Patent Application
20110198337
This invention is related to the manufacture of an improved porcelain stoneware panel for use as a thermal accumulator and transmission element in heating devices.
Within the huge variety of products of the ceramics industry, porcelain stoneware is one of the most important. This material originated in the 1980s as a product with high technical performance, characterised by its ability to reproduce nature and come closer, more than any other ceramic product, to the concept of natural rock or stone. It gave rise to proposals for original and at that time unknown combinations. Porcelain stoneware is included in the BIa group (dry-pressed flagstone with water absorption E<0.5%) of regulations ISO13006 and UNE 67-087. It is a vitrified product in its entire mass and very compact, having a very low porosity as an essential characteristic, which confers excellent mechanical and chemical properties and resistance to freezing, making it useful for surfacing or exterior covering in cold areas. It also has a high resistance to chemical agents and cleaning products and also maintains a very good resistance to abrasion and has a high breakage point. To this should be added its ease of cleaning, which makes this an ideal material for surfacing in spaces where hygiene is of utmost importance.
The manufacturing process for traditional porcelain stoneware for surfacing comprises the following stages:
The use of traditional porcelain stoneware panels for surfacing in the field of heating as an element to which heating elements or devices are attached is known. The applicant (of this patent application), taking advantage of benefits inherent in porcelain stoneware, has started to use it as an accumulator and radiator in heating systems, generating various utility models and national and international patents, such as Spanish patent ES 2 265 783 “Gres porcelánico con cobertura de metal sintético” (porcelain stoneware with synthetic metal covering), Spanish Utility Model ES1 042 460 “Radiador eléctrico perfeccionado” (Improved electrical radiator), Spanish patent ES 2 265 784 “Disposición para el calefactado de placas en gres porcelánico para su actuación como acumulador y radiante para calefaccián” (arrangement for the heating of porcelaneous stoneware panels for use as an accumulator and a radiant element for heating) and international patent PCT/ES2006/00464 of the same title.
However, the application of traditional porcelain stoneware for surfacing in heating systems entails a series of limitations. These limitations are:
In view of the foregoing, there is a need to provide a thermal accumulation-transmission panel and a method of obtaining it that solves all of the drawbacks mentioned; in particular, to improve the thermal accumulation performance, furnish better mechanical properties and enable an increase in natural convection with respect to traditional panels of porcelain stoneware.
Surprisingly the inventors have found that changing the starting materials and the manufacturing process of traditional porcelain stoneware panels, it is possible to confer on these panels a three-dimensional disposition that is especially advantageous for its application in heating. The improved porcelain stoneware panels thus obtained, or the panels of the invention, show excellent thermal properties as a result of a combination of chemical composition and novel geometry. In particular, the porcelain stoneware panels of the invention improve thermal accumulation performance, exhibit better mechanical properties and increase natural convection with respect to traditional porcelain stoneware panels.
A first aspect of the invention is directed to a thermal accumulation-transmission panel that comprises porcelain stoneware, characterised in that the chemical composition of the porcelain stoneware comprises between 80.0% and 90.0% SiO2, and between 5.0% and 15.0% Al2O3, and in that the geometry of the panel presents parallelepiped projections on one of its faces and has a thickness of at least 12 mm.
According to a specific embodiment, the panel of the invention comprises between 82.0% and 86.0% SiO2, preferably 84.6%. According to another specific embodiment, the panel of the invention comprises between 8.0% and 10.0% Al2O3, preferably 9%.
The presence of parallelepiped projections on the part adjacent to the heat source facilitates, as will be seen later, thermal transmission by convection and radiation, as well as thermal accumulation.
Likewise, the width enables the panel to conserve its mechanical properties and enhances the thermal accumulation capacity with respect to traditional porcelain stoneware panels, which are narrower. According to a preferred embodiment, the thickness of the porcelain stoneware panel of the invention is between 12 mm and 16 mm, preferably 14 mm.
In another preferred embodiment, the porcelain stoneware panel of the invention presents on the face adjacent to the heat source blind peripheral slots, obtained during the process of moulding, for housing attachment systems of the panel to various heat sources.
In a second aspect, the invention refers to the manufacturing process of the improved porcelain stoneware panel or the process of the invention. This process is based on a modification of the manufacturing process of traditional porcelain stoneware for surfacing and is characterised by using a force of at least 3000 tonnes in the pressing stage and including a total firing time of at least 60 minutes.
In an additional aspect, the invention is directed to a heating device that comprises an improved porcelain stoneware panel and a heat source.
In order to complement the description which follows below and with the aim of helping towards a better understanding of the characteristics of the invention, in accordance with a preferred example of a practical embodiment thereof, a set of drawings is included as an integral part of this description wherein, in an illustrative and non-limitative manner, the following are represented:
a and 2b show respectively the energy-dispersive X-ray analysis on porcelain stoneware for normal surfacing use and on improved porcelain stoneware for use in heating systems, which is the object of this invention.
The chemical composition of the improved porcelain stoneware panel (1) comprises a higher silica content and a lower alumina content compared with the composition of a traditional porcelain stoneware panel. Specifically, the composition of the porcelain stoneware of the invention comprises:
The silica and alumina contents expressed in this invention are those obtained after an analysis by calcination at 900° C.
For the purposes of this invention, silica is understood in its commonly accepted meaning, i.e. SiO2 in its various polymorphic forms. Also, for the purposes of this invention, alumina is understood in its commonly accepted meaning, i.e., Al2O3 in its various polymorphic forms.
According to a specific embodiment, the silica content is between 82.0% and 86.0% and preferably 84.6%. According to another specific embodiment, the alumina content is between 8.0% and 10.0% and preferably 9.0%.
