WO1997006907A1 - Die casting devices - Google Patents

Abstract

A device mountable in a die casting installation which defines a flow path for the supply and flow of a heat transfer medium adjacent to a region of a die component of the installation, whereby the extraction of heat energy at said region from a metal being cast in the installation is able to be retarded or accelerated such as by selection of the heat transfer medium and/or its flow rate along the flow path. The device can be mountable adjacent to a sprue region of the installation such that, with the supply of the heat transfer medium at a sufficient flow rate, the cooling of metal in the sprue region is able to be accelerated where the medium is a coolant or sprue region is able to be heated where the medium is adapted to provide heat energy input. Alternatively, the device can include a conduit system mountable in the die component of the installation and through which the heat transfer medium is able to be supplied for the extraction of heat energy from a section of metal cast in a die cavity defined by the installation, and an insert at a leading end thereof which is adapted to control the extraction of heat energy from a localised region of the metal at said section and to conduct the heat energy to heat transfer medium in the conduit system, wherein the device is adapted to be received in the die component such that a surface of the insert defines a part of, and is exposed at, the cavity so as to be in direct thermal contact with the cast metal at said localised region.

Description

DIE CASTING DEVICES This invention relates to improvements applicable to die casting, in particular low pressure die casting, of light alloys such as aluminium alloys.

In the die casting of light alloy components, efficient operation requires rapid solidification of the casting and maintenance of the shortest practical cycle time consistent with the production of quality castings, by the use of cooling and/or heating. However, the sequence of operations performed in each cycle make it difficult to achieve a substantially constant thermal variation in successive cycles. For example, cooling or heating is achieved by an appropriate medium, such as air, water, oil or combinations thereof, supplied to the die components to control temperature, the die is opened for removal of a casting, after which the die is cleaned, fresh cores may be positioned, and the die is closed for the next forced feeding of molten metal. The relative time for these operations can vary, as can the temperature of the molten metal, introducing variability in the control necessary and overall time of successive cycles.

The present invention is concerned with devices which enable more precise die thermal and casting solidification control in successive cycles and, hence, attainment of a shorter average cycle time, while maintaining a required level of casting quality and safety of operation.

According to the invention there is provided a device mountable in a die casting installation, wherein the device defines a flow path for the supply and flow of a heat transfer medium adjacent to a region of a die component of the installation, whereby the extraction of heat energy at said region from a metal being cast in the installation is able to be retarded or accelerated such as by selection of the heat transfer medium and/or its flow rate along the flow path.

In one aspect, the invention provides an improved sprue region cooling and/or heating device (hereafter referred to as "sprue control device") for supplying heat transfer medium in the sprue region of a die casting component, that is, in a lower die component in the case of a low pressure die casting operation. The sprue control device is mountable adjacent to the sprue region at a position such that, with the supply of heat transfer medium at a sufficient flow rate, solidification and/or subsequent cooling of metal is accelerated where the medium is a coolant or retarded where the medium is adapted to provide heat energy input. The sprue control device preferably substantially encircles the sprue. In one arrangement, it is provided around a sprue bush of its die component, preferably, so as to be separable therefrom.

The sprue control device may be of annular form, with adjacent or circumferentially spaced inlet and outlet ducts for heat transfer medium. However, the sprue control device preferably is of penannular form, with adjacent inlet and outlet ducts which are slightly spaced at a gap resulting from that form. The sprue control device preferably has at least one thermocouple associated therewith for monitoring such aspects as the heating and/or cooling performance of a thermal control system. The penannular form is well suited to this since temperature monitoring is readily able to be achieved by at least one thermocouple located in the sprue bush, between the inlet and outlet ducts. Preferably two thermocouples are provided, with these being spaced along the length of the sprue bush, that is, in the direction of metal flow through the sprue bush or, alternatively, circumferentially around the sprue bush.

The sprue control device may define a gallery which provides for the flow of cooling and/or heating medium and which is thermally connected, via the sprue bush of its die component, with metal in the sprue. However, the thermal connection preferably is substantially limited to a radially circumferential inner region of the gallery. Thus, the gallery may be insulated, at least to a degree, at a radially outer circumferential region thereof and preferably also at ends thereof spaced axially of the sprue, that is, spaced in the direction of metal flow through the sprue bush. In one convenient arrangement, the gallery is defined by an annular or penannular metal conduit which, around a radially inner circumferential surface thereof, is in direct thermal contact with an outer peripheral surface of the sprue bush and which, at a radially outer and each axial end surface thereof, is insulated from the sprue bush and its die component, such as by an air cavity therebetween.

