WO2006103535A1

WO2006103535A1 - Method and apparatus for fabric calendering

Info

Publication number: WO2006103535A1
Application number: PCT/IB2006/000721
Authority: WO
Inventors: Angelo Manenti
Original assignee: T.M.T. Manenti S.R.L.
Priority date: 2005-03-29
Filing date: 2006-03-29
Publication date: 2006-10-05
Also published as: EP1863964B1; ATE539188T1; ITTO20050200A1; CN101166861A; CN101166861B; EP1863964A1

Abstract

An apparatus for continuous calendering of fabrics comprises a first operating unit (20) with devices for surface moistening (27) of the fabric (3) and/or means for impregnation (28) of the fabric (3) with treatment liquids, and with cylinders (23, 24) for exerting on the fabric (3) a mechanical action of lateral pressing, and at least one second operating unit (30, 30a) for subjecting the fabric (3) to a condition of intense lateral pressing without the aid of a water-repellent belt.

Description

"Method and apparatus for fabric calendering"

* * *

Field of the invention

The present invention relates to a method and an apparatus for fabric calendering.

In the textile sector, the term "calendering" identifies a finishing treatment in which a fabric is subjected to hot drawing in order to reduce its thickness, eliminate any possible creases therefrom and bestow thereupon a tendentially shiny appearance on at least one face.

State of the prior art

In the known art three systems of calendering exist, which are preferably used selectively in the various textile sectors (synthetic fibres, vegetal fibres, and animal fibres) according to the tradition of use and the expectations of the fashion market, and namely: a) shoe calendering, b) roll calendering, and c) belt calendering. As represented schematically in Figure 1, in systems of the first type a heated cylinder 1 is made to rotate against a fixed concave shoe 2, which presses against the cylinder itself with the fabric 3 being treated set in between. Said technique is used mainly in the wool sector and presents the drawback of stretching the fabric, on account of the friction of the latter against the fixed surface of the shoe. The machine is a single-acting one, and the effect is obtained on just one face of the treated fabric. As represented in Figure 2, roll calenders, or "cotton calenders", provides instead for two or more rolls or cylinders Ia, Ib, Ic set on top of one another, i.e., stacked up in "tower" fashion, where at least one of the cylinders is heated (the cylinder Ib, in the example illustrated) , and the cylinders rotate against one another at a very high pressure, with the fabric 3 set in between. The cylinders may be made of metal or else be coated with various materials, all having in any case as common characteristic high hardness. Said characteristic has the purpose of limiting the section deformed in the point of contact between the cylinders, and hence concentrate the pressure in very little space. The machine can be a single-acting one or else a multiple-acting one, but the direction of passage and the face of the fabric involved (with respect to the heat source) is always the same.

Belt calenders, which have been introduced relatively recently, implement a process that resembles as regards effect and results that of shoe calenders. In this technique, as is represented schematically in Figure 3, the fixed shoe is replaced by a deformable and as a whole impermeable belt 4, configured as an endless belt, guided via rollers 5 and subjected to marked tensioning. In this way, no major stretching of the fabric is noted, as instead typically occurs in the case of traditional shoe calenders. The machine is a single-acting one, and the effect involves just one face of the treated fabric. The process of impermeable- belt calendering has then an important secondary effect: the moisture present or induced on the fabric, exposed in a hot and closed environment (i.e., the space between the cylinder and the belt) causes formation of steam, which is an excellent aid to the process for many textile materials.

In all of the aforesaid known calendering processes the main purpose is, as has been said, to bring about a marked reduction in the thickness of the fabric, via lateral mechanical pressure with the administration of thermal energy (the word "lateral" is here to be understood with the typical meaning that it has in the textile field, i.e., in relation to the larger sides or faces of the fabric, referred to in jargon as "front" and "back") . As a second effect, which is also important, a considerable surface variation of the treated fabric is observed, which becomes markedly shiny. Unfortunately, also this aspect, which is at times sought according to the prevailing fashion trend, is extremely temporary and unstable.

In order to solve the problem and bestow a permanently shiny appearance, it is necessary to aid the process with a subsequent operation of stabilization or else to use chemical products during the process itself. Chemical agents are used above all in belt calendering where the prolonged thermal effect seems, even today, to help considerably the development of chemical products and their permanence on the fabric. The present invention is based upon recognition of the fact that the conventional calendering systems mentioned above present technological limits, which preclude a real effectiveness thereof.

