RU2250147C1 - Method for helical piercing of cast billet - Google Patents

Abstract

FIELD: rolled stock production, plastic working of metals, namely helical piercing processes.

SUBSTANCE: method comprises steps of guiding heated billet to working rolls turned by angle of feeding and expansion; piercing billet by means of plug mounted in pass formed by rolls and guiding tool. Feed angle value is in range 12 - 18°; expansion angle value is in range 6 - 10°. Reduction degree in restriction portion is in range 21 -35 % and it is realized with use of rolls having inlet cone angle equal to 4 -8°. Reduction degree of billet in front of nose of plug is normalized by means of mathematical expression given in description of invention.

EFFECT: possibility for making tubes with high accuracy geometry size and high quality inner and outer surfaces.

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Description

The invention relates to the field of metal forming and relates to the production of hollow billets from continuously cast billets or ingots.

Currently, a known method for producing tubular products, including flashing a solid billet with compression in diameter of 8-20% at feed angles of 10-18 degrees [1]. The disadvantage of this method is the inability to obtain high-quality cast metal sleeves, because with these firmware modes, the metal is destroyed in the axial zone of the workpiece in front of the toe of the mandrel.

Closest to the technical nature of the claimed technical solution is a method of screw flashing a cast billet, including feeding the heated billet into work rolls deployed at the feed and rolling angle, and flashing the workpiece with a mandrel installed in a caliber formed by rolls and a guiding tool [2].

The disadvantage of this method is the impossibility of obtaining a high-quality inner surface of the liners, as well as the elaboration of the structure along the wall thickness with high accuracy of geometric dimensions.

The objective of the invention is to improve the quality and accuracy of the geometric dimensions of the sleeves when flashing from cast metal. This goal is achieved by the fact that in the method of screw flashing a cast billet, including feeding the heated billet to work rolls deployed at the feed and rolling angle, and flashing the workpiece with a mandrel installed in the caliber formed by the rolls and the guiding tool, the flashing is carried out at a feed angle not less than 12 degrees, the rolling angle of 6-10 degrees with a compression in the clamp 21-35%, while using rolls, the angle of the input cone of which is 4-8 degrees, and the amount of compression of the workpiece in front of the mandrel is determined t by the relation:

where u ₀ is the relative compression of the workpiece in front of the toe of the mandrel;

φ is the angle of inclination of the input cone of the roll, deg;

β is the feed angle, deg;

γ - rolling angle, deg.

The claimed combination of distinctive features ensures the achievement of the purpose of the invention, namely, improving the quality and accuracy of the geometric dimensions of the sleeves when piercing from cast metal. A decrease in the feed angle of less than 12 degrees leads to the appearance of captures on the inner surface of the sleeve due to the destruction of the metal in front of the mandrel toe. Setting the rolling angle to less than 6 degrees in combination with a small feed angle leads to localization of deformation in the outer layers of the rolled pipe and to the absence of a study of the structure of the pipe wall; an increase in the rolling angle above 10 degrees causes a deterioration of the gripping conditions. Firmware with crimps with a diameter of less than 21% in diameter does not provide for the elaboration of the cast structure, and an increase in compression of more than 35% leads to a decrease in the ductility of the metal. When the angle of the input cone of the roll is less than 4 °, the metal is destroyed in the axial zone of the workpiece, an increase in the taper angle of more than 8 ° leads to a deterioration of grip. The amount of compression of the workpiece in front of the toe of the mandrel is determined from the ratio:

The invention is illustrated in the drawing, which shows a longitudinal section of the deformation zone with a vertical plane. It can be seen from the drawing that the relative compression of the workpiece in front of the mandrel toe is determined in a plane perpendicular to the rolling axis and passing through the first point of contact with the metal of the mandrel toe passing along the rolling. The value of the relative compression is usually calculated by the formula:

u ₀ = (D ₃ -D ₀ ) / D ₃ ,

where u ₀ is the relative compression of the workpiece in front of the toe of the mandrel;

D ₃ - the diameter of the initial billet, mm;

D ₀ is the diameter of the workpiece in a plane passing through the point of contact with the metal of the mandrel sock, mm

Knowing the amount of compression in front of the mandrel toe, you can determine the position of the latter in the deformation zone.

