A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals

Abstract

The present invention belongs to the technical field of material surface treatment, and discloses a method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals, which includes the following steps: grinding and cleaning the surface of the armature to be enhanced; designing the selective laser melting and injecting structure on the surface of the armature into different shapes according to the electromagnetic emission working conditions and the ablation characteristics of the armature; setting laser parameters, feeding refractory metal powder onto the surface of the armature to be enhanced based on the shape of the selective laser melting and injecting structure, and using the laser to perform laser melting and injection on the surface of the armature to be enhanced to form a melted and injected layer. After multiple meltings and injections, an enhanced armature composite structure with an alternating distribution of strengthened area melted and injected layers and non-strengthened areas is obtained on the surface of the armature. The present invention can solve the transition ablation problem caused by severe ablation of the armature in existing electromagnetic railguns.

Description

Technical Field

[0001] The present invention belongs to the technical field of material surface treatment, and more specifically, relates to a method for laser selective melting and injection of refractory metals to enhance the ablation resistance performance of an armature. Background Art

[0002] The electromagnetic railgun is an advanced kinetic energy killing weapon made by using electromagnetic launch technology. Compared with traditional guns, its projectiles have a faster speed, a longer range, and more powerful lethality. During the ultra-high-speed launch of the electromagnetic railgun, the aluminum alloy armature and the rail are subjected to the coupling action of extremely high power, extremely high current, and extremely high speed in a very short time, resulting in serious current-carrying wear, surface melting, and ablation. On the one hand, a large thickness of aluminum accumulation is formed on the surface of the rail, affecting the subsequent launch process; on the other hand, the strength of the armature is significantly reduced, and in severe cases, even the fin is fractured, deteriorating the contact state between the armature / rail, reducing the service life of the rail, and restricting the development of electromagnetic energy launch technology to a great extent.

[0003] In order to improve the contact state between the armature / rail, some researchers have prepared a low-melting-point lubricating coating on the surface of the armature, reducing the friction between the armature / rail, and significantly improving the electromagnetic launch efficiency (Chen Jianwei, Lv Qingao, Zhang Qian, Xing Yanchang. Application research on sliding electrical contact conductive coating for electromagnetic railguns [J]. Aerodynamic Missile Journal, 2018, 8: 79-85.).

[0004] However, with the increase in the outlet kinetic energy of the electromagnetic energy device, the low-melting-point lubricating coating will melt and ablate in an "avalanche" manner, deteriorating the contact effect between the armature / rail and even leading to transition ablation.

[0005] In the prior art, the patent document CN110029344B discloses a method for laser melting and injection to strengthen the surface of 7075 aluminum alloy. This method uses an aluminum-chromium mixed powder prepared by a special preparation method combined with laser melting and injection technology to strengthen the surface of 7075 aluminum alloy. However, the disadvantage of this method is that the melting point of the molten metal powder is relatively low, which will cause violent melting and ablation, and it is difficult to be used in the field of electromagnetic rails. In addition, the conductive and thermal conductivity of the coating prepared by full-area laser melting and injection decreases, which will also affect the electromagnetic launch effect. Summary of the Invention

[0006] In view of the deficiencies of the prior art, in order to improve the armature / rail contact characteristics and extend the service life of the rail, on the one hand, it is necessary to increase the melting point, melting heat enthalpy, and high-temperature strength of the armature material to avoid severe ablation of the armature; on the other hand, the aluminum alloy armature should be appropriately melted to form a liquid aluminum film with a certain thickness at the armature / rail interface, that is, to achieve the "controlled melting" of the armature material during the electromagnetic launch process to ensure good contact characteristics between the armature and the rail. Therefore, the purpose of the present invention is to provide a method for selective laser melting and injecting refractory metals to enhance the ablation resistance of the armature to solve the problems of transition ablation and aluminum accumulation on the rail caused by severe ablation of the armature in existing electromagnetic railguns.

