Apparatus for Preventing Solidification of Molten Metal in an Electro-Magnetic Pump for Supplying the Molten Metal

The present invention relates to an apparatus for preventing solidification of molten metal in an electromagnetic pump. In particular, the apparatus according to the present invention is adapted to be used when the molten metal in a container is supplied to molds or the like by means of an electromagnetic pump with the supply of molten metal being intermittently suspended for considerably long time.

In supplying molten metal to a mold by means of an electromagnetic pump mounted on a metal container, the molten metal received in the container is held in high temperature due to the high insulating characteristic of the container itself by actuating the heater provided thereon, thus being prevented from solidifying at least for a certain period.

However, the molten metal in the electromagnetic pump provided on the container will alter into solid state as the temperature thereof is lowered after certain period of suspension in supplying molten metal into the molds or the like, although no problem is caused in the course of continuous supply. This is a matter of natural consequence because the molten metal of unit volume received in the electromagnetic pump must contact with the inner wall surface of lower temperature and of larger area than in the container. Therefore, it was heretofore necessary in the operation of molten metal supply to limit the amount of molten metal in the container to a certain amount of an uninterrupted and exhaustive supply of molten metal. Such manner of supply has caused the inconveniences in the operation of molten metal supply.

To overcome the above mentioned difficulties, it was proposed to inverse the direction of travelling magnetic field in the electromagnetic pump. By inversing the direction of travelling magnetic field, the surface of the molten metal in the electromagnetic pump is lowered in relation to the level of molten metal surface in the container, while the circulation of molten metal is generated as will be explained below.

The driving force in electromagnetic pump to push molten metal into the container is largest in the central portion thereof and is decreased at the both sides thereof by degrees. (This is well known as the lateral edge effect and is substantiated through experiments.) Such distribution of driving force generates the circulation of molten metal wherein the central flow is directed to the container and the side flows are directed to the outlet of the pump. Since the driving force generated by travelling magnetic field is so feeble at the position where the electromagnetic pump is connected to the container, the molten metal around the position of connection fails to be transferred to the full inside of the container and tends to return, that is, to flow upwardly along the both sides of molten metal conduit. (The decrease of driving force at the longitudinal edge is well known as longitudinal edge effect.)

It was found that the above mentioned circulation of molten metal flow functions to check solidification of molten metal to a certain extent, but it was impossible to substantially prevent the drop of molten metal temperature, thus bringing about the defects such as nonuniformity or the inferiority of resulted articles. Summary of the Invention

It is therefore the object of the present invention to keep the molten metal in electromagnetic pump in substantially the same temperature as that in a container in spite of the suspension of molten metal supply, by means of partition walls provided on the molten metal inlet in the electromagnetic pump where the pump is connected to the container. These partition walls serve to continuously exchange the molten metal in the pump with that in the container.

The detailed construction of the apparatus according to the present invention will be explained hereinafter with reference to the accompanied drawings wherein:

FIG. 1 is a sectional view of the entire device according to the present invention;

FIG. 2 is a view of the essential portion of the device according to the present invention and indicates the principle of function obtainable by the present invention;

FIG. 3 is a sectional view taken along the line A--A' in FIG. 2;

FIG. 4 is a sectional view of the second example of the present invention;

FIG. 5 is a sectional view taken along the line A--A' in FIG. 4;

FIG. 6 is a sectional view of the third example of the present invention;

FIG. 7 is a sectional view taken along the line A--A' in FIG. 6;

FIG. 8 is a sectional view of the fourth example of the present invention; and

FIG. 9 is a sectional view taken along the line A--A' in FIG. 8.

A container which is referred to in each of the drawings by numeral 1 is made of refractory material and receives molten metal 2 which is liquidized through melting process. Numeral 3 indicates a heater which is mounted on the container 1 to continuously supply heat to the molten metal 2 for preventing drop of the temperature thereof. Numeral 4 indicates an electromagnetic pump which exemplifies the present invention and which comprises a refractory wall 4b defining a molten metal conduit 4a, a molten metal supply outlet 4c attached to the top of the molten metal conduit 4a, an iron core 4d disposed around the refractory wall 4b to receive the conduit 4a between the upper and lower portions of the core, an AC coil 4e received in grooves 4d' of the iron core 4d and partition walls 4b' incorporated to the refractory wall 4b as an independent member or in one unit. The partition wall 4b' will be explained below in detail.

