BE1024868B1 - METHOD OF SURFACING A ROCK - Google Patents

Abstract

The present invention relates to a surfacing method of a rock having at least one surface to be treated in a device comprising a flame unit followed by a water jet treatment unit, comprising: - feeding said rock onto a strip conveyor, towards said flaming unit which comprises at least one flaming head provided with at least two flaming nozzles fueled and oxidant and facing said at least one surface to be treated, - flaming said at least one a surface by means of said flaming head - feeding of said rock towards said water jet treatment unit - application of at least one jet of water at high pressure by means of said water jet head in the direction of said at least one surface, - obtaining an anthracite gray colored shade rock.

Description

BELGIAN INVENTION PATENT

FPS Economy, SMEs, Middle Classes & Energy Publication Number: 1024868 Filing number: BE2017 / 5800 Intellectual Property Office International Classification: B28D 1/00 B28D 7/02 Date of issue: 04/06/2019

The Minister of the Economy,

Considering the Paris Convention of March 20, 1883 for the Protection of Industrial Property;

Given the law of March 28, 1984 on patents for invention, article 22, for patent applications introduced before September 22, 2014;

Given Title 1 “Invention Patents” of Book XI of the Economic Law Code, article XI.24, for patent applications introduced from September 22, 2014;

Having regard to the Royal Decree of 2 December 1986 relating to the request, the issue and the maintenance in force of invention patents, article 28;

Given the patent application received by the Intellectual Property Office on 07/11/2017.

Whereas for patent applications falling within the scope of Title 1, Book XI of the Code of Economic Law (hereinafter CDE), in accordance with article XI. 19, §4, paragraph 2, of the CDE, if the patent application has been the subject of a search report mentioning a lack of unity of invention within the meaning of §1 of Article XI. 19 above and in the event that the applicant does not limit or file a divisional application in accordance with the results of the search report, the granted patent will be limited to the claims for which the search report has been drawn up .

Stopped :

First article. - It is issued to

CARRIERES DU HAINAUT, Rue de Cognebeau 245, 7060 SOIGNIES Belgium;

represented by

GEVERS PATENTS, Holidaystraat 5, 1831, DIEGEM;

a Belgian invention patent with a duration of 20 years, subject to payment of the annual fees referred to in article XI.48, §1 of the Code of Economic Law, for: PROCESS FOR SURFACING A ROCK.

INVENTOR (S):

SEQUARIS Philippe, Chemin des Roquettes 17A, 7061, THIEUSIES;

PRIORITY (S):

DIVISION:

divided from the basic request:

filing date of the basic application:

Article 2. - This patent is issued without prior examination of the patentability of the invention, without guarantee of the merit of the invention or of the accuracy of the description thereof and at the risk and peril of the applicant (s) ( s).

Brussels, 04/06/2019,

By special delegation:

BE2017 / 5800 "Surfagggg process, dfone rock"

The present invention relates to a method of surfacing a rock, preferably a sedimentary rock carbonate limestone fossiliferous with crinoids.

In general, a carbonate sedimentary rock calcareous fossiliferous with crinoids. whether treated or not, shaped as an article or not. may also be referred to as "blue stone",

Blue stones are widely used as a noble material, for example to form window sills, patio doors or facade cladding. Blue stone is defined as a fossiliferous crinoid limestone according to the nomenclature of PTV 844 level 5 precision, registered at ΙΊ8Ν (Beige Institute for Standardization} on September 23, 2005 - (NBN EN 12670). The upper Tournai stratigraphic age also meets the descriptions written in MIT 220 “The blue stone of Belgium known as Petit Granit of Tournai geological age” and NIT 228 “Natural stones of the BBRI (Scientific and Technical Center of Construction ia, Belgium). stones also respond to the name of sedimentary carbonate limestone fossiliferous crinoid rocks.

The document WQ 393 22 62 relates to a method for treating the abrasive surface of a stone slab. This teaching proposes to apply a treatment by water jets to provide a final product with an improved external appearance compared to a product obtained by application of a flame.

According to this document, the use of a flame treatment is restrictive and does not make it possible to provide a quality product with an improved appearance, in particular because of the thermal shock resulting from such treatment.

