Andersen, Uffe (Amtsvejen 82 Merløse Skævinge, DK-3320, DK)
| 1. | Method of casting articles having an axis of rotational symmetry (15) in a string (12) of vertically parted sand mould parts (5) of a mouldstring plant, the sand mould parts (5) defining between them at least one runner (9) and at least one mould cavity (6), eventually provided with one or more cores (13, 14), characterised by the steps of arranging the at least one mould cavity (6) such that said axis of symmetry (15) is substantially vertical, arranging the most downstream part of the runner (9) to fall substantially together with said axis of symmetry (15), and introducing molten metal into the mould string (12) to fill the casting cavities (6). |
| 2. | Method according to claim 1, characterised in that the molten metal is introduced into the mould string (12) by countergravity delivery. |
| 3. | Method according to claim 2, characterised in that the runner (9) debouches into the centre of the at least one mould cavity (6). |
| 4. | Method according to claim 2, characterised in that the runner (9) splits into a number of radial channels through which the molten metal enters the at least one mould cavity (6). |
| 5. | Method according to claims 2 to 4, characterised in that the runner (9) continues upwardly from the centre of the mould cavity (6) to form an feeder (21,22). |
| 6. | Method according to any of claims 1 to 5, characterised in that the mould cavities (6) are placed in the mould string (12) one above another in one or more stacks (8). |
| 7. | Method according to claim 6, characterised in that the runner (9) continues upwardly from the centre of the lowest mould cavity (6) of a stack to the centre of each of the casting cavities (6) above the lowest mould cavity (6). |
| 8. | Method according to any of claims 1 to 7, characterised in that at least one core (13,14) is provided in the mould cavity (6), placed within the circumference of the article to be cast to form at least a part of the side surface of the article. |
| 9. | Method according to claim 8, characterised by two cores (13,14) being provided in the mould cavity (6), each core (13,14) being placed within the circumference of the article to be cast to form at least a part of the respective side surface of the article. |
| 10. | Method according to claim 9, characterised in that the two cores (13,14) rest upon one another. |
| 11. | Method according to any of claims 1 to 10, characterised in that the mould parts (5) are of the boxless type. |
| 12. | Mould string of vertically parted sand mould parts (5) of a mouldstring plant for casting articles having an axis of rotational symmetry (15), the mould string (12) defining at least one mould cavity (6) and a runner (9) between the sand mould parts (5), the at least one mould cavity (6) optionally being provided with one or more cores (13,14), characterised in that the axis of symmetry (15) is arranged substantially vertically and the most downstream part of the runner (9) being arranged to fall substantially together with said axis of symmetry (15). |
| 13. | Mould string according to claim 12, characterised in that the molten metal is introduced into the mould string (12) by countergravity delivery. |
| 14. | Mould string according to claim 13, characterised in that the runner (9) discharges the molten metal into the centre of the at least one mould cavity (6). |
| 15. | Method string according to claim 13, characterised in that the runner (9) splits into a number of radial channels through which the molten metal enters the at least one mould cavity (6). |
| 16. | Mould string according to claims 13 to 15, characterised in that the runner (9) continues upwardly from the centre of the mould cavity (6) to form an feeder (21,22). |
| 17. | Mould string according to any of the claims 12 to 16, characterised in that the casting cavities (6) are placed in the mould string (12) one above another in one or more stacks (8). |
| 18. | Mould string according to claim 17, characterised in that the runner (9) continues upwardly from the centre of the mould cavity (6) of a stack to the centre of each of the casting cavities (6) above the lowest mould cavity (6). |
| 19. | Mould string according to any of claims 12 to 18, characterised in that at least one core (13,14) is provided in the mould cavity (6) placed within the circumference of the article to be cast to form at least a part of the side surface of the article. |
| 20. | Mould string according to claim 19 characterised by two cores (13,14) being provided in the mould cavity (6), each core being placed within the circumference of the article to be cast to form at least a part of the respective side surface of the article. |
| 21. | Mould string according to claim 20, characterised in that the two cores (13,14) rest upon one another. |
| 22. | Mould string according to any of claims 12 to 21, characterised in that the mould parts are of the boxless type. |
| 23. | Article cast in a mould string (12) according to claims 12 to 22. |
| 24. | Article cast with the method according to claims 1 to 11. |
| 25. | Article according to claim 23 or 24, characterised in that the article is a wheel. |
| 26. | Article according to claim 25, characterised in that the article is a lightalloy wheel. |
| 27. | Article according to claim 26, characterised in that the article is a lightalloy wheel for a motor vehicle. |
BACKGROUND ART Vertically parted mould parts, e. g. green sand mould parts of a mould-string plant like the"DISAMATIC"moulding plant manufactured and marketed by the applicants, are used for casting articles with a great variety of shapes. The Application Manual of the DISAMATIC 2070 MK2-B discloses a method of casting articles having an axis of symmetry such as differential case castings, gear wheels, wheels for motor vehicles, brake drums, or clutches with the axis of rotational symmetry being arranged horizontal. The runner is for practical reasons normally formed in the parting surfaces of the mould. Consequently, the runner must meet the mould cavity at its often relatively thin circumferential periphery and the molten metal is introduced into the thin circumferential peripheral area of the flat article. The orifice at the point where the runner meets the mould cavity, through which the molten metal enters the mould cavity, is thus a narrow slot and has consequently a small cross-sectional area. When casting for example light-alloy wheels, which have a relatively low wall thickness at their circumference compared to the hub in the centre of the wheel, all the molten metal has to flow through a narrow opening at the circumference into the mould cavity. Moreover, the molten metal has a long way to go to reach the opposite side of the article. Due to these two factors the filling rate is low and problems arise for example with early solidification.