[0007] To achieve the above object, the present invention provides a method for selective laser melting and injecting refractory metals to enhance the ablation resistance of the armature, including the following steps:

[0008] S1. Grind and clean the surface of the armature to be enhanced;

[0009] S2. Design the selective laser melting and injecting structure on the surface of the armature into different shapes according to the electromagnetic launch conditions and the ablation characteristics of the armature;

[0010] S3. Set the laser parameters, feed the refractory metal powder onto the surface of the armature to be enhanced based on the shape of the selective laser melting and injecting structure, and use the laser to perform laser melting and injection on the surface of the armature to be enhanced. After multiple meltings and injections, an enhanced armature composite structure with an alternating distribution of the melt injection layer in the strengthening area and the surface of the armature in the non-strengthening area is obtained.

[0011] Further, the shape of the selective laser melting and injecting structure is a number of melt injection lines arranged in parallel on the surface of the armature; preferably, the width range of each melt injection line is 1 mm - 6 mm.

[0012] Further, the shape of the selective laser melting and injecting structure is a grid formed by the vertical and horizontal intersection of a number of the melt injection lines.

[0013] Further, the shape of the selective laser melting and injecting structure is a number of melt injection points evenly distributed on the surface of the armature; preferably, the diameter of the melt injection points is 3 mm - 6 mm.

[0014] Further, the selective laser melting and injecting structure is a melt injection surface with a preset shape covering a part of the surface of the armature.

[0015] Further, the thickness of the selective laser melting and injecting structure is 0.5 mm - 1.2 mm; preferably, the thickness of the selective laser melting and injecting structure is 0.8 mm - 1.0 mm.

[0016] Even further, the ratio of the surface area of the selective laser melting and injecting structure to the surface area of the armature is

[0017] Further, in step S3, during laser melt injection, the laser is moved from the previous melt injection track to the next melt injection track according to a preset offset distance.

[0018] Furthermore, the preset offset distance is preferably 1 mm - 12 mm; more preferably, the preset offset distance is 1.5 mm - 10 mm.

[0019] Further, in step S2, the spot size in the laser parameters is set to 2 mm - 6 mm, the laser power is set to 2000 W - 4000 W, the scanning speed is set to 100 mm / min - 1900 mm / min, the powder feeding rate of refractory metal powder is 4 g / min - 22 g / min, the powder feeding gas flow rate is set to 5 L / min - 12 L / min, and the protective gas flow rate is set to 8 L / min - 15 L / min.

[0020] Through the above technical solutions conceived by the present invention, compared with the prior art, the following main advantages are presented:

[0021] 1. In the present invention, by introducing refractory metals such as W, Mo, Nb, etc., the refractory metal powder is used in the selective laser melt injection technology, that is, it is sent to the area to be strengthened of the armature through the powder feeding device of the laser. The surface of the armature to be strengthened melts to form a molten pool under the action of the laser. After the refractory metal powder enters the molten pool, it is slightly melted or not melted. During the subsequent solidification process of the molten pool, the refractory metal powder particles are condensed in the molten pool to form a melt injection layer, so as to obtain a reinforced armature composite structure in which the strengthened area melt injection layer and the non-strengthened area are interwoven and distributed on the surface of the armature. This kind of reinforced armature composite structure can increase the melting point of the laser strengthened area on the surface of the armature, thereby further improving the ablation resistance of the armature.

[0022] 2. In the present invention, the forms of the selective laser melt injection structure are diversified, and different selective laser melt injection structures can be designed according to different requirements, such as dot array shape, side-by-side linear array shape, horizontal and vertical cross-grid shape, etc. In the selective laser melt injection structure, due to the presence of refractory metals in the strengthened area, its melting point is high and it will only be slightly melted during actual operation, while the melting point of the aluminum alloy in the non-strengthened area is low and it will melt to form a film during the working process. This kind of film can play a lubricating role, thereby ensuring good contact between the armature and the guide rail and avoiding transition ablation.

