Leather (Hide or Skin) Manufacturing Processes

Leather Manufacturing Processes
Presented By:
Engr. S. M. Murshidur Rahman

Leather
Leather is one kind of protein which is called collagen. The collagen is obtained from animal hides and skins,
which is turned as leather by the process of tanning.
Hide
The outer coverings of large animals are called ‘‘hides’’’. They are large in size, thicker in substance and heavier
in weight. Example: Buffalo, Cow, horse etc. Wet salted cow below 7 kg weight is called calves, between 7 to 12
kg is called kips and above 12 kg is called hide.
Skin
The outer coverings of small animals are called ‘‘skins’’. They are small in size, thinner in substance and lighter
in weight. Example: Goat, Sheep, Deer etc.
The outer covering of wild animals is also called skins like tiger, lion etc.
Raw materials

Different Sections of Hides and Skins
No. Region Parts of Region % based on whole surface area
01 Butt or bend Shell, back and butt edge 45-50
02 Neck Shoulder, head and face 20-25
03 Flank/Belly Belly, fore shank and hind shank 20-25

Parts of a hide/Skin

Leather making processes
Raw hide/skin process according to operations:
1. Wet blue: Up to beamhouse operation.
2. Crust: Before to finishing. After post-tanning operations.
3. Finishing: Apply finishing coat to give desired characteristics and appearance.

Leather making processes
According to processes:
a. Beamhouse Operations:
1. Sorting
2. Trimming
3. Curing & Storing
4. Soaking
5. Unhairing and Liming
6. Painting and Liming
7. Fleshing
8. Splitting
b. Tanyard Operations:
1. Washing
2. Deliming
3. Bating
4. Degreasing
5. Pickling
6. Tanning
7. Basification
8. Samming and setting
9. Splitting
10. Shaving
c. Post-Tanning Operations:
1. Neutralization
2. Bleaching
3. Re-tanning
4. Dyeing
5. Fatliqouring
6. Drying
d. Finishing:
1. Mechanical Process
2. Applying a surface
coat
Note: All of above processes are not required for all types of leather. It depends on some factors such as uses of
finished leather, defects of leather, purposes, customer requirements, types of hide/skin etc.

Beamhouse operations
Beamhouse operations are the steps leather must go through before being cured and tanned. The Beamhouse
process is made up of several steps. The aim of this part of the task is to clean the hide, removing all hair and
dirt.
The processes in leather manufacture that take place following curing and preceding the actual tannage of the
skin. These processes include some or all of the following: curing, soaking, unhairing and liming, scudding,
fleshing, deliming, bating, degreasing, pickling, tanning not necessarily always in the order given. The skin
may also be split before tanning. The principal objectives of beamhouse operations are to rid the stock of
substances not wanted in the finished leather, notably the class of proteins known as keratin, and to put the
skins into the proper chemical and physical condition for subsequent processing. To produce satisfactory
leather, beamhouse operations must be carried out in such a manner that no damage is done to the fibrous
(collagen) part of the skin that is converted into leather, nor to its internal structure. The term derives from
the "beam," a convex wooden slab sloping upward from the floor, over which the raw stock is placed for
trimming, fleshing, unhairing, or scudding by hand.

1. Sorting: On receipt, hides and skins may be sorted into several grades by size, weight, or quality. Hides are
also sorted by sex. Hides and skins are generally stored as they are received by the tannery on pallets in
ventilated or air conditioned and/or cooled areas, depending on the method of curing chosen. From storage
the hides and skins are taken to the beamhouse.
2. Trimming: Trimming is generally carried out during the sorting process. Some of the edges (legs, tails, face,
udders, etc.) of the raw hides and skins can be cut off. Usually this process step is done in the abattoir, but it
can also be carried out in tanneries.

3. Curing: Curing is a process that prevents the degradation of hides and skins from the time they are flayed
in the abattoir until the processes in the beamhouse are started. When the raw material cannot be
processed immediately ("green"), it must be cured.
The methods for curing for long-term preservation (six months) are: salting, brining, drying and salt drying.
Methods for short-term preservation (2 - 5 days) are cooling, using crushed ice or refrigerated storage, and
biocides.
Curing is done in the abattoir, at the hide market, or at the tannery. In certain cases it might be necessary to
repeat the step in the tannery, e.g. if chilled hides are salted for longer storage or salting was not efficient
enough.

