A method for in-situ crushing and pulverizing of ores based on high-pressure gas high-speed unloading

Abstract

The embodiment of the application discloses a high-pressure gas high-speed unloading ore in-situ crushing and pulverizing method, relates to the technical field of mineral exploitation and separation, and is invented to solve the problem of high energy consumption in the mining and selecting process. The high-pressure gas high-speed unloading ore in-situ crushing and pulverizing method comprises the following steps: according to the working face area and geological structure of a roadway mining area, the roadway mining area is divided into an outer area and an inner area; first crushing holes are evenly arranged on the working face, and the tail ends of the first crushing holes are located in the inner area of the roadway mining area; high-pressure gas is filled into the first crushing holes, and the first crushing holes are blocked after the high-pressure gas fills the first crushing holes and the ore cracks in the inner area; the ore in the outer area is crushed to release the high-pressure gas in the ore cracks in the first crushing holes and the inner area; and the ore in the inner area is crushed to obtain ore particles. The embodiment of the application is suitable for the scene of mineral exploitation and pulverization in the roadway mining area.

Description

Technical Field

[0001] This application relates to the field of mineral mining and sorting technology, and in particular to a method for in-situ crushing and pulverizing ore based on high-pressure gas high-speed unloading. Background Technology

[0002] In the process of mining ore, explosives are typically used to crush the ore within the mining area, obtaining larger ore fragments. These fragments are then transported to a concentrator for further crushing and grinding to obtain smaller ore particles, which are then sorted and smelted. This process is energy-intensive and cumbersome, requiring the transportation of all the ore fragments to the processing site. Furthermore, the further crushing of the fragments into smaller particles consumes even more energy, resulting in high energy consumption in the current mining and beneficiation processes. Summary of the Invention

[0003] In view of this, the embodiments of this application provide a method for in-situ crushing and pulverizing of ore based on high-pressure gas high-speed unloading, which facilitates the reduction of energy consumption in the mining and beneficiation process.

[0004] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0005] This application provides a method for in-situ crushing and pulverizing ore based on high-pressure gas high-speed unloading, comprising: dividing the roadway mining area into an outer area and an inner area according to the working face area and geological structure of the roadway mining area; uniformly opening a first crushing hole on the working face, with the end of the first crushing hole located in the inner area of ​​the roadway mining area; filling the first crushing hole with high-pressure gas, and sealing the first crushing hole after the high-pressure gas has filled the first crushing hole and the ore cracks in the inner area; crushing the ore in the outer area to release the high-pressure gas in the first crushing hole and the ore cracks in the inner area, and crushing the ore in the inner area to obtain ore particles.

[0006] According to one specific implementation of this application, after uniformly opening the first breaking hole on the working face, the method further includes: opening the second breaking hole on the working face based on a preset rule, the end of the second breaking hole being located in the outer area of ​​the roadway mining area; after sealing the first breaking hole, the method further includes: filling the second breaking hole with explosives and sealing the second breaking hole; crushing the ore in the outer area, including: detonating the explosives in the second breaking hole to crush the ore in the outer area.

[0007] According to one specific implementation of this application, after uniformly opening the first breaking hole on the working face, the method further includes: uniformly opening sealing holes in the circumferential edge region of the working face of the roadway mining area, with the end of the sealing hole located in the inner region of the roadway mining area; before filling the second breaking hole with explosives, the method further includes: grouting the sealing hole to seal the ore cracks on the boundary of the roadway mining area.

[0008] According to one specific implementation of this application, an explosive in the second breaking hole is detonated to break the ore in the outer region, thereby releasing the high-pressure gas in the ore fissures in the first breaking hole and the inner region, and breaking the ore in the inner region to obtain ore particles. This includes: detonating the explosive in the second breaking hole to break the ore in the outer region, forming a free surface at the junction of the outer and inner regions; and the high-pressure gas in the ore fissures in the first breaking hole and the inner region expanding and releasing energy to break the ore in the inner region and obtain ore particles.

