Grinding Media Descriptions

Polymers

Polystyrene: Non-abrasive, spherical in shape, non-toxic and dust free. A variety of levels of cross linked polymers are available in sizes as small as 100-200 microns. Standard and Toughened Polystyrene beads can have a strong odor from free styrene but this can be eliminated with Norstone’s proprietary process. Also available in food grade, porous, toughened and narrow particle distributions. Norstone can provide full laboratory testing for residuals, heavy metals and microbials if required. Density: 1.05 gm/cc. Bulk Density: 0.63 kg/l; 1.4 #/l; 2.3 kg/gal; 5 #/gal

PMMA: Non-abrasive, spherical in shape, non-toxic, no odor and dust free. Available in sizes under 150 microns. Not solvent resistant. No data on abrasion resistance. Density: 1.05 gm/cc. Bulk Density: 0.63 kg/l; 1.4 #/l; 2.3 kg/gal; 5 #/gal

Polyamide (Nylon): Non-abrasive, cube or cylindrical shape, high chemical resistance, non-toxic, dust free. Can swell in water. Smallest size available is 0.5mm x 0.5mm x 0.87mm diagonal. Also available in balls down to 2.0 mm and cylinders down to 0.5 mm.  Density: 1.20 gm/cc. Bulk Density: 0.68 kg/l; 1.5 #/l; 2.5 kg/gal; 5.5 #/gal

Polycarbonate: Higher density polymer, non-toxic, cylinder shape, dust free. Smallest size is 0.5mm x 0.71mm. Also available in balls down to 2.0 mm.  Density: 1.20 gm/cc. Bulk Density: 0.72 kg/l; 1.6 #/l; 2.6 kg/gal; 5.8 #/gal

Polyurethane: High density, non-toxic balls used for delumping, mixing and blending of powders. milling water-based liquids and screen de-blinding.  Certain sizes are available with steel cores. Very long wearing and gentle on the mill/mixer. Smallest size is 3/16″.  Density: 1.20 gm/cc. Bulk Density: 0.72 kg/l; 1.6 #/l; 2.6 kg/gal; 5.8#/gal.

PTFE: PTFE (Teflon) balls with steel cores.  Difficult to get so there may be minimum quantity requirements and very expensive.  However, these are excellent for high temperature and aggressive chemical applications.

Other: Many other polymer options are available such as polyethylene, acetal, PEEK, polypropylene.  Let us know what you need.

SILICAS

Sand: This media is still used because of its low price but it can be costly in the long run. It is abrasive to the mill due to its irregular shape as it is more needle-like than spherical and the tips tend to break off. Waste disposal of this short term media can also be expensive. Available with a resin coating but this will eventually wear off and go into the product.  Alternative medias are glass, alumina silicate and magnesium silicate. 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. 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. Chinese glass contains small levels of lead and arsenic. They should not be used.  Density = 2.5 gm/cc. Bulk Density: 1.5 kg/l; 3.3 #/l.; 5.5 kg/gal; 12 #/gal.  Color: Clear, can have a green, blue or gray tint.

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 better. Density = 2.6 gm/cc. Bulk Density: 1.6 kg/l; 3.5 #/l.; 6.0 kg/gal; 13.3 #/gal. Color: Clear, can have a green tint.  Pure borosilicate glass (PYREX grade) is also available and is extremely expensive.

Molded Soda Lime Glass: This is the cleanest & clearest glass bead with a blue tint.  Large sizes are available.  This media has a very tight particle size distribution with the same specs as Soda Lime Glass.
Density = 2.5 gm/cc. Bulk Density: 1.5 kg/l; 3.3 #/l.; 5.5 kg/gal; 12 #/gal.

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 high aspect ratio thus giving it a lot of surface area for product contact in the mill. They are still available but getting to be expensive. A good alternative is Steatite which is a produced ceramic. 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 4.0 mm available in beads and 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 has the same density. Density = 2.6 gm/cc. Bulk Density: 1.6 kg/l; 3.5 #/l; 6.0 kg/gal; 13.3 #/gal. Color: Off White

ALUMINAS

Alumina Silicate (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.  Colors: Off-White, Yellow, Gray, Brown and Black

Standard Alumina/85%-92%: 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. Colors: Off White, Matt White, Polished White

Higher Density Alumina/93%-97%: Alumina media found in this range is generally imported and has a higher density so the liner hardness must be considered prior to using this. The 93% alumina bead is spherical and excellent for use in both liquids and powders.  Available in Polished and Standard. Density: 3.7 gm/cc. Bulk Density: 2.3 kg/l; 5.1 #/l; 8.4 kg/gal; 18.5 #/gal.  Color: Polished White

Higher Purity Alumina/98%-99.99%: 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.  We have medias with purity of 99.99%. Density: 3.8 gm/cc. Bulk Density: 2.4 kg/l; 5.3 #/l; 8.6 kg/gal; 19 #/gal.  Color: Matte White, Off white translucent.

