RU2150342C1 - Method for cold pilger rolling of tubes - Google Patents

Abstract

FIELD: rolled tube production, namely, manufacture of tubes from hard-to-form titanium alloys by cold lengthwise rolling in roll grooved pass. SUBSTANCE: method comprises steps of performing before rolling process cold drifting of blank inner diameter by value consisting (1.5-3.0) of elastic deformation value until occurring residual deformation; sizing wall with absolute reduction value of wall equal to (0.1-0.25)(1-dt/d3)t3; reducing tube by wall and diameter along portion of drift having conicity degree 2tgα_o=0.007-0.013; in addition realizing free reduction of tube by diameter, reducing wall at sizing tube and performing free reduction of tube by diameter on transition portion. In order to realize it, multicone drift is used. Said drift has next relation between total length of portions for reducing tube by diameter and length of tube portions reduced by wall and diameter: lred dr/lred t = (0.3-0.7) δ_in.p.•lnμt/δ_in.b.•lnμd, where δ_in.p.,δ_in.b. - yield strength values of metal of ready tube and blank; μt,μd - elongation values of tube reduced by wall and diameter; t_b,d_b,d_t - wall thickness value of blank, diameters of blank and tube respectively. EFFECT: enhanced accuracy of geometry of tubes made of hard-to-form alloys such as titanium alloys. 1 dwg, 1 ex

Description

 The invention relates to pipe rolling production and can be used in the manufacture of cold-deformed pipes by longitudinal rolling in a gauge formed by rolls.

 A known method of manufacturing cold rolled pipes, including rolling with pilgrim rolls on the mandrel of the workpiece, which before rolling is distributed with an increase in the inner diameter of the pipe by 1-5% (USSR AS N 1224025, class B 21 B 21/00, 23/00 publ. . 1986 Bull. N 14).

 The disadvantage of this method is that cold rolling, carried out after the distribution of the inner diameter of the billet, does not correct the inherent experimental difference obtained by flashing it and additionally induces the difference of the pipe. As a result, the finished pipe has a large difference.

 A known method of cold pilgrim rolling pipes, adopted for the prototype (a. With. The USSR N 1126343, class B 21 B 21/00, publ. 1984 Bull. N 44), comprising feeding a portion of metal and deforming it into the working cone pilger rolls with reduction, compression in diameter and wall thickness, repeated reduction with a degree of deformation of 5 - 15%, wall and diameter calibration. This rolling method allows to increase the accuracy of the finished pipes by reducing the eccentric difference in the workpiece.

 The disadvantage of this method of pipe production is the appearance of an additional induced difference arising during free reduction in the precalibration zone, which is not corrected by the calibrating section of the gauge stream, since the pipe does not touch the mandrel in the calibrating section. In addition, when rolling pipes of non-ferrous metals, in which the elastic modulus is approximately 2 times lower than the elastic modulus of steel, in order to ensure plastic deformation during repeated reduction in the precalibration section, it is necessary to repeatedly carry out a large reduction of the caked metal. This leads to the formation of folds on the inner surface of the pipes and cracks. The large taper in the precalibration reduction zone requires an increase in the length of the calibrating section on the gauge stream and leads to increased wear of this section.

 The technical result of this invention is to increase the accuracy of the geometric dimensions of the finished pipes from hardly deformable alloys with a small modulus of elasticity, for example, from titanium alloys.

где σ_вт,σ_вз - соответственно пределы прочности трубы и заготовки;
μ_t,μ_d - вытяжки соответственно по стенке и по диаметру.The technical result is achieved by the fact that in the proposed method for the production of pipes before cold pilgrim rolling, the pre-mechanically bored tube billet is mandreled on a mandrel without compression of its external diameter by 1.5 ... 3.0 elastic deformations of the diameter until permanent deformation occurs, the process reductions with wall calibration are carried out with absolute wall compression equal to (0.1 ... 0.25) • (1-d _t / d _s ) • t _s , wall and diameter reductions are carried out in the mandrel section with taper 2tgα ₀ = 0.007 ... 0.013, in addition, p free reduction in diameter, reduction with wall calibration, and free reduction in diameter in the transition section are carried out, and wall and diameter reductions are carried out on a multicone mandrel, in which the ratio between the total length of the reduction section in diameter and the length of the reduction section on the wall and diameter is determined from expressions:

where σ _W , σ _VZ - respectively, the strength limits of the pipe and the workpiece;
μ _t , μ _d - hoods, respectively, along the wall and in diameter.

