
Sheet coils
Sheet coils when produced are handled internally in steel mills, stored in logistic warehouses and shipped to end customers to be processed to products. Along such process chains, coil magnets from TRUNINGER are widely used. Many decades of experience in coil magnet design combined with our controller's highest safety standards created a striking alternative to mechanical lifting gear.
Applications
Sheet coils require specific lifting magnets, for cold-rolled, hot-rolled or slit coils different solutions are applied.
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Cold-rolled sheet coil handling
Transporting coils gently
Steel mills, logistics companies and service centres set high standards in terms of coil quality. Such quality must be maintained for all transport processes weather in house or outside the company. No pressure marks, damaged edges or residual magnetism are tolerated.
An excellent alternative to mechanical lifting devices, such as tongs or C-hooks, are electro magnets. TRUNINGER produces special magnets for cold-rolled sheet coils weighing up to 50 tons. Each of these magnets can handle a wide range of different coil diameters and widths.
Figure 1: Cold-rolled sheet coils in stock area
Coil magnets grip the coil peripheral from above and do not touch the eye such as tongs or lifters. Damages of the coil eye or side faces are thus absent.
TRUNINGER coil magnets are also equipped with proximity sensors as standard. These sensors allow the magnet to be set down gently on the coil.
Using a magnet system yields the following benefits:
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Figure 2: Densely stored coils in a warehouse
Video 1: Efficient loading of a ship directly out of the coil warehouse
Handling of hot-rolled coils
Reliable and safe
Every day steel mills and logistic companies handle huge volumes of hot-rolled coils either internally as semi-finished products or externally as sales products. TRUNINGER coil magnets enable quick, safe and reliable handling, as well as loading and unloading of lorries, railway wagons and ships.
Figure 1: Magnetic coil transport applied to ships and railway wagons
In contrast to cold-rolled coils, hot-rolled coils are not tightly wound due to contraction of the material in the cooling process. Air gaps formed in-between the windings of steel significantly reduce the magnet’s lifting force (see figure 3); the larger the air gaps the greater the impact on the lifting force. For safety reasons this loss of lifting force needs to be compensated.
Coil magnets with deeply-penetrating magnetic field have been developed to match hot-rolled coil properties.
At TRUNINGER for dimensioning and design of such magnets FE method is applied. Finite element simulation helps to optimise existing magnet designs and to develop new, client-specific magnet solutions.
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TRUNINGER design features
- Coil magnets can be equipped with two independent magnet coils each of them being powered and monitored separately by the magnet controller.
- Should one electric circuit fail, the remaining circuit will continue to carry the load. The controller generates a visual and audible alarm and sends a signal to the crane. When this happens, the load must be set down and the magnet switched off (see ‘Fully redundant system’).
Figure 2: Moving a hot-rolled coil — note the air gap!
- Using signals from proximity sensors mounted between the magnet poles the crane control system is able to reduce the approach speed of the hoist. This allows to guarantee soft touch down of the magnet on the coil.
Figure 3: Carrying hot-rolled coils in a outdoor stock yard
- Special design magnets equipped with temperature-resistant magnet coils guarantee a long service life also when used to carry hot coils in harsh environments.
Slit coil handling
Transport of coated, sensitive coils
In rolling mills red-hot slabs get rolled down to a final thickness of 1 to 18 mm and sent on as hot-rolled sheet coils for further processing. Cold-rolled products are also present in thicknesses of under 1mm. Depending on the size ordered by the customer, coils get slit lengthways to form narrower strips, known as slit strips. Slitting the coils in this way produces numerous coil sizes and thicknesses.
Figure 1: Slitting the coil lengthways to form slit strip rings
Slit coils are also zinc-plated, galvanised or painted. The slit coils get further processed into finished products in the metalworking industry, e.g. in forming and diecutting operations or in tube manufacturing.
No matter what needs to be done, there is always a TRUNINGER magnet for the job, e.g.:
- Lifting a slit coil pack
- Carrying individual slit coils
Figure 2: Stacking a vertical slit coil in a tube manufacturer’s warehouse
Using an electromagnet is an alternative to using purely mechanical lifting devices, e.g. a chook. For production reasons in steel mills or slitting plants the entire pack of slit coils gets carried away and placed into storage in one lift (see figure 3).
Carrying slit coils magnetically requires a powerful magnet with a deep field penetration in order to ensure that the necessary force is applied to the narrow coil width for a safe and secure transport.
Figure 3: Handling a pack of slit coils in one lift
TRUNINGER magnet system yield the following advantages and benefits:
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Special application: Slit coil tilting device
Depending on the type of handling equipment, slit coils may be delivered either:
- Eye-up, axis vertical
- Standing upright, axis horizontal
However, subsequent processing of slit coils often requires to rotate from horizontal to vertical position or vice versa. For this purpose, TRUNINGER has developed a slit coil magnetic tilting device (see ‘Coil rotator’ and figure 4).
Figure 4: Coil tilting device with ring magnet