Environment-friendly filter bag and preparation process

Abstract

The invention relates to the technical field of liquid filtration, and discloses an environment-friendly filter bag which is formed by welding filter cotton cloth, and the filter cotton cloth is prepared from high-strength polypropylene fibers, macromolecular polyethylene fibers and additives; the invention further discloses a preparation process of the environment-friendly filter bag. The preparation process comprises the following steps: S1, opening and mixing the raw materials: mixing the high-strength polypropylene fibers and the high-molecular polyethylene fibers into mixed fiber cotton; s2, carding the mixed fiber cotton, namely carding the mixed fiber cotton, and adding an additive to form mixed short fibers, S3, lapping and pressing, namely pressing the mixed short fibers into coarse cotton cloth; s4, needling: needling the hopcotton cloth; s5, calendaring and batching: calendaring and shaping the hopcotton cloth; s6, welding the filter bag: welding the filter cotton cloth to form the filter bag. According to the filter bag prepared by the invention, the fracture tension at the welding point is large, the welding is firm, and the filter bag is difficult to tear; the filter bag can be used for filtering high-pressure and high-pollutant liquid and is low in use cost.

Description

Technical Field

[0001] The invention relates to the technical field of liquid filtration, in particular to an environmentally friendly filter bag and a preparation process thereof. Background Art

[0002] Polypropylene filter bags are widely used in the fields of liquid filtration, particle filtration and dust collection. In the field of liquid filtration, they are often used in water treatment, chemical, pharmaceutical, food and beverage industries to remove suspended matter, impurities, particles and microorganisms. They can achieve fine filtration in the liquid processing process to ensure product quality. They are low cost, good chemical resistance and easy to move.

[0003] However, due to the loose welding at the bottom of the filter bag, it is easy to crack and break under high pressure and high pollutant conditions. Therefore, it can only be used to filter low-pressure and low-impurity liquids. To filter high-pressure and high-pollution liquids, other large-scale filtering equipment can only be used, which greatly increases the cost of use. Summary of the invention

[0004] The object of the present invention is to provide an environmentally friendly filter bag and a preparation process to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An environmentally friendly filter bag is formed by welding filter cotton cloth, wherein the filter cotton cloth is prepared from high-strength polypropylene fiber, high-molecular polyethylene fiber and additives, wherein the mass ratio of the high-strength polypropylene fiber, the high-molecular polyethylene fiber and the additive is (80-100): (10-12): (0.4-0.6).

[0007] As a further scheme of the present invention: the additive consists of a stabilizer, an antioxidant and an antistatic agent, and the mass ratio thereof is 1:1:1; wherein the stabilizer is one or more of an organotin stabilizer, a barium zinc stabilizer, and a calcium zinc stabilizer, such as the organotin stabilizer is tin mercaptide and tin maleate, the barium zinc stabilizer is composed of barium stearate and zinc oxystearate, and the calcium zinc stabilizer is composed of calcium stearate and zinc oxystearate; the antioxidant is one or more of an ascorbic acid antioxidant, a phenolic antioxidant, and a sulfite antioxidant, such as the ascorbic acid antioxidant is L-ascorbic acid fatty acid ester, the phenolic antioxidant is tert-butylphenol hydroxybenzoate, and the sulfite antioxidant is sodium bisulfite; the antistatic agent is one or two of a quaternary ammonium salt antistatic agent and an alkyl amino acid salt antistatic agent, such as the quaternary ammonium salt antistatic agent is bis(2-ethoxyethyl)dimethylammonium chloride, and the alkyl amino acid salt antistatic agent is alkyldiaminoethylglycine hydrochloride.

[0008] As a further solution of the present invention: the thickness of the high-strength polypropylene fiber is 2.5D-3.5D, and the length is 49-75mm; the thickness of the high-molecular polyethylene fiber is 1.5D-3D, and the length is 30-48mm.

[0009] A preparation process of an environmentally friendly filter bag comprises the following steps:

[0010] S1, opening and mixing of raw materials: 80-100 parts by mass of high-strength polypropylene fibers and 10-12 parts by mass of high-molecular polyethylene fibers are respectively fed into a cotton blending machine for opening, and then mixed and rolled out to form mixed fiber cotton;

[0011] S2. Combing mixed fiber cotton: Take 0.4-0.6 parts of additives by mass and add them to 100 parts of distilled water, stir evenly to form a mixed liquid for use; comb the mixed fiber cotton with a carding machine, and mix the liquid during the combing process to form mixed short fibers.

