FR2707537A1 - Method and machine for moulding cores in moulding sand - Google Patents

Abstract

The method includes a phase of injecting sand into a cavity of a core box and a phase of hardening the sand inside the core box (9). Suction is produced in at least one part of the cavity of the core box (9), at least during the initial phase of injecting the sand into the cavity. Gas is blown into the same part of the cavity of the core box (9) after hardening of the core. The core-moulding machine includes a suction and blowing means (22, 23, 24) in at least one part of the core box (9).

Description

 The invention relates to a method and a machine for molding cores in foundry sand making it possible to produce cores of complex shape and in particular having tightened parts with small cross-section. The invention is particularly applicable to the molding of foundry cores for the manufacture of parts for the automotive industry such as engine blocks.

 Methods are known for molding foundry cores consisting in injecting sand containing various additives and in particular a hardenable synthetic resin in a core box, so as to fill one or more cavities for molding cores delimited by tool parts of the core box machined by etching.

 Foundry sand is injected inside the core box using a feed pot or shot pot which is filled with foundry sand at a filling station in a first phase and then moved to the injection position in the core box, the sand then being injected by means of injection nozzles or shooting nozzles which constitute the outlets of the shooting pot through which the sand is expelled by compressed air.

 After filling the molding cavities of the core box with foundry sand, the shot pot is replaced at the filling station and a heating head in the case of molding the cores in a hot box or a gas injection head in the case of the molding of the cores in a cold box is placed in the injection position above the core box. Is then carried out, either the heating of the cores, or the injection of a reactive gas, inside the core box, so as to ensure the hardening of the resin and therefore of the sand cores in their form of molding .

 In the case of foundry cores having a complex shape and in particular having parts of reduced cross section, the complete filling of the mold cavity of the core can be difficult, since air forming a mattress can be trapped in certain parts of the cavity of small cross section and to oppose a complete and satisfactory filling of the cavity during the injection of foundry sand. The trapped air in these areas may also produce turbulence which hinders correct filling of the parts of the cavity with a small section.

 As a result, the quality of production of certain delicate parts of the cores is insufficient.

 After the core has been produced and removed from the mold, there may remain in certain parts of the cavity of small section, sand concretions, which risk opposing correct filling of the cavity, during a subsequent core molding operation.

 In particular, for the production of automotive engine parts such as cylinder blocks, it is necessary to mold cores allowing the lining of the cylinders and the cooling water passage channels inside the cylinder block . These water passage channels having reduced sections and connecting to certain parts of the core intended to carry out the lining require, for their molding, the filling of certain parts which are difficult to access of the cavity of the core box.

 The object of the invention is therefore to propose a process for molding cores in foundry sand by injecting sand into at least one cavity of a core box and hardening of the sand inside the core box which allows to produce with a very high manufacturing quality parts which can be of complex shape and which in particular comprise parts with a small cross section.

 For this purpose, suction is produced in at least part of the cavity of the core box, during at least part of the phase of injecting the sand into the cavity.

 In order to clearly understand the invention, a description will now be given, by way of nonlimiting example, with reference to the appended figures, of a machine for molding cores in foundry sand and a method of molding cores according to the invention. 'invention.

 Figure 1 is an elevational view in partial section of a machine for molding cores in foundry sand for implementing the method according to the invention.

 Figure 2 is an elevational view in partial section of a core box and a suction and blowing device for implementing the method according to the invention on a molding machine as shown in the figure 1.

 FIG. 3 is a perspective view in partial section of a part of the core box and of the suction device shown in FIG. 2.

 Figure 4 is an elevational view in partial section of a suction and blowing device for the implementation of the method according to the invention on a machine for casting foundry cores.

 FIG. 1 schematically shows the assembly of a machine for molding cores in foundry sand by injecting sand into the cavity of a two-part tool under the effect of a gas under pressure.

Such a machine is generally called a machine for pulling out pits of sand.

 The core molding machine or core pulling machine generally designated by reference numeral 1 comprises a frame 2 constituted by a horizontal base 3, vertical columns 4 and an upper part 5 which is substantially horizontal and fixed on the upper end of the columns 4.

 The base 3 is pierced with a through opening 6 in which is mounted a lifting cylinder 7 of a table 8 for supporting a core box 9 consisting of two parts attached to one another. The lower part 9a of the core box resting on the table 8 is generally called the lower tool and the upper part 9b attached to the lower tool 9a is generally called the upper tool.

