ITMC20130029A1 - INJECTION MOLDING MACHINE WITH DOSING TANKS. - Google Patents

Description

DESCRIPTION

accompanying a patent application for an industrial invention entitled:

“INJECTION MOLDING MACHINE WITH DOSING TANKS”.

TEXT OF THE DESCRIPTION

The present patent application for industrial invention relates to an injection molding machine with dosing tanks.

In multi-cavity injection molding of traditional thermoplastic materials, the perfect balance of the injection system is not always a sufficient condition to guarantee a perfect weight balance between the different cavities; this is because unevenness in temperature levels are always possible. Sometimes, even a few degrees of difference between the different cooling zones can lead to weight imbalances.

Also for this reason, after the injection of thermoplastic material, a maintenance phase is always used. In fact, keeping a fluid material under pressure within a series of communicating cavities involves an almost complete balance in the filling of the cavities.

However, it is not always possible to use a maintenance phase in injection molding. In fact, some materials have such characteristics that they cannot be compacted. This is the case, for example, of those polymers added with blowing agents, or in the context of thermosetting agents, of Liquid Silicone (LSR).

These drawbacks are solved at least in part by the use of dosing tanks, also called "Shooting Pot", to introduce a dosed volume of thermoplastic material or other material into a mold.

WO 2011/081694 and US6491509 describe the use of dosing tanks.

However, the molding systems with dosing tanks, according to the known art, are particularly complex and difficult to manufacture and manage.

In fact, the dosing tanks and the relative feeding channels are positioned completely inside the molds. As a result, there are high costs due to the construction of suitable seats of the dosing tanks, to the oversizing of the molds that must house said dosing tanks, to the maintenance or replacement of parts, since the mold must be completely disassembled with long production stops.

In addition, the mold must be designed and built according to the use of the dosing tanks. In fact, it would not be possible to adopt such systems in pre-existing molds not specifically designed.

The dosing tanks of the known art have functional inefficiencies, because they are fed with a LIFO (Last in First Out) logic. In fact, the dosing tank is generally fed from the same hole which is then used for the subsequent injection.

Although WO 2011/081694 describes the feeding of the dosing tank from a hole other than that of the injection, and arranged in an intermediate position of the dosing tank, in any case this tank works according to a LIFO logic. In fact, the material that enters first is the last to be then injected into the mold, with an evident lengthening of residence times and consequently an increase in the risks of degradation or prevulcanization in the case, for example. liquid silicone (LSR).

According to the known technique, the dosage in the shooting pot is achieved by adjusting, for each cavity, the distance of withdrawal or advancement of an injection piston present inside the dosage tank.

US6491509 describes this type of regulation, through a series of contrasts which also act as actuators of the piston of the shooting pot. These contrasts are perpendicular to the pistons of the shooting pots. The pistons of the shooting pots extend through special channels obtained in the mold and even in the press surfaces.

This conformation is very complex, expensive and not very flexible, since the mold must also provide a series of suitable channels in order to accommodate said contrasts / actuators. Once these channels have been made, it will no longer be possible to move them to any other position except by modifying the mold. Clearly it is not possible to use such a system in a traditional press that is not equipped with press plates drilled in correspondence with the position of the contrasts / actuators.

The object of the present invention is to obviate the drawbacks of the known art by providing an injection molding machine with dosing tanks that is versatile, economical, simple to manufacture and able to minimize the overall dimensions and costs of the molds.

Another object of the present invention is to provide such an injection molding machine with dosing tanks that is reliable, efficient and effective.

These objects are achieved in accordance with the invention with the characteristics listed in the attached independent claim 1.

Advantageous embodiments appear from the dependent claims.

The injection molding machine according to the invention includes:

- a base,

- two sides fixed to the base,

- a feeding unit fixed to the sides, into which the fluid material to be printed is fed,

- an upper cross member fixed to the sides,

- a plurality of injection nozzles mounted on the upper crosspiece, for injecting fluid material into a mold, - a plurality of metering tanks mounted on the upper crosspiece, in which each metering tank is connected to the supply unit and to the respective injection nozzle to feed fluid material to the injection nozzle,

- an injection plate mounted vertically sliding between the two sides and supporting a plurality of actuators that act within the respective dosing tanks to push the fluid material towards the injection nozzles,

- drive means for moving said injection plate so as to allow the transfer of fluid material from the dosing tanks to the injection nozzles,

in which said metering tanks, said injection plate and said actuators are separate and independent from the mold.

The machine according to the invention is capable of volumetrically dosing and transferring the quantity exactly necessary for the production of the required piece into the cavity of a mold. This occurs by means of the dosing tanks which are in a 1 to 1 ratio with the mold cavities. That is, each cavity of the mold has its own dosing tank.

The machine according to the invention can adapt to changes in production needs by decreasing the number of cavities to be fed and managed and the volumes required even with different volumes in the same mold.

The machine according to the invention guarantees correct molding even in all those cases in which the balancing of the cavities inside a multi-cavity mold can be problematic, such as in the case of injection of Liquid Silicone (LSR).