The invention also provides a die casting installation which includes a die having a plurality of die components which are co-operable to define a die cavity, with one of the components including a sprue bush through which molten metal is able to be supplied to the cavity in each of successive casting cycles, and which further includes a sprue control device according to the invention mounted around the sprue bush for achieving thermal control of solidification and subsequent cooling of metal in the sprue bush at a required stage in each cycle. The installation may be for low pressure die casting, with the one component being a lower die component through which the sprue bush extends upwardly to the die cavity. The installation may be provided with more than one sprue bush, with the one component for example having two sprue bushes each able to receive molten metal from a respective arm of a "Y" feeder by which molten metal is forced from a molten metal supply. Where there is more than one sprue bush, each preferably is provided with a respective sprue control device.

In operation with the die casting installation, the temperature of the (or each) sprue bush is monitored, in the course of solidification of molten metal in the die cavity towards the sprue bush. At an appropriate stage, coolant is supplied to the (or each) sprue cooler, to achieve solidification of molten metal in the sprue bush.

Means, including the thermocouple(s), for monitoring the temperature of the sprue bush may provide an output signal for a control system operable for controlling the supply of heat transfer medium to the sprue control device. The control system may be operable, in response to that output, to determine the onset time and duration of supply of, and also the flow rate for, the medium. Also, the control means may suitably activate supply means to provide a required supply of the medium. When the sprue is to be reheated after ejection of a casting from the die cavity, and before the commencement of the next casting cycle, the monitoring means may provide an output indicative of the sprue bush temperature and in response to which the control system may be similarly operable to supply heated medium to preheat the sprue control device. Until molten metal is solidified in the sprue bush, pressure under which molten metal is supplied to the die cavity is maintained. In the course of solidification of molten metal in the die cavity, the supply of molten metal to the cavity is maintained to allow for shrinkage in metal volume on solidification. With appropriate monitoring of the temperature of molten metal in the sprue bush, it is found that the monitored temperature fluctuates rapidly over a relatively small temperature range, apparently due to periodic inflow of molten metal compensating for shrinkage. An output of monitored temperature, showing such fluctuations, enables control over both the timing of the supply and the flow rate of coolant to the sprue cooler and hence determination of an optimum stage for solidification of molten metal in the sprue bush.

Particularly with a large casting, such as a cylinder head for an automotive engine, the sprue control device is adapted to provide cooling and/or heating at its sprue bush by circulation of heat transfer medium, such as coolant comprising water. The medium is circulated around the sprue control device for a sufficient period, at a sufficient flow rate, to achieve a required rate of solidification of metal contained in the sprue bush. Where, for example, the heat transfer medium is coolant water, the supply of the coolant water may be at a rate of from about 5 to 15 l/min for a period of from 5 to 20 seconds.

For other castings, water also can be used as the coolant. However, at least with smaller castings, the coolant can comprise air or an air/water mist. In each case, a cooling rate in the sprue bush of at least about 1 to 3°C/sec or higher, is desirable. However, as indicated above, the heat exchange medium can be required to retard loss of heat energy from the sprue region, while it also can be used for preheating that region. In the latter cases, the heat exchange medium can be heated water or oil, steam or other suitable heat exchange medium. In another aspect, the invention provides an improved cooling and/or heating device, utilising a heat transfer medium - supplying fountain (hereinafter referred to as a "fountain device"), for accelerating or retarding cooling of metal in a section of a casting. The fountain device utilises a conduit system which is mountable in a die casting component, and through which the medium is able to be supplied to control the extraction of heat energy from cast metal at the section of the casting. The fountain device, at a leading end thereof, has an insert which is adapted to control the extraction of heat energy from a localised region of the cast metal, such as to conduct the heat energy to the conduit system for extraction by a coolant medium.

The fountain device is adapted to be received in its die component such that a surface of the insert defines a part of and is exposed at the die cavity and is in direct thermal contact with cast metal. The fountain device may be configured such that a substantial part of heat energy extracted by it from the cast metal is conducted from the cast metal via the exposed surface of the insert, so as to minimise the amount of heat energy conducted to the insert from a surrounding region of the die component. In one arrangement, the fountain device is of elongate form between leading and trailing ends, with the insert defining the leading end, and the conduit means extending from within the insert to the trailing end. The conduit means has inner and outer co-axial conduits between which an annular fluid flow passage is defined, with the outer conduit having a closed end within the insert and the inner conduit having an open end within the insert, such that heat transfer medium is able to circulate through the fountain device, via inlet and outlet ports at the trailing end, by flow through the inner conduit and then through the annular passage, or by flow through the annular passage and then through the inner conduit. In that arrangement of the fountain device, the insert may be cup-shaped in having a basal wall of which an outer surface is to be exposed at the die cavity, and a peripheral wall which projects from the basal wall towards the trailing end and within which an end of the conduit means is received. A leading end portion of the conduit means which is received in the insert is in direct thermal contact with the basal wall and the peripheral wall of the insert, with the contact with the peripheral wall preferably being by screw threaded engagement to maximise the area of contact therebetween.

