EP0882526B1 - Method and device for preventing or reducing trumpet-shaped widenings on a pipe end by skew rolling of thin-walled pipes - Google Patents

Abstract

The prevention or reduction of the trumpet like expansion of the pipe end during rolling of thin walled pipes on an Assel mill comprises reducing the degree of radial forming of the blank as the front end of the hollow blank enters into the mill, in comparison to the stationary state of rolling, and/or increasing the resistance torque of the blank cross section at the front end by reduction of the tangential material flow. At least one roll and preferably all rolls (A) are provided quick acting hydraulic closing and opening units which allow the rolls to be set radially against the rolled material (C, D), in a short time interval and also against the rolling force. The maximum closure distance of each movable roll is equal to the corresponding shoulder height or to the maximum wall thickness reduction.

Description

The invention relates to a method and an apparatus for performing the Procedure for avoiding or reducing trumpet-shaped widenings on Pipe end when diagonally rolling thin-walled pipes on an Assel mill.

Such a method and such Device are according to the preambles of Claims 1 and 7 from DE 44 28 530 A known.

Instationäre Phase:

Anwalzen des Hohlblockes bzw. des vorderen Hohlblockendes bis zum vollständigen Füllen der Umformzone in axialer Walzrichtung.

Stationäre Phase:

Walzen des Hohlblockes zur Luppe nach dem Füllen der Umformzone unter annähernd gleichmäßigen Temperatur- und Reibungsbedingungen bis zum

Beginn des Leerens der Umformzone, d.h. wenn die hintere Stirnfläche des

Hohlblockes die Stelle des ersten Kontaktes zwischen Hohlblock und Walze im Einlaufteil passiert.

Instationäre Phase: Auswalzen des hinteren Hohlblockendes vom Beginn des Leerens bis zum Ende des Leerens der Umformzone, d.h. wenn die hintere Stirnfläche der Luppe die Stelle des letzten Kontaktes zwischen Luppe und Walze im Auslaufteil passiert.

Until now, the use of woodlice mills was limited to the production of thick to medium-walled tube blanks. In recent years, thanks to the introduction of various innovations, the field of application has been expanded to thin-walled blanks up to about D / S ∼ 40 and beyond. Even if D / S ∼ 10 ... 12 is exceeded, a trumpet-shaped diameter enlargement or widening occurs at the front end of the head (at the head of the head), which complicates, hinders or makes impossible the further transport and further processing of the head. The cause of the trumpet-shaped expansion can be explained as follows. The Assel rolling process is divided into three different phases:

Transient phase:

Rolling on the hollow block or the front end of the hollow block until the forming zone is completely filled in the axial rolling direction.

Stationary phase:

Rolling the hollow block to form a blank after filling the forming zone under approximately uniform temperature and friction conditions up to

Start of emptying of the forming zone, ie when the rear face of the

Hollow block passes the point of first contact between the hollow block and roller in the inlet part.

Unsteady phase: Rolling out the rear end of the hollow block from the start of emptying to the end of emptying of the forming zone, ie when the back face of the blank passes the point of last contact between the blank and the roller in the outlet part.

In the unsteady phases the normal steady state is in Rolling stock, i.e. not yet in the hollow block or rock material (front end) or no longer available (rear end); because the axial tension is missing Direction completely or partially. Because the material speed and the material flow in the Assel rolling, which is an oblique rolling process, in the circumferential direction of the tube is significantly larger than in the longitudinal direction, promote or increase higher Rolling speeds, especially in the rolling stage without longitudinal tension. the stretching of the material. The material flow caused by the radial deformation, i.e. is enforced by reducing the wall thickness, therefore preferably goes in the tangential direction, less in the longitudinal (axial) direction, so that the circumference or diameter of the plate is increased. This locally and temporarily process-related diameter enlargement manifests itself on the head as trumpet-shaped expansion.

The driving force for this expansion is the material displacement per unit of time that occurs in the absence of longitudinal tensile stress, which is mainly influenced by the degree of wall reduction and the feed angle, whereby the geometry of the hollow block used also plays an important role in preventing the undesired flow of material. If the wall thickness of the bobble exceeds a certain dimension or if its ratio D _L / S _L falls below a certain amount, for example 10, the expansion-related formation of trumpets on the bobble head is small or practically imperceptible.

