Spray nozzle for a spray tool

In a spray nozzle with a nozzle housing including a dosing chamber for accommodating a release agent to be sprayed into a mold via a discharge line including a check valve and a nozzle body and a venting unit integrated into the nozzle housing for venting air from the spray nozzle, the volume of the dosing chamber is adjustable and the venting unit is activatable by an activation signal by which the venting unit is moved from a dysfunctional position to a venting and opening position in which the check valve is held open by the venting unit for venting the dosing chamber and the discharge line, via the nozzle body.

BACKGROUND OF THE INVENTION

The invention relates to a spray nozzle for a spraying tool for the application of a release agent to a casting mold.

Such a spray nozzle is disclosed in DE 10 2008 035 632 B4. This spray nozzle includes in a nozzle housing a dosing chamber into which a release agent can be introduced. The volume of the dosing chamber can be changed via a discharge piston. By actuating the discharge piston the release agent is displaced from the dosing chamber and conducted, via a discharge passage, to a nozzle body which includes an outwardly open cavity in which spray air is added to the release agent before its discharge.

The dosing chamber is provided with a venting channel for the venting of a gas volume in the dosing chamber.

It is the object of the present invention to provide a spray nozzle for a spraying tool which can be effectively vented by simple measures.

SUMMARY OF THE INVENTION

In a spray nozzle with a nozzle housing including a dosing chamber for accommodating a release agent to be sprayed into a mold via a discharge line including a check valve and a nozzle body and a venting unit integrated into the nozzle housing for venting air from the spray nozzle, the volume of the dosing chamber is adjustable and the venting unit is activatable by an activation signal by which the venting unit is moved from a dysfunctional position to a venting and opening position in which the check valve is held open by the venting unit for venting the dosing chamber and the discharge line, via the nozzle body. Preferably the spray nozzle operation is controlled by a common control air supply which, below a certain threshold pressure, controls the dosing chamber volume but, above a certain, higher, threshold pressure activates additionally the venting unit while holding the check valve open when the venting unit is activated.

The dosing element is in the form of an expulsion piston which can execute a control movement in the direction of the longitudinal piston axis.

During a regular normal operation the release agent displaced from the dosing chamber by the control movement of the dosing element is discharged from the nozzle housing via a discharge channel to a nozzle element. If appropriate, a spray medium, in particular compressed air, is added to the release agent in order to discharge the release agent from the nozzle element in the form of a spray cloud.

The spray nozzle includes an integral active venting unit for venting the dosing chamber and, if applicable, the discharge channel which is in communication with the dosing chamber. Venting is required when air has collected in the dosing chamber or, respectively, in the discharge channel whereby a discharge of the release agent is prevented or at least negatively affected. Because of the compressibility of the air in the dosing chamber the control movement of the dosing element is not or only partially converted into a displacement of the release agent. For a proper functioning of the spray nozzle any air collected in the dosing chamber needs to be vented.

The air is vented via the active venting unit in that an activation signal is applied to the venting unit whereupon the venting unit is automatically adjusted from a dysfunctional position to a venting and opening position. With a proper functioning of the spray nozzle that is without any air collected in the dosing chamber by the release agent, the venting unit or a component operated by the venting unit is moved to the venting and opening position permitting the release agent to pass the venting unit. If air is present in the dosing chamber the venting unit or a component activated by the venting unit can be moved by application of the activation signal automatically to the venting and opening position in which the dosing chamber is vented. Upon completion of the venting, the venting unit is again returned from the venting and opening position to the dysfunctional position whereby the normal functional operability of the spray nozzle is re-established and normal operation of the spray nozzle can be resumed.

Because of the automatic operation of the venting unit a manual opening and closing for the venting procedure is eliminated. The venting unit is activated by the activation signal which supplies the energy for transferring the venting unit from the dysfunctional position to the venting and opening position and which controls the movement of the venting unit. Movement of the venting unit into the dysfunctional position is obtained either also in an active manner by applying an activation signal to the venting unit or in a passive manner by a force permanently applied to the venting unit in a direction toward its dysfunctional position such as the spring force of a spring element or the force generated by the weight of the venting unit or another component which acts on the venting unit. The movement of the venting unit from the dysfunctional to the venting and opening position is obtained by the activation signal acting in a direction opposite the direction of the return force biasing the venting unit into the dysfunctional position.

