CZ235395A3 - Grooving of rolls of inclined rolling device - Google Patents

Abstract

The invention concerns set-up of the rolls of a skew rolling mill, in particular, an Assel mill for production of pipes out of pre-pierced hollow blanks on a mandrel by means of at least three rolls. Such rolls are separated from one another by a circumferential angle of 120 deg., incline at a spreader angle towards the rolling axis, and are additionally pivoted through a transport angle (alpha ) relative to this axis. Each roll consists of a run-in cone (2), a shoulder (3), a smoothing section (4) and a rounding cone (5). Roll set-up is characterised by combination of the following features; a) the pivot axis of each roll for forming the transport angle (alpha ) cuts the axis of the blank at a right angle, and passes through the middle of the smoothing section (4); b) the section (4) has a concave shape corresponding to the local pipe diameter; c) the length of the section (4) is chosen so that the overlap of three rolls varies from 115 to 150%; d) the transport angle (alpha ) varies from 7 to 15 deg., and preferably is 10 deg.

Description

Calibration of rollers of inclined rolling equipment

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the calibration of rolls of an inclined rolling apparatus for rolling tubes from punched tubular billets through a mandrel, in particular an Assel rolling apparatus having at least three rollers offset by 120 ° relative to each other. they always have a tapered cone, a working part (step), and a smoothing part followed by a rounding cone.

BACKGROUND OF THE INVENTION

In various known oblique rolling devices for punching and drawing of massive and perforated billets of metal according to Mannesmann, Stiefel, Diescher and Assel, they occur on the billets, respectively. pipe, the spiraling unevenness of the wall thickness, the so-called helix. These manifest themselves in the cross-section of the billets as eccentricity, i.e. the deviation of the centers of the inscribed and circumscribed circle, and in the longitudinal section, as the periodic and alternating wall thickening and weakening. These deviations can lead to a deterioration in the quality of the pipe at the corresponding size. In general, however, rolled tube manufacturers try to achieve the highest possible shape accuracy to avoid unwanted rejects.

The cause of the helix is mainly due to insufficient calibration of the cylinders. With an oblique punch rolling machine as a pre-rolling tube, this may still be permissible if the obligatory subsequent rolling operation is longitudinal rolling. This can be rolling on a mandrel, on an extrusion mill, or on a continuous rolling mill. During longitudinal rolling, the helices can be straightened if not completely removed.

However, if the next rolling operation is again an oblique rolling process, for example in a Diescher or Assel rolling apparatus, the helixes are not completely smoothed out of the punching operation, but instead new helices are formed which may lie on the existing helices and thus strengthen them further.

The Assel rolling method for producing rolling bearings and thick-walled tubes for rotating parts with a diameter / wall ratio of about 16: 1, developed about 60 years ago by Walter Assel, has evolved into a powerful elongation method through continuous improvement. It is used in the manufacture of tubes with medium or large wall thickness, especially those which are intended to have perfect surfaces and narrow tolerances, as is the case with tubes for rolling bearings. The Assel rolling device operates on the principle of inclined rolling over a mandrel rod, wherein three conical cylinders are engaged which are inclined to the axis of the rolled goods and are offset by 120 ° to each other. In addition, the rollers are adjustable perpendicular to the axis of the rollers so that a number of tube diameters can be produced on a single Assel rolling machine. The working rolls of the Assel rolling device consist essentially of a leading-in part, a working part (shoulder), a smoothing part and an outlet and rounding part. The main forming work is carried out in the working part on the shoulder. Against the Diescher method, in which it is known to employ two so-called barrel rollers, the Assel method has the advantages of better guiding the rolled goods by fitting at least three rollers and eliminating the need to fit the guide discs. A particular advantage is that the Assel rolling mill needs a substantially smaller diameter of the rolls, which results in these machines being generally smaller than the corresponding Diescher rolling mill.

In the Assel method, the perforated tubular billet protrudes directly into the forming zone and stabilizes its wall of the just rolled tube just beyond the forming zone, in the so-called roll-on zone of the roll, by its thick wall, thereby avoiding excess triangulation. Thus, diameter / wall thickness ratios of greater than 35: 1 are possible when certain precautions are taken to allow the pipe ends to be rolled without the formation of funnels (DE 38 23 135).

