Page 16 - MetalForming January 2012

The Basics of Coil Processing, Part 1:
Unwinding the Coil
This is the first article in a series that MetalForming and Coe Press Equipment will present in 2012 on the basics of coil processing.
BY JIM WARD
Modern coil-handling and feeding equipment has dramatically increased the efficiency and through- put of pressrooms around the world, as well as helped to eliminate the dangers and repetitiveness of hand feeding. Metalformers can select from among a variety of coil- feeding methods and types of equipment to accommodate their unique needs. When doing so, they must consider sev- eral parameters to ensure selecting a system that best meets the requirements of the application, including price, oper- ating cost, coil weight, material type and thickness, feed length and speed requirements, material finish, floor-space availability and controls compatibility.
In this series of articles, we will discuss such basic oper- ations as unwinding and straightening the coil, and feeding the press. Along the way we will discuss the various types of equipment used for each process, helping to provide basic guidelines for investing in new coil-processing lines.
The focus of this article: The various approaches to coil unwinding— coil cradles (or coil boxes), centering reels and pallet decoilers. Look for part two later this year, where we will explore straightening options for coil lines.
Coil Cradles
Coil cradles hold a coil by the outside diameter, cradling it on powered rollers called nest rolls. This approach prima- rily finds use in medium- to heavy-gauge applications when material marking is not an issue. The cradle contains the coil
Jim Ward is general sales manager, Coe Press Equipment, Sterling Heights, MI: 586/979-4400; www.cpec.com.
Fig. 1—A combination cradle/straightener unwinds the coil off of the top to a powered straightener and into a horizontal loop. Of the three coil-cradle configurations, this style requires the greatest amount of floor space due to the horizontal loop.
within a box or framework that provides protection for the operator, by preventing the coil from telescoping. The outer wrap is contained between the weight of the coil and the nest roll as it unwinds, helping to prevent clockspring as well as controlling the coil for threading, particularly useful when feeding heavy-gauge or high-strength materials. However, this same feature also can cause problems with thin or cosmet- ically sensitive material, as it tends to mark or distort the sheetmetal.
A rule of thumb: Avoid use of coil cradles for processing material less than 0.06 in. thick.
Another disadvantage of the cradle-style unwinder is that it can operate inefficiently when rewinding and rebanding partially run coils. After running in a cradle for a period of time, the coil tends to clockspring internally and the wraps become loose, making it impossible to re-band into a nice, tight coil. Additionally, coil cannot be rebanded until it is lift- ed off and out of the nest rolls.
Manufacturers offer coil cradles in three basic configu- rations. A combination cradle/straightener (Fig. 1) unwinds the coil off of the top to a powered straightener and into a
14 MetalForming/January 2012
www.metalformingmagazine.com