O-Rings, Press-in-Place, Gaskets and More
In any mechanical device made of multiple components, the mating faces of two parts create a clear path for the internal lubricants or fluids to leak. While that seam could be welded together to ensure permanent, leak-free sealing, it is not very conducive to maintenance of the equipment. Instead, these components are typically bolted together in some way and a seal is used to close the gap between the components. The nature of the sealing system can range from a simple die-cut gasket mirroring the mating faces, to a complex molded shape that integrates multiple components.
One of the most common solutions to section sealing is a die-cut gasket. Gaskets are made from a variety of materials, ranging from soft foam to reinforced fiber gaskets. A soft foam can accommodate a surface that features uneven or damaged faces. The soft foam fills in any voids or disparities and creates a seal in a low pressure environment. Those same benefits cause issues for the joint in higher pressures. The ability to flow and conform causes the gasket to extrude right out of the gap and allow fluid to leak.
As the complexity of the joint increases, so does the need for rigidity in material. Similar to rubber o-rings, gasket material comes in a variety of compounds and hardness. While foam falls on the low end of the hardness spectrum, solid rubber sheets can reach 90 Shore A on the durometer scale, and even higher in some urethane formulations. The fluid and temperature of the application play a part in determining the material choice, while the pressure, mating surface conditions, and bolt load help complete the seal determination.
At the upper end of the die-cut spectrum are fiber composite materials. These fiberglass-like materials have a higher resistance to extrusion and can be used in more extreme environments than an equivalent in rubber. The fiber is blended typically with a rubber compound to gain the sealing properties of the base material (temperature, fluid resistance, etc.) while the fiber increases the base polymer’s capabilities in terms of pressure and extrusion resistance.
Even with the wide variety gasket options, there are situations where a die-cut gasket will not work. Most commonly the pressure is just too high for a gasket to effectively seal, or the section face does not provide enough space between ports or the outside edge to allow for enough gasket material. In these cases, there may be a need to machine a groove into the section face and install an o-ring. O-rings are a tried and true sealing method used for decades throughout the world. Standard sizes cover a wide range of needs and accommodations and material options support a wide range of application. Groove dimensions for standard size product is driven by international standards to remove guesswork or extensive research for design.
An o-ring sealing solution can be very effective, but only when the o-ring is installed correctly and installation requirements do not create situations where the seal can fall out. Assemblies where an o-ring falls out of place or is forgotten can cause lost productivity if the unit fails at final test, or worse, at the end customer. For these more complex or time consuming areas, a press-in-place design can prove helpful.
Press-in-place designs commonly use existing seal grooves and feature a custom design profile that creates interference in the groove. This allows the seal to hold the groove so it will not fall out of the groove during assembly, even when inverted. These seals are molded to conform to any groove shape as well so a seal interface that is not round can be easily accommodated without trying to form an o-ring into an irregular shape.
When designed for a new application, groove design can complement a press-in-place design, to allow for easier assembly, easy removal tabs for servicing, and integration of other components like plugs or end caps and cater to the unique operating parameters of the specific applicaiton. This allows for reduction in components for final assembly, and peace of mind that the seal will stay where it is designed to operate throughout the assembly process.
Other Section Sealing Methods
A sealing interface that requires multiple o-rings can create confusion if multiple sizes or compounds are required. In these cases, an integrated seal with a metal gasket carrier and various o-ring shapes molded onto the carrier can be helpful. One gasket-like component can eliminate the need for multiple o-rings and the associated machining needed to create glands. This style of product appears similar to a die-cut gasket, but the carrier material is metal rather than rubber or fiber. The metal acts as its own gland for each of the integrated seals, reducing costs for the mating components, and creating the same extrusion resistance a gland would provide.
Rubber covered metal gaskets are another option for higher pressure interfaces. The thin coating of rubber on the metal gaskets creates the seal against each of the mating components, while embossed areas throughout the gasket create high stress concentrations that provide excellent sealing under pressure.
A hybrid approach to many of these sealing methods is a Select-a-Seal gasket. These fiber gasket carriers have a rubberized internal edge to each of the sealing cavities. While the rubber does provide a sealing elements, the rubber material also seeps into the fiber gasket material creating a barrier for fluid, preventing the “wet edge” appearance many fiber gasket materials are known for.