The bulk weight of grinding balls

In the grinding material process at ball mills becomes necessary to calculate the bulk weigh of used grinding media. The bulk weigh of the grinding balls is necessary to understand the grinding balls mass in the cube, the grinding balls mass loaded into the mill, the prevention of mill overloading with grinding balls, etc. These data often used in operational management of grinding process.

Consider a definition technique the bulk weight of new grinding balls. Methodological tables in specialized handbooks indicated the bulk weight of grinding balls different sizes. The indicators were calculated more than 20 years ago. Currently, these data can give an error more than 10%. This is a big error in production operational management. This error is caused by the fact that in the modern grinding balls production apply many materials (different grades of steel, «white» and «gray» cast iron) in contrast to past years. Besides, the actual diameter (size) and shape of grinding media affect the bulk weigh value.

Experts of «Energosteel» company have developed a common methodology together with technical specialists of Ukrainian and CIS countries mining & processing enterprises. This methodology allows to accurately determining a bulk weigh of grinding balls. Below, we give the main points that reveal the determining process the bulk weigh of grinding media (grinding balls).

To measure the bulk weigh of grinding media uses container with regular geometric shape (cube) and volume no less than 1.0 cubic meter. Pay your attention, calculations results will be more accurate if cube has large capacity. Cube capacity should not have flaws («waves», protrusions, holes, etc.). For the reliability of the results, measurements carry out with using the same capacity for all grinding media types. Measurements, calculations and commission inspection of the container carried out in the presence of responsible persons: representatives of grinding media producer and representatives of enterprise where grinding media used. Container fills by the same ways for all grinding media types.

Container fills by grinding media and lifted to a height of 10-12 cm from the concrete floor, then the crane operator disengages the lifting-lowering mechanism and container freely hits the floor. These ups-downs carry out at least 3 times. The capacity fills with grinding media to the upper edge level, after each shake. This procedure carried out at least 3 times with one grinding media type.

If it’s technically impossible to carry out the «shake-up» process (because of safety rules, lack of vibration surface, etc.), then grinding media loaded into container by a «washer» with 200-250 kg. The grinding media evenly distributed over the container into the hand way, after each unloaded «washer». Grinding media should be evenly distributed in cube; surface of them should be smooth in the container.

The container is weighing, when it filled by grinding media as much as possible.  Weighing can be done by any measuring instruments: crane scales, stationary scales, etc. It is important that weighing takes by the same measuring instruments and under the same conditions.

Bulk density (bulk weight) determined by the formula:

Ý = (G1-G) / V  (t / m³)

Where:

G1 – container weight with grinding media (t);

G – container weight (t);

V – capacity volume (m³).

Based on the weighing results, needs to make an act (report) about the bulk weigh of each grinding media type. The act introduces the average value of bulk weight by 3 weighing results. The obtained result of bulk weight determination can be used in operational accounting, control of grinding process.

In our next articles we will consider the methodology for determining the bulk weight of grinding media in a working ball mill.