US3498096A - Hot piercing mill with skew rolls for the production of seamless metal tubes - Google Patents

Description

' March 3, 1970 c. M ONTAGNA 3,493,096

HOT .PIERCING MILL WITH SKEW ROLLS FOR THE PRODUCTION OF SEAMLESS METAL TUBES Filed 0ct'.v20, 1967 l 2 Sheets-Sheet 1 INVENTOR.

CHRLO MONT/76AM March 3, 19-70 C.&MONTAGNA 3,498,096

v MILL WITH {.SKEW ROLLS FOR THE OF SEAMLESS METAL TUBES 301 PIERCING 2 Sheets-Sheet 2 raonucwxon and Oct. 20, 196? 4 H nvvawrag C4250 MONTAGNA United States Patent Oflice 3,498,096 Patented Mar. 3, 1970 3,498,096 HOT PIERCING MILL WITH SKEW ROLLS FOR THE PRODUCTION OF SEAMLESS METAL TUBES Carlo Montagna, Via Luciano Manara 15, Milan, Italy Filed Oct. 20, 1967, Ser. No. 676,823 Claims priority, application Italy, Nov. 3, 1966, 29,542/ 66 Int. Cl. B21b 19/04 U.S. C]. 72-97 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novel hot piercing mill for the production of seamless metal tubes from round blooms using skew rolls.

In the novel hot piercing mill one of the rolls is hollow and the other one, of traditional barrel design, is positioned inside said hollow roll, the bloom to be pierced being positioned between the inner surface of the hollow roll and the outer surface of the barrel roll.

DESCRIPTION OF THE INVENTION Having briefly summarized the disclosure, the present invention relates to hot piercing mills with skew rolls for the production of seamless tubes and more particularly to a new piercing mill with one hollow roll having in the inside the second roll.

In the production of seamless tubes, for the hot piercing of round blooms (ingots or billets) a skew-rolls mill, Mannesmanns type, having two or more barrel type rolls or similar, is normally used.

It is known that the combined action of the two rolls, while advancing the bloom with roto-traverse motion, starts also the breaking off (disgregation) of its axial core. Said effect is later completed by the action of a plug suitably shaped, which is fitted to a bar on the extension of the bloom axis. This plug Widens and smooths the bore produced by the skew rolling. It is also known that in order to obtain such a rate of deformation of the bloom to cause breaking off at the center, it is necessary to have the rolls act on the bloom with a strong rolling force. The result of this force is a stress in each element of the bloom.

In each cross-section through the bloom, ahead of the position where the breaking off of the core starts, the unitary compressive stress diagram, along the diameter perpendicular to the direction of the compressive force, is a very steep one (with a maximum of the axis of the bloom).

The compressive stresses, which cause the breaking off of the axial core, are concentrated in a limited central part of the bloom, where they reach a high absolute value. We have, therefore, in said part great differences of stress among one point and those immediately adjacent. This (together with the action of ovalization of the bloom due to the rolls) causes tearings in the material, which can spread out also to some distance from the axis and which will not be eliminated by the further widening action of the plug, thus originating a defective bore surface.

With the present invention, we have found a remedy for this trouble, as it realizes working conditions suitable for getting a much more flat diametrical diagram of the compressive stress for the central part. We have, i.e., in comparison with the previous case, a lower absolute value of the stress in correspondence of the axis of the bloom; moreover we have in the central core, where the breaking off occurs, lower differences between the stress in one point and that in the adjacent points. The above mentioned danger of tearing the material is thus eliminated. That (together with a less pronounced action of ovalization) enables to obtain hollow blooms with a sounder inside surface.

According to the present invention the hot piercing mill has one hollow roll, duly profiled on the inner surface, and one traditional barrel roll of known design profiled in agreement with said inner surface, positioned inside said hollow roll in a manner that between the inner surface of the hollow roll and the outer surface of the barrel roll there is sufficient room for the positioning and working of the bloom.

Objects and advantages of the present invention will be readily apparent from the following detailed description, when considered in connection with the accompanying drawings in which:

FIG. 1 shows diagrammatically the piercing mill in a cross section according to a plane normal to the axis of the bloom.

FIG. 2 shows the same mill in cross section according to the horizontal plane II-II; and

FIG. 3 represents the cross section according to the vertical plane III-III.