With the aim of enhancing thermal accumulation, the panel (1) of the invention has a thickness of at least 12 mm, preferably between 12 mm and 16 mm and still more preferably of 14 mm. Traditional panels of porcelain stoneware present a lower thickness, usually between 9 mm and 11 mm, due to the difficulty of maintaining the mechanical properties of the material at higher thicknesses. However, due to the manufacturing process, the panel (1) of the invention can have higher thicknesses than panels of traditional stoneware, with its mechanical properties being unchanged.
Additionally, during the manufacturing processes it is possible to confer on the porcelain stoneware panel (1) of the invention an original configuration in the form of parallelepiped projections (2) on at least one of its faces (5). Preferably, one face (5) furnished with said series of parallelepiped projections (2) is the face (5) that will be placed adjacent to a heat source, thereby substantially improving the processes of thermal transmission and accumulation. The parallelepiped projections (2) of the panel of the invention are distributed in a central area on this face (5) in order to encourage convection.
These projections (2) enable the creation of natural convection chimneys that on the one hand improve the thermal transmission by natural convection and, on the other hand, encourage heat transmission from the face adjacent to the heat source to the distal face. As an additional effect, the projections (2) increase the surface area of the panel (1) and therefore improve thermal accumulation and radiation.
In the context of this specification, a panel adjacent to a heat source can relate to a relationship of closeness if the heat source is not appropriate for contact with the panel, for example in the case of a resistance of fins, or of contact, if it is for example a resistance by cables or a water recirculation system.
In a preferred embodiment, the panel (1) additionally presents a peripheral ridge (3) of higher thickness on the face furnished with parallelepiped projections. Consequently, when the panel (1) is placed adjacent to a heat source, said ridge (3) encourages the creation of hot air pockets, laterally closes the equipment to encourage the chimney effect, diverts the convection of hot air from the upper part of the panel, so reducing excessive heating of the part of the equipment most likely to be touched by a user and brings higher resistance to an anchoring element, as will be seen below.
In the previous embodiment of the panel (1) of the invention, equipped with a peripheral ridge (3), the central zone whereon the parallelepiped projections are distributed occupies approximately the entire face (5), except for the peripheral zone occupied by the ridge (3).
In another preferred embodiment, the improved porcelain stoneware panel (1) presents on the face (5), adjacent to the heat source, peripheral blind slots (4), which can be created during the moulding process and which make possible the insertion of fastening elements of the panel to systems which will be placed thereagainst and over which the heat source will be incorporated. In a still more preferred embodiment, the peripheral blind slots (4) are arranged on the peripheral ridge (3) of a panel (1) equipped with a peripheral ridge (3). Consequently, greater resistance is provided to the anchoring element as the slots (4) are made in an area of the panel (1) of higher thickness.
The geometry of the shape of the over-thick panel, together with the possibility of using the peripheral blind slots (4) as supporting and fastening elements, make the porcelain stoneware panel (1) of the invention optimal for use in any heating system, irrespective of the heat source used. Therefore, this heat source can be of any type, such as, for example, electricity or water.
The manufacturing process for the improved porcelain stoneware panel, or process of the invention, is based on a modification of the manufacturing process of traditional porcelain stoneware for surfacing. The process of the invention enables the manufacture of porcelain stoneware panels that exhibit a substantial improvement in thermal accumulation and transmission capacity with respect to traditional porcelain stoneware, retaining their mechanical properties.
The manufacturing process starts with a careful selection and combination of natural raw materials. The base material for the process of the invention comprises a lower content of clays with respect to the base material for traditional stoneware for surfacing, and in contrast also includes whitening additives. The following table shows a comparison between the composition of the base material for traditional porcelain stoneware for surfacing and of improved porcelain stoneware according to a specific embodiment of the invention.
Feldspars act as fluxes and among the whitening additives are, for example, zirconium oxide.
Once the base material has been selected, it is homogenised, micronized and atomised in the same way as in the manufacturing process for traditional porcelain stoneware for surfacing. However, the pressing and firing stages differ compared with respect to said process.
While the pressing force used in industrial processes for obtaining porcelain stoneware for surfacing varies between 2500 Tn and 2800 Tn, in the case of this invention it is necessary to use a force of at least 3000 tonnes, preferably between 3500 and 4000 tonnes, and still more preferably 3800 tonnes.
Also, the process of the invention increases the total firing time, i.e., the combination of heating, firing and cooling, with respect to the manufacturing process of traditional porcelain stoneware for surfacing, which is around 54 minutes. The total firing time according to the process of the invention is at least 60 minutes, preferably between 60 and 80 minutes and still more preferably 70 minutes.
In an additional aspect, the invention is aimed at a heating device that comprises the porcelain stoneware panel (1) of the invention and a heat source. As previously described, the heat source can be of any type, such as, for example, an electrical heat source or the recirculation of a fluid with thermal accumulation capacity (water, oil, etc.). Preferably, the porcelain stoneware panel (1) and the heat source are bound by means of the insertion of fixing elements into the peripheral blind slots (4) of the panel itself.
The following table shows, for comparative purposes, the chemical composition of a sample of normal porcelain stoneware for surfacing.
The following table shows the chemical composition of a sample of improved porcelain stoneware for heating applications. This chemical composition differs from that of normal porcelain stoneware for surfacing by approximately 7% in the silicon and aluminium oxide content:
As can be seen in
b (improved porcelain stoneware) shows the content of Si, Al and the presence of Zr in comparison with traditional porcelain stoneware of
In the test shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 08380246.2 | Aug 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/060067 | 8/4/2009 | WO | 00 | 4/28/2011 |
