HK1061541B - Shielding gas device for pressure die casting machines - Google Patents

Description

The invention relates to a protective gas device for a dielectric dielectric machine which includes at least one furnace, particularly for processing magnesium melt, with openings in the furnace for the supply of the protective gases, with various protective gas sources, with a container connected to it to receive a mixture of individual protective gases and with at least one dosing device connecting the container to the furnace openings.

To prevent the reaction of magnesium with oxygen in the air, the magnesium melt contained in the melting furnace of die casting machines must be covered with an inert gas mixture. For this purpose, mixtures of carrier gases and sulphur hexafluoride (SF6) or sulphur dioxide (SO2) such as N2 and SF6, dry air and SF6 or dry air with SO2 are used, with the aim of keeping the concentration of the inert gas components in the mixture as low as possible.

In the known systems for the production of the protective gas mixture, the individual components are filled at relatively low pressure (0,8 to 1,5 bar) by a quantitatively adjusted feed into a container from which the gas mixture is withdrawn and fed to the melting surface.

In the current equipment, the type of mixing process usually leads to stratification or it cannot be guaranteed that it does not occur. Stratification can also occur if the gas has not mixed properly and then settles due to gravity. A homogeneous mixture is not formed.

The gas mixture is fed into the furnace by one or more inlet openings with the lowest possible flow resistance, the quantity to be dosed being adjusted by volume flow.

If the inlet openings are grouped together and connected to different dosing devices, e.g. for one or several ovens, changes in the dosing of one inlet will affect the dosing of the other inlet openings. Adjustment is usually very difficult. In addition, local over- or under-dosing may also occur in the oven. Areas of SF6 enrichment and SF6 depletion may occur above the melting chamber, which is known as concentration shading. If a change in dosing is desired in the known types of operation, for example, in different operating modes, clean, emergency, then the adjustment must be determined and adjusted in a simple manner.

Disclosure WO 99/02287 A1 discloses a protective gas device for a die casting machine for processing magnesium melt, comprising a dry air and SO2 gas source, a mixed unit connected to these gas sources, each with a flow controller for the two protective gases and a control unit to monitor and control the composition and amount of gas mixed. Behind the flow controllers, the two gas supply lines join to form a downstream line in which the two gases mix and from which the gas is introduced into one or more melting furnaces, the latter having associated gas-flow controls with flow-measuring elements and a distribution of the protective gas to each melting furnace.

The present invention is based on the design of a protective gas device of the type described at the outset in such a way as to achieve a simple and non-retroactive protective gas charge on the melt and to avoid the problems mentioned above.

To solve this problem, a protective gas device with the characteristics of claim 1 is provided.

Err1:Expecting ',' delimiter: line 1 column 391 (char 390)

Err1:Expecting ',' delimiter: line 1 column 499 (char 498)

The operating pressure of the metering device, which is kept constant, is adjusted to the type of inlet nozzles and thus also to the desired distribution principle of the gas mixture in the furnace. To this end, it is of course advantageous to monitor the input pressure at the metering unit, i.e. the pressure in the pressure storage unit, so that the operating pressure for the metering device can be maintained.

The control of the operating pressure makes the dosing, i.e. the desired quantity of gas, completely independent of other consumers in the same gas mixture, which allows different groups of intake nozzles to be operated without feedback over several dosing units.

In this way, the invention allows several dosing devices to be connected in parallel to each other and supplied by the pressure storage for different furnaces. Each dosing unit can be equipped with a device for setting the dosing volume, with each dosing unit being assigned a type of operating key by which the operator can determine the dosing volume. Each dosing unit can also be equipped with a control logic that receives signals about the furnace state in further development of the invention. In this way, an automatic regulation of the protective gas concentration can also be achieved.

The invention incorporates a mixer with a mixing chamber in front of the pressure storage tank, in which the gases forming the protective gas mixture are brought together under pressure. The system pressure of this mixer can be adjusted to the operating pressure of the dosing devices. The system pressure of the mixer must be sufficiently higher than the operating pressure of the dosing devices.

The invention also incorporates nozzles for the supply of mixed gases at the mixing chamber, with pressure control devices attached to the supply lines to the mixing chamber and pressure regulators to maintain the same pressure to achieve uniform pressure control between the carrier gas and the protective gas.

This design has the advantage that the mixing gases, i.e. the components of the protective gas, are formed under turbulent flow in the set mixing ratio in the mixing chamber and then fed to the pressure vessel. The mixing of the gases works without any electrical energy expenditure. Even in the event of a power failure, the mixture can therefore be produced exactly as long as sufficient mixing gases are present. The concentration is not changed. The system's main mixing and dosing device is also thus able to maintain the concentration exactly even in the event of a power failure. Only the dosing is set to a fixed continuous emergency gas dose.

