[0001 ] The invention relates to devices intended for protecting means arranged for measuring a parameter of a distant element.

[0002] In some technical domains, such as metallurgy, measuring devices are used for measuring a parameter of a distant element, such as a steel sheet produced by a mill or a hot strip mill. For instance, the measuring device may be a pyrometer intended for measuring the temperature of a steel sheet. When the distant element is located in an environment comprising dust particles and/or water droplets, at least the optical part of the measuring device needs to be protected, otherwise it becomes "polluted" and therefore the parameter measurements are erroneous.

[0003] To prevent the dust particles and/or the water droplets to reach the optical part, and notably its lens, this optical part may be fixed in an end part of a hollow body and a pressurized gas may be injected, with an angle typically equal to 30° and in the direction of the distant element, into the internal space delimited by this hollow body, through an inlet defined in an intermediate part.

[0004] However, despite the pressurized fluid, some dust particles and/or some water droplets still enter the hollow body and reach the optical part, and therefore the parameter measurements become rapidly erroneous, which may be questionable when they are used for permanently controlling a process, such as cooling a steel sheet at a fixed temperature, by spraying water, before coiling it. In such a situation quality defects appears on the steel sheet and maintenance operations must be done continuously, almost each day, for cleaning the optical part. These maintenance operations are very complex, and may induce damages on the optical fiber and/or lens of the measuring device (for instance a pyrometer), which are costly. [0005] To improve the situation, it has been proposed to set a grid inside the hollow body before the optical part. But, such a solution cannot be used when the measuring device comprises a laser producing a light beam for aiming at a precise area of the distant element. More the holes of the grid become gradually obstructed, which prevents obtaining the parameter measurements.

[0006] It has been also proposed to add one or two shutters to the hollow body and to set the shutters in an open position each time a measure must be done. But, such a solution introduces a lot of complexity and fragility (due to the mechanical pieces and control means), and increases the cost and bulkiness.

[0007] So, an objective of the invention is to improve the situation without introducing complexity and fragility. [0008] To this end, the invention relates notably to a device, intended for protecting a means for measuring a parameter of a distant element, and comprising a hollow body delimiting an internal space and having:

- an intermediate part comprising an inlet arranged for feeding the internal space with a pressurized gas,

- a first end part extending a first extremity of the intermediate part and intended for facing the distant element, and

- a second end part extending a second extremity of the intermediate part and comprising at least an optical element of the measuring means. [0009] This protecting device is characterized in that the intermediate part further comprises, inside the internal space, a piece comprising a rear face facing the second end part, a front face facing the first end part and comprising a plurality of holes, an internal channel defined between these rear and front faces and tightly communicating with the inlet to feed these holes with the pressurized gas, and a central through hole surrounded by this internal channel and crossing through the rear and front faces to allow a communication between the first and second end parts. [0010] The protecting device of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations:

- the intermediate part may be coupled to the first and second end parts by screwing;

- each hole may have a diameter comprised between 1 mm and 3 mm;

- the inlet may comprise a conduct inclined by a chosen angle with respect to a wall of the intermediate part that delimitates partly the internal space and to which the piece is secured fixedly; > the chosen angle may be comprised between 25° and 90°;

• the chosen angle may be equal to 50°;

- the central through hole may have a diameter comprised between 10 mm and 30 mm;

- the hollow body may have a circular cross-section. In this case, the piece is a circular plate;

- the piece may be an integral part of the intermediate part;

- the first end part may comprise an end face intended for facing the distant element and inclined by a chosen angle with respect to a wall that delimitates partly the internal space; - the second end part may comprise a frame of the optical element on which the optical element a lens is mounted and to which an optical fiber is coupled;

- the second end part may comprise at least an optical element of a pyrometer intended for measuring a parameter that is a temperature. [001 1 ] The invention also relates to a mill arranged for producing a metal sheet defining a distant element, and comprising at least one protecting device such as the one above introduced and facing this metal sheet. [0012] The invention also relates to a method intended for making an intermediate part of a protecting device such as the one above introduced, and being an additive manufacturing method.

[0013] The invention also relates to a computer assisted design file which comprises digital information for the implementation of a method such as the one above introduced, when loaded onto a machine.

