JP6287713B2 - Lubricating composition for hot pipe making - Google Patents

Description

  The present invention relates to a lubricating composition, and more particularly to a lubricating composition for hot pipe making.

  In a seamless steel pipe manufactured by the Mannesmann method, after a piercing and rolling by a piercing machine, a drawing and rolling by a mandrel mill is performed.

  In the drawing and rolling by the mandrel mill, first, a mandrel bar is inserted into the hollow shell. Next, stretch rolling is performed on the hollow shell in which the mandrel bar is inserted. After stretching and rolling, the mandrel bar is pulled out from the hollow shell.

  During drawing and rolling, the hollow shell is drawn in the rolling direction. At this time, the roll peripheral speed of the mandrel mill is different from the moving speed of the mandrel bar in the rolling direction. Therefore, the surface of the mandrel bar slides against the inner surface of the hollow shell, and friction is generated. If the friction coefficient becomes excessively large, seizure occurs or wrinkles occur on the inner surface of the hollow shell. If the friction coefficient becomes excessively large, uniform deformation of the hollow shell is further inhibited. Therefore, the mandrel bar during drawing and rolling is required to have lubricity with respect to the hollow shell.

  On the other hand, the mandrel bar after drawing and rolling is pulled out from the hollow shell. This extraction operation is called burst ripping. If the friction coefficient is excessively large even during burst ripping, the mandrel bar is difficult to pull out. Therefore, the mandrel bar is required to have not only the lubricity during stretch rolling but also the lubricity during burst ripping.

  In order to improve the lubricity of the mandrel bar as described above, a lubricating composition is used. Lubricating compositions applied to mandrel bars have been proposed as follows.

  The lubricating composition for hot working disclosed in Japanese Patent No. 2910592 (Patent Document 1) has an average particle size of 40 μm or less and a purity of 81% or more of 5-35 parts by weight of graphite and an average particle size of 40 μm or less. 5 to 20 parts by weight of a water-dispersed polymer or water-soluble polymer, 3 to 15 parts by weight of boric acid having a purity of 81% or more, 3 mica having an average particle diameter of 40 μm or less and a purity of 81% or more -35% by weight and 15-86 parts by weight of water (see paragraphs [0015] and [0016] of Patent Document 1). Patent Document 1 describes that the lubricating composition can reduce a coefficient of friction generated during stretching by a mandrel mill and can effectively prevent fusion between a tool and a workpiece (see paragraph [0044]). ).

  The lubricant composition for high temperature processing disclosed in JP-A-9-78080 (Patent Document 2) is composed of potassium tetrasilicon mica, sodium tetrasilicon mica, natural gold mica, bentonite, montmorillonite, and vermiculite. One or more particulate oxide layered materials selected from the group consisting of boron oxide, boric acid, alkali metal borates, sodium carbonate, potassium carbonate, and sodium silicate having a melting point of 1000 ° C. or lower; One or two or more binders selected from the group consisting of potassium silicate are blended at a weight ratio of 1: 4 to 1: 1 (see paragraph [0013] of Patent Document 2). Since the lubricating composition does not contain graphite, it is described that a carburized layer is not formed on the rolled steel material, and no scratches are generated (see paragraph [0039]).

Japanese Patent No. 2910592 JP-A-9-78080

  However, Patent Documents 1 and 2 describe the lubricity (coefficient of friction) during stretching and rolling, but do not mention the lubricity during burst ripping. In the lubricating compositions of Patent Documents 1 and 2, the lubricity during burst ripping may be low.

  An object of the present invention is to provide a lubricating composition for hot pipe making that exhibits excellent lubricity during stretching and burst ripping.

The lubricating composition for hot pipe making according to the present embodiment contains mica, graphite, boric acid, and water, F1 defined by the formula (1) is 30 to 80% by mass, and the formula (2 F2 defined by) is 40 to 60%.
F1 = [mica] / ([mica] + [graphite]) (1)
F2 = [Boric acid] / ([Mica] + [Graphite] + [Boric acid]) (2)
Here, the mica content (mass%) in the lubricating composition is substituted for [mica] in the formulas (1) and (2). In [Graphite], the content (mass%) of graphite in the lubricating composition is substituted. [Boric acid] is substituted with the content (% by mass) of boric acid in the lubricating composition.

  The lubricating composition according to the present embodiment is excellent in lubricity at the time of stretch rolling and also excellent in lubricity at the time of burst ripping.

