The world can be a very dirty place and applications require sealing tasked with keeping that dirt out of the moving parts. Many solutions exist to prevent dirt and mud ingression into a system, each with unique benefits and drawbacks.
Metal Face Seals
Arguably the most robust exclusion system available is a Metal Face Seal, sometimes called Duo-Cone, Cat, or Toric seal. These seals operate by loading two finely lapped metal surfaces against each other using rubber elements as energizers and static seals around the exterior of the seal. The finely polished metal surfaces must be perpetually lubricated by internally retained fluid, creating a thin film on which the seal faces ride. From the exterior, the two metal components mate so tightly, there is virtually no avenue for dirt ingression. Though these seals work very well once installed, installation can be challenging and incorrect assembly can cause premature wear or immediate leakage. This style of seal also requires a design with minimal axial movement or misalignment during application.
Another popular exclusion method is the use of a wiper style seal. This method is common on the rod end side of a hydraulic cylinder and in other situations where dirt exclusion is required, but a more robust solution would be unnecessary. This style of seal could utilize either an integrated metal can which is pressed into the housing, or molded from a rubber or urethane material allowing installation into a specially designed groove. These styles are designed for axial movement and can tolerate some misalignment, but do not provide an overly robust sealing solution in heavy dirt and mud applications.
Custom Designed Exclusion Sealing Solutions
In many cases, a unique and custom solution is required to meet the specific needs of the customer. Though every application is different, there are some core concepts that carry through the custom design process:
Minimize the Ingression Area
- Minimizing the opening for contamination helps restrict the overall size of the contamination and reduces the volume that reaches the sealing components. In a heavy mud environment, shielding the seal area for rocks, debris, and other large objects adds life to the seal and prevents damage to the seal outside of normal wear and tear through use. It also acts as a restrictor for the contaminants so a smaller volume reaches the actual seal or sealing elements.
Convolute the Path the Contamination Must Take
- A convoluted path through the sealing area creates a longer path for dirt ingression, and allows for additional sealing elements such as lips and pockets of grease. More sealing elements can result in a longer overall life for the seal. A single lip seal will begin to wear once dirt reaches it, but in a seal with three lips, contamination must reach and wear out each of the three lips in succession before the overall seal will fail.
Allow the Contamination to Purge Itself
- While no seal will last forever, creating a design that allows for the purging of any contamination can add additional life. A design that encourages contamination to fall back out when not in a heavy dirt environment is essential to prevent continued compaction of additional material and increased wear on the sealing components. Creating a seal that allows for a grease purge can result in a seal cleared of contamination when performing equipment maintenance, ensuring a longer seal life.
An application specific solution is often the best solution for a complicated exclusion requirement. Developing a robust solution by thoroughly evaluating the complete application, end use environment, and worst-case scenarios allow for long life and serviceability.