EP3004400B1

EP3004400B1 - Leathers drying and/or conditioning method and drying and/or conditioning plant suitable to implement such a method

Info

Publication number: EP3004400B1
Application number: EP14731064.3A
Authority: EP
Inventors: Antonio Galiotto
Original assignee: Erretre SpA
Current assignee: Erretre SpA
Priority date: 2013-05-30
Filing date: 2014-05-27
Publication date: 2022-02-09
Anticipated expiration: 2034-05-27
Also published as: BR112015029571B1; CN105431556B; ITPD20130150A1; BR112015029571A2; EP3004400A1; CN105431556A; WO2014191910A1

Description

The present invention relates to a drying and/or conditioning method of leathers or similar laminar surfaces, especially tannery leathers typically although not exclusively wet leathers just undergone working of retanning, dyeing and greasing for example in a machine known as "drum" in the tannery field, or leathers still partially soaked with moisture which must be stabilized by a process known as "conditioning" in the tannery field itself.
The particularity of the method of the invention stands in the fact of providing an accurate control phase of the level of expansion, distension, enlargement, extension or traction of the leathers just introduced in the operative tunnel of a drying and/or conditioning plant, in order to standardize the level of tension among the leathers of the same batch, and/or during the gradual transition of the leathers themselves through the aforesaid operative tunnel, in order to avoid damage to the leathers due to a potential excessive traction applied to them. Furthermore, the present invention also relates to a drying and/or conditioning plant of leathers or similar laminar surfaces, especially suitable to implement such a method. Notoriously, in the tanning field drying (or desiccation) of the leathers is a basic working that is typically performed in the middle phase of the entire production process of tanning (in which the leathers already taken the connotation of semi-finished products) with the aim of drying the leathers from the excess of water accumulated in the previous workings. When they have to undergo the process of drying, leathers, indeed, have been already subjected to at least chemical and mechanical processes such as soakage, calcination, stripping of flesh, splitting, de-calcination, degreasing, tanning, retanning, shearing, dyeing and greasing, in their proper and established operative sequence, and present themselves as wet semi-finished products.
At the current state of the art, working of drying is carried out with various plant solutions, depending on the type of leathers and the final destination of the finished product: in this regard, suspension or hanging drying, nailing drying, "pasting" drying, vacuum drying are cited in this seat, by way of example.
The conditioning is, instead, an operation through which the animal leather is kept in an environment at standard temperature (T) and relative humidity (RH) (for example T = 20°C and RH = 65%) up to that the conditions of equilibrium with the environment are reached and the desired mechanical processes with the necessary effectiveness and efficiency can thus be carried out.
Considering the essential features, a typical leathers drying and/or conditioning plant of the prior art includes an operative tunnel that mainly develops along a linear direction and is provided with air conditioning devices, (such as, for example, fans of axial type) and/or traction organs (such as pneumatic organs installed in the operative tunnel), suitable to work on the leathers so as to respectively dry and/or stretched them according to predefined treatment and/or tensioning cycles.
A known drying and/or conditioning plant also comprises a plurality of support frames, each of which accommodates at least one leather in such a way as to keep it stretched, as well as moving means, operatively connected with the support frames in order to convey them along said linear direction according to a predetermined speed inside the operative tunnel, to allow drying and/or tensioning of the leather, and outside the operative tunnel itself to allow discharge of these leathers dried and/or tensioned in a given treatment cycle and load of other leathers to be dried and/or tensioned in the next treatment cycle.
An operator, but much more often at least a pair of operators provides to couple by nailing the leathers with the respective support frames which are conveyed one at a time inside the operative tunnel of the plant where their drying (or their conditioning) is got by properly varying and modulating, depending on the settings chosen, the inner temperature and humidity conditions along the longitudinal development of the operative tunnel.
Before stably coupling them with the support frames (at least one leather for at least one side face of the latter), the operators expand, widen or put in traction the leathers by means of an initial manual action that, however carefully performed and however the skill and experience of the operators involved are proven, is inherently empirical and does not take into account the type, shape and condition of the various leathers, which, as it is well known, vary from batch to batch, and sometimes even from leather to leather inside the same batch. Moreover, the same physical state and/or tiredness of the operators vary within one working day and from a working day to another, so that the force with which they are able to stretch or open the tannery leathers on the support frames is obviously variable over time.
Such a situation actually represents a drawback widely felt in the field of tanning when it is considered how, in the prior art, the leathers thus loaded on the support frames by the operators are further and mechanically extended or stretched by actuation means of which, as known, the drying and or conditioning plant concerned is provided with: it should be seen in this connection prior art document GB1432966 A .
Indeed, as soon as the support frames, complete with leathers to be dried, reach or approach the operative tunnel, they are subjected to the mechanical action of the actuation means that widen the support frames typically according to a vertical direction (as known, for example from the prior art document GB1432966 A , these support frames are composed of two halfportions partially telescopic and spaced apart each other) with consequent extension of the surface of the leathers supported and previously fixed to the support frames by one or more operators in the loading stations.
Alternatively, as shown in the prior art document FR2187913 A1 , the actuation means act directly on the leather stretched in order to widen them at a plurality of perimetrical points at which they have been engaged to the support frame by means of pliers.