[0023] 3. The present invention reasonably designs the shape of the laser melt injection structure, such as designing the laser melt injection structure into several melt injection lines arranged in parallel on the surface of the armature, several melt injection lines intersecting vertically and horizontally to form a grid-shaped melt injection layer, several melt injection points evenly distributed on the surface of the armature, etc., and reasonably designs its thickness, area and distribution method, such as designing the thickness to be 0.5 mm - 1.2 mm, and the surface area ratio of the selective laser melt injection structure to the surface area of the armature is By selecting laser melting and injection structures with the same thickness and different area ratios, the thickness of the molten metal film melted at the armature / guide rail contact interface can be regulated as needed, and the liquid film can be evenly distributed at the armature / guide rail interface to obtain a better lubrication effect. If the thickness of the laser melting and injection structure exceeds the above range, less melting of the aluminum alloy substrate will occur, and a good lubrication effect cannot be formed between the armature and the guide rail. At the same time, the staggered design of the strengthening area and the non-strengthening area of the present invention can avoid the "avalanche-type" melting and ablation of the armature under extreme working conditions, so that the contact state and lubrication effect between the armature and the copper guide rail can be flexibly adjusted according to the emission working conditions.

[0024] 4. In the method of the present invention, during laser melting and injection, the melting laser moves according to a preset offset distance of 1-12 mm. The reason for designing this moving distance is that by selecting an appropriate laser offset distance for processing, a molten injection layer with a compact texture and a complete shape can be obtained.

[0025] 5. In the method of the present invention, the spot size in the laser parameters is set to 2 mm - 6 mm, the laser power is set to 2000 W - 4000 W, the scanning speed is set to 100 mm / min - 1900 mm / min, the powder feeding rate of the refractory metal powder is 4 g / min - 22 g / min, the powder feeding gas flow rate is set to 5 L / min - 12 L / min, and the protective gas flow rate is set to 8 L / min - 15 L / min. Its function is to make the refractory metal powder particles evenly distributed in the molten injection layer by selecting appropriate processing parameters to obtain a high-quality strengthened alloy layer. Description of the Drawings

[0026] Figure 1 is a schematic diagram of the process of selective laser melting and injection of refractory metal-reinforced aluminum alloy in an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of the cross-sectional metallographic structure of the molten injection layer of the selective laser melting and injection of tungsten particle-reinforced aluminum alloy with anti-ablative performance in an embodiment of the present invention;

[0028] Figure 3 is a schematic diagram of the composite structure of the selective laser spot melting and injection of refractory metal-reinforced aluminum alloy in an embodiment of the present invention;

[0029] Figure 4 is a schematic diagram of the composite structure of the selective laser line melting and injection of refractory metal-reinforced aluminum alloy in an embodiment of the present invention;

[0030] Figure 5 is a schematic diagram of the composite structure of the selective laser grid melting and injection of refractory metal-reinforced aluminum alloy in an embodiment of the present invention;

[0031] Figure 6It is a schematic diagram of a laser surface selective melting and injecting refractory metal reinforced aluminum alloy composite structure according to an embodiment of the present invention.

[0032] In the drawings: 1 - laser beam, 2 - powder hopper, 3 - aluminum alloy matrix, 4 - refractory metal particles, 5 - molten pool, 6 - molten injection layer, 7 - laser beam scanning direction. Specific embodiments

[0033] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] The present invention provides a method for laser selective melting and injecting refractory metals to enhance the ablation resistance performance of an armature, including the following steps:

[0035] S1. Grind and clean the surface of the armature to be enhanced. The material of the armature includes but is not limited to 7xxx aluminum alloy, such as 7005 aluminum alloy, 7075 aluminum alloy, etc. Then clean the surface of the polished armature. Acetone can be used to clean the oil stains on the surface during cleaning.

[0036] S2. Design the shape of the laser selective melting and injecting structure on the surface of the armature based on the electromagnetic emission working condition and the ablation characteristics of the armature. Specifically, based on the electromagnetic emission working condition and the ablation characteristics of the armature, if the ablation at the front end of the armature is not the most serious, design the shape of the laser selective melting and injecting structure on the front end surface of the armature as a line shape, the shape of the laser selective melting and injecting structure in the middle of the armature as a dot shape or multi-line shape, and since the ablation at the tail end of the armature is serious, design the shape of the laser selective melting and injecting structure on the tail end surface of the armature as a surface shape.

