RU2233720C2 - Seamless hot rolled tube manufacturing method - Google Patents

Abstract

FIELD: rolled tube production, namely processes for making seamless hot rolled mean and large diameter tubes, possibly in tube rolling plants with pilger mills.

SUBSTANCE: method comprises steps of heating blank-ingots, piercing them in helical 777rolling mill and rolling them in pilger mill at fixed feed value lowered from beginning to end of rolling process; rolling tubes in pilger mill at feed whose value is decreased from beginning of rolling process to its end depending upon elongation factor, wall thickness, tube diameter, rolling temperature, linear expansion coefficient of steel. Feed value is determined according to expression m=k*μ*S*D*α*t* where μ - elongation factor; D - diameter of tube, mm; S - wall thickness, mm; α - linear expansion coefficient of steel, 10^-6*/^oC; t - current temperature value of rolling process, C; k - coefficient equal to 0.038 1/mm for tubes with diameter 273-325 mm; 0.033 for tubes with diameter 351 mm; 0.03 - for tubes with diameter 377 mm and 0.026 - for tubes with diameter 426 mm.

EFFECT: lowered lengthwise wall thickness difference of tubes, enhanced operational reliability, improved effectiveness of mill.

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Description

The invention relates to pipe rolling production, and in particular to a method for the production of seamless hot-rolled pipes of medium and large diameters, and can be used in the production of them on pipe-rolling plants with pilgrim mills.

In pipe-rolling production, there is a known method for the production of seamless hot-rolled pipes of medium and large diameters in pipe-rolling plants with pilgrim mills, where the main deformation (work) is carried out on pilgrim mills (F.A. Danilov, A.Z. Gleiberg. VB Balakin, Hot pipe rolling. Moscow, 1962, p. 280). The main disadvantage of this method is the longitudinal difference in the pipes with an average fixed feed rate from the beginning of the steady-state process to the end due to the increase in pressure due to a decrease in the temperature of the sleeves. On pipe rolling plants with automatic mills, the average drawing coefficient for flashing is 4.0–4.5, and on an automatic mill, it usually does not exceed 2.0. On pipe rolling plants with pilgrim mills, the drawing coefficient on piercing mills is 1.9-2.1, and on pilgrim mills it reaches 15-16. Therefore, the sleeve after the piercing mill is thick-walled and of relatively short length (2.5-3.5 m). The pilgrim rolling cycle consists of seed, steady-state process and rolling of the pilgrim head. When rolling thin-walled pipes (lash length 35-42 m), the steady-state process is from 88.0 to 90% of the total rolling time, and when rolling thick-walled pipes from 80.0 to 84.0% (pipe length from 4.0 to 7.0 m). The value of the total metal pressure on the roll during rolling of one pipe (whip) varies significantly and depends on the irregularity of supply during the rolling process and the temperature drop of the sleeve by the end of rolling, because the machine time for rolling one pipe (whip) with a length of 36 m is from 4.2 to 5.5 minutes, depending on the diameter, wall thickness and steel grade. With an increase in the metal pressure on the rolls from the beginning of rolling to the end, the system (pilgrim stand, bearings, rolls, compression screws) experiences increasing loads, i.e. deformation of the cage and rolls occurs, clearances in the bearings and pressure screws are selected, and therefore, the size of the gauge increases from the beginning of the steady rolling process to the end and, as a result. the pipe wall thickness increases by an amount equal to half the increase in caliber size. The unevenness of the flow rate affects the pressure value to a greater extent. Cases of breakdowns of rolls and spindles due to excessive feeding accompanied by impacts are a frequent occurrence in the practice of pilgrim installations.

The closest technical solution is a method for the production of seamless hot-rolled pipes of medium and large diameters on tube-rolling plants with pilgrim mills, including heating billets (ingots), piercing them on a cross-screw rolling mill in thick-walled sleeves and rolling on a pilgrim mill in pipes with a fixed feed rate , decreasing from the beginning to the end of rolling as it cools (F.A. Danilov, A.Z. Gleiberg, V.G. Balakin. Hot rolling of pipes, Moscow, 1962, p. 304).

However, the known method has the following disadvantages. This method does not provide a qualitative and quantitative estimate of the decrease in the feed quantity of a portion of the sleeve metal to the roll center of the pilgrim mill, depending on the geometric dimensions of the sleeves, pipes, the linear expansion coefficient of the rolled metal and the decrease in the temperature of the sleeve during the rolling process. A decrease in the feed rate, only due to a decrease in the temperature of the sleeve, without taking into account the plastic (strength) characteristics of the metal and the geometric dimensions of the rolled profiles (pipes), can lead to exceeding the critical loads on the mill line (breakage of safety bolts, rolls and spindles) when rolling large pipes diameters with relatively thin walls and pipes made of alloyed hard to deform steel grades and alloys, as well as to an unreasonable decrease in the feed rate when rolling smaller pipe diameters with relatively thick walls made of carbon steel grades.

