Metal production is a core industry and a hard one: temperatures are extreme, loads are heavy and hot or else difficult and hard to handle. Julian Champkin reports.
Making metal is challenging. Ores and scrap must be heated to high temperatures; molten metal is moved at height in open vessels, then poured, still red-hot, into casting moulds. Heat and dust, dangerous loads and continuous production demands are inherent to the process.
Before you even reach that foundry stage you have to get the raw materials into the furnace; and after it you have to transport and warehouse your finished product.
All of this demands specialised lifting equipment – sometimes very specialised equipment indeed. We can start at the beginning of the production process, with scrap metal and ore.
Mining the ore of course is a process in itself with its own specialised equipment which we shall not deal with here. But scrap metal is another primary ingredient in steel-making; and lifting and moving it is surprisingly hard.
Scrap-handling is made complex by the random and unsorted nature and size of the load. It can arrive at the mill by truck, rail or barge; scrap is a high-volume and mass material which makes transporting it by water particularly efficient. Speed, stability and sturdiness are extremely important criteria in unloading. ‘Interlocking pieces of the material cause extraordinary forces to be imparted to cranes and material handling machines,’ say Liebherr, who supply dockside equipment for the application. “Those strains can quickly impair the longevity of the equipment. The handling of scrap steel metal and other metals is one of the toughest applications in industrial material handling.”
Material handlers, crawler cranes and static and mobile dockyard cranes are all used, depending on the size of the port and the vessels involved. Liebherr has two material handling machines, its LH 30 M Industry Litronic and LH 60 M Industry Litronic, that are specifically designed for scrap handling. The operating weight of the former is from 26.5t to 29.1t, and its engine output 140 kW; for the latter the figures are 55t to 61t and 190 kW.
At the Alba terminal in Amsterdam Maja Stewadoors has a Liebherr LHM550 harbour crane for scrap unloading; Koster Metalen at the port of Beverwijk, Países bajos has a LH 150 C High Rise Industry Litronic for the same purpose.
And in southern Alemania waste disposal contractor Schrott- und Metallhandel M, Kaatsch, one of the largest handling companies for scrap metal in the region, operates its own port facilities on the river Neckar loading scrap that arrives by rail onto barges for delivery to steelworks. Barges on the waterway now have a capacity of up to 2,000 tons of scrap; to increase speed of loading them the company uses an LH 120 C Litronic machine with a 15m industrial-type angled boom, a 12m stick and a 2.5 cubic metre capacity grapple. A large, square-design crawler undercarriage allows a 7 ton load at the machine’s maximum radius of 25 metres.
Once the scrap arrives at the foundry, the next stage is moving it to the furnace. Konecranes agree with Liebherr on the joys, or reverse, of handling the material: “Scrap is difficult to handle. It has no defined shape for a hook or tong to fit onto, and it is often mixed, so it requires sorting. A scrapyard crane has to fit the size of the vehicles that deliver the scrap and must be able to access the right materials quickly from all parts of the storage area.” A speciality of theirs is overhead gantry cranes for the purpose, installed at the foundry: “They are heavy-duty, high-speed cranes that can handle scrap in the yard and load it into buckets or ladles for transport to the melt shop. These cranes are equipped with lifting magnets, a hydraulic grab or both together to move a load of scrap weighing up to 40 tons.”
We are now in the region of heat, dust and molten metal, and of cranes that can cope with those conditions.
The scrap coming from the scrapyard is loaded in the furnace with an overhead charging crane. Its main hoisting machinery lifts the bucket to the furnace for melting, and an auxiliary hoist on the crane opens and closes the bucket during loading.
In most mills the scrap is added to iron ore already in the furnace; from the initial furnace blast a teeming crane helps mix the molten metal in the right proportions. Once the mix and temperature are right the liquid steel is poured into giant ladles carried by tundish cranes which carry them to the casting moulds when the molten metal is poured out to cool and solidify.
The charging crane, cucharón de la grúa, teeming crane, and tundish crane are all quite similar, say Konecranes, - usually overhead traveling cranes that are fitted with special attachments to lift the giant ladles - and can be defined by their location and function in the plant rather than by differences in design.
They often perform more than one function and are used as backup for each other. Increased working coefficients, a differential gear reducer, redundancy in all critical systems, a backup brake on the rope drum, and motion limiters are just some of the technologies that are fitted.