In this connection, it is to be considered that, in general terms, fibres and fabrics are materials "with memory", which, if they are left free to relax (in a natural way or else subjected to a mechanical beating action) , tend to assume a resting condition as close as possible to their original dimensional condition (with phenomena of crimping of the fabric thread, relaxing of the twisting of the fibres, relaxing of the stresses applied mechanically in the various processes, hygroscopic dilation, etc.).

One of the purposes of textile finishing is hence to apply a series of mechanical, physical and chemical processes that tend to fix in a relatively permanent way a certain aspect of the fabric. Calendering is precisely a tendentially stabilizing treatment, both at a structural level and as regards the visual appearance of a fabric, in which the reduction in thickness and the tactile; aspect assumes particular importance.

In order to obtain this results, traditional textile technology teaches that it is necessary to administer simultaneously to the fabric undergoing treatment various forms of energy, and in particular a mechanical action, which brings about a structural modification by squeezing, and a thermal action, which supplies the energy necessary to enable the molecules of the fibre to settle more easily in the new condition. In many cases, especially for animal fibres such as wool, a more or less high presence of moisture or of chemical agents concurs to enhancing the effect.

The mechanical and thermal energies have an effect that depends directly upon the .time required to apply said energies, upon the stay time of the effect applied, and upon the type of reverse process with which said energies are released (thermal shock) . In practice, then, there exists a first stage, i.e., a "heating" time, followed by a stage of structural modification, i.e., a "positive transition" time, where the intimate structure of the fabric assumes the new condition. After the modification phase, it is necessary to perform, at least in the case of many materials, a cooling stage, i.e., a "negative transition" time, which must be fast and incisive in order to prevent the structural modification obtained during the positive transition from vanishing to a fair extent on account of the aforesaid memory effect of fibres . In shoe calendering the specific pressure on the fabric is medium, and the time of application is short. In addition, the fabric is exposed to air, which implies fast evaporation of its water content, and is subject to stresses by stretching. The consequence is that the physical transformation has a strong cohesive component that vanishes very easily.

On the other hand, in roll calendering the pressure or pressures is/are relatively high and are obtained with high hydraulic pressures acting on semirigid cylinders made of paper-wool or polyamide (with hardnesses of around 85° Shore D - equivalent to 98- 100° Shore A); the temperatures can even exceed 200°C, but the time of application is very short. For these reasons, said process can be used exclusively on fabrics with high sensitivity to temperature and with low hysteresis, as in synthetic fibres, or with high sensitivity to mechanical deformation, as in vegetal fibres. In either case an appreciable and 'permanent result is obtained only with a marked flattening of the fibre, which in this way looses, however, a major part of its own three-dimensional structure and assumes a marked metallic visual appearance and a "papery" tactile effect.

Finally, in belt calenders, the treatment time is decidedly prolonged but the specific pressures are relatively modest (1-5 kg/cm² of distributed mean pressure) , which, according to the angle of winding between the belt and the cylinder, can create an arc- shaped distribution of the forces (with a pressure peak that is twice the distributed mean pressure) . The generally impermeable nature of the belt enables a control on the water content, in practice preventing a continuous evaporation and maintaining the rate of moisture constant throughout the process. For these reasons, the process is used especially for treatment of animal fibres.

As has already been mentioned, in this case chemical products can be used, which, thanks to chemical bonds known to people skilled in the sector, bestow upon the fabric a marked shiny appearance, at times "plastified" according to the requirements of fashion trends .

However, heavy use of the aforementioned chemical products presents three important disadvantageous aspects:

- the chemical products, in proportion to the amount used, attack also the structure of the fabric itself, weakening it;

- the chemical products themselves and their vapours attack the components of the machine, especially the silicone-coated belt and the overhead structures, considerably shortening the life of the calender; and

- chemical agents have a cost, which, together with premature wear of the machine components, leads to increased costs of production of the fabric thus treated.

Methods and apparatuses for continuous refining of fabric are known, in which, during treatment, operatively associated to the fabric is a water- repellent belt subjected to strong tension. For example, the document No. WO-93/17167 describes a method for continuous decatization, which consists in causing the fabric already impregnated or moistened with a treatment liquid to pass through pressure means constituted by the aforesaid water-repellent belt subjected to tension, which sandwiches the fabric against a heated cylinder.

