Bar quality improvements follow refurbishment

Edited by the Engineeringtalk editorial team Nov 23, 2000

Bar quality improvements have followed the completion of the Metalock mill refurbishment at Llanwern carried out by Metalock.

To restore stands R2 and R3 of the roughing mill to their original manufacturing tolerances for squareness, straightness and dimensional accuracy and eliminate risk of cambered bars at Corus Llanwern hot strip mill, Metalock Industrial Services, Coventry, United Kingdom in conjunction with the mill management, carried out extensive in-situ machining work during the recent summer shutdown.

Metalock has a wealth of experience in this type of work and has developed equipment and expertise enabling it to undertake such projects effectively.

Llanwern is an integrated steel plant producing strip products.

The roughing mill is the first rolling stage of the hot strip mill which is capable of producing 80,000 tonnes of rolled product per week.

The project involved machining the vertical wear plate faces (windows) and wrap around edges on R2 and R3 mill housings.

The 1.7m wide x 6m high vertical windows and new wrap around edges on each of the four columns required machining to full height.

This allowed oversize hardened wear plates to be fitted and original dimensions restored.

Additionally, over two hundred 1.25in BSW holes were to be refurbished by drilling and tapping oversize to M48 holes, then fitting screwed inserts with a central 1.25in BSW tapped hole.

Wear plate securing holes tend to become damaged during routine roll changes due to the 30-ton roll and chock assemblies sometimes colliding with the edges of the wear plate.

The only protection provided to the wear plate bolts from this shearing action, were two dowel pins per plate, but these proved inadequate.

Corus's solution to this problem has been to redesign the wear plates to incorporate wrap around edges to closely position the plates thus preventing sideways movement in the event of a collision with the roll chocks.

From information collected during a series of pre shutdown surveys it was evident that the vertical wear plate faces had worn and would require each face to be machined to clean up and at the same time to ensure square and true surfaces to the mill centreline axis.

For the vertical wear plate faces and wrap around edges machining operations, special purpose milling machines, designed and built previously by Metalock, were adapted to suit the larger mill housings at the Llanwern plant.

These machines are designed to reach the full height of mill housing windows in one setting and are set to the predetermined datums, using optical measuring instruments.

Further optical checks are performed as work progresses.

A feature of Metalock's machines is their ability to remove material rapidly using powerful 50HP (38kW) hydraulically driven milling heads.

Metalock recognised that drilling and tapping such a large number of M48 holes on the wear plate faces, many of which had broken studs still in place below the surface, would be a time consuming task and could not be allowed to hinder the face machining operations.

To overcome this, Metalock engineers designed and manufactured two special-purpose drilling machines mounted on 6m long jig plates that covered the full face and facilitated rapid access to every hole.

By using two special purpose milling machines, the operator side windows on both stands were machined concurrently.

At the same time, two drilling rigs were used to drill and tap the holes in the drive sides of both stands.

On completion of those four operations, the machines were changed over to drill and tap the operator sides and machine both drive side windows.

Organizing concurrent operations on each stand this way enabled the project to be completed well within programme and budget.

The task of stripping down the mills to provide access for the machining operations and rebuilding on completion was subcontracted to GES Ltd, a local company who also provided fitting and welding services throughout the shutdown.

Specialist alignment services were contracted to Davian Ltd.