What is a Plastic Seal?
This is generally referring to a device that is used to retain lubricants (such as oil or grease) within a system and prevent contaminants (such as dust, dirt or liquids) from entering. They can be either static or dynamics seals.
Benefits of Plastic Seals vs Other Materials
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Low Friction – For dynamic seals running on a hard surface, such as steel, plastics such as Tetron S, Polystone 7000, Ertacetal C and Ertalon LFX, tend to have low friction compared to rubbers and polyurethanes, which results in lower drive forces (and energy consumption) and heat generation.
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High Speed – due to the low friction and heat generation, plastics can tend to tolerate higher surface speeds.
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Corrosion Resistance – Plastic seals are often resistant to corrosion, making them suitable for use in challenging environments where exposure to moisture, chemicals, or other corrosive substances is a concern.
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Reduced wear – Plastics have very good wear and abrasion resistance, resulting in improved service life.
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Cost-Effectiveness – machined plastics seals don’t require the up-front cost of tooling, therefore are cost effective for short production runs.
Dotmar has qualified engineers that can provide direct support with plastic seal material selection to suit the application needs.
Shaft Seal
A traditional seal used on a rotating shaft. These can also be energised with an o’ring, other elastomers or metal bellows.
Rod Seal
Also known as a wiper seal, the movement is along the length of a rod or shaft.
Cup Seal
A lateral sliding seal that acts on the outer diameter.
Deckle Seal
This seal is a long section that has a belt run over it. Mainly used in the Pulp & Paper industry
Labyrinth Seal
This non-contact seal uses the principle of pressure drop between each labyrinth.
Vee Rings
These rotary seals are predominantly used in pumps to seal the drive shaft.
Material selection is a critical consideration when choosing a plastic for seals, as it directly impacts the performance, durability, and maintenance requirements of these components. Here are some key material selection considerations for plastic seals:
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Speed
The higher the surface speed the higher the potential to generate heat beyond the capability of a material. The co-efficient of friction as well as the temperature capability of the material, directly influence its capacity to handle higher surface speeds.
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Time
The duration of operation is critical and will significantly affect the speed capability of materials for seals.
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Temperature
The surrounding temperature (opposed to heat generated from friction) for both short- and long-term exposure is important, as materials can withstand higher temperatures for short term periods compared to long term or constant exposure, which in turn affect their speed capacity. In the case of extreme temperatures, materials such as Tetron S and Ticomp S, as often suitable materials for seals
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Wear and Abrasion
Abrasive conditions provide different challenges to clean environments, and therefore the material selection, which can include Ticomp S and Polystone 7000.
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Lubrication
Consider whether the seal is in direct contact with a lubricant or is dry-running. This together with the speed will influence the material selection.
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Friction
The co-efficient of friction of materials will influence the forces required to drive the system, as well as the heat generated.
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Regulatory Requirements
Does the application have regulatory requirements such as food contact, drinking water, anti-static or flame retardant. The food industry may also require materials to be metal detectable, x-ray detectable and/or visually detectable by being coloured blue.
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Other considerations
At times there may be other considerations such as chemical resistance, dimensional stability, and machinability. Some high performing materials can carry a higher cost, therefore balancing the cost vs performance benefits should also be considered.
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