 The lower tool 9a and the upper tool 9b are internally machined to delimit a cavity whose shape corresponds to the shape of the core to be produced by injection and hardening of foundry sand in the cavity.

 The jack 7 makes it possible to move the table 8 and the core box 9 in the vertical direction in one direction and in the other, as shown by the double arrow 7 ', between a high position not shown and a low position shown in the figure.

 The upper part 5 of the machine for pulling the cores 1 comprises guide and support means 10 placed horizontally and which can be constituted by a rail or a slide.

 A supply pot for the foundry sand core box or firing pot 12 resting on the guide and support means 10 is connected to a displacement means 14 which can be constituted by a hydraulic cylinder making it possible to ensure a rapid movement of the firing pot 12 between a first position vertically above the core box 9 and a second position 12 ′ vertically and below an installation 15 for filling the firing pot 12 in foundry sand, position 12 'being shown in broken lines in Figure 1.

 The shooting pot 12 is produced in the form of a capacity intended to receive a load of sand in its filling position 12 ′ and comprising, at its lower part, a closing plate or shooting flange 17 on which are fixed shooting nozzles 18 of vertical direction.

 The shooting nozzles which are produced in the form of tubular steel parts comprise a lower end part or elastomer nose or a metal part having a cone-on-cone bearing to ensure sealing.

 The internal passages of the nozzles 18 constitute the outlet orifices of the firing pot 12.

 In its vertical position of the core box 9, the firing pot 12 is placed in the extension of a firing unit 16 ensuring the sending of compressed air under pressure into the pot 12 to ensure the evacuation of sand by the nozzles 18 and injection into the core box, when the core box 9 has been placed in the high position by the jack 7, its upper part abutting against the firing flange 17.

 The nozzles 18 ensure, in this position, the supply of foundry sand to the mold cavities of the tooling of the core box 9.

 Foundry sand contains various additives which are incorporated and mixed homogeneously with the sand grains.

 These additives comprise at least one hardenable synthetic resin, a catalyst ensuring the hardening of the resin, during an addition of heat or in the presence of reactive gas, a preservative allowing the long-term storage of the sand protected from the air and heat and a heat-resistant lubricating substance such as an oil or grease containing silicones.

 The core pulling machine 1 also has a head 20 for blowing hot heating air or a reactive gas into the core box 9, when this head is placed in the operating position, above the box. cores 9, at the injection station of the firing pot 12.

 The head 20 can be connected to the firing pot 12, so that it can be moved simultaneously to the firing pot, by the displacement means 14, in the horizontal direction. In this way, when the firing pot 12 is in its injection position above the core box 9, the head 20 is in its out-of-service position, as shown in the figure.

 When the firing pot 12 is moved into its position 12 ′ at the filling station situated vertically from the filling installation 15, the head 20 is automatically placed vertically above the core box 9.

 In this phase, the mold cavities of the core box were filled with sand, the hardening of which can be ensured by the head 20.

 In the case of a hot box process, the hardening of the core sand is ensured by heating under the effect of a high temperature gas blown through the head 20 into the core box 9. The core box is then brought to a temperature close to 280 "C.

 In the case of a cold box process, hardening is ensured in a known manner by blowing a reactive gas constituted by dimethylethyl acetate through the head 20, inside the core box 9.

 In the case of a core box 9, the lower 9a and upper 9b tools of which are internally machined to delimit a cavity of complex shape which may include parts with small cross section, the filling of the cavity of the core box 9 by injection sand through the nozzles 18 may present difficulties because the air trapped in the parts of the small section cavity cannot be easily evacuated at the time of injection and produces turbulence disturbing the flow of sand to inside the cavity.

 After hardening and demoulding of the core, there may also remain in the small section of the cavity of the resin-impregnated sand concretions which obstruct the passages with small section, so that the cores produced during subsequent operations using the core box may have unacceptable defects.

 According to the invention, the core box 9 is connected at the level of the lower tool 9a and at the level of the upper tool 9b or even at the level of the lower tool or the upper tool only, to conduits such as 21a and 21b which are themselves connected to the cylinder of a suction and blowing pump 22 in which a piston 23 moves, the rod of which is connected to an actuating cylinder 24.

 The chamber of the jack 24 is connected to a control unit 25 for the various members of the core molding machine comprising means for supplying hydraulic fluid to the jack 24.

 The displacement of the jack 24 can be controlled in one direction or the other by the unit 25 during the operating phases of the molding machine, to cause the displacement of the piston 23 in one direction or the other as indicated by the double arrow 26.

