Description A Roller Kiln Technical Field The invention relates to a roller kiln comprising means for applying heat and a treatment chamber internally of which a roller plane is located, on which roller plane objects under treatment are placed and transferred from an entrance to an exit thereof. Specifically, though not exclusively, the invention is usefully applied in firing ceramic materials and/or manufactures.

Background Art At present electrically-heated roller kilns are used in various industrial fields, such as the glass, metallurgical and ceramics industries, and are constituted by a rectangular-section heating chamber in which, above and below the roller plane on which the objects to be treated are transiting, heating panels are provided; electrical resistance elements are either sunk into or located on these heating panels. Good heat radiation is thus obtained inasmuch as the vault and the bottom of the chamber are in close proximity to the products on the rollers. The technique does, however, present some drawbacks.

Often it is necessary to protect (using a screen) the bottom heating panels, as fall of powders and/or flakes, possibly caused by friction of the products as they move along the rollers, can cause damage to the elements.

Protecting the panels leads to a constructional complication, but can also determine a reduction in thermal efficiency of the kiln, both in terms of speed of response and in terms of overall performance.

Large maintenance hatches also have to be provided, or even more complex arrangements such as raisable vaults, in order that access can be gained to the

inside of the kiln should one of the panels have to be substituted.

Obviously in such cases the whole kiln has to be shut down and cooled first.

High density of heating potential (W/m) cannot be achieved since the panels cannot support resistances having large sections and arranged very close to each other.

Finally, the vault panels cannot be positioned very close to the material transiting on the rollers because there is always the risk that, in case of accidents inside the kiln, the material will pile up on the rollers and touch the panels, damaging them.

Safety distances are usually around 10-12 cm. and are the cause of a drop in heat- exchange performance between the panel and the materials being fired; they also perforce increase the volume of the firing chamber more than would be necessary for optimum functioning.

The aim of the present invention is to obviate the drawbacks and limitations in the prior art by providing an electric-powered roller kiln which is highly efficient while at the same time being very easy to realise.

An advantage of the invention is that very much higher concentrations of power can be reached, as the heating and rotating rollers have diameters of between 42 and 45 mm. and are arranged at distances from each other which might be 58, 60 or 62 mm.

A further advantage, apart from the phenomenon of transmission of heat by radiation from the vault, bottom and reflecting walls, lies in the fact that there is also transmission by conduction, inasmuch as the material to be fired advances by rolling in direct contact on the heat source.

A still further advantage is that the temperature in the chamber can be better controlled, as each single roller can be heat-adjusted, so that effectively differentiated sets of temperatures can be obtained every 58, 60 or 62 mm.

A further advantage is that the heating elements can be easily substituted without

having to shut down the whole kiln, as each roller can be removed and substituted during normal kiln operation. This does away once and for all with the need for complicated constructional solutions for access to inside the kiln.

A final and not negligible advantage is the maximisation of kiln heating performance; as there is no need to create room to house the heating panels, it becomes possible to dimension the firing chamber, both in terms of volume and in terms of vault, bottom and wall geometry, so as to have maximum energetic performance and minimum heat waste.

These aims and advantages and more besides are all attained by the object of the invention, as it is characterised in the appended claims.

Disclosure of Invention Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of some preferred but non-exclusive embodiments of the invention, illustrated purely by way of a non-limiting example in the accompanying figures of the drawings, in which: figure 1 shows a schematic transversal section in vertical elevation; figure 2 is a schematic section made according to line II-II of figure 1 ; figure 3 is the same view as figure 1 but of a further embodiment of the invention.

With reference to the figures of the drawings, 1 denotes the treatment chamber of a continuous roller kiln 10, which can preferably be used for firing ceramic slabs or tiles 6. A roller plane 2 is provided inside the chamber 1, on which the ceramic slabs or tiles 6 are placed to be transferred.

Heat is generated by at least a part of the rollers 3 of the roller plane 2, which are hollow and internally exhibit special means for producing heat energy. The means for producing heat energy preferably comprise electrical resistances 4 arranged longitudinally so as to create a predetermined distribution of heat energy along

the axis of each single roller 3.

The electrical resistances 4, which can be made of spirals of high-resistance conductive material, are arranged longitudinally so as to create uniform distribution of heat energy along the axis of each roller 3, and precisely over a predetermined portion of each roller 3.

The electrical resistances 4 are connected to the electrical source by rotating contacts 5 situated at an end of each single roller 3-the other ends of the rollers 3 being rotated by a conventional mechanism.

The efficiency of the kiln is guaranteed by the fact that at least a part of the internal surfaces of the treatment chamber 1 above the roller plane 2 are reflective, i. e. able to reflect back the majority of the energy emitted by radiation.

In the second embodiment of the invention, illustrated in figure 3, two parallel roller planes 2 are provided, one located above the other, having the task of firing a considerably thick tile or slab. The aim is to achieve a homogeneous and symmetrical heating of the objects under treatment, i. e the ceramic products transiting on the lower roller plane 2.

Two further advantages of the invention, to be added to all the other advantages already mentioned, are that the easily-adjustable heating enables the firing temperature curve to be precisely achieved, and a uniform heat (and therefore temperature) distribution can be obtained across a generic transversal section.