ES2371769T3 - APPARATUS AND PROCEDURE FOR CONTROLLING COMPACTION THROUGH ISostatic MOLDS. - Google Patents

Abstract

Apparatus for controlling the compaction of the powder in a mold for ceramic products by means of a punch of the isostatic type comprising an air space within which an amount of oil is provided that is sufficient to support the elastic pressing membrane, characterized in that said The air space is put in communication with a tank (6) and a feed pump (7) by means of a volumetric measuring device (5) that sends the desired amount of oil to the mold air space, said device being associated for measuring with a means of detection and reading (56) of the amount of oil sent to the air space of the mold, and being associated with valve means (81, 82, 83) for supplying, blocking and discharging the oil to the , in and from the mold air space, to ensure the presence in said air space of a predefined volume of air for each stage of the compaction cycle.

Description

Apparatus and procedure for controlling compaction by isostatic molds.

The present invention relates to an apparatus and a method for controlling the compaction of the powder in a mold for ceramic products by means of an isostatic punch according to the preamble of claims 1, 5, respectively.

In order to ensure the homogeneous compaction of the powder, necessary to avoid variations in the size of the finished product, one of the punches of the mold for normal ceramic products comprises a metal base in which an air gap is defined. This air space is closed by a deformable membrane designed to come into contact with dust and filled with a liquid, usually oil.

The air space may comprise a grid that defines a series of intercommunicated cells to whose upper edge the membrane is fixed.

The filling of the air space by oil takes place by regulating the pressure inside the punch, causing an elastic deformation of the membrane that remains in contact with the upper part of the grid to which it is fixed.

Variations of the isostatic mold are known, in which the membrane is supported on the metal base and is attached thereto only in distributed areas, so that adjacent communication zones are defined in which the membrane is simply supported on the base. metallic

The supply of pressurized oil between the membrane and its level of support causes the deformation of the membrane with a series of undulations designed to counteract the pressing pressure in an isostatic way.

Both known forms of isostatic mold are characterized in that they contain an amount of oil that remains constant throughout the duration of the molding, with the exception of possible leaks or losses.

Known isostatic molds often provide that the isostatic punch equipped with a membrane is the lower punch of the mold, which defines the base of the mold cavity in which the powder to be pressed is received.

The widespread use of isostatic molds has revealed a number of drawbacks that take place in the powder press cycle produced by the raw tile that is then put on fire.

The most obvious drawbacks arise from the fact that the amount of oil contained in the mold air space remains constant during the cycle.

In fact, the oil modifies its own physical-chemical characteristics with aging and can become aggressive over time with regard to the membrane: taking into account the very high tension to which it is subjected, which can reach hundreds of kg per square cm, this phenomenon considerably shortens the life of the mold.

In addition, it is impossible to avoid small leaks and losses of oil during the life of the mold, leaks and losses that modify the behavior of the punch, favoring, for example, the phenomenon called transparency, due to which, the design of the grid of the mold or the back grid of the tile, which generally coincide with each other, is visible on the side when the tile itself is observed. In addition, in any case, both coinciding with the loading of the powders and the discharge of the powders from the mold, the undulations of the membrane are the origin of the phenomenon of deterioration.

During the discharge of the powders, they induce an irregular distribution of the powder itself with possible compaction differences between the areas of the membrane deformed by the oil and those attached to the iron base.

During the removal of the tile from the inside of the cavity in which it was formed, the elastic action of the punch can cause defects or breakage of the tile itself.

During the expulsion of the tile, the undulations of the membrane project beyond the upper face of the matrix of the mold, and the tile that comes out rubs with them, which causes premature localized wear and deterioration.

JP 2003 260600 discloses an apparatus for controlling powder compaction in a mold for ceramic products according to the preamble of claim 1, and shows a system for feeding oil to

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pressure to a mold to print integrated circuit cards. Said apparatus comprises a piston and double cylinder group, consisting of two cylinders, the cylinder being arranged in series and each of said cylinders having two parts and a common axis for both cylinders. The cylinder arranged above the mold is a double acting cylinder and can act in both directions in a compression and expansion manner. During compression, said upper cylinder acts, by means of the common axis, connected by means of a connecting element, on the lower cylinder by compressing a mold chamber and, as a consequence, increases the oil pressure in said mold; The same cylinder can act to decompress the oil, reducing the pressure in the mold.

The hydraulic circuit is divided into two parts, because in the branch of the circuit that is connected to the mold a thermal oil is used, while in the rest of the circuit, with separation between fluids with respect to the branch that contains the thermal oil, It contains another type of oil. In addition, a blocking valve is not provided under the cylinder acting directly on the mold. As a consequence, during the pressing operation, the pressure in the mold moves back to the cylinder.

Document GB 1 234 978 shows a pusher that can be stopped in a plurality of operating positions during the pressing cycle.

