Выражение встречается в следующем контексте:
Ladle Refining Bells consist of a patented steel framework that is fully encased by high temperature monolithic refractory based on the successful Injection Lance technology. The pre-cast bells or snorkels are supplied ready to use and designed to permit easy removal and reassembly from the CAS-OB or RH/DH Degasser station. Use of FOSCAST® RH snorkels and CAS-OB bells has been shown to significantly reduce costs by increasing the service life as well as to render the process more environmentally compatible.
Заранее спасибо, Наталья