Picking the “right” bead – how to select the most appropriate bead for your application.
1. Chemical compatibility. Is the grinding media going to introduce any chemical contamination issues? All grinding media will contaminate the product being ground to some extent or another even if the contamination is in the ppm or ppb range, so it’s important to consider what’s acceptable and what isn’t. While steel grinding media is attractive because of its relative density and low cost it can produce graying of product especially one that is white or light-colored. Certain products, for electronics and eye-care for example, can have no metallic contamination so the choice is limited.
2. Physical compatibility. The relative hardness and abrasiveness of grinding media, grinding chamber and product need to be considered. Since the grinding media is inexpensive compared to the equipment it should wear more rapidly.
3. Grinding media density. The range of specific gravity for commercially available grinding media runs from sp.gr. 1.0 for plastics to sp.gr. 15 for tungsten carbide. It makes sense that you wouldn’t select a very light grinding bead for a highly viscous system or a very dense grinding bead for a low-solids aqueous suspension.
4. Grinding bead diameter. The same composition of grinding media is often available in different size ranges. Typically the larger the in-feed material, the larger the grinding bead you need to use to do the work. It also follows that the finer the grind you need the smaller the grinding bead. Other size considerations include whether screens or gaps are being used to separate the media from the product – as a rule of thumb the smallest grinding bead diameter should be three times the size of the opening in the screen or gap.
5. Budget considerations. Here there are multiple issues to consider:
a. Initial cost. Generally grinding media that exhibit the best wear properties are more expensive than other options. Also the smaller the grinding media the more expensive it can become.
b. Grinding bead life. As grinding beads wear they need to be replaced. The longer a grinding bead lasts the cheaper it may be in the long run because of the costs associated with downtime, new beads, disposal and labor.
c. Mill wear. Low cost, hard grinding beads may lead to expensive equipment repairs.
d.Quality of product. Grinding media with less debris (under-sized or misshapen pieces) will tend to have a longer service life than cheaper material that might contain these artifacts.
Follow the links below to more information on these common media classes – if you don’t see what you need, click “Request info” and tell us what you are looking for.
- Plastics (sp.gr. 1.0 to 1.2)
- Glass (sp.gr. 2.2 to 3.0)
- Ceramics, includes Aluminum Oxide and Zirconium Oxide (sp.gr. 3.5 to 6.1)
- Steel (sp.gr. 7.8)
- Tungsten Carbide (sp.gr. 15)
- Artistic Glass
- Precision Balls
Click here for up-to-date pricing on grinding media. Last revision March 2015. (PDF – 116kb)