Rolling Unit Research Articles

The hot-rolling batch scheduling method based on the prize collecting vehicle routing problem

This paper studies a hot-rolling batch scheduling problem, which is a challenging problem commonly arising in the iron-steel industry. This problem deals with forming steel strips into rolling units and determining the rolling sequences while minimizing changes in characteristics (e.g., width, thickness and rigidity) of all neighbor steel strips and maximizing the machine utilization. Based on technical rules used in iron-steel production practice, we formulate this problem as a prize collecting vehicle routing problem, which is a hard combinatorial multi-objective optimization problem. We develop a new heuristic approach to solve this problem by enhancing the framework of particle swarm optimization (PSO). The key features of our approach are the utilization of number mapping function, which allows the PSO algorithm to deal with discrete problems, and the employment of tabu search at the end of every PSO iteration. We investigate and measure the performance of the proposed approach using three real life datasets obtained from a well-known iron-steel production company in China. The results suggest that our approach is very efficient and effective in providing high-quality and practical solutions, and our approach outperforms traditional PSO and tabu search algorithms based on these datasets.

Improvements & Innovations in the Continuous Casting Process at POSCO

Continuous casting is the essential process converting liquid steel to solid in the form of slabs or billets/blooms in the steel plant. The economy and quality of the steel products are greatly dependent on how successfully the continuous casting is performed. New technologies have been actively developed in the process during the last decades in order to increase the productivity and, therefore, to decrease the operational cost. Since its first commissioning of a slab caster in 1976, POSCO has constructed a number of continuous slab, bloom and billet casters including a thin slab caster not only for plain carbon steels but for stainless steels. Through the operation of various types of continuous casters for more than 30 years so far, POSCO has steadily developed fundamental technologies and operational know-how and achieved the equipment innovations to improve the surface and internal qualities of cast products as well as to extend the productivity of continuous casters. Furthermore, POSCO has deepened the basic understanding on the solidification phenomena of liquid steel and also accumulated the engineering backgrounds to design the most optimal continuous casters. It has also devised the indispensable and auxiliary equipments and the key technologies to control the process precisely and efficiently in order to guarantee the quality and productivity. An innovative technology under development is the POCAST process, where controlled amount of the pre-molten mold flux instead of conventional powder mold flux is continuously fed into free surface of molten steel through the plunger-type feeding system from the flux melting furnace. In order to prevent the molten flux from freezing at the meniscus, a reflective insulation cover is installed, leading to the suppression of thermal radiation from the molten steel and flux. It is generally understood that, as casting speed increases, the occurrence of breakout increases since mold lubrication becomes insufficient due to the lack of mold flux flow from the meniscus into the solid shell/mold boundary. However, by utilizing the especially composition controlled pre-molten flux, it becomes possible to eliminate the formation of slag bear in the mold. Therefore, the mold flux consumption rate is increased even at the reduced oscillation rate & stroke and more importantly, the mold flux infiltration becomes more uniform throughout the boundary between the mold and the solidified shell. This consequently results in drastic reduction of the formation and depth of the oscillation mark and the occurrence of surface hooks without increasing the possibility of breakout, as has been proved in the casting trials carried out with the 10 ton pilot slab caster in Pohang. A key trend in the development of the continuous casting process is to reduce the thickness of cast products. Examples include thin slab casting and strip casting. In the thin slab casting process, a major drawback is the relatively low casting speed and, as a result, the inefficient equipment layout in the plant where two casters are connected to a hot rolling unit. The drawback could be resolved if the casting speed exceeds a certain limit. At the high casting speed, the productivity of casting becomes equivalent to that of hot rolling, and the thin slab casting plant is to be designed so that one strand

Study of refractory materials for the production of aluminum alloy thin strips

Computer tomography of refractories that are used in foundry systems for casting and rolling units in order to prepare thin foil aluminum billets is performed. The question is considered of recycling refractory materials with the aim of their further use in foundry equipment.

Optimisation of pinch roll load in thin slab continuous casting

An analytical model has been developed to investigate the optimum pinch roll load and resulting slab thickness reduction during the continuous casting of a steel, constant thickness, thin slab in a vertical type machine. The pinch roll unit consists of two driven pinch roll sets, which support the solidified hot slab weight and take up the reaction forces owing to slab bending. Optimum conditions prevail when the pinch roll load required to support the slab weight is equally shared by the two pinch roll sets and has the minimum value allowing proper control of the slab speed. The model has been validated by being applied to an existing industrial case of thin slab continuous casting of plain low carbon steel. The effects of pinch roll radius, slab thickness, casting speed, slab temperature and the material carbon percentage on minimum pinch roll load and slab thickness reduction ratio have been investigated. Expressions have been obtained for the optimum pinch roll load and slab thickness reduction ratio related to the prevailing process parameters, which the plant operator can directly apply to determine the optimum pressure setting for the hydraulic cylinders fitted to the movable roll ends. The bending roll load is shown to be small compared with the pinch roll load.