Widening or stretching value of the leathers to be dried is currently preset and adjusted as a fixed distance (which determines the application of a given tension to the fibres of the leathers) for a certain batch (for example, 200 mm), varying instead from batch to batch: it follows that it does not disadvantageously take into account in any way of the initial expansion conditions of the leathers allocated by the operators and of the size of the leathers belonging to the same batch, properties that, as just said, are inevitably or often variable.
It is obvious that this situation, seen on daily basis in the tanning industry, means that, at the end of the drying cycle, the leathers of a given batch are evenly stretched or expanded in terms of distance, but to such an expansion corresponds a uneven tension of the fibres of the material dried: such an effect currently leads to lacks of homogeneity among batches of the same product coming from the processing of different leathers and typically results in a generally expected quality reduction (with consequent choice downgrading).
In addition, in the course of the drying and/or conditioning cycle in the operative tunnel, wet leathers inevitably and automatically shrink due to the loss by evaporation of water with which they are drenched: this at different level depending on the type of leather - which depends on the morphological features of the animal - and the type of treatment to which the leathers themselves have been previously subjected - which depends on the applied temperature and humidity conditions and from tanning, retanning and dyeing chemicals used in leathers processing.
In such a phase, therefore, as a result of their drying inside the operative tunnel of the drying and/or conditioning plant, the fibres of the tannery leathers, at the beginning manually hooked to the support frames by the operators and subsequently mechanically expanded by the actuation means, are thus subject to a higher tension, which cannot be measured or modified during the drying phase and which often provokes damage to the leathers, with the consequent generation of disadvantageous downgrades or production waste: such a negative aspect is associated with the already mentioned prior art documents FR2187913 A1 and GB1432966 A .
Starting, therefore, from the knowledge of the drawbacks mentioned above of the current state of the art, the present invention intends to give them full remedy.
In particular, main purpose of the present invention is to provide leathers, especially tannery ones, drying and/or conditioning method, at the end of which the leathers of a same given batch treated during the method present an uniform and controllable level of tension, contrary to what is allowed by the current operating technologies.
Within this purpose, it is task of the present invention to develop leathers drying and/or conditioning method more efficient than equivalent methods of the prior art, able to provide dried tannery leathers having a greater surface extension, with resulting higher producer's satisfaction and operating margin.
It is a second purpose of the invention to implement leathers drying and/or conditioning method which guarantees to the tanning leathers themselves, during crossing of the entire operative tunnel, to maintain a constant tension, predetermined at design stage, or to appropriately modify it according to what is deemed optimal for a given batch of production.
In the conceptual sphere of this second purpose, it is task of the invention to provide tannery leathers drying and/or conditioning method which allows to avoid, or at least drastically reduce compared to the prior art, on one hand damages, often irreparable, of leathers due to an excess of tension of their fibres during drying and/or conditioning process, on the other hand not appropriate and not optimal levels of expansion of the leathers due to a lack of tension of their fibres.
It is another purpose of the invention to operate a drying and/or conditioning method of leathers that compared with the current state of the art allows to reduce the percentage of tannery leathers just dried that it is necessary to downgrade or devote to waste.
It is another purpose of the invention to devise animal leathers drying and/or conditioning plant which contributes to efficiently achieve the aforesaid purposes and tasks even from a structural point of view.
It is a last but not least purpose of the invention to provide technologically advanced, versatile and reliable leathers drying and/or conditioning plant.
Said purposes are achieved through leathers drying and/or conditioning method according to the appended claim 1, as hereinafter referred for the sake of exposure brevity.
Further applicative features of detail of the method of the invention are set forth in the corresponding dependent claims.
Also a drying and/or conditioning plant of leathers, particularly suitable to implement the method just indicated, according to the attached claim 9, as again hereinafter referred for the sake of exhibition brevity, contributes to the solution of the above cited drawbacks.
More constructive features of detail of the plant of the invention are contained in the relevant dependent claims.
The above claims, in the following specifically and concretely defined, are integral part of the present description.
Advantageously, the leathers of a given production batch treated according to the drying and/or conditioning method of the invention have an uniform surface expansion and, mostly, tension level, unlike what happens in the tannery leathers treated with similar known methods.
Still advantageously, the drying and/or conditioning method of the invention allows the leathers, during crossing of the entire operative tunnel, to maintain a constant tension considered optimal in a specific operating situation, without them being subjected to excessive stresses as it happens instead in the known art, thanks to the possibility to modify the traction force with which the actuation means operate on the support frames which stably accommodate the leathers.
This thanks to the fact the method according to the invention includes a step of controlling the level of expansion of the leathers which, in turn, comprises the following operations:

establishing a predetermined nominal tension value of the leathers;
detecting the tension value of the fibres of the leathers expanded as a result of the operation of the actuation means on the support frames at the operative tunnel of the drying and/or conditioning plant;
comparing the measured tension value with the predetermined nominal tension value, measuring tension deviation thereof;
adjusting operation of the actuation means depending on the measured tension deviation in such a way as to keep the leather spread and/or tensioned substantially to the predetermined nominal tension value,

