Denim Manufacturing: Yarn Processes


Process Flow for Denim Manufacturing

 

Warp yarns used in indigo denim fabrics must go through numerous unique processing steps before they are ready to be placed on the weaving machine.

 

If the warp yarns are to be indigo dyed on a long chain or rope range, the yarn is ball warped and then rope dyed, followed by re-beaming onto section beams. The warp yarns are then slashed before being woven.


Yard Numbering

 

Yarns used in denim fabrics are termed “short-staple spun yarns,” because they are formed from fibers having a staple length of less than 2.5 inches. The cotton fiber usually is just over an inch long. One of the key pieces of yarn information for the development and manufacture of denim is the choice of yarn size. The terms “yarn number,” “yarn count,” and “yarn size” are used interchangeably to refer to the linear density of a given yarn.


Yarn Spinning Systems

 

The two most common spinning systems used to produce yarns for denim fabrics are ring spinning and open-end rotor spinning.


Warping

 

“Warping” is the process of transferring multiple yarns, each on a separate yarn package, onto a single collecting package.


Dyeing

 

Most denim fabric is yarn-dyed; the warp yarns are dyed with indigo, and the filling yarns are left undyed.

 

However, solid shades are becoming more popular and can be dyed by various methods.


Slashing

 

The main purpose of sizing warp yarns is to encapsulate the yarn with a protective coating. This protective coating reduces yarn abrasion during weaving. The size also reduces yarn hairiness, preventing adjacent yarns from becoming entangled. For many years, native or slightly modified starches with corresponding binders were regarded as the most economical size for indigo warps.

The change to garment-washed denim led to the development of new sizing recipes.  The type and quantity of size used depend on what finishing operations will be used and whether the product is loomstate or mill-finished denim.