Backup rolls

01

Fix the roll size from the stand drawing and the scrap diameter

Steel Authority of India (SAIL) purchase specifications for roll-shop items give each backup roll as barrel diameter × barrel length × total length with a scrap diameter and a weight, tied to a drawing number. Examples: a single-stand four-high cold reversing silicon-steel mill roll of 1,220 mm × 1,270 mm × 3,715 mm, scrap 1,105 mm, 17.5 t; five-stand tandem cold mill rolls of 1,425 mm × 1,420 mm × 4,047 mm, scrap 1,295 mm, 25.5 t; hot strip mill finishing rolls of 1,310 mm × 1,700 mm × 4,715 mm, scrap 1,180 mm, 25 t; hot strip mill-II rolls of 1,550 (+0.5/−0) mm × 2,230 mm × 5,934 mm, scrap 1,400 mm, about 47.6 t; and a new 4.3 m wide plate mill roll of 2,200 (+0.5/−0) mm × 4,300 mm × 9,860 mm, scrap 2,000 mm, about 170,200 kg. [1]

The plate-mill specification also asks for run-out, roundness and concentricity within 0.05 mm throughout the roll and a barrel surface finish of 0.80 micron (min.), and individual specifications state what must be fitted to the necks before delivery: thrust rings shrunk on the neck of an older plate-mill roll; pins, lock plates with socket-head bolts and rest buttons on the hot strip mill-II rolls; pins and neck keys on the new plate-mill roll. [1]

Editorial calculation: the usable radial layer is half the difference between new and scrap diameter — (2,200 − 2,000)/2 = 100 mm for the plate-mill roll, (1,550 − 1,400)/2 = 75 mm for the hot strip mill-II rolls and (1,220 − 1,105)/2 = 57.5 mm for the cold reversing mill roll — and the hardness requirement must hold through that layer. [1]

Give the supplier the mill, stand and position (top or bottom), the roll drawing with barrel diameter and tolerance, barrel length, total length, neck diameters and tapers, scrap diameter, weight, run-out and roundness, surface finish, neck fittings to be assembled, chock and bearing interface, and the quantity per year.

02

Set the hardness profile, steel and guaranteed tonnage

The SAIL specifications give barrel and neck hardness in Shore D (JIS) with Leeb equivalents and a floor at scrap diameter: 55–60 Shore D barrel and 40–45 neck for hot strip mill finishing and roughing rolls, at least 50 Shore D at scrap; 65–70 barrel and 40–45 neck for cold mill rolls, at least 60 at scrap; 65–71 barrel and 37–43 neck for hot strip mill-II rolls, at least 60 at scrap; and 53–58 barrel and 47–52 neck for the new plate-mill roll, at least 50 at scrap. In the same documents the indefinite chill double-poured work rolls of the hot strip mill are specified at 80–85 Shore D, so the backup roll is the softer, tougher partner. [1]

All the SAIL backup rolls are alloy forged vacuum-degassed steel. Minimum alloy contents range from Cr 1.5%, Mo 0.30% and V 0.10% on the older plate-mill roll to Cr 3.0% with Mo, Ni and V on the cold-mill rolls; the new plate-mill roll is given an indicative C 0.38–0.48%, Cr 2.5–3.6%, Mo 0.50–0.80%, V 0.08–0.15%, Ni 0.60% max, P and S 0.025% max and retained austenite 4% max. Each item also carries a minimum guaranteed tonnage, from 100,000 t for the cold reversing mill roll to 4,000,000 t for the new plate-mill roll (written 1,00,000 MT and 40,00,000 MT in the document). [1]

Sidenor describes its forged backup rolls as made from vacuum-degassed steel forged in hydraulic presses for a high degree of reduction, offered in 3% Cr and 5% Cr forged steel for continuous hot strip mills, Steckel mills and cold rolling mills, and states that their structural homogeneity allows higher hardness together with toughness and performance above cast backup rolls. [2] [3]

State the barrel hardness range, neck hardness range, minimum hardness at scrap diameter (Shore D and Leeb), the steel and its limits on S, P and retained austenite, melting, degassing and forging route, heat treatment, ultrasonic and hardness inspection reports, and the guaranteed tonnage and how it will be measured.

03

Choose the roll design for the mill

In a four-high stand two work rolls are braced against backup or support rolls; Google Patents US4480459A describes a stand in which the support rolls are controlled-deflection rolls — a shell turning about a stationary beam on hydraulic support elements whose force is set individually or in groups — and notes this helps thickness and flatness control, for example on cold-rolled aluminium foil, while a simplified version uses one solid support roll. [4]

US5001820A describes a sleeved roll in which a sleeve is shrink- or expansion-fitted over a roll core supported by bearings, and notes that such variable-crown rolls can serve as work, intermediate or backup rolls; it identifies the risk that the sleeve shifts axially on the core under rolling-force deflection and leaves the roll eccentric, which makes thickness across the strip uneven. [5]

Editorial note: solid forged rolls are what the SAIL specifications buy for plate, hot strip and cold mills [1]; ask a supplier quoting a sleeved or controlled-deflection roll for the fit, the means of preventing sleeve shift and the hydraulic service it needs.

Name the mill type (plate, hot strip roughing or finishing, Steckel, tandem cold, reversing cold, temper or skin-pass), whether the roll is solid forged, sleeved or controlled-deflection, and any crown or profile on the barrel.

04

Know the backup roll parts and fittings

This is a functional reference built from the sources cited; it is not one maker's design.

05

Fill the specification fields with values for your mill

A backup roll quotation needs values from your stand drawing and rolling programme. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the stand, drawing and hardness data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Mill: [plate; hot strip; Steckel; cold tandem; reversing]
Stand: [position; drawing number]
Size: [barrel diameter; length; total length; scrap diameter; weight]
Hardness: [barrel; neck; minimum at scrap diameter]
Material: [steel; S, P limits; process]
Fittings: [pins; keys; thrust rings; rest buttons]
Supply: [quantity; guaranteed tonnage; inspection reports]

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