 In a first direction of movement (from left to right in FIG. 1), the piston 23 produces a suction in the parts of the cavity of the core box delimited by the lower tool 9a and by the upper tool 9b . In the other direction, (from right to left in FIG. 1) the piston 23 blows inside the cavity delimited by the lower tool 9a and by the upper tool 9b of the core box 9.

 The control of the piston 24 for displacement of the piston 23 is programmed, so that the piston 23 begins to move in the direction corresponding to the suction just before the start of the injection of sand into the core box 9. The suction continues during at least part of the phase of injecting the sand into the core box 9 during which the parts of small section of the cavity of the core box fill with sand, without this filling being disturbed by air trapped in these small section sections.

 Indeed, the suction pump 22 is connected via the conduits 21a and 21b to these parts with a small section in which the air is sucked in from the start of the injection phase.

 The phase of injecting the sand into the core box 9 is preceded by a tightening phase one against the other of the tools 9a and 9b, this tightening being able to be achieved by jacks not shown after the upward movement of the tray 8 and the core box 9.

 The start of the suction in the parts with a small section of the mold cavity via the conduits 21a and 21b can be advantageously controlled simultaneously with the tightening of the tools 9a and 9b of the core box 9.

 At the end of the core molding cycle, after their hardening, the tools 9a and 9b constituting the core box 9 are loosened and separated from one another to allow the core to be recovered from foundry sand. A blowing is then carried out inside the two parts of the mold via the conduits 21a and 21b by controlling the movement of the jack 24 and of the piston 23 of the pump 22, in the desired direction. This blowing allows the possible unblocking of the parts with a small cross section of the mold cavity and of the suction and blowing circuit itself. The start of blowing is controlled by the programmable controller of the control unit 25 of the core molding machine. Blowing is generally carried out at the time of dusting of the cores after they have been removed from the mold.

 In Figures 2 and 3, there is shown a tool for implementing the method according to the invention, in the case of molding of foundry cores intended for the manufacture of engine blocks comprising four pistons in line. In Figure 2, there is shown the lower tool 29a and the upper tool 29b of a core box 29 in which one can carry out the molding of a set of cores in foundry sand 28 used during the manufacture of engine blocks, the cores such as 28 being introduced into a casting mold of the cylinder block, before the casting of the metal of the cylinder block to allow reserving around each of the engine cylinders, a space for circulation of the coolant motor and supply and connection ducts to ensure the circulation of the coolant.

 As can be seen in FIG. 2, the core 28 comprises parts with a small section 30, the production of which is difficult, insofar as these parts of small thickness intended to reserve passage channels between two successive cylinders are produced by molding in openings 36 of small section joining two parts of the main cavity 35 of the core box 29.

 The mold cavities 36 of the parts 30 of small cross section of the core 28 are machined inside the lower tool 29a of the core 29.

 These cavities are connected by means of three conduits 31 machined in the lower tool 29a, to a distribution pipe 32 delimited between a surface of the lower tool 29a and an attached plate 43.

 The distribution and suction pipe 32 is connected to a pump 33 actuated by a jack 34 allowing suction or blowing into the reduced section cavities of the lower tool 29a, according to the phases of the molding of the cores , in the same way as the pump 22 which has been described with reference to FIG. 1.

 In FIG. 3, the lower tool 29a of the core box 29 is shown, in which three cavities are machined making it possible to mold the lower part of three cores in foundry sand 28 intended for the casting of a block. -cylinders of an engine comprising four cylinders in line.

 It is quite obvious that the upper tool comprises a cavity making it possible to mold the complementary upper part of the three cores 28 shown in FIG. 3.

 In general, it is possible to use core boxes having any number of cavities or imprints at least equal to two to carry out the simultaneous molding of the same number of cores.

 The cavities machined in the lower tooling and in the upper tooling of the core box have the shape of a hollow wall comprising successive portions substantially in the form of a cylinder portion connecting according to the successive junction zones 27a, 27b and 27c.

 Each of the tools such as the lower tool 29a is produced in several parts which are machined to allow different parts of the cavity to be obtained which are attached to each other during assembly of the tool to produce a continuous cavity .

 At the connection zones 27a, 27b, 27c of the successive parts of substantially cylindrical shape of the tool cavity, there are provided the transverse openings 36 for joining the two parts of the cavity located on either side of the line of cylinders.

