Corus Port Talbot - reverse/roughing mill stand m/cing

To restore the reversing roughing mill to its original manufacturing tolerances for squareness, straightness anddimensional accuracy and further improve the quality of rolled product produced on the hot strip mill at Corus,Port Talbot, Metalock Engineering, in conjunction with Universal Engineering Design Ltd (UED), carried outextensive in-situ machining work during a recent shutdown. Coventry based Metalock has a wealth of experi-ence in this type of work and has developed equipment and expertise enabling it successfully to undertake suchprojects within customer time and budget allowances.

Over recent years the mill housings had worn and suffered corrosion necessitating shims and oversize wearplates. The 80-inch reversing roughing mill, complete with edge rolls, is the first stage of the hot strip productionline with the steel being passed through the rolls up to seven times. Due to the wear problem caused by descalingingress it was becoming difficult to present the desired quality of strip to the coil box and subsequently thefinishing mill.

Work had been carried out in the top work roll area in 1995 using shims and oversize wear plates to eliminatedamage there. During a later inspection of the bottom work roll and bottom back-up roll areas at it was deter-mined that damage and erosion had reached an unacceptable 4.00mm. Corus management and Sheffield-based UED, their project managers, decided that remedial work would necessitate removing 6mm from thehousing faces in the damaged areas and the fitting of new wear plates. Metalock Engineering was selectedjointly by Corus and UED to undertake the in-situ machining work based on successful similar operations at CorusLlanwern previously.

However, following an inspection after the strip-down to carry out the work, it was discovered that the top workroll area had sustained damage since the original survey. Corus sought to have this re-machined as well as partof the work programme. Checks were made to establish that the rig and set-up to be used by Metalock tomachine the bottom roll areas would be capable of extending to the top work roll area as well.

A few modifications were required and in the words of UED’s project manager Howard Duke, “Metalock providedan excellent service and completed 25% more machining than envisaged within the programme”.

Metalock’s special purpose milling machines, designed and built themselves are are designed to attach to thehousing using existing bolt holes and the roll change rails and, depending upon the areas to be machined can beselected to reach the full height of the housing. To speed the machining process both incoming and outgoinghousing faces are machined simultaneously using hydraulically driven milling heads equipped with 160mmdiameter cutters. The operator side housing is done first and then the milling machine vertical column is tra-versed through to the drive side housing to continue the machining op-eration.

In addition to the face machining, Metalock also restored M30 bolt holesin the housings used to secure the wear plates as during an examinationit was found that 60/70% of them were a sloppy fit. Again, to speed theoperation, drilling and tapping of the drive side housing was being carriedout whilst the operator side was being milled. Once completed, drillingand milling rigs were changed over to drill/tap the operator side and millthe drive side.

Due to the design and the manner in which the milling machine is set upoptically, Metalock engineers are able to achieve tight tolerances basedon a central datum. In the case of the Port Talbot mill, the housing waswithin 0.002-inch (0.0508mm) which was possibly an improvement onthe original set-up when the mill was new.

By extending its specially designed milling and drilling columnfor mill housings, Metalock was able to machine the topwork roll area as well as the bottom roll faces. The rig isattached using existing bolt holes and the roll change rails.