Kanpur has always been famous for its leather manufacture process. There was a lot of demand for leather at Kanpur even before the establishment of factories. Leather was manufactured by local village craftsmen and the cottage industry used to meet their demands. The goods were made from buffalo and processed by several technologies and steps.
Leather: a material made from the hide of an animal by tanning or similar process. Leather is a prominent industry in India and has a large demand in fashion, footwear, furniture, interior, automotive industry.
In India, the leather is prepared from the raw hides of different animals like buffalo, goat, cow, and sheep. The process involves various processes.
Leather manufacture process
More than 15% of India’s exports of leather and leather products comes from the city of Kanpur. The land and the rivers are often polluted by the biproducts of the leather processing. The UNIDO, launched the Kanpur leather development project in 2015 along with the Government of India. The objective was to generate awareness about cleaner tanning technologies and to create a better working environment.
The Leather manufacturing is a big procedure which uses many chemicals and mechanical operations.
The steps manufacture process are as follows:
The hides are removed immediately after the cow is killed, and salted to prevent decay. 55% of water in the hide is removed after salting. The animal skin is then dried for 3 to 6 days. The raw hides are then sold to tanneries.
The dry salted hides are washed and the salt is removed to have a proper tanning process. The hides are soaked in water and chemical agents(similar to household detergent) and disinfectants are added for 8 to 20 hours, it depends on the thickness of the hides. This procedure removes the dirt from the hides.
They have to undergo hair removal as these Leather materials are made from animal hides. Hair shaving machines are nowadays used to avoid hairs getting chemically dissolved into the rivers. The hair is separated by machines and can then be used as fertilizers on farms.
The fleshing machine removes all excess flesh, fat, muscles from the hides.
The hides are made free of all the chemicals. The hides are washed in ammonium sulfate or ammonium chloride and clear water in big drums. These chemicals not only clean the existing chemicals but also adjust the acid-alkaline to the proper point for receiving the bate. It destroys most of the remaining unwanted constituents of the hide.
The leather needs to be made ready to accept tanning material. The hides must be kept in low ph, because chrome tanning agents are not soluble under alkaline conditions. Salt and acid are added to the hides. This process can keeps the hides in proper condition and for long period of time without rotting.
These hides are then added to a big revolving drum in which chrome tanning agents are added. These are thus converted from raw hides to stable products. The hide’s dimensional stability can be improved by these tanning agents along with its abrasion resistance, resistance to chemicals and heat, the ability to flex without breaking, and the ability of repeated cycles of wetting and drying.
The hides are then placed through two large rollers to remove the rest of the moisture from them.
The hides are then split into their desired thickness. The average thickness is generally around 5mm. The thickness of the hides varies according to the product needed. The hides are put through the splitting machine and cut according to the desired thickness. The splitting cuts the top grain first and then another layer and sometimes two. These layers are called splits.
The thickness of the hide should be uniform allover. It is done using the shaving machine. Hides are run through it. The cutting blade is hellical in shape. This makes the hide better for chemical processing.
Leather Re-tanning process:
This is done to understand the special end-use properties with other tanning chemicals. The solidity is added in the leather, variations are reduced in the characteristics of leather that existed with the help of retaining substances.
Leather Coloring process
The tanning process is followed by the coloring process of the hides. Aniline dyes (that are obtained directly from petroleum)and hot water, are added to rotating drums and the hides are colored according to the desired color.
The hide is then dipped into a wet chemical solution, this softens the hide and thus increases the leather’s tensile strength.
This process removes excess moisture. The hides are stretched and squeezed. This prepares the leather for proper drying conditions.
The hides are then stretched in a frame and clipped, these clippers are called toggles. One hide is taken and each side of the frame is clipped and slid into a drying oven.
This leather manufacture process makes the leather very flexible. Staking is the final process to increase the firmness or softness of the leather.
The hides is then dipped in a large dry drum and rolled into it. It is then collapsed to get the desired softness.
The final appearance of the hide is improved by removing the scratches, healed scars, etc. Sanding is done on the surface of the hides. The hide gets better.
Finishing of Leather manufacture process
Layers are added if required in this process. This process also adds some film-forming material coating, as well as a protective coating.
Leather Plating process:
The hides are passed passed through heated surface. This is the final step in leather manufacture process.