Acceptance Rules and Quality Control Methods Of Grinding Balls

The quality control the grinding balls hardness and surface checked every hour of the mill’s work, as well as new steel grade rolling in the beginning.

Quality control the grinding balls surface, dimensions and hardness carried out by a shift master or laboratory assistant in accordance with the requirements to current regulatory documentation.

The grinding balls hardness control carried out in accordance with DSTU 3499-97.

Ten grinding balls select from five different batch locations to check the dimensions, quality and surface hardness.

If surface hardness control results are unsatisfactory, this indicator checked again on a doubled grinding balls quantity selected from the same batch. If more than two grinding balls don’t meet the requirements during the second test then batch transferred to a lower hardness group.

Three balls select from three different locations in each 20-th batch for hardness control of grinding balls the 4th group on 0.5 R depth. If surface hardness control results are unsatisfactory at least for one grinding ball then provide test again on a doubled grinding balls quantity selected from the same batch.

If repeated measurements show unsatisfactory results, then needs to perform tests on two consecutive batches until acceptable results.

Requirements to normative documentation allow no more than 10% nonconforming grinding balls by size and surface quality.

The surface hardness of the grinding ball determines on two diametrically opposite sites.

Four measurements perform at each site during hardness determination by the Rockwell hardness method. The first three measurements performed at the vertices of imaginary equilateral triangle with a side length from 5 to 8 mm. These measurements are tentative and the results are not recorded in the test report. The fourth measurement carried out in the center of the triangle. This measurement result enters in the test report.

One measurement performs at each site during hardness determination by the Brinell hardness method. This measurement result enters in the test report.

The hardness determined as the average value of all grinding balls measurements.

The grinding ball hardness at 0.5 R depth o determined on a flat surface area, prepared in accordance with the requirements GOST 9012 and GOST 9013 by removing grinding ball metal to desired depth. At distance of 1/2 radius perform four hardness measurements on two mutually perpendicular lines. The minimum and the maximum hardness values ignore, and the hardness defined as arithmetic average value of the other two dimensions.

Hardness determination allowed to cross templet during delivery (delivery according to DSTU 3499). Cross templet cuts perpendicular to grinding ball technological “belt”.  Cross templet surface prepared in accordance with the requirements GOST 9012 and GOST 9013.

Volumetric Hardness (VH) determined in two mutually perpendicular directions on the templates cut from the central part of the grinding ball. Templet surface prepares in accordance with the requirements of GOST 9012 and GOST 9013. Volumetric hardness (VH) calculated by formula:

VH= 0,289 Т_surf+ 0,436 Т_0,25 + 0,203Т_0,5 + 0,063Т_0,75 + 0,009 Т_c

Т_sur ; Т_0,25 ; Т_0,5 ; Т_0,75 ; Т_c  – hardness values in radius parts from the surface of the ball.  They determined according to paragraph 7.2.1.8.

The impact resistance control of grinding balls performs according to procedure MI-01.01: 2010. The 10 grinding balls take from five different batch locations for testing. If impact resistance control results for 2 grinding balls are unsatisfactory, this indicator checked again on a doubled grinding balls quantity selected from the same batch. The grinding balls batch reject when repeated testing results are unsatisfactory. The laboratory assistant records all quality control results of grinding balls in register “Grinding balls measurement of hardness and diameter”. It’s necessary to specify the batch number, tank number, diameter of grinding balls, shift, Rockwell hardness or Brinell hardness, results of external inspection and measurement in register.