In addition, H appeared that current treatments allow BE2017 / 5800 to give blue stones a dark shade, preferably anthracite gray, making the surface of blue stones particularly smooth. Indeed, the surface treatments currently applied '' to give the blue stones a dark shade are essentially based on polishing, which inevitably makes the treated stones particularly smooth. However, these smooth surfaces can be dangerous when the stones are used as slabs or paving stones laid outside, to achieve for example, a door threshold, a path or a terrace. Indeed, because of their smooth surface, these stones can be particularly slippery, this phenomenon being further accentuated during precipitation during which the stones are likely to be covered with a film of water, the surfaces being even more gHssantes and therefore all the more dangerous for people stepping on it.

Another drawback of the current treatment methods lies in the service life of the product obtained, as regards the maintenance of a dark shade over time. When stone slabs are laid outside, these tend to lose their dark color over time and become more and more lighted, which makes them much less aesthetic and requires their replacement. This lightening phenomenon is observed even when a pretreatment by polishing to make the blue stones darker has been applied. This is partly due to pollution, bad weather and the stresses that the surface of blue stones can undergo when they are placed outside.

2S There is a real need to provide a more efficient, even more cost-effective rock surface treatment process which increases the life of the final product. In addition, there is also a need to provide a method suitable for forming a non-slip surface, while ensuring that the dark hue of the rock is retained over time, particularly when the rock is exposed in an outdoor environment. .

To solve these problems, there is provided according to the present invention a method of surfacing a rock, preferably a sedimentary rock carbonate limestone fossiliferous with crinoids, having at least one surface to be treated in a surface treatment device comprising a unit of flame followed by a water jet treatment unit, said method successively comprising the following steps:

brought from said rock on a conveyor bed, having a predetermined displacement speed along a plane A, in the direction of said flaming unit which comprises at least one flaming head provided with at least two flaming nozzles, at least 3 flame nozzles, supplied with fuel and with oxidizer and facing said at least one surface to be treated, said flame head being arranged to be oriented in the direction of movement of said conveyor belt by tilting at a predefined angle ,

- flaming said at least one surface by means of said flaming head giving a dark and matte shade to said at least one surface,

- brought from said rock having said at least one flame-treated surface in the direction of said water jet treatment unit which comprises a water jet head provided with several openings,

2ϋ - application of at least one high pressure water jet by means of said water jet head towards said at least one surface previously treated with flame to form on said at least one surface of said rock a structure rough, and obtaining a rock of overall anthracite gray hue, studded with several fossil fragments, of crystals, preferably of the calcite type, whose cleavage planes sparkle in the light and have a relief of non-slip surface.

The method according to the invention is more cost-effective compared to known treatment methods since it can be applied to rocks which are normally discarded. This is totally surprising given the state of the art. Indeed, it is known that, certain rocks, such as by

BE2017 / 5800 example, your bluish stones present within them flaws as for example free of ch ^ bonnées veins, generally of black color. In addition to being unsightly, these defects represent points of weakness which can reduce the resistance of the blue stone to external constraints, 5 Typically, these types of rock are generally not valued are therefore downgraded because they do not have a level of sufficient quality for your rock selectors, more specifically slice.

For these reasons, these rocks having veins are therefore discarded by rock operators because their use cannot be valued, which generates a serious shortfall for the operators of these rocks.

However, the process according to the invention allows this product, normally discarded, to be valorized by the application of a first flame step followed by a water jet treatment step,

In effect, the process according to the invention has the effect of stripping the surface by removing the parts of rock which may have points of weakness, without however affecting the rock in depth. It results in particular that the resistance of the treated rock is reinforced. This process therefore makes it possible to reduce the quantity of rocks placed in the trash, after extraction in quarries. The operators of rocks and particularly blue stones can thus market a larger quantity of rocks, which increases the value of this product, and makes the process of extracting rock from quarries profitable.

In addition, the process according to the invention makes it possible to provide a rock of which at least one of the surfaces, the treated surface, has a dark shade, preferably anthracite gray. This shade is particularly sought after by the consumer.

In this regard, it has been found that the process according to the invention makes it possible to increase the duration of the final product obtained since the preservation of the dark shade is guaranteed over time. It has been possible to demonstrate that the dark shade of rock, for example of blue stones treated by the process according to the invention, is maintained significantly more

BE2017 / 5800 for a long time, even in external conditions, compared to similar rocks, for which another surfacing process (a polishing for example) has been applied for the same purpose.

