The present invention concerns a leather tanning drum.
In the leather tanning process the drum, which, as it is known, is a big-sized, cylindrical-shaped machine rotating horizontally on its axle and large enough to contain several hundred kilos of skins, is generally used in at least three different phases of the aforesaid process, and more specifically in the soaking and liming, in the tanning and in the dyeing phase.
Each one of these phases has its own specific, indispensable function and implies the use of specific chemical solutions and compounds.
Drums currently used, which are in wood planking, often need massive and expensive washings as, though made of highly resistant wood, they undergo some degree of impregnation from the particularly aggressive chemical elements and compounds that are used in the tanning process.
The use of steel drums, also introduced on the market, failed to solve the problem, as the particular aggressiveness of the chemical agents causes a fast deterioration of this kind of drums, this deterioration being due to both a general and homogeneous attack to the material from the chrome tanning salts, with a consequent gradual reduction of the steel wall thickness, and to the widespread and localized attacks to the drum internal surface from the chlorides, or similar substances, used in some of the processes, like the bleaching of the skins.
It has to be noticed, furthermore, that the above-mentioned steel drums imply, for the performance of the process, a global energetic waste which results to be remarkably increased, due to the material high thermal conductivity.
So, few examples of steel drums are now used, only in connection with specific works, as those of the drum shown in US-A-4,441,342, i.e. laboratory dyeing tests or milling, but, also in these specific works, the use of steel material is not an optimal one; for instance, in milling operation, a problem arises from the low thickness of the steel surface of the treatment chamber, where the skins can be damaged by the edges of holes or other openings provided in said surface, said edges being increasingly sharpened during the use.
Another problem involved with current drums concerns the difficulties linked to the carrying out of the bath recycle.
Indeed, specific technical solutions have been developed in order to avoid the frequent interruption of the drum rotation to permit the removal of the waste substances produced during some phases of the process, as well as to carry out the filtering, checking and changing of the tanning bath chemical solution, these measures being based on the fact that the drum main rotation shaft is internally hollow so as to allow both the entering and exit of the substances composing the bath, or included in it, during the drum rotation.
At the hollow shaft external end, a tank is generally placed where waste products deposit and from which cochlea devices, or similars, keep collecting them; it is from this same tank that the chemical solution, after having been cleaned up and regenerated, enter the drum again through the same hollow shaft.
Machines including this hollow shaft solution are disclosed, for example, in JP 62 020600, US-A-4,122,692 and again in US-A-4,441,342.
Just the two last cited documents constitute interesting cases to show how different solutions of the problem concerning the bath circulation inside the drum may strongly depend on particular operative contexts. In fact, the structural lay-out of US-A-4,441,342 drum is very simple in respect of the other one's, the simplicity deriving substantially from the fact that, in this case, the hollow shaft is not axially passing through the drum. The operative context of said drum (milling, laboratory dyeing tests) is different fom that of the US-A-4,122,692, which concerns a general purpose drum.
So, in US-A-4,441,342, the bath circulation has not a relevant role; it only needs to assure the entering and exit of the bath liquor without stopping the drum rotation; in US-A-4,122,692, instead, the bath ciculation must be done in such a way to assure, also, a good exchange of the liquor between the two ends of the internal volume of the drum, in order to achieve a bath as homogeneus as possible. The liquor exchange between the two internal ends is obtained just employing a hollow shaft, axially passing, which comunicates with the treatment compartment by means of connecting ducts located at both front ends of the drum. Obviously, in this second solution, the presence of a shaft in the center of the drum would cause the winding of the skins around the same shaft during the rotation of the drum. Therefore, in order to avoid said handicap in such drums, radial partition walls are used, but this introduces other disadvantages, as, the drum unsuitableness to specific works, the necessity of separate charging openings for each treatment chamber, and the increasing, in general, of structural complexity and total costs.
From the above it is easily understable the seeking of solutions regarding general purpose drums in which an efficacious bath circulation without the axially passing shaft drawback is assured.
About the recycle, we have to add that some solutions have been adopted involving blades arranged inside the drum, which are positioned both all along the cylindrical surface and in correspondence with the lateral surface whereto said hollow shaft is connected, these blades having been specifically designed in order to make the gathering of waste materials and their conveying outside together with the bath liquid solution as effective as possible.
Considering that the entering and the exit of the bath liquor and of the above waste substances is done by the same hollow shaft, it results evident that the bath recycle efficacy is strictly linked to the internal shape of the drum; in other words we can say that the recycle action risks to be annulled unless the drum bath in and out fluxes are accurately kept apart.