The die component with which the fountain device is used defines a bore therethrough for receiving the fountain device. However, the fountain device preferably has a cross-section such that, when received in the bore of the die component, it is in thermal contact with the die component substantially only adjacent the basal wall of the insert. For this, the insert preferably has an enlarged cross-section adjacent to its basal wall by which it engages a surface of the die component which defines the bore, such that at least part of the axial extent of the peripheral wall of the insert, preferably a major part of that extent, is spaced from that surface of the die component. Also, over the axial extent of the conduit beyond the insert, the conduit means is spaced from the surface of the die component which defines the bore.

The insert of the fountain device preferably is of a metal which enhances the control of extraction of heat energy, and which is compatible with molten alloy to be cast. In one preferred form, the insert is of a copper-beryllium alloy. The conduit means also is to be of a metal which enhances the control of heat energy extraction, although the choice of its metal is less important than for the insert, and the conduit means can, for example, be of copper or stainless steel.

The fountain device may be mounted in the bore of its die component such that contact between the component surface which defines the bore and a peripheral surface of the insert around the basal wall is substantially air-tight. Where this is the case, the basal wall of the insert, or a separable part thereof, may be adapted for venting of air from the die cavity during the feeding of molten metal. For this purpose, the basal wall or its separable part may define vent slots which extend upwardly from the exposed surface towards the interior of the insert. To facilitate the venting of air, the insert preferably defines at least one passageway which provides communication between the vent slots and the peripheral surface of the insert, such that vented air is able to discharge via the bore of the die component.

The fountain device preferably includes locking means by which it is clamped in the bore of its die component. The locking means, in one convenient arrangement, comprises a sleeve through which the conduit means extends, with the sleeve having a threaded flange at its trailing end by which it is able to be threadedly engaged with an outer end of the bore, so that its leading end abuts the trailing end of the insert to clamp the insert in position. With such arrangement, the insert and the bore preferably are stepped to define respective shoulders providing for clamping of the insert in position. The invention also provides a die casting installation which includes a die having a plurality of die components which are co-operable to define a die cavity, with at least one of the components defining at least one bore which extends between inner and outer surfaces thereof, and the installation further includes at least one fountain device according to the second aspect of the invention. The or each fountain device is mounted in the or a respective bore such that a surface of its insert defines part of and is exposed at the die cavity so as to be exposed to direct thermal contact with molten metal supplied to the cavity. The installation may be for low pressure die casting, with the one component being an upper die component, and the or each bore thereof being positioned such that the fountain device mounted therein is operable to control the extraction of heat energy from the molten metal at a heavy section for a casting. The arrangement may be such as to facilitate solidification of the molten metal substantially from the one component, towards a sprue region at an opposite die component. The installation may include a sprue control device according to the first aspect of the invention, with the sprue control device mounted around a sprue bush through which molten metal is supplied to the cavity.

A heat exchange medium for use with the fountain device may be as described above in relation to the sprue control device. The medium may be a coolant, such as to enhance heat extraction from a heavy section of a casting. Alternatively, it may be a heated medium for retarding heat energy extraction, such as from a thin or light section of a casting adjacent to a heavy section, or for preheating a region of its one die component. The die component having a fountain device mounted therein preferably has at least one thermocouple which is closely adjacent and monitors the temperature of the insert of the device. Means which include the thermocouple may provide an output signal for a control system, and this may be the same or different control means for a sprue control device according to the invention. In any event, such control system preferably is operable to determine the onset time and duration for the supply of, and the flow rate for, heat transfer medium to be supplied to the conduit system, and suitably activate supply means by which the medium is passed to the conduit system.

The invention now will be described with reference to the accompanying drawings, in which: Figure 1 is a sectional view through a bottom die component of a low pressure die casting installation;

Figure 2 is a section view, taken on line II-II of Figure 1;

Figure 3 is a top plane view of a top die component of the installation;

Figure 4 is a partial sectional view of the die component of Figure 3, taken on line IV-IV;

Figures 5 and 6 are further partial sectional views of the die component of Figure 3, showing typical locations for thermocouples;

Figure 7 shows smoothed thermocouple temperature traces obtained with use of the bottom die component of Figures 1 and 2; and Figure 8 shows smoothed thermocouple traces obtained with use of the top die component of Figures 3 to 6.