In practice, therefore, the method of the invention provides the possibility to vary, depending on the operational requirements, the expansion force applied by the actuation means on the tannery leathers supported by the support frames, compensating for any but rather probable initial differences of tensioning between leather and leather resulting from the variability of the manual force with which the operators engage them to the support frames, with the aim of keeping constant the tension of the fibres of the leathers of a given batch.
The traction force automatically applied by the actuation means on the tannery leathers does not simply and aseptically consider the length of opening or stretching of the leathers themselves, hooked to the support frames, necessary to reach a prefixed standard expansion value (and a consequent nominal tension value), as it happens in the prior art (for example in the prior art documents FR2187913 A1 and GB1432966 ), but the actual state of traction in which the tannery leathers stand during the entire drying process, so that, in method of the invention, the force actually applied by the actuation means compensates for the manual force applied by the operator and any tannery leather of a given production batch is stretched or spread of the same and constant predetermined nominal tension value of the fibres of the leather, deemed optimal by the manufacturer for that production batch.
Equally advantageously, the leathers drying and/or conditioning method prevents or at least greatly reduces compared with the prior art the damages, often irreparable, suffered by the leathers themselves and due to the excessive traction exerted on them by the actuation means in the operative tunnel during the drying process, resulting in the favourable lowering of the percentage of tannery leathers just dried to be downgraded or allocated to waste.
The same advantages obtained by the invention could be in practice achieved by greatly reducing the speed of drying of the leathers and the extension (or widening) of the support frames, with the double disadvantage of a reduction in the productivity of the drying and/or conditioning plant and a decrease in the surface yield of the leather (it should be noted that, normally, in the tannery field the finished leathers - understood as leathers just treated through tanning, retanning and dyeing - which are processed by a tanning industry are purchased by weight as raw materials and sold by square metres as finished products).
The invention method, since it ensures timely and accurate control of the tension applied to the leathers during the drying phase, allows instead to accelerate the speed with which the support frames, complete with leathers to be dried, run through the operative drying tunnel. The method of the invention, in essence, allows also to achieve a good compromise between speed of drying of the leathers and drying efficiency, placing the drying and/or conditioning plant in the condition to be quick and efficient in processing the leathers to be dried.
Said purposes and advantages, as well as other ones that will emerge later one, will result at a greater extent from the description that follows, relating to a preferred embodiment of the drying and/or conditioning plant of the invention and to a preferred applicative embodiment of the method of the invention implemented by such a plant, given by indicative and illustrative, but not limitative, way with reference to the accompanying drawings, in which:

figure 1 is a simplified assonometric view of the tannery leathers drying and/or conditioning plant of the invention;
figure 2 is an assonometric view of a constructive assembly of figure 1;
figure 3 is the side view of figure 2;
figure 4 is a schematic hydraulic circuit used by the plant of figure 1 for implementing the preferred applicative embodiment of the method of the invention;
figure 5 is a schematic and simplified front view of the plant of figure 1 with the actuation means in the operating position;
figure 6 is an enlargement of a constructive detail of figure 5;
figure 7 is the enlarged detail of figure 6 but with the actuation means in the release position;
figure 8 is a simplified and partial assonometric view of an inner glimpse of the plant of figure 1;
figure 9 is the schematic and partial assonometric view of a constructive assembly of figure 8;
figure 10 is a truncated and enlarged view of figure 9.

The industrial leathers, particularly but not necessarily tannery leathers, drying and/or conditioning plant, object of the present invention, is shown in figure 1 where it is globally numbered with 1.
As it can be seen, such leathers drying and/or conditioning plant 1 includes:

an operative tunnel 2 mainly developing along a linear direction Z and provided at the top with air conditioning devices, overall indicated with 3 and typically consisting of axial fans of the known type, which, when operating, work on the leathers so as to dry them according to predefined treatment cycles;
a plurality of support frames 4, each of which suitable to accommodate on both the side faces 4c, 4d at least one of these leathers in such a way so as to keep it in a stretched, preferably vertical, position;
actuation means, overall numbered with 5, operatively connected with the support frames 4 and suitable to be operated in such a way as to spread the leathers to a prefixed standard expansion value;
moving means, as a whole reported with 6, operatively connected with the support frames 4 in order to convey them along the linear direction Z according to a predetermined speed inside the operative tunnel 2, to allow drying of the leathers, and outside the operative tunnel 2 to allow discharge of the leathers dried in a working cycle and load of the leathers to be dried in the next working cycle.

