What Material Is Used for Seals?

A seal is a ring cover consisting of one or several parts that are fixed to one ring or gasket of a bearing and contact or form a narrow labyrinth gap with another ring or gasket to prevent leakage of lubricant and the intrusion of foreign bodies. Object. A seal is a rubber ring with a circular cross-section. Due to its O-shaped cross-section, it is called an O-shaped seal. It is one of the most widely used hydraulic and pneumatic transmission systems. It is commonly referred to as an O-ring in Taiwanese and Japanese companies.

Defining materials

Generally speaking, elastomers are organic polymers that are elastic, allowing them to deform slightly under pressure but are flexible enough to prevent permanent deformation or flow. In an O-Ring seal, the material creates a seal between two smooth surfaces, such as flanges, by slightly flowing into microscopic imperfections in the flange and maintaining the internally stored force to keep the seal in place as it opens and closes time and time again. It is helpful to characterize a ‘rubber’ material rather than a material such as PTFE, which takes on a different shape when compressed and retains that shape when the compression force is removed.

O-ring materials are difficult to characterize because they are not clearly defined compounds. To add to the confusion, many possible variations are encountered within a single material category.

PYG-type End-Face Sealing Ring

PYG-type End-Face Sealing Ring

This means that they are ‘compounded’ from a variety of component materials, such as base resins, elasticity-enhancing fillers, plasticizers, and curing agents. Within a given generic category, there will be many variations in the actual compounding and molding process, many of which will be considered proprietary. For example, the filler may be carbon black or it may be diatomaceous earth. This tells us that there will be a great deal of variation in any of the properties of the materials and it is necessary to take this into account when using them or designing them into vacuum systems and processes.

The most common generic groups of O-ring materials are NBR (e.g. Buna N), butyl rubber, fluoroelastomers (e.g. Viton and Fluorel) and perfluoroelastomers (e.g. Chemraz and Kalrez). Each of these groups has widely different vacuum-related properties, so it is not possible to make general statements about which material is the best. Instead, it is necessary to try to find the best material for a particular application, where the specific properties of the elastomer will make it a better choice.

Sealing ComponentsCDType Sealing Components

Precautions for O-Ring maintenance

Although O-rings can be used as convenient reusable vacuum seals, they can also be a good way to introduce contaminants into other cleaning systems. Handling and fitting them with bare fingers can introduce skin oils, so they should always be handled with lint-free gloves. Plastic gloves can transfer plasticizers to surfaces and should be avoided.

Never use solvents to clean O-rings as they will absorb solvents and cause swelling, which in turn greatly increases permeability. Ultrasonic cleaning can lead to water absorption. It is best to wipe them with a lint-free paper towel unless a release powder is detected, and then a damp paper towel will suffice.

Never lubricate O-rings unless there is a practical need that cannot be avoided (e.g. scratched sealing surfaces), but touching up scratches with a stone or Scotchbrite is a better solution.

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