Materials are selected on the basis of their chemical andthermal stability relative to the medium to the sealed.
Care should also be taken to determine whether the anticorrosive properties of the metallic components are sufficient.
|Protection against corrosion
In the standard models, the reinforcing ring is of phosphatised deep-drawn sheet and the radial spring from size 111 or 211 upward of bright-drawn spring strip steel.
Seal sizes 100 to 110 and 200 to 210 are equipped with radial springs of stainless spring strip steel as standard.
From size 111 or 211 upward, the seals can also be equipped with stainless radial springs upon request.
Radial springs of spring-hard brass sheet are frequently employed for special sizes and designs.
|Dependability of seal||
In order to ensure a dependable sealing effect, the pressureexerted by the medium to the sealed may not lift thesealing lip up off the mating surface. The maximum
permissiblepressure per seal size can be seen on the tables at page "Type VI, VA, DI".
It is only permissible to increase the sealing lip prestress by increasing the spring force if
a dependable seal cannot be ensured in any other manner. Otherwise, an increase in the sealing lip prestress would result in unnecessary friction and heat-up, leading to
Peripheral and rotational speed
In order to avoid unnecessary heat-up and wear of the sealing lip, it is necessary to limit the peripheral speed at the sealing lip in accordance with the selected seal material.
The permissible rotational speeds for Perbunan® and Viton®, by seal size, can be seen from the tables on pages VI, VA and DI.
The diagram (down) provides a rapid
overview for Perbunan®.
Permissible speed for Perbunan:
|Friction and dissipated output:
In order to determine the required drive output, information is necessary regarding the coefficient of friction at start-up and the dissipated output under normal operating
conditions. During start-up, static friction is initially encountered, followed by dynamic friction.
The coefficient for static friction is assumed to be μo = 0.48, the coefficient for dynamic friction a maximum of p = 0.24 (0.12–0.24).
These figures apply for lubricated steel/
PERBUNAN and steel/VITON sealing surfaces.
MRO = 5 · 10-4 · Fa · dm · μo [J]
PR = 52,5 · 10-6 Fa · dm · n · μ [W]
Fa = Contact pressure force (sealing lip) [N]
dm = Mean diameter of sealing lip [mm]
n = Speed [min-1]
μo = Coefficient of friction, static
μ = Coefficient of friction, dynamic
Coefficient of friction dissipated output
|Permissible peripheral speed
The peripheral speed at the sealing lip may not exceed
the following values:
Perbunan® 20 m/s, Viton® 30 m/s
Perbunan® 10 m/s, Viton® 15 m/s
Perbunan® 9 m/s, Viton® 13 m/s
These values assume sufficient lubrication and heat dissipation at the sealing surface. Should these conditions not be provided, the limits shown at the left must be appropriately reduced, in accordance with the specific application.
Peripheral speed: v (m/s)
Speed: n (min-1)
Axial force: Fa (N)
Pressure: p (Pa)
Moment of friction: MRO (J)
Dissipated output: PR (W)
Width/length, Diameter: b, l, d (mm)
Coefficient of friction, static: μo ( )
Coefficient of friction, dynamic : μ ( )
Conversion of units:
1 N = 0,102 kp
1 Pa = 0,102 mmWS = 10-5 bar
1 J = 0,102 kpm = 1 Nm
1 W = 1,36 · 10-3 PS