Furthermore, as regards the global safety level associated with the drum operating phases, it has to be considered that during the carrying out of particular works requiring a high quantity of liquid mass inside the drum, there is a greater possibility for the internal pressure to raise up to dangerous levels.
It arises, so, the need of employing suitable automatic devices in order to avoid any of the related risks.
One of the most practicable way to achieve that may consist in intervening on the closing means of the charging openings, introducing convenient and innovative safeting devices.
The aim of the present invention is just to propose a drum provided with constructive and structural improvements which enable the getting over of all the aforementioned problems.
This aim is achieved with a leather tanning drum comprising a cylindrical main body rotatable on a horizontal axis, a hollow shaft communicating with the outside and located in corrispondence to one of the cylindrical main body circular surfaces, wherein a plurality of cavities, or pockets, are longitudinally arranged along the internal circumferential surface of said main body, a plurality of radial cavities and an annular cavity are located in correspondence of the circular surface whereon said hollow shaft is located, said radial cavities connecting said longitudinal cavities and said annular cavity with said hollow shaft, said longitudinal cavities and said annular cavity being in communication with the internal volume of the drum through openings arranged in such a way to obtain, during the drum rotation, a continuous recycle and a continuous exchange of the chemical bath between the two ends of the internal volume of the drum.
The drum comprises exactly four longitudinal cavities, or pockets, placed in diametral opposed positions, and one radial cavity for each longitudinal cavity, the radial cavities being separately connected, at one of their ends, with sections of said hollow shaft.
The above annular cavity is located peripherally to the circular surface where the hollow shaft is located; it comprises peripheral cavities which are in communication with said longitudinal cavities and which are, further, in communication with the interior of said main body through openings provided in sectors of said peripheral cavities located in different radial positions in respect of said longitudinal cavities, or pockets.
The longitudinal pockets are in communication with the interior of said main body through openings placed in proximity of the circular surface facing the surface in correspondence of which said annular cavity is located
The drum cylindrical main body is in polymeric material; a metal framework with evident structural characteristics is externally connected to said main body, said framework being specifically designed to allow the thermal dilatations of the polymeric material main body.
At least one door for the introduction and removal of leathers in and from the drum is kept closed by the help of elastic means regulated so as to assure a perfect seal under normal operating conditions and, at the same time, working as a safety-valve in the event of anomalous raisings of the drum internal pressure.
The drum of the present invention includes also other constructive improvements that fit with the above-mentioned innovative structural features and contribute to improve its general hardiness and resistance in agreement with the special operating conditions.
The advantages deriving from the drum constructive and structural improvements re clearly evidentely when we take into consideration the improved operative flexibility involving an easier passage from one phase of the tanning process to the next, due to the ineffective action of the various chemical agents on the drum material, to the excellent working performances linked to the bath re-circulation circuit new conformation, and, finally, to the high safety and durability levels attained.
However, for a better understanding of the above-mentioned advantages and the characteristics of the present invention, this will now be described by way of an embodiment example, with reference to the accompanying drawings, in which:
Referring now to fig.1, it is indicated with [10] a leather tanning drum according to the present invention.
It is composed of a main cylindrical body [11], in polymeric material, horizontally rotating on its axle by the help of a gearmotor unit [12] having an output pinion [13] engaging with a gear [14] directly coupled to said cylindrical body [11].
The partially sectioned view of fig.1 shows that the rotation shaft [15] of the drum [10] is internally hollow and divided in four sections separated by two orthogonal dividing plates [16, 17] which are more clearly illustrated in figures 2 and 3, said dividing plates being rotating together with the shaft [15] which is supported, free of rotating, en the structure [18].
Externally fixed to the main cylindrical body [11] there is a metal framework [19] composed of two 6-spoke structures placed in correspondence of the main body [11] circular surfaces [20, 21], and linked to one another by double C-shaped longitudinal bars [22], as it is clearly shown in fig.2 and 11.
The connection between the framework [19] and the drum main body [11] is obtained using both screw means [23] linking the lateral 6-spoke structures to the circular surfaces [20, 21] and other screw means [24] fastening the longitudinal bars [22] to the cylindrical body [11] side surface.
It is to be pointed out that the screw means [24] are useful also to fasten the so-called pegs [25] to the main body [11], said pegs being arranged on the inside of the drum so as to help the leathers dragging during the rotation; their fastening is obtained according to the connection scheme illustrated in fig.11. As regards the rows of pegs [25] which are not positioned in correspondence with the external bars [22], the fastening scheme is the one illustrated in fig.10.