FIG. 1 is a diagram showing the relationship between F1 and the coefficient of friction μ1 obtained in the simulated stretch rolling test. FIG. 2 is a schematic diagram of a simulated stretch rolling test. FIG. 3 is a diagram showing the relationship between F1 and the friction coefficient μ2 obtained in the simulated burst ripping test. FIG. 4 is a schematic diagram of a simulated burst ripping test. FIG. 5 is a diagram showing the relationship between F2 and the friction coefficient μ2. FIG. 6 is a diagram showing the relationship between F2 and the friction coefficient μ1.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Lubricating composition]
The lubricating composition of the present embodiment is used for hot pipe making, and in particular, for drawing and rolling using a mandrel mill equipped with a mandrel bar. The lubricating composition is applied to the surface of the mandrel bar before drawing and rolling. The lubricating composition contains mica, graphite, boric acid, and water.

[Mica]
At the start of stretching and rolling, the temperature of the hollow shell is as high as about 1100 to 1250 ° C. A mandrel bar is inserted into such a high-temperature hollow shell, and drawing and rolling are started. For this reason, excellent lubricity is required during stretch rolling in such a high temperature range.

  Mica reacts with boric acid, which will be described later, to form a lubricating coating during the drawing and rolling performed in the high temperature range. By forming a lubricating coating on the surface of the mandrel bar, the coefficient of friction of the mandrel bar in drawing and rolling is reduced and the lubricity is improved.

Mica is a pulverized product of silicate mineral containing Al, K, Mg, Na, Fe and the like. The mica may be natural mica (natural mica) or artificial mica. Examples of mica include potassium tetrasilicon mica {KMg _2.5 (Si ₄ O ₁₀ ) F ₂ }, sodium tetrasilicon mica {NaMg ₂ .5 (Si ₄ O ₁₀ ) F ₂ }, natural gold mica {KMg ₃ (AlSi ₃ O). ₁₀ ) (OH) ₂ } and the like. The lubricating composition may contain two or more mica.

  The minimum with preferable mica content in a lubricating composition is 4.5 mass%, More preferably, it is 6 mass%. The upper limit with preferable mica content in a lubricating composition is 12 mass%, More preferably, it is 9 mass%.

[graphite]
As described above, since the hollow shell temperature in the drawing and rolling is high (about 1100 to 1250 ° C.), the mandrel bar is required to have lubricity in a high temperature range. On the other hand, the hollow shell temperature at the start of burst ripping after drawing and rolling is low, about 500 to 650 ° C. Even during burst ripping, the mandrel bar requires lubricity. That is, the lubricating composition is required to have lubricity in a high temperature range of about 1100 to 1250 ° C. and lubricity in a low temperature range of about 500 to 650 ° C.

  Graphite improves lubricity in a low temperature range and makes it easy to pull out the mandrel bar from the hollow shell during burst ripping. The graphite may be natural graphite or synthetic graphite. The preferable average particle diameter of graphite is 100 μm or less. The lubricating composition may contain two or more types of graphite.

  The minimum with preferable graphite content in a lubricating composition is 3 mass%, More preferably, it is 6 mass%. The upper limit with preferable graphite content in a lubricating composition is 10.5 mass%, More preferably, it is 9 mass%.

[boric acid]
In this specification, boric acid means boric acid and / or a boric acid compound. Boric acid reacts with mica at the time of drawing and rolling to form a lubricating film, and improves the lubricity at the time of drawing and rolling. The boric acid compound is, for example, an inorganic compound containing an alkali metal borate, boron oxide, or boron. Examples of the alkali metal borate include potassium borate, sodium borate, and lithium borate. Inorganic compounds containing boron are, for example, amine borate. The lubricating composition may contain two or more boric acids.

  A preferable lower limit of the boric acid content in the lubricating composition is 10% by mass. The upper limit with preferable boric acid content in a lubricating composition is 22 mass%.

[water]
Water is mixed with mica, graphite, and borate to form a slurry. When the lubricating composition contains water, the lubricating composition becomes a slurry. Therefore, it is easy to apply the lubricating composition uniformly on the surface of the mandrel bar before drawing and rolling.

  The minimum with preferable water content in a lubricating composition is 63 mass%, More preferably, it is 66 mass%. The upper limit with preferable water content in a lubricating composition is 75 mass%, More preferably, it is 73 mass%.

[About F1 and F2]
In the lubricating composition of the present embodiment, F1 defined by the formula (1) is 30 to 80% by mass, and F2 defined by the formula (2) is 40 to 60% by mass.
F1 = [mica] / ([mica] + [graphite]) (1)
F2 = [Boric acid] / ([Mica] + [Graphite] + [Boric acid]) (2)
[Mica] is substituted with the content (mass%) of mica in the lubricating composition. In [Graphite], the content (mass%) of graphite in the lubricating composition is substituted. [Boric acid] is substituted with the boric acid content (% by mass) in the lubricating composition. That is, when the “boric acid” contained in the lubricating composition is boric acid in a narrow sense (that is, when boric acid itself is used as a raw material), the content of boric acid is substituted. When “boric acid compound” is used as a raw material of the lubricating composition, the content of the boric acid compound is substituted for [boric acid] in F2.

