Method for piercing titanium alloy solid billet

Abstract

A method for piercing a titanium alloy solid billet, the method including: 1) providing a Mannesmann rotary piercer including two rollers, a feed channel, a plurality of centering devices, and a mandril including a plug; fixing the mandril using the plurality of centering devices, where the Mannesmann rotary piercer has a feeding angle of 6-18°, a cross angle of 15°, and a roll speed of 30-90 rpm; 2) heating a titanium alloy solid billet to 930-990° C.; 3) transferring the titanium alloy solid billet to the feed channel of the Mannesmann rotary piercer; and 4) aligning the titanium alloy solid billet with the plug of the mandril, and driving the titanium alloy solid billet to pass through the plug of the mandril, thereby piercing the titanium alloy solid billet and yielding a titanium alloy tube.

Claims

1. A method, comprising: 1) providing a Mannesmann rotary piercer comprising two rollers, two guide plates disposed in an arrangement of plane symmetry and have a first symmetry plane intersecting the two rollers and a second symmetry plane perpendicular to the first symmetry plane, a feed channel, a plurality of centering devices, and a mandrel comprising a plug; fixing the mandrel using the plurality of centering devices; wherein the mandrel defines a passing line; the Mannesmann rotary piercer has a feeding angle of 6-18°, a cross angle of 15°, a roll speed of 30-90 rpm, and a plug advance of 5-15 mm; the feeding angle refers to a projection of an included angle between an axis of one of the two rollers and the passing line on the second symmetry plane, and the cross angle refers to a projection of an included angle between the axis of one of the two rollers and the passing line on the first symmetry plane; the plug advance refers to a distance between a front end of the plug and a roll gorge along the passing line, the roll gorge refers to a position of the two rollers where a distance between the two rollers is minimum; and a diameter reduction ratio of the billet is set as 6-12%; 2) heating a titanium alloy solid billet to 930-990° C.; 3) transferring the titanium alloy solid billet to the feed channel of the Mannesmann rotary piercer; and 4) aligning the titanium alloy solid billet with the plug, and driving the titanium alloy solid billet to pass through the plug, thereby piercing the titanium alloy solid billet and yielding a titanium alloy tube; wherein the Mannesmann rotary piercer comprises three cams for each centering device; an included angle of each two of the three cams is 120°, and the mandrel is disposed in a hole enclosed by the three cams for each centering device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of a method for piercing a titanium alloy solid billet according to one embodiment of the disclosure;

(2) FIG. 2 is a schematic diagram of a Mannesmann rotary piercer in one angle of view showing the feeding angle of two rollers according to one embodiment of the disclosure;

(3) FIG. 3 is a schematic diagram of a Mannesmann rotary piercer in another angle of view showing the cross angle of two rollers according to one embodiment of the disclosure;

(4) FIG. 4 is a sectional view taken from line A-A in FIG. 2;

(5) FIG. 5 is a photograph of the microstructures of the different parts of the billet with a length of 230 mm;

(6) FIG. 6 is a flat view of a mandril and a centering device in a Mannesmann rotary piercer;

(7) FIG. 7 is a top view of the mandril and a centering device of FIG. 6 from another perspective; and

(8) FIG. 8 is a schematic diagram of the mandril and a centering device of FIG. 6 from the direction of the axis of the mandril.

DETAILED DESCRIPTION

(9) To further illustrate, embodiments detailing a method for piercing a titanium alloy solid billet are described below. It should be noted that the following embodiments are intended to describe and not to limit the disclosure.

(10) As shown in FIG. 1, provided is a flow chart of a method for piercing a titanium alloy solid billet. The method is detailed as follows:

(11) 1) Providing a Mannesmann rotary piercer comprising two rollers 201, two guide plates 204, a feed channel 301, a plurality of centering devices 302, and a mandril 202 comprising a plug 203; fixing the mandril using the plurality of centering devices. Specifically, three centering devices are provided, that is, one primary centering device 302A and two secondary centering devices 302B. The mandril comprises a free end 202A and a fixed end 202B. The distance between the one primary centering device and the fixed end 202B is approximately 513 mm. The distances between the two secondary centering devices and the fixed end and the free end are approximately 342 mm and 102.6 mm, respectively. The uneven distribution of the centering devices improves the stability of the mandril, and reduces the occurrence of the rolling block phenomenon (the alloy billet is stuck in the middle of the rotary piercer). The distance Ddx between the two guide plates is 1.05-1.1 times the distance Dgx of the two rollers in a cross section perpendicular to the axis of the billet, and a minimum distance between the two rollers is D×(1−diameter reduction ratio), where D is the diameter of the titanium alloy solid billet with a unit of millimeter.

