SAND CORE MAKING MACHINE WITH IMPROVED ELECTRICAL CONTROL

Abstract

 The invention is directed to a core making machine (2) comprising a main frame (4); a lower support assembly (6) mounted on the main frame (4), for supporting a core box; a core box closing frame (10), vertically movable on the main frame (4); a head (14) for sand filing and compacting, above the core box closing frame (10) and vertically movable on the main frame (4); electromechanical cylinders (18, 20) mounted on the main frame (4) and configured for moving the core box closing frame (10) and the sand filing and compacting frame (14) and exerting a pressing force on the core box; and a control unit of the electromechanical cylinders (18, 20), configured for varying the force exerted by said electromechanical cylinders during sand filling and/or sand compacting.

Description

Technical field

[0001] The invention is directed to the field of the production of sand cores for iron and aluminium casting. A core is a device used in casting and core boxing processes to produce internal cavities and re-entrant angles (an interior angle that is greater than 180°). The core is normally a disposable item that is destroyed to get it out of the piece. They are most commonly used in sand casting, but are also used in die casting and injection core boxing.

Background art

[0002] Machines for making sand cores are known since many years. They consist essentially in a main frame; a lower support assembly mounted on the main frame, for supporting a core box; a core box closing frame, vertically movable on the main frame; a shooting head, above the core box closing frame and vertically movable on the main frame. For producing a sand core, a corresponding empty lower box is brought inside the machine underneath the shooting head of the machine. Once in the lower box is in position, the upper box carried by the core box closing frame and the shooting head are lowered for core box closing. Thereafter the sand is injected into the core box. At the end of the shooting cycle the head is moved up to allow the gassing unit going in. Once the gassing unit is inside the head is again lowered for sand curing through the injection of gas. During shooting and curing both head and upper box support hydraulic cylinders exercise their maximum force to ensure the core box closing and prevent sand and gas leaking. The force is usually comprised between 100 kN and 1000 kN. The hydraulic unit must then be dimensioned for, on one side, achieving that high pressing force, and on the other side, being able to move the shooting head and the core box closing frame at a sufficient speed when loading and unloading the core box.

[0003] Prior art patent document published CN 108262452 A discloses a sand core casting machine equipped with electromechanical actuators for moving the shooting head whereas the core box closing frame is mechanically driven by a rack and pinion transmission between the frame and the vertical guiding rods. For achieving a high pressing force during the compaction phase, the machine is equipped with a mechanical linkage mechanism designed for progressively increasing the resulting force applied in the head when the latter approaches and contacts the core box. This solution is interesting in that it avoids the need of a hydraulic unit as in the above prior art. The presence of the mechanical linkage mechanism is however disadvantageous in that it occupies space, increases the manufacturing costs and can lead to unbalance in the forces applied by each electromechanical cylinder and therefore to a non-homogeneous pressing force on the core box.

Summary of invention

Technical Problem

[0004] The invention has for technical problem to overcome at least one of the drawbacks of the above cited prior art. More specifically, the invention has for technical problem to provide a sand core casting machine achieving a better control of the casting process at a lower cost.

Technical solution

[0005] The invention is directed to a sand core making machine comprising: a main frame; a lower support assembly mounted on the main frame, for supporting a core box; a core box closing frame, vertically movable on the main frame; a head for sand filing and compacting, above the core box closing frame and vertically movable on the main frame; electromechanical cylinders mounted on the main frame and configured for moving the core box closing frame and the head and exerting a pressing force on the core box; wherein the core making machine comprises a control unit of the electromechanical cylinders, configured for varying the force exerted by said electromechanical cylinders during sand filling and/or sand compacting.

[0006] Varying the force exerted by the electromechanical cylinders during sand filling and/or sand compacting is during core phases of these operations, i.e. not at the transient starting and ending phases of these operations, during which the force is applied and released, respectively. Each of these transient starting and ending phases can last less than 1 second, even less than 0.5 second.

[0007] Compacting the sand the core box can comprise a curing operation of an adhesive mixed with the sand.

