EP2358485B1 - Method for producing seamless tubes by means of a three-roll bar rolling mill - Google Patents

Description

The invention relates to a method for producing seamless pipes by means of a three-roll bar rolling mill according to the preamble of claim 1.

A generic method is used in Steel tube manual (Vulkan-Verlag, Essen, 12th edition 1995, p.107-111 ) andi in the EP-A 1889669 described.

Bar rolling mills, e.g. Working according to the tube contour method are used for the production of seamless tubes. They have the task to strip a previously produced by means of oblique rolling hot hollow block to a mother tube. This mother tube is then reduced in a Maß- or stretch-reducing mill to the desired final size.

Basically, there are bar rolling mills in two embodiments, with two or three rolls per stand. The number of scaffolds usually varies between four and eight.

It is known that bar rolling mills are very sensitive to variations in the wall thickness and the diameter of the incoming hollow block. However, such variations can not always be avoided in the cross rolling process, over which the hollow block is normally made.

In particular, cross-rolling mills with Diescherscheiben as a guide produce hollow blocks with diameters that differ in the head and foot from the "fillet". In the rod rolling process, these deviations can lead to caliber underfill, wall thickening, holes and caliber overfilling.

In order to minimize such errors, it is also known to precede the rod rolling process with a hollow block reduction stand (void reduction stand). In a two-roll bar rolling mill has such a framework four rolls and three rolls in a three-roll mill.

A disadvantage of known Hohlblockreduziergerüsten is that change the rolling conditions in the bar mill at different diameters of the hollow block yet.

The result of this is that different entry conditions arise for the bar rolling mill during the deformation (input clearance, hollow block to bar, outer diameter reduction in the 1st stand), which in turn can have negative effects on the quality of the tube.

Object of the present invention is for a three-roll bar mill, the calibration and the driving of Void Reduction Stand (VRS) set so that even with different diameters of the hollow block almost the same rolling conditions apply to the forming in bar mill.

It is important to balance the diameter deviations in the hollow block or from hollow block to hollow block for rolling in the bar mill as possible while preventing underfilling or overfilling of the caliber.

This object is achieved according to the preamble in conjunction with the characterizing features of claim 1. Advantageous developments are the subject of dependent claims.

According to the teachings of the invention, a method is used to solve this problem, in which the rolls of the upstream scaffold up and shut down to the same extent as the deformation stands of the bar rolling mill, the Kalibergrundradius the rolls of the upstream scaffold extends over 60 ° and this a flank radius follows with a tangential transition, which is so dimensioned that even with maximum infeed of the rolls in the region of the edge almost no reduction in diameter of the largest expected hollow block diameter takes place.

The great advantage of the present invention is that with the proposed procedure and the corresponding calibration on the one hand the fluctuation range of the diameter of the incoming into the bar mill hollow block can be significantly reduced, on the other hand, it is possible by the calibration of the invention, even at different diameters of the hollow block tube almost same conditions for to adjust the bar rolling, which manifests itself in a much more uniform quality in the geometry of the tube.

In an advantageous embodiment of the invention, the employment of the upstream scaffold is adjusted according to the employment of the first stand of the rod rolling mill, that the average game to the rod for the employment of the 1st scaffold remains the same in its absolute size.

A constant rod clearance at the outlet of the hollow block reducing framework leads to uniform deformation conditions during rolling and thus to a significantly improved tube quality.

According to a further advantageous feature of the invention, all stands of the bar rolling mill can be employed for a given rod diameter to achieve the desired wall thickness behind the bar mill by the same amount, this amount also corresponds to the setting of the upstream scaffold.

In contrast to the constant input game, this does not require any complicated calculation for the change in employment. This has the further advantage that no over- and underfilling of the caliber can take place for the bar mill, d. H. the input conditions related to the outside diameter for rolling in the bar rolling mill are almost constant.

According to further advantageous features of the invention, the employment of the upstream scaffold corresponds only to the employment of the first stand of the rod rolling mill in its absolute size. The cooperation of hollow block reduction scaffolding and subsequent 1st scaffolding is crucial for the quality of the rolling process. Alternatively, it is also possible that the employment of the upstream scaffold corresponds to the employment of the first stand of the rod rolling mill in its relative size.

The employment in its relative size has the advantage that in addition to the almost constant input conditions for the rod rolling mill and the wear is taken into account (wear compensation) and so the maturities are improved.

