The present invention relates to a method of transferring a melt from a bath of molten metal to a receiving station sit¬ uated above the bath surface, wherein a given amount of melt from said bath is - in accordance with the principle of open¬ ly communicating vessels - diverted by self -flowing to a space, separate in relation to the bath until the levels of the melt in the bath and in the space are in agreement, whereafter communication between the molten bath and the space is in¬ terrupted and a predetermined quantity of gas is forced into the space above the melt until a predetermined volume of melt is pressed out from said space and taken to the receiving station, whereafter the gas forced in is lead off from the space and said communication is opened so that the difference in level between the melt in the space and in the bath is once again evened off. The invention also relates to an appai?- atus for carrying out the method of transferring melt from a bath of molten metal to a receiving station situated above the surface of the bath.

In the art of casting it is previously known to transfer por- tions of a melt from a bath of molten metal to a receiving station situated above the surface of the bath. Such methods are utilized in conjunction with continuous or discontinuous casting, many different kinds of conveying and metering or portioning apparatus being used for the melt. Electromagnetic pumps, mechanical buckets or collectors as well as siphon apparatus can be mentioned as examples in this connection.

Even if these previously known methods and aids for portion¬ ing or conveying melt are utilized per se, there are how- ever important problems, inter alia In conjunction with the difficulty of being able to divert and convey within narrow tolerances predetermined portions of the melt from a bath containing it to the receiving station situated above the surface of the melt bath.

A particular serious problem occurring in this connection in the use of a siphon metering furnace, i.e. a furnace for molten metal in which the siphon principle is utilized for taking the melt up out of the bath, consists in that the surface level ofthe melt in a storage bath of melt must, for technical reasons, vary so considerably in height with time, that it is necessary to use complicated and expensive monitoring and control equipment, which is also difficult to handle, to portion the melt equally, as well as transporting portions of the melt to a position above the holding bath, which has a surface varying in height. The reason for this i that portioning is substantially dependent on three paramete namely the difference in level between the surface of the me in the metering furnace and at the receiving station, the pressure acting on the melt and the time during which the pr ure acting on the melt and the time during which the pressur acts.

When starting up the work cycle of the siphon furnace, the automatic control equipment must thus be able to adjust the gas pressure and/or the duration thereof, acting on the melt so that a predetermined volume of the melt is obtained withi the correct limits. When setting the parometers of pressure and duration, the automatic equipment must be thus able to b adjusted to the appropriate height of the melt surface.

In continued operation, the unavoidable level alteration of the melt must be considered, and the automatic monitoring and control equipment must consequently be able to correct pressure and/or duration so that portioning accuracy is main tained. This means, for example, that when starting the pro¬ cess, it is necessary to try out suitable increments of pres ure and/or time to retain the metering accuracy, and subsequ ly gradually increase these variables automatically in relat to the continuously sinking level of the melt in the bath. I most such furnaces.^ these setting procedures must be carried

out again each time the bath is charged , which naturally signifies that on each such occasion there i s a new starting point for the level of the melt .

Another substantial disadvantage in the known siphon furnace technology is that with the intention of counteracting sub¬ stantially height variations of the melt level in the holding bath, these baths are kept in large furnace rooms , in whi ch the surface area of the melt is considerable. Consequently, when such furnace rooms are subjected to gas pressure , the furnace walls will be subj ect ed to extreme pressure- loads , resulting in strength and safety problems . Since the furnace rooms must be accessible for charging new melt as well as for cleaning and maintenance purposes , the furnace must be open- able .- In turn, this requires that the roof or hatches are connected pressure tight to the furnace with the aid of pack¬ ing and heavy bolted joints . Holding baths with large pressure- loaded surf aces thus have considerable drawbacks .

In connection with the above , it may be mentioned that large furnace volumes are striven for, to avoid charging new smelts at short intervals .