The fact that the fabric stays for a certain time at a certain temperature in a wet/moist environment under the mechanical constraint imposed by the pressure of the water-repellent belt leads to the intimate modification of the fabric, bestowing thereupon permanent characteristics that are both of a structural nature and possibly of a visual nature.

The presence of the water-repellent belt constitutes a problem, in so far as said belt entails problems of reliability both in terms of defects on the results of treatment of the fabric and in terms of resistance to use over time. In addition, the use of the water-repellent belt entails very high replacement costs, as well as extremely complex and burdensome possible operations of replacement. Summary of the invention The purpose of the present invention is to provide an apparatus and a method that enable the problems and drawbacks referred to above with reference to the prior art to be eliminated.

Another purpose of the present invention is to provide a method and an apparatus for fabric calendering that enable improved effects of continuous permanent stabilization to be obtained, both at a structural level and as regards the visual appearance of the fabric, as compared to the prior art, and that can be used indifferently for treatment of synthetic fibres, of fibres of vegetal origin, and of fibres of animal origin.

A further purpose of the invention is to provide a method and an apparatus for fabric calendering designed to ensure an appreciably higher rate of treatment.

Yet a further purpose of the invention, which expressly regards the case of calendering with the aid of chemical products, is the reduction in the consumption of chemical products, and the use of components that, both as regards fabrication and as regards maintenance, require shorter operating times and lower operating costs.

With a view to achieving said purposes, a subject of the present invention is a calendering method having the characteristics of Claim 1. Additional characteristics of the method are set down in the dependent Claims 2-10.

The subject of the present invention is also a calendering apparatus having the characteristics specified in Claim 11 and in the claims depending thereupon.

The fundamental idea underlying the present invention lies in the original intuition that the action of the conventional water-repellent belt can be obtained in an equally, if not more effective way by contrast cylinders with elastically deformable surfaces radially pushed in pressure contact against the corresponding heated cylinders of the second operating unit, thus creating at least two areas of intense squeezing, through which the fabric is subjected to the marked mechanical constraint generated by the pressure of the contrast cylinder. The mechanical constraint imposed in said area can be rendered decidedly greater than that obtained in an equal area by using conventional tensioned water-repellent belts. Of course, its amount will depend upon the mutual pressure of the cylinders coming into contact. In order to increase the productivity of the apparatus, said area may be repeated a number of times. Considering the operation as a whole (mechanical effect plus thermal effect) , experimentally it has been possible to show how an effective and powerful mechanical/thermal action, if compared to the case of belt calendering, produce by itself a good level of surface shininess, much higher than that obtained with the traditional process, and how, advantageously, in order to fix permanently this shiny effect, much smaller amounts of chemical products are sufficient. In the case of certain fabrics, indeed, a so-called "KD" fixing action (i.e., a process of wool fixing with the aid of steam) without the addition of chemical products is more than sufficient to obtain the desired level of sheen.

Brief description of the drawings The invention will now be described with reference to the annexed plate of drawings, which is provided purely by way of non-limiting example, and in which:

- Figures 1, 2 and 3 are schematic illustrations of a known process of shoe calendering, a known process of roll calendering, and a known process of belt calendering, respectively;

Figure 4 is a schematic illustration of a continuous-calendering line made according to the invention; and - Figure 5 is a schematic illustration of a possible variant of the continuous-calendering line according to the invention. Detailed description of the invention

Figure 4 is a schematic illustration of an apparatus or line for continuous calendering of fabrics according to a first embodiment of the invention. The calendering line, designated, as a whole, by the reference number 10, comprises the following contiguous operating units: - a unit for moisture control or fabric- conditioning unit 20, provided with a device for controlled surface moistening 27 and/or a device for impregnation 28 with chemical products, and a pair of cylinders 24-23, which are possibly also heated, between which the fabric is subsequently; - a calender unit with two pairs of motor-driven cylinders stacked in tower fashion, designated by 30; and a possible drying and cooling device, not illustrated in so far as it is generally conventional, set downstream of the second calender 30.