In a further advantageous development of the invention, the caliber base radius has an eccentricity which is dimensioned so that it becomes zero at maximum acceleration of the upstream framework.

It is advantageous here that the so-forming contact surface roller rolling has a positive effect on the roller wear on the calibration jump. Furthermore, this has the positive effect of reducing outer surface imperfections, such as caliber strips.

Further features, advantages and details of the invention will become apparent from the following description of an embodiment shown in a drawing. In the single figure, the inventive calibration of the upstream framework of a Void Reduction Stand (VRS) is shown and will be described in more detail below.

Prior art reducers are usually calibrated in an oval fashion. For this purpose, a Kaibergrundradius Al is defined, which is constantly enlarging into a Kaliberflankenradius BI passes.

In contrast, according to the invention, a round calibration is proposed, in which a basic radius R1 transitions tangentially into an edge radius over an angular length of 60 °, whose working area per flank is 30 ° ( FIG. 1a ). Is shown in FIG. 1a in addition, the roll axis (1), the caliber contour (2), the eccentricity (3) of the caliber base radius R1, the caliber base radius R1 (4) and the caliber flank radius R2 (5).

The advantage of this calibration is that it can halve the variation in the hollow block diameter from the hollow block reduction frame (VRS) compared to the oval calibration.

This is explained in more detail in the following example. In this case, the size BI is used for the distance between the roll axis and the caliber base, and the size AI is used for the distance between the roll axis and the caliber flank.

The hollow blocks produced by the cross rolling mill generally have a tolerance in the outer diameter of z. B. 2.5%.

The VRS should be able to record the maximum hollow block diameter x 0.99 to 1.00 (2 x AI). The diameter in the center of the caliber (2 x BI) should correspond to the minimum hollow block diameter x 0.99 to 1.00.

The two calibration methods lead to the following results:

Oval calibration

Radius with BI at center of caliber and continual increase to Al in gauge jump. The mean caliber diameter is 2 x (BI + (AI - BI) / 2)

around calibration

Radius with BI to center of caliber above 60 degrees (+/- 30 degrees) and continual increase to Al in caliber jump (each 30 degrees). The average caliber diameter results in a good approximation to 2 x (BI + (AI - BI) / 4)

Example:

Hollow block diameter maximum 102.50 mm Hollow block diameter on average 100.00 mm Hollow block diameter minimal 97.50 mm Input tolerance maximum 5.00 mm

Oval calibration

AI = 1.00 x hollow block diameter max. / 2 51.25 mm BI = 1.00 x hollow block diameter min. / 2 48.75 mm VRS diameter min. = 2 x BI 97.50 mm VRS diameter max. 2 x (48.75 + (51.25 - 48.75) / 2) 100.00 mm

Thus a hollow block with a diameter> = 100 mm leaves the VRS with 100 mm. A smaller diameter remains in its size.
Output tolerance maximum 2.50%

around calibration

AI = 1.00 x hollow block diameter max. 51.25 mm BI = hollow block diameter min. / 2 48.75 mm VRS diameter min. = 2 x BI 97.50 mm VRS diameter max. 2 x (48.75 + (51.25 - 48.75) / 4) 98.75 mm

Thus, a hollow block with a diameter> = 98.75 mm leaves the VRS with 98.75 mm. A smaller diameter remains in its size.
Output tolerance max. 1.25% (relative to the nominal hollow block diameter)

The oval calibration achieves a tolerance improvement from 5 to 2.5% (50%) and the round calibration improves from 5 to 1.25% (75%).

Different wall thicknesses are rolled on the same roll bar. To do this, the work scaffolds must be opened and closed. The VRS should approximate this approach and retraction, as only in this way does the cooperation between VRS and the scaffolds remain approximately the same.

In FIG. 1b shows the VRS framework (left) and the 1st framework of the bar rolling mill (right). c and c 'correspond to the nominal position VRS stand and 1st stand of the three-roll bar mill, where c' is the opening gauge of the caliber of the VRS and c is the opening gauge of the caliber of the bar mill at nominal position.

a and a 'symbolize the positive change in employment (driving) of the bar rolling mill and the VRS stand.

b and b 'symbolize the negative change of shutdown (closing) of the bar rolling mill and the VRS stand.

calculation "absolutely the same":

