FR2591133A1 - Method and machine for manufacturing a foundry half-mould by means of green sand moulding - Google Patents

Abstract

Foundry. The machine according to the invention comprises: - a means 31 for support and guiding carried by the frame, superposed on and parallel to the means 14 and extending under the filling station and the compacting head, - a sand filling frame 32 movable on this means 31, - a scraping means 36, - and a pressing plate 33 carried by the means 31. Application to machines for moulding by means of compacting by shock wave.

Description

 The present invention relates to the technical field of manufacturing sand molds for obtaining castings.

 In this technique, the general problem to be solved is that of making a sand mold whose imprint is the most faithful and precise possible reproduction of the model and keeps this characteristic, even during the casting of the molten metal, so that the casting obtained is the exact representation of the model.

 In other words, the problem to be solved is that of making a sand mold, the imprint of which undergoes little or, preferably, no deformation, at the time of the production of the mold, its handling and its setting. in work or use.

 The current technique for manufacturing a mold by green sand molding can be briefly described as consisting in producing at least one open mold and, more generally, two complementary half-molds which are then assembled by any suitable means for delimit together and, on either side of their joint plane, the overall casting footprint.

In what follows, the phrase "mold element" will be used to designate any type of green sand mold.

 Each mold element is made from a mixture of sand and additional components comprising, mainly, water, bentonite and adjuvants known to those skilled in the art. For reasons of convenience, the mixture is referred to as sand in the following.

 A determined dose of sand is poured into a molding box formed by a frame comprising a frame placed on a bottom plate bearing the positive representation of the model. The sand is then compacted by one or more compaction processes by pressing, shaking, blow-blowing or shock wave produced by the explosion of a gas or the sudden expansion of a compressed fluid acting on the upper layer of the mixture.

 It seems that the shock wave compaction process is the one that currently provides the best results.

 One of the particular advantages of this process lies in the fact that this compaction method makes it possible to confer increasing cohesion and compaction with the depth of the layers from the surface of application of the shock wave. This is favorable for maintaining a certain porosity necessary for the evacuation of gases and fumes during the casting of the molten metal into the cavity.

 The analysis of the results obtained by the implementation of this process makes it possible, however, to note that it is not yet fully satisfactory for the following reasons.

 First of all, scraping must be carried out after demolding the model, so as to give the mold element and opposite the impression, a flat face necessary for its handling and its subsequent support. This scraping phase subjects the compacted mass of sand to a stress generally applied in an inclined direction resulting from the application of vertical pressure and relative horizontal translation. This constraint has the effect of causing a deformation of the imprint when the latter is separated from the scraped upper layer by a relatively small thickness of compacted sand. Indeed, in such a case, the application pressure and its direction tend to repel and repress the compacted layers of sand forming this thickness and to cause a local deformation of the imprint of the mold element. first drawback.

 As mentioned above, the shock wave compaction process gives increasing compaction from the layers underlying the upper application surface of the wave to the layers forming the plane of the joint. the mold element and corresponding to the sand in contact with the model plate.

Thus, when the imprint to be delimited involves a large thickness of layers, those corresponding to the bottom of the imprint considered from the surface corresponding to the joint plane, will be less compacted than those close to this surface.

 If this is favorable for the evacuation of gases and fumes, on the other hand, when a mold is made up of two complementary mold elements produced in this way, the lower half-mold will also have your same characteristics. This therefore amounts to saying that the less compacted layers of the imprint of the lower half-mold will be those which will have to withstand the greatest metallostatic pressure during the casting of the molten metal.

It will therefore inevitably result in a deformation of the imprint of the lower half-mold. This is a second drawback.

 Thus, the shock wave and scraping compaction process, as recalled above, does not make it possible to solve the problem posed, because it leaves two significant risks of deformation of the imprint remaining at manufacturing stages at which none retouching cannot then be made.

 Furthermore, in the above process, it is understood that each mold element obtained or at least one dg two to be paired must be the subject of an additional intervention aimed at sparing the pouring cone allowing the introduction of molten metal into the footprint.

 Generally, this intervention includes a milling operation carried out from the erected upper surface of the mold element to provide a cone opening into a duct or jet which is delimited in the mold element, in relation to the imprint, by a shape carried by the model plate.

 This milling operation is also sometimes responsible for a deformation of the impression, depending on the conformation of the latter and the choice of the position of the casting jet. Furthermore, the execution of the cone by milling leads, inevitably, to leaving inside the cone, in the casting jet and also sometimes in the imprint, particles of sand which are subsequently responsible for poor quality. of the part obtained by inclusion in the metallic mass of these sand particles.

 The object of the invention is to remedy the drawbacks of the manufacturing technique by shock wave compaction and scraping, in order to eliminate the risks of deformation of the imprint during manufacture.

To achieve this objective and, consequently, to solve the general problem posed, the invention proposes improvements to the known method and consisting in producing each mold element in such a way that interventions on the mass of compacted sand intervene, in all cases. , before demoulding of the model plate, so as to eliminate the risk of deformation of
The footprint during manufacturing.

 The improved method according to the invention also consists in involving a post-compacting phase making it possible to impart greater compactness to the layers corresponding to the "bottom" of the imprint, so as to give these layers sufficient cohesion for resist the metallostatic casting pressure when the half-cavity constitutes after pairing with a complementary mold element the lower half-cavity.

 In order to preserve the good homogeneity of the precompaction in the shock wave compaction process, the process according to the invention provides that the post-compaction phase only takes place after the removal by scraping of an excess layer of sand. .

The quantity left, after this scraping, for the post-compaction, is adjustable and between 2 and 10% of the final height of the mold element to be obtained. This setting allows, after
Post-compaction, optimum and reproducible hardness of the imprint.

 The method of the invention also aims to eliminate the intervention phases by milling and proposes, in this sense, to execute by punching, during the post-compacting phase, the different complementary impressions provided from the upper surface. erect of a half-mold.

To achieve the above goals, the method of the invention consists in
- fill the box with a load such as after
compaction, the upper level of compacted sand
is located above the joint plane between the
between the chassis and the riser,
- clear, at least partially, the enhancement
after compaction by vertical displacement
relative,
- subject the upper layer of compacted sand
scraping while leaving a thickness
determined surplus,
- exert by a clamping plate a force of
pressing on the scraped upper surface of the
compacted sand,
- release the model plate,
- then to evacuate the chassis and the half-mold
manufactured it contains.

The invention also relates to a machine for implementing the method, characterized in that it comprises
- a means of support and guidance carried by the
frame, superimposed and parallel to the middle and
extending under the filling station and the
compaction head,
- a mobile extension on this means,
- a scraping means,
- And a pressing plate carried by the means.

 Various other characteristics will emerge from the description below made with reference to the appended drawings which show, by way of nonlimiting example, an embodiment of the subject of the invention.

 Fig. 1 is a longitudinal sectional elevation of the machine according to the invention.

 Fig. 2 is a cross section taken, substantially along the line II-II of FIG. 1.

 Figs. 3 to 9 are schematic views illustrating the implementation of the method according to the invention.

 According to fig. 1 and 2, a machine for manufacturing a foundry mold element by green sand molding, according to the method of the invention, may comprise a frame 1 of any suitable shape, which is illustrated by two side plates 2 joined together between them by spacers or cross members 3. The frame 1 supports, at its upper part, a station 4 doser-distributor of sand, which can be constituted by a simple transfer hopper or, again, by a tank hopper associated with a dosing and dispensing mechanism. The frame 1 supports, moreover, a compacting head 5 which is arranged parallel to the vertical axis of the station 4. The compacting head 5 comprises a lower expansion chamber 6 whose open base is defined by a support flange 7.The top of the expansion chamber 6 is formed by a partition 8 separating this chamber from a reservoir 9 for storing a charge of compressed fluid. The reservoir 9 can be connected to a source of distribution of a compressed fluid, such as air, by a pipe 10 equipped with a valve 11.

 The partition 8 delimits at least one and, preferably, several passages 12 controlled by as many shutters 13 which are, for example, of the valve type. The abrupt opening of these valves can be ensured in various ways known in the art of shock wave compaction heads.