In the line 10, the fabric 3 being treated is wound off a respective feeding means, which, in the example represented, is a support 11 on which the fabric is lapped, to be drawn and guided, via means in themselves known - designated as a whole by the reference number 12 - into the conditioning unit 20. After conditioning in the conditioning unit 20 the fabric 3 passes, with a short passage through the air, into the calendering unit 30, purposely drawn and guided with means, in themselves known. The fabric 3 leaving the calender 30 then passes into the possible drying and cooling apparatus (not illustrated) , and is finally drawn and guided - via means 15 in themselves known to a generic lapping unit 16, which deposits the fabric 3 on an adequate accumulation support, designated by 17.

The conditioning unit 20 is envisaged for all applications that involve use of water or chemical fixing products. As has already been described, calendering in the most general sense of the term can be obtained with the fabric dry and then undergo fixing during other subsequent finishing processes. Certainly, however, the best results according to the present invention can be obtained by applying, during the process itself, small amounts of water or products to enhance and impress permanently the shiny appearance.

The conditioning unit 20 can advantageously be used as entry calender. This comprises a structure 21, which supports two cylinders 23, 24 with parallel axes, at least one of which preferably (but not necessarily) is heated. At least one cylinder 23 is pushed towards the other cylinder 24 via pneumatic pressure, i.e., via pneumatic actuator means, not illustrated in detail. The main characteristics of the cylinders 23, 24 can correspond to those of the cylinders of the calender unit 30 that will be described hereinafter.

The above configuration can advantageously be used for complete impregnation of the fabric in the first pressing step, with consequent variation of the visual and tactile results.

This amount of moisture must remain high until within the treatment area between the two cylinders 24- 23. For this purpose, the fabric must tend to enter in a direction that is perpendicular (horizontal, in the example) to the squeezing axis (vertical, in the example) .

An inclination exceeding 20° upwards or downwards could cause premature contact of the damp fabric against one of the surfaces of the cylinder, possibly heated. The contact would cause, in fact, a sudden evaporation of the moisture and/or of the chemical product, and this would reduce considerably the total effectiveness of the process. The calendering unit 30 comprises a structure 31, which supports at least two cylinders 33, 32 with parallel axes, and preferably two pairs of cylinders 33-32 and 35-34 stacked on top of one another in tower fashion, at least one of which may be heated. At least one cylinder of each pair is pushed towards the other cylinder via pneumatic pressure, i.e., via pneumatic- actuator means (not illustrated in detail but within the reach of the person skilled in the art) . Supply of the actuator means with air enables, if need be, an adaptation of the relative position between the axes of the cylinders in order to enable passage between the cylinders themselves of any hems, even thick ones, or of elements of the fabric that are in relief. It should be noted that said passage is problematical in traditional calenders, in which the two cylinders are pushed against one another via hydraulic actuators,, which do not enable adaptation of position between the cylinders .

Preferably, the pressure exerted via the pneumatic- actuator means is such that a pressure of at least 20 kg per linear centimetre will be exerted on the fabric 3 in order to obtain an evident effect of drawing. At least ₍ one of the cylinders of each pair 33- 32 and 35-34 is preferably coated with material suited for working at high temperature and with hardness not higher than 95° Shore A. In this way, an adequate elastic surface deformation of the coating is enabled in order to create between the cylinders a pressing area provided with relatively low rigidity and a pressing action that is extended in time, such as not to destroy completely the "three-dimensional" structure that may be present on the fabric and to enable the fabric to remain for a certain time in a closed environment, without any evaporation, under a heavy mechanical constraint.

The temperature during passage between the two cylinders of each pair 33-32, 35-34 can be set selectively and is preferably in the order of 80-200⁰C. Also the pressure between the two cylinders of each pair can be adjustable in a selective way. For this purpose, the calendering unit 30 can be equipped with adjustment means, not represented, acting on the pneumatic actuator/actuators of the unit 30 with a pressure that can be adjusted up to beyond 100 kg/cm. In one embodiment, the cylinders can also have differentiated surface hardness: this can be obtained, for example, via a coating with rigid polymers, rubbers or silicones for at least one cylinder, in such a way that the maximum specific pressure will be concentrated in a minimum point of contact between the cylinders.

By passing through the calendering unit 30, thanks to the characteristics thereof, there is instead created a more intense squeezing of the fabric 3.

It may be noted that the device for controlled moistening 27 and/or the impregnation device 28 of the conditioning unit 20 enable considerable enhancement of the feel and sheen on various types of fabrics, such as, for example, animal fibres that are markedly sensitive to humidity or to steam resulting from administration of thermal energy. It should be noted that a moistening stage of this sort is not envisaged in traditional roll-calendering systems.

