Run-out table for a hot strip mill: driven table rollers and water cooling banks between the finishing mill and the down-coiler

01

Strip front-end flying, threading speed and table length to the down-coiler

Nippon Steel's patent US 5,921,127 describes the strip cooling line of a hot strip mill as a run-out table of hundreds of motor-driven rollers with a water spray or laminar-flow cooling device. When strip is conveyed at high speed on this roller table its front end can fly upward and is then hard to guide into the down-coiler, so the patent states that conveyance speed had to be held at about 700 m/min until the front end was wound round the coiler mandrel, short of the finishing mill's maximum of approximately 1,500 m/min. The patent proposes a front-end arresting device that pulls the strip head to the coiler under tension, with pinch rollers and sprays that move toward the strip after it passes, so that the run-out table can be shortened. [3]

Nippon Steel's technical report on cooling control states that the run-out table between finishing rolling and coiling is more than 100 m long and that strip head ends flutter violently on the table rollers, so pyrometers must measure from a distance to avoid being hit. [1]

Editorial calculation: 700 m/min is about 11.7 m/s and 1,500 m/min 25 m/s; at 11.7 m/s the strip head crosses 100 m of table in about 8.6 s, and at 25 m/s in 4 s.

Give the supplier the strip width and thickness range, finishing exit speed and threading speed, table length from last stand to coiler, steel grades and target coiling temperatures, cooling water supply and tank head, and the coilers it must serve.

02

Cooling banks, header flow and where the strip temperature is measured

In Nippon Steel's description, the run-out table water supply is divided into cooling banks: zone 1 has six banks and zone 2 ten, each with pipe laminar nozzles above the pass line and full-cone spray nozzles below between the table rollers, more than 300 nozzles in all, and water is switched on and off bank by bank under a cooling control model. Its fountain pyrometers purge the optical path with water and work at 0.83 µm or less (FP1) or around 1.1 µm (FP2), where water absorbs little; feedforward control using them raised the strip length within ±20 °C of the target coiling temperature by 5.8% for 440 MPa steel, 9.7% for 590 MPa steel and 6.4% for low-temperature coiling steel. [1]

Primetals describes upgrading the laminar cooling line of Wuhan Iron and Steel's 2,250 mm hot strip mill: the first 16 laminar header sets, each of one top and three bottom headers, were replaced by 18 Power Cooling sets of two top and two bottom headers with a total maximum flow of about 14,000 m³/h, and turbo-laminar headers were added later in the line. Headers are fed by gravity from a new overhead tank, with frequency-controlled booster pumps for higher flow and a quasi-laminar mode that switches to pressure cooling in less than a second. Eight top and 24 bottom headers were removed to leave a gap for intermediate temperature measurement, a laser speed gauge was added for strips shorter than the distance from the last stand to the coiler, the roller table in the Power Cooling area was replaced for drainage, and the plant was down for 15 days. [2]

Patent US 4,899,547 describes measuring the temperature profile across the strip with an infrared sensor and adjusting a coolant manifold with independently controllable outlets spaced across the width, so that the controller evens out the transverse temperature profile. [4]

03

Run-out table elements named in mill sources

Each element below is named in one of the cited mill reports or patents; the mills described are different, so no single table is shown with all of them.

04

Send the strip range, speeds and cooling targets together

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

Strip: [width; thickness; grades]
Speed: [finishing exit; threading; maximum]
Table: [length; roller diameter and pitch; drives]
Cooling: [banks; headers; flow; tank head; pumps]
Targets: [coiling temperature; cooling rate; interrupted cooling]
Measurement: [pyrometer positions; speed gauge]

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