EP2470315B1 - Method for producing hot-rolled hollow profiled elements having a rectangular cross-section and small edge radii - Google Patents

Description

The invention relates to a method for producing hot-rolled hollow sections made of steel according to the preamble of claim 1. In particular, this is deviating from the circular shape hollow sections, such as hot-finished hollow sections according to EN 10210-2.

The known as MSH ^® profiles hot rolled hollow sections can be produced with essentially round initial cross-section of both cold-finished longitudinally welded as well as from hot-finished seamless Vorrohren.

When using cold-finished longitudinal welded Vorrohre a round tube is first prepared from a formed to a slit pipe steel strip, usually by HFI welding, which is hot rolled after heating to forming temperature in corresponding roll mills to form a hollow profile, such. In JP 8 238520 A , When using hot finished seamless billets they are reheated either at the same heat or at rolling temperature and then formed with appropriate rolls to a hollow profile with the required rectangular or square cross-section.

Correspondingly produced hollow sections, are used as construction tubes in addition to the classic field of application of structural steel increasingly increasingly in industrial, sports facilities, bridge and mechanical engineering, construction machinery, special vehicles, commercial vehicles and agricultural machinery as well as steel and building construction.

Increasing demands for environmentally friendlier and more economical construction methods led to the development of hot-rolled hollow profiles, which are characterized by a lower weight or a larger cross section with the same nominal dimension (edge length x nominal wall thickness) in relation to the required area moment of inertia or resistance, and compared to hollow profiles, the z. B. are produced by cold production of bent sheet metal, have significantly smaller edge radii or visible edges.

Since the edge radii of the hollow sections are not uniform in practice, EN 10210-2 does not specify the outer radii of curvature but the lengths of the rounding areas, referred to below as visible edges.

The advantages of small visible edges in hollow sections are on the one hand a larger area moment of inertia and greater bending and torsional stiffness, on the other hand results in connections in the profile edge region a smaller weld gap and thus a more appealing appearance, which is very important in visual constructions.

Furthermore, there is a wider contact surface for cross sections to be connected, whereby the carrying capacity is increased. In addition, a force can be introduced at least partially straight into a standing parallel to the force profile wall when the visible edge is smaller than the wall thickness, which is advantageous for the static design.

However, hot-finished hollow sections with a maximum visible edge length of ≤ 3.0 x t (t = wall thickness) according to EN 10210-2 are no longer sufficient for all areas of application.

Here, for example, is the scope of application for climbing tower cranes for high-rise construction. With these cranes, the height of the tower and thus the crane and hook heights are gradually increased by inserting additional tower elements, thus adapting to the construction progress.

The tower elements are composed of square or rectangular hollow profiles, wherein the vertically extending Turmelementeckprofile, the so-called "corner stems", are interconnected by bolts arranged centrally in the hollow profile.

To increase the tower elements, a guide frame along the vertical tower element corner profiles is used, in which the guide rollers must run because of space reasons because of the bolt connection very close to the profile edge. at To large visible edges, the guide rollers would run too far in the hollow profile center, so that the individual tower elements could not be connected by the bolts.

Other applications for hollow sections with smaller visible edges are z. B. the lower chords of the boom of trolley tower cranes to obtain a wider bearing surface for the trolley rollers or generally when loaded on bending profiles, z. B. for that from the DE 10 2007 031 142 well-known crane track carrying system made of steel for high demands and that from the DE 10 2006 010 951 known supporting system made of steel for roof structures.

The maximum permissible value for visible edge lengths C ₁ and C ₂ of ≤ 3.0 xt for hot-finished hollow sections according to EN 10210-2 is clearly too high for the aforementioned application areas. In accordance with EN 10210, a value of 1.5 xt is therefore generally used as the basis for calculation.

So far, it has not been successful in terms of rolling technology to reduce the visible edge lengths of hollow sections made of cold-fabricated welded or hot-finished seamlessly produced delivery tubes in such a way that they can be used economically for the described fields of application. It was therefore always sought after a compromise between rolling the hollow profile, wear of the rolls and the visible edge length, but this did not lead to the desired success.

For these applications, hollow profiles welded together, for example, consisting of two L-shaped legs, which have very small visible edge lengths of ≦ 1.0 × t and have thus far fallen below the standard specification for hot-finished hollow sections, have been used.

However, these hollow profiles, which are welded together from individual profiles, have the disadvantage of inhomogeneous material properties and, due to the weld seam stresses, an increased risk of warping due to the weld seam and are expensive to produce.

The object of the invention is therefore to provide a method for producing hot-rolled hollow sections with rectangular or square cross section of welded or seamless Vorrohren, with the simple and cost-effective manner in the course of Walzan production of the hollow sections also visible edge lengths with C ₁ or C ₂ ≤ 1.5 xt can be realized.

This object is achieved according to the preamble in conjunction with the characterizing features of claim 1.

According to the teachings of the invention, a method is used to solve this problem, in which for a given profile cross-section introduced into the roll mill Vorrohr based on the previously default standard Nennaußendurchmesser an enlarged diameter, which can be reached from a degree of reduction of the front pipe and to be reached Hollow profile dimensions is determined, wherein the degree of reduction to be achieved in a range of -2.0% to -13% and is determined according to the following formula: $$\mathrm{Reduction\; grade\; R}\left[\%\right]=\left[\left(\mathrm{2}\times \left(\mathrm{H}+\mathrm{B}\right)\right)-\mathrm{\pi }\times \mathrm{D}\right]\times \mathrm{100}\%/\left[\mathrm{2}\times \left(\mathrm{H}+\mathrm{B}\right)\right]$$

In the course of extensive experiments, it was surprisingly found that for a given caliber of the rollers, the use of a larger diameter of the front pipe than a standard pipe diameter leads to a significantly improved caliber filling in the edge areas, with the result that significantly smaller visible edges can be realized.

