Modernising tried and tested technology

Christine Gassel Freie Journalistin in München

Because of increasing competition, the productivity and maintenance costs of finishing lines are being increasingly scrutinised by production management. This is equally true for machines which have been giving good service for decades, but for which it is increasingly difficult or impossible to obtain spare parts and the efficiency of which has been left behind by technical progress and new regulations. Buying a new machine involves a high investment coupled with loss of production time due to on-the-job-training, the period of job familiarisation and loss of production during installation. An alternative method of bringing the line technically up-to-date is by retrofitting the existing machines which involves only optimising individual components.

Thus it was that the Wieland-Werke AG in Vöhringen, a company specialised in manufacturing semi-finished products made of copper or copper alloys decided to have their stretch bend levelling line professionally retrofitted. Within only 6 months the specialist supplier Burghardt + Schmidt GmbH in Remchingen had produced a modernisation plan corresponding to the exact needs of the customer which comprised obtaining the necessary components right up to installation on site. Since implementation, the machine has been working at a higher speed, has increased productivity and is much easier to service.

The core competence of the Wieland-Werke AG includes the production of strips, wires and tubes made of copper, brass or bronze alloys, including bearings and other system components. In order to meet the highest possible demands regarding surface quality and evenness the strips have to be rolled and aligned very precisely. Undesirable deviations of shape or form can thus be reduced to a minimum. The Vöhringen factory near Ulm has since 1976 been using a stretch bend levelling line and straightening system, both of which have four braking and drawing-in rollers. In 2006 the company realised that this old and trusted machine no longer corresponded to modern requirements.

“On one hand the machine no longer conformed to the latest safety regulations concerning machine operation and handling“, explains Dipl.-Ing. (FH) Wolfgang Benischke, Head of the Planning Section of the Rolling Group. „On the other hand there could be no guarantee for continuous production in the medium-to-long term, because it was sometimes not possible to obtain spare parts for the electrical equipment. Moreover, there were more and more breakdowns in production and the costs for remedying these were excessively high.” However, the mechanical components were still in good condition, and for this reason the company decided against the acquisition of a new machine. “Decisive for us was the realisation that retrofitting would involve fewer costs than a new acquisition“, he remembers.

The aims of the modernisation were soon defined: the machine should be mechanically modernised and its performance enhanced. And, as the line speed needed to be increased, the performance of decoiling and recoiling as well as that of the brake rollers needed to be improved. Basic plant parameters such as the thickness range from 0,1 to 0,8 mm and widths from 70 to 420 mm, or the stretching limit of a maximum of 630N/ sq.mm needed to be retained. The order for the necessary renewal of electrical parts was given to DAA Delta Technik GmbH, a close partner of Burghardt + Schmidt. The order comprised a comprehensive series of measures ranging from the disassembly of the old control cabinets up to the complete new wiring and integration of a visualisation system based on WinCC.

The world’s leading producer of stretch bend levelling lines, Burkhardt + Schmidt, recommends in addition the replacement of all existing drives for reels and rollers by 3-phase A/C motors. “In this way, not only less maintenance is needed, but braking energy can be recovered which increases energy efficiency”, explains Volker Lüdecke, Technical Director of the company. Finally the new motors had to be set on new bases, the existing clutches with drum brakes had to be replaced with others using disc brakes and instead of the existing shoe brakes, brake callipers needed to be used as standstill brakes. Moreover, because of the new situation, gear boxes with new gear ratios were installed and the reels were fitted with a new intermediate shaft and a second clutch.

In order to ensure that the metal strip is correctly positioned at all times and runs centrically in the straightening press, the recoiling reel, hitherto fixed, had to be retrofitted with a strip edge guide. To achieve this, the lower side of the reel had to be re-worked in order to mount linear guides. The edge guide itself, including strip light, was fitted in a frame located after the bridge table but before the final steering roller for the recoiling reel. In order to exactly control the positioning with a tolerance of less than 1 mm for the guided edge it was necessary to fit the recoiling reel with a linear path transducer linked to a digital strip controller. The strip is moved by means of hydraulic cylinders with a +/- 100 mm stroke. As a fix-point for the strip it was necessary to integrate a 250 mm deflection roller between the edge detector and the recoiling reel. This, as well as the gear coupling, was fitted with protective devices for the safety of the machine operator. Moreover, the necessary tubes and pipes including valve blocks for the hydraulic and pneumatic supply were provided for the new or modified parts of the machine.

Wieland had specified a tight window of only 6 months for the complete modernisation – from ordering to test running. “The most important thing was to minimise the down-time for the modification of the straightening machine and the resulting costs“, explains Lüdecke. In order to ensure this, Burghardt + Schmidt stocked all the necessary materials in advance and pre-assembled as much as possible in their own workshops. This saved time during the disassembly and reassembly of the machine on site. “The core down-time was 3 weeks“, confirmed Benischke, „and the whole project was completed with no problems“. The staff of the company were retrained to cope with changes in the machine operation during the running-in period. As they had been involved in the planning of this modernisation, the switch-over was achieved without major difficulties.

In the meantime the modernised stretch bend levelling line in the Wieland factory has been working reliably for several years – with an increase to both the performance and to the quality of production. „Due to the strip edge guidance the coiling of the strip has been much improved“, records Benischke. At the same time the guidance as well as the stronger tape tension have improved the evenness of the straightened metal strip. In addition both the number and duration of down-times were significantly reduced, while at the same time it has proved to be easier to obtain spare parts for the new system. The new and more detailed documentation supplied and the improvements to the visualisation system have played an important part in the search for errors and have simplified operation. The investment in the plant, which will soon be 38 years old, has more than paid for itself. •