Back to Mobile Stacking Systems 
Leaching methods at the time stacked materials parallel to shiftable conveyors that had to be moved numerous times by a dozer, typically about 3 feet (1 meter) at a time. While shifting was going on, the stacking process was disrupted.
Also, belt tripper design at the time used rail wheels that were subject to derailment, brakes that became useless after derailment, and a sometimes jerky propulsion movement due to wire rope stretching.
These issues were addressed by two new designs finalized by TNT in 1998, for which the Patents 6,085,890 and 6,098,780 were granted in 2000. These two designs - a new heap leach process and a new tracking, propulsion, and braking system for bridge tripper / hopper cars - have led to the development of larger portable conveyors that are safer to use and have much less downtime during operation.
Starting with rubber-tired conveyors averaging 125 feet in length, TNT was able to install in 2004 the first self-propelled, treaded conveyor under the "Super Portable"® name. By 2007, the Super Portable's original 215-foot length had reached 250 feet, TNT's current standard.
The Super Portable® technology uses tube steel profiles to provide the best weight-to-strength ratio, and to keep ground-bearing pressure within the specified range. This conveyor offers the optimum combination of constructability, maneuverability and operational benefits. A hydraulic power unit supports several functions that assist in achieving maximum production and minimizing scheduled shutdowns. The crawler tracks are driven by electrical drives, which are more efficient than hydraulic drive units. A diesel generator provides self-propulsion.