The electromagnetic pump 4 having the above mentioned members is connected to the container 1 in such manner that the edge of the conduit 4a opposed to the outlet 4c is secured to the outelt 1a of the container located in the lower part of the container 1. The pump 4 is directed upwardly and slantedly.

The conduit 4a is influenced by the travelling magnetic field across its full width. The above mentioned partition walls 4b' according to the present invention are, as shown in FIG. 2 and FIG. 3, located in the molten metal conduit 4a so as to divide the conduit into three passageways. A central passageway P is larger than side passageways P' in width, and this is because the driving force applied to molten metal at the central portion of a passageway is larger in the broader passageway than in the narrower passageway as a result of variation in inductive efficiency.

Next, the arrangement of the partition walls 4b' in its longitudinal direction comes into question. With regard to this it is preferable that the partition walls 4b' extrudes over the edge of the pump 4 into the container 1 as shown in FIG. 2 so that the molten metal in the electromagnetic pump 4 may be sure to be introduced into the container 1 through the central passageway by virtue of the travelling magnetic field directed to the container 1. It will be however understood that, for the purpose of facilitating production of the apparatus, the edge of the partition walls 4b' may be recessed from the edge or the set position of the pump 4 so far as the molten metal in the pump 4 can be guided through the central passageway P into the container 1. On the other hand, the partition walls 4b' extend upwardly and slantedly toward the molten metal exit 4c but terminate at the level lower than the possible molten metal surface in the conduit 4a at the time of reverse operation when the electromagnetic pump 4 or the travelling magnetic field push the molten metal into the container 1. In other words, the disposition of the partition walls 4b' is such that they are entirely immersed into the molten metal 2 even when the travelling magnetic field is in reverse operation, while the lower ends thereof extend in the length enough to introduce the molten metal 2 into the container 1 through the central passageway P by means of the travelling magnetic field directed to the container 1.

When it is required, in the above mentioned embodiment of the present invention, to supply molten metal 2 into a mold through the molten metal exit 4c, the AC coil 4e in the electromagnetic pump 4 is energized to generate a travelling magnetic field in the direction designated by arrow line in FIG. 1.

When the molten metal supply is to be suspended, the travelling magnetic field reverse to the arrow line is generated in the AC coil 4e by a suitable switch means. The functions derived from such reverse operation will be described below with reference to FIG. 2.

The traversal distribution of driving force in the electromagnetic pump 4 is as shown in graph (a) at the place where the partition walls 4b' are not present. Since the driving force in the central portion is larger than that in the side portions, the molten metal 2 in the central portion commences to advance toward the container 1, and runs into the central passageway P defined by the partition walls 4b'. This flow of molten metal 2 in the central passageway P is curved from the partition walls 4b' and pours intensively into the container 1 from the inner edge or lowermost portion of the partition wall 4b'.

At this time the driving force generated by travelling magnetic field is distributed longitudinally along the electromagnetic pump 4 as shown in graph (b), which indicates that the driving force is weakend at the edge of the electromagnetic pump 4 due to the longitudinal edge effect. The driving force in the molten metal conduit 4a is still further weakened because the eddy current in molten metal 2 is divided by the partition walls 4b' into branch currents in passageways P, P' thus resulting in the decrease of the effective driving force. However, the molten metal 2 introduced into the passageways P, P' is still under the influence of the driving force which greatly affects the prevention of molten metal solidification. Molten metal 2 introduced into the central passageways P pours into the container 1 by the driving force of travelling magnetic field in the central passageway P. In compensation for this flow, the circulation of molten metal 2 between the container 1 and the electromagnetic pump 4 can be stimulated by decreasing, as far as possible, the driving force applied to molten metal in the side passageways with relation to the driving force in the central passageway P. For the purpose of relatively decreasing the driving force in the side passageways P' directed to pressured molten metal in the container 1, the central passageway P is configurated to be larger in its width than that of the side passageways as shown in FIG. 2. The modifications thereof will be shown hereafter. So, the driving force is very small in the central passageway P and side passageways P', and consequently the flow of molten metal 2 directed upwardly to molten metal exit 4c as shown by arrow line is generated in the side passageway P' wherein the driving force is so feeble. This flow serves to compensate the molten metal 2 which runs through the central passageway P and pours into the container 1. By such function of the reverse magnetic field it is made possible to successively exchange the molten metal 2 in the electromagnetic pump 4 with the molten metal of high temperature in the container 1, even at the time of suspension in teeming molten metal by electromagnetic pump 4.

