A Layman's Guide to Blending Zircon Flours

By

Nipendra P. Singh

S&A Consulting Group LLP

Cleveland, Ohio USA

 

ABSTRACT

In mid 1970, a new zircon crisis emerged. Prices skyrocketed but quality plunged. One foundry, faced with a warehouse full of unusable zircon, developed a simple method for blending the poor quality flour into a more usable product. While not sophisticated as current blending techniques, this method has merit for some zircon users who wish to improve the rheology of their slurries.

This paper will discuss the technology of zircon slurries and provide a working method for blending zircon. In the past, this method was found to give about 90 per cent reliability when care was taken. The method required some laboratory capability to evaluate the zircon on hand. The method has been modified so simple slurry tests in the plant can be used.

INTRODUCTION

There have been several material shortages over the history of the modern investment casting industry. This has ranged from alloying additions, like nickel, to the ceramic materials for shell and core, like fused silica and zircon. The basis of this talk comes from the zircon shortage of the mid 1970’s.

You may recall that zircon was, at that time, a by-product of the mining for titanium oxide used in the paint and other industries. For every 2000 tons of TiO2, the process would yield about a ton of zircon. As the market for this mineral waned, the available zircon was quickly consumed. The price zoomed from $95 per ton to over $1800 per ton. This compares to about $500 per ton now. And sorry to say, the quality of zircon for ceramic slurries nose-dived.

Because suppliers were not prepared to replace out of spec material, many companies used it as it was, or stockpiled what could not be used and bought more. Our company did the latter. At one time, this inventory reached a million pounds of out of spec zircon.

Needless to say, drastic measures were required. Fortunately, our lab and plant were prepared to blend the zircon. The problem lay in that no reliable and reproducible method was available. So bad material was simply stored and more blends were made. The plant was working 7 days a week.

In those days, small particle screen analysis was done semi-automatically with micro-sieves and some use of the Coulter Counter, a machine used to determine blood count. The Setagraph, a particle settling machine, gave a general description of particle distribution, but was very slow. The modern laser units, such as the Micro-Trac, were not yet available.

A curious note about the Coulter Counter was that it was calibrated by use of ragweed pollen, which is very uniform in size. I always knew immediately when the unit was calibrated, because the release of the pollen made itself known as I began sneezing.

This paper will describe the lab data that was employed and the procedure for formulating the zircon flour. With the right zircon available, successful blends gave the desired viscosity about 90% of the time. Also, the plate weight (PW) of the slurry only reached about 90% of the estimated PW. A new method will be shown.

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