A METHOD FOR COMPACTING MOULDING SAND

Abstract: The invention relates to a method for compacting moulding sand in a moulding box in which a model is present, which model is embedded in moulding sand. The moulding box is thereby vibrated by means of imbalance weights, which are each to be rotated about an axis of rotation during operation. At least four imbalance weights being rotatable about parallel axes of rotation are used, which can be shifted in phase relative to each other.

Description: A method for compacting moulding sand. The invention relates to a method for compacting moulding sand in a moulding box in which a model is present, which model is embedded in moulding sand, wherein the moulding box is vibrated by means of imbalance weights, which are each to be rotated about an axis of rotation during operation. The term imbalance weight is understood to mean a mass to be rotated about an axis of rotation by means of a suitable driving source, whereby the centre of gravity of said mass is located some distance away from the axis of rotation in question. As is described in US patent no. 4,600,046, such a method is used in particular when using foam models, which evaporate when molten metal is poured into the moulding box, whereby the vapours being formed will escape through the compacted moulding sand. With the construction described in US patent no. 4,600,046, the moulding box is supported on a spring-supported platform. A vibrating unit, which comprises two imbalance weights rotating in opposite directions during operation, is connected to the moulding box at a point located some distance above the springing platform. The two imbalance weights rotating in opposite directions generate a horizontally oriented vibration force during operation, which can only be varied in magnitude by increasing the frequency or by shifting the imbalance weights relative to each other during standstill of the device, but as a result of the spring support of the moulding box by means of the springing platform, it will not be possible to prevent the moulding box from making a tumbling movement as well during operation. Furthermore, when the counterweights are rotating, a vibration force only in substantially horizontal direction will constantly be generated. According to the invention, at least four imbalance weights are used, which can be shifted in phase relative to each other. When using the method according to the invention, vibration in vertical direction as well as in horizontal direction can be generated as desired, whereby also the magnitude of the vibration force can be varied independently of the frequency of the movement of the imbalance weights. Preferably, this will be done in such a manner that the resulting vibration force will pass through the centre of gravity of the moulding box. Furthermore it is possible to arrange that no vibration forces will be exerted on the moulding box when the imbalance weights are rotating, which makes it possible in an advantageous manner to run the imbalance weights up to the desired speed first, and only then produce a vibration force by means of the imbalance weights. It is possible thereby to avoid vibration of the moulding box at a frequency corresponding with the natural vibration frequency of the moulding box during the starting and stopping of the rotation of the imbalance weights, whereby undesirable movements affecting the intended compacting of the moulding sand may occur. According to another aspect of the invention, a device which is particularly suitable for carrying out the above-described method comprises a frame for supporting a moulding box, whilst the frame supports four imbalance weights which are rotatable about axes of rotation extending parallel to each other, and means are provided for driving the imbalance weights and shifting them in phase relative to each other. The invention will be explained in more detail with reference to the accompanying figures. Figures 1 - 9 diagrammatically show various possibilities for rotating and shifting imbalance weights relative to each other when using the method according to the invention. Figure 10 is a diagrammatic sectional view of a device in which a moulding box can be clamped down, and by means of which the method according to the invention can be used. Figure 11 is a sectional view of Figure 10, seen along line XI-XI in Figure 10. Figures 1 - 9 diagrammatically show a moulding box 1 to be vibrated, as well as four imbalance weights 2 - 5. Two imbalance weights 2, 3 are disposed one above the other on one side of moulding box 1, and the two other imbalance weights 4 and 5 are disposed one above the other on the other side of moulding box 1, thus effecting a symmetric position of the imbalance weights relative to moulding box 1. As is indicated by arrows A and B, the imbalance weights 2 and 3 rotate in opposite directions in the embodiment according to Figures 1 - 6. Similarly, imbalance weights 4 and 5 of the embodiments shown in Figures 1 - 6 likewise rotate in opposite directions, as