WO1993019208A2

WO1993019208A2 - Dryer for the continuous drying and conditioning treatment of hides or fabrics

Info

Publication number: WO1993019208A2
Application number: PCT/EP1993/000654
Authority: WO
Inventors: Angelo Guarise
Original assignee: Baggio Tecnologie Srl
Priority date: 1992-03-19
Filing date: 1993-03-18
Publication date: 1993-09-30
Also published as: IT1258562B; ITVI920046A1; WO1993019208A3; ITVI920046A0

Abstract

The invention concerns the making of a dryer for the continuous drying and conditioning treatment of hides or fabrics, which includes: a loading unit (3, 203) composed of an entry belt (31, 231) on which the goods (10, 210) to be treated is placed, and of a feed belt (33, 233) overlooking a feed counterbelt (36, 236). These receive between them the goods to be treated (10, 210) from the entry belt (31, 231). Furthermore, it includes a drying chamber (2) containing a number of drying cylinders (40, 47, 51), one on top of the other, which receive the goods (10, 210) conveyed by the feed belt (33, 233). This is made advance inside the drying chamber up to an unloading belt (4), with a winding course. The advance speed of the feed belt (33, 233) is higher than the advance speed of the entry belt (31, 231).

Description

DRYER FOR THE CONTINUOUS DRYING AND CONDITIONING TREATMENT OF HIDES OR FABRICS. This invention consists of a dryer for the continuous drying and conditioning treatment of hides or fabrics particularly for hides. The drying and conditioning of goods made of hide or fabric are carried out by means of dryers, basically composed of a drying chamber, into which products are inserted and which is provided of a heating and dehumidification system. A continuous hide dryer is already well-known, which is the object of Italian patent n° 1207906, where hides are in- serted into the drying chamber. They are placed between two continuous porous belts, one on top of the other, which run through the drying chamber with a winding course, among a number of cylinders. The first inconvenience of the above-mentioned dryer is its difficulty in maintaining the tension of the joined belts constant throughout their course, due to their considerable length . In order to maintain said tension as constant as possible , the higher belt is forced against the lower belt , in the hide loading area , which may damage hides already in the phase of ins ertion into the dryer . .In f act , the strong adherence of the higher belt to the lower belt accentuates pos sible folds in the hide , which become def ects in the finished product after drying . A further inconvenience is represented by the f act that near each winding cylinder rotating with a constant number of revolutions , the peripheral speed of the external belt is higher than the speed of the internal belt and , conse- quently , there is s liding between the two belts . Such sliding is transmitted to the hide placed between the two belts , on which wrinkling and folds may appear . At the end of drying these become permanent folds and , therefore , further defects . The aim of this invention is to eliminate, or at least reduce, the above-mentioned inconveniences . In particular, the main aim of this invention is to make a dryer in which the tension of the belts conveying hides remains practically constant throughout the drying course. A further aim of this invention, is to make a dryer which prevents folds or wrinkling from forming on hides, espe- cially in the phase of insertion between the two belts. Another aim of this invention is to make a dryer in which hides remain perfectly outstretched between the guide belts throughout the drying course. A further aim of this invention is to make a dryer in which the hide near the points of the belt winding round the cylinders do not undergo wrinkling, because of the sliding between the same belts, due to different peripheral speeds. Last but not least is the aim to make a dryer whose heating system can have an easy maintenance. The above-mentioned aims are achieved by making a dryer for the continuous drying and conditioning treatment of hides or fabrics which, according to the main claim, comprises: - a loading unit composed of an entry belt on which the goods to be treated are placed and of a feed belt overlook- ing a feed counterbelt, both of them are substantially in- clined between which are disposed the goods to be treated, coming from the entry belt; - a drying chamber containing a first drying belt overlook- ing a drying counterbelt, both of them are substantially horizontal and suited to receive between them the goods conveyed by the feed belt, said chamber containing further drying belts, superposed each one below the first drying belt, where each of said drying belts receives the goods from the previous belt and convey them to the following belt; - an unloading belt conveying the goods outside the dryer, at the end of treatment; - means for heating and dehumidifyinσ the air in the drying chamber; - means for the dehumidification and conditioning of the product, and it is characterized in that these belts are closed-ring wound between one or more cylinders, at least one of which is