Media Stocked and Distributed from EMImills Machinery, Inc.
types of grinding media are available from Engineered Mills, 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.
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
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.
it be used to provide:
a. Dispersion or de-agglomeration
or the separation of bound aggregates
or agglomerates that yield individual
Milling and grinding; where finite particles are reduced to a more desirable
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:
EMI 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