Finally, the fact of applying a flaming step and then a water jet treatment makes it possible to impart a certain roughness to the treated surface of the rock, which gives it non-slip properties,

It has also been observed that the surfacing treatment according to the invention makes it possible to obtain blue stones, the surface of which is studded with several fossil fragments, of crystals, preferably of the calcite type, whose cleavage planes sparkle in the light. . This light flickering effect is particularly unexpected.

Preferably, said flaming step is accompanied by the addition of a quantity of water, preferably cold, on said at least one surface of said rock to cause a temperature shock.

It has been observed that the application of water, preferably cold on the surface of the treated rock, causes a phenomenon of flaking of the surface. This variation comes from the thermal shock created by the application of water after the passage of the flame during the flaming stage. This flaking allows both to provide a certain roughness on the surface of the stone and to further decrease a little more ia the presence of defects such as carbonaceous veins on the surface of the treated rock. This phenomenon is particularly astonishing given that it is known from the state of the art that thermal shocks must be avoided at all costs so as to preserve the resistance of the rock.

Preferably, the lad flaming head is further arranged to be moved transversely relative to the direction of movement of said conveyor belt at a translation speed between 45 and 120 cm / min, preferably between 50 and 100 cm / min, more preferably between 65 and 90 cm / min, more preferably still 30 equalizes at 75 cm / min.

BE2017 / 5800 the transverse displacement of the flaming head makes it possible to treat the whole of said at least one surface in a substantially manner

BE2017 / 5800 homogeneous.

Preferably, said openings of said water jet head are rotatably mounted and each have a speed of rotation of between 30 ° rpm and 700 rpm, preferably between

Ί00 rpm and 600 rpm, more preferably between 450 and

550 rpm.

This allows you to choose the most suitable rotation speed to provide a surface rendering as desired.

Advantageously, said speed of said conveyor belt is between 50 cm / min and 150 cm / min, preferably between 100 cm / min and 110 cm / min.

This makes it possible to manage the time of exposure or treatment, of said hive in each unit, in this case flaming and water jet treatment.

Preferably, said rock is in the form of a slice obtained by cutting said rock, said slice having a thickness of between 1 and 30 cm, preferably ranging from

1.5 cm to 20 cm, more preferably between 3 and 10 cm.

It is preferable to opt for a slice with a thickness included in one of the abovementioned ranges in order to be able to provide a final product which can be used in various fields of application.

Preferably, said flaming head is inclined in the direction of movement of said conveyor belt at an angle between 0

This makes it possible to treat said at least one surface with a flame angle which can make it possible to give a precise surface structure. The goal is to provide a non-slip end product.

Advantageously, each nozzle of said flaming head has a distal end situated at a distance from said at least one surface of said rock, said distance being between 25 and 35 mm, preferably between 29 and 31 mm.

Preferably, said flame head is provided with 3 nozzles arranged so as to form the edges of a triangle.

Advantageously, each nozzle of said flame head has an opening diameter of between 3.5 and 4.5 mm, preferably between 3.8 and 4 mm.

Preferably, each nozzle of said flame head has a length of between 70 and 90 mm, preferably between 75 and 85 mm, more preferably between 79 and 81 mm.

Advantageously, the flaming step is carried out at a temperature between 0 ° C and 4000 "C, preferably between 1000'C and 3000C, even more preferably between 1000 and 1500 ° C.

Preferably, the method according to the invention comprises a step of supplying said nozzles with a propylene / oxygen mixture, preferably in a ratio 1.1: 5 (expressed by volume).

Other embodiments of the process according to the invention are indicated in the appended claims.

The present invention also relates to a calcined fossiliferous crinoid carbonate sedimentary stone obtained by the process according to the present invention, characterized in that it has a coefficient of friction of at least 0.71 and a slip angle of at least 35 * evaluated according to the Difv 51130 standard, which corresponds to a slip resistance class Ri 3.

Other embodiments of the stone obtained directly by the process according to the invention are indicated in the appended claims.

The present invention also relates to a calcined fossiliferous carbonate sedimentary stone with crinoids obtainable according to any one of the preceding claims having an overall anthracite gray hue, studded with several fossil fragments, crystals of

BE2017 / 5800

S calcite whose cleavage planes sparkle in the light and have a non-slip surface relief, obtained by the application of a flaming followed by a high pressure water jet.