is indicated by means of arrows C and D. Each of the imbalance weights 2 - 5 is driven by its own power source, for example an electric motor. The rotational speeds of the various imbalance weights can be adjusted independently of each other. The construction is thereby such that the number of revolutions per unit time of an imbalance weight can be briefly increased and/or decreased as desired during operation, independently of the speed at which the other imbalance weights are driven, for a purpose yet to be described in more detail . In the arrangement of the imbalance weights 2- 5 which is shown in Figure 1, the two imbalance weights 2 and 3 disposed one above the other are in phase with each other, and the same applies to the two imbalance weights 4 and 5 disposed one above the other, whilst imbalance weights 4 and 5 are shifted 180 ° with respect to imbalance weights 2 and 3. If the imbalance weights arranged in this manner are rotated in the directions indicated by arrows A, B, C and D, the forces generated by the imbalance weights will be in equilibrium, so that no vibration force will be exerted on the moulding box. This arrangement of the imbalance weights 2 - 5 will be used when the vibration is started and when the vibration is stopped, which makes it possible when accelerating or decelerating the imbalance weights to a desired speed to prevent a vibration force being exerted on the assembly of moulding box and on the means supporting the moulding box at a frequency which corresponds with the natural frequency of said assembly. The fact is that such an event might severely disturb the obtained compactness of the moulding sand, in particular during deceleration of the imbalance weights. In this arrangement of the imbalance weights, the moulding box may also be placed into and/or removed from a frame (as described hereafter) supporting the moulding box, without having to stop the motors driving the imbalance weights. Starting from the position of imbalance weights 2 - 5 which is shown in Figure 1, the rotating imbalance weights 2 and 3 can for example be shifted in opposite directions through and angle β of 90 ° relative to each other, as shown in Figure 2, so that imbalance weight 3 lags 180 ° in phase relative to imbalance weight 2. The counterweights 4 and 5 are thereby maintained in the relative positions as shown in Figure 1. When the imbalance weights arranged in this manner are rotating, the forces generated by imbalance weights 2 and 3 will offset each other, whilst the two rotating imbalance weights 4 and 5 will generate a force F = ^Fmax. Another possible arrangement of the imbalance weights is shown in Figure 3, wherein the rotating imbalance weights 2 and 3 are shifted through 180 ° relative to the position shown in Figure 1, so that they are in phase with imbalance weights 4 and 5. When the imbalance weights arranged in this manner are rotating, the force generated in horizontal direction will be F = Fmax. In the arrangement of the rotating imbalance weights which is shown in Figure 4, imbalance weights 2 and 4, which are disposed one beside the other, are in phase with each other, whilst imbalance weights 3 and 5, which are likewise disposed one beside the other, being in phase with each other, are shifted in phase through 180 ° relative to imbalance weights 2 and 4. When the imbalance weights 2 - 5 arranged in this manner are rotating again in the direction of indicated by arrows A, B, C and D respectively, the forces generated by the rotating imbalance weights will offset each other, so that no vibration force will be exerted on moulding box 1. When, starting from the above-described arrangement as shown in Figure 4, two imbalance weights disposed one beside the other, imbalance weights 3 and 5 in the embodiment of Figure 5, are shifted in phase in opposite directions through an angle β of 90 ° relative to the arrangement as shown in Figure 4, the forces generated by imbalance weights 3 and 5 will offset each another during rotation of the imbalance weights arranged in this manner, and the two imbalance weights 2 and 4 will generate a vertically oriented vibration force of a magnitude F WFmax. Another possibility is to shift the imbalance weights 3 and 5 from the position shown in Figure 4 through an angle β of 180 ° , as is shown in Figure 6, so that all imbalance weights will be in phase with each other. In this arrangement, the rotating imbalance weights will generate a vertically oriented vibration force F = Fmax. It will be apparent that the above-described arrangement and configuration of the rotating imbalance weights during operation makes it possible to choose whether or not to subject moulding box 1 to a vibration force while the imbalance weights are rotating, whereby both the magnitude and the direction of the vibration force being exerted can be varied independently of the frequency of the vibration force at a constant rotational speed of the imbalance weights. The magnitude of the vibration force will depend on the rotational speed of the rotating