  When F1 is 30 to 80% by mass and F2 is 40 to 60% by mass, the lubricating composition exhibits excellent lubricity during stretch rolling and burst ripping. Hereinafter, this point will be described.

[About F1]
[Lower limit of F1]
FIG. 1 shows the relationship between F1 and the coefficient of friction μ1 during stretch rolling. FIG. 1 was obtained by the following simulated stretch rolling test.

  A plurality of lubricating compositions differing in F1 shown in the examples described later were prepared. F2 of each lubricating composition was 52% by mass. A simulated stretch rolling test shown in FIG. 2 was performed on each lubricating composition.

  With reference to FIG. 2, the simulated stretching and rolling test apparatus 10 includes a roll 11 and a plate-shaped tool material 14. A steel plate 12 assuming a hollow shell was prepared. The chemical composition of the steel plate 12 corresponded to SUS304 defined in JIS G4304 (2012). The chemical composition of the tool material 14 corresponded to SKD61 defined in JIS G4404 (2006).

  The lubricating composition 13 was applied to the upper surface of the tool material 14. The average film thickness of the applied lubricating composition 13 was 50 μm. A steel plate 12 heated to 1100 ° C. in a nitrogen atmosphere was placed on the upper surface of the tool material 14 to which the lubricating composition 13 was applied. Further, the roll 11 was pressed against the steel plate 12 with a load P1, and rolling was performed at a reduction rate of 30%.

  During actual stretching and rolling, the roll peripheral speed V1 of the mandrel mill is different from the moving speed V2 of the mandrel bar in the rolling direction. Friction occurs between the hollow shell and the mandrel bar due to the difference between the peripheral speed V1 and the speed V2.

  Therefore, in the simulated stretching rolling test, the peripheral speed V1 of the roll 11 was set to 78.5 mm / s, and the moving speed V2 of the tool material 14 in the rolling direction was set to 40 mm / s. V2 / V1 was 0.51. Before rolling, the tool material 14 was scaled to form a scale on the surface of the tool material 14. The temperature of the tool material 14 during rolling was 400 ° C.

The steel plate 12 was rolled under the above conditions, and the coefficient of friction μ1 during stretch rolling when each lubricating composition was used was determined by the following equation.
Friction coefficient μ1 = Friction force F applied to the tool material 14 / Load P1 for pressing the roll 11 against the steel plate 12

  In actual stretching and rolling, a mandrel bar once coated with the lubricating composition is used for stretching and rolling a plurality of times. Therefore, in this test, for each lubricating composition, the simulated stretching and rolling test was performed twice on the tool material 14 after applying the lubricating composition, and the first (first pass) and the second (second pass). ) Was determined. Based on the test results obtained, FIG. 1 was created.

  “♦” in FIG. 1 indicates the friction coefficient μ1 in the first pass. “◇” indicates the friction coefficient μ1 in the second pass. In actual stretching and rolling, it is preferable that excellent lubricity is obtained even after performing multi-pass stretching and rolling. Therefore, in this test, the lubricity was evaluated by the friction coefficient μ1 in the second pass.

  Referring to FIG. 1, when F1 is less than 30% by mass, friction coefficient μ1 is large and exceeds 0.11. Therefore, in this case, the lubricity in actual stretching and rolling is low, and seizure is likely to occur. When F1 is 30% by mass or more, the friction coefficient μ1 is as small as 0.11 or less. Therefore, the lubricating composition exhibits excellent lubricity during stretching and can suppress the occurrence of seizure. Therefore, the lower limit of F1 is 30% by mass.

[About the upper limit of F1]
FIG. 3 is a diagram showing the relationship between F1 and the friction coefficient μ2 at the start of burst ripping. FIG. 3 was obtained by the following simulated burst ripping test.

  A plurality of lubricating compositions identical to those in the simulated stretch rolling test described above were prepared. F2 of each lubricating composition was 52% by mass. A simulated burst ripping test shown in FIG. 4 was performed on each lubricating composition.

  Referring to FIG. 4, the simulated burst ripping test apparatus 20 includes a ring-shaped tool material 21 simulating a mandrel bar and a heating coil 23. The heating coil 23 was disposed around a cylindrical steel material 22 simulating a hollow shell.