[0009] According to one specific implementation of this application, before dividing the tunnel mining area into an outer area and an inner area based on the working face area and geological structure of the tunnel mining area, the method further includes: determining the tunnel mining area based on a single mining advance; dividing the tunnel mining area into an outer area and an inner area based on the working face area and geological structure of the tunnel mining area, including: determining a blasting area in the tunnel mining area based on the working face area and geological structure of the tunnel mining area; dividing the blasting area into an outer area, and dividing the remaining area outside the blasting area into an inner area.

[0010] According to one specific implementation of this application, high-pressure gas is filled into the first breakage hole, and after the high-pressure gas fills the first breakage hole and the ore fracture in the inner region, the first breakage hole is sealed, including: filling the first breakage hole with high-pressure gas until the pressure in the first breakage hole stabilizes, and then sealing the first breakage hole.

[0011] According to one specific implementation of this application, crushing the ore in the outer region to release the high-pressure gas in the first crushing hole and the ore crack in the inner region, and crushing the ore in the inner region to obtain ore particles includes: after a second preset time of stillness, crushing the ore in the outer region to release the high-pressure gas in the first crushing hole and the ore crack in the inner region, and crushing the ore in the inner region to obtain ore particles.

[0012] According to one specific implementation of this application, the explosive includes nitroglycerin explosive, emulsion explosive and trinitrotoluene; filling the second rupture hole with the explosive includes: filling the second rupture hole with nitroglycerin explosive, emulsion explosive and / or trinitrotoluene.

[0013] According to one specific implementation of this application, the high-pressure gas includes high-pressure liquid carbon dioxide, nitrogen, argon, or air.

[0014] According to one specific implementation of this application, the pressure of the high-pressure gas is 1-30 MPa.

[0015] Compared to blasting-based mining methods for obtaining ore fragments, this application provides a high-pressure gas high-speed unloading in-situ ore crushing and pulverization method. Based on the working face area and geological structure of the roadway mining area, the roadway mining area is divided into an outer and inner region. This allows for two main advantages: firstly, first crushing holes can be evenly opened on the working face, with their ends located in the inner region of the roadway mining area. High-pressure gas is then filled into these first crushing holes, and after the high-pressure gas has filled the first crushing holes and the ore fissures in the inner region, the first crushing holes are sealed. Secondly, it facilitates the determination of the crushing area within the roadway mining area. By crushing the ore, the high-pressure gas in the first crushing holes and the ore fissures in the inner region is released, crushing the ore in the inner region to obtain ore particles. This reduces the need for further crushing and grinding of the ore fragments, thus lowering energy consumption in the mining and beneficiation process. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of one embodiment of the in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading according to this application. Detailed Implementation

[0018] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0019] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0020] The present invention provides a method for in-situ crushing and pulverizing of ore based on high-pressure gas high-speed unloading, which facilitates the reduction of energy consumption in the mining and beneficiation process.

[0021] The following combination Figure 1 The embodiments of this application will be further described below.

[0022] Figure 1A schematic flowchart of an in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading, as described in this application, is shown below. Figure 1 As shown, the in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading includes:

[0023] S101. Based on the working face area and geological structure of the tunnel mining area, the tunnel mining area is divided into an outer area and an inner area.

[0024] The outer area refers to the working face area close to the roadway mining area, while the inner area is the working face area far away from the roadway mining area.

[0025] Geological structure includes surrounding rock strength, surrounding rock porosity, and surrounding rock permeability.

[0026] For example, a first reference table can be pre-constructed, which may include multiple sets of one-to-one corresponding working face areas, geological structures, and outer region thicknesses. In this way, the thickness of the outer region of the tunnel mining area can be determined based on the working face area and geological structure of the tunnel mining area, thereby dividing the tunnel mining area into an outer region and an inner region.

[0027] S102. The first breaking holes are evenly opened on the working face, and the end of the first breaking hole is located in the inner area of ​​the roadway mining area.