In accordance with the invention, the leathers drying and/or conditioning plant 1 includes:

detection means 7, generally indicated with 7, operatively connected with the actuation means 5 and having the function of measuring the tension value of the fibres of the leathers expanded due to operation of the actuation means 5 on the support frames 4;
adjustment means, generally indicated with 8, operatively connected with the actuation means 5 on which work depending on the tension deviation between the measured tension value and a predetermined nominal tension value so that to keep the leather spread and/or tensioned substantially to the predetermined nominal tension value.

Preferably but not necessarily, the detection means 7 comprise a system for measuring the pressure of the operating fluid of the actuation means 5: such a measurement system is overall indicated with 9 and is visible in figure 4.
The adjustment means 8 include, in turn, a supply circuit of the operating fluid of the actuation means 5: such a supply circuit is indicated as a whole with 10 and is also visible only in figure 4.
More in detail, the actuation means 5 are any of the linear actuators selected from the group consisting of mechanical actuators, oil-pressure (or hydraulic, preferred solution by the applicant of the present invention and illustrated in the figures that follow) actuators, pneumatic actuators, combinations thereof and/or similar.
In particular, the oil-pressure actuators, by using an incompressible operating fluid (oil) allow to perform the aforesaid operations provided in the method of the invention with greater constructive simplicity of the adjustment means 8: the force with which the oil is put under pressure exactly corresponds, indeed, to the force transmitted on the leathers in order to stretch or draw back them, depending on the case.
On the basis of the preferred embodiment of the actuation means 5, the measuring system of the pressure of the operating fluid 9 comprises, for example, a pressure transducer 11, electrically connected on one side with a bidirectional pipe 12 containing pressure fluid of the hydraulic actuator 13 of the actuation means 5 and, on the other side, with a central processing and control unit 14 (or PLC).
Furthermore, the supply circuit of the operating fluid 10 includes, by way of example and as well illustrated in figure 4:

a control valve of the flow direction 15, of the four-way type;
a suction pump 16;
an oil tank 17 from which a suction pipe 18 departs (communicating with the bidirectional pipe 12) and in which a drain pipe 19 flows into;
a safety valve 20;
a displacement transducer 21 operatively connected with the force stem 22 of the hydraulic actuator 13 and electrically connected with the central processing and control unit 14.

According to the preferred embodiment described herein of the invention, the actuation means 5 are arranged at a loading buffer station 23, placed upstream the operative tunnel 2 which it communicates with and adapted to receive the support frames 4, when the actuation means 5 work on the support frames 4 in order to expand the leathers to the predetermined nominal tension value.
The actuation means 5 are also placed inside the operative tunnel 2 where, during the proper drying phase, work on the support frames 4 in order to adjust the tension value of the leathers to the predetermined nominal tension value (established in recipe): therefore, the tension value of the leathers can be varied also along the operative tunnel 2, either increasing or decreasing it, with the aim of keeping it consistent with the recipe.
It is stated precisely that the support frames 4 are stably kept in the optimal position, such that the tension of the leathers is equal to the predetermined nominal value, by mechanical locking means, not illustrated in the accompanying drawings and of the type known per se to the man skilled in the art, arranged laterally to the support frames 4 with which are operatively connected and comprising for example a tooth which snap-engages in a rack. When necessary, these locking means are released by actuating means, preferably of pneumatic type, which determine the temporary ineffectiveness of the locking means: it is evident how, in this operating condition, the support frames 4 are supported only by the actuation means 5.
Since, in the embodiment here described and illustrated in the accompanying drawings (in particular in figures 1-3), the operative tunnel 2 is divided into a plurality of consecutive drying chambers 24, physically separate and operatively independent each other, possibly bounded by dividing means (or bulkheads, not visible) but communicating each other to allow passage of the support frames 4, the actuation means 5 are arranged in the initial part of the loading buffer station 23 and in the initial part of each drying chamber 24: in the latter case, the actuation means 5 are, then, arranged inside the operative tunnel 2 in order to control, by means of the detection means 7 and the adjustment means 8, the state of tension of the tannery leathers during the drying phase and to intervene when the measured tension value exceeds the predetermined nominal tension value, established in the recipe.
It is also underlined that figures 1-3 show the example of a drying and/or conditioning plant 1 in which the operative tunnel 2 is divided into three consecutive drying chambers 24: this is a purely indicative example, proposed only for explanatory purposes to fully explain one of the technical aspects of the invention, considering that other embodiments of the invention, not illustrated, could provide for an operative tunnel comprising a number of consecutive drying chambers different from three, although not less than two.
Similarly, in other embodiments of the drying and/or conditioning plant of the invention, not accompanied by reference drawings, the actuation means could be arranged at only one or some of the various consecutive drying chambers of the operative tunnel, based on the design choices and the type of tannery leathers to be treated.
As it can be seen in particular in figure 5, the actuation means 5 are associated with and work at both the lateral sides 4a, 4b of each of the support frames 4: such a configuration is particularly suitable for stretching leathers of traditional type, having the classical shaped similar to a shield, arranged substantially symmetrically with respect to the axis of symmetry of the support frames 4.
Further embodiments of the drying and/or conditioning plant of the present invention, not yet represented in the accompanying drawings, could provide that the actuation means are arranged at only one of the lateral sides of the support frames, being especially suitable to stretch leathers of less conventional shape and which occupy at least one of the side faces of the support frames in an asymmetrical way.
Figure 5 and the subsequent figures highlight that, preferably but not necessarily, the actuation means 5 are movable along the linear direction Z being coupled through sliding means, as a whole numbered with 25 and operatively connected with motorization means (visible in figures 8-10 where are overall indicated by 26), with a base framework 27 that contributes to define the operative tunnel 2 and which supports the support frames 4 in such a way as to keep them suspended from a reference surface S on which the base framework 27 insists.
Such a design feature allows to move the actuation means 5 in such a way that they, as well as the detection means 7 and the adjustment means 8 connected with them, one by one contact the support frames 4, complete with leathers to be dried, while the latter temporarily remain stationary in both the loading buffer station 23 and in the various consecutive drying chambers 24: it follows, in the invention described herein, a detailed, progressive and continuous monitoring of the state of tension to which the leather to be dried are subjected near the entry and inside the operative tunnel 2.
In particular, in function of the multi-cell constructive design of the operative tunnel 2 here described by way of preferred example, the actuation means 5, as mentioned arranged at the initial part of each of the consecutive drying chambers 24 (resulting distinct each other from a drying chamber 24 to the adjacent one), are made movable by the moving means 6 along the linear direction Z for a maximum longitudinal stroke which substantially coincides with the transverse width of each of the consecutive drying chambers 24.
Preferably but not necessarily, the loading buffer station 23 integrally receives a predetermined group of support frames 4 before such a predetermined group of support frames 4 is transferred in block (or pack) inside the operative tunnel 2 by the moving means 6, in such a way that the support frames 4 of the predetermined group simultaneously reach the inside of the operative tunnel 2 and the tannery leathers supported by the support frames 4 of the predetermined group are simultaneously subjected to the treatment of the air conditioning devices 3 (typically axial fans).
In a preferred but not limiting manner, each of the consecutive drying chambers 24 integrally houses in block a predetermined group (or pack) of support frames 4 initially grouped or accumulated in the buffer loading station 23 and is provided with air conditioning devices 3 that are adjusted independently for each of the drying chambers 24: this ensures a more effective control of the tension applied on the leathers by the actuation means 5 during the drying phase in the operative tunnel 2.
As far as the moving means 6 are concerned, as illustrated in figure 3, they comprise, in a purely illustrative and indicative way:

