The final variations of edge-sealing systems are systems that seal on the outside of the skirtboard steel. The most effective design combines multiple layer seal effectiveness with the simplicity of single-strip systems.
When conveyor maintenance workers prepare for cold weather activities they dress in layers. They know it is better to put on multiple layers of clothing—undershirt, shirt, sweatshirt, and jacket—than to wear one thick layer. The same concept can be used for transfer-point sealing: it is better to work with several thin layers than one thick, general-purpose layer. In sealing, the first layer is provided by the wear liner installed inside the chute. Extending down close to the belt, the wear liner keeps the large particles of material well away from the belt edge. The next layer is provided by the sealing system.
Multiple-layer seal designs feature rugged single-strip elastomers manufactured with a molded-in flap that serves as a secondary seal. This outrigger, or secondary strip, typically forms one or more channels that would capture the fines and gently carry them along the belt before depositing them back into the main body of material.
The system’s primary seal is clamped against the outside of the chute work, extending vertically down and lightly touching the belt. It is applied with light pressure onto the belt, and the clamp applies force horizontally toward the chute, rather than down onto the belt. Because the clamping force is horizontal, the primary strip contains the material without the application of high pressure on the belt that would increase wear and conveyor power consumption. This primary strip will contain most of the material that has escaped past the wear liner.
As an outrigger, the secondary seal requires only the force of its own elasticity to provide sealing pressure, and, consequently, will wear a long time without the need for adjustment.
Belt sealing and support components work together to ensure an effective seal to prevent the escape of fugitive material.
Installing the preferred one-piece design is a simple procedure: unroll the seal to the proper length, cut it, and attach it to the skirtboard using a clamping system. A one-piece seal avoids any unnecessary joints and the handling of multiple pieces. Sealing systems should be provided in different thicknesses, to handle different duty applications, and in different materials, to handle different needs such as food grade, high temperature, and underground applications.
Advantages of outward sealing are:
- Long lasting, because they are positioned away from material flow and sheltered by the skirtboard and wear liner.
- Can be self-adjusting
- Low required sealing pressure due to “labyrinth” or multiple-layer seal design
- Adapt to existing clamp systems
Disadvantages of outward sealing are:
- Require greater belt-edge distance (or free-belt distance)
- Vulnerable to damage if belt mistracks from underneath the seal
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