TECHNICAL FIELD

The present invention regards a device and a method for processing a layer of powder material, mainly within a method for forming ceramic tiles or slabs. BACKGROUND ART

There are known devices for forming ceramic tiles comprising a slidable transport surface on which there is progressively supplied a ceramic powder, so as to form a layer. The transport surface is generally defined by a slidable and fixable conveyor belt, the layer of powder is advanced by the transport surface through a compacting station of the continuous type, i.e. which is adapted to compact the layer of powder as it progressively advances on the transport surface.

The compacting station generally comprises two flexible compacting surfaces, mutually superimposed and both slidable in the same direction of the transport surface. Also the compacting surfaces are usually defined by a respective slidable and flexible belt. The lower compacting surface is arranged beneath and at contact with the transport surface, so that it supportingly rests thereon, while the upper compacting surface is arranged at a given height above the transport surface. At a predefined area, the compacting surfaces are guided to slide between special pressing means, for example between a pair of superimposed rollers, which maintain the upper compacting surface locally pressed towards the lower compacting surface, so as to press the layer of powders which is located on the transport surface. The compacting station usually also comprises two parallel lateral edges and slidable substantially in the same direction and at the same speed as the transport surface, which are adapted to laterally contain the layer of ceramic powder on the transport surface during compacting, so as to make the apparent density of the layer of powder more uniform in the direction of the width. These lateral edges are elastically yieldable, so as to be able to be compressed under the effect of the compacting surfaces. Downstream of the compacting station, the transport surface lastly advances the layer of compacted powder through a subsequent cutting station, which is adapted to divide it into single slabs of desired dimensions.

A need regarding these forming devices lies in the fact that the forward advancement of the layer of powder upstream of the compacting station has an almost constant thickness in the direction of the width, so as to ensure that the forward advancement of the compacted layer in the outlet has the most uniform possible apparent density. However, the powder deposited on the transport surface upstream of the compacting station usually tends to be arranged so as to form a layer with trapezoid-shaped transverse section, which thus does not have a sufficiently constant thickness in the direction of the width and may lead to a faulty compacted layer, at least along the edges. With the aim of attaining this drawback, it is known to arrange upstream of the compacting station of the means for laterally containing the layer of powder. These containment means comprise generally a pair of parallel edges which are mounted in fixed position above the transport surface. The powder is supplied on the transport surface in the space comprised between these two lateral containment edges, which support the powder along the entire path towards the compacting station, conferring to the layer of powder a substantially rectangular-shaped section. Thus however, between the fixed containment edges and the layer of powder which advances on the transport surface there occurs a mutual sliding friction, which however requires a considerable reduction of the thickness of the layer of powder at the edges, still determining a non-uniform density of the compacted layer exiting from the compacting station as well as a local deformation of possible graphic effects made on the layer of powder.

DISCLOSURE OF THE INVENTION

An object of the present invention is to overcome, or at least efficiently reduce, this drawback of the prior art, through a simple, rational and inexpensive solution.

Such object is attained by the characteristics of the invention indicated in the independent claims. The dependent claims outline preferred and/or particularly advantageous aspects of the invention. In particular, the invention provides a device for processing a layer of powder material, comprising a slidable transport surface adapted to support and advance the layer of powder material, a compacting station adapted to compact the layer of powder material while it advances on the transport surface, and means for trimming the lateral edges of the layer of powder material upstream of the compacting station.

More in particular, said trimming means are generally adapted to separate and thus remove two small lateral strips of powder material from the layer which advances on the transport surface upstream of the compacting station, so as to reduce the width thereof.

Due to this solution, the fixed edges for laterally containing the layer of powder are no longer required. Actually, though the powder material usually tends to form a layer with trapezoidal section, said layer of powder material can be initially made having a greater width respect to what is required at the inlet of the compacting station, so that the trimming means may subsequently remove the inclined lateral edges of this layer of powder material, reducing the width thereof to the required value and conferring to the transverse section of the layer of powder material a square shape with an almost constant thickness.