The oil feed to the pusher is regulated by a control system to which information about the pusher positions is fed. Said device provides position transducers, such as a potentiometer that generates an electrical signal corresponding to the adjustment of the pump that drives the pusher and an indicator of the position of said pusher. However, said press is not an isostatic press.

Document DE 43 20 203 shows a hydraulic press which provides on both sides of the mold elastic membranes that can vibrate.

The oil pressure is fed from a pump associated with a reservoir and the hydraulic circuit opens and closes quickly by means of a device that drives a valve that opens and closes the oil inlet to the cylinder. In this way, a variable and pulse pressure is created on the elastic membranes.

In this case, a blocking valve is also not provided below the cylinder, so that the pressure in the mold returns to the cylinder.

EP 0 659 572 shows a method and an apparatus for the manufacture of ceramics with an isostatic mold. A hydraulic cylinder and piston group is provided that drives a hydraulic press connected to a hydraulic circuit which, in turn, provides a valve group and a pressure multiplier. During any individual pressing action, the valve opens when a pressure is lower than the maximum operating pressure of the cylinder and hydraulic piston group, while the opening in the opposite direction of the valve group acts on repositioning the pressure multiplier . Thus, under the membrane in the compressed area between the pattern in which the bases of the tile are formed, a hydraulic pressure is achieved that is sufficient to raise the tile in the final phases of pressing.

US Patent No. 4,718,842 shows a press provided with a position transducer and optoelectronic means to reference the position of a first press plate.

The objective of the present invention is to eliminate the aforementioned drawbacks with the intention of obtaining a simple and economical solution.

This objective is achieved by means of an apparatus and a method for controlling the compaction of the powder in a mold for ceramic products by means of a punch of the isostatic type according to claims 1 and 5, respectively.

The pressing system according to the invention provides for the use of an isostatic mold substantially of the known type, associated with means for feeding and controlling the oil contained therein.

Said feeding and control means comprise a volumetric measuring device adapted, in each pressing cycle, to insert a precise and desired volume of oil into the punch, means adapted to discharge all the oil contained in the punch in each cycle of Pressed and, finally, means for sending to an oil tank contained inside the pad, with the modes defined below.

At the beginning of the use of the punch, the operator decides the measured amount of oil that should be in the pad. At the beginning of the pressing cycle, the amount of oil contained in the punch is equal to zero or, in any case, it is an amount that does not deform the elastic membrane.

This situation is maintained during the powder loading stage, and during the low pressure corresponding to the dust deaeration stage.

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At the end of these stages, or partially during them, the desired volume of oil is inserted into the mold, so that it is in the normal operating configuration at the time it receives the impact of compaction, and distributes the pressure of compaction in an isostatic way.

When the compaction is completed, the previously inserted oil is removed from the mold, which is again in the starting state.

The advantages and structural and functional characteristics of the invention will be apparent from the following detailed description, illustrated in the figures in the tables of the attached drawings and which are provided by way of non-limiting example.

Figure 1 schematically illustrates an isostatic punch according to the invention with a related hydraulic scheme.

As can be seen in the figure, the punch 1 is inserted into a mold of which only matrix 2 can be seen; known wear plates 11 are fixed peripherally to said die level with the upper edge. The punch comprises a metal body 10.

The upper surface of the body 10 provides a network of grooves 12 and a corresponding network of conduits 13, whose vertical segments lead to the center of the areas defined by the grooves.

The ducts 13 lead to a single manifold 14 which, in turn, leads laterally to the outside of the body

10.

The areas defined by the grooves 12 are covered by a non-stick substance before casting and the elastic membrane 3 is vulcanized or polymerized in situ; thus, said elastic membrane is adherent to the metal body only in the grooves and along the periphery.

The powder 4 to be compressed is supported on the membrane 3. When oil is inserted through the ducts 13, it is distributed in the areas between the grooves, swelling the upper membrane which, thus, gives the punch the isostatic property.

The volumetric measuring device 5 is shown in the figure, schematized as a cylinder 51, in which a hermetic piston 52 slides, dividing the interior of the cylinder into two chambers 54 and 55.

The rod 53 is associated with a detection and measurement device 56 of the piston translations, which defines the volume of oil fed by the measuring device.

The chamber 54 of the cylinder is connected to an oil tank 6 via the pump 7 and the valve 81.

The chamber 55 of the measuring device is connected to the manifold 14 with the interposition of a valve 82, and to the conduit connecting the pump 7 and the valve 81 with the interposition of the valve 83.

The manifold 14 is connected directly to the reservoir 6 with the interposition of a two-way valve 84.

The operation of the device is as follows.

The configuration of the system illustrated in the figure corresponds to the elevated position of the upper transverse element of the press, which is not illustrated.