movable translation means, only partially visible in figure 3 and therefore not indicated for the sake of simplicity, coupled with the base framework 27 through support members;
motorization means, overall numbered with 30, arranged at the initial portion of the base framework 27 and facing the loading buffer station 23, coupled through transmission means, not visible, with the movable translation means in order to make them slide along the linear direction Z according to a first way, causing advancement of the support frames 4 (in this case by pack) inside the operative tunnel 2;
thrust means, as a whole numbered with 31, coupled with the movable translation means and cooperating directly with the support frames 4 in order to determine their advancement along the linear direction Z as a result of the operation of the motorization means.

In a preferred but not binding way, the motorization means act on the movable translation means in such a way as to make them slide along the linear direction Z according to a second way, opposite to the first way, causing retraction of the movable translation means, when the drying cycle of the predetermined group of support frames 4 is completed and the predetermined group of support frames 4 is conveyed to an unloading station 28 located downstream and outside the operative tunnel 2: by doing so, the movable translation means are made available to the advancement along the first way of the linear direction Z of a subsequent predetermined group of support frames 4 in the meantime introduced into the loading buffer station 23.
As said, integral part of the present invention is also leather, particularly but not exclusively tannery leathers, drying and/or conditioning method.
Such a method comprises the following steps:

establishing a prefixed standard expansion value of the leathers (for instance 200 mm);
loading at least one of these leathers on both the side faces 4c, 4d of each of the support frames 4;
conveying the support frames 4, thus provided with leathers, towards the operative tunnel 2 of the drying and/or conditioning plant 1 described before;
operating the actuation means 5 in order to mechanically work on the support frames 4 in such a way as to stretch the leathers to the prefixed standard value.

