DD223467A1 - METHOD FOR DRYING POROESES AND FIBER SOFT MATERIALS, PREFERABLY LEATHER, FUR FURSES AND FURSES - Google Patents

Abstract

The invention relates to the drying of leather, skins, furs and similar porous and fibrous materials. The object of the invention is to accelerate the drying process and to improve the quality of the porous and fibrous materials. According to the invention periodic changes in the physical state of a drying medium are caused, which propagate in the context of the actual transport of the drying medium. The changes in the physical state are achieved by flowing around an obstacle body, by changing the flow opening of the drying medium or by an adjusted Druckpulsationselement in a vacuum chamber. The invention is applicable to the drying of leather, artificial leather, skins, furs, paper, textiles, ceramics and the like.

Description

Process for drying porous and fibrous materials, preferably leather, skins and furs

Application of the invention

The invention relates to the drying of leather, skins and furs and similar porous and fibrous materials using a drying medium.

Characteristic of the known technical solutions

Leather, skins, furs and similar porous and fibrous materials are generally dried by a stream of drying medium which absorbs the moisture and releases it outside of the material to be dried. The flow of the drying medium acts on the material to be dried throughout the drying process at constant pressure. The drying medium is usually heated air. The drying process is composed of the moisture transport in the porous or / and fibrous structure of the material to be dried on its surface, where a so-called boundary layer is formed, and from the moisture transport from the boundary layer into the drying medium. With respect to the passage of time, this drying process can be subdivided into two time periods. During the first period of time, a constant drying speed is achieved, that is to say that the same amount of moisture delivered to the drying medium is attributed to each time unit. This first period ends when the moisture transport in the porous or / and fibrous structure

Door begins to slow down to the boundary layer, wherein the drying medium would possibly still be able to dissipate the same amount of moisture. At this moment begins the second period of the .Drocknungsprozesses, during which the conditions for the unwanted sticking together and shrinking of the fibers of the material to be dried arise. There are various drying methods of leather and similar porous and fibrous materials known to limit the extent to which the above deficiencies to varying degrees.

According to DE - OS 3010000 a drying process is known in which the leather is enclosed between two films in a chamber. The chamber is part of a vacuum drying plant and the leather has a constant negative pressure throughout the drying process. The negative pressure is chosen to achieve a low boiling point of the liquid substance contained in the leather. Although the intensity of the moisture removal from the material to be dried is thus higher, in the final phase of the drying process, in turn, there is a drop in the drying rate and thus also undesired adhesion and shrinkage of the leather fibers.

Also known is the drying process, in which the leather is introduced into a high-frequency electrostatic field. The leather thus absorbs part of the high-frequency energy into its structure, where it transforms into heat, which vaporizes the moisture contained in the leather. The high-frequency energy advantageously adversely affects the surface tension of the moisture boundary layer, which increases the drying speed. The drying rate also depends on the amount of heat absorbed, which very easily leads to local overheating, which manifests itself in undesired adhesion and shrinkage of the fibers. Furthermore, a drying method is known in which the leather is exposed to the action of a drying medium which simultaneously forms an acoustic field. (Boucher, R.M.G .: "Ultrasonic in Processing", Chemical Engineering, 68, 1961, No. 20). The acoustic field transmits acoustic energy;

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resulting in the production of pressure changes of the drying medium, resulting in a relatively small mutual movement between the fiber structure of the leather and the liquid contained in the pores of the fibers. The magnitude and velocity of the periodic changes in this movement correspond to the amplitude and frequency of the acting one acoustic field. The transmitted acoustic energy thus produces a mechanical effect which can be described as a "shaking out" of the liquid from the pores of the fiber structure of the leather, which has a positive influence on the drying speed, especially in the section of decreasing drying speed. By the action of the acoustic energy and the drying medium is set in motion, which so advantageously affects the surface tension of the drying boundary layer, whereby also the Trocknungsgeachgeschwindigkeit is increased. The absorption of the acoustic energy also leads to a warming of the leather and thus to an acceleration of the drying process. The disadvantage of this drying method is that the changes in the physical state achieved in the acoustic field in their order of magnitude are small and thus have a low mechanical, transferred to the leather effect. When using sirens as a generator of the acoustic field, it should be noted that these are technically complex and delicate, especially with regard to the high humidity and aggressiveness of the tanning agents used.

Object of the invention

The object of the invention is to accelerate the drying process and to improve the quality of the materials to be dried.

