Leather production – from the raw-hide to the leather
Leather production is a complex and complicated refining process. Each hide or skin has to pass approximately 40 processing steps until the raw material has become the natural product leather. A leather which meets the requirements of the processors as well as the consumers diverse and fashion orientated desires.
In order to convert the perishable raw material into stable long lasting, sellable leather, several weeks are still required despite modern tanning processes. Leather production is an elaborate manufacturing process which requires a great deal of expertise and experience of the tanner.
The manufacturing process is shown in simplified form below.
1 - Storage and Sorting
The raw-hides are delivered and then either immediately processed or temporarily stored in cool rooms.
2 - Soaking
By soaking, the raw material is freed from dirt and preservation salt and regains its original water content.
3 - Liming
The hairs are released from the hides by adding lime and sulphuric compounds. After liming the hide is called pelt.
4 – Fleshing and Splitting
During the fleshing process tissue, meat and fat residues are removed with sharp knife rollers. In order to obtain an evenly thick grain leather, the hide is being split. The left over split leather can be further processed to suede, for example.
5 – Bating, Deliming and Tanning
The liming chemicals in the pelt are neutralized during the deliming process by use of acid and salts. The tanning agents bond chemically with the hides fiber tissue during the tanning process. The raw hide has now become leather.
6 – Sammying
The wet leathers are drained by the sammying process.
7 – Shaving
The leather thickness is “roughly” pre-defined by the splitting process, shaving whit knife cylinders are then used for the fine adjustment of the leather thickness.
8 – Neutralization, Filling, Dyeing and Greasing
First the tanning acid is neutralized. Depending on the type of leather, a filling and dyeing with water-soluble dyes follows. By addition of greases the required softness of the finished leather is achieved.
9 – Drying
The following methods are used to dry the leather:
- drying by vacuum, where the boiling point of the water is lowered by the vacuum, this happens on heated plates
- chamber toggle drying, where the leathers are toggled onto a straining frame and run through a drying chamber
- suspension drying, where the leathers are air-dried hanging under the ceiling
10 – Sorting
The leathers are sorted according to various quality criteria (for example defects, thickness and disposition).
11 – Milling and Staking
After the drying process the leather is softened by mechanically treatment either in mill drums or by staking to prepare it for the further processes of finishing.
12 – Finishing
This finishing surface treatment gives the leather its final characteristics and visual appearance. The wear-and-tear capabilities depend heavily on the quality and the amount of pigments, binders and varnishes. The design of the leather can also be changed by the various embossing patterns.
The art of finishing lies in the application of very thin layers without affecting the visual appearance and the favourable characteristics like suppleness and breathability. This happens by the spray-finish.
13 – Checkup
Quality is tested repeatedly between all workflows. The final inspection ensures that the individual production parts correspond to the leather type or sample template in all requirements. The leather is also sorted according to different quality characteristics.
14 – Dispatch
The leather is electronically measured, packaged and then dispatched.