Preparation method of high-strength cold-rolled titanium strip coil for coiled tubing

Abstract

The invention relates to the technical field of titanium strip coils, in particular to a preparation method of a high-strength cold-rolled titanium strip coil for coiled tubing, which comprises the following steps: S1, cold rolling: a hot-rolled pickled coil with the thickness of 5.5-6.5 mm is subjected to cold rolling by adopting 20 rollers, and the hot-rolled pickled coil comprises the following components in percentage by mass: 0.26-0.33% of Fe, 0.27-0.33% of O and the balance of Ti; s2, degreasing is conducted, specifically, the titanium strip coil obtained after cold rolling is subjected to degreasing treatment; s3, annealing is conducted, specifically, a vertical bell-type furnace is filled with argon for protection for annealing treatment, furnace cooling is conducted after annealing is completed, and a titanium strip coil with the thickness being 3-4.5 mm for the coiled tubing is obtained; a cold rolling mode is adopted, the thickness of the titanium strip coil is rolled to 3.0-4.5 mm, a bell-type furnace annealing mode is adopted, an oxide layer is prevented from being generated on the surface, the bending performance of the titanium strip is enhanced, cracks are prevented from being formed on the surface during pipe manufacturing, the compressive strength, the yield strength and the ductility of the product are high, and the bending angle (6T) is large.

Description

Technical Field

[0001] The invention relates to the technical field of titanium strip coils, and in particular to a method for preparing a high-strength cold-rolled titanium strip coil for a continuous oil pipe. Background Art

[0002] Titanium materials have the advantages of high specific strength and strong corrosion resistance. When used in continuous oil pipes, they can improve the corrosion resistance of the oil pipes and reduce the weight of the oil pipes themselves. They have incomparable advantages over alloy steel and nickel-based alloys. Titanium materials with low cost, easy forming, moderate strength, high oxygen content and high iron content have become the preferred materials for continuous oil pipes. At present, the high-oxygen and high-iron industrial pure titanium materials used in continuous oil pipes are mainly produced in the form of titanium strip coils. According to the requirements of continuous oil pipes, the thickness of the titanium strip coils is between 2 and 6 mm, and titanium strip coils above 3 mm are produced by hot rolling.

[0003] Titanium strip coils with a thickness of more than 3mm are usually produced by hot rolling and continuous annealing processes. The oxide layer formed on the hot-rolled surface is removed by shot peening and pickling. Since the material itself has high strength and low plasticity, shot peening will form a hardened layer on its surface, resulting in microcracks on the surface during the tube bending process. In severe cases, it will cause the welded pipe to crack. In addition, the stress layer formed by shot peening will cause an additional stress layer on the surface of the continuous tube, affecting the fatigue performance of the continuous tube.

[0004] In order to solve the above problems, the present invention designs a method for preparing a high-strength cold-rolled titanium strip coil for continuous oil pipe. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a high-strength cold-rolled titanium strip coil for a continuous oil pipe.

[0006] A method for preparing a high-strength cold-rolled titanium strip coil for a coiled oil pipe comprises the following steps:

[0007] S1. Cold rolling:

[0008] A hot-rolled pickled coil with a thickness of 5.5 to 6.5 mm is cold-rolled by 20 rollers for 3 to 8 passes, and the total deformation of the cold rolling is 30 to 55%, so as to obtain a cold-rolled titanium strip coil; wherein the hot-rolled pickled coil comprises, by mass percentage, 0.26 to 0.33% of Fe, 0.27 to 0.33% of O, and the balance of Ti;

[0009] S2, degreasing:

[0010] Degreasing the cold-rolled titanium coil to obtain a degreased titanium coil;

[0011] S3, Annealing:

[0012] The degreased titanium strip coil is annealed in a vertical bell furnace filled with argon for protection, with an annealing temperature of 630-660°C, a heating time of 6-8h, and a holding time of 12-15h. The titanium strip coil is cooled to 60-100°C with the furnace and then taken out of the furnace to obtain a titanium strip coil with a thickness of 3-4.5mm for continuous oil pipe.

[0013] Furthermore, in step S1, the deformation amount of the first pass of the cold rolling is 10-15%, and the deformation amount of the remaining passes is 5-10%.

