東邑精密陶瓷股份有限公司

No.10, Lane 273, Sec. 4, Changxing Rd., Luzhu Shiang, Taoyuan County 338, Taiwan (R.O.C.)
Customer Service : service@oc-tec.com
Tel : 03-3125869
Fax : 03-3125862

應用技術

Q1:Does the milling efficiency increase if mixed size beads are used?

Negative.
Narrow bead size distribution is a key factor for high speed milling.
The following problems will occur if mixed size beads are used ,

  1. Separation of big beads and small beads happens during high speed milling. Small beads tends to be pushed to edge of the chamber and the slurry outlet.
    A local high pressure occurs, and unexpected movement of the small beads will lead to damage of the agitation blades and wall of the chamber.
  2. Big beads tends to damage the small beads. It will cause deformation of small beads and accelerate the problem that described in item 1.
  3. Broadened particle size distribution in the slurry. It is due to different gaps between beads. Slurry tends to "escape" from the narrow gaps which have higher shear while higher shear is an important contribution of milling efficiency.
The picture below shows that small beads deformation by mixing two different size beads.

Data source : Customer Service of EE-TEC
Bead mill machine : Netzsch
Media : 0.65mm + 0.4mm YSZ beads
Slurry : Inorganic slurry

Q2:Is roundness of the media important?

Yes!
Roundness of the media plays a very important rule for both horizontal and vertical milling machines.
Gaps between beads decide shear force. Uniform gaps make sure particles in slurry are subjected to similar micro environment.
While big gaps will let slurry "escape" from small gap, and leads to broadened particle size distribution.
On the other hand, beads with poor roundness move slower than round ones.
They tends to be pushed to edge of the chamber wall to cause damage of the chamber.

Data source : Customer Service of EE-TEC
Bead mill machine : Netzsch
Media : 0.65mm + 0.4mm YSZ beads
Slurry : Inorganic slurry

Q3:What are the meaning of "true density" and "packing density" of media?

(1)For the same material, higher true density means fewer pores inside the body. Meanwhile, better physical properties including wear resistance. The following pictures and experiment prove the correlation between true density and wear resistance.

SEM picture of cross section of poor density YSZ bead ( 1mm, N-brand ) SEM picture of cross section of high density YSZ bead (1mm, EE-TEC) After 80 hours of milling in pure water, N-brand seriously contaminates the water (left) while EE-TEC beads keep water clean.
(2) Packing density : media weight per specified volume Except for calculate packing volume in the milling chamber, the packing density reveal the following important Properties :
- True density. Media has higher packing density has higher true density.
- Roundness of the media. As the pictures below , bead with perfect roundness has highest packing density (left) while elliptic bead has loose packing.
High roundness, high packed
Poor roundness, loose packed