The driving band is part of an artillery shell, a band of soft metal near the middle of the shell, typically made of copper or lead. When the shell is fired the pressure of the propellant squeezes the metal into the rifling of the barrel, both providing for a seal as well as providing a driving surface to spin the shell. In a rifle, the entire bullet is typically covered in copper, as so the entire bullet is its own driving band.
One downside to the driving band is that it must be placed at the widest point on the shell, and also near the balance point. This is not nessessarily the best point from an aerodynamic perspective, at high supersonic speeds the widest point should be far to the rear of the balance point. Another downside is that with increasing shell weight the driving band becomes more difficult to build properly. Instead of the propellant gasses driving the shell up the barrel, it can simply blow the driving band right off the shell.
Gerald Bull worked extensively on ways to eliminate the driving band, leading to the development of his Extended Range, Full Bore ammunition for his GC-45 howitzer, which is now rapidly replacing older artillery world-wide.
The bands and chains are driven from a single motor and the speed of the confronting and adjacent runs of bands and chains must be carefully controlled in order that there is no speed differential between various portions of the bag.
The band sealer is indicated in general by numeral 10 and includes one or more pair of endless heat transfer bands 11 and 12 arranged to have confronting and closely spaced heat transfer runs 11.1 and 12.1 for engaging and transferring sealing heat into and from the bag tops B which are passed therebetween.
The space immediately above the driving wheels is open and unobstructed and the band wheels are driven directly from the conveyor chains, the speed of which is accurately coordinated with the rotary speed of wheels 13 and the linear speed of the bands 11 and 12.