It has been proposed (DE 44 28 530 A1), the funnel-shaped widenings at the rear end of the bobbin in that the rolling stock into a Constriction of the axially advanced dome rod is rolled in, so that in the rolling direction at the back a short pipe end with a thickened wall Apart from the fact that this suggestion arises only at the back end of the bob applicable, it usually requires constant hollow block length, rolling time or Rolling speed so that the paragraph of the dome bar when rolling out the End of bobbin is always exactly in the right place between the rollers, what can practically never be realized. If the slab is shorter, the offset part comes to late between the rollers and the intended effect does not occur. Is the sloop longer, then the separated part is too early between the rollers and that thick-walled end becomes too long, which means increased material losses. This means that the dome rod is always different when the length of the hollow block fluctuates would have to be positioned. To avoid this, the prior art proposed to accelerate the dome bar at the end of the rolling process or to stop; an effort that is technological and in terms of Wear is not ideal. The use of the known prevention method Trumpet-shaped widenings at the back end of the bob cannot be attributed to this transfer the front end of the slab so that other ways must be found.

From DE 19 39 778 it is known that the roll adjustment by an overdrive change in a short time to influence the formation of different To take wall thicknesses.

According to DE 36 22 678 this can also be achieved if with an axial movable dome is worked, the different outer diameter having. The wall thicknesses can not only in the end areas of the pipe can be varied, but also via the pipe run itself.

Especially for influencing the end area of the pipes to be rolled designed the scaffolding according to DE 22 19 941, but not only a relative here rapid opening of the caliber, that is to say moving the rollers apart, is provided is, but also a twist of the scaffolding parts to achieve different Feed speeds.

This state of the art is concerned with a trumpet-shaped upgrade of the pipes Technology not.

The object of the present invention is to provide a method and an apparatus for Perform the method to find the one with which the trumpet-shaped Expansion of thin-walled blanks at their front end when rolled into one Woodlice mill avoided or at least in its dimensions on a harmless Dimension can be reduced.

To solve the problem, the invention proposes that when the front hollow block area in the woodlouse mill the radial forming of the blanks compared to the stationary rolling condition and / or that Section modulus at the head end due to obstruction of the tangential material flow is increased. This will cause the transient Phase during the rolling of the tube blank in the wood mill, conditions created, that come close to the stationary rolling condition. The material flow in tangential Direction is reduced so that the missing tension in the axial direction is partially compensated. The result is a reduction depending on the tube wall thickness or avoided formation of trumpets at the front end of the cap.

In order to reduce the radial deformation of the blank, a special one is used Feature of the invention proposed that at least one of the rollers of the Asselwalzwerkes while rolling the head piece against the stationary state is at least partially open and after filling the Forming zone is closed quickly. This results in a front end of the head with a thicker wall than the target wall thickness, so that the tendency to form trumpets is severely hindered or restricted. After rolling on, i.e. after the first filling of the forming zone is finished, the Work rolls as quickly as possible by moving into their end position or target work position hazards. Now the target plate wall can be created and the The target diameter is set. This procedure can be practiced by Opening and closing (quick closing) with a roller, preferably the top roller or is carried out simultaneously with two or preferably three rollers.

Favorable parameters for the opening of the rollers according to the invention are in Claim 3 specified. The opening path Δ DHP is upwards as a result limited that the gripping of the hollow block by the rollers in the inlet part or in The stretched part must still be guaranteed. If necessary, gripping the slug in supported or forced the rollers by pressing with the hollow block inserter become. All rollers should preferably be in the starting position by the same amount be open and at the same time after triggering a signal or command End position to be closed.

In addition to the opening of the rollers according to the invention, there is another Feature of the invention proposed that for rolling the blank during the Running the head piece into the woodlice mill the speed of the rolls temporarily by 10 to 70%, preferably by 40 to 60% over the Rated speed is reduced. By lowering the circumferential roller speed the circumferential stretch, i.e. the widening of the bob something can be reduced. However, this method is usually large when it occurs trumpet-shaped enlargements on the scabbard alone are not sufficient, one Use together with the opening of the rollers according to the invention is therefore advantageous.

Another possibility is to reduce the stretch in the circumferential direction in reducing the feed angle of the rolls when rolling or otherwise expressed, the rolling with a smaller feed angle, as it is to avoid triangulation is practiced at the back end of the head. According to the invention, the inclination of the roller axes, the feed angle of the Rolling, reduced to 0 ° to 5 °, preferably to 3 ° to 4 °. Such a solution has not yet been technically implemented for rolling on the front end of the blank.

Another feature of the invention is characterized in that the Dome pole with a conical or cylindrical front end with rounded or angled transition is positioned so that the Wall thickness reduction is reduced. The rolling then takes place with a initial wall thickness reduction of about 0.5 to 3 mm, which also causes the Widening of the front tube end is reduced.

