Добавил:
ivanov666
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Fur Processing Technologies. Тutorial
.pdf
11
• chemical composition (mass fraction of moisture, fat, ash, chromium
Indicator
Maximum,
points
Acceptable limits of
quality assessment
decrease, points
Hair dressing quality
16
2−3
Hair color
10
1
Fur skin dressing quality
14
2−4
Total
40
2−8
salts, acidity).
The combination of hair and skin properties chatacterizes the performance properties of fur skins. They are determined by heat saving, waterproof and wearproof properties as well as by skin size and weight.
The hair ability to hold air (heat protective properties) depends on
the hair structure, density, and the degree of hair compression during
the wearing of a finished product. The best heat protective properties have
the skins of polar fox, beaver, fox, reindeer, fur sheepskin. Skins with rare
and low hair (barn rat, calyx, foal, ground squirrel) have low heat-saving
properties.
The wear resistance of the fur depends on the strength of the hair and its
connection with the dermis, fragility, abrasion, felting and lightfastness of
the color, the methods of skin processing, the thickness and density of the
topographic areas.
The weight of the skin depends on its size, the thickness and density of
the fur skin, the density and length of the hair, the hunting period and the
habitat of animals, the methods of dressing and dyeing the skin. The weight
of fur has a great influence on the ergonomic properties of semi-finished and
final fur products.
The quality of a fur semi-finished product is assessed by the following
methods:
• organoleptical analysis (Table 1);
• wear-testing;
• instrumental methods.
Table 1. Organoleptical analysis of fur semi-finished products
Instrumental (laboratory) methods of quality assessment include microscopic, chemical, physicochemical analysis. Instrumental methods are used
12
to evaluate different properties such as hygienic and performance properties,
serviceability and invariability.
Microscopic analysis is used to study the elements of the hair and skin
microstructure and changes occurring in the skin and hair during the processing. This analysis also defines the distribution of substances introduced
into the semi-finished product. Using a microscope, you can study the plexus
of collagen fibers, the angle of inclination of the beams, etc.
Chemical analysis determines the content of moisture, ash, fatty substances, acid in the fur skin and hair, as well as the compliance of the chemical composition of fur with the requirements of standards. The analysis is
used to control technological processes. This method allows us to manufacture uniform products in practice. After establishing the compliance of
the chemical composition with the requirements of the relevant standards,
the fur is tested physically and mechanically, and then sorted and subdivided
into quality categories.
Physical and mechanical testing includes a number of various laboratory
methods. These methods are used to determine and measure properties indicating quality of fur products such as reliability and durability. The properties for the fur skin are tensile strength, plasticity, strength of the face layer,
lightfastness of color, etc. The properties for the hair are soiling, density,
resistance to abrasion, heat protection, color stability, elasticity, lightfastness
of color, etc. The crease of fur is also determined.
Aesthetic indicators of the fur are luster, color and shade, softness, density, length and height, pubescence, wear resistance, moiriness of the hair.
1.4. Types of technological processes
The peculiarity of the fur and sheepskin manufacture is the simultaneous
processing of fur skin and hair. Therefore, it is necessary to keep and improve
the natural properties of the hair and obtain a soft and plastic fur skin. The variety of types of fur raw materials leads to the development of a great number
of techniques and methods for fur processing.
13
The processing of fur skins is a set of sequentially performed technological operations, as a result of which the raw materials turn into semi-finished products with required consumer properties. According to the applied
technologies these operations are divided into two groups.
The first group includes operations based on chemical or physicochemical processes occurring in liquid media. These operations are used to prоcess
batches of raw materials or semi-finished products. Therefore, they are often
called batch processes.
The second group includes mechanical operations using machines. Typically, these operations are used to process a pieсe of fur product. The second
group of operations takes short time compared to the batch proceses, which
may take hours.
