Abstract:
A device for treating pieces of a substrate at high pressure, piece by piece or in batches, with a treatment medium in the supercritical or near-critical state, includes a first pressure chamber, a pipe system for supplying and discharging the treatment medium, to and from the pressure chamber under high pressure and an electric motor, which is fixed to the housing in the first pressure chamber or in a second pressure chamber coupled to the first pressure chamber under the high pressure, for driving an actuator to carry out a mechanical action in the treatment medium. The electric motor is in this case open to the treatment medium and is disposed and designed to be accessible to the treatment medium, in such a manner that during the treatment of a substrate the treatment medium flows through and around the electric motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Dutch Patent Application No. NL 1028037, filed Jan. 14, 2005, the contents of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The invention relates to a device for treating pieces of a substrate with a supercritical or near-critical treatment medium, which may for example comprise CO 2 , N 2 O, lower alkanes, such as ethane and propane, or mixtures thereof, at high pressure in a pressure chamber, piece by piece or in batches, with a mechanical action being carried out in the treatment medium.  
       BACKGROUND OF THE INVENTION  
       [0003]     The prior art has disclosed a number of variants of a device of this type, in which an electric motor is used as drive for carrying out the mechanical action. However, the said treatment media have the drawback of dissolving many polymers therein. This can give rise to problems with regard to sticking, softening and expansion or even bursting of the polymer if it comes into contact with the treatment medium. This problem becomes more serious the higher the density of the treatment medium, such as for example in liquid or supercritical phases of the treatment medium under ever higher pressures. This may give rise to considerable problems in the event of an electric motor coming into contact with treatment media of this type, for example short-circuiting as a result of the electrical insulation of the motor windings being affected, leaks caused by damage to any sealing rings, and jamming caused by fretting of plastic bearing components. Furthermore, treatment media of this nature are able to dissolve may oils and greases. This leads to removal of grease from anything which comes into contact with the treatment medium. This problem is likewise exacerbated as the density of the treatment medium rises. In the case of the electric motor, this can give rise to problems with lubricated surfaces in the bearing of the motor shaft, as well as with any bearings used in the mechanical actuator.  
         [0004]     To avoid the above complications, the electric motor can be positioned outside the sphere of influence of the treatment medium, i.e. outside the pressure chamber. The mechanical actuator provided inside the pressure chamber is then driven by a drive shaft which passes through a wall of the pressure chamber. However, this presents specific problems with the need to seal the drive shaft. Sealing problems of this nature are exacerbated at higher pressures of the treatment medium, resulting in an expensive structure.  
         [0005]     An alternative is to make use of a magnetic coupling between the electric motor and the mechanical actuator, as shown for example in U.S. Pat. No. 5,267,455. There is no need for seals in this case. However, at high pressures, the wall thickness of the pressure chamber increases and consequently the magnetic coupling is more difficult to realize, certainly if high powers need to be transmitted. This leads to very expensive structures.  
         [0006]     WO 00/63483 also discloses a device showing a washing machine drum which is driven by an electric motor. In this case, the washing machine drum and the electric motor are both located in a treatment space which is partially filled with highly pressurized liquid CO 2  at room temperature. The document describes the electric motor having to be disposed as high as possible within the top part of the treatment space, so that the electric motor substantially, i.e. barring a few splashes of liquid CO 2 , only comes into contact with gaseous CO 2 .  
         [0007]     One drawback in this case is that this known device is susceptible to faults and problems may still arise as a result of standard polymer components of the electric motor being adversely affected. Furthermore, the working range of the permitted pressure and temperature are limited, and consequently in some cases so is the effectiveness of the washing treatment which is intended in this case.  
       SUMMARY OF THE INVENTION  
       [0008]     It is an object of the invention to at least partially overcome the abovementioned drawbacks and/or to create a useable alternative. In particular, it is an object of the invention to create a reliable and efficient device for treating pieces of a substrate at high pressure, piece by piece or in batches, with a treatment medium in the supercritical or near-critical state.  
         [0009]     This object is achieved by a device according to the present invention. In this case, the device comprises a first pressure chamber, which is provided with a closable feed opening for placing pieces of substrate in the pressure chamber, and a pipe system for supplying and discharging the treatment medium, which may comprise, for example, CO 2 , N 2 O, lower alkanes, such as ethane and propane, or mixtures thereof, to and from the pressure chamber under high pressure. In the first pressure chamber or in a second pressure chamber coupled to the first pressure chamber under the high pressure, there is an electric motor for driving an actuator to carry out a mechanical action in the treatment medium. The electric motor is in this case open to the treatment medium and the electric motor is disposed and designed to be accessible to the treatment medium, in such a manner that during the treatment of a substrate the supercritical or liquid treatment medium flows through and around the electric motor.  
