Patent Document

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a spray gun for atomizing paints, lacquers or similar media that can be supplied to a workpiece by means of an air flow, in which case the spray gun can be actuated by means of a lever mounted in a pivoting arrangement on a sleeve which accommodates an atomiser nozzle and the air flow can be generated by an air turbine assigned to the spray gun. 
   2. Description of the Prior Art 
   A spray gun of this type is described in FR 80 145 66. In this embodiment, the electric motor driving the air turbine can be removed together with the air turbine and is arranged in a separate component on the housing of the spray gun perpendicular to the atomizer nozzle of the spray gun, so that the air flow generated by the air turbine has to have its direction changed several times before it emerges from the atomizer nozzle. 
   This generates significant flow noise as well as flow losses, therefore this spray gun does not provide a reasonable level of efficiency. A further disadvantage is that the drive motor of the air turbine is only provided with inadequate cooling; this is because the only air flowing past the drive motor is the air drawn in by the air turbine and this air flow is not controlled, meaning that sustained operation is often impossible. Also, this spray gun does not provide any counterbalance because the reservoir container for the medium to be processed and the drive motor with air turbine are arranged ahead of the handle, therefore a high tilting torque is generated whilst the medium is being processed and this tilting torque has to be counteracted by the operating personnel. The principal disadvantage, however, is that the level of noise generated by the air turbine spinning at high speed is only inadequately muffled by the component that houses the motor. As a result, this spray gun has not proved effective in practical use. 
   The purpose of the present invention is therefore to create a spray gun for atomising medium of the aforementioned type that not only has a straightforward design structure and can be easily operated, but in which above all the operating noise does not attain disruptive levels and there are almost no flow losses which would be caused by changes in the direction of the air flow. Furthermore, the components of the spray gun should be distributed in such a way that either no or only slight tilting torques are generated, therefore permitting work over long periods without leading to fatigue. 
   In accordance with the present invention, this is achieved in a spray gun of the aforementioned type in that the air turbine and its electric drive motor are arranged coaxially or almost coaxially to the atomiser nozzle of the spray gun on the side of a handle opposite to the sleeve that carries the atomiser nozzle so that the air flow from the air turbine can be supplied in or almost in a straight line through the sleeve of the atomiser nozzle and that the air turbine is provided with a muffler. 
   In this case, it is advantageous for the muffler, the air turbine and its drive motor to be arranged axially one after the other in the flow direction of the air flow and installed in an attachment formed onto or attached to the handle, so that a high counterweight to the reservoir container attached on the opposite side of the sleeve is created. In addition, a cavity should be provided between the muffler and the air turbine by means of which the flow noise is reduced. 
   Furthermore, it is advantageous for the movement sequence of the lever that actuates the spray gun to be adapted to a switch associated with the drive motor of the air turbine and that can be influenced by the lever in such a way that the drive motor can be switched on before the atomiser nozzle opens and can be switched off after the atomiser nozzle closes. In this way, it is assured that the medium will only be sprayed when sufficient air flow is available for this and no droplets will be formed when the spray gun is switched on and off. 
   In order to avoid deflections in the air flow within the spray gun and therefore to avoid flow losses, the attachment that accommodates the muffler, the air turbine and its drive motor should be arranged at an angle α from 0° to 60°, in a preferred embodiment approx. 20°, in relation to the longitudinal axis of the sleeve that carries the atomiser nozzle, opposite to the handle. 
   Furthermore, the drive motor of the air turbine should be equipped with a jacket that is closed in the axial direction and radially supported in the attachment, it being possible for this jacket to be connected to the sleeve with a connection that can, in a preferred embodiment, be separated. The jacket therefore forms a pressure chamber through which the air flow is guided close to the drive motor of the air turbine so the air flow provides effective cooling. 
   In accordance with a further embodiment, there is provision for installing a protective grille between the drive motor of the air turbine and the sleeve, with the protective grille being supported, in a preferred embodiment, in the jacket and which should be manufactured from a vibration-damping material, with the possibility of mounting the end of the drive motor of the air turbine that faces away from the air turbine in the protective grille. As a result, satisfactory support for the drive motor is assured. 
   It has also proven to be extremely advantageous to form the attachment and/or the jacket directly onto the handle and, with a separable connection, on the sleeve that carries the atomiser nozzle, for example by means of a bayonet lock, in which case a container cover can be attached to the sleeve and the container cover should be provided with a holding element, for example in the form of a lug, into which it is possible to engage a web projecting from the handle in order to lock the connection between the attachment or the jacket and the sleeve. In this way, it is possible for the drive part of the spray gun to be separated from its components that are used for atomisation and for the air flow to be used for other purposes, e.g. as a jet of air for blowing out workpieces. 