The aim of the proposed method is to reduce the longitudinal difference in the pipes, to prevent breakage of the safety bolts, rolls and spindles of the pilgrim mill when rolling pipes from alloyed hard to deform steel grades and alloys and thin-walled large-diameter pipes made of carbon steel grades due to incorrectly selected feed rates, as well as increasing mill productivity due to an unreasonable reduction in feed when rolling pipes of medium diameters from carbon steel grades.

This goal is achieved by the fact that in the known method for the production of seamless hot-rolled pipes, including heating the billets (ingots), piercing them on a cross-helical rolling mill and rolling on a pilgrim mill with a fixed feed rate, decreasing from the beginning to the end of rolling, rolling the pipes on a pilgrim the mill is produced with a feed, the value of which is reduced from the beginning of rolling to the end, depending on the drawing ratio, wall thickness, pipe diameter, rolling temperature, linear expansion coefficient st ali and determine from the expression

m = k · μ · S · D · α · t,

where μ is the drawing coefficient;

D - pipe diameter, mm;

S is the wall thickness, mm;

α is the coefficient of linear expansion of steel, 10 ^-6 · 1 / ° C;

t is the current value of the rolling temperature, ° C;

k - coefficient 0.0381 / mm for pipes with a diameter of 273-325 mm, 0.033 for pipes with a diameter of 351 mm, 0.03 for pipes with a diameter of 377 mm and 0.026 for pipes with a diameter of 426 mm.

Using this expression to determine the feed rate of the sleeve into the deformation zone of the pilgrim mill, which takes into account the geometric dimensions of the rolled profile (pipe) with the coefficients k, μ, S and D, the metal properties by the linear expansion coefficient α, and the current value of the rolling temperature - t, we can determine the maximum value at the start of rolling m _max and the minimum at the end m _min , and then carry out the rolling process in manual mode with values gradually decreasing from m _max to m _min, or in automatic mode if there is a device, fi coding feed rate. Using this method of production of seamless hot-rolled pipes will make it possible to exclude the possibility of breakage of the rolls and spindles of the pilgrim mill due to the rolling process at optimal feed rates from the beginning to the end of rolling, to improve the quality of pipes by geometric dimensions (wall thickness) due to rolling with optimal feed values and, accordingly, increase the performance of the pilgrim installation. A comparative analysis of the proposed solution with the prototype shows that the claimed method differs from the known one in that the pipes are rolled on a pilgrim mill with a feed, the value of which is reduced from the beginning of rolling to the end depending on the drawing ratio, wall thickness, pipe diameter, rolling temperature, coefficient linear expansion of steel and determined from the expression

m = k · μ · S · D · α · t,

where μ is the drawing coefficient;

D - pipe diameter, mm;

S is the wall thickness, mm;

α is the coefficient of linear expansion, 10 ^-6 · 1 ° C,

t is the current value of the rolling temperature, ° C;

k - coefficient 0.0381 / mm for pipes with a diameter of 273-325 mm, 0.33 for pipes with a diameter of 351 mm, 0.03 for pipes with a diameter of 377 mm and 0.026 for pipes with a diameter of 426 mm. Thus, the claimed method meets the criteria of the invention of "novelty."

Comparison of the proposed solution (method) not only with the prototype, but also with other technical solutions in the art did not allow them to identify signs that distinguish the claimed solution from the prototype, which allows us to conclude that the criterion of "significant differences".

The method has been tested and implemented on a pipe-rolling installation with pilgrim mills 8-16 of ChTPZ OJSC. Comparative rolling of 325 × 8 and 426 × 9 mm pipes from 20 steel ingots of 470-500 × 1700 and 540-585 × 1700 mm was carried out (thin-walled pipes according to GOST 8732-78) and pipes 325 × 30 and 426 × 40 mm in size from forged drilled steel billets of grade 15X1M1F 500 × 100 × 1750 and 600 × 100 × 1750 mm in size (thick-walled boiler tubes according to TU 14-3- 460-75).

40 ingots with a diameter of 14 "(470-500 mm), 40 ingots with a diameter of 16" (540-585 mm) of steel of the grade 20, 40 billets with a diameter of 550 and 40 billets with a diameter of 600 mm of steel of the grade 15X1M1F were set in production. Half of the ingots and billets were rolled into pipes of 325 × 8, 426 × 9, 325 × 30 and 426 × 40 mm in size using the existing technology, and the second half — according to the proposed method, with the determination of the maximum and minimum feed rates by the proposed formula and with a gradual decrease the feed rate by the roller in manual mode.

