With coil processing equipment, feeders can generally respond much more quickly than most uncoilers, also known as coil reels. This is due to the fact that uncoilers are responsible for starting and stopping the coil, which has a larger inertial load than the feeder. In some cases, the uncoiler is additionally required to straighten. For an uncoiler to respond as quickly as a feeder does would require a much larger drive as well as the ability to position, as is the case with a combination coil reel/feeder/straightener. This is why most systems have a slack loop.
The purpose of a loop is to provide a reservoir of slack material for the quick-response feed to draw from at start-up, while the slower uncoiler gains velocity to match line speed. And, conversely, a loop allows the straightener to absorb material that is unwound while the coil reel decelerates at a slower rate when the line stops. The loop also allows the coil reel to run at a fairly constant speed during continuous operation, even though the rate of consumption is constantly changing due to the intermittent feed motion.
Types of Configurations
Slack loops can take a variety of forms: