RU2194583C2 - Mandrel for making tubes in die rolling mills - Google Patents

Abstract

FIELD: tube production, possibly in mills for die rolling of tubes. SUBSTANCE: mandrel includes variable-conicity profile. Conicity value of back end of mandrel α_H consists 0.7 α_T and it is inversely proportional to wall thickness of rolled tube. Length value l of mandrel portion with less conicity consists l=(0.3 - 0.5)Ltot and it is proportional to wall thickness of rolled tube. α_H - conicity value of portion with profile of less conicity; α_T - conicity value of mandrel portion with profile of larger conicity; l - length of portion with less conicity; Ltot - total length of working portion of mandrel. EFFECT: enhanced accuracy of tube size due to reduced wall thickness difference, lowered metal consumption. 2 dwg

Description

 The invention relates to pipe production and can be used in mills for periodic rolling of pipes.

Known mandrel with constant taper (α _t ), which is determined taking into account the thermal expansion of the mandrel during the rolling process and the absolute value of the entire tolerance field on the wall thickness of the rolled pipe, which determines the longitudinal difference between the pipes (dS _t ) [1].

In FIG. 1 are schematically shown:
ABB ¹ - forming mandrel with profile according to [1];
dS _t - longitudinal difference when rolling the pipe on a mandrel with a profile according to [1];
α _t - the taper of the mandrel section with a profile according to [1].

 The main disadvantage of a mandrel with such a profile, designed for the entire field of tolerance for wall thickness, is the receipt on it of a significant number of pipes with wall thickness outside the tolerance field.

 Known mandrel with a variable profile, including from the rear end to the middle of the conical section and the rest in the form of a cylinder [2].

 The disadvantage of a mandrel with such a profile is that after rolling a certain number of pipes on it, significant difficulties arise due to a sharp deterioration in the descent of the pipe from the mandrel during rolling and its removal from the pipe at its end. This is due to local wear of the mandrel located in the place of its greatest heating from the rolled blanks.

 The length of the wear section is more than 1 meter, and the depth of wear exceeds the cone drop over this length, i.e. a sufficiently long section with inverse taper (gh) is formed, which causes these difficulties. When rolling thin-walled pipes, this drawback is compounded by the fact that the axial loads acting on the pipe when it is shifted from the mandrel often exceed the longitudinal stability of the pipes and cause them to collapse ("accordion").

In FIG. 1 are schematically depicted:
ABC - forming mandrel with profile according to [2];
egh - mandrel wear line;
gh is the inverse taper mandrel section.

 The technical result is achieved by improving the quality of pipes by reducing the longitudinal difference, reducing metal consumption, reducing machine downtime and increasing the tool life in the manufacture of pipes by periodic rolling using a mandrel, the profile of which is made with variable conicity, smaller in the section from the rear end of the mandrel .

The solution to this problem is achieved by the fact that in the known design, the mandrel for the production of pipes on batch rolling mills with constant tapering of the working surface [1] part of it from the rear end is made with a taper less than from the front end. In this case, the taper of the mandrel from the side of the rear end α _n is up to 0.7 α _t and is inversely dependent on the wall thickness of the rolled pipe. The length of the mandrel section with less taper (Fig. 2) is l = (0.2-0.6) L _total and is directly dependent on the wall thickness of the rolled pipe.

In FIG. 2 are schematically depicted:
ADC - forming mandrel with a new profile;
α _n - the taper of the plot with a profile of less taper;
l is the length of the section of the mandrel with less taper;
L _total - the total length of the working section of the mandrel.

 When determining the length of the mandrel section with reduced taper, the longitudinal stability of the rolled pipes is taken into account. With a greater longitudinal stability of the pipes, the length of the section with reduced taper can reach a maximum, and with a lower longitudinal stability of the pipes, it can be a minimum.

 The use of the invention will improve the quality of pipes by reducing their longitudinal difference, reduce metal consumption, reduce machine downtime, increase tool life in the manufacture of pipes by periodic rolling.

BIBLIOGRAPHIC DATA
1. P.T. Emelianenko. Pilgerstans. ONTI, NKTP. DNTVU. 1937, p. 124-130.

 2. Yu. M. Matveev, Y.D. Vatkin. Calibration tool pipe mills. - M.: Metallurgy, 1970, p. 166-171.

Claims (1)

Dorn for the production of pipes in batch rolling mills, having a variable profile, characterized in that the profile is made with variable taper, while the taper of the mandrel from the rear end side α _n is up to 0.7 α _t and is inversely dependent on the wall thickness of the rolled pipe , and the length of the section of the mandrel with less taper is l = (0.3 ÷ 0.5) L _total and is directly dependent on the thickness of the rolled pipe, where:
α _n - the taper of the plot with a profile of less taper;
α _t - taper of the mandrel section with a profile of greater taper;
l is the length of the section of the mandrel with less taper;
L _total - the total length of the working section of the mandrel.

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