[0008] According to a preferred embodiment, the electromechanical cylinders comprise a first set of vertical electromechanical cylinders operatively attached, at one end of each electromechanical cylinder, to the main frame and, at the other end of each electromechanical cylinder, to the core box closing frame and a second set of vertical electromechanical cylinders operatively attached, at one end of each electromechanical cylinder, to the main frame and, at the other end of each electromechanical cylinder, to the head.

[0009] According to a preferred embodiment, the control unit is configured for commanding the electromechanical cylinders during the shooting cycle and/or the compacting cycle such that each of the electromechanical cylinders exerts a pressing force on the core box and that the pressing force of the first set of electromechanical cylinders adds on to the pressing force of the second set of electromechanical cylinders.

[0010] According to a preferred embodiment, the second set of vertical electromechanical cylinders comprises a pair of electromechanical cylinders arranged on each lateral side of the head, and the first set of vertical electromechanical cylinders comprises a pair of electromechanical cylinders arranged laterally outwardly to the pair of electromechanical cylinders of the second set of electromechanical cylinders.

[0011] According to a preferred embodiment, the main frame is a tubular frame forming a cuboid with a main vertical direction, the first set of vertical electromechanical cylinders being arranged in side walls of the cuboid - shaped tubular frame and the second set of vertical electromechanical cylinders being arranged inside the cuboid.

[0012] According to a preferred embodiment, the core box closing frame comprises brackets attached to the electromechanical cylinders of the first set of vertical electromechanical cylinders, said brackets extending horizontally through the side walls of the cuboid-shaped tubular frame.

[0013] According to a preferred embodiment, the electromechanical cylinders are all arranged with main axes thereof in a same vertical plane.

[0014] According to a preferred embodiment, the machine further comprises four vertical guiding rods fastened to the main frame, a first set of linear bearings slidably mounted on the four vertical guiding rods and attached to the core box closing frame, and a second set of linear bearings slidably mounted on the vertical guiding rods and attached to the head.

[0015] According to a preferred embodiment, the four vertical guiding rods are arranged so as to form a rectangular shape, the vertical plane comprising the main axes of the electromechanical cylinders being median to the rectangle.

[0016] According to a preferred embodiment, the control unit is configured for achieving, during the compacting, an increasing phase of the pressing force and thereafter a diminishing phase of said pressing force.

[0017] According to a preferred embodiment, the diminishing phase lasts at least 40%, preferably at least 50%, of the compacting.

[0018] According to a preferred embodiment, each of the electromechanical cylinders comprises a ball screw drive or a planetary screw drive, and an electric motor for driving said screw drive.

[0019] According to a preferred embodiment, at least one, preferably each of the electromechanical cylinders comprises a position measuring unit of said electromechanical cylinder, operatively connected to the control unit.

[0020] The invention is also directed to a method for operating a sand core making machine comprising a main frame; a lower support assembly mounted on the main frame, for supporting a core box; a core box closing frame, vertically movable on the main frame; a head for sand filing and compacting, above the core box closing frame and vertically movable on the main frame; and electromechanical cylinders mounted on the main frame and configured for moving the core box closing frame and the sand filing and compacting frame and exerting a pressing force on the core box; wherein the method comprises: electrically commanding said electromechanical cylinders such as to vary the pressing force on the core box during sand filling and/or sand compacting.

[0021] According to a preferred embodiment, varying the pressing force on the core box is achieved by varying a command signal to electronic drive units of the electromechanical cylinders, resulting in a variation of current and/or voltage applied to said electromechanical cylinders.

[0022] According to a preferred embodiment, varying the pressing force during the compacting comprises an increasing phase of the pressing force and thereafter a diminishing phase of said pressing force where the diminishing phase lasts at least 40%, preferably at least 50%, of the compacting.

[0023] According to a preferred embodiment, the method comprises electrically detecting the position of some, preferably each, of the electromechanical cylinders, comparing said positions for the core box closing frame and/or for the head, and in the presence of a difference exceeding a predetermined value, issuing a warning signal and/or compensating said difference by accordingly commanding said electromechanical cylinders in a differentiated manner.

[0024] According to a preferred embodiment, the method comprises electrically detecting the position of some, preferably each, of the electromechanical cylinders, and commanding said electromechanical cylinders during opening.

