EP0703014B1 - Method for rolling hollow blocks in an Assel rolling mill - Google Patents

Description

The invention relates to a method for reducing the outer diameter and the wall thickness by rolling a cylindrical hollow block which is inserted with its front part into an Assel rolling mill, wherein a device for reducing the diameter and / or the wall thickness of the rear end part of the is provided on a mandrel bar threaded hollow block, the pre-reduction rollers reducing the end of the hollow block can be set against the hollow block and can be guided away therefrom.

• 1. die Rohroberfläche zu glätten und
• 2. Wanddickenunterschiede auszugleichen.

Seamless tubes, especially steel, are manufactured in three main forming steps, namely punching, drawing and finish rolling. Often, massive round blocks are first punched in a Mannesmann cross-rolling mill and later introduced into the so-called sizing or stretch-reducing mill for finish rolling. Various methods are known for the intermediate stretching; the Assel method has established itself as an independent method with which the present invention is concerned. It is used in the manufacture of pipes with medium and thick wall thicknesses, and in particular those that should have flawless surfaces and close tolerances, as is the case, for example, for the manufacture of steel bearing steel pipes. The Assel rolling mill works on the principle of cross-rolling over mandrel bars, whereby three conical work rolls are in engagement, each of which is offset by 120 degrees relative to the rolling axis. In addition, the work rolls are adjustable perpendicular to the roll axis, so that a large number of pipe diameters can be produced on an Assel mill. The work rolls of the Asselwalzwerkes essentially consist of an inlet cone, a working part (the work shoulder), a smoothing part and an outlet and rounding part. The smoothing part has the purpose of partially detaching the tube from the mandrel bar and

• 1. smooth the pipe surface and
• 2. Compensate for differences in wall thickness.

When rolling, in particular, thin-walled tubes, it has proven to be disadvantageous that the Assel rolling process forms a trumpet at the rear end of the tube, which is usually triangular in cross section. One speaks of the triangulation, which ultimately means a scrap end to be separated on the rolled pipe. In the case of particularly strong triangulation, the slug can get stuck in the woodlice mill, so that the rollers have to be opened with all conceivable disadvantages.

The reason for the triangulation lies in the tendency to widen in the rolling mill and is process-related. If the longitudinal tensile stress in the billet drops towards the end of the rolled stock because there is no longer enough material to be formed in the inlet cone of the Assel mill, the tendency to increase the proportion of tangential forming increases. This means that the radial deformation causes more tangential and less longitudinal deformation. This in turn causes an increase in diameter. If the tangential exit speed between the rollers and the mandrel becomes greater than the pull-in speed of the following roller, there is a material jam in the free spaces between the three rollers, which can block the longitudinal feed movement.
A method of the type mentioned at the outset is known from WO 90/00449. To solve the problems described, it was proposed there
to install a pre-reduction device on the inlet side of the Assel mill, which consists of three or four adjustable pre-reduction rollers, the axes of which have a slight inclination to the rolling stock axis or stand axis of the Assel mill. This angle of inclination can be adjustable or fixed and is based on the average feed angle of the wood mill. With this known pre-reduction device, the triangulation at the rear end of the slug can be avoided or reduced during the Assel process, so that the slug can be removed without problems Asselwalzwerk can emerge without the need to lift the rollers. This results in a diameter and / or wall thickness reduction carried out in the pre-reduction device at the end of the hollow block entering the wood mill. It is therefore the aim of this pre-reduction to reduce the driving force for the widening of the ends, namely the radial forming in the forming zone of the Assel mill, if possible, but at least to reduce it to such an extent that there are no longer any faults in the Assel mill and high end losses. The object of the invention is to optimize the speed and forming conditions and thus the effect of the pre-reduction in a method of the type mentioned at the outset.
This object is achieved by the characterizing features in claim 1.
The present invention has recognized that it is not sufficient to simply reduce the ends of the hollow blocks arbitrarily before entering the wood mill, rather certain speed and forming conditions must be observed if the pre-reduction does not lead to a deterioration of the hollow block ends or the intended effect should even be abolished. It was also found that the conditions depend on which pipe diameter and wall thickness are rolled in the Assel mill.

