Coil Processing – Metal Forming ABCs

The fabrication and metal manufacturing world can be difficult to understand if you’re not a veteran on shop floor. Not only that, but when you want to look something up, clear explanations can be hard to come by. That’s why we’re starting up a blog series on metal forming terminology – a handy ABC dictionary for any metal forming professional to refer to. Whether you’re looking for answers or testing your knowledge, find the answers here!

This week’s post…

Coil Processing

  • Accumulator – A device that stores materials in a defined amount so a new coil can be installed and then welded to the old coil, ensuring a non-interrupted material flow to the roll forming machine.
  • Center Buckle – Occurs when the center of the material is longer than the edges. Can only be corrected by a leveler.

center buckle coil

  • Coil – A length of steel wound into coil form. Typically 16-20″ ID x 60-72″ OD.
Steel coil

Steel coil

  • Coil breaks (crossbreak) – Coil breaks are a defective condition composed of ridges or marks across the width of sheet or coil caused by improper coiling or leveling. Creases or ridges which appear as parallel lines, transverse to the direction of rolling, and which generally extend across the width of the sheet. A discontinuous curvature in the strip in the direction in which the material was rolled or uncoiled hot rolled strip.
  • Coil Set – A lengthwise curve or set found in coiled strip metals following its coil pattern. A departure from longitudinal flatness, it can be removed by roller or stretcher leveling from metals in the softer temper ranges.
    coil set

    Coil Set

  • Coiling – Coiling is the process of winding flat material while it is still hot. As it exits the extrusion rollers at the mill immediately after it has been formed.
  • Coils – Sheet metal rolled from slab or ingot that has been wound into coiled roll. Coils are considered the most efficient way to store and transport sheet metal. Master coils are produced at the mill and slit coils are converted from the master coils in narrower
    widths through the slitting process.
  • Cold reduction mill – Sheet and strip are cold reduced to the desired thickness for the following reasons:
    1. To obtain the desired surface.
    2. To impart desired mechanical properties.
    3. To make gauges lighter than the hot strip mill can produce economically.
    4. To produce sheet and strip of more uniform thickness.
  • Cold rolled base – Coils that are cold worked or reduced to gauge on the tandem mill.
  • Cold rolling – Term applied to the operation of passing unheated metal through rolls for the purpose of reducing its gauge.
  • Cold rolling mill – A mill that reduces the cross sectional area of the metal by rolling at approximately room temperature.
  • Cold strip mill – A mill that rolls strip without first reheating.
  • Cold work – Plastic deformation at such temperatures and rates that substantial increases occur in the strength and hardness of the metal. Visible structural changes include changes in grain shape and, in some instances, mechanical twinning or banding.
  • Crossbow – A bow in the underside of the coil sheet, i.e. when the bottom side of the coil is shorter than the top side. The crossbow increases from each side as you reach the center. Can be corrected using a precision straightener or leveler.


  • Crown – When the coil sheet is thicker at the center than at the edges.

crown coil

  • Cut-to-length – Process to uncoil sections of flat-rolled steel and cut them into a desired length. Cut-to-length product is normally shipped flat-stacked.
  • Edge Wave – When the edges of the coil are longer than the center, resulting in a wave-like appearance to the edge of the sheet. Can be corrected/removed by leveler equipment.

edge wave coil

  • Sheet – A wide, but thin (down to .05″), flat rolled metal mass in widths typically provided in widths from 24″ to 80″. It can be sold either in cut-to-length pieces or rolled into large, heavy coils.
  • Slit Edges – The edges of sheet or strip metal resulting from cutting to width by rotary  slitters.

Slitting unit

  • Slitting 
    1. The process of taking the wide rolls or sheets provided by the mills and cutting them down to narrower width strips or rolls by service centers to meet the needs of their customers, such as roll formers.
    2. Cutting or shearing along single lines to cut strips from a sheet or to cut along lines of a given length or contour in a sheet or workpiece.
    3. Cutting sheet or strip metal to width by rotary slitters.
  • Uncoiler – A device that supports the coil while allowing the material to be fed into the roll forming machine without causing extreme drag and overrun.
high speed uncoiler with hold downs

Uncoiler device


Related Posts

Commenting area

  1. Thanks for sharing the information about Coil Processing and terms like -Cut-to-length Cold rolled base, which are used in this process in detail.

Comments are now closed for this article.