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Grinding Media Definitions & Tips
Media:  Plastic | Silica | Alumina | Zirconia Silica| Zirconia Oxide| Steel | Exotics

The Grinding Media Depot ^® offers all standard types of  grinding medias  as well as some out of the ordinary and/or experimental sizes and materials.  We continually look for the best value which means high quality reasonably priced.  We conduct wear tests on the media to ensure that the quality meets our requirements for wear resistance.  Feel free to call us to discuss your application, 800-726-1366.

• Remember: grinding medias from different vendors should never be mixed even if they are purported to be the same bead.
  • Not all glass beads are the same.
  • Mixing of medias will lead to increased wear rates and shorten the life of the media.
• Never run a mill empty with media or with a low viscosity fluid such as solvent or water as this will cause premature wear of the media and mill.
• Always consider the plant culture when deciding upon a grinding media. There is no point to paying a lot of money for a long wearing media if it has a tendency to end up on the floor or down the drain.
• Don't hesitate to call Norstone to discuss your specific application.

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SILICA Click here to view Silica Media.

Sand:  This media is still used because of its low price but can be costly in the long run. It is abrasive to the mill due to its irregular shape as it is more needlelike than spherical and the tips tend to break off.  Waste disposal of this short term media can also be expensive.  Alternative medias are glass and mullite. Density:  2.50 gm/cc.  Bulk Density:  1.5 kg/l; 3.3 #/l;  5.5 kg/gal;  12 #/gal

Soda Lime Glass:  This is the most popular glass sphere used for grinding media.  The larger beads are molded.  Some brands are produced from virgin glass while others are produced from recycled glass.  Air inclusions also vary which can determine the life span of the bead as it determines the strength of the bead.  This is an excellent bead for low viscosity material or low heat processes. Density = 2.5 gm/cc.  Bulk Density:  1.5 kg/l;  3.3 #/l.; 5.5 kg/gal;  12 #/gal

Low Alkali/Borosilicate Glass:  There are several grades of borosilicate glass beads.  This bead is used for low alkali applications as well as food and pharmaceutical.  There is also a high crush strength bead which is more abrasion resistant than the soda lime glass.  It is more expensive than the soda lime but the value is there. Density = 2.6 gm/cc.  Bulk Density:  1.6 kg/l; 3.5 #/l.;  6.0 kg/gal;  13.3 #/gal
Borosilicate glass (PYREX grade) is also available.

Flint Pebble: A natural resource that is getting harder to find in its natural state.  It is basically quartz having similar density to glass but harder with irregular shapes and surfaces.  The benefit of the pebble is the aspect ratio thus giving it a lot of surface area for contact in the mill.  They are still available but getting to be expensive.  A good alternative is Steatite. Density: 2.6 gm/cc.  Bulk Density:  1.6 kg/l;  3.5 #/l; 6.0 kg/gal;  13.3 #/gal

Steatite:  This media is a fused magnesium silicate composite made up of 62% SiO2.  The minimum size is 6.0 mm available in satellite balls, cylinders and spheres.  This is an excellent alternative to flint pebbles or large glass balls. It lasts longer than glass but is the same density. Density = 2.6 gm/cc.  Bulk Density:  1.6 kg/l;  3.5 #/l; 6.0 kg/gal;  13.3 #/gal

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ALUMINA Click here to view Alumina Media.

Mullite/45%-70%: This media is most often referred to as MULLITE with approximately 35% SiO2.  It has the advantage of being higher in density than glass and lower density than other aluminas.  Beads are available in several different alumina concentrations and densities, with or without bauxite. It is available in small beads, satellites and cylinders. It lasts longer than glass and is not as abrasive as other aluminas. Density:  3.25 gm/cc.  Bulk Density:  1.74 kg/l;  3.8 #/l; 6.7 kg/gal; 14.5 #/gal

Standard Alumina/85%-90%: 85%-90%:  This is still the most common range of alumina media used for particle size reduction in both powders and liquids.  Beads are available as well as satellites and cylinders. Some sizes are available in both dry pressed and iso pressed.  The beads can be abrasive. Density: 3.6 gm/cc.  Bulk Density:  2.2 kg/l; 4.9 #/l; 8.2 kg/gal; 18 #/gal

Higher Density Alumina/92%-97%: Alumina media found in this range is generally imported and have a higher density so the liner hardness must be considered prior to using this.  The 94% alumina bead is spherical and excellent for use in both liquids and powders.  Density:  3.7 gm/cc.  Bulk Density:  2.3 kg/l; 5.1 #/l; 8.4 kg/gal; 18.5 #/gal