         [0010]     Surprisingly, it has been found that, despite the drawbacks described in the prior art, it is none the less readily possible for an electric motor to be designed in such a manner that it can be exposed from the inside and the outside to the supercritical or near-critical liquid treatment medium and is able to withstand it. In the invented device, the electric motor is located in the process tank at the high process pressure; this high pressure prevails both outside and inside the electric motor. The pressure inside the motor casing is then advantageously substantially equal to the pressure outside the electric motor, i.e. in the relevant pressure chamber. As a result, the electric motor can be of simpler and less expensive design. Inter alia, there is no need for a seal between the motor shaft and the motor casing, and the casing does not need to have any additional structural strength in order to withstand high pressure differences. Another advantage is that the supercritical or near-critical liquid treatment medium contributes to cooling the electric motor. Put another way, the heat which is dissipated by the electric motor can advantageously be used to keep the treatment medium at process temperature during the treatment of a substrate.  
         [0011]     The motor windings of the electric motor may be insulated using insulation material which is resistant to the specific treatment medium, and it is possible to use a lubrication-free bearing for a motor output shaft of the electric motor. These measures make it more readily possible for the device to function without problems under various operating conditions, in particular even at pressures and temperatures which are so high that the treatment medium is in the supercritical or near-supercritical phase.  
         [0012]     The electric motor may comprise a motor casing which is provided with inlet openings for allowing the treatment medium to flow into the electric motor as far as around the motor windings. The inlet openings allow the treatment medium to flow freely through the interior of the electric motor, with the result that successful cooling of the motor windings can be achieved. For example, there is no longer any need for cooling fins on the motor casing.  
         [0013]     Further preferred embodiments are defined in the subclaims.  
         [0014]     The invention also relates to the use of a device for treating pieces of textile substrate at high pressure, piece by piece or in batches. Additionally, the invention relates to use of a device for treating pieces of a substrate at high pressure, piece by piece or in batches, with a treatment medium wherein the pressure and temperature at which the treatment medium is supplied to a pressure chamber during treatment are such that the treatment medium is in a supercritical or near-critical state, and in which an electric motor for driving an actuator for carrying out a mechanical action in the treatment medium is located in the treatment medium, which is in the supercritical or near-critical state, with the treatment medium flowing through and around it. Further, the invention relates to use of a device for treating pieces of a substrate at high pressure, piece by piece or in batches, with a treatment medium in particular according to one of the preceding claims, wherein the pressure and temperature at which the treatment medium is supplied to a pressure chamber during treatment are such that the treatment medium is at least partially in a liquid phase, and in which an electric motor for driving an actuator for carrying out a mechanical action in the treatment medium is submerged in the treatment medium, which is in the liquid phase, with the treatment medium flowing through and around it.  
         [0015]     The invention also relates to an electric motor for a device which is open to the treatment medium and is designed to be accessible to the treatment medium, in such a manner that during treatment of a substrate with a treatment medium, the treatment medium can flow through and around the electric motor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The invention will be explained in more detail with reference to the appended drawing, in which:  
         [0017]      FIG. 1  shows a diagrammatic view of an embodiment of a pressure chamber with an electric motor fixed to the housing therein, for a device according to the invention with pump;  
         [0018]      FIG. 2  shows a cross-sectional view through an electric motor which can be used in a device as shown in one of  FIGS. 1, 4 ,  5  and  6 ;  
         [0019]      FIG. 3  shows a side view of  FIG. 2 ;  
         [0020]      FIG. 4  shows a variant of  FIG. 1  with the direction of flow reversed;  
         [0021]      FIG. 5  shows a variant of  FIG. 1  with a washing machine drum; and  
         [0022]      FIG. 6  shows a device according to the invention in which an electric motor with pump is accommodated in one pressure vessel, a beam dyeing machine interacting with it. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]     In  FIG. 1 , the pressure chamber device as a whole is denoted by reference numeral  1 . The device  1  comprises a pressure chamber  2 , which is in this case formed by a pressure vessel and is provided with an opening, which can be closed by a cover  3 , for mounting an electric motor  7  with pump  9  in the pressure vessel. There is also a pipe system  5  with a feed  5   a  and a discharge  5   b . An electric motor  7  is disposed in the pressure chamber  2 . A pump  9  is mounted on the motor output shaft  8  of the electric motor  7 . The pump  9 , which is formed for example by a centrifugal pump with an impellor, is in this case mounted directly on the motor shaft  8 . The pump  9  is accommodated in a pump casing  10  which comprises an inlet  11  and an outlet  12 . The outlet  12  is connected to the discharge  5   b .  