   It is also advantageous for the end of the handle to run in the same plane as the standing surface of a reservoir container attached to the spray gun and if the end of the handle is formed as a stand foot, so that the spray gun can be securely put down after use. To reduce the operating noise of the air turbine even more, a sound-absorbing insert should also be arranged between the attachment and the jacket of the drive motor. 
   The muffler used in the spray gun in accordance with the present invention is, in order to achieve effective acoustic insulation of the intake noise of the air turbine, characterized in that the muffler has a spiral-shaped air duct arranged in a cylindrical housing between an air inlet opening and an air outlet opening, this air duct being formed by two thin-walled partition walls that run in a spiral and are arranged at a lateral distance from one another on a base and/or on a cover of the housing that, in a preferred embodiment, is cylindrical in shape and which project at right angles from the housing, these partition walls combining with the base and the cover to enclose a closed cross-sectional area, that the air inlet opening of the air guide duct is worked into the outer wall of the housing and/or the cover, for example in the form of slots, and that the air outlet opening is arranged centrally in the housing in the base of the housing. 
   In this case, it is advantageous for the air guide duct to consist of two or more sections running in an almost mirror image arrangement to one another and, in a preferred embodiment, with point symmetry so that the air supply can be evenly distributed over 360°. 
   Furthermore, it is advantageous for the air guide duct or the two sections that form the air guide duct to be provided with a guide surface in the area of the air outlet opening, the guide surface being spatially curved, and in the case that the air guide duct is composed of two or more sections then the individual sections in the area of the air outlet opening are to be separated from one another by wall sections extending in the axial direction of the air guide duct. 
   Furthermore it is advantageous for the cross-sectional area of the air guide duct or the sections that form it to be always consistent along its length, in which case if the base and/or the cover of the housing are configured with a funnel shape then the distance between the two partition walls enclosing the air guide duct or enclosing the sections forming the air guide duct is continuously changed in such a way that the enclosed cross-sectional area of the air guide duct is kept constant at all times. 
   In particular in a housing with a tapered base, the air outlet opening should be followed by an air distributor in the form of a guide body with a tapered configuration. 
   The housing and/or the cover and the partition walls formed onto them should be configured as an injection-moulded plastic part, in which case it is advantageous for the housing and/or the cover and/or the partition walls formed onto them to be manufactured from a plastic which absorbs or reflects sound, in a preferred embodiment from a plastic incorporating air bubbles and/or pores and, furthermore for the housing and/or the cover and/or the partition walls to be provided with a coating which absorbs and/or reflects sound. 
   If the partition walls that form the air guide duct are formed onto the base of the housing then it is advantageous for a preferably rubber-like seal to be inserted between them and the cover, the seal corresponding approximately to the inner jacket surface, or for the seal to be attached to the cover. 
   In order to reduce the noise additionally, it is advantageous for one or more air inlet openings to be provided, e.g. in the form of slots, in the attachment of the spray gun, with the air inlet openings being arranged in a preferred embodiment offset at 90° or 180° in the circumferential direction and/or axially displaced in relation to the air inlet openings worked into the housing and/or the cover of the muffler. 
   The muffler embodied in accordance with the present invention can form the end air connection of the air turbine and be arranged directly in its intake area. 
   In a spray gun is embodied in accordance with the present invention, it is possible to atomise a medium with the help of a high-volume air jet without thereby giving rise to unpleasant noise or impeding the handling of the spray gun. The air flow is namely guided almost in a straight line through the attachment accommodating the air turbine as well as the sleeve that carries the atomiser nozzle, there are no deflections in the air flow and the flow resistance values are also minor. 
   Furthermore, it is advantageous that the arrangement of the sleeve with the atomiser nozzle and the reservoir container on one side of the handle and of the attachment accommodating the air turbine and the drive motor on the other side of the handle provides for an almost even distribution of weight. It is therefore possible to work with the spray gun configured in accordance with the present invention for long periods without uneven loadings leading to fatigue. Also, in particular in the separable embodiment of the spray gun, the spray gun can be used for many different applications by connecting a hose with an air nozzle, for example, to the air turbine in order to be able to perform cleaning work. 
   The muffler assigned to the air turbine furthermore permits a very effective insulation of the intake noise of the air turbine, since the sucked-in air flow is if necessary divided into several individual flows, sucked in over a long distance and only deflected to a minimum extent in this case. The resistance opposing the sucked-in air is only minor in this case, therefore the air flow rate through the muffler is only impeded to a slight extent. 