Due to the elimination of the fixed containment edges, the layer of powder material is no longer subjected to sliding during the advancement towards the compacting station, thus preventing the adverse effects due to friction. Hence, the layer of powder material at the inlet of the compacting station may substantially have the same thickness both at the centre and at the edges, thus making the apparent density of the compacted layer at the outlet more uniform and maintaining possible graphic patterns made on the layer of powder material.

According to an aspect of the invention, the aforementioned trimming means may comprise a pair of blades arranged in fixed position above the transport surface. This aspect of the invention has the advantage of providing a particularly simple solution for trimming the lateral edges of the layer of powder material. Each of said blades can be defined by a thin sheet oriented orthogonally with respect to the transport surface. The use of a thin sheet has the advantage of allowing an extremely clear trimming of the layer of powder material, eliminating or however considerably reducing possible adverse effects that could be caused by the mechanical action of the blade on the powder material.

According to another aspect of the invention, the device may also comprise means for regulating the mutual distance between the aforementioned blades. Thus, it is advantageously possible to vary the width of the layer of powder material at the inlet of the compacting station.

According to another aspect of the invention, the device may also comprise means for moving away from the transport surface the powder material separated by the trimming means. This aspect of the invention has the advantage of allow the recovery of the removed powder material, which may thus be advantageously reutilized for forming a new layer of powder material at the beginning of the process.

According to a further aspect of the invention, said means for moving away may comprise suction means for suction the powder material separated by the trimming means. This solution has the advantage of being particularly simple and allowing an easy recovery of the powder material.

Each suction means may comprise a hood positioned above the transport surface, which is provided with an inlet for the powder material which advances on the transport surface and an outlet connected with means for creating vacuum adapted to suction the powder material through the outlet same. This solution has the advantage of being particularly efficient and productive.

Furthermore, the invention provides a method for compacting a layer of powder material, comprising the steps of:

- advancing the layer of material on a slidable transport surface,

- trimming the lateral edges of the layer of powder material, and subsequently

- compacting said layer of powder material while it advances on said transport surface. This method substantially attains the same advantage of the device outlined previously, i.e. that of allowing the layer of powder material at the inlet of the compacting station to substantially have the same thickness both at the centre and at the edges, thus making the apparent density in the compacted layer at the outlet uniform and maintaining possible graphic patterns made on the layer of powder material.

According to an aspect of the invention, the method may comprise the further step of moving away from the transport surface the powder material separated from the layer following the trimming step, so as to be able to advantageously recover and reutilize it in the process.

In order to make this step of moving away particularly simple and efficient, the same can be performed by suctioning the powder material which was separated from the layer following the trimming step.

BRIEF DESCRIPTION OF DRAWINGS

Further characteristics and advantages of the invention will be apparent from reading the following description provided by way of non-limiting example, with reference to the figures illustrated in the attached drawings.

Figure 1 is a schematic view - in plan view - of a device for processing a layer of powder material according to the invention.

Figure 2 is the section ll-ll of figure 1.

Figure 3 is the section Ill-Ill of figure 1 in enlarged scale, and in which there are schematically shown some details of the compacting station.

Figure 4 is the section IV-IV of figure 3, in a further enlarged scale.

Figure 5 is the detail V of figure 1 in enlarged scale.

Figure 6 is the perspective lateral view of the detail of figure 5, in which the layer of powder material was omitted for the sake of clarity.

BEST MODE FOR CARRYING OUT THE INVENTION

The mentioned figures show a device 100 for processing a layer M of powder material, typically of ceramic powder within a method for forming ceramic tiles or slabs.

As illustrated in figure 2, the device 100 comprises a flexible conveyor belt 105, which is closed-loop-like wound around a plurality of rollers 110 with horizontal axis, including a series of idle return rollers and at least one motorised drive roller adapted to actuate the conveyor belt 105 to slide. The conveyor belt 05 can be made of plastic material, so as to have a low cost, a low extent of dirtiness and an easy operating maintenance. The upper section of the conveyor belt 105, substantially horizontal, defines a slidable transport surface 106 adapted to support the layer M of powder material and advance it in a predefined direction of advancement A.