[0014] Note: By performing a large deformation in the first pass, a large rolling deformation can be achieved, which improves production efficiency. At the same time, the surface roughness of the hot-rolled pickled coil of the parent coil is relatively large. The large deformation in the first pass is conducive to quickly reducing the surface roughness and avoiding uneven roughness and color difference caused by small deformation.

[0015] Furthermore, in step S1, the rolling parameters are adjusted according to the thickness difference between the entrance thickness and the exit thickness of each cold rolling pass, and the rolling parameter adjustment method is as follows:

[0016] When the thickness difference reaches more than 10%, the rotation rate of the rolling roller is 640-680 rpm, and the rolling rate is adjusted to 140-150 m / min;

[0017] When the thickness difference is 10% or less, the rotation rate of the rolling roller is 540-600 rpm, and the rolling rate is adjusted to 120-130 m / min;

[0018] After the cold rolling deformation reaches 90-95% of the total deformation, the rotation rate of the rolling roller is adjusted to 360-450 rpm and the rolling rate is adjusted to 80-100 m / min.

[0019] Note: The raw material used for the first rolling is the titanium strip coil after hot rolling, annealing and pickling. After online continuous annealing, the plate shape is better, which is conducive to cold rolling deformation. Therefore, at the beginning of cold rolling, the thickness difference is large, and the rotation rate and rolling rate of the rolling rollers used are large. However, with the cold rolling deformation, the thickness difference gradually decreases, and the plate shape of the titanium strip coil deteriorates. Reducing the rolling speed is conducive to plate shape regulation. At the same time, due to the high strength of the material, the high rolling pressure, and the large amount of heat generated, reducing the rolling speed is conducive to reducing the rolling deformation heat; after the deformation amount tends to the total deformation amount, the rolling speed is further reduced to further reduce the rolling deformation heat and regulate the plate shape.

[0020] Furthermore, in step S1, during cold rolling, the front and rear tensions are adjusted as follows: the tension of the first pass is controlled at 200-250 MPa, the tension of the second pass is controlled at 250-300 MPa, and the tension of the remaining passes is controlled at 300-350 MPa.

[0021] Note: In order to ensure smooth rolling, increasing the front and rear tensions is beneficial to reducing the rolling deformation force and avoiding excessive strength of the rolled material, which may cause the equipment to overload. During the first rolling, the material has a low strength after annealing, and the tension used is 30-40% of the material yield strength. With the rolling deformation, the material is hardened, the yield strength increases, and the front and rear tensions are increased accordingly. At the same time, since the material deformation at the roller outlet is greater than the deformation at the entrance, the front tension is 20-50MPa higher than the rear tension.

[0022] Furthermore, in step S2, the degreasing method is: passing the cold-rolled titanium coil through a degreasing tank filled with degreasing liquid, the temperature of the degreasing liquid is 50-75°C, the online degreasing operation speed is 20-30m / min, and then the degreasing liquid attached to the titanium coil is cleaned with clean water, and the surface is dried with 100-120°C hot air.

[0023] Description: Use degreasing liquid to remove residual rolling oil and titanium powder on the surface of the titanium coil to prevent the titanium coil from reacting during the subsequent annealing process and affecting the performance of the titanium coil itself.

[0024] Compared with the existing titanium strip coil preparation method, the beneficial effects of the present invention are:

[0025] (1) The present invention uses a cold rolling method to roll the hot-rolled pickled coil obtained by hot rolling pickling to a thickness of 3.0 to 4.5 mm, and then uses a bell furnace annealing method after degreasing to avoid the formation of an oxide layer on the surface, thereby removing the hardened layer formed on the surface of the titanium strip during shot peening during hot rolling pickling, thereby enhancing the bending performance of the titanium strip, avoiding the formation of cracks on the surface during pipe making, and improving the forming performance and bending fatigue performance of the welded pipe.

