Mills Don't Have To Be Big To Go Gearless

Often, when thinking about gearless mill drives (GMD), large diameter semi-autogenous grinding (SAG) mills come to mind, with high power ratings of around 28 MW, well above the feasible range of geared mills. Interestingly though, of all the GMDs awarded globally in the last two years, the average GMD power was ‘only’ 18.7 MW. During this time, just two SAG mill GMDs of 18 and 24 MW were ordered, compared to a total of 10 ball mill GMDs – ranging from 16 MW upwards, and averaging 18.3 MW. Over the last four decades, more than 200 GMDs for wet grinding have been sold to the mineral processing industry. In the first two of those decades, 67% of those GMDs were for (S)AG mills, and 33% for ball mills. Whereas, in the last two decades it was the opposite: only 37% of the GMDs were for (S)AG mills, and 63% for ball mills.

Most gearless mills today are ball mills

There are several reasons why most GMDs sold today are for ball mills rather than SAG mills. Firstly, there are often more ball mills than SAG mills in a typical SAB(C) circuit. Secondly, certain greenfield projects, and some existing operations with SAG and ball mills that are now reaching deeper levels of the deposit, are processing more competent and harder ore: the high competence increases the attractiveness of a high-pressure grinding roll (HPGR) over a SAG mill, and the higher hardness increases the power requirement of the ball mill. Although HPGRs produce additional micro-fractures compared to SAG mills, they also produce less fines (i.e. finished product), and may require rather large ball mills, especially for relative hard ores. Furthermore, the GMD provides inherently variable speed, combined with the highest drivetrain efficiency and almost no limit to installed mill power. Most importantly, the gearless solution offers the highest mill availability: all mechanical drivetrain components are eliminated, so they cannot fail, and the GMD is significantly better monitored than most ring-gear mill drives. For the past 15 years, ABB GMDs have led the way with online monitoring and remote troubleshooting tools that have paved the way for predictive and prescriptive maintenance, resulting in minimised unplanned downtime.

Read the article online at: https://www.globalminingreview.com/special-reports/31032025/mills-dont-have-to-be-big-to-go-gearless/