 The molding of the parts 30 of small section of the core 28 is carried out inside the transverse openings 36 of small section of the cavity 35 of the molding of the core 28 communicating at each of their ends with the main parts of the cavity 35 constituting two walls continuous on both sides of the line of cylinders.

 It is quite obvious that the foundry sand which is injected into the main cavity of the mold 35 hardly reaches the interior of the transverse openings 36 intended to constitute the parts with small cross-section 30 of the core 28.

 The air present inside the openings 36 is hardly expelled outside the cavity of the tool 29a, so that the filling of the openings 36 risks being carried out in a defective manner.

 To facilitate the filling of the transverse openings 36 intended to constitute the parts of small section 30 of the core 28, the openings 36 are each connected by a channel 31 machined inside the tool 29a, to a suction pipe such as 32a delimited between the added plate 33 and the lower surface of the tool 29a.

 The tool 29a comprises three parallel suction lines 32a, 32b and 32c each corresponding to the cavity 35 for molding the core 28 of a line of cylinders.

 Each of the cores 28 corresponding to a line of four cylinders further comprises, at each of the cooling spaces of a cylinder, parts of small section 38 whose molding is carried out inside parts of small section 39 in form of conduits extending the cavity 35 downwards, to come out into the corresponding suction line such as 32a.

 The parts 38 of small cross section of the core 28 are intended to provide conduits for supplying and leaving coolant in the cooling space around the cylinders.

 In reality, the core 28 has four parts with a small cross section such as 38 at each of the parts of the core corresponding to a cylinder. To simplify the representation of the core and the cavities in FIG. 3, only two parts with a small section 38 have been shown at each of the cylinders opening into a suction pipe such as 32a.

Two other parts with a small cross-section in the form of conduits of the cavity 35 are machined at each of the core parts corresponding to a cylinder and open into a suction line, not shown, parallel to the lines such as 32a, 32b and 32c.
Each of the suction pipes such as 32a, 32b and 32c and the pipes located in parallel at each of the cavities 35 for molding a core 28 is connected by a pipe such as 41a, 41b and 41c to a manifold. suction or nurse 40 connected by a flexible hose 44 to the suction and blowing pump 33 whose piston is actuated by the jack 34. A filter 45 is interposed between the end of the pipe 44 opposite the nurse 40 and the pump 33, so as to stop the sand particles which can be sucked inside the core box, during the suction phase inside the parts with small section of the cavities of the core box.

 The pump 33 has an opening or valve 46 allowing the exhaust or the air intake during the suction and blowing phases inside the mold cavity.

 The cylinder 34 is controlled in the manner described above, so that the piston of the cylinder 33 moves in the direction of suction inside the mold cavity just before and during part of the injection phase of sand in the core box 29.

 Aspiration into the cavity 35 occurs at the transverse openings 36 between the cylinders, via the conduits 31 and at the conduits 39 with a small section.

 This produces and empties the air contained in these parts with a small section of the cavities 35, which allows very good filling with a satisfactory density of these parts with a small section.

 It also avoids the effects of discharge and turbulence of the air contained in these parts with a small cross-section, during injection.

 It is quite obvious that the blowing of air by reversing the direction of displacement of the jack makes it possible to expel the sand particles possibly deposited or agglutinated inside the parts with small section 36 and 39 of the mold cavities 35 of the cores 28.

 In FIG. 4, the pump 33 is shown in more detail, which comprises a cylinder 47 in which a piston 48 is mounted movable and sealed, thanks to segment seals such as 49.

 The piston 48 is integral with a rod 50, itself connected via a hinge 51 to the rod of the jack 34. The body of the jack 34 is hinged mounted on a support 52 resting on the floor of the molding machine nuclei.

 The wall of the cylinder 47 is crossed by the opening 46 allowing the air to be drawn in or out during the movements of the piston 48.

 The device according to the invention which is of very simple structure makes it very easy to ensure excellent conditions for filling the cavity of the core box, in its parts with a small section which are put under vacuum from the start of the phase. injection or slightly before this phase.

 The method and the device according to the invention therefore make it possible to appreciably improve the quality of the cores obtained even in the case of cores of complex shape having numerous parts with small cross section.

 Manual interventions on the tool for molding the cores, for example to remove sand concretions in parts with a small section of the cavity are reduced or even eliminated.

 This results in extremely reduced production losses through the use of the process according to the invention.

 The suction and blowing device which can be produced in a very simple form nevertheless has great efficiency and can be controlled very precisely as a function of the stages of carrying out the operation of molding the cores.