[0026] (2) The thickness of the titanium strip coil prepared by the present invention is 3 to 4.5 mm, which belongs to the thickness range with relatively high rolling difficulty. The total cold rolling deformation is controlled at more than 30%. The cold rolling deformation evenly breaks the grains in the material to ensure the uniformity of the rolling deformation structure, thereby playing a role in refining the grains, which is beneficial to improving the strength and plasticity of the final product. The titanium strip coil used in the present invention has high oxygen and iron content, high material strength and poor plasticity. The maximum rolling deformation is controlled below 55%, avoiding the risk of breaking the strip during the rolling process caused by excessive rolling deformation. Compared with the general pure titanium strength of about 400MPa, the compressive strength of the material of the present invention can reach 700MPa, and the yield strength is greater than 580MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a comparison chart of the tensile strength results of the present invention's exploration 1;

[0028] Figure 2 It is a comparison chart of the elongation results of the present invention's exploration 1;

[0029] Figure 3 It is a comparison diagram of the bending angle results of the present invention's exploration 1;

[0030] Figure 4 It is a comparison chart of the tensile strength results of the present invention's exploration 2;

[0031] Figure 5 It is a comparison chart of the elongation results of the present invention's exploration 2;

[0032] Figure 6 It is a comparison diagram of the bending angle results of the present invention's exploration 2;

[0033] Figure 7 It is a comparison chart of the tensile strength results of the present invention's exploration 3;

[0034] Figure 8 It is a comparison chart of the elongation results of the present invention's exploration 3;

[0035] Fig. 9 It is a comparison diagram of the bending angle results of the present invention's exploration 3;

[0036] Fig.10 It is a comparison chart of the flatness results of the present invention's exploration 4. DETAILED DESCRIPTION

[0037] In order to further illustrate the method and effect of the present invention, the technical solution of the present invention will be clearly and completely described in combination with experiments.

[0038] Embodiment 1: A method for preparing a high-strength cold-rolled titanium strip coil for a coiled oil pipe, comprising the following steps:

[0039] S1. Cold rolling:

[0040] A hot-rolled pickled coil with a thickness of 6.0 mm and a width of 1240 mm is cold-rolled by 20 rollers for 4 passes, with a total deformation of 33% during cold rolling, a rotation rate of 500 rpm, and a rolling rate of 120 m / min, to obtain a titanium strip coil with a thickness of 4.0 mm after cold rolling; the deformation of the first pass is 12%, and the deformations of the second to fourth passes are 10%, 8%, and 8%, respectively; wherein the constituent elements of the hot-rolled pickled coil, by mass percentage, include: 0.31% Fe, 0.29% O, a total content of other impurities of 0.15% and the balance of Ti;

[0041] The tension after rolling of the first pass is controlled at 225MPa, the tension after rolling of the second pass is controlled at 275MPa, and the tension after rolling of the remaining passes is controlled at 325MPa, and the tension before rolling of each pass is 35MPa greater than the tension after rolling; the tension is controlled by the tension system of the coiler installed before and after the rolling mill, the tension before rolling is the tension applied by the coiler installed before the rolling mill to the hot-rolled pickled coil before entering the rolling mill, and the tension after rolling is the tension applied by the coiler installed after the rolling mill to the hot-rolled pickled coil after entering the rolling mill;

[0042] S2, degreasing:

[0043] The cold-rolled titanium coil is degreased to obtain a degreased titanium coil; the degreasing method is as follows: the degreasing tank is filled with a degreasing liquid, the temperature of the degreasing liquid is 62° C., the online degreasing speed is 25 m / min, the degreasing liquid attached to the titanium coil is cleaned with clean water, and the surface is dried with 110° C. hot air; the degreasing liquid can be a GS-503 degreasing agent;

[0044] S3, Annealing:

[0045] The degreased titanium strip coil was annealed in a vertical bell furnace under argon protection, with an annealing temperature of 645°C, a heating time of 7h, and a holding time of 13.5h. The titanium strip coil was cooled to 80°C with the furnace and then taken out of the furnace to obtain a titanium strip coil with a thickness of 4mm for continuous oil pipe.

[0046] Example 2: This example is different from Example 1 in that the thickness of the titanium strip roll is 3 mm.

[0047] Example 3: This example is different from Example 1 in that the thickness of the titanium strip roll is 4.5 mm.

[0048] Embodiment 4: This embodiment is different from Embodiment 1 in that the constituent elements of the titanium strip coil, by mass percentage, include: 0.26% Fe, 0.33% O and the remainder Ti.

[0049] Embodiment 5: This embodiment is different from Embodiment 1 in that the constituent elements of the titanium strip coil, by mass percentage, include: 0.33% Fe, 0.27% O and the remainder Ti.