[0014] Other characteristics and advantages of the invention will emerge clearly from the description of it that is given below by way of an indication and which is in no way restrictive, with reference to the appended figures in which:

- figure 1 illustrates schematically, in a perspective view, a part of a hot strip mill comprising an example of embodiment of a protecting device according to the invention, with its three parts not yet coupled together,

- figure 2 illustrates schematically, in a longitudinal cross section view, the protecting device illustrated in figure 1 , after coupling of its three parts, and

- figures 3A and 3B illustrates schematically, and respectively in longitudinal and transversal cross section views, the intermediate part of the protecting device illustrated in figures 1 and 2.

[0015] The invention aims, notably, at proposing a protecting device 1 intended for protecting means 6, 7 for measuring a parameter of a distant element 2.

[0016] In the following description it will be considered, as an example, that the distant element 2 is a steel sheet produced by a mill 16, and more precisely by a hot strip mill. But the invention is not limited to this type of distant element. Indeed it concerns any type of element (or piece) located in a difficult environment, for instance comprising dust particles and/or water droplets, and having a parameter that has to be measured by a measuring means, periodically or occasionally. So, such an element may be part of a device, apparatus or system that is different from a mill.

[0017] More, in the following description it will be considered, as an example, that the parameter to be measured is the temperature. So, the measuring means is a pyrometer.

[0018] Still more, in the following description it will be considered, as an example, that the protecting device 1 , according to the invention, belongs to the hot strip mill 16, and therefore is installed permanently near the distant element 2. But the protecting device 1 could be external to the hot strip mill and brought in the vicinity of the distant element 2 when a parameter measurement must be done.

[0019] An example of embodiment of a protecting device 1 according to the invention is illustrated in figures 1 and 2. As mentioned above, in this non-limiting example the protecting device 1 belongs to a hot strip mill 16 that produces an element 2, which is a steel sheet whose temperature must be periodically measured in order to remain at a constant temperature to be coiled. For instance, and as illustrated in figure 1 , the hot strip mill 16 comprises spraying means 17 intended for spraying water on top of the steel sheet 2 for cooling it as a function of its temperature measured by at least one protecting device 1 located under this steel sheet 2.

[0020] As illustrated, a protecting device 1 according to the invention comprises a hollow body 3 delimiting an internal space 4 and having an intermediate part 3-1 , a first end part 3-2 extending a first extremity of this intermediate part 3-1 , and a second end part 3-3 extending a second extremity of this intermediate part 3-1 , opposite to its first extremity. [0021 ] In the non-limiting example illustrated in figures 1 and 2 the intermediate part 3-1 and the first 3-2 and second 3-3 end parts are three independent parts that must be coupled one to the other. More precisely, in this example the intermediate part 3-1 is coupled to the first 3-2 and second 3-3 end parts by screwing, thanks to internal and external threads defined on their extremities. But other types of coupling between the intermediate part 3-1 and the first 3-2 and second 3-3 end parts could be used. More, the intermediate part 3-1 and the first 3-2 and second 3-3 end parts could be an integral part of a single piece defining the hollow body 3.

[0022] For instance, and as illustrated in figure 1 , the hollow body 3 may have a circular (transversal) cross-section. This means that in this case the intermediate part 3-1 and the first 3-2 and second 3-3 end parts have a circular (transversal) cross-section, preferably with the same diameter.

[0023] The first end part 3-2 is intended for facing the distant element 2 (here a steel sheet). For instance, and as illustrated in the non-limiting example of figures 1 to 3A, when the hollow body 3 is inclined with respect to the distant element 2, the first end part 3-2 may comprise an end face 15 intended for facing the distant element 2 and inclined by a chosen angle with respect to its wall 14 that delimitates partly the internal space 4. This option is intended for avoiding a part of the dust particles and water droplets to penetrate into the internal space 4.

[0024] The second end part 3-3 comprises at least an optical element 7 of a measuring means 6 (here a pyrometer) that is arranged for measuring a parameter of the distant element 2. As mentioned above, in this example the parameter is the temperature.

[0025] For instance, the optical element 7 may comprise a frame, fixed to the extremity of the second end part 3-3 that is opposed to the one coupled to the intermediate part 3-1 , on which a lens is mounted and to which an optical fiber (not illustrated) is coupled. This optical fiber allows to transfer the collected photons (originating from the distant element 2) away from the distant element environment, in a protected area where the sensor and measurement means of the pyrometer 6 stand. [0026] The intermediate part 3-1 comprises an inlet 5 arranged for feeding the internal space 4 with a pressurized gas, and a piece 8.

