Applications for silicon fluid buffers
Front impact buffer
» Front buffers and cartridges
» Front / rear protection
» Couplers
» Semi-automatic couplers
» Permanent couplers (inter-car)
» Shock absorber for auto coupler
Infrastructure/End-of-track stop
» Shock absorber for end-of-track stop (sliding)
» Shock absorber for end-of-track stop (fix)
Major advantages of Silicon Fluid (SF) in comparison to Hydraulic
- Self regenerative product (no need for gas or spring to reset in nominal position after impact)
- Easier to protect against leakage due to high pressure and viscosity of the fluid
- Silicon fluid is less sensitive to temperature change. (for example: for temperature increase of 20oC, the reaction force is divided by 2 for hydraulic buffer, against 1,05 for silicon fluid buffer)
- Not sensitive to remaining air in reservoir during assembly (at a pressure of 500 bars the air volume is divided by 500)
- High capability for energy absorption in limited space envelopes
- Durable and maintainable product (average of 10 to 15 years of service until first maintenance service)
Basic construction
The design of silicon fluid buffers utilizes the unique compression and shear characteristics of specially formulated silicone elastomers. These characteristics allow the energy absorption and return spring functions to be combined into a single unit without the need for an additional gas or mechanical spring stroke return mechanism.
A KONI silicon fluid buffer is mainly constituted of a reservoir, a guide ring (equipped with specific seals), a piston and silicon fluid.
Main characteristics of silicon fluid
1. Compressibility –> SPRING function
≈ 15% volume reduction from 1 to 4000 bar
2. Viscosity –> DAMPING function
10 to 30 million centistokes (oil is 500 cSt)
The higher the viscosity –> the lower the ability to flow.
Principle of the Spring Function
The displacement of the piston leads to a change of the volume of the silicon fluid. If the silicon fluid is compressed, its pressure increases and acts against the displacement of the piston. This is called the Spring Function, or compressibility.
S= Surface area
P= Pressure
E= Effort
X= Stroke
Principle of the Damper Function
When the piston is equipped with a head, the displacement leads to a lamination of the fluid. In this case, the force developed by the unit depends on the velocity of the displacement. This is called the Damping Function, or viscosity.
1 –> We add a head to the piston
Our testing process
The dynamic test is used at conception phase to adjust the clearance between the reservoir diameter and the piston head and obtain the requested reaction force, stroke and dissipated energy. If possible, the behavior should be tested under real impact conditions of velocity and mass.
After the dynamic test, the buffer is tested under static conditions which will provide the static signature of the device. This static signature is called “validation grid” and is used to release all future serial production of the corresponding unit.