The layer M of powder material is advanced from said transport surface 106 through a compacting station 115 of the continuous type (schematically indicated with a square in figure 1 but detailed in figure 2), which is adapted to compact the layer M of powder material progressively as it advances.

The compacting station 115 comprises two flexible compacting belts, mutually superimposed, including a lower compacting belt 120 and an upper compacting belt 125. Both the compacting belts 120 and 125 may be made of plastic material, so as to have a low cost, a low extent of dirtiness and an easy operating maintenance.

The lower compacting belt 120 is closed-loop-like wound around a pair of rollers 121 with horizontal axis, including an idle return roller and a motorised drive roller adapted to actuate the compacting belt 120 to slide, the upper section of the compacting belt 120, substantially horizontal, defines a slidable compacting surface 122 which is arranged beneath and at direct contact with the transport surface 106, so that it supportingly rests thereon, the compacting surface 122 is further actuated to slide in the same direction of advancement A and substantially at the same speed as the transport surface 106, so as to prevent mutual friction.

The upper compacting belt 125 is in turn closed-loop-like wound around a pair of rollers 126 with horizontal axis, including an idle return roller and a motorised drive roller adapted to actuate the compacting belt 125 to slide, the lower section of the compacting belt 125 defines a slidable compacting surface 127 which is arranged above the transport surface 106, and it is spaced therefrom so as to leave defined an interspace for the passage of the layer M of powder material, the compacting surface 127 is actuated to slide substantially in the same direction of advancement A and substantially at the same speed as the transport surface 106, so as to prevent mutual friction with the layer M of powder material.

The compacting station 115 further comprises special pressing means, which are adapted to locally maintain the upper compacting surface pressed 127 towards the transport surface 106, so as to compress the layer M of powder material interposed therebetween. In the illustrated example, the pressing means comprise a pair of mutually superimposed pressing rollers, including a lower pressing roller 130 and an upper pressing roller 135, having rotation axes horizontal and orthogonal with respect to the direction of advancement A. The lower pressing roller 130 is arranged beneath and at direct contact with the lower compacting surface 122, and it is positioned at a height such to maintain the planarity of the transport surface 106. The upper pressing roller 135 is instead arranged above and at direct contact with the upper compacting surface 127, and it is positioned at a height such to locally approach said upper compacting surface 127 towards the transport surface 106, so as to reduce the thickness of the interspace defined therebetween and thus compact the layer M of powder material. While the lower pressing roller 130 is mounted fixed, the upper pressing roller 135 is carried by jacks 136 that allow modifying the height thereof, i.e. the distance with respect to the lower pressing roller 130, for example as a function of the thickness of the layer M of powder material to be compacted and/or the compacting pressure intended to be applied thereon.

In order to make the compacting of the layer M of powder material more gradual, the pressing means may also comprise a pair of mutually superimposed roller units, including a lower roller unit 140 and an upper roller unit 145, which are positioned upstream of the pressing rollers 130 and 135 with respect to the direction of advancement A. Both roller units 140 and 145 comprise rollers having rotation axes horizontal and orthogonal to the direction of advancement A. The rollers of the lower roller unit 140 are arranged beneath and at contact with the lower compacting surface 122, they are arranged on a plane parallel to the direction of advancement A, and they are positioned at a height such to maintain the planarity of the transport surface 106. the rollers of the upper roller unit 145 are instead arranged above and at contact with the upper compacting surface 127, they are arranged on an up-down inclined plane with respect to the direction of advancement A, and they are positioned at a height such to progressively approach the upper compacting surface 127 towards the transport surface 106, so as to progressively reduce the thickness of the interspace defined therebetween and thus gradually compacting the layer M of powder material. In order to improve the compacting uniformity of the powder material in the direction of the width of the layer M, the compacting station 115 also comprises means for laterally containing the layer M of powder material. In the illustrated example, said containment means comprise a pair of slidable belts, respectively 150 and 155, which are both positioned above the conveyor belt 105. Each slidable belt 150 and 55 is flexible and it is closed- loop-like wound around a respective plurality of rollers 160 with horizontal axis, including a series of idle return rollers and possibly a motorised drive roller which allows the belt to slide. In particular, the slidable belts 150 and 155 are configured and actuated so that the lower section of each of them, substantially horizontal, is adapted to slide in the same direction of advancement A and substantially at the same speed as the transport surface 106. As illustrated in figure 4, said lower sections of the slidable belts 150 and 155 are both positioned resting on the transport surface 106, in an interposed position between the latter and the upper compacting surface 127, thus defining two parallel and mutually spaced edges 151 and 156 which are adapted to laterally contain the layer M of powder material during compacting. The slidable belts 150 and 155 are made of a quite yieldable material in the direction of the thickness, for example made of rubber or any other plastic material, so that the containment edges 151 and 156 defined thereby may be elastically compressed between the compacting surfaces 122 and 127.

