MXPA99006054A - Surt method and apparatus - Google Patents

Abstract

An apparatus for dispensing a liquid material from a container (12) is described, the apparatus comprises a first container (11), which forms an intermediate chamber and which is arranged to receive material from the container (12), a second container (10) which forms a dispensing chamber and which is arranged to receive material from the intermediate chamber (11), first pressurizing means by means of which the intermediate chamber (11) can be pressurized, second pressurizing means by means of which the dispensing chamber (10) can to be pressurized, first valve means (13) operable to allow the material to be admitted to the intermediate chamber (11) of the container (12), second valve means (14) operable to allow the material to be admitted to the supply chamber (10) from the intermediate chamber (11) and a duct (19) extending from inside the dispensing chamber (11) whereby the material can be supplied through the duct (19) of the supply chamber (10) by pressurizing the supply chamber (1

Description

METHOD AND ASSORTMENT APPARATUS Description of the invention This invention relates to an assortment apparatus or dispensing apparatus for dispensing a liquid metal and to a method for supplying a liquid metal to a mold by means of such an apparatus. The transfer of liquid metal, in particular liquid aluminum, into molds for producing molded parts is usually carried out by simple pouring under the force of gravity. There are a variety of severe disadvantages in this technique, in particular the entrainment of air and oxides as the metal falls in a relatively uncontrolled manner. To overcome the worst characteristics of this mold filling method, the low pressure (LP) molding process was developed. In this technique, the metal is maintained in a large bath or crucible, usually of at least 200 kg of liquid metal capacity that is contained within a pressurizable enclosure or enclosure known as a pressure vessel. Pressurization of this container with a low pressure (usually a small fraction such as 0.1 to 0.3 atmospheres) of air or other gas drives the liquid up an ascending pipe and into the mold cavity that is mounted above the pressure vessel .