[0037] S3. Place refractory metal powders, such as tungsten, molybdenum, etc., in the powder feeding device of the laser, then set the corresponding laser parameters, and use the laser selective melting and injecting technology to perform laser melting and injection on the surface of the armature to be enhanced according to the shape of the laser selective melting and injecting structure, so as to obtain a reinforced armature composite structure in which the molten injection layer in the strengthened area and the surface of the armature in the non-strengthened area are interwoven and distributed.

[0038] In a preferred embodiment, the laser selective melting and injecting structure is composed of several molten injection lines arranged in parallel on the surface of the armature, that is, the thickness of the molten injection lines is the same, the shapes are roughly the same, and multiple molten injection lines are arranged side by side in the molten injection area to form a molten injection layer.

[0039] In a preferred embodiment, the laser selective melting and injecting structure is a grid-shaped molten injection layer composed of several molten injection lines intersecting vertically and horizontally. The thickness and shape of the vertically and horizontally intersecting molten injection lines are roughly the same, and multiple horizontally arranged side-by-side molten injection lines and multiple vertically arranged side-by-side molten injection lines are arranged perpendicular to each other and intersect. The thickness at the intersection of two molten injection lines is also the same as the thickness of the molten injection line, that is, the thickness of the molten injection layer in the entire selected area is uniform.

[0040] In a preferred embodiment, the selective laser melt injection structure is composed of a plurality of melt injection points uniformly distributed on the surface of the armature; in a more preferred embodiment, the diameter of the melt injection points is 3 mm - 6 mm, that is, the melt injection points are circles of a certain size.

[0041] In a preferred embodiment, the selective laser melt injection structure is a melt injection surface of a preset shape covering a part of the surface of the armature, that is, the melt injection layer of the selective laser is a melt injection surface of a specific shape with a larger area that is the same as the size and shape of the selected area, such as a rectangular melt injection surface, a special-shaped melt injection surface, etc.

[0042] In a preferred embodiment, the thickness of the selective laser melt injection structure of the foregoing various shapes (i.e., the entire melt injection layer) is 0.5 mm - 1.2 mm. Preferably, the thickness of the selective laser melt injection structure is 0.8 mm - 1.0 mm. Its function is to make the refractory metal powder particles evenly distributed in the melt injection layer and ensure good contact between the armature surface and the electromagnetic track.

[0043] In a more preferred embodiment, the ratio of the surface area of the selective laser melt injection structure to the surface area of the armature surface is For example, the ratio of the area of the rectangular melt injection surface to the area of the entire armature surface is Its function is to make the melting amount of the aluminum alloy armature appropriate and ensure good lubrication between the armature and the guide rail.

[0044] In a preferred embodiment, in step S3, each time laser melt injection is performed, the laser beam is moved from the previous processing track to the next processing track according to a preset offset distance to ensure that a melt injection layer with a dense texture and a complete shape is obtained.

[0045] In a more preferred embodiment, the foregoing preset laser offset distance is 1 mm - 12 mm, that is, one track is melt injected every 1 mm - 12 mm of offset. After multiple multi-track melt injections, a reinforced aluminum alloy composite structure with a uniform structure and an alternating arrangement of strengthened areas and non-strengthened areas is finally formed; in a more preferred implementation, the offset distance of each laser melt injection is 1.5 mm - 10 mm.

[0046] In a preferred embodiment, in step S2, the spot size in the laser parameters is set to 3 mm - 6 mm, the laser power is set to 3000 W, the scanning speed is set to 700 mm / min, the powder feeding gas flow rate of the refractory metal powder is set to 6 L / min, and the protective gas flow rate is set to 12 L / min. At these parameters, the melting amount in the strengthened area can be greatly reduced, thus achieving the effect of "controlled melting".

[0047] To illustrate the present invention, the foregoing method provided by the present invention will be described in detail below in conjunction with embodiments, but the following embodiments should not be construed as limiting the protection scope of the present invention.