A device for performing the method is characterized in that at least one of the rolls, preferably all rolls of the wood mill, with hydraulic quick release or quick closing devices are provided with which the rollers can also be adjusted radially to the rolling stock in a short time against the rolling force are, the closing path of each movable roller at most the respective Shoulder height or the maximum wall thickness reduction. The The device according to the invention must be able to roll in to reduce the distance between the rolls for a short time, from partially open to the closed state (in the working position). According to a further feature of the invention, the closing path should preferably be used be infinitely variable or in small increments of preferably 0.5 to 1 mm. This can e.g. through a stroke limitation, such as the addition of spacers, respectively.

The closing process must be triggered automatically by a signal or how it Invention provides can be initiated by an automatic control. In a Favorable embodiment of the invention provides that as a signal for control of the closing process the increase in the armature current in the drive motor below Use of a timer is usable. Another option is there in that the signal to control the closing process from one to the Transport path of the tube switch switched radiation sensor is removable So can a thermal or radiation sensor (a photo cell) immediately before the inlet of the Hollow block inserted between the rollers or from the outlet side become. The time from the detection of the hollow block to the exit from the Forming zone or until the rollers start to close should be calculated approximately, but should be better for each shell dimension can be determined empirically under constant technological conditions.

The advantages of the present invention can be summarized as follows: Avoiding or reducing the trumpet-shaped expansion of the front The end of the bobbin can be bumped into the outlet of the woodlouse mill and avoid behind. This increases the process stability when rolling thin-walled blanks with a diameter to wall thickness ratio D / S 10 ... 50th Roll stands of the downstream one that are usually additionally required Sizing or reducing roller mill for reducing trumpet-shaped widenings are saved. It also tears open the end of the bob (Longitudinal cracking) safely avoided at the head of the cup.

Figur 1

die Stellung der Asselwalzen in der stationären Phase

Figur 2

die trompetenförmige Aufweitung am Rohrluppenende

Figur 3

das Anwalzen der Luppe mit teilangestellten Asselwalzen

Figur 4

die stationäre Phase nach dem Anwalzen

Figur 5

das erfindungsgemäße Anwalzen auf abgesetzter Domstange und

Figur 6

die stationäre Phase nach dem Anwalzen gemäß Figur 5

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

Figure 1

the position of the woodlice in the stationary phase

Figure 2

the trumpet-shaped widening at the end of the tube blank

Figure 3

rolling the slug with partially employed woodlice rollers

Figure 4

the stationary phase after rolling

Figure 5

the rolling according to the invention on stepped dome bar and

Figure 6

the stationary phase after rolling according to FIG. 5

In the drawing figure 1 is the stationary phase for rolling a tube blank shown. A denotes the woodlouse, B denotes a cylindrical one Dome pole inside the tube; the direction of rolling is given at WR. The in Hollow block C introduced in the rolling direction is turned into the die D in the woodlling process rolled out. The woodlouse is composed of the inlet part G, the stretching part and the Shoulder E, the smoothing part F and the outlet and rounding part H together. With X is denotes the outlet-side wall at the front end of the cap. As in Figure 1 The disc D is recognizable due to the material flow during the cross rolling process expanded in the radial direction, being at the front end of the slat to the trumpet-shaped expansion comes as shown in Figure 2 on the right side of the Hole D are recognizable.

FIG. 3 shows the proposal according to the invention for an Assel rolling mill, which includes a roller quick-locking device. The same parts are the same designated. The outlet-side front end of the bobbin is labeled D1. The Rolling takes place as shown in the drawing figure with partially opened rollers, see above that at the front end D1 a head with a thicker wall than that Target wall thickness D (Figure 1) results. The tendency to form trumpets becomes strong Dimensions hindered or restricted by the main driver of the expansion, the Wall reduction, is greatly reduced when rolling on. After the done Rolling, i.e. after the first filling of the forming zone is finished the work rolls as quickly as possible by moving them into their end positions or Desired working position driven. This state is shown in Figure 4. Now that can Should be rolled billet wall D2, the target diameter is set. This Procedure can be practiced by opening and closing with a roller or is carried out simultaneously with two or three rollers. This is preferred Closing and opening with all three rollers.

Another possibility for carrying out the method according to the invention is in Figures 5 and 6 shown. One of the conical or in the form of a cylindrical heel with a rounded or angled transition trained dome rod B used, which is positioned during rolling (Figure 5) must be that in the beginning only a wall thickness reduction of approx. 0.5 to 3 mm he follows. This also reduces the expansion; a thicker wall is created on front end of the head.

As FIG. 6 shows, after the rolling and filling of the forming zone, the Dome bar is pushed forward and in the stationary rolling process the target slab wall generated. In both cases, i.e. in the procedural steps after the Figures 3 and 4 as in Figures 5 and 6 can be those shown in Figure 2 Avoid trumpet-like flared ends, because according to the invention radial deformation of the billet compared to the stationary rolling condition reduced and the section modulus at the head end Hindrance of the tangential material flow is increased.