Overload protection, an ‘emergency stop’ system bypassed from the normal control system, derailment supports, and end limit switches are standard features.
All parts of the mechanical and electrical equipment are designed so that they are easily accessible from permanent service platforms for adjustment, lubrication, inspection, maintenance and repair. Out-of-service times must be reduced to a minimum, so emphasis is placed upon quick replacement of faulty or worn parts as opposed to repair.
Illustrating the challenges of these conditions is a charging crane installed by Konecranes for steel company Rautaruukki in Finlandia.
Its Raahe plant produces 2.8 mmt of hot rolled steel and special steel products a year. The existing charging crane in its foundry was installed in 1975 and was reaching the end of its useful life.
Konecranes designed a 220/60t replacement crane. The crane is central to the manufacturing process, so reliability and near-constant availability were essential. The replacement also needed to be able to fulfil the increased production rates planned for the plant.
The new crane was equipped with several redundant features; for example the variable frequency drive and network braking units were both given redundancies. fitted. State-of-the-art motion control technology gave safe operation at higher speeds to address the capacity requirements.
The operator emphasised maintenance and user-friendly operator interface as important. Here again digital technology came into play: the crane is equipped with Konecranes’ crane monitoring system for efficient maintenance and smart control features such as sway control and semi-automatic positioning for user-friendliness in operation. Everything was designed and carried out with close cooperation with the customer. The crane has now been installed; demand needs have been met, as have the needs of reliability and maintainability. A lifespan of at least 30 years is expected from the crane.
On top of the extreme environmental demands on them, foundry cranes have to do the job quickly. Matthias Meisberger, is head of technical planning at SLR Giesserei St.Leon-Rot in Baden-Württemberg, Germany. It is a foundry that specialises in sophisticated components made of spheroidal-graphite cast iron – an iron casting material whose properties match that of steel and with which SLR produces, for example, high-strength travel unit components for construction and agricultural machinery. “If the cranes fail, the foundry will come to a standstill,” says Meisburger. “And that doesn’t just apply in the event of a lengthy period of downtime. We have a maximum period of 15 minutes to transport the material from the melting furnace to the mould line. If the spheroidal-graphite cast iron has not been cast by then, the treatment effect wears off and it turns into conventional grey iron, which is of no use to us.”
His foundry uses two Demag foundry cranes to transport molten cast iron from the melting furnaces to the casting cars that take the material to the mould line. The extreme conditions include abrasive dust as well as heat.
Demag had supplied the cranes in 2002. Despite heavy use, these cranes had by no means reached the end of their lifecycle after 16 years. However, growing demand for SLR’s casting expertise required the use of ladles for handling up to 3t of molten material. Since the empty ladles themselves weigh more than 2t the existing cranes would then have exceeded their 5t load capacity.
Demag has therefore replaced the 50.5-metre-long crane runway and installed two EKDE suspension cranes rated for foundry duty with a load capacity of 10t. The cranes are based on Demag’s universal crane range but numerous extra design features adapt them to the extreme requirements of foundry duty.
The cranes transport ladles of molten cast iron at a temperature of around 1500°C. The new cranes are designed for maximum availability: the drive is protected by heat shields and the crane bridge enclosure is installed exactly in the centre of the bridge because the heat is higher at the girder ends. The crane bridge itself is exceptionally rigid to avoid deflection and extreme oscillation.
For safety and redundancy, all four trolleys of the travel unit are driven and equipped with a manual brake release function, which enables the crane also to operate with only two working drives.
An automatic centrifugal emergency brake serves as a catching device in the (unlikely) event that the drive unit in the hoist fails.
The cranes are equipped with collision protection and each is controlled by a Demag D3 radio control system. This ensures the operator can maintain a safe distance from the load. The DMR rope hoist has a bottom block with a hook as a load handling attachment and, like the entire crane, is designed for an ambient temperature of up to 55°C. An integrated weighing device, also suitable for high temperatures, shows the operators the weight of the filled ladles, which can weigh up to 8t. Other options are aimed at high availability in the not only hot, but also dusty environment. For example, there are self-adjusting brushes that continuously sweep the abrasive dust off the crane runways.
