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| | Passing the toughness test with honors in the german steel industry |
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The venerable European cathedral city of Wetzlar was a free city within the Holy Roman Empire, the medieval state that embraced most of central Europe and Italy under the rule of the German kings from 962 to 1806.
Wetzlar's modern-day history has been shaped by local iron and steel industries founded during the Industrial Age. Starting in the mid-19th century, Wetzlar developed into a center for the German steel industry.
Geographically, the city is situated in western Germany, near France, and is home to a number of major steel producers, such as Buderus Edelstahlwerke AG and its rolling mill in Wetzlar. Like all steel mills, Buderus has to contend with removing the large quantities of scale that accumulate during steel production - a problem that is as old as the steel industry itself. At Buderus, up to 380 tons of scale can accumulate on the company's 850 bloom line, which has a monthly production of 20,000 tons of steel.
Closed scale flushing circuit
To achieve the highest cost efficiency, the Buderus mill has designed its scale flushing circuit as a closed cycle, in which the scale drops into a conical tank during the rolling process. The tank is then flushed with water supplied by pumps.
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In a rolling mill, heated ingots pass through a rolling mill, a massive set of rollers that reduce the ingots to one of several predetermined shapes, such as blooms (a square or oblong shape) or a slab (rectangular shape). Blooms can also be further processed into smaller square sections called billets.
At the Buderus mill, scale generated in the rolling process drops downwards and collects in a flushing tank. The scale is flushed back into the settling tank, where it goes through preliminary separation. Scale that settles on the bottom of the tank is removed manually at regular intervals.
The flushing water, which contains abrasive scale, flows into a settling tank. After preliminary cleaning, the water flows into the pump sump. From the sump, the flushing water is pumped into the conical scale-collecting tank and the flushing process starts again.
Highly abrasive flushing water
Since scale flakes are heavier than water, larger particles deposit in the settling tank. A grapple empties the tank at regular intervals. The finer particles remain in the flushing water, however, and are consequently present in the recycled flushing water, making it a highly abrasive medium to pump.
The mill's original grey-iron pumps were thus subjected to much wear, particularly their impellers, and had to be replaced approximately every six months, causing long and expensive production downtimes. Eager to find a swift solution to the problem, Buderus consulted IIT Flygt and installed an IIT Flygt HP 5550, a submersible heavy-duty pump designed for severe abrasive slurry handling functions.
The ITT Flygt submersible pumps incorporate new technologies and design features providing important advantages for high-wear applications:
| The pumps have a split volute to permit simple, fast replacement of the abrasion-resistant hard chrome steel liner. A new volute casing can be installed in a single shift. The high chrome liner, designed for slurries with sharp particles, also provides good corrosion resistance. | | | | | The pump operating range is wide to minimize cycling. | | | | | The pump casing is made from solid cast iron. All parts coming into contact with the pumped media are primed and coated with chlorinated rubber. | | | | | Other design features include wear ring trimming, two sets of mechanical seals, a seal isolation zone, back pull-out for fast access to wear parts and a protected wet end. |
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In addition, the pumps are integral units, made up of a close-coupled motor and impeller, and operate on the sump floor. If maintenance or repairs are required, a pump is simply hoisted out of the pit along guide rails and serviced on ground level.
Five-year life
Based on experience from previous installations, the high-chrome impeller of the 5500 series has a normal life of five years when pumping return scale slurry in rolling mill conditions. Buderus tested the HP 5500 for a six-month period - the normal duty period for the dry-mounted pumps before maintenance was required - and detected no wear. The HP 5500 pump has been in permanent operation since mid-1993 and downtime is no longer a worry or problem at the Buderus mill.
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| Buderus Edelstahlwerke AG Rolling Mill |
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| Pump type: |
Submersible ITT Flygt HP 5500, 22 kW, abrasion-resistant slurry pump for high-wear applications |
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| Wear parts and impeller material: |
High chrome |
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| Flow rate: |
120 l/s, head 9.4 m |
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| Pumped medium: |
Scale slurry from flushing circuit of mill train |
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| Size of solids: |
10 mm max. |
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| Solids content: |
10 g/l max. |
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