Step Seal: Structure, Materials and Applications

Step Seal is a single-directional, high-performance sealing component widely used in hydraulic cylinder piston rod seals. It is named for its unique stepped (Step-shaped) structure design and is renowned for its extremely low friction and outstanding sealing performance.

 1. Structure of Step Seal

Step Seal is a two-part combined sealing component:

 Main Sealing Ring: Usually made of filled polytetrafluoroethylene (PTFE) or its improved materials (such as Turcon® etc.). This is the core component of the seal, with a unique "step-shaped" cross-section. This step structure forms a low-pressure area and a high-pressure area.

 Low-pressure side (atmospheric side): Usually has a shallow groove.

 High-pressure side (piston cylinder side): Designed to be more robust to withstand system pressure.

 Elastic Loading Ring (O-Ring): Usually made of elastic materials such as Nitrile (NBR) or fluororubber (FKM) as an O-ring. It is installed in the groove of the main sealing ring and is located on the low-pressure side.

 Working Principle:

 When the system is without pressure, the elastic O-ring provides initial preload to the main sealing ring, achieving low-pressure sealing. When the system pressure increases, the pressure medium enters the stepped groove, acting on the back of the main sealing ring, pushing it further towards the piston rod surface, forming a self-enhanced sealing effect. The higher the pressure, the greater the sealing force.

 2. Differences between Step Seal and Glyd Ring Structure

 Glyd Ring is another common piston rod seal, consisting of PTFE Glyd Ring and O-ring. Although both are combined seals and use similar materials, they have key differences in structure and performance:

 Characteristics

 Step Seal  

 Glyd Ring (Glyd Ring)  

 Structural Shape

 Step-shaped, asymmetric cross-section, with high and low pressure sides

 Rectangular or similar rectangular runway shape, with basically symmetrical cross-section

 Sealing Lip

 Has a very low and smooth sealing lip

 Sealing Lip is more obvious

 Friction Characteristics

 Extremely low start-up and running friction, almost no "slipping" phenomenon

 Friction coefficient is lower, but usually slightly higher than Step Seal

 Application Direction

 Strictly single-direction sealing, installation must correctly distinguish the high-pressure side and low-pressure side

 Single-direction sealing, but the structural symmetry is slightly higher, and the distinction is not as strict as Step Seal

 Dynamic Response

 Responds very quickly to pressure changes, and the sealing effect improves with pressure increase

 Response is good, but the self-enhancement effect and dynamic characteristics are slightly inferior to Step Seal

 Summary of Core Differences:

 Step Seal achieves lower friction and better dynamic response characteristics than Glyd Ring through its unique stepped design, especially in low-speed and low-pressure conditions, effectively avoiding "creeping" phenomenon, and has more outstanding performance. Glyd Ring is a more economical and widely used mature solution.

 3. Structural Advantages of Step Seal

 Extremely low friction coefficient: The PTFE material itself has a very low friction coefficient, and with the optimized lip design, it significantly reduces start-up and running resistance, improves system efficiency, and reduces energy consumption and wear.

 Zero-leakage Sealing: Excellent static and dynamic sealing capabilities, can achieve no-leakage sealing, meeting high standards of environmental protection and equipment requirements. Non-stick slip phenomenon: Specifically suitable for low-speed and light-load conditions, it can completely eliminate the "creeping" or "jerk" (Stick-Slip) during the piston rod movement, ensuring smooth operation.

High pressure resistance: The stepped structure brings about a self-reinforcing effect, enabling it to withstand up to 60 MPa or even higher system pressure.

Wide temperature range: Depending on the selected material combination (such as PTFE paired with FKM O-rings), it can be applied in a wide temperature environment ranging from -50°C to +200°C.

Long life and high wear resistance: PTFE material has excellent wear resistance and performs well even in the presence of contaminants, with a long service life.

Four. Materials and Required Characteristics

Main sealing ring material:

Common materials: Filled polytetrafluoroethylene (PTFE).

Common fillers:

Glass fiber: Improves wear resistance and hardness.

Graphite: Enhances self-lubrication and temperature resistance.

Molybdenum disulfide (MoS₂): Improves self-lubrication and reduces friction.

Bronze: Improves thermal conductivity and wear resistance.

Materials should possess the following characteristics:

Low friction coefficient

High wear resistance

Good thermal conductivity (to dissipate friction heat)

Resistance to chemical media and hydraulic oil

High mechanical strength (resistant to compression, creep)

Elastic loading ring (O-ring) material:

Common materials: Nitrile rubber (NBR) (suitable for most mineral-based hydraulic oils and general conditions), Fluororubber (FKM) (suitable for high temperatures, harsh chemical environments and synthetic hydraulic oils).

Materials should possess the following characteristics:

Good elasticity (providing continuous preload)

Compatibility with the main sealing ring and grooves

Oil-resistant, temperature-resistant

Small compression permanent deformation

Five. Common Application Scenarios

Stefan is used due to its high performance in demanding engineering machinery, industrial equipment and hydraulic systems:

Construction machinery: Hydraulic cylinder piston rods for excavators, loaders, cranes, bulldozers, etc. This is its most mainstream application field.

Injection molding machines: Injection and mold closing oil cylinders requiring smooth and precise actions.

Machine tools and presses: Main cylinders and auxiliary oil cylinders, especially in scenarios requiring low-speed and smooth operation.

Aerospace: Seals for landing gear, actuators, etc., requiring high reliability and wide temperature performance.

Servo hydraulic cylinders: Situations requiring extremely high control accuracy and dynamic response, extremely low friction.

Adverse conditions: Suitable for conditions with certain contamination, large temperature variations or requirements for long life and maintenance-free operation.

In summary, Stoffen is a high-end sealing component that combines the low friction properties of PTFE with the pre-tightening force of elastomers through an ingenious stepped structure design. It is a proven preferred solution in one-way piston rod sealing applications that require low friction, no leakage, no crawling, and high pressure resistance.

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