         [0024]     The pressure chamber device shown may be incorporated as a second pressure chamber in a high-pressure circuit with a first pressure chamber for treating a substrate.  
         [0025]     The electric motor  7 , which is shown in more detail in  FIGS. 2 and 3 , comprises motor windings  20  which are insulated by an insulation material that is able to withstand a treatment medium that is specifically to be used, comprising CO 2 , N 2 O, lower alkanes, such as ethane and propane, or mixtures thereof. The insulation material preferably consists of polyester. Tests have shown that this is an eminently satisfactory material. Other materials, such as kapton or Nomex, are also possible.  
         [0026]     Furthermore, the electric motor  7  comprises bearings  21  for the motor output shaft  8 . The bearings  21  are of the lubrication-free type, i.e. no greases or oils are required for the bearings to function correctly. The bearings  21  may comprise ceramic balls or a PEEK or bronze ball cage. It is advantageous for the bearings  21  to comprise a self-lubricating contact layer, for example in a groove in the bearings. The self-lubricating contact layer is preferably formed by a carbon-nitride layer. It has been found that such a material is well able to withstand the treatment medium (in particular supercritical CO 2 ), while sufficient lubrication of the bearings  21  is also achieved.  
         [0027]     The bearings  21  are mounted in bearing blocks  23 , which also form a type of covers for a motor casing  24  surrounding the electric motor  7 . The bearing blocks  23  are made from a corrosion-resistant material, for example stainless steel or anodized aluminium.  
         [0028]     Through-flow openings  26  (cf.  FIG. 3 ) are provided in the bearing blocks  23  of the motor casing  24 . This means that the electric motor  7  is of an open type and the treatment medium is free to circulate through the interior of the electric motor  7 . This ensures successful cooling of the motor windings  20  and has the advantage that the motor casing  24  can be of more lightweight design, since the pressure inside the motor casing  24  is substantially equal to the pressure outside it. Furthermore, there is no need for any cooling fins, on account of the thermal properties of the treatment medium, and the motor shaft does not have to be passed through the motor casing  24  in such a manner as to be sealed with respect to the treatment medium at the supercritical process pressure.  
         [0029]     The electric motor  7  is supplied with power via an electrical connection  27 , which is provided with insulation material that is able to withstand the treatment medium, for example Nomex, aramid paper, kapton, polyester film and/or yarns. The electrical passage of the connection  27  through the wall of the pressure chamber  2  is provided with a tensile stress reliever which is able to withstand the treatment medium, for example a Buna-N ring or potting resin.  
         [0030]     During operation, treatment medium is fed to the pressure chamber  2  via the feed  5   a , and the electric motor  7  with the pump  9  is set in operation. Some of the treatment medium flows freely through the motor casing  24 , where it has a cooling action, is sucked in by the pump  9  via the inlet  11  and is pumped by the mechanical action of the pump  9  to the outlet  12  or discharge  5   b , leaves the pressure vessel  2  and enters another (first) pressure chamber (not shown), where the pieces of substrate are located, where it carries out a treatment on the pieces of substrate. After it has left the first pressure chamber, the treatment medium is fed back to the feed  5   a , via an associated pipe. After the treatment medium which is circulating in this way has been able to act on the pieces of substrate for a desired time, the electric motor is stopped and the treatment medium is discharged from the system until the system is at ambient pressure, and then the treated pieces of substrate can be removed from the first pressure chamber again.  
         [0031]     The pressure across the pump casing  10  in which, for example, an impellor of the pump is rotating is at most equal to the boost pressure provided by the pump  9 , and is therefore advantageously only a few bar, while the treatment medium in the pressure chamber  2  may be at a high pressure.  
         [0032]      FIG. 4  shows a variant, in which identical components are denoted by the same reference numerals. The pressure chamber  2  is now provided with a feed  30  which is connected to an inlet  31  of the pump casing  10 . There is also a discharge  32  which is in direct, open communication with the pressure chamber  2 . Furthermore, through-flow openings  33  are now provided in the peripheral wall of the motor casing of the electric motor  7 .  