In accordance with the innovative features of the invention, the method comprises a step of controlling the level of expansion of the leathers which comprises the following operations:

establishing a nominal predetermined tension value of the leathers (for instance 50 bar);
detecting the tension value of the fibres of the leathers expanded as a result of the operation of the actuation means 5 on the support frame 4 at the operative tunnel 2 of the drying and/or conditioning plant 1;
comparing the measured tension value to the predetermined nominal tension value, measuring the tension deviation thereof;
adjusting operation of the actuation means 5 depending on the measured tension deviation, by varying the value of expansion of the leathers, in such a way as to keep the leathers spread and/or tensioned substantially to the predetermined nominal tension value,

In appropriate but not exclusive way, the operation of operating the actuation means 5 in order to mechanically work on the support frames 4, the operation of detecting the tension value of the fibres of the leathers expanded, the operation of comparing the measured tension value with the predetermined nominal tension value, by measuring the tension deviation and the operation of adjusting operation of the actuation means 5 depending on the measured tension deviation and the operation of activating or releasing the mechanical locking means occur automatically, being managed by the central processing and control unit (or PLC) 14, shown schematically in figure 4, available to the operators by means of a control panel.
It is confirmed that the actuation means 5 used in the method of the invention are any of the linear actuators selected from the group consisting of mechanical actuators, oil-pressure (or hydraulic) actuators 13, pneumatic actuators, their combinations and/or similar.
The operation of detecting the tension value of the fibres of the tannery leathers expanded is performed through a system for measuring the pressure of the operating fluid 9 of the actuation means 5 which exploits the mechanical and operational connection of the actuation means 5 with the support frames 4: the system for measuring the pressure of the operating fluid 9 comprises, preferably, the pressure transducer 11 electrically connected with the central processing and control unit 14.
The operation of adjusting operation of the actuation means 5 depending on the measured tension deviation takes place through the supply circuit of the operating fluid 10 of the actuation means 5 which acts on the support frames 4 modifying the length thereof: the supply circuit of the operating fluid 10 comprises, in this case, purely by preferred way, a displacement transducer 21, electrically connected with the central processing and control unit 14, and an auxiliary hydraulic plant of the type described above, generally indicated with 29 in figure 4.
Preferentially, the operation of adjusting operation of the actuation means 5 takes place in such a way as to spread the support frames 4 and increase the expansion of the tannery leathers by a length (or distance) corresponding to the measured tension deviation: the actuation means 5 thus work as tensioners so as to increase the tensioning level of the tannery leathers.
In particular, the operation of spreading the support frames 4 due to operation of the actuation means 5 in order to increase the expansion of the leathers is performed when the support frames 4, equipped with these leathers to be dried, are placed in an initial loading buffer station 23, arranged in front of the operative tunnel 2 and suitable to receive the support frames 4, of the drying and/or conditioning plant 1.
In a preferred but not exclusive manner, the operation of adjusting operation of the actuation means 5 also takes place in such a way as to restrict/spread the support frames 4 and decrease/increase the expansion of the leathers of a length (or distance) corresponding to the measured tension deviation, so that the actuation means 5 work as de-tensioners/tensioners lowering/increasing the tensioning level of the aforesaid leathers, bringing it back to the predetermined nominal value (by the recipe).
More specifically, the operation of restricting/spreading the support frames 4 due to operation of the actuation means 5 in order to decrease/increase the expansion of the leathers is performed when the support frames 4, provided with leathers to be dried, are arranged inside the operative tunnel 2 of the drying and/or conditioning plant 1 and are undergoing drying by the air conditioning devices 3.
Advantageously, the operation of operating the actuation means 5 to mechanically work on the support frames 4 to expand the leathers to the predetermined nominal tension value takes place in a differentiated manner from opposite sides of the support frames 4 in order to compensate for irregularities and/or asymmetries in profile and/or shape of the leathers loaded on the support frames 4, for example when the leathers take a shape substantially similar to a triangle or a trapezoid.
In this case, the entire control step of the level of expansion of the tannery leathers appropriately and conveniently takes place in a differentiated manner from the opposite sides of the support frames 4.
In such a way, the method of the invention is functional even in case of leathers, especially tannery ones, of less traditional shape which it happens to manage in the tanning field.
In essence, therefore, the purpose of the method of the invention is keeping constant at the predetermined nominal value, fixed at design level, the tension to which the fibres of the leathers are subjected during the process of drying and/or conditioning, checking and if necessary modifying it accordingly: such a purpose - change of the tension of the fibres of the leather up to the predetermined nominal value - is achieved by increasing or, predominantly, decreasing the level of expansion of the leathers on the support frames 4. Increasing or decreasing the level of expansion of the leathers on the support frames 4 takes place by spacing out or approaching each other, generally along a vertical direction, the two telescopic semi-portions in which each of the support frames 4 receiving at least one leather on at least one of its side faces 4c, 4d is divided, taking into account that, as mentioned, the process of drying and/or conditioning involves the progressive restriction of the leathers and the consequent increase of the tension of their fibres which, therefore, must be managed to avoid damages due to overtensions.
The method of the invention provides for stopping spreading (namely opening or spacing out the two semi-portions that make them up) of the support frames 4 when a given pressure/force of the actuation means 5 which work on them is reached, while all the current systems that manage these operations, however being carried by a fluid, stop on reaching a given distance: in prior art, therefore, the pressure on the leathers can be disadvantageously transmitted even in excess since the fluid actuation means stop at the prefixed distance.
The invention allows, instead, to set the opening of the support frames as a function of a predetermined nominal tension value different from leathers to leathers and, also, provides, during the drying and/or conditioning process, an operation which cannot be found in the prior art, namely the adjustment of the operation of the actuation means according to the measured tension deviation with respect to a predetermined nominal tension value, by varying the value of expansion of the leathers, so as to keep them spread and/or tensioned substantially for such a predetermined nominal value.
On the basis of the foregoing, it is understood, therefore, that the leathers drying and/or conditioning method and the drying and/or conditioning plant suitable to implement such a method, object of the present invention, achieve the purposes and reach the advantages mentioned above.
In executive stage, changes could be made to the leathers drying and/or conditioning plant of the invention, consisting, for example, in a constructive conception of the moving means different from that one just described and shown in the drawings that follow.
In particular, the leathers drying and/or conditioning plant or method of the invention, preferably applied by means of a discontinuous pack (or block) moving of the support frames as described above, is obviously applicable, with appropriate tricks, also by means of a continuous moving of the individual support frames.
Beyond to that, in other embodiments of the present invention, not shown, the drying and/or conditioning plant could include detection means - which measure the tension value of the fibres of the leathers expanded as a result of the operation of the actuation means on the support frames - different from those ones previously described in relation to the preferred embodiment.
Moreover, in other embodiments of the drying and/or conditioning plant of the invention, not illustrated, the adjustment means could assume a structural design different from that one shown in the course of the description, while remaining capable of acting on the actuation means according to the deviation between the measured tension value and a predetermined nominal tension value so that the leathers remain stretched substantially to the predetermined standard tension value.
In addition, further embodiments of the drying and/or conditioning plant of the invention, not shown, could provide that at least one of the support frames retain only a leather in one of the side faces, or a single leather in each of the side faces.
It is also stated precisely that the number of support frames, provided with at least one leather in at least one of its side faces, could be any, such a number being able to vary on the basis of the manufacturer's constructive choices, operative needs and/or spaces available at the client's factory.
It is, finally, clear that several other changes could be made to the drying and/or conditioning method and plant concerned, without departing from the principle of novelty intrinsic in the inventive idea expressed herein, as it is clear that, in the practical implementation of the invention, materials, shapes and sizes of the illustrated details could be changed, as needed, and replaced with others technically equivalent.
Where the constructive features and techniques mentioned in the following claims are followed by reference numbers or signs, those reference signs have been introduced with the sole objective of increasing the intelligibility of the claims themselves and therefore they have no limiting effect on the interpretation of each element identified, by way of example only, by these reference signs.