[0028] The depth of the first fracture hole can be determined based on the thickness of the tunnel mining area. For example, the depth of the first fracture hole can be the same as the thickness of the tunnel mining area. When determining the depth of the first fracture hole, it can be combined with the actual engineering situation, such as based on the surrounding rock strength, surrounding rock porosity, surrounding rock permeability, and the pressure of the high-pressure gas mentioned below.

[0029] The number of first fracture holes, or the spacing between them, can be appropriately increased or decreased based on the surrounding rock strength, porosity, permeability, and the pressure of the high-pressure gas described below. For example, if the surrounding rock strength, porosity, and permeability determine that the surrounding rock is relatively firm, and the pressure of the high-pressure gas is relatively low, then the number of first fracture holes can be appropriately increased.

[0030] S103. High-pressure gas is filled into the first breakage hole, and after the high-pressure gas fills the first breakage hole and the ore cracks in the inner area, the first breakage hole is sealed.

[0031] For example, a compression pump can be used to fill the first fracture hole with high-pressure gas. A pressure sensor can be used to determine whether the ore fractures in the first fracture hole and the inner area are filled with high-pressure gas. Based on the geological structure of the tunnel mining area, a suitable plug can be selected to seal the first fracture hole. For example, if the porosity is high, a fluid plug can be selected to seal the first fracture hole.

[0032] For example, the high-pressure gas may include high-pressure liquid carbon dioxide, nitrogen, argon, or air.

[0033] S104. Crush the ore in the outer region to release the high-pressure gas in the first crushing hole and the ore crack in the inner region, and crush the ore in the inner region to obtain ore particles.

[0034] After the ore in the outer region is crushed, the high-pressure gas in the first crushing hole and the ore cracks in the inner region can expand rapidly and release a large amount of energy, which can form a shock wave, thereby crushing the ore in the inner region and obtaining ore particles.

[0035] Compared to blasting-based mining methods for obtaining ore fragments, the in-situ crushing and pulverizing method based on high-pressure gas high-speed unloading provided in this application divides the mining area into an outer and inner region according to the working face area and geological structure. This allows for the uniform opening of first crushing holes on the working face, with their ends located in the inner region of the mining area. High-pressure gas is then filled into these first crushing holes, and after the high-pressure gas has filled the first crushing holes and the ore fissures in the inner region, the first crushing holes are sealed. Furthermore, it facilitates the determination of the crushing area within the mining area. By crushing the ore, the high-pressure gas in the first crushing holes and the ore fissures in the inner region is released, and the ore in the inner region is crushed to obtain ore particles. This reduces the need for further crushing and grinding of the ore fragments, thus lowering energy consumption in the mining and beneficiation process.

[0036] In one embodiment, the pressure of the high-pressure gas is 1-30 MPa. The pressure of the high-pressure gas can be determined based on the geological structure of the tunnel mining area; if the porosity and permeability are low, the pressure of the high-pressure gas is increased, and if the porosity and permeability are low, the pressure of the high-pressure gas is decreased.

[0037] In one embodiment, after uniformly opening the first breaking hole on the working face, the method further includes: opening a second breaking hole on the working face based on a preset rule, wherein the end of the second breaking hole is located in the outer region of the roadway mining area.

[0038] Creating a second breaking hole on the working surface may include a second breaking hole in the outer contour area of ​​the working surface and a second breaking hole in the central area. The second breaking hole in the central area may be staggered with the first breaking hole.

[0039] In the preset rules, the diameter of the second breaking hole is 30-100 mm. In one embodiment, the diameter of the second breaking hole is 30 mm. In another embodiment, the diameter of the second breaking hole is 65 mm. In yet another embodiment, the diameter of the second breaking hole is 100 mm. Specifically, the diameter of the second breaking hole can be determined based on the geological structure and engineering practice.

[0040] The spacing between adjacent second fracture holes can be 1.5 to 2 times the hole diameter. For example, the spacing between adjacent second fracture holes can be 1.5 times the hole diameter, and the specific spacing between the second fracture holes can be determined based on the geological structure and engineering practice.

