WO2023099980A1 - Injector for wax, plastic, resin or other material to be injected - Google Patents

Abstract

Described is an injector (1) for wax, plastic, resin or other material to be injected into moulds to be filled, comprising, on a load-bearing frame (9), a main tank (2) for the material to be injected which has a pressure (Ps) less than the external pressure (Pa), at least during a step of the work cycle. The tank (2) is equipped with means for heating the material to be injected in such a way as to guarantee its fluidity. There are also injection means (3, 31, 32, 33) in communication with the main tank (2), which comprise an injection syringe (3) for containing the material to be injected and designed to have a pressure (Pi). The syringe (3), by means of an exchange valve (5), is in communication with the main tank (2) and is connected to an injection nozzle (6) for a mould to be filled. Moreover, the exchange valve (5) is interposed between the main tank (2) and an auxiliary tank (4), in turn designed to place in communication the main tank (2) and the mould to be filled. The exchange valve (5) also comprises means (51, 52, 53) for simultaneous regulation of the locking pressure of the mould to be filled and the injection pressure of the material to be injected. In this way, the distribution of the material to be injected is allowed according to the pressure differential created between the various components of the injector (1).

Description

Injector for wax, plastic, resin or other material to be injected

Technical field

This invention relates to an injector for wax, to be used in the goldsmith's, silversmith's and costume jewellery sector, which allows the injection of wax, plastic, resin or other materials which can be injected into rubber moulds to be filled, for fusion or micro-fusion with a lost wax mould.

According to the prior art, the injectors for wax, plastic, resin or other material to be injected into rubber moulds are formed by two medium-large tanks, positioned one inside the other, the first, outer tank, under pressure, designed to contain the wax to be injected under pressure and the second, inner tank, in which the vacuum is substantially formed.

These injectors place the tank under pressure and the injection channel is opened to inject the wax directly from the outer tank into the mould, using a special nozzle.

However, machines of this type are not very precise because a considerable amount of air remains in the outer tank (under pressure) which, acting as a cushion/spring, does not allow a precise injection.

In addition, wax is in contact with air in the outer tank, which is under pressure, absorbing moisture and favouring the formation of microbubbles. Moreover, as the tank gradually empties the wax reduces, while the air, which is compressible, increases. This leads to the injection of wax with a non-constant weight, with two macroscopic consequences: firstly, the wax models produced in rubber moulds are not perfect, but have obvious burring; even more seriously, the final parts will have different weights, which is a serious problem if the products are made of precious metal, such as gold, platinum, etc.

Background art

In order to overcome this problem, in some cases the vacuum has been created in the mould by means of the inner tank (using the nozzle), however, in order to reach a satisfactory vacuum level the injector takes a considerable amount of time.

Another drawback of prior art injectors is due to the use of a distribution valve which in turn mounts a non-return valve with elastic operation. In practice, the non-return valve, by means of an abutment spring interposed between a wall of the housing defined inside a duct for communication between the wax containment tank and injector means and a slider, opens and closes an injection channel.

In this way, the non-return valve is able to modulate the opening and closing of the injection channel in a very simple manner, however, since it is not moved mechanically, it is affected by the soiling of the wax which over time causes an imperfect closing of the injection channel.

Another problem with these injectors is due to the fact that the excess wax settles in the vacuum tank and remains there forcing the operator to empty the wax from the vacuum tank by hand to carry out the cleaning.

Summary of the Invention

The aim of the invention is to overcome the above-mentioned drawbacks of prior art injector types for wax, plastic, resin or other material to be injected into moulds to be filled which allows wax models to be obtained which are substantially identical to the negative rubber mould, without burrs and of homogeneous weight.

In the context of the above-mentioned purpose, an aim of the invention is to provide a wax injector, which reduces the injection times.

Another aim of the invention is to allow a facilitated cleaning of the parts of the machine, in particular the wax tank.

Another aim of the injector according to the invention is to eliminate the need to perform the degassing of the wax in advance.

Yet another aim of the invention is to provide a wax injector, with means which are readily available on the market and using materials of common use, in such a way that the device is economically competitive.

This purpose, as well as these and other aims, which are described in more detail below, are achieved by a wax injector according to the invention comprising the technical features described in one or more of the appended claims. The dependent claims correspond to possible different embodiments of the invention.