REF .: 30708 The LP molding process suffers from the filling of the crucible or internal bath. The metal has to be introduced to the container via a small door, through which a kind of funnel is inserted to guide the liquid metal from a filling bucket through the door opening and into the pressure vessel. The fall to the tunnel, the turbulent flow through the funnel and the final fall to the residual melt reintroduce all to the liquid metal air and oxides, the same pollutants that the process seeks to avoid. Additional problems of mold filling control arise because the large size of the molding unit involves two additional penalties: (i) the large volume of gas above the melt is of course highly compressible, and thus provides control rather "soft" or "spongy" about the filling speed; In addition (ii) the problem is complicated due to the large mass of metal in the furnace that needs to be accelerated by the application of gas pressure. The problem is similar to trying to accelerate (and subsequently decelerating) a ram weighing 200 kg or more, by traction in a few weak elastic bands. The so-called Cosworth process was designed to avoid this problem by providing melting and containment furnaces for the liquid aluminum that were attached to a common level, so that the metal flowed from one to the other in a quiet manner. The liquid is finally transferred to the mold cavity by an uphill transfer, using an electromagnetic (EM) pump that is permanently immersed in the melt and that takes its metal from below the surface of the liquid and moves it to an ascending pipe. to the mold cavity without moving parts. The control over the flow rate of the metal is improved due to the volume of work in the pump and its supply tube is only a few kilograms. However, the driving force is only the linking of magnetic flux lines, which resemble the elastic bands in the mechanical analogy, so that the control is not as accurate as one might think for the first time. Although there are many advantages to the solution of Cosworth, the EM pump is not without its problems: (i) It is expensive in capital and operating costs. The high maintenance costs arise mainly as a result of the special moldable refractory grade for the submerged sections of the pump. These require regular replacement by an experienced person. In addition, they are subject to catastrophic failures due to the various types of EM pumps having a deficient reputation for reliability. The disappointing reliability is complicated by its extreme complexity and delicacy. (ii) Relatively narrow passages in the pump are prone to blockage. This can occur gradually by accretion or suddenly by a single piece of foreign material. (iii) Occasional voltage fluctuations cause annoying spills when the system is in operation with the metal at the standby level (sometimes called the polarization level). (iv) At metallostatic low heads, application of full power to the pump to accelerate the metal as quickly as possible sometimes results in restriction of flow into the pump as a result of the electrical compression effect on a high current density. If the compression completely interrupts the liquid metal channel, arcing of electrical current will occur to cause damage and temporarily stop the flow. The pump has difficulty recovering from the condition during that particular molding, with the consequence that the molding is filled at too low a speed and thus is defective. A variety of attempts have been made to simulate the Cosworth process by using pneumatic metering devices that are certainly capable of raising the liquid to the mold cavity. However, in general these attempts are impaired by the problem of turbulence during the filling of the pressurizable container and by the large volume of the apparatus, in order to suffer from the twin problems of a large mass being accelerated and a large volume of compressible gas to effect this action One of the first inventions to respond to these critical points effectively is described in British patent 1 171 295, filed on November 25, 1965 by Reynolds and Coldrick. That invention provides a small pressure vessel that is lowered to a source of liquid metal. An opening in its base allows metal to enter. When the levels inside and outside are practically equal, the opening of the base is closed. The small internal gas space above the closed liquid metal is now pressurized, to force the metal into an ascending pipe and into the mold cavity. After the molding has solidified, the pressure in the pump can be allowed to fall back to atmospheric pressure, to allow the metal to drain back into the riser. The opening of the base can be reopened to refill the container, which is then ready for the next molding. The compact pneumatic pump has proven to work well in service. It has been found that the only major problem in the service when pumping liquid aluminum is the creation of oxides in the riser. These are created each time the melt rises and falls. Thus, the riser tube can not only be blocked, but also oxides which are released are transported towards molding and deteriorate their quality, to possibly result in molding scraping. The object of the present invention is to combine the advantages of the EM pump with the simplicity of a pneumatic supply or supply system, without the disadvantages of either providing a compact pneumatic pump that has the ability to hold the liquid metal to a high level, just below the top of the rising tube all the time during the sequential production of molded parts, to minimize the creation of oxides. The invention provides in a first aspect, an apparatus for dispensing a liquid material from a container of liquid material, the apparatus comprises a first container forming an intermediate chamber and arranged to receive material from the container, a second container forming a chamber Assortment that is arranged to receive material from the intermediate chamber, first media or pressurization elements through which the intermediate chamber can be pressurized, second pressurizing means by which the dispensing chamber can be pressurized, first valve means operable to allow the material to be admitted to the intermediate chamber of the container, second operable valve means to allow the material to be admitted to the dispensing chamber of the intermediate chamber and means forming a conduit extending from inside the dispensing chamber, by means of which the material can be supplied through the conduit from the dispensing chamber by pressurizing the dispensing chamber. Such an apparatus can be used to supply molten metal, for example, aluminum or magnesium in molds for the manufacture of molded parts. For devices for supplying liquid aluminum, the main vessels, cap rods and riser can all be purchased at a moderate cost from existing crucible suppliers, thermocouples and tubes, in commonly available materials, such as clay / graphite or clay refractories / Sic. Also, such materials are designed to be especially tolerant of temperature damage, which becomes hard as their joined vitreous phase partially softens. At the operating temperature, such materials are designed to deform instead of falling in a brittle manner. For devices suitable for supplying liquid magnesium, the main vessels, lid rods and riser can all be manufactured from iron, low carbon iron or ferrite stainless iron. Thus, the materials and manufacturing cost are again low and the material is resistant to faults due to temperature fragility, such that the device is in itself robust. The pressurizing gas may be dry air or anhydrous carbon dioxide, both cheap gases, but rendered inert by mixing up to about 2 volume percent sulfur hexafluoride (or other more environmentally benign gas). To supply liquid metals at a higher temperature, the materials of the apparatus will become progressively more expensive. Such materials as SiC, SiN and SiAlON (ceramics based on silicon / aluminum oxy-nitride) and possibly several oxide-based ceramics may become necessary. A truly inert pressurizing gas such as argon will also be required for such service. The invention provides in a second aspect a method for dispensing molten metal into molds, by means of an apparatus according to the first aspect, the method comprising a repeated cycle of operations comprising: (i) pressurizing a dispensing chamber containing molten metal to cause the metal to be discharged through a duct ascending the chamber to a mold; (ii) reducing the pressure in the supply chamber in order to decrease the level of the riser metal to a waiting level; (iii) pressurizing an intermediate chamber containing molten metal in order to transfer the metal from the intermediate chamber to the dispensing chamber to recharge the dispensing chamber while maintaining the metal level in the riser to a level or above of the waiting level; and (iv) recharging the intermediate chamber of a molten metal container, flow passages between the intermediate chamber and the dispensing chamber and between the container and the intermediate chamber that is opened as required to allow the metal to be transferred to the chambers . The present invention will be illustrated only by way of example in the following description and with reference to the accompanying drawings. In the drawings, (where similar numbers denote similar parts); Figure 1 is a longitudinal section through an apparatus according to the first aspect of the present invention; Figures 2A, 2B, 2C, 2D and 2E in sequence, schematically show a process according to the second aspect of the present invention using the apparatus of Figure 1; Figure 3 is a preferred form of a valve for the use of the apparatus of Figure 1.

