Improved device for glazing objects

Abstract

An improved device for glazing objects such as slabs and tiles comprises, operating in association with a mobile conveying surface (20) for conveying objects to be glazed, such as slabs and tiles (30) and the like, at least one glaze dispensing bar or plate (1). This bar is located at a predetermined distance above the mobile conveying surface (20) and, in turn, comprises a lower wall (11) on which a first plurality of contiguous glaze dispensing modules or modular dispensers (10) is arranged. Each of these modules is equipped with at least a first series of front dispensing nozzles or holes (12a), which have dispensing axes arranged in parallel and contained on the same plane, transversally positioned with a predetermined inclination relative to the direction of motion of said mobile conveying surface (20) for the manufactured articles to be glazed (slabs or tiles 30). Each said glaze dispensing module (10) also comprises at least a second series of rear dispensing nozzles or holes (12b), which have axes arranged in parallel and contained on the same plane, transversally positioned with a predetermined inclination relative to the direction of motion (22) of said mobile conveying surface (20) for the manufactured articles to be glazed (slabs or tiles 30). The axes of the dispensing nozzles or holes (12b) of the second series are incident on the glazing plane of the manufactured articles, slabs or tiles (30), in an area between the two incidence points on the same glazing plane of two contiguous axes of two front modular dispensing holes (12a) belonging to said first series of modular dispensers (10).

Description

[0001] IMPROVED DEVICE FOR GLAZING OBJECTS

[0002] DESCRIPTION

[0003] The present invention relates to an improved device for glazing objects. Specifically, but not exclusively, it finds useful application for performing glazing in the ceramic industry, mainly dedicated to the production of ceramic tiles and / or slabs for flooring or wall coverings in construction.

[0004] Glazing, which involves depositing a continuous and as uniform and homogeneous as possible layer of glaze on surfaces intended, for example, to subsequently receive a decoration, represents a part of the production process for ceramic slabs or tiles that's normally carried out on their production line. Here, the glaze is deposited on the moving products to be glazed.

[0005] Various in-line glazing techniques are known and have been developed over time, starting from spray glazing. This technique uses glazing stations made up of various types of glazing booths arranged along the line. At each of these, atomized glaze is sprayed onto the surface of the passing tiles and / or slabs. The adoption of actual booths is necessary to contain the atomized glaze within a confined environment strictly required for the operation and to prevent, or at least limit, its dispersion into the surrounding environment. While the resulting surface glazing quality is good, it's economically improvable. This is because a large portion of the atomized glaze isn't actually used during the process; it fails to be deposited on the slabs or tiles. Consequently, it must be aspirated (from 30%, up to over 50% of the dispensed glaze, depending on the glazing technique used) to keep the application booth clean and prevent the dispersed atomized glaze mist from entering the environment. This then requires it to be captured and conveyed by a special system for abatement and subsequent disposal. Another glazing technique is continuous curtain glazing. Here, an application veil of glaze is generated, with its width depending on the format of the tiles and slabs to be glazed. These products, transferred onto a transport system, impact the veil, acquiring a portion that forms a continuous and uniform layer on their surface. Various constructive forms are used, such as waterfall, bell, or die. In this case too, the quality of the glazing performed is more than good. However, due to the application methods, the quantity of glaze that needs to be dispensed is still substantial, making it not particularly suitable for the current types of tiles and slabs most produced by the ceramic industry, such as porcelain stoneware, for which the quantities of glaze to be applied must be limited. It's estimated that these glazing techniques are used in about 10% of national ceramic industry production and slightly more, between 30% and 40%, in the rest of the world.