Higher Purity Alumina/98%-99.9%: Alumina with this higher purity is used in grinding materials which cannot tolerate contamination other than alumina.  It can be dramatically more expensive and is also more brittle than other alumina formulations.  It is available in spheres, satellites and cylinders.  Density:  3.8 gm/cc.  Bulk Density:  2.4 kg/l; 5.3 #/l; 8.6 kg/gal; 19 #/gal

ZirTA-NOR (Zirconia Toughened Alumina):  Zirconia Toughened Alumina: This product isrelatively new and has proven to be an excellent media in the medium density range. It is solid, white, round, has high fracture resistance with lower amounts of zirconia and no radioactivity. Sizes start at 0.6 mm and can be made up to 2" in balls and cylinders. Density: 4.2 Bulk Density: 2.6 kg/liter

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ZIRCONIA SILICA Click here to view Zirconia Silica.

Zirconia Silicate:  This is a popular, medium density,  bead which is SINTERED.  This bead has a hard outer crust and a soft inner core so it should be used in less aggressive types of small media mills.  Sizes above 3.0 mm are not practical because of the inherent structure which weakens the bead and causes it to crack and break. This bead can be abrasive to the mill. Density: 4.0 gm/cc.   Bulk Density:  2.45 kg/l; 5.3 #/l;  9.27 kg/gal; 20.4 #/gal

Zirconia Silica: This bead is also a popular medium density bead which looks almost identical to the Zirconia Silicate but they can NEVER be mixed.  This bead is FUSED and is consistent from the crust to the core.  It lasts longer than a sintered bead but should not be used in sizes above 2.0 mm because of the inherent air inclusions known as hollows in the bead. This bead can crack and break and cause abrasion problems in the mill.  Preconditioning the beads is strongly recommended. Density: 3.8 gm/cc.  Bulk Density:  2.4 kg/l;  5.0#/l; 8.6 kg/gal;  19 #/gal

High Density Zirconia Silica: This is a relatively new bead  which is a fused zirconia silica containing a higher amount of zirconia than the more common formulation.  Density: 4.6 gm/cc.  Bulk Density:  2.8 kg/l; 10.6 kg/gal; 23.3#/gal; 6.2 #/l

Toughened Zirconia Silica:  This is a relatively new bead which is a fused zirconia silica toughened with yttria and alumina.  This bead is excellent as a medium density media with longer wear and durability than the standard zirconia silicas on the market. The bead has the added advantage of being available in very small sizes. Density: 4.6 gm/cc.  Bulk Density:  2.8 kg/l;  6.2 #/l; 10.6 kg/gal; 23.3#/gal

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ZIRCONIA OXIDE Click here to view Zirconia Oxide Media.

Magnesium Stabilized Zirconia Oxide:  A very popular high density ceramic satellite or cylinder for all types of milling.  While this form of the media is excellent, the bead is very poor in that it is abrasive to both the mill and itself. Density: 5.5 gm/cc.  Bulk Density:  3.2 kg/l; 7.0 #/l; 11.8 kg/gal; 26 #/gal

Cerium Stabilized Zirconia Oxide: This is a relatively new high density media but has become very popular due to its durability and value pricing.  The bead will not crack and break. The media is available in beads, satellites, cylinders and spheres. Density:  6.0/6.25 gm/cc.  Bulk Density:  3.6/4.0 kg/l;  7.9/8.8 #/l; 12.7/15.1 kg/gal; 28/33 #/gal

Yttria Stabilized Zirconia Oxide:  This is the highest, longest lasting and toughest high density media.  This media is very hard and non-porous so that it will not break.  It is non-porous thus cleaning easily. It is available in several grades. Beads, spheres and cylinders are available in a wide range of sizes. Density: 6.0 gm/cc.  Bulk Density:  3.7 kg/l; 8.1 #/l; 14 kg/gal; 30.1 #/gal

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EXOTICS Click here to view Exotics.

Tungsten Carbide:  This media continues to grow in interest due to its high density. Beads and satellites are available in limited sizes.  The mills using this media must be built to handle the high density. Density: 15 gm/cc.  Bulk Density:  8.2 kg/l; 18 #/l; 30 kg/gal;  66 #/gal

Silicon Nitride:  This is a media mostly available as grit.  Not widely used.

Silicon Carbide:  This is a low density ceramic available in limited sizes.  The balls and satellites are usually custom made.

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