[0012] S3. Laying and pressing: Lay the mixed staple fibers layer by layer in the mold according to the thickness requirements, and form a cheesecloth through vibration and compaction;

[0013] S4, acupuncture: the cheesecloth is needled five times using a needle-punching machine, and after repeated compaction and kneading, its structure is uniform, and then the cheesecloth is tested to prevent broken needles from falling into the cheesecloth;

[0014] S5. Calendering and rolling: Use a three-roll calender to calender and shape the raw cotton cloth, press the cotton cloth into a smooth surface on one side and a semi-smooth surface on the other side to form a filter cotton cloth, and then cut the filter cotton cloth and roll it up;

[0015] S6. Filter bag welding: After the filter cotton cloth is cut into suitable sizes, it is welded by an ultrasonic welding machine so that the upper end is open and the lower part is closed to form a filter bag.

[0016] As a further solution of the present invention: in the step S1, the specific preparation method of the mixed fiber cotton is as follows:

[0017] S11, taking 80-100 parts of high-strength polypropylene fibers by weight, and conveying them to the entrance of the cotton mixer through a belt conveyor, and then conveying them into the cotton mixer through a cotton suction fan, and opening them for 25-35 minutes;

[0018] S12, taking 10-12 parts of high molecular weight polyethylene fiber by weight, and conveying it to the entrance of the cotton mixer through a belt conveyor, and then conveying it into the cotton mixer through a cotton suction fan, and opening it together with the high-strength polypropylene fiber, and mixing it for 55-65 minutes;

[0019] S13, rolling the mixed fiber cotton out of the cotton mixer through a polygonal angle roller to form mixed fiber cotton; wherein the rotation speed of the polygonal angle roller is 180-220r / min, and the feeding speed of the mixed fiber cotton is 0.8-1.2m / min.

[0020] As a further solution of the present invention: in the step S2, the rotation speed of the carding machine is 750-850 r / min, the carding amount is 140-160 kg / min; the density of the mixed staple fiber is 18-22 g / m 2 .

[0021] As a further solution of the present invention: in the step S3, the stacking speed is 7 to 9 m / min, and the total number of stacked layers is 24 to 26 layers.

[0022] As a further solution of the present invention: in the S4 step, the frequency of the first pass is 350-450 times / min, the frequency of the second pass is 750-850 times / min, the frequency of the third pass is 950-1050 times / min, the frequency of the fourth pass is 1150-1250 times / min, and the frequency of the fifth pass is 1250-1350 times / min.

[0023] As a further solution of the present invention: in the step S5, the temperature of the upper roller is 100-120°C, the temperature of the middle roller is 220-240°C, and the temperature of the lower roller is 85-95°C; the calendering speed is 3.2-3.4 m / min, and the width of the filter cotton cloth after calendering is 2000-2200 mm, the thickness is 2.4-2.6 mm, and the density is 490-500 g / m 2 The width of the cut filter cotton cloth is 500-520mm and the length is 90-110m / roll.

[0024] As a further solution of the present invention: in the step S5, the frequency of the ultrasonic welding machine is 15KHZ, the power is 2.2-4.2KW, the welding time is 3-4s, and the welding pressure is 0.6-0.7MPa.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The filter bag prepared by the present invention is formed by welding filter cotton cloth, wherein the filter cotton cloth is prepared from high-strength polypropylene fiber, high-molecular polyethylene fiber and additives. The breaking tensile force at the welding point in the filter bag is large, the welding is firm and not easy to tear; the filter bag can be used to filter high-pressure and high-pollutant liquids, and the use cost is low. DETAILED DESCRIPTION

[0027] Example 1

[0028] In an embodiment of the present invention, an environmentally friendly filter bag and a preparation process are formed by welding filter cotton cloth, wherein the filter cotton cloth is prepared from high-strength polypropylene fiber with a thickness of 2.5D and a length of 51 mm, high-molecular polyethylene fiber with a thickness of 1.5D and a length of 30 mm, tin mercaptan, sodium bisulfite and alkyldiaminoethylglycine hydrochloride, wherein the mass ratio of high-strength polypropylene fiber, high-molecular polyethylene fiber, tin mercaptan, sodium bisulfite and alkyldiaminoethylglycine hydrochloride is 80:10:0.15:0.15:0.15.

