EP1008400A2 - Method for reducing trumpet-shaped widenings on the leading end of a pipe - Google Patents

Abstract

Leading end trumpet formation prevention during thin-walled tube skew rolling involves moving apart and swiveling the rolls as the conical portion of the mandrel rod moves through the roll gap.

Description

The invention relates to a method for reducing trumpet-shaped widenings on front pipe end when diagonally rolling thin-walled pipes on an Assel mill, at which is conically offset at the front end between two cylindrical areas Mandrel bar positioned according to its starting position when entering the front Hollow block area in the Assel mill is moved axially controlled in the rolling direction.

The invention is based on DE 197 24 233 A1 in which it is proposed when running in of the front hollow block area in the woodlice mill the radial forming of the billet compared to the stationary rolling condition and / or the section modulus of the cross section of the cap at the head end by obstructing the tangential material flow to increase. As a result, in the unsteady phase when rolling the tube blank in the Asselwalzwerk conditions created that the stationary rolling condition to come close. The material flow in the tangential direction is reduced so that the missing tension in the axial direction is partially compensated. The result is one Depending on the tube wall thickness, reduced or avoided formation of trumpets on the front The end of the bobbin is recognizable, but the further transport and further processing of the bobble is not more difficult or hindered. The disadvantage, however, is that the wall thickness of the Tube end enlarged, so that a significant amount of material cut off as scrap must become. So it would be better if the material accumulation by increasing the Wall thickness would not even arise.

In recent years, the area of application of woodlice mills became thanks to introduction various innovations on thin-walled blanks up to about D / S ∼ 40 and beyond expanded. If D / S ∼ 10 ... 12 is exceeded, however, the front is created Luppe end a trumpet-shaped diameter enlargement or widening that the Further transport and further processing of the slug is difficult, impeded or impossible makes. The cause of the trumpet-shaped expansion can be explained by the fact that in the unsteady phase when rolling the hollow block or the front hollow block end up to completely fill the forming zone in the axial rolling direction of the normal stationary one Stress condition in the rolling stock, i.e. not yet in the hollow block or rock material is available; because the tension in the axial direction is missing completely or partially. There, compared to the steady state, the material speed and the material flow essential when rolling wood in the circumferential direction of the tube in the unsteady state is greater than in the longitudinal direction, promote or increase higher rolling speeds of the Material in the circumferential direction of the slug or in the tangential direction at the stage of Rolling without longitudinal tension, the stretching of the material in the circumferential direction. The Material flow that is caused by the radial deformation, i.e. by reducing the wall thickness is therefore preferably in the tangential direction, less in the longitudinal direction (Axial) direction, so that the circumference or diameter of the plate is enlarged. This locally and temporarily process-related diameter enlargement manifests itself at the bowl head as a trumpet-shaped expansion.

It has been proposed (DE 44 28 530 A1), the funnel-shaped expansions on to influence the rear end of the slab by constricting the rolling stock controlled axially advanced mandrel rod is rolled in so that in the rolling direction at the back there is a short pipe end with a thickened wall. Apart from that this proposal is only applicable at the rear end of the bob, it is usually required constant hollow block length, rolling time or rolling speed, so that the sales of Mandrel bar always in exactly the right place when rolling out the end of the slug stands between the rollers, which can hardly ever be achieved. If the sloop is shorter, the offset part comes too late between the rollers and the intended effect occurs not a. If the blank is longer, then the part that has been removed is too early between the rollers and the thick-walled end becomes too long, which means increased material losses. This means that the mandrel rod is constantly positioned differently when the length of the hollow block fluctuates should be. To avoid this, the prior art proposes that To accelerate or stop the mandrel bar at the end of the rolling process; an effort which is not ideal in terms of technology and wear. The Application of the known method for preventing trumpet-shaped widenings on the rear end of the bob cannot be transferred to the front end of the bob, so that other ways need to be found.

The object of the present invention is to find a method with which the trumpet-shaped expansion of thin-walled slugs at their front end when Rolling in an Assel mill reduced in size to a harmless level can be.

To solve the problem it is proposed that when rolling the tube on the Rolling wall thickness set woodlice rollers while maintaining their between the Cone of the mandrel rod and the smoothing part of each wood roll formed nip at the same time with the displacement of the mandrel rod and analogous to the increasing course of the cone The mandrel rod is moved apart and at the same time pivoted so that the smoothing part the woodlouse roller runs essentially parallel to the cone of the mandrel bar. With this Proposal is an annoying trumpet formation of the front pipe end during woodlice rolling avoided, although the nominal wall thickness at the pipe end is maintained. With the The method according to the invention enables lossless woodlice rolling. Pipe ends with thickened wall no longer occur.

An essential part of the process is the use of a mandrel bar attached to its free End has a cone and then has a cylindrical piece, the Diameter is smaller than the actual mandrel rod diameter. The mandrel bar is in Rolling direction shiftable at controlled speed.