[0041] For example, the depth of the second fracture hole can be the same as the thickness of the outer region. The depth of the second fracture hole can be determined based on the thickness of the outer region, according to the geological structure and engineering conditions.

[0042] After sealing the first rupture hole, the method further includes: filling the second rupture hole with explosives and sealing the second rupture hole. For example, explosives can be filled into the second rupture hole, and the second rupture hole can be sealed with stemming material.

[0043] As one possible implementation, the explosive may include nitroglycerin explosive, emulsion explosive and trinitrotoluene; filling the second rupture hole with the explosive may include: filling the second rupture hole with nitroglycerin explosive, emulsion explosive and / or trinitrotoluene.

[0044] For example, an explosive device can be formed by filling the second break-through hole with nitroglycerin explosive and emulsion explosive in proportion to increase safety during transportation.

[0045] Crushing the ore in the outer region can specifically include detonating explosives in the second crushing hole to crush the ore in the outer region. In this way, the explosives can rapidly crush the ore in the outer region within a short time, achieving a rapid release of high-pressure gas in the first crushing hole and the ore fissures in the inner region. This causes the high-pressure gas in the first crushing hole and the ore fissures in the inner region to expand rapidly, releasing a large amount of energy and forming a shock wave that crushes the ore in the inner region, obtaining ore particles.

[0046] After the explosive is loaded into the second rupture hole, a fuse can be connected to the explosive to detonate it.

[0047] In addition, a second breaking hole can be opened on the working face of the roadway mining area based on the smooth blasting method.

[0048] In one embodiment, after uniformly opening the first breaking holes on the working face, the method further includes: uniformly opening sealing holes circumferentially on the contour edge region of the working face in the roadway mining area, with the ends of the sealing holes located in the inner region of the roadway mining area. This facilitates sealing the boundary of the inner region of the roadway mining area, creating a closed area for the pulverized portion to be mined.

[0049] For example, the contour edge region of the working surface can be a region 0.2 meters away from the contour of the working surface. The sealing holes can be staggered with the second breaking holes within the contour edge region.

[0050] Before filling the second break hole with explosives, the method also includes grouting the sealing hole to seal the ore cracks at the boundary of the roadway mining area.

[0051] Sealing ore cracks at the boundary of the mining area can create a closed boundary for the tunnel, allowing the energy generated by the explosion of explosives to be released in the outer area of ​​the mining area, reducing energy loss and more effectively damaging the ore.

[0052] In one embodiment, the explosive in the second break-through hole is detonated to break the ore in the outer region, thereby releasing the high-pressure gas in the first break-through hole and the ore fissures in the inner region, and breaking the ore in the inner region to obtain ore particles. Specifically, this includes: detonating the explosive in the second break-through hole to break the ore in the outer region, forming a free surface at the junction of the outer and inner regions; and rapidly expanding and releasing energy in the high-pressure gas in the first break-through hole and the ore fissures in the inner region to break the ore in the inner region and obtain ore particles.

[0053] The free surface is the surface where the ore comes into contact with air, and it can be used to control the crushing effect of high-pressure gas on the ore in the inner region.

[0054] After the ore in the outer region is broken to form a free surface, the inner side of the free surface is the inner region of the tunnel mining area, and the outer side of the free surface is air. The first break hole and ore fractures in the inner region of the tunnel mining area are filled with high-pressure gas, that is, there is a high pressure difference between the inner and outer sides of the free surface. Therefore, the high-pressure gas in the first break hole and ore fractures in the inner region will expand rapidly. During the rapid expansion, the high-pressure gas will release energy. The shock wave generated by the release of energy can break the ore in the inner region and obtain ore particles.

[0055] In one embodiment, before dividing the tunnel mining area into an outer area and an inner area based on the working face area and geological structure of the tunnel mining area, the method further includes: determining the tunnel mining area based on a single mining advance.

