Technical Multiwire Drawing Line Solutions

The ability to offer high quality lines for wire and strand market constitutes a competitive advantage. Product development is therefore oriented in two parallel directions: the development of new products and the continuous improvement of existing products within a context of continuous market evolution, to ensure that final users always have the best.

In a high competitive market, wire manufacturers ask to increase the product quality and the production reliability, whereas production costs and scrap rate are to be reduced.

The wire drawing and annealing in-line process of aluminium wire add new challenges compared to the process of bare copper wire. In particular, the aluminium multiwire drawing system presents technical challenges in the surface as the wire is hard and abrasive and the dust and powder generation is higher. Annealer contact band life is critical due to sparking, and the oxidation of the wire surface changes the contact resistance between wire and contact ring. A lower tensile strength requires accurate tension control to avoid lack of roundness of the finished wires in reels.

The multiwire drawing machine is a slipping gearbox machine; therefore, a high number of drafts causes a high cumulative slip in the wire inlet side. For example, in a 22-draft machine setup, the cumulative slip at the wire inlet is approximately 30-35% (considering a slip of 1.5% for each die, and 4% at the final die). High slip has a negative effect on the quality of wires. This phenomenon increases the frequency of wire breaks, reduces the life span of drawing capstans and increases energy consumption and noise level of the multiwire line.

Wire drawing machine
Photo 3 Multiwire drawing line

The Sampsistemi DM multiwire drawing platform (see Photo 3) is based on the splitting of gear transmission into two or more independent sections, with separate AC servomotors. This allows slip recovery between each section and at the inlet side. A 22-draft machine with three motors has a maximum slip at the wire inlet of 10-12% and reduces the slip at the separation by ca. 5%.

Power splitting also enables the use of compact AC servomotors with compact drives that allow a more precise regulation in the operation and high efficiency of transformation current in mechanical torque at drive end.

A control motion system (see Fig. 2) is used for synchronization of all motors. The reduction of slipping and the improvement in the quality of gear transmission, bearings, seals, etc., have allowed a reduction in the energy consumption by up to 10-15%, consequently abating production costs. In order to reach the best wire quality surface, zirconium oxide pulling rings have been adopted.

 

Multiwire drawing machine
Fig. 3: Chart of “slipping recovery”

The drawing of aluminium wires requires an increased amount of lubricant compared to bare copper, a better control of temperature and cleaning.

Die holders have spray jets on both the inlet and outlet cones to improve wire lubrication within the die, to reduce friction and to facilitate cleaning of the inlet/outlet cones themselves, thereby enhancing product quality and prolonging life span of the dies. There is also a spray for pulling rings to reduce the friction with the wire.

The lubrication of the final die is critical as it is here that the wire attains its minimum diameter. At maximum speed, the lubrication is usually only on the entrance die cone. For these reasons, the designed multiwire drawing machines have a pressurized separate lubricant supply circuit for their final dies.

Net oil or emulsion can be used in the multiwire drawing process for lubricating and cooling. The constant developments in the field of emulsions is giving promising results in terms of life span of the dies, wire surface quality and cleanliness of the wire, which is the basic condition for a successful in-line annealing process.

TO BE CLONTINUED ...