The operator decides in advance the volume of oil that he wishes to insert into the punch depending on the geometry of the pad, properly reading the device 56 which is a position transducer, and making sure that the conduction and the chambers 54 and 55 of the Measuring device are full of oil.

Once this stage has been carried out, the valves 81, 82, 83 and 84 together with the device 56 are connected to the mold control system, for example a PLC, which regulates the following operations in relation to the stage of the press cycle.

During the descent of the transverse element, and the operation until a pressing cycle stage that can be initiated by the operator, normally the deaeration stage, the system configuration does not change.

Once the above mentioned stage is completed, the control system causes almost simultaneously:

the start of the pump 7, the movement (to the left in the figure) of the valve slide 81 and the

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movement (to the right in the figure) of the valve slide 82.

As a consequence, the pump feeds pressurized oil into the chamber 54 of the measuring device and the piston moves, transferring the oil contained in the chamber 55 of the measuring device into the mold.

As soon as the device 56 indicates that the desired oil volume has been transferred under the membrane 3, which takes place before the necessary pressing to ensure the final compaction of the tile, the valve slider 81 is repositioned in the center , and the valve slide 82 is repositioned to the left.

In this way, the punch is isolated from the measuring device and acts as a normal isostatic punch in the subsequent pressing stages.

During the last pressing, when the tile has already been compacted, a certain thrust is maintained in said tile, and the valve slide 82 is repositioned to the right as well as the valve slide 81. The thrust acting on the tile compresses the membrane 3 which, in turn, pushes the oil present in the pad. In this way, the oil can leave the punch towards the chamber 55 of the measuring device which, like the valve slider 81 has moved to the right, is connected to the reservoir 6; thus, the piston 52 moves to the left, returning to its initial position.

The control system waits for the punch to be completely discharged by the pressure transducer 56, then the valve slide 82 is repositioned to the left, the valve slide 81 is repositioned in the center and the cycle continues pressed normally.

Whenever you want to change the oil inside the pad, the following cycle is carried out:

the valve slider 82 moves to the right as well as the valve slider 84, the valve slider 81 moves to the left, so that it connects the chamber 54 with the pump line, while the punch and the chamber 55 of the measuring device is arranged in connection with the reservoir 6, so that the piston 52 moves to the right and the oil present in the punch is sent to the reservoir. When the piston reaches a defined position detected by transducer 56, the valve slider 82 moves to the left, the valve slider 84 moves to the left, the valve slider 83 moves to the left and, finally, the valve slider 81 moves to the right, so that chamber 55 communicates with the pump, while chamber 54 communicates with the reservoir and, thus, piston 53 moves towards left until it reaches a position detected by transducer 56.

Finally, the valve slide 83 moves to the left, the valve slide 84 moves to the left and the valve slide 81 returns to its initial position.

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Claims (5)

1. Apparatus for controlling the compaction of the powder in a mold for ceramic products by means of a punch of the isostatic type comprising an air space within which an amount of oil is provided that is sufficient to support the elastic pressing membrane, characterized in that said air space is communicated with a reservoir (6) and a feed pump (7) by means of a volumetric measuring device (5) that sends the desired amount of oil to the mold air space, being said measuring device associated with detection and reading means (56) of the amount of oil sent to the mold air space, and being associated with supply, blocking and discharge valve means (81, 82, 83) 10 of the oil to, in and from the mold air space, to ensure the presence in said air space of a predefined volume of air for each stage of the compaction cycle. 2. Apparatus according to claim 1, characterized in that the air space of the mold is in Direct communication via a valve (84) with the air reservoir (6) without passing through the measuring device (5). 3. Apparatus according to claim 1, characterized in that the measuring device (5) is composed of a cylinder divided into two parts (54, 55) by means of a piston (52), of which one (54) is connected to the pump (7) by means of a three-way valve (81), while the other (55) is connected to the mold air gap by 20 means of a two-way valve (82) and to the pump supply line (7) by means of a two-way valve (83). 4. Apparatus according to claim 3, characterized in that the piston (52) comprises a rod associated with a position transducer (56). 25 5. Method for controlling the compaction of powders in a mold for ceramic products by means of an isostatic punch comprising an air gap in which an amount of oil is disposed using the apparatus according to any of claims 1 to 4, which includes the following operations: 30 - feed a measured amount of oil into the air space that is sufficient to support the elastic pressing membrane;

-

the stage of loading the powder into the mold cavity and carrying out a first stage of light compaction

corresponding to the dust deaeration stage; 35

-

insert a measured volume of desired oil into the air space so that, in its normal operating configuration at that time, it receives the impact of the final compaction and distributes the compaction pressure in an isostatic manner;

40 - extract from the air space at least the previously inserted oil which, once again, returns to the starting state. E06075716 11-15-2011