EP0200658B1 - Heating cylinder for products such as films, foils, slabs or the like - Google Patents

Abstract

A heater drum has an outer cylindrical wall centered on and rotatable about an axis, an inner cylindrical wall fixed concentrically within the outer wall and defining therewith an annular chamber, and a body of a heat-transmitting fluid in the chamber in heat-transmitting contact with both walls. A core body fixed nonrotatably about the axis inside the inner wall is heated to a high treatment temperature. This heat is transmitted radially from the core body to the inner wall. The walls are rotated jointly about the axis relative to the core body to distribute the heat of the inner wall via the fluid body to the outer wall. The chamber is at subatmospheric pressure and the fluid is partly vaporized and partly liquid at the high treatment temperature. The core body is of part-cylindrical section generally centered on the axis and has an outer surface spaced slightly radially inward of the inner wall. In addition the heat-transmission is via another body of heat-conducting liquid in contact with the outer surface of the core body and the inner wall. This liquid can be a fluorine compound or a silicone oil.

Description

Heating rollers are used in a very large number of branches of industry whenever it is a question of bringing to a given temperature or drying a product in the form of a film, a sheet or a 'a plate. This is particularly the case in the leather, stationery, plastics, rubber, etc. industries.

There is a very wide variety of this type of cylinder which can be used for such or such branch of industry according to the degree of temperature precision required.

The simplest heating method consists, as shown in FIG. 1, of placing inside a cylinder (2) a certain number of electrical resistors (3) rotating with the cylinder and supplied by the rotor (4). . This type of cylinder has significant drawbacks, however, since the impossibility of performing a very fine distribution of the electrical resistances results in significant temperature differences along a generator and along a circumference.

In order to obtain acceptable temperature accuracy (of the order of 3 to 4 ° C), it is necessary to provide significant metallic masses so as to equalize, by thermal conductivity, the irregularity of the intake of calories due resistance. In this way, temperature regularity is improved, but the large metal masses and consequently the high thermal inertia result in an extremely long reaction time to temperature variations, whether these are caused by the device. temperature regulation or result from the process itself.

Another important drawback lies in the fact that the regularity of temperature of the surface of the cylinder ultimately depends on an “intelligent” distribution of a metallic mass and of the heating resistors and that this distribution can only be done by making a number of assumptions about the nature of the product carried by the cylinder and its calorie needs. Such a cylinder therefore only allows an empirical approach to the optimal heating conditions for a given temperature range, for a given product and for a given production speed.

For its reasons, this type of cylinder is very little used today.

• - transfert de calories entre le système générateur et le cylindre;
• - répartition régulière de ces calories à proximité des points de consommation de façonil maintenir la température régulière sur la surface utile des cylindres sur toute la plage des régimes de fonctionnement prévus.

To overcome these drawbacks, the most commonly used cylinders involve a so-called heat transfer fluid, the circulation of which performs a dual function:

• - transfer of calories between the generator system and the cylinder;
• - regular distribution of these calories near the consumption points so as to maintain the regular temperature over the useful surface of the cylinders over the whole range of the operating modes provided.

The cylinders currently used, in particular in the paper, rubber and plastic processing industries, are almost always of this type. The fluids used are, depending on the applications and the temperature ranges, water, heat pipe oils, steam or specialized fluids.

Whatever the fluid, in most cases, and as shown in Figure 2, the calorie production system (5) is external to the consumer cylinder (6), whether it is a centralized system (for a cylinder bank) or an individual system for each cylinder. Calories are supplied by electric resistors (7), oil, gas and coal (steam) burners in the generator outside the cylinder. A temperature sensor (8) measures the temperature of the fluid and regulates it.