Preferably, the aforementioned stone also has a variation in oiorimetric measurement measured according to standard DIN 6174, less than or equal to 1, after having been exposed in an outdoor environment for a period of two months.

The variation in colorimetric measurement is determined by subtracting the colorimetric value indicated after 2 months of exposure in an external medium from that taken, at time zero, in this case before exposure in external medium. The subtraction of these two values being less than or equal to 1.

Advantageously, said stone has a surface relief of between 0 and 1 mm, preferably between ü, l and 0.8 mm.

Other embodiments of the stone obtainable according to the invention are indicated in the appended claims.

A carbonate limestone fossiliferous crinoid sedimentary rock was extracted in the form of a block within a quarry then placed in a cutting unit where the rock is recovered in the form of a slice having a thickness of between 1.5 and 20 cm.

Thus, several slices are recovered and need to be visually evaluated by experts in order to classify them according to their degree of quality.

The slices which have the lowest degree of quality and which should normally be discarded are kept for processing and thus valued using the process according to the present invention. Such slices have dark or even black tones.

In the method according to the invention, these slices having veins can be placed in the treatment device according to the invention cm .zw

BE2017 / 5800 which includes two units. The first flaming unit comprises one so as to constitute the vertices of a triangle. The second unit is a water jet treatment area. The combination of these two treatments constitutes the heart of the present invention.

In practice, the wafer is brought to a conveyor belt which has a displacement speed of between 50 cm / minute and 150 cm / minute along a plane A, in the direction of said flame unit. The flame head is supplied with fuel and oxidizer so that the nozzles can generate a flame which faces the surface of the wafer. In addition, the head of flame has been previously manipulated to be inclined in the direction of movement of said conveyor belt 10 in a range 15 to 45 ^I: with respect to an axis perpendicular to the plane A.

In addition, the flame head moves by translation, transverse to the plane A (in the direction of the width of the wafer) to sweep the wafer across its entire width. In this way, the flame treatment is carried out homogeneously, that is to say over the entire surface to be treated, at a temperature between 1000 and 4000 ’C.

During this flaming step, this can be accompanied by the addition of water which is injected at the surface of the flame-treated wafer in order to form a scuff. from the surface.

After passing through the flame unit, the wafer is brought to the water jet treatment unit which comprises a water jet head provided with several openings. This step is carried out with a water jet pressure of between 500 and 2000 bars, preferably around 1000 bars to give the rough surface to the surface of the wafer.

This makes it possible to obtain a rock of hue of overall anthracite gray hue, studded with several fossil fragments, of crystals, preferably of calcite type, whose cleavage planes sparkle in the light and having a non-slip surface relief.

Preferably, said openings of said water jet head are each formed by a nozzle. water jet and are mounted on a tray. Preferably, said tray comprises 20 nozzles.

BE2017 / 5800

Preferably, said plate has a speed of rotation

BE2017 / 5800 between 300 rpm and 700 rpm, preferably between

400 rpm and 600 rpm, more preferably between 450 and

550 rpm.

Advantageously, each nozzle of said flame head has a distal end located at a distance from said at least one surface of said rock, said distance being between 25 and 35 mm, preferably between 29 and 31 mm.

In particular, said flame head is provided with

nozzles arranged to form the edges of a triangle.

Advantageously also, each nozzle of said flame head has an opening diameter of between 3.5 and 4.5 mm, preferably between 3.8 and 4 mm.

In addition, each nozzle of said flame head can have a length of between 70 and 90 mm, preferably between 75 and 35 mm, more preferably between 79 and 81 mm.

Other characteristics, details and advantages of the invention will emerge from the description given below, without implied limitation and with reference to the attached drawings.

In the context of the present invention, the determination of a colorimetric value can be carried out using a spectrophotometer, for example of the MiniScan® EZ brand supplied by Huntertab.

The principle of measurement is to determine the color on a scale from D to 100, where û corresponds to the color black and. 100 to 25 white color.

In the context of the present invention, the surface relief of between 0 and 1 mm, preferably between 0.1 and 0.8 mm is determined using a profile feeler having graduations, such as for example the Profilmeister supplied parStaiaa.

Using this tool, it is possible to determine the surface relief of the rock precisely.

Figure 1 is a perspective view of the flame unit of the surface treatment device according to the invention in the presence of a slice of rock whose surface must be treated.

