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Lechler Ltd
1 Fell Street, Newhall
Sheffield, S9 2TP, England
Tel: +44(0)114 249 2020
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Application Know-How

Application Know-How

Whilst the principal objective of the selective roll cooling system is to achieve optimum strip flatness and efficient heat transfer from the roll; ensuring this is achieved by applying minimum coolant volume is a key engineering and production priority.

This results in a consequential reduction in the coolant volume being applied and reprocessed for recovery as spent coolant, which can significantly reduce primary operating costs. 

Efficient application of the coolant and lubrication media also ensures minimal generation of detritus and particulates in the process consequentially improving surface quality, strip brightness and rolled in defects such as micro-inclusions.

Lechler systems are "designed in" to the existing mill configurations as an integral part of the rolling process ensuring optimum interaction and integration with the rolling process.

Lechler provides participative contributions to ensuring clients' process needs are considered a priority.  

Symmetrical / Asymmetrical shape correction

Symmetrical / Asymmetrical shape correction

Symmetrical deviations in strip flatness can be controlled by mechanical actuators, such as roll skewing, roll bending, and roll shifting systems, to correct product flatness (shape) defects.

Where flatness deviation is asymmetrical (off strip centre line - one sided) these systems offer limited capability 

Selective zone cooling such as the Lechler Selectospray system however affords precise control and correction of deviations in shape at any point across the strip width. 

Regardless of the nature of the symmetry of the shape defect, for fine tuning of flatness deviations, Selective Roll Cooling is the most efficient solution to counteract  the very minute transient changes in the thermal profile of the work rolls most commonly caused by :


  • Localised deviations in friction / lubrication and subsequent thermal changes
  • In-process roll surface wear

     And additionallyvariables incoming via;

  •  Random variations in the strip surface characteristics
  •  Minute physical changes  in strip cross-section which transpose into significant “shape” defects

Selective cooling principle

Selective cooling principle

Lechler’s Selectospray roll cooling system is essentially a dedicated slave / actuator device reacting to a signal from the sensor roll of the Automatic Flatness Control System (AFC).


The Shape roll measures the longitudinal strip stress at regular equispaced points across the rolling width on the work roll and detects;


  • When the longitudinal stress is low (buckled / wavy zone) because of increased local reduction and a corresponding increased longitudinal extension. This indicates a localised, "thermal radial expansion" in the roll surface, corresponding to the zone exhibiting the waves or buckles in the strip; this corresponding zone on the roll is then selectively cooled.                                           
  • Conversely where a longitudinal zone in the strip is exhibiting a higher stress deviation, there is less reduction / extension; the longitudinal zone (in the strip) is shorter.  The corresponding zone on the work roll is then allowed to expand under controlled conditions with the spray switched off until the roll grows radially in that zone, reducing the stress in the longitudinal zone in the strip.

System Overview

System Overview

The integrated Selective Cooling System (Selectospray) comprises of engineered headers, spray valve assemblies, actuated by control cabinet and control hoses utilising signals fed back from a flatness (shape) measurement roll.

  • Zoned spray banks in the Selectospray headers can be operated independently to cool the hot zone on the roll body which  has expanded radially, counteracting the thermal expansion, effectively reducing its expanded  radius, eliminating the "over-rolling” that can result in corresponding buckles or wavy zones in the rolling direction, on the strip.
  •  The shape roll comprises of an array of circular segments or rotors, each housing several radial mounted stress measuring sensors; typically a 26mm or 52mm pitch measuring the stress across the strip width as the strip (under tension) passes over the Shape-roll.
  • Each coolant valve / nozzle (spray) is controlled by feedback from a corresponding stress sensor on the shape roll or any other shape control system.
  • To achieve controlled selective cooling, the work roll barrel is cooled by dedicated banks of spray nozzles uniformly spaced across its width and precisely aligned to the stress-measuring sensors (segments or rotors) on the shape roll.
  • Nozzle and valve assembly are controlled by a dedicated solenoid valve receiving the electrical signal through an I/O unit from the shape meter control computer.
Selectospray® applications cover hot, cold and foil rolling in Steel, aluminium and other non-ferrous flat strip operations and additionally can incorporate hot edge compensation for specific rolling applications such as aluminium, as well as for rolling copper alloys, and cold rolling of steel and tinplate



Lechler outlines the benefits of employing the Selectospray system thus:


  • Dynamically controls heat  transfer in to the roll surface, generated by deformation / friction in the roll bite
  • Significantly improves strip flatness and counteracts asymmetric "shape" deviations and roll wear.
  • Facilitates a significantly wider operating range for other actuators and contributes to extended work roll campaigns and consequent work roll life.
  • Reduces applied volumes through more efficient application and improves recovery costs of coolant and lubrication