A mechanical seal is used to seal the open pressure pipe from the drive gears in the fuelling machine, which can run at speeds of 261 rev/minute and generate pressure of up to 120 bar.
Here, the seal also needs to perform during maintenance operations without any lubrication.
“For this purpose, a truly profound knowledge of physics, chemistry and material science is required,” said Dr. Ravi Bactavatchalou, head of the tribology department at FTI.
“The challenge is to understand what is happening in the tribological contact from macroscopic into atomistic scale,” added Bactavatchalou.
Atomic Simulations uses computer-aided methods to describe the organisation, movement, and interactions of molecules and atoms on surfaces when they rub against each other.
This, said the FTI expert, provided answers to questions, such as which material pairings cause less friction under extreme conditions, which do not, why this is, and under which conditions we can achieve ultra-low friction and longer lifetime of developed tribological systems.
“From an understanding of what´s happening at the atomistic level, we were able to design the final seal solution: a crystalline diamond coated silicon carbide against a silicon carbide sliding face, containing a high level of amorphous carbon,” said Bactavatchalou.
The material pairing reduces friction significantly and avoids the so-called “cold welding effect”.
This is due to strong bonding between carbon-carbon contact happening at the molecular level within milliseconds by sliding two diamond surfaces.
When the seal starts to rotate once again, extremely high torque results due to the higher adhesion bonding.
“This surprising and negative effect had never been discovered for this type of tribosytem,” Freudenberg added.
The diamond silicon carbide seal has been billed by Freundenberg as “a quantum leap forward for power plant applications.”
The seal’s operational life is claimed to be approximately four years, compared to ten months for “the old seal [from Freudenberg]”.
The new seal ”prevents unforeseen failures and ensures safe operations in the critical hot zone of a nuclear reactor, improving employee and customer safety,” said Reischl summing up the benefits.