DISCLOSURE OF THE INVENTION It is the object of the invention to provide a method and a mould string for casting articles having an axis of rotational symmetry in which the above mentioned problems are avoided or at least considerably reduced. This object is achieved with the method according to claim 1 and a mould string according to claim 12.
By arranging the axis of symmetry substantially vertically, and by arranging the most downstream part of the runner to fall substantially together with the axis of symmetry, it is possible to arrange the opening of the runner into the mould cavity in the central part of the article. Thus, an opening of the runner into the mould cavity with a relatively large cross-sectional area can be used so that the mould cavity can be filled up quickly without exceeding the limits of the flow speed.
Further, by arranging the opening of the runner into the mould cavity central, the maximum distance between the opening and the periphery of the mould cavity is reduced.
In the method and the mould string, the molten metal may according to an embodiment be introduced by counter-gravity delivery.
The runner continues in an embodiment upwardly from the centre of the mould cavity to form a feeder.
The casting cavities may according to an embodiment be placed in the mould string, one above another in one or more stacks.
The runner continues in an embodiment upwardly from the centre of the lowest mould cavity of a stack to the centre of each of the casting cavities above the lowest mould cavity. Between the mould cavities in a stack, the runner can be formed with an enlarged cross-sectional area to form feeders for the mould cavity below.
At least one core may be provided in the mould cavity placed within the circumference of the article to be cast from a part of the side surface of the article.
Alternatively, two cores may be provided in the mould cavity, placed within the
circumference of the article to be cast to form a part of the respective side surface of the article. According to an embodiment, the two cores rest upon one another.
Articles that can be produced with the method and the mould string are for example light-alloy wheels for a motor vehicle. The method and the mould string offer in particular advantages in connection with casting such light-alloy wheels. The cores, which are usually made of a finer sand quality than the mould parts, are in accordance with the invention placed on the sides of the wheel to be cast. This is particularly advantageous since the side wheel that will be visible when the wheel is used on a motor vehicle has the highest surface quality demands. The finer sand quality of the core facilitates obtaining the required surface quality of the visible side of the wheel. A further advantage of placing the cores at the side of the wheel is that the core defines the"design"of the visible side of the wheel. Nowadays, a wide variety of designs are offered in order to comply with the customer trends and demands. Hereto only the design of the side surface is changed, while the rest of the wheel remains unchanged. Thus, the method and mould according to the present invention offer an advantage in that the"design"of the visible side of the wheel can be changed by simply interchanging the core.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a diagrammatic side view of a mould-string plant, Fig. 2 shows a detailed cross-sectional view of a part of a mould string with cast articles including the runner therein in accordance with the invention, Fig. 3 shows a view at the parting surface of one mould part with two cast articles including the runner and the cores therein, with the other mould part that defined the mould cavity being removed, Fig. 4 shows an elevated view of two cast articles together with the runner, and Fig. 5 shows an exploded view of the cores.
DETAILED DESCRIPTION OF THE INVENTION Fig. 1 is a diagrammatic longitudinal sectional view through a string moulding plant
comprising a combined mould making and casting apparatus, e. g. of the "DISAMATIC @"type. This apparatus as such is dealt with in GB-848,604, which describes the mode of operation, and for this reason it is only dealt with briefly in this specification.
Box-less mould parts 5 made from green sand, i. e. sand with moist clay as binder supplied from a hopper 1 to a moulding chamber 2 defined between a pattern located on a movable piston 3 and a pattern located on a movable and upwardly pivotable counter pressure plate 4 in a downwardly pivoted position (not shown) of the counter pressure plate 4. In the moulding chamber 2, the green sand is compacted by the piston 3 to form a mould part 5, the counter-pressure plate is conveyed forward and pivoted upwards to the position shown in Fig. 1, after which the mould part is conveyed by the piston 3 to abut against the mould string formed by previously produced mould parts 5, said mould strings being conveyed over a distance corresponding to the thickness of a mould part 5 in the direction indicated by the arrow A. In the mould string, the front side of a mould part 5 together with the rear side of the previous mould part 5 defines at least one mould cavity 6 and a runner 9 for guiding the molten metal to a mould cavity 6.
It will be appreciated that the casting of the mould cavity 6 takes place while the mould string is stationary, i. e. within the intervals between each time the piston 3 advances the mould string through a distance corresponding to a thickness of a mould part 5 in the direction of the arrow A.
The filling takes place at a filling station (not shown) after which the mould parts are further advanced stepwise through a casting zone to a shake-out grill (not shown).
