Method and apparatus for making a curved ceramic slab

Abstract

Described is a method for making a curved ceramic slab comprising the following steps: - Providing a flat ceramic slab (L), extending between a first end (L1) and a second end (L2); - providing a shaping template (2), having at least one curved profile and made of refractory material; - positioning the ceramic slab (L) resting on the shaping template (2), with at least the first end (L1) projecting in cantilever fashion from the shaping template (2); - applying a bending force (FP) at the first end (L1), perpendicular to a bending axis about which the flat slab (L) is bent, preferably by placing a bending weight (31) at the first end (L1); - applying a counterweight force (FC), at the second end (L2); - placing the shaping template (2) and the flat slab (L) inside a kiln (1); - applying a thermoforming cycle (CT), until reaching a bending temperature inside the kiln (1), between 700°C and 1000°C.

Description

[0001] METHOD AND APPARATUS FOR MAKING A CURVED CERAMIC SLAB

[0002] Technical field

[0003] This invention relates to a method and a system for making a curved ceramic slab.

[0004] Background art

[0005] In the sector of processing ceramic products which have already been fired there are some prior art solutions which comprise methods for bending the ceramic product.

[0006] These methods are based on the principle of weakening the material, to make weaker zones which allow an easier bending. For this reason, as is known, solutions are provided in which a flat slab is milled in order to make zones with a reduced thickness, on which a curvature is formed.

[0007] However, these solutions have several drawbacks. Firstly, the forming of a point of weakness, whilst it helps in the curvature, correspondingly facilitates a failure of the material when it is put into use. Secondly, in a transversal view of the curved slab, it will be noted that the profile is not uniform (due to the milling) and the aesthetic features of the product are therefore unsatisfactory.

[0008] Amongst the prior art solutions in the sector for processing ceramic products there are some documents which illustrate solutions for bending ceramic slabs but which nevertheless have important drawbacks and which do not allow the significant bending that the method according to this invention can achieve. These documents are as follows: CN1 12008900A, JPH01242428A, JPH08247666A, US2018327301 A1 , CN218504800U and CN1566003A.

[0009] Aim of the invention The aim of this invention is to provide a method and a system for making a curved ceramic slab which overcome the above-mentioned problems of the prior art.

[0010] Said aim is fully achieved by the method and system according to the invention as characterised in the appended claims.

[0011] An aspect of the invention provides a method for making a curved ceramic slab. The method comprises a step of preparing a flat ceramic slab, extending along a bending direction between a first end and a second end. The bending direction is perpendicular to a bending axis, about which the flat slab is bent. The slab is a slab already fired and, if necessary, already provided with the necessary decoration.

[0012] It should be noted that the definition of axis and direction is different and identifies, in one case, a single infinite straight line about which the ceramic product is bent and passing, basically, through the centre of rotation.

[0013] The method comprises a step of preparing a shaping template, having at least one curved profile and made of refractory material. The refractory material is a clayey material having a very high thermal inertia. Moreover, the refractory material is not very invasive on the ceramic slab and there is no risk of ruining it. The template rests on the bottom of the kiln. The template is rested along a direction perpendicular to the weight force, that is, it is rested on the bottom of the kiln which is positioned horizontally.

[0014] According to an embodiment, the template is made as a single piece. According to an embodiment, the template comprises a contact surface, where the ceramic slab makes contact at the end of the bending.

[0015] The method comprises a step of positioning the ceramic slab resting on the shaping template, with at least the first end projecting in a cantilever fashion with respect to the template.

[0016] The method comprises a step of applying a bending force at the first end.

[0017] The method comprises a step of applying a counterweight force. The counterweight force is preferably applied at the second end, but it could also be applied between the first end and the second end, provided it is such as to counterbalance the bending force, avoiding a tipping of the ceramic slab. In this regard, the bending force and the counterweight force determine corresponding rotations in opposite directions.

[0018] The method comprises a step of inserting the template and the flat slab inside a kiln.

[0019] The method comprises a step of applying a thermoforming cycle, inside a thermoforming kiln, until reaching a bending temperature inside the kiln. The bending temperature is between 700°C and 1000°C.

[0020] Preferably, the step of applying a bending force is performed by positioning a bending weight at the first end. Thus, the bending force is a weight force, determined by the bending weight.

