Continuous Extrusion of Solid Aluminium Conductors, Profiles and Multivoid Tubes
Continuous Extrusion of Solid Aluminium Conductors, Profiles and Multivoid Tubes
Meltech-Confex continuous rotary extrusion is able to extrude solid aluminium conductors (SAC) sections for the cable industry at average production rates of between 500 and 2000 Kgs per hour. The size of the extruder used determines the maximum production rate possible, but the average rate depends on several factors that are described later in this white paper.
The SAC sections can be extruded in the range 16 to 2000mm2 to both BS and DIN standards. To change from one size to another is simply a case of changing the die. Of course, there are other sections that are also produced for electrical use including transformer tapes and lightning conductors. Bespoke dies are also available for manufacture of complex profiles and multivoid tubes.
Maximum Production Rates
The maximum production rates that can be achieved using a Meltech-Confex MC310 size machine, for example, with an extrusion wheel diameter of 310 mm, are related to the size of feed rod or rods that are used. The fitted power to the machine and the available torque dictate the maximum rod size that can be used. Meltech-Confex offers a variety of machine sizes and drive packages tailored to meet individual customers requirements. Some examples, with maximum production rates, are :
using a 150 kW DC drive with maximum wheel speed of 40 rpm
feed stock : single Ø9.5 mm rod : 375 Kgs / hr output
feed stock : twin Ø9.5 mm rods : 750 Kgs / hr output
using a 200 kW DC drive with maximum wheel speed of 40 rpm
feed stock : twin Ø12.5 mm rods : 1200 Kgs / hr output
There is a limitation on the maximum production rate for products of small cross sections which is also dependant on the width : thickness ratio. Practically, a maximum product speed of 120 metres per minute can be considered, although speeds of up to 200 metres per minute are possible in some instances.
Feed Stock Selection
The feed stock used for SAC extrusion is in the form of rod that has generally been produced by the cast and roll process. Although SAC producers can use a single rod feed, on the basis that the larger the rod section the greater the productivity of the machine, the cost can be prohibitive. For this reason most producers opt for lower costing Ø9.5 mm rod, to use this rod size and yet still achieve high production rates a twin (2) rod feed system is commonly used.
Advantages of Continuous Rotary Extrusion for SAC Manufacture over other Production Techniques
Other processes used to make SAC include conventional extrusion and rolling. However, the continuous rotary extrusion process has distinct advantages over both of these approaches.
A conventional extrusion press is only able to extrude discreet lengths of product, limited by the size of the billet used. To achieve the long lengths required by cable manufacturers, up to 10-15,000 meters, a system of billet-to-billet extrusion is used. This results in the extruded section having differing properties along its length - due in part to a layer of aluminium oxide formed at the end of each billet. In the extruded product this layer can be seen as an elongated cone shape along a length of the SAC which forms a barrier to the conductivity of the product.
Using a rolling mill to form SAC requires many sizes of aluminium feed rod to enable a range of sizes to be made. The process of rolling induces work hardening into the product and thus annealing is necessary before it can be made up into a cable, also a lubricant has to be used which needs to be removed later, adding further cost to the process. Rolling the relatively sharp corners required for BS specification SAC is difficult and many tooling changes are necessary to produce the section. Moreover, a rolling mill can only make a limited number of sections.
By contrast, the continuous rotary extrusion process requires only one feed rod diameter to make any required size and produces SAC exactly as required by the cable manufacturer. To change from one section size to another takes about 10 minutes - which is the time needed from stopping production of one size to starting the next. Meltech-Confex extruders can also make many other extrusion profiles that are impossible to achieve both technically and economically with conventional extrusion and rolling.
Other Aluminium Products
The Meltech-Confex extruder can also be used for many other products. In the electrical field these include rectangular sections for transformer winding, magnet wires, etc. Also, various profiles for use in fibre optic cable construction, these include many sizes of spacer section or carrier as well as tube and ‘C’ section for sheathing. Aluminium cladding of a steel core wire, ASWire is also carried out using the continuous rotary extrusion process. Apart from EC aluminium various electrical alloys are extruded using Meltech-Confex machines including 6201, 6101 and 3000 series alloys.
Non electrical extrusions include many hollow sections - round tubes for refrigerators, single and multiport tubes for car radiators and air conditioning systems. The extrusion of multiport tubes has been one of the most interesting recent developments. Micro multiport tubes for parallel flow condensers used in car air conditioning systems are now extruded with between 5 and 20 voids (holes) at 0.38 - 0.75kg / metre in sizes from 15 - 35mm wide x 1.3 - 3.0mm thick and with wall thickness down to as low as 0.2mm. Larger sizes are also extruded up to 105mm wide for use in truck radiators but generally the continuous extrusion process is more economical than a conventional press for these products at up to about 45 mm wide. Meltech-Confex have developed a complete line for this product including an in-line zinc spray system.
It is impossible to list all the other products that have been or are extruded by the continuous process, but a few examples are wire for cathodic protection, polygon tubes for electromagnets, special sections for such diverse uses as thread inserts and even special strips for the trim tabs on racing car wings. Finally, one particularly interesting use of the process has been for the manufacture of AlTiB, AlSr and other alloy grain refining rod where a continuously cast bar of about 1100mm2 is used as feed and the product is Ø9.5mm rod.
In Conclusion
The use of a Meltech-Confex continuous rotary extrusion line for the production of aluminium products is a well proven and cost-effective method. The versatility of the process allows quick changes from one product to another resulting in short lead times. It is feasible to install a line that can be used for the extrusion of several different products, for example both electrical and hollow sections. Using automated take-up / coiling systems allows uninterrupted production, enabling longer production runs and greater economy-of-scale savings.
With continuous development over the past twenty years, Meltech-Confex continuous extrusion equipment today is more reliable as well as being easier to operate and maintain. Production costs have also been reduced making the process even more economical. Even today we are still striving to improve the process although gains that can be achieved are not as significant as they have been over the past twenty years.
For more information on the Meltech-Confex Continuous Rotary Extrusion lines call Meltech-Confex Ltd on
+44 (0)1254 691488, e-mail sales@meltechconfex.com