TECHNICAL FIELD

The present invention relates to a device and a method for treating a strip or layer of powder material, mainly relating to a process for forming ceramic tiles or slabs. In particular the invention relates to a device and a method such as the one described in document WO 2013050845 to which the reader is referred in relation to the depositing means of the powder on a belt, and to the compacting means of the layer of powder formed on the belt.

BACKGROUND ART

In particular this device comprises a sliding conveyor surface able to support and advance the layer of powder material in the form of a strip, and a compacting station able to compact the layer of powder material while it advances on the conveyor surface.

The transversal section of the strip or the layer of powder deposited on the belt can be assimilated to an isosceles trapezium the sides of which are inclined by an angle depending on the angle of friction of the powder.

In this way two decreasing edges or lateral zones are defined in the strip or layer of powder.

Since in the compacting station the layer must have a constant rectangular section, the decreasing lateral edges of the layer of powder must be trimmed. For this purpose trimming means are provided for the lateral edges of the layer of powder material upstream of the compacting station.

Known trimming means comprise a pair of separating blades located in a fixed position above the conveyor surface, each orientated perpendicularly with respect to the conveyor surface and parallel to the advancing direction thereof.

The blades are aligned with lateral containing means of the powder present in the compacting station and are located internally of the uniform loading zone, leaving the two edges external, i.e. the two zones or portions of the strips in which the powder is arranged according to the angle of friction thereof. Means are provided for adjusting the reciprocal distance of the blades.

Also included are means for distancing the powder material separated by the blades from the conveyor surface, which means comprise a hood positioned above the conveyor surface and provided with an inlet for the powder material advancing on the conveyor surface, and an outlet thereof connected to means for creating a depression able to aspirate the powder material through the outlet of the hood.

The method described in document WO 2013050845 comprises, upstream of the compacting activity, the activity of trimming the lateral edges of the layer of powder material, and recuperating the powder material separated from the layer following the trimming activity, and recycling the powder to the depositing means.

The recuperating of the material occurs by aspiration of the powder material separated from the layer, and lying externally of the blades.

Both the device and the method have been shown to be effective for modest thicknesses of the powder layer, i.e. for layer thicknesses destined to create slabs of up to 6-8 mm; for larger layer thicknesses the known device and method have been seen to have some drawbacks originating from the excessive quantity of powder to be recuperated and recycled.

DISCLOSURE OF THE INVENTION

The aim of the present invention is to remedy the above-cited drawbacks, with a solution that is simple and economical.

This aim is attained by the invention thanks to a device and a method exhibiting the characteristics cited in the independent claims; the dependent claims relate to further advantageous characteristics of the invention.

In substance, the invention includes, in a plant of the type illustrated in document WO 2013050845, positioning the blades which cause the trimming no longer internally of the rectangular section of the powder layer, but internally of the decreasing section of the edges of the layer, so as to subdivide the section into two parts having substantially identical sections.

In a case where the decreasing section of the edges has a substantially triangular conformation, the blades will be located about halfway along the base of the triangular section of the edges of the layer.

In this way the edges of the powder layer exhibit, in proximity of the blades, an insufficiency of powder, while the quantity of powder externally of the blades is not only very much smaller, but is substantially identical to the quantity of powder missing internally of the blades and required so as to obtain a regular and rectangular section of the layer.

The invention includes recuperating the material which is external of the blades and transferring it internally of the blades.

For this purpose the invention includes, at the upstream end of the blades, in the advancing direction of the powder, transfer means of the powder from externally to internally of the blades.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and the constructional and functional advantages of the invention will clearly emerge from the detailed description that follows, relating to the figures of the accompanying tables of drawings and having as object some preferred embodiments of the invention.

Figure 1 is a plan view of a section of conveyor with an overlying layer of powder. Figure 2 shows section ll-ll of figure 1■

Figure 3 is a plan view of a first embodiment of the invention.

Figure 4 is a plan view of the blank metal sheet used for forming the first embodiment of the invention.

Figure 5 is a lateral view of figure 3.

Figure 6 is a plan view of a second embodiment of the invention.

Figure 7 is a front view of figure 6.

Figure 8 is a larger-scale view of a part of figure 6.

