There is no need to prove that a stationary mill will not produce grinding effect. Only the movement of the grinding cylinder can affect the movement of the grinding medium inside the mill, resulting in grinding action. Therefore, the motion state of the mill cylinder affects the motion state of the medium inside the mill, which also affects the grinding effect.

 

The motion state of the steel ball in the mill is influenced by many factors, but the most influential factors are the rotational speed n (r/min) of the mill cylinder and the filling rate of the steel ball in the mill ψ (%). Observational tests on the motion state of the steel ball inside the mill indicate:

 

(1) When the ball is loaded inside the mill and is constant, as the mill speed increases, the steel ball inside the mill will change from falling to throwing, and even appear in a centrifugal operation state, indicating that the movement state of the steel ball is closely related to the speed of the cylinder.

 

(2) When the speed of the mill is constant, only one ball will jump at the lowest position of the mill. When the number of balls is increased in sequence, the balls will be arranged in a line at the lowest position and jump. After a certain amount of ball loading is reached, the ball load forms a slope inside the mill. When the ball reaches the top of the slope, it rolls down along the bedding surface in a downward flow state. As the number of balls increases, the height at which the ball load rises increases until a swinging motion occurs. Therefore, the motion state of the ball load is also related to the filling rate of the ball ψ (%) closely related.

 

(3) The shape x of the lining plate of the inner grinding cylinder also reflects the motion state of the ball. When the convex edges of the lining plate are high, the lifting force on the ball load is greater, and the ball skills are improved slightly. The smooth lining plate has a weak lifting effect on the ball.

 

(4) When only steel balls are installed in the mill, the sliding between the steel balls is severe. If mineral sand is installed, it prevents the sliding between the steel balls. Even the slurry concentration C (%) inside the mill also affects the motion state of the steel ball.

 

(5) Even if they are all steel balls, the large steel ball slides heavily, while the small steel ball slides weakly. The larger size of the steel ball occupies the inner layer, while the smaller size occupies the outer layer, which also affects the movement state of the steel ball.

 

(6) Whether the mill is dry or wet grinding, and even the properties of the ore material, all affect the movement status of the steel balls inside the mill. Therefore, the motion state u of the steel ball in the mill is a state function, which varies according to several factors, and can be expressed as:

U=f (n ψ、χ、 c. D...)

 

The state of the steel ball in the mill is a variable state function, which makes it difficult to quantify the state of the steel ball by mathematical means. Its motion state varies according to the variable parameters, and if there are many types of variable parameters, the state of the steel ball is also complex. Moreover, the impact of many factors on the state is currently difficult to express in functional relationships. Researchers have captured the motion states of ball loads inside the mill and selected three typical motion states.

 

2、 The grinding effect of various steel ball motion states

As previously analyzed, the motion state of the steel ball inside the mill is complex, and three typical states have been determined, with several transition states between the three typical states. Now analyze the grinding effect under three typical states.

 

When the steel ball is in a state of falling motion, the ball load moves up with the cylinder wall, and after reaching a certain height, it moves down the slope from top to bottom. During the upward and downward rolling process of the steel ball along the cylinder wall, it grinds with each other during the rolling process, and the mineral particles sandwiched between the ball loads are ground to fine. The steel ball drops from the slope to the bottom lining plate, producing a certain impact effect and having a strong impact crushing effect on the ore particles. Therefore, the grinding action under the downward flow type is mainly grinding, supplemented by impact.

 

When the steel ball is in a throwing motion, there is a grinding effect between the steel ball and the lining plate, as well as between the steel ball and the steel ball, during the rising process of the steel ball, which grinds the ore. When the steel ball rises above, it is thrown downwards. During the throwing process, the falling speed between the balls and between the balls and the ore particles is the same, and there is no relative motion, so there is no grinding effect. But when the steel ball falls to the foot of the ball load, it forms a strong impact on the lining plate and ball load below, causing a strong impact and crushing effect on the ore particles. The steel ball in the foot area is very active and has a strong grinding effect. Therefore, when the steel ball is thrown and dropped, the grinding effect is mainly impact, supplemented by grinding. Due to the stronger relative motion of the steel ball under the throwing type compared to the pouring type, the grinding effect under the throwing type is stronger than that under the pouring type. The productivity should also be higher.

 

When the steel ball undergoes centrifugal operation, there is no relative movement between the steel ball and the lining plate, as well as between the steel ball and the steel ball, thus there is no grinding effect on the ore particles. Therefore, centrifugal movement should be avoided as much as possible during the movement of the mill.