Claims

Leathers, particularly tannery leathers, drying and/or conditioning method comprising the following operations:
- establishing a prefixed standard expansion value of said leathers;

- loading at least one of said leathers on at least one of the side faces (4c, 4d) of one or more support frames (4);

- conveying said support frames (4), provided with at least one of said leathers, towards an operative tunnel (2) of a drying and/or conditioning plant (1);

- operating actuation means (5) in order to mechanically work on said support frames (4) in such a way as to stretch said leathers to said prefixed standard expansion value, -establishing a predetermined nominal tension value of said leathers;

- detecting the fibres tension value of said leathers expanded following said operation of said actuation means on said support frames at said operative tunnel (2),
characterized in that it comprises a step of controlling the level of expansion of said leathers just introduced in said operative tunnel (2) and/or during the gradual transition of said leathers through said operative tunnel (2) of said drying and/or conditioning plant (1) by the following operations:
-

- comparing said measured tension value with said predetermined nominal tension value, measuring tension deviation thereof; and

- adjusting the operation of said actuation means depending on said measured tension deviation in such a way so as to keep said leathers spread and/or tensioned to said predetermined nominal tension value,
wherein said operation of adjusting said operation of said actuation means (5) depending on said measured tension deviation takes place through a supply circuit of an operating fluid (10) of said actuation means (5) which acts on said support frames (4) modifying the length thereof.
Method according to claim 1), characterized in that said operation of detecting said fibres tension value of said expanded leathers takes place through a system for measuring operating fluid (9) pressure of said actuation means (5) exploiting the mechanical and operative connection of said actuation means (5) with said support frames (4).
Method according to any of the preceding claims, characterized in that said operation of adjusting said operation of said actuation means (5) takes place in such a way as to spread said support frames (4) and increase the expansion of said tannery leathers by a length corresponding to said measured tension deviation, so that said actuation means (5) work as tensioners increasing the tensioning level of said leathers.
Method according to claim 3), characterized in that said operation of spreading said support frames (4) due to said operation of said actuation means (5) to increase said expansion of said leathers is performed when said support frames (4), provided with said leathers, are placed in a loading buffer station (23) arranged upstream said operative tunnel (2) of said drying and/or conditioning plant (1) and suitable to receive said support frames (4).
Method according to any of the preceding claims, characterized in that said operation of adjusting said operation of said actuation means (5) takes place in such a way as to restrict/spread said support frames (4) and decrease/increase the expansion of said leathers tannery by a length corresponding to said measured tension deviation, so that said actuation means (5) work as de-tensioners/tensioners lowering/increasing the tensioning level of said leathers.
Method according to claim 5), characterized in that the operation of restricting/spreading said support frames (4) due to said operation of said actuation means (5) to decrease/increase said expansion of said leathers is performed when said support frames (4), provided with said leathers, are placed inside said operative tunnel (2) of said drying and/or conditioning plant (1).
Method according to any of the preceding claims, characterized in that said operation of operating said actuation means (5) to mechanically work on said support frames (4) and expand said leathers to said predetermined nominal tension value takes place in a differentiated manner from opposite sides of said support frames (4) in order to compensate for irregularities and/or asymmetries in profile and/or shape of said leathers loaded on said support frames (4).
Method according to claim 7), characterized in that said step of controlling the level of expansion of said leathers takes place in a differentiated manner from said opposite sides of said support frames (4).
Leathers, particularly tannery leathers, drying and/or conditioning plant (1) comprising:
- an operative tunnel (2) mainly developing along a linear direction (Z) and provided with air conditioning devices (3) suitable to work on said leathers so as to dry them according to predefined treatment cycles;