More specifically, according to a first aspect, the invention relates to an injector for wax, plastic or resin to be injected into moulds to be filled, which comprises, on a load-bearing frame, a main tank for the material to be injected which has a pressure less than the external pressure (substantially equal to the atmospheric pressure) at least during a step of the work cycle and injection means in communication with the main tank. The main tank is also equipped with means for heating the material to be injected, in such a way as to guarantee its fluidity, that is to say, a substantially liquid state. The injector has an injection syringe which has a pressure less than that of the main tank during at least one step of the work cycle. The injection syringe is interposed and in communication between the main tank and the mould to be filled, that is to say, with a nozzle for the mould, by means of an exchange valve. Moreover, the exchange valve is interposed between the main tank, the auxiliary tank and the injection means and has means for simultaneously regulating the locking pressure of the mould and the injection pressure. In this way, advantageously, the distribution of the wax or the material to be injected is allowed, according to the pressure differential created between the various components of the injector.

Preferably, the auxiliary tank is in turn interposed between the main tank and the mould to be filled.

Advantageously, again for reasons of overall size and practicality, the exchange valve comprises: an injection channel for the passage of the wax between the syringe and the nozzle; a refilling channel connecting the main tank and the syringe; a vacuum channel connecting between the auxiliary tank and the nozzle; and a cleaning channel connecting the main tank and the auxiliary tank. The Applicant has understood that, by suitably moving the regulating means, in such a way as to open/close the above-mentioned channels, the injector could completely serve an injection station, satisfying all the needs linked to the injection of wax into moulds, including cleaning of the tank and parts of the machine.

Advantageously, the Applicant has provided that the main tank can be made available for a further injection unit, the latter comprises second injection means identical to the injection means already described, a second auxiliary tank also similar to that described previously, as well as a second exchange valve equal to the other exchange valve.

Preferably, the regulating means comprise three pistons.

Description of the drawings

Further features and advantages of the invention are more apparent in the detailed description below, with reference to a preferred, non-limiting embodiment of the wax injector, illustrated by way of example and without limiting the scope of the invention, with the aid of the accompanying drawings, in which:

Figure 1 shows a plan view of an example embodiment of the injector 1 ;

Figure 2 shows a side view of the injector 1 of the previous drawing;

Figure 3 is a cross section substantially normal to the ground of the injection syringe 3, with enlargement in the joint between the piston 31 and the plunger 33;

Figure 4 is a perspective view of the injection syringe 3 of the previous drawing;

Figures 5A-5E schematically illustrate the operation of the exchange valve 5.

Detailed description

The above-mentioned drawings show a preferred embodiment of a wax injector, according to the invention, which is denoted in its entirety with the numeral 1 and which comprises, on a load-bearing frame 9, firstly a main tank 2 for the wax, which has an operating pressure Ps less than the external pressure (atmospheric Pa) and which is therefore substantially a vacuum at least during the work cycle. In this way, all the bubbles and the microbubbles from the wax are advantageously eliminated and, moreover, moisture is removed from the wax.

In particular, the vacuum in the tank 2 is created by means of a motor driven vacuum pump in an oil bath, electronically controlling the start time and the value reached, so as to remain between 250 and 350 mbar during the working operation.

Alternatively, a Venturi tube can be used.

The tank 2 is suitably heated, using heating means of essentially known type, to guarantee the fluidity of the material to be injected, which must be substantially liquid during the work cycle. In this regard, the main tank 2 is preferably made of aluminium and, if necessary, thermally insulated; however, according to other embodiments, the tank 2 is made of other materials: according to a variant embodiment, for example, it has a single chamber which has an inner jacket made of steel or aluminium, for containing the wax, and an outer layer for the vacuum.

The injector 1 also comprises injection means, such as an injection syringe 3 which comprises a piston 31 , with a different volume on the basis of the model, preferably of the pneumatic type, which acts in a cylinder 32 by means of a plunger 33. The piston 31 is controlled by a proportional valve (or proportional regulator) 35, during suction and discharging, along its movement in the direction of extension 30. The valve 35 is in turn controlled by an electronic control unit (not illustrated) which may be a PLC or an electronic card with parameters set by an external screen or by any graphical interface for controlling the injection station.

Obviously, in the case of a double injection station, there would preferably be a second interface for controlling the second injection means, the second auxiliary tank and the second exchange valve.

Advantageously, the piston 31 and the plunger 33 are mutually interconnected in such a way as to form a clearance sufficient to allow the loading and injection of the wax without creating stresses inside the cylinder 32.