As already mentioned, a mixing unit with a pressure storage unit can supply several dosing units, which either supply different groups of nozzles in a furnace or several melting furnaces, the dosing volumes of which are independent.

As mentioned above, the pressure in the pressure storage is monitored and for this purpose, for example, a pressure monitoring device may be provided in the connection line between the mixing chamber and the pressure storage.

Finally, in a further development of the invention, a gas analyzer can be attached to the mixing chamber to control the concentration of the mixture, which can easily compare the gas mixture in the mixing chamber with a reference mixture and, in the event of any deviation, give a signal to the mixing device to control the supply of the mixture.

The invention is illustrated by an example of an embodiment in the drawings and is explained as follows: Figure 1a block-shaped representation of a protective gas device according to the invention,Figure 2a diagrammatic representation of the mixing device used in the protective gas device of Figure 1,Figure 3a diagrammatic representation of a dosing device of Figure 1,Figure 4a schematic longitudinal section through the melting furnace of Figure 1,Figure 5,a drawing of the melting furnaces of Figures 4 andFig. 6and finally an enlarged representation of an inlet nozzle for the protective gas interlayer of Figures 4 and 5.

Figure 1 shows a pointed frame of a melting furnace 1 whose bath is to be covered with protective gas. This melting furnace 1 is shown in detail in Figures 4 and 5 and is described in more detail there. The gas mixing and dosing unit for the loading of the melting furnace 1 with protective gas consists first of a gas mixture 2 whose structure is shown in Figure 2. This gas mixture is fed on the one hand by the protective gas used, i.e. SF6 or SO2 in the sense of Figure 3, and a carrier gas, for example nitrogen N2 in the sense of Figure 4.The gas mixture is then held in a pressure vessel inside the gas mixture, from which the gas is passed from the gas mixture via the connecting lines 5 and 6 to the metering lines 7 and 7a. The structure of these metering lines is shown in Figure 3. Other metering lines can be connected to the 6' line. From the metering lines 7 and 7a, the gas is passed through the connecting lines 8 and 8a to the intake nozzles 9 and 9a, respectively, and enters the chamber of the melting furnace 1 above the melt. This is described in detail in Figures 4 and 5.

Fig. 2 shows that the protective gas, e.g. SF6 through connector 3 and the carrier gas, e.g. N2, through connector 4, is fed into the mixing device 2, with both mixing gases passing through a filter 10 into the pipes 11 and 12 respectively. From a central monitoring logic 13, an input pressure monitoring 14 is carried out and the pressure in these inlet pipes 11 and 12 is indicated by corresponding pressure gauges 15 respectively. A pneumatic pressure control 16 ensures that the pressure in the two supply lines 11 and 12 of the mixed gases supplied is equal. The gases are kept at a pressure of at least 5 bar.

The concentration of the protective gas carried by the line 11 is set at point 17 and a corresponding throttling point 18 is located in the parallel line 12 of the carrier gas and both pressure lines 11 and 12 are directed to a mixing chamber 19 where the two gases are released from nozzles 20 under pressure and can be carried in the resulting turbulent flow to a homogeneous mixture. This homogeneous gas mixture is then passed to a pressure storage tank 21 via line 22 whose pressure is monitored by an output pressure monitoring 23 of the monitoring logic 13 and again by a pressure gauge 15. In the pressure storage line 21 a homogeneous mixture is thus stored depending on the input pressure (gas 4 - 5 bar) which can then be directed to a 5 or more dosing devices.

Fig. 3 shows as an example the dosing device 7 of Fig. 1 which supplies the mixed gas under pressure through the line 5. Again, a filter 10 is advanced to a further line 24 whose pressure is monitored via the device 25 and a central dosing and monitoring device 26 and is also centrally regulated via the devices 27 and 28 and the central control 29 to a specific operating pressure of about 1.8 to 3.0 bar. This pressure can be made visible via a manometer 10. In the example of line 24, two out of the three controls 30, 31 and 32 are selected to carry out the mixed gas injection and each control is set to a different amount of gas.

The central dosing system also has signal inputs 35 from the die casting machine and the melting furnace 1 and corresponding signal outputs to the furnace and the die casting machine are indicated by the arrows 36.

Figures 4 and 5 show that the melting furnace 1 shown in the example has a sampling chamber 39 and a storage chamber 40, separated by a wall 41 in both chambers, containing melt up to level 42 and the chambers 43 and 43a above the melting melt being filled with the protective gas mixture. In the sampling chamber 39 the melting furnace 1 is a hot-chamber casting machine, and the melting furnace is located in a familiar way. The pressure lines 8 and 8a, which lead to the pressure-gas mixture 9 and 9a, respectively, are geometrically separated.