The apparatus shown in Figures 1 and 2A through 2E acts in the manner of a liquid metal pump and will be referred to hereinbelow as such. The pump comprises a dispensing chamber 10 which is surrounded by and adapted to receive liquid metal from an intermediate chamber 11. The intermediate chamber 11 is stocked in and adapted to receive liquid metal from a liquid metal container 12. The reception of the liquid metal from the container 12 to the intermediate chamber 11 and from the intermediate chamber 11 to the dispensing chamber 10 is carried out through the valves 13 and 14 respectively. The valve 13 can be closed by means of a plug-rod 15, which in turn is operatively associated with a bellows 16 to allow vertical movement of the rod and a gas-tight seal in relation to the pump. Similarly, the valve 14 can be closed by means of a plug-rod 17 operatively associated with a bellows 18. A riser tube 19 extends from the dispensing chamber 10 to a mold 30. The riser tube is sealed in relation to the chamber by means of a gas-tight seal 20 (which may be, for example, a thermally insulating ceramic fiber packaged gland). The pressure in the two chambers is changed as required by the application of a vacuum through the valve 21 and / or the admission of a pressurizing gas through the valve 22. The pressure is indicated by means of a manometer shown schematically at 23. A pair of heat shields 24 minimize heat loss from the two chambers 10 and 11. When the pump is lowered into the container 12 of molten metal, the liquid metal enters both of the chambers 10 and 11 via the Valves 13 and 14 to equalize all the metal levels that provide the gas in the chambers can be poured into the atmosphere via the vent hole 21 and the riser tube 19. The closing of the valve 13 and the introduction of pressurized gas via the valve 22 pressurizes both chambers, with the result that the metal is forced up the riser 19 and into a mold 30 to make a casting 31. The resulting molding pressure and overpressure are indicated by arrow XX 'in Figure 2B. (As shown in FIG. 2B, the level in chamber 10 is raised almost imperceptibly as a result of compression of the gas volume). Once the molten piece 31 has solidified, the gas pressure at 22 can be allowed to fall, to cause the metal level to be decreased to the holding level indicated by dashed lines YY 'in Figures 2C, 2D and 2E .

The precise amount of the fall is verified by the gauge 23, since the relative constancy of the height of the liquid in the inner chamber means that any pressure head verified by 23 will correspond to a precise height in the riser tube 19. The valve 14 It is closed, sealed and isolates the camera 10 in such a way that the waiting level YY 'is maintained. This level is only about 50 mm below the top of the metal supply point in the mold 30. The valve 13 is now open and the vent 21 open to allow depressurization of the chamber 11, which is now You can allow it to be refilled. This filling phase can of course be accelerated simply by closing the vent hole 21 and applying a moderate partial vacuum by 22. In this way, the pump cycle time can be greatly increased. In addition, the technique of using vacuum to assist pump filling may be useful if the general level of liquid in container 12 falls very low. Maintaining the standard level in chamber 11 (by means of appropriate probes or detectors) allows the pump to continue running without changes or other pressure settings and thus allows the pump to operate repeatedly despite changes in metal level in the container 12.

When the chamber 11 is refilled (Figure 2E), the valve 13 can be closed and the valve 14 can be opened.