[0048] Example 1

[0049] Laser selective area melting and injection of refractory metal W on the surface of 7xxx aluminum alloy. In this example, 7005 aluminum alloy is selected, combined with Figure 1 - Figure 2 , and the specific method includes the following steps:

[0050] S1. First, polish the surface of 7005 aluminum alloy with sandpaper and clean the surface oil stain with acetone;

[0051] S2. Design the laser selective area melting and injection structure as several injection lines arranged in parallel on the armature surface;

[0052] S3. Then, place refractory metal particles 4 with a mesh size of 400 - 500 (W metal particles are selected in this example) in the powder hopper 2, and set the powder feeding amount of refractory metal particles 4 to 16 g / min; Set the laser parameters, adjust the spot size of the laser beam 1 to 4 mm, set the laser power to 3000 W, set the scanning speed to 700 mm / min, set the powder feeding gas flow rate to 6 L / min, and set the protective gas flow rate to 12 L / min; Open the powder hopper 2, turn on the laser, and along the structure of the laser selective area melting and injection line, use the laser beam 1 to melt the surface of the aluminum alloy substrate 3 to form a molten pool 5; The powder hopper 2 feeds the refractory metal particles 4 into the molten pool. Since the temperature of the molten pool 5 does not reach the melting point of metal W, then as the molten pool solidifies, the W particles will be "frozen" in the molten pool 5, and finally a molten injection layer 6 is formed. The molten injection layer is the metallographic structure as shown in Figure 2 ; Offset the laser beam along the direction perpendicular to the laser beam scanning direction 7, and inject an injection line every 10 mm. After multiple multi - channel melting and injection, finally, an enhanced aluminum alloy composite structure with a thickness of 0.8 mm and parallel and staggered strengthened and non - strengthened regions of laser linear selective area melting and injection of W metal as shown in Figure 4 is obtained.

[0053] After laser selective area melting and injection of refractory metal W, the melting amount in the strengthened region of 7xxx aluminum alloy is greatly reduced compared with the non - strengthened region on it, achieving the effect of "controllable melting".

[0054] Example 2

[0055] In this example, laser selective area melting and injection of refractory metal Nb is carried out on the surface of 7xxx aluminum alloy. 7075 aluminum alloy is selected in this example, combined with Figure 1 , and the specific method includes the following steps:

[0056] S1. First, polish the surface of 7075 aluminum alloy with sandpaper and clean the surface oil stain with acetone;

[0057] S2. Design the laser selective area melting and injection structure on the surface of the aluminum alloy substrate armature as an injection surface with a specific shape of a relatively large area in the selected area;

[0058] S3. Place refractory metal particles Nb with a mesh size of 400 - 500 in powder hopper 2, and set the powder feeding rate of refractory metal particles Nb to 10 g / min; set the laser parameters, adjust the spot size of laser beam 1 to 4.5 mm, set the laser power to 2500 W, set the scanning speed to 1000 mm / min, set the powder feeding gas flow rate to 5 L / min, and set the shielding gas flow rate to 10 L / min; open powder hopper 2, turn on the laser, and along the structure of the laser selective melting and casting surface, use laser beam 1 to melt the surface of aluminum alloy substrate 3 to form a molten pool 5; powder hopper 2 feeds refractory metal particles Nb into the molten pool. Since the temperature of molten pool 5 does not reach the melting point of metal Nb, then as the molten pool solidifies, Nb particles will be "frozen" in molten pool 5, and finally a casting layer 6 is formed; offset the laser beam along the direction perpendicular to the laser beam scanning direction 7, and cast a casting line every 1.5 mm. After multiple multi - pass castings, finally obtain Figure 6 the enhanced aluminum alloy composite structure with a laser surface selective melting and casting Nb metal layer with a thickness of 0.6 mm as shown.

[0059] Example 3

[0060] The difference between this example and Example 2 is that the laser selective melting and casting structure is designed as the dot - shaped casting layer as shown in Figure 3 and the grid - shaped casting layer as shown in Figure 5 According to the same processing steps as in Example 1 and Example 2, adjust appropriate laser processing parameters for powder - feeding laser melting and casting processing, so as to obtain an armature structure with a dot - shaped casting layer or a grid - shaped casting layer with an appropriate thickness.

