Falcon UF Autopac
"AUTOPAC" is Sepro Mineral Systems' acronym for "Programmable Automation Controller". Sepro has decided, after a careful review of the many options available, to build its automation system around variable frequency drives coupled to PLC control. The rationale for this decision is compelling:
Many independent researchers have verified Sepro's claim that metallurgical performance is a function of the centrifugal field applied. This is established fact in credible research circles. Where the target mineral is fine, say finer than 40 microns, both experience and research have shown it to be necessary to apply a larger centrifugal field than where the target mineral is relatively coarse, say coarser than 100 microns. Some applications require application of as little as 60G's. Sepro Mineral Systems made changing the centrifugal field into a simple keypad entry back in 1989 as opposed to having a massive, costly mechanical changeover. Machines that offer a single centrifugal field are at an obvious disadvantage.
Mechanical Performance
Enhanced gravity concentration machines which must be started "across-the line" may subject their drive components to extreme overloads in each start cycle, sometimes 5 or 6 times the full load amperage of the motor. This can cause premature failure of not only the electric motor, but also drive belts and bearings. A variable frequency drive is designed to control the loads applied to the drive components to within acceptable limits, thus extending component life when compared to "across-the-line". In addition, constant speed machines offered today must coast to rest. In applications where the machine must start and stop as part of an operating or maintenance routine, coasting to rest adds considerable and unnecessary downtime to the machine. By integrating a dynamic brake with the variable frequency drive, downtime is reduced to an absolute minimum without jeopardizing drive components. Clearly, the variable frequency drive offers a superior control strategy.
Vibration
The designer has the option of using a large, balanced rotating mass in an enhanced gravity concentration machine if a vfd/dynamic brake is utilized. It is well known that increasing the balanced, rotating mass of such a machine will tend to dampen vibration caused by transitory imbalance. If a vfd is not available the designer must keep the inertia of the rotating mass low enough to allow "across-the-line" starting. This approach results in a machine with a tendency to vibrate severely with even the most modest transitory imbalance. The designer is then faced with accommodating the tendency to vibrate with vibration isolation mounts. These mounts in turn cannot withstand the high loads induced by the high centrifugal fields that are possible with the Falcon Concentrator. The use of a variable frequency drive then is critical to the unqualified success of the Falcon Concentrator.
Cost
When variable frequency drives were first introduced, they were expensive, unreliable and of limited ability, just like the computers of the 1950's. Now, just like modern computers, costs are way down, reliability is way up, and the ability of even the most basic vfd was not available at any price ten years ago.
Future Considerations
Mineral processing plants in the future will rely even more heavily on PLC's than they do now. On stream analysis techniques will also be used much more extensively. This fact has not been lost on vfd manufacturers. Sepro's vfd's can be configured to give to or receive from, instructions from PLC's and many other electronic devices.
