Hardide CVD Hard Coatings for Mechanical Face Seals

Introduction

Hardide coatings, an advanced surface coating company, manufactures Hardide chemical vapour deposition (CVD) tungsten carbide/tungsten coatings for application on mechanical seals that are used in heavy-duty rotating equipment for the chemical, oil and gas industries. Mechanical face seals are used in rotating equipment including turbines, compressors, and pumps to lubricate the mechanical assemblies, exclude abrasive media, and prevent leaks. Seal reliability is a key parameter for overall equipment reliability because seal failure can cause damage to expensive equipment, thus resulting in high downtime costs.

Hard Materials

Hard materials are widely utilized for heavy-duty mechanical face seals, especially in the making of highly durable ‘primary' sealing surface that can resist three-body abrasion, corrosion and erosion. Solid hard materials including sintered tungsten carbide, ceramic or silicon carbide are often utilized but they are expensive, brittle and difficult to produce, particularly if the seal design has finer features. There is a substantial difference between thermal expansion properties of solid hard materials and steel. This causes jamming when there is change in temperature.

Hard Coatings

A more efficient technique involves the application of hard coating on mechanical seal components made of steel, which is low cost, tough and much easier to machine. This method also paves the way for better seal design. There are different designs of mechanical seals available but normally these include the primary sealing surfaces, often created as two rings or disks, of which one is a stationary part and second is a rotating part. During the rotation of the seal at a rate of 1000 to 60,000 rpm and more, the mechanical face seal’s operation relies on the fluid layer isolating the primary seal components to lubricate their surfaces for friction reduction and overheating prevention. Coating these hard faces of a mechanical seal prevents scratching by hard particles and the creation of scratch asperities that may rupture the lubricating fluid film.

Hardide CVD Coatings

Hardide CVD tungsten carbide/tungsten coatings fulfill all the key prerequisites for mechanical seal applications. Although the optimal hardness for mechanical seal applications is between 1100 and 1800 Hv, Hardide produces its coatings with a hardness ranging between 450 and 3500 Hv. The typical thickness of Hardide coatings is 50 µm but the company produces thinner or thicker coatings of 5 to 100 µm for certain seal designs. It is possible to polish Hardide coatings to a good finish, typically reaching an Ra better than 0.3 µm by simply polishing without using expensive grinding. Hardide coatings’ uniform structure provides an even wear pattern that enables coated components to maintain an optimum finish for longer period even in the most abrasive environments. These coatings comprise tungsten carbide and tungsten, which resist chemically aggressive and corrosive media, especially acids. Their mechanical properties can be improved by alloying them with small quantities of fluorine or fluorocarbons.

Conclusion

With Hardide CVD hard coatings, users in high wear applications such as valves, pumps and down hole tools operating in power generation, cryogenic equipment, refineries, food manufacturing, and oil and gas facilities can reduce expenses by optimizing part life and improving product performance.

Tungsten Carbide Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten-carbide.com.cn
Tel.: 86 592 5129696; Fax: 86 592 5129797
Email: sales@chinatungsten.com
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