The venting of the spray nozzle can also be manually initiated by providing the activation signal manually so that the venting unit is moved from the dysfunctional position to the venting and opening position. Alternatively the automatic adjustment movement of the venting from the dysfunctional position to the venting and opening position may be initiated by monitoring a system value, for example the pressure of the release agent in the area of the nozzle body or in the discharge channel and automatically activating the venting unit by applying the activating signal to the venting unit depending on the height of the system value. As system value for example also an optical surveillance of the spray pattern of the release agent out of the nozzle body may be taken into consideration wherein the venting unit is activated when it is optically determined that the release agent is not sprayed out or not in the desired form.

In an advantageous development the activation signal for the venting unit is the same as the activation signal for the dosing member which is used for a volume change of the dosing chamber and the discharge of the release agent from dosing chamber. The activation signal is for example based on pressurized control air which is applied to the dosing member as well as to the venting unit. The control air for the dosing member and the venting unit may be supplied via a common control air duct also to the spray nozzle. Alternatively, the control air for the dosing member and the control air for the venting unit may be supplied via separate control air ducts.

The control air is pressurized wherein below a certain air pressure threshold value, only the dosing member is activated and, above the air pressure threshold value, both the dosing member and the venting unit are activated.

Advantageously, there is a lower compressed air threshold value and a higher, upper, compressed air threshold value which are for example at 6 bar and 8 bar, wherein below the lower threshold value only the dosing member is activated and above the upper threshold value both, the dosing member as well as the venting unit are activated. This procedure has the advantage that, during normal operation, with the venting unit in the dysfunctional position, the dosing member can be activated by the pressurized air and/or with control pressure corresponding to the lower threshold value whereas, for the venting, the control air pressure value only needs to be increased to the upper threshold value in order to move the venting unit into the venting and opening position. Because of the pressure difference between the lower and the upper pressurized air threshold value there is a security spacing which prevents an unintended activation of the venting unit. Since for the venting procedure both, the dosing member and the venting unit are activated it is made sure that, with the activation of the dosing member, any air is removed from the dosing chamber via the nozzle body in spite of the high compressibility of the air in the dosing chamber.

Also other activation values may be taken into consideration for activating the venting unit. As another activation value for example, an electric current may be used by which an electric venting unit, for example, in the form of an electromagnetic activator is energized. Also the dosing member may be electrically activated. Alternatively, the venting unit and/or the dosing member may be hydraulically activated.

It is advantageous to use the same activation medium for both, the dosing member and the venting unit. But, alternatively, it is also possible to use different activation media for the dosing member and the venting unit, for example control air for the dosing member and electric current or hydraulic pressure for the venting unit.

In the discharge channel a check valve is arranged which can be activated by the venting unit from a blocking position to an open position for venting the system. For the duration of the venting process the check valve remains in the open position in which the air in the dosing chamber and possibly residual release agent is discharged from the dosing chamber via the discharge channel and the nozzle body. Also, during normal operation, wherein the venting unit is in the dysfunctional position, the check valve is opened during the discharge of the release agent. At the end of the discharge procedure—during normal operation as well as at the end of the venting procedure—the check valve returns to the blocking position in which the discharge channel is blocked.

In an advantageous embodiment, the check valve comprises a blocking ball which is arranged in the discharge channel and is movable therein between a blocking and an opening position.

In an advantageous embodiment of the invention the venting unit is in the form of a venting piston which is movable along its longitudinal axis between the dysfunctional position and the venting and opening position. During normal operation without any air in the dosing chamber, the venting piston is in the axially retracted dysfunctional position. Upon activation of the venting piston, in particular by control air whose pressure is above an upper air pressure threshold value, the venting piston is moved axially out of the dysfunctional position into the venting and opening position and presses the check valve, that is in particular the blocking ball, out of its blocking into its opening position in which the check valve remains for the duration of the venting procedure. To end the venting procedure activation of the venting piston is stopped whereby the venting piston returns to its dysfunctional position for example by its weight. However, the venting piston may also be spring-biased for returning it to its dysfunctional position.