Only a relatively short period was available to dismantle the old installation and install the new runways and crane; all this had to be done during the two-week factory break. The power supply also had to be renewed and structural changes made. After the end of the holiday, the foundry staff were able to work with the new cranes, which have since proven their worth under the demanding conditions.
“It was important that the cranes run smoothly from the start,” says Meisburger, “and they do. Finishing touches are being made gradually.” The finishing touches include modification of the tilting mechanism on the ladles. The hand wheels for manual operation can still be seen in the picture. SLR has now, however, switched the casting ladles to electric motorised tilting at the touch of a button as planned – for good reason.
“The smaller crucibles were still easy to operate manually,” says Meisburger. “With the new, larger crucibles, however, the operators would have to use the hand wheel to tilt 3 tons of molten material more than 80 times per shift. The electric tilting mechanism makes the work much easier and also improves safety.”
ArcelorMittal is the world’s leading steel and mining company, producing 71.5 million metric ton of steel a year. Recently ArcelorMittal Francia commissioned Spanish cranemakers Jaso to manufacture a scrap loading crane for its plant in Dunkerque.
The crane, which is currently nearing commissioning, will transport the scrap and charge the converter with it. Its maximum load capacity is 300 tons with a span of 24.4 metres. It has a special and unusual configuration, of three girders joined by an end carriage; the design provides the rigidity, robustness and durability necessary in the hot and rigorous environment of the converter.
Four trolleys will allow two baskets to be handled simultaneously. The front lifts will be carried out by two 115-ton trolleys that have a crossbeam with two slat hooks for hooking the basket. Rear Lilting is by two 75-ton trolleys with a slat hook for tilting the baskets to unload the scrap into the converter. Motion control will be by regenerative variators that allow the energy released during lowering of the load or braking movements to be harnessed and returned to the grid.
To protect the electrical equipment from the harsh conditions it will be Located inside one where it will be perfectly conditioned: electrically insulated and insulated also from heat; the enclosure is equipped with industrial air conditioning with redundancy. The air system also pressurizes the inside of the enclosure to prevent the entry of steel dust through leaks or when it is accessed.
In terms of safety, the crane will meet all the requirements of the Performance level D standard.
It will have a ‘degraded’ or ‘emergency operation mode’ so that in case of failure of some of the equipment, the lifting and translation motions can continue to operate until the load is brought to a safe place.
The latest data processing technology related to Maintenance 4.0 is fitted. Control will be via a cab located at one end for good visibility of the working area.
The cabin includes industrial air conditioning, insulation for steel mill conditions and an electrically operated front glass protection system that comes into operation before the converter is loaded to avoid the impact of hot or hard projectiles generated during the process.
The crane has been designed to allow access to all areas and equipment for maintenance while complying at all times with the customer’s safety regulations in terms of crane entry permits and the movement of people.
This Large-scale project is scheduled for commissioning in 2022.
When steel has been cast and fabricated it needs to be distributed. Street Crane recently installed overhead cranes for Tata Steel’s distribution centre at Redcar in North Yorkshire.
The centre provides steel and processing facilities to meet specific requirements of local customers. Plate and sections for use in engineering and marine fabrications or structural steelwork can be cut, shot blasted and painted prior to delivery to customers ready for the next stage of manufacture.
The company required bespoke overhead cranes to significantly improve order turnaround.
Street supplied and installed four 12-ton overhead travelling cranes of a radically different design. These were configured by Street to handle the high rates of material flow to significantly improve processing and speed of delivery.
The cranes are of a double bridge design. Two linked beams span the 20 metre bays; on these a 27m crane bridge is fitted bearing twin six ton hoists with magnets. This allows zoned material flow in the processing bay, with transfer through the shot blast and painting processes before the finished steel is shipped out to customers.
The hoists on each crane can be operated singly or in tandem, to give additional stability for heavier or awkwardly-shaped loads.
Anti-collision systems permit safe crane movement on a common gantry: audible alarms and amber flashing lights warn of another crane approaching. Crane control is via a push button infra-red link, complying with Tata's stringent requirements and the crane bridge platforms feature taut-wire safety lines and 10 safety harness anchor points at key locations such as panels, crabs and end carriages. To sustain uptime and efficiency ‘hours of service’ metering is on all crane motions to assist with planning and proactive maintenance.
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