The following dimensions result in two exemplary embodiments of the invention: example 1 Example 2 SH = hollow block wall thickness 14 mm 10 mm SL = wall thickness 7 mm 4 mm ΔS = wall thickness reduction 7 mm 6 mm ΔS _on = reduced wall thickness reduction for rolling, assumed 14% of ΔS = 0.14 * 7 ∼1 mm ∼3 mm ΔDHP = opening path per roller assumed 0.86 * ΔS = 0.86 * 7 ∼6 mm ~3mm SL _on = wall thickness after rolling in accordance with the proposal SL _an = S _L + ΔDHP = 7 + 6 = 13 mm 4 + 3 = 7mm SL _an = SH - ΔS _an = 14-1 = 13 mm 10-3 = 7 mm

Claims (12)

1. Method for avoiding or reducing trumpet-shaped expansions at the tube end during the diagonal rolling of thin-walled tubes from a hollow block (C) on an Assel rolling mill,
   characterised in that
   as the leading end of the hollow block passes into the Assel mill, the radial deformation of the loop (D) relative to the steady state roll condition is reduced and/or the moment of resistance of the hollow block cross-section at the head end is increased by reducing the tangential material flow.
2. Method according to Claim 1,
   characterised in that
   to reduce the radial deformation of the tube mouth, at least one of the rolls of the Assel mill is partially opened relative to the steady state condition during the initial rolling of the head portion, and is rapidly closed once the deformation zone has been filled.
3. Method according to Claim 2,
   characterised in that
   the amount by which the rolling gap DHP is enlarged compared with the technologically necessary rolling gap for the respective tube mouth size, is determined such that the wall reduction on entry

   

   S_an is only 0% - 80% and preferably 10% - 50% of the nominal wall reduction

   

   S, from which it follows that:

   

   and

   

   so that the total reduction

   

   In the above:

   

   S_an is the reduced wall thickness reduction during initial rolling

   

   DHP/roll is the opening travel of the roll

   

   S is the nominal wall reduction

   H_S is the roll shoulder height.
4. Method according to any of Claims 1 to 3,
   characterised in that
   to feed in the tube mouth, during the entry of the head portion into the Assel rolling mill the rotation speed of the rolls is temporarily reduced by 10 - 70% and preferably by 40 - 60% compared with the nominal rotation speed.
5. Method according to any of Claims 1 to 4,
   characterised in that
   by reducing the inclination of the roll axes, the feed angle of the rolls is reduced to 0° - 5° and preferably to 3° - 4°.
6. Method according to any of Claims 1 to 5,
   characterised in that
   a mandrel bar with a conically or cylindrically narrowed front end and a rounded or angular transition, is positioned during initial rolling in such manner that the wall thickness reduction is reduced, and after rolling has begun, the mandrel is displaced axially so as to produce the nominal wall thickness.
7. Device for the diagonal rolling of thin-walled tubes, having rolls (A) that can be adjusted radially relative to the rolled material and having also an axially displaceable mandrel bar (B) with a conically or cylindrically narrowed front end and a rounded or angular transition, designed for implementing the method for avoiding or reducing trumpet-shaped expansions at the tube mouth end during the diagonal rolling of thin-walled tubes from a hollow block (c) on an Assel rolling mill in accordance with any of Claims 1 to 6,
   characterised in that
   at least one of the rolls (A) of the Assel mill is provided with hydraulic rapid-opening and -closing mechanisms by means of which the rolls (A) can be adjusted radially with respect to the rolled material in a short time even against the rolling force, and the closing travel of each displaceable roll is at most equal to the respective shoulder height or to the maximum wall thickness reduction.
8. Device according to Claim 7,
   characterised in that
   the closing travel of the rolls (A) can be varied continuously or in small steps, preferably of 0.5 to 1 mm.
9. Device according to either of Claims 7 or 8,
   characterised in that
   the closing process of the rolls (A) can be initiated by an automatic control unit.
10. Device according to any of Claims 7 to 9,
    characterised in that
    as the signal which triggers control of the closing process, the increase of the armature current in the drive motor can be used, with the participation of a time switch.
11. Device according to any of Claims 7 to 9,
    characterised in that
    the signal which triggers control of the closing process can come from a radiation sensor connected in the transport path of the tube mouth (D).
12. Device according to Claim 7,
    characterised in that
    all the rolls of the Assel rolling mill are provided with hydraulic rapid-opening and -closing mechanisms.

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