[0021] The bending weight is calculated as a function of the thickness of the slab, the width of the slab, defined as the distance between the first and the second ends of the slab and / or as a function of a final curvature radius of the slab. In particular, the weight increases with increasing thickness, decreasing width and / or increasing curvature radius.

[0022] Preferably, the bending weight comprises a body. The body, according to an embodiment, is made of refractory material, for example for bending weight values less than a predetermined value. According to an embodiment, the body is made of metallic material, for example for bending weight values greater than the predetermined value.

[0023] Preferably, the bending weight comprises a ballast weight. The ballast weight is preferably positioned on the opposite side of the slab relative to the template. The bending weight comprises an anchoring hook. The anchoring hook is configured to be hooked at the first end, making contact with the surface of the slab facing the template, in such a way as to keep stable the bending weight following a bending of the slab.

[0024] Preferably, the thermoforming cycle comprises a thermoforming step whose duration is greater than 9 hours, preferably greater than 11 hours.

[0025] According to an embodiment, in the step of positioning the slab on the template, the second end of the slab also projects in a cantilever fashion. The step of applying a counterweight force is performed by positioning at the second end a counterweight weight, having the same weight as the bending weight.

[0026] In fact, in this case, the counterweight contributes to performing a bending on the opposite side of the first end of the slab relative to the centre of the template.

[0027] The step of positioning the slab on the template comprises a step of supporting the slab. In said step, a supporting element is positioned beneath the first end of the slab, to prevent the application of the bending force from tipping the slab before the counterweight force is applied.

[0028] The step of positioning the slab on the template comprises a step of removing the supporting element after performing the step of applying the counterweight force.

[0029] According to an embodiment of the method, the kiln comprises a guide axis. The template comprises a corresponding guide groove. The guide groove is configured to house the guide axis when the template is positioned inside the kiln.

[0030] According to an embodiment, the thermoforming cycle comprises one or more of the following steps:

[0031] - a step of preheating, until reaching a preheating temperature of between 300°C and 500°C in a time interval of between 2 hours and 5 hours;

[0032] - a first step of dwelling at the preheating temperature for a time interval of between 0.5 hours and 2 hours;

[0033] - a step of thermoforming, until reaching the bending temperature of between 800°C and 1100°C in a time interval of between 10 hours and 15 hours;

[0034] - a second step of dwelling at the bending temperature for a time interval of between 0.5 hours and 2 hours;

[0035] - a first step of cooling, until reaching a cooling temperature of between 400°C and 600°C in a time interval of between 2 hours and 4 hours; - a third step of dwelling at the cooling temperature for a time interval of between 0.5 hours and 2 hours;

[0036] - a second step of cooling, until reaching a slab unloading temperature, substantially equal to the ambient temperature outside the kiln, in a time interval of between 2 hours and 6 hours.

[0037] According to an embodiment, in the thermoforming step the ceramic slab is bent until obtaining a radius of curvature of between 100 mm and 500 mm, preferably less than 300 mm. The template is a curved template having a radius of curvature of between 100 mm and 500 mm, preferably less than 300 mm.

[0038] An aspect of the invention provides an apparatus for making a curved ceramic slab.

[0039] The apparatus comprises a thermoforming kiln. The thermoforming kiln is configured for thermoforming a flat ceramic slab, extending along a bending direction between a first end and a second end.

[0040] The apparatus comprises a shaping template (that is to say, also a plurality of shaping templates distributed in the kiln). The shaping template has at least one curved profile. The shaping template is made of refractory material.

[0041] The shaping template is positioned inside the kiln and is configured for receiving and supporting the ceramic slab, with at least the first end projecting in a cantilever fashion relative to the template.

[0042] The apparatus comprises one or more bending elements, configured for applying a bending force at the first end.

[0043] The apparatus comprises one or more counterweight elements, configured for applying a counterweight force at the second end of the slab, wherein the bending force and the counterweight force determine corresponding rotations in the opposite direction. It should be noted that, according to some embodiments, the counterweight force defines a second bending force, which contributes to bending (folding) the flat slab.

[0044] The thermoforming kiln is configured for applying a thermoforming cycle, until reaching a bending temperature of between 700°C and 1000°C inside the kiln.

[0045] Preferably, the kiln is an electric kiln. The electric kiln includes heating elements. The heating elements are mounted at the bottom of the kiln to allow the slab to be uniformly heated.

