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Decatising or decatizing, also known as crabbing, blowing, and decating, is the process of making permanent a textile finish on a cloth, so that it does not shrink during garment making.[1][2][3] The word comes from the French décatir, which means to remove the cati or finish of the wool. Though used mainly for wool, the term is also applied to processes performed on fabrics of other fibers, such as cotton, linen or polyester. Crabbing and blowing are minor variations on the general process for wool, which is to roll the cloth onto a roller and blow steam through it.
Decatized wool fabric is interleaved with a cotton, polyester/cotton or polyester fabric and rolled up onto a perforated decatizing drum under controlled tension. The fabric is steamed for up to ten minutes and then cooled down by drawing ambient air through the fabric roll. The piece is then reversed and steamed again in order to ensure that an even treatment is achieved.
There are several quite different types of wool decatizing machines including batch decatizing machines, continuous decatizing machines, wet decatising machines and dry decatizing machines.
For egample: In the 1920s, James Bailey textile engineers (Slaithwaite, Yorkshire) developed a successful and efficient means of decatising by essentially putting two blowing machines back to back. These were used by most if not every woollen & worsted finishers in the UK, and became the mainstay of Batch Decaters throughout the mid 20th century. In the early 1950s, They re-patented the Bailey 'Empire blowing, steaming or decatising machine' advertising a new design, better finish, increased output, and less steam consumption. This design sold very well, as they were simply the best built and most effective machines in the world at the time. In the UK, these machines are still used to this day at worsted cloth finishers as Crabbing machines.
Crabbing (sometimes called greasy blowing) is a type of special decatising done mostly to worsted fabrics in the 'grey state', or when they come off the weaving loom. It is the first step in the traditional finishing process of fine worsted cloths in the UK, after the cloth is weighed. The objective of crabbing is to achieve a 'preliminary set' on the cloth before it is scoured/washed in soap. This stabilises the cloth in place during the washing and milling process and can prevent warping of the cloth and distortions occurring.