4. Soaking: Soaking is carried out to allow hides and skins to re-absorb any water which may have been lost
after flaying, to clean the hides and skins (removal of dung, blood, dirt etc.), and to remove interfibrillary
material.
The soaking methods depend on the state of the hides. The process is mostly carried out in two steps: a dirt
soak to remove the salt and dirt and a main soak. The process is carried out in processing vessels, such as
mixers, drums, paddles, pits, or raceways. Raceways and pits are more commonly used for the processing of
sheepskins. The duration of soaking may range from several hours to a few days.
Depending on the type of raw materials used, soaking additives can be used such as surfactants, enzyme
preparations and bactericides.

5. Unhairing and liming: The function of liming and unhairing is to remove hair, interfibrillary
components and epidermis and to open up the fibre structure.
Hair removal is performed by chemical and mechanical means. The keratinous material (hair, hair roots,
epidermis) and fat are eliminated from the pelts mainly with sulphides (NaHS or Na2S) and lime. Alternatives
to inorganic sulphides include organic compounds such as mercaptans or sodium thioglycolate in
combination with strong alkali and amino compounds. Enzymatic preparations are sometimes added to
improve the performance of the process.
The process of liming and unhairing can be carried out in process vessels such as drums, paddles, mixers, or
pits.

6. Painting and liming of sheep skins: The aim of painting is to bring about the breakdown of the wool
root within the skin so that as much undamaged wool fibre as possible can be pulled easily from the pelt.
Paint, generally consisting of a mixture of sodium sulphide and lime, is applied to the flesh side of the skin
and left for several hours. Enzymes is also used for unhairing. Application of the paint can be through a
spraying machine or manually. After several hours the wool can be ‘pulled’ from the skin, either manually or
mechanically. After pulling, the skins are limed in process vessels, with the same purpose as the liming of
bovine hides. Wool-on skins are not painted, unhaired or limed. Specially this process is done to save
hair/wool before liming process.

7. Fleshing: Fleshing is a mechanical scraping off of the excessive organic material from the hide (connective
tissue, fat, etc.). The pelts are carried through rollers and across rotating spiral blades by the fleshing machine.
Fleshing can be carried out prior to soaking, after soaking, after liming or after pickling. The process of fleshing
is called green-fleshing if the removal is done prior to liming and unhairing. If fleshing is performed after the
liming and unhairing it is called lime-fleshing. Sheepskins may be fleshed in the pickled state.
To see video visit: https://www.youtube.com/watch?v=ltFFcZ9-gUs

8. Splitting: By mechanical splitting the thickness of hides and skins is regulated and they are split
horizontally into a grain layer and, if the hide is thick enough, a flesh layer. Splitting is carried out on splitting
machines, fitted with a band knife. Splitting can be done in limed condition or in the tanned condition.

To see leather manufacturing process video: https://www.youtube.com/watch?v=cUu3EXORw0M
https://www.youtube.com/watch?v=xKWK5rDeJlA
For more video visit: https://www.youtube.com/playlist?list=PLtkxsvTf9L6FT1fZvEtLxAnaVP0-eBwBq
https://www.youtube.com/c/MurshidurRahman
To get slide visit: https://www.slideshare.net/Murshidur_Rahman/leather-processingpptx

Tanyard operations
1. Washing: Th aim of washing is to remove excessive lime from pelt.
2. Deliming: The aim of deliming is to remove residual lime from the pelts and to take the pelts to the
optimum condition for bating. This involves a gradual lowering of the pH (by means of washing and addition of
deliming chemicals), an increase in temperature and the removal of residual chemicals and degraded skin
component.
Generally, deliming is performed in a processing vessel such as a drum, mixer or paddle.

