Patent Publication Number: US-6663020-B1

Title: Mist generating head

Description:
The invention relates to a mist generating head. Such known mist generating heads are employed, for example, in appliances used to increase the moisture content of ambient air or also in industrial installations, in which, for example, a film of oil or a coating of adjacent oil droplets is applied to the surface of a workpiece. 
     What the known mist generators have in common is that it is difficult to produce mist also from liquids of higher viscosity for, in said case, the gas jet meeting the liquid stream delivered by the liquid nozzle may no longer subdivide the liquid stream into individual droplets because the cohesion in the liquid stream is too great. Also, with the known mist generators, the generated mist quantity may not be adjusted to very low values because atomization of the liquid by means of a gas jet presupposes a specific minium flow rate of liquid through the liquid nozzle and of gas through the gas nozzle. 
     The object of the present invention is therefore to develop a mist generating head in a way that allows also small quantities of a liquid of higher viscosity to be reliably atomized. 
     According to the invention said object is achieved by a mist generating head having the features disclosed in the present invention. 
     In the mist generating head according to the invention, there is forced subdivision of the fed liquid into small packages by the valve body associated with the liquid nozzle. Said small liquid volumes, which are delivered each time the valve body opens, are then split up further by the gas flow so that, on the whole, a fine mist is obtained. 
     Good preliminary dispersion of the liquid at the liquid nozzle is obtained when the valve body cooperating with the liquid nozzle is operated at the frequency disclosed in the present invention 
     The pressure value indicated in the present invention for the liquid to be atomized and the pressure value indicated in the present invention for the gas are advantageous likewise in view of fine, reliable nebulization of the liquid. 
     The geometry of the mist generating head as disclosed in the present invention has the advantage that, on the one hand, the liquid droplets derived by the liquid nozzle reach and pass through the gas jet and, on the other hand, a specific concentration and spatial confinement of the mist is effected by the gas jet and, moreover, the mist generation as a whole is effected symmetrically and uniformly. 
     The effect achieved by disposing the valve body axially outside of the liquid nozzle as disclosed by the present invention is that the valve body acts simultaneously as a deflector, by means of which the liquid droplets delivered by the liquid nozzle are distributed in peripheral direction. 
     In a mist generating head of the present invention, the gas nozzle, viewed in flow direction, may be disposed downstream of the liquid nozzle such that the stream of droplets delivered by the liquid nozzle may widen slightly before the fine atomization by the gas flow is effected. The result is better surfaces for the gas flow to act upon. 
     According to the present invention, the gas nozzle at the inlet side has a recess that serves to collect the mixture of droplets and gas before running into the gas nozzle, which has only a small diameter. 
     When an injection nozzle unit of the type indicated in the present invention is used to realize the liquid nozzle and the valve body, the cost benefits, stability under load and reliability of injection nozzles for i.c. engines may be turned to good use for nebulization of a liquid. 
     The development of the invention is advantageous both in view of a compact design of the mist generating head and in view of the uniformity of the generated mist. 
     With the development of the invention, a shaping and/or confinement of the mist stream generated by the mist generating head is obtained. 
     According to the present invention, the cross-sectional shape of the mist stream may easily be increased or decreased in size. 
     This may be realized according to the present invention by means which are mechanically extremely simple. 
     The effect achieved by the development of the invention is that the cross section of the mist stream may be adjusted to suit prevailing requirements by means of a control device. 
    
    
     There now follows a detailed description of embodiments of the invention with reference to the drawings. Said drawings show: 
     FIG.  1 : an exploded diagrammatic view of an installation for producing thin films of oil on metal sheets which are to be fed to a press; 
     FIG.  2 : transverse cross section through the lubricating chamber of the installation shown in FIG. 1; 
     FIG.  3 : an axial section through a mist generating head of the type used in the installation according to FIG. 1; 
     FIG.  4 : a transverse section through the mist generating head shown in FIG. 3 along the cutting line IV—IV indicated there; 
     FIG.  5 : a plan view of the bottom end face of the mist generating head according to FIG.  3  and 
     FIG.  6 : a view similar to FIG. 4 but showing a mist generating head with a controllable mist stream cross section. 
     In FIG. 1,  10  denotes the frame of a lubricating station denoted as a whole by  12 . 
    
