Today we would like to consider a simple, but very important issue. We often say, “you need to choose the right diameter of the balls”. However, the products of all manufacturers are different, and now there is no single generally accepted standard for classifying grinding balls by diameter. Therefore, we decided to expand this concept and help you not to make a mistake when choosing the required size of grinding media.
As you know, the quality (technical characteristics and classification) of grinding media, which are produced and used in Ukraine, is regulated by the state standard: DSTU 8538-2015. This document specifies the requirements for the physical and chemical parameters of steel grinding balls produced by any of the methods (casting, forging / stamping, cross-helical rolling) and the classification of these products depending on their characteristics. It also spells out the requirements for the size of the grinding media and the possible deviation in the diameter.
Here is a table from DSTU 8538-2015, which indicates the classification of steel grinding balls according to geometric dimensions (diameter).
According to the table there are two concepts: conditional diameter and nominal diameter.
The conditional diameter is the name of the classification group whose grinding balls diameters are as close as possible and are interchangeable when forming the assortment.
The nominal diameter is the actual size of the grinding ball, i.e. depending on the production method, the technical condition of the equipment; diameter may vary.
Deviation to the nominal diameter is the permitted range of deviation in the size of the grinding ball within one classification group.
Let’s look at an example. The client asks to deliver to his address grinding balls with a diameter of 100 mm in accordance with DSTU. The client and the manufacturer (seller) understand that 100mm is a conditional diameter, but in fact, this group includes balls with a diameter of 100mm to 108mm.
In foreign grinding media markets, such a tool as DSTU (GOST) is not available. On the one hand, each manufacturer of grinding balls determines the classification of its own products according to the standard size and determines for itself what deviation can be. The deviation range mainly depends on the production method and the condition of the production equipment. Therefore, “casters” lay a deviation in the geometry of +/- 10%. Those balls with a diameter of 90mm to 110mm are considered 100mm grinding media. Grinding ball manufacturers that use the forging or cross-rolling method typically allow for a tolerance of +/- 3%. There are cases when the manufacturer indicates the range in millimeters. The only thing that is obligatory for the manufacturer, in addition to the deviation range, is to indicate from which diameter value this deviation applies.
On the other hand, the client can request a specific ball diameter and indicate the deviation range acceptable according to his technological requirements.
In other words, there is no concept of conditional and nominal diameter abroad. Therefore, sometimes, during export deliveries, there may be a misunderstanding between the parties. This is to be taken into consideration at the beginning stage of negotiations to clearly form an idea of what size of grinding balls will be discussed.
We hope that our information will be useful to you, and you will never encounter misunderstandings on this issue.