Method of glazing a ceramic article

Abstract

The invention relates to a method for glazing a ceramic article, in particular a hollowware (1) with a perforated base (2). Furthermore, the invention relates to a device (4) for carrying out the method.To enable a less complex, high-quality glazing of ceramic articles, especially hollowware with openwork feet, a method with the following steps is proposed: - Glazing a first part (5) of the ceramic article (1) with a first glaze (6) by wave glazing, - subsequently cleaning the ceramic article (1) by removing the excess parts of the applied first glaze (6) such that a defined boundary line (19) of the first glaze (6) is created, and - subsequently glazing a second part (27) of the ceramic article (1) with a second glaze (24) by dipping, whereby during dipping the second glaze (24) is applied up to the boundary line (19) of the first glaze (6).

Description

[0001] The invention relates to a method for glazing a ceramic article, in particular a hollow article with a perforated base edge.

[0002] Ceramic items, especially hollowware, can have a rim and a foot rim. These foot rims can be openwork. The perforations in the foot rim are also called water grooves, and a foot interrupted by such water grooves is also called a wash foot. Ceramic items that can have feet with water grooves include cups, mugs, and other ceramic drinking vessels.

[0003] The glazing of articles with wash feet on the inside and outside has so far been carried out predominantly using the technique of spray glazing, as this is a comparatively simple and more reliable technique, particularly in view of the fact that when dipping the article into the glaze using the alternative dip glazing technique, it is always necessary to hold the article at the edge of the foot and an additional, subsequent glazing step is required to glaze the edge of the foot, which can lead to quality problems due to the often varying glazing results.

[0004] During spray glazing, a large amount of glaze is routinely lost because it is not applied to the item. The overspray must be laboriously collected and recycled.

[0005] DE 198 10 710 A1 describes a process for glazing hollow clay or porcelain ware. Part of a mug or cup is glazed using dip glazing, while another part of the mug or cup is glazed using flow glazing. A combination of these two glazing techniques is also known from DE 12 66 199 B for glazing ceramic plates.

[0006] An object of the present invention is to enable a low-cost, particularly high-quality glazing of ceramic articles, in particular hollowware with openwork foot edges.

[0007] This object is achieved by a method according to claim 1. Advantageous embodiments of the invention are specified in the subclaims.

[0008] The inventive method for the preferably fully automated glazing of a ceramic article, in particular a hollowware with a perforated base rim, comprises the following steps: glazing a first part of the ceramic article with a first glaze by means of flow glazing, subsequent cleaning of the ceramic article by removing the superfluous parts of the applied first glaze such that a defined boundary line of the first glaze is created, and subsequent glazing of a second part of the ceramic article with a second glaze by means of dip glazing, wherein during dip glazing the second glaze is applied exactly up to the boundary line of the first glaze. In this way, after completion of glazing, the boundary line of the flow glazing forms the dividing line between the two glazes.

[0009] With the inventive method for glazing ceramic articles with openwork feet, the use of spray glazing can be dispensed with. Instead, the techniques of flow and dip glazing can be used. The process is therefore not only simpler but also more cost-effective. The disadvantages of spray glazing, particularly the overspray problem, are avoided. At the same time, a very high glazing quality is achieved. In particular, a very precise parting line and a particularly smooth transition between the glazes can be achieved.

[0010] According to one embodiment of the invention, the second part of the ceramic article is a part of the article that is not provided with the first glaze. In other words, the second part of the ceramic article is a different part than the first part of the ceramic article, i.e., the second part can be completely different from the first part.

[0011] According to one embodiment of the invention, the second part of the ceramic article or a portion of this second part is a part of the article that (because it has already been cleaned) is no longer provided with the first glaze. In other words, the glazed parts or parts to be glazed of the ceramic article can also overlap, i.e., the second part or a portion of the second part of the ceramic article can be the first part or a portion of the first part of the ceramic article, or vice versa.

[0012] According to one embodiment of the invention, the second part of the ceramic article is the entire remaining part of the article, apart from the first part of the article, so that together with the first part, the entire ceramic article is glazed. Alternatively, the first part and the second part together may also form only a part of the ceramic article, wherein the remainder of the article not formed by the first or second part has been or will be glazed in the same or a different way, or will not be glazed.

