Pin toe-in is an understood and accepted phenomenon in all pre-bake aluminium smelters and VHE has been working to solve the problem. Toe-in is caused by the difference in expansion rates of the steel yoke or spider and the carbon anode as they heat up in the reduction cell. The yoke expands more than the anode, bending the pins which are already sealed in the anode block.
The pins bend inwards just above the iron thimble, and can no longer be correctly located in the anode holes. After some further time the pins will no longer fit into the holes.
It used to be that smelters would continue to use rods until the pins would no longer fit into the anode. The bent pins would then be cut off and new ones welded onto the yoke. Today, it is generally accepted a pin straightener has a cost benefit. Straight pins reduce operational problems and improve the pin-carbon volt drop.
VHE of Iceland has proven designs appropriate to different reduction technologies. Ambient temperature straightening is suitable for smaller pin diameters and is an economical solution. VHE has supplied a number of such machines to smelters worldwide.
For larger pin diameters, hot straightening is usually the best approach. Pins heated to 650°C may be straightened with much smaller forces, and the cost of an induction heating unit is to a large extent off-set by savings in the heavier duty steelwork and hydraulic systems which would otherwise be needed. VHE has delivered such pin straighteners for diameters up to 180mm to a number of smelters internationally.
Velaverkstaedi Hjalta Einarssonar - VHE is a major mechanical fabricator, offering a comprehensive range of design, manufacturing and site services. VHE now provides all Stimir solutions to the primary aluminium industry, with particular focus on the Rodding Plant. All aspects of design and fabrication are undertaken at VHE's own facilities, ensuring total quality control and on-time delivery.