Patent ID: 12186801

DETAILED DESCRIPTION

It is to be understood that the detailed figures are for purposes of illustrating the exemplary embodiments only and are not intended to be limiting. Additionally, it will be appreciated that the drawings are not to scale and that portions of certain elements may be exaggerated for the purpose of clarity and ease of illustration.

The use of a centrifugal molten metal pump in the process of die casting is highly challenging. A typical die casting cycle time is 30 to 90 seconds, which requires a shot sleeve to be filled in approximately 3 to 10 seconds. Furthermore, the delivered quantity of molten metal should be within about 2% of the expected quantity. Similarly, it is desirable to provide an initial “slow” speed fill period (e.g. ¼ cycle time), an intermediate “high” speed fill period (e.g. ½ cycle time), and a third pressurized hold period (e.g. ¼ cycle time). The present disclosure is directed to a system that can fulfill these requirements.

With reference toFIG.2, a die-casting machine100comprises a stationary die clamping plate102onto which a stationary die half103is mounted. This stationary die half103together with a moveable die half104, fastened to a moveable die clamping plate106, define a die cavity107. An external after-pressure arrangement108can be optionally added to the die cavity107. After pressure arrangement108can be linked to a control unit114by a data communication line128.

A shot sleeve109having a filling hole110is fastened to the stationary die half103. A casting piston111is displaceable in this shot sleeve109by means of a hydraulic drive unit113which acts upon its piston rod112in order to press metal, that has been filled into the shot sleeve109through the filling hole110, into the die cavity107. The hydraulic drive unit113is controlled by control unit114via data communication line123which may encompass both electric-electronic components as well as at least part of the hydraulics. To this end, a position sensor and or velocity sensor and/or acceleration sensor115as well as other sensors, such as pressure sensors, are coupled to the control unit114via data communication line116, as is known.

A vacuum valve117may be provided within the region of the parting plane of both die halves103,104. Vacuum valve117can be controlled, in the present case, by a quickly reacting metal front sensor118interfaced with control unit114via data communication line119. The reaction speed of this sensor118is such that the valve is still able to close a vacuum conduit120in the region of the die halves103,104within a time period which passes up to the moment when the metal arrives from the sensor118to the valve117. The vacuum conduit120, instead of comprising a separate control unit which includes a vacuum pump and a vacuum tank (as a vacuum source) and so on, is advantageously coupled to that control unit114which also controls the movement of the casting piston111so that the parts belonging to the control of the evacuation device are accommodated in the housing where the control unit of the piston111are mounted, and no separate control parts have to be provided.

In a typical die casting establishment, the die casting machine100is disposed on a floor130into which a molten metal receiving well132can be formed. Molten metal well receiving well132is in fluid communication with a refractory furnace from which molten metal134is received. Of course a variety of alternative molten metal retention environments exists, such as, for example, a well in which molten metal is deposited from a remote furnace location via transporting equipment. It would similarly be feasible for molten metal to be delivered to the well via launder system. Nonetheless, the present invention is directed to the utilization of a centrifugal pump140to provide molten metal via a conduit142extending between the molten metal base144to the die casting fill hole110. It is noted that the run of conduit142inFIG.2appears lengthy but this depiction is provided only to illustrate the details of the various components. Moreover, it is envisioned that the pump and shot sleeve in practice will be situated significantly closer to one another. Molten metal pump140can be the type disclosed in US 2014/0044520, the disclosure which is herein incorporated by reference.

Molten metal pump140is in communication with the controller114. For example, data communication line150can be provided between an inverter152and the controller114. Similarly, a data communication line154can be provided between an RPM sensing device, such as an encoder155, and the controller114.

The controller114is used to adjust the RPM of the pump motor153. By controlling the pump RPM, the shot size and rate of molten metal flow can be controlled. A typical control system will include a programmable logic controller (PLC), a human—machine interface (HMI), and an inverter. An electronic motor encoder155may also be present to provide the PLC with a feedback loop coupled with the inverter to monitor pump speed. The motor illustrated inFIG.2is a 3-phase variable frequency drive inverter. However, a DC servo motor would be equally suitable.

With reference toFIG.3, a precise shot weight can be provided by employing the depicted feedback loop logic control. The PLC logic includes a command speed sent to the pump motor, then utilizing a RPM sensing device, the speed of the pump motor is relayed to the PLC and verified. The PLC program then makes adjustments to the command speed of the pump motor. This cycle is repeated many times per second for accurate RPM control of the pump motor.

Some of the parameters used to calculate the shot volume/quantity can include: 1) cycle time in seconds; 2) RPM of the pump motor; and 3) evaluation of the inverter settings including acceleration, deceleration, speed feedback calculating parameters (other conditions may also be monitored).

The controller can also be in communication with a sensor such as laser sensor164(seeFIG.2) to determine the molten metal level within the associated furnace. Moreover, it is believed that molten metal depth may be an important variable effecting shot sleeve fill. Accordingly, the PLC receiving data concerning molten metal depth level will adjust the pump RPM appropriately.

The programming of the shot weight can be automatically calculated from data tables included in the controller programming based on time of fill that an operator inputs via the HMI (SeeFIG.4). The operator can manually adjust the shot weight by changing the RPM on one or more entry points and/or the system can use feedback from the die cast machine where, for example, biscuit length is communicated to the controller and fill cycle points automatically adjusted to achieve the correct fill shot weight. (A biscuit is the remaining metal in a shot sleeve after the molten metal is rammed into the die).

Accordingly, the present system may include automatic RPM adjustment features dictated by feedback from the pump inverter and optionally an encoder which are each instructive on the relative performance of the pump. Similarly, automatic RPM adjustment may be made in view of other sensed conditions such as molten metal depth and/or biscuit size. In addition, the system can be manually adjusted by an operator using the HMI of the controller.

With reference toFIG.4, the HMI screen is depicted. The illustrated screen provides the programmed pump RPM at ½ second intervals throughout a sleeve shot fill cycle. It is envisioned that these entries can be adjusted by an operator. In addition, the HMI interface will include features such as cycle pause, and start keys. Similarly, the ability to monitor pump motor RPM based on inventor data can be provided. It is further envisioned that a pump control pause will be accessible.

With reference toFIG.5, elements of the molten metal pump assembly200of the present disclosure are illustrated. More particularly, the elongated shaft216includes a cylindrically shaped elongated orientation having a rotational axis that is generally perpendicular to the base member220. The elongated shaft has a proximal end228that is adapted to attach to the motor (seeFIG.2) and a distal end230that is connected to the impeller222. Impeller222is rotatably positioned within the pump chamber218such that operation of the motor rotates the elongated shaft216and the impeller222within the pump chamber218.

In certain embodiments, it may be advantageous to provide the motor controlling the rotation of the molten metal shaft with an electronic brake (i.e.199inFIG.2).

The base member220defines the pump chamber218that rotatably receives the impeller222. The base member220is configured to structurally receive the refractory posts P (seeFIG.2) through passages231. Each passage231is adapted to receive the metal rod component of the refractory post to rigidly attach to a platform PL (seeFIG.2). The platform supports the motor153above the molten metal.

In one embodiment, the impeller222is configured with a first radial edge232that is axially spaced from a second radial edge234. The first and second radial edges232,234are located peripherally about the circumference of the impeller222. The radial edges may be formed of the impeller body (e.g. graphite) or may be bearing rings (e.g. silicon carbide) seated to the impeller body. The pump chamber218includes a bearing assembly235having a first bearing ring236spaced from a second bearing ring238. The first radial edge232is facially aligned with the first bearing ring236and the second radial edge234is facially aligned with the second bearing ring238. The bearing rings are made of a material, such as silicon carbide, having frictional bearing properties at high temperatures to prevent cyclic failure due to high frictional forces. One of the bearings is adapted to support the rotation of the impeller222within the base member such that the pump assembly does not experience excessive vibration. More precisely, one bear ring has a close tolerance with the impeller radial edge to reduce excessive vibration. The second bearing ring is spaced from the radial edge of the impeller and provides a wear surface for the leakage path described below. The radial edges (or bearing ring seated thereon) of the impeller may similarly be comprised of a material such as silicon carbide. For example, the radial edges of the impeller222may be comprised of a silicon carbide bearing ring.

In one embodiment, the impeller222includes a first peripheral circumference242axially spaced from a second peripheral circumference244. The elongated shaft216is attached to the impeller222at the first peripheral circumference242. The second peripheral circumference244is spaced opposite from the first peripheral circumference244and aligned with a bottom surface246of the base member220. The first radial edge232is adjacent to the first peripheral circumference242and the second radial edge234is adjacent to the second peripheral circumference244.

A bottom inlet248is provided in the second peripheral circumference244. More particularly, the inlet comprises the annulus of a bird cage style of impeller222. Of course, the inlet can be formed of vanes, bores, or other assemblies known in the art. As will be apparent from the following discussion, a bored or bird cage impeller may be advantageous because they include a defined radial edge allowing a designed tolerance (or bypass gap) to be created within the pump chamber218. The rotation of the impeller222draws molten metal into the inlet248and into the chamber218and the continued rotation of the impeller222causes molten metal to be forced out of the pump chamber218to an outlet250of the base member220. Outlet250can be in fluid communication with conduit142(seeFIG.2).

A close tolerance is maintained between radial edge232of the impeller222and the first bearing ring236of the bearing assembly235. For example, the first radial edge232surrounds the first bearing ring236such that the radial edge232rotates while maintaining contact with bearing ring236to provide rotational and structural support to the impeller222within the chamber218. It is envisioned that such contact may be in the form of a thin lubricating layer of molten metal.

A bypass gap260is provided to manipulate a flow rate and a head pressure of the molten metal. The bypass gap260allows molten metal to leak from the pump chamber218to an environment outside of the base member220at a predetermined rate. Moreover, the predetermined rate can be controlled by the relative size of the bypass gap. The leakage of molten metal from the pump chamber218during the operation of the pump assembly allows an associated user to finely tune the flow rate or volumetric amount of molten metal provided to the associated shot sleeve. The leakage rate of molten metal through the bypass gap260improves the controllability of the transport of molten metal and is at least in part because a static hold condition can be maintained while the impeller shaft assembly rotates.

The bypass gap260can be formed by the second bearing ring238wherein the second bearing ring238includes a larger internal diameter than the external diameter of the second radial edge234. Moreover, it is envisioned that one of the two bearing sets has a radial edge engaging and rotatably supported against the bearing ring while the other radial edge is spaced from the associated bearing ring to provide a bypass gap. Optionally, it is contemplated that the bypass gap260may be provided between the first radial edge232and the first bearing ring236.

In one embodiment, operation of the pump assembly of the present disclosure includes an ability to statically position molten metal pumped through the outlet at approximately 1.5 feet of head pressure above a body of molten metal. In one embodiment the impeller rotates approximately 850-1000 rotations per minute such that molten metal is statically held at approximately 1.5 feet above the body of molten metal. The bypass gap manipulates the volumetric flow rate and head pressure relationship of the pump such that an increased amount of rotations per minute of the impeller would allow the reduction of head pressure as the flow rate of molten metal is increased.

With reference toFIG.6, an alternative bottom, feed shot sleeve embodiment is depicted. The depicted apparatus is largely the same as shown inFIG.2. Accordingly, much of the associated numbering has been retained. However, in this embodiment, a shot sleeve209having a filling hole210located in a lower surface212is provided. This design is considered highly beneficial because it facilitates low turbulence filling of the shot sleeve and associated improved metal quality. Moreover, by providing the molten metal inlet to the shot sleeve in a lower half thereof, a relatively low turbulence fill can be performed. It is noted that the present use of a centrifugal pump to provide molten metal directly to the shot sleeve allows for a lower half inlet, a feature not easily achievable via a ladle fill or pressurized furnace.

It is also noted that the present pump is considered suitable for use with any type of casting apparatus. Moreover, it can be used in vertical and horizontal casting. Furthermore, it can be used with a vertical or horizontally oriented shot sleeve. Similarly, it can be used with a sleeve having a top, bottom or side inlet location and wherein the shot sleeve is in any orientation. Advantageously, this allows die casting operators significantly greater flexibility in the design layout of a casting apparatus and/or multiple casting apparatus.

The present embodiment is advantageous in that the need to expose metal to the atmosphere during ladling can be avoided. Similarly, a filter(s) can be associated with the molten metal pump to deliver high quality metal that is provided from a furnace. In this context, the pump (e.g. adjacent the molding apparatus) may be remote from the furnace and fed by a heated launder system.

It is envisioned that the subject apparatus may benefit by inclusion of a shut-off valve positioned adjacent to the inlet of the permanent mold body. For example, the shut-off valve can be placed between the outlet nozzle from the mold pump and the inlet to the permanent mold body. The shut-off valve may be particularly suitable for use in a mold system including a vertical bottom feed or a horizontal feed into the lower portion of the permanent mold body. More particularly, it is envisioned that the shut-off valve can have value in preventing a back-flow of molten metal. In this regard, while the molten metal pump of the present disclosure is capable of holding molten metal statically, it must remain engaged with the permanent mold during solidification of the casting for the static positioning to prevent leakage. Therefore, the molten metal pump cannot be used immediately to fill a subsequent mold.

In this context, it is contemplated that the shut-off valve can be closed after mold fill, allowing the immediate disengagement of the pump nozzle from the mold body and the re-registration of the pump nozzle with a next mold cavity to be filled. The shut-off valve can be used to prevent the leakage of molten metal from the previously filled cavity during the solidification process. The inclusion of a shut-off valve can increase the process efficiency by allowing the mold pump to more rapidly engage the next mold cavity to be filled.