After the heat transfer fluid has been brought to the desired temperature of the receiver, either directly or indirectly by mixing, it is conveyed by a system of pumps (9) and is introduced into the cylinder by a rotary joint (10) ensuring the sealing. According to the requirements of regularity of temperature, the fluid circulates either inside the cylinder (technique known as the hollow body), or in an annular space created at the periphery of the cylinder between the outer ferrule and a second inner ferrule, or in even more efficient systems inside spirals or rectilinear channels (12) judiciously distributed and crossed. The objective is to ensure a circulation at high speed of the heat transfer fluid, so that the calories consumed by the treated product are replaced as quickly as possible without preferential heating on one side or another.

In the case of fluids, the existence of a fluid accelerator element (pump) is essential. In the case of steam, the pressure difference is sufficient to ensure the circulation of the fluid at high speed, the supply of calories taking place by conduction and partially by condensation.

Whatever system is used, there is always in this group of cylinders a calorie generator external to the cylinder and a member for pressurizing the fluid intended to ensure circulation at high speed.

• - rendement thermique faible dû à des déperditions calorifiques importantes au niveau de la chaudière extérieure, des canalisations de transmission, des vannes, du joint tournant...,
• - consommation d'énergie importante au niveau de l'organe de mise en pression (généralement pompe). Plus les exigences de régularité de température sont importantes, ptus la consommations ce niveau est élevée puisque le coefficient d'échange dépend directement de la vitesse de circulation du fluide, elle-même dépendante de la différence de pression,
• - présence inévitable d'un joint tournant qui présente de nombreux inconvénients pour un certain nombre d'applications. Ces inconvénients sont: l'encombrement des systèmes, l'entretien élevé auxquels ils sont assujettis, la difficulté de les rendre complètement étanches, ce qui présente un grave inconvénient pour les applications dites propres (film technique, bandes magnétiques, etc....). En outre, quel que soit le type de joint tournant utilisé, ces joints présentent un couple parasite dû à l'existence de plaques d'étanchéité en rotation l'une contre l'autre qui est gênante pour certaines applications.

This type of cylinder is satisfactory in a multitude of uses. However, it has the following drawbacks:

• - low thermal efficiency due to significant heat losses at the level of the external boiler, transmission pipes, valves, rotary joint ...,
• - significant energy consumption at the pressurizing member (generally pump). The higher the requirements for regularity of temperature, the higher the consumption, since the exchange coefficient depends directly on the speed of circulation of the fluid, itself dependent on the pressure difference,
• - inevitable presence of a rotating joint which has many drawbacks for a certain number of applications. These disadvantages are: congestion of systems, maintenance high to which they are subject, the difficulty of making them completely waterproof, which has a serious drawback for so-called clean applications (technical film, magnetic tapes, etc.). In addition, whatever the type of rotary joint used, these joints have a parasitic torque due to the existence of sealing plates rotating against each other which is troublesome for certain applications.

Despite their drawbacks, these systems are currently in common use, except in a certain number of applications where these drawbacks are unacceptable.

For certain other applications, in particular in the textile field, it is however necessary to use other types of cylinders. There are indeed in this branch of industry frequently problems of cylinders rotating at very high speed (4000-5000 rpm) having a compact volume and for which the turning point technique would be unacceptable. cylinders being subjected to large instantaneous load variations, must be able to react extremely rapidly by adding calories during a variation in speed at a particular point of the cylinder.

In such cases, the so-called rotating heat pipe technique is used, in which, as shown in FIG. 3, the cylinder (13) comprises, in the immediate vicinity of the product to be treated, an annular space (14) placed under a high vacuum and partially filled with a heat transfer liquid (15) located, due to the high depression of the chamber (14) in which it remains, in a state of constant vaporization over the entire temperature range of use of the cylinder.

The function of this heat transfer fluid is to ensure, in the same way as the fluid in the cylinders described above, a circulation of steam at very high speed (immediate compensation for temperature differences) and supply of calories by condensation.

For this type of cylinder by the heating mode of the “short-circuit transformer” (16) consisting in creating, from a fixed coil inside the cylinder, a magnetic field which by looping in short-circuit in the metallic mass of the cylinder (in rotation) releases by joule effect the calories necessary for the system.