With reference to Figures 1 and 2, the bottom die component 10 has an upper die cavity defining surface 12, and a lower surface 14. Mounted in component 10, there is a sprue brush 16 which defines a sprue passage 18 by which molten metal is supplied to the cavity, in one convenient arrangement, component 10 has two adjacent bushes 16, each of which is coupled to a respective arm of a "Y" feeder (not shown) by which molten metal is able to be supplied to the cavity through the passage 18 of each sprue bush 16.

Around bush 16, component 10 is provided with a sprue region cooling device 20, which is operable to solidify molten metal in passage 18. Device 20 is mounted around a cylindrical outer surface 22, below a radial flange portion 24, of bush 16. The arrangement is such that device 20 is substantially located in an annular chamber 26 defined between component 10 and bush 16, with chamber 26 being closed below device 20 by an annular cover plate 28 secured by bolts (not shown) to component 10.

Device 20 includes a penannular collar 30 of inverted U-section and a collar insert 32. As shown, the inner periphery of each side flange 30a of collar 30 is stepped to as to receive collar insert 32 therein with collar 30 and collar insert 32 defining a penannular coolant water gallery 34. A suitable seal is provided between collar 30 and collar insert 32, to preclude leakage of water from gallery 34, while bolts, welds or the like (not shown) are provided to secure collar insert 32 in position.

As shown in Figure 2, device 20 includes an inlet arm or duct 36 and an outlet arm or duct 38, each communicating with gallery 34 at a respective one of adjacent ends of collar 30. The radially outer end of duct 36 has a coupling 36a by which it is connectable to a line (not shown) for the supply of coolant water, while duct 38 has a similar coupling 38a by which it is connectable to a coolant discharge line (not shown). The arrangement is such that, when required, coolant water is able to be supplied to duct 36, for flow around gallery 34 and discharge via duct 38, with the water supply line having valve controls enabling the flow of water around gallery 34 at a required flow rate, and at a required time and for a required duration. However, the arrangement also is such that pressurised air can be caused to flow around gallery 34, to purge gallery 34 of water, at a suitable time in a casting cycle.

The part of device 20 defined by collar 30 and collar insert 32 is of rectangular cross-section, although other cross-sections can be used. The arrangement is such that a radially inner, circumferential surface 30a of collar 30 is in direct thermal contact with surface 22 of sprue bush 16. Thus radial extraction of heat energy from molten metal in passage 18 is facilitated, around substantially the full circumferential extent of bush 16, with flow of coolant around gallery 34. However, the radial extent of collar 30 is such that chamber 26 provides an insulating air gap 26a at the radially outer circumferential surface 30b, such that extraction of heat energy from component 10 is minimised. Similariy, chamber 26 provides an air gap 26b between plate 28 and the lower extent of collar 30 and collar insert 32, so as to limit the extent to which heat energy is extracted from molten metal in passage 18, below device 20. Thus, the length of a sprue formed on a casting can be controlled.

Chamber 26 provides a further air gap 26c between top surface 30c of collar 30 and flange 24 of bush 16. However, the lower surface of flange 24 is stepped at 24a such that, adjacent a radially inner part of surface 30c, collar 30 is in direct thermal contact with bush 16, at flange 24. This contact facilitates extraction of heat energy from molten metal in the upper extent of passage 18, above the level of device 20, to preclude the possibility of solidification of metal in passage 18 at the level of device 20 while molten metal remains at the junction of passage 18 and the die cavity.

As shown, device 20 includes upper and lower thermocouples 40, each retained by a compression fitting 40a. As seen most clearly in Figure 2, each thermocouple 40 is located between ducts 36 and 38 such that its hot junction is able to be located in bush 16, below flange 24 but substantially at the level of device 20. The thermocouples 40 thus are able to monitor the temperature of the sprue bush 16, and provide outputs enabling determination of the timing for the supply of coolant water flow around gallery 34.

