From Garbage to Gold

Conveyor Belt Scale

From Garbage to Gold

Belt Scale Applications made easy even in demanding Environments
What if you could reduce a time-consuming, complicated task from every other day to once a month? An integrated solid waste management company in India tried just that. Organic waste from the local municipality arrives at the company's facility and is loaded onto a conveyor. The company uses a belt scale to control and totalize the feed of material. The totalized amounts are used to calculate the price of waste from the city, so the company required accuracy and reliability.
(ed. WoMaMarcel - 25/9/2015)
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Weighing Gold per Belt Scale

Rings, watches, necklaces – you’ll see shiny gold jewellery is found in all shapes and sizes. Yet this expensive material starts out like any other mineral: in the ground, dirty, and waiting to be discovered.

A precious minerals processing plant in northeastern Russia uses a conveyor to transport gold ore into a ball mill. The site consists of an on-site flotation concentrator and a high-grade refractory gold deposit. The refractory ore is processed by conventional flotation on site. Then the concentrate is shipped to another plant where gold bars will be produced using pressure oxidation and cyanidation technologies.

The conveyor has a 1300 mm (51-in) wide belt and runs at 0.64 m/s (2 ft). The gold ore is transported in at a nominal flow rate of 110 t/h (121 sht). A gravimetric tensioner is on the conveyor to ensure a constant belt tension along its 143-m length, with idlers spaced on the conveyor every one meter (3.2 feet).

The customer already had a scale installed from a competitor: a full frame four-idler design. Unfortunately the scale was installed in an area that is not desirable for accurate weighing performance near the drive pulley. The reason was due to its size and the fact that the conveyor is curved, limiting the options for installation based on these constraints.

Installation of the Milltronics MMI belt scale and Sitrans WS300 speed sensor was quick and easy.

The four-idler model was reporting an accuracy above 1% and also experienced issues with temperature influences, producing a significant error at sub-zero temperatures due to deformation of the large frame under the thermal expansion and contraction forces. This was creating erroneous signals on the load cells being measured as product weight.

The customer required that the scale met metrological approvals of the Russian GOST Metrological agency. Siemens is one of the few companies in the world that has this approval for its belt scales, and offered a Milltronics MMI belt scale, a combination of two MSI belt scales in tandem. The compact design of the single idler model allowed for quick and easy installation, as well as for lower space requirement. This in turn allowed for a more suitable area in the conveyor to be selected. A Sitrans WS300 speed sensor mounted on a self-cleaning bend pulley, a calibration test chain, and a Milltronics BW500 integrator completed the belt scale system.

The integrator was connected to the plant network via the Profibus DP option, allowing for total integration of the scale into the plant automation system. The Sitrans WS300 also features special electrical circuitry, which eliminates false speed sensor signals from vibration. The bushed calibration test chain is a reliable option for calibration when material tests are not possible to help simulate material being transported on the belt. Siemens recommends the use of test chains on trade-approved applications for this reason.

After a fast and headache-free installation and commissioning, monitoring the scale obtained the accuracy to be 0.15%, which more than satisfied the needs of the customer.

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