Media Information

Media Stocked and Distributed from Eiger Machinery, Inc.

Various types of grinding media are available from Eiger Machinery, Inc. Most common are glass (2.5 SG) zirconium silica (3.8 SG), yttrium stabilized zirconium silica (4.6 SG), yttria stabilized zircon ia (5.9 sg), YTZ (6.1 sg) and steel balls (7.1 SG) with common sizes ranging from 0.25 to 3 mm diameter. Each bead type chosen because of their individual characteristics in relation to the rheological properties of the product to be ground.

It is important beads be of a superior grade, spherical and uniform in shape, able to withstand wear and impact. Spherical and uniform beads have the greatest surface to weight ratios that provide predictable patterns as they are propelled through product by the rotating agitators. Wear is gradual and uniform.

In choosing grinding media three major areas must be considered:

1. It must first be determined what the primary requirement of the grinding bead is.

      Will it be used to provide:

a. Dispersion or de-agglomeration or the separation of bound aggregates
or agglomerates that yield individual finite particles.

      Or..
b. Milling and grinding; where finite particles are reduced to a more desirable size.

In some cases both functions are necessary.

Larger beads will yield greater impact, which will accelerate reduction rates, while smaller beads, having a greater count per volume, providing excellent dispersion and particle polishing forces.

2. Secondly, the rheological properties are considered. What bead mass is required to move through the product. High viscosity pastes will necessitate the need for heavier Zirconium Silicate or steel beads. Relatively thin or low viscosity (less than 5000 cps) can normally be dispersed with glass. Too dense a bead may even provide particle destruction or over milling.

3. The composition of the bead is considered and abrasiveness of the product. Thin low viscosity, low solid materials that exhibit little or no lubricity or inter-particle hydraulic protection will have excessive media and component wear. Steel or zirconium Silicate beads may be a problem

The chart shows the effect on bead count when using smaller media. The increased number of contacts points provide excellent hydraulic shearing and impact forces. In addition the smaller media provide a filtering media bed which creates finer and finer particles by allowing the smaller particles to pass through the void spaces more easily while they slow down the passage of the larger particles.

Generally the smallest, lightest bead is the most desirable. Product purity may dictate which media will be compatible. In some cases discoloration or metal contamination may exclude steel media as a viable choice and in others it is advantageous for production of heavy pastes, including inks. Here magnetic filtering can be used to insure product cleanliness.

New advances in ceramic grinding media formulations provide many manufacturing benefits even though the cost is higher. Many of these have a higher density, increased hardness, provide long bead life and low wear on equipment. The increased density will help when milling with smaller diameter beads, typically less than 0.6 mm diameter.

Grinding Media  is used in a variety of equipment:

Eiger supplied media can be used in all laboratory and production equipment used for wet milling, fine grinding and dispersion.
• Horizontal Bead Mills
• Vertical Mills
• Attrition Mills
• Batch Bead Mills