[0006] A more recent glazing technique, still under study and development, is digital ink-jet glazing, borrowed from ink-jet or digital printing, which is now very widespread in the ceramic sector for executing all types of decoration. However, some problematic aspects still need to be overcome for the use of such ink-jet technology transferred to glazing. Among these is certainly the cost of the glaze, which is 6-8 times higher than that normally used with traditional techniques. This is due to the higher production cost of glazes and the necessary media in their composition, attributable to the cost of preparing the glazes, which requires extra-fine grinding to avoid clogging of the print heads, and the cost of preparing the chemical media indispensable for preserving the print heads. These latter, moreover, are particularly polluting when burned in the firing kiln. This condition has limited the spread of ink-jet technology for glazing, also considering that the quantities of glaze applied in glazing are still greater than those normally used for the same surface area in decoration. Another obstacle is the overall cost of the plant (machine), which is significantly higher than that of machines using known technologies for glazing slabs or tiles. Furthermore, these latest generation ink-jet glazing techniques are based on the idea of using glazing units, each essentially comprising a glaze application bar placed transversally to the direction of advancement of the slabs or tiles. From its lower face, an equal number of glaze droplet flows are dispensed (through a series of small nozzles or holes) onto the underlying surfaces of the slabs or tiles, using various hydraulic and mechanical dispensing methods. These impact the underlying surface to be glazed, depositing rows of small glaze spots aligned in directions transversal to the longitudinal direction of advancement of the slabs or tiles and spaced from each other by a pitch of a few millimeters, corresponding in turn to the interaxis existing between adjacent holes of the ink-jet dispenser. This fails to guarantee optimal aesthetic results (specularity of the glazed surface), due in particular to the limit imposed by the minimum distance of, on average, 2-3 mm between the axis of each nozzle or hole and that of the immediately adjacent nozzle. This condition often tends to highlight undesirable longitudinal streaks in the glazed surface. One way to try to mitigate this effect has been to increase the amount of glaze to "flood" the surface more and thus improve spreading, with the introduction of a second row of holes alongside the first and placed in intermediate positions with respect to the holes of the first series.

[0007] However, even these latest embodiments aren't free from problems and drawbacks. Some concern increased production costs, others are induced by specific characteristics of the initial raw material, meaning the ceramic slabs or tiles to be glazed.

[0008] The present invention aims to overcome the drawbacks and limitations of the known art by means of a new glazing device that is economically advantageous both in terms of plant cost and operating cost for glazing products (slabs, tiles), and that has a low environmental impact. This impact depends not only on the quality of the components but also on the quantity of glaze used and consumed, compared to the known systems currently widespread and used in the known art. This is also considering that these glazing techniques are applied under typical production conditions of the ceramic industry production lines, where the product to be glazed can present quite different initial conditions: hot (between 70° and 100°C) and with a high degree of absorption towards water-based fluids.

[0009] Another object of the present invention is to provide a glazing device with a modular structure that allows for easy use for all types of formats.

[0010] The present invention aims to provide a glazing device as described in the description, illustrated in the attached figures, and claimed in the claims. The most evident advantages it provides are:

[0011] • Equalizing or improving the level of glaze spreading on the surface compared to current methods in use.

[0012] . Being simple to use for industry operators.

[0013] • Requiring an accessible investment compared to the known art currently in use.

[0014] . Making the new glazing process economically sustainable, thanks to the use of glazes with characteristics and costs very similar to current ones (and not 6-8 times higher like those used for Ink Jet technology).

[0015] . Allowing substantial glaze savings (at least 30%) compared to the most widespread current glazing method (spray application).

[0016] . Allowing significant savings for the abatement and disposal of waste, together with the undeniable and much more important beneficial result of reduced environmental pollution. . Allowing less water usage, both for grinding glaze components and for the frequent washings required by known application devices (such as spray booths and similar).

[0017] • Containing atmospheric emissions of harmful combustion gases generated in subsequent production stages.

[0018] The recent progressive trend towards the use of glazing devices or dispensers that use modular systems consisting of ink-jet heads or dispensing modules arranged aligned on bars placed transversally to the feeding direction of the slabs or tiles to be glazed. The modular structure simplifies the adaptation of the bars to the width of the slabs or tiles to be glazed for dispensing glaze for coating (glazing) the flat surfaces of the slabs or tiles.

[0019] This configuration allows for the linear extension of the format (application front) through the assembly of ink-jet heads or dispensing modules. These modules are assembled on at least one bar or plate of adequate dimensions, positioned in two rows spaced from each other in the longitudinal direction (that of the advancement of the product to be treated), to conveniently bring closer the extreme emission points of the fluid of each module (in the transversal direction).

[0020] Typically, in the mentioned techniques, operation occurs on product surfaces at ambient temperature, often with very low absorption, and with fluids whose drying isn't particularly rapid. Therefore, the distance between the two rows of modules has little or no physical impact on the result.

[0021] Conversely, the influence on the good glazing result is significantly accentuated when the technique is applied to ceramic tiles or slabs (in the crude phase). Here, due to the specific production conditions of the production line, the product is generally hot (between 70° and 100°C) and has a high degree of absorption towards water-based fluids. Furthermore, as an additional aggravating factor, the quantities of fluid applied in the glazing process are quite high (from 200 to 700 g / m2), and consist of approximately 50% water (very volatile in the presence of temperature).

