Analysis on the grinding operation condition of ball mill and rod mill

Date: 2019-06-28 Views:

The ball mill and the rod mill are the most commonly used grinding equipment in the dressing plant, so what is the difference between the operation of the two grinding equipment? Sometimes we think, why do we have a ball mill for a dressing plant, but with a rod mill, why? Today we analyze the problem from the point of view of the operation. to make a difference

First, the loading system of grinding media

1. Media size


The size of the grinding medium is mainly determined by the ore property. The harder the ore is, the more coarse it is to the ore, it is preferable to use a large-sized grinding medium to produce a large impact-grinding effect. The grinding medium with small size is used for grinding the soft fine-grained material, so as to enhance the grinding effect. The grinding media with different diameter shall be provided to meet the requirements of the non-uniformity and operating conditions of the ore property when the size of the material is different from that of the material.

2. Medium shape and material


The grinding medium test shows that the spherical and long rod medium grinding effect is the best. The collision of spherical medium is point contact during grinding, so the ball milling efficiency is high and it is easy to grind fine, but compared with rod grinding, the phenomenon of over grinding is serious. When the grain size of ore feeding is below 30mm and the particle size of grinding product is less than 1mm, the rod grinding efficiency is higher.
Steel and iron grinding media are generally used in production. Compared with iron ball, steel ball has high density, high strength, strong wear resistance and good grinding effect. However, the outstanding advantage of iron ball is that the price is cheap and the manufacture is convenient. In production, large ball commonly used steel, small ball commonly used iron. Steel balls should be used for rough grinding and iron balls for fine grinding. In recent years, rare earth medium manganese ductile iron balls have been successfully used instead of steel balls. The production practice shows that the wear resistance of this ball is more than twice as high as that of low carbon or medium carbon forged steel balls, and it is a cheap "substitute steel" material.

Second, mill speed and medium filling rate


The medium fill rate refers to the percentage of the grinding media in the mill volume. The medium fill rate reflects the amount of filling of the medium in the mill. For different grinding modes, mill structure, operating condition and medium shape, the medium filling rate has a suitable range, and it is too high or too low to affect the grinding effect. The filling rate of the ball mill is 40-50%, the rod mill is 35-45%, the filling ratio of the self-grinding machine is 25-40%, and the filling rate of the gravel mill is about 43%.

From the point of view of maximum production capacity per unit energy consumption, the rotation rate of ball mill is 65% ~ 78%. The rod mill usually works in the state of laxation movement, the rotation rate is about 50% ≤ 70%, the rotation rate of the self-grinding machine is usually 70% ≤ 80%, and the rotation rate of the gravel mill is 77% ≤ 85%.

And when the filling rate is low, the actual critical speed of the rolling machine is high, and the rotating speed of the medium achieving the "diarrhea" working state is high; and when the filling rate is high, the medium can be dropped even when the filling rate is high. The medium filling rate must be one of the measures to increase the rate of rotation when working within the critical speed. but the rotating speed is increased to pay attention to the mechanical problems such as the abrasion of the lining plate and the like

The optimum medium filling rate should be at a certain speed to maximize the mechanical energy. In practice, the media should be supplemented regularly to maintain the proper ratio and filling rate of the medium.

III. Grinding concentration


Grinding concentration is usually expressed as a percentage of the quality of solid materials in pulp. It not only affects the production capacity, product quality and power consumption of the mill, but also affects the overflow particle size of the grading machine, thus affecting the separation effect. When the grinding concentration is too low, the solid in the grinder decreases, so the effective grinding effect of the grinding medium is reduced. With the proper increase of grinding concentration, the grinding efficiency may be improved, but the coarse particles are easy to be discharged from the mill, which makes the particle size of the product thicker. When the grinding concentration is too high, the slurry flowability becomes smaller, the impact and grinding effect of the medium becomes worse, the production capacity and grinding efficiency of the mill are reduced, and even the "bulging belly" is caused by too little discharge. Suitable grinding The ore concentration should be determined by the test.

In practice, rough grinding (product particle size 0. 5%). When the grinding density is above 15mm, the grinding concentration is 75% ≤ 85%, and the grinding concentration is 65% ≤ 75% when the fine grinding (the particle size of the product is smaller than 0.15mm) or the ore with low density. When grinding in two stages, the grinding concentration in the first stage should be higher (75% ≤ 85%) and the grinding concentration in the second stage should be lower (65% ≤ 75%). The grinding concentration of wet self-grinding machine or wet rod mill is generally about 65%. The grinding concentration is generally adjusted by adjusting the grinding and filling water, which is added by the sand return port of the grader.

IV. Classification efficiency and sand return ratio


In closed circuit grinding, the grader has a significant influence on the work of grinding and grading unit. The higher the classification efficiency, the less qualified particle size in the return sand, and the lighter the overgrinding phenomenon, so the grinding efficiency is also higher.

The increase of the return sand ratio is beneficial to the improvement of the mill output. However, the over-load of the grinding machine and the classifier is caused by the general assembly, and the normal operation is destroyed. The sand-returning ratio of the ball mill is 100-400%, is used for 200-350%, and the sand-returning ratio of the rod mill is not more than 200%, and is generally 150-200%. The return-to-sand ratio is generally adjusted by adjusting the amount of water supplied from the mill. The ore feeding of the grinding machine shall be continuous and uniform, and the "air-beating" and "flaccidity" of the grinding machine shall be avoided.

Among the above factors, such as equipment type, specification, mill speed, feeding particle size and other parameters cannot be easily changed in the production process, and the working conditions of the mill can be adjusted frequently to make the grinding grading unit operate under the most suitable conditions.


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