Paint & Coatings Industry - May 2008 - (Page 54)

High-Performance A Cost-Effective Solution he advantages of using the highest st specification grinding media in milling operations are well documented and understood. Higher density provides the potential to increase productivity, often significantly over other traditional ceramic and glass materials. Improved toughness and durability result in extended bead lifetimes and machine maintenance periods. T Yttria-Stabilized Zirconia Generally accepted as the best option is yttria-stabilized zirconia. This material is an engineering-grade ceramic, with controlled stabilization of the zirconia phase and fine crystal grain size. The resulting beads have increased strength, fracture toughness and wear resistance. The material tends to be favoured over other highdensity forms; particularly due to its compatibility with all machine types, reduced abrasion of mill parts and above all, its consistency of performance. The material has found particular application in demanding and high-specification operations, where precision, control and contamination are of primary importance. It has not, however, been generally adopted as an industrial standard. The main reason for this has been the high purchase price and the subsequent prohibitive cost of filling production machines. The cost of the media is a function of the complicated chemical and powder processing technology required to produce a high-quality product. To give FIGURE 1 | Basic production flow chart for yttria-stabilized zirconia. Zircon sand Dissolution Zirconia chemical an idea of the requirements, a simplified production o ments simpli flow sheet is detailed in Figure 1. Various attempts have been made to limit the level of processing in order to restrict overall media cost. Reduction in the degree of micronization and lower sintering temperatures have been the main target. But these have generally resulted in the production of inferior materials. An alternative has been the substitution of the stabilizing ion (yttria) with other oxides, such as magnesia and ceria. Some of the produced materials have had merit and have resulted in beads, which have found niche applications. In general, however, these beads have never matched the high performance of a top-quality yttria zirconia media. Zirmil.2 The challenge to develop a cost-effective, high-performance, yttria-stabilized bead has been the focus of a two-year project at the central laboratories of Saint-Gobain ZirPro. The engineers at ZirPro had an ideal basis for the investigation. The company is one of the world’s largest suppliers of zirconium oxide and was a pioneer in introducing ceramic micro-grinding media into the market place some 30 years ago. The result of the project is the newly launched product, Zirmil.2. With an advanced ceramic formulation, this engineered media maintains the highest standards for this type of material. The bead has superior density, sphericity and size specification, with excellent wear and lifetime characteristics. The media is detailed in Figure 2. Extensive testing has been carried out on the new material to ensure that the high-performance expectations are achieved. One series of tests, which particularly compares the performance of the media, is the ‘exaggerated wear test’. Here a small horizontal mill is operated at high speed with a standard 85% fill of media, using only water. This type of operation is very aggressive and results in accelerated media wear. Comparative data was collected for similar sized beads; some of the results are detailed in Figure 3. It can be seen from Figure 3 that Zirmil.2 far outperforms ceria-based media and has comparable per- Milling Zirconim oxide Calcination Compounding Shaping Sintering Bead product Finishing By Dr. Paul Hassall, Technical Support Manager | Saint-Gobain ZirPro, France 54 MAY 2008 | W W W . P C I M A G . C O M http://WWW.PCIMAG.COM

Table of Contents Feed for the Digital Edition of Paint & Coatings Industry - May 2008

Paint & Coatings Industry - May 2008 Contents Viewpoint Industry News Calendar of Events Company News Mergers and Acquisitions Names in the News Charlotte Dining Guide Exhibits-in-Print Waterborne Alkyds Break Through the Performance Barrier New Matting Agents for Waterborne Coatings and Varnishes Silicon-Based Technology for the Coatings Industry High-Performance Microgrinding The Development of New SMA Esters as Pigment Dispersants for Waterborne Coatings and Inks The Right Choice New Coating Technology Expands Color Choices for Vinyl Building Products BioPreferred Federal Biobased Products-Preferred Procurement Program European Union's REACH Regulation Sustainability - The New Nano Improved Dirt Pickup Resistance Critical to Future Coating Innovation NanoNews Protective Coatings NDT - Energy-Saving Paint Static Electricity - The Hidden Danger in Hazardous Areas Wacker Chemie - A Profile of Success Materials Watch Products and Literature Classifieds Advertiser Index

Paint & Coatings Industry - May 2008

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