[0029] A preparation process of an environmentally friendly filter bag comprises the following steps:

[0030] S1. Opening and mixing of raw materials:

[0031] S11, 80 parts by mass of high-strength polypropylene fibers with a thickness of 2.5D and a length of 51 mm are conveyed to the entrance of the cotton mixer by a belt conveyor, and then conveyed into the cotton mixer by a cotton suction fan, and opened for 25 minutes;

[0032] S12, taking 10 parts by mass of high molecular weight polyethylene fiber with a thickness of 1.5D and a length of 30 mm, and conveying them to the entrance of the cotton mixer through a belt conveyor, and then conveying them into the cotton mixer through a cotton suction fan, and opening them together with the high-strength polypropylene fiber, and mixing them for 55 minutes;

[0033] S13, feeding the mixed fiber cotton onto the polygonal angle roller at a speed of 0.8 m / min, and then rolling the mixed fiber cotton out of the cotton mixer through the polygonal angle roller at a speed of 180 r / min to form mixed fiber cotton;

[0034] S2. Combing of mixed fiber cotton: Take 0.15 parts of tin mercaptan, 0.15 parts of sodium bisulfite and 0.15 parts of alkyl diaminoethyl glycine hydrochloride by mass, add them to 100 parts of distilled water, stir evenly, and form a mixed solution for use; comb the mixed fiber cotton with a carding machine at a speed of 750r / min and a carding amount of 140kg / min, and during the carding process, the mixed solution is mixed to form a density of 18g / m 2 Mixed staple fibers;

[0035] S3, laying and pressing: according to the thickness requirement, the mixed short fibers are laid layer by layer in the mold at a speed of 7m / min for 24 layers, and then vibrated and compacted to form a cheesecloth;

[0036] S4. Acupuncture: The cheesecloth is needled at a frequency of 350 times / min for the first pass, 750 times / min for the second pass, 950 times / min for the third pass, 1150 times / min for the fourth pass, and 1250 times / min for the fifth pass, and the cheesecloth is repeatedly compacted and kneaded to make its structure uniform, and then the cheesecloth is tested to prevent broken needles from falling into the cheesecloth;

[0037] S5. Calendering cloth: raise the temperature of the upper roller of the three-roll calender to 100℃, the temperature of the middle roller to 220℃, and the temperature of the lower roller to 85℃; then calender the cotton cloth at a speed of 3.2m / min, so that the cotton cloth is pressed into a smooth surface on one side and a semi-smooth surface on the other side, with a width of 2000mm, a thickness of 2.4mm, and a density of 490g / m 2 The filter cotton cloth is cut into a width of 500mm and then wound at 90m / roll.

[0038] S6. Filter bag welding: After cutting the filter cloth into suitable sizes, use an ultrasonic welding machine with a frequency of 15KHZ and a power of 2.2KW to weld the filter cloth at a pressure of 0.6MPa for 4s, so that the upper end is open and the lower part is closed to form a filter bag.

[0039] Example 2

[0040] In an embodiment of the present invention, an environmentally friendly filter bag and a preparation process are formed by welding filter cotton cloth, wherein the filter cotton cloth is prepared from high-strength polypropylene fiber with a thickness of 3D and a length of 51 mm, high-molecular polyethylene fiber with a thickness of 1.5D and a length of 48 mm, tin mercaptan, sodium bisulfite and alkyldiaminoethylglycine hydrochloride, wherein the mass ratio of high-strength polypropylene fiber, high-molecular polyethylene fiber, tin mercaptan, sodium bisulfite and alkyldiaminoethylglycine hydrochloride is 90:11:0.17:0.17:0.17.