powered, where the advance speed of the feed belt is higher than the advance speed of the entry belt. According to a preferred embodiment, the dryer is provided with a system for the heating and dehumidification of the drying chamber with heat pump where the heat exchange between the condensing/evaporating batteries of the heat pump and the drying chamber interior takes place by means of the interposition of freon/water heat exchangers. Furthermore, the invented dryer can be provided with a high-frequency unit for controlling humidity and, therefo- re, for the conditioning of hides going out. Furthermore, the invented dryer is provided with gate valves controlled by thermometers and hygrometers, for changing the air inside the dryer with air taken from the outside when, under the same temperatures, the humidity of the external air is lower than the humidity of the air inside the drying chamber. Therefore, the invented dryer offers the advantage to obtain a better quality in the finished product than the quality achievable with the dryers of the well-known type, having the same potentiality, and with energy saving. The above-mentioned aims and advantages will be better highlighted during the description of a preferred embodi- ent of invention given just as an indication, which does not intend to be restrictive, and represented in the en- closed drawings where: - fig. 1 shows the lateral section view of the dryer of this invention; - fig. 2 shows the front view of the dryer in fig. 1; - fig. 3 shows the detail of the loading unit of the dryer in fig. 1; - fig. 4 shows the details of some re-conveyance belts, each one placed at the hide unloading end from the respec- tive drying belt; - fig. 5 shows a cross section of the dryer in fig. 1 with a schematic view of the heat-pump heating and dehumidifica- tion system; - fig. 6 shows the detail of the bearing system for drying belts in axonometry; - fig. 7 shows an alternative version of execution of the invented dryer. As can be seen in fig. 1, the dryer of this invention, which is collectively referred to as 1, is composed of a drying chamber, collectively referred to as 2. In the front part of this chamber there is a loading unit, collectively referred to as 3, through which the hides to be dried are inserted into the drying chamber, while in the lower part of the same chamber there is an unloading belt 4 through which the dried hides are conveyed outside. The dryer is also composed of a high-frequency unit, col- lectively referred to as 5, for controlling hide humidity. Furthermore, as can be seen in fig. 5, the heat-pump hea- ting and dehumidification system that is collectively referred to as 6 also belongs to the dryer 1. This system is used both to heat the hide-drying air and to remove the steam that forms inside the drying chamber 2 during the treatment, by condensation. It should be noted that in a different embodiment the high- frequency unit may not be present. The loading unit collectively referred to as 3 is shown in fig. 1 and in greater detail in fig. 3 where one sees that it is composed of an entry belt 31, basically horizontal, on which the hide to be dried 10 is placed. This belt advances by means of a powered cylinder 32 at a predeter- mined speed in direction 11. The entry belt 31 runs on a support plane 8 whose end 12 is rounded, so that it can be used as a transmission element for the powered cylinder 32 of the entry belt 31. Then it conveys the hide 10 towards a feed belt 33 belonging to the loading unit 3 and running on a fixed plane 7, and the rotation of the powered cylinder 35 round which it is wound, makes it advance in direction 34. A feed counterbelt 36 is associated with the feed belt 33 and overlooks the same. This counterbelt advances in the same direction 34 and at the same speed as the feed belt 33, moved by at least one of the cylinders round which said counterbelt is wound. The feed counterbelt 36 is made of a soft and elastic material so that it can adapt itself to the superficial shape of the hide, maintaining the same outstretched, and guide it up to the insertion into the drying chamber. In this way, an interspace forms between the feed belt 33 and the counterbelt 36 that overlooks it, where the hide 10 coming from the entry 31 is placed. The advance speed in direction 34 of the feed belt 33 turns out to be higher than the advance speed of the entry belt 31. For this reason, the hide 10, when passing from the entry belt 31 to the feed belt 33, is attracted by the latter with a tension proportional to the speed difference between the belts, which allows one to maintain the hide in tension and, therefore, perfectly outstretched. Furthermore, one can see that in the area 38 where the hide 10 passes from the entry belt 31 to the feed belt 33, the feed counterbelt 36 lays between two cylinders 39 whose centers are aligned along a direction 13, forming an angle 14 with the horizontal direction. The value of this angle 14 and the diameter of cylinders 39 are dimensioned in such a way that in the area 38 it is possible to achieve the conditions allowing this passage to take place with a sufficiently gentle bending and such as