Technical information

To assure that the sealing lips are permanently pressed against the contact surfaces, spring-energized seals made from PTFE and PE compounds require metal spring elements that are integrated in the plastic casings. In special cases, these may be elastomer O-rings as well. Most seals, however, have metal springs. The spring assures constantly even contact pressure of the sealing lip across the entire temperature range. For the different types of seals different types of springs are available with particular spring characteristics. These spring characteristics and properties have a major influence on sealing performance, friction and wear behavior of the groove seal.

U- and/or V-Spring

These standardized spring types are used in all U-shaped versions, such as the standard URI, URA, URS rod and piston seals and the URF shaft seals. Both types are primarily used in dynamic sealing applications, as relatively low spring forces are achieved with large spring travel. In high-speed applications this results in low wear of the dynamic sealing lips. With their maximum pre-loading force, the spring ends directly act on the sealing edges of the sealing lips, thus generating optimum compression development. The highly flexible springs are capable of providing better compensation for larger groove tolerances, coaxiality flaws and misalignments.

C-spring

The C-spring is a spiral type wound from metallic tape and excels at offering high spring forces even at low rates of spring travel. These springs are recommended primarily for use in static and/or slow-moving and high-pressure sealing applications. The high pre-loading forces ensure excellent sealing performance both with fluid and gaseous media. This spring type is particularly well suited for low-temperature applications

Special Springs

Additional special spring types available on request.

This map shows the various spring characteristics related to the individual nominal cross-sections, clearly revealing the differences between U-, V- and/or C-springs. This data based on a 20 mm length of spring. Purpose-manufactured special springs for friction-optimized seals assure minimum contact pressures with large rates of spring travel. This enables us to make pinpoint calculations and proposals for seals offering high wear reserves and thus prolonged service life.

U-Spring compared to C-Spring

C-Spring
U-Spring

Spring Characteristics U-Spring

U 332 (spring thickness 0,10 mm)
U 116 (spring thickness 0,08 mm)
U 104 (spring thickness 0,25 mm)
U 108 (spring thickness 0,12 mm)
U 308 (spring thickness 0,20 mm)
U 104 (spring thickness 0,15 mm)
U 316 (spring thickness 0,10 mm)

Spring Characteristics C-Spring

C 116 (spring thickness 0,08 mm)
C 332 (spring thickness 0,08 mm)
C 108 (spring thickness 0,08 mm)
C 316 (spring thickness 0,12 mm)
C 104 (spring thickness 0,15 mm)

As a general rule, seals must be stored in such a way that any damage resulting from external shock or pressure is precluded. Sealing lips must be protected from deformation under all circumstances. Springenergized seals made from PTFE compounds have a virtually unlimited shelf life.
PE-based seals should be placed and picked using the First-in-First-out principle.
Maximum storage period is app. 1 year, provided the seals are stored in dry conditions and protected from exposure to UV light.

The crucial factor affecting the sealing function, sealing performance and service life of the seal is the surface quality of the contact surface. Grooving, scoring, scratching and traces of machining must be avoided. In a sealing system, any of these will lead to leakage as well as damage to the sealing lips. The following surface roughness values of the dynamic and static sealing surface are recommended:

Surface hardness of shaft seals ≥ 58 HRC non-twisting. Particularly with piston and rod seals, e.g. types URI, URA and URS, the material content/ bearing content of the surface is crucial. As such, even roller-burnished or ground/polished stainless steel rods or needles achieve a high material content of ≥ 75% measured at a cut depth of c = 25% of the Rz-value based on a reference value of 5% .

The following surface structures illustrate this point:
Ideal contact surface for piston and rod seals, e.g. achieved by rollerburnishing, honing, grinding/ polishing. For shaft seals, e.g. type URF, we recommend hardened steel shafts ground without twists. Many applications also use coatings such as chromium oxide, tungsten carbide, carbon coatings, etc. When such coatings are used, a very good surface quality (Rz ≤ 1.0 μm) must be assured. Otherwise, these extremely hard coatings cause excessive wear of the sealing lip. We also recommend you consider having our development department perform respective wear tests in such cases.

Ideal dynamic contact surface

Material content 75% at Rz-value 1.0 μm

• good sealing effect
• long service life
  
  

Cracked contact surface, not optimally suited

Material content 20% at same Rz-value of 1.0 μm

• lower sealing effect
• wear of sealing lip