Model or formula to predict time needed to cool down steel billets. Smile
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Posted by: capterdi ®

02/24/2007, 20:14:30
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Hi,

I´m looking for a model or formula to calculate the time that
is needed to cool under natural conditions (not forced air flow, water, etc.) a pile of steel billets produced at a melt shop. The process is as follows: steel billets with square
cross section of 140 mm x 140 mm and 12.7 m. long are produced via the casting of liquid steel. These billets are placed separated one from the other on a cooling bed, until they reach aprox. 450 °C. Then they are stored in a yard, where they are
placed side by side. Here they sit tightly close one to another; each billet touches the next one along the face that has a horizontal measure of 12.7 m. When the yard has 20 contiguous billets (we can call this a bed of 20 billets), then the next
billets are piled on top of this bed, until another bed of 20 billets is formed. The process continues in such way, until 25 beds are completed. So, we have a pile 2.8 m wide, 3.5 m. high
& 12.7 m. depth.

I´m faced with this problem: these steel billets will be shipped later to another industrial plant, that is far away. So flat bed trailers will be used to transport the billets. The platforms of the trailers are made from steel and wood; so the billets will
sit on top of wood, and we have to be careful in allowing the billets to cool down to a temperature of 150 °C or less, in order to rest assured that the wood won´t catch fire.

I have observed that it´s not the same to ship billets from the top beds; these ones have cooled to a lower temperature. Suppose that we want to ship the hole pile, truck after truck, with no loading delays. We will see that after finishing with the uppermost beds, the next ones will be hotter, due to the temperature gradient that exists from the center of the pile to each of the sides.

So, I´m looking for a model or formula to predict the temperature of the center of a billet depending on the bed (lowest one, second lowest, etc.), the time that has
passed since the pile was formed and the initial temperature.

Thank you.








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Re: Model or formula to predict time needed to cool down steel billets.
Re: Model or formula to predict time needed to cool down steel billets. -- capterdi Post Reply Top of thread Forum
Posted by: randykimball ®
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02/25/2007, 08:57:36
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Being that you are adding and removing billets at intervals you may have to place sensors or at least take readings amoung the stack at controled time intervals to develop your own model. You should be able to work up a spread sheet matrix with the data obtained from those readings which will soon demonstrate a pattern. From this pattern you can develop a model (prediction) based on the control (pre-written data). Then you tweak your model based on the comparison between its predictions and your continued real time readings to effect a more accurate model. Be sure to log the ambent air temperature, wind speed, sun shine %, humidity, and other weather conditions with your readings. After a few cycles you should have a good grasp of the time/heat losses accordingly to how you add to or remove from what quantity in what weather.

It sounds like you may want to experment with the way you stack the billets. That some are cooling quicker than others may effect the consistency properties of the billets. If they are going on to a foundry for additional processing is one thing but if they are going on for forging or machine work, this could be a problem.





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Modified by randykimball at Sun, Feb 25, 2007, 09:08:30


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Re: Re: Model or formula to predict time needed to cool down steel billets.
Re: Re: Model or formula to predict time needed to cool down steel billets. -- randykimball Post Reply Top of thread Forum
Posted by: capterdi ®

02/26/2007, 14:16:43
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OK. This is a good solution, that at the end will render a working model that could be used from then on.

But at this moment, say the starting point of my project, I´m wondering about the existence of a theoretical model (eg. on a Heat Transfer text book, Manual, lecture, etc.)that could be used as a preliminary or basic approach to the solution.

About the adding and removing of billets: we can assume at this point that once they are piled, they will remain were they are, until the time for shipment comes. Then, let´s assume that once we begin removing billets from top, and continuing toward the bottom of the pile, the time for this operations is equal to zero, so that there is no additional complication for the theoretical model. In other words, what I would like is this:

Input data: initial temperature (eg. 450 °C)
Size of solid body: as described above

Based on this, there is an amount of energy stored in the form of heat, and a temperature gradient begins to develop. I would like the model to predict which is the innermost temperature of the body (eg. center) after 24, 36, ...etc. hours.

Thank you








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