to avoid the for a- tion of folds. As one can see in fig. 2 and fig. 3, the feed counterbelt 36 is maintained adherent to the hide 10 and, therefore, also to the feed belt 33 by the presence of pressure ele- ments 20, composed of a number of elastic ribbons 9 which exert a constant pressure, uniformly distributed throughout the hide surface and prevent this from going back. These ribbons are fixed to the higher part of the loading unit 3 and arrange themselves on the counterbelt 6 for gravity. Furthermore, they are locked in the final part by means of a locking element 19 which is fixed to the struc- ture of the loading unit 3 and is used to prevent the counterbelt 36 from accidentally dragging the ribbons during its movement. The pressure of the elastic ribbons 9 is uniformly distributed throughout the hide surface, thanks to the characteristics of softness of the feed counterbelt 36. When the hide 10 arrives at the final part of the feed belt 33, it is guided downward by the feed counterbelt 36 and by the respective exit cylinder 37. So, it is forced to meet the first drying belt 40 which is placed horizontally and is ring wound between two entry cylinders 15 and two exit cylinders 16. Furthermore, the rotation of said cylinders, round which the belt is wound, makes it advance in direc- tion 41. The advance speed of the drying belt 40 in direction 41 is higher than the advance speed of the feed belt 33. For this reason, the drying belt 40 recalls the hide 10 from the feed belt 33 with a tension proportional to the difference of their speed. Such tension allows one to maintain the hide outstretched on the drying belt 40, even in this case. From this moment the hide that is being treated 10 begins its course inside the drying chamber 2, without having undergone violent pressures between the cylinders and the belts . Therefore , the formation of folds is avoided, while the presence of possible wrinkling has been eliminated by the stretching caused by the speed difference of the same belts . As one can see in fig. 1, the hide in the course of manu- facture is maintained adherent to the first drying belt 40 by a drying counterbelt 42, placed in the higher part of the drying belt 40. As one can see in fig. 4, when the hide 10 arrives at the end of this first drying belt 40, it meets the reconveyance belt 43 which winds the drying belt 40 round the higher cylinder 44 belonging to the two exit cylinders 16, with a moderate pressure, avoiding in this way the formation of folds on the hide. Then the reconveyance belt 43 guides the cylinder also for a part of its descending tract 45. In this way, the reconveyance belt 43 guides the hide 10 up to the lower cylinder 46 where the hide is placed on a second drying belt 47, completely similar to the previous one. This belt makes the hide advance in direction 48, opposite to the previous one 41. The reconveyance belt is made of elastic and soft material so that it can function as guide and control of pressure on the hide 10 that is being treated, in an optimum way. In particular, fig. 4 shows that the reconveyance belt 43 is wound between a higher cylinder 49 and a lower cylinder 50. Since both of said cylinders are placed behind the higher cylinder 44 of the drying belt 40, the higher cylin- der 49 allows the hide to be inserted between the first drying belt 40 and the reconveyance belt 43 in a gentle way, while the lower cylinder 50 functions as a guide for the hide 10 when this comes off the previous belts and begins to place itself on the second drying belt 47. Furt- her ore, the lower cylinder 50 controls the hide 10 throu- ghout its phase of stretching on the second drying belt 47 until completely coming off the belts. While traveling on the drying belts, the hide tends to stiffen because of the drying action. For this reason it has increasing difficulties in adapting itself to the ben- ding of the exit cylinders of the drying belt and, in particular, of the higher cylinder where the hide is placed between the drying belt and the respective reconveyance belt. This situation is shown in fig. 4, where one can see that the hide 10 in phase of advanced drying, in the passage from the drying belt 51 to the unloading belt 4 below, when it is wound round the higher cylinder 52 of the two exit cylinders 53 of the drying belt 51, forces against the internal branch 54 of the reconveyance belt 55. Therefore, in order to avoid the interference of the internal branch 54 against the external branch 56, a stiff core (60) is placed between the two branches, which is used as a separa- ting element between the two branches and the reconveyance belt 55. Furthermore, apart from taking up and neutralizing the thrust of the hide 10 it guides it along a normal return course, until depositing on the belt below. When the hide reaches the lower part of the drying chamber, it is placed on the unloading belt shown in fig. 1 and collectively indicated with 4, where the high-frequency unit 5 is located, through which the hide passes before being unloaded outside. The hide conditioning takes place in this high-frequency unit 5 and, practically, the percen- tage of humidity that the hide