[0050] Example 6: This example is different from Example 1 in that three cold rolling passes are performed, and the total deformation of the cold rolling is 30%, the deformation of the first cold rolling pass is 10%, and the deformation of the remaining passes is 10%.

[0051] Example 7: This example is different from Example 1 in that the cold rolling is performed 8 times, the total deformation of the cold rolling is 55%, the deformation of the first cold rolling pass is 15%, and the deformation of the remaining passes is 5%.

[0052] Example 8: The difference between this example and Example 1 is that the cold-rolled titanium coil is passed through a degreasing tank filled with degreasing liquid, the temperature of the degreasing liquid is 50°C, the online degreasing operation speed is 20m / min, and then the degreasing liquid attached to the titanium coil is cleaned with clean water, and the surface is dried with 100°C hot air.

[0053] Example 9: The difference between this example and Example 1 is that the cold-rolled titanium coil is passed through a degreasing tank filled with degreasing liquid, the temperature of the degreasing liquid is 75°C, the online degreasing operation speed is 30m / min, and then the degreasing liquid attached to the titanium coil is cleaned with clean water, and the surface is dried with 120°C hot air.

[0054] Example 10: This example is different from Example 1 in that the annealing temperature is 630°C, the heating time is 6h, the holding time is 12h, and the titanium strip coil is cooled to 100°C after the holding is completed and then taken out of the furnace.

[0055] Example 11: This example is different from Example 1 in that the annealing temperature is 660°C, the heating time is 8h, the holding time is 15h, and the titanium strip coil is cooled to 60°C after the holding is completed before being taken out of the furnace.

[0056] Embodiment 12: This embodiment differs from Embodiment 1 in that the rolling parameters are adjusted according to the thickness difference between the entrance thickness and the exit thickness of each cold rolling pass. The rolling parameter adjustment method is as follows:

[0057] When the thickness difference reaches more than 10%, the rotation rate of the rolling roller is 660 rpm, and the rolling rate is adjusted to 145 m / min;

[0058] When the thickness difference is 10% or less, the rotation rate of the rolling roller is 570 rpm, and the rolling rate is adjusted to 125 m / min; (It can be understood that the thickness difference of 10% means that the ratio of the inlet thickness to the outlet thickness reaches 10%)

[0059] After the cold rolling deformation reaches 93% of the total deformation, the rotation rate of the rolling roller is adjusted to 405 rpm and the rolling rate is adjusted to 90 m / min.

[0060] Example 13: This example differs from Example 12 in that, when the thickness difference reaches more than 10%, the rotation rate of the rolling roller is 640 rpm, and the rolling rate is adjusted to 140 m / min.

[0061] Example 14: This example differs from Example 12 in that, when the thickness difference reaches more than 10%, the rotation rate of the rolling roller is 680 rpm, and the rolling rate is adjusted to 150 m / min.

[0062] Example 15: This example differs from Example 12 in that, when the thickness difference is 10% or less, the rotation rate of the rolling roller is 540 rpm, and the rolling rate is adjusted to 120 m / min.

[0063] Example 16: This example differs from Example 12 in that, when the thickness difference is 10% or less, the rotation rate of the rolling roller is 600 rpm, and the rolling rate is adjusted to 130 m / min.

[0064] Example 17: The difference between this example and Example 12 is that, until the deformation amount of cold rolling reaches 90% of the total deformation amount, the rotation speed of the rolling roller is adjusted to 360 rpm and the rolling speed is adjusted to 80 m / min.

[0065] Example 18: The difference between this example and Example 12 is that, until the deformation amount of cold rolling reaches 95% of the total deformation amount, the rotation speed of the rolling roller is adjusted to 450 rpm and the rolling speed is adjusted to 100 m / min.

[0066] Example 19: This example is different from Example 1 in that the tension after rolling of the first pass is controlled at 200 MPa, the tension after rolling of the second pass is controlled at 300 MPa, and the tension after rolling of the remaining passes is controlled at 300 MPa.

[0067] Example 20: This example is different from Example 1 in that the tension after rolling of the first pass is controlled at 250 MPa, the tension after rolling of the second pass is controlled at 250 MPa, and the tension after rolling of the remaining passes is controlled at 350 MPa.

[0068] Example 21: This example differs from Example 1 in that the tension before each rolling pass is 20 MPa greater than the tension after rolling.