         [0033]     During operation, the treatment medium flows via the feed  30  and the inlet  31  into the pump casing  10  and from there flows partly through the electric motor  7  and partly around it into the pressure chamber  2  and then back out via the discharge  32 .  
         [0034]      FIG. 5  shows an application in which an electric motor  40  and a drum  41  driven by it are positioned together in the same pressure chamber  42 . Treatment medium can be fed to and discharged from the pressure chamber  42  (pipes not shown). The electric motor  40  is provided with through-flow openings  44 , while the abovementioned measures according to the invention are preferably once again taken for the motor windings and the bearings used. The pressure chamber  42  is provided with a cover  43  which can be opened in order for pieces of substrate that are to be treated to be put into and taken out of the drum  41 . The drum  41  can be used both for washing and for dyeing.  
         [0035]      FIG. 6  shows a cylindrical pressure vessel  50  which is provided at both ends with feed openings which can be closed off by covers  51 ,  51   a  and  51   b . Both the pressure chamber for the electric motor with actuator and the pressure chamber for the pieces of substrate are integrated in this pressure vessel  50 . The cover  51   a  can be opened in order for a rolled-up piece of textile substrate  53  to be introduced into the pressure chamber on a perforated tube  52 . The cover  51   b  is provided with a feed  55  and a discharge  56  for treatment medium. A pump casing  58 , in which an electric motor  59  and a vane pump  60  are jointly accommodated, is directly connected to the feed  55 . The pump casing  58  holding the electric motor  59  and the vane pump  60  can be mounted in the pressure vessel  50  when the cover  51   b  is open. The vane pump  60  is advantageously disposed upstream of the electric motor  59 , which contributes to better flow of the treatment medium past and if desired through the electric motor  59 , resulting in better cooling. From the pump casing  58 , the treatment medium can flow via an outlet  62  into the tube  52  and from there, via the holes, through the substrate  53  that is to be treated, performing its treating action on the substrate. Finally, the treatment medium can leave the pressure chamber  50  again via the discharge  56 . On account of the fact that the treatment medium has been laden with dye outside the pressure chamber  50 , it is in this way possible to dye the textile substrate. The pressure drop across the textile substrate is approximately 1 bar.  
         [0036]     In a preferred use, the treatment medium is supplied to the pressure chamber of the above-described devices at a pressure and temperature which are such that the treatment medium is in a supercritical or near-supercritical state. The entire pressure chamber, including the “open” electric motor, is then at the pressure and under the influence of the supercritical or near-supercritical treatment medium. Surprisingly, it has been found that this does not present any problems, in particular if the motor windings are insulated with insulation material that is able to withstand the treatment medium and if the bearing is of a lubrication-free type. For CO 2  as treatment medium, the supercritical state is reached at a pressure of at least 73 bar and a temperature of at least 31 degrees.  
         [0037]     In a variant, the treatment medium is supplied to the pressure chamber of the above-described devices at a pressure and temperature which are such that the treatment medium is at least partially in a liquid phase. The “open” electric motor is then preferably submerged in the liquid treatment medium. Surprisingly, this too has been found not to present any problems, in particular if the motor windings are insulated with insulation material that is able to withstand the treatment medium and if the bearing is of a lubrication-free type.  
         [0038]     In addition to the embodiments shown, numerous variants are possible. For example, it is also possible for other types of actuators in addition to the pump and the drum to be used to move the substrate and the medium with respect to one another, for example a propeller, an agitator or a stirring mechanism. In addition to washing or dyeing pieces of a textile substrate, the device can advantageously also be used to treat other types of substrate or to treat a substrate in another way, for example clean or degrease it. Examples of articles which can also be suitably treated using the device and the use according to the invention include fabrics, such as woven and nonwoven fabrics formed from materials such as cotton, wool, silk, leather, rayon, polyester, acetate, glass fibre, fur, etc. These fabrics may be formed into pieces, such as clothing, work gloves, cloths, leather goods (for example handbags and briefcases), etc. The present device and the use can also be used to treat, in particular wash, clean or degrease, other items, such as semiconductors, micro-electromechanical systems, opto-electronics, fibre optics and machined or cast metal components. It is also possible to treat foodstuffs and contaminated soil using the device and the use according to the invention.  
         [0039]     Therefore, the invention provides a user-friendly, efficient device which allows an electric motor that can be of simple and inexpensive design to be positioned within the sphere of influence of a specific, aggressive type of treatment medium under various conditions of use in a pressure chamber.