will contain when it reaches the dryer dump, is defined in this unit. Furthermore, this unit is aimed at making this humidity uniform throughout the surface with a percentage value predetermined by the user. This high-frequency unit 5 is basically composed of a number of electrodes 24 placed over and under the unloading belt 4, on which the hide 10 is placed. They are electri- cally connected to a high-frequency generator 25. Therefo- re, these electrodes 24 produce a high-frequency field which produces a heating due to the friction of the molecu- les of the water contained in the hide, when it passes between the electrodes . Since the energy irradiated by the electrodes 24 is proportional to the humidity taken, the intensity of the electric field is piloted in such a way as to produce a higher or lower water evaporation in the area of the hide containing a greater or smaller quantity of humidity, respectively. In this way, the humidity is uni- formly distributed throughout the hide. In other words, it is possible to obtain a hide conditioned with a pre-esta- bushed humidity value, at the end of drying. Fig. 1 also shows that, while moving, both the first drying belt 40 and the second drying belt 47, and similarly any further drying belts are supported by bearing elements referred to as 70, which develop longitudinally in the direction in which each belt advances. Fig. 6 shows a partial axonometric view of these bearing elements, where one can see that they have a tubular shape and present a transversal circular section 71 suitable to guarantee a sufficient support to the belt during its movement, without strong frictions and without preventing hot air from pass- ing among the same belts. The longitudinal axis of these bearing elements 70 develops parallel to the belt in the direction of its length 74. However, it should be noted that the section of these bearing elements can also be other than tubular and take different shapes from the circular one. As far as the heating and dehumidification of the drying chamber 2 is concerned, the improved heat-pump unit is usefully used, the object of Italian Patent Application n. VI92A000044, which in fig. 5 is collectively referred to as 6. It can be seen that it is composed of a compressor 61, a heating battery 62 and a condensing battery 63, which are inserted in the heat pump cycle by means of the interposi- tion of exchangers 64 and 65, respectively. The interposi- tion of these heat exchangers 64 and 65 is aimed at insuia- ting the compressor circuit 66 in which the refrigerant, for example freon, flows from the thermal exchange circuits 67 and 68, of the condensing battery 63 and of the heating battery 62, respectively, in which, vice versa, only water circulates. In this way, if the heating battery 62 and the condensing battery 63 should be corroded by acids present in the hides, which are circulated during drying, it is possible to replace them by closing the on-off valves 69, without intervening on the refrigerating circuit of the heat pump. This is a great advantage, since maintenance can be effected also by non-qualified personnel, which other- wise would need the intervention of refrigerator techni- cians. A fan 80 is included for air circulation, which takes air from the higher part 87 of the drying chamber 2. Air enters the fan in the direction indicated by the arrow 81 and is conveyed with the direction indicated by the arrow 82 in the room below and against the heating battery 62. In this area, air recovers the heat that the compressor 61 produces during its operation and, furthermore, is heated when passing through the heating battery 62. This heating batte- ry 62 is connected to a second exchanging element 101, by means of the circuit 68. This exchanging element 101 be- longs to the heat exchanger 64, which receives heat from a first exchanging element 102, also belonging to the same exchanger 64, which is the heat pump condenser. Furtheππo- re, the exchanging element 102 is series connected to the refrigerant circuit 66 and in this element 102 the conden- sation of the refrigerant circulating in the circuit 66 takes place. This refrigerant, by condensing, gives the condensation heat to the second exchanging element 101 and this, in its turn, gives it to the heating battery 62, which heats the air entering the dryer. This hot air enters the drying chamber 2 in direction 83, where it rises upward in the direction indicated by the arrow 84, passing through the drying belts with winding direction. Since the air entering the lower part of the drying chamber 2 is dry hot air, as can be seen in fig. 5, a part of it is also conveyed inside the high-frequency unit, in which it favours the drying of the hide being conditioned. When the air reaches the higher part 87 of the drying chamber 2, it is attracted by the fan 80 and thus flows in direction 85 through the condensing battery 63 where it is cooled and dehumidified by means of the condensation of the steam that it has accumulated during the course in the drying chamber. This humidity settles by dripping in the small tank 86 of the condensing battery 63. In fact, through the circuit 67, this condensing