Toughened Alumina: Bauxite, XMB, Toughened Alumina: This product has proven to be an excellent media in the medium density range. It is solid, white, round, has high fracture resistance. 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.  Color: Off White, Matte White

ZIRCONIA SILICAS

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.  Color: Matte White

Zirconia Silica: This bead is 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.  These beads are sold preconditioned.  Density: 3.8 gm/cc. Bulk Density: 2.4 kg/l; 5.0#/l; 8.6 kg/gal; 19 #/gal.  Color: Matte White

High Density Zirconia Zilicate: This is a sintered zirconia silicate containing a higher amount of zirconia than the more common formulation. This bead has excellent performance and value.  Highly durable for its class. Density: 4.6 gm/cc. Bulk Density: 2.8 kg/l; 10.6 kg/gal; 23.3#/gal; 6.2 #/l.  Color: Polished Gray, Polished White

ZIRCONIA OXIDES

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.  Color: Yellow

Cerium Stabilized Zirconia Oxide: High density ceramic media.  Very popular due to its durability and value pricing. The bead will not crack and break unless the mill isn’t assembled or operated properly. 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.  Colors: Toffee, Golden Brown, Dark Brown and Black

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 unless the mill isn’t assembled or operated properly. 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. All brands are not the same with some wearing quicker than others. Density: 6.0 gm/cc. Bulk Density: 3.7 kg/l; 8.1 #/l; 14 kg/gal; 30.1 #/gal.  Colors: Matte White/Polished White/Pearl White

STEELS

Steel Shot: There are many sources for steel shot but all are not equal since much of the steel shot is used for shot peening or ballast. Make sure that the shot is designed as a grinding media or it could tear up the mill. Steel shot is one of the least expensive grinding medias with the benefit of high density and the availability of a wide range of sizes for small media. The more narrow size ranges of shot will last longer. Density: 7.6 gm/cc. Bulk Density: 4.5 kg/l; 9.9 #/l; 17.8 kg/gal; 38 #/gal.  Color: Black Polishes to Silver.

Standard Steel Balls Case Hardened: These are hardened only on the crust but look the same as the through hardened balls. A case hardened ball can flatten from weight or during operation. Density: 7.6 gm/cc. Bulk Density: 4.5 kg/l; 9.9 #/l ; 17.8 kg/gal; 38 #/gal.  Color: Silver

Standard Steel Balls Thru Hardened: This is a very strong grinding ball, through hardened. It has flats on opposite sides. This ball is available in polished and unpolished. Density: 7.6 gm/cc. Bulk Density: 4.5 kg/l; 9.9 #/l; 17.8 kg/gal; 38 #/gal.  Color: Silver

52100 Chrome Alloy Balls: This is a through hardened chrome alloy steel ball. It is highly polished and mono-sized with a hardness of 63-65 Rockwell C. The pricing is reasonable for an almost ball bearing quality media. It is slow to rust and is a long last steel media. Density 7.6 gm/cc. Bulk Density: 4.5 kg/l; 9.9 #/l ; 17.8 kg/gal; 38 #/gal.  Color: Highly Polished Silver.

Stainless Steel Shot: This is similar to the steel shot but made from 300 series stainless steel. The shot is considerably softer than steel shot and work hardens making it brittle. It is relatively inexpensive but doesn’t last long. Flats are always present.  Density 7.6 gm/cc. Bulk Density: 4.5 kg/l; 9.9 #/l; 17.8 kg/gal; 38 #/gal.  Color: Silver

Stainless Steel Cut Wire: This is cut wire which can then be used as cylinders or conditioned so that it is somewhat round in shape. It is available in various types of stainless. Density 7.6 gm/cc. Bulk Density: 4.5 kg/l; 9.9 #/l; 17.8 kg/gal; 38 #/gal.  Color: Silver

Stainless Steel Balls: Through hardened balls which are available in various types of stainless. These balls can be expensive but generally used when other types are not acceptable. Available in 300 and 400 series.  400 series is magnetic.  Density 7.6 gm/cc. Bulk Density: 4.5 kg/l; 9.9 #/l; 17.8 kg/gal; 38 #/gal.  Color: Polished Silver

Stainless Steel Cylinders: Not typically a popular media but still available. Density 7.6 gm/cc. Bulk Density: 4.5 kg/l; 9.9 #/l; 17.8 kg/gal; 38 #/gal. Color: Polished Silver

Jewelry Mix: This media is most commonly used in the finishing and polishing of jewelry.  It is stainless steel and consists of a variety of shapes like pins, barrels, satellites, cones, balls, diagonals.

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. Available with flats, bands, and spherical.  Minimum order might be required..  Spheres are very expensive.  Density: 15 gm/cc. Bulk Density: 8.2 kg/l; 18 #/l; 30 kg/gal; 66 #/gal.  Color: Charcoal

Silicon Nitride: Very expensive.  Available in beads and balls. Density: 3.4 gm/cc

Silicon Carbide: This is a low density ceramic available in limited sizes. The balls and satellites are usually custom made. Density: 3.21 gm/cc

Diamond & Cubic Boron Carbide: Used as a grinding media for the most severe applications and nothing else has worked. It is excellent for extremely hard materials. The shape is irregular aggregates. The cost is very high. However, it is worthwhile to consider as it will last an extremely long time and only introduce carbon as a contaminant.