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BTU Bridle Technology has received an order from SES Engineering LLC covering the design, construction and supply of three Umlauf Bridles for a revamp of a push-pull pickle line operated by Steel Dynamics Flat Roll Group (SDI). After the revamp that pickle line will be the first in the world to use exclusively Umlauf Bridles to transport the strip through the line. Umlauf Bridles build up strip tension high enough to ensure that also thick-gage and high-strength strip will leave the pickling line leveled. Once revamped, the pickle line will be able to operate at much higher speeds than before, as scale breaking will be much more intensive.

SDI expects from the pickling line revamp in Columbus/Mississippi, for which SES acts as general contractor, above all a solution capable of producing very high strip tension in the line. Therefore SES chose the Umlauf Bridle technology from BTU. Thanks to their special design, Umlauf Bridles of the latest 3.0 generation are able to apply much higher forces onto strip in processing lines than conventional bridle roll units. What is more, Umlauf Bridles distribute the strip tension extremely uniformly across the complete width of the strip.

The first of the three Umlauf Bridles will be arranged directly behind the pay-off reel. There it will immediately bite the very first centimeters of the head of the up to 13 mm thick and up to 1,880 mm wide strips and guide them into the stretch-leveler. The stretch-leveler will be supplied by SES. In connection with the second Umlauf Bridle arranged behind the leveler, strip tensions of up to 1,250 kN can be reached during stretch-leveling. A very intensive scale breaking effect will result from the thus achieved elongation rates of 0.5 to 1.0 percent. This will make it possible to operate the line at speeds of up to 150 m/min.

As the strip is actively pulled through the leveler by the Umlauf Bridle, no roller drive equipment is required in the leveler. This reduces investment and maintenance costs and prevents roller slipping.

The second Umlauf Bridle pushes the leveled strip into the pickling tank, and the third one will be arranged at the run-out to bite the head of the pickled strip and guide it into the recoiler. At the same time, it creates the strip tension needed to produce exactly wound coils.

Daniel Cullen, Senior Sales Manager of SES Engineering, explains the reasons for choosing the Umlauf Bridle technology: “The most important aspect for us was to find a technology that would be able to reach very high strip tension and allow us to control that strip tension in a very precise way. Apart from that, the simplicity of the Umlauf principle convinced us: we will be able to set the right strip tension exactly where in the line we need it – without any conventional bridle rolls, driven rollers in the leveler or an additional braking unit. Moreover, in future stretch-leveling will require less strain energy as there is no bending of strip in the Umlauf Bridles.”

According to Michael Umlauf, Commercial Manager of BTU Bridle Technology, by moving the strip exclusively in a linear way the Umlauf Bridles are superior to bridle rolls in several respects: “Using Umlauf Bridles in connection with stretch-levelers means that leveling is performed primarily by stretching and only to a minor degree by bending. Actually, up to 90 percent of the leveling work comes from the stretching effect.”

The pickle line is scheduled to come back on stream after the revamp in January 2019.

Background: The Umlauf principle

Umlauf Bridles consist of two crawler-type units covered with an elastic coating. One unit is arranged above and one below the strip. They guide and transport the strip linearly, i.e. without any deflection, at different positions within strip processing lines. Thanks to their extreme compactness, they can be arranged at virtually any position in the line.

By applying the force over an area – and not concentrated in one point – any local concentrations of forces or relative movements between the crawler unit and the strip surface are prevented. Therefore, the risk of surface damage is ruled out, making this technology highly suitable for delicate strip surfaces.

A single Bridle unit may be used to apply large forces to the strip, for example, in order to pull it through side trimmers, slitting shears or levelers. This aspect is of particular interest especially when processing thick strips. The unit may also be installed to decouple the strip tension of a line section from upstream processes or even reduce the strip tension to “zero”. By reducing strip back-tension to “zero”, an Umlauf Bridle makes it possible, for example, to measure the flatness of the strip without any interfering effects.

As the Umlauf Bridles are arranged within the strip processing line, they build up strip tension before the coiler bites the strip head. This significantly increases the usable coil length, in other words the yield. In certain strip processing lines this may lead to a plus of 20 meters per coil.

Umlauf Bridles can be rotated very precisely through their vertical axis, for example, in order to reduce strip camber during leveling or adjust the strip position during side trimming. At cut-to-length lines, they position the strip edge perfectly perpendicular to the shear. The advantages of this solution: perfectly rectangular cut-to-length strip.