Aluminium rolling models: aligning mill productivity

mill productivity reversing mill

Aluminium rolling models: aligning mill productivity

Over the years we have developed a suite of process models for the aluminium rolling industry. Recently we’ve shown in several blog posts how you can use these models to increase mill productivity.

In July Vicente Martin described how using the Innoval Rolling Model can determine the ground camber of work rolls. Now I’m going to explain how you can use the same model to help balance the output between consecutive rolling mills. This is another great tool to maximise mill productivity.

Matching mill productivity values

A common configuration for a hot line is the single stand reversing mill followed by a 3-stand hot tandem mill. A key requirement for productivity is to ensure that you match the time taken on each of these mills. Ideally, neither mill should wait for the other. This is because the overall productivity of the hot line is equal to the smaller of the two individual mill productivity values. Of course, given that softer alloys allow bigger reductions than harder alloys, it’s not always possible to meet these ideal conditions.  Furthermore, there is usually a coil temperature requirement from the tandem mill. This can be another constraint.

Trying to get close to optimum conditions can be quite hard if you use a trial-and-error approach. Tandem mill speed directly influences the coil temperature. Consequently, automation schemes often use the measured coil temperature to control the tandem mill speed. However, this may exacerbate the problem of matching the two mill productivity values. The Innoval Rolling Model can quickly demonstrate this. It uses an inbuilt sensitivity tool to look at how the coil temperature alters with the mill speed.

mill productivity Tandem mill speed

Figure 1: The variation in coil temperature with mill speed for a specific tandem mill running an AA3xxx product.

Accounting for entry temperature

The coil temperature also depends on the entry temperature to the tandem mill. The same tool within the rolling model can generate this sensitivity as shown in Figure 2.

mill productivity slab temperature

Figure 2: Variation of coil temperature with entry temperature to the tandem mill.

Having a lower entry temperature into the tandem mill allows the mill to run faster to get the same target coil temperature. However, it has an adverse impact on the rolling load, especially for the first stand.

mill productivity stand load

Figure 3: Impact of entry temperature on rolling load of the first stand.

If this is still okay, then there is the task of modifying the reductions in the reversing mill schedule to achieve the lower transfer temperature.

Models such as the Innoval Rolling Model give you a quick and efficient way to look at these problems as a whole. Consequently, you can generate pass schedules for both mills that minimise the waiting time, and so deliver close to optimal productivity.

If you want to know more about our rolling model, you can watch a short animation here.

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Dan Miller

Dan is one of our Process Improvement consultants and a recognised expert in aluminium rolling. He’s worked in most of the former Alcan rolling operations across the globe, as well as a huge number of plants since Innoval was formed.

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