  The chemical composition of the tool material 21 corresponded to SKD61 defined in JIS G4404 (2006). The tool material 21 had a diameter of 60 mm, a wall thickness of 20 mm, and a height (length) of 30 mm. The chemical composition of the steel material 22 corresponded to SUS304 defined in JIS G4304 (2012). The diameter of the steel material 22 was 50 mm, and the height (length) was 60 mm.

  The lubricating composition 24 was applied to the lower end surface of the tool material 21 and dried. The film thickness of the lubricating composition after drying was 250 to 300 μm.

  The steel material 22 was heated to 1200 ° C. by the heating coil 23. After the heating, the lower end surface of the tool material 21 on which the lubricating composition 24 was formed was pressed against the upper end surface of the steel material 22 with a load P2 = 800 kgf, and held as it was for 10 seconds. Thereafter, the steel material 22 was rotated around the axis at 100 rpm for 1 minute while the tool material 21 was pressed against the steel material 22 with the load P2. During the rotation, the temperature of the steel material 22 was maintained at 1200 ° C. (first step).

  After completion of the rotation, heating was stopped, and the steel material 22 was allowed to cool to 600 ° C. After the steel material 22 reached 600 ° C., the steel material 22 was rotated again around the axis at 100 rpm for 1 minute while the tool material 21 was pressed against the steel material 22 with a load P2 = 800 kgf (second step).

In the above test, the first step simulates the “stretching and rolling step”, and the second step simulates the “burst ripping step” after the drawing and rolling. During the second step, the pressing load P2 applied to the tool material 21 and the torque T applied to the steel material 22 were measured. In the case of burst ripping, the friction coefficient is highest at the start of burst ripping (that is, immediately after the start of sliding). Therefore, the load P2 and torque T at the start of the second step (immediately after the start of sliding) were measured, and the friction coefficient μ2 at the start of the second step was determined based on the following equation.
Friction coefficient μ2 = (T / d) / P
Here, d is the torque arm length. The friction coefficient μ2 obtained by the above method corresponds to the friction coefficient at the start of burst ripping. FIG. 3 was prepared based on the friction coefficient μ2 obtained in the above test.

  Referring to FIG. 3, if the friction coefficient μ2 is 0.5 or less, the mandrel bar can be easily pulled out in burst ripping. Referring to FIG. 3, when F1 exceeds 80 mass%, friction coefficient μ2 exceeds 0.5. Since the ratio of graphite to mica decreases, it is considered that the lubricity in a low temperature range where burst ripping is performed is lowered. From FIG. 3, when F1 is 80% by mass or less, excellent lubricity is exhibited even during burst ripping.

  As mentioned above, if F1 is 30-80 mass%, a lubricating composition will show the outstanding lubricity at the time of extending | stretching rolling, and can suppress seizure even if it uses a mandrel bar for several times of extending | stretching rolling. Furthermore, it exhibits excellent lubricity even during burst ripping.

  A preferred lower limit of F1 is 40% by mass. A preferable upper limit of F1 is 60% by mass.

[About F2]
FIG. 5 is a diagram showing the relationship between F2 and the friction coefficient μ2 at the start of burst ripping. FIG. 5 was obtained by the following test method.

  A plurality of lubricating compositions having different F2 values shown in the examples described later were prepared. F1 of each lubricating composition was 33% by mass. The above-mentioned simulated burst ripping test was performed on each lubricating composition to obtain a friction coefficient μ2. FIG. 5 was created based on the obtained friction coefficient μ2.

  Referring to FIG. 5, regardless of the value of F2, friction coefficient μ2 is 0.5 or less. That is, the lubricity during burst ripping does not depend on the proportion of boric acid content in the lubricating composition.

  On the other hand, the lubricity (friction coefficient μ1) during drawing and rolling depends on the proportion of boric acid content in the lubricating composition. FIG. 6 is a diagram showing the relationship between F2 and the friction coefficient μ1 during stretching. FIG. 6 was obtained by the following method. As in the case of FIG. 5, a plurality of lubricating compositions having different F2 were prepared. F1 of each lubricating composition was 33% by mass. The above-described simulated stretching and rolling test was performed on each lubricating composition to obtain a friction coefficient μ1. FIG. 6 was created based on the obtained friction coefficient μ1.

  In FIG. 6, “♦” indicates the friction coefficient of the first pass, and “◇” indicates the friction coefficient of the second pass. Referring to FIG. 6, the friction coefficient μ1 in the second pass markedly decreased with an increase in F2, and became 0.11 or less when F2 was 40% by mass or more. On the other hand, when F2 further increased, the friction coefficient μ1 increased, and when it exceeded 60 mass%, it exceeded 0.11. That is, in FIG. 6, the relationship between F2 and the friction coefficient μ1 is a downwardly convex graph having an inflection point in the vicinity of F2 = 50 mass%.