    
     A housing  14  is shown removed from a lubricating device, which is denoted as a whole by  18 . Said housing comprises an upper housing part  16   a  and a lower housing part  16   b , which together delimit an inlet slot  20  and an outlet slot  22 , through which metal sheets (not shown) to be lubricated may pass. 
     As may be seen from the drawing, the lubricating station  12  is substantially symmetrical relative to the conveying plane of the metal sheets. Where necessary, functionally equivalent components situated above and below the conveying plane are distinguished by the suffixes a and b respectively. 
     For feeding and carrying away the metal sheets to be lubricated a charging conveyor, which is not shown in the drawings, and a discharge conveyor  24 , which is illustrated only diagrammatically in the drawings, are used. For greater clarity the discharge conveyor, like the housing  14 , is shown moved away from the actual lubricating device  18 . 
     The lubricating device  18  comprises profiles  26 ,  28 , which are arranged transversely relative to the conveying direction of the metal sheets. Of the profiles  26 , one ( 26   a ) is disposed above and the other ( 26   b ) below the conveyor of the metal sheets. A set of upper mist generating heads  34   a  and a set of lower mist generating heads  34   b  are attached in each case by an obtuse-angled retaining plate  30  to the profile  26   a  and  26   b  respectively so as to be uniformly distributed in a transverse direction relative to the conveying direction of the metal sheets. 
     In the interior of the housing  14  supporting rollers  38  carry the metal sheets which are to be lubricated. 
     As FIG. 2 reveals, the axes  40   a ,  40   b  of the mist streams generated by the mist generating heads  34   a ,  34   b  are tilted out of the vertical through approximately 15° in conveying direction of the metal sheets. Disposed in the two housing parts  16   a ,  16   b  are baffles  44  and  46  respectively, which are spaced apart from the housing walls and at the bottom end each have an obliquely upward- and inward-extending end portion  48  and  50 . Between the baffles  44 ,  46  and the vertical walls of the housing parts  16   a ,  16   b  there remains in each case a gap  52 ,  54 , which is connected by lines  56 ,  58  to a suction channel  60 , upon which an extractor (not shown in the drawing) operates. 
     The vertical walls of the housing parts  16   a ,  16   b  at the bottom end have in each case end portions  62 ,  64 , pairs of which form in each case an admission hopper and a discharge hopper for the metal sheets which are to be lubricated. 
     As FIGS. 3 to  5  reveal, the mist generating heads  34  each have a housing  66 , in which a central, multi-stepped bore  68  is provided. An injection unit  70  of the type used for fuel injection in diesel engines is inserted into the stepped bore  68 . The injection unit  70  has a housing  72 , which at its outside has a plurality of shoulders and in its bottom end face has a liquid nozzle  74 . The liquid nozzle  74  simultaneously has at the outlet side a valve seat  76  in the shape of a truncated cone, which cooperates with a valve body  78  carried by a valve stem  80 . 
     The valve stem  80  extends, in the drawing, up through the housing  72  and is connected at the top end to the armature of an electromagnet  82 , which is excited from a control unit  84 . The latter receives from a master control device  86  signals which specify the frequency, at which the electromagnet  82  is activated, the pulse duty factor between open and closed time of the valve body  78  and optionally the amplitude of the supply current fed to the electromagnet  82  (and hence the opening travel of the valve body  78 ). 
     The valve may operate at a frequency of about 10 to about 100 Hz. In an advantageous embodiment, the valve operates at a frequency of approximately 60 Hz. 
     The stepping of the bore  68  and the graduation of the outer surface of the housing  72  give rise in the bottom portion of the housing  72  to an annular space  88 . The latter communicates via an inlet  90  with a compressed-air line  92 . The latter contains a pressure regulator  94 . 
     An air nozzle disk  96  is screwed by means of a threaded ring  98  tightly up against the bottom end face of the housing  66 . The air nozzle disk  96  in its top boundary surface has a truncated-cone-shaped recess  100 , which surrounds the bottom end of the housing  72  with clearance and leads as a funnel to a likewise truncated-cone-shaped nozzle aperture  102 , which opens out into the bottom free end face of the air nozzle disk  96 . 
     As FIG. 4 reveals, branching off from the inlet  90  is a lateral channel  104 , in which a truncated-cone-shaped valve seat not provided with a reference character is formed and cooperates with a needle valve body  106 , which has a conical tip, runs in a thread of the housing  66  and may be operated at a knurled end portion  108 . Emanating from the portion of the lateral channel  104  situated downstream of the valve seat formed in the lateral channel  104  is an axial control air channel  110 , which leads to a further annular space  112  situated between the underside of the housing  66 , the top of the air nozzle disk  96  and the inner surface of the threaded ring  98 . 
     Via bores  120 ,  122  of the housing  66 , which are closed by stoppers  116 ,  118 , a further vertical control air channel  124  is acted upon, which opens into the annular space  112  diametrically opposite the entry point of the control air channel  110 . 
     Opening out into the free end face of the air nozzle  96  are control nozzle channels  126 ,  128 , which emanate from the annular space  112  and are a continuation of the control air channels  110 ,  124 , as FIG. 5 reveals. 
     A liquid feed channel  130  of the injection unit  70  is connected to a distribution line  132 , in which a pressure regulator  134  keeps the liquid to be atomized (oil) at a pressure of 2 to 8 bar, preferably approximately 4 to 5 bar. The pressure adjusted by the pressure regulator  94  in the compressed-air line  92  is approximately 2 to 4 bar. 
     The pressure values actually used in each case depend on the nature, in particular the viscosity of the liquid to be atomized in each case and the size of the desired droplets as well as the desired velocity of the mist stream. 
     During operation, the electromagnet  82  is excited by the control unit  84  in each case at the adjusted frequency and with the set pulse duty factor. Each time the electromagnet is excited, a preset small liquid volume is delivered through the liquid nozzle  74  and is subjected simultaneously to preliminary atomization. 
     On leaving the liquid nozzle, said liquid droplets come into intimate contact with the sleeve-like air jet flowing around the bottom end of the injection unit  70  and are split up further in said air jet. At the outlet of the nozzle aperture  102  a fine liquid mist is obtained. 
     When the needle valve body  106  is in the closed position, the external contour of said liquid mist corresponds to a cone. By opening the needle valve body  106 , the mist cone may be pressed flat from two opposite directions so that the transverse cross-section of the mist assumes a shape similar to a rectangle. 
     In the modified example according to FIG. 6, the needle valve body  106  is supported so as to be displaceable in axial direction in the housing  66  and is firmly connected to the armature of an electromagnet  136 . Via the supply current of the electromagnet  130  the control unit  86  may therefore easily control the cross-sectional shape of the mist stream.