[0013] According to one embodiment of the invention, the first part of the ceramic article is at least an inner side of a hollow ware, and the second part is at least a part of an outer side of this hollow ware. According to one embodiment of the invention, the first part of the ceramic article is glazed with a first glaze, and the second part of the ceramic article is glazed with a second glaze that is different from the first glaze. According to one embodiment of the invention, the second glaze has a different color than the first glaze. In this way, the invention can also be used to create a two- or multi-color glaze, as is often desired for hollow ware.

[0014] According to one embodiment of the invention, the ceramic article is cleaned in such a way that the boundary line is created in the area of the rim of the ceramic article. This meets the desire, in two-color glazes, to glaze the inside with one color and the outside with the other color, so that the color dividing line between the inside and outside of the article created by dip glazing is located in the area of the rim.

[0015] According to one embodiment of the invention, the ceramic article is held during flow glazing by a first article holder operating according to a first functional principle, and during dip glazing by a second article holder, preferably operating according to a different functional principle from the first holding principle. In this way, optimized holding methods can be used for the respective process step. This is particularly advantageous when the article is a hollow article with a perforated base edge, since an article holder can then be used whose holding principle is adapted to a perforated base edge.

[0016] According to one embodiment of the invention, the ceramic article is held by the first article holder during cleaning. This eliminates the need for a transfer device between the flushing station and the cleaning station.

[0017] According to one embodiment of the invention, during dip glazing, the ceramic article is immersed in a glaze basin located in a storage basin. The second glaze is transported from the storage basin into the glaze basin and flows from the glaze basin over its edge back into the storage basin. This creates a very smooth glaze surface into which the ceramic article is immersed.

[0018] It is generally customary for the glaze in the dipping tank to be constantly circulating, as otherwise the glaze will sediment. One embodiment of the invention deviates from this method and the transport of the second glaze from the storage tank to the glaze tank is interrupted from time to time. Advantageously, such an interruption occurs during the immersion of the ceramic article in the glaze tank or in a defined temporal connection with this immersion. In this way, a particularly calmed glaze is created with a very smooth glaze surface, which is unusual for dip glazes, as previously calmed glazes were not used in dip glazing, but instead the glaze was constantly circulated. Sedimentation does not occur despite the interruption in the glaze transport, as the interruption is only for a short period of time.

[0019] According to one embodiment of the invention, before the ceramic article is immersed in the glaze basin, preferably immediately before immersion, an air stream is generated over the glaze surface using a blowing device. This air stream is preferably designed as an air blast and is directed such that it flows directly over the glaze surface. It serves to remove any foam, the so-called haze, from the glaze surface before the article is immersed in the glaze. This foam can form on the glaze surface when the colored glaze is not agitated or is only slightly agitated. Removing this haze prevents it from accumulating on the article, which would lead to undesirable glaze defects on the article after firing.

[0020] The invention makes it possible to mechanically and automatically provide ceramic articles, in particular hollowware such as mugs or cups, on the inside and outside with different, in particular differently colored glazes. The invention not only makes it possible for these ceramic articles to have openwork base edges, but also allows particularly precise boundary lines between the glazes or particularly precise dividing lines between the glazes to be realized. If different colored glazes are used, an exceptionally sharp color separation can be achieved with the method according to the invention. At the same time, a very smooth transition between the glazes can be created in the area of the dividing line, which is particularly advantageous for cups. If the dividing line between the two glazes is located in the area of the rim of the cup, as is generally desired, a particularly smooth rim can be achieved with the method according to the invention.This is particularly important because irregularities on the surface of the rim of the cup can be particularly easily perceived by the very sensitive lips.

[0021] The method according to the invention is particularly suitable for the fully automated glazing of ceramic articles. However, the method according to the invention is also suitable for the semi-automated glazing of ceramic articles, in which individual steps of the actual glazing process or the feeding or removal of the ceramic articles to or from the glazing machine are performed manually.

