It gives you all about leather processing. Leather tanning is completely decribe in this slide. What is Leathe, its manufacturing process and all about leather tanning is decribe in this slide. It will help u a lot. It's process management. The Raw material we need in leather manufacturing process is used in it.

1. Leather Processing & Tanning

2. What is leather?
• It is a durable and flexible material created via the tanning of
putrescible animal raw
• hide and skin, primarily cattle hide.
• It is animal skin that has been processed to retain its flexibility,
toughness, and waterproof nature.

3. Leather Manufacturing Process
• The leather manufacturing process is divided into three sub-
processes: preparatory stages, tanning and crusting. All true leathers
will undergo these sub-processes. A further sub-process, surface
coating may be added into the sequence. The list of operations that
leathers undergo vary with the type of leather.

4. Production management
• The leather making process is in general restricted to batch
processing, but if the surface coating sub-process is added then some
continuous processing can be included. The operation flow has to
follow the preparatory → tanning → crusting → surface coating sub-
process order without deviation, but some of the sub-processes can
be omitted to make certain leathers (or partially tanned/ untanned
products).

5. RAW MATERIALS
• – from cows, pigs, goats, and sheep;
• – exotic animals such as alligators, ostriches, and kangaroos
• TANNING MATERIALS
• Vegetable - extracts from the bark and wood of trees (oak, wattle
etc.).
• Mineral - in the main, trivalent chromium sulphate.

6. Preparatory stages
• The preparatory stages are when the hide/skin is prepared for tanning.
During the preparatory stages many of the unwanted raw skin components
are removed. Many options for pretreatment of the skin exist. Not all of
the options may be performed. Preparatory stages may include
- the hide/skin is treated with a method which renders it
temporarily imputrescible.
- water for purposes of washing or rehydration is reintroduced.
- unwanted proteins and "opening up" is achieved.

7. - the majority of hair is removed.
- subcutaneous material is removed.
- the hide/skin is cut into two or more horizontal layers.
- the hide/skin is further treated to achieve more "opening up"
or more protein removal.
- liming and unhairing chemicals are removed from the pelt.
- proteolytic proteins are introduced to the skin to remove further
proteins and to assist with softening of the pelt.
- natural fats/oils are stripped or as much as is possible from
the hide/skin.[4]
- physical removal of the fat layer inside the skin.[5] Also similar
to Slicking.

8. - chemical modification of dark pigments to yield a lighter
coloured pelt.
- lowering of the pH value to the acidic region. Must be done
in the presence of salts. Pickling is normally done to help with the
penetration of certain tanning agents, e.g., chromium (and other
metals), aldehydic and some polymeric tanning agents
- raising of the pH out of the acidic region to assist with
penetration of certain tanning agents

9. What is tanning?
• Leather is made from animal skins or hides which have been
chemically treated to preserve quality and natural beauty. The
chemical procedure used to ready raw animal hides for use is called
"tanning." A piece of hide or skin which has been tanned produces a
strong, flexible leather which is able to resist decay and spoilage.

10. Step 1: Soaking
• Hides are re-hydrated or re-soaked and
washed in large rotating drums

11. Step 2: Hair Removal
• •Hair is removed by chemical digestion
• Lime and sodium sulphide solution
• Hairless hides are then neutralized with acids and treated with
enzymes
• – Removes deposits
• – Increases softness

12. Step 3: Deliming
• Hairless hides are then neutralized with acids and treated
with enzymes
• – Removes deposits
• – Increases softness

13. Step 4: Pickling
• •Hides are soaked in a solution of water, salt,
• and hydrochloric (or sulphuric) acid

14. Step 5: Tanning
• Tanning
• Two main methods: Chrome and Vegetable
• Chrome is more common
• Vegetable tanning produces stiffer leathers;
• chrome tanning produces softer leather

15. Step 5: Chrome Tanning
• Most upholstery, shoes, garments, bags
• Hides placed in rotating drums and washed in a chemical containing
trivalent chrome
• After 8 hours, the chrome is “fixed” with an alkaline chemical (sodium
carbonate)

16. Step 5: Vegetable Tanning
• Used on shoe soles, luggage, belts, and some
upholstery
• Slower, 2-4 days
• Uses tannic acid, which is extracted from tree bark

17. Step 6: Dyeing
•Placed in rotating drums with hot water, dyes, and
synthetic tanning materials to obtain desired color

18. Step 6: Rolling
• Rolled through a machine to
make stronger
• Dried by hanging or dry tumbling

19. Step 7: Finishing
• Finished with coatings of
acrylic, urethane, vinyl, wax,
nitrocellulse, dye, or other
materials.

20. Environmental Impact
• Air pollution
• ammonia gas, hydrosulphuric gas and volatile organic compounds
• Water contamination
• residual baths for hide treatment and washings containing chemical
products
• Contamination of the soil
• flesh, hairs, hide chippings and scrapings
• Large amount of water consumption
• Chrome has high level of contamination

21. Ways to Reduce
• Reuse water
• Recover and reuse chrome*
• New process- improved chrome syntan with more than 90% uptake of
chrome
• Use ammonia-free deliming
• Use less salt (although will decrease “shelf-life”)