Mechanical Seal Manufacturing: Purpose, Types, Materials, and Casting Solutions

Mechanical seals are indispensable components across a multitude of industrial applications, playing a critical role in preventing fluid or gas leakage from rotating equipment such as pumps, compressors, and mixers. Their reliable performance is very much needed to guarantee operational efficiency, safety, and environmental protection. In this article, I will delve into specialized mechanical seal manufacturing, focusing specifically on the precision achieved through investment casting and the enduring quality offered by various grades of stainless steel mechanical seals.  

I will also explain the diverse range of stainless steel grades available for these components, so then you could make decisions for specific application needs. Ultimately, I will guide you in selecting a reliable manufacturer capable of delivering high-performance solutions.

Purpose and Types of Mechanical Seals

At their core, mechanical seals serve the fundamental purpose of preventing fluid or gas leakage from rotating equipment. This is achieved by creating a dynamic seal between a rotating component (typically a shaft) and a stationary housing, effectively containing the process fluid or gas within the equipment. Without effective sealing, leakage can lead to product loss, environmental contamination, and safety hazards, not to mention increased maintenance costs and equipment downtime. Industries and applications like oil and gas, chemical processing, industrial machinery, and water treatment commonly rely on mechanical seals, especially in valves and pumps, including various pump types, compressors, and mixers.

To address the diverse needs of various industries, numerous mechanical seal types have been developed. Each design is designed to meet specific application requirements, considering factors such as pressure, temperature, fluid characteristics, and rotational speed.

Pusher Seals

These are among the most basic and widely used seals. They utilize a spring or bellows to push a rotating face against a stationary face, maintaining a continuous seal. They are versatile and suitable for a broad range of applications.  

Cartridge Mechanical Seals

These are pre-assembled units designed for ease of installation and maintenance. They are self-contained, reducing the risk of installation errors and simplifying seal replacement.

Balanced Seals

These seals are designed to handle high-pressure applications. They incorporate design features that reduce the hydraulic pressure acting on the seal faces, minimizing wear and extending seal life.  

Gas Seals

Specifically engineered for gas applications, these seals utilize spiral grooves or other design features to create a controlled gas film between the seal faces, minimizing leakage. They are vital in industries dealing with hazardous or expensive gases.  

Pump Seals

This is a broad category including various seal types designed for use in pumps. The specific requirements of pump seals vary depending on the type of pump and the fluid being handled.  

The selection of the appropriate mechanical seal type is often prioritized for achieving optimal performance and reliability.

Several factors must consider the specific application requirements, including the type of fluid or gas being sealed, the operating pressure and temperature, and the rotational speed of the equipment.

Casting Process

Investment casting is among the most refined casting processes for manufacturing high-precision, high-quality mechanical seals. This method is very well known for producing the intricate geometries and tight tolerances often required.

In brief, the investment casting process involves creating a precise wax pattern that replicates the desired seal component. This pattern is then repeatedly dipped into a ceramic slurry, forming a robust ceramic shell. Once the ceramic shell is hardened, the wax is melted away (“dewaxing”), leaving a hollow ceramic mold. Molten stainless steel, the material of choice for durable and corrosion-resistant stainless steel mechanical seals, is then poured into this mold. After solidification and cooling, the ceramic shell is broken away, revealing the near-net-shape casting. Finally, finishing operations, such as machining and polishing, are performed to achieve the required surface finish and dimensional accuracy.

The precision and superior surface finish achieved through investment casting are necessary for ensuring the reliable performance of these components. This process allows specialized investment casting manufacturers like SIMIS to create complex designs with minimal machining, reducing material waste and production costs. Strict quality control measures are implemented throughout the investment casting process to guarantee that each mechanical seal meets the high standards demanded by various industrial applications.

Mechanical Seals Materials

The selection of the appropriate stainless steel grade is paramount in the manufacturing of high-performance stainless steel mechanical seals. Stainless steel, often preferred for its excellent corrosion resistance, durability, and strength, is a fantastic material for these components operating in diverse and often demanding environments. At Taiyuan SIMIS, we offer various stainless steel grades, each possessing unique properties that cater to specific application needs.

AISI 304/304L

This austenitic stainless steel is widely used due to its good corrosion resistance and formability. AISI 304 is suitable for general-purpose mechanical shaft seal applications in moderately corrosive environments. 304L, the low-carbon version, is preferred for welding applications to minimize carbide precipitation and maintain corrosion resistance.

