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Project: Complete assembly of bell, protective cover, base, diffuser and plenum

This R&D project carried out in 2019 saw the construction of a complete plant with all its components, specifically bell, protective cover, diffuser and plenum. Over the years Nicro has gained consolidated experience in the study and construction of plants of this kind, in which the mentioned components are used.

Specifically, for the project, the customer, having to build a large plant for the first time, relied on the technical/construction collaboration gained by Nicro.



The base, as can already be seen from the name, is a structure that serves to support, in addition to the components of which it is made, also what is loaded onto it.

Another element constituting the system was the use of a protective cover with the aim of mitigating the heat that is radiated from the outside, by means of radiant tubes, first to the bell and then to the material that must undergo the treatment.

The use of the cover also has another important function: the recirculation of air directed so as to have a temperature uniformly distributed within the system.

The bell is the element that, heated by the radiant tubes placed outside it, radiates heat inside it first by heating the protective cover and then the material to be treated. In addition, it is also the essential component to start the ignition of the entire furnace, because once lowered onto the base, it closes the system.

The continuous distribution of air inside the system, completely static, is guaranteed by a fan. It is connected to an engine and turning on itself allows a continuous distribution of hot air from the bottom to the top and from the top to the bottom.

It is important that the various elements are well matched to each other in order to have the best possible performance during the operation of the system.

Read more: Bell furnaces: structure and advantages


Starting from these assumptions and following indications received by the customer, we proceeded to study in detail the distribution of the load to be heat treated, which would have affected the base and the details of which it is made, diffuser and plenum.

  • In this first phase, particular attention was into to the study of the type of substrate to be used: whether with reverse edging (as built for other bases but smaller in size) or flat edging (as supported by Nicro ).
  • The further step was the study of the diffuser and plenum which must be positioned above the base and which have the respective function of directing the air inside the system and supporting the charge to be treated.
  • For the hood and shirt, the focus was on the thicknesses to be adopted and the space to be left between the two pieces. A very important detail because the fan, positioned between the base and the diffuser, must push the hot air upwards of the bell and then descend downwards inside the protective cover, thus investing the material that must be treated.
  • Finally, the last step was to check the coupling between the various elements of the project to verify the validity of the technical and functional choices adopted for the construction of the plant as a whole.

Project: Complete assembly of bell, protective cover, base, diffuser and plenum

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