[0041] A preparation process of an environmentally friendly filter bag comprises the following steps:

[0042] S1. Opening and mixing of raw materials:

[0043] S11, 90 parts by mass of high-strength polypropylene fibers with a thickness of 3D and a length of 51 mm are conveyed to the entrance of the cotton mixer by a belt conveyor, and then conveyed into the cotton mixer by a cotton suction fan, and opened for 30 minutes;

[0044] S12, taking 11 parts of high molecular weight polyethylene fiber with a thickness of 1.5D and a length of 48 mm by weight, and conveying them to the entrance of the cotton mixer through a belt conveyor, and then conveying them into the cotton mixer through a cotton suction fan, and opening them together with the high-strength polypropylene fiber, and mixing them for 60 minutes;

[0045] S13, feeding the mixed fiber cotton onto the polygonal angle roller at a speed of 1 m / min, and then rolling the mixed fiber cotton out of the cotton mixer through the polygonal angle roller at a speed of 200 r / min to form mixed fiber cotton;

[0046] S2. Combing of mixed fiber cotton: Take 0.17 parts of tin mercaptide, 0.17 parts of sodium bisulfite and 0.17 parts of alkyl diaminoethyl glycine hydrochloride by mass, add them to 100 parts of distilled water, stir evenly, and form a mixed solution for use; comb the mixed fiber cotton with a carding machine at a speed of 800r / min and a carding amount of 150kg / min, and during the carding process, the mixed solution is mixed to form a density of 20g / m 2 Mixed staple fibers;

[0047] S3, laying and pressing: according to the thickness requirement, the mixed short fibers are laid layer by layer in the mold at a speed of 8m / min for 25 layers, and then vibrated and compacted to form a cheesecloth;

[0048] S4. Acupuncture: using a needle loom, the cheesecloth is needled at a frequency of 400 times / min for the first pass, 800 times / min for the second pass, 1000 times / min for the third pass, 1200 times / min for the fourth pass, and 1300 times / min for the fifth pass, and after repeated compaction and kneading to make the structure uniform, the cheesecloth is tested to prevent broken needles from falling into the cheesecloth;

[0049] S5. Calendering cloth: raise the temperature of the upper roller of the three-roll calender to 110℃, the middle roller to 230℃, and the lower roller to 90℃; then calender the cotton cloth at a speed of 3.3m / min, so that the cotton cloth is pressed into a smooth surface on one side and a semi-smooth surface on the other side, with a width of 2100mm, a thickness of 2.5mm, and a density of 495g / m 2 The filter cotton cloth is cut into a width of 512mm and then wound at a rate of 100m / roll.

[0050] S6. Filter bag welding: After cutting the filter cloth into suitable sizes, use an ultrasonic welding machine with a frequency of 15KHZ and a power of 3.2KW to weld the filter cloth at a pressure of 0.65MPa for 3.5s, so that the upper end is open and the lower part is closed to form a filter bag.

[0051] Example 3

[0052] In an embodiment of the present invention, an environmentally friendly filter bag and a preparation process are formed by welding filter cotton cloth, wherein the filter cotton cloth is prepared from high-strength polypropylene fiber with a thickness of 3D and a length of 75 mm, high-molecular polyethylene fiber with a thickness of 3D and a length of 48 mm, tin mercaptan, sodium bisulfite and alkyldiaminoethylglycine hydrochloride, wherein the mass ratio of high-strength polypropylene fiber, high-molecular polyethylene fiber, tin mercaptan, sodium bisulfite and alkyldiaminoethylglycine hydrochloride is 100:12:0.2:0.2:0.2.

[0053] A preparation process of an environmentally friendly filter bag comprises the following steps:

[0054] S1. Opening and mixing of raw materials:

[0055] S11, 100 parts by mass of high-strength polypropylene fibers with a thickness of 3D and a length of 75 mm are conveyed to the entrance of a cotton mixer by a belt conveyor, and then conveyed into the cotton mixer by a cotton suction fan, and opened for 35 minutes;

[0056] S12, taking 12 parts by mass of high molecular weight polyethylene fiber with a thickness of 3D and a length of 48 mm, and conveying them to the entrance of the cotton mixer through a belt conveyor, and then conveying them into the cotton mixer through a cotton suction fan, and opening them together with the high-strength polypropylene fiber, and mixing them for 65 minutes;

