MINING SCREENS
General Kinematics STM-SCREEN™ solution for Copper Mountain
At the Copper Mountain Mining ( CMM ) operation in BC , Canada , the SAG / ball / flotation circuit was initially designed for 35,000 t / d . A secondary crushing circuit was installed to exceed the original design and push the mill tonnage rate to 40,000 t / d . The increased circulating load led to
the original SAG mill discharge screen overloading . The initial screen was supplied and rated for a total infeed , including circulating load , of 2,298 t / h with 13 mm deck openings . “ Brute force screen design inherently dampens vibration under load , which adversely affects the screening efficiency . Once a brute force machine is overburdened , effective screening stops , and screen body and structure stresses increase significantly .”
CMM , along with their previous screen supplier , committed time and resources trying to increase the screen capacity . First , they declined the screen , expecting the increased angle would throw the material toward the discharge end faster . The change helped reduce overloading , but the screen ’ s structural failures continued , as did the screening efficiency was affected negatively .
Copper Mountain Mining successfully deployed General Kinematics ’ STM-SCREEN™ featuring Two-Mass Technology to up capacity and reduce maintenance costs
Second , the original screen OEM increased the wheel force and horsepower of the drive . Again , the change helped reduce overloading , but the screen ’ s structural failures continued and became more frequent . Each time the SAG mill had a surge ( or ‘ burp ’), the screen would become overloaded , increasing stresses and leading to additional maintenance .
General Kinematics comments : “ Brute force vibratory screens require significant horsepower and eccentric forces to operate . The increased horsepower induces a tremendous amount of stresses on the screen body , ultimately creating structural failures in just months . CMM experienced this first-hand and began scheduling downtimes to replace the screen entirely every quarter . The screen that came out of service would be rebuilt , costing them tens of thousands of dollars with each occurrence . Furthermore , each attempt to increase the throughput in the circuit also increased the frequency of repairs .”
With a stretch target of 50,000 t / d , CMM knew that the current screen bottleneck would need to be addressed . The new SAG mill discharge screen would need to achieve a sustained capacity of 2,400 t / h , with periodic surges to 2,700 t / h . This increase in capacity represents a 30 % increase over the existing screen ’ s sustainable capacity - in the same screen footprint .
To raise operational uptime and increase average daily capacity , the Operations & Maintenance team determined that reducing downtime associated with the screen was an essential requirement . Finally , the new screen would require minimal changes to the existing support structure , saving installation time and financial resources .
“ After extensive research , CMM selected General Kinematics ’ STM-SCREEN™ , featuring Two-Mass Technology . The engineering principles behind Two-Mass Technology are inherently more suited for the rigors of heavyduty screening applications like the SAG mill discharge . The Two-Mass drive system responds to rapid increases in material loading by sustaining stroke . Whereas the brute force
The STM-SCREEN™ stroke stays consistent even with large variations in the product infeed . This allows for uniform screening to always occur with no reduction in efficiency
screen loses stroke and screening efficiency during surge conditions . Since the STM- SCREEN™ does not dampen , screening efficiency and production continue to be maintained even during surge conditions .”
General Kinematics provided a 3.6 m x 8.5 m STM-SCREEN™ for CMM ’ s application . GK designed the screen to fit the existing mounting arrangement to reduce modifications and the related downtime during the switch . The new GK STM-SCREEN™ required no significant changes to the support structure to facilitate installation . Screen cracking issues have also been eliminated ( successful operation for more than two years with no structural problems ). “ The Two-Mass drive system distributes drive forces evenly along the length and across the width of the screen and , therefore , dramatically reduces
concentrated forces at any point . The reduction of these concentrated forces reduces / eliminates the cracking of side structures that lead to planned and unplanned downtime as well as the related expense .”
CMM reports maintenance costs have been significantly reduced by eliminating the quarterly screen rebuild program . With zero structural failures since installation , CMM has saved an estimated $ 800,000 annually in time , material , and labour annually since installation . CMM also reports that the screen is no longer the bottleneck restricting the increased daily throughput of the mill . The successful operation of the new screen will allow CMM to increase hourly / daily tonnage to an average hourly capacity of 2,400 t / h ( including circulating load ) with surges to 2,700 t / h once the new ball mill ( BM # 3 ) comes online .
OCTOBER 2021 | International Mining