Advantages of the invention

[0025] The invention is particularly interesting in that the use of electromechanical cylinders directly attached to the core box closing frame and to the head, i.e. without intermediate linkage mechanisms, provides a simpler and more compact constructions whereas sophisticated functions can be achieved thanks to the electric command of the electromechanical cylinders.

Brief description of the drawings

[0026] 

Figure 1 is front view in perspective of a sand core making machine according to the invention.

Figure 2 is rear view in perspective of a sand core making machine of figure 1.

Figure 3 is a schematic representation of the electromechanical cylinders of the sand core making machine of figures 1 and 2.

Figure 4 a schematic representation of the connection between the electromechanical cylinders of the sand core making machine of figures to 3 and a control unit thereof.

Figure 5 is a curve of the pressing force exerted on the core box during compaction that can be achieved by the electromechanical cylinders.

Description of an embodiment

[0027] Figures 1 and 2 are front and rear perspective views of a sand core making machine according to the invention.

[0028] The sand core casting machine 2 comprises a main frame 4 that is for instance of the tubular type, i.e. essentially made of an assembly of beams, for instance steel beams. As this is apparent the main frame is generally cuboid extending along a main vertical direction. A lower support assembly 6 is provided at a lower portion of the main frame 4. That assembly 6 comprises a support surface for receiving the core box or box and for supporting the high pressing forces exerted during compacting that will be described later in this description. The lower support assembly 6 can comprise a conveyor, as visible in figure 1, for loading the core box onto the machine 2 and for unloading such core box after casting one or several sand cores in the core box. The loading is usually achieved from the front side of the machine, as visible in figure 1, and the unloading usually achieved on the rear side, as visible in figure 2. The loading and unloading could however be achieved differently without any influence on the principle of the invention that will follow.

[0029] The machine 2 can also comprise a side pressing assembly 8 arranged directly above the lower support assembly 6, for pressing core box parts showing a generally vertical contact plane.

[0030] The machine 2 comprises a core box closing frame 10 which is not well visible in figures 1 and 2 for it is hidden by other parts of the machine. It is better visible in the schematic illustration in figure 3 that will be described later in this description. That frame is slidably mounted on the four vertical guiding rods 12 attached to the main frame 4. The core box closing frame 10 can for instance be made of two sub-frames, i.e. one on each side lateral side of the machine 2. That frame is intended to carry a lid or upper part of the core box and to lower that lid onto the core box once the latter is properly loaded into the machine 2.

[0031] The machine 2 comprises also a head 14 that is slidably mounted on the main frame 4. For instance that frame is slidably mounted on the four vertical guiding rods 12, similarly to the core box closing frame 10. The head 14 is located above the core box closing frame 10. The head 14 is more voluminous and complex than the core box closing frame 10, for it achieves several functions, for instance and roughly contacting the lid of the core box for "shooting" the sand into the cavity or cavities of the core box, placing a gassing unit between the frame 14 and the lid of the core box for diffusing a catalysing gas, like dimethylethanamine, for curing, i.e. polymerizing the resin(s) mixed with the sand, and thereafter diffusing air for cleaning the core(s) from the catalysing gas. To that end, the head 14 comprises, at an upper portion, a hopper 14.1 for collecting the sand previously mixed with one or several resins, and a chamber 14.2 that is closed, once filled with the sand, and fed with compressed air stored in the tank 16 for injecting or more commonly said "shooting" the sand into the core box.

[0032] The above functions of the head 14, the core box closing frame 10, the side pressing assembly 8, and the lower support assembly 6 are as such known from the person skilled in the art and therefore does not need to be further detailed.

[0033] The machine 2 of the invention is however characterized by the way these frames are arranged on the main frame 4 and even more by the way they are moved vertically. Indeed, the core box closing frame 10 will be moved by a first set of two electromechanical cylinders 18 and the head 14 is moved by a second set of two electromechanical cylinders 20. For instance, these electromechanical cylinders 18 are arranged vertically and are directly attached to the main frame 4 and to the corresponding frame. The electromechanical cylinders 18 and 20 are not well visible in figures 1 and 2. Their arrangement relative to the main frame 4 and the core box closing and heads 10 and 14 will be detailed in relation with figure 3.