Despite the wide range of processed raw materials, the technological
processes consist of the similar operations according to their purposes. Some
differences in technology are determined by the characteristics of certain
types of raw materials or special requirements for semi-finished products.
The technological processing of fur skins can be divided into several
groups:
1) The first group refers to preliminary processes and operations aim
ed
at obtaining a semi-finished product with required geometric parameters,
chemical composition and microstructure of the leather and fur, which are to
be cleaned of dirt, grease and other components of organic and mineral
origin. This group includes such operations as batching, soaking, washing,
degreasing, fleshing, cutting, squeezing, and shaving.
2) The second group refers to processes and operations designed for the
irreversible fixation of fur raw materials. They are used to obtain required
structural elements of the fur product with high resistance to moisture, heat
and bacteria. This group is usually called dressing, and it includes pickling,
softening, tanning and fatliquoring.
3) The third group includes finishing processes and operations, which
are used to obtain fur products with required aesthetic properties. The operations include drying, drumming, and finishing of fur and leather. The processes of dyeing of semi-finished products (neutralization, pickling, bleaching, dyeing, salting) also refer to this group. The finishing processes (drying,
drumming, printing) are used after dyeing.
Fur raw materials with a beautiful natural hair color are not dyed.
The production cycle of their processing ends with the finishing of the semifinished product.
14
The production cycle of dyeing of fur raw materials is carried out in two
ways: discontinuous and continuous. Discontinuous production cycle includes all operations. Continuous production cycle does not include the intermediate finishing of unpainted semi-finished products. The discontinuous
method is long and more laborious. However, the intermediate finishing of
the semi-finished product provides more softness and plasticity of the leather
and uniform color of the hair. It is used for dyeing astrakhan fur, rabbit skins,
fur sheepskins. The continuous method is more economical. This method allows us to reduce the processing cost by 30%, and the cost of finished products – by 35 %.
1.5. Technological process parameters
The processing parameters are set according to the results of research
and industrial experience. The parameters that provide high quality products,
the least cost of materials and processing time are called optimal. Depending
on the types of raw materials or processing methods, the parameters may
differ significantly. The standard technologies for the processing of certain
fur raw materials were developed on the basis of optimal parameters.
The standard takes into account all features of raw materials. The standard
describes the sequence of all chemical and mechanical operations, which
provide the optimal processing parameters for a certain raw material.
The standard specifies how to complete a finished batch of products and how
to control the technological process. It indicates the rates of material consumption, the duration of the production cycle, and the characteristics of
equipment. The standard includes the table of interchangeability of used materials and describes the processes for preparing working solutions. It is
a mandatory document for industrial companies working in the field of the
fur processing. An unauthorized change in the parameters and processing
modes is considered as a gross violation of the production process.
The results of achievements in the field of science and engineering, as
well as the advanced experience of fur companies, are taken into account and
included to the standard. This improves the processing of fur raw materials.
15
However, there is a great number of fur companies which are independent
from state standards. These companies may use the latest developments of
Russian and international manufacturers as well as the most effective chemical materials. They develop more optimal industrial procedures. Therefore,
modern schemes for processing fur skins differ significantly from the traditional ones indicated in the Standard.
The size of the production batch (in kg) is set according to the capacity
of the equipment, float ratio and weights of skins. For most types of raw
materials, the weight of the hides is measured after their air drying. For other
preservation methods, a conversion factor is set for calculating weight of the
hides according to the hides after air drying.
The main parameters of fur manufacturing processes are float ratio, process duration, reagent concentration, temperature, and mechanical mixing.
Float ratio is an indicator, which has a great influence on the capacity of
the equipment, the correct flow of technological processes, the uniformity of
washing raw materials with processed liquids, the absorption intensity of reagents and their efficient use, as well as volume and contamination of
wastewater.