[0057] S13, feeding the mixed fiber cotton onto the polygonal angle roller at a speed of 1.2 m / min, and then rolling the mixed fiber cotton out of the cotton mixer through the polygonal angle roller at a speed of 220 r / min to form mixed fiber cotton;

[0058] S2. Combing of mixed fiber cotton: Take 0.2 parts of tin mercaptan, 0.2 parts of sodium bisulfite and 0.2 parts of alkyl diaminoethyl glycine hydrochloride by mass, add them to 100 parts of distilled water, stir evenly, and form a mixed solution for use; comb the mixed fiber cotton with a carding machine at a speed of 850r / min and a carding amount of 160kg / min, and during the carding process, the mixed solution is mixed to form a density of 22g / m 2 Mixed staple fibers;

[0059] S3, laying and pressing: according to the thickness requirement, the mixed short fibers are laid layer by layer in the mold at a speed of 9m / min for 26 layers, and then vibrated and compacted to form a cheesecloth;

[0060] S4. Acupuncture: The cheesecloth is needled at a frequency of 450 times / min for the first pass, 850 times / min for the second pass, 1050 times / min for the third pass, 1250 times / min for the fourth pass, and 1350 times / min for the fifth pass, and the cheesecloth is repeatedly compacted and kneaded to make the structure uniform, and then the cheesecloth is tested to prevent broken needles from falling into the cheesecloth;

[0061] S5. Calendering cloth: raise the temperature of the upper roller of the three-roll calender to 120℃, the middle roller to 240℃, and the lower roller to 95℃; then calender the cotton cloth at a speed of 3.4m / min, so that the cotton cloth is pressed into a smooth surface on one side and a semi-smooth surface on the other side, with a width of 2200mm, a thickness of 2.6mm, and a density of 500g / m 2 The filter cotton cloth is cut into a width of 520mm and then wound at a rate of 110m / roll.

[0062] S6. Filter bag welding: After cutting the filter cloth into suitable sizes, use an ultrasonic welding machine with a frequency of 15KHZ and a power of 4.2KW to weld the filter cloth at a pressure of 0.7MPa for 3s, so that the upper end is open and the lower part is closed to form a filter bag.

[0063] In order to better illustrate the technical effects of the present invention, the following embodiments are described:

[0064] The high molecular weight polyethylene fiber, tin mercaptan, sodium bisulfite and alkyl diaminoethyl glycine hydrochloride in Example 2 of the present invention are deleted; the remaining components and preparation process are the same as those in Example 2, as Comparative Example 1;

[0065] The breaking tensile forces at the welding points of the filter bags prepared in Example 1, Example 2, Example 3 and Comparative Example 1 were respectively measured and recorded in the following Table 1;

[0066] Table 1 Breaking Tensile Force Analysis

[0067]

[0068]

[0069] It can be concluded from Table 1 above that there is no significant difference in the breaking tensile force at the welding point of the filter bags in Example 1, Example 2 and Example 3; while the breaking tensile force at the welding point of the filter bag in Comparative Example 1 is significantly smaller than that in Example 1, Example 2 and Example 3; furthermore, it can be concluded that the breaking tensile force at the welding point of the filter bag prepared by the present invention is large, the welding is firm, and it is not easy to tear; the filter bag can be used to filter high-pressure and high-pollutant liquids.

[0070] What is described above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An environmentally friendly filter bag, characterized in that: The filter is formed by welding filter cotton cloth, wherein the filter cotton cloth is prepared from high-strength polypropylene fiber, high-molecular polyethylene fiber and additives, wherein the mass ratio of the high-strength polypropylene fiber, the high-molecular polyethylene fiber and the additive is (80-100): (10-12): (0.4-0.6).

2. The environmentally friendly filter bag according to claim 1, characterized in that: The additives are composed of a stabilizer, an antioxidant and an antistatic agent, and the mass ratio thereof is 1:1:1; wherein the stabilizer is one or more of an organic tin stabilizer, a barium zinc stabilizer, and a calcium zinc stabilizer; the antioxidant is one or more of an ascorbic acid antioxidant, a phenolic antioxidant, and a sulfite antioxidant; and the antistatic agent is one or two of a quaternary ammonium salt antistatic agent and an alkyl amino acid salt antistatic agent.

