Leather manufactures – Work stretcher or holder – Stretcher
Patent
1993-05-13
1994-03-08
Crowder, Clifford D.
Leather manufactures
Work stretcher or holder
Stretcher
69 21, C14B 126
Patent
active
052917592
DESCRIPTION:
BRIEF SUMMARY
The invention refers to a process for stretching leather and similar flat materials, such as e.g. skins, furs, but also in certain cases sheet blanks and similar.
From the DE-OS 30 10 003 it is known that pieces of leather--usually referred to as "skins" for short, are clamped in a gap between two elastically extendable membranes pressed against each other through negative pressure and sealed against each other along the length of their perimeters and that the stretching process is executed by simultaneous stretching of the two membranes with frictionally engaged conveyance of the membrane clamped between them. In this way, an evenly distributed and permanent surface enlargement of considerable extent and which is free of folds is achieved over the surface of the leather. Required also for each of the two membranes is a stretching device whose effects are spread over the perimeter of the membranes. A more or less equal stretching of the membranes must be ensured because of the friction contact between the two membranes and the leather.
Task of the invention is the creation of a stretching process in contrast to this which enables the same quality stretching result to be achieved without the comparably time-consuming stretch loading of both leather surfaces. The solution provided by the invention to this task is determined by the combination of the following features.
a) at least one part of the initial surface of a piece of leather is mounted on a bearing surface which is particularly smooth with regard to the leather;
b) the piece of leather is loaded with the pressure forces spread over at least one part of the bearing surface which work against the bearing surface.
c) stretching forces, which are at least approximately tangential with reference to a leather surface as well as at least approximately polydirectional in the direction of the edge of the leather piece, are put into effect to stretch the leather at a strain relative to the bearing surface on at least one part of the second surface of the piece of leather.
As a result of the detailed examinations, it has been proved that excellent results can be achieved with regard to extent and similarity of form of the surface enlargement using this type of single-sided surface loading of the leather.
This is generally dependent on the essentially even simultaneous and polydirectional straining of the leather relative to the bearing surface. The required smooth sliding of the bearing surface can generally be assured without difficulty by taking into account the properties (in particular the moisture content) of the leather in each case in selection of the usual trade materials. Surprisingly, it has been shown that the pressure forces can also be produced by loading the leather with negative pressure (with reference to the ambient atmosphere). This negative pressure is used to advantage in a gap in which the leather is enclosed.
In addition to this, the invention provides other possibilities for carrying out other functions for processing the leather connected with the stretching process. This includes firstly the combination of a stretching process with heating which can also be used to improve the stretching results. In this case, the invention also includes the combination of the stretching process with drying. Surprisingly it has been shown that multiple treatment can be carried out without encountering fundamental problems. This is a significant step towards rationalization when considering the great importance of the setting of certain humidity values during leather production and leather processing.
In practice, it has proved advantageous to load the second surface of the leather with suction negative pressure during the stretching process.
A further task set for the invention is the creation of a stretching device for leather and similar, which is particularly suited to execution of the process according to the invention. The solution to this task is determined by the following characteristics.
a) provision of a bearing appliance for retaining the sp
REFERENCES:
patent: 3727437 (1973-04-01), Dokoupil
patent: 3872695 (1975-03-01), Busek
Crowder Clifford D.
Neas Michael A.
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