Planetary-centrifugal milling

Planetary centrifugal mill AGO-2 (acceleration 60g), stainless steel vial 35mL. 5mm balls (75g), substrate hydrazlne NaHS04 10 2 0.2 mol, silica gel grinding auxiliary 10g. 

Planetary Ball Milling This is a method of increasing the gravitational force acting on balls in a ball mill. For example, refractoiy metals and carbides can be ground to 1 to 2.6 [Lm in 5 to 20 min in an apparatus capable of applying a centrifugal force of 10 to 50 G. [Dobrovol sldi, Poroshk. MetalL, 7(6), 1-7 (1967)]. 

Ball, planetary-centrifugal, vibratory or ultrasonic mills are used for milling TiB2 and ZrBj powders. The milling elements are balls of cemented carbide (WC-Co) or ball-bearing steel. 

In planetary ball mills, several ball mill chambers are mounted on a frame in a circular pattern. The balls are all rotated in one direction (clockwise or counterclockwise), and the frame is rotated in the opposite direction, generating substantial centrifugal forces (10 to 50 g, depending on the device). 

In planetary ball mill (Figure 17.3d), vials filled with balls and powder are placed onto a rotating disc (sun disc), so far as, alike planets, a vial turns around (revolves) and rotates about its own axis. Thenceforth, the name planetary mUl. For commercial mills, the ratio of angular velocity of sun disc and vials are fixed. The ball movement in a vial is the result of a superimposition of centrifugal forces. At one moment, the ball is detached from the vial wall and impacts an opposite side. 

Further developments - e.g., based on fundamentally different comminuting actions such as those of the centrifugal forces in planetary ball mills or of the pressure waves associated with electrical discharges — do indeed open up some interesting prospects, but such processes are still very much in the experimental stage and nowhere near full development for use on an industrially meaningful scale. 

There are other advantages of employing magnetic ball mills besides the control of mechanical milling modes. Since the centrifugal force becomes a secondary factor in milling, and the reactor shell rotates at low RPM, contamination from balls and shell wear is lower than in a vibrational or a planetary mill there is less ball wear involved and contaminations with Fe from steel become less of the problem. Also lower rotations and uniaxial movement of reactors paced on horizontal axle allow... 

Mechanochemical reactions are carried ont by means of mechanical activation in high energetic apparatus. Grinding devices with high load rates are used for this purpose, such as planetary, vibratory centrifugal, shock-reflective and ring roll mills, attritors, etc. 

Another type of miU commonly used in studies of mechanochemical processing is the planetary mUl. As implied by the name, the milling container is rotated about two separate paraUel axes in a manner analogous to the rotation of a planet around the sun. The miUing action of a planetary mill is similar to that of a conventional horizontal tumbling mUl. However, the velocity of the grinding media is not limited by centrifugal forces. 

With planetary mills the container is rotated about two separate parallel axes, similar to the rotation of the earth about the sun. The kinematics of planetary and tumbling mills are similar, however, the speed, and hence milling time, of a planetary mill is not limited by centrifugal forces. A number of studies have analysed ball motion and collision energies in planetary mills (Burgio et al. 1991, Dallimore et al. 1994). It has been shown that ball/container slip can have an important effect on ball trajectories, limiting collision... 

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