Figure 2 is a cross-sectional view of the flame head according to the invention.

FIG. 1 represents a flaming unit 3 according to the invention comprising a flaming head 5 and a conveyor belt 4 conveying a rock 1 cut into slices of a certain thickness 7 in the direction x.

The flaming head 5 is inclined at a predefined angle y defined with respect to an axis perpendicular B to said plane A and comprises three flaming nozzles 6 directed towards the surface 2 of the rock 1, to be treated.

FIG. 2 is a cross section through the 3 flame nozzles S of the flame head 5 arranged so as to form the vertices of a triangle.

A carbonate limestone fossiliferous crinoid sedimentary rock was extracted in the form of a block within a quarry and then sawn so as to form a slice 1.5 cm thick. your slice is then brought into the surface treatment device.

The wafer is placed on a conveyor belt moving at a speed of 105 cm / min and is first introduced into a flaming unit which is provided with a flaming head having three nozzles arranged in a triangle, each having a diameter opening of 3.98 mm and a length of 80 mm. The flame nozzles are supplied with a mixture of oxygen and propylene (5: 1.1: v / v) and generate a flame having a height of 30 mm towards the surface of the wafer in order to treat it. The flaming head is inclined relative to a plane perpendicular to said surface of said wafer at an angle of 71 °, De

BE2017 / 5800 plus, Its flaming head is placed at a distance of 30 mm from the surface of the treated wafer.

During the flaming step, the flaming head performs a translational movement at a speed of 75 cm / min in a direction 5 perpendicular to the direction in which the wafer is transported by the conveyor belt. During the passage of the flame, tap water at about 10 ”C is applied to the surface of the rock by a water jet.

The wafer is then conveyed by the conveyor belt to the water jet treatment unit. A water jet head comprising a series of nozzles generates at least one water jet at a pressure of 1000 bars in the direction of the surface of the wafer. During the water jet treatment step, the water jet head also performs a translational movement at a speed of 40 cm / min in a direction perpendicular to the direction in which the wafer is transported by the conveyor belt. . Additionally, the water jet head includes a turntable comprising. 20 nozzles forming as many openings from which water jets are directed towards the surface of the wafer. In addition, during treatment, the rotary table performs a rotational movement at a speed of 500 rpm and is at a distance of 30 mm from the surface of the treated wafer.

At the end of the treatment, the slice obtained after treatment has an overall shade of deep anthracite gray and is studded with numerous fossil fragments, of calcite crystals which have cleavage planes scintillating in the light. The surface of the wafer has a friction coefficient of at least 0.71 and a slip angle of at least 35 ° evaluated according to the DIM 51130 standard, which corresponds to a slip resistance class R13. The colorimetry index measured, preferably according to DIN standard 6174, is 39,985 using a MîniScan * EZ brand spectrophetometer supplied by Hunterlab. The color scale chosen has a value of zero for the color black and a value equal to 100 for the color white.

BE2017 / 5800

BE2017 / 5800

The conditions of Example 1 were reproduced, except that a sanding step was carried out in place of the flaming and the water jet.

The lifetimes (by measurement of colorimetry) of a calcined fossiliferous crinoid carbonate sedimentary rock treated according to Example 1 and of a calcined fossiliferous crinoid carbonated sedimentary rock treated according to the comparative example were compared.

For this, two tiles were placed close to each other outdoors, so that they both undergo the same exterior conditions in terms of exposure to UV, rain, wind and to pollution.

Before external exposure, the treated surface of the slab according to Example 1 has a calorimetric value of 39.985 and a value of 40.240 after 2 months of exposure.

The treated surface of the wafer according to the comparative example has, before exposure, a color value of 24,751 and, after exposure for one month, a value of 30,506.