In one embodiment of the invention, the hollow block is located at the beginning of the rolling with its front edge in front of the shoulder of the woodlice. If this point is reached, the Mandrel bar advanced at a set speed in the rolling direction. At the same time, the woodlice are moved apart and pivoted so that the The distance between the mutually parallel surface lines remains constant, i.e. the Pipe wall thickness is maintained. When the end of the cone is reached, the woodlice rolls no longer spread apart. Then the woodlice rolls so far pivoted back that now the surface line of the smoothing part parallel to the surface line of the (cylindrical) mandrel bar lies. The distance between the surface lines corresponds to each other continue to the rolled tube wall thickness, thickened ends do not occur.

Favorably, the woodlouse rollers are pivoted about their roller centers, whereby the rolling centers lie on a vertical of the longitudinal axis of the roll, which is the smoothing part the rollers cut in the middle.

When the beginning of the pipe passes through the woodlice, one still occurs Triangle formation. But since the pipe start practically on the cone of the mandrel bar rolled down a smaller diameter and the pipe circumference is reduced, the triangle disappears as it passes through the rounded part of the woodlice. On In this way, the beginning of the pipe is given a diameter that largely corresponds to that of the Corresponds to the mother tube or is slightly smaller.

Fig. 1

die Stellung der Dornstange bei Walzbeginn und

Fig. 2

die Stellung der Dornstange im stationären Betrieb.

An embodiment of the invention is shown in the drawing and is described below. It shows:

Fig. 1

the position of the mandrel bar at the start of rolling and

Fig. 2

the position of the mandrel bar in stationary operation.

The two drawing figures give a rough schematic of the conditions in woodlice rolling a thin-walled tube again. Shown are one of the woodlice 7 and the Mandrel bar 1, which has a cone 2 of e.g. 150 mm long and attached to it then again a cylindrical piece 3 of e.g. 120 mm long. The Diameter 4 of this cylindrical piece is e.g. 15 mm smaller than the real one Mandrel rod diameter 5. The mandrel rod 1 is controlled in the rolling direction 6 Slidable speed.

At the start of rolling (FIG. 1), the mandrel rod 1 with its cone 2 is in a stationary state Position between the Asselwalzen 7, the end 8 of the conical part under the Shoulder 9 of the woodlice 7 lies. The roller longitudinal axis a - a is now around the Roll center M pivoted in the direction of arrow X so that the surface line 10 of the smoothing part the woodlice is approximately parallel to the opposite surface line 11 of the cone 2. The distance between the two lines gives the wall thickness of the rolled pipe. A however, the exact parallel position of the surface lines of both bodies only results if the Transport angle of the woodlice is 0 °. Since a transport angle is used to advance the rolling stock is necessary, the surface lines are not actually parallel, but spatially oblique to each other and strive away from the center of the smoothing part. The result The resulting dimensional deviation of the wall can be neglected in practice. The The slightest deviation arises when the pivot axis 12 is drawn through the center as shown of the smoothing part passes through.

At the start of rolling, the hollow block 14 is located with its front edge 15 in front of the shoulder 9 of the Asselwalzen 7. When this point is reached, the mandrel bar 1 with a fixed Speed advanced in the rolling direction. At the same time the woodlice 7 so moved apart that the distance of the surface lines 10 and 11 from each other constant remains, i.e. the pipe wall thickness is maintained. When the end of cone 2 has been reached the Asselwalzen 7 no longer moved apart. Then the Asselwalzen 7 pivoted back in the direction of arrow Y (Fig. 2) that now the surface line 10 of the smoothing part is parallel to the surface line 13 of the cylindrical part 3 of the mandrel bar 1. The distance between the surface lines 10 and 13 from each other continues to correspond to the rolled Pipe wall thickness.

When the beginning of the pipe passes through the woodlice 7, one continues to occur Triangle formation. However, since the pipe start is practically on the cone 2 of the mandrel rod 1 rolled down to a smaller diameter 4 while reducing the pipe circumference the triangle disappears as it passes through the rounded part of the woodlice 7. In this way, the beginning of the pipe gets a diameter that that of the mother pipe corresponds or is somewhat smaller.

Claims (3)

Method for reducing trumpet-shaped widenings at the front pipe end when cross-rolling thin-walled pipes on an Assel rolling mill, in which the mandrel rod, which is tapered at the front end between two cylindrical areas and is appropriately positioned in its starting position, is moved axially controlled in the rolling direction when the front hollow block region enters the woodlice rolling mill,
characterized, that the Assel rolls set to the wall thickness to be rolled when the pipe is rolled, while maintaining their roll gap formed between the cone of the mandrel bar and the smoothing part of each Assel roll, are moved apart and pivoted at the same time as the mandrel bar moves and analogously to the increasing course of the cone of the mandrel bar, that the smoothing part of the woodlouse roller runs approximately parallel to the cone of the mandrel bar. Method according to claim 1,
characterized, that at the start of rolling the hollow block lies with its front edge in front of the shoulder of the woodlouse roller and the mandrel bar is positioned so that its conical part is in a resting position between the woodlice rollers and its transition from thin cylindrical part to the conical part is under the shoulder of the woodlice roller The method of claim 1 or 2,
characterized, that the pivoting of the woodlum rolls takes place around their roll centers and that the roll centers lie on a perpendicular to the roll longitudinal axis, which cuts the smoothing part of the rolls in the middle.

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