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Rod and bar rolling of special steelsInnovation has been a cornerstone of Morgårdshammar’s operations throughout its history. The rolling of special steels requires specialist equipment to maximise output without compromising on product quality. Examples of innovations and recent applications are described.

In December 2006 Morgårdshammar celebrated its 150th anniversary when one of their most famous

engineers, Erik Norlindh, if still alive, would have been 97 years old. He had a significant impact on the development of Morgårdshammar and of long products rolling generally, and his innovative spirit lives on in the company.

Norlindh’s innovations in the steel industry are well documented. Some of his ideas were:` Universal coupling` Roller guide` Oval repeater operating from upper to lower position` Housingless stands` Three high universal stand` Single family rolling – a method of minimising resetting

time` Jumping three high stand` Conti-loop wire rod mill ` Fixed pass line rolling` Housingless concept for heavy plate mills` AGC system for Steckel mill housingless stands` Continuous hot strip rolling via fast stand changing

technology

MORGÅRDSHAMMAR TODAY – THE HERITAGE OF AN INVENTORThe housingless stand This was initially built in both two-high and three-high versions. With this design Norlindh could shorten the loaded length compared to conventional roll stands with heavy housings, therefore a housingless stand became much lighter than a comparable housing stand. Also, the elastic strain of the stands was reduced dramatically and thus the variation of deflection in a pass was reduced and the tolerances improved. Today housingless stands are standard in the industry and by looking at the different designs available in the market, many of the features Norlindh already had in 1944 can be recognised.

During the 1960s, a new generation of housingless stands was developed (see Figure 1). All chocks were supplied with nuts, and the stay bolts were manufactured as free bolts made from high strength engineering steels, which

Author: Giacomo VerliniMorgårdshammar AB

r Fig 1 New generation housingless stand

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further improved the stiffness of the stand, and thus the tolerances. The screwdown mechanism was then designed as a separate unit placed on top of the stand, out of the loaded area. The stay bolts are right- and left-threaded with nuts in the chocks, which makes it possible to set the rolls on a symmetrical rolling line. The new generation housingless stands are also supplied with cylindrical roller bearings and with a special thrust support, consisting of double angular roller bearings assembled face to face. The inner rings are fixed on the rolls while the outer rings are fixed in the thrust box, bolted to the chocks and fixed by

bolts to a rigid ruler when the stand is positioned in the rolling line.

The first installation of this type was a continuous line. All roll units with exit guides, posts, couplings, combined pinion stand and reduction gear as well as the drive motor were mounted as a complete unit on a tilting head. The centre of tilting was the pass line, and the units rested on tiltable pads below the motor. All stands were placed on sledges and clamped in position when the correct groove was positioned in the rolling line by special spring-loaded clamps. The spring force was loosened by means of hydraulics when the stands needed to be moved or changed. a

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This system ensured that the stands were not pressurised during operation, and is common technology for most mill manufacturers today.

The flexibility to roll rounds, squares, flats and spring sections was dramatically improved, and it became possible to take the edging passes in any stand in the straight rolling line. The fixed pass line was an advantage, particularly for the rolling of wide flats, because by keeping the rolled bar in the same line no side shifting was necessary and the rolled material became straighter.

The heavy housingless billet mill As it is still not possible to continuously cast some steel grades there is a need for billet rolling mills to roll blooms to the required billet size and consolidate the core. Morgårdshammar developed the heavy billet rolling stand P979 B for this purpose. Figure 2 shows the new stand, which has a lower roll fixed but which is adjusted to the height of the work roller table. The design is based on experiences of heavy plate rolling.

The stand is very light, but is still stiffer than most billet mills, thanks to the housingless design. In Figure 3 (with the stress path marked in black), the P900 B series stand is compared on the same scale, to a conventional stand of equal capacity. Spherical radial bearings and a special thrust arrangement, designed as a closed unit with double conical roller bearings give the stand optimum radial and axial rigidity. The rest bars hold the chocks together and axial rigidity is guaranteed by a special thrust support, mounted on the free end of the rolls, in the same way as on the common P600 series of stands.

Screw jacks adjust the height of the entire stand to the roller table height, not only to compensate for the difference from new roll diameter to scrap diameter, but also to compensate for the different pass height on the bullhead and in the deeper box grooves. This is a unique capability, which has been made possible thanks to the fact that the roll forces are discharged on the four screw downs inside the stand. By full utilisation of the adjustable height, the bite conditions in the early passes are improved, and the ski end problem solved, since all passes can enter perfectly horizontally. The stand is also supplied with the common fast roll changing system, which reduces the downtime dramatically compared to conventional blooming mills.

