THE TANNING PROCESS
Rawhides
· Hides are about 70% water and become hard and inflexible after drying.
· They can be easily attacked by bacteria and rot if not kept refrigerated or the water content removed
· Hides are contaminated and dirty with blood, dung, hair etc.
Leather for automotive interiors should be:
· Dry, flexible and stable
· They should have colour, softness and durabilityTanning makes the leather resistant to bacteria. Chrome tanning is the most popular method. The modern leather processing can be divided into three parts:
1. Preparation of wet blue.
2. Modification of the properties as needed in the final leather.
3. Finishing on the surface.
The processes in 1 and 2 are usually done inside drums in water. A few operations are carried out in special machines on individual hides/skins
Preparation of wet blue
Hides are washed with water and special detergents. This is known as Soaking. Hides are scrapped of any loose flesh. This is known as Fleshing. Hair is removed from the hide using special chemicals
The chemicals used in tanning modify the colour, softness and other properties. The fibre network should be opened up and most other non-fibrous material removed. This is done in Liming. This requires a special soaking which uses lime to increase the water entering the fibre network. Natural grease is also removed.