It has not yet been solved how to prevent or assassin the Assel method. strongly reduce, by the introduction described helix formation. Although in the usual Assel method, i.e. relatively thick walls, narrow tolerances are known to be achieved in a wall thickness of ± 4 to ± 8%, the accuracy is not yet perfect. It is desired, especially with regard to thin walls, to further improve these tolerances in the Assel method by avoiding or reducing the helix. This is the object of the present invention.

SUMMARY OF THE INVENTION

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To achieve this goal, the present invention proposes a combination of the following measures:

a) The axis of rotation X-X, according to which each cylinder is rotated to form a conveying angle γ, intersects the axis Y-Y of the rolled goods at a right angle and passes through the center of the trowel of the cylinder;

b) The smoothing part of the cylinder is formed concavely with the pipe diameter (rod diameter + 2 times the wall thickness) available.

(c) The length of the roller scraper is chosen so that the overlap of the scraper parts of the three cylinders is 115 to 150%.

d) The conveying angle γ of the roll is 7 ° to 15 °, preferably 10 °.

The range given for the conveying angle γ takes into account the fact that, in theory, the caliper according to the invention can be optimally used for only a single pipe diameter. However, since in practice different tube diameters are rolled on an Assel rolling device, the rounding is primarily designed to correspond to the mean tube diameter. This results in a slight deterioration in the wall thickness tolerance, but this can be corrected by the fact that the conveying angle γ can be varied in a given region, whereby an optimum position of the sheathing line of the wiper portion to the pipe can be set.

The proposed measures make it possible to achieve considerable improvements in wall thickness tolerances, especially for thin walls.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 One of the three Assel rolls of a conventional Assel rolling apparatus in the longitudinal median plane of the tube with a so-called divergent rolling position.

Fig. 2 A top view of an Assel cylinder with a conveying angle γ = 0 °.

FIG. 3 is a top view of an Assel cylinder rotated according to the invention.

FIG. 4 is a front view of an Assel cylinder calibrated according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The cylinder 2 consists, according to FIG. 1, of the taper cone 2 'of the working part (shoulder) 3, the trowel part 4 and the rounding cone 5. The taper cone 2 and the trowel part have straight sheath lines, the taper cone 2 can also be divided into two cones with different conical angle. This is also known with rounding cone 5. Rounding cones with convex sheath lines are also known. On the tapered cone 2, the perforated tubular bar 6 is gripped, rotated and stretched onto the cylinder 2. Hereby, the outer and inner diameters of the tubular bar 6 are reduced to such an extent that the perforated tubular bar 6 touches the mandrel bar with its inner surface. The wall thickness is not substantially reduced here. The wall thickness is decisively reduced only below the shoulder 3. The smoothing part 4 serves to equalize the wall thickness of the pipe Ί. When rolled under the shoulder 3 in the smoothing portion 6, the tube expands and takes on a polygonal cross-section, as the wall extends into the spaces lying between the rollers. On the adjacent rounding cone 5, the polygonal tube 7 is rounded.

As can be seen from the front view of Figure 1, the cylinder 1 is rotated to the longitudinal axis YY by an angle g, with the axis of the cylinder ZZ intersecting the longitudinal axis YY at point A. However, from the top view of the cylinder (Figure 2) in this case it is only 0 ° and the rolls cannot perform any feed of the perforated billet 6. Therefore, the rolls are set to a conveying angle χ> 0 ° by rotating about the axis of rotation XX in Figure 1. rotating XX by the apex of the cylinder, which is the largest diameter of the barrel-shaped oblique cylinders, and in the case of the Assel cylinders, the diameter of the cylinder at the outer edge of the shoulder. This is the same case for all three cylinders.

In the geometrically ideal case according to FIG. 2, namely, at a conveying angle of χ = 0 °, the liner 9 of the smoothing portion 4 lies absolutely parallel to the opposite liner liner 10 of the mandrel rod 8 / as shown in FIG. ZZ and the longitudinal axis YY at the point of intersection A. In this position, that is to say with parallel lines 9 and 10 of the two shells, the rolling gap ppd has the wiper portion 4 everywhere.