 The machine for implementing the invention comprises means 14 for supporting, presenting and transferring a molding frame from station 4 to the compacting head 5. In the present case, the frame is , mainly, constituted by a frame 16. The means 14 comprise a guide track 17 which is, for example, constituted by two rails 18 fixed on the plates 2. The guide track 17 extends under the station 4 and under the compaction head 5 and supports a mobile assembly 19 which can be brought directly above the station 4 or the compaction head 5. The mobile assembly 19, associated with a drive mechanism 20, comprises a cradle 21 supporting at least a hydraulic cylinder 22 with a vertical axis, the piston rod 23 of which can be controlled in adjustable extension-retraction strokes. The rod 23 supports a horizontal table 24 on which a removable base plate 25 can be mounted. The plate 25 supports, on its upper face, a partial model 26 corresponding to the positive shape of the imprint to be formed in a mold element to be manufactured. In general, the partial model 26 is associated with a shape 27 whose subsequent function is to provide a blind hole or casting jet in the half-mold.

 The cradle 21 delimits, at its upper part, a section 28 of the track extending in a horizontal plane superimposed on the track 17 and in a direction perpendicular to the latter. The section 28 is normally placed, when the crew 19 is in the standby position under the station 4, between a supply conveyor 29 and an evacuation conveyor-30 extending in the same direction on both sides. other from cradle 21.

 The section 28 is intended to support the frame 16 which is brought to the manufacturing machine by the conveyor 29 and extracted from this machine by the conveyor 30. The frame 16 is chosen, in correspondence with the model plate 25, so that its lower joint plane can cooperate with the upper surface of this plate. The section 28 is formed on the cradle 21, so that, in the position of maximum retraction of the piston rod 23, the modetal plate 25 is placed below and at a distance from the frame 16.

 The means 14 comprise a second guide track 31 extending superimposed on the track 17 and above the section 28 having a direction parallel to the track 17. The guide track 31 extends under the metering station- distributor 4, under the compacting head 5 and beyond the latter. The guide track 31 supports an extension 32 normally occupying a standby position under the metering-dispensing station 4. The extension 32 can be moved freely on the track 31 which also carries a movable plate 33 associated with a member motor 34. This motor member is designed to immobilize the plate in a waiting position outside of the head 5 and to control the movement of this plate from this waiting position to under the head 5 and vice versa.

 The plate 33 has a lower face 35 located substantially in the plane of the lower joint plane of the extension 32. The plate 33 is provided, on its front edge oriented in the direction of the extension 32, with a rigid scraper blade 36 s 'extending in a plane below the face 35 which can be equipped with punch accessories 37 whose particular function appears in the following.

 The process for manufacturing a dem, -moulding mold, using a machine as described above, takes place as follows.

 Fig. 3 shows the machine in its initial standby position in which the mobile assembly 19 and the extension 32 are placed directly above the station 4. In this state, the jack 22 maintains the model plate 25 in the low position under a frame 16 brought to the section 28. The station 4, in the case where it is constituted by a transfer hopper, is then fed so as to contain a load of sand 40 corresponding to that necessary for manufacturing a foundry mold element. The plate 33 is held in its extreme position according to FIG. 1 and the corpactage head 5 is controlled so as to confine in the reservoir 9 a charge of compressed fluid.

 The first phase of the process consists in ensuring the supply of the jack 22, as illustrated in FIG. 4, to raise the table 24 and bring the model plate 25 into contact with the lower joint plane of the frame 16. The supply to the jack 22 is ensured so that the extension stroke of the rod 23 lifts the frame 16 by relative to the section of track 28 and brings the top of this frame to cooperate with the lower joint plane of the riser 32.

The model plate 25, the frame 16 and the extension 49 then constitute, together, a molding box 41 with an open top placed under the hopper 4 which is commanded to open to pour the load of sand 40 into the bottle 41.

 The second phase of the process, illustrated in fig. 5, consists in closing the hopper 4 to fill it again with a load 40a which will be used for the manufacture of a future mold element. Simultaneously, the mechanism 20 is actuated, so as to bring the mobile assembly 19 directly above the compacting head 5.