It may also be expedient to provide additionally for a manual venting procedure for venting the spray nozzle. To this end a by-pass may be provided which can be opened manually for the venting of the dosing chamber.

In accordance with a further advantageous embodiment, the dosing volume of the dosing chamber may be adjustable by means of a displacement element which may, for example, be in the form of a set screw which is screwed into the dosing chamber housing and which can be adjusted from without. The front end of the set screw forms an abutment and support area for the dosing member, the base position of which depends on the position of the set screw. With an adjustment movement of the set screw the volume of the dosing chamber can be changed.

The invention will become more readily apparent from the following description of a particular embodiment thereof described below with reference to the accompanying drawings.

DESCRIPTION OF A PARTICULAR EMBODIMENT

In the figures identical components are designated by the same reference numerals.

FIGS. 1 and 2are perspective views of a spray nozzle1for spraying a release agent, for example an oil, into a cavity or onto the surface of a mold. The spray nozzle1, which may be part of a spraying tool, comprises a nozzle housing2from which a nozzle body3extends which is in the form of a nozzle body ball and is supported in the nozzle housing2in a corresponding ball joint so that the nozzle body3can be pivoted about up to three rotational axes. Via the nozzle body3the release agent is sprayed out in the discharge direction4in the form of a spray cloud.

As apparent from the perspective view of the spray nozzle according toFIG. 2there are several inlet openings5to8at the bottom side of the spray nozzle1via which different media can be supplied to the spray nozzle1. Via the inlet opening5spray air is introduced which is mixed with the release agent to generate a spray cloud which is discharged via the nozzle body3. The spray air and the release agent are mixed in the nozzle body3within an outwardly open cavity18or already upstream of the nozzle body3in a passage19via which the release agent is supplied to the nozzle body3.

The release agent is supplied to the nozzle housing2via another inlet opening6. There are further two more inlet openings7and8via which control air is supplied to the spray nozzle1. The control air is pressurized and is used for controlling the movement of a dosing member for changing the volume of the release agent to be discharged and for controlling the movement of the venting unit in the spray nozzle.

FIGS. 4 and 5are sectional views taken along line A-A ofFIG. 3. They show a cross-section of the nozzle housing2of the spray nozzle1. Shown therein is a dosing member9in the nozzle housing2, inFIG. 4in the initial position and inFIG. 5in the displacement position, which dosing member is used for the displacement of the release agent from a dosing chamber10via a discharge channel11to the nozzle body3. The dosing member is in the form of a dosing piston9whose front end delimits the dosing chamber10so that an axial displacement along the longitudinal piston axis of the dosing piston9results in a volume reduction of the dosing chamber10and a release agent displacement of the same volume out of the dosing chamber10toward the nozzle body3. The dosing piston9is axially movably supported in an operating chamber12provided in the nozzle housing2. In the area above the dosing piston9control air under an operating or control pressure of for example 6 bar is admitted to the operating chamber12whereby the dosing piston9is moved from its initial position as shown inFIG. 4to its displacement position as shown inFIG. 5. This movement is performed against the force of a spring element13(FIG. 4) which is supported in the nozzle housing2so as to bias the dosing piston9into its initial position. After completion of the spraying procedure the pressure of the control air in the upper area of the operating chamber12above the dosing piston9is reduced whereby the dosing piston9is returned by the force of the spring element13to its initial position.

The volume of the dosing chamber10can be adjusted by a set screw21(FIG. 4) which forms a control element. The set screw21, can be adjusted from without for changing the position of the set screw21within the housing. The front end of the set screw21forms a stop—or support surface for the dosing piston9, so that its initial position depends on the position of the set screw21.

