The leather manufacturing process英语口语900句文本 is divided into three sub-process: preparatory stages, tanning and crusting. All true leathers will undergo the sub-process. A further sub-process, surface coating may be added into the quence. The list of operations that leathers undergo vary with the type of leather.
Production management[edit]
Theunierm 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-process can be omitted to make certain leathers (or partially tanned/ untanned products).
The preparatory stages are when the hide/skin is prepared for tanning.[1] 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:[2]
∙ prervation- the hide/skin is treated with a method which renders it temporarily imputrescible.
∙ soaking - water for purpos of washing or rehydration is reintroduced.
∙ liming - unwanted proteins and "opening up" is achieved.
∙ unhairing - the majority of hair is removed.
∙ fleshing - subcutaneous material is removed.
∙ splitting - the hide/skin is cut into two or more horizontal layers.
sounds是什么意思∙ reliming - the hide/skin is further treated to achieve more "opening up" or more protein removal.
∙ deliming - liming and unhairing chemicals are removed from the pelt.
∙ bating - proteolytic proteins are introduced to the skin to remove further proteins and to assist with softening of the pelt.[3]
∙ degreasing - natural fats/oils are stripped or as much as is possible from the hide/skin.adiz是什么意思[4]
∙ frizing - physical removal of the fat layer inside the skin.[5] Also similar to Slicking.
∙ bleaching - chemical modification of dark pigments to yield a lighter coloured pelt.
∙ pickling - lowering of the pH value to the acidic region. Must be done in the prence 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
治青春痘的妙招
∙ depickling - raising of the pH out of the acidic region to assist with penetration of certain tanning agents
vitamin water
Tanning[edit]
Main article:四级几分可以算过 Tanning (leather)
Barrel for leather tanning,Igualada Leather Muum, Spain
Tanning is the process that converts the protein of the raw hide or skin into a stable material which will not putrefy and is suitable for a wide variety of end applications. The principal difference between raw hides and tanned hides is that raw hides dry out to form a hard inflexible material that can putrefy when re-wetted (wetted back), while tanned material dries out to a flexible form that does not become putrid when wetted back. A large number of different tanning methods and materials can be ud; the choice is ultimately dependent on the end application of the leather. The most commonly ud tanning material is chromium, which leaves the leather, once tanned, a pale blue colour (due to the chromium), this product is commonly called “wet blue”.
The acidity of hides once they have finished pickling will typically be between pH of 2.8-3.2. At this point the hides are loaded in a drum and immerd in a float containing the tanning liquor. The hides are allowed to soak (while the drum slowly rotates about its axle) and the tanning liquor slowly penetrates through the full substance of the hide. Regular checks will be made to e the penetration by cutting the cross ction of a hide and obrving the degree of penetration. Once an even degree of penetration is obrved, the pH of the float is slowly raid in a process called basification. This basification process fixes the tanning material to the leather, and the more tanning material fixed, the higher the hydrothermal stability and incread shrinkage temperature resistance of the leather. The pH of the leather when chrome tanned would typically finish somewhere between 3.8-4.2.[6]
Crusting[edit]
Drying of leather in East Timor
Crusting is when the hide/skin is thinned, retanned and lubricated. Often a coloring operation is included in the crusting sub-process. The chemicals added during crusting have to be fixed in place. The culmination of the crusting sub-process is the drying and softening operations. Crusting may include the following operations:
∙ wetting back - mi-procesd leather is fecklessrehydrated.
∙ sammying - 45-55%(m/m) water is squeezed out the leather.
∙ splitting - the leather is split into one or more horizontal layers.
∙ shaving - the leather is thinned using a machine which cuts leather fibres off.
∙ neutralisation - the pH of the leather is adjusted to a value between 4.5 and 6.5.
西安美容培训∙ retanning - additional tanning agents are added to impart properties.
∙ butter facedyeing - the leather is coloured.