[0046] Preferably, the thermoforming kiln comprises an infeed hatch, from which the slab resting on the template can be inserted. The infeed hatch is located on a first side of the kiln. The thermoforming kiln comprises an outfeed hatch. The curved slab can be unloaded from the outfeed hatch. The outfeed hatch is located on a second side, opposite the first side.

[0047] According to an embodiment, the apparatus comprises a loading trolley, located at the front of the infeed hatch. The loading trolley is configured to autonomously load in the kiln the flat slab resting on the template. According to an embodiment, the apparatus comprises an unloading trolley. The unloading trolley is positioned in front of the outfeed hatch. The unloading trolley is configured to autonomously unload from the kiln the curved slab resting on the template.

[0048] According to an embodiment, the kiln comprises a guide axis. Moreover, the template comprises a guide groove, configured to receive the guide axis of the kiln, in such a way as to stabilise the template in the kiln during thermoforming.

[0049] Brief description of the drawings

[0050] This and other features will become more apparent from the following description of a preferred embodiment of the invention, illustrated by way of non-limiting example in the accompanying tables of drawings, in which:

[0051] - Figure 1 schematically illustrates an apparatus for making a curved slab used in a method for making a curved slab;

[0052] - Figures 2A and 2B schematically illustrate a detail of the apparatus of Figure 1 in a first step and in a second step of preparing a slab on a respective template; - Figure 2C illustrates a further embodiment of the apparatus and of the relative end product obtained;

[0053] - Figure 3 schematically illustrates a detail of the apparatus of Figure 1 ;

[0054] - Figure 4 illustrates a schematic plan view of an apparatus for making a curved slab used in a method for making a curved slab;

[0055] - Figure 5 schematically illustrates a graph relative to a thermoforming cycle for the bending of a flat slab according to this invention.

[0056] Detailed description of preferred embodiments of the invention

[0057] With reference to the accompanying drawings, the numeral 100 denotes an apparatus for thermoforming a flat ceramic slab L, aimed at obtaining a curved ceramic slab C.

[0058] The apparatus 100 comprises a kiln 1 , preferably an electric kiln.

[0059] According to an embodiment, the kiln is an electric kiln muffle or simply a muffle, which is able to reach temperatures of from 1000°C to 1800°C, depending on the power and efficiency of the refractory material with which it is produced.

[0060] More specifically, the kiln 1 comprises a heating system with heating elements 10. In order to obtain a homogeneous heating of the ceramic slab L positioned in the kiln, the heating elements 10 are positioned on the bottom of the kiln 1 and / or, partly, in a lower lateral zone of the kiln 1 . According to an embodiment, the apparatus 1 comprises a guide axis 11. The guide axis 11 is positioned on the bottom of the kiln 1 and is elongate along a direction parallel to a bending axis, about which the slab L is bent. The guide rod 11 may have a dovetail profile or a square or rectangular profile.

[0061] Preferably, the thermoforming kiln 1 comprises an infeed hatch 12, from which the slab L can be inserted. The infeed hatch 12 is located on a first side of the kiln 1. The thermoforming kiln 1 comprises an outfeed hatch 13. The curved slab can be unloaded from the outfeed hatch 13. The outfeed hatch 13 is located on a second side of the kiln 1 , opposite the first side. The apparatus 100 comprises at least one template 2, preferably a group of templates 2, which are spaced along the bending axis. A single template can be used for ceramic slabs L which are not very long whilst, for longer slabs, it is preferable to use more templates 2 spaced from each other.

[0062] According to an embodiment, each template is free of grooves (when the guide axis 11 is not present) and it is therefore simply rested on the bottom of the kiln 1 . Each template 2 is preferably made of refractory material.

[0063] According to other embodiments, each template comprises a guide groove 21 , positioned on its side resting on the kiln 1. The guide groove 21 houses the guide axis 11 , in such a way that the template 2 is constrained and does not move along a direction perpendicular to the bending axis.

[0064] When the guide axis 11 has a dovetail profile, the template 2 is also connected vertically.

[0065] The templates 2 may have various profiles, for example they may have a semicircle profile, a profile with a curve having a subtended angle of 90° combined with a rectilinear stretch. In general, the profile of the template 2 is complementary to the bend to be imparted to the slab L.