In this regard, the shank 31 A of the piston 31 has a housing compartment 31 B, preferably in the shape of an inverted “LT, designed to be engaged by a protrusion 33B, preferably T-shaped, defined on the head 33A of the plunger, in such a way that the protrusion 33B and the compartment 31 B are mutually interlocked along the direction of extension 30 of the piston 31 (Figures 3 and 4).

The Applicant has understood that by making the protrusion 33B and the plunger 33 in a single-block made of aluminium, an improved operation and an improved assembly could be achieved.

There is also an auxiliary tank 4 where a “strong" vacuum is formed, that is to say, with a pressure Pv of the tank 4 less than the pressure inside the main tank 2, Ps, during operation, which is used to form the vacuum in the rubber mould.

The vacuum in the mould is formed by another solenoid valve by means of a motor driven vacuum pump, which is also in an oil bath, which reaches a final high vacuum pressure (Pv).

One feature of this injector is to provide an exchange valve 5 which is able to regulate the flow "traffic" between the tank 2, the auxiliary tank 4 and the mould to be filled, obviously by using the syringe 3.

For this purpose, the exchange valve 5 comprises at least four channels: an injection channel 81 for the passage of the material to be injected between the syringe 3 and the nozzle 6; a refilling channel 82 for connection between the tank 2 and the syringe 3, which allows the hot wax to be sucked from the main tank 2; a vacuum channel 83, connecting the auxiliary tank 4 and the nozzle 6, for creating a vacuum in the mould; and a cleaning channel 84 for connecting the tank 2 to the auxiliary tank 4, which is able to suck the wax remaining in the tank 4 and return it to the main tank 2.

According to a first embodiment, the means for simultaneously regulating the locking pressure of the rubber mould and the injection pressure of the wax, formed inside the valve 5 consist of two pistons, which can be moved independently of each other, made of standard steel or aluminium: a primary piston, for opening and closing the injection channel 81 , and a secondary piston, for opening and closing at least one between the refilling channel 82, the vacuum channel 83 and the cleaning channel 84.

According to the preferred embodiment, on the other hand, the valve 5 is formed by three pistons: a first piston 51 , which opens/closes the channel between the main tank 2 and the syringe 3, in such a way as to load wax into the syringe 3, a second piston 52 and a third piston 53 which, used to maintain the closed position when the machine is stationary, form the vacuum in the mould to be filled, inject the wax (also plastic or resin) and during cleaning, since they open and close at least one between the refilling channel 82, the vacuum channel 83 and the cleaning channel 84.

In addition, the Applicant has preferably provided the pistons 51 , 52 and 53 with sealing gaskets located at the ends of the pistons.

Preferably, the pistons 51 , 52 and 53 act slidably on respective housing cavities 55, 55' and 55" formed in the drawer valve 5.

The Applicant has found that forming the two bodies, that is to say, the cavities 55, 55' and 55" and pistons 51 , 52 and 53, both made of steel, the seal arrives only thanks to the tolerances which are centesimal, otherwise the valve 5 does not operate.

Since the achievement of tolerances of this type is extremely expensive, in order to reduce the cost of making the drawer valve 5 and the injector 1 , just the inner walls of the cavities 5 and the pistons 51 , 52 and 53 have been made of aluminium.

In order to compensate for the different tolerances created during heating of the machine - where the operating temperature can also reach 70/80°C - and which are due to the different thermal behaviour of the two metals (steel and aluminium), the Applicant has advantageously provided seals made of silicone material, preferably the commercially available material known as Viton®, to be mounted in the pistons 51 , 52 and 53, in such a way as to prevent further machining on the pistons.

The pistons 51 , 52 and 53 are preferably moved electrically or pneumatically by means of a solenoid valve and, advantageously, all have a shaped shank, that is to say, equipped with recesses and protrusions for locking or releasing the injection 81 , refilling 82, cleaning 83 and vacuum 84 channels at least one at a time. In this way, the movement of the piston 51 , 52 or 53 along the respective axis of symmetry 50, 50', or 50" substantially normal with respect to the direction of extension 30, determines the opening or closing of the corresponding channel.

With reference to Figures 5A-5F, the operating logic of the exchange valve, preferably actuated through an electronic control unit, is as follows.