According to a preferred embodiment, the molten metal is supplie to the mould cavity by counter-gravity delivery. Hereto, the casting apparatus comprises a heated and sealed reservoir containing molten metal and comprises in short the following operational components: -A supply of molten metal contained in a substantially closed furnace 7, -A source of gas in the pressure 17 for supplying gas under the pressure to apply a suitably controlled gas pressure to the space inside the fumace so as to cause the molten metal to flow out,
-A filling tube 10 extending upwardly to a mouthpiece 11 adapted for temporary connection to the mould being in a position for filling, and -A shutter mechanism to close the inlet after filling the mould to enable forward transportation of the mould string before the inlet freezes naturally.
Optionally, one or more cores 13,14 are placed in the mould cavity as shown in Fig.
1 by a core setter apparatus (not shown).
Turning now to Fig. 2 which shows a cross-sectional view of a part of the mould string in more detail. Two mould parts 5 together define the mould cavities 6, the runner 9 and the gating system. As can be best seen from Figures 3 and 4, the runner 9 starts at the lower part of the side of the mould string and continues upwardly towards the centre of the mould cavity 6 of the lower one of the moulding cavities 6. The runner is provided with a feeder 20. The runner 9 continues with an enlarged section 21 which functions as an feeder for the lowest mould cavity, thereafter continues towards the higher mould cavity. The runner 9 continues then with an enlarged section 22 functioning as a feeder for the upper mould cavity 6.
The article, in this case a light-alloy wheel for a vehicle, is placed in the mould string such that the axis of symmetry of the wheel is substantially vertical. The runner 9 meets the mould cavity 6 at the centre of the wheel and thus at the place where the wall thickness of the wheel is highest. Thus, the orifice between the mould cavity 6 and the runner 9 is as large as possible. The massive central part of the wheel can thus be cast relatively quickly without causing too high flow velocities, i. e. without creating turbulent flow. From the central part of the wheel, the molten metal flows through the spokes which are obscured in Figure 2 by the parts of the cores 13,14 filling the space between the spokes to the rim of the wheel. The rim of the wheel is relatively thin-walled and extends over a relatively long distance, so that it is advantageous that the rim is filled through many channels formed by the spokes.
The rim can thus be filled relatively quickly because there are many inlets to the part of the mould cavity that forms the rim. The rim can be better seen in Fig. 4 which shows the cast wheels together with the runner 9 and the feeders without the mould 5 and the cores 13,14.
Light-alloy metals shrink relatively a lot during cooling down and solidification. The central hub of the light-alloy wheel is the most massive part of the article and
consequently, it has the highest need for after feeding in order to compensate for shrinkage during solidification of the molten metal. By placing the feeders 21 and 22 directly above the casting cavities 6, this need is met in an optimum manner.
Fig. 5 shows an exploded view of the stack of cores 13,14. A core 13 is used to define the side surface of the wheel that will be visible when the wheel is used on an automotive vehicle. The core 13 of the upper mould cavity 6 rests on the core 14 forming the other side surface of the wheel, i. e. the side facing towards the vehicle.
This second core 14 rests directly on the core 13 of the mould cavity 6 below. This core 13 which forms the visible side surface of the lower wheel rests again directly on the core 14 of the lower mould cavity 6 which forms the inner not visible side surface of the lower wheel. The visible side surface of the wheel is thus formed by the core 13. The cores are usually made of a finer sand-quality. Consequently, the surface quality of the wheel is highest at the place where it is required.
According to an embodiment of the invention (not shown), more than one stack of cores and cavities is formed between two mould parts 5. It is also possible to have more than two casting cavities 6 in one stack. This is both possible with only one stack formed between two mould parts 5 and with the embodiment with more than one stack of moulding cavities formed between two mould parts 5.
When there is a need to change the design of the visible side surface of the wheels, the production may be changed very quickly by setting new cores 13,14 in the moulding cavities which have the shape according to the new design. The mould parts 5 do not need to be changed if only the design of the wheel is changed. The mould parts 5 only have to be changed if the size, i. e. width or diameter, of the wheel has to be changed. Therefore, with one single type of mould parts and a variety of cores, a corresponding variety of designs of wheels can be produced.
LIST OF REFERENCE NUMERALS 1 HOPPER 2 MOULDING CHAMBER 3 MOVABLE PISTON 4 COUNTER-PRESSURE PLATE 5 MOULD PART 6 MOULD CAVITY 7 FURNACE 8 STACK 9 RUNNER <BR> <BR> <BR> <BR> <BR> 10 FILLING TUBE<BR> <BR> <BR> <BR> <BR> 11 MOUTHPIECE 12 MOULD STRING <BR> <BR> <BR> <BR> <BR> 13 CORE<BR> <BR> <BR> <BR> <BR> 14 CORE 15 AXIS OF SYMMETRY 16 RESERVOIR 17 SOURCE OF GAS UNDER PRESSURE 20 FEEDER 21 FEEDER 22 FEEDER
Next Patent: CO-SINTERING OF SIMILAR MATERIALS