Struk Sergey Valerievich

Fizical Metallurgical Faculty

Chair of Heat-Transfer Phisics

The Speciality: Heating engineer

The Theme of final work:

The Accelerated cooling of metal in cristalizer

The Supervisor: Ginkul Stanislav Ivanovich

The Accelerated cooling of metal in cristalizator

Introduction

In up-date volumes of metal production and in creasing demand for it the refinemention and in creasing demand for it the refinement of quality of metal production decreasing of metal rejects during its production and metal working becomes the main task. To realise the programme of economy of ferrouse metal the actions which decrease scaling and improve mechanical properties of rolling take an imprtant part. Nowdays accelerated metal cooling has become an important and integral part of technogical ptocess in number of mills. It can be used as anindependent pperation nut sometimes sa a part of other technogical prosess. Accelerated metal-cooling is used in different areas of the production of rolling, in particular after rolling releasing from finishing stand after thermal prosessing in diferent heating appliance, between mills.

Subject urgency

Accelerated cooling of sectional bars helps to solve problems connects with improvement of mechanical properties of rolling to increase its uniformity to decrease scaling to improve properties of rolled surface. Accelerated cooling has both social and ecological aspects, as it helps to improve work environment, to protect waters and enveronment from contimination.

Ains and objects of work

To determine optimal accelerated cooling parameters, construction, main setting.

Work results practical value

Getting necessary running ability of metal depends on the temperature of rolling. To reach this aim the mathematical model has been developed which helps to determine settings (rolling rate, speedof cooling of liquid, its physical properties, etc). On the base of the results of differential equation in order to recived given thermal field.

main body

We can get mechanic metal properties and srtucture needed dereasing of scaling by controlled cooling of rolling. Controlled metall cooling consists in the choice of the necessary heat - transfer coefficient, which could provide bulk temperature required, which could provide getting all the necessarry properties. We can get temperature field in the course of cooling by solving differential equation of thermal conduction. For cylinder it is the following.



With the entry condition at τ = 0, t = f(r) and boundary conditions

;

where λ(t), c(t), ρ(t) – heat conductivity factor, Vt/(ì²·K) ; thermal capacity, Dg/(ì·Ê); density, êã/ì³ ; α_îõë- factor thermal capacity at cooling by water , Vt/(ì²·K); factor Thermal capacity at cooling define under the formula [1]



Metal cooling researcheres have been done where metal diameter was 0,0065ì, cooling chamber lenght was 1m, alignment chamber's lenght 6m, ïrolling cooled with backflow, intial metal tempereture was 1000ºC. Figure 1 shows the change of temperature cooling in water. With the same rolling rate we hae different bulk temperature distribution in cut depends on speed of the flow.



Figure 1 - Rolling temperature field dinamic with speed 20m/s

Conclusion

When spped of rolling increases heat-transfer coefficient of cooling increases too that leads to the change of refrigeration rate and after alignment temperature chamber we have bulk temperature, relative accuracy might not exceed given one|t_sr0 - t_srm|/t_sr0≤ε. In the calculation the relative accuracy was 0,05. When the rolling rate is the same - 20m/s and bulk temperature is defferent the water flow speed should be different. When water flow speed changes coefficient of heat-transfer changes too. When temperatures are equal heat-transfer coefficient α_Σ decreases with the fall of bulk temperature? as portion or radiant energy decreases. So we see that water flow speed both with backflow and forward flow modelling depends on bulk temperature given. The speed we have helps us to determine heat-transfer cooling coefficient and rollong temperature field.