Linear encoders used in automatic saw application

Stimir, an Icelandic supplier of plant and machinery to the primary aluminium industry, is using SHG-TT incremental linear encoders from Newall Measurement Systems in groundbreaking automatic stub saw and MIG welding systems for leading aluminium smelters. The machines, four of which have been installed and commissioned, require precise positioning capabilities from its encoders, TTL output and high levels of contamination protection.

Used in anode rodding plants, Stimir's innovative automated stub saw machines use bandsaw technology, resulting in energy conservation, noise reduction, cleaner cut surfaces and easy and inexpensive blade replacement. The saw cuts stubs horizontally while the rod remains hanging in the overhead conveyor.

The latest installation at Balco in India is the first stub repair installation in the new pre-bake smelter and is energy-efficient and quiet. The smooth and precise cut surfaces generated by the Stimir saw enable much improved control of welding, producing mechanically stronger joints with significantly lower electrical resistance. The system control specified by Balco enables the selection of any of three cut lengths on any combination of the four stubs on each anode rod. After cutting, the rod moves on the overhead conveyor to an automatic MIG welding station where the correct length of new stub is fitted and welded in place. This is the fourth recent shipment for Stimir's automatic stub saw and follows orders from Alcan Iceland, Alcan Steg of Switzerland and Soeral in Norway.

High-quality, reliable components

Stimir's technical director Ingi Rutsson says: "Less-than-perfect fabrication and assembly can render even the best design useless. At Stimir we put extra effort into the mechanical and electrical assembly of our products, using experienced staff and high-quality, reliable components. The selection of the right linear encoder was crucial in the development of these machines. Positioning of the saw to reflect correct removal of the damaged stub is essential, as is welding head positioning. Furthermore, the operating environment for these machines is far from clean, so protection from the ingress of contamination is a significant factor."

Newall's SHG-TT incremental encoder is capable of achieving high accuracy and provides a differential quadrature output at RS422 TTL levels. Importantly it is sealed to IP67 and is resistant to severe shock, vibration and RFI, making it well suited to Stimir's requirement. The SHG can deliver real-time feedback at traverse speeds of up to 20m/s. A comprehensive measuring length range is offered giving travels ranging from 0.50-11m for a single scale, with modular versions available in excess of 30m.

Mr Rutsson comments: "We considered a number of encoders but it was clear Newall's SHG-TT most closely matched our needs. It is rugged in construction, easy to mount and available on short delivery."

This was Newall's first OEM account in Iceland and continues the trend of global penetration into new markets worldwide with its range of linear encoders and digital readout systems.

About Stimir

Stimir was established in 1995 by former employees of the Icelandic Aluminium Company (ISAL), now a part of the Alcan group. Stimir's founders originate from a number of departments at ISAL and have brought to Stimir a valuable insight and understanding of the needs and demands of its customers in the aluminium industry. Located at Hafnarfjrdur, south of the capital Reykjavik, the company is taking advantage of the country's growing aluminium sector. As part of a $50million-turnover, 280-employee group, the company still obtains 70 per cent of its revenue from the Icelandic market.