The obj ect of the invention i s thus to eliminat e the above- mentioned drawbacks within the known siphon-furnace technology.

This is achi eved in accordance with the method of the present invention in that the bath of molten metal i s kept at a sub¬ stantially constant level by the addition of molten metal from an external source thus to provide a consistant reference level for portioning.

The apparatus for carrying out -the method in accordance with

- the invention comprises a holding oven, arranged to keep a buffer supply of smelt at a predetermined temperature and

provided with an inlet for charging new smelt at substant¬ ially the same temperature , this oven communi cating via a bottom canal with a separate pressure-tight furnace chamber communicating via a closable outlet canal for smelt commun- icates with said receiving station and via a gas pipe i s alternatingly connectable to a source of gas for driving out one portion of smelt at a time via the outlet canal fro the furnace chamber to the reception station , the smelt bat freely communi cating with an outside supply of smelt at a substantially constant surface level .

The invention will now be described in detail while referri to an embodiment thereof schematically ill ustrat ed on the accompanying drawing and further distinguishing features of the invention will be di sclosed in conj unction therewith.

Figure 1 on the drawing is a schematic verti cal longitudinal section of a furnace constructed in accordance with the in¬ vention , built together with equipment for distributing molt en metal , Figure 2 is a top plan view seen of Figure 1 and Figure 3 Is a schematic diagram of the di stribution equipmen illustrat ed In Figure 1 „

On the drawing , with special reference to Figure 1 , the lowe portion of a f urnace installati on for molten meltal in acc¬ ordance with the invention is denoted by reference 10 , and a roof or cover for the furnace by 11.

On one side , the cover 11 clos es off a holding oven or room 12, arranged to keep an accumulator store of melt 13 at a pr determined t emperature , A s eparate pressure-tight furnace chamber 14 on the right hand side of the holding oven in Figure 1 has s ubst anti ally small er dimensions than the hold¬ ing furnace 12, and has a limited amount of melt in its lowe part . The melt 13 in the holding oven 12 communi cates vi a a bottom canal 16 with the melt 15 In the s eparat e , pressure- tight furnace chamber 14. The latter communi cat es in its tur

via a melt outlet canal 17, with a receiving station gener¬ ally denoted by the numeral 18 for receiving portions of melt supplied from said furnace chamber, said station being situated above the level of the melt 13 in the holding oven 12. The furnace chamber 14 is closed pressure-tight upwardly by means of a removable furnace cover 19, which is heavily and sealingly attached to the upper part of an intermediate wall 20 of the furnace body 10 » The chamber 14 is further connectable by means of a gas pipe 21 to an outside gas supply (not shown), preferably air, such that the chamber 14 can alternatingly be subjected to an excess pneumatic pressure and relieved therefrom.

In the Figure there is also illustrated an opening 22 for supplying molten metal to the holding oven from an outside store 23 comprising, for example, a plurality of elongate horizontal conveying troughs for said metal, wherein the smelt is automatically kept at a constant level.

The method, and apparatus for carrying out the method in accordance with the Invention can be applied, inter alia, for sand-casting, gravity di-casting, dicasting, or low-pressure dicasting. For all the above-enumerated casting processes it is necessary to have a closure valve between the accumulator supply or 'holding oven 12 and the furnace chamber 14. Such a closure valve 24 is shown in Figures 1 and 2, and has the form of a slide which can 'be adapted to be raised and lowered automatically in suitable guides. In the embodiments, Figures 1 and 2, the slide valve 24 is displaceably arranged between plate-like walls 25, 26, 27 and 28. As is clearest shown in Figure 1, the mutually opposing plates 25 and 26 have a through-flow duct 29 and 30, respectively, whereby open communication can be maintained between the accumulator supply 12 and the furnace chamber 14 when the slide 24 is in a raised position and whereby communication between these two is broken off when the slide is in its lowest position.

