The basic elements of creating a strong face seal are relatively easy to understand. The main function of a seal is to eliminate the potential of fluid leakage from high to low pressure by utilizing a sealing gap. Missteps in basic sealing lead to increased maintenance time, halted operations, and overall system component replacements. Considering the specifications of your sealing system must be the foremost concern when outlining the build and machinery of your platform.
In short, a face seal is a complete closure in which the surfaces to be sealed are normalized to the axis of said seal. Face seals prevent fluid leakage and thus eliminate resulting complications from chemical contaminants stemming from leakage. Static seals are at the mercy of preloading, which helps attain sealing. Preloading is achieved when the seal height is greater than the sealing gap. During compression of machine parts, seal elasticity is deformed, spurring internal stressors forcing both the top and bottom sealing gap to close. Subsequential fluid pressure is attributed to additional internal stress, fomenting preloading and leakage prevention.
Face seal functionality centers around the successful contact between the gasket and sealing faces at some or all locations surrounding the sealing gap where the fluid pressure is greatest. Three cornerstone considerations must be implemented to successfully construct a face seal. They include the following elements: axial squeeze, gland fill, and interference fit.
Axial Squeeze (Preload): Without calculation of the axial squeeze, proper sealing becomes impossible. The axial squeeze is also known as the preload of the seal. Calculating the percentage of axial squeeze follows a predetermined formula:
% Axial Squeeze = H0-Hc / H0
H0 = Original Seal Height
Hc = Compressed Seal Height
Traditionally axial thickness is typically deflected by 25% of its original height measurement when the two surfaces forming the sealing gap are in their final positions. Keep your sealing system’s manufacturing tolerances in mind throughout the entirety of your design. Designing the correct system the first time will save you time and money. Axial squeeze tolerance should fall between the ten and forty percent mark.
Gland Fill: Glad fill describes the percentage of volume seal grooves take up. The percentage may be calculated with the following formula:
% Gland Fill = VS / VG
VS = Seal Volume
VG = Gland Volume
Taking care not to overtax the gland is essential to successful operation of sealing systems. In environments where the gland fill is overburdened, weighty seal volumes will cause direct damage to the seal and their corresponding sealing surfaces. Commonly, gland fill manufacturing capacity weighs in at 95 percent.
Interference Fit: The final stepping stone in creating a comprehensive sealing solution is determining the geometrical definition of the sealing system. Interference fit varies depending upon where the greatest amounts of pressure are exuded. Should the greatest pressure be expressed on the inside of the seal, outside diameter (O.D.) interference is recommended.
However, in systems where the greatest pressure resides outside of the sealing system, an inside diameter (I.D.) interference is recommended. Manufacturing tolerances should be designed within a one to five percent range. Automated assembly systems or specialized machines may prevent traditional interference fit design methods.
Radial seals and face seals vary in the direction in which compression is achieved for sealing. Radial seals compress to both the outside diameter and inside diameter. Face seals differ in compression (or squeeze), which is applied to both the top and bottom of the sealing system’s cross sections. Radial seals specialize in cap and plug, piston and bore type utilization. Face seals are typically leveraged solely in static environments, whereas radial seals herald applications in both static and dynamic environments. Design parameters vary greatly between designs. The following considerations vary when developing face and radial sealing systems: squeeze, fill, stretch, gap size, clearance gap, and the angle of the installation chamber.
Static radial seals describe sealing systems in which there exists no motion in relation to the seal and mating surfaces achieving sealing. The only activity static seals experience is the mating of sealant surfaces. Wear and tear is typically slow developing in static sealing solutions, as there are fewer components involved constantly wearing down sealing components. Static systems can accommodate an increased seal squeeze, greater clearance gaps, rougher finishing for sealing surfaces, and higher rates of fluid pressure.
Dynamic radial seals move through a set range of motions including reciprocation, rotation, and oscillation between mating surface elements. Sealing systems mobilize themselves either on a continuous basis or are expressed in recurrent cycles. Operating motions are performed via the moving piston and rod. Rotary environments exhibit both internal and external rotation surrounding the area of the shaft axis in a singular fashion. Fans are excellent examples of this type of relationship. Similarly, rotary seals oscillate forward and backward again.
Rotating and oscillating selections exist within some specialized models, but their use is uncommon. Dynamic radial seals carry intrinsic friction between mating sealant surfaces. Maintenance is necessary to respond to deteriorating elements of sealing systems for optimal performance.
We’ve been pioneering industrious sealing solutions for nearly 50 years! Here at Wyatt Seal, we’re dedicated to helping our customers outfit the custom solutions they need to improve their turnaround times. We offer thousands of manufactured seals, rotary seals, gaskets, O-rings, and specialized sealing products. We also offer custom fabrication for sealing solutions which do not yet exist on the market. Contact us directly for immediate ordering and custom inquiries.
Dupont’s variety of products serve countless uses. Among these is the Kalrez 1050LF. This specific product is part of Dupont’s Kalrez line of parts, known across the manufacturing space as a top material for long-term sealing in some of the harshest chemical environments out there.
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