Leather production – from the raw-hide to the leather
Leather production is a complex and complicated refining process. Approximately 40 processing steps have to pass through a hide or skin until the natural raw material has become leather from the biological raw material. A leather that meets the requirements of the processors as well as the diverse and fashionable wishes of the consumers.
In order to convert the perishable raw material into stable, sellable leather, still several weeks are still required despite modern tanning processes. Leather production is an elaborate manufacturing process that requires a great deal of expertise and experience with 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 stored temporarily in cooled rooms.
2 - Soaking
By soaking, the raw material is freed from dirt and preservation salt and retains its original water content.
3 - Liming
The hairs are dissolved from the hides by adding lime and sulphuric compounds. The hide is called pelt after the liming process.
4 – Fleshing and Splitting
During the removal process tissue, meat and fat residues are removed with sharp knife rollers. In order to obtain a uniformly thick grain leather of a certain thickness, the leather is being split. The resulting split leather can be further processed, for example to suede.
5 – Bating, Deliming and Tanning
The liming chemicals in the pelt are neutralized during the deliming through the use of acid and salts. The tanning agents bond chemically with the fiber tissue of the hide during the tanning process. The raw hide has become leather now.
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 is used for the fine adjustment of the leather thickness through knife cylinders.
8 – Neutralization, Filling, Dyeing and Greasing
The acid from the tannic acid is first neutralized. Depending on the type of leather, a filling and dyeing with water-soluble dyes follows. The addition of greases ultimately results in the softness required for the finished leather.
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 under the ceiling
10 – Sorting
The leathers are sorted according to various quality criteria (for example defects, thickness and use).
11 – Milling and Staking
The leather is treated after the drying mechanically in the mill drums or through staking to make it softer so that it is optimally prepared for the finishing operation.
12 – Trimming
This process gives the leather the final characteristics and visual appearance. The wear-and-tear capabilities depend heavily on the quality and the amount of the 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 in all requirements correspond to the leather type or sample template. The leather is also sorted according to different quality characteristics.
14 – Dispatch
The leather is electronically measured, packaged and then dispatched.