[0022] The invention therefore aims to eliminate or minimize the problems arising from the difference between the deposition of the fluid between the two distinct rows of dispensers. The undesired defect to be solved relates to the longitudinal streaks that appear at the margin points between the traces / portions applied by the different dispensers, due to the differential drying of the glaze layer dispensed at different moments (even if the time elapsed is very short, between 30 and 120 milliseconds, depending on the translation speed of the tiles or slabs to be glazed).

[0023] Further features and advantages of the present invention will become clearer from the following detailed description of some preferred embodiments, illustrated by way of example, but not limitation, in the attached figures, in which:

[0024] . Figure 1 shows, with reference to a first embodiment, a schematic vertical elevation view, partially sectioned along a vertical plane parallel to the direction of motion of the mobile transport plane for the tiles to be glazed.

[0025] . Figure 2 shows part of a schematic top plan view of Figure 1 .

[0026] . Figure 3 shows a schematic section made along a plane parallel to the transport plane 20 a short distance from the dispensing nozzles or holes 12, 13.

[0027] . Figure 4 shows a schematic top plan view of Figure 3 made at the level of the glazing plane 22, which schematically highlights the arrangement of the glaze points (in reality, small spots) produced in the "downstream" part of the slab or tiles represented in Figure 3. In the attached figures, the central part of an improved glaze dispensing device is shown, consisting of a plurality of glaze dispensing modules 10 made in accordance with the invention. This device is arranged with a transversal orientation at a predetermined distance above the support surface of a mobile transport plane 20, which is held by the assembly of two transport belts 21 on which tiles or slabs to be glazed 30 are placed and orderly transferred.

[0028] The dispensing device comprises, operating in association with the mobile transport plane 20 for the objects to be glazed, at least one glaze dispensing bar or plate, generally indicated by 1. This is located at a predetermined distance above said mobile transport plane 20 and comprises, in turn, a lower wall 11 on which a first and a second row, parallel to each other, of glaze dispensing modules or modular dispensers 10 are arranged. Each of these is equipped with at least a first series of front dispensing nozzles or holes 12 and a second series of rear dispensing nozzles or holes 13.

[0029] The axes of the front dispensing holes 12 are arranged parallel to each other and contained on the same plane of trace a, which is transversally positioned with a predetermined inclination with respect to the direction of motion of said mobile transport plane 20 for the manufactured articles to be glazed (slabs or tiles 30). The rear dispensing nozzles or holes 13 of the second series have axes arranged parallel to each other and contained on the same plane p, which is transversally positioned with a predetermined inclination with respect to the direction of motion of said mobile transport plane 20 for the manufactured articles to be glazed (slabs or tiles 30).

[0030] In particular, the axes of the rear dispensing nozzles or holes of the second series are incident on the glazing plane of the manufactured articles, slabs or tiles 30, in an area between the two incidence points on the same glazing plane of the two contiguous axes of two front dispensing holes 12 belonging to said first series of said modular dispensers 10. In this way, the jet dispensed from a dispensing hole 13 of the second series centers the empty surface between the intersections with the glazing plane of the two axes of the two adjacent holes of the first series. This results in the wetting of the portion of the surface in the area between the two impact zones of the jets produced by the adjacent dispensing holes 12 of the first series.

[0031] As can be easily seen from the figures, the deposition of drops from the dispensing holes 12 and from the dispensing holes 13 occurs almost simultaneously along the intersection with the glazing plane 22. This achieves, above all, substantially uniform impact conditions on the underlying slab or tile, which is favorable for the simultaneous distribution and deposition of individual glaze spots on the surface to be glazed and the drying of the glaze spots originated by the impact of glaze droplets produced and directed by the dispensing holes 12 and 13.

[0032] Said glaze dispensing holes or nozzles are calibrated and of equal diameter. Furthermore, they are arranged aligned and equidistant from each other. Their pitch and diameter are made according to the nature and rheological characteristics of the glaze and the quantities to be applied. The range of pitches between the holes is approximately between 0.5 mm and 3 mm, with a more frequent use interval of 1 mm-2 mm. The range of diameters of the holes themselves is between 0.1 mm and 0.6 mm, with a more frequent interval of 0.2 mm-0.4 mm for the glazes most frequently used in the ceramic industry, depending on the grammage (quantity of glaze per unit area) to be applied and the transit speed of the tiles or slabs 30.