Burning of the workpiece is carried out with a relative strain equal to ε = (1.5 ... 3.0) • σ _tz / E,
where ε is the relative strain;
σ _TS - yield strength of the workpiece material;
E is the longitudinal modulus of elasticity of the tube billet.

During subsequent cold rolling of pipes on a mandrel of variable cross section with calibrated pilgrim rolls, the deformation of the tube stock is carried out sequentially in several zones (see drawing): reducing - 1 ed. - (without touching the inner surface of the tube stock with a mandrel), reducing with wall calibration - 1 _ed. ^k - the absolute compression wall equal to (0,1 ... 0,25) • t _h • (1-d _r / d _z (t _s - wall thickness tubular blank; d _h - the outer diameter of tubular blank; d _t is the diameter of the finished pipe), by reducing on the transition zone of the gauge stream (1 _ed. ^p ), which consists of two sections of free reduction; the section of the pipe leaving the mandrel with a taper α _p and a taper forming a transition zone of caliber α $\genfrac{}{}{0ex}{}{\text{to}}{\text{P}}$ (1 _ed. ^P ) and the landing site calibrated along the wall of the pipe to the crimp portion of the mandrel with a taper α _o (1 _ed. ^About ); crimp (1 _crimp ), in which the workpiece is mainly crimped to the wall thickness of the finished pipe, and calibrating (1 _k ), on which the irregularities of the working cone of the pipe obtained during previous deformation in the corresponding zones are smoothed, and the outer diameter of the finished pipe is calibrated .

Burning of the inner mechanically bored surface of the workpiece with a relative deformation ε = (1.5 ... 3.0) • σ _tz / E allows to reduce the roughness of the inner channel of the tube billet, increase its geometric accuracy and create a hardened layer on this surface. This layer prevents the occurrence of folds, cracks, bumps on the inner surface of the pipe during its reduction and contributes to a better correction of the incorporated eccentric difference during reduction.

 From the theory and practice of cold pipe rolling (Shevakin Yu.F. Calibration and efforts in cold rolling of pipes. M., Metallurgy, 1963) it is known that the eccentric difference in the tube billet decreases when the pipe is reduced without wall compression. However, the possible magnitude of this reduction is very limited due to the appearance of defects in the form of bumps, folds and cracks on the inner surface of the pipe. Therefore, usually after a small reduction zone, the diameter is reduced with intensive wall compression. However, at this stage of deformation, the relative value of the incorporated eccentric difference varies insignificantly.

Experimental studies have shown that if, when reducing the diameter, insignificant wall compression is performed within (0.1... 0.25) • (1-d _t / d _s ) • t _s , then the intensity of correction of the eccentric difference during rolling remains the same as with free reduction, however, defects do not form on the inner surface of the working cone and the finished pipe. Wall compressions with a value of less than 0.1 (1-d _t -d _s ) • t _s in this section lead to the appearance of defects on the inner surface of the pipe. Wall compressions with a value greater than 0.25 (1-d _t / d _s ) • t _s significantly reduce the correction intensity of the eccentric difference.

 The compression of the wall of the workpiece is carried out at the next stage of deformation of the working cone - crimp section. In this section, the relative eccentric difference does not practically change, however, the induced transverse difference appears due to the flow of metal into the outlets of calibers during its deformation.

It is known from theory that the width of the gauge release, and consequently the transverse induced difference, decreases with decreasing taper of the mandrel in the crimp section. However, experiments have shown that with increased feeds and hoods of difficult to deform materials there is a range of optimal tapering of the mandrel in the crimp section of the working cone. It is equal to 2tgα ₀ = 0.007 ... 0.013. A decrease in the taper of the mandrel below 0.007 leads to an increase in the effort to disrupt the working cone of the pipe from the mandrel when the workpiece is fed, to the front support in the deformation zone and to the intensive flow of deformable metal into the outlets, which increases the magnitude of the induced transverse difference of the finished pipes. The use of mandrels with a taper in the crimp zone above 0.013 also leads to an increase in the transverse induced difference.

Experimental studies during pipe rolling showed that the stability of the process depends on the ratio of the total length of the reducing section and the length of the crimp section of the mandrel. The rational range of this ratio is
(0,3 ... 0,7) • σ _W • lnμ _t / σ _taken • lnμ _d
In this case, the spacer force acting on the work rolls in the zones of the crimping and reducing walls with calibration is approximately equal to each other.