Based on the problems and disadvantages and the inadequacies of existing devices, it is proposed according to the invention to slowly and continuously turn the rollers of the pre-reduction device against the hollow block and to comply with the conditions for the axial path for the effect of the pre-reduction device as set out in claim 1. If these conditions are observed, optimal results in terms of the task can be achieved. If the path is chosen too short, the rollers of the pre-reduction device do not reach their end position, which means that the wall thickness is not reduced sufficiently and triangulation occurs. If, on the other hand, the reduced length is too long, a belly is created, ie a thickening of the hollow block at the end, so that triangulation can also occur there. It should be noted that the rear end of the hollow block should be as perpendicular as possible to the longitudinal axis, it is best to use sawn blocks. Oblique hollow block ends and large ones Differences in wall thickness at the end also lead to partial (one-sided) triangulation.
Advantageous refinements of the invention result from the subclaims. In a further embodiment of the invention, it has been found that the diameter of the tangential circle between the rollers of the pre-reduction device is of particular importance in the employed state. Favorable results can be expected if the guide values specified in claim 2 are observed. In connection with the teaching of the first claim, a hollow block end is created if the specified criteria are met, which ends after a conical transition with a cylindrical reduced hollow trestle wall. In the extreme case, the length of the cylindrical part of the reduced hollow block end can be zero.

According to a further feature of the invention, feed angles are specified for the rolls of the wood mill, which likewise reduce the widening in conjunction with the features of the invention explained above. It was recognized that in addition to the reduction in wall thickness, the feed angle also influences the widening, this angle must be at least sufficiently small, at least for the rolling out of the rear hollow block end, so that not too much material enters the roll gap per revolution. Claim 3 indicates a preferred feed angle γ between 3.5 and 6 degrees, in which the invention can be carried out particularly cheaply. If, however, the feed angle is too small, the axial exit speed is low, and on the other hand the widening that occurs as a result makes it more difficult to detach the cap from the mandrel bar.

According to a further feature embodying the invention, it is proposed in the fourth claim that the circumferential roller speed is between 1.5 and 6 m / s, preferably between 4.0 and 4.5 m / s. adjust.

It is favorable for the rolling of thin-walled blanks if the smoothing part of the woodlouse roller is relatively short when the rollers have a large run-out angle. Claim 5 specifies dimensional ranges for the length of the smoothing parts based on different hollow block diameters. The run-out angle related to the smoothing part of the woodlice should be 4 to 6 degrees. It is advantageous if the transition between the smoothing part and the outlet part is rounded off by a radius, that is to say a sharp edge is avoided. It is also possible to make the entire outlet part curved, ie to completely replace the conical or linear part by a rounded part.

Finally, it has proven itself in a further embodiment of the measures according to the invention if, when rolling thin-walled blanks, the spreading angle δ, which for example is 3 degrees in conventional divergent wood mills, is slightly opened, i. H. is increased by 0.3 to 0.7 degrees to then 3.3 to 3.7 degrees.

Another proposal of the invention provides for the rollers to be moved into a position near the surface of the hollow block before the rollers of the pre-reduction device are closed. Corresponding information is given in claim 7. Advancing the rollers of the pre-reduction device has the advantage that the rollers represent an additional guide for the hollow block during rolling in the wood mill and greater security is achieved in order to achieve the necessary reduced length.

With a pre-reduction device, which is connected upstream of an Assel rolling mill for rolling preferably thin-walled tubes, favorable results can be achieved with the above-described method, the triangulation at the end of the rolled hollow block being largely avoided and at least reduced so much that it no longer can interferes with the process flow.

An embodiment of the invention is explained below; For a better understanding of the process, reference is made to the drawing figure. The schematic illustration shows two of three woodlice rolls of a woodlice mill, designated 1, which process the hollow block 2 to reduce the diameter and wall thickness. The pre-reduction device, the three rollers of which are denoted by 3, is connected upstream of the wood rollers 1. The dome 4 can be seen in the interior of the hollow block 2. The roller of the woodlouse mill consists of the inlet part 5, the working part (shoulder) 6, the smoothing part 7 and the outlet or rounding part 13. The spreading angle of the rollers 1 is denoted by δ.

The surfaces of the three rollers 3 of the pre-reduction device facing the roller axis are touched in their illustrated working position by a tangential circle which has the diameter D _NEL . The hollow block 2 is reduced to an outer diameter, which is indicated by dashed lines at 8. When the hollow block is advanced in the direction indicated at 9 by the drive of the Assel rolls in the direction indicated at 10 and the rollers 3 of the pre-reduction device are turned on, a conical transition area arises from the outer diameter of the hollow block D _H to the diameter D _NEL corresponding to the tangential _circle , such as shown in sections below the rollers 3. The conical transition area is designated 11 there. The total length between the start of the conical region 11 following the hollow block diameter D _H to the end of the hollow block 12 is L _NEL .