 The invention is not limited to the embodiments which have been described.

 Thus the means of suction and blowing in certain parts of the cavity of the core box can be different from the piston and cylinder device which has been described above.

 The arrangement of the suction and blowing conduits inside the core box may be different from those which have been described and adapted to the shape of the cores and to the parts of these cores in which it is desirable to apply a depression or blowing.

 Suction and blowing can be carried out both in the lower tooling part and in the upper tooling part of a two-part core box which are attached to each other to form the internal cavity molding cores.

 The molding method and machine according to the invention can be used for molding cores in foundry sand different from cores for the production of motor vehicle engine blocks comprising ducts of small section.

 The invention can be applied in all cases in which the molding of cores of complex shape is carried out requiring the use of a molding cavity comprising ducts of small section or blind holes which it is difficult to ensure. filling with foundry sand and evacuation of the air contained, at the start of sand injection.

Claims (11)

 1.- process for molding cores (28) in foundry sand comprising a phase of injecting sand into at least one cavity (35) of a core box (9, 29) and a phase of hardening the sand to the interior of the core box (9, 29), characterized in that suction is produced in at least part of the cavity (35) of the core box (9, 29) during at least part of the phase of injecting the sand into the cavity (35).  2.- molding process according to claim 1, characterized in that a gas blowing is carried out in at least part of the cavity (35) of the core box (9, 29), after the curing phase sand inside the core box (9, 29).  3.- molding method according to any one of claims 1 and 2, characterized in that a suction is produced in at least one part (36, 39) of the cavity (35) of the core box (9 , 29) having a reduced section, so as to evacuate the air present in the reduced section part (36, 39) of the cavity (35) at the start of the injection phase and to facilitate the filling of the part reduced section (36, 39) by sand, during the injection phase.  4.- Method according to any one of claims 1 to 3, characterized in that one begins to produce the suction in the part (36, 39) of the cavity (35) of the core box (9, 29) prior to the phase of injecting the sand into the cavity (35).  5.- Process for molding cores (28) in a core box (9, 29) comprising a lower tool (9a, 29a) and an upper tool (9b, 29b) which are brought together and tightened before the sand injection phase to form the cavity (35), characterized in that the suction is controlled in the part (36, 39) of the cavity (35) simultaneously with the tightening of the lower tooling (9a, 29a) and the upper tool (9b, 29b) against each other.  6.- Machine for molding cores in foundry sand comprising a core box (9, 29) comprising a lower tool (9a, 29a) and an upper tool (9b, 29b) attached to each other to constitute a mold cavity (35), a device for injecting sand (12) into the core box (9, 29) and a head (20) for injecting a sand hardening gas into the core box (9, 29), characterized in that it further comprises at least one suction and blowing duct (32, 32a, 32b, 32c) formed inside at least part of the box cores (9, 29) and communicating with at least part of a molding cavity (35) of the core box (9, 29) and a suction and blowing device (22, 33) connected to the pipe suction and blowing (32, 32a, 32b, 32c) inside the core box (9, 29).  7.- Device according to claim 6, characterized in that the suction device 33, is constituted by a cylinder (47) in which is movably mounted a piston (23, 48) integral with a rod (50) connected to the rod of an actuating cylinder (24, 34).  8.- Device according to claim 7, characterized in that the cylinder (24, 34) is connected to a control unit (25) of the molding machine (1), to be controlled according to the actuation phases of the molding machine.  9. Molding machine according to any one of claims 6 to 8, characterized in that the suction and blowing device (23, 33) is connected to the suction duct (32, 32a, 32b, 32c ) inside the core box (9, 29), via a duct on which a filter (45) is arranged.  10. Molding machine according to any one of claims 6 to 9 for molding cores (28) intended to reserve a cooling jacket around the cylinders of an engine, during the manufacture by molding of cylinder blocks of motor, characterized in that the suction duct (32, 32a, 32b, 32c) is connected to parts (36, 39) of small section of the cavity (35) for molding the cores (28) in which are made of core parts (30, 38) used to reserve water passages during the molding of the cylinder block.  11.- Device according to claim 10, characterized in that the core box (9, 29) comprises at least two cavities (35) for molding at least two cores (28) comprising parts of reduced section (36 , 39) connected to at least two suction and blowing lines (32a, 32b, 32c) arranged in parallel and connected via a suction and blowing manifold (40) to the installation of suction and blowing (33).