Modeling rolling batch planning as vehicle routing problem with time windows

This paper considers the rolling batch planning problem of grouping and sequencing a given set of slabs into several rolling units in iron and steel industry. The existing mathematical methods often used for the problem are traveling salesman problem (TSP) and vehicle routing problem (VRP), but these methods are not precise, because the position limitation of some slabs in a rolling unit scheduling is not considered. Therefore we suggest a new model, vehicle routing problem with time window (VRPTW) to describe the rolling batch planning problem, in which the position limitation of slabs are quantified as the time constraints. Several solution methods including the genetic algorithm are presented for solving the problem and the computational results show that the genetic algorithm is superior to other methods. In this paper, the vehicle routing problem with time window (VRPTW) of combinational optimization is used to analyze and model the rolling batch planning problem. Genetic algorithm and heuristic are used to solve the problem. Simulation results based on the actual production data show that this model is precise and the genetic algorithm based method is very promising.

Operational results with CCR cassette type compact rolling stands and super high load cantilever stands on bar and wire rod mills

The CCR Cassette Type Compact Rolling Stand is a design for extremely rapid programme change and allows a flexible production planning and, in conjunction with the high level of automation, the production of small order lots with high mill efficiency.Super High Load Cantilever Stands are used as rolling units for prefinishing or finishing blocks in wire rod mills. The design features predestinate this type of stand to roll high alloy steel grades and superalloys with high deformation resistance.

単ロール急冷凝固法によるアルミニウム合金広幅クラッド箔の製造および箔特性

A single roll unit for rapid solidification of wide clad aluminum foils was designed and assembled. Two nozzles were attached tandem over the roll to produce clad foils. These nozzles have positional freedoms for the roll to investigate influences of the nozzle position on the clad foil formation. High purity aluminum and Al-4mass%Si, Al-12mass%Si and Zn-22mass%Al alloys were used. A molten alloy was poured by nitrogen pressure at 0.01 to 0.3MPa onto the roll rotating at 55m/s through the first nozzle, and another alloy was poured onto the first flow through the second nozzle. Clad aluminum alloy foils are succesfully prepared. A linear and undisturbed interface lies between the base foil and the overlying foil, acros which unappreciable alloying elements diffuse. The base and overlying foils are not teared each other by repeated bending.

単ロール急冷凝固装置の試作と作製したＡｌ‐Ｓｉ共晶合金広幅はくの特性

A single roll unit for rapid solidification of wide aluminum foils was designed and assembled. A nozzle having 0.5×160mm slit is attached to the bottom of crucible. The nozzle is dividable into two blocks at the slit. A water cooled copper roll 300mm in diameter and 200mm in width can be rotated at 0 to 4000rpm. The nozzle has 6 positional freedoms for the roll to investigate influences of the nozzle position on the foil formation. Al-12 wt%Si alloy 1kg melted in air in a crucible was poured onto the roll through the slit. Foils uniform in width at 160mm of the nozzle width and in thickness are successfully prepared. Diagrams to estimate dependences of such fundamental factors as rotating speed of the roll and ejection pressure on the thickness and quality of foils are drawn. The foil has tensile strength higher in the longitudinal direction than that in the transverse direction.

Metal ducts for casting and rolling copper rod

Metal ducts made of a high-alumina composite material satisfy the conditions of service and operate reliably in copper rod casting and rolling units.

Rolling of special steel in mechanized light-section and lNire-rod mills

In modern rolling mills for special steel the degree of mechanization has greatly increased. Mechanized roughing with both heavy and light billets has been introduced, and flats as well as bars are continuously rolled. When rolling wire in a contiloop mill the tension on the bar between the rolling stands is avoided by loop regulation in a 180° repeater. In new designs the roll diameter has been reduced, allowing rolling of different qualities in the same roll pass design. By means of the installation of several exits from the mills and mechanical equipment for quick changing, use of the mills is increased. Special steel is rolled as 5·5-8 mm dia. wire at a speed of 35 m/s. A production capacity of over 11000 t/month for the rolling of special steel in the range 5·5-26 mm dia. has been achieved. There are new rolling units for rolling at 50 m/s in order to increase the production when rolling the smallest dimensions. A new patenting method, the ED (easy drawing) process, with coiling directly into a hot-water bath, is in operation in Europe, Africa, and Asia. This method demands less space than conventional methods.

Mechanization and automation of the tube rolling unit

Mechanization and automation of the tube rolling unit