Copper alloys for fabricated rotors - Interview with Aurubis

06/05/2015 06
By Nuno Fernando

When it comes to providing the rotating machinery industry with copper, for example to fabricate copper motor rotors, one of the leading suppliers worldwide is Aurubis. Jo Rogiers, Business Line Manager Bars and Profiles, and Jan Janssen, R&D Director, describe the Aurubis portfolio for this industry sector.

 

Can you briefly introduce Aurubis?

Rogiers: Aurubis is the largest copper producer in Europe and the world’s largest copper recycler. We are headquartered in Hamburg, Germany, and have production and service sites in Europe, Asia and North America. The company was founded in 1866, and currently has about 6,500 employees in over 20 countries. Aurubis produces over one million tons of copper products annually.

What do you provide to the rotating machinery industry?

Rogiers: We supply two types of products: bars and nuggets for die-casting. These are used mainly in the automotive and locomotive industries, and the white goods sector. Their contribution to the one million tons of copper that Aurubis produces is rather small, but nevertheless it’s an important and growing area of business for us.

What is the current state of the market?

Rogiers: In Europe the market is fairly flat due to the economic climate, but elsewhere in the world, for example in China, the demand for copper for the rotating machinery industry is growing significantly.

Janssen: In this market the key demand of our customers is for copper with a high dimensional accuracy, followed by very smooth surfaces.

What is a typical order quantity?

Rogiers: This industry works mainly with relatively small batches, certainly when compared to bus bars. A typical order is 200-300 kg. Very occasionally we get an order for one or two tons.

Janssen: One reason for the small order size is that a lot of ad hoc design seems to be done in this industry: small rotors for diverse motors, a lot of differentiation, and high demands on the product. Consequently we have more dies for this market than for all the other markets combined. So it’s a niche market, with a lot of complexity required.

What are the main alloys you provide?

Rogiers: We basically supply four grades of copper to this industry. Two of these grades are our standard materials: oxygen-free copper (Cu-OFE) and Electrolytic Tough Pitch copper (Cu-ETP). These are complemented by two varieties of copper-silver alloys (CuAg OF): one with 0.04% and one with 0.1% silver. Our products are made from high grade cathodes ensuring very low impurity content.

Janssen: We have heard of other companies conducting trials with alloys such as copper-magnesium phosphor and copper-iron phosphor, but we don’t see a market demand for such alloys yet.

What advantages do copper-silver alloys give?

Rogiers: The addition of silver increases the resistance to recrystallization and improves creep properties up to 250°C. It also enhances performance at high temperatures without any effect on conductivity. Adding silver means a machine – such as an electric motor – can be run at higher temperatures.

Janssen: On the other hand, adding silver does not necessarily lead to a higher tensile strength or yield strength, as these properties depend on the deformation grade of the material used. Customers are always looking for the Holy Grail – the perfect combination of very high conductivity, very high strength and usability at high temperatures – but copper is a soft material and it’s very difficult to combine all these properties. Developments are in progress to make more optimal alloys but the electro-technical industry is a slow-moving industry, with standards to adhere to and barriers to overcome. So acceptance of new grades proceeds rather steadily.

What processes are used to produce these alloys?

Rogiers: We use a series of different “in-house” technologies, ranging from casting to extrusion and cold deformation. It’s a process chain that Aurubis has fine-tuned over decades using innovative technology and our own internal know-how and experience. There is a high quality demand on the product, so we have to control the process correctly.

What are the specific quality challenges you face?

Janssen: Maintaining a high surface quality and dimensional accuracy of the product. The tolerances of what we are allowed to deliver are narrow when compared to standard extrusion processes. For standard bus bars in an enclosure the tolerances are much greater. For a copper rotor, for example, anything less than perfection is unacceptable.

How long does it take to deliver a batch?

Rogiers: If we already have the die in-house, two to three weeks. If it’s for a new design and we need to make the die, then it will take an additional three or four weeks. Our plant in Olen, Belgium, is specialised, amongst other complex profiles, in the production of bars and nuggets for the rotating machinery industry. The plant is fully integrated and is set up to allow production to switch easily and quickly from Cu-OFE over to Cu-ETP and silver-copper alloys. From our Olen plant we supply to customers throughout the world.

 

For more information on the Aurubis copper portfolio, visit http://belgium.aurubis.com/