[0022] An apparatus for carrying out the method according to the invention, also referred to herein as a glazing machine, comprises at least one device for flow glazing ceramic articles, at least one device for subsequently cleaning the ceramic articles, and at least one device for subsequently dipping the ceramic articles. These devices are designed to carry out the corresponding steps of the method according to the invention. The glazing machine may further comprise devices for feeding and removing the ceramic articles (feed devices, removal devices) and / or devices for transferring the ceramic articles from one station of the glazing machine to another station of the glazing machine (transfer devices).

[0023] An embodiment of the invention is explained in more detail below with reference to the drawings. Fig. 1 is a schematic representation of the internal glazing of the ceramic article, Fig. 2 is a schematic representation of the sponging of the ceramic article, Fig. 3 is a schematic representation of the external glazing of the ceramic article, Fig. 4 is a schematic representation of the unglazed ceramic article, Fig. 5 is a schematic representation of the splash-glazed ceramic article, Fig. 6 is a schematic representation of the cleaned ceramic article, Fig. 7 is a schematic representation of the dip-glazed ceramic article.

[0024] All figures depict the invention not to scale, but merely schematically and with only its essential components. Like reference numerals correspond to elements with the same or comparable function.

[0025] The ceramic article to be glazed is a hollowware 1, namely a cup. The base rim 2 of the hollowware 1 is openwork and has a water groove 3 ( Fig. 4 The glazing of the hollowware 1 is carried out fully automatically using a glazing machine 4.

[0026] After the hollowware 1 has been fed to the glazing machine 4 by means of a suitable feed device (not shown), for example a feed device for synchronized feeding, a first part 5 of the hollowware 1 is glazed with a first glaze 6 in a first color by means of flow glazing. For this purpose, a device 7 for flow glazing, which is designed as part of the glazing machine 4, is used. The first part 5 of the hollowware 1 is essentially the inner side 8 of the hollowware 1 ( Fig. 5 ). The first glaze 6 is therefore the interior glaze.

[0027] For the splashing, the hollowware 1 is held at its foot edge 2 by a first article holder 9 and moved with its mouth edge 11 oriented downwards towards a splash nozzle 12 of the splash glazing device 7, from which the first glaze 6 emerges in the manner of a fountain ( Fig. 1 ). The first article holder 9 is a vacuum suction cup arranged on a support arm 13 of the glazing machine 4. The first article holder 9 acts on the foot edge 2 of the hollowware 1 and sucks it in with negative pressure. In this way, the hollowware 1 is held at the foot edge 2. The hollowware 1 can then be moved into the desired position above the surge nozzle 12 and back by rotating (see double arrow 14) and / or linearly moving (see double arrow 15) the support arm 13. The first article holder 9 is designed to hold a perforated foot edge 2. As an alternative to a vacuum suction cup, another suitable article holder can also be attached to the support arm 13.

[0028] In addition, during the flow glazing, the mouth rim 11 and a section 16 of the outer side 17 of the hollowware 1 are provided with the first glaze 6 by immersing the hollowware 1 with its mouth rim 11 into a glaze container with which the first glaze 6 emerging from the flow nozzle 12 is collected.

[0029] The hollowware 1 is immersed into the glaze container at least to such an extent that it is ensured that the mouth rim 11 is completely covered with the first glaze 6 on the inside and outside ( Fig. 5 ) .

[0030] If the pump used for the surge glazing (not shown) is operated in a non-pulsating mode so that a uniform discharge of glaze 6 from the surge nozzle 12 occurs, a very uniform glaze thickness can be achieved.

[0031] Following the application of this flow glaze, the hollowware 1 is cleaned by removing the superfluous parts of the applied first glaze 6 in such a way that a defined, sharp boundary line 19 of the first glaze 6 is created ( Fig. 6 ). For this purpose, a device 21 designed as part of the glazing machine 4 is used for cleaning ( Fig. 2 ).

[0032] Cleaning is carried out, for example, by sponging the mouth rim 11. The surface of the hollowware 1 is wiped by moving the hollowware 1 against a rotating cleaning sponge 22 of the cleaning device 21. A dry or wet sponge 22 can be used for this purpose. If the cleaning device 21 is arranged adjacent to the flow glazing device 7, the hollowware 1 can be pressed against the cleaning sponge 22 using the same article holder 9 immediately after the flow glazing. A transfer device between these two stations is then not required. Alternatively, the sponge 22 can also be moved against the hollowware 1.