The form and location of device 20 enables enhanced determination of the timing and duration of the supply of coolant for the solidification of molten metal in passage 18, at the end of a casting cycle. For efficient cooling, collar 30 in particular, but preferably also collar insert 32, is made of a metal providing for adequate heat energy extraction, such as copper or stainless steel. In use, with cooling by means of device 20, the cooling operation consists of a short run of water around gallery 34, followed by an air purge to expel water from gallery 34, at the appropriate time in the casting cycle. This appropriate time is determined by the solidification pattern for a particular casting, as indicated for example by the output of thermocouples 40 and/or other thermocouples in die component 10. The cooling cycle, by the flow of water around gallery 34, constitutes only a short duration in the total casting time, with device 20 not being operative to provide cooling over the remainder of the total time of casting. However, in the casting of automotive cylinder heads, for example, use of the device 20 enables a reduction of the overall process cycle time of up to about 30%, with a corresponding increase in productivity. The mounting of device 20 in component 10 is simple, and necessitates only a firm friction fit of collar 30 onto surface 26 of bush 16 to achieve good thermal contact therebetween. Due to this, and the simple form of both device 20 and modification of component 10 and its bush 16, rapid detachment of device 20 is possible when it is required.

The penannular form of collar 30 and insert 32 of device 20 is such that a shrink-fit effect will occur during a cooling cycle, in which coolant such as water is circulated around gallery 34, to enhance the transfer of heat energy from sprue bush 16 to collar 30. When cooling is stopped, preferably by purging by an air flow through gallery 34, collar 30 heats up quickly and expands, thus reducing the heat energy transfer at surface 30a due to a resultant looser fit between collar 30 and sprue bush 16. In the arrangement of Figures 3 to 6, there is shown a top die component 50 of a low pressure die casting installation. The component 50 is of an installation for casting a cylinder head for an automotive engine. For each of a plurality of locations at which the casting is to define a boss which is of enlarged thickness, relative to adjacent regions, component 50 is provided with a bore 52 which extends between its lower, die cavity defining surface 54 and its upper surface 55. A respective boss cooling fountain device 56 is mounted in each bore 52. Component 50 also has other bores 58 which extends inwardly from surface 55 to a die core 60, in each of which is provided a core cooling fountain device 62. Additionally, component 50 has conventional bores 64 through which casting ejection pins 66 are slidable.

Each boss cooling fountain device 56 is of elongate, generally cylindrical form, and includes a conduit means 68, a heat extracting insert 70 at its leading end, and a retaining sleeve 72 by which means 68 and insert 70 are clamped in a required position in the respective bore 52. Conduit means 68 includes an outer conduit 74 which is closed at its leading end 74a, and an inner conduit 76 which extends co-axially within conduit 74 and is open at its leading end 76a. Means 68 also includes a connector head 78 mounted on the trailing end of conduits 74 and 76.

Head 78 has an inlet port 78a by which it is connectable to a line 80 for the supply of coolant water, and an outlet port 78b for connection to a coolant water discharge line. In fact, while line 80 is shown in Figure 4, the heads 78 of the two devices 56 are not shown as connected to it, for simplicity of illustration. Also, in Figure 5, each head 78 is shown as having two ports 78a, although only one is used as is convenient for simplicity of plumbing, and the other is provided with a sealing plug 81. However, the overall arrangement is such that, when required, coolant water is supplied to a port 78a, flows down passage 82 of conduit 76, upwardly in the annular passage 84 defined around conduit 76 by conduit 74, and discharges via port 78b.

Insert 70 is cup-shaped and has a basal wall 86 and a peripheral wall 87. The leading end 74a of conduit 74 is received in insert 70, with end 74a firmly abutting wall 86. Also, for maximum surface to surface contact, the lower extent of conduit 74 is threaded and screwed into internal thread provided around wall 87 of insert 70.

Insert 70 is stepped around wall 86 to provide a reduced diameter leading end, while bore 52 is correspondingly stepped to a reduced diameter adjacent to lower surface 54. The arrangement is such that insert 70 defines a shoulder 88 which abuts shoulder 89 of bore 52, when device 56 is properly located, with surface 90 of insert 70 flush with surface 54.

Above its shoulder 88, insert 70 is stepped around wall 87 such that, over the major part of the length of insert 70, there is an annular insulating air gap 91. Thus, only the lower extent of insert 70 is in thermal contact with die component 50, such that device 56 is operable to extract heat energy predominantly via surface 90 when that surface is in contact with molten metal.

Retaining sleeve 72 is concentric with conduit means 68, but is spaced from conduit 74 and die component 50 by respective annular, insulating air gaps 93 and 94. At its upper end, sleeve 72 has an externally threaded flange 95 which is engaged with a threaded, enlarged diameter portion 52a of bore 52. Sleeve 72 is screwed down in bore 52 so that its lower end engages the upper end of peripheral wall 87, to thereby clamp shoulders 88 and 89 into firm engagement. This arrangement permits removal of insert 70 without total disassembly of die component 50. To enable air venting, the basal wall 86 of insert 70 is counter bored to define a recess 95, in which a vent 96 is mounted. The vent 96 defines axially extending vent slots 96a such that, while insert 70 preferably provides a gas seal therearound with bore 52, gas in the die cavity is able to vent through slots

96a. At its upper extent, wall 86 defines a lateral passage 97 and an axial groove 98 in the external surface of wall 87, by which vented gas is able to discharge into air gaps 91 and 94. However, air venting (if in fact required) can also be provided for by flats machined into the surface of the peripheral wall 86.