imbalance weights, of course. Figures 7 - 9 show an arrangement wherein the counterweights 2 and 3 disposed on one side of moulding box 1 rotate in the same direction, as indicated by arrows E and F, whilst the counterweights 4 and 5 disposed one above the other likewise rotate in one direction as indicated by arrows G and H, albeit in a direction opposed to the direction of rotation of imbalance weights 2 and 3. In the arrangement which is shown in Figure 7, the two imbalance weights 2 and 4 disposed on either side of moulding box 1 are in phase with each other, as are the two imbalance weights 3 and 5 disposed on either side of moulding box 1, whereby imbalance weights 3 and 5 are shifted in phase through 180 ° relative to imbalance weights 2 and 4, however. In this arrangement of the imbalance weights, the forces generated in the direction indicated by the arrows during rotation of the imbalance weights will offset each other, so that no vibration force will be exerted on moulding box 1, even though the imbalance weights are rotating. Two imbalance weights disposed on beside the other, the lower imbalance weights 3 and 5 in Figure 8, can be shifted in phase in opposite directions through an angle β of 90 ° relative to each other from the position shown in Figure 7. In this arrangement, the forces generated by rotating imbalance weights 3 and 5 will offset each other, whilst the rotating imbalance weights 2 and 4 will generate a vertical vibration force of a magnitude FWFmax. According to another possibil ity, two imbalance weights disposed one beside the other, the lower imbalance weights 3 and 5 in Figure 9, are shifted in phase through an angle β of 180 ° from the position shown in Figure 7, so that all four imbalance weights 2 - 5 will be in phase with each other. In this arrangement of the imbalance weights, the imbalance weights will exert a vertically oriented vibration force F = Fmax on moulding box 1. It will be apparent that also with the arrangement and direction of rotation of the imbalance weights as shown in Figures 7 - 9, the magnitude of the vibration force can be changed independently of the frequency of the vibration force, whilst also an arrangement wherein no vibration force at all is exerted on the moulding box during rotation of the imbalance weights is conceivable. Figures LO and 11 diagrammatically show a device for carrying out the method. The device comprises two spaced-apart supports 6 and 7, which are attached to foundation beams 8 which are anchored in the ground. Supports 6 and 7 support a supporting frame 9, which, as is shown in Figure 10 as well as in Figure 11, comprises a symmetrical construction with respect to a vertical centre plane. Frame 9 thereby comprises two vertical and parallel frame-shaped side walls 10 and 11, which are spring-supported in supports 6 and 7 by means of supports 12 and 13 respectively. The spaced-apart side walls 10 and 11 are interconnected by two frame-shaped connecting walls 14 and 15 disposed one above the other and extending in horizontal direction, seen in Figures 10 and 11, and by parallel cross walls 16 and 17, which are provided with a large number of holes. The above walls thereby bound a space 18, in which a moulding box 1 containing a model and moulding sand can be arranged and vibrated. Supports 19, on which the moulding box can be placed, are attached to cross walls 16 and 17 for the purpose of supporting the moulding box. Clamping elements 20 for clamping down the moulding box on supports 19 are furthermore provided some distance above supports 19, which clamping elements are mounted on the ends of levers 22, which can pivot about horizontal pins 21. Levers 22 can be pivoted by means of setting elements 23 of any desired form. It will be apparent that once a moulding box is present on supporting elements 19, the clamping elements 20 can be pressed against the moulding box by means of setting elements 23 so as to clamp the moulding box down firmly in space 18 of frame 9. As is furthermore apparent, in particular from Figure 10, horizontally extending supporting plates 24 and 25 are secured to the sides of cross walls 16 and 17 that face away from each other, on which supporting plates the motors 26 - 29 for driving the counterweights 2 - 5 (not shown), which are likewise supported by supporting plates 24, 25, are mounted. It is preferred to use electric motors, which can be controlled by means of a control unit which is known per se, in such a manner that a brief deceleration or acceleration of the rotating motors can be effected so as to shift the imbalance weights in the manner described above. It will be apparent, that the moulding box and its contents, which is thus clamped down in frame 9, can be vibrated as desired in the above-described manner. Preferably, the construction of frame 9 and the arrangement of the imbalance weights are thereby such that the resulting vibration force generated by the imbalance weights passes at least substantially through the centre of gravity of the filled moulding box.