The shiftable rougher for special steel production Morgårdshammar’s modern roughing technology of is the reversible and shiftable, housingless design (see Figure 4). This technology can be applied to the P635, P641 and P653 stands. As special steels are very sensitive to surface cracking due to severe cooling of the surface layer in contact with the rolls, long roll/material contact time must be avoided. A fully continuous mill is, therefore, not

r Fig 2 P979 B housingless billet mill stand

r Fig 3 Comparison between P979 B (right) and conventional billet stand (left)

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a

suitable due to the long contact time in the early passes where the speed is low and the contact length is fairly long due to the large roll diameter and heavy linear draught. The preferred option is a reversing rougher.

The lateral shifting rougher has a shorter interpass time than conventional mills where the stand has a fixed position and the bar turners move across the work roller table to position the bar in front of the actual groove. With lateral shifting the work roller table is narrow and no lateral movement of the bar is made, thus the bars remain straight during rolling. Thanks to its high speed operation the heat losses can be kept low, resulting in more even temperature along the bar than in continuous rolling, since the head and tail alternate each pass. This operation is fully automated, very reliable and requires no operator.

The high speed reversing roughing with short interpass times makes it possibile to obtain high rolling capacity. This is normally consistent with the capacity requirements in special steels mills, like mills for stainless steels, and many installations have been made in recent years.

A NEw pARADIGM IN wIRE ROD AND bAR ROLLINGSince Norlindh’s time, the development of automation systems has dramatically changed the options available in rod rolling mills. Modern speed control systems are fast enough to be able to control the loops at speeds up to 20-25m/s without the need for repeaters.

Since the late 20th century, fully continuous wire rod and bar mills have dominated the market, however, when rolling special steel grades, the cooling of the rolled bar surface can produce serious surface defects on the bars as well as deep fire cracking in the roll surface. Also, the ever increasing billet sizes, dictated by the need for shrouded and higher productivity casting, has required changes

in rolling practices. To solve these problems alternative technologies have been developed, as well as processes for improving the material properties and to avoid intermediate heat treatments.

The H-V wire rod block with intermediate stand shear One of the most significant developments in wire rod rolling is the wire rod block, characterised by 6-10 cantilever stands assembled in a common frame, and driven by common motor over gears with fixed gear ratio. The blocks on the market are designed mostly with the roll shafts inclined at 225 and 315°, as seen in the rolling direction, with the origin in the rolling line, and with common trigonometric definition of positive angles. This kind of block is called a Delta block, Vee block or X block and it is particularly stable, since all the stands are mounted symmetrically as seen from the rolling line, and with the main shafts, and all gears close to the common foundation. The rolling speed can be very high (120-140m/s). In Morgårdshammar the block design has been more focused on special steel, small rolling lots and ergonomic design for fast roll changing.

By designing the blocks with only horizontal and vertical rolls (0-270° or 180-270°; see Figure 5), the mounting and dismounting of the roll rings is easier to perform, and down time for roll ring changing can be reduced. The rolling speed in this kind of block does not normally exceed 95m/s. However, this is no problem for special steel rolling where, for Si-Mn alloyed welding wire, tyre cord wire and common austenitic grades, 80m/s is a practical maximum rolling speed. Duplex stainless steels and Ni-base alloys are normally not rolled at more than 60m/s and tool steels and high speed steels are at even lower speeds in order to avoid partial melting of the segregated material in the core of the wire. These high alloy steels are also rolled

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r Fig 4 Shiftable rougher in operation r Fig 5 Morgårdshammar H-V high speed wire rod block

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highly alloyed tool steels is favourable for consolidation of the billet core. The common Danieli Morgårdshammar housingless stand design is extremely light, but still stiffer than conventional billet mills. Spherical radial bearings and a special thrust arrangement with double conical roller bearings give the stand optimum radial and axial rigidity. The rest bars hold the chocks together and axial rigidity is guaranteed by a special thrust support. The supply will be for the complete mechanical package from Sweden by Morgårdshammar AB with electrical and automation from Danieli Automation, Italy.

