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SKF Assists In The Development Of State-of-the-art Hydraulic Piston Seals
Sep 25, 2018

                        SKF assists in the development of state-of-the-art hydraulic piston seals

Piston seals are the key to the performance of hydraulic cylinders. The seal is located in the groove of the outer diameter of the piston and must resist high pressure hydraulic fluid and does not impede movement of the piston along the hydraulic cylinder. Since most hydraulic cylinders move in both directions, the seal must be able to withstand pressure on either side. The design of piston seals requires engineers to strike a balance between friction and sealing performance. If too much fluid leaks from the high pressure side of the cylinder to the low pressure side, the seal performance will be reduced. On the other hand, excessive friction on the cylinder wall can lead to increased wear and shortened operating life. Complete failure of the piston seal, ie internal leakage, can cause significant operational and safety hazards, such as loss of control of the load on the building or material handling equipment.

To overcome the shortcomings of PTFE seals, SKF's team of engineers tried to develop a sealing technology that could replace it based on the company's proven ECOPUR polyurethane material.

Manufacturing polyurethane seals that match the good performance of PTFE seals is far from paper. Wolfgang Swete, director of strategic product line development for SKF Fluid Seals, explains, “The gap between the piston and the barrel means you need an anti-extrusion A material with good enough performance to maintain its shape under all operating conditions."

SKF tested prototype seals made from its hardest Ecopur polyurethane and found that it could not achieve its goals. However, SKF has made a special grade of Ecopur material with its own advantages in material development and manufacturing capabilities, specifically for piston seals. This new material - X-Ecopur PS - is currently the hardest polyurethane produced by SKF.

With the right materials, the SKF team began to design a reasonable sealing section. This is a familiar area for SKF engineers. They use a fairly mature product development process, combined with a large number of computer simulations using finite element techniques, using CNC equipment to quickly develop prototypes and then customizing static and dynamic test equipment. Perform physical tests on it.

In SKF's new design, an oil groove is added to the side of the slip ring to ensure that pressure is quickly applied to the elastomer. This design allows the seal to switch position based on rapid changes in pressure direction, reducing the possibility of internal leakage and loss of hydraulic cylinder function. The side oil grooves also reduce the pressure between the slip ring and the elastomer, which can also result in loss of hydraulic cylinder function.

SKF has now developed a full range of innovative piston seals for a wide range of hydraulic applications. Light duty LPV series with O-ring elastomer for manufacturing machines for indoor and stationary applications. This series of seals is suitable for pressures up to 250 bar, speeds up to 0.5 m/s and temperatures ranging from -20 to 100 °C. The medium to heavy duty MPV series is suitable for demanding applications such as mobile equipment such as agricultural and construction machinery. MPV seals are suitable for metric grooves for pressures up to 400 bar, speeds up to 1 m/s and temperatures ranging from -20 to 110 °C. The third seal series is modeled as DPV and offers the same operating parameters as the MPV series for inch grooves.

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