- a plurality of support frames (4), each of which suitable to accommodate on at least one of the side faces (4c, 4d) at least one of said leathers in such a way as to keep it in stretched position;

- actuation means (5) operatively connected with said support frames (4) and suitable to be operated in such a way as to spread said leathers to a prefixed standard expansion value;

- moving means (6), operatively connected with said support frames (4) in order to convey them along said linear direction (Z) according to a predetermined speed inside said operative tunnel (2), to allow drying of said leathers, and outside said operative tunnel (2) to allow discharge of said leathers dried in a working cycle and load of said leathers to be dried in the next working cycle,

- detection means (7), operatively connected with said actuation means (5) and suitable to measure the fibres tension value of said leathers expanded following operation of said actuation means (5) on said support frames (4);
characterized in that it comprises:
- adjustment means (8), operatively connected with said actuation means (5) and suitable to work on said actuation means (5) depending on the tension deviation between said measured tension value and a predetermined nominal tension value so as to keep the leathers spread or tensioned to said predetermined nominal tension value when said leathers are just introduced in said operative tunnel (2) and/or during the gradual transition of said leathers through said operative tunnel (2), said actuation means (5) being arranged:

- at a loading buffer station (23), placed upstream said operative tunnel (2) which it communicates with and suitable to receive said support frames (4), when said actuation means (5) work on said support frames (4) in order to expand said leathers to said predetermined nominal tension value, and/or

- inside said operative tunnel (2) when said actuation means (5) work on said support frames (4) in order to restrict said leathers to said predetermined nominal tension value, wherein said adjustment means (8) include a supply circuit of the operating fluid (10) of said actuation means (5).
Plant (1) according to claim 9), characterized in that said detection means (7) comprise a system for measuring the pressure of the operating fluid (9) of said actuation means (5).
Plant (1) according to claim 10), characterized in that said actuation means (5) are any of the linear actuators selected from the group consisting of hydraulic actuators, pneumatic actuators, mechanical actuators and their combinations.
Plant (1) according to claim 10) or 11), characterized in that said actuation means (5) are movable along said linear direction (Z) being coupled through sliding means (25), operatively connected with motorization means (26), with a base framework (27) that contributes to define said operative tunnel (2) and which supports said support frames (4) in such a way as to keep them suspended from a reference surface (S) on which said base framework (27) is suitable to insist.
Plant (1) according to any of the claims 10) to 12), characterized in that said actuation means (5) are associated with and work in correspondence of at least one of the lateral sides (4a, 4b) of each of said support frames (4).
Plant (1) according to any of the claims 11) to 13), characterized in that said loading buffer station (23) integrally includes a predetermined group of said support frames (4) before said predetermined group of said support frames (4) is transferred in block within said operative tunnel (2) by said moving means (6), in such a way that said support frames (4) of said predetermined group simultaneously reach the inside of said operative tunnel (2) and said leathers supported by said support frames (4) of said predetermined group are simultaneously subjected to the treatment of said air conditioning devices (3).
Plant (1) according to claim 14), characterized in that said operative tunnel (2) is divided into a plurality of consecutive drying chambers (24), physically separate from and operatively independent each other, communicating each other to allow passage of said support frames (4), each of which is suitable to accommodate in block said predetermined group of said support frames (4) initially present in said loading buffer station (23) and provided with said air conditioning devices (3) suitable to be adjusted independently for each of said drying chambers (24) in such a way as to ensure a more effective control of the tension of said leathers during the drying phase inside said operative tunnel (2).
Plant (1) according to claim 15), characterized in that said actuation means (5) are arranged at the initial part of each of said drying chambers (24) and are made movable by said moving means (6) along said linear direction (Z) for a maximum longitudinal stroke which coincides with the transverse width of each of said drying chambers (24).