The pump is now ready to repeat its cycle once a new mold 30 is placed in position on the molding station. Security interlock means, known per se, prevent the operation of the pump without the mold being in its position and properly clamped. Other safety features, such as an electrode that surrounds the mold platform on the molding station, can detect the escape of liquid metal if a mold leaks and can automatically stop the molding cycle. Then, the pressure in chamber 11 is raised to that in chamber 10 and valve 14 is then opened. By continuing with the gas transfer to the chamber 11, the liquid metal will then move to refill the chamber 10. A simultaneous escape of the chamber 10 will be necessary during this time to maintain a constant pressure above the melt and thus maintain constant the level of the liquid on the top of the riser 19. The sequence of operation is shown in Figure 2 as A-BCDE-BCDE-BCDE, etc. The valves 13 and 14 can be constructed in a variety of ways. An automatic or passive closure can be effected by the use of a ball 40 of a refractory material of greater density than that of the liquid metal, which is located in a countersunk taper fit 41 which forms the inlets of the valves 13/14 (as it is shown in figure 3). However, such devices are subject to failure if a scrap piece prevents proper seating of the ball. An active closing mechanism is favored in which the openings are closed by means of a cover rod 15/17. The closing force can be adjusted to reduce the incidence of leaks and a partial rotation of the rod after closure can be used to assist in the effectiveness of the closure. The additional advantage of the active seal is that the pump can be drained quickly if necessary. The advantages of the pump are many: 1. A compact size and extreme simplicity, to give a low capital expenditure. 2. A reduced gas demand to allow inert gas to be used economically. This improves the quality of the molded part while prolonging the life of the pump. 3. The reduced volume of gas gives an improved potential for precision control with respect to flow and pressure. 4. The pressure is under direct control by pressure gauges and computers, etc. (and not indirectly via voltage or current and a characteristic of voltage / pressure / flow involved for example, which in this case is variable from time to time). 5. The capacity of pump feeding speed is high for any metal system due to the large feed tubes. This is in contrast to EM pumps that have limited performance with respect to aluminum, and are somewhat less developed for magnesium and until now, not capable for heavy liquid metals. 6. The design is not susceptible to blockage. 7. The pump can be placed in an open oven to allow the melt to be treated immediately before being molded (in most LP systems the melt is enclosed in a pressure vessel and thus is inaccessible). 8. It can keep the melt at the waiting level, to reduce melt oxide contamination and reduce the delay of the fade arrival time when it is required for the next casting. 9. Maintenance of the melt at the holding level is perfectly stable and safe while the valve 14 remains closed. This contrasts with the operation of the EM pumps where the effects of the programming elements or voltage fluctuations cause the melt to spill unpredictably from the molding station. This is a serious threat to the safety of operating personnel. 10. The pump load is from below the surface of the melt, which does not involve surface turbulence and thus no degradation of metal quality. 11. The recharge can be carried out in the cycle of time with the help of filling aided by vacuum if necessary (most LP systems require an interruption to the molding while the pressure vessel is loaded). 12. The recharge can be carried out at the same internal height inside the pump, when using a filling aided by vacuum. Thus, the pump can be put into operation in a way that is completely insensitive to wide fluctuations in the level in the furnace bath (this contrasts with the behavior of EM pumps which are especially sensitive to changes to outside restricted limits). narrow). 13. Mechanical failures of the pump are not expected to be associated with any danger to personnel or equipment. In effect, the unit has intrinsic safety features. This is because: a. Even for a pump capable of feeding large volumes of liquid metal, the unit can be integrated well below the limit of 250 bars-liters, this is the energy level at which a container is considered to constitute a pressure vessel for the law. Below this limit the contained energy is considered too low to be of any significant danger. b. If the pump is accidentally overpressurized, which could lead to a possible dangerous condition, the assembly is simply arranged so that the cover rises against a specially calibrated spring pressure, so as to dissipate the excess pressure in a non-hazardous manner. Alternatively, a bursting disc can be provided. Such a gas leak is necessarily above the level of liquid metal and thus is safe. This is in contrast to an LP unit. Failures of a crucible in an LP oven can endanger the interior of the oven and destroy the heating elements. The faults of the pressure vessel itself could be much more serious. The possibility of accidental opening of the loading door while the oven is under pressure is a reason why some LP operators will not use the equipment provided to maintain the liquid level at a holding height. It is noted that, with regard to this date, the best method known to the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention.

Claims (8)

1. Claims Having described the invention as above, the content of the following claims is claimed as property: 1. An apparatus for dispensing a liquid material from a container of liquid material, the apparatus is characterized in that it comprises a first container forming an intermediate chamber and which is arranged to receive material from the container, a second container forming a dispensing chamber that is arranged to receive material from the intermediate chamber, first pressurizing means by which the intermediate chamber can be pressurized, second pressurizing means by which the supply chamber can be pressurized, first valve means operable to allow material to be admitted to the intermediate chamber from the container, second valve means operable to allow material to be admitted to the chamber supplying the intermediate chamber and means forming a conduit that that extends from within the dispensing chamber by means of which the material can be supplied through the conduit from the dispensing chamber by pressurizing the dispensing chamber.
2. 2. The apparatus according to claim 1, characterized in that it is adapted to supply molten metal to the molds.
3. 3. The apparatus according to claim 2, characterized in that the metal is aluminum.
4. 4. The apparatus in accordance with the claim 2, characterized in that the metal is magnesium.
5. 5. The apparatus in accordance with the claim 3, characterized in that at least the first and second containers are made of a refractory material of clay / graphite or clay / silicon carbide. The apparatus according to claim 4, characterized in that at least the first and second containers are manufactured from iron, low carbon steel or ferrite stainless steel. The apparatus according to any of claims 1 to 6, characterized in that the pressurization means consist essentially of an inert gas, for example air or carbon dioxide, optionally mixed with up to about 2% by volume of sulfur hexafluoride. . 8. A method for dispensing molten metal into molds by means of an apparatus according to any of the preceding claims, the method is characterized in that it comprises a repeated cycle of operations comprising: (i) pressurizing a dispensing chamber containing molten metal for cause the metal to be discharged through a duct ascending the chamber to a mold; (ii) reducing the pressure in the supply chamber in order to decrease the level of the metal in the riser to a waiting level; (iii) pressurizing an intermediate chamber containing molten metal for the purpose of transferring metal from the intermediate chamber to the dispensing chamber to recharge the dispensing chamber while maintaining the level of the metal in the riser at a level of or about wait level; and (iv) recharging the intermediate chamber of a molten metal container, flow passages between the intermediate chamber and the dispensing chamber and between the container and the intermediate chamber that is opened as required to allow the metal to be transferred to the chambers .