The rolling method is as follows. The heated workpiece is set in the work rolls, where it is crimped by them in a gauge formed by the mutual contact of the contact surfaces of the rolls, the axes of which are inclined to the axis of the workpiece. The angle between the rolling axis and the projection of the roll axis onto the plane passing through the rolling axis and the segment, which is the shortest distance from the rolling axis to the roll axis, is the rolling angle, and the angle between the rolling axis and the projection of the roll axis onto the plane perpendicular to the rolling plane and passing through the rolling axis is the feed angle. When a workpiece is crimped by rolls, the metal fills the deformation zone and meets a mandrel that is stationary in the axial direction, the length of the deformation zone section from touching the workpiece to the roll until it meets the mandrel toe is determined by the amount of compression in front of the mandrel toe, which is caused by the ratio:

The selected compression value u ₀ provides reliable secondary capture, i.e. the created reserve of friction forces is sufficient to overcome the resistance of the mandrel when the metal moves in the deformation zone.

A depression is formed at the end of the workpiece, which, as the workpiece moves along the deformation zone, turns into a cavity, the maximum compression of the workpiece in diameter is from 21 to 35%, which ensures a good study of the cast structure of the starting material.

An example implementation of the method.

For rolling pipes with dimensions of 108 × 10 on a TPA with a three-roll rolling mill, a continuously cast billet with a diameter of 156 mm was stitched. According to traditional technology, a circle of 120 mm is used for their production. The preforms were heated in a ring furnace to a temperature of 1240 ° C. Before flashing, the distance between the rolls was B = 112 mm, the compression in the pinch was 28%, between the bars L = 120 mm, the ovalization coefficient was 1.07. The angle of the inlet cone of the roll was φ = 6 °, the rolling angle γ = 8 °, the diameter of the mandrel 88 mm, the feed angle β = 14 °. The amount of compression of the workpiece in front of the toe of the mandrel was determined from relation (1).

sin6 ° Cos14 ° = 0.1045.97 = 0.1014

Thus, the amount of compression in front of the mandrel nose should be not less than 6.4%, but also not more than 10.1%, respectively, the magnitude of the extension of the mandrel toe beyond the pinch rolls was chosen according to these values. The wall thickness is adjusted by moving the mandrel in the specified range of compression changes.

In total, 6 tubes were rolled according to the proposed option; in addition, after flashing, 4 sleeves were removed from the stream for analysis of the quality and shape-changing parameters. Inspection of the inner and outer surfaces of pipes and sleeves showed no defects. The quality pipes met the requirements of GOST. Metallographic studies showed a complete study of the cast structure, the absence of discontinuities and cracks.

Thus, the proposed rolling method ensures the production of pipes of high accuracy in geometric dimensions with high-quality internal and external surfaces.

Sources of information

1. USSR author's certificate No. 738697 B 21 at 19/00, 8/00, publ. BI No. 21, 1980

2. Rolling production. Reference, vol. 2. Edited by E.S.Rokotyan. M .: Metallurgizdat, 1962, pp. 391-411, 430-431.

Claims (1)

The method of screw flashing a cast billet, including feeding the heated billet to work rolls deployed at the feed and rolling angle, and flashing the workpiece with a mandrel installed in caliber formed by rolls and a guiding tool, characterized in that the flashing is carried out at a feed angle of at least 12 degrees , the rolling angle is 6-10 degrees with a compression in the clamp 21-35%, using rolls, the angle of the inlet cone of which is 4-8 degrees, and the relative compression of the workpiece in front of the mandrel nose is determined and h ratio

Where u ₀ - the relative compression of the workpiece in front of the toe of the mandrel; φ is the angle of inclination of the input cone of the roll, deg .; β - feed angle, deg .; γ - rolling angle, deg.