Texts on specialities
Processes in leather manufacture
New words and word-combinations to be remembered:
adipose tissue жирова тканина
tannage, tanning дублення
tannery шкіряний завод
green-salted skins мокро-засолені шкури
hide велика шкіра
pelt шкіра, сировина
drenching киселювання (м’якшиння в киселі)
buffing шліфування, полірування, пушення
seasoning глянцювання, лакування, апретування
The first stage in leather manufacture comprises those operations which remove the epidermis and hair (or wool) and which render the adipose tissue so swollen that it is easily removed by fleshing. The second stage is the tannage of the corium by permeating it with a tanning agent or material to render it proof against putrefaction. The final or third stage consists of finishing, currying, dyeing or dressing, etc.
The processes that precede the actual tanning or conversion of hides and skins into leather are: washing, cleaning, fleshing, splitting, soaking, unhairing, do-liming, bating, puering, drenching, pickling.
As hides and skins are brought to the tannery in cured condition (green-salted, dry-salted and dried), the object of all these processes is to bring the hides and skins to the natural soft condition it is in when removed from animal and in addition to remove blood, dirt, salt.
At the tannery skins and hides are properly washed and cleaned in large washing machines. To remove the excess flesh and fat from the skins tanners use fleshing machine. Next operation is soaking. The object of the soaking process is to soften the hides and skins and to remove the salt dung, blood and dirt adhering to them.
The skins and hides are soaked in a lime solution to loosen the hair and epidermis so that it can be easily removed by the machine. Lime used for unhairing must be as free as possible from impurities. The period of liming has a marked influence on the finished product.
Limed hides and skins contain some lime which would interfere with the tanning process so it is advisable to remove it from the surface layers of the pelt.
Ordinary de-liming may be accomplished by weak organic acids or certain chemicals, while bating, puering and drenching, all of which tend to produce soft leather, must be brought about through fermentative, bacterial or enzyme action.
After drenching of sheep, goat pelts and of bated calf and light hide pelts, they are usually pickled with salt and sulphuric acid. Sheep-skin pelts are pickled to preserve them.
The series of processes by which the natural skins are converted into leather is covered by the term «tanning». The purpose of tanning is to convert raw hides and skins into leather, to render the hide imputresci-bility, that is resistant to putrefectiom.
Hides and skins tanned absorb certain properties of the agents with which they are tanned.
There are several methods of tanning, each producing special type of leather with special characteristics: vegetable, chrome, oil, alum, formaldehyde, synthetic, zirconium and combination tanning.
The finishing processes that follow tanning are numerous and of great importance in converting a harsh, stiff material into the beautiful finished leather.
They are: setting-out, drying, stuffing, currying, staking, fat-liquoring, buffing, seasoning, rolling, glazing, polishing, ironing, embossing, dressing, dyeing, etc,
These final operations are numerous and depend in large part upon the type of finished leather required.
I. Answer the following questions:
1. What are the main stages in leather manufacture?
2. What are the processes that precede the actual tanning?
3. What is the object of soaking, fleshing, liming, unhairing?
4. What is the chief purpose of tanning?
5. What finishing processes do you know?
II. Speak on the processes in leather manufacture using the following word-combinations:
— three stages in leather manufacture;
— the processes that precede the actual tanning: washing, cleaning, fleshing, soaking, unhairing, etc.;
— the purpose of tanning, the methods of tanning;
— the finishing processes that follow tanning;
— to depend upon the type of finished leather required.