[0033] However, the excess glaze 6 can also be removed in other ways. For example, the glaze 6 can be scraped off with a cleaning knife from a suitably equipped alternative cleaning device (not shown).

[0034] By this cleaning, a sharp boundary line 19 of the first glaze 6 is achieved ( Fig. 6 ). The cleaning process can be adjusted so that this boundary line 19 runs exactly where desired on the hollowware 1. In other words, the position of the boundary line 19 is freely adjustable. The arrangement of the cleaning knife or the position and shape of the cleaning sponge 22 can be adjusted accordingly. In the example described here, the boundary line 19 runs directly in the area of the mouth rim 11 of the hollowware 1.

[0035] After cleaning, the inside 8 of the hollowware 1 as well as the mouth rim 11 up to the sharp border line 19 are completely covered with the first glaze 6, while the outside 17 of the hollowware 1 is unglazed up to this border line 19 ( Fig. 6 ). In this way, on the one hand, the inner glaze 6 located on the outer side 17 of the hollowware 1 in the area of the mouth rim 11 after the flow glazing is prevented from mixing with the outer glaze 24 when the hollowware 1 is immersed in the outer glaze bath 23. On the other hand, the cleaning defines a particularly sharp boundary line 19, as is necessary so that after the outer side 17 of the hollowware 1 has been glazed with the second glaze 24, a precise dividing line 25 is present between the glazes 6, 24, as described below.

[0036] After the interior glaze 6 from the flow glazing process has been cleaned off, the hollowware 1 is either transferred directly to a device 26 for dip glazing using a transfer device (not shown), or the hollowware 1 is stored or subjected to another intermediate step, such as a drying step. Furthermore, the hollowware 1 does not need to be cleaned off immediately after the flow glazing process. The glaze 6 can also be removed after a waiting period. The hollowware 1 can therefore also be temporarily stored and / or transported, for example, after the flow glazing process.

[0037] After the cleaning step, a second part 27 of the hollowware 1 is glazed with a second glaze 24 in a second color different from the first color by means of dip glazing. This is done by a dip glazing device 26 designed as part of the glazing machine 4. This second part 27 of the hollowware 1 is essentially the outer side 17 of the hollowware 1. The second glaze 24 is thus the outer glaze. A section 28 of this second part 17 of the hollowware 1 is a part of the section 16 of the first part 5 of the hollowware 1 that is no longer provided with the first glaze 6 because it has already been cleaned, namely that part of the outer side 17 of the hollowware 1 that was provided with the first glaze 6 during immersion in the glaze container during the flow glazing ( Fig. 6 ). The remaining part of the second part 27 of the hollowware 1 was unglazed until then.

[0038] For dip-glazing the outer side 17 of the hollowware 1, including the cup base, the hollowware 1 is held by a suitable second article holder 29. This article holder 29 is designed such that it engages exclusively with the inner side 8 of the hollowware 1. For this purpose, a stamp (not shown) sealingly inserted into the hollowware 1 is suitable, for example, which secures the hollowware 1 to the article holder 29 by creating a vacuum. Alternatively, the hollowware 1 can also be held on its inner side 8 with a vacuum-free gripper (not shown).

[0039] The second article holder 29 is also attached to a support arm 31, which can move the hollow article 1 into the desired immersion position and back by rotation and / or linear movement. For highly precise positioning of the hollow article 1 in the immersion tank 23, servo motors 32 are preferably used to drive the support arm 31.

[0040] The hollowware 1, held in this way by its inner side 8, is immersed into the outer glaze bath 23 for dip glazing with its base edge 2 facing downwards and covered with the outer glaze 24. The second glaze 24 is applied exactly up to the boundary line 19 of the first glaze 6, so that after dip glazing is complete, the boundary line 19 of the flow glazing forms the dividing line 25 between the two glazes 6, 24. In other words, the two glazes 6, 24 each end at the dividing line 25 without any overlap of the glazes 6, 24 or any defects occurring. This achieves a very precise transition between the glazes 6, 24.

[0041] The dipping basin 23, into which the hollowware 1 is immersed during dip glazing, is designed as an inner basin which is arranged in an outer storage basin 33, wherein the second glaze 24 is pumped from the storage basin 33 from below into the dipping basin 23 and flows from the dipping basin 23 over its edge 34 on all sides back into the storage basin 33.

