Patent Publication Number: US-2009230215-A1

Title: Apparatus for generating and spraying an aerosol

Description:
The instant invention relates to an apparatus for generating and spraying an aerosol which contains liquid particles in a gas stream and for pointedly supplying the aerosol to a lubricating location, especially for use in minimum quantity lubrication techniques where minute amounts of lubricating oil must be fed to the location at which a material treating process is performed, e.g. a place of cutting or deforming objects. 
     In a known apparatus of this kind (WO 98/28085) an injector device is provided to produce a mixture of gas and liquid which exits in the form of a gas/liquid jet from an outlet, hitting the structured surface of an impact body, such as a stepped pyramid, and thereby forming a gas/liquid mist. 
     Another known apparatus for producing a gas/liquid mixture operates according to the injector principle, whereby a gas/liquid jet generated by an injector is sprayed onto the tip of a pyramid which is set into rotating motion by a drive means (DE 203 09 452 U1). 
     The liquid particles in a gas stream issuing from a spraying device, such as a nozzle, should be extremely small, i.e. in an order of magnitude of 1 μm or less, so that they may be kept afloat after spraying across the longest possible distance and thus be conveyed directly to the place of application. 
     It is, therefore, an object of the invention to provide an apparatus of the kind specified initially by which an aerosol containing minute liquid droplets can be produced economically, the consistency of said aerosol when sprayed and conveyed being maintained all the way to the place of application even across great conveying distances. 
     Claim  1  serves to meet the object defined above. Claim  1  specifies an apparatus which comprises:
         (a) a vessel containing a supply of liquid and a pressure space above the level of the liquid supply,   (b) an atomizer disposed in the pressure space above the level of the liquid supply and comprising:   (i) a spraying device for spraying the aerosol,   (ii) a liquid feed line connected at one end to the liquid supply and at its other end to the spraying device and including a pump for feeding the liquid,   (iii) a gas feed line connected at one end to a pressure gas source and at its other end to the spraying device,   (iv) at least one apertured wall disposed in the way of the trajectories of the spray jets from the spraying device and having holes for passing liquid particles of a predetermined size while separating greater liquid particles at the apertured wall, and   (c) an aerosol line which connects the pressure space with a machining location to be wetted by the aerosol.       

     The apparatus according to the invention is devised so as to provide an aerosol containing liquid particles of smallest dimensions which are maintained as such even after a rather long conveying distance to the place of application, for example a location where a cutting process or cold deformation is performed. The spraying takes place without any relative movement between the spraying device and the apertured wall and without electric energy input, simply by the pressure energy of the gas/liquid stream. The operating pressure of the gas used, e.g. air, may be adjusted to values between 1 bar and 7 bars, depending on the respective case of treatment, e.g. cutting or milling. 
     In a preferred embodiment of the invention, the apertured wall is of cylindrical shape and the spraying device is disposed in the centre of the apertured wall and adapted to spray the aerosol all around in outward direction against the apertured wall. In this manner, an aerosol mist uniformly distributed around the apertured wall is generated in the pressure space radially outside of the apertured wall. 
     The dimensions of the liquid particles carried along in the mist can be successfully diminished further by arranging another apertured wall downstream and spaced from the outside of the first mentioned apertured wall. 
     Testing in practice proved that a particularly useful embodiment is obtained when three cylindrical apertured walls are arranged concentrically around the spraying device. 
     The or each apertured wall preferably is made from thin sheet material of corrosion resistant metal which is easily bent into the desired shape, such as especially stainless steel. The holes in the apetured wall or walls should have hole dimensions of less than 500 μm, preferably less than 200 μm. 
     The holes in the apertured wall may be provided in a regular pattern and be separated by webs whose width is smaller than the hole diameters. The holes in an embodiment which proved successful in testing are of diamond shape. The holes may be arranged in mutually offset rows in the manner of honeycombs and they may be of hexagonal or round shape. 
     In a preferred embodiment of the invention the spraying device comprises a nozzle head including a mixing chamber and a twist body arranged in the mixing chamber. At least one helical groove with a baffle face is formed in the circumference of the twist body to cause a twist of the gas/liquid streams as described in DE 196 08 485 C2. 
