CitectSCADA system implemented in new greensand plant

Orthos Projects Ltd has successfully completed a turnkey contract to design and build a new state-of-the-art greensand preparation plant, part of a complete new casting facility for Scaw Metals, South Africa's leading producer of high-chrome grinding media for the mining industry. The turnkey project, part of Scaw's multi-million-Rand expansion programme in its high-chrome foundry, employs a CitectSCADA system to provide plant visualisation and operator interface. In addition, the Citect system has a modem connection allowing remote observation, fault diagnosis and troubleshooting by Orthos technical staff from anywhere in the world.

"We have used CitectSCADA successfully on several of our international foundry projects," says Alan Piper, Project Engineer for Orthos Projects. "It is an extremely fast and easy-to use system. We like the way it enables us to do just what we need to do, even down to data logging, and the way it expands easily and flexibly as the requirements of our customers grow. A major benefit is that we do not need to purchase development licences for CitectSCADA. This reduces our costs substantially, and also helps our clients, who can make changes to their systems without the added cost of a development system."

The Scaw Metals project consolidates Orthos Projects' growing reputation within the South African marketplace. It required Orthos to design and install a new state-of-the-art 45tph greensand preparation plant as part of a complete new casting facility. Greensand plants are systems used in many foundries for the production of cast iron assemblies. They employ moulds made from a number of materials, primarily sand; hence there is a need for systems to produce this sand automatically. New raw materials (typically silica sand, clay, coal dust and water) are weighed and mixed with old, previously-used sand in order to provide the ideal 'green sand' for a molding machine. A mixer is used to combine all these materials, typically mixing around 4 tons at a time. Finally, a moulding machine forms and compresses the sand, ready for the molten metal to be poured.

High-technology, high-efficiency control

The specification for the greensand plant supplied to Scaw Metals demanded the very latest high-technology, energy-efficient equipment, with integrated computer, PLC and SCADA control systems. However, with over 25 years of experience in foundry engineering, Orthos Projects proved that it had the technical merit, track record and innovative capability to produce the exact specification of sand plant required.

Engineering was carried out in the UK and the plant was supplied complete with all key components. This factor, combined with a local supply for structural steelwork and construction labour, enabled an extremely quick project turnround of just over nine months from order placement to first production.

A new tower building houses the 45tph sand preparation plant capable of supplying the Disamatic moulding machines requirements; incorporated within the plant is an Eirich intensive batch mixer, chosen for its high degree of sand preparation, reliability and low maintenance. Sand cooling is achieved using an Orthos pre-mixer cooler, which reduces sand temperatures to below 40degC from inlet temperatures in excess of 90degC, while maintaining consistent return sand moisture.

Level control in all silos and storage hoppers is carried out using load cell weighing. PLC-controlled batch weighing of return sand, bentonite, coal dust, new sand, dust-filter fines and water, together with the Eirich moisture controller, ensures high-quality, consistent moulding sand to be produced. Online testing of compactability and shear strength using the Eirich Qualimaster provides closed-loop control of moisture to suit compactability requirements and bentonite levels according to the required green shear strength.

Twenty screens of graphical information

Providing plant visualisation and operator interface functions across all of these operations is the CitectSCADA system. Housed on two PCs with a secondary system, the SCADA provides twenty screens of graphical information. "We are able to produce impressive results, even for the most demanding applications using Cicode programming," says Alan Piper. "It allows us to do things that we cannot do with other systems. All objects are interactive, so our operator interface is simple, intuitive and flexible, and because all the graphics were developed with optimisation in mind, our run-time performance is excellent."

In common with all CitectSCADA systems, the SCAW Metals installation offers the benefits of flexibility and scaleability to handle from the smallest to the largest tasks (450,000 I/O +). The package also has built-in DCS-style multi-level redundancy that is easy to configure and can be incorporated at all levels. The significance of this for the user is the ability to tolerate hardware failures anywhere in a system, with no loss of functionality, performance, communication or system reliability. In addition, the SCAW Metals system is equipped with a modem connection, allowing remote observation, fault diagnosis and troubleshooting by Orthos technical staff from anywhere in the world.