Seal for Extreme Conditions

The combination of seals, wipers, and guides in hydraulic cylinders is determined by the application in which the machines are used, the arrangement of the cylinders, and the prevailing operating conditions. In order to meet the requirements of applications running in extreme conditions in an economical manner, Simrit developed the new high-performance HDR-2C U-packing. This new seal combines two polyurethane materials and their respective properties in a single seal in a way that makes optimum use of the specific advantages of each material.

The development of this innovation would not have been possible without the help of modern simulation and analysis methods, which provided an accurate insight into all functional areas of a seal¾even under load. These methods showed that because of their functions, the demands made on the sealing material by sealing edges, which are exposed to static and dynamic loads, are completely different to those made by the groove base or when bridging gaps. The press fit (Fig. 1, section 1) prevents axial movement of the seal in the housing. For this, a very stiff material with low permanent set and excellent adhesion is required. Static tightness (Fig. 1, section 2) prevents leakages via the groove base and ensures pressure buildup. To this end, the sealing material must boast good elasticity and a high contact force pressure. It is important that dynamic sealing is guaranteed at the sealing edge (Fig. 1, section 3) even at low temperatures and that leakages are prevented via the moving rod. At the same time, however, this area must also ensure pressure buildup when exposed to transverse loads on the rod even after a lengthy downtime in low temperatures. The ideal material for this function boasts excellent dynamic properties, low relaxation at low temperatures, low friction, and high tightness. The gap-bridging zone (Fig. 1, section 4) must be extrusion-resistant and must prevent the seal from being pressed into the gap under high pressure. This requires a sealing material with a high level of stiffness and hardness.