This type of cylinder is extremely efficient in terms of temperature regulation, thanks to the heat transfer fluid and in terms of calorie creation by transformer effect. On the other hand, it has the drawback of being relatively expensive in terms of implementation, due to the high cost of the electrical windings required, which generally limits its application to cylinders of very small dimensions.

An additional difficulty results from the fact that the temperature distributing fluid, as well as the release of calories taking place inside the rotating part itself (which is desirable to give the system a rapid response time), it is necessary, to ensure acceptable temperature regulation of the system, that the temperature measurement probe (17) is itself in the rotating casing. The temperature measurement probe (1) is therefore in rotation like the entire system, and it is therefore necessary to bring out the signal by electronic systems (18) with induced field, which are themselves extremely expensive and complicated. to implement.

This is an important difference compared to the previous type of cylinder where the fluid is warmed up outside the rotating cylinder, it is simple to measure the temperature of the fluid before it enters the system, the thermocouple then being static and the regulation system therefore having an acceptable cost.

The document FR-A-2321103 describes a method and a device for heating cylinders comprising a cylindrical shell integral in rotation with the cylinder shaft and having two concentric walls delimiting an annular volume containing a heat transfer fluid which is located between a vapor phase and a liquid phase. Inside the ferrule, is arranged parallel thereto and integral in rotation with this another ferrule, which delimits with the interior wall of the first ferrule a space in which is housed the heating device which can be constituted by electrical resistances or by steam or oil which is circulated after introduction into said space.

The present invention aims to remedy these drawbacks.

To this end, the cylinder which it concerns, of the type comprising a cylindrical ferrule integral in rotation with the cylinder shaft, having two concentric walls delimiting an annular volume containing a heat transfer fluid which is located between a vapor phase and a liquid phase , is characterized in that inside the ferrule is disposed a fixed body extending substantially over the entire length thereof on a cylindrical sector located below the axis of the cylinder, is temperature regulated at a temperature close to the temperature of use of the cylinder, a blade of liquid, stable at the temperature of use of the cylinder, ensuring the transmission of calories between the fixed body and the inner wall of the shell.

The fixed body is regulated to a temperature close to the temperature of use of the cylinder by various devices, which can be either a circulation of hot fluid, or electrical resistances, or other means capable of bringing or removing from the body the calories necessary to allow it to reach the desired thermal balance.

The calorie supply is extremely simple, since the hot body is fixed inside the cylinder, avoiding components, such as rotary joints for a fluid system, or rotary contacts for an electrical supply, which would be necessary if the body was mobile.

Advantageously, the annular volume, delimited between the two walls of the shell, is maintained in permanent depression, and is partially filled with a fluid, which is, due to its thermodynamic characteristics and the degree of vacuum, in permanent equilibrium between a vapor phase and a liquid phase, over the entire temperature range of use of the cylinder.

This high-performance heat transfer fluid system located in the rotating part of the cylinder ensures temperature balance over the entire surface of the cylinder due to the circulation of steam at very high speed in the closed and vacuum enclosure formed by the annular volume delimited by the two walls of the shell.

In the context of cylinders heated to temperatures of the order of 150 to 160 ° C., different liquids can be used to ensure the transmission of heat between the fixed body and the inner wall of the shell, and in particular fluids of the fluorinated type. or silicone oils, which are particularly well suited, since they allow operation at atmospheric pressure without risk of degradation or generation of dangerous products. However, it is preferable that, in order to avoid leaks by spraying, or during gear changes, the rotary part of the cylinder constitutes a closed volume inside which the heating fixed body is located.

In accordance with another characteristic of the invention, the fixed body extends over a sector, for example a quarter of a circle situated below the axis of the cylinder, and the level of the contact liquid is also situated below the cylinder axis.

Since a very small amount of contact liquid is sufficient, the seal provided by the rotating part of the cylinder may be sketchy, since the level of liquid does not exceed the level of the axis. It is therefore a type of sealing that has no common measure with that required by rotary seals which are required to be absolutely sealed, even under relatively high operating pressures.

