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Drycooling for Wieland's hot-rolling millFrom non-ferrous metal block to high-tech strip: Hot rolled andcold showered

Aerial photo: Full view of the Wieland plant in Vöhringen with modern hot-rolling mill

Line of busi-ness:

EPC

Application: Machine cooling

Country / City: Germany / Vöhringen

Fluid: Glycol

Product: Drycooler GFH

Wieland-Werke AG, Ulm, have recently re-placed their approximately 30-year-old rollingmill for non-ferrous metals in the Vöhringenplant with a modern hot-rolling facility. In thenew system, blanks 8 m long and weighing upto 14 tonnes can be “stretched” to a lengthof 100 m during the course of several rollingprocesses. The doubling of the rolling capacitybrought with it a change-over from ground-wa-ter cooling to air cooling. Two drycooling sys-tems, for plate cooling and the rolling frame,with a cooling power of 5 MW and 3 MW,

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respectively, are installed, and work indepen-dently of each other. On the basis of the almosthistoric business relationship, Wieland decidedon Güntner drycoolers of type GFH.

Wieland is one of the world's leading suppliers of spe-cial copper pipes for refrigeration and air-conditioning.

In return, Güntner cover the greater part oftheir demand for copper pipes from Wieland.The manufacture of semi-finished goods innon-ferrous metals is a very heat-intensiveprocess. After the actual smelting, the rawblocks have to be put in the standard shapesfor trade, such as coils, strips or cut plates. Forthis step of the process – called warm rolling –the raw block is first heated and then deliber-ately cooled down during the rolling process.Most of this withdrawn heat is at a compara-tively low temperature, so utilisation of the heatis limited to only a few applications. The pri-

mary goal is to control the cooling process insuch a way as to achieve optimum quality ofmaterial. Ground water has been used hithertofor cooling the 30-year-old rolling train.

Dry cooling preferred

After deciding on a new rolling train, Wielandwere again faced with the question of how tocool the plates and rollers. Permission for useof water is mostly tied to usage – even if olderwater rights exist – that is, they are not transfer-able to new plants or expansions. Oswald Abler,Project Engineer at the Wieland-Werke AG inVöhringen and jointly responsible for the ener-gy supply, therefore had to plan the drycoolingsystem for the new rolling train from scratch:“The law on water rights has changed a lotin recent years. It is no longer permitted touse ground water for cooling in systems of thissize, as we did in the old system. We thereforeplanned for a cooling system with dry coolingright from the start.”

A direct comparison between the various cool-ing processes, i.e. wet cooling towers, hybridcoolers and drycoolers, showed clear benefitsfor dry cooling. Abler says, “For several yearsnow, we have been installing dry coolers bypreference in other areas of the plant, too. Al-though air-cooled coolers take up more spacefor the same performance, they are quite sim-ply more economical for many applications. Inthe case of water cooling systems, the permis-sion application procedure is more difficult, be-cause of vapour formation, for instance. Andwith air cooling, we can dispense with the treat-ment of water and the disposal of sludge.”

Better quality through a cold shower

Because of the different cooling processes inthe rolling mill and plate cooling, the drycool-ing plant is in two parts. The “rolling frame”cooler, with total cooling power of 3 MW, sup-plies the following rolling equipment with cool-ing water:

• Motor and bearings of the two warmrollers (electrical connection 2 x 2.0MW)

• Emulsion tank• Thickness measuring equipment

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• Hydraulics (LP and HP)• Oil lubrication system• Coiler

Six Güntner type GFH drycoolers are installed,each with twelve fans (530 rpm; 770 W perfan). Each drycooler is 12 m long and 2.4 mwide, and weighs about 3 tonnes. The coolantis a 60:40 mixture of water and glycol. The wa-ter in the rolling-frame circulates at a rate ofaround 330 cu.m. per hour; there are two elec-tric circulation pumps (operational/ reserve)with 75 kW power.

