DE4206397A1 - Method for stretch-reducing of steel rolling mill loops - is used in multi-stand mill, each succeeding stand moves at higher speed than previous one - Google Patents

Abstract

The ends of steel loops are edged, calibrated, upset, and the loops are then joint into long lengths, perhaps into continuous lengths, by electron-beam welding. The loop lengths are then moved to the stretch-reducing rolling mill. End calibration produces reproducible even loop ends. The loops can be produced cold or warm. Increased wall thickness also protects against tearing off in the mill. The upset wall sections help to identify joints after the stretch-reducing. Other similar welding processes may be used. USE/ADVANTAGE - Prevents thickened ends during stretch-reducing, internal surface of loops remains free of folds.

Description

Steel pipes are common, but especially in modern ones Pipe mills - such as continuous lines, push bench systems or Extrusion - one stretch in the last operation subjected to reduction rolling.

This procedure has compared to the simple reducer roll the great advantage that the wall thickness of the rolling mill luppen - in future only called Luppen - not again increases, and the inner surface of defects, namely Wrinkles, remains free.

This is achieved by the fact that in the multi-stand rolling mill each subsequent scaffold has a higher speed than the exit speed of the roughing stand.

This creates on the pipe string with an increase in The number of scaffolding is an ever stronger train. So the Luppe will not only reduced in diameter, it is also in the Length drawn. In this way, the slab wall is preserved or even desirably reduced. At the same time this avoids the appearance of wrinkles on the Inner surface, with changing internal pressure loads can lead to failure of the pipe. Cold drawing of such pipes are also serious Damages are not always avoidable.  

However, this method has the fundamental disadvantage that that the train can only be built up gradually. The full train is only reached after up to 6 scaffolds.

The end of the strand is subject to the same criteria as when simply reducing.

It is easy to see that consequently both the beginning as well as the end of the reduced pipe string with decrease the train is subject to the same criteria as a reduced one Pipe.

The wall thickness at the ends of the strands is therefore greatly thickened and only reaches the at some distance from the ends desired wall and quality.

It is understood that these pipe parts are intended Not intended purpose, but eliminated and to be scrapped. The business disadvantage is significant.

As a result, there have been many efforts to thicken ends to avoid. The relevant patent literature gives this Information desk. The success has so far failed to materialize. Especially the close one lying attempt to reduce the loops before stretching to weld together an endless strand if in doubt, to get only fillet pieces, can be ge fails to be viewed.  

The following facts stand in the way of success:

• 1. The slugs consistently on a cross-section different wall thicknesses. You can't make mistakes freely (dislocations) welded together. In the welding area, the train leads to the Tear off in the stretch-reducing mill.
• 2. The welding processes in use (Fusion welding) change the chemical Composition of the fillet in the welding area and thus their firmness. Decreased strength leads inevitably in the stretch-reducing mill Weld area to overstretching, which leads to Demolition.
• 3. The outside and inside diameters of the blanks fluctuate in areas, welding together is flawless not possible.
• 4. Loops are out of round in areas and elude a flawless welding process.
• 5. Arises in all fusion welding processes inevitably notches. They lead to Tearing off the pipe run in the stretch-reducing mill.

The idea of the invention is based on 4 individual steps:

• 1. There are individual groups - after the flutter has been separated end - with relatively short production lengths (state of the art) joined together.
• 2. The ends of the slugs are calibrated.
• 3. The outermost ends of the slugs are slightly compressed.
• 4. The slugs are primarily made with the help of an electron beam welded together and in doubt in endless strands fed to the stretch-reducing mill.

Sheet 1 shows in the upper partial section two - possibly more - segment clamping jaws ( 3 ), which encompass the end of the armature ( 1 ) and calibrate the outer diameter. At the same time, the slab section is given a circular shape.

In the second step, the mandrel ( 2 ) - lower drawing - calibrates the outermost end of the bob and slightly compresses the end.

In addition to a noticeable reduction in the eccentricity of the Bracket ends should have a wall reinforcement of at least 10% the nominal wall can be achieved. At this point there are interior and The outside diameter is absolutely the same and the bowl is circular.

This operation guarantees that all those attached to the troops Deviations from the ideal size are eliminated and thus the The prerequisite for error-free welding is given.  

Sheet 2 shows a possible arrangement for electron beam welding. The tail ends ( 4 ) + ( 5 ) are pushed precisely with the help of the clamping jaws ( 3 ) and pressed together with axial pressure. It doesn't matter what the temperature of the ends of the holes are.

The ring ( 2 ) has a through hole for the electron beam. It is connected to the electron beam gun and ensures that the vacuum necessary for welding can be kept in the room ( 6 ).

The clamping jaws rotate the pipe string through 360 ° during the Electron beam welded the joint.

The advantage of electron beam welding is that

• 1. only a negligible amount of material is welded on.
• 2. 1. means that there is no chemical change in the weld area.
  No changes to the mechanical properties.
• 3. The wall thickness reinforcement provides additional Safety against tearing off and serves when necessary Removal after reduction rolling to find the exact separation point.  
• 4. Electron beam welding avoids any kind of penetration notches, welding beads and cant inside and outside.
• 5. The electron beam welding allows a very high welding speed and therefore continuous Sequence of slag rollers and stretch reduction.

Sheet 3 shows a plant, like Luppen in a heat from the Luppen Rolling mill continuously joined and the reducing roll factory can be fed.

In Fig. 3, the rooms marked with ( 1 ) are keeping warm or reheating chambers.

The operations are running in rooms ( 2 )

• a) Trim flutter ends
• b) calibration and upsetting and
• c) electron beam welding

from.

In the rooms ( 3 ) there are the drives for axial and transverse transport as well as for the turning of the strand of strands around its own axis, which is necessary during welding.

Figure 3 also shows how, starting from the bottom and continuing upwards, a void is successively added to the pipe string that is already developing.

With 10-fold strands, the loss of thickened drops Ends already from 6 to 0.6%. Economically this represents a significant improvement in the level of output.

Claims (6)

1. A method for avoiding thickened ends during stretching of steel rolling mill slabs, characterized in that the ends of the slugs are trimmed, calibrated, compressed and mainly joined together by means of electron beam welding to long lengths, optionally to form endless strands, and then fed to the stretch-reducing roll mill. 2. The method according to claim 1, characterized in that the end calibration reproducibly even batches ends are generated. 3. The method according to claim 1, characterized in that the Rolling mill slugs in the cold as well as in the warm condition can be processed. 4. The method according to claim 1, characterized in that the Wall thickness reinforcement against additional security Tear off in the stretch-reducing mill. 5. The method according to claim 1, characterized in that the Wall thickness upsetting to identify the separation points after stretch reduction serves. 6. The method according to claim 1, characterized in that except the electron beam welding also the flash off stump welding, arc welding, autogenous welding or Friction welding can be used.