It is envisioned that after all molds are filled, the permanent mold body can be removed from the casting location and a new permanent mold body brought into association with the casting location. It is noted that the shut-off valve can be disposable such that as each mold body is emptied and prepared for re-use the spent shut-off valve is removed and replaced with a new insert. Alternatively, the shut-off valve assembly may be of a reusable design. Without limitation, exemplary casting equipment with which the present shut-off valve could be utilized include equipment manufactured by Anderson Global, Maumee Pattern, TEI Tooling Equipment International, and Valiant. The present shut-off valve may have value in association with a rotary casting process. An exemplary rotary casting system is described in U.S. Pat. No. 6,637,496, the disclosure of which is herein incorporated by reference.

Turning now toFIGS.7-9, the shut-off valves depicted therein efficiently (cost, speed, size) allow flow to be shut-off in a permanent mold in which metal such as aluminum has been cast to prevent metal from leaking. It can advantageously be actuated with a high degree of certainty in a short period of time, such as less than two seconds, or less than 1.5 seconds, or less than 1 second. The shut-off valve can be less than approximately 6″ long, particularly as used in association with permanent mold carousels.

Turning toFIG.7, a heated ceramic nozzle701is connected to a centrifugal molten metal pump shown schematically as702but which can be the type as shown in the preceding figures. However, it is noted that the shut-off valve described herein is not necessarily required to be associated with the mold pump described hereinabove but could be utilized with other mold filling apparatus such as low pressure systems.

The pump702and nozzle701can be provided with vertical movement, for example, in the range of about 1″ to 2″. This vertical movement can facilitate the engagement and disengagement of nozzle701with a permanent mold703. Intermediate the nozzle701and permanent mold703is a shut-off valve assembly705.

Shut-off valve assembly705can include a body portion707comprised of, for example, steel. Body portion707can be a separate or an integral component of the permanent mold703. Body portion707can, for example, form a generally cylindrical space configured to receive insert709. Insert709can, for example, be a cylindrical disc shaped body. However, the insert is not considered limited to this shape. Insert709can be comprised of a resilient material, preferably a compressible material, such as, but not limited to, vacuum formed ceramic fiber or low density ceramic board.

Insert709can define a passage710intended for alignment with the inlet711to the permanent mold703for filling a cavity formed therein. Body portion707can have a slightly tapered (e.g. between 1° and 5° innermost wall713configured for receiving and registering a similarly tapered end portion714of nozzle701.

An air cylinder715is in communication with a pump PLC744or other probe associated with the mold such that the air cylinder715can be actuated and push plunger717horizontally along line719through passage720in body portion707. Plunger717engages a shut-off plug721and actuates the valve by pushing plug721into the passage710sealing the same. Preferably the air cylinder715and plunger717will have a short stroke length, for example 2″. The shut-off plug721can be formed with angled (e.g. between 1° and 5° side walls. It is also envisioned that the insert709will be comprised of the same or a higher or a lower density material than the plug721. It is further envisioned that a plug receiving recess723may be formed in an opposed wall of the insert709.

With reference toFIG.8, an alternative embodiment is depicted wherein the shut-off valve insert body is a one piece construction. Particularly, the plug is formed integrally with the remainder of the insert. Insert809can be constructed to have tapered (e.g. 30°) sidewalls817for easy registration with the mold inlet. Moreover, an insert809can be comprised of the resilient material such as vacuum formed ceramic fiber wherein a plug821is partially formed by cutting the material along lines823and825to create a preferential weakness from which the plug821can be separated from the remainder of the insert809when acted upon by the plunger819and air cylinder827(the body portion of the shut-off valve has been omitted in this view). The uncut half round sections can be formed with a cutting blade inserted on each side of the plug about one-half way to the bore. Preferably, sufficient cutting is performed to allow the air cylinder to disengage the plug from the remainder of the body and push it into the molten metal flow. Upon separation, plug821enters passage829blocking molten metal flow. This results in a stable flow cutoff device for metal solidification.

Turning next toFIG.9, an alternative configuration is depicted wherein a valve901is constructed without a plug but formed of sufficiently resilient and deformable material such that the air cylinder903fitted with a wedge shaped ram905engages a side wall causing deformation and pinching of the passage907to seal the molten metal path. It may be desirable to provide a back-side stop909to facilitate pinching passage907shut. It is envisioned that the valve can again be formed of resilient fiber reinforced ceramic or a polymeric material. It may be advantageous for the ram905to stay engaged during the solidification of the metal in the inlet portion but nonetheless the removal of the engagement of the mold pump nozzle and re-association with a subsequent empty cavity is feasible to increase the efficiency of the mold filling operation. In certain embodiments it may be desirable to form the passage of the insert in an ovoid shape (longer in direction x than in direction y) wherein the ram can engage the insert in a direction transverse to the longer axis such that a decreased amount of deformation is required to shut the passage.

The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.