An extended product rolling mill is one of the most demanding programs for motor drives. The rolling process consists of transferring from a hot steel billet through a "rolling train". The modern-day rolling train includes numerous rolling stands arranged in an in-line setup. Every single rolling stand consists of a highest and a bottom roll, driven with a gear box by an electric motor. The rolls of the stands have contours or "grooves" machined into the rolls, so the hot billet transferring in between the grooves is lessened in size and shaped by each subsequent stand. Common motor sizes for modern-day mills is around 600kW to 1200kW for every single stand. Typically specific amount of stands are used depending on the size of the feed billet as well as the finished product. There is additionally a basic completing rate followed nowadays.
The tension in between each stand must be properly controlled, as the slightest change in tension will impact the shape of the item. Furthermore as the billet head end gets in each subsequent rolling stand, the performance drop must recover extremely quick, so as not have an effect on the tension control. The motor drives are managed by a sophisticated stream or stress or loop command program, with must take into account the design reduction of every stand, and the efficient roll groove size which is constantly changing because of roll wear and heat range changes.
As the hot billet passes through the rolling train it is processed, lowered in proportions, and lengthened with the mill stands. The item will then be transferred to a walking beam cooling base, via a superior speed switch method (braking slide/aprons). Scissors in the rolling train generate head and tail crops, and separate the material to suit the cooling base.
Drive Assortment
Due to the effect tons involved, the motors and drives should be chosen to allow for momentary high overloads. NEMA standard MG-1 specifies the temporary (1 min) overloads of at least 200 percent. In reality the actual demands may be dissimilar. Whenever the actual lots duty cycle is understood, the excess dimensioning of the motor and drive need to be inspected by seasoned rolling mill applications specialists using dimensioning program devices offered by the majority of drive and motor makers.
From experience it has long been revealed that in order to satisfy the tension control demands the motor speed must be managed to about less than 1 %. Fortunately numerous modern-day AC and DC digital drives can fulfill this static accuracy rating. The more essential requirements is the dynamic performance rating of the drive which is needed to lessen the rate drop from the bar head getting in each stand. The performance drop is affected by the inertia of the stand or gearbox or motor mix as well as the compelling efficiency of the drive. The ideal velocity fall must be restricted to a certain quantity of percentage. Frequently it is recommended to for a rolling mill to mix different suppliers of gearbox, motors and drives to achieve the optimum combo of system inertia and vibrant efficiency.
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