Claims: CLAIMS . 1. A method for compacting moulding sand in a moulding box in which a model is present, which model is embedded in moulding sand, wherein the moulding box is vibrated by means of imbalance weights, which are each to be rotated about an axis of rotation during operation, characterized in that at least four imbalance weights are used, which are rotatable about parallel axes of rotation and which can be shifted in phase relative to each other. 2. A method according to claim 1, characterized in that said moulding box is placed between said imbalance weights, in such a manner that two imbalance weights are arranged symmetrically on either side of the moulding box. 3. A method according to claim 2, characterized in that two imbalance weights disposed on one side of said moulding box are rotated in opposite directions during operation. 4. A method according to claim 3, characterized in that the imbalance weights disposed on either side of the moulding box are positioned one above the other, and that the two upper imbalance weights disposed on either side of the moulding box as well as the two lower imbalance weights disposed on either side of the moulding box are rotated in opposite directions relative to each other. 5. A method according to any one of the preceding claims, characterized in that said imbalance weights are rotated whilst the imbalance weights disposed on the same side of the moulding box are in phase with each other and 180 ° off phase relative to the imbalance weights disposed on the other side of the moulding box, which are in phase with each other. 6. A method according to claim 5, characterized in that once a specified rotational speed of the imbalance weights is reached, two imbalance weights disposed on either side of the moulding box are shifted in phase through 90 ° or 180 ° . 7. A method according to claim 1 or 2, characterized in that the imbalance weights disposed on one side of the moulding box are rotated in the same direction during operation, as are the imbalance weights disposed on the other side of the moulding box, wherein the direction of rotation of the imbalance weights disposed on said one side of the moulding box is opposed to the direction of rotation of the imbalance weights disposed on the other side of the moulding box. 8. A method according to claim 7, characterized in that the imbalance weights are rotated with the imbalance weights disposed on a respective side of the moulding box being 180 ° off phase, whilst imbalance weights disposed on either side of the moulding box are in phase in pairs. 9. A method according to claim 8, characterized in that once the imbalance weights are rotating, two imbalance weights disposed on either side of the moulding box are shifted in phase through 90 ° or 180 ° . 10. A method according to any one of the preceding claims, characterized in that the position of the imbalance weights relative to the moulding box is selected such that the resulting vibration force passes at least substantially through the centre of gravity of the moulding box. 11. A device, in particular for carrying out a method according to any one of the preceding claims, characterized in that said device comprises a frame for supporting a moulding box, whilst the frame supports four imbalance weights which are rotatable about axes of rotation extending parallel to each other, and means are provided for driving the imbalance weights and shifting them in phase relative to each other. 12. A device according to claim 11, characterized in that said frame comprises a box-shaped supporting frame, in the interior of which a moulding box can be disposed. 13. A device according to claim 12, characterized in that said supporting frame comprises two walls extending parallel to each other, which walls bound the space in which the moulding box can be disposed, whilst imbalance weights and motors driving said imbalance weights, which are supported by said walls, are mounted on the sides of said walls that face away from each other. A device according to any one of the claims 11 - 13, characterized in that the frame comprising the imbalance weights connected thereto is of symmetrical construction.

Inventors: VAN HEEREVELD DANIEL JACOBUS P, VAN HEEREVELD, DANIEL, JACOBUS, PETRUS
Applicants: GEMERT JOHANNES GERARDUS VAN, HEEREVELD DANIEL JACOBUS PETRU, VAN GEMERT, JOHANNES, GERARDUS, VAN HEEREVELD, DANIEL, JACOBUS, PETRUS
Application year: 1998
Main classification: B22C15
IPC codes: B22C15