According to the closed configuration of the valve 5, which is the initial configuration (that is to say, when the injector 1 is at rest), the piston 51 blocks the refilling channel 82 interfering in the flow of wax between the main tank 2 and the syringe 3, whilst the pistons 52 and 53 block the injection channel 81 , preventing the wax from being fed by the nozzle 6. In this configuration, the piston 52 closes the passage of the vacuum channel 83 and the cleaning channel 84 is also closed by the piston 53. In practice, all the channels 81 -84 are locked by the pistons 51 -53 (Figure 5A).

At this point, the piston 52 translates along the axis 50', in such a way as to open the vacuum channel 83 and allow air to be sucked in from the nozzle 6, connected to the mould. On the other hand, at the same time, the vacuum is formed in the auxiliary tank 4. In this way, the air sucked in flows along the channel by pressure difference, since a pressure Pv is produced in the tank 4 which is less than the atmospheric pressure present in the mould: PV<Pa. The other pistons 51 and 53 remain in the initial position keeping the channels 81 , 82 and 84 closed. In this way it is possible to remove all the air from the mould (Figure 5B).

Once the vacuum is created in the mould, the piston 53 translates along the axis 50" (in the opposite direction with respect to the previous translation of the piston 52) in such a way as to close the channel 83 but opening the injection channel 81 which passes the wax up to the nozzle 6, so as to allow the injection of hot wax into the mould. The other channels, 82 and 84, remain closed (Figure 5C).

The injection pressure is variable and can be regulated electronically by means of the proportional regulator 35 (Figure 2).

In the meantime, the pressure in the auxiliary tank 4 reaches a value equal to the external one (Pv=Pa) and the piston 52 therefore moves, returning to the initial position and unlocking the cleaning channel 84 which, open in this way, allows the wax remaining in the tank 4 and in the nozzle 6 (in the injection step) to move towards the main tank 2 due to the pressure difference created: Ps<Pv(=Pa). The other pistons 51 and 52 remain in their previous position in such a way as to close the other channels 81 -83 (Figure 5D).

At the end of the cycle, after the cleaning as described in the previous step, the pistons 51 and 53 move simultaneously along the respective axes 50 and 50" in the opposite direction with respect to each other: the piston 51 frees the refilling channel 82 allowing the syringe 3 to suck the wax from the tank 2 thanks to the raising of the piston 31 (Ps>Pi), whilst the piston 53 closes the cleaning channel 84. In other words, the injection syringe 3 is filled by giving opposite pressure to the piston 31 and creating a pressure difference thanks to the greater vacuum formed in the cylinder 32 than that present in the main tank 2: Pi<Ps (Figure 5E).

Once refilling is completed, the piston 51 moves in the opposite direction along its axis 50 by closing the channel 82 and returning the exchange valve to the initial configuration, that is to say, with all the channels 81 -84 closed (Figure 5F).

The closed configuration of the valve 5 is maintained when the machine is stationary and does not work: it is used to close the vacuum channel 83 and the wax injection channel 81 .

Figures 5A-5F also show plugs 91 for closing the machining grooves formed for making the channels 81 -84.

Preferably, the operating pressures Ps and Pv, respectively referred to the main tank 2 and the tank 4, are controlled by means of electronic sensors, of perse known type.

From the above description it may be seen how the invention achieves the preset purpose and aims and in particular it should be noted that an injector is made for wax, plastic, resin or other material to be injected into moulds which makes it possible to obtain wax models identical to the negative rubber mould and without burrs.

In particular, the making of the injection syringe in which the wax is practically already degassed (the degassing occurs in the main tank) offers an extremely precise injection, without the large quantity of air normally located in the pressurised tank forming a cushion, causing the air to float due to its compressibility.

Another advantage of the invention is due to the fact that an injector of this type, thanks to the injection syringe, guarantees a substantially homogeneous density of all the wax during the machining cycle, avoiding the formation of moisture and microbubbles in the injectable material, so as to ensure that even the micro-cast pieces of jewellery will be cleaned and similar in shape and weight.

Another advantage of the invention is to allow a facilitated cleaning of the parts of the machine, by suitably programming the exchange valve.

Lastly, the use of means which are easily available on the market and the use of common materials makes the device economically competitive.

The invention can be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

Moreover, all the details of the invention may be substituted by other technically equivalent elements.

In practice, the materials used, as well as the dimensions, may be of any type, depending on requirements, provided that they are consistent with their production purposes.