Decrease in this ratio below 0,3σ _W • lnμ _t / σ _taken • lnμ _d leads to an increase in crest taper stream crimping zone, increasing stream Razvalki, induced an increase in the transverse variation in overheating of the mandrel into the ends of the crimp portion and lowering of its durability. In the crimp zone of the working cone, the spacer forces acting on the work rolls increase.

Increasing the ratio of total length to the length of the reducing section of the crimp portion above 0,7σ _W • lnμ _t / σ _taken • lnμ _d leads to a decrease in the geometric accuracy of tube due to the increase the proportion eccentric planted and increase variation in the rolling force in the expander reduction zone with a calibration wall.

 The invention is illustrated in the drawing, which shows a reamer caliber, mandrel and working cone rolled tube billet with the designation of the lengths of the rolling zones.

Example. We rolled a tube billet from VT1-0 titanium alloy along the route 9 70x9 - ⌀ 48x6 at the KhPT "RN-3 ^1/2 " mill. The working part of the sweep of the profile of the stream of calibers was 475 mm (fifteen-zone calibration of 31.7x15).

The diameter hood was 1.45 (the natural log of 0.3732) and the wall hood was 1.5 (the natural log of 0.4055). The length of the transition zone 1 _ed. ^{p is} taken equal to 31.7 mm, and the total length of the reducing and crimping zones was 475.0 mm and is divided in the ratio l ^Σ peg / l _crim = 241.3 / 233.7 taking into account the mechanical properties of the tube billet (σ _W = 500 MPa ) and the finished pipe (σ _b = 700 MPa, as well as the natural logarithms of hoods on the wall and diameter.

The taper of the reducing part of the mandrel α _p was equal to 2tgα _p = 0,041. The taper of the crimp part of the mandrel α _o was equal to 2tgα _o = 0.007, which corresponds to the recommended taper interval for the crimp section.

The taper of the generatrix of the transition zone is taken equal to the half-sum of the reducing and crimping zones of the two-cone mandrel and amounted to 2tgα $\genfrac{}{}{0ex}{}{\text{to}}{\text{P}}$ = 0.024. The feed during rolling was 8.. . 12 mm on a double course of the stand. The fixed difference in the initial tube billet ranged from: longitudinal - 7.3 ... 12.6%, transverse - 8.4 ... 13.1%.

 The tube stock was torn into a “cold” mandrel, the diameter of which was 0.31 mm larger than the inner channel of the blank. Distribution by burnishing was carried out on a 10-ton drawing mill.

Laminated pre-machined and mandrel tube blanks had an outer diameter difference of not more than 0.05 mm, the longitudinal difference in wall thickness varied within 3.7 ... 5.5%, and the transverse difference varied within 4.2 .. .7.1%. This result was achieved due to the fact that in the reduction zone, the wall compression during diameter calibration was only 0.59 mm, and the wall compression in the crimp section of the mandrel was performed at a taper of 2tgα _o = 0.007 with the corresponding partition of the reducing and crimping sections of the mandrel depending on the mechanical properties of the pipe billet and finished pipe and process parameters (hoods in diameter and wall).

 Thus, the proposed method of cold pilgrim rolling allows to increase the accuracy of the geometric dimensions of pipes from difficultly deformed alloys, such as titanium, with a small modulus of elasticity.

Claims (1)

The method of cold pilgrim rolling of pipes, including feeding the workpiece and deforming it into a working cone on the mandrel with reciprocating rolls with sequential reduction of the diameter of the workpiece with wall calibration, compression by diameter and wall and diameter calibration, characterized in that cold rolling is performed before rolling the inner diameter of the workpiece by the amount of (1.5 - 3.0) elastic deformation of the diameter before the appearance of permanent deformation, the reduction process with wall calibration odyat absolute compression wall equal to (0,1 - 0,25) • (1 - d _r / d _z) • t _s; compression along the wall and diameter is carried out in the mandrel section with a taper of 2tgα ₀ = 0.007 - 0.013, in addition, free reduction in diameter, reduction with wall calibration and free reduction in diameter at the transition section are performed, and compression along the wall and diameter is carried out on a multiconus mandrel , in which the ratio between the total length of the reduction section in diameter and the length of the compression section of the pipe along the wall and diameter is determined from the expression:

where σ _W , σ _VZ - the ultimate strength of the metal of the finished pipe and billet;
μ _t , μ _d - hoods on the wall and diameter;
t _z , d _z , d _t - wall thickness of the workpiece, the diameters of the workpiece and pipe.