Silicones, silicone oils, sprays
Casting and potting resins)
A flap closes slowly and evenly in the pattern. The order form states "silicone oil, 1,000 cSt". For a repeatable movement, two parts of the description are still missing: the conditions under which the oil possesses this viscosity, and the mechanism in which it is used.
The practical selection criterion is therefore, for example: This component should close between two defined positions within a specific time frame – under the intended start and operating conditions. Viscosity helps in the preliminary selection; the movement test answers the question of functionality.
First, correctly assign the unit
cSt stands for centistokes and denotes kinematic viscosity. 1 cSt corresponds to 1 mm²/s. This is distinct from dynamic viscosity, measured in mPa·s, for example.
Both quantities are related via density: kinematic viscosity = dynamic viscosity ÷ density. For a conversion, the temperature and pressure of the values must be the same. Therefore, the numerical values of different units cannot simply be equated. Anton Paar: Viscosity and Viscometry
Temperature is part of the value even without conversion. "1,000 cSt at 25 °C" describes more than "1,000 weight oil". Whether the candidate covers the entire application range will be determined by its viscosity-temperature information and testing in the damper.
Replacing an oil by its number leaves other properties unknown
Elkem describes silicone fluids with varying degrees of polymerization and corresponding viscosities, as well as chemical variants with different property profiles. The products can also be supplied pure, in solution, or as an emulsion. Elkem: industrial silicone fluids
For a filled damper, the intended fluid type must first be identified. An emulsion for surface application, even with a similar viscosity, cannot replace the oil filling.
Equally important are the housing, moving parts, and seals. For an already functioning setup, the complete fluid designation used previously serves as the best point of comparison. This makes it clear which material is being changed during the test.
Example: Good pattern, open during cold start
Let's assume the flap is currently only tested at room temperature. Later, it should close reliably after a cold night as well as after prolonged use. The first test will then have recorded one operating state; the remaining tests still need to be carried out.
For comparison purposes, the mechanism, its existing settings, the amount of fluid added, and the defined starting position remain constant. The same movement between the same positions is measured. The permissible time range is predetermined based on the application. Additionally, jerking, fluid leakage, and changes following the intended actuation sequence can be assessed.
This makes it possible to describe a deviation: Which candidate behaves differently under which condition? The statement "feels tougher" is replaced by a functional criterion.
Check the limits of use on the correct variant
The viscosity rating does not replace the temperature limits or compatibility information for the intended fluid. For comparison purposes, these specifications are assigned to the specific variant. Data for a lower viscosity oil or a differently composed fluid are not applied to the damper candidate.
The selection process therefore uses the technical data sheet and safety data sheet of the intended product. Special requirements such as food contact, skin contact, or medical use necessitate the corresponding product documentation.
The decision ultimately combines two results: The fluid is suitable for the materials and operating conditions; the damper thus achieves the desired movement.
Frequently asked questions
Can I equate 1,000 cSt with 1,000 mPa·s?
The units denote different viscosity measurements. For conversion, the density under the same temperature and pressure conditions is required.
What measurement is more helpful than "the flap feels right"?
For example, the time between two defined positions under a defined setup and temperature conditions. The acceptable time range is determined by the application; jerking or fluid leakage can also be evaluated.
Sources
- Anton Paar: Viscosity and Viscometry. Retrieved 2026-10-25.
- Elkem: Silicone fluids for industrial applications. Retrieved 2026-10-25.