Data on the results of rolling and delivery of pipes of 325 × 8, 426 × 9 in accordance with GOST 8732 and 325 × 30, 426 × 40 mm according to TU 13-3-460-75 are given in the table. The table shows that the average length of pipes (lashes) of 325 × 8 mm in size, rolled according to the existing technology, was 40.2 m, which were cut into four pipes (krata). The average pipe length at delivery was 35.7 m: of which the first three pipes were put on the wall of 8 mm with a positive tolerance, and the fourth pipes with an average length of 8.8 m were put on the wall of 9 mm. The average weight of the pipes was 2.302 tons, and the expenditure coefficient of the metal was 1.265. The average length of pipes (lashes) measuring 325 × 8 mm at the rental, rolled according to the proposed technology, was 42.3 m, and at delivery 36.9 m. All pipes were put on the wall 8.0 mm. The average weight of pipes at delivery was 2.308 tons, and the expenditure coefficient of the metal was 1.260. A similar picture was obtained when rolling pipes with a size of 426 × 9 mm. The expenditure coefficient of the metal for pipes rolled according to the existing technology amounted to 1.271, and according to the proposed method - 1.264. The average length of pipes 325 × 30 mm in size, rolled according to the existing technology, at the rental was 11.84, at delivery - 10.89 m, and the expenditure coefficient of the metal was 1.245. The average length of pipes of 325 × 30 mm in size, rolled by the proposed method, is 11.5 at the rental, 10.97 at delivery, and the metal expenditure coefficient is 1.236. A similar picture was obtained when rolling pipes with a size of 426 × 40 mm. The expenditure coefficient of the metal pipes rolled by the existing technology amounted to 1.264, and according to the proposed method - 1.251. Thin-walled pipes according to GOST 8732, rolled according to the existing technology, had a longitudinal difference, as a result of which the third pipe edges 325 × 8 mm in size were put on an 8 mm wall with a positive tolerance field, and the last (fourth edges) on a 9.0 mm wall . A similar picture when rolling pipes with a size of 426 × 9 mm. The second krat (pipes) surrendered with a positive tolerance field, and the third krat on the wall - 10 mm. The delivery of pipes to the wall of 9 and 10 mm is not custom-made products that go to the warehouse and wait for new customers. According to the proposed method for the production of pipes in accordance with GOST 8732, a decrease in the expenditure coefficient of the metal from 5.0 to 7.0 kg per ton was obtained, depending on the assortment. A similar picture is observed when rolling thick-walled pipes according to TU 14-3-460. Since the margin of tolerance for the wall on the pipes of this assortment is + 20 / -5%, they were delivered to the wall of 30 and 40 mm in theoretical weight, but when rolling the pipes according to the existing method, the average wall along the length of the pipe is slightly higher, because pipes rolled by the proposed method, obtained longer by thinning the wall under the pilgrim head, which allowed to reduce the expenditure coefficient of the metal, respectively, by 9 and 13 kg.

Thus, the table shows that when rolling thin-walled pipes according to GOST 8732 according to the proposed method, a reduction in the expenditure coefficient of the metal from 5 to 7 kg was obtained, the production of a non-custom part of the pipes was excluded, i.e. pipe rental to the warehouse. When rolling thick-walled pipes of 325 × 30 mm and 426 × 40 mm in size according to TU 14-3-460 according to the existing technology, the metal expenditure coefficient was 2.245 and 1.264, and according to the proposed method, 1.236 and 1.251, respectively, i.e. a decrease from 9 to 11 kg per ton was obtained due to thinning of the wall under the pilgrim head and an increase in the average length of pipes by 8 mm.

Using the proposed method for the production of seamless hot-rolled pipes of medium and large diameters in tube rolling plants with pilgrim mills will reduce metal consumption in the production of thin-walled pipes according to GOST 8732 and thick-walled pipes according to TU by reducing the longitudinal difference, i.e. increase the average wall thickness from the beginning to the end of rolling, significantly reduce or completely eliminate the non-custom part when rolling thin-walled pipes by transferring the last lash pipes to thicker walls, eliminate the breakage of safety bolts, rolls and spindles of the pilgrim mill when rolling pipes from alloyed hard to deform steel grades and alloys and thin-walled large-diameter pipes made of carbon steel grades due to excess loads from incorrectly selected feed rates, increase productivity mill because of the unreasonable decrease in the feed when rolling pipes of medium diameter from carbon steel grades, and therefore, reduce the cost of pipes.

Claims (1)

A method for the production of seamless hot-rolled pipes, including heating ingot billets, piercing them on a cross-helical rolling mill and rolling on a pilgrim mill with a fixed feed rate, decreasing from the beginning to the end of rolling, characterized in that the tubes are rolled on the pilgrim mill the value of which is reduced from the beginning of rolling to the end, depending on the drawing ratio, wall thickness, pipe diameter, rolling temperature, coefficient of linear expansion of steel and is determined from the expression m = k · μ · S · D · α · t, where μ is the drawing coefficient; D is the diameter of the pipes, mm; S is the wall thickness, mm; α is the coefficient of linear expansion of steel, 10 ^-6 · 1 / ° С; t is the current value of the rolling temperature, ° C; k is a coefficient of 0.0381 / mm for pipes with a diameter of 273-325 mm, 0.033 for pipes with a diameter of 351 mm, 0.03 for pipes with a diameter of 377 mm and 0.026 for pipes with a diameter of 426 mm.