Claims (5)

1. Method for surfacing a rock (1), preferably a rock (1) sedimentary carbonate limestone fossiliferous with crlnoids, having at least one surface (2) to be treated in a surface treatment device comprising a flame unit ( 3) followed by a water jet treatment unit, said method successively comprising the following steps: - brought from said rock (: 1) onto a conveyor belt (4), having a displacement speed (x) predetermined along a plane A. in the direction of said flaming unit (3) which comprises at least one flaming head ( 5) provided with at least two flame nozzles (6), preferably at least 3 flame nozzles (6). supplied with fuel and with oxidizer and facing said at least one surface (2) to be treated, said flame head (5) being arranged to be oriented in the direction of movement of said conveyor belt (4) by tilting at an angle predefined, - flaming said at least one surface (2) by means of said flaming head (If imparting a dark and matte tint to said at least one surface (2), - brought from said rock (1) having said at least one flame-treated surface (2) in the direction of said water jet treatment unit which comprises a water jet head provided with several openings, · application of at least one high pressure water jet by means of said water jet head towards said at least one surface (2) previously treated by flame to form on said at least one surface (2) of said rock ( 1) a rough structure, and · obtaining a rock in a tint of anthracite gray overall, studded with several fossil fragments, of crystals, preferably of the caldte type, whose cleavage planes sparkle in the light and presenting B E2017 / 5800 non-slip surface relief. 2. The method of claim 1, wherein said flaming step is continued by applying an amount of water, preferably cold, on said at least surface (2) of said rock (1) to cause a temperature shock. 3. Method according to claim 1 or 2, wherein said flaming head (5) is further arranged to be moved transversely relative to the direction of movement of said conveyor belt (4} at a translation speed between 45 and 120 cm / min, preferably between 50 and .100 cm / min, more preferably between 65 and 90 cm / min, more preferably still equal to 75 cm / min. 4. Method according to any one of the preceding claims, in which said openings of said water jet head are rotatably mounted. each have a rotation speed of between 300 rpm / 700 and 700 rpm, preferably between 400 rpm and 600 rpm, more preferably between 450 and 550 rpm. .5. A method according to any one of the preceding claims, wherein said speed (x) of said conveyor belt (4) is between 50 cm / min and 150 cm / min, preferably between 100 cm / min and 110 cm / min. 6. Method according to any one of the preceding claims, in which said rock (1} is in the form of a slice obtained by cutting out said rock (1), said slice having a thickness of between 1 and 30 cm, preferably ranging from 1.5 cm to 20 cm, more preferably between 3 and 10 cm. 7. Method according to any one of the preceding claims, in which said flaming head (5) is inclined in the direction. I JW of movement of said conveyor belt (4) at an angle (y; cornpri between 0 and 75 ^:: , preferably between 10 and 45 °, more preferably between 15 and 35 °, defined with respect to an axis (8j perpendicular to said pian A. 8. Method according to any one of the preceding claims, in which each nozzle (6) of said flaming head (5) has a distal end situated at a distance from said at least one surface (2) of said rock (1) , said distance being between 25 and 35 5 mm, preferably between 29 and 31 mm. 9. Method according to any one of the preceding claims, in which said flaming head (5) is provided with 3 nozzles (6) arranged so as to form the edges of a triangle. W. Method according to any one of the claims 10 above, wherein each nozzle (6) of said flaming head (5) has an opening diameter between 3.5 and 4.5 mm, preferably between 3.8 and 4 mm. 11. Method according to any one of the preceding claims, in which each nozzle (6) of said flaming head (.5) 15 has a length of between 70 and 90 mm, preferably between 75 and 85 mm, more preferably between 79 and 81 mm. 12. Method according to any one of the preceding claims, in which the flaming step is carried out at a temperature between 0 ° C and 4000 C, preferably between 1000X and 20 3000 ”C, even more preferably between 1000’C and 1500’C. 13. Fossiliferous limestone carbonate sedimentary stone with crinoids obtained by the method according to any one of claims 1 to 12, characterized in that it has characterized in that it has a coefficient of friction of at least 0.71 and . a slip angle of at least 35 ° 25 evaluated according to standard DIIM 51130, which corresponds to a slip resistance class R13. 14. Fossiliferous limestone carbonate sedimentary stone with crinoids obtainable according to any one of the preceding claims of overall anthracite gray hue, studded with several fossil fragments, of calcite crystals whose cleavage planes sparkle in the light and having a non-slip surface relief, obtained by the application of a flame followed by a high pressure water jet. BE2017 / 5800 15. Stone according to claim 14, further having a variation in colorimetric measurement, preferably measured according to DIN6174 standard, less than or equal to 1, after having been exposed to an outdoor environment for a period of two months. 16. The blue stone according to claim 15, having a surface relief of between 0 and 1 mm, preferably between 0.1 and 0.8 mm.