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Surface Technology & Steel Mill Caster Rolls |
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Mill Roll Cladding Technology
Whether you have full-body rolls, split rolls or I-star rolls; whether your caster is a bow type, a vertical-bend type or a curved mould type; whether you produce slabs, blooms or thin slabs; whether you suffer from cracking, wear, corrosion or a combination of all the above, there is a Corewire material and surface engineering technique that can help improve your productivity and reduce your service costs. |
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At Corewire our approach to materials development is a simple one: 'design the solution to fit the problem', and in respect of this we apply the idea of 'zoning' to continuous casters.
Steel Mill Caster Roll Zoning
Zoning divides up the caster according to the operating conditions in each particular area. For example, at the very top of the caster, above the zero segment, the foot or mould |
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rolls are subject to the combined actions of very high temperatures, a basic mould powder and elevated chloride levels in cooling water, all of which produce a highly corrosive/erosive environment and limit the roll's service life to around 100,000 tonnes of steel through put. For these rolls Corewire recommend Weldclad 900, which has increased the roll's service life by around seven times. |
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Further down the caster, ahead of and into the straightener segments, thermal cycling & mechanical loading become more significant, which is reflected in the increase in thermal fatigue cracking, surface wear and roll bending failure mechanisms.
Here alloys such as the now famous Weldclad 3, and newer materials like Weldclad 2000 are proving very effective. |
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However, the operating conditions of every caster varies, even two machines from the same manufacturer on the same plant will have different characteristics.
Bespoke Solutions
Therefore the first priority in recommending welding consumables is to identify your operating conditions, and evidence of your operating conditions can be found by look at your primary mechanism for roll failure. For example, do you need remove your rolls from service because of corrosion or thermal fatigue cracking; because of roll bending or excessive wear?
Excessive corrosion can usually be attributed to the quality of the cooling water. For example, recommended chloride levels should not exceed 100ppm, however concentrations in excess of 500ppm have been seen. However, water quality can also be responsible for thermal fatigue failures. Suspensions present in poor quality water can be deposited in the roll’s cooling bores, reducing the volume of water passing through, and allowing the roll’s operating temperature to increase. With the majority of the cooling burden now falling on external sources such as misting or sprays the temperature gradient across the roll’s diameter can be significant.
Roll bending can usually be attributed to the base material of your rolls, and is unique to full-body roll caster designs. The more expensive base materials such as 42CrMo4 and 21CrMoV511 generally have sufficient strength to resist deformation, and if bending was found in these cases it could most probably be attributed to caster operation, for example the machine stopping for a period. Where bending is an issue, for example with straight 13Cr materials that have been operating for some time, Corewire have developed Weldclad 75, a buffer material that reproduces the mechanical properties of 21CrMoV511 to add strength to the roll. |
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