   The thin-walled partition walls forming the air guide duct furthermore only take up a minor proportion of the interior of the housing, so that almost the entirety of the housing can be used for the air flow. Also, the partition walls formed onto the base and/or the cover and contacting the opposite part ensure a high level of stability, by means of which the noise is further reduced. When the muffler in accordance with the present invention is used, it is therefore possible significantly to reduce the environmental impact resulting from the use of the high speed air turbines which generate loud noise. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings show sample embodiments of a spray gun configured in accordance with the present invention, the details of which are explained below. In the drawings, 
       FIG. 1  shows a longitudinal section through the spray gun with atomizer nozzle, air turbine and muffler; 
       FIGS. 2 and 3  each show a partial section through the spray gun in accordance with  FIG. 1  in various operation positions; 
       FIG. 4  shows a projection of a variant of the spray gun in accordance with  FIG. 1 , in a separable embodiment; 
       FIG. 5  shows an axial section of a muffler installed in the spray gun in accordance with  FIG. 1 , with a one-piece air guide duct; 
       FIG. 6  shows the spray gun in accordance with  FIG. 5 , with an air guide duct formed from two sections; 
       FIG. 7  shows a perspective view of the muffler in accordance with  FIG. 6 ; 
       FIG. 8  shows an axial section through the muffler in accordance with  FIG. 7 ; and 
       FIG. 9  shows the muffler in accordance with  FIG. 8 , with sections of the air guide duct having different cross sections. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The spray gun shown in  FIGS. 1 ,  2 ,  3  and  4  and identified with  1  or  1 ′ is used for atomising paints, lacquers or similar media  3  located in a reservoir container  2 , it being possible to supply the media  3  to a workpiece by means of an air flow. In the illustrated embodiment, the air flow for atomisation is generated by an air turbine  5  that can be driven by an electric motor  4 . In addition, the air turbine  5  is provided with a muffler  6  in order to reduce the intake noise, whilst a cavity  7  is created between the muffler  6  and the air turbine  5  for the same purpose. 
   The spray gun  1  principally consists of a sleeve  11  to which the reservoir container  2  is attached, of an atomiser nozzle  12  equipped with an axially adjustable nozzle needle  13  and also attached to the sleeve  11 , of a handle  21  and of an attachment  31  formed onto the handle  21 , the attachment  31  being firmly connected to the sleeve in the case of the spray gun  1  and which accommodates the air turbine  5 , its drive motor  4  and the muffler  6 . The spray gun can be actuated by means of a lever  15  that operates against the force of a spring  14  and that pivots about an articulated pin  16 . 
   The handle  21  has an electrical switch  22  built into it, to which electrical power can be supplied through a cable  23  and that is inserted in the circuit of the electric motor  4 . By means of a button  24  that can also be moved by the lever  15  against the force of a spring  25 , it is possible to switch the circuit of the electrical motor  4  in such a way that the air turbine  5  is switched on before the atomiser nozzle  12  opens and for the air turbine  5  only to be switched off once the atomiser nozzle  12  has itself already been closed. 
   For this purpose and as shown in the various operating positions in  FIGS. 1 ,  2  and  3 , the operating sequence of the lever  15  is accordingly adapted to the movement of the nozzle needle  13  and the button  24  for switching the drive motor  4  on and off. This approach avoids a situation in which the medium  3  can emerge from the atomiser nozzle  12  before a sufficient air flow is available for processing it, or that droplets are formed on the atomiser nozzle  12  before the start of work or after work has finished. 
   In order to make this movement sequence possible, a slot  18  is worked into the lever  15  of which the adjustment travel is to be adjusted using a setscrew  29  at the level of the nozzle needle  13 , and a pin  17  attached to the nozzle needle  13  engages in the slot  18 . The nozzle needle  13  is therefore not entrained and moved until the drive motor  4  has already been switched on by the actuation of the switch  22 , due to the necessity of overcoming the idle travel created by the slot  18 . 
   The drive motor  4  and the air turbine  5  that spins at high speed are inserted in a jacket  32  that, in the embodiment illustrated in  FIGS. 1 to 3 , is firmly connected to the sleeve  11  together with the attachment  31 . The jacket  32  therefore forms a pressure chamber for the air flow generated by the air turbine  5  that is guided past the drive motor  4  and provides cooling for the drive motor  4 . Furthermore, the jacket  32  accommodates a protective grille  33  made from a vibration-damping material that is supported on the jacket  32  and in which is mounted the end of the drive motor  4  opposite to the air turbine  5 . An insert  34  made from a sound-absorbing material is arranged between the jacket  32  and the attachment  31 , and this insert  34  significantly insulates the noise created by the air flowing into the sleeve  11  through the protective grille  33  in the suction and pressure area. 
   In order to increase the stability of the connection between the sleeve  11  and the attachment  31  or the jacket  32 , a lug  27  is attached to a cover  26  formed onto the sleeve  11 , this cover  26  being for the container  2  that is held in a separable connection, and a web  28  projects from the handle  21  and is engaged in the lug  27 . Furthermore, the end of the handle  21  at the level of the base of the container  2  is formed as a stand foot  30  so that the spray gun can be put down securely. 