[0061] In the present invention, by introducing refractory metal, the refractory metal powder is sent to the area to be strengthened of the armature through the laser powder feeding device for melting and casting. The surface of the armature to be strengthened melts under the action of the laser to form a molten pool. After the refractory metal powder enters the molten pool, it is slightly melted or not melted. During the subsequent solidification process of the molten pool, the refractory metal powder particles are condensed in the molten pool to form a casting layer, so as to obtain an enhanced armature composite structure in which the strengthened area casting layer and the non - strengthened area are interlaced and distributed on the surface of the armature. This enhanced armature composite structure can increase the melting point of the laser - strengthened area on the surface of the armature, thereby further improving the anti - ablation performance of the armature.

[0062] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for laser selective melting and injection of refractory metals to enhance the ablation resistance of armatures, characterized in that Including the following steps: S1. Grind and clean the surface of the aluminum alloy armature to be strengthened until it is smooth; S2. According to the electromagnetic emission working conditions and the ablation characteristics of the aluminum alloy armature, design the laser selective melting and deposition structure on the surface of the aluminum alloy armature into different shapes; S3. Set the laser parameters, feed the refractory metal powder onto the surface of the aluminum alloy armature to be strengthened based on the shape of the laser selective melting and deposition structure, and use the laser to perform laser melting and deposition on the surface of the aluminum alloy armature to be strengthened. After multiple melting and depositions, a reinforced aluminum alloy armature composite structure with an alternating distribution of a strengthened area melting layer and a non-strengthened area armature surface is obtained.

2. The method for enhancing the ablation resistance performance of the armature by selective laser melting and injecting refractory metals according to claim 1, characterized in that, The shape of the laser selective melting and deposition structure is a number of melting lines arranged in parallel on the surface of the aluminum alloy armature.

3. A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals as described in claim 2, characterized in that, The width of each melting line is 1 mm - 6 mm.

4. A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals as described in claim 1, characterized in that The shape of the laser selective melting and deposition structure is a grid formed by the vertical and horizontal intersection of a number of melting lines.

5. A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals as claimed in claim 1, characterized in that, The shape of the laser selective melting and deposition structure is a number of melting points evenly distributed on the surface of the aluminum alloy armature.

6. A method for enhancing the ablation resistance of an armature by selective laser melting and injecting refractory metals as claimed in claim 5, characterized in that, The diameter of the melting point is 3 mm - 6 mm.

7. A method for laser selective area melting and injecting refractory metals to enhance the anti-ablative performance of an armature, as described in claim 1, wherein The laser selective melting and deposition structure is a melting surface with a preset shape covering a part of the surface of the aluminum alloy armature.

8. A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals according to any one of claims 1-7, characterized in that, The thickness of the laser selective melting and deposition structure is 0.5 mm - 1.2 mm.

9. A method for laser selective melting and injecting refractory metals to enhance the anti-ablative performance of an armature according to claim 8, characterized in that, The thickness of the laser selective melting and deposition structure is 0.8 mm - 1.0 mm.

10. A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals as claimed in claim 1, characterized in that The surface area ratio of the selective laser melting injection structure to the surface area of the aluminum alloy armature is - .

11. A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals as described in claim 1, characterized in that In step S3, during laser melting and deposition, move the laser from the previous melting track to the next melting track according to a preset offset distance.

12. A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals as described in claim 11, characterized in that, The preset offset distance is 1 mm - 12 mm.

13. A method for laser selective melting and injection of refractory metals to enhance the ablation resistance performance of an armature according to claim 12, characterized in that, The preset offset distance is 1.5 mm - 12 mm.

14. A method for enhancing the ablation resistance performance of an armature by selective laser melting and injecting refractory metals as claimed in claim 1, characterized in that, In step S2, set the spot size in the laser parameters to 2 mm - 6 mm, the laser power to 2000 W - 4000 W, the scanning speed to 100 mm / min - 1900 mm / min, the powder feeding rate of the refractory metal powder to 4 g / min - 22 g / min, the powder feeding gas flow rate to 5 L / min - 12 L / min, and the protective gas flow rate to 8 L / min - 15 L / min.

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