Kolubara Metal Vreoci in Serbia was established in 1953 as a part of Kolubara-a large industrial mining conglomerate. Kolubara Metal is a manufacturing and engineering company specializing in mining equipment, equipment maintenance, repairs, and other engineering machinery used in the mining industry.
To facilitate the assembly and maintenance of mining machines, an improved method needed to be found for weighing the superstructures of mining machines.
Weighing was the procedure of choice for determining the weight and location of the center of gravity on mining machine superstructures. It can be performed on different types of mining machines (bucket-wheel excavators, spreaders, mobile transfer conveyors, etc.) and can also be used on various steel structures in other industrial applications.
Weighing has been carried out at Kolubara Metal since 1988. The measurement laboratory and research service was established in 2002. It was accredited in accordance with SRPS ISO/IEC 17025:2006 in 2009.
Weighing of mining machines needs to be performed after a factory is built, or after major reconstruction, at periodical intervals. The overall assessment of stability of mining machines is based on weighing results (several mining machines in Serbia had previously crashed due to the center of gravity being unknown).
Weighing is a complex method because it involves lifting the entire superstructure (up to 50m in length and 40m in height, with a mass of 1500 t) off the ball-bearing undercarriage by means of hydraulic jacks as well as determining the individual jack loads.
The method used is based on two measuring systems operating in parallel:
- Hydraulic measurement, which measures the hydraulic oil pressure
- Measurement of the electrical resistance, i.e. the measured change in the resistance of a strain gauge-based force transducer
The position on the mining machine where the force transducer is installed is known as the jacking point, and it is custom designed. Mining machines usually have three or four jacking points, however, the company is able to measure six points simultaneously.
The loads at the jacking points are measured online, and measured data is displayed in numerical and graphical formats. During weighing, the loads can be observed at the various points. The figure shows the moment when the superstructure is lifted off the ball-bearing undercarriage (flat line). The oscillation of the superstructure can also be observed during the measurement sequence.
The center of gravity is determined using Varignon's theorem.
The measurement laboratory and research service has accomplished 120 weighing assignments since 2002
Branko Nikolić, MSc Mechanical Engineering
Rajko Spasojević, BSc Electrical Engineering
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