[0056] Among them, mining footage is an indicator used to measure the depth of tunnel mining, which represents the depth of excavation from the boundary of the mine or the existing mining area inward; single mining footage represents the depth of ore that can be broken in a single crushing operation during the excavation process from the boundary of the mine or the existing mining area inward.

[0057] The mining area of ​​a roadway can be determined based on the footage of a single mining operation and the area of ​​the working face.

[0058] In one embodiment, the tunnel mining area is divided into an outer area and an inner area based on the working face area and geological structure of the tunnel mining area, including: determining the blasting area in the tunnel mining area based on the working face area and geological structure of the tunnel mining area; dividing the blasting area into the outer area and dividing the remaining area outside the blasting area into the inner area.

[0059] Based on the working face area and geological structure of the roadway mining area, the depth of ore crushing in the roadway can be determined, and based on this depth and the area of ​​the working face of the roadway, the blasting area of ​​the roadway mining area can be determined.

[0060] When determining the crushing depth of ore in a roadway, if the working face area of ​​the roadway mining area is large, the crushing depth of ore in the roadway can be deeper; if the ore in the roadway has high hardness and low porosity, the crushing depth of ore in the roadway can be shallower. The specific crushing depth of ore in a roadway can be determined based on the actual engineering situation.

[0061] When high-pressure gas is injected into a hole, if the pressure in the hole is stable, it indicates that the hole is filled with high-pressure gas. Therefore, in one embodiment, high-pressure gas is filled into the first crushing hole, and after the high-pressure gas fills the first crushing hole and the ore fractures in the inner area, the first crushing hole is sealed. This includes filling the first crushing hole with high-pressure gas until the pressure in the first crushing hole stabilizes, and then sealing the first crushing hole. This facilitates the determination of whether the first crushing hole is filled with high-pressure gas and improves mining efficiency.

[0062] As an optional implementation, filling the first breakage hole with high-pressure gas, and sealing the first breakage hole after the high-pressure gas fills the first breakage hole and the ore cracks in the inner area, may include: filling the first breakage hole with high-pressure gas, stopping the filling of high-pressure gas after a first preset time, and sealing the first breakage hole.

[0063] The high-pressure gas filled into the first crushing hole can diffuse into the ore fractures connected to the first crushing hole. After the high-pressure gas filling stops, the high-pressure gas can continue to diffuse into the connected ore fractures to fully fill the ore fractures in the inner area.

[0064] In one embodiment, crushing the ore in the outer region to release the high-pressure gas in the first crushing hole and the ore crack in the inner region, and crushing the ore in the inner region to obtain ore particles includes: after remaining still for a second preset time, crushing the ore in the outer region to release the high-pressure gas in the first crushing hole and the ore crack in the inner region, and crushing the ore in the inner region to obtain ore particles.

[0065] The second preset time is 30-60 minutes, which can be determined based on the geological structure of the tunnel mining area. If the porosity and permeability are low, the first preset time is extended; if the porosity and permeability are high, the first preset time is shortened. The purpose of allowing the gas to stand for the second preset time is to ensure that the high-pressure gas fills the inner area of ​​the tunnel mining area and does not diffuse into areas outside the tunnel mining area.

[0066] As an optional implementation, preparations for detonating the explosives in the second rupture hole can be carried out within a second preset time period.

[0067] The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading provided in this application embodiment can seal ore cracks on the boundary of the roadway mining area by setting sealing holes in the edge contour area of ​​the working face of the roadway mining area, forming a closed boundary of the roadway, and more effectively destroying the ore.

[0068] By setting a first break hole located on the inner side of the roadway mining area and a second break hole located on the outer side of the roadway mining area, explosives can be placed in the second break hole and high-pressure gas can be filled in the first break hole. This allows the high-pressure gas to fill the ore fractures in the first break hole and the inner side of the roadway mining area, so that the outer side of the roadway mining area can be blasted by the explosives, releasing the high-pressure gas in the inner side of the roadway mining area. This crushes the ore in the inner side of the mining area, obtaining ore particles. This reduces the need for further crushing and grinding of ore fragments, and facilitates lower energy consumption in the mining and beneficiation process.