Furthermore, the basic thickness shows the wall thickness S _H and the tangential circle in the "high point" of the woodlice and is denoted by D _HP . The outside diameter of the billet leaving the Assel mill is designated D _L , the wall thickness of the billet is designated S _L. The diameter of the dome bar is shown at D _M.

D_H =

185,7 mm vom Lochwalzwerk kommend

S_H =

17,9 mm vom Lochwalzwerk kommend

D_M =

139,7 mm Domstangendurchmesser

D_HP =

158,8 mm Abstand der Asselwalzen im hohen Punkt (Tangentialkreisdurchmesser)

D_L =

177,8 mm Durchmesser der das Asselwalzwerk verlassenden Luppe

S_L =

9,5 mm Wandstärke der das Asselwalzwerk verlassenden Luppe

γ =

4,5 Grad Vorschubwinkel des Asselwalzwerkes

δ =

3,7 Grad Spreizwinkel des Asselwalzwerkes

v_U =

4,2 mm/sek. Umfangsgeschwindigkeit der Asselwalze im hohen Punkt

D_W =

403 mm Durchmesser der Asselwalze am hohen Punkt

t_NEL =

0,4 sek. Schließzeit der Walzen der Vorreduktionseinrichtung vom ersten Kontakt bis zur Endstellung

D_NEL =

155,2 mm vorgewählter Abstand der Walzen (Tangentialkreisdurchmesser) der Vorreduktionseinrichtung ohne Einwirkung der Umformkraft

L_NEL =

230 mm Weg der Wirkung der Vorredukionseinrichtung

L_K =

32 mm Länge des Glätteils der Asselwalze

An Assel mill according to the invention, as shown schematically in the drawing figure, can have the following dimensions and values, for example:

D _H =

185.7 mm coming from the piercing mill

S _H =

17.9 mm coming from the piercing mill

D _M =

139.7 mm dome rod diameter

D _HP =

158.8 mm distance between the woodlice at high point (tangential circle diameter)

D _L =

177.8 mm diameter of the billet leaving the woodlill mill

S _L =

9.5 mm wall thickness of the billet leaving the woodlill mill

γ =

4.5 degree feed angle of the woodlouse mill

δ =

3.7 degree spreading angle of the woodlouse mill

v _U =

4.2 mm / sec. Circumferential speed of the woodlice in high point

D _W =

403 mm diameter of the woodlice at the high point

t _NEL =

0.4 sec Closing time of the rollers of the pre-reduction device from the first contact to the end position

D _NEL =

155.2 mm preselected distance of the rollers (tangential circle diameter) of the pre-reduction device without the influence of the forming force

L _NEL =

230 mm way of the effect of the pre-reduction device

L _K =

32 mm length of the smoothing part of the woodlice

A pre-reduction device for performing the method according to the invention works hydraulically. The maximum pressure force of the rollers of the pre-reduction device is predetermined for a given hydraulic cylinder and choice of pressure, the hydraulic pressure is generally constant. The closing speed can be set by means of a valve via the flow rate per unit of time, working at low speeds. The start of the closing process of the rollers of the pre-reduction device can be triggered by photocells, the closing time must be chosen depending on the hollow block diameter. It is also conceivable to determine the axial speed in the inlet with two sensors and a microprocessor using a time measurement for a defined measuring section. The start of the closing process can thus be adapted to the speed. The opening of the rollers of the pre-reduction device can also be triggered by a photo cell.

Claims (7)

1. A method for reducing the external diameter and the wall thickness by rolling a cylindrical hollow shape, which is introduced by its front part into an Assel rolling mill, with a means for reducing the diameter and/or the wall thickness of the rear end part of the hollow shape threaded on to a mandrel bar being provided before the Assel rolling mill when viewed in the direction of introduction, the pre-reduction rolls of which, which reduce the hollow shape end, being adjustable against the hollow shape and being able to be moved away therefrom,
   characterised in that
   the pre-reduction rolls are adjusted against the hollow shape slowly and continuously at such a screw-down speed that the axial path (L_NEL) for the action of the pre-reduction rolls, measured from the point of impact of the pre-reduction rolls on the surface of the hollow shape to the end of the hollow shape is $$\begin{array}{c}\begin{array}{c}{\text{L}}_{\text{NEL}}{\text{= 0.8 .... 2.0 D}}_{\text{H}}\\ {\text{preferably L}}_{\text{NEL}}{\text{= 1.0 .... 1.25 D}}_{\text{H}}\text{,}\end{array}\end{array}$$