     In order for the gas/liquid mixture prepared in the mixing chamber to be sprayed as uniformly as possible onto the inner circumference of the apertured wall, the spraying device may comprise a nozzle mouth formed with a ring of outlet orifices which are directed at a deflector face of a jet deflecting body inserted in the nozzle mouth to guide the issuing spray jets in the direction of the apertured wall. 
     The invention will be described further, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a diagrammatic illustration of an apparatus for generating and spraying an aerosol according to the invention; 
       FIG. 2  is an axial sectional elevation along line II-II in  FIG. 4  showing a spraying device of the apparatus according to the invention; 
       FIG. 3  is a perspective view of the axial sectional elevation according to  FIG. 2 ; 
       FIG. 4  is a top plan view of the spraying device shown in  FIG. 2 ; 
       FIG. 5  is a view of a nozzle head of the spraying device, shown on an enlarged scale; 
       FIG. 6  is a sectional view along line VI-VI in  FIG. 5 ; and 
       FIG. 7  is a greatly enlarged partial view of a section of an apertured wall according to the invention, having diamond-shaped holes. 
       FIG. 1  diagrammatically illustrates the entire apparatus for generating and spraying an aerosol. 
    
    
     The apparatus comprises a pressure-sealed vessel  1  containing a supply of oil  2  in its lower part, while a pressure space  4  is defined above the level  3  of the oil supply. The surface of the level  3  is monitored by a level sensor  5 , and the pressure in the pressure space  4  is monitored by a pressure sensor  6 . 
     A solenoid valve  9  connected to the pressure sensor  6  by a pressure signal line  10  is inserted in a compressed air feed line  7  coming from a pressure source  8 . The compressed air feed line  7  is connected to an air inlet connecting piece  11  of a spraying device designated generally by reference numeral  12 . The pressure sensor  6  functions to switch off and on the supply of compressed air when a pressure maximum is exceeded and a pressure minimum is fallen short of, respectively. The operating pressure may be adjustable between 1 bar and 7 bars, depending on the particular case of treatment. 
     An oil inlet connecting piece  13  connected to an oil feed line  14  is provided below the air inlet connecting piece  11 . The other end of the oil feed line  14  is connected to the oil supply  2  in the vessel  1 . A gear pump  15  is installed in the oil feed line  14  and, when in switched-on state, it pumps oil from the oil supply  2  through the oil inlet connecting piece  13  into the spraying device  12 . When a predetermined minimum level is fallen short off the level sensor  5  emits an alarm signal “refill vessel”, and when a maximum level is surpassed it emits a signal “stop oil supply”. Both the air inlet connecting piece  11  and the oil inlet connecting piece  13  extend through the wall of the vessel  1  fixedly so that the spraying device  12  is kept stationary within the vessel  1 . 
     A check valve  16  is mounted in the compressed air feed line between the solenoid valve  9  and the air inlet connecting piece  11 . A check valve  17  is mounted in the oil feed line  14  between the gear pump  15  and the oil inlet connecting piece  13 . 
     A vertical longitudinal bore  18  is provided in the spraying device  12 . Both the air inlet connecting piece  11  and the oil inlet connecting piece  13  open into this longitudinal bore  18 , the oil flowing inside a capillary hose  19  through the oil inlet connecting piece  13  and the lower part of the longitudinal bore  18  to a nozzle head  20 . An oil/air mixture produced in the nozzle head  20  is sprayed by the nozzle head  20  radially in all directions outwardly into the pressure space  4 , passing successively through three apertured walls  27 ,  28 ,  29  embodied by three concentric cylindrical, thin-walled sheets having perforated hole patterns. Thus the pressure space  4  is filled by the generated aerosol of the oil/air mixture. 
     An aerosol line  21  leads out of the pressure space  4  and is adapted to be blocked and unblocked by means of a ball valve  22 . The ball valve  22  is controlled through air activating lines  23   a,    23   b  by a solenoid valve  24  which is operable through the air feed line  7  by compressed air from the source  8 . 
