New sounds for old bells: innovative method from Czech Technical University can repair historic bells without welding
Bells across Czechia may now get a new lease of life, thanks to a technique developed by scientists at the Czech Technical University in Prague, which uses fast-moving metal particles to repair parts cracked or worn down over time.
The clear ringing sound of a bell at the Faculty of Nuclear and Physical Engineering in Prague demonstrates the effects of a new way to repair old metal objects, without welding on additional material. Named ‘supersonic kineticisation’, the method works by firing metal particles so quickly (at speeds of around 3,700 kilometres per hour) that they bond with an object upon impact. Jan Čížek from the Czech Academy of Sciences’ Institute of Plasma Physics explains the process:
“Now high-pressure nitrogen is flowing into the pipe. You can already hear it starting to flow through the outlet nozzle. This is high-pressure nitrogen, with a pressure of 70 atmospheres. We produce it ourselves from liquid nitrogen, which has a temperature of minus 200 °C … The way it works is that at the end of the metre-long cannon, there is a nozzle, through which the high-speed accelerated nitrogen gas enters, and in another place, through the tube, the powder that you want to apply enters. In our case, this is the material for repairing the bell. Here at the end of the nozzle, the accelerated particles emerge, flying at an incredible speed towards the damaged bell or part of it. There they land and connect to it very firmly, and so you can restore the damaged part.”
Damage to old bells is typically caused by long-term usage, as the clapper repeatedly strikes two sides of the bell’s internal surface. Historically, this damage was remedied by rotating the clapper’s swing thirty degrees, but, as Dr. Čížek notes, this rotation solution can only be done a limited number of times. Removing damaged parts and welding on new material may harm the sound of a bell, so this innovative alternative from Czech scientists promises to restore the historic objects without threatening their distinctive chime. Researcher Ondřej Kovářík describes the current process of testing:
“Supersonic kineticisation can produce a material that is equivalent to the material of the [original] bell; that is, we could make an entire bell out of it. Then we test its various properties: how long the material lasts when we pull on it, or what happens when we stress the material cyclically. These are all parameters that are very important for using a bell, which is made of a very mechanically stressed material.”
This method is used not only for repairing old artefacts, but also in many modern industries: for example, in aviation, in the energy industry (in which turbine blades can be repaired with this method), in the automotive industry, and in the space industry, in which this method is used to produce nozzles for rocket engines.