[0069] Example 22: This example differs from Example 1 in that the tension before each rolling pass is 50 MPa greater than the tension after rolling.

[0070] Experimental Example: The description of this experimental example is based on the scheme described in Example 1, and is intended to illustrate the practical application effect of the present invention.

[0071] The head and tail of the titanium strip coil after annealing in Example 1 were sampled respectively to test the strength, elongation and bending angle in the vertical direction of rolling. The test results are shown in Table 1 below. The yield strength meets R p0.2≥580MPa, bending angle meets the requirement of α≥105°.

[0072] Table 1 Performance parameters of each section of the titanium strip coil in Example 1

[0073]

[0074] According to the diameter of the coiled tubing of Ф50.8mm, the titanium strip coil is slit on the slitting machine, with a slitting width of 159.5 and a width tolerance of ±0.2mm. The surface of the strips is smooth and meets the requirements for the use of coiled tubing.

[0075] Table 2 Performance parameters of titanium strip coils obtained by hot-rolling pickled coils and continuing hot rolling to 4 mm

[0076]

[0077] It can be seen from the results in Table 2 that the performance parameters of the titanium coil obtained by hot rolling are lower than those of the titanium coil obtained by cold rolling in this method, and the bending angle and tensile strength are significantly lower than those in Example 1. Therefore, the performance of the titanium coil obtained by cold rolling in this application is significantly better than that of hot rolling.

[0078] Table 3 Effect of iron oxide content on the performance of titanium strip

[0079]

[0080] It can be seen from the results in Table 3 that the elongation of the low-iron and low-oxygen and low-iron and high-oxygen titanium strip coils is improved compared to the high-iron and high-oxygen titanium strip coils of the present application, but the strength is significantly reduced. High iron and high oxygen will cause the material to have high strength, poor plasticity, difficulty in cold rolling, difficulty in deformation, and easy strip breakage. Therefore, the present invention overcomes the difficulties brought about by high iron and high oxygen and improves its comprehensive performance.

[0081] 1. Explore the effects of the target thickness of the titanium strip and the proportion of its components on its performance.

[0082] Depend on Figures 1 to 3 The results show that, compared with Examples 1 to 5, if the thickness of the titanium strip is too thin or too thick, or the iron content in the composition elements is too high, the plasticity and toughness of the alloy may be reduced. Similarly, although oxygen has a significant strengthening effect, excessive oxygen will increase the brittleness of the titanium alloy and affect its overall performance, which will reduce the tensile strength, elongation and bending angle of the titanium strip.

[0083] 2. Investigate the influence of cold rolling and annealing parameters on the performance of titanium strip.

[0084] Depend on Figures 4 to 6The results show that, compared with Examples 1, 6 to 11, rolling parameters that are too small or too large, the difference in deformation between passes that is too small or too large, and annealing parameters that are too small will reduce the tensile strength, elongation and bending angle of the titanium strip coil. The degreasing treatment parameters have little effect on the performance of the titanium strip coil. The performance of the titanium strip coil in Example 11 is better than that in Example 1, but the required annealing parameters are larger and the performance improvement is smaller. Therefore, from an economic point of view, the parameter effect of Example 1 is relatively better; among them, since the temperature of the degreasing treatment has a smaller effect, no data comparison is performed.

[0085] 3. Investigate the effect of adjusting the rolling rate by the thickness difference of each pass on the performance of titanium strip during cold rolling.

[0086] The difference between the comparative example 1 and the example 12 is that as the deformation amount increases, the rotation rate of the rolling roller and the rolling rate increase;

[0087] The difference between the comparative example 2 and the example 12 is that the rolling parameters when the thickness difference is above 10% and when it is below 10% are opposite;

[0088] Depend on Figures 7 to 9 The results show that, compared with Examples 1, 12 to 18 and Control Examples 1 to 2, Control Examples 1 to 2 changed the adjustment rules and significantly reduced the performance improvement of Example 1 compared with Examples 12 to 18. Therefore, the rolling rate adjustment method of the present invention has certain advantages in improving the performance of titanium strip coils.