[0033] The axes of the dispensing holes 13 of the rear series and those 12 of the front series of each dispensing module 10 are both inclined with respect to the normal to the direction of motion of the mobile transport plane 20 by angles a and p, where the more commonly used reference values are a = 30° and p < 10°. More generally, the acute angle between the two said planes is between 25° and 45°.

[0034] The glaze dispensing modules 10 of each of the two parallel rows of dispensing holes are aligned in two parallel rows. The dispensing modules 10 of the first row are offset with respect to those of the second row, presenting opposite ends partially overlapping on the glazing plane 22 for a length of a few millimeters (3-10mm). The presence of this partially overlapping section on the transport plane 20 is characterized by an arrangement and distribution scheme of the dispensing nozzles or holes designed so that the overall quantity of glaze for the projected total coverage (which occurs due to the overlapping of the ends of the modules of a first row with those of the second) is dispensed 50% by the modular dispenser 10 of the first row and 50% by the modular dispenser 10 of the second row of the projected total coverage.

[0035] This situation is schematically illustrated in Figure 4, which shows the coverages performed through the patterns of the impact points generated by the execution of the glazing operations as obtained from the portion of the device represented in Figures 3 and 4, i.e., from the dispensing module 10 of the first row and from the two dispensing modules 10 of the second row.

Claims

CLAIMS1). An improved device for glazing objects such as ceramic slabs and tiles characterised by the fact that the said device comprises - operating in association with a mobile conveying surface (20) for conveying objects to be glazed, such as slabs and tiles (30) - at least one glaze dispensing bar (1), which is located at a pre-established distance above the said mobile conveying surface (20) and comprising, in turn, a lower wall (1 1) on which a first row is arranged, composed of a plurality of contiguous dispensing modules or modular glaze dispensers (10), each of which is equipped with at least a first series of front dispensing nozzles or holes (12) with dispensing axes arranged in parallel and lying on the same plane, which is positioned transversally with a pre-established inclination with respect to the direction of motion of the said mobile conveying surface (20) for conveying objects to be glazed, slabs, or tiles (30); it being envisaged that each of the said glaze dispensing modules (10) comprises at least a second series of rear nozzles or dispensing holes (13) with axes arranged in a mutually parallel fashion and lying on the same plane, which is transversally positioned with a pre-established inclination with respect to the direction of motion of the said mobile conveying surface (20) for conveying objects to be glazed, slabs, or tiles (30); each of the axes of the nozzles or dispensing holes (13) in the second series being incident on the surface for glazing the objects, slabs, or tiles (30) in an area included between the two points of incidence on the same glazing surface of two contiguous axes of two front modular dispensers (12) in the said first series of modular dispensers.2) A device according to Claim 1 characterised by the fact that the said dispensing holes are sized, have the same diameter, and are arranged aligned and mutually equidistant; the pitch of the holes and diameter thereof being sized according to the nature of the glaze and the amounts to be applied; thepitches between the said holes ranging from approximately 0.5 mm to 3 mm, with a most frequently used range being 1 mm to 2 mm; the diameters of the said holes ranging from 0.1 mm to 0.6 mm with a more frequent range being from 0.2 mm to 0.4 mm for the glazes most commonly used in the ceramic industry depending on the weight ratio (amount of glaze per unit of surface area) to apply and the transit speed of the tiles or slabs (30).3) A device according to Claim 3 characterised by the fact that the axes of the dispensing holes (10) in the rear series and those in the front series are both inclined with respect to the direction of motion of the mobile conveying surface (20) so as to form acute angles a p with respect to the normal in the said direction of motion.4) A device according to Claim 4 characterised by the fact that the glaze dispensing modules (10) in each of the said two parallel rows are aligned in two parallel rows and are staggered, having the opposite ends partially overlappable by a few millimetres (3-10 mm) above the glazing surface, the said distance being envisaged with a pattern of nozzles or dispensing holes (12) and ends arranged so that the overall quantity of glaze is dispensed at a rate of 50% by the dispenser in the first row and 50% by the dispenser in the second row with respect to the total coverage envisaged, which occurs as a result of the overlapping of the ends of the modules in the first row and those in the second row above the said glazing surface.

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