Immediately downstream of the pressing means, the compacting station 115 is also provided with means for contrasting the expansion to which the layer M of powder materials is spontaneously subjected to after the compacting step. More in particular, these contrast means have the function of "accompanying" the expansion of the powder material, i.e. slowing it, so as to prevent the formation of cracks and/or fissures in the layer M after compacting.

As illustrated in figure 4, the means for contrasting the expansion comprise a lower plate 165, which is positioned beneath and at direct contact with the lower compacting surface 22. The lower plate 165 is substantially horizontal and it is positioned at a height such to maintain the planarity of the transport surface 106. The contrast means further comprise an upper plate 170, which is superimposed to the lower plate 165 and it is positioned above the upper compacting surface 127. While the lower plate 165 is fixed, the upper plate 170 is supported by means of jacks 175 of the hydraulic type which allow varying the distance thereof with respect to the transport surface 106, for example as a function of the thickness of the layer M of powder material. Furthermore, as observable from the figures, the upper plate 170 may oscillate with respect to the jacks 175 so as to be able to be inclined with respect to the transport surface 106. The upper plate 170 has the function of maintaining the upper compacting surface pressed 127 towards the upper section of the conveyor belt 105, subjecting the layer M of powder material to a pressure for contrasting the expansion. Generally, this contrast pressure will be lower than the compacting pressure exerted by the pressing rollers 130 and 135, so that the powder material can still expand, but without causing the formation of cracks or fissures in the compacted layer M.

As illustrated in figure 1 , immediately upstream of the compacting station 115, the device 100 comprises means for trimming the edges of the layer M of powder material which advances on the transport surface 106. More precisely, these trimming means are generally adapted to separate and remove two small lateral strips S of powder material from the edges of the layer M which advances on the transport surface 106, so as to reduce the width thereof and confer them a configuration with substantially square- shaped transverse section. In the illustrated example, the trimming means comprise a pair of blades, each of which is defined by a sheet 200 oriented orthogonally to the transport surface 106 and parallel to the direction of advancement A. Said sheets 200 are mounted in fixed position above the transport surface 106, so as to remain immobile with respect to the layer M of powder material which advances, cutting the lateral strips S.

The sheets 200 may be made using any material but more preferably made of metal, for example made of steel. In order to obtain a clear and precise cut of the layer M of powder material, the sheets 200 are generally quite thin, for example they may have a thickness between 0.1 mm and 2 mm. The sheets 200 also have a quite small dimension in the direction of advancement A, preferably lower a 300 mm, so as to reduce the frictions that are created between them and the lateral edges of the layer M of powder material that slides towards the compacting station 115 to the maximum. With the aim of further reducing these frictions, the sheets 200 may be coated, at least on the inner face thereof, made of anti-adhesion material, for example of teflon. In the illustrated example, each sheet 200 is fixed to a support body 205, which is in turn fixed to a fixed framework (not shown) of the device 100, by means of a respective connection bracket 210. In particular, the support body 205 is fixed to the outer face of the respective sheet 200, so as to be substantially aligned with the lateral strip S of powder material which is cut by said sheet 200. The connection bracket 210 carries the support body 205 and the respective sheet 200 above the transport surface 106, almost at contact with the latter, so as to avoid sliding but allow the sheet 200 to cut the layer M of powder material substantially over the entire thickness thereof. With respect to the direction of advancement A of the transport surface 106, each sheet 200 is substantially aligned with a respective containment edge 151 and 156 of the subsequent compacting station 115. Thus, the sheets 200 are adapted to reduce the width of the layer M of powder material so that the latter can be received substantially fittingly between the said containment edges 151 and 156. Possibly, to the sheets 200 there may be associated means (not illustrated) adapted to adjust the mutual distance thereof. Said means may comprise devices adapted to allow a movement of the connection brackets 210 with respect to the fixed framework of the device 100, such as for example of the jacks or linear actuators. In order to ensure that the layer M of powder material at the inlet of the compacting station 115 has the square-shaped section conferred thereto by the sheets 200, the distance between the end downstream of said sheets 200 and the end upstream of the containment edges 151 and 156 (always with respect to the direction of advancement A), should be preferably null or however extremely small, so as to prevent lateral losses of powder material.

