SU755348A1 - Mandrel for screw expanding of tubes - Google Patents

Description

The invention relates to pipe production, in particular to the mandrels used when rolling ^g pipes in three-rolls-rolling roll mills.

Known mandrel, mainly for hot rolling of pipes, having a tapered section and a section of greater taper in the tail section at a length equal to: 0.2 0.2 0.5 of the total length of the mandrel {1].

A mandrel of such dimensions, when rolled on pilgerstan, allows to obtain a billet of different thicknesses along the length with a thinned wall at the rear end for subsequent reduction. one·

The closest to the invention to the technical essence is the mandrel for screw rolling, containing a cylindrical section, an adjacent cone section with a smaller base and a cylindrical flange (2). The conical section of small length serves exclusively to smoothly mate the flange with the cylindrical part 21 of the mandrel.

The disadvantage of this mandrel is that when using

mandrels in the process of rolling the pipe

exercise almost constant

2

deformation on the wall of the workpiece.

When rolling the end sections (rear ends) of pipes, mainly with the ratio of the external diameter to the wall thickness of 5.5 - 8.0, the contact forces determined by the amount of compression along the wall of the workpiece, it becomes insufficient for the axial feed of the latter; there is a breakdown of the process. The increase in compression due to an increase in the diameter of the mandrel in the place of its conjugation of the cylindrical part with the flange cannot provide a sufficient increase in the deformation along the wall of the sleeve, since the length of the end defect of the type “nedokat ¹ ” is usually 1.0 - 2.5 outer diameter of the pipe.

The aim of the invention is to reduce the end defects on the pipes and increase the speed of rolling by increasing the contact forces' acting on the workpiece, by increasing the degree of deformation along the wall of the workpiece at the time of rolling the rear ends of the pipes.

. The goal is achieved in that the mandrel for screw rolling, which includes a cylindrical section adjacent to it a smaller base of

755348

four

Nose and cylindrical

The flange, the length of the conical section, is 1.2–3.0 of the diameter of the cylindrical section, and its angle of taper is 1–4 °.

When using such a mandrel in the process of rolling the rear end of the pipe, the degree of deformation along the wall on a section whose length is equal to the length of the end defect of the type “under-rolled” in case of rolling on a cylindrical mandrel increases. Increasing the degree of deformation increases the contact forces acting on the workpiece in the process of rolling its rear end, which prevents the process from stalling. The mandrel area, providing an increase in strain, must be conical so that the degree of compression along the wall gradually increases as the deformation zone is released and thus the fall of the active contact forces applied to the workpiece is compensated as a result of reduction. the contact surface of the metal with the rolls during the release of the deformation zone.

The parameters of the transition section are chosen from the following considerations: the length of the section should be approximately equal to the length of the end defect when rolling on a cylindrical mandrel, i.e. 1.2 - 3.0 diameters of the cylindrical part of the mandrel. If you choose a length of less than 1.2 diameters of the mandrel, the contact forces (compression) will increase in a very short area and will not provide the feed of the workpiece. If the length of the section is more than 3.0 of the mandrel diameter, the process will not fail, however, the section with the thinned wall on the pipe will be large, which will determine the Increased level of pipe cut-off;

the angle of tapering is chosen based on the fact that usually the gap between the inner surface of the sleeve and the mandrel is 3-5 mm. When the taper angle is less than 1 °, the flange will have a diameter smaller than the internal diameter of the workpiece, and the mandrel will not fix relative to the workpiece.

When the taper angle is more than 4 ^{, the} flange of the mandrel will have a diameter greater than the external diameter of the pipe and rolling will be impossible.

The drawing shows the proposed mandrel in the deformation zone.

The mandrel has a cylindrical section 1, a conical section 2 and a cylindrical flange 3.

Example 1. Preventing the appearance of end defects of the type '' under-rolled ' ¹ when rolling tubes with a ratio of diameter to wall thickness of 5.5 - 8.0.

Sleeve 4, obtained on the firmware *

mill, is fed into the receiving groove of the three-roll mill, where

a mandrel having a cylindrical part 1, a cone section 2 and a flange 3 is inserted. The mandrel is inserted into the sleeve until its flange / 3 comes into contact with the rear end of the sleeve. Thus, the position; The mandrel will be fixed relative to the liner during rolling.

Next, the mandrel and the sleeve set in rolls; rolling begins, resulting in a pipe. When rolling the rear end of the pipe, the inner surface of the liner is deformed by the conical section of the mandrel, the deformation along the wall increases, the contact forces and the total force acting on the workpiece increase, which prevents the appearance of a “under-rolled” - the process in the final stage proceeds without breaking the axial feed stable After rolling, the mandrel is removed from the tubes and used when rolling other tubes.

PRI mme R 2. Prevention of end defects of the type "socket" when rolling pipes with a ratio of diameter to wall thickness more than 8.5,

The proposed mandrel can be used with the positive effect of direct rolling thin-walled tubes.

In this case, when rolling the rear end of the pipe on the tapered portion of the mandrel, rolls should be bred.

This will compensate for the increase in compression along the wall by increasing the diameter of the mandrel. The fact that when rolling the rear end of the pipe the gap between the inner surface of the sleeve and the mandrel is very small will have a positive effect on the stability of the rolling of the rear end. The latter will allow the rolls to be diluted at a shorter part of the rear end of the pipe than when rolling on a conventional cylindrical mandrel, which will reduce the end cut on the pipes.

Claims (1)

Claim Mandrel for helical rolling of tubes, including a cylindrical section, a conical section adjacent to it with a smaller base and a cylindrical flange, characterized in that, in order to increase the speed of pipe rolling with the ratio of diameter to wall thickness · 5.5 - 8.0, the length of the conical section is 1.2 - 3.0 diameter of the cylindrical section, and its angle of taper is 1 - 4 °.