# Method for making mandrels of pilger mills

FIELD: rolled tube production, namely method for making pilger mill mandrels from heat resistant steel for rolling hot rolled tubes.

SUBSTANCE: method for making mandrels used for rolling hot rolled tubes with large and mean diameters in range 273-550mm comprises steps of casting ingots of hear resistant steel; forging cylindrical solid or hollow blanks, roughly working of them, performing heat treatment and finishing mandrels at forming conicity 1 - 2 mm on length of their working portion while taking into account designed linear expansion coefficient during rolling process; determining diameter size by means of expression δ = dn - Δ/1 + α·t. One portion of mandrel from lock along length of half of working portion of mandrel is in the form of cone with diameters of cone bases determined form given expression and second portion is in the form of cylinder or truncated cone whose diameters are determined according to next expression

EFFECT: lowered lengthwise thickness difference of tubes.

3 cl, 1 dwg, 1 tbl

The invention relates to pipe production, namely the method of manufacture of mandrels piligrimage mills of heat-resistant steel for rolling hot-rolled pipes of large and medium diameters (273-550) mm

A known method of manufacture of mandrels piligrimage mills for rolling hot-rolled pipes of large and medium diameters, including the casting of ingots of heat-resistant steel (50HN or HF), forging them into a cylindrical solid or hollow billet (forgings) size 280-570×6000 mm with ukonom 2,25-2,5, rough machining with allowance on a diameter of 10-15 mm taking into account leashes forgings during heat treatment, heat treatment domowych blanks, machining of dies on the finishing size of the taper in one to two millimeters on the working part with the subsequent rolling or grinding surface and commissioned them to failure on the grid razgonnyj cracks, longitudinal cracks, and "wave" (Faganello, Ashlaring, Wegmarken. Hot rolling pipe, Metallurgizdat, Moscow, 1962, s-305.

The disadvantage of this method is that the average diameter of the mandrels piligrimage mills determine the temperature conditions, taking into account their uniform heating to a temperature of ≈500°C during the rolling process, and the linear expansion by the formula

where d_{n}in the morning the diameter of the pipes after piligrimage mill,
mm;

α - the coefficient of linear expansion, 10^{-6}1/°C;

t∂ - the temperature of the mandrel at the end of the rolling, °C.

Taking t∂≈500°s and α=12,5*10^{-6}*1/°get δJS=0,994 d_{n}. When taper mandrels 1-2 mm have

δD.Z.=δJS+(0,5-1,0) mm;

δD.P.=δds.-(0,5-1,0) mm,

where δD.Z. the diameter of the rear end of the mandrel (with side locking parts), mm;

δD.P. - diameter front end of the mandrel (from seed), mm.

This method of manufacture of mandrels does not account for the difference (gap) between the inner diameter of the pipes after piligrimage mill and the diameter of the mandrels formed by rolling them in rolls with tangential issues, resulting in the internal diameter of the pipes in the deformation zone is larger than the diameter of the mandrel. Gap Δ depends on the geometrical dimensions of calibers piligrimage rolls, i.e. the diameters of rolled tubes and the angle of the transverse release piligrimage rolls. With increasing diameters of the rolls (pipe) and the angle of the transverse release of the gap between the mandrel and the inner diameter of the pipe increases, due to which the pipe is freely get away with Dorn.

Main parameters determining the quality of the pipes are raznesennost and accuracy of the outer diameter. The question of the accuracy of the pipe outside diameter is solved by calibrating the mill, and the different is cinnosti pipes after piligrimage mill to fix nothing. When configuring piligrimage mill for rolling pipe with a nominal wall thickness of tapered mandrels on the front ends of the tubes are observed thickening of the walls towards the middle part, reaching 0.85 mm or more, due to lower temperature of the front end of the mandrel and its taper, i.e. smaller diameter of the mandrel relative to the δds. (0,25-0,5) mm plus half the difference between the diameters due to the difference in their temperatures. The existing method assumed that the mandrel during the rolling process is heated evenly along the length to a temperature of ≈500°C. However, due to increased lengths of pipes (lashes) on piligrimages mill with 25 to 35 to 40 meters, increases the contact time of the mandrels with hot shells-pipes, and, consequently, increases the temperature of the mandrels by the end of the rolling 600-650°S, depending on pipe sizes and steel grades. On the other hand, the working part of the mandrel is 5.0 to 5.5 meters, and the deformation (flattening) of the liner into the pipe starts at a distance of about 1,500 to 1,700 mm from the front end of the mandrel and depends on the way the rollback of the feeding apparatus, which, in turn, depends on the diameter of rolled pipes, i.e. katysheva radius of the rolls. With the increase in diameter of the rolls path rollback pickup apparatus increases. Therefore, the front sections of the mandrels are not in the zone of deformation of the metal rollers, and are dissipated in the contact zone with their pipes. Therefore, these sections of the mandrels are heated to lower temperatures. In other words the temperature interval of dies increases from the front end toward the middle, and then decreases towards the tail end. The drawing shows the temperature along the length of the working part of the mandrels with a diameter of 409/410 mm after cooling in the bath with the lubricant (1) and after rolling pipe size s×32000 mm (3). From the drawing it is seen that the temperature of the mandrel along the length of the as-rolled pipes ranges from 350 to 600°C. After entering chilled mandrel to a temperature of 150-200°in a sleeve, which has a temperature of ≈1150°With that comes heat, and therefore, thermal expansion. The absolute value of the expansion reaches the large diameters of the mandrels during rolling of thin-walled tubes, i.e. depends on the time of rolling (time of contact of the mandrel with hot sleeve-pipe).