As has been said, the specific function of the calendering unit 30 is that of fixing, tendentially but not necessarily in progression, the process of squeezing of the fibre. According to the primary characteristic of the invention, said calendering unit 30 does not use a water-repellent belt, but, as has been seen, pairs of particular calendering cylinders 32-33 and 34-35, through which the fabric 3 is maintained in conditions of lateral mechanical constraint and which can present elastically deformable lateral pressure surfaces, possibly also with differentiated deformability. The cylinders of each pair 32-33 and 34-35 of the unit 30 can be optionally heated and, as has also already been said, the mutual contact pressure can be selectively variable, as a result of their relative displacement in the radial direction, with modalities not illustrated in so far as they are within the reach of the person skilled in the art.

Associated to the two pairs of cylinders 32-33 and 34-35 are respective sets of transmission rollers, for example arranged in the way represented in Figure 4, designed to determine through each pair a substantially rectilinear passage of the fabric 1, i.e., tangential to the surfaces of said rollers, and hence substantially without running over said surfaces.

In this way, through the calendering unit 30 the fabric 3 is squeezed for a short time at a certain temperature under the marked mechanical constraint imposed by the pressure between the cylinders 32-33 and 34-35. The mechanical constraint, in terms of surface loading applied on the fabric 3, can be rendered appreciably higher than that obtained on the same area using a conventional tensioned water-repellent belt.

In order to increase the effectiveness and productivity of the apparatus, various solutions can be adopted; for example, the calendering unit 30 may be doubled, as indicated by 30a in Figure 5, or even repeated a number of times; in this case, a number of pairs of heated cylinders and contrast cylinders will, for example, be provided, arranged one after the other along the path of advance of the fabric 3. In addition, the pairs of cylinders 32-33, 34-35 of the calendering unit 30 can be driven by an single motor drive or else by independent motor drives, and in this case each pair of cylinders will be preceded or followed by a convenient system for synchronization of the speed with that of the preceding or ensuing pair.

Practical tests conducted by the Applicant have made it possible to verify how the method and the apparatus according to the invention enable the pre-set purposes to be achieved effectively, through a balanced ratio between the forms of energy and times involved, without any significant pauses between the various passes, which would lead to a considerable loss of effect. For this purpose, the temporal aspect of the process according to the invention must be emphasized, understood as time that passes between application of the various forms of energy. The various actions of heating, squeezing, and subsequent cooling are made in a fast temporal sequence: in this way, before the relaxing reaction of the fabric - due to the aforesaid memory effect - which follows upon a first action becomes- appreciable, a new action is applied. It should be noted that a mode of operation of this sort cannot be obtained by treating the fabric with machinery of a known type, which is typically single-acting and requires operating times that are considerably longer.

The method and apparatus described can be defined as being of universal application, in so far as they can be used with advantageous results for dry, wet and/or moistened treatment of fabrics, whether they are synthetic fibres, vegetal fibres or animal fibres.

Wet calendering or impregnation calendering performed according to the invention achieves very marked natural shiny effects and hence requires reduced amounts of chemical products as compared to the belt technique. The material of the cylinders is decidedly more robust and insensitive than the silicone materials of the belt, and, in addition, the costs and times involved in production and replacement of a cylinder are by far more contained as compared to a belt system. It is clear that numerous changes are possible to the apparatus and method described by way of example for the person skilled in the art. For example, the calendering unit 20 could also comprise two or more pairs of calendering cylinders similar to the cylinders 23 and 24. Of course, the details of construction and the embodiments may vary widely with respect to what is described and illustrated herein, without thereby departing from the scope of the present invention as defined in the ensuing claims. Thus, for example, the elastic deformability of the contrast cylinder or each contrast cylinder 33, 35 may be obtained, instead of with a coating of elastic material such as silicone, by making the entire cylinder of such a material.

Claims

1. Method for fabric calendering, of the type in which a fabric (3) is continuously moved for being subjected to a reduction in thickness through lateral mechanical pressure with administration of thermal energy, the method comprising a first phase during which a mechanical action of lateral pressing of the fabric (3) is applied, characterized in that the method further comprises carrying out at least one second phase of stabilization of the fabric (3), during which the fabric itself is subjected to conditions of intense lateral pressing, higher than that of the first step, without the aid of a water-repellent belt.

