosion behavior, and sintering response.
For example, a custom tungsten carbide seal ring for abrasive but chemically mild service may require a different grade strategy from one operating in chloride-rich or acidic process fluid.
The key manufacturing lesson is that material selection and process selection cannot be separated. A change in binder composition or WC grain size may require corresponding changes in milling, pressing, sintering, and finishing conditions.
Weigh, Mix, and Mill the Carbide Powder
The raw powder system must be homogenized before forming.
Depending on the approved manufacturing route, powder preparation can involve controlled weighing, wet or dry mixing, milling, binder addition, and granulation. The goal is not simply to make the powder finer. Milling also helps distribute the metallic binder uniformly around WC particles and produces a consistent feedstock for pressing.
Excessive milling, contamination, poor binder distribution, or uncontrolled particle-size changes can all influence the final microstructure.
Press the Seal-Ring Blank
Prepared powder is compacted into a body using an appropriate forming process.
Depending on ring geometry, size, production quantity, and tooling strategy, manufacturing routes may include uniaxial die pressing, isostatic pressing, or other powder-consolidation methods.
The body has the basic ring shape but has not yet achieved the density or strength of finished cemented carbide.
At this stage, dimensions intentionally differ from final dimensions because the component will shrink during sintering. The exact shrinkage is process- and composition-dependent, so using a universal percentage for all tungsten carbide rings would be technically misleading.
Where required, features that are easier to create before sintering may be introduced through controlled green machining. The compact is still comparatively fragile, so edge damage and cracking must be avoided.
Sintering Create the Cemented Carbide
Sintering transforms the fragile compact into a dense engineering material.
Cemented-carbide literature describes this as one of the most important stages in the entire production chain. During the cycle, temporary forming agents are removed and the binder phase enables densification and bonding of the WC structure.
Sintering control influences:
● Final density
● Residual porosity
● WC grain growth
● Carbon balance
● Binder distribution
● Hardness and toughness
● Final blank distortion
Carbon control is especially important. Metallographic standards for hardmetals specifically address porosity, uncombined carbon, and eta-phase because these conditions reveal problems that cannot be detected from dimensional inspection alone.
What About Sinter-HIP?
Some demanding Carbide Components use pressure-assisted densification such as sinter-HIP as part of the manufacturing route.
The purpose is to reduce residual internal porosity under controlled high-temperature and gas-pressure conditions.
However, HIP should not be presented as a magic process that automatically makes every seal ring superior. The need for pressure-assisted densification depends on the grade, application, quality specification, component size, and risk profile.
Good manufacturing still depends on correct powder chemistry, compaction, carbon control, and sintering before the HIP stage becomes meaningful.
Grinding Establishes Final Geometry
Once sintered, cemented carbide is extremely difficult to machine using conventional cutting tools. Diamond grinding is therefore an established finishing method for WC-based hardmetals.
For seal rings, grinding may establish:
● Finished OD
● Finished ID
● Thickness
● Parallel faces
● Steps and shoulders
● Chamfers
● Required concentric relationships
Grinding is not merely a dimensional operation. Grinding causes damage beneath the surface of tungsten carbide. Grinding-wheel condition and process parameters also influence grinding force, energy, and resulting surface integrity.
That means aggressive stock removal is not automatically efficient if it leaves microchipping, cracks, or excessive surface damage that must later be removed.
I regard grinding allowance as a balance: enough material must remain after sintering to achieve final geometry, but unnecessary grinding stock increases machining time and the opportunity for edge damage.
Lapping Creates the Functional Seal Face
Grinding brings the ring close to its final geometry. Lapping performs a different job.
Mechanical seal faces operate in very close proximity with a thin lubricating film between rotating and stationary surfaces. Surface topography and flatness therefore affect the ability of the pair to control leakage and maintain stable contact conditions.
Lapping is used to refine the working face toward the flatness, surface texture, and thickness relationship required by the actual seal design.
Double-sided lapping is also an established precision process for components such as seal rings where flatness and thickness uniformity matter.
A critical distinction is that lapping should not be expected to correct every upstream problem.
It can remove small amounts of material and improve face geometry. It cannot remove a deep grinding crack without significant rework, correct excessive sintering distortion economically, or repair internal porosity.
For more detail, see our guide to seal-face flatness and lapping quality.
Final Inspection Must Check More Than a Shiny Face
A visually reflective sealing face is not proof that the ring meets the drawing.