For the preliminary processes and processes of dressing, the float ratio
is equal to 5–10. For the processes of dyeing it is 12–15. For currying processes, the float ratio is up to 5. The float ratio depends on the type of processed raw materials. For processing sheep, rabbit, goat, astrakhan fur,
the float rate is 10. For gopher, fur seal and otter skins, it is 6. For fox, arctic
fox, sable and soft marten skins, it is 25.
The float ratio is lower for processing of the hides with smooth, straight
hair, than the float ratio for the hides with soft and curly hair. Wrong choice
of the value of the float ratio during the processing of long- and soft-haired
hides, may lead to the hair felting. The float ratio is greater for stationary
processes compared to the processes with stirring.
The process duration affects the diffusion of a reagent into the raw material or semi-finished product, its uniform distribution over the layers and
binding to proteins. An excessive increase in the duration of some processes
can lead to a decrease in the strength of the fibrous structure of a semi-finished product, as well as to a weakening of the connection between the hair
and the skin.
The concentration of reagents during operations in liquids is one of
the main parameters of fur processing technologies. An increase in the concentration of the reagent leads to an increase in its diffusion into the semifinished product. Thus, the impregnation of the semi-finished product is
16
accelerated, and the interaction intensity of the reagent with proteins increases. A significant increase in the concentration of the main reagent without taking into account the action of the other components of the processing
fluid can cause enhanced fixation of the reagent in the surface layers and
blockage of diffusion pathways, as well as a sharp change in the size of structural elements. This may cause various defects on the semi-finished product.
The temperature of the processing fluid affects the duration of processes
and the properties of semi-finished products. An increase in temperature accelerates the diffusion, distribution and binding of reagents in the dermis,
skin or hair. It speeds up the process. However, it should be noted, that an
increase in the temperature of the processing fluid leads to the loosening and
decomposition of proteins.
Mechanical mixing speeds up the process. However, intensive and continuous mixing of fur raw materials or semi-finished products in launchs can
cause felting of the hair.
Each of the above listed parameters determines the quality of final products.
1.6. Technological operations of fur processing
1.6.1. Preliminary processes and operations
Soaking. Soaking is the second stage of the technological process after
conservation. Chemicals are used during this process. The purpose of soaking is to reabsorb water in the leather, remove chemical preservatives and
soluble protein substances, and wash away contaminants. Therefore, at this
stage, aqueous solutions containing antiseptics, exacerbators, surfactants, enzymes and mixtures of these substances are used.
The soaking parameters are to be determined by the method of preservation of raw materials, since it influences the moisture content in the skin.
The moisture content in a percentage of the weight of raw materials is approximately 65–70 for raw materials without conservation, 10–15 for fresh-
17
dry and dry-salted raw materials, and 45–50 for wet-salted and acid-salted
raw materials.
The fastest process of soaking is for wet-salted raw materials, since they
lose a small amount of moisture during conservtion. It is easily watered even
in clean water within a few hours. Typically, the process takes place in a solution of sodium chloride washed out of the hide. It is also quite easy to soak
the raw material after the conservation by pickling. A significant amount of
interfiber proteins is removed during pickling that accelerates the process of
soaking. The hides of the acid-salt conservation are to be be rinsed firstly
with clean water to remove the aluminum salts contained in the conservation
mixture. This is done due to the uneven distribution of aluminum salts over
the skin, which leads to uneven watering and, as a result, to the rupture of
the skins during fleshing. In addition, aluminum salts complicate the degreasing of the hair. Therefore, the soaking of acid-salted raw materials takes
more time in comparison with soaking wet-salted raw materials.
There are some problems for soaking dry-salted and freshly dry raw materials. During the conservation of raw materials by these methods, part of
the moisture is lost, and its reverse transition to the skin is quite difficult.
To accelerate the soaking process, the first period of watering is carried out
with the increased temperature of the soaking solution in the presence of accelerators. The dry-salted skins soak faster than the fresh-dry ones.
The structure of the skin has a great influence on the parameters of soaking. The larger the hide and the thicker and denser its skin, or the more carbohydrates in the skin, the more difficult process of its soaking.