2. Method as per Claim 1, wherein in the first phase the fabric (3) is moistened and/or impregnated with treatment liquids.

3. Method as per Claim 1, wherein the first phase comprises a step of calendering in which the fabric (3) passes through at least one pair of rotating cylinders with parallel axes (23, 24) .

4. Method as per Claim 1, wherein the second phase comprises a step of calendering during which the fabric (3) is pressed against the side surface of at least one rotating cylinder possibly heated (32, 34), by means of a contrast cylinder (33, 35) , which has an elastically deformable lateral pressure surface and is rotatable about an axis parallel to the axis of said heated cylinder (32, 34) .

5. Method as per Claim 1, wherein the second phase is followed by a step of drying and cooling of the fabric (3) .

6. Method as per Claim 1, wherein, with short time intervals within one another, there are provided: a first step of roll calendering, aimed at reducing the thickness of the fabric (3) moistened and/or impregnated with treatment liquids;

- a second step of roll calendering, in which the stabilization of the structure obtained in the first step is favoured by intense pressing of the fabric (3) without the aid of a water-repellent belt; and

- a cooling step.

7. Method as per Claim 6, wherein at least one cylinder is pneumatically pressed towards the other cylinder. 8. Method as per Claim 6, wherein at least one cylinder has an elastically deformable surface.

9. Method as per Claim 6, wherein selective regulation of the temperature of at least one cylinder is provided. 10. Method as per Claim 6, wherein selective adjustment of the contact pressure between said cylinders is provided.

11. Apparatus for calendering fabrics, in which a fabric (3) is continuously moved so as to be subjected to a reduction in thickness through lateral mechanical pressure with administration of thermal energy, the apparatus comprising an operating unit (20) having means (23, 24) for exerting on the fabric a mechanical action of lateral deformation, characterized in that it comprises at least one second operating unit (30, 30a) having means (32, 33; 34, 35) for subjecting the fabric (3) to a condition of intense lateral pressing without the aid of a water-repellent belt.

12. Apparatus as per Claim 11, wherein the first operating unit comprises means for surface moistening

(27) of the fabric (3) and/or means for impregnation

(28) of the fabric (3) with treatment liquids.

13. Apparatus as per Claim 11, wherein the first operating unit is a calender with possibly heated cylinders (20) . 14. Apparatus as per Claim 11, wherein the second operating unit (30, 30a) includes at least one pair of heated rotating cylinders (32, 34) against the side surface of each of which the fabric (3) is pressed via a respective contrast cylinder (33, 35) having an elastically deformable lateral pressure surface.

15. Apparatus as per Claim 11, wherein, at short spatial distances from one another, there are provided:

- a first calender (20), with means for surface moistening (27) of the fabric (3) and/or means for impregnation (28) of the fabric (3) with treatment liquids, and at least one pair of cylinders (23, 24);

- at least one second calender (30, 30a) including a pair of rotating cylinders (32, 34), against the side surface of each of which the fabric (3) is pressed via a respective contrast cylinder (33, 35) having an elastically deformable lateral pressure surface; and

- a cooling apparatus.

16. Apparatus as per Claim 15, wherein in the first calender (20) :

- at least one cylinder (23, 24) is pressed towards the other cylinder via pneumatic means (25) ; and/or

- at least one cylinder (23, 24) has an elastically deformable surface; and/or - at least one cylinder (23, 24) is coated with material which can work at high temperature and has a hardness not higher than 95° Shore A.

17. Apparatus as per Claim 16, wherein means are provided for regulating selectively at least one of: - the temperature of at least one cylinder (23, 24); and

- the contact pressure between the cylinders (23, 24)

18. Apparatus as per Claim 16, wherein the surface hardness of one cylinder (23, 24) is different from the surface hardness of the other cylinder.

19. Apparatus according to Claim 11, wherein said second operating unit comprises two separate sets (30, 30a) , each of which includes a respective pair of heated cylinders (32, 34), and corresponding contrast cylinders (33, 35) with elastically deformable lateral pressure surfaces.

20. Apparatus according to Claim 14 or Claim 19, wherein said pairs of cylinders (32, 33; 34, 35) (30, 30a) are stacked on top of one another in tower fashion.