The device 100 further comprises means adapted to move the powder material of the lateral strips S cut by the sheets 200 away from the transport surface 106. In the illustrated example, said means for moving away comprise a system for the suctioning of the powder material which, due to each sheet 200, comprises the relative support body 205. As illustrated in figure 6, the support body 205 is actually configured as a hood, i.e. it has an inner cavity facing downwards and closed at the lower part by the transport surface 106. The support body 205 is further provided with a lateral inlet 215 which faces the opposite direction with respect to the direction of advancement A, so as to allow the powder material of the lateral strip S to enter into the inner cavity. The support body 205 is also provided with an outlet duct 220 communicating with the inner cavity. Said outlet duct 220 is connected through a flexible pipe 225 with means, schematically represented in figure 1 and indicated with 226, which are adapted to create a vacuum, for example with using a powerful fan. Such vacuum generates an air current which suctions the powder material from the inner cavity of the support body 205, making it to pass through the outlet duct 220 and the flexible pipe 225. The suctioned material may be subsequently separated from the air current, for example through a cyclone device, and be received in a suitable container (not shown).

In the light of what is described above, the use of the device 100 provides for depositing on the transport surface 106 a layer M of powder material initially having a width greater than the one required at the inlet of the compacting station 115, i.e. greater than the distance between the containment edges 151 and 156. Given that there are not provided systems for the lateral containment of the powders upstream of the sheets 200, the powder material initially deposited on the transport surface 106 shall tend to be arranged freely, obtaining a layer M with trapezoidal-shaped transverse section, i.e. with the edges inclined as observable in figure 2. Advancing on the transport surface 106, the layer M subsequently passes through the sheets 200, which provide for re-trimming it along the edges, removing the two lateral strips S of powder material. In other words, the sheets 200 remove the inclined edges of the layer M of powder material, conferring it a configuration with substantially square-shaped section. At the same time, the sheets 200 reduce the width of the layer M of powder material, so as to make them coincide with those provided for at the inlet of the compacting station 115, i.e. substantially coinciding with the distance between the containment edges 151 and 156. The layer M thus re-trimmed is thus advanced by the transport surface 106 through the compacting station 115, in which it is compacted in the usual manner, the powder material of the lateral strips S there is progressively advanced by the transport surface 106 into the cavity of the support bodies 205, from which it is continuously suctioned and moved away. The powder material thus suctioned may be received subsequently and thus reutilised for the formation of a new layer M at the beginning of the process.

Obviously the compacting device 100 described above may be subjected - by a man skilled in the art - to numerous technical-applicational modifications without departing from the scope of protection of the invention according to the following claims. REFERENCES

100 device

105 conveyor belt

106 transport surface

1 0 rollers

115 compacting station

120 lower compacting belt

121 rollers

122 lower compacting surface

125 upper compacting belt

126 rollers

127 upper compacting surface 130 lower pressing roller

135 upper pressing roller

136 jacks

140 lower roller unit

145 upper roller unit

150 belt

151 edge

155 belt

156 edge

160 rollers

165 lower plate

170 upper plate

175 jacks

200 sheet

205 support body

210 connection bracket

215 inlet port

220 outlet duct

225 flexible pipe means for creating vacuum direction of advancement layer of powder material lateral strips of powder material