Braking device for retractable screens / preloading device.

When the viscodynamic brake starts to operate, the finned rotor turns inside its shell. The special design of the fins and the precise viscosity of the oil create friction and thus generate the braking force.

The brake only operates in one direction, namely the phase of releasing and rewinding the insect screen. During closure, the finned rotor is disabled by the silent one-way device.

The one-way devices are mounted in two patented versions: spring-loaded and ratchet. The type of one-way device does not alter brake operation and its choice is purely dictated by the constructional details of your screen system.

The silicone oil.

The viscosity of the oil is a decisive characteristic for the qualitative performance of the brake. The passing of time and changing climatic conditions must not impair efficiency.

Research for the ideal viscosity has spurred Fandis engineers to create six machines dedicated exclusively to mixing oils. The machines, designed and constructed in-house, guarantee maintaining the quality and values set in the design phase.

The testing process.

Wear, time and climatic changes: the viscodynamic brake is ready for every eventuality. Brake devices are tested inside the Fandis laboratories for 20,000 usage cycles. Well beyond the normal expectations of any screen system.

Trend - viscosity vs. temperature.

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The braking device is now available with four viscodynamic oil variants, corresponding to different force levels and individually colour-coded. This graph shows the theoretical viscosity values of the four oils against temperature.

Viscosity is the property that indicates sliding resistance. It depends on the type fluid and temperature. An increase in temperature is always followed by a drop in viscosity, and hence in the resistance force.

The cSt (centistoke) is the unit of measurement that indicates the kinematic viscosity of a fluid.
The numbers where the dashed line crosses the coloured lines indicate the viscosity values of the oils at the reference temperature of 25 °C.

Although this table can be of help, it should be remembered that the behaviour of the braking device does not just depend on the operating temperature, but also on the force of the return spring and the type of system for which braking is required.

Braking force vs. speed.

This graph, obtained in the Fandis laboratories, shows how the braking force varies with rewind speed (18mm diameter blue brake).