[0042] The pumping of the second glaze 24 into the dipping basin 23 is interrupted immediately before each immersion of a hollow ware 1 for the duration of the dipping process, so that during the dipping glazing the second glaze 24 is not circulated and the glaze 24 no longer overflows into the storage basin 33. Therefore, immediately before the immersion of the hollow ware 1, there is an overfilled dipping basin 23 in which, due to surface tension, the second glaze 24 forms a glaze mound (not shown) projecting beyond the basin rim 34 with a very flat surface that serves as a glaze surface 35. The pump for pumping the outer glaze 24 is in Fig. 3 For reasons of simplification, the transport lines for the interior glaze 6 are not shown in Fig. 1 .

[0043] Immediately before the hollowware 1 is immersed in this glaze surface 35, an air stream is also generated by means of an air nozzle 36 attached to the dipping tank 23, which air stream flows over the glaze surface 35 and blows the silicate foam (not shown) away from the glaze surface.

[0044] After the dip glaze is applied, the hollowware 1 is completely glazed. The hollowware 1 is then dried and can be transferred to a suitable removal device (not shown) by means of a transfer device (not shown), by means of which the hollowware 1 is removed from the glazing machine 4.

[0045] Furthermore, physical features of the device can be reformulated to be used as process features, and process features can be reformulated to be used as physical features of the device. Features reformulated in this way are automatically disclosed. List of reference symbols

[0046] 1 Ceramic article, hollowware, cup 2 Base rim 3 Water groove 4 Glazing machine 5 First part of the hollowware 6 First glaze, interior glaze 7 Device for flow glazing 8 Inside of the hollowware 9 First article holder, vacuum suction cup 10 (free) 11 Mouth rim 12 Flow nozzle 13 Support arm 14 Linear travel direction 15 Direction of rotation 16 Outside section 17 Outside of the hollowware 18 (free) 19 Boundary line 20 (free) 21 Cleaning device 22 Cleaning sponge 23 Immersion tank, exterior glaze bath 24 Second glaze, exterior glaze 25 Parting line 26 Immersion tank 27 Second part of the hollowware 28 Part cleaned of the first glaze 29 Second article holder 30 (free) 31 Support arm 32 Servo motor 33 Storage tank 34Dip tank edge 35Glaze mirror 36Air nozzle

Claims

1. Method for the preferably fully automated glazing of a ceramic article, in particular a hollowware (1) with a perforated foot rim (2), comprising the steps of - glazing a first part (5) of the ceramic article (1) with a first glaze (6) by means of cascade glazing, - subsequent cleaning of the ceramic article (1) by removing the excess portions of the applied first glaze (6) in such a way that a defined boundary line (19) of the first glaze (6) is produced, and - subsequently glazing a second part (27) of the ceramic article (1) with a second glaze (24) by means of dip glazing, the second glaze (24) being applied up to the boundary line (19) of the first glaze (6) during the dip glazing.

2. Method according to claim 1, wherein the first part (5) of the ceramic article (1) is at least an inner surface (8) of a hollowware (1) and the second part (27) is at least a part of an outer surface (17) of this hollowware (1).

3. Method according to claim 1 or 2, wherein the first glaze (6) has a different colour than the second glaze (24).

4. Method according to one of claims 1 to 3, wherein the cleaning of the ceramic article (1) is carried out in such a way that the boundary line (19) is formed in the region of the mouth rim (11) of the ceramic article (1).

5. Method according to one of claims 1 to 4, wherein the ceramic article (1) is immersed in a dipping basin (23) arranged in a supply basin (33) during the dip glazing, wherein the second glaze (24) is transported from the supply basin (33) into the dipping basin (23) and flows out of the dipping basin (23) over its edge (34) back into the supply basin (33).

6. Method according to claim 5, wherein the transport of the second glaze (24) from the supply basin (33) into the dipping basin (23) is interrupted from time to time.

7. Method according to claim 5 or 6, wherein, before the ceramic article (1) is immersed in the dipping basin (23), an air flow guided over the glaze surface (35) is generated with the aid of a blowing device (36).

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