Fresh raw materials contain a large number of microorganisms capable
of dissolving proteins. When raw materials are preserved, the microorganisms are not destroyed, but only their development is slowed down. Typically, bacterial contamination is the most widespread for fresh-dry and drysalted raw materials. To prevent the development of bacteria during the soaking process, especially when this process is carried out at elevated temperatures, antiseptics or antibiotics are added to the soaking solution. In this case,
the pH of the medium should be controled, since at a pH of less than 4.5,
the growth of bacteria stops. However, at a pH of less than 3, the process of
swelling is possible, and an alkaline environment may lead to the damage of
the hair follicles.
A long period in the soaking liquid leads to the flabby and rag surface
of the skin. In addition, it disrupts bonds between the hair and skin.
A number of neutral and acidic salts, such as sodium chloride (NaCl),
hydrogen sulfate (NaHSO
), sodium sulfite and hydrogen sulfite (Na2SO3
4
18
and NaHSO3) are used as accelerators of soaking. Acid salts (sulfite and hydrosulfite) promote the extraction of soluble proteins from collagen and increase the permeability of the skin. Sodium sulfite in the presence of sodium
fluorosilicate also intensifies the soaking of the skin. Sodium hydrosulphite
is especially effective for soaking skins with a skin thickness of 0.3–0.5 mm,
since it affects the proteins of the reticular and subcutaneous fat layers, weakens the connection between them and facilitates the removal of the subcutaneous fat layer during fleshing. However, due to the unpleasant odor caused
by the release of sulfur dioxide, its use is limited.
The accelerators also have certain bactericidal properties. Sodium chloride promotes the reproduction of bacteria at its concentration of up to
6 g/dm
3
, and it reduces their number at a concentration above 20 g/dm3. It has
weak bactericidal properties and slightly reduces the growth of bacteria during short-term processing (up to 12 hours) and temperatures up to 20 ºС.
In such conditions, most types of raw materials preserved by the fresh-dry or
dry-salted method do not soak. Under more severe conditions for soaking,
sodium chloride as an independent antiseptic is not recommended. Sodium
sulfite plays the similar role. It is used to facilitate the process of subsequent
fleshing (0.5 g/dm
creased by adding 1-2 g/dm
50 g/dm
3
of chloroform.
Formalin in a weakly acidic environment (pH is less than 4) at a con-
centration of 0.5-1.0 g/dm
3
). The bactericidal effect of soaking solutions can be in-
3
of zinc chloride, 0.5 g/dm3 of sodium fluoride,
3
increases the bactericidal activity of the solution
while reducing the tanning effect.
The use of strong antiseptics may lead to an increase in the soakingtemperature to 35 ºC. It reduces the time of soaking significantly. Sodium fluorosilicate has high bactericidal properties, especially in the presence of sodium
bisulfite, fluorosilicate of ammonium, acid, and alkali.
Fatty substances in the hide prevent the absorption of water and its wetting. To increase the wettability of the skin and accelerate the diffusion of soaking solutions through difficult-to-permeate layers, various surfactants are
added to them. In this case, the soaking solution has a good wetting ability and
easily diffuses into the skin. It accelerates the soaking of the skin. In addition,
contaminants are washed off from the hair and the skin.
Enzymes are used to accelerate the soaking process and improve product
quality. As a result of partial hydrolysis of the interfiber substance, the permeability of the subcutaneous fat layer increases, the monolithicity of the structural elements of the skin is disrupted and the degree of its soaking increases.
This has a positive effect on the fleshing process since less effort is required
19
for removing the subcutaneous fat layer. It also reduces the number of skin
breaks, which leads to more economical consumption of raw materials.
Proteo and mucolytic enzymes accelerate significantly the process of
soaking. The proteo enzymes dissolve non-collagen proteins (albumins,
globulins, etc.). However, their use is undesirable due to the dehairing effect.