• "relativ gleich":
  Der Verfahrweg (positiv = Auffahren, negativ = Zufahren) des VRS-Gerüstes zum ersten Gerüst des Stangenwalzwerks ist relativ gleich, d. h. es ist eine Funktion aus Nominalstellung (c, c') und dem Verfahrweg des 1. Walzgerüstes (a, b)
• "absolut gleich": $$b\ge a$$
  
  $$\mathit{aʹ}=a$$
  
  $$\mathit{bʹ}=b$$
  
  
  oder
• "relativ gleich": $$\frac{a+c}{c}=\frac{\mathit{aʹ}+\mathit{cʹ}}{\mathit{cʹ}}$$
  
  $$\mathit{aʹ}=\left(\frac{a+c}{c}\right)\cdot \mathit{cʹ}-\mathit{cʹ}$$
  
  
  bzw. $$\mathit{bʹ}=\left(\frac{c-b}{c}\right)\cdot \mathit{cʹ}-\mathit{cʹ}$$
  
  
  z. B. c =100mm ; a = 1mm ; c' = 88mm $$\mathit{aʹ}=\left(\frac{1+100}{100}\right)\cdot 88-88=0,88$$
  

The travel path (positive = ascent, negative = approach) first stands of the bar rolling mill and the VRS stand are absolutely equal in their amount (a '= a and b' = b).

• "relatively equal":
  The travel path (positive = ascending, negative = closing) of the VRS stand to the first stand of the bar rolling mill is relatively the same, ie it is a function of nominal position (c, c ') and the travel path of the first rolling stand (a, b)
• "absolutely the same": $$b\ge a$$
  
  $$\mathit{a\text{'}}=a$$
  
  $$\mathit{b\; \text{'}}=b$$
  
  
  or
• "relatively equal": $$\frac{a+c}{c}=\frac{\mathit{a\text{'}}+\mathit{c\; \text{'}}}{\mathit{c\; \text{'}}}$$
  
  $$\mathit{a\text{'}}=\left(\frac{a+c}{c}\right)\cdot \mathit{c\; \text{'}}-\mathit{c\; \text{'}}$$
  
  
  respectively. $$\mathit{b\; \text{'}}=\left(\frac{c-b}{c}\right)\cdot \mathit{c\; \text{'}}-\mathit{c\; \text{'}}$$
  
  
  z. C = 100mm; a = 1mm; c ' = 88mm $$\mathit{a\text{'}}=\left(\frac{1+100}{100}\right)\cdot 88-88=0.88$$
  

LIST OF REFERENCE NUMBERS

No. description 1 roll axis 2 groove contour 3 eccentricity 4 Caliber base radius R1 5 Caliber flank radius R2 a, a ' relative change of employment (positive) VRS and 1st framework b, b ' relative change in employment (negative) VRS and 1st framework c, c ' Nominal position VRS and 1st framework

Claims (6)

1. Method for producing seamless tubes from metal, in particular from steel, wherein a previously produced hot hollow ingot is stretched by means of a three-roll bar rolling mill on a mandrel to form a parent tube and, before running into the bar rolling mill, the hollow ingot is provided with a rolling step that makes the diameter uniform by means of an upstream stand,
   characterised
   in that the rolls of the upstream stand are opened and closed to the same extent as the deforming stands of the bar rolling mill, the pass base radius of the rolls of the upstream stand extending over 60° and this radius being followed by a side radius with a tangential transition which is dimensioned such that, even with maximum closure of the rolls, in the region of the side virtually no diameter reduction of the largest hollow ingot diameter to be expected takes place.
2. Method according to Claim 1,
   characterised
   in that, for a given bar set, all stands of the bar rolling mill are adjusted by the same amount for attaining the desired wall thickness downstream of the bar rolling mill, this amount also corresponding to the setting of the upstream stand.
3. Method according to Claim 1 and 2,
   characterised
   in that the absolute value of the setting of the upstream stand corresponds to the setting of the first stand of the bar rolling mill.
4. Method according to Claim 1 and 2,
   characterised
   in that the relative value of the setting of the upstream stand corresponds to the setting of the first stand of the bar rolling mill.
5. Method according to one of Claims 1 to 4, characterised
   in that the setting of the upstream stand is adjusted in accordance with the setting of the first stand of the bar rolling mill such that the absolute value of the average clearance relative to the bar remains constant for the setting range of the first stand.
6. Method according to one of Claims 1 to 5, characterised
   in that the pass base radius has an eccentricity which is dimensioned so as to become zero with maximum opening of the upstream stand.

Images