In addition, the contact liquid having only a simple function of transmission of calories by thermal conductivity between the fixed body and the rotating shell, it is not necessary, contrary to the conditions required in conventional cylinders, ensuring a high circulation speed for the liquid in order to carry out the transfer of calories, and simultaneously balancing of temperatures, this being ensured by the heat transfer fluid inside the shell.

The simple rotation of the cylinder is sufficient to ensure this transfer.

This cylinder is also equipped with a temperature regulation device comprising a measurement probe, located in the fixed body near the connection liquid between the fixed heating body and the inner wall of the shell.

In any case, the invention will be clearly understood with the aid of the description which follows, with reference to the appended schematic drawing, of which FIG. 4 represents a perspective view of this heating cylinder, one end of which is partially cut away.

This cylinder comprises a cylindrical ferrule comprising two concentric walls, respectively, exterior (20) and interior (22), delimiting an annular volume (23), this ferrule being integral in rotation with the shaft (24) of the cylinder. The annular volume (23) is permanently depressed, and is partially filled with a fluid (25) which, due to its thermodynamic characteristics and the degree of vacuum, is in permanent equilibrium between a vapor phase and a liquid phase, over the entire operating temperature range of the cylinder.

Inside the ferrule, is arranged a fixed body (26) having, in cross section, a shape of circular sector, corresponding to a quarter of a circle, of axis corresponding to the axis of the cylinder and of slightly smaller radius to the radius of the inner wall of the ferrule.

This fixed body (26) is equipped with heating means constituted by resistors (27) in the embodiment shown in the drawing. Between the fixed body (26) and the rotating part, and more precisely the inner wall (22) thereof, heat transfer is provided by a blade of a liquid (28) the level of which is located below the axis of the cylinder, and which is chosen to have good stability at the operating temperature of the cylinder.

This cylinder finally has a temperature regulation device, the probe (29) of which is disposed in the fixed body (26) near the liquid ensuring contact between the fixed body (26) and the inner wall (22) of the shell.

As is apparent from the above, the invention brings a great improvement to the existing technique by providing a heating cylinder of simple design, because the hot body is fixed and requires only simple means of implementation both on the plan of the creation of the calories that of the regulation of the temperature, that the heat transfer fluid, located in the rotating part of the cylinder, ensures an excellent temperature balance on all the surface of the cylinder, and finally that the transfer of calories between the body fixed and the rotating part, is obtained by a liquid which does not require strict sealing conditions.

Claims (5)

1. Heating cylinder of the type comprising a cylindrical shell which is rotationally rigid with the shaft of the cylinder, comprising two concentric walls (20, 22). defining an annular space containing a heat-bearing medium which is between a vapour phase and a liquid phase, characterised in that there is inside the shell a fixed body (26) extending substantially over the entire length of the shell, over a cylindrical segment situated below the axis of the cylinder and of which the temperature is regulated to a temperature close to the temperature at which the cylinder is used, a sheet of liquid (28) stable at the temperature of use of the cylinder and providing for transmission of heat between the fixed body (26) and the inner wall (22) of the shell.

2. Heating cylinder according to claim 1, characterised in that the annular space (23) defined between the two walls (20, 22) of the shell is maintained permanently at a negative pressure and is partially filled with a fluid (25) which by virtue of its thermodynamic properties and the degree of vacuum involved, is permanently in a state of equilibrium between a vapour phase and a liquid phase, over the full range of temperatures at which the cylinder is used.

3. Heating cylinder according to claim 1, characterised in that the liquid (28) which ensures contact between the fixed body (26) and the inner wall (22) of the shell is chosen from among the fluorinated liquids or silicon oils.

4. Heating cylinder according to claim 1, characterised in that the level of contact liquid (28) is likewise below the axis of the cylinder.

5. Heating cylinder according to any one of claims 1 to 4, characterised in that it comprises a device for regulating the temperature and comprising a sensor (29) for measuring the temperature between the fixed body (26) close to the space filled by the connecting liquid between the fixed heating body and the inner wall of the shell.

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