After the cavity of the die installation has been filled with molten metal, solidification of the metal commences at surface 54 of die component 50, and proceeds down towards a lower die component, such as towards a sprue region of a die component 10 of Figures 1 and 2. Such directional cooling is facilitated by circulation of coolant through conduit means 68, and the similar conduit means of devices 62. However, each device 56 has its leading end in thermal contact with the metal at a heavy section of the casting, and the features of insert 70 and its relationship to conduit means 68 and component 50 enhance extraction of heat energy from each heavy section. Thus, by control over coolant flow through conduit means 68, it is possible to ensure solidification of molten metal at the larger sections does not lag behind solidification at thinner adjacent sections, with risk of encapsulated regions of molten metal and resultant formation of voids or cavities in a casting.

The fountain devices 62 are similar to devices 56 except for the geometry of the insert 102, and termination of their bores short of surface 54, adjacent to a die core 100. In so far as relevant, parts of devices 62 have the same reference numerals as part of devices 56. No specific venting arrangement is incorporated in insert 102 as venting can be provided by the clearance in the bore 64 for each ejector pin 66, in accordance with normal practice. The insert 102 may be located by the sleeve 103. Air gaps 104a and 104b are provided to limit heat energy removal from die component 50. The insert 102 may be kept firmly in position by a die core 105 located under the die component 50.

As shown in Figures 5 and 6, thermocouples 101 are mounted in die component 50, adjacent to at least representative ones of devices 56 and 62. These enable differences in the molten and solidified metal temperature and/or thermal gradients in the die insert 102 to be monitored. Thus, the relative rate of supply of coolant water to the respective sets of devices 56 and 62 can be controlled, so as to enhance the attainment of substantial uniformity of solidification away from surface 54 of component 50.

Figure 7 shows operation with device 20 of the bottom die component 10 of Figures 1 and 2 in the casting of an automotive engine cylinder head by low pressure die casting of an aluminium alloy. The smoothed thermocouple traces were obtained from the upper thermocouple 40 between ducts 36, 38 of device 20. Trace A was obtained with no heat exchange medium supplied to gallery 34. Also, in each case, traces B and C were obtained with a flow of water around gallery 34, initiated 140 seconds after the commencement of casting, at a respective flow rate of 5 l/minute for 10 seconds and 10 l/minute for 10 seconds. The water flow was followed by air-purging of gallery 34.

Trace A shows a relatively smooth increase in the temperature of sprue bush 16 in the course of solidification of alloy in the die cavity towards the sprue passage 18. This increase commenced after a period of relative stability at a preheat temperature of about 485°C resulting from a preceding similar cycle.

By comparing trace A with traces B and C obtained in cases where water cooling is operational, it can be seen that the sprue bush temperature recovers to within 15°C of the temperature obtained by the uncooled sprue, after an initial temperature deficit of about 60°C due to the cooling effect of the sprue control device. This enables the correct thermal balance in the die to be preserved before the start of the next cooling period.

After an initial interval in which the temperature was stable, at about 424°C and 414°C, due to lower residual heat energy content from a preceding similar cycle, traces B and C follow a similar path to trace A until the onset of water flow around gallery 34. With the onset of the water flow, the temperature of sprue bush 16 decreased at about 1°C/second under the conditions providing trace B and about 2.1°C/second under the conditions providing trace C. As indicated, the lower traces were obtained with the upper thermocouple 40, although traces obtained with the lower thermocouple 40 were essentially the same. The water flow rates used achieved rapid cooling of metal in sprue passage 18, enabling earlier release of molten metal supply pressure and draining of molten metal from a feeder pipe by which molten metal had been supplied to the die cavity via sprue bush 16. As shown, this cooling continued at a slightly declining rate after the 10 second interval of water flow, indicating that it was further assisted by the air purge. The cooling of sprue bush 16, via the water flow around gallery 34, also resulted in a slight increase in the rate of solidification of molten metal in the sprue gate above device 20. However, this was due primarily to a greater temperature differential between the top and bottom die components, resulting from the lower initial heat energy content of the lower die component 10 under the conditions of water flow providing lower traces B and C. Using the cooling cycle of 10 seconds duration initiated at 140 seconds, enabled a reduction in process cycle time of approximately 30%, compared with conventional practice for the casting in question, while still providing sound castings of a good standard.