Figure 9 is a larger-scale view of a part of figure 7.

Figures 1 and 2 are plan views of the powder layer 2 deposited on the belt 1. BEST WAY TO CARRYING OUT THE INVENTION

In the illustrated example the section of the layer (figure 2) has a central zone 1 1 having a constant thickness, by the sides of which two lateral zones, or decreasing edges 12 having a triangular section, are formed, the width L of which is a function of the angle of friction of the powder.

If one of the lateral zones 2 is divided by an ideal plane 3 perpendicular to the conveyor plane 1 , and located at the halfway point of the width L of each lateral zone or edge 12 of the strip 2, each of the zones 12 is sub-divided such that the two parts 121 and 122 (see figure 2) have substantially the same section.

The lateral edges or zones 12 might not have an exactly triangular section, since the section thereof depends not only on the angle of friction of the powder, but also on other unpredictable factors.

In any case it is possible to divide the lateral edges or zones, by means of a vertical plane, into two portions having a substantially identical section.

With reference to the first embodiment of the invention illustrated in figures from 3 to 5, a curved section of sheet metal can be observed, in the form of a ploughshare 5, which starts from a horizontal section 51 and curves up to terminating with a vertical section 52.

The ploughshare 5 is fashioned from a flat metal sheet 50 (figure 4) having the shape of a rectangular trapezium the smaller base A of which is equal to the width of the portion that is to be trimmed, and the larger base of which is equal to 2A; the hypotenuse is inclined by 45° with respect to the bases.

Having identified the axis XX perpendicular to the hypotenuse and passing through the end of the axis coinciding with the smaller base, the metal sheet is curved by rotating the hypotenuse about the axis XX, so that it is vertically arranged; the ploughshare 5 thus assumes the definitive configuration thereof, with the horizontal section 51 thereof in front of the part 121 of the section of the powder, starting from the plane 1 , and with the vertical section, corresponding to the hypotenuse of the rectangular trapezium, which is located exactly at the halfway plane 3 of the triangular section of the powder layer.

The end downstream of the ploughshare is followed by one of the containing planes 6 of the powder, sent on to following work operations. The configuration of the device at the other edge of the powder layer, to the right of the central zone 1 1 , is exactly symmetrical to the above-described configuration.

During the advancing of the powder layer, the horizontal section 51 collects the powder from the conveyor and transfers the powder internally of the plane 6, in the zone denoted by 122 in figure 2.

The layer of powder internally of the containing planes 6 therefore has a rectangular section, and the thickness of the layer is constant.

It is specified that as a simple variant of the ploughshare 5, a vertical wall could be used, converging towards the centre of the conveyor, not illustrated, which starts at the edge of the powder layer and terminates against the end of the containing wall 6.

A second embodiment is illustrated from figure 6 to figure 8, where the numerical references denote the details that are the same as in the preceding figures.

The figures show that two rotors 7 are located on the conveyor plane 1 , each activated by an electric motor 70.

The two rotors 7, with the respective motors 70, have the axis thereof perpendicular to the conveyor plane and are suspended on the conveyor plane 1 so that the conveyor plane 1 is brushed by the base of the rotors 7.

The suspension means comprise the possibility of transversally adjusting the position of the rotor.

Each rotor 7 is positioned in such a way as to be tangential to the plane 3 separating the two parts 121 and 122 of the lateral section of the strip (see figure 2). As in the preceding embodiments, the lateral wall 6 for containing the strip is located at the plane 3 downstream of the rotor.

Each rotor 7 comprises a cylindrical core from which a spiral ribbing 700 branches.

The direction of the ribbing 700, and the rotation direction of the rotor 7 are such that the ribbing collects, from the conveyor plane 1 , the material of the zone 121 which encounters the rotor during the advancing of the conveyor plane and raises it up to the zone 122.

The rotor 7 can advantageously be closed in a cylindrical casing 71 which is open only at the loading and unloading zone substantially tangential to the plane 3. The rotor 7 can be rotated at a variable velocity so as better to adjust the final profile according to which the powder is arranged in proximity of the containing walls.

It is understood that the invention is not limited only to the described examples, and that any variants and improvements can be made thereto without forsaking the scope of protection of the claims that follow.