AISI 316/316L

This molybdenum-enhanced austenitic stainless steel offers superior corrosion resistance compared to 304/304L, particularly in chloride-containing environments. AISI 316 is ideal for pump seals and other mechanical seal types operating in aggressive chemical and marine environments. 316L, similar to 304L, is used when welding is required.

AISI 410/420

These martensitic stainless steels are known for their high hardness and wear resistance. They are often used in pump seals and other applications where high wear resistance is crucial. These grades can be heat treated to increase hardness.

AISI 347

This austenitic stainless steel is stabilized with niobium, offering excellent resistance to intergranular corrosion, especially at elevated temperatures. AISI 347 stainless steel is suitable for applications involving high-temperature fluids and corrosive environmsents, often found in specialized gas seals and high-temperature pump seals.

2205 (Duplex Stainless Steel)

This duplex stainless steel combines austenitic and ferritic properties, providing high strength and excellent corrosion resistance, including resistance to stress corrosion cracking. It is utilized in demanding applications that require high mechanical strength and resistance to aggressive chemical environments, like certain high pressure cartridge mechanical seals.

2207 (Super Duplex Stainless Steel)

This super duplex stainless steel provides even higher corrosion resistance and strength than 2205, making it suitable for extremely aggressive environments, such as those encountered in offshore oil and gas applications.

17-4PH (Precipitation Hardening Stainless Steel)

This martensitic precipitation hardening stainless steel offers a unique combination of high strength and corrosion resistance. It is used in applications requiring high strength and moderate corrosion resistance, and where heat treatment can be used to increase hardness.

The selection of the appropriate stainless steel grade for a mechanical seal depends on several factors, including:

• The type of fluid or gas being sealed.
• The operating temperature and pressure.
• The corrosive nature of the environment.
• The required mechanical properties, such as strength and hardness.

As a professional investment casting company with rich experience in mechanical seal casting, we thoughtfully consider these factors to make sure the selection of a stainless steel grade that provides optimal performance and longevity for the specific application. We also offer guidance to our clients on material selection to achieve the optimal balance of budget and performance requirements.

Advantages of Investment Castings for Mechanical Seals

The combination of investment casting and stainless steel offers a compelling solution for the production of high-performance mechanical seals. Using this manufacturing technique leads to seals with enhanced reliability and extended lifespans, suitable for a diverse range of uses.

Firstly, the precision inherent in investment casting allows for the creation of intricate and complex geometries that are often required for modern mechanical seal types. This is particularly beneficial for cartridge mechanical seals, where precise dimensions and tight tolerances are often needed for optimal performance. The near-net-shape capabilities of investment casting minimize the need for additional machining, reducing material waste and production costs.  

Secondly, stainless steel mechanical seals produced through investment casting exhibit exceptional durability and corrosion resistance. The wide range of stainless steel grades available, as discussed earlier, allows us to select the optimal material grade for specific application environments. For instance, 316L provides superior corrosion resistance in aggressive chemical environments, while duplex stainless steels offer enhanced strength and resistance to stress corrosion cracking, essential for demanding applications like offshore oil and gas.  

Last but no least, the smooth surface finish achieved through investment casting minimizes friction and wear on the seal faces, leading to extended seal life and reduced maintenance requirements. This is exceptionally relevant for seals in pumps and gas equipment, as their stable operation and dependability are vital.

Why Choose Our Investment Casting Services for Mechanical Seals

For high-quality components, specifically mechanical seals, Taiyuan Simis Investment Casting Co., Ltd offers specialized investment casting with a focus on stainless steel. To achieve precise and consistent output, we employ state-of-the-art machinery, which includes robotic shell construction, automated drying systems, vacuum melting, and CMM technology. Our ISO 9001 accreditation and rigorous quality control, encompassing material testing and NDT, guarantee top-tier products. We specialize in custom manufacturing of these components, catering to diverse needs with expertise in numerous stainless steel grades (304/316/410/347/2205/2207/17-4PH).

For other stainless steel grades, please contact us with your specific requirements. As a reliable manufacturer and supplier of these components, we provide comprehensive support from design to delivery. At Simis, we also offer customized investment casting services, providing you with full flexibility to cast bespoke investment castings to your required specifications, including sizes, weights, materials, tolerances, treatments, logos, and markings. We also offer comprehensive tooling services. Contact us today for tailored solutions for your projects.