FIG. 4 and FIG. 5 indicate an improved construction according to the present invention for reducing the driving force applied to side passageways. As shown in these drawings, refractory walls 4b which define the side passageways P' are covered by magnetic shielding plate such as copper plate 4f. By the provision of this copper plate, the driving force caused by the travelling magnetic field and applied to the molten metal in the side passageway P' is remarkably weakened, and in turn the driving force directed to the container 1 in the central passageway P is relatively strengthened than that in the side passageways P'. Hence in this improved instance of the present invention the size or the width of both of central passageway P and side passageways P' do not affect the circulation of molten metal in contrary to the aforementioned first instance.

The next embodiment of the present invention is shown in FIG. 6 and FIG. 7, wherein the molten metal conduit 4a is enlarged at the particular position corresponding to the longitudinal length of the partition walls 4b'. According to such construction, the both sides of the enlarged portion of the conduit 4a protrude laterally from the iron core 4d for generating travelling magnetic field, thus substantially nullifying the drive force generated by the travelling magnetic field in side passageways P'. Therefore, in this case too, the proportion of the width of side passageways to that of central passageway does not affect the function of molten metal circulation.

In these embodiments of the present invention, the cross section of the molten metal conduit is made rectangular in shape, and means for generating travelling magnetic field is located at least at one side of the conduit. But it is of course possible to have the travelling magnetic field arranged evenly arround the condity by using, for example, a cylindrical electromagnetic pump. As shown in FIG. 8 and FIG. 9, the cylindrical electromagnetic pump may have a partition wall 4b of cylindrical configuration and is provided with a molten metal passageway Q extending between the outer circular face of the partition wall 4b' and the inner circular face of the refractory wall 4b. Support limbs 4g serve to secure the partition wall 4b' to the refractory wall 4b to form a united construction.

It will be understood that the above mentioned construction shown in FIG. 8 and FIG. 9 serves to generate the circulation of molten metal which runs through the above mentioned passageway Q and the central passageway Q' defined by the partition wall 4b'. By virtue of such circulation, the replacement of molten metal in the container 1 with that in the electromagnetic pump is carried out, and the driving force in the passageway Q is by far larger than that in the passageway Q' because the passageway Q is exposed to the strong magnetism generated by the travelling magnetic field generator just adjacent thereto, when the travelling magnetic field is generated in the pump 4 toward the container 1.

As a result the molten metal is supplied into the container 1 through the passageway Q and, to compensate for the discharge of molten metal, the molten metal of high temperature in the container 1 is introduced into the electromagnetic pump 4 through the passageway Q' thus effecting a continuous replacement of the molten metal in the electromagnetic pump 4 with that in the container 1. Reference numeral 4h indicates a refractory member for guiding molten metal into the container, and reference numeral 4i indicates the support limb therefor.

The embodiments of the present invention as explained hereinbefore are directed to the apparatus for supplying molten metal to a mold through the molten metal outlet of an electromagnetic pump, wherein the electromagnetic pump extends upwardly and slantedly from the bottom of a side portion of a container. However, it is clear that the present invention is not limited to these embodiments but can be applied to any of the devices for controlling the discharge of molten metal from a container by means of an electromagnetic pump for generating travelling magnetic field.

As explained above, the present invention has developed the device for eliminating the defect of the former electromagnetic pump, that is, the drop of molten metal temperature in an electromagnetic pump. Thus the present invention solved the problem of replacing molten metal in the electromagnetic pump with that in the container, which otherwise can not be carried out at the time of suspension in supply. The difficulties due to the noticeable decrease of the driving force caused by the longitudinal edge effect at the lowermost or the connecting portion of the pump was overcome by the present invention.

In summary, the device according to the present invention is provided with the partition walls for forming two or three passageways to bring about the augmented gap of the effect of the travelling magnetic field. The molten metal in the electromagnetic pump is guided through the passageway subjected to strong magnetic field into the container, and the molten metal in the container is introduced through the passageway subjected to weak magnetic field into the electromagnetic pump. By virture of such construction, the molten metal discharged from the container through the travelling magnetic field can be always maintained in the same temperature as that in the container, and the danger of generating uneven structure in the finished article was eliminated in the process of teeming molten metal into a mold or the like.