During this movement, the extension 32 is carried by the frame 16. When this position is reached, the jack 22 is again supplied to cause the extension stroke of the rod 23, so as to ensure the application of the plane upper seal of the extension 32 under the joint plane 7 of the expansion chamber 6.

 The compacting head 5 is then controlled so that its operation produces a shock wave in the chamber 6 and ensures the compaction of the fuzzy sand charge 40 in the molding box 41.

A third phase of implementation of the method, as illustrated in FIG. 6, then consists in controlling the retraction stroke of the rod 23, so as to lower the riser 32 on track 31. The retraction stroke is also controlled to lower the frame under the riser, by a measure at least equal to
The thickness of a residual excess layer C of sand rising above the upper joint plane of the frame 16 after the compacting phase. The retraction stroke of the rod 23 is also controlled, so that the upper joint plane of the frame 16 is located below and at a distance from a fictitious horizontal plane passing through the base of the scraper blade 36, by a measure e lower than layer C.

 In this state, the motor 34 is supplied with power to control the movement of the plate 33 in the direction of the compacting head 5. The movement of the plate also has the effect of displacing the extension 32 in the direction of the vertical position 4. To this end, provision is made to have at the front edge of the plate 33, already provided with the scraper blade 36, a thrust and spacing buffer 42 making it possible to cause the retraction of the riser 32, before the blade scraper 36 is brought into contact with the excess layer of compacted sand.

 The linear progression of the plate 33 causes the scraper blade 36 to scrape off the excess layer overcoming the thickness e and to evacuate this layer in a receiving tank 43.

 This scraping phase, carried out at work, that is to say on the mass of compacted sand but still contained and confined in the molding box 41, makes it possible to avoid deformation of this mass of sand and, in particular, the half-footprint defined by the model 25 which still occupies it.

 As indicated above, the adjustment of the retraction stroke of the rod 23, prior to the third phase, is carried out so as to allow to remain, after scraping, a thickness e of compacted sand rising above of the upper joint plane of the chassis 16.

 Fig. 7 illustrates a fourth phase of the process, occurring after the above scraping phase when the plate 33 is placed exactly plumb and above the frame 16.

In this state, the jack 22 is again supplied to cause the extension stroke of the rod 23 which raises the molding box 41 in the direction of the face 35 of the plate 33. This has the effect of pressing the thickness e and to carry out an overcompaction by tightening the mass of compacted sand in the box 41, without risk of deformation, since the mass of compacted sand is always contained in the box 41.

 This overcompaction interests, more precisely, the upper layers of precompacted sand and thus confers a greater compactness on these layers. This part of the mold has, in this way a greater local resistance capable of supporting, without risk of deformation of the imprint, your metallostatic casting pressure applying, more particularly, to the lower half-mold of a mold. The retraction stroke of the rod 23 is adjusted so as to leave a thickness e corresponding to the desired overcompaction effect.

 This pressing phase also makes it possible to have an upper face of compacted sand erected on a regular horizontal plane and thus to give the subsequent mold element a flat upper reference face which can be used to facilitate subsequent handling during its use.

 Fig. 8 illustrates a fifth phase of the method consisting in controlling the mechanism 20 to bring the mobile assembly 19 back to the base of the station 4. Simultaneously, the drive member 34 is controlled to bring the pressing plate 33 back to its original position outside the vertical envelope for compacting the compacting head 5. In this position, the jack 22 is then supplied to control the retraction stroke of the rod 23, so as to lower the frame 16 on the track 28.

 Fig. 9 shows that the retraction stroke of the rod 23 is then definitively controlled to release the model plate 25 relative to the frame 16 which surrounds a mold element 60 offering, in its lower surface, a half-cavity 61 and a casting jet 62.

 According to the method of the invention, provision is made to have, on the lower face 35 of the pressing plate 33, an accessory punch, such as 37, illustrated in FIG. 1. This punch ensures, during the secondary compaction phase by pressing, the formation, from the upper surface of the mold element 60, of a hollow imprint defining a pouring cone 63 opening into the jet of casting 62.

 This phase of the process eliminates the usual phase of milling and eliminates all the risks it entails. As the punching of the cone 63 occurs at post and before demoulding of the model plate 25, no deformation of the impression is to be feared.