The method in accordance with the invention is intended for application inter alia to the processes mentioned above, by utilizing the apparatus illustrated on the drawing in the manner as hereinafter described.

In the initial situation illustrated in Figure 1 or carry¬ ing out the process, the melt in spaces 23, 12, 14 and 17 is at the same level, since the slide valve 24 has previous¬ ly been lifted up into its upper position, so that levelling out has taken place ₀ In this condition of the installation, the furnace chamber 14 is connected via the gas pipe 21 to the outside gas source (not shown on the drawing), the melt 15 in the furnace chamber 14 being pressed downward by a gas cushion and upwards through the outlet canal 17 to the receiving station 18 above the surface level of the melt in all the previously mentioned spaces. A portion of melt can be supplied from the receiving station 18 to a sand mould, gravity-dicasting mould etc., alternatively, the portion can be supplied to the filling hole in the pressure chamber of a dicasting machine,, The quantity of melt transferred is substantially controlled by regulating the size of the gas cushion forced in via the pipe 21. When the metal metering is terminated, the slide 24 is lifted to its upper position, the melt levelling off in the whole of the installation by gas being drawn-out of the chamber 14 by suction through the

The metering procedure in the furnace chamber 14 is explain ed with reference to Figure 3, which schematically illustrat the installation in Figure 1.

The gas pipe 21 is connected to a gas source which in its simplest form can comprise a pressure piston-cylinder arrang ment with adjustable stroke for the piston and adapted for

alternatingly supplying the furnace chamber 14 with a pre¬ determined gas quantity, suitably air, and after each com¬ pression stroke of the piston sucking out the same quantity of gas during the return stroke.

This principle of moving the same quantity of gas backwards and forwards is one of the main characteristic features of the present invention and differs significantly from the state ^* of the art in siphon metering furnaces, wherein one has consistantly worked with variable quantities of air supplied from a compressed-air mains network etc. at sub¬ stantially room temperature, the air being heated In the furnace and subsequently blown out with a high heat content directly into atmosphere. This is naturally unsatisfactory both from the point of view of the process and heating econ¬ omy.

With the present inventive subject, all these previous draw¬ backs are circumvented by working with one and the same quantity of gas, the heat content of which is substantially retained.

With the embodiment of the invention just described, good precision of the metered melt quantity can be obtained, especially if the stroke of the piston is pre-set, the pistons speed is balanced in both directions and any tendency to piston-stroke reversal is delayed.

As will be seen from Figure 3, the gas source may consist of a closed pneumatic cylinder 31, to the upper end of which the gas pipe 21 is connected at the point 32. A piston 33 works in the cylinder 31, and is carried by a long piston rod 34, which is slideably mounted in a seal 35 in the lower end wall 36 of the cylinder,,

Beneath the cylinder 31, coaxial therewith, there is placed a further pneumatic cylinder 37 of substantially the same length as the cylinder 31.

As will be seen from the Figure, the long piston rod 34 extends through the whole of the cylinder 37 and downwards out -of it. The piston rod 34 slides through a seal 38 in the upper wall 39 of the cylinder 37 and also carries a piston 40 rigidly attached to it, the piston 40 being inside the cylinder 37. The cylinder 37 carries an axially position able end wall 41 or the like so as to adjust the stroke of the pistons 33 and 40 and consequently the volume of the gas to be passed between the upper chamber of the cylinder 31 and the furnace chamber 14.

Although the piston-cylinder device 31 - 41 shown in Figure 3 has the form of a tandem piston cylinder, it is also poss- ible to use only one single or double-acting piston-cylinder which is either pneumatically or hydraulically driven. Even other embodiments are equally possible.

Furthermore, the cylinder used as a gas source may preferabl be associated with a pneumatic and electrical control equip¬ ment (not shown) which may suitably vary the various opera¬ tional parameters of the apparatus.

Thus, the present invention is not limited to the embodiment described and illustrated herein, but may be varied within the scop.e of the following claims.