battery 63 is connected to a second exchanging element 103, belonging to the heat exchanger 65, which gives heat to a first exchan- ging element 104, also belonging to the same exchanger 65 and series connected to the refrigerant circuit 66. This represents the heat pump evaporator. In the first exchan- ging element 104 the evaporation of the refrigerant circu- lating in the circuit 66 takes place. By evaporating, this refrigerant absorbs the heat from the second exchanging element 103, which, in its turn, absorbs it from the con- densing battery 63, which cools and dehumidifies the air going out of the dryer. Then, this dried air is sent to the lower chamber, in direction 82, where the compressor 61 is present and starts again to circulate in the closed circuit, as previously described . In the higher part 87 of the drying chamber 2 , a lateral opening 9 0 and a higher opening 9 1 are inc luded , both communicating with the outside . They can be closed by means of a shutter, 92 and 93 respectively. The opening and closing of these shutters is driven by a control device, including a hygrometer, which is not shown in the figure. These openings are used to discharge the air of the drying chamber 2 outside, when its humidity is higher than the humidity of the external air. In fact, when the drying air reaches the higher part 87 of the drying chamber 2, it is full of humidity. Therefore, if the humidity of the exter- nal air is lower than the humidity of the air circulating inside, in the higher part of the drying chamber, it is more convenient to discharge the latter with direction 94 through the lateral opening 90 and suck new air from the outside, through the higher opening 91 with direction 95 and convey the latter through the condensing battery 63, improving, in this way, the thermal exchange efficiency.

Fig. 7 shows an other embodiment of the invented dryer, where one can see that the entry belt 231, which forms the loading unit, collectively referred to as 203, is inclined. Furthermore, the feed belt 233 and the first drying belt 240 belong to the same belt 200, whose advance speed is higher than the advance speed of the entry belt 231. This favours the stretching of the hide 210 that is being dried. The inclination of the entry belt 231 and the integration of the first drying belt 240 with the feed belt 233 in a single belt 200, in some cases favours the hide stretching, preventing clogging and folds while it advances, and fa- vours its stretching, too. On the basis of what has been described, it is possible to understand how the invented dryer achieves the pre- established aims. The first aim that is achieved is to dry the hide less violently than in the well-known dryers and, above all, guiding it constantly. In this way it is possible to pre- vent the formation of folds which would be prejudicial to quality, after drying. Furthermore, the presence of the reconveyance belts at the exit end of each drying belt prevents the formation of wrinkling on the hide, caused by different rim speeds of the guide belts, when the hides that are being treated are conveyed to the following belt by one of these drying belts. Furthermore, thanks to the high-frequency unit, the inven- ted dryer allows one to obtain a hide exactly conditioned at the desired percentage humidity degree at the exit. It has also been noted that the utilization of an improved- heat-pump heating system in which the refrigerant circuit is separated from the condensing/heating batteries through the interposition of freon/water heat exchangers, simpli- fies maintenance. In fact, if the heating and/or condensing batteries should be changed, this replacement can also be carried out by non-qualified personnel, since it is neces- sary to intervene only on the pipes connecting the batte- ries to the heat exchangers on the side in which water circulates. It is not necessary to intervene on the refri- gerating circuit. In phase of execution, changes can be brought about to the invented dryer, in order to improve or simplify its manufac- ture or aimed at improving its operation. Therefore, for example, the air entering the drying chamber could also take place by means of heat exchangers of a well-known type, such as resistance exchangers, steam exchangers, or something similar, instead of heat pumps. Similarly, air dehumidification could take place by means of high-frequency filters or other types of filters. Furthermore, as far as the high-frequency unit for hide conditioning is concerned, which in the solution of execu- tion has been prearranged at the end of drying, it can also be placed in any intermediate position in the drying cham- ber or even more than one high-frequency units could be included. Furthermore, the unloading belt can also be placed in such a way as to unload the hide on the opposite side of the entry side and this, for example, would allow one to join the dryer to continuous systems. Moreover, the elastic ribbons can be replaced by chains or other elements which can distribute a uniform pressure on both the belt and the hide. However, it should be noted that all these possible ver- sions are protected by this invention.

