| Résumé : |
Following a description of the defect and its characteristics a bibliographical review follows.
Mechanised flaying is highlighted as the culprit of the sharp increase in the number of damaged skins reported recently. Also highlighted is the need to discover, inside the slaughterhouses, the reasons for these defects.
Previous studies dealing with the physical properties of skin are also reviewed due to their relevance to the problem in question. From this review, the following conclusions have been reached :
Directional changes in the external muscle fibres of the animal's body also determine anatomical variations and changes in the collagen fibre tissue of the adjacent skin, including changes in the direction of hair follicles.
From these anatomical variations, directional and strength variations are produced in terms of values of the skin's physical resistances.
The flanks of sheepskins, due to their structure and thinness, are less resistant to damage than the central part of the skin. This resistance is even less in situations of traction parallel to the backbone rather than in those perpendicular to it.
A consignment of sheepskins from a recently mechanised slaughterhouse gave 93,5 % strained skins. Th seriousness of this damage gave rise to this extensive progrramme of study.
By contrast, a manual slaughterhouse with skilled workers was producing crack-free skins. Using these skins to measure the forces associated with grain strain produced the following results :
Forty kg of traction, parallel to the backbone and applied perpendicularly to the backbone, did not produce any cracks.
The cracks alwaysopened perpendicularly (ie. at right angles) to the line of traction, tending to be located in the flancks of the skin.
With a "large ball" burst test, the action of the slaughterman's punch was imitated, this did not crack the grain even when the skin was perforated.
Further tests were carried out consisting of manually pulling the wool which clearly showed that pulling mainly in the weak areas of the skin, would crack the grain.
Two raw skins were sub-divided into 4 cm wide strips, each of which was stretched to 20 kg, load under tensile test. Cracks only occurred in the strips of the flanks cut parallel to the backbone.
In view of these results, three flaying variations were applied in a mechanised slaughterhouse. These clearly showed that hand-easing of the skin onn all four legs, before mechanically stripping, noticeably reduces the cracks produced.
By eliminating strong pulls on the skin during hammock work and avoiding pulling the wool we believe that : even in mechanised work, total elimination of cracks can be achieved.
The study concludes by giving the following recommendations :
Don't pull the wool.
Don't strain the flanks of the skin, especially parallel to the backbone. |
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Accueil
Grain strain in sheepskins produceed during flaying : Part I in JOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC), Vol. 74 (Année 1990)
