The art of tanning is one of the oldest craftman’s trades of mankind. Out of these handicraft businesses developed worldwide acting enterprises during the industrialization. Heller Leder was founded in the early 20th century in Hehlen at the river Weser.
Pull the cursor along the timeline from “then” to “today” and learn more about important events in the company tradition which made Heller-Leder to what we are today. The tanning industry calls hides and skins customarily the raw-hides. They contain three different layers: epidermis, corium and subcutis. Only the corium can be used for the leather production. The corium is composed mainly of structured proteins. Hides are delivered salt-cured or fresh. The advantage of the salt-cured preservation is the good stock-ability. Fresh hides, however, need to be put into work immediately, but avoid chlorides, i.e. salt in the waste water. The natural condition of the hide is restored through the soaking operation, in other words,the loss of water during the preservation is compensated again and the raw hides are cleaned from dung and blood rests, or the like. The hairs and non-leather providing collagens are dissolved from the hides by adding lime and sulphur compounds during liming and activated tanning groups are built. The hide is called pelt after the liming process. The remaining tissue, flesh and fat is removed by rotating cylinders knives. This generates the so-called lime-leather which is used among others as a resource for the generation of bio-gas. The pelt is split horizontally into two layers in order to achieve an evenly thick full-grain of a defined thickness. The split-leather and the flesh-split are produced this way. The liming chemicals in the pelt are neutralized during the deliming through the use of acidic reacting salts and/or weak organic as well as inorganic acids or with carbon dioxides. The fiber tissue of the pelt is cleaned by enzymes from scud and opened-up. The tanning agents bond chemically with the fiber tissue of the hide during the tanning process and cross-link the fibers as a result. The hides is thereby modify in a way so that they remain permanently flexible, i.e. neither rots nor parches in heat. The raw hide became in this way leather. The chrome tannage, applied since the 1960s, has including the combined tanning procedures today worldwide with appr. 85% share the main importance, as a leather type can be produced with this process that can be refined for most of the characteristics the market is requiring. Only complex-forming salts of the trivalent chromium have a tanning effect. Further, tanning processes with glutardialdehyde, vegetable tanning agents, fats or aluminum salts have also a larger importance. The wet leathers are drained by the sammying process and thereby prepared for the next steps like sorting and shaving. Chrome or chrome free tanned leathers are either sold as wet-blue or wet-white or processed further in the tannery’s next departments dye-house and finishing to finished leathers. 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. The final character of the leather is determined by neutralization, dyeing and stuffing according to the intended use and the relevant fashion. These processes happen in one go in this compact process. Further characteristics like the filling, softness and grain firmness are here especially important, next to measurable physical properties. Applied are re-tanning agents, dye-stuff and fatting agents of various kinds. 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 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. There exists the further possibility to buff the grain side in order to produce e.g. the leather type Nubuk. This process gives the leather the final characteristics and visual appearance. For more information contact Mrs Suzanne Zervos, office and Management Assistance.