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Typical strip & coolant temperatures


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In the process of rolling the most significant aspect is the generation of heat through friction and deformation in the roll bite.The most important aspects are:
a) Maintaining uniform, stable roll temperatures, circumferentially around the roll and transversely across the roll width.
b) Creating optimum thermal crowns and minimum differential in temperature in the upper and lower work rolls with optimum heat extraction.

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Typical strip & coolant temperatures

  1. 1. Emulsion Temp- Generally in any reversible type Reduction Roll Mill (can be 4- Hi or 6-Hi type) for Multi pass, the emulsion temp should be in the range of 48 ~ 55 deg C. At this temp the emulsifier package / other lubricate gets mix up and work well. Sometimes case to case basis the emulsion temp in the Tank is to maintained at a bit high, say app 55 ~ 58 deg C to get better lubrication property from a special lubricate package inside the particular rolling oil. But at no point of time the emulsion temp should be more than 60 degC, otherwise some of base oil and some emulsifier may lose its property. At the same time at no point of time emulsion temp should go down below 40 deg C, because below 40 deg C, bacteria start growing in the emulsion and emulsion Ph start changing its value. Once Ph change the total property gets change. Typical Strip & Coolant Temperatures:-
  2. 2. W/R temp  Generally in any Mill the temp of entry strip at 1st pass would be at ambient temp. No problem for this at the Roll byte. I could learn Quaker that for a reduction app 25 ~ 30% , the roll biting temp under rolling load could rise app 120 ~ 200 deg C depending on the speed. But it is not necessary that W/R temp would be that high. Now for a ideal Mill where flow has been designed properly and the emulsion temp is being maintained at around 48 ~ 52/53 deg C, one can expect the W/R temp after final pass would be app 5 to 6 deg more than the emulsion. If it is so then perfect heat balance is taking place in side the mill during
  3. 3. Strip Temp-  This is a bit controversial topics so far a Customer for a Rolling Oil supplier is concern. Any rolling oil supplier should maintain by designing the proper rolling oil ( which should have the optimum lubrication at the Roll bite) the exit strip temp after final pass should be less than 100 deg. But it is next to impossible to maintain the exit strip temp below 100 deg C, while rolling thin gauge say below 0.25 mm.  Now here I will put my hands on experience in the field as Mill Operation and subsequently as Rolling oil expert, pl take a look at below table-
  4. 4. Input Thickness( mm) Output Thickness( mm) % of Total Reduction Final Speed ( mpm) Final Strip Temp ( Deg C) 4 1.2 70 900 85~90 3.5 0.8 77 1000 85~90 3.5 1.2 66 900 85~90 3 0.6 80 1200 90 ~100 2.5 0.5 80 1200 or more 90 ~100 2 0.3 85 1200 or more app 105 ~110 2 0.2 90 1200 or more app 110 ~ 115 1.8 0.2 89 1200 or more app 110 ~ 115 1.8 0.18 90 1200 or more app 110 ~ 115 1.6 0.15 91 app 110 ~
  5. 5.  If the actual strip temp comes above temp. mentioned in the table, then I would say it is excellent design for Rolling mill as well as Rolling Oil .   In any case the entry strip temp at 1st pass would be at ambient temp. But in subsequent pass it would be better if there is strip cooling header before entering into roll byte. Customer may use it or not, there should be a provision for that. During thin gauge one should use it. While thicker gauge Customer may not use that.  In case of tandem Mill that is why both side flow is designed. But I would opt for a strip coolant header for any reversible Mill.  In my experience I have observed a strip temp after rolling down to 0.18 mm gone upto 140 deg C. Then after investigation it was found that pump pr. Drop down drastically below 4.0 kg/cm2. Generally the pump pr. should be in the range of 5 ~ 6 kg/cm2 at suction point and by the time it reaches to Mill it should be app 4.8 ~5.5 kg/cm2. Flow should be designed based on Mil Motor power. Excessive flow/ inadequate flow or high pr / low pr from pump also lead to higher temp of the strip. 