(12) 2) As shown in FIGS. 2, 3 and 4, the Mannesmann rotary piercer has a feeding angle of 6-18°, a cross angle of 15°, a diameter reduction ratio of 6-12%, a roll speed of 30-90 rpm, and a plug advance of 5-15 mm. Specifically, the Mannesmann rotary piercer has a feeding angle α of 15°, a cross angle β of 15°, a diameter reduction ratio of 8%, and a roll speed of 60 rpm. The feeding angle refers to the projection of an included angle between the axis of one of the two rollers and the axis of the titanium alloy solid billet on a plane passing the axis of the billet and parallel to the A-A line, and the cross angle refers to the projection of an included angle between the axis of one of the two rollers and the axis of the titanium alloy solid billet on a plane perpendicular to the plane passing the axis of the billet and parallel to the A-A line. The plug advance L.sub.PA refers to the distance between the plug nose and the roll gorge 205 along the axis of the billet; the plug nose refers to the front end of plug; the roll gorge 205 refers to the position of minimum distance between the two rollers.

(13) 3) Heating a titanium alloy solid billet to 930-990° C.

(14) In this disclosure, the titanium alloy solid billet is prepared by melting in vacuum consumable electric arc furnace, forging and machining. Specifically, three titanium alloy solid billets TC4 are provided, with dimension of Φ45×200 mm, Φ45×280 mm, and Φ45×420 mm, respectively. The microstructure of each part of the billets is even, and no defects such as inclusions and pores are found. The phase transformation temperature of the titanium alloy cylindrical billets is 1000° C.±5° C.; the initial microstructure of each part of the cylindrical billets is bimodal microstructure with 44% primary α phase, and the average grain size of primary α phase is 20 μm.

(15) The three titanium alloy cylindrical billets are heated in a heating furnace. The heating temperature is 960° C.±10° C. and the heating time is 60 min. The shape of two rollers are all conical roll with double helix; As shown in FIGS. 6-8, The Mannesmann rotary piercer comprises three cams 401 for each centering device; the included angle of each two of the three cams is 120°, and the mandril is placed in the holes enclosed by three cams for each centering device.

(16) 4) Transferring the titanium alloy solid billet to the feed channel of the Mannesmann rotary piercer. The transit time is less than or equal to 5 seconds.

(17) 5) Aligning the titanium alloy solid billet with the plug of the mandril, and driving the titanium alloy solid billet to pass through the plug of the mandril, thereby piercing the titanium alloy solid billet and yielding a titanium alloy tube.

(18) The rolling temperature of the titanium alloy solid billet is 860-1000° C.

(19) Following 5), the titanium alloy tube is cooled in air, and the head and tail of the titanium alloy tube are machined.

(20) After the piercing, the dimensions of the head and tail of the three titanium alloy tubes are shown in Table 1.

(21) TABLE-US-00001 TABLE 1 Dimensions of three titanium alloy tubes Head of titanium alloy tubes Tail of titanium alloy tubes Outer Inner Wall Outer Inner Wall dia- dia- thick- dia- dia- thick- meter meter ness meter meter ness Items (mm) (mm) (mm) (mm) (mm) (mm) Φ45 × 47.10 19.90 13.20 46.90 19.80 13.55 200 mm Φ45 × 47.20 20.10 13.40 47.00 20.00 13.50 280 mm Φ45 × 47.00 19.80 12.70 46.80 19.80 13.8  420 mm Variance —  0.09  0.01  0.05  0.02  0.03

(22) As shown in Table 1, the variances between the inner diameter and the wall thickness of the three tubes with different lengths is less than 0.1, which indicates that the piercing method of the disclosure is accurate and stable, and the tubes with a diameter thickness ratio of about 3.5 are obtained.

(23) The microstructure of different parts of the billet with a length of 230 mm is studied. The samples are selected from the head, middle part and tail of the tube for metallographic analysis. As shown in FIG. 5, each sample is provided with three observation points along the radial direction. The three observation points of the head are a, b, and c along the radial distribution. The three observation points of the middle part are d, e, and f, respectively. The three observation points of the tail are g, h, and i. The radial and axial microstructure of the tube with bimodal microstructure is even across the section. According to statistics, the primary α phase of each part accounts for 15%-35%.

(24) The obtained titanium alloy tubes of the disclosure have a bimodal microstructure. The primary α phase is equiaxed and accounts for 15%-35%. The diameter-thickness ratio of the titanium alloy bimodal microstructure tube is less than 4. The disclosure adopts a conical roll with double helix, a large feeding angle and cross angle, and the rolling parameters such as diameter reduction rate and the roll speed are reasonably designed, which can effectively avoid the temperature rise in the whole process of rotary piercing, and obtain a titanium alloy tube with bimodal microstructure.

(25) By reasonably designing the feeding angle, cross angle, roll speed, diameter reduction rate of the Mannesmann rotary piercer and the length of the plug, the temperature rise of the alloy billet in the process of rotary piercing can be effectively controlled, thereby avoiding the formation of the Widmanstatten microstructure, and improving the quality of the titanium alloy tube with bimodal microstructure. The centering devices of the Mannesmann rotary piercer are unevenly distributed, thus improving the strength and rigidity of the centering devices acting on the mandril, and reducing the occurrence rate of the rolling block phenomenon.

(26) It will be obvious to those skilled in the art that changes and modifications may be made, and therefore, the aim in the appended claims is to cover all such changes and modifications.