Claims

1) An injector (1 ) for wax, plastic, resin or other material to be injected into moulds to be filled, comprising, on a load-bearing frame (9): a main tank (2) for the material to be injected, designed to have a pressure (Ps) less than the external pressure (Pa) at least during a step of the work cycle and provided with means for heating the material to be injected in such a way as to guarantee its fluidity; injection means (3, 31 , 32, 33) in communication with said main tank (2), comprising an injection syringe (3) for containing the material to be injected and designed to have a pressure (Pi) and which, by means of an exchange valve (5), is in communication with said main tank (2) and is connected to an injection nozzle (6) for a mould to be filled; said exchange valve (5) being interposed between said main tank (2) and an auxiliary tank (4), in turn designed to put in communication said main tank (2) and the mould to be filled; said exchange valve (5) also comprising means (51 , 52, 53) for simultaneous regulation of the locking pressure of the mould to be filled and the injection pressure of the material to be injected, in such a way as to allow the distribution of the material to be injected according to the pressure differential created between the various components of the injector (1 ).

2) The injector (1 ) according to the preceding claim, wherein said injection syringe (3) is designed to be interconnected between said main tank (2) and the mould to be filled.

3) The injector (1 ) according to the preceding claim, wherein said injection syringe (3) comprises, inside it, a piston (31 ) controlled by a proportional valve (35) for suction and discharge along a relative direction of extension (30), which is in turn controlled by an electronic control unit, and engagement for a cylinder (32) by means of a plunger (33); said piston (31 ) and said plunger (33) being mutually interconnected in such a way as to form a clearance sufficient to allow the loading and injection of the wax without creating stresses inside said cylinder (32); the shank (31 A) of said piston (31 ) having a housing compartment (31 B) designed to be engaged by a protrusion (33B) defined on the head (33A) of said plunger (33) and made of a metal monoblock, preferably made of aluminium.

4) The injector (1 ) according to any one of the preceding claims, wherein said exchange valve (5) comprises: an injection channel (81 ) for the passage of the material to be injected between said injection syringe (3) and said nozzle (6); a refilling channel (82) for connection between said main tank (2) and said injection syringe (3); a vacuum channel (83) for connection between said auxiliary tank (4) and said nozzle (6); and a cleaning channel (84) for connection between said main tank (2) and said auxiliary tank (4).

5) The injector (1 ) according to any one of the preceding claims, wherein said regulating means (51 , 52, 53) comprise at least two pistons (52, 53), a first piston (52) and a second piston (53), defined inside the frame (50) of said exchange valve (5) and designed to be moved independently of each other.

6) The injector (1 ) according to the preceding claim, wherein said first piston (51 ) is for opening/closing said injection channel (81 ) and said second piston (52) is for opening/closing at least one between said refilling channel (82), said vacuum channel (83) and said cleaning channel (84).

7) The injector (1 ) according to the preceding claim, comprising a third piston (53) defined inside said frame (50) and designed to be moved independently of said first piston (51 ) and of said second piston (52); said third piston (53) being, in conjunction with said second piston (52), for opening/closing at least one between said refiling channel (82), said vacuum channel (83) and said cleaning channel (84).

8) The injector (1 ) according to any one of claims 5 to 7, wherein each of said at least two pistons (51 , 52, 53) has a shaped shaft equipped with recesses and protrusions for locking or unlocking at least one at a time between said injection channel (81 ), said refiling channel (82), said vacuum channel (83) and said cleaning channel (84), in such a way that its movement along an axis of symmetry (50, 50', 50") determines the opening or closing of the respective injection channel (81 ) and/or said refiling channel (82) and/or said vacuum channel (83) and/or said cleaning channel (84).

9) The injector (1 ) according to any one of claims 5 to 8, wherein said drawer valve (5) comprises at least one housing cavity (55, 55' and 55") designed to be slidably engaged by a respective one of said pistons (51 , 52, 53) and comprising an inner wall, preferably made of steel, of the same metallic material as that used to make the outer surface of said respective pistons (51 , 52, 53).

10) The injector (1 ) according to the preceding claim, wherein a seal made of silicone material is mounted on said at least one of said pistons (51 , 52, 53), in such a way as to compensate for the construction tolerances following the thermal deformation of the processing cycle between said at least one of said pistons (51 , 52, 53) and the respective housing cavity (55, 55', 55").