[0066] The apparatus 100 comprises a bending system 3. The bending system 3 is configured for applying a bending force FP on the slab L, in a direction which determines a curvature of the slab about the bending axis.

[0067] The bending system 3 is configured for applying a counterweight force FC on the slab L, which prevents the falling of the slab L from the template 2. Preferably, the slab L has a first end L1 and a second end L2. The bending force FP is exerted on the first end L1 , which projects in a cantilever fashion from the template 2, whilst the counterweight force FC is exerted on the second end L2.

[0068] According to an embodiment, illustrated in Figure 2B, the bending force FP and the counterweight force FC coincide and are applied on the two ends of the slab L in equilibrium, thereby doubling the bending force and making the operations faster. According to a further example which nevertheless remains within the scope of protection claimed and which is useful only for example purposes, the template 2 has the shape of a double curvature.

[0069] According to this example, the template has a first straight stretch T1 , which rises from the base of the kiln, a first curve C1 , a second central straight stretch T2, a second curve C2 and a third straight stretch T3. The second straight stretch T2 is interposed between the first curve C1 and the second curve C2.

[0070] The slab L rests on the template 2 at the second rectilinear stretch T2, whilst, in an initial thermoforming step, the two ends L1 and L2 of the slab project in a cantilever fashion from the side of the first curve C1 and of the second curve C2, respectively.

[0071] As mentioned above, the bending force FP and the counterweight force FC coincide and are applied on the two ends of the slab L.

[0072] When the bending force Fp and the counterweight force FC bend the slab L this forms with the same curvature provided by the template 2, creating a ceramic slab with a double curvature.

[0073] More specifically, according to this invention, there is the protection also independent of the method of a thermoformed ceramic slab including: a first rectilinear portion PT1 , a first curved portion PC1 , a second rectilinear portion PT2, a second curved portion PC2 and a third rectilinear portion TP3. Preferably, the first rectilinear portion PT1 is perpendicular to the second rectilinear portion PT2. Preferably, the third rectilinear portion PT3 is perpendicular to the second rectilinear portion PT2. In other words, the angle subtended by the first and second curved portions PC1 , PC2 is ninety degrees. Obviously, the angle subtended by the first and second curved portions PC1 , PC2 is adjustable on the basis of the bending force FP and the counterweight force FC exerted as well as by the time the slab remains in the kiln (that is, during the thermoforming time).

[0074] According to an embodiment, the bending force FP is a weight force determined by a bending weight 31. The bending weight 31 comprises a ballast 311 and a hook 312. The hook 312 anchors to the first or to the second end L1 , L2 in such a way that the ballast 311 remains preferably on the surface of the slab L opposite to that which comes into contact with the template 2. The hook 312 anchors on the surface of the slab L facing the template 2.

[0075] According to an embodiment, the counterweight force FC is a weight force determined by a counterweight weight 32. The counterweight weight 32 comprises a respective ballast 321 and a hook 322. The hook 322 anchors to the first or to the second end L1 , L2 in such a way that the ballast 321 remains preferably on the surface of the slab L opposite to that which comes into contact with the template 2. The hook 322 anchors on the surface of the slab L facing the template 2.

[0076] The presence of the hooks 312, 322 prevents, with the bending of the slab L, that the bending weight 31 or counterweight weight 32 can rotate and fall from the slab L.

[0077] According to an embodiment, the apparatus comprises a supporting element 4, used to support the slab L whilst the bending weights 31 and / or counterweight weights 32 are positioned.

[0078] According to a particularly simple embodiment, the supporting element is a supporting foot. The supporting element 4 is adjustable in length to adapt to the size of the templates 2. The supporting foot 4 has an end 4A (on which could be provided a plate) which comes into contact with the slab L and a second end 4B which is rested on the bottom of the kiln 1 .

[0079] At the end of the positioning of the bending weights 31 and / or the counterweight weights 32, the supporting foot 4 is removed, since the system is in equilibrium by merely the balancing of the weights.

[0080] According to an embodiment, the apparatus 100 comprises a loading trolley 14, positioned in front of the infeed hatch 12. The loading trolley 14 is configured to autonomously load in the kiln the slab L resting on the template 2. According to an embodiment, the apparatus comprises an unloading trolley 15. The unloading trolley 15 is positioned in front of the outfeed hatch 13. The unloading trolley 15 is configured to autonomously unload from the kiln the curved slab resting on the template 2.