Ovako Imatra, Finland Morgårdshammar received an order in May 2007 to supply a new P969 B housingless reversing blooming stand and auxiliaries to replace the existing housing-type stand in the 250kt/yr bloom/billet mill. This is another major modernisation stage after the previous upgrading step (also carried out by us in 2002), which included the installation of two reversible shiftable P653 roll stands and associated auxiliaries. The installation will provide greater operational flexibility, shorter changing time, increased plant efficiency and higher product tolerances. The new 830mm diameter roll stand will produce the feed material for the downstream finishing stands to produce large size quality bars in the range of 90-200mm diameter rounds and 80-150mm squares, in high carbon, spring and bearing steels.

The same stand will also produce 135mm semi-finished squares for feeding the special steel bar mill (also supplied by Morgårdshammar in the late 1980s) which produces 25-85mm diameter quality rounds and flat bars. Start up of the new mill is scheduled for summer 2008. With the supply of the new blooming stand, all rolling mill equipment at Ovako Imatra will be of Morgårdshammar origin.

Sidenor Azkoita Sidenor Azkoitia (formerly GSB Acero) special steel bar mill will undergo a major upgrade in order to enhance plant productivity, efficiency and final product quality for stainless and spring steel products. The order in 2007 foresees the addition of a fully automatic two-high reversing shiftable type P653 roughing stand, a set of horizontal, vertical and combined stands for the intermediate/prefinishing mill, lengthening and widening of the pack-annealing type cooling bed, and new product handling and finishing equipment after the Morgårdshammar cold shear.

The new mill configuration will retain the existing Kocks/Danieli roughing and sizing block (RSB; started up in 1998) as the finishing mill for the range of special bar quality (SBQ) round bars, while the flats will be finished at the upstream stand No. 12.

The upgraded mill will have a design capacity of 60 t/hr and will be suitable for producing 20-65mm diameter SBQ

at lower reductions, which require different gearing of the blocks, hence Morgårdshammar delivers blocks with 20% average reduction for carbon and low alloy steels, and with 16% per pass for special steels.

Roll gap adjustment is copied from the P600 series housingless stands. No eccentric sleeves are employed enabling all load-carrying contacting surfaces to be pre-stressed by the same ‘counter nut’ system as employed in our mill stands. The elimination of eccentric sleeves for roll gap adjustment means that the Morgårdshammar block has a considerably larger diameter roll shaft in relation to roll ring diameter than any of our competitors: 120mm for our 150mm stand and 160mm for our 200mm stand. This, of course, means very significant reductions in roll shaft bending under load, which contributes to the ease of maintaining close tolerances on a wide range of finishing products. In addition, no eccentric sleeve means the difference between maximum and minimum roll diameters, 20 and 25mm respectively, for P815 and P820 exceeds that of most competitors resulting in significantly greater roll economy.

In order to simplify maintenance the roll unit can easily be separated from the gearboxes as only the roll unit is removed when the sleeve bearings need replacement. The gearbox with its demands for precision gear meshing and alignment remains mounted on the main frame.

A unique feature of the Morgårdshammar blocks, designed for special steels, is the intermediate stand crop shear positioned after the fourth stand in the block. By cropping the head ends, steels sensitive to head end splitting, like free cutting steels, sulphurised austenitic stainless steels, tool steels and high speed steels, can be rolled at full security, and cobbles due to split ends are avoided.

Morgårdshammar wire rod blocks are found in very demanding applications for the rolling of stainless steels, nickel alloys, carbon steels and rebar at sites including: Acerinox in Spain and USA, Talley Metals, USA, Ugine Savoie, France, Outokumpu, Sheffield, UK, Nucor, Nebraska, USA, Sumitomo, Japan, Mukand, Bhilai, ISWP TATA and Usha Martin, India.

REFERENCE pLANT EXAMpLESMetal Ravne, Slovenia This leading European producer of high alloy steel, chose Danieli Morgårdshammar to replace the old blooming mill and install a heavy P979 B billet rolling stand. Production in the mill covers all engineering steels, special steels and high alloyed tool steels. Slabs in widths up to 510mm (designed up to 800mm) as well as billets will be rolled in hot and cold worked tool steels.

The roll stand with a fixed lower roll and a large roll diameter (930mm) guarantees that the stress state in the

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groove two-high P635 top driven vertical stand, plus associated auxiliaries and services, will also be supplied.