Ί same width, ie. here the rolled wall of the tube 4 is equally thick at any point below the smoothing roller 4. When the screed portion is long enough and there is a sufficient degree of overlap with the other rollers, no helices are formed on the tube 7).

and

However, since the rollers are rotated by a conveying angle X for the spiral forward movement of the rolled goods, the liner liner 9 moves away from the liner liner liner 10 with an increasing distance from the narrowest point that lies at the top of the shoulder. The distance between the lines 9 and 10 of the two tires increases. In the same direction, an increase in the wall thickness of the tube 7 in the region of the smoothing portion 4 is also observed. Since the tube 7 rotates in accordance with the peripheral speed of the rollers and the displacement of the conveying angle γ, while taking into account the displacement effect, the tube 7 in this way acquires a spiraling surface roughness, simply called a helix. The helix is multiple according to the number of rollers.

Experimental rolling yielded a helix depth of 0.3 mm, with the helix depth meaning the difference between the strongest and the weakest wall thickness of the helix. The measurement is confirmed by numerical testing of the helix thicknesses as shown in the following example:

*

Taking the conveying angle γ = 10 ° ¹ and the pipe diameter below the smoothing part of cylinder 1 as possible. D = 250 mm, the helix pitch is about 46 mm in three cylinders. The length of the screed would have to be slightly longer than this dimension in order to completely overlap the screed parts of all three rollers.

Assel rolling equipment. The widest line spacing

9, 10 of the two skins is 0.25 + .5 mm, provided that the narrowest point lies exactly on the outer edge of the shoulder 13 of the cylinder. The symbol s indicates the wall thickness of the pipe.

The invention proposes a combination of measures to prevent the formation of helix on the pipe. By moving the cylinder rotation axis X1-X1 to the center of the trowel portion 4 of the cylinder 11 as shown in Figure 4, the narrowest point between the lines 9, 10 of the two skins is moved from the bottom of the shoulder 3 to the center of the trowel portion 4. 9, the distances between the lines 9, 10 of the two shells are divided on both sides of the axis of rotation X1-X1 and thus reduced by about half. In this way, a considerable improvement in the wall thickness tolerance of the pipe is already achieved. By providing a smoothing portion 14 with slightly inwardly curved, i.e. concave, skin lines, a further improvement is achieved. In this case, the curvature of the liner line is formed in such a way that the liner line 9 of the smoothing portion 4, which lies directly opposite the line 10 of the mandrel bar 8, has the same distance to the liner line 10 over its entire length. In this way, the wall of the tube 7 contained in the smoothing part 4 is rolled with a uniform wall thickness and the formation of a helix is avoided. The length of the scraper portion is selected such that the overlap is 115-150%.

In theory this means that this cylinder shape can only be used with a single pipe diameter. However, since in practice different tube diameters are rolled on an Assel rolling device, the curvature of the scraper portion 4 is designed to correspond to the mean tube diameter. This again leads to a slight deterioration of the pipe wall thickness tolerances, but this can be corrected by varying the conveying angle [gamma] in the determined area. In this way, it is possible to set the optimum relative position of the lines 9, 10 of the two skins.

The combination of the proposed measures results in a considerable improvement in the wall thickness tolerances of Assel rolling.

Claims (2)

PATENT CLAIM 1. Calibrating the rollers of an inclined rolling machine:) k (i ₎ rolling tubes from perforated tubular billets through a mandrel. 2 in particular, an Assel rolling mill having at least three rollers> --- offset by 120 ° relative to each other, tilted against the rolling axis by an angle α and rotated against the rolling axis by a conveying angle γ, each having a taper, working part (shoulder) and smoothing the part to which the rounding cone extends, characterized by a combination of the following measures: a) the axis of rotation (X-X) according to which each roller is rotated to form a conveying angle (γ), intersects the axis (Y-Y) of the rolled goods at right angles and passes through the center of the roller trowel (4) b) the smoothing part (4) of the cylinder (1) is made concavely with the diameter of the tube (rod diameter + 2 times the wall thickness) available c) the length of the trowel (4) of the roller (1) is chosen such that the overlap of the trowel (4) of all three rollers (1) is 115 to 150% d) the conveying angle (γ) of the cylinder (1) is 7 ° to 15 °, preferably 10.