[0081] The apparatus is configured for performing a method for making a curved slab L which comprises, in short, two main steps: a step of preparing the flat slab resting on the template 2 and a step of thermoforming in the kiln 1.

[0082] In the step of preparing the flat slab resting on the template 2 the operator positions the template 2 resting on the bottom of the kiln 1 or resting on the loading trolley 14. Subsequently, the slab L is positioned on the template 2, in such a way that the centre of the slab L is aligned with the bending axis. This makes it possible to have a situation of partial stability of the slab L for positioning the weights.

[0083] The method comprises positioning, manually or automatically, the supporting element 4 below the first end L1 of the slab L, in such a way that this cannot fall from the side of the template 2 where the first end L1 of the slab L is located.

[0084] Subsequently, the method comprises placing the bending weight 31 on the first end L1 , hooking it to said end. Moreover, the method comprises positioning the counterweight weight 32 on the second end L2, hooking it to said end.

[0085] Lastly, the supporting element 4 is removed, as it is no longer required, given the stability of the structure positioned in this way.

[0086] At this point, the slab L resting on the template 2 is inserted in the kiln 1 from the loading trolley 14, if it is not already inside the kiln 1 .

[0087] The method comprises starting a thermoforming cycle CT, which comprises the following steps:

[0088] - a step of preheating (A), until reaching a preheating temperature of between 350°C and 450°C in a time interval of between 2.5 hours and 4.5 hours;

[0089] - a first step of dwelling B at the preheating temperature for a time interval of between 0.5 hours and 2 hours; - a step of thermoforming C, until reaching the bending temperature of between 800°C and 1000°C in a time interval of between 11 hours and 14 hours;

[0090] - a second step of dwelling D at the bending temperature for a time interval of between 0.5 hours and 2 hours;

[0091] - a first step of cooling E, until reaching a cooling temperature of between 450°C and 550°C in a time interval of between 2 hours and 4 hours;

[0092] - a third step of dwelling F at the cooling temperature for a time interval of between 0.5 hours and 2 hours; - a second step of cooling G, until reaching a slab unloading temperature, substantially equal to the ambient temperature outside the kiln, in a time interval of between 3 hours and 5 hours.

[0093] Subsequently, the curved slab C is removed from the kiln through the outfeed hatch 13 and positioned on the unloading trolley 15.

Claims

CLAIMS1. A method for making a curved ceramic slab, comprising the following steps:- providing a planar ceramic slab (L) extending along a bending direction between a first end (L1 ) and a second end (L2), the bending direction being perpendicular to a bending axis, about which the planar slab (L) is bent;- providing a shaping template (2), having at least one curved profile and made from refractory material;- positioning the ceramic slab (L) supportably on the shaping template (2), with at least the first end (L1 ) projecting in cantilever fashion from the template (2);- applying a bending force (FP) at the first end (L1 );- applying a counterweight force (FC) at the second end (L2), where the bending force (FP) and the counterweight force (FC) cause corresponding rotations of the slab (L) in opposite directions;- placing the template (2) and the planar slab (L) into a kiln (1);- applying a thermoforming cycle (CT), until reaching a bending temperature of between 700°C and 1000°C inside the kiln (1 ).

2. The method according to claim 1 , wherein the step of applying a bending force (FP) is performed by placing a bending weight (31 ) at the first end (L1 ).

3. The method according to claim 2, wherein the bending weight (31 ) is calculated as a function of the thickness of the slab (L), the width of the slab (L), defined as the distance between the first and the second end (L1 , L2) of the slab and / or as a function of a target curvature radius (L), so that the weight increases with increasing thickness, decreasing width and increasing curvature radius.

4. The method according to claim 3, wherein the bending weight (31 ) comprises a block, made from refractory material for values of bending weight (31 ) lower than a predetermined value, and from metallic material for values of bending weight (31 ) higher than the predetermined value.

5. The method according to any one of claims 2 to 4, wherein the bending weight (31) comprises a ballast weight (311 ), positioned on the opposite side of the slab with respect to the template (2), and an anchoring hook (312) configured to be hooked to the first end (L1 ), in contact with the surface of the slab (L) facing the template (2), so as to hold the bending weight (31 ) stably in place after bending the slab (L).

6. The method according to any one of the preceding claims, wherein the thermoforming cycle (CT) comprises a step of thermoforming whose duration is longer than 9 hours.