[0089] Compared with Examples 12 to 18, when the thickness difference reaches more than 10%, the rolling parameters are too small or too large; when the thickness difference is 10% or less, the rolling parameters are too small or too large, and after the rolling deformation reaches the total deformation, the rolling parameters are too small or too large, which will reduce the performance improvement of the titanium strip coil. Therefore, in comprehensive comparison, the parameter effect of Example 12 is relatively better.

[0090] 4. Investigate the effect of adjusting the rolling tension of each pass on the performance of titanium strip during cold rolling.

[0091] The difference between Comparative Example 3 and Example 1 is that the rolling tension of each pass remains unchanged;

[0092] Depend on Fig.10The results show that, compared with Examples 1, 19 to 22 and Control Example 3, Control Example 3 has no change in tension after rolling, and significantly reduces the flatness performance compared with Examples 19 to 22. Therefore, the rolling tension adjustment method of the present invention has certain advantages in improving the surface quality of titanium strip coils; and the surface of the strip coil with poor flatness is prone to scratches, pits and other problems, which will affect the appearance quality of the strip coil and further affect its application effect; the strip coil with poor straightness is prone to stress concentration during processing and use, thereby affecting its mechanical properties, such as tensile strength, yield strength, etc.

[0093] Compared with Examples 1 and 19 to 22, if the rolling tension is adjusted too small or too large, the straightness of the titanium strip coil will be relatively worse. Therefore, in comprehensive comparison, the parameter effect of Example 1 is relatively better.

Claims

1. A method for preparing a high-strength cold-rolled titanium strip coil for a coiled oil pipe, characterized in that: The following steps are involved: S1. Cold rolling: A hot-rolled pickled coil with a thickness of 5.5 to 6.5 mm is cold-rolled by 20 rollers for 3 to 8 passes, and the total deformation of the cold rolling is 30 to 55%, so as to obtain a cold-rolled titanium strip coil; wherein the hot-rolled pickled coil comprises, by mass percentage, 0.26 to 0.33% of Fe, 0.27 to 0.33% of O, and the balance of Ti; S2, degreasing: Degreasing the cold-rolled titanium coil to obtain a degreased titanium coil; S3, Annealing: The degreased titanium strip coil is annealed in a vertical bell furnace filled with argon for protection, with an annealing temperature of 630-660°C, a heating time of 6-8h, and a holding time of 12-15h. The titanium strip coil is cooled to 60-100°C with the furnace and then taken out of the furnace to obtain a titanium strip coil with a thickness of 3-4.5mm for continuous oil pipe.

2. The method for preparing a high-strength cold-rolled titanium strip coil for a coiled oil pipe according to claim 1, characterized in that: In step S1, the deformation amount of the first pass of the cold rolling is 10-15%, and the deformation amount of the remaining passes is 5-10%.

3. The method for preparing a high-strength cold-rolled titanium strip coil for a coiled oil pipe according to claim 1, characterized in that: In step S1, the rolling parameters are adjusted according to the thickness difference between the entrance thickness and the exit thickness of each cold rolling pass. The rolling parameter adjustment method is as follows: When the thickness difference reaches more than 10%, the rotation rate of the rolling roller is 640-680 rpm, and the rolling rate is adjusted to 140-150 m / min; When the thickness difference is 10% or less, the rotation rate of the rolling roller is 540-600 rpm, and the rolling rate is adjusted to 120-130 m / min; After the cold rolling deformation reaches 90-95% of the total deformation, the rotation rate of the rolling roller is adjusted to 360-450 rpm and the rolling rate is adjusted to 80-100 m / min.

4. The method for preparing a high-strength cold-rolled titanium strip coil for a coiled oil pipe according to claim 1, characterized in that: The tension after rolling of the first pass is controlled at 200-250MPa, the tension after rolling of the second pass is controlled at 250-300MPa, and the tension after rolling of the remaining passes is controlled at 300-350MPa, and the tension before rolling of each pass is 20-50MPa greater than the tension after rolling.

5. The method for preparing a high-strength cold-rolled titanium strip coil for a coiled oil pipe according to claim 1, characterized in that: In step S1, the degreasing method is: the cold-rolled titanium coil is passed through a degreasing tank filled with degreasing liquid, the temperature of the degreasing liquid is 50-75°C, the online degreasing operation speed is 20-30m / min, and then the degreasing liquid attached to the titanium coil is cleaned with clean water, and the surface is dried with 100-120°C hot air.

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