   Since the attachment  31  is located at an angle α of approx. 20° upwards in relation to the sleeve, the air flow generated by the air turbine  5  travels into the sleeve  11  and therefore into the atomiser nozzle  12  almost without any deflection. As a result, flow losses and flow noise are largely avoided. Also, the insert  34  and the muffler  6  keep the operating noise of the spray gun  1  within a range that can be supported by the operating personnel in spite of the fact that the air turbine  5  is rotating at high speed. 
   In the embodiment illustrated in  FIG. 4 , the handle  21  and the attachment  31  are both connected to the sleeve  11  in a separable arrangement. A bayonet lock  19  and  20  is used for this purpose, with its interlocking components being formed onto the sleeve  11  and the jacket  32 . As a result, a hose line  9  can be connected to the jacket  32 , there being an air nozzle  10  connected to the hose line  9 . In this way, the air flow generated by the air turbine  5  can be used for blowing out workpieces, for example. 
   The muffler  6  used in the spray gun  1  or  1 ′ consists, as can be seen in detail in particular in  FIGS. 5 to 9 , of a cylindrical housing  41  and a cover  42  on the housing  41 , with the interior of the muffler  6  featuring an air guide duct  43  that is formed by thin-walled partition walls  47  and  48  arranged at a lateral distance from one another. The partition walls  47  and  48  are formed onto a base  46  of the housing  41  and/or on the cover  42  and project at right angles from it. In addition, the air guide duct  43  is equipped with an air inlet opening  44  worked directly into the outer wall of the housing  41  and an air outlet opening  45  provided centrally in relation to the base  46 . In the muffler as illustrated in  FIG. 5 , the air outlet opening  45  is provided with a spatially curved guide surface  49  in order to deflect the air flow and direct it towards the air turbine  5 . 
   In the embodiment shown in  FIGS. 6 and 7 , the air guide duct  43  is formed by two sections  43   a  and  43   b  in an almost mirror-image arrangement, which are therefore arranged in point symmetry to one another. Accordingly, two air inlet openings  44 ′ and  44 ″ are worked into the outer wall of the housing  41  and the air outlet openings  45 ′ and  45 ″ are in turn provided with guide surfaces  49 ′ and  49 ″. In addition, the sections  43   a  and  43   b  are separated from one another in the area of the air outlet openings  45 ′ and  45 ″ by means of two wall sections  51  and  52  that are connected to one another by a hub  53 , with the effect that the two air flows to be supplied to the air turbine  5  via the sections  43   a  and  43   b  do not come together in the area of the air outlet openings  45 ′ and  45 ″. 
   The cross-sectional area F of the air guide duct  43  in the muffler  6  is always the same along its length. However, in the muffler  6 ′ shown in  FIG. 8 , the base  46  of the housing  41  has a tapering shape, therefore the distance between the two partition walls  47 ′ and  48 ′ or  47 ″ and  48 ″ has to change continuously in order to keep the same cross-sectional area F in both sections  43   a  and  43   b  at all times. The increase in the axial distance between the base  46  and the cover  42  in the outer area compared to the inner area is therefore compensated for by a reduction in the lateral clearance between the partition walls  47 ′ and  48 ′ or  47 ″ and  48 ″. 
   In the muffler  6 ″ shown in  FIG. 9 , in contrast, the base  46 ′ of the housing  41 ′ runs in parallel to the cover  42 . The distance between the partition walls  47 ′ and  48 ′ or  47 ″ and  48 ″ is therefore also constant in order to achieve a constant cross-sectional area F 1 . 
   In accordance with  FIG. 8 , the air outlet opening  45 ′,  45 ″ can be followed by a tapering air body  50  that is attached to the hub  53  by means of a screw  54 , in order to deflect the air flow radially outwards and to insulate noise. Furthermore, the partition walls  47 ,  48  can be provided with a sound-absorbing coating  55  and a rubber-like seal  56  can be inserted between the partition walls  47 ,  48  and the cover  42  in order to provide an air-tight seal in the air guide duct  43  or the sections  43   a,    43   b  in the area of the cover  42 . In addition, an air filter  58  can be inserted between the rotating edge of the cover  42 , in which air slots  57  can be worked, and the housing  41 . 
   In the spray gun  1 , the air for generating a high-volume air flow is supplied to the muffler  6  through air inlet openings  35  worked into the attachment  31 . The air inlet openings  35  in this case are offset in relation to the air inlet openings  44  of the muffler both around the circumference and in the axial direction of the attachment  31 , this arrangement also having the effect of reducing noise. The deflections in the air guide duct  43  of the muffler  6  are small, therefore practically no flow noise occurs here. Furthermore, the operating noise of the air turbine  5  is significantly reduced by the muffler  6  that is arranged on the end of the air turbine  5 , as a result no impairment to persons working with the spray gun  1  through excessive operating noise needs to be feared.

Technology Category: 7