In these last two figures we can see how, in correspondence with the drum areas which are subjected to high structural tensions, like the ones where the connection means [24, 24'] are positioned, the main body [11] thickness, which is significantly lower than that of the traditional wooden drums, is properly increased by reinforcement strips [26, 27], also in polymeric material, which can have a circular shape, as it is the case of fig.10, or a longitudinal one, as in fig.11.
Furthermore, in the case of fig.10 an auxiliary internal support [28] is used, of rectangular or similar shape, affecting the pegs fixing area only and also made in polymeric material; differently, we can see in fig. 11 how the peg is internally inserted on longitudinal supports [29] shaped so as to help. supporting the side edges of the panels [30] which constitute the internal walls of the longitudinal cavities [31] dedicated to the re-circulation of the liquid mass in which the leathers are soaking.
The above panels [30] are in fact provided with several holes [32], clearly shown in fig. 5, connecting the cavities [31] with the drum [10] internal space; said cavities [31] are also connected with other cavities [33], positioned in correspondence with the circular surface [20] of the main body [11], these cavities (33) being formed through side panels [34, 35, 36] fixed with said surface by heat seal, through a diametral panel [37], and through other closing panels [38] also fixed to said panels [34, 35, 36, 37] by heat seal. It is to be noticed that the closing panels [30] of the cavities [31] are fixed to the respective supports [29] by screw means, in order to allow the inspection and cleaning of said cavities whenever necessary.
As regards the lateral cavities [33], there is no need of inspecting or cleaning them, as their specifically designed configuration facilitates the outflow of the chemical bath and all the substances contained in it.
Fig. 2 and 3 just show the shape of said lateral cavities [33], two of which, for comprehension purposes, are clearly illustrated in detail, without their closing panel, while the other two, symmetrical to the former ones in respect of the shaft [15] position, are illustrated with the closing panel [38] regularly closed.
As we can see, the cavity transversal section is gradually reducing as we proceed towards the shaft [15], with a consequent increase in the speed of the flux out-flowing; furthermore, each of the cavities [33] is independently connected with each one of the sections the hollow shaft [15] is divided into; this obviously facilitates the exchange of the liquid and the substances in it towards the external depuration tank, which has not been shown in the annexed drawings as being of known technique.
The connection between the lateral cavities [33] and the drum internal space is achieved not only through the longitudinal cavities [31], but also through the cavities with triangular section [39] positioned on the edge of the circular surface [20]; in fact, on the panel [40] delimitating these cavities [39] we can find two diametrically opposed areas [41] suitably provided with holes.
Also the area where the lateral cavities [33] are connected with the hollow shaft [15] is obviously protected by a closing panel similar to panel [38], which has not been shown in fig. 2 and 3 only for reasons of drawing simplicity.
The introduction and removal of the leathers in and from the drum are carried out, in this embodiment example, through a unique door [42]; this is translated from its closing position, showed in fig. 1, to its opening position, and vice-versa, through hydraulic actuators [43] engaging with toothed sliding seats [44], which are connected with a hatch [45] fixed to the main body [11] by screw means [46]. It has to be noticed that the cylindrical main body [11] has been suitably reinforced in its door area through an internal panel [47].
The door [42], when in its closing position, is kept pressured against the hatch [45] through helical springs [48] positioned at the four corners of the door. In particular, with the help of fig. 6 and 7, we can observe that the springs are compressed between caps [49], which are fixed, by screws [50], to grooved pieces [51] coupled to the hatch [45], and to the spring supporting brackets [52], which are connected to the door [42] by screw means [53].
The door opening is performed by translating it along the sliding seats [44] after having lifted the door up from the position shown in fig. 7 to the one of fig. 8; this lifting is made possible by the action of the small hydraulic cylinders [54] fixed to the spring supporting brackets [52] by screws [55]. In fact, the pistons [56] of said small cylinders [54] act against the grooved pieces [51] causing the springs [48] to be more compressed and, consequently, the brackets [52] move from the hatch [45] to which the pieces [51] are radially coupled.
A rubber ring [57] is positioned all around the door edge [42] in order to assure a perfect seal between the door and the hatch. Suitable cylindrical pieces [58], fixed to the brackets [52], are positioned inside the springs [43], acting as guiding elements.
