Julian Champkin explores the world of process cranes

Cranes used in metal foundries must withstand the worst of working environments and for safety must do so with absolute reliability. Julian Champkin explores the world of process cranes.

The metal-foundry industry combines hazardous environments of extreme heat, choking dust, hot metal and naked flame. Melt shops require heavy and dangerous loads to be transported; their cranes must be able to lift and carry buckets of liquid metal safely and reliably. The special conditions of a foundry demand special requirements of the cranes and hoists.

“These are workhorses,” says Rich Warriner, director of business development at Virginia Cranes. “Safety is paramount; and foundries operate 24 hours a day, seven days a week, so downtime is not wanted and ease of maintenance is a necessity.”

Turkish crane-makers BVS Cranes echoes and amplifies the point: “Generally in the metal foundry industry the melting shops operates continuously for three shifts 24 hours a day,” says Mehmet Erol, deputy general manager at BVS Cranes. “The environment is full of dust and the ambient temperature is up to 70–80°C. Therefore, cranes that are to work in metal foundries are specialised equipment with extremely critical pre-requisites. The process and melting shops of a foundry are some of the hardest places for the working of cranes.”

Heatproofing, redundancy, safety of operatives—generally nowadays increased by using remote control—and reliability and ease of maintenance are some of the more obvious requirements. Precision in handling is another. Technological advances in smart technology data recording and the like have enabled and improved many of these in recent years—and this in turn has led to productivity gains, and to sales.

“The metal foundry market has considerable growth potential because new technologies allow customers to save money and run their businesses in a more sustainable manner,” says Steve Gagnuss, senior vice president for industrial cranes at Konecranes APAC. “Konecranes’ metal process cranes are designed with smart features which reduce structural stress, increase efficiency and prolong equipment life. We see lots of potential, in the Asia- Pacific region in particular.”

The cranes involved go by the names of ladle cranes, charging cranes, teeming cranes and tundish cranes, according to their particular location and function in the foundry; but they have similarities and characteristics in common. They are usually overhead travelling cranes that are fitted with special attachments to lift the giant ladles that contain liquid metal. They often perform more than one function and are used as backup for each other. Auxiliary hoists can be attached for scrap charging and maintenance functions, such as cleaning the empty ladles or lifting the furnace shell.

Gagnuss explains the processes involved: “The ingredients for steel come from two main sources: original raw materials—iron ore and coking coal—and scrap. These are treated separately in the foundry. Iron ore and coking coal are combined in a furnace in a direct reduction process to produce metallic iron. The melted iron is mixed with scrap to create molten steel.

“The scrap, transported from a scrapyard, is loaded into the furnace by an overhead charging crane. The main hoisting machinery lifts the bucket to the furnace for melting. An auxiliary hoist on the crane opens and closes the bucket during loading.”

BVS Cranes says: “Charging cranes are used for feeding scrap to the arc furnace. Ladle handlers are used for transferring molten metal, at a temperature of 1500- 1600°C, then returning the empty pots for re-charging.

“So these two type of cranes are the most critical equipment in melting shops. Any crane failure would mean that steel manufacturing would have to stop at the facility. This means that the charging cranes and ladle handlers have to be manufactured to the highest standards, and the highest class of safety factors has to be incorporated. Security and safety are always in the foreground.”

The worst nightmare, of course, would be a ladle full of molten metal dropped from a height. An unmovable ladle of molten metal jammed overhead is also to be avoided. “If it cools to the point of solidifying, you have lost the metal and your ladle as well,” says Warriner. For these reasons multiple layers of redundancies are built into foundry process cranes.

“The national code in the US demands two sets of holding brakes, wire rope strength of an 8:1 safety factor, and that is pretty much all it demands,” says Warriner. “But best practice is more rigorous and application specific.”

Elsewhere regulations are more prescriptive. “They vary between regions and countries,” says Gagnuss, “but the overarching theme that guides them is safety. Typical regulations in the crane industry outline safe use, inspection and maintenance requirements, and design working periods.

“In Australia, for example, over the last five years the standards have been updated to include the requirement to ascertain the remaining design working period (DWP) according to processes and calculations summarised in a new section (9) of AS2550.1. DWP is then used to determine when a major inspection and subsequent general overhaul is due. Similar standards apply throughout Asia.

“This can have significant implications on maintenance costs, because if DWP is not estimated according to the correct process, the design life—and the intervals between required major inspections—can be reduced by as much as a third of the crane’s original design life.”

He adds that the only method of duty estimation that does not require DWP to be reduced by a safety factor is one that uses a recognised type of recording system. Konecranes Control Pro is one such.

There are also products available such as Truconnect, which provides real time data via a modem so equipment owners can log in and see exactly how their equipment is operating and more accurately plan predictive maintenance schedules.

Interpretation of standards is an area for experts in the field, says Gagnuss. “There is a clear need for expert and independent guidance in interpretation of standard provisions and ensuring, where work is needed, that service partners are trained to the appropriate standards required.”

