Nokian Renkaat, a leading producer of tyres for northern conditions,broke new ground in spring 1998 in choosing ABB's ACS 600 MultiDrivesystem to control the speed and torque of the motors driving thelatest batch mixer at the company's production facility in Nokia,Finland. According to factory service manager Timo Ylikoski, an ACsystem was chosen instead of the customary DC solution with a view toassessing the options for future investments.

"There were no reference installations to visit, but the torque response demonstration in ABB's test yard convinced us that the AC solution could offer the required performance," Ylikoski says.
Reliable speed control is the main requirement this application puts on the drive system. The ACS 600 product family features ABB's Direct Torque Control (DTC) technology. In DTC drives, inverter switching directly controls the flux and torque of the motor. Overload
characteristics come into play during process disturbances requiring the mixer to be restarted with a full load.
The new mixer of Nokian Renkaat has a motor power rating of 1500 kW. The mixer is used both for mixing raw rubber and additives into rubber compounds and for adding vulcanising agents to the compounds Mixers are in
continuous production, operated in three shifts seven days a week. Mixer operation is fully automated, with the drive system integrated in the process control system.
The mixing cycle, which lasts some five minutes in all, requires high torque at the beginning. The cycle starts with the differentially timed feeding of the lumps of raw rubber or sheeted rubber compound and the additives into the mixer through different routes.

Torque and speed control
"The load curve of the rubber mixer is rather peculiar, with very high torque required at the start of the mixing cycle. AC drives have a certain edge over DC drives in this respect," says Timo Ylikoski.
The ACS 600 MultiDrive system at Nokian Renkaat attains the required torque step rise with an inverter power rating of 3040 kVA. Accurate speed control is important throughout the cycle as a means of attaining the desired quality and capacity.
Reliability of the drive system is essential in continuous production. The advantage of the AC drive system is, that it needs minimal maintenance. The system with a 12-pulse rectifier is also friendly towards the electricity network, says Ylikoski.



Low motor noise
A distinct advantage during operation is that, thanks to direct torque control, the low audible motor noise is appreciably lower than in the alternative solution. At Nokian Renkaat, noise control includes sound-insulation of the mixer gearbox. As a result, the noise level of the DTC-controlled system including the mixer, gearbox and motor is well below 80 dB.
Commissioning went without a hitch. Initially, the mixer went into continuous production for five days a week. Once the training of new operatives is completed, the mixer will operate 24 hours a day seven days a week. There have been no problems. Says Timo Ylikoski, "The drive system is performing as it should when we can leave it to get on with the job."

Technical data
Converter: Supply unit: ACA633-5200-6, 12 pulse
Inverter unit: ACA610-3040-6
Control: Encoderless speed control,
analogue reference from process control system

Operating cycle: Filling: 2 x nominal torque (TN) 12 s,
Mixing: nominal torque (TN=14325 Nm) 248 s,
Discharging: torque decreases from nominal to zero (TN=>0) 40 s.

For further information please contact:

ABB Industry (Pty) Ltd
David V. Sheldon
P.O. Box 11494
1457 Randhart, South Africa
Tel: +27 11 864 5340
Fax: +27 11 908 2061
http://www.abb.com/vsd

Asea Brown Boveri S.R.O.
Vladimir Lexa
Sokolovská 84-86
Praha 8 - Karlin
18600 Prague, Czech Republic
Tel: +420 2 2283 2327
Fax: +420 2 2283 2310
http://www.abb.com/vsd

ABB Industry Oy
Drives / System AC Division
Panu Rahikka, Sales Manager
PO Box 184
FIN-00381 Helsinki
Finland
Tel: +358 10 222 3281
Fax: +358 10 222 2681
http://www.abb.com/vsd

ABB Systemen B.V.
Postbus 2714
3000 CS Rotterdam
Marten Meesweg 5
3068 AV Rotterdam
Hans Damen
hans.damen@nlsys.mail.abb.com
Tel.: 010-4078 262
Fax: 010-4078 433
http://www.abb.com/vsd

S.A. ABB N.V.
Peter van de Moortel
Roge Wei 27
1930 Zaventem
Tél. 02 718 63 40
Fax. 02 718 66 64
http://www.abb.com/vsd

ABB Industria S.P.A.
Fausto Belotti
Viale Edison 50
20099 Sesto San Giovanni, Milano
Tel. 02 2623 2792
Fax 02 2623 2979
http://www.abb.com/vsd

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