The same applies to storage chamber 40 where the chamber 43a above the melting level 42 is charged by the pressure nozzles 9a, which are placed at greater distance from each other in chamber 43a on the side opposite the cleaning and charging vent 46 and which, as indicated by the arrows 47 in each case, also achieve a uniform flow in chamber 43a which, together with the pressure charge selected by the intake nozzles 9, 9a, ensures a uniform protection gas concentration above the melting level.

Figure 6 shows an example of one of these pressure-inlet nozzles 9 equipped with a screw-in 48 for attachment to corresponding pressure lines and a throttle 49 or a shutter behind which the gas flowing under pressure undergoes a radial expansion which creates a turbulent blurring which ensures an even distribution in chambers 43 and 43a.

Of course, a protective gas charge is also possible in the case of other types of furnaces, such as single-chamber furnaces or those not used for hot-chamber pressurized casting machines.

Claims (18)

1. A shielding gas device for a pressure die-casting machine having a melting furnace (1), preferably for processing magnesium melts, comprising:

   - openings in the melting furnace for supplying shielding gases,

   - a plurality of different gas sources,

   - a container (21) downstream the gas sources for receiving a mixture of individual ones of the shielding gases, and

   - at least one metering device (7, 7a) connected to the container through a connection line (5, 6) and to the openings of the melting furnace through terminal lines (8, 8a),

   characterized in that

   - the container is a pressure reservoir (21),

   - the openings of the melting surface (1) are respectively provided with an inlet nozzle (9, 9a) comprising an orifice or a throttle (49), and

   - the metering device (7) comprises means for regulating an operating pressure for the shielding gas mixture supplied from the pressure reservoir to the inlet nozzles, which operating pressure is equal to or less than the pressure in the pressure reservoir and effects a jet broadening of the gas output from the orifice or throttle of the respective inlet nozzle.
2. The shielding gas device according to claim 1, characterized in that metering device is configured to deliver the shielding gas mixture to the inlet nozzles continuously or discontinuously.
3. The shielding gas device according to claim 1 or 2, characterized in that the inlet nozzles (9, 9a) are distributively arranged on the melting furnace (1).
4. The shielding gas device according to any of claims 1 to 3, characterized in that the inlet nozzles (9, 9a) are placed on the melting furnace (1) such that a gas flow is generated towards potential leakage points (45, 46) of the furnace.
5. The shielding gas device according to any of claims 1 to 4, characterized in that the inlet nozzles (9, 9a) are arranged such that they are protected from being contaminated or clogged by being wetted by molten material.
6. The shielding gas device according to any of claims 1 to 5, characterized in that the operating pressure regulating means are configured to adjust the operating pressure to the type of the inlet nozzles (9, 9a).
7. The shielding gas device according to any of claims 1 6, characterized in that the operating pressure regulating means are configured to activate a signal device (37) in case of deviations from a desired operating pressure.
8. The shielding gas device according to any of claims 1 to 7, characterized in that multiple metering devices for different sections (39, 40) of the melting furnace or for different melting furnaces are connected in parallel and are fed by the pressure reservoir (21).
9. The shielding gas device according to any of claims 1 to 8, characterized in that each metering unit (7, 7a) is provided with a device (33, 34) for adjusting the metered quantity.
10. The shielding gas device according to any of claims 1 to 9, characterized in that an operating mode button (34) is associated with each metering device for determining the metered quantity.
11. The shielding gas device according to any of claims 1 to 10, characterized in that each metering device (7, 7a) is provided with a control logic (26) that receives the status signals (35) concerning the melting furnace.
12. The shielding gas device according to any of claims 1 to 11, characterized in that a mixing device (2) having a mixing chamber (19) for combining the shielding gases forming the shielding gas mixture under pressure is associated to the pressure reservoir (21).
13. The shielding gas device according to claim 12, characterized in that pressure nozzles (20) for supplying the shielding gases to be mixed are provided on the mixing chamber (19).
14. The shielding gas device according to claim 12 or 13, characterized in that pressure regulating devices (14, 16) are provided which are associated to supply lines (11, 12) leading to the mixing chamber (19).
15. The shielding gas device according to any of claims 12 to 14, characterized in that a pressure regulating device (16) for maintaining equal pressure is associated to supply lines (11, 12) leading to the mixing chamber (19).
16. The shielding gas device according to any of claims 12 to 15, characterized in that a device (23) for monitoring pressure is provided in a connection line (22) between the mixing chamber (19) and the pressure reservoir (21).
17. The shielding gas device according to any of claims 12 to 16, characterized in that a gas analyzer is associated with the mixing chamber (19) to monitor the concentration of the gas mixture.
18. The shielding gas device according to claim 17, characterized in that the gas analyzer is configured to compare the gas mixture of the mixing chamber (19) to a reference mixture, and to output a signal to the mixing device (2) in case of deviations.