Metallurgical apparatus – Means for melting or vaporizing metal or treating liquefied... – With means to discharge molten material
Reexamination Certificate
2000-03-15
2001-10-23
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for melting or vaporizing metal or treating liquefied...
With means to discharge molten material
C222S591000
Reexamination Certificate
active
06306338
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a melt withdrawal device for melt furnaces for charging casting machines, comprising a melt conveying pump including a pump tube forming a lower melt inlet and an upper melt outlet and a pump shaft extending inside the pump tube and carrying a pump rotor.
DESCRIPTION OF THE PRIOR ART
A prerequisite for the proper charging of casting machines or similar means is the possibility of a functionally reliable and dosable melt conveyance from the storage space of melt and holding furnaces, where so far, as is disclosed in EP 0 609 197 B, DE 195 41 093 A or DE 44 20 655 A, screw pumps have mostly been used as conveying pumps, whose delivery rate depends, however, on the pressure conditions in the melt inlet area of their pump tubes and thus on the respective pump head, which leads to a considerable impairment of the dosability of the pump delivery rates, since the melt level heights in the melt storage space of the melt furnaces vary considerably during operation.
From U.S. Pat. No. 4,398,589 A a pumping device for liquid metal is already known, which operates according to the electromagnetic principle and in which a feedback control of the delivery rate is possible. The pumping device must, however, be disposed outside the melt furnace, which leads to considerable thermal difficulties.
SUMMARY OF THE INVENTION
It is therefore the object underlying the invention, to create a melt withdrawal device as described above, which is characterized by its delivery rates largely independent of changes in the melt level.
This object is solved by the invention in that before the melt conveying pump a charging means is provided for keeping constant the pump head, which charging means comprises a charging tank accommodating the pump tube with the melt inlet and a charging pump capable of filling the charging tank with melt up to a melt overflow determining the charging height, where the delivery rate of the charging pump exceeds that of the conveying pump. Since the charging tank is filled with melt up to the melt overflow, this charging means with its charging tank and the charging pump ensures constant pressure conditions in the melt inlet area of the melt conveying pump during the withdrawal operation, so that even with external variations in the melt level a constant melt level height, i.e. charging height, determining the pressure conditions is effective for the melt conveying pump, and independent of the respective melt level heights in the storage space of the melt furnaces a constant pump head is obtained for the melt conveying pump, and thus the delivery rates can exactly be metered as desired. The overflow itself will lie in the vicinity of the maximum melt level, in order to adapt the pressure conditions to the actual circumstances and to avoid the maintenance of unnecessary charging heights. The charging pump should also be adjusted to the conveying pump, so that on the one hand a sufficient excess of melt is conveyed into the charging tank, in order to exclude a decrease of the melt level inside the charging tank below the melt overflow during a withdrawal of melt, but on the other hand to be able to ensure a constant pump head with a rather low melt overflow. As melt conveying pump and as charging pump all suitable conveying pumps can be used, and there are also obtained all kinds of embodiments for the charging means itself.
The charging tank may, for instance, be comprised of a chamber which surrounds the melt inlet and includes a lower intake opening and a rising pipe extending upwards and forming the melt overflow, and the charging pump may have a charging rotor seated in the vicinity of the intake opening. There is obtained a compact constructional unit of melt conveying pump and charging means, where the flow cross-section of the rising pipe will be dimensioned rather small in consideration of the risk of solidification-related obstructions and the like.
To prevent in a simple way that in the case of a standstill of the pump the melt level height inside the charging tank decreases down to the respective melt level height in the storage space, which without an additional control effort for prefilling the charging tank before the actual withdrawal of melt would involve initial variations in the pump head, the intake opening has associated thereto a backflow check valve with a valve body closing the intake opening opposite to the intake direction, so that with the charging pump standing still the backflow check valve will close the intake opening and prevent the melt from flowing out of the charging tank, whereby also at the beginning of the withdrawal substantially unchanged pressure conditions and charging heights are ensured.
As valve body of the backflow check valve suitable valve plates or the like may be inserted in corresponding valve housings, but advantageously it is also possible that the charging rotor itself, which is vertically movably disposed above the intake opening, forms the valve body, so that the charging rotor moving upwards with a drive rotation will clear the intake opening and the driveless charging rotor moving downwards under the influence of its own weight will again close the intake opening.
An expedient construction is obtained when the charging tank is arranged coaxial to the pump tube, which allows the formation of charging chamber and rising pipe as a stepped tube portion.
It is basically irrelevant according to which operating principle conveying pump and/or charging pump are operating, but a coaxial arrangement of pump rotor and charging rotor involves certain advantages. The pump shaft may for instance extend downwards from the pump tube and with its protruding end serve as drive shaft for the charging rotor, so that a common drive for both pumps is obtained.
The charging rotor may of course also be seated on a separate drive shaft extending through the hollow pump shaft, whereby a greater adaptability of the charging pump capacity to the respective circumstances is achieved.
Another expedient embodiment of the charging means consists in that the charging tank comprises two partial tanks, a charging part accommodating the pump tube and closed at the bottom and a filling part accommodating the charging pump and having the lower intake opening, where filling part and charging part are in flow connection with each other via an overflow edge and the filling part forms the melt overflow. The charging part ensures the constant charging height and due to its closed bottom this charging part at the same time prevents this charging height from decreasing in the case of a standstill of the pump, so that in essence a constant pump head is always ensured. The filling part with the charging pump ensures the filling or melt application of the charging part with a corresponding excess of melt, so that again uniform pressure conditions independent of external variations in the melt level are obtained for the melt conveying pump.
An expedient constructional unit is in turn obtained when charging part and filling part are arranged coaxial to the pump tube and the filling part surrounds the charging part, where the charging pump has a charging rotor seated below the charging part on a drive shaft extending from the charging part. The filling part inwardly verges into the charging part and with its upper marginal edge forms the melt overflow to the outside. As a drive shaft for the charging pump the bottom end of the pump shaft may be used, but there may also be provided a separate drive shaft for the charging rotor, which extends through the hollow pump shaft.
When in accordance with another constructional solution charging part and filling part are arranged one beside the other and the charging pump of the filling part has a drive shaft which is parallel to the pump shaft and includes a lower charging rotor, a pumping means completely independent of the melt conveying pump may be provided as charging pump, which pumping means provides for an optimization of the charging operation, for instance by prefilling the fill
Ehrentraut Otto
Rauch Erich
Sigmund Alfred
Collard & Roe P.C.
Ing. Rauch Fertigungstechnik Gesellschaft m.b.H.
Kastler Scott
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