[0034] Figure 3 is a schematic vertical and median sectional view of the machine of figures 1 and 2. Each of the electromechanical cylinders 20 of the second set are attached at their upper ends to an upper portion of the main frame 4. More specifically, these electromechanical cylinders 20 are attached at their upper ends to upper side beams 4.1 extending in the loading direction (perpendicular to the plane of the drawing) and which are interconnected by a front and a rear transversal longer beam 4.2 (only the rear beam is visible in figure 3). The lower ends of these electromechanical cylinders 20 are attached to the head 14. The latter comprises four linear bearings 14.3 mounted on the four vertical guiding rods 12, respectively and attached to flat frame body 14.4 supporting the chamber 14.2 and the hopper (not represented in figure 3). The flat frame body 14.4 supports also a guiding frame for selectively inserting a gassing unit below said flat frame body 14.4 for the compaction phase. This guiding frame is visible in figure 2: it protrudes horizontally from the rear side. Such a guiding frame is known as such and therefore does not need to be further detailed.

[0035] Still with reference to figure 3, the electromechanical cylinders 18 of the first set are arranged laterally and outwardly to the second set 20. More specifically, the electromechanical cylinders 20 of the second set are arranged inside the cuboid formed by the main frame 4 whereas the electromechanical cylinders 18 of the first set are arranged in the side walls (though not closed) formed by the main frame 4. The electromechanical cylinders 18 are attached at their upper ends to intermediate side beams 4.3 parallel to and below the upper side beams 4.1, and at their lower ends to the core box closing frame 10. More specifically, the later can be formed to two independent sub-frames, i.e. one on each lateral side of the machine. For instance, the core box closing frame 10 comprises four linear bearings 10.1 mounted on the four vertical guiding rods 12, similarly the linear bearings 14.3 of the head 14. The core box closing frame 10 comprises on each lateral side of the machine a main bracket 10.2 rigidly fastened to two linear bearings 10.1, and an outer side bracket 10.3 rigidly fastened to the main bracket 10.2 and extending essentially horizontally and outwardly therefrom for being attached to the lower end of the corresponding electromechanical cylinder 18. Each of the two outer side brackets 10.3 extends between two lateral vertical beams 4.4 of the main frame 4. The core box closing frame 10 comprises also on each lateral side an inner side bracket 10.4 rigidly fastened to the main bracket 10.2 and extending essentially horizontally and inwardly therefrom for supporting the lid or upper portion 22 of the core box (not represented).

[0036] In operation, once the core box or box is loaded into the machine 2, the core box closing frame is lowered by electrically commanding the electromechanical cylinders 18 until the lid or upper portion 22 contacts the core box (not represented). Thereafter the head 14 is lowered by commanding the electromechanical cylinders 20 until it contacts the lid or upper portion 22. Sand contained in the hopper is then injected to shot into the core box cavity or cavities. Thereafter the head 14 is lifted and a gassing unit is moved horizontally by means of the guiding frame (visible in figure 2) and the head 14 is lowered again, whereby the gassing unit (not represented) is sandwiched between the lid or upper portion 22 and the head 14. A flow of catalysing gas is injected into the core box for curing the resin(s) contained in the sand and thereby solidify the core(s). During that phase, a high pressure on the sand is required for ensuring a proper contact of the grains and a proper cohesion during curing. That high pressure is achieved by combining the forces of the electromechanical cylinders of the first and of the second sets 18 and 20. The head 14 comes in abutment against the core box closing frame 10 so that the resulting pressing force of the electromechanical cylinders 20 of the second set is transmitted by the lid or upper portion 22 to the core box and also the resulting pressing force of the electromechanical cylinders 18 of the first set is applied to the lid or upper portion 22 and therefore added to the resulting force applied onto the core box.

[0037] The above constructions is particularly interesting on a structural point of view and also an on operational point of view, essentially in that the forces exerted by the electromechanical cylinders 18 and 20 are supported by the lateral portions of the main frame 4, causing nearly no bending, and in that the forces add up for reaching a high closing pressure on the core box during the critical compacting phase while limiting the respective capacity of the electromechanical cylinders.