[0027] This piece 8 is located inside the portion of the internal space 4 that is delimited by a wall 17 of the intermediate part 3-1 and comprises a rear face 9, a front face 10, an internal channel 12, and a central through hole 13. In the case where the hollow body 3 has a circular cross-section, the piece 8 is a circular plate.

[0028] The rear face 9 faces the second end part 3-3. The front face 10 faces the first end part 3-2 and comprises a plurality of holes (or nozzles) 1 1 . The internal channel 12 is defined between the rear 9 and front 10 faces and tightly communicates with the inlet 5 to feed the holes 1 1 with the pressurized gas. The central through hole 13 is surrounded by the internal channel 12 and crosses through the rear 9 and front 10 faces to allow a communication between the first 3- 2 and second 3-3 end parts.

[0029] So, the pressurized gas reaches the inlet 5, then reaches the internal channel 12, then flows inside the internal channel 12 and reaches the second end part 3-3 through all the holes (or nozzles) 1 1 . The flows of gas, canalized through the holes 1 1 , are guided by the wall 14 of the second end part 3-3 in the direction of its end face 15 facing the distant element 2, which allows rejecting outside the dust particles and the water droplets. Indeed, there is no flow of dust particles or water droplets that can reach the optical part 7 of the pyrometer 6 despite the central through hole 12 of the piece 8.

[0030] For instance, each hole 1 1 may have a diameter comprised between 1 mm and 3 mm. In this case, this hole diameter may be equal to 2 mm, for instance.

[0031 ] Also for instance, the central through hole 12 may have a diameter comprised between 10 mm and 30 mm, especially when the diameter of the internal space 4 is comprised between 25 mm and 40 mm. In this case, this central through hole diameter may be equal to 20 mm, for instance. It is important to note that the above-mentioned values are in fact fixed by the measuring means 6 characteristics (and more precisely here by the view angle of the pyrometer 6) and the relative position of the object to measure, because the hollow body 3 does not have to interfere with the view angle.

[0032] As illustrated in the non-limiting example of figures 1 to 3B, the inlet 5 may comprise a conduct that is inclined by a chosen angle with respect to the wall 17 of the intermediate part 3-1 that delimitates partly the internal space 4 and to which the piece 8 is secured fixedly.

[0033] For instance, this chosen angle may be comprised between 25° and 90°. In this case, this angle may be equal to 50°, for instance.

[0034] Also as illustrated in the non-limiting example of figures 1 to 3B, the piece 8 may be an integral part of the intermediate part 3-1 . But this is not mandatory. Indeed it could be inserted inside the intermediate part 3-1 and then secured fixedly by welding to the inner face of the wall 17 in the area comprising the output hole of the inlet 5.

[0035] It is important to note that the diameter of the internal space 4, the length of the hollow body 3 and the position of the piece 8 must be appropriately chosen in order not to interfere with the view angle of the pyrometer 6.

[0036] According to the invention, at least the intermediate part 3-1 of the hollow body 3 may be produced by implementing an additive manufacturing method in three dimensions, especially when the piece 8 is an integral part of the intermediate part 3-1 as mentioned above. One means here by "additive manufacturing method" a three-dimensional printing process. Such an additive manufacturing method allows to consolidate every element in a single part, which guarantees the tightness. [0037] This additive manufacturing method may be operated with a three- dimensional (or 3D) printer, or by selective laser sintering with metal powder as raw material, or by a binder jetting method also starting with a metal powder, or else by a laser cladding technology with metal wire as raw material, for instance. The selective laser sintering is interesting in the present case because it does not require an important post-process and gives more accuracy.

[0038] For instance, the metal powder may be a powder of stainless steel 316 which allows resisting to high temperature and humidity conditions. But it could be another metal supporting the high temperature (typically 700°C) and the humidity conditions. Also for instance, it is possible to use a selective laser sintering machine such as an EOS M280 ® made by EOS GmbH (Electro Optical Systems GmbH).

[0039] In order to make at least the intermediate part 3-1 according to the invention with a 3D printer, it is necessary to create a computer assisted design file comprising digital information defining all the geometrical features of this intermediate part 3-1 and allowing implementation of the method describe above, and then to load this computer assisted design file into a machine. [0040] The first 3-2 and second 3-3 end parts could be also produced by means of a 3D printer. But this is not mandatory. Indeed, they could be also produced by machining. Moreover the first 3-2 and second 3-3 end parts are preferably made in the same material as the intermediate part 3-1.