The machine according to the invention provides a system of independent and external dosing tanks to the mold, with its own motor and related drive controls. This allows you to easily use the machine according to the invention as a secondary injection unit to a traditional molding and also offers the possibility of using the machine according to the invention even in an assembly line.

Advantageously, the actuator of each dosing tank comprises a piston with a chamber and a stem with a duct for the passage of fluid material. Therefore, both the filling and the emptying of the dosing tank takes place coaxial to the piston following a FIFO logic. In practice, the first material to enter the tank is the first to be injected, thus minimizing the permanence of the tank material, reducing the risk of degradation or vulcanization.

The dosing tanks have a coaxial feed. The coaxial feeding of the dosing tanks and the fact that the toy car is made in an independent structure external to the mold allows you to easily combine each shooting pot with its own independent dye supply with its own static mixer. In practice, in the same mold each piece could have a different color.

In the machine according to the invention, the piston of the dosing tank does not require any adjustment, thanks to the provision of the first sleeve integral with the fixed table and the second sleeve integral with the injection plate connected to the mobile table. The adjustment of the material dosage takes place through a micro threaded ring nut of the first sleeve. This ring nut is completely external to the mold and housed in a separate structure. This means that the adjustment is very simple, fast and safe, as it must be carried out in an easily accessible area far from the hot mold. This construction method also makes it possible to control the threaded ring nuts even with servo actuators that can be set from the control panel.

Advantageously, each dosing tank is connected to a low pressure supply and to a colorant feeder. In this way, each single piece cavity could have a different color from the others.

Further characteristics of the invention will become clearer from the detailed description that follows with reference to the attached drawing tables, having only an exemplary and non-limiting value, in which:

Fig. 1 is a perspective view of the injection molding machine according to the invention;

Fig. 2 is a front view of the machine of Fig. 1; Fig. 3 is a sectional view, taken along the section III-III of Fig. 2, in which the dosing tank is full, at the beginning of the injection phase;

Fig. 3A is an enlarged detail of Fig. 3;

Fig. 4 is a view like Fig. 3, in which the metering tank is empty, at the end of the injection phase;

Fig. 4A is an enlarged detail of Fig. 4;

Fig. 5 is a perspective view like Fig. 1, but also illustrating the mold; And

Fig. 6 is a sectional view like Fig. 3, but also illustrating the mold.

With the aid of the Figures, the injection molding machine according to the invention is described, indicated as a whole with the reference number (100).

For now, with reference to Figs. 1 and 2, the machine (100) comprises a base (1), two sides (2) fixed to the base, an upper crosspiece (3) fixed to the two sides (2), and a plurality of injection nozzles (4) mounted on the upper cross member (3). Each injection nozzle (4) is fed by a respective dosing tank (shooting pot) (S) mounted in the upper crosspiece (3).

A fixed table (5) is fixed to the two sides (2) and a mobile table (6) is mounted sliding vertically between the two sides, below the fixed table (5).

The mobile table (6) is connected to an injection plate (7), by means of columns (8) which cross the fixed table (5). The injection plate (7) is mounted vertically sliding between the two sides (2) above the fixed table (5). On the injection plate (7) actuators are mounted which act within the respective dosing tanks (S) connected to the injection nozzles (4) for the injection of fluid material, as will be described in detail below.

A motor (10) is mounted on the crankcase (1). The motor (10) is preferably an electric motor of the brushless type, equipped with a servo-drive.

With reference to Fig. 3, the motor (10) comprises a motor shaft (11) with a vertical axis which crosses the base (1). A pulley (12) is mounted on the crankshaft (11) which drives a belt (13) to transmit a rotary motion to a screw (14). The screw (14) has a vertical axis parallel to the axis of the shaft (11) of the motor.

The screw (14) breads in a nut screw (15) integral with the mobile table (6). In this way the mobile table (6) can translate vertically, thanks to the rotation of the screw (14) which moves the nut screw (15). Preferably the nut screw (15) is ball recirculating.

A feeding / mixing unit (20) is fixed to the sides (2). The mixing unit (20) has the shape of a substantially U-shaped bracket, seen in plan, so as to protrude in front of the sides (2).

In the mixing group (20) there is a power inlet (21) for feeding the fluid material to be printed. A plurality of static mixers (22) are connected to the mixing group (20) to mix dyes with the material to be printed.

With reference to Fig. 3, each static mixer (22) comprises:

- a channel (23) communicating with the power input (21), e

- a colorant inlet (24) communicating with the channel (23) of the static mixer.

With particular reference to Fig. 3A, each dosing tank (S) comprises a body (30) within which a chamber (31) is formed which communicates with the injection nozzle (4) through a channel (32) obtained in the upper cross member (3). In particular, the injection nozzle (4) is of the shut-off type and includes a needle (70) regulated by a cylinder (71).

A piston (40) is slidably mounted in the chamber (31) of the storage tank body. The piston (40) has a rod (41) which protrudes from the lