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Grinding Media Tips

inside a grinding mill with ceramic grinding media

Follow These Tips for Better Grinding Results

Specify CoorsTek high-density media for particle size reduction and dispersion processes in minerals, ceramics, white cement, abrasives, and paint applications.

For general purpose grinding, CoorsTek supplies two materials:

Alumina 90 (90% AI203) – offering superior density and abrasion resistance.

Alumina 995 (99.5% AI203) – a higher-purity material, ideal for harsh-duty environments where corrosives may attack the media, or media-induced product contamination is a concern.

Boost productivity, cut operating costs, and improve product purity with CoorsTek high-density, non-porous Media – the tougher charge with exceptionally long useful life.

Grinding Media Ball Mill Chambers

SELECTING THE CORRECT Grinding Media SHAPE

Generally, the ball shape is preferred for converting large size feed materials into finely ground products. The size depends primarily on the material to be ground and on the work to be done. 

Natural-Shaped Media
With its sliding, mortar-and-pestle action, the Natural Shape is best when there is little requirement for primary size reduction. However, when you desire the largest amount of fine product, it's an extremely efficient shape for dispersing solids into a vehicle.

Rod-Shaped Media
When a uniformly fine product of limited size range is required, CoorsTek Rod Media should be used. Rod media are particularly effective in vibratory mills. The line contacts between the media provide more interface areas, spreading the grinding energy over many particles to keep the amount of size reduction constant.

Ball-Shaped Media
A general-use media, CoorsTek Ball Media is superior for maximum surface contact.

SELECTING MEDIA SIZE

Generally, the largest media selected should be at least 5 times larger than the largest feed particle. The balance of the charge should depend on the characteristics of the remaining feedstock.

Requirements differ with the material being ground or dispersed, the feed size, and the finish size. 

CHARGING AND MAINTAINING BATCH & CONTINUOUS BALL MILLS

Smaller Media = More Contacts

Since particle size reduction takes place when the material being ground is sandwiched between the media, it is best to choose the smallest feasible grinding media combination as smaller media provide many more contacts than larger media.

A Balanced Blend of Media Sizes

Always use a balanced blend of between two to four media sizes when making up a new media charge, and then add the largest size as makeup to maintain a balanced media level. This ensures size reduction of the large particles with simultaneous grinding of the smaller particles.

Charge Level

Maintain the CoorsTek media charge at 48%-55% of total mill volume in batch-type mills and 38%-42% in continuous mills. In most cases, production efficiency decreases and wear of the media increases rapidly if the level of the media charge is allowed to drop below these recommended amounts, or if the media are not properly covered with material.

Batch mills should be charged to a level of 1 to 3 inches of product over the top of the grinding media.

Continuous mills should be charged to a product level just above and a media level just below the discharge grates.

Batch Material Consistency

Increase the consistency (viscosity or % of solids) of your batch material well above that used in mills charged with lighter grinding media. This keeps the grinding media working against the material and not expending its energy on itself and on the lining of the mill. Noisy media indicate that you are grinding the grinding media-and producing excessive heat, wear, and noise.

The material to be ground should completely cover the media, filling all the voids in the media charge.

Grinding Cycle Time

Because CoorsTek media grinds faster, it is mandatory that you shorten the time cycle for batch mills or increase the feed rate for continuous mills. This, of course, also results in greater output of ground product.

 

Selecting Efficient Mill Speeds

At 100% critical mill speed, all media are centrifugally forced to the outside, and no grinding occurs. CoorsTek recommends 50% to 70% of critical mill speed for optimum grinding performance.

100% critical mill speed = 76.63 / √D, where D is mill ID in feet

Dry grinding requires faster mill speeds than wet grinding. Lifter bars may be required at very low mill speeds.

 

EFFICIENT MILL SPEEDS – WET GRINDING

Grinding media ball mill efficient speeds during wet grinding

 

BALL MILL LOADING

Grinding Media Ball Mill Loading Graphic

Batch-Type Mill Recommendations
(Pounds per linear foot for three lining thicknesses)

Grinding media batch-type mill charging recommendations

CONTINUOUS-Type Mill Recommendations
(Pounds per linear foot for three lining thicknesses) 

Grinding Media Continuous-Type Ball Mill Loading Recommendations

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