       FIGS. 2 to 4 , once more, show the spraying device  12  on an enlarged scale and separate from the other component parts of the overall apparatus. The individual components of the spraying device  12  are to be seen more clearly in these figures than in  FIG. 1 . That is true in particular of the three apertured walls  27 ,  28 ,  29  with their holes through which the oil/air mixture formed within the nozzle head  20  is sprayed in radial direction from the inside to the outside. Greater droplets cannot pass the small holes in the apertured walls  27 ,  28 ,  29 . Instead, they are separated at these apertured walls, whereas smaller oil droplets in passing through the holes are communicated still further so that they will be set floating in the aerosol which finally forms in the pressure space  4 . 
     It may be taken from  FIGS. 2 and 3  that the spraying device  12  comprises an upper casing portion  25  which contains the air inlet connecting piece  11  and the oil inlet connecting piece  13  as well as the longitudinal bore  18  and the nozzle head  20 . It also comprises a lower casing portion  26  which is coaxial with the upper casing portion  25 . 
     The two casing portions  25  and  26  have coaxial spigots  25   a  and  26   a,  respectively, facing in opposite directions and holding the innermost apertured wall  27  between them. Moreover, the upper and lower casing portions have coaxial, radially further outwardly located shoulders  25   b,    26   b  which support the middle apertured wall  28 . Finally, the upper casing portion  25  has an outer flange  25   c  and the lower casing portion  26  has an outer shoulder  26   c,  the flange  25   c  and shoulder  26   c  being axially aligned so that they can retain the outer apertured wall  29 . 
     The upper and lower casing portions  25  and  26 , respectively, are connected tight together by three screws  31  arranged equidistantly in a circle x as indicated by dash-dot lines, thereby firmly holding the apertured walls  27 ,  28 ,  29  between them. As  FIGS. 2 and 6  show, the nozzle head  20  is threaded firmly into the upper casing portion  25 . 
     The nozzle head  20  of the spraying device  12 , shown on an enlarged scale in  FIGS. 5 and 6 , comprises a nozzle member  32  in which a twist body  33  is received. The inner end of the oil carrying capillary hose  19  is immersed with clearance in a central bore  34  formed in the twist body  33 . A helical groove  35  is formed in the outer circumference of the twist body  33  to present a baffle face for generating twisting of the flow in the groove. The groove  35  communicates through a transverse bore  36  with the central bore  34  in the twist body  33 . Therefore, gas and liquid can mix intimately inside the groove under the twisting effect and pressure. To that end compressed air is introduced in the direction of arrows “a” and “b” into the groove  35  and the clearance between the capillary hose  19  and the central bore  34 . 
     The helical groove  35  opens into the mixing chamber proper  32   a  of the nozzle head  20  via an inferior front wall  37 . The oil/air mixture flows on through a ring of outlet orifices  38  formed in a nozzle mouth  39  of the nozzle member  32  and impinges on an obtuse-angled deflector face  41  of a deflector head  40  which is screwed by a threaded trunnion  42  into a threaded hole in the nozzle mouth  39 . 
     The mixed jets issuing from the outlet orifices are conveyed outwardly from the deflector face  41  approximately in radial direction (see dashed arrows in  FIG. 6 ) against the cylindrical apertured wall  27 . With thicker droplets being separated, the jets continue on their way through the holes of the other apertured walls  28  and  29  and into the pressure space  4  where finally an aerosol is formed containing most finely divided oil droplets of the minutest dimensions in an order of magnitude of less than 1 μm, preferably in the range of 0.5 μm. The aerosol thus obtained in the pressure space  4  ultimately is passed on through the aerosol line  21  and the ball valve  22  to a treatment location. This may be a place where cutting or cold deformation is performed, and it may be located at a great distance of, for example, 30 m and more. The aerosol is conveyed all the way without any impairing of the floating state of the minute oil particles in the pressure air. 
     The features disclosed in the specification above, in the claims, and drawings may be essential to the realization of the invention in its various modifications both individually and in any combination.