3. The environmentally friendly filter bag according to claim 1, characterized in that: The thickness of the high-strength polypropylene fiber is 2.5D-3.5D, and the length is 49-75mm; the thickness of the high-molecular polyethylene fiber is 1.5D-3D, and the length is 30-48mm.

4. A process for preparing an environmentally friendly filter bag according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, opening and mixing of raw materials: 80-100 parts by mass of high-strength polypropylene fibers and 10-12 parts by mass of high-molecular polyethylene fibers are respectively fed into a cotton blending machine for opening, and then mixed and rolled out to form mixed fiber cotton; S2. Combing mixed fiber cotton: Take 0.4-0.6 parts of additives by mass and add them to 100 parts of distilled water, stir evenly to form a mixed liquid for use; comb the mixed fiber cotton with a carding machine, and mix the liquid during the combing process to form mixed short fibers. S3. Laying and pressing: Lay the mixed staple fibers layer by layer in the mold according to the thickness requirements, and form a cheesecloth through vibration and compaction; S4, acupuncture: the cheesecloth is needled five times using a needle-punching machine, and after repeated compaction and kneading, its structure is uniform, and then the cheesecloth is tested to prevent broken needles from falling into the cheesecloth; S5. Calendering and rolling: Use a three-roll calender to calender and shape the raw cotton cloth, press the cotton cloth into a smooth surface on one side and a semi-smooth surface on the other side to form a filter cotton cloth, and then cut the filter cotton cloth and roll it up; S6. Filter bag welding: After the filter cotton cloth is cut into suitable sizes, it is welded by an ultrasonic welding machine so that the upper end is open and the lower part is closed to form a filter bag.

5. The process for preparing an environmentally friendly filter bag according to claim 4, characterized in that: In the step S1, the specific preparation method of the mixed fiber cotton is as follows: S11, taking 80-100 parts of high-strength polypropylene fibers by weight, and conveying them to the entrance of the cotton mixer through a belt conveyor, and then conveying them into the cotton mixer through a cotton suction fan, and opening them for 25-35 minutes; S12, taking 10-12 parts of high molecular weight polyethylene fiber by weight, and conveying it to the entrance of the cotton mixer through a belt conveyor, and then conveying it into the cotton mixer through a cotton suction fan, and opening it together with the high-strength polypropylene fiber, and mixing it for 55-65 minutes; S13, rolling the mixed fiber cotton out of the cotton mixer through a polygonal angle roller to form mixed fiber cotton; wherein the rotation speed of the polygonal angle roller is 180-220r / min, and the feeding speed of the mixed fiber cotton is 0.8-1.2m / min.

6. The process for preparing an environmentally friendly filter bag according to claim 4, characterized in that: In the step S2, the rotation speed of the carding machine is 750-850 r / min, the carding amount is 140-160 kg / min; the density of the mixed staple fibers is 18-22 g / m 2 .

7. The process for preparing an environmentally friendly filter bag according to claim 4, characterized in that: In the step S3, the stacking speed is 7 to 9 m / min, and the total number of stacked layers is 24 to 26 layers.

8. The process for preparing an environmentally friendly filter bag according to claim 4, characterized in that: In the step S4, the frequency of the first pass is 350-450 times / min, the frequency of the second pass is 750-850 times / min, the frequency of the third pass is 950-1050 times / min, the frequency of the fourth pass is 1150-1250 times / min, and the frequency of the fifth pass is 1250-1350 times / min.

9. The process for preparing an environmentally friendly filter bag according to claim 4, characterized in that: In the step S5, the temperature of the upper roller is 100-120°C, the temperature of the middle roller is 220-240°C, and the temperature of the lower roller is 85-95°C; the calendering speed is 3.2-3.4 m / min, and the width of the filter cotton cloth after calendering is 2000-2200 mm, the thickness is 2.4-2.6 mm, and the density is 490-500 g / m 2 The width of the cut filter cotton cloth is 500-520mm and the length is 90-110m / roll.

10. The process for preparing an environmentally friendly filter bag according to claim 4, characterized in that: In the step S5, the frequency of the ultrasonic welding machine is 15KHZ, the power is 2.2-4.2KW, the welding time is 3-4s, and the welding pressure is 0.6-0.7MPa.

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