Thursday, May 15, 2014

Basic of shoes-Leather Upper

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 This is the second part of basic of shoe. See the first part.
  • Shoe Materials
    • Upper: The type of materials commonly used in shoe uppers are:
      • Leather 
      • Synthetics
      • Fabrics
      • Rubber
  • Leather: Leather can be made from the skin of any animal:
    • Cattle 
    • Sheep
    • Fish
    • Bird
    • Reptile
             Cattle, Cow or buffalo are the main source of supply although exotic materials such as ostrich, crocodile, etc. are sometimes used.
  • The skin of most animals consists of three main layers, the:
    • Grain: The grain is the outermost on the animal. Best leather have the grain layer intact. Flawed leather have the grain buffed or corrected before finishing. Buffing is done by applying a surface of an abrasive wheel to give the grain a degree of nap or "Sueding". Examples of buffed leather are the "brushed" pigskin, buck, nubuck (calf-imitating buck). "Velvet" suede's are also lightly buffet as well as some grain leathers, just enough to give a Matt surface without masking the grain pattern. Thick leather are split into two separate layers known as the "grain split" and the "flesh split." The latter is used as a "suede split" with either the flesh side ot the split side uppermost. Most suede's are made from splits without the grain.
    • Corium: The corium is the main or central layer. The corium has thicker fibers that provide most of the material strength.
    • Flesh: The flesh is a thin layer between the corium and the actual flesh of the animal. The flesh is of little value in the finished leather and it is usually partly or wholly removed.
  • The skin is converted to leather through process called tanning. The two types of tanning are:
    • Chrome: Chrome tanning is the most widely used tanning process today. The hides are placed in large revolving drum, where they are soaked and agitated in a solution of chromium sulfate. The leather turns blue or green as a result of the tanning. After removal from the drums the skins are split and shaved for even thickness.
    • Vegetable: Vegetable tanning is a slow process. It uses extracts of bark, wood, etc. It is now used only for sole leather.
  • The hide is divided into:
    • Five sections for upper leather
      • Bend: The bend is the central part of the hide. It has the best quality and it is the most wear resistant. It is used for vamps.
      • Shoulder: The shoulder is the neck part of the animal. It has some defects (Wrinkles around the neck). It is used for making tongues.
      • Butt: The butt is the back part of the animal and it is not very good quality. It is used for linings.
      • Head and Feet: The head and feet are the worst part of the hide and they are not generally used.
      • Belly: The belly being the part of the body which subjected to most movements, it has a different structure than other parts. It has longer fibers, which make it easier to stretch. It is one of the poorest parts of the hide.
    • Three sections for sole leather
      • Bend: The bend covers the back of the animal from the groin to the first wrinkle of the neck. It is a good quality leather and it is the most wearesistant are. It is the best leather for soles.
      • Shoulder: The shoulder is the part covering the neck. It is of a lesser quality and it is used for making insoles, counters, etc.
  • The skin stretch varies according to the particular area of the body of the animal. A shoe component must always be cut so that the direction of stretch follows the width of the piece.
 This is to avoid cutting the stretch direction along side the piece. It must be tight in the heel-to-toe direction.

Leather stretch area

    • The properties of leather for uppers are:
      • Plasticity: The properties and appearance of leather makes it very suitable for shoe uppers. Plasticity is the ability to retain a stretched shape. It enables the upper to take the shape of the last in shoe making and to "give" in wear should the shoes be fitted a little tight, but not so much that the shoes lose their shape completely.
    • Perspiration absorption and transmission of it as water vapor: Leather usually absorbs large quantities of perspiration and, depending on the finish, transmits it as water vapor. The ability to do this is most desirable for foot comfort, especially in men's footwear. The ability to transmit moisture is affected by the type of finish applied to the outer surface. A patent finish, for example, is impermeable, as are scuff-resistant coatings used on some children's shoes.
                The permeability of leather means that normally, it is not completely waterproof. However, most types are sufficiently water-repellent for normal wear that does not involve long periods of wear under wet conditions. (The water resistance can be improved by special treatments).
  • Resistant: Most leathers have good resistance to flexing in walking.
  • Expensive: Leather is one of the most expensive materials used for shoe uppers.
  • Traditional: Leather has been used for hundreds of years in shoe construction.
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