[0069] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0070] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for in-situ crushing and pulverizing ore based on high-pressure gas high-speed unloading, characterized in that, include: Based on the working face area and geological structure of the tunnel mining area, the tunnel mining area is divided into an outer area and an inner area. The first breaking holes are uniformly opened on the working surface, and the end of the first breaking hole is located in the inner area of ​​the roadway mining area; High-pressure gas is filled into the first break hole, and after the high-pressure gas fills the first break hole and the ore cracks in the inner region, the first break hole is sealed. The ore in the outer region is crushed to release the high-pressure gas in the first crushing hole and the ore crack in the inner region, and the ore in the inner region is crushed to obtain ore particles. After uniformly opening the first breaking holes on the working surface, the method further includes: Based on preset rules, a second breaking hole is opened on the working face, and the end of the second breaking hole is located in the outer area of ​​the roadway mining area. After sealing the first fracture hole, the method also includes: Explosives were loaded into the second rupture hole, and the second rupture hole was then sealed. Crushing the ore in the outer region includes: The explosive in the second break hole is detonated to break the ore in the outer region.

2. The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading as described in claim 1, characterized in that, After uniformly opening the first breaking holes on the working surface, the method further includes: Evenly spaced sealing holes are made circumferentially along the edge of the working face in the roadway mining area, with the ends of the sealing holes located in the inner area of ​​the roadway mining area. Before filling the second rupture hole with explosives, the method further includes: Grouting is injected into the sealing holes to seal the ore cracks at the boundary of the roadway mining area, creating a closed environment for the ore body to be extracted by high-speed gas unloading.

3. The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading according to claim 1, characterized in that, Detonating the explosive in the second break-through hole to break the ore in the outer region includes: Detonate the explosive in the second breaking hole to break the ore in the outer region and form a free surface at the junction of the outer region and the inner region; The high-pressure gas in the first crushing hole and the ore crack in the inner region expands and releases energy, crushing the ore in the inner region to obtain ore particles.

4. The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading according to claim 1, characterized in that, Before dividing the roadway mining area into an outer and inner area based on the working face area and geological structure, the method further includes: The mining area of ​​the roadway is determined based on a single mining advance. Based on the working face area and geological structure of the tunnel mining area, the tunnel mining area is divided into an outer area and an inner area, including: Based on the working face area and geological structure of the tunnel mining area, the blasting area in the tunnel mining area is determined; The blasting area is divided into an outer region, and the remaining area outside the blasting area is divided into an inner region.

5. The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading according to claim 1, characterized in that, Filling the first fracture hole with high-pressure gas, and sealing the first fracture hole after the high-pressure gas has filled the first fracture hole and the ore fractures in the inner area, includes: High-pressure gas is filled into the first breakage hole until the pressure in the first breakage hole stabilizes, and then the first breakage hole is sealed.

6. The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading according to claim 1, characterized in that, The ore in the outer region is crushed to release the high-pressure gas in the first crushing hole and the ore cracks in the inner region. The ore in the inner region is then crushed to obtain ore particles, including: After a second preset time of stillness, the ore in the outer region is crushed to release the high-pressure gas in the first crushing hole and the ore crack in the inner region, thereby crushing the ore in the inner region and obtaining ore particles.

7. The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading according to claim 1, characterized in that, The explosives include nitroglycerin explosives, emulsion explosives, and trinitrotoluene; The second rupture hole is filled with explosives, including: The second break hole is filled with the nitroglycerin explosive, the emulsion explosive and / or the trinitrotoluene.

8. The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading according to claim 1, characterized in that, The high-pressure gas includes high-pressure liquid carbon dioxide, nitrogen, argon, or air.

9. The in-situ crushing and pulverizing method for ore based on high-pressure gas high-speed unloading according to claim 1, characterized in that, The pressure of the high-pressure gas is 1-30 MPa.

Images