With reference to FIGS. 1, 2, and 3, wherein similar reference characters indicate like parts, the novel hot piercing mill comprises essentially the hollow roll 1, the usual barrel roll 2, the round bloom 3 to be pierced and the piercing plug 4.

Referring to FIG. 2, roll 1 has an inner convex surface as shown and is journalled in suitable roller bearings 10 into a casing (not shown in the figure) equipped with the necessary positioning and control means of known type. On roll 1 an annular rotor is fitted, bearing a ring gear 5 which is driven through a pinion 6, by a known drive system consisting of gearbox and motor (not shown in the figure).

Again referring to FIG. 2, roll 2 has an outer convex surface which is in agreement with the convex surface of the roll 1 and is journalled on suitable bearings 8 supported in a fork shaped chock (not shown in the figure) not connected with the above mentioned casing which is also equipped with positioning and control means of known type.

The two rolls have a different speed of revolution, in relation to the respective diameters. They can have a common drive in which case the ratio among their respective numbers of revolutions is fixed, or each roll may have its own drive system and, therefore, an independent speed control. The piercing mill is completed by two fixed guide shoes 7, which serve both to contain the ovalization of the bloom during the skew-rolling, and to keep the bloom in the desired working position.

When the two rolls have a separate drive, it is possible to eliminate the guides as the bloom position can be controlled acting on the speed control of the rolls. It is clear that (as shown in FIG. 3) also in the piercing mill object of the present invention, the axes of the two rolls have to be skewed of a certain angle in respect to the axis of the bloom (or mill centerline) in order to obtain the conditions of skew rolling on which process is based.

The size variations of the hollow blooms to be produced can be obtained either by varying the relative positions of the two rolls or by duly modifying their relative speeds, in order to bring the work piece in a position suitable to the desired diameter, moving its axis out of the plane of symmetry of the mill.

This latter possibility is shown by setting 3 (in shortdashed line) of FIGURE 1, which represents a hollow bloom with a smaller diameter than that of setting 3, which is being worked without altering the relative position of the two rolls, but simply moving the bloom axis out of the plane of symmetry of the mill by means of a suitable speed adjustment of the two rolls.

Inasmuch as various changes may be made in the form, location and relative arrangement of the parts without departing from the essential characteristics of the invention, it is to be understood that the invention is not limited to or by the foregoing disclosure of the exemplary embodiment the inventive scope being defined in the appended claims.

What is claimed is:

1. A hot piercing mill with skew rolls for the production of seamless metal tubes from a solid bloom, comprising one hollow roll, duly profiled in the inner surface with a convex surface, and one traditional barrel roll having an outer surface profield with a convex surface in agreement with said inner surface, said barrel roll being positioned inside said hollow roll in a manner that between the inner surface of said hollow roll and the outer surface of said barrel roll there is sufficient room for the positioning and working of the bloom.

2. A hot piercing mill with skew rolls for the production of seamless metal tubes from a solid bloom, comprising one hollow roll, duly profiled in the .inner surface with a convex surface, and one traditional barrel roll having an outer surface profiled with a convex surface in agreement with said inner surface, said barrel roll being positioned inside said hollow roll in a manner that between the inner surface of said hollow roll and the outer surface of said barrel roll there is sufficient room for the positioning and working of the bloom which is kept in the desired working position by two fixed guide shoes;

3. A piercing mill according to claim 1 further comprising a separate driving system for each of the two rolls with an independent speed control.

4. A hot piercing mill as set forth in claim 1 further comprising a piercing plug between said inner surface and said outer surface for piercing the solid bloom during working thereof.

5. A hot piercing mill as set forth in claim 4 which further comprises a pair of fixed guide shoes between said inner surface and said outer surface for containing the ovalization of the bloom and the position of the bloom during working.

6. A method of producing seamless metal tubes from a solid bloom comprising the steps of feeding a hot round solid bloom between a convex surface of a rotating annular roll and a corresponding convex surface of a barrel shaped roll, rotating the barrel shaped roll within the annular roll on an axis inclined with respect to the Z axis of rotation of the annular roll, and piercing the core 459,752 9/1891 Jackson et al 72-97 CHARLES W. LANHAM, Primary Examiner L. A. LARSON, Assistant Examiner

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