FIGS. 7 and 8are further cross-sectional views of the spray nozzle taken along line B-B ofFIG. 6. The cross-sectional area of the view is angularly displaced with regard to the cross-sectional views ofFIGS. 3 to 5. InFIGS. 7 and 8a venting unit14is shown which serves to vent the dosing chamber10and possibly also the discharge channel11if air has collected in the dosing chamber10or, respectively, in the discharge channel11. In that case normal operation of the spray nozzle that is the spraying of release agent is not possible since, because of the high compressibility of the air in the dosing chamber, the movement of the dosing piston9does not result in a proper discharge of the release agent but essentially only to a compression of the air or gas volume in the dosing chamber10.

The venting unit14is in the form of a venting piston which extends in the nozzle housing2parallel to the dosing piston but in spaced relationship therefrom. The venting piston14is axially movable between the dysfunctional position shown inFIG. 7and the venting and opening position shown inFIG. 8. The front end of the venting piston14faces a check valve15in the form of a check valve ball which is arranged in the flow passage of the release agent from the dosing chamber10to the nozzle body3in a section11aof the discharge channel11. The check valve ball15is movable between a blocking position and an opening position. In the blocking position (FIG. 7) a flow of release agent or air through the discharge channel11is prevented; in the opening position (FIG. 8) the flow is possible.

During regular operation—that is without any air in the dosing chamber10—the release agent is discharged by the operating movement of the dosing piston9via the discharge channel11and the nozzle body3. Herewith the check valve ball15is lifted out of the blocking position as shown inFIG. 7to the opening position as shown inFIG. 8. The opening position is above the blocking position. Upon completion of the discharge procedure the check valve ball15moves spring-based from the opening position back to the blocking position.

The venting piston14is normally in the retracted initial position as shown inFIG. 7, in which the venting piston does affect the movement of the check valve ball15. But by the movement of the venting piston14out of the dysfunctional position as shown inFIG. 7to the venting and opening position as shown inFIG. 8in which the venting piston is raised. The top end of the venting piston14pushes the check valve ball15off its blocking position to its opening position in which the flow passage through the discharge channel11is cleared. With an operating movement of the dosing piston9the free volume of the dosing chamber10is reduced and air present in the dosing chamber10and possibly in the discharge channel11is discharged via the now open discharge channel11and the nozzle body3. The venting procedure is terminated when the dosing piston9returns again to its initial position and the venting piston14returns to its dysfunctional position.

The venting piston14is lifted from the dysfunctional position as shown inFIG. 7to the venting and opening position as shown inFIG. 8by means of control air. The venting piston14is movably supported in an operating chamber16within the nozzle housing2. Into the area of the operating chamber16at the bottom side of the venting piston14control air can be introduced which lifts the venting piston14out of the dysfunctional position into the venting and opening position.

The lifting level of the venting piston14depends on the pressure of the control air at the bottom side of the venting piston. Advantageously the control air needs to reach or exceed a pressure threshold value of for example 8 bar in order to lift the venting piston14. This pressure threshold value is above the normal pressure of for example 6 bar which is applied to the dosing piston to move it against the force of the spring element13. The pressure difference between the normal control pressure for the operation of the spray nozzle (the lower air pressure threshold value) and the higher air pressure threshold value for the lifting of the venting piston14into the venting and opening position ensures that the venting piston remains during normal operation in its lower dysfunctional position. During normal operation a control pressure is also effective at the lower side of the venting piston14which, however is not high enough to lift the venting piston into the venting and opening position. Only when the control pressure exceeds the upper air pressure threshold value can the venting piston14be moved to the venting and opening position.

Upon completion of the venting procedure the pressure of the control air is reduced whereby the venting piston14is returned by the spring element20from the raised venting and opening position to the lower dysfunctional position. Subsequently the normal operating mode of the spray nozzle can again be resumed.

FIG. 10is a cross sectional view of the spray nozzle1taken along line M-M ofFIG. 9, andFIG. 11is a cross-sectional view of the spray nozzle1taken along line N-N ofFIG. 9. The cross-sections extend through the inlet opening6for the release agent (FIG. 10) and, respectively, the inlet opening7for the control air (FIG. 11). The release agent is supplied via the inlet opening6and a check valve17to the dosing chamber10. The control air is supplied via the inlet opening7and—via the additional inlet opening8—to the operating chamber12above the dosing piston9and to the operating chamber16below the venting piston14.