[0038] Electromechanical cylinders suitable for the present invention are commercial available, as an example and in a non-limiting manner, at the company Rexroth® under the series EMC-HD where EMC stands for ElectroMechanical Cylinder and HD stands for High Duty. Such cylinder are of the screw cylinder type, e.g. with ball or planetary roller screw drive driven by an electric motor coupled to the body of the cylinder. Such electromechanical cylinders are commanded by means of a specific electronic drive unit that converts an input signal into a command electrical supply of the electromechanical cylinders.

[0039] The electromechanical cylinders can be equipped with coders or any other means providing a feedback information of the position, i.e. the extension, of the electromechanical cylinders.

[0040] Figure 4 is a schematic representation of the electric layout of the connection of the electromechanical cylinders 18 and 20 with a central control unit 24. This is quite schematic in that the central control unit can comprise several drive units specific to each of the electromechanical cylinders. The central control unit 24 advantageously receives information of the longitudinal positions of the electromechanical cylinders and thereby any unbalance or difference between the lateral sides of the machine. The central control unit 24 can comprise a microcontroller with a memory loaded with code instructions specifically designed for achieving various functions of the machine.

[0041] Figure 5 illustrates one of the functions that the above control unit 24 can achieve, namely a reduction of the pressing force F_c exerted onto the core box during the compacting phase expressed in seconds. Indeed, a maximum pressing force is required at the beginning of the polymerization of the resin(s) mixed with the sand, for ensuring a proper compaction of the sand and thereby a proper solidification of the core(s). The compacting phase lasts usually between 10 and 15 seconds, whereas the maximum pressing force is required during a first phase when curing has not yet really started. The pressing force can then follow a second phase where it substantially diminishes, e.g. during at least 40% or even 50% of the compacting phase. This then provides a substantially reduction in current consumption of the electromechanical cylinders. During compacting, the electromechanical cylinders are energized with high currents and/or voltages for outputting high pressing forces while possibly slightly moving toward the core box for ensuring an optimal compaction of the sand. This is major advantage of using electromechanical cylinders.

[0042] The control unit 24 can achieve other functions, like commanding the electromechanical cylinders at higher speeds when lifted away from the core box and also when lowered to the core box before contact. Also depending on the height of the core box, the core box closing frame 10 and the head 14 do not need to be lifted to the maximum for loading the core boxs. Thanks to the position signals provided by the electromechanical cylinders to the control unit 24, the latter can then optimize the movements of the core box closing frame 10 and the head 14.

[0043] Also, the position signals provided by the electromechanical cylinders to the control unit 24 allow the latter to better control the respective lateral positions of the core box closing frame 10 and the head 14.

Claims

1. A sand core making machine (2) comprising:

- a main frame (4);

- a lower support assembly (6) mounted on the main frame (4), for supporting a core box;

- a core box closing frame (10), vertically movable on the main frame (4);

- a head (14) for sand filing and compacting, above the core box closing frame (10) and vertically movable on the main frame (4);

- electromechanical cylinders (18, 20) mounted on the main frame (4) and configured for moving the core box closing frame (10) and the sand filing and compacting frame (14) and exerting a pressing force on the core box;

characterized in that
the core making machine (2) comprises a control unit (24) of the electromechanical cylinders (18, 20), configured for varying the force exerted by said electromechanical cylinders during sand filling and/or sand compacting.

2. The core making machine (2) of claim 1, wherein the electromechanical cylinders (18, 20) comprise a first set of vertical electromechanical cylinders (18) operatively attached, at one end of each electromechanical cylinder, to the main frame (4) and, at the other end of each electromechanical cylinder, to the core box closing frame (10) and a second set of vertical electromechanical cylinders (20) operatively attached, at one end of each electromechanical cylinder, to the main frame (4) and, at the other end of each electromechanical cylinder, to the head (14).

3. The core making machine (2) of claim 2, wherein the control unit (24) is configured for commanding the electromechanical cylinders (18, 20) during the sand filling and/or the sand compacting such that each of the electromechanical cylinders (18, 20) exerts a pressing force on the core box and that the pressing force of the first set of electromechanical cylinders (18) adds on to the pressing force of the second set of electromechanical cylinders (20).

