Wool milling

W00L MILLING

 Milling is an essential process for woollen material. It is otherwise known as Felting. The ability to Felt is the characteristic feature of wool. The felting property is used in the finishing process to alter the appearance, body, elasticity and the strength of the wollen fabric.

Different types of wool vary in their ability to felt and this depends on length, fineness, scaliness, waviness etc.

The object of Milling is to make the fabric fuller and denser as a result of which the woven pattern becomes more or less obscure. Both dyed and undyed fabrics are milled. The milled cloth is suitable for producing a raised finishing

Classification of milling

Milling is classified into two types;

(1) Acid milling and

(2) Alkaline milling (including soap milling)


Both are carried out in stock or in rotary milling machine The three essential requirements for felting to occur are;

1) Moisture,

2) Heat and

3) Pressure.

ALKALINE MILLING

This may be carried ont with soap and soda ash or with allkali alone. For best results, the following conditions may be used.

        Sodium Carbonate 6-7 Tw

        pH 9 to 11

        Temperature 88°C

 This is suitable for unsecured wool of low quality It is not suitable for fine fabrics.

ADVANTAGE OF ALKANIL MILLING 

Both scouring and milling is carried out in one operation There is a 30% saving of cost compared to soap milling

SOAP MILLING

It is a very widely used method For the process, the following conditions may be used;


    Soap solution 8 10 % strength

    2.5 gallons is sufficient for 100kg of cloth.

   Temperature 40°C

After milling, the material is given a short and warm wash to remove all! Traces of soap.

ADVANTAGE

1. Softer cloths are milled with less risk of damage.

2. No previous scouring is necessary.

DISADVANTAG

1. It is a slightly a costlier process.

ACID MILLING

Sulphuric acid is the best milling agent.

Sulphuric cid  0.2 – 0.5%

pH - 2

Temperature 45°C

But the 0.2 - 0.5% sulphuric acid is diluted with 2 lbs of dark oil Vitriol for every 100 ibs of cloth. After milling, the febrile Should he washed thoroughly

ADVANTAGE

This method is used for even very stronger fabrics Always employed for colored woven goods due to less bleeding of color. This method is useful to mill cross breed wool which is difficult to mill with soap solution

DISADVANTAGE

It is suitable only for Animal fibres since it destroys the cellulosic fibres. It produces unwanted Harshness. Before milling, it should be thoroughly scoured to remove any traces of soap, as the soap precipitates the acid. Normally Rotary Milling machine is preferred for milling processes.