Heat shielding is one obvious requirement for foundry cranes. “It is more important in open ladles than in closed tipping,” says Warriner. “Our company produces custom designed cranes that tap the molten metal from the furnace or cupola—the terms are interchangeable. It can then either feed the molten metal into smaller ladles that in turn carry them to the moulds and pour; or if the product is rather a large one then the first ladle can fill the mould directly.”

The bucket-shaped container with one or more holes in the base that funnels molten metal into the mould is known as a tundish; the smaller cranes that pour into them are the tundish cranes.

“The biggest problem here is radiant heat rather than ambient heat,” he explains. “So you need heatshields around the hook and the bottom block, and underneath the controls. Almost all these cranes are radiocontrolled. There are not too many cab

options nowadays. And pendant controls too are unusual, except as a backup. “In a foundry the loads would be from 3t to 50t; in a steel mill it can be up to 500t, which is a whole different world.”

Given a ladle crane of 250t capacity, half of that is the ladle, half is the molten load. The biggest problem from the crane operators’ and designers’ point of view, says Warriner, is not pouring the molten metal but charging the furnace with scrap iron: “In a mini mill they melt the scrap iron in an electric arc furnace. First you need a prime to be inside the furnace, so it is already at molten iron temperature before you add the scrap. When the material in the drop charge is put in, gases and fly ash from the furnace envelop the crane, at very hot temperatures. Electrical wiring has to withstand that—SRML (Silicone Rubber Motor Lead) high-temperature wire has to be used, which is expensive. Controls must be cooled and air-conditioned.”

Redundancy is an equally obvious requirement of foundry process cranes. Should, for example, a motor fail, it is unacceptable for the load to remain suspended and immovable. BVS Cranes foundry cranes provide a textbook example of how to minimise the risk, says the company: “At BVS Cranes we manufactured a 500t capacity crane according to foundry specifications for MMK in 2009 and it is still operating. This crane weighs about 700t unladen, and with a full load approximately 1,200t. The control class of this crane has been designed according to EN 954-1, category 3 failsafe. All electrical equipment has been chosen according to this standard. It is an extremely safe crane, with double motors on planetary reducers for hoisting. The trolley and bridge travelling have main inverters and spares for hoisting, and double inverters and spares for lifting. The trolley and bridge travelling have four motors. The system has double security brakes, and there is a special reeving system with four ropes.

“Using the planetary reducer this crane can operate with one motor at full load at full speed, and in case of any failure can operate with one motor at full load at half speed.”

Konecranes also design-in safety, redundancy and back-up. “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 we employ,” says Gagnuss. “Automation of repetitive movements and an air-conditioned, ergonomic cabin keep the driver comfortable and able to concentrate on the task at hand. To help the cranes last, exposed areas are protected against heat and dust.”

Technological advances have added to safety and reliability, adds Gagnuss: “Cranes can be fitted with remote monitoring so that operators can follow the operating statistics of the crane throughout its lifecycle. Routine maintenance helps to prevent unexpected faults, minimise downtime and maximise the productivity of the crane.

“Konecranes’ metal handling technologies include unmanned full automation, remote operation stations, and remote monitoring and maintenance reporting products.” These in particular are focused on applications such as scrap metals and foundries.

One example from Konecranes’ Smart Features is sway control. This controls the bridge and trolley acceleration and deceleration rates to automatically minimise swaying of the load, so giving precise load positioning and reduced load cycle times; it also reduces collisions and equipment damage.

Shock load prevention allows for smooth load pick-up. The hoist drive monitors the load. If it is picked up abruptly, the hoisting speed is automatically reduced until the load is lifted. This prevents shocks to the load and the crane, reducing wear of the crane’s steel structure and mechanical parts. Slack rope prevention is another safety feature. As the load is lowered, the hoist drive detects when the load has landed and stops the movement. The hoist ropes do not slacken so the ropes do not slip out of the hook block and the lifting device does not tip.

When lifting a load simultaneously with two hooks, hoisting synchronization supervises and controls both hooks so that they run at the same speed, even if there is imbalanced loading between the hoists.

Target positioning allows up to 120 pre-set target positions and eight home positions. The crane drives itself to the selected target position then automatically lowers the load to a pre-defined height. End positioning is similar, designed to speed up the final positioning of the load to an X-Y coordinate. It is especially useful in work cycles involving stationary machines or structures where the operator must repetitively position loads in the same places. The operator can define up to 16 end positions. When the load is moved into a positioning window around the target and the ‘end positioning’ button is pressed, the crane moves the load to the centre of the window. Then the operator takes over manually and lowers the load.

Working limits can be thought of as temporary virtual walls at which the crane stops automatically. Protected areas are permanent no-go areas which the crane operator cannot override or adjust, allowing protection of the most valuable production machinery or working areas from possible operator error.

Foundries are one of the most dangerous and difficult operating environments for hoists and cranes. Developments such as these are adding safety and reliability. It remains an evolving field.

Bagikan di Facebook

Tweet di

Ikuti kami

Simpan