  From the above results, the following matters can be considered. If F2 is too low, the boric acid content in the lubricating composition is too low. In this case, since mica and boric acid cannot sufficiently react during the drawing and rolling, the amount of the lubricating coating produced by the reaction is insufficient. Therefore, the friction coefficient μ1 is increased, and the lubricity during the drawing and rolling is decreased. On the other hand, when F2 is too high, the boric acid content in the lubricating composition is too high. In this case, although a lubricating coating is formed, the viscosity of the lubricating composition is low because of too much boric acid. Therefore, the lubricating composition is not easily held by the mandrel bar, and is easily dropped off from the mandrel bar. As a result, the friction coefficient μ1 is increased, and the lubricity during stretching is reduced.

  When F2 is 40 to 60% by mass, the lubricating coating is sufficiently formed, and the viscosity of the lubricating composition does not become excessively low. Therefore, the friction coefficient μ1 at the time of drawing and rolling is low, and excellent lubricity is exhibited.

[Others]
The lubricating composition of this embodiment may contain other compounds along with mica, graphite, boric acid, and water. The lubricating composition may contain, for example, a known dispersant. The lubricating composition may also contain an adhesive. If an adhesive is contained, the adhesive force with the surface of a mandrel bar will increase. The pressure-sensitive adhesive is, for example, an organic binder, for example, an alkaline resin.

[How to use the lubricating composition]
An example of a method for using the above lubricating composition will be described. First, a lubricating composition is prepared. Apply the lubricating composition to the surface of the mandrel bar. The application method is not particularly limited. For example, the lubricating composition is applied by spraying. After application, the lubricating composition is dried. The dried mandrel bar is used for drawing and rolling.

  Through the above steps, the lubricating composition can be used for stretching rolling using a mandrel bar.

  Lubricating compositions with test numbers 1 to 18 having the components shown in Table 1 were prepared.

  The above-described simulated stretch rolling test was performed on the lubricating compositions of Test Nos. 1-18. In the simulated stretching and rolling test, the test was carried out twice consecutively assuming that the mandrel bar was used continuously in the first pass and the second pass. The friction coefficient μ1 was determined for each time (first pass, second pass). Furthermore, the above-described simulated burst ripping test was performed on the lubricating compositions of Test Nos. 1-18.

[Test results]
Table 1 shows the test results. Referring to Table 1, the components of the lubricating compositions of Test Nos. 1 to 7 were appropriate, and both F1 and F2 were appropriate. As a result, the friction coefficients μ2 of Test Nos. 1 to 7 were all 0.5 or less, indicating excellent lubricity during burst ripping. Furthermore, the friction coefficients μ1 in the second pass of Test Nos. 1 to 7 were all 0.11 or less, and showed excellent lubricity during stretch rolling.

  On the other hand, F1 of test number 8 was too low. Therefore, the friction coefficient μ1 in the second pass exceeded 0.11, and the lubricity during stretching was low.

  F2 of test number 9 and test number 10 was too low. Therefore, the friction coefficient μ1 in the second pass exceeded 0.11, and the lubricity during stretching was low.

  F2 of test number 11 and test number 12 was too high. Therefore, the friction coefficient μ1 in the second pass exceeded 0.11, and the lubricity during stretching was low.

  F1 of test number 13 and test number 14 was too low. Therefore, the friction coefficient μ1 in the second pass exceeded 0.11, and the lubricity during stretching was low.

  F1 of test numbers 15-17 was too high. Therefore, the friction coefficient μ2 exceeded 0.5, and the lubricity during burst ripping was low.

  Both F1 and F2 of test number 18 were too low. Therefore, the friction coefficient μ1 in the second pass exceeded 0.11, and the lubricity during stretching was low.

The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

Claims (1)

A lubricating composition for hot pipe making,
With mica,
Graphite,
Boric acid,
Containing water,
Lubricating composition whose F1 defined by Formula (1) is 30-80 mass%, and F2 defined by Formula (2) is 40-56 mass %.
F1 = [mica] / ([mica] + [graphite]) (1)
F2 = [Boric acid] / ([Mica] + [Graphite] + [Boric acid]) (2)
Here, the content in mass% of the mica in the lubricating composition is substituted for [mica] in the formula (1) and / or the formula (2). [Graphite] is substituted with the content in mass% of the graphite in the lubricating composition. [Boric acid] is substituted with the boric acid content in mass% of the lubricating composition.

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