Sunflag I&S – Special Steels, Nagpur A new high-speed wire rod line for special steels was commissioned in August 2006. It comprises a 10-pass high-speed block and controlled cooling system. The line produces 5.5-16mm diameter stainless, carbon and alloy steel wire rod at speeds of up to 90m/s. The new wire rod line is a consequence of customer satisfaction from the previously installed Morgårdshammar garret line project, producing a range of large rounds from 10-36mm at speeds up to 15m/s in 1,500kg coils.

SAIL – bhilai Steel plant In 2006 the merchant mill was upgraded with a new roughing mill from Morgårdshammar. Another wire rod line was commissioned in 2007. The project consisted of the installation of a new wire rod line with two cantilever stands in front of the new eight-pass wire rod block, water quenching boxes, new laying head and cooling conveyor line. The wire rod block will produce 5.5-12mm carbon and low alloy steel rod at a maximum speed of 60m/s.

Mukand Ltd The existing special steel bar and rod mill has undergone major modernisation. Plant upgrading, including a new reversing shiftable roughing stand, new bar-in-coil line, modifications to the wire rod line and new straight bar outlet, are designed for higher production capacity, an enlarged range of products and enhanced final product quality. The modernised mill will produce 5.5-15mm wire rod, 15-35mm diameter coiled bars (up to 1.5t), and 20-45mm diameter straight bars in low to high carbon and special steels, including ferritic, austenitic, and martensitic stainless steels at rates of up to 55t/hr.

A LOOK AHEADMorgårdshammar has brought the innovative spirit of Erik Norlindh into a new era by developing new and revolutionary equipment for rolling mills and refining the processes for special steel production. Some of these innovations have been presented here, and many reference plants bear witness to the innovative spirit of Morgårdshammar. In the near future, revolutionary ideas in automatic gauge control will be introduced for heavy plate mills, and high productivity coiling technology for heavy rounds is under patent application. Today, as in the 20th century, the steel industry worldwide can rely on the innovative team at Danieli Morgårdshammar. MS

Giacomo Verlini is Vice President Sales and Projects, Morgårdshammar AB, Smedjebacken, Sweden.

CONTACT: giacomo.verlini@morgardshammar.se

bars and 50-130mm (round and sharp-corner) flat bars, in carbon, cold heading, ball bearing, spring, and stainless (austenitic and martensitic) steel grades.

The new housingless-type reversing shiftable rougher will play a significant role in the rolling process of stainless steels. The order for this additional unit reconfirms the leadership of Danieli Morgårdshammar, after the success of the similar mills in operation around the world. The cooling bed with pack-annealing system is a technological milestone in the production of spring steel flats.

The supply will be for the complete mechanical package from Sweden by Morgårdshammar AB and electrical and automation from Danieli Automation, Italy.

Special Metals wiggin Ltd, UK A new bar mill for the production of super alloys has been sold to Special Metals, part of Precision Castparts Corp., a worldwide manufacturer of complex metal components and products such as Inconel, Incoloy, Nimonic, Udimet, Monel and Nilo alloys.

Special Metals is a world leader in the invention, production and supply of the high-nickel, high-performance alloys used for difficult jobs in engineering.

The order, awarded in late 2007, consists of a new generation shiftable housingless P635 rougher and a continuous rolling mill to finish straight bars through a cooling line. The supply will be for the complete mechanical package from Sweden by Morgårdshammar AB and the electrical and automation from Danieli Automation, Italy.

With this new installation Special Metals Wiggin will quadruple production and expand the product range of rounds. The company is a long-term Danieli Morgårdshammar customer, with all its existing rolling facilities supplied from Sweden.

DANIELI MORGÅRDSHAMMAR IN INDIADanieli Morgårdshammar’s success in India continues with recent orders and successful plant commissioning – reconfirming and consolidating leadership in the field of long products production. The most recent projects include:

Usha Martin Ltd, Jamshedpur An order for the modernisation of the existing wire rod mill and completion of a new bar mill was awarded at the end of 2006. The wire rod mill – already modified by Morgårdshammar in an earlier upgrade – will undergo another major upgrade, aimed at increasing the finishing speed to 95m/s and at enhancing the quality of the in-line heat-treated wire rod. The supply will include the replacement of three pre-finishing roll stands with new roll units, modification to the existing high-speed finishing block to enable the finishing speed to increase, a new water cooling line, new ‘oil- film-bearing’ laying head, plus extension and completion of the existing controlled-cooling conveyor. A new multi-

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