As indicated, the cooling rate increased significantly with an increase in water flow rate from 5 to 10 l/minute. The system used with device 20 is capable of a flow rate of about 18 l/minute and the indications are that faster cooling rates or a longer duration of water cooling can be used in the production of good castings at further reduced cycle times.

Figure 8 shows operation with the device 56 of a top die component 50 of Figures 3 to 6, in the casting of an automotive cylinder head by low pressure die casting of an aluminium alloy. The smoothed thermocouple traces were obtained with the left hand thermocouple 101 as shown in Figure 6, with each trace showing temperature variation throughout a complete cycle about 5.5 minutes and also showing the start of a next cycle.

The device 56 was located in die component 50 as detailed above, with its surface 90 flush with die cavity defining surface 54 for direct thermal contact with a region of cast molten metal where the cylinder head is to have a heavy section, such as a boss. The temperature trace of Figure 8 shown in solid line indicates the variation of the temperature in die insert 102 as obtained with a flow of water through passages 82, 84 at a flow rate of 6 l/minute, initiated 25 seconds after the commencement of casting for an interval of 25 seconds and followed by air-purge of passages 82, 84. The temperature trace shown by a broken line indicates the temperature in die insert 102 with no cooling water supplied to passages 82, 84. As is evident from the trace of Figure 8 for no cooling, the temperature of die insert 102 rises readily over an interval of about 70 seconds, and thereafter declines relatively slowly through to the end of the casting cycle. This is indicative of slow solidification of molten metal in the heavy section relative to adjacent light sections, and a resultant substantial risk of a cavity forming in the heavy section.

With the supply of cooling water, the rise in temperature of insert 102 is arrested, with its temperature then declining rapidly during and for a time after the period of cooling, and the temperature of insert 102 then increasing relatively slowly. This is indicative of enhanced solidification of molten metal in the heavy section, downwardly from the top of the die cavity, preventing this solidification from lagging behind solidification in adjacent light sections. Thus, conditions for directional solidification in the casting are enhanced and the feeding of metal shrinkage by make-up molten metal in the casting is facilitated, to avoid the risk of a cavity in the casting. Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

Claims

1. A device mountable in a die casting installation, wherein the device defines a flow path for the supply and flow of a heat transfer medium adjacent to a region of a die component of the installation, whereby the extraction of heat energy at said region from a metal being cast in the installation is able to be retarded or accelerated such as by selection of the heat transfer medium and/or its flow rate along the flow path.

2. A device according to claim 1 , wherein said device is mountable adjacent to a sprue region of the installation such that, with the supply of the heat transfer medium at a sufficient flow rate, the cooling of metal in the sprue region is able to be accelerated where the medium is a coolant or sprue region is able to be heated where the medium is adapted to provide heat energy input.

3. A device according to claim 2, wherein the device is adapted to substantially encircle a sprue bush of the installation.

4. A device according to claim 3, wherein the device is provided around the sprue bush so as to be separable therefrom.

5. A device according to any one of claims 2 to 4, wherein said device is of annular form and has an inlet duct and an outlet duct such that heat transfer medium is able to be supplied to the inlet duct, and discharge from the outlet duct after flow around the flow path.

6. A device according to any one of claims 2 to 5, wherein the device is of a penannular form and has adjacent inlet and outlet ducts each located at a respective end of the flow path.

7. A die casting installation, wherein a die component of the installation has a device according to any one of claims 2 to 6, said component has a sprue through which molten metal is able to be supplied to a die cavity of the installation and said device is mounted adjacent to the sprue.

8. An installation according to claim 7, wherein at least one thermocouple is associated with said device to enable monitoring of temperature of metal in the sprue by means of a thermal control system.

9. An installation according to claim 7, wherein said device is of a penannular form and mounted around a sprue bush of the component, and wherein at least one thermocouple is associated with the device by being mounted between respective ends thereof.

10. An installation according to claim 9, wherein two thermocouples are mounted between said ends and are spaced longitudinally with respect to the direction of molten metal flow through the sprue bush into the die cavity.

11. An installation according to any one of claims 7 to 10, wherein said device defines a gallery which provides for the flow of heat exchange medium around the flow path, and the gallery is thermally connected via the sprue bush with metal in the sprue by means of a thermal connection substantially limited to a radially inner circumferential region of the gallery.