   

   D_H designating the external diameter of the hollow shape before entry into the Assel rolling mill.
2. A method according to Claim 1, characterised in that the following relationships apply as standard values for the diameter of the tangential circle between the pre-reduction rolls in the adjusted state:
      for medium wall thicknesses ( ${\text{D}}_{\text{L}}{\text{/S}}_{\text{L}}\text{≤ 12}$

   

   ) $$\begin{array}{c}\begin{array}{c}{\text{D}}_{\text{NEL}}{\text{= D}}_{\text{M}}{\text{+ (1.8 ... 2) x S}}_{\text{H}}\\ {\text{SH}}_{\text{E}}{\text{= (0.9 ... 1.0) x S}}_{\text{H}}\text{and}\end{array}\end{array}$$

   

      for small wall thicknesses (D_L/S_L ▷ 12) $$\begin{array}{c}\begin{array}{c}{\text{D}}_{\text{NEL}}{\text{= D}}_{\text{M}}{\text{+ (2.0 ... 2.2) x S}}_{\text{L}}\\ {\text{SH}}_{\text{E}}{\text{= (1.0 ... 1.1) x S}}_{\text{L}}\text{and}\end{array}\end{array}$$

   

      for thin-walled hollow shapes $${\text{D}}_{\text{NEL}}{\text{= a + b x D}}_{\text{HP}}\text{[mm],}$$

   

   in which

   D_NEL =   the diameter of the tangential circle between the pre-reduction rolls in the adjusted state

   S_H =   the wall thickness of the hollow shape

   SH_E =   the theoretical reduced wall thickness at the end of the hollow shape

   D_L =   the diameter of the hollow shape after the Assel rolling mill

   D_M =   the diameter of the mandrel rod

   S_L =   the wall thickness of the hollow shape after the Assel rolling mill

   D_HP =   the diameter of the tangential circle between the Assel rolls at the high point in the working position, and in which:

   a = 0 to 10, preferably 6,35

   b = 0.9 to 1.0, preferably 0.938.
3. A method according to Claims 1 and 2, characterised in that the rolls of the Assel rolling mill are operated with a small feed angle γ of between 3 and 14 degrees, preferably 3.5 to 6.0 degrees.
4. A method according to Claims 1 to 3, characterised in that the peripheral speed of the rolls of the Assel rolling mill is set to v_U = 1.5 to 6.0 m/s, preferably 4.0 to 4.5 m/s.
5. A method according to one or more of the preceding claims, characterised in that for rolling thin-walled hollow blanks with a short smoothing section the rolls are manufactured with a large exit angle, wherein for a distance D_HP between the rolls of the Assel rolling mill measured at the high point of

   D_HP = 90 ... 150 mm

   a smoothing section length L_K = 10 ... 50 mm,

   preferably L_K = 20 ... 30 mm, is provided,
   and for a distance of

   D_HP = 150 ... 200 mm

   a smoothing section length L_K = 20 ... 80 mm,

   preferably L_K = 30 ... 40 mm, is provided,
   the exit angle of the Assel rolls - relative to the smoothing section - being between 4 and 6 degrees.
6. A method according to one or more of the preceding claims, characterised in that when rolling thin-walled tube blanks $${\text{δ = δ}}_{\text{Nenn}}\text{+ 0.0 ... 1.5 degrees,}$$

   

   preferably ${\text{δ = δ}}_{\text{Nenn}}\text{+ 0.3 ... 0.7 degrees}$

   

   ,
   wherein δ_Nenn designates the spreading angle set by the rolling mill design for the roll calibration.
7. A method according to one or more of the preceding claims, characterised in that before adjusting the pre-reduction rolls the rolls are moved into a position close to the surface of the hollow shape, with the following applying for the tangential circle of the pre-set rolls: $$\begin{array}{c}\begin{array}{c}{\text{D}}_{\text{NEL0}}{\text{= D}}_{\text{H}}\text{+ 4 ... 20 mm,}\\ {\text{preferably D}}_{\text{NEL0}}{\text{= D}}_{\text{H}}\text{+ 8 ... 16 mm.}\end{array}\end{array}$$

   

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