RU2271885C2 - Tube rolling method in plant with automatic mill - Google Patents

Abstract

FIELD: processes for producing seamless tubes in plants with automatic mills.

SUBSTANCE: method comprises steps of heating billet; piercing it to sleeve; rolling sleeve out in automatic mill; rolling it out in rolling out mill and sizing; before rolling in automatic mill, heating leading end of sleeve till temperature exceeding that of sleeve body no more than by 50°C; determining period of such heating according to formula t = (100 x S x (D -S)/a)x (T _{end ah} - T_{end bh})/(T _torch - T _{end bh}) where t - time period of heating, s; S - thickness of sleeve wall, m; D - diameter of sleeve, m; a -thermal conductivity, sq. m /h; T _{end a h} = T + (0 - 50)°C, temperature of sleeve end after heating, °C; T - temperature of sleeve body, °C; T_{end b h} - temperature of sleeve end before heating, °C; T _torch -torch temperature, °C.

EFFECT: improved strength of mandrel, elimination of flaws on inner surface of tubes.

Description

The invention relates to pipe production, and in particular to a method for the production of seamless pipes, and can be used in the production of pipes in pipe rolling plants with automatic mills.

In pipe production, there is a known method for producing pipes in plants with an automatic mill, including heating the workpiece, piercing the workpiece in a cross-helical rolling mill, rolling the liner in the machine tool, rolling in the rolling mill and calibration [Danilov F.N., Gleiberg A.Z., Balakin V.G. Hot rolling pipes. Metallurgizdat, 1962, p.150].

The disadvantage of this method is the rapid failure of the mandrels of the automatic machine, which leads to the formation of marks and scoring on the inner surface of the pipes.

The closest technical solution is the method of rolling pipes in an automatic machine, which consists in periodically turning the mandrel after the pipe leaves the caliber. [At 21 to 17/08, A.S. No. 239905, declared 50966, publ. 12/21/73.].

This solution to some extent will reduce the wear of the mandrel, but does not coordinate the problem. When flashing, the front end is uneven, i.e. there is no perpendicularity to the axis and, therefore, when the sleeve is set into the mill, the more advanced part of the end face will somehow get on the mandrel, i.e. mandrel rotation is ineffective.

The aim of the proposed method is to increase the durability of the mandrels, i.e. elimination of tearing and sagging of metal on the surface of the mandrels and, accordingly, elimination of defects on the inner surface of the pipes.

This goal is achieved by the fact that the front end of the sleeve before rolling in the automatic machine is heated to a temperature of 0-50 ° C above the body temperature of the sleeve, while the duration of heating is carried out according to

where t is the duration of heating, s;

S is the wall thickness of the sleeve, m;

D is the diameter of the sleeve, m;

a - thermal diffusivity, m ² / h;

Т _З = Т + (0 ÷ 50 ° С) - temperature of the end face of the sleeve after heating, ° С;

T is the body temperature of the sleeve, ° C;

T _t - temperature of the end face of the sleeve before heating, ° C;

T _f - flame temperature, ° C.

The main reason for the quick failure of the mandrel is the cold front end of the sleeve.

When the sleeve is set by the pusher in the mill, a blow occurs on the work rolls, which is mitigated by the rotation of the rolls, then the bend of the end of the sleeve and a hard blow to the conical part of the stationary mandrel occur, which leads to tearing of the metal or the formation of metal sagging on the mandrel and, accordingly, the formation of marks and scoring on the inner pipe surface.

Comparative analysis with the prototype shows that the proposed method of rolling in a plant with an automatic mill is characterized in that the front end of the sleeve before rolling in the automatic machine is heated to a temperature of 0-50 ° C above the body temperature of the sleeve, while the duration of heating is carried out according to

Thus, the proposed method meets the criterion of "novelty."

Comparison of the proposed solution not only with the prototype, but also with other technical solutions in this technical field did not allow us to identify in them the features that distinguish the proposed solution from the prototype, which allows us to conclude that the criterion of "significant differences".

The method was tested on a plant with an automatic mill 140 "ChTPZ".

In the production of tubing with a size of 73 × 5.5 mm (sleeve size 106 × 8 mm), the mandrels are forced to change through 2-3 rolled pipes. Due to the small mass of the pipe metal, the front end end cools quickly to 750-800 ° C.

In the middle of the inclined grating between the firmware axis and the caliber axis of the automatic machine, a stopper and four jet-torch burners were installed, aimed at the end of the sleeve.

Gas was opened when the end of the sleeve approached the burners and ignition occurred from the temperature of the pipe.

Preliminarily, the temperature of the end face of the sleeve (750-800 ° C), the temperature of the pipe body (1120-1170 ° C), and the torch temperature of 1400 ° C were measured.

After a heating time of 2.0-2.5 s, the gas was turned off and the operation was repeated.

When using this method, mandrels were replaced on average through 32 pipes, i.e. resistance has increased by more than 10 times. At the same time, the mandrels were replaced not due to scratches and scoring on the inner surface of the pipes, but to increase the pipe wall thickness (wear).

An increase in the temperature of the front end by more than 50 ° C with respect to the body of the pipe leads to cases of bending of the pipe edge and stuck on the mandrel, and at a temperature below the body of the pipe reduces the resistance of the mandrels.

Thus, the use of the inventive rolling method in a plant with an automatic mill will increase the resistance of the mandrels and improve the quality of the inner surface of the pipes.

Claims (1)

A method of rolling pipes in a plant with an automatic mill, including heating the billet, flashing the sleeve, rolling it out in the automatic machine, running in the rolling mill and calibrating, characterized in that the front end of the sleeve before heating in the automatic machine is heated no more than 50 ° C above body temperature sleeves, the duration of heating is determined by the formula

where t is the duration of heating, s; S is the wall thickness of the sleeve, m; D is the diameter of the sleeve, m; a - thermal diffusivity, m ² / h; T _s = T + (0 ÷ 50 ° C) - temperature of the end face of the sleeve after heating, ° C; T is the body temperature of the sleeve, ° C; T _T - temperature of the end face of the sleeve before heating, ° C; T _f - flame temperature, ° C.