Case Study: Metal powder process control

Company profile:

	Atomization process Ferro Silicon for separation systems
	Leading supplier in RSA Iron ore mines Heavy metal oxide producers
	Plant built in 1996
	Cutting edge of separation technology Adds significant value to downstream processes Correct PSD is essential

Background

In 1996, the company started producing gas-atomized ferrosilicon powder. Gas atomization is a widely used process where control of the molten metal and high pressure gas allows tailoring of the microstructure of a powder as well as its chemical composition. Nozzle dimensions are critical and measuring PSD in real time enables tight specifications to be met, reducing costs and improving quality.

The quality of the Kumba ferrosilicon and its application is at the cutting edge of technology and is adding significant value to the company's iron ore business. Kumba's ferrosilicon powders are made by melting a blend of steel scrap and silicon in an induction furnace. The molten metal is poured through a narrow nozzle and blasted with high-pressure nitrogen gas resulting in small, roughly spherical, particles of ferrosilicon. This powder is then fed through a cyclone to a cooling bed. Any undersized particles from the cyclone are filtered into a bag house and the filter is periodically discharged into the product hopper. The discharge from the cooling bed is passed through a 212 nm screen and into the product hopper, from where it is dispensed into large bags for shipment. The Insitec replaced a manual screening procedure which was not only time-consuming but also lagged production by several hours. On-Line laser diffraction is now used for process control. However, final quality assurance is still performed using screens. Since the down-stream processes include bag filters which empty periodically and storage hoppers where settling occurs, there is continued need for screening before shipping the product.

Cooling and Classification

Kumba Installation

Using the Insitec system, particle size is measured close to the atomizer outlet, so that process parameters can be adjusted to achieve the desired PSD.

Following atomizing the material is transported by nitrogen into a cyclone. After cooling it is falling under gravity. The Dv50 is around 100 micron (100% expected below 300 micron) and the SG is around 7.2. Although the material is considered abrasive the particles are close to being spherical. PSD figures are fed back directly to the operators (via a display in the control room). The display comprises %-45 and %+212 µm together with 'out of limit' indicators and this immediate reporting allows the immediate detection of any changes in particle size and allows process parameters to be adjusted accordingly. Time history files are examined allow the tracking of performance during nightshift and other periods.

Typical PSD history

Atomizer Start-Up

The benefits of Insitec

Since PSD determines the density of the material and hence the efficiency of the separation processes for which it is used consistency is essential. Smaller particles give higher densities and the final product is sold according to its size range.

Before installation of the Malvern Insitec system, particle size distribution of the company's ferrosilicon powder was subject to variations that meant a significant proportion of the production did not meet the required specifications. This led to a growing stockpile of product with no market and delays in producing product that was in demand. Since the installation of the Insitec system, stockpiling has been eliminated, production times and costs have been reduced and the company has introduced a new product in a new size range.

Overall:

Stock holding eliminated
Production times reduced
Production costs down
Downtime reduced, with maintenance being predicted
New products introduced
Production is "right first time"
Insitec has become essential to plant operation