 Although this is not shown, it should be considered that the face 35 can also support other accessories for delimiting imprints in the upper surface of the mold element 60 during the pressing compacting phase, for delimit a peripheral chute or, again, grooves favoring the evacuation of gases and fumes.

 Following the lowering of the model plate 25, the frame 16 and the half-mold 60 can be removed by the conveyor 30. The section 28 can then be occupied by another frame 16 intended for the manufacture of a another half-mold according to the cycle described above.

 It should be considered that the method of the invention could involve different means 14 in structure and in operation. Thus, these means could be provided to impose on the molding box 41 a transfer path according to horizontal, or vertical or combined horizontal / vertical modes with linear or polygonal or rotary paths and alternating or continuous movements.

 The invention is not limited to the example described and shown, since various modifications can be made thereto without departing from its scope. In particular, it should be considered that the scraping could be carried out in a different way. It would be possible, in particular, to assume the function of a scraper on the riser 32 by providing for a vertical relative clearance between the latter and the molding box, of a measurement corresponding to the excess thickness to be reserved, then , then, to control its relative horizontal displacement, so that the internal edge of the interested part of its periphery acts in the manner of a scraper.

Claims (11)

CLAIMS:  1 - Method for manufacturing a foundry mold element by green sand molding and shock wave compaction, of the type consisting in delimiting a molding box by a model plate forming the bottom and by a movable frame associated with an extension and defining together the perimeter wall, to fill this box with a load of fuzzy sand, to apply to the upper surface of the load of sand a shock wave by a compacting head,  characterized in that it consists of:  - fill the box with a load such that after  compaction, the upper level of compacted sand  is located above the joint plane between the  chassis and extension,  - clear, at least partially, the enhancement  after compaction by vertical displacement  relative,  - subject the upper layer of compacted sand  scraping while leaving a thickness  determined surplus,  - exert by a clamping plate a force of  pressing on the scraped upper surface of the  compacted sand,  - release the model plate,  - then to evacuate the chassis and the half-mold  manufactured it contains.  2 - Method according to claim 1, characterized in that  - fully releases the extension,  - scrapes by horizontal displacement  relative between a scraper and the molding box.  3 - Method according to claim 1, characterized in that:  - partially releases the extension,  - performs a relative movement between the box  molding and the heightening which assumes by it-  even a scraper function.  4 - Method according to claim 1, 2 or 3, characterized in that it consists in performing, by the clamping plate and simultaneously with the pressing phase, at least one imprint in the scraped upper face of the mass of compacted sand .  5 - Method according to one of claims 1 to 4, characterized in that the thickness of the scraped sand layer is adjusted.  6 - Machine for manufacturing a foundry mold element by green sand molding and shock wave compaction, of the type comprising a frame (1) supporting, on the one hand, a metering-dispensing station (4) sand and a compacting head (5) arranged in two parallel vertical orientations and, on the other hand, means (14) for support, presentation and transfer of a chassis (16) from the station (4) to the post (5),  characterized in that it comprises:  - a means (31) for support and guide carried  by the frame, superimposed and parallel by means  (14) and extending under the filling station  and the compaction head,  - a mobile extension (32) on this means (31),  - a scraping means (36),  - And a pressing plate (33) carried by the  medium (31).  7 - Machine according to claim 6, characterized in that the scraping means is constituted by a part of the edge of the riser.  8 - Machine according to claim 6, characterized in that the scraping means is constituted by a scraper blade (36) carried by the front edge of the plate (33) mounted movably on the means (31).  9 - Machine according to claim 6 or 8, characterized in that the extension (32) is mounted freely on the track (31) and in that the pressing plate (33) is associated with a motor (34) drive moving from a waiting position to an extreme scraping and tightening position and vice versa.  10 - Machine according to claim 6, characterized in that the underside of the plate (33) comprises accessories (37) for marking and / or conformation.  11 - Machine according to claim 6, characterized in that the means (14) comprise a movable assembly (19) carrying a plate (24) intended to support a model plate (25), the plate being associated with a jack (22 ) with adjustable stroke capable of adjusting the vertical position of the box constituted by the chassis and the plate to define the thickness of the layer remaining after scraping.