The use of mucolytic enzymes is more desirable since they remove mucopolysaccharides from the skin. In this case, so-called voids are formed, which
improves the water permeability and soaking of the skin. The enzymes allow
us to combine watering and softening processes. The optimal pH value in
this case is equal to 4.5–5, since a higher pH value reduces the bactericidal
properties of antiseptics.
The development of the enzymatic soaking regime began with the addition of enzymes to the solution at the first soaking. However, since the raw
materials are often very dirty, which leads to severe contamination of the solution, consistent positive results have not been obtained. The addition of
enzyme preparations to the solution during the second soaking (when using
surfactant solutions in the first soaking for 4–5 hours) show good results.
In the process of soaking, the parameters of bacteriality of the raw material are controlled. The main parameters of the prcess regime are also controlled. They are process duration and temperature, degree of watering and
elasticity of the skins after soaking. The criterion for the sufficiency of soaking is also an increase in the weight of raw materials (soaking weight). After
soaking, the skins should be soft over the entire area, contain at least 67 %
moisture and not more than 2 % sodium chloride.
Recently, a number of complex chemicals have been developed to speed
up and improve the quality of soaking. As a rule, the compositions of these
chemicals is not disclosed by manufacturers. The use of some chemicals will
be described below when explaining the methods for producing specific
types of raw materials.
Samming. The purpose of the samming process is to remove excess
moisture from the fur product. Depending on the area of fur skins and type
of raw materials, the process of samming can be carried out in flesh machines
with blunt knives or in centrifuges or hydraulic presses. For example,
the samming of the hair of sheepskins is performed in flesh machines with
blunt knives. The sheepskins are wrung out completely in a centrifuge.
The samming of rabbit skins is performed in a centrifuge.
20
Fleshing. Typically, fleshing operations are performed after the process
of soaking to remove the muscle-fat layer over the entire area of the skin and
suture torn skins.
The fleshing of insufficiently watered raw materials may lead to a signifcantly reduction of the useful area of the skin, mainly in the peripheral
topographic areas. It may be a result of breaks due to imperfections in the design of fleshing machines as well as the processing of bacterially damaged
skins. Therefore, weak skins are to be scoured after the process of pickling.
This process allows us to make skins denser. It is widely used for the skins
of a rabbit, muskrat, gopher, etc.
The simplest device for manual fleshing is a brace or braid. Valuable
species of furs are fleshed using these tools. The process of fleshing using
these devices is performed by cutting off the flesh layer with a sharply sharpened blade.
Washing. The next process is washing. It is performed in the same
equipment as the the process of soaking. The purpose of washing is to remove various inorganic and organic contaminants from the hair (sand, dirt,
blood, etc.). The contaminants may cause the damage of hides. Washing is
carried out in surfactant solutions, which are usually used as anionic pastes
with high detergency. The optimum action of the paste is at a pH of 8–9.
Sodium carbonate is added to the washing bath to create the appropriate alkalinity of the solution.
Degreasing. The hides of sheep, marmots, ground squirrels, seals, and
fur seals are characterized by a significant content of fatty substances. The fat
content of a sheepskin may exceed 25 %. Fat makes the skin heavier and
rougher. In addition, the fat may lead to the oxidation of hides during their
storage.
The fat can lead to technological disruptions in the processing of fur
(soaking, dyeing, refining). The removal of naturally occurring fatty substances from the hide is performed during the degreasing process. Fatty substances of animal origin are to be removed because they, being in fat cells,
are not able to lubricate collagen fibers. This leads to the reduction of softness and elasticity of skins.
There are several methods of degreasing:
• adsorptive (using solid adsorbents - special clays);
• enzymatic (decomposition of fat by lipolytic enzymes);
• extraction (extraction of fat with organic solvents);
• emulsion (processing of skins in aqueous solutions of surfactants).
Соседние файлы в предмете [НЕСОРТИРОВАННОЕ]