7. The method according to any one of the preceding claims, wherein, in the step of positioning the slab on the template, the second end (L2) of the slab (L) is also positioned in cantilever fashion, and wherein the step of applying a counterweight force (FC) is performed by placing at the second end (L2) a counterweight (32) having the same weight as the bending weight (31 ).

8. The method according to any one of the preceding claims, wherein the step of positioning the slab on the template comprises the following steps:- supporting the slab (L), wherein a supporting element (4) is positioned beneath the first end (L1 ) of the slab (L) to prevent the bending force (FP) from tipping the slab before the counterweight force (FC) is applied;- removing the supporting element (4) after performing the step of applying the counterweight force (FC).

9. The method according to any one of the preceding claims, wherein the kiln (1 ) comprises a guide shaft (11) and wherein the template (2) comprises a matching guide groove (21 ), configured to accommodate the guide shaft (11 ) when the template (2) is placed inside the kiln (1 ).

10. The method according to any one of the preceding claims, wherein the thermoforming cycle (CT) comprises the following steps:- a step of preheating (A), until reaching a preheating temperature of between 300°C and 500°C in a time interval of between 2 hours and 5 hours;- a first step of dwelling (B) at the preheating temperature for a time interval of between 0.5 hours and 2 hours;- a step of thermoforming (C), until reaching the bending temperature of between 800°C and 1100°C in a time interval of between 10 hours and 15 hours;- a second step of dwelling (D) at the bending temperature for a time interval of between 0.5 hours and 2 hours;- a first step of cooling (E), until reaching a cooling temperature of between 400°C and 600°C in a time interval of between 2 hours and 4 hours;- a third step of dwelling (F) at the cooling temperature for a time interval of between 0.5 hours and 2 hours;- a second step of cooling (G), until reaching a slab unloading temperature, substantially equal to the ambient temperature outside the kiln, in a time interval of between 2 hours and 6 hours.

11. The method according to any one of the preceding claims, wherein, in the step of thermoforming (C), the ceramic slab is curved until obtaining a curvature radius of between 100 mm and 500 mm and wherein the template is a template having a curvature radius of between 100 mm and 500 mm.

12. An apparatus (100) for making a curved ceramic slab, comprising:- a thermoforming kiln (1 ), configured for thermoforming a planar ceramic slab (L) extending along a bending direction between a first end (L1 ) and a second end (L2), the bending direction being perpendicular to a bending axis, about which the planar slab is bent;- a shaping template (2) having at least one curved profile and made from refractory material, the shaping template (2) being positioned inside the kiln and being configured to supportably receive the ceramic slab, where at least the first end (L1 ) projects in cantilever fashion from the template (2);- one or more bending elements (31 ), configured for applying a bending force (FP) at the first end (L1 );- one or more counterweight elements (32) configured for applying a counterweight force (FC) at the second end (L2) of the slab (L), where the bending force (FP) and the counterweight force (FC) cause corresponding rotations in opposite directions, wherein the thermoforming kiln is configured for applying a thermoforming cycle (CT), until reaching a bending temperature of between 700°C and 1000°C inside the kiln.

13. The apparatus (100) according to claim 12, wherein the kiln (1 ) is an electric kiln including heating resistors (10), positioned at the bottom of the kiln (1 ) to allow the slab to be uniformly heated.

14. The apparatus (100) according to claim 12 or 13, wherein the thermoforming kiln (1 ) comprises an infeed hatch (12), through which the slab (L) can be supportably placed on the template (2) and which is located on a first side of the kiln (1 ), and an outfeed hatch (13), through which the curved slab can exit the kiln and which is located on a second side, opposite the first side.

15. The apparatus (100) according to claim 14, comprising a loading trolley (14), positioned in front of the infeed hatch (12) and configured to autonomously load the planar slab into the kiln supportably on the template, and an unloading trolley (15), positioned in front of the outfeed hatch (13) and configured to autonomously unload the curved slab, supported on the template, from the kiln.

16. The apparatus (100) according to any one of claims 12 to 15, wherein the kiln (1 ) comprises a guide shaft (11 ) and wherein the template (2) comprises a matching guide groove (21 ), configured to receive the guide shaft (11 ) of the kiln so as to stabilize the template (2) in the kiln during thermoforming.

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