By appropriate choice of the degree of reduction of the front pipe or the Vorrohrdurchmessers now not only visible edge lengths of ≤ 1.5 x t can be realized but even visual edge lengths of ≤ 1.0 x t or ≤ 0.6 x t.

However, as the tests have shown, the danger of the rolling plug increases if the pre-pipe diameter is too large, that is to say to a large degree of reduction compared with the standard pre-pipe diameter, in which the pipe to be reshaped by the rolls undergoes no advance in the rolling stand before it leaves the forming zone and gets stuck in the rolling stand.

In addition, there is the danger above a certain front tube diameter that material enters the roll gap and thus creates a burr or bead, which subsequently has to be laboriously processed.

In the case of a small diameter of the delivery pipe, which is too small a reduction factor compared to the standard delivery pipe diameter, the caliber charge in the radius ranges is insufficient and a sufficiently small visible edge is not generated.

The inventive enlargement of the Vorrohrdurchmessers by maintaining the required degree of reduction are thus set relatively narrow limits, the degree of reduction of -2.2% to -4.0% for visible edge lengths ≤ 1.0 xt but of <-4.0% for visible edge lengths ≤ Is 0.6 xt. In an advantageous development of the invention, these values can even be achieved without a change in the calibration of the rolls in comparison to the use of a standard pre-pipe diameter.

The advantage of the method according to the invention is that compared with the hollow profiles welded together from individual profiles, hot-rolled hollow profiles that can now be produced very economically can also be used for applications that could not be used there due to the visible edge lengths that were previously too great.

The following examples illustrate the operation of the invention.

Customer requirement: C ₁ or C ₂ ≤ 1.0 xt according to EN 10210-2

Example 1:

required dimension of the hollow section (H x W x t): 220 x 220 x 16 mm Circumference of the warm pre-pipe (U): 889.07 mm Calculated degree of reduction: -1.02 measured visible edge length C ₁ or C ₂ : 21 mm determined factor C ₁ / t or C ₂ / t: 21/16 = 1.3 (not met)

Example 2:

required dimension of the hollow section (H x W x t): 220 x 220 x 16 mm Circumference of the warm pre-pipe (U): 907.92 mm Calculated degree of reduction: -3.08 measured visible edge length C ₁ or C ₂ : 14 mm determined factor C ₁ / t or C ₂ / t: 14/16 = 0.9 (fulfilled)

Example 3:

required dimension of the hollow section (H x W x t): 220 x 220 x 16 mm Circumference of the warm pre-pipe (U): 927.43 mm Reduction ratio: -5.11% measured visible edge length C ₁ or C ₂ : 9 mm determined factor C ₁ / t or C ₂ / t: 9/16 = 0.6 (fulfilled)

The following is an application example for the use of a hollow profile according to the invention is described in detail with reference to a sectional view.

In the single figure , a section of a tower element of a tower crane is shown, are used in the inventively produced hollow profiles with small visible edges as a construction element.

The hollow section 1 of the tower element is designed as a vertically extending tower element corner profile "corner post". The visible edges of the hollow profile are denoted by C ₁ and C ₂ .

The connection with the aufzustockenden tower element is done by means of a centrally through the opposite leg of the hollow section 1 plugged through bolt 2, which connects the Turmelementeckprofile the lower with those of the tower element mounted thereon.

The hollow profile 1 is provided in the region of the bolt connection with reinforcing tabs 4, 4 'and the bolt 2 secured by splints 3, 3' against loosening.

To increase the tower elements, a guide frame 5 along the vertical tower element corner profiles used in the guide rollers 6, 6 'because of the bolt connection for reasons of space must run very close to the profile edge. This can now be easily realized with the hot rolled hollow profile produced according to the invention because of the very small visible edge length. <B> LIST OF REFERENCES </ b> No. description 1 hollow profile 2 bolt 3, 3 ' cotter pins 4, 4 ' reinforcing tabs 5 guide frame 6, 6 ' guide rollers H, B Edge lengths of the hollow profile (height, width) in mm D Diameter of the warm pre-pipe before the start of rolling in mm U Circumference of the warm pre-pipe before the start of rolling in mm t Wall thickness in mm C1, C2 Visible edge lengths in mm

Claims (2)

1. A process for the manufacture of hot finished hollow sections made from steel with a rectangular or square cross section whereby an essentially round seamless hollow made by hot rolling or a welded hollow made by a cold manufacturing process with a defined nominal external diameter is first produced and then formed into a hollow section with the required cross section at the forming temperature and the exposed corners C₁ and C₂ of the hollow sections have a value ≤ 1.5 x t (t = wall thickness) characterised in that
   for a specified cross section of the hollow section the hollow to be introduced into the profiling rolling mill has a nominal external diameter which is calculated from a reduction factor of the hollow which is to be attained and the hollow section dimensions which are to be attained, whereby the reduction factor lies in the range of -2% to -13% and is calculated using the following formula: reduction factor R [%] = [(2 x (H + B)) - π x D] x 100 % / [2 x (H + B)] whereby for an exposed corner length C₁ and C₂ of the hollow sections of ≤1.0 x t the reduction factor of the hollow is < -2.2 to -4% but
   for an exposed corner length C₁ and C₂ of the hollow sections of ≤ 0.6 x t the reduction factor of the hollow is < - 4.0%,
   whereby:

   H = the height of the hollow section in mm

   B = the width of the hollow section in mm and

   D = the diameter of the hot hollow in mm before rolling commences.
2. A process according to claim 1,
   characterised in that
   the forming into a hollow section is done with the same roll gaps of the profile rolls for the use of a hollow with a standard hollow diameter.

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