Aerial photo: Main Wieland Plant in Ulm

The “plate cooling” drycooler is used to chillthe warm, rolled “strips” with an emulsion –the so-called quench water – from 600 °C to150 °C. This quality-boosting process requiresa large quantity of water in a very short time,so cooling power of 5 MW is needed. Here, too,the coolant is a 60:40 water glycol mixture ina closed circulation system. The flow volumeis in the region of 450 cu.m. per hour, provid-ed by two circulation pumps (operational/re-serve), each with 75 kW of electrical power.

The actual process cooling is designed as anopen, secondary circulation system with elab-orate periphery, such as fin clarifiers, scale col-lector and sand filter etc. In this process, thereis automatically a higher level of cooling tem-perature, so in winter the available warmthis introduced to the ventilation system in thebuilding. This way, about 2,000 kW of wasteheat can be utilised to heat the building savinga corresponding amount of primary energy.

The waste heat from the process is dissipatedby eight Güntner GFH drycoolers of the sametype and size as those used for cooling therollers, but with more powerful fans (1.05 kWelectrical power per fan at 620 rpm).

Standard version meets noise protection cri-teria

The new rolling train is situated right next toa residential area, so noise control was giventop priority right from the planning stage of thedrycooling plant. Although the final drycoolingperformance was not yet defined at this stage,it was possible to size the new drycooling plantwith sufficient precision on the basis of over-all noise expertise that was available for theVöhringen plant. Otto Schmid from the Günt-ner Sales Office South describes how the deci-sion was reached: “Because we had the noiseprotection expertise, we were able to use themaximum permissible values as a yardstick.Our philosophy is not to sell the customer thegreatest possible number of drycoolers, butrather one drycooler of reasonable size andwith acceptable noise emission. With the largerange of fans we are able to cover a wide rangeof performance, even with a standard productlike the GFH drycooler.”

Immission control according toVDI guideline 2058

The new drycooling plant is not the first projectwith Güntner products at Wieland. OswaldAbler says, “We have been working togethervery constructively for years now. With OttoSchmid from Technical Sales at Güntner, wehave solved every cooling problem up to nowquickly and without any red tape.”

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From continuous casting to high-tech se-mi-finished products

Archaic as the smelting of metals and alloysmay seem even today, the degree of automa-tion and precision in the further processing ofingots to strips, plates and tubes is all the moreimpressive. In the new rolling train at Wieland,the ingots, which are cast in moulds and areeight metres long, 200 - 250 mm high and upto 800 mm wide, are first heated to deforma-tion temperatures of between 750 and 1050°C – depending on the alloy – in a gas-heatedrocker bar furnace. The downstream hot rollerthen reduces the thickness of the blank to 10to 15 mm in a back-and-forth movement. Theraw block lengthens with each run through therollers until, at the end of the rolling process, itreaches a length of 100 m. The rolled-out cast-ing dross and the oxides that have formed dur-ing rolling are then milled off at a cutting speedof 30 m per minute, leaving bare metal surfacevisible. In readiness for further processing, the“strip” is wound by a “coiler” (500 kW motor),or deposited in the strip store.

Comparison of heat transfer coeffi-cient in smooth and interior-ribbed tubes

With process annealing and cold rolling, thecoils or plates are given the final thickness thecustomer wishes, or given the ordered hard-ness. Slitting shears then cut the strips to thecorrect width. Most of the strips up to 0.5 mmthick are made into fabricated materials forelectrical goods and electronics, such as leadframes for semiconductor elements, plug con-nections for telecommunications and vehicleelectrics, high-frequency and underwater ca-

bles, or transformers. Other major precisionstrip costumers are the manufacturers of con-sumer goods such as metal ornaments, cutleryor musical instruments. Wieland is also one ofthe world’s main suppliers of special coppertubes for refrigeration and air-conditioning ap-plications.

Smooth and interior-ribbed tube