To complete the description of the drum [10] components, we can see longitudinal blades [59] fixed to the internal surface of the main body [11]; they are positioned alternatively to the pegs [25] and have the function of increasing the bath turbulence, said blades being suitably reinforced through side brackets [60], clearly shown in fig. 4 and 5.
As regards the metal framework [19], we have to notice that, in the enlarged view of fig. 9, the connection between the framework and the cylindrical main body [11] is designed so as to let some free space [61] between the framework itself and the drum main body in correspondence with the peripheral areas of the circular surfaces [20, 21]; this free space allows the necessary degree of dilatation of the main body [11], in polymeric material, due to the thermal excursions caused by the different treatments of the skins, which are being performed.
The drum of the present invention operates as follows.
After introducing the leathers and liquid mass containing the necessary chemical substances, the door [42] is moved to the closing position by sending the suitable input to the supplying hydraulic circuit of the actuators [43]; at this point, the hydraulic circuit of the small cylinders [54] is released, in order to let the drum door to be pressed against the hatch [45]. The drum is, then, ready to be started in its rotation movement by activating the motorgear unit [12].
With reference to fig. 3, given R as the drum rotation sense, we can see that cavities 33a and 33c are dedicated to the liquid and various substances outflow from inside the drum, while cavities 33b and 33d are intended to the re-entering of the liquid in the drum after it has been depurated in the external tank.
We must consider, in fact, that in the angular position shown in fig.3, and in those ones immediately following it, cavity 33a begins to be interested by the liquid, present inside the drum at about the level indicated in the figure, which reaches the cavity itself [33a] through the peripheral cavity [39], wherein the liquid has already flowing through the holes of area 41a; the same is not possible for the other cavity [33d], as it, in this moment, is not communicating with area 41a of cavity 39 but with area 41b, which, in that angular position, or in those ones immediately following int, is positioned on the drum upper part, not reached by the liquid. Therefore, when the drum, in its rotation, reaches the angular position of fig. 2, the quantity of depurated liquid coming from the external tank, where the average level is higher than that of the hollow shaft [15], is almost entirely flown to cavity 33d, and only in a small amount to cavity 33a; so, in the continuing of the rotation, until the position symmetrical to that of fig.3 is reached, the liquid outflow from cavity 33d to the drum takes place through the communicating longitudinal cavity 31d, while, starting from this angular position, cavity 33a, now positioned on the superior half plane, starts pouring its content towards the outside through section 15c of the hollow shaft [15].
The same happens, obviously, during the successive half rotation for cavities 33c and 33b, which are exactly symmetrical to cavities 33a and 33d respectively.
When the rotation sense is inversed, cavities 33b and 33d become the ones dedicated to the liquid outflow towards the outside, while cavities 33a and 33c are intended to let the depurated liquid re-enter the drum.
It can be noticed that, indeed, the chemical bath re-circulation is homogeneous and involves the whole liquid mass, as, like we see in fig.5, while the liquid flowing from the drum to the outside comes from the drum right side, where we find areas 41 feeding the exit cavities 33a and 33c, the depurated liquid re-enters the drum through the holes 32, which are connected with the entering cavities 33b and 33d and which are positioned on the drum left side.
Obviously, in order to improve the bath re-circulation efficacy, various modifications to the described embodiment of the present invention will be envisaged.
The connection scheme among the different cavities might, for example, be varied, in particular between the exit lateral cavities and the drum areas from which the liquid is collected, or else, new unidirectional devices for the flux exiting or entering the lateral cavities [33] might be employed; further, both the lateral and longitudinal cavities shape might be modified; the latter might, for example, be positioned obliquely along the drum internal surface rather than longitudinally; these all represent modifications that might be easily carried out in the industry thanks to the material composing the drum main body and its various internal devices, it consisting, in particular, of polypropylene.
Further variations might involve, obviously, the external metal framework, both as a whole and in its specific components, but always respecting its structural coherence with the drum main body in polymeric material.
The closing door [42], too, might undergo constructive variations, as, in some cases, for example, its manual operation might be preferred; or else, the number of doors might vary, in case the drum, just thanks to the optimal re-circulation efficacy, is divided into two or more compartments by longitudinal perforated panels, which perforated panels being commonly used when, for example, the skins to be treated are particularly long, or the drum loading capacity has to be increased.
It is to be understood that the drawings show only an example provided solely as a practical demonstration of the invention, and that this invention may vary in its form and dispositions. Any reference numbers in the appended claims have the purpose of facilitating the reading of the claims with reference to the description and to the drawings.