4. The core making machine (2) of one of claims 2 and 3, wherein the second set of vertical electromechanical cylinders (20) comprises a pair of electromechanical cylinders (20) arranged on each lateral side of the head (14), and the first set of vertical electromechanical cylinders (18) comprises a pair of electromechanical cylinders (18) arranged laterally outwardly to the pair of electromechanical cylinders (20) of the second set of electromechanical cylinders (20).

5. The core making machine (2) of any one of claims 2 to 4, wherein the main frame (4) is a tubular frame forming a cuboid with a main vertical direction, the first set of vertical electromechanical cylinders (18) being arranged in side walls of the cuboid-shaped tubular frame (4) and the second set of vertical electromechanical cylinders (20) being arranged inside the cuboid, and preferably wherein the core box closing frame (10) comprises brackets (10.3) attached to the electromechanical cylinders (18) of the first set of vertical electromechanical cylinders, said brackets extending horizontally through the side walls of the cuboid-shaped tubular frame.

6. The core making machine (2) of any of claims 1 to 5, wherein the electromechanical cylinders (18, 20) are all arranged with main axes thereof in a same vertical plane.

7. The core making machine (2) of any of claims 1 to 6, further comprising four vertical guiding rods (12) fastened to the main frame (4), a first set of linear bearings (10.1) slidably mounted on the four vertical guiding rods (12) and attached to the core box closing frame (10), and a second set of linear bearings (14.3) slidably mounted on the vertical guiding rods (12) and attached to the head (14).

8. The core making machine (2) of claims 6 and 7, wherein the four vertical guiding rods (12) are arranged so as to form a rectangular shape, the vertical plane comprising the main axes of the electromechanical cylinders being median to the rectangle.

9. The core making machine (2) of any of claims 1 to 8, wherein the control unit (24) is configured for achieving, during the compacting, an increasing phase of the pressing force and thereafter a diminishing phase of said pressing force, and preferably wherein the diminishing phase lasts at least 40%, preferably at least 50%, of the compacting.

10. The core making machine (2) of any of claims 1 to 9, wherein each of the electromechanical cylinders (18, 20) comprises a ball screw drive or a planetary screw drive, and an electric motor for driving said screw drive.

11. The core making machine (2) of any of claims 1 to 10, wherein at least one, preferably each of the electromechanical cylinders (18, 20) comprises a position measuring unit of said electromechanical cylinder, operatively connected to the control unit (24).

12. A method for operating a sand core core boxing machine (2) comprising a main frame (4); a lower support assembly (6) mounted on the main frame (4), for supporting a core box; a core box closing frame (10), vertically movable on the main frame; a head (14), above the core box closing frame (10) and vertically movable on the main frame (4); and electromechanical cylinders (18, 20) mounted on the main frame (4) and configured for moving the core box closing frame (10) and the sand filing and compacting frame (14) and exerting a pressing force on the core box;
characterized in that the method comprises:
electrically commanding said electromechanical cylinders (18, 20) such as to vary the pressing force on the core box during sand filling and/or sand compacting.

13. The method according to claim 12, wherein varying the pressing force on the core box is achieved by varying a command signal to electronic drive units of the electromechanical cylinders (18, 20), resulting in a variation of current and/or voltage applied to said electromechanical cylinders.

14. The method according to one of claims 12 and 13, wherein varying the pressing force during the compacting comprises an increasing phase of the pressing force and thereafter a diminishing phase of said pressing force where the diminishing phase lasts at least 40%, preferably at least 50%, of the compacting.

15. The method according to one of claims 12 to 14, comprising electrically detecting the position of some, preferably each, of the electromechanical cylinders (18, 20), comparing said positions for the core box closing frame (10) and/or for the head (14), and in the presence of a difference exceeding a predetermined value, issuing a warning and/or compensating said difference by accordingly commanding said electromechanical cylinders (18, 20) in a differentiated manner, and/or comprising electrically detecting the position of some, preferably each, of the electromechanical cylinders (18, 20), and commanding said electromechanical cylinders during opening.

Drawing