Final inspection for precision tungsten carbide seal rings may include:
● OD, ID, thickness, and special geometry
● Face flatness
● Surface texture
● Parallelism or runout where specified
● Edge chips and microdamage
● Hardness and density
● Material-grade verification
● Traceability and inspection documentation
Flatness and surface roughness should be treated as separate characteristics. A face can be smooth but geometrically distorted, or flat but finished with an unsuitable surface texture.
This distinction is particularly important in mechanical seals because the final face operates as part of a mating pair rather than as an isolated polished component.
The Manufacturing Chain: What Each Stage Can and Cannot Fix
| Stage | Main Control Objective | What a Later Stage Cannot Easily Repair |
| Powder preparation | Composition and uniformity | Incorrect binder chemistry or contamination |
| Pressing | Consistent green density and shape | Severe density gradients or green cracks |
| Sintering | Densification and controlled microstructure | Porosity, abnormal phases, major distortion |
| Grinding | Final size and geometry | Internal metallurgical defects |
| Lapping | Functional sealing-face condition | Deep grinding damage or poor bulk material |
| Final inspection | Verify compliance | It detects defects; it does not manufacture quality |
When customers focus only on the final lapped surface, they are looking at the last visible stage of a much longer process.
In practice, I consider the most reliable seal rings to be the result of cumulative control.
The correct powder system provides the intended microstructure. Stable forming gives the sintering process a uniform starting point. Controlled sintering produces a sound blank. Grinding establishes the functional geometry without introducing excessive damage. Lapping then finishes a sealing surface that was already supported by good material and good geometry.
Langsun Carbide manufactures custom tungsten carbide seal rings for mechanical seals from WC-Co and WC-Ni material systems according to customer drawings and operating requirements, with precision grinding, lapping, dimensional inspection, and material-quality verification applied according to the agreed specification.
The final lapping operation should refine quality—not rescue the component from defects created five stages earlier.
FAQ
Why are seal rings oversized before sintering?
The compact shrinks during densification. The required green dimensions and finishing allowance depend on the specific material composition, tooling, pressing route, and sintering process.
Why is diamond used to grind tungsten carbide?
Cemented carbide is extremely hard after sintering. Diamond abrasives provide an established method for achieving precision dimensions and surface finishes on WC-based hardmetals.
What is the difference between grinding and lapping?
Grinding establishes dimensions and geometry with relatively higher material-removal capability. Lapping removes much smaller amounts of material to refine face flatness, surface condition, and thickness consistency.
Can lapping remove defects caused during sintering?
Not internal defects. Lapping can improve the near-surface geometry but cannot repair porosity, abnormal microstructure, deep cracks, or incorrect material composition.
Technical References
1. Raihanuzzaman, R. M., Xie, Z., Hong, S. J., Ghomashchi, R., Powder Refinement, Consolidation and Mechanical Properties of Cemented Carbides—An Overview, Powder Technology, Vol. 261, 2014, pp. 1–13. DOI: 10.1016/j.powtec.2014.04.024.
2. Cemented Carbide Microstructures: A Review, International Journal of Refractory Metals and Hard Materials, 2019. The review describes the conventional production chain from powder mixing and spray drying through pressing, dewaxing, sintering and post-sintering grinding.
3. ISO 4499-2:2020, Hardmetals — Metallographic Determination of Microstructure — Part 2: Measurement of WC Grain Size.
4. ISO 4499-4:2016, Hardmetals — Metallographic Determination of Microstructure — Part 4: Characterisation of Porosity, Carbon Defects and Eta-Phase Content.
5. 3D FIB/FESEM Tomography of Grinding-Induced Damage in WC-Co Cemented Carbides, Procedia CIRP, Vol. 87, 2020, pp. 385–390. DOI: 10.1016/j.procir.2020.02.070.
6. Effect of Bond Type and Process Parameters on Grinding Force Components in Grinding of Cemented Carbide, Procedia Engineering, Vol. 149, 2016, pp. 122–129. DOI: 10.1016/j.proeng.2016.06.646.
7. Description of Surface Topography of Sealing Rings, Wear, Vol. 271, Issues 3–4, 2011, pp. 571–575. DOI: 10.1016/j.wear.2010.04.036.
8. Theoretical and Experimental Investigations on Thickness Uniformity in Double-Sided Lapping, Chinese Journal of Mechanical Engineering, Vol. 38, Article 83, 2025.