The closest technical solution is the method of manufacture of mandrels taking into account thermal expansion of the mandrels before and after rolling (Ugoma, Ibibo, Ascarelli, Dec. Technological processes, equipment and information management systems used by the firm Mannesmann-Demag, Germany, during rolling of pipes on units with piligrimage mills (Ferrous metallurgy, Bulletin of the scientific and technical information No. 10, S. 15-31, Moscow, 1987, and Guidera, Galesburg, Chicleros technologies and devices for the method of hot polerowanie. Report on the Symposium of the firm "Mannesmann-Demag", 1986, Moscow).

The temperature of the mandrel to rolling (after cooling) and after rolling (after removing the mandrel from the pipe) is ≈, 250°C. After entering chilled mandrel to a temperature of ≈200°in a sleeve, which has a temperature of ≈1150°With, is its thermal expansion. The absolute value of the expansion reaches a significant value on the large diameters of the mandrels during rolling of thin-walled tubes. For example, the diameters of the mandrels 409/410 mm by rolling pipe size 426×9×32000 mm thermal expansion in the Central part is 2,04 mm In the rolling process the temperature of the liner is reduced from 1150 to 950°With heat generated by deformation of the metal. In this regard, the increasing pressure of the metal on the rolls that must be taken into consideration when designing stands for the system, jacking screws - pillows - piligrimage rolls, had the lowest deformation, i.e. greater rigidity, which would not change the size of the caliber of the rolls.

The disadvantage of this method is that the average diameter of the mandrels is also determined from the temperature conditions of rolling with the increase of temperature during the rolling process on the ≈250°With evenly along the length of the working part. As can be seen from the drawing, the actual temperature in the Central working part d is rnow after rolling pipe size HH mm up to 600° Or more, and the temperature along the length of the working part ranges from 350 to 600°C. the Lowest temperature of the mandrel for rolling tubes of this size have side domowego lock (rear end), the highest temperature in the middle part, i.e. in the zone of maximum duration of deformation over time. When calculating the average diameters of the mandrels to take the temperature 250°With, as recommended by the authors, we will get the average diameters of the conical mandrels smaller during rolling which will receive the thickened ends of the pipes from the seed and when decade piligrimage heads, and this will lead to significant longitudinal varying wall thickness of the pipe. The drawing shows the actual average change of temperature intervals along the length of the working part of the conical mandrel diameter 4098/410 mm by rolling pipe size 426×9×32000 mm, i.e. when the length of deformation (time rolling one pipe) from 5.0 to 6.0 minutes. If to calculate the diameter of the working part of the mandrels to take the temperature of the mandrels after cooling or even heating along the length of the mandrels on S°it will increase the calculated wall thickness and increase the longitudinal varying wall thickness, and if the calculations diameters to take the temperature of the mandrels after rolling tubes, i.e. the maximum value, it will lead to thinning of the wall thickness in the middle part of the TRU is.

The purpose of the proposed method is the reduction of the longitudinal varying wall thickness of the pipe, and hence increase their accuracy on the wall.

This objective is achieved in that in the known method of manufacture of mandrels piligrimage mills for rolling hot-rolled pipes of large and medium diameters, including the casting of ingots of heat-resistant steel, the forging of a cylindrical solid or hollow workpieces, rough machining, heat treatment, machining of dies on the finishing size of the taper in one to two millimeters of the length of the working part and exploitation to education grid razgonnyj cracks, machining of dies on the finishing size is produced taking into account the estimated coefficient of linear expansion in the rolling process, and the sizes of the diameters determined from the expression

where d_{n}- internal diameter of pipe after piligrimage mill, mm;

Δ - the difference between the internal diameters of the pipes after piligrimage mill and the diameters of the mandrels by rolling in the rolls with tangential issues, mm;

α - the coefficient of linear expansion of steel, 10^{-}6*1/°C;

t∂_{}- the estimated temperature of the mandrels along the length of the rolling process, °C.

Dorn from castles, to the length of one second working parts are made con is red, the diameters of the bases which determine from the above expression, and the second part cylindrical or with a reverse taper, the diameter of which is determined from the expression

where D is the outer diameter of the pipe after piligrimage mill, mm;

S - wall thickness of pipe, mm;

A=0.5 to the minimum value of the inverted cone mandrel, mm;

K=0,07 - coefficient taking into account the geometrical dimensions of rolled pipes.