12. An installation according to claim 11 , wherein the gallery is at least partially insulated at a radially outer circumferential region thereof.

13. An installation according to claim 11 or claim 12, wherein the gallery is at least partially insulated at ends thereof spaced axially of the sprue with respect to the direction of molten metal flow through the sprue bush to the die cavity.

14. An installation according to claim 12 or claim 13, wherein the gallery is insulated by an air cavity between the gallery and an adjacent surface of the die component.

15. An installation according to any one of claims 7 to 14, wherein said installation is adapted for low pressure die casting and said die component thereof is a lower component through which the sprue extends upwardly to the die cavity.

16. An installation according to claim 15, wherein said component has at least two sprue bushes, with each sprue bush provided with a respective said device.

17. A device according to claim 1 , wherein said device includes a conduit system mountable in the die component of the installation and through which the heat transfer medium is able to be supplied for the extraction of heat energy from a section of metal cast in a die cavity defined by the installation, the device has an insert at a leading end thereof which is adapted to control the extraction of heat energy from a localised region of the metal at said section and to conduct the heat energy to heat transfer medium in the conduit system, and wherein the device is adapted to be received in the die component such that a surface of the insert defines a part of, and is exposed at, the cavity so as to be in direct thermal contact with the cast metal at said localised region.

18. A device according to claim 17, wherein said device is configured such that, when mounted in said component, a substantial part of extracted heat energy is conducted from the cast metal, via the exposed surface, whereby the amount of energy conducted to the insert from a surrounding region of the component is minimised.

19. A device according to claim 17 or claim 18, wherein the conduit system is of elongate form between leading and trailing ends with the insert defining the leading end, the conduit system has inner and outer substantially co-axial conduits between which an annular flow passage is defined, the outer conduit has a closed end at or within the insert and the inner conduit has an open end at or within the insert, whereby heat transfer medium is able to circulate via inlet and outlet ports at or adjacent to the trailing end by flow through the inner conduit and then through the passage or by flow through the passage and then through the inner conduit.

20. A device according to any one of claims 17 to 19, wherein said insert is cup-shaped with a basal wall which defines said surface and a peripheral wall which projects from the basal wall, and wherein a leading end portion of the conduit system is received within and is in direct thermal contact with said peripheral wall.

21. A device according to claim 20, wherein said end portion is in direct thermal contact with said peripheral wall by screw threaded engagement therebetween.

22. A device according to claim 20 or claim 21 , wherein said device is adapted to be received in a bore defined by said die component and has a transverse cross-section such that, when received in the bore, there is direct thermal contact between the insert and the component only at or adjacent to the basal wall of the insert and the conduit system is not in direct thermal contact with the component.

23. A device according to claim 22, wherein the insert has an enlarged cross-section at or adjacent to the basal wall by which it is adapted to engage the bore in direct thermal contact.

24. A device according to any one of claims 17 to 23, wherein the insert if of a copper-beryllium alloy.

25. A device according to any one of claims 17 to 24, wherein the conduit system is of copper or stainless steel.

26. A device according to any one of claims 17 to 25, wherein the device is adapted to be mounted in a bore of the die component such that contact between a peripheral surface of the insert around the basal wall and a surface of the component which defines the bore is substantially air-tight.

27. A device according to claim 26, wherein the basal wall of the insert or a separable part of the basal wall is adopted for venting air from the die cavity during the feeding of molten metal to the die cavity.

28. A device according to claim 27, wherein the basal wall or separable part thereof defines vent slots which extend upwardly from the exposed surface towards the interior of the insert.

29. A device according to claim 28, wherein the insert defines at least one passageway which provides communication between the vent slots and the peripheral surface of the insert.

30. A device according to any one of claims 17 to 29, including locking means by which the device is adopted to be clamped in a bore of the die component.

31. A device according to claim 30, wherein the locking means comprises a sleeve through which the conduit system extends, with the sleeve having a threaded flange at its trailing end by which it is adapted to be threadedly engaged in an outer end of the bore and whereby a leading end of the sleeve abuts a trailing end of the insert to clamp the insert in position.

32. A die casting installation wherein a die component of the installation defines a bore in which a device according to any one of claims 17 to 31 is secured such that the surface of the insert at the leading end of the device defines a part of, and is exposed at, a die cavity defined by the installation.

33. An installation according to claim 31 , wherein the die component defines at least two bores in each of which a respective said device is secured.

34. An installation according to claim 32 or claim 33, wherein the installation is for low pressure die casting and the die component is an upper die component.

35. An installation according to claim 34, wherein the installation has a lower die components having a device according to any one of claims 2 to 6.