Explanation of the essence of the invention

The invention has for its object to develop a method with which in porous and fibrous materials, preferably leathers, skins and furs, moisture contained

can be brought out faster and removed from the structure of the material to be dried using a drying medium. , According to the invention the object is achieved in that periodically triggered changes in the physical state in. Spread out the frame of transport of the drying medium. Periodic changes of the physical state are achieved,.

when the flow of drying medium flows around an obstruction body,

- By changing the diameter of the outlet nozzle of the flow of the drying medium

- By a set element of the pressure pulsations.

The advantage of the drying process of this invention is that the action of the transported drying medium with the periodically induced changes in physical state increases the mechanical effect, thereby increasing the rate of drying and substantially reducing the bonding and shrinkage of the fibers of the material to be dried. Upon initiation of periodic changes in that the flow of the drying medium flows around an obstacle body, Carman vortices are formed, which periodically fall on the material to be dried, where they exert a mechanical effect. Upon initiation of periodic changes by varying the diameter of the discharge nozzle of the stream of drying medium, the stream is divided into parts having different physical states. These items of drying medium impact the material to be dried, where they exert a mechanical action. Upon initiation of the periodic changes by an adjusted element, the drying medium periodically changes its physical states and these changes cause a mechanical effect on the material to be dried.

The periodic changes in the physical state, together with the interactions with the material to be dried, manifest themselves as periodic pressure fluctuations, which produce a mechanical effect which is mutual

Movement between the Paserstruktur and the liquid contained in the pores of the .u.trocknenden material expresses. Thus, there is an advantageous "shaking out" of the liquid from the fibers, which loosen up at the same time, whereby the dried material better softness and flexibility is achieved. Part of the mechanical energy gained by the mechanical action converts to heat, which manifests itself in the increase of the diffusion coefficient. Due to the mutual movement between the fiber structure and the liquid, the moisture transport in the fiber structure accelerates towards the boundary layer, which advantageously accelerates the entire drying process, especially its second section, where the drying speed slows down. This reduces energy consumption and significantly restricts sticking and shrinkage of the fibers of the material to be dried. On the surface of the material to be dried there is an impairment of the surface tension of the moisture barrier layer and thus to an increase in the intensity of the heat transfer from the drying medium into the fiber structure and moisture from the fiber structure in the drying medium. The initiation of the periodic changes in the physical state of the drying medium bound to its transport is characterized by relatively low demands as to the energy supplied and the construction of the plant. In this case, relatively large changes in the physical state of the drying medium are achieved and thus also a great mechanical effect on the material to be dried. An advantage of the drying method of this invention is that, when combined with other known drying methods, the benefits of both methods are retained.

embodiment

The invention will be explained in more detail below on three Aususführungsbeispielen.

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example 1

The leather to be dried is exposed to streams of heated air, with each of these streams in front of the. Impact on the leather to be dried flows around an obstacle body. The circulation of the obstacle body forms the known Carman vortices, which occur as a pressure fluctuation, by which a periodic mechanical effect on the leather to be dried is achieved,

Example 2

The leather to be dried is exposed to the action of streams of heated air, the nozzles of the individual streams are provided with elastic attachments. Due to the flow of heated air, the elastic cap periodically changes its diameter, which in turn causes periodic changes in the velocity, density and pressure of the stream of heated air. As a result, the exiting streams are periodically subdivided into individual parts with different pressure values. They strike the material to be dried and cause a mechanical effect.

Example 3

The leather is enclosed between a heated base plate and a porous pressure plate. Both plates are arranged in the vacuum chamber of a Yakuumtrocknungsanlage. In the suction circuit of the vacuum chamber, a set pressure pulsation element (eg, a rotary valve) is mounted, which periodically closes the space of the vacuum chamber of the vacuum drying plant from the environment. Thus, periodic pressure changes, which produce a mechanical effect, act on the material to be dried. In this case, the actual benefits of vacuum drying are retained, especially the lowering of the boiling point of the liquid contained in the pores of the fiber structure of the leather and thus also the increase in the intensity of the removal of the vaporized liquid.

Claims (3)

- 7 - invention claim A process for drying porous and fibrous materials, preferably leather, skins and furs, using a drying medium whose physical state changes periodically, characterized in that the transport of the physical changes takes place through the drying medium itself. 2. The method according to item 1, characterized in that for periodic change of the physical state, an obstacle body is arranged in the flow of the drying medium. 3. The method according to item 1, characterized in that for the periodic change of the physical state, the opening of the outlet nozzle of the drying medium is formed variable « A-. Method according to item 1, characterized in that a set pressure pulsation element is arranged for the periodic change of the physical state in the intake circuit of a vacuum chamber »