The inventive method of manufacture of mandrels piligrimage mills, namely a method of calibrating them by working length, taking into account the estimated coefficient of linear expansion, forms of caliber rolls (gaps between the internal diameters of the tubes and mandrels) and the geometric dimensions of the pipe (L/S)was significantly lower longitudinal raznesennost. Comparative analysis of the proposed solutions with the prototype shows that the inventive method differs from the known fact that the machining of dies on the finishing size is produced taking into account the estimated coefficient of linear expansion in the rolling process, and the sizes of the diameters determined from the expression

where d_{n}- internal diameter of pipe after piligrimage mill, mm;

Δ - the difference between the internal diameters of the pipes after piligrimage mill and the diameters of the mandrels through the rolling walkah with tangential issues, mm;

α - the coefficient of linear expansion of steel, 10^{-6}*1/°C;

t∂ - the estimated temperature of the mandrels along the length of the rolling process, °C.

Dorn from castles, to the length of one second working parts are made conical, the diameter of the bases which determine from the above expression, and the second part cylindrical or with a reverse taper, the diameter of which is determined from the expression

where D is the outer diameter of the pipe after piligrimage mill, mm;

S - wall thickness of pipe, mm;

A=0.5 to the minimum value of the inverted cone mandrel, mm;

K=0,07 - coefficient taking into account the geometrical dimensions of rolled pipes. Thus, the claimed method meets the criteria of the invention of "novelty."

The comparison of the proposed solutions (way), not only the prototype, but also with other technical solutions in this field of technology is not allowed to reveal in them the features distinguishing the claimed solution to the prototype that allows to conclude that the criterion of "substantial differences".

The method was tested on pipe installation piligrimage mills 8-16 "JSC "Chelyabinsk tube rolling plant". Was made and set in the production of a new mandrel diameter 361/362 for rolling pipe size 377×9 mm, an existing method with the taper on the working side of 1.0 mm, p is antigenome method with a taper on one half of the working part from domowego castle 1.0 mm and a cylindrical second part (361,5/360,5/360,5), the proposed method with a taper on one of the second working section 1.0 mm from domowego castle and reverse cone 1.0 mm on the second part of the mandrel (361,5/360,5/361,5). Similarly, it was made by three of the mandrel for rolling pipe size 377×40, 426×9 and 426×40 mm Data by geometric sizes of mandrels made by the existing and proposed methods, and the average wall thickness along the length of the tubes, laminated on the mandrels shown in the table. The table shows that during rolling of pipe size 377×9 mm on the mandrels made on existing technology, the average longitudinal raznesennost was 1.8 mm, the mandrels are made of the proposed method with a taper on one half of the working part from domowego castle 1.0 mm and a cylindrical second part, the average longitudinal raznesennost amounted to 1.3 mm, and the mandrels are made of the proposed method with a taper on one half of the working part from domowego castle 1.0 mm and a reverse taper rate of 1.0 mm on the second part, the average longitudinal raznesennost amounted to 1.15, i.e. when rolling tubes on the mandrels produced by the proposed method longitudinal raznesennost decreased accordingly 1.38 and 1.57 times. When rolling the rough size h mm reduced longitudinal varying wall thickness was 1.38 and 1.47 times pipe size h mm of 1.62 and 1.75, and pipe size mm respectively 1.69 and 1.83 times. Thus, the reduction prodolny of varying wall thickness depending on sortmenu pipes was from 1,38 up to 1.83.

The use of the proposed method of manufacture of mandrels piligrimage mills for rolling hot-rolled tubes of larger and medium diameters will significantly reduce the longitudinal raznesennost pipes, and consequently, to reduce the consumption of metal in the redistribution of the ingot (billet) - pipe, to reduce the output is not ordered part of the pipe, and therefore, reduce their value.

1. The method of manufacture of mandrels piligrimage mills for rolling hot-rolled pipes of large and medium diameters, including the casting of ingots of heat-resistant steel, the forging of a cylindrical solid or hollow workpieces, rough machining, heat treatment, machining of dies on the finishing size of the taper in one to two millimeters of the length of the working part and exploitation to education grid razgonnyj cracks, characterized in that the machining of dies on the finishing size is produced taking into account the estimated coefficient of linear expansion in the rolling process, and the sizes of the diameters determined from the expression

where d_{n}- internal diameter of pipe after piligrimage mill, mm;

Δ - the difference between the internal diameters of the pipes after ilgrimage mill and the diameters of the mandrels, by rolling in the rolls with tangential issues, mm;

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

- the estimated temperature of the mandrels along the length of the rolling process, ° C.

2. The method according to claim 1, characterized in that the mandrel from the locks on the length of one second working parts are made conical, the diameter of the bases which determine from the above expression, and the second cylindrical part.

3. The method according to claim 2, characterized in that the second part of the mandrels are made with reverse cone, the diameter of which is determined from the expression

where D is the outer diameter of the pipe after piligrimage mill, mm;

S - wall thickness of pipe, mm;

A=0.5 to the minimum value of the inverted cone mandrel, mm;

K=0,07 - coefficient taking into account the geometrical dimensions of rolled pipes.

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