Claims

CLAIMS 1) Dryer for the continuous drying and conditioning treatment of hides or fabrics comprising: - a loading unit (3;203) composed of an entry belt (31;231) on which the goods (10;210) to be treated are placed and of a feed belt (33;233) overlooking a feed counterbelt (36;236), both belts substantially inclined between which are disposed the goods to be treated (10;210), coming from the entry belt (31;231); - a drying chamber (2) containing a first drying belt (40;240) and a drying counterbelt (42) overlooking the belt (40), both of them are substantially horizontal and suited to receive between them the goods (10;210) conveyed by the feed belt (33;233), said chamber containing further drying belts (47, 51), superposed each other, below the first drying belt (40;240) where each of said belts (47, 51) receives the goods (10;210) from the previous belt (40;240) and convey them to the following belt; - an unloading belt (4) which conveys the goods outside the dryer, at the end of treatment; - means for heating and dehumidifying the air circulating in the drying chamber; - means for dehumidifying and conditioning the product, characterized in that all these belts (31,231; 33,233; 36,236; 40, 41, 42, 47, 51) are closed-ring wound between one or more cylinders, at least one of which is powered, where the advance speed of the feed belt (33;236) is higher than the advance speed of the entry belt (31;231). 2) Dryer according to claim 1), characterized in that said feed belt (233) and said first drying belt (240) form a single continuous ring (200). 3) Dryer according to claim 1), characterized in that the advance speed of said feed belt (33) is lower than the advance speed of the first drying belt (40). 4) Dryer according to claim 1), characterized in that a reconveyance belt ( 43 , 55 ) overlooks each drying belt ( 40 , 240 ; 47 , 51 ) at the exit end, which is c los ed-ring wound between at least two cylinders ( 49 , 50 ) , of which at least one is powered, where said reconveyance belt ( 43 , 55 ) guides the treating goods ( 10 ; 210 ) and maintains them adherent to the drying belt ( 40 , 240 ; 47 , 51 ) when such goods pass from a drying belt (40 , 240 ) to the drying belt below ( 47 , 51 ) . 5) Dryer according to claim 3), characterized in that in each reconveyance belt (43, 55) a stiff reconveyance core (60) is placed between the two branches (54, 56) that constitute the same reconveyance belt. 6) Dryer according to claim 1), characterized in that the feed counterbelt (36, 236) is maintained adherent to the feed belt (33, 233) by means of pressure elements (20) which are placed on the surface of the same feed counter- belt (36, 236) by means of gravity and are fixed to the loading unit (3, 203) in their higher and lower ends. 7) Dryer according to claim 1), characterized in that the heating and dehumidification elements for the air circulating in the drying chamber (2) are a heat pump (6) composed of a compressor (61) which maintains a refrigerant in circulation in a closed circuit (66), operatively con- nected both to a condensing battery (63), through which the damp air going out of the drying chamber (2) circulates and is dehumidified and to a heating battery (62), through which dry air circulates and is heated before entering the same drying chamber (2). 8) Dryer according to claim 5), characterized in that each battery (62, 63) is operatively connected to the refrigerant circuit (66), through at least a heat exchanger (64, 65), provided with first exchanging elements (102, 104) series connected to the refrigerant circuit (66), making the thermal exchange with second exchanging elements (101, 103), connected to the corresponding battery (62, 63), with which they effect a further closed circuit (68, 67), which is separated from the refrigerant circuit (66). 9) Dryer according to claim 7), characterized in that the first exchanging element (104), belonging to each heat exchanger (65) relating to each condensing battery (63) is the evaporating element in which the refrigerant evapora- tion takes place. 10) Dryer according to claim 7), characterized in that the first exchanging element (104) belonging to each heat exchanger ( 64) -relating to each heating battery (62) is the condensing element in which the refrigerant condensation takes place. 11) Dryer according to claim 1), characterized in that the higher part (87) of the drying chamber (2) communicates with the outside through openings (90, 91), each one inter- ceptable through at least a shutter (92, 93) where this shutter is driven in relation to the external air humidity. 12) Dryer according to claim 1), characterized in that the means for dehumidifying and conditioning the goods are at least a high-frequency unit (5), which is composed of a plurality of electrodes (24), electrically connected to a high-frequency generator (25), through which the goods (10) pass. 13) Dryer according to claim 5), characterized in that the pressure elements (20) are a plurality of elastic ribbons (9) . 14) Dryer according to claim 5), characterized in that the pressure elements (20) are a plurality of chains.