The Swedish company SSAB Oxelösund claims to be the first in the world to guarantee the precision of their AccuRollTech rolled steel plate. The guarantee covers thickness tolerances and applies both to ordinary steel and the Hardox and Weldox grades, in plate dimensions from 4 mm to 150 mm. These close thickness tolerances for rolled plate have been made possible by means of a new and advanced four-high rolling mill. "Today we can produce plate with a thickness tolerance down to +/-0.2 mm", says Johan Anderson, Business Development Manager for the company. Such close tolerances save weight and material, and have many other advantages too.

The current standard for thickness tolerance, EN 10029 Class A, specifies +0.8/-0.4 mm.
"We can manufacture wide and thin steel plate to tolerances as close as one-third of the amount permitted by the EU standards," continues Johan Anderson. Having a precise thickness enables designers to calculate detail weights very accurately, and can thus design optimally, without excessive allowances for safety and wear.

Exact characteristics
Close tolerances give the product exact characteristics and combine low weight with high structural strength and minimum material. This is particularly important in the heavy vehicle industry, to keep manufacturing costs down and maintain the vehicle load capacity. High precision also facilitates processing; laser cutting and robot welding demand close tolerances to maximise cutting speed and welding quality. An exact thickness also permits even and smooth bending, and the same degree of spring-back for every part.
The AccuRollTech guarantee applies both to wear-resistant heavy plate (Hardox) - which is used among other things for mechanical shovels and dump truck tipping bodies - and to high structural strength plate (Weldox) for such applications as cranes.
"A deviation within +/- 0,2 mm is in the extra-close tolerance class. The thinnest plate has a guaranteed tolerance of +/- 0,35 mm (see the diagram in Figure 2)", asserts Johan Anderson. The plating is thoroughly worked and can be supplied in thickness intervals of 0.1 millimetre. The minimum nominal thickness is four mm and the maximum is 150 mm.
The new four-high rolling mill, representing an investment of SEK 1,600 million, is driven by two 11 200 kW continuous power electric motors. During starting, each motor can supply as much as 33 000 kW, which is equivalent to about 12% of the output of a medium-size nuclear power plant. The rolling force is a huge 10 000 tons, which is said to be the most powerful in the world.
SSAB Oxelösund, a part of SSAB Svenskt Stål AB, is Scandinavia's leading heavy plate manufacturer and a world leader in the field of quenched and tempered steel.
The head office is at Oxelösund and the company has offices in 40 countries. The total annual manufacturing volume 500 000 tons of heavy plate. There are about 2 400 employees, and the turnover in 1999 reached SEK 4,000 million.

Captions:
Figure 1: The new four-high rolling mill exerts a force of 10 000 tons, and it is said to be the most powerful in the world.

Figure 2: A deviation within +/- 0.2 mm is in the extra-close tolerance class. For the thinnest plate, the guaranteed tolerance is +/- 0.35 mm.

For further information please contact:
SSAB Swedish Steel Ltd
Christer Nylund, Directeur
100-801 Belgrave Way
Annacis Island
Tél. : 604-526 4399
Fax : 604-526 4379
Email : christer_nylund@ssab.ca
Internet : www.ssab.ca

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