3. Bating: Bating is a partial degradation of non-collagenic protein achieved by enzymes to improve grain of
hide and the subsequent run and stretch of leather. In this process the rest of the unwanted hair roots and scud
can be removed.
Tanyard operations

4. Degreasing: Excess grease must be eliminated from fatty skins (sheep, pig) to prevent the formation of
insoluble chrome-soaps or prevent the formation of fat spues at a later stage. Degreasing is most relevant in
processing sheepskins, where the natural fat content is about 10 % - 20 % on dry weight. The nature of this
fat makes it difficult to remove because of the presence of cerides and a high melting temperature.
The three different methods commonly used for degreasing are:
a. degreasing in aqueous medium with organic solvent and non-ionic surfactant
b. degreasing in aqueous medium with non-ionic surfactant
c. degreasing in solvent medium.
Tanyard operations

5. Pickling: Pickling is carried out to reduce the pH of the pelt prior to mineral tanning and some organic
tannages (e.g. chrome tanning, glutardialdehyde tanning, vegetable tanning).
The choice of the exact pickling parameters depends on the subsequent tanning step.
Very often tanning is carried out in the pickle liquor; however, pickled pelts, e.g. sheepskins, can be traded.
Pickeled pelt sheepskins must contain fungicides to protect them from mould growth during storage.
Tanyard operations

7. Tanning: In the tanning process the collagen fibre is stabilised by the tanning agents such that the hide is no
longer susceptible to putrefaction or rotting. In this process, the collagen fibres are stabilized by the cross-
linking action of the tanning agents. Furthermore, their dimension stability, resistance to mechanical action
and heat increase.
The various agents can be categorized in three main groups:
• mineral tannages
• vegetable tannins
• alternative tanning agents, which can be subdivided into
– syntans
– aldehydes
– oil tannage
Chromium and vegetable tanning agents are the most commonly used tanning agents.
Tanyard operations

8. Basification: This basification process fixes the tanning material to the leather, and the more tanning
material fixed, the higher the hydrothermal stability and increased shrinkage temperature resistance of the
leather. The pH of the leather when chrome tanned would typically finish somewhere between 3.8 and 4.2.
Tanyard operations

9. Samming and setting: After tanning, the leathers are drained, rinsed and either horsed up to age
(Basification process), or unloaded in boxes and subsequently sammed to reduce the moisture content prior
to further mechanical action, such as splitting and shaving.
The setting out operation can be carried out to stretch out the leather. Machines exist which combine the
samming and setting action.
After samming and setting, hides and skins can be sorted into different grades after which they are processed
further or sold on the market.
Tanyard operations
To see video visit: https://www.youtube.com/watch?v=-tATfiXn-48

10. Splitting: The function of the splitting operation is to cut through skins or hides at a set thickness. If the
hide/skin is thick enough splitting can yield a grain split and a flesh split which can both be processed into
finished leather. Splitting can be performed before tanning, after tanning or after drying.
Tanyard operations
To see video visit: https://www.youtube.com/watch?v=UH56-GPHmfk

11. Shaving: The shaving process is carried out to achieve an even thickness throughout the skin/hide, and it
can be carried out on tanned or crusted leather. Shaving is carried out where splitting is not possible or where
minor adjustments to the thickness are required.
Tanyard operations
To video visit: https://www.youtube.com/watch?v=aUtG76rScv8

Post-tanning operations
Post-tanning involves neutralization and washing, followed by re-tanning, dyeing and fatliquoring, mostly
done in a single processing vessel. At this stage of the process, specialist operations may also be carried out to
add certain properties to the leather such as water repellence or resistance, oleophobing, gas permeability,
flame retarding, abrasion, anti-electrostatics.
1. Neutralization: Neutralization is the process by which the tanned hides are brought to a pH suitable for the
process of re-tanning, dyeing and fatliquoring.

2. Bleaching: Vegetable tanned skins and leathers with wool or hair may need to be bleached in order to
remove stains, or to reduce the colouring in the hair, wool, or leather prior to re-tanning and dyeing.

3. Re-tanning: The re-tanning process can be carried out with the following objectives:
• to improve the feel and handle of the leathers
• to fill the looser and softer parts of the leather in order to produce leathers of more uniform physical
properties and with more economical cutting value to the customer
• to assist in the production of corrected grain leathers
• to improve the resistance to alkali and perspiration
• to improve the wetting back property of the hides which will help the dyeing process.
A wide variety of chemicals can be used for the re-tannage of leather. They can generally be divided into the
following categories: vegetable tanning extracts, syntans, aldehydes, mineral tanning agents and resins.

4. Dyeing: The dyeing process is carried out to produce level colours over the whole surface of each hide and
skin and exact matching between hides in a commercial pack. Typical dyestuffs are water based acid dyes. Basic
and reactive dyes are less commonly used.

5. Fatliquoring: Leathers must be lubricated to achieve product-specific characteristics and to re-establish the
fat content lost in the previous procedures and to fix dyeing and tanning components. The oils used may be of
animal or vegetable origin, or might be synthetics based on mineral oils.
Stuffing is an old technique used mainly for heavier vegetable-tanned leather. The sammed leather is treated in
a drum with a mixture of molten fat.
The re-tanned, dyed, and fatliquored leather is usually washed before being piled on a 'horse’ to age (let the fat
migrate from the surface to the inside of the pelt).

6. Drying: The objective of drying is to dry the leather whilst optimizing the quality and area yield. There is a
wide range of drying techniques and some may be used in combination. Each technique has a specific influence
on the characteristics of the leather.
Drying techniques include samming, setting, centrifuging, hang drying, vacuum drying, toggle drying and paste
drying. Generally samming and setting are used to reduce the moisture content mechanically before another
drying technique is used to dry the leather further.
After drying, the leather may be referred to as crust. Crust is a tradable intermediate product.

Finishing
The overall objective of finishing is to enhance the appearance of the leather and to provide the performance
characteristics expected of the finished leather with respect to:
• colour
• gloss
• handle
• flex, adhesion, rub fastness, as well as other properties including extensibility, break, light- and
perspiration fastness, water vapour permeability and water resistance as required for the end use.
Generally, finishing operations can be divided into mechanical finishing processes and applying a surface coat.

1. Mechanical finishing processes: A wide range of mechanical finishing operations may be carried out to
improve the appearance and the feel of the leather. The following list of operations includes commonly used
mechanical finishing operations. However, the list is not exhaustive and many other operations exist for
special leathers such as sole leathers, wool-on skins, and special effects leathers:
• conditioning (optimizing the moisture content in leather for subsequent operations)
• staking (softening and stretching of leather)
• buffing/dedusting (abrading of the leather surface and removing the resulting dust from
the leather surface)
• dry milling (mechanical softening)
• polishing
• plating/embossing (flattening or printing a pattern into the leather).
These operations may be carried out before or after applying a coat, or between the application of
coatings.
Finishing

Finishing
Leather staking process: The process whereby the fibers of a leather are separated to a degree, thus softening the
leather and improving its feel and handle. The process involves flexing the skin, either by hand or machine.
Staking by hand is done by pulling the skin in all directions across a blunt blade fixed in a stake. The staking
machine consists of a table that is divided into two parts with an opening of about 10 inches between them. The
machine is equipped with two jaws, one above and one below the table. The upper jaw has a rubber roll at its end,
while the lower jaw has a bladed opening into which the roll of the upper jaw may sink. The operator slides a
portion of the skin between the jaws, which then come together and pull back. As they do so, they force the leather
to flex sharply over the blades of the lower jaw and around the roll of the upper jaw. The operator holds the skin in
place against the backward movement of the jaws and shifts the position of the skin after each motion of the jaws.
There are also machines with automatic clamps that hold the skin when the jaws are staking it. Instead of a roll in
the upper jaw, some machines have a smooth blade which forces the skin into a slot; both blade and slot pull
backward with the skin between them, flexing it sharply along their path.

Finishing
After drying, the leather is further softened on different machines (tumbling, stacking).
To see video visit: https://www.youtube.com/watch?v=MLhGw3E6OWg

Finishing
Leather buffing process: Sometimes, buffing is carried out before applying a binder-based pigment colour
layer and embossing the leather. The result is then a corrected grain. This technique is done to make skin
damages invisible and to obtain a uniform grain pattern in order to reduce the cutting waste. Such leather is not
classed as superior quality, because the finish and the embossing reduces softness and naturalness. Aniline
leather and semi-aniline leather are not buffed and are rarely embossed and are therefore higher quality and more
beautiful leather.
Some leathers are only slightly buffed and embossed and feel beautifully soft and warm. But they are an exception.
Sanding leather involves applying an abrasive paper on a rotating roller to the surface (grain side) or reverse (flesh
side). This results in a uniform surface. In the earlier times of leather production, such work was purely done
manually.
When sanding the grain side, you get a light velvet-like pile. The leather is then called nubuck. If a smooth
leather is sanded to make the surface smoother, the tanner also calls this buffing. The flat sanding of scars in the
leather, which results in nubuck, is also called buffing. After buffing dedusting is carried out to remove buffing
dust from leather surface. Engr. S. M. Murshidur Rahman

Finishing
Leather buffing process
To see leather buffing process: https://www.youtube.com/watch?v=4QUnax2EwaY

Finishing
Leather milling process: Milling is a key process to soften leather for adequate compliance. It is, however, still
not well understood for its effects on leather structure and mechanical properties. To consistently produce high
quality leather, it is essential that the tanner understands the impact and effects of every mechanical operation in
the leather-making process. This investigation is devoted to gaining a better understanding of milling effects on
pliability and other properties of concern to the leather industry, such as mechanical strength and toughness.
Observation showed milling leads to a decrease in Young's modulus, consequently an improved compliance and
softness. Data also showed, however, there is little change in tensile strength and toughness. Moreover, leather
products in service are constantly being stretched. For understanding the mechanical behavior of leather products
under cyclic stretching, we measured the energy loss (hysteresis) during cyclic tensile tests using an advanced
computing program. Data showed that hysteresis is the greatest for the first cycle, thereafter, the rest of hysteresis
values are relatively unchanged. We also discovered that drum milling significantly decreases the hysteresis. This
implies that a structural change occurs during milling, resulting in a removal of the residual stress that was
introduced during the leather making process.

Finishing
Leather milling process
To see video: https://www.youtube.com/watch?v=ks3bbscmR3U

Finishing
Leather embossing process: Embossing is the art of producing raised patterns on the natural grain of an animal
skin. The design is created by pressing rolling, or stamping. Embossments can cover the entire surface of a skin or
just selected areas.
Types of embossing:
• Blind Embossing, blind printing, blind finishing: Embossing of leather without colour.
• Gold embossing: The transfer of gold leaf into the embossing.
• Colour imprint: The transmission of colour by colour films in the embossment.
The parameters that influence the embossing:
• The amount of pressure used to stamp the tools into the leather -> The higher the pressure, the stronger
and more durable the embossing.
• The time required for the stamping -> The longer the stamping pressure, the stronger and more durable
the embossing.
• The temperature used -> The hotter the tool, the stronger and more durable the embossing.
• The moisture content of the leather -> Imprints in damp leather are clearer and more durable.

Finishing
Prior to embossing, leather may be bonded with foam and lining on the back so that the embossed pattern sits
neatly and retains its depth. Sometimes a fabric is glued to the back to prevent stretching and flattening of the
embossed motif. Deeply imprinted motifs need to be stabilised with fillers. There is a wide variety of filling
materials that can be used, from papier mâché to hot glue, but the decisive factors are their stability and flexibility.

2. Applying a surface coat: The purpose of applying a surface coat is:
• to provide protection from contaminants (water, oil, soiling)
• to provide colour either to modify dyed colour or reinforce that provided by the dyes, to even the colour
or to disguise defects
• to provide modifications to handle and gloss performance
• to provide attractive fashion or fancy effects
• to meet other customer requirements.
Finishing

There is a wide range of application methods each of which has its advantages and disadvantages. A
combination of methods can be used to achieve the desired effect on the finished product. In principle the
following types of application methods can be distinguished:
• padding or brushing the finishing mix onto the leather surface
• spray coating, which involve spraying the finishing material with pressurized air in spray cabinets
• curtain coating, which is passing the leather through a curtain of finishing material
• roller coating, which is an application of finishing mix through a roller
• transfer coating, which is the transfer of a film/foil onto leather previously treated with an adhesive.
Finishing

Finishing
Applying a surface coat
To see video visit: https://www.youtube.com/watch?v=g1fd6skW6KY
https://www.youtube.com/watch?v=-caaBKdHkTE

Finishing
Final checking and Sorting

For more details……
Email: murshidurkhulnabd@gmail.com
Facebook: https://www.facebook.com/murshidur.rahman.5203
LinkedIn: www.linkedin.com/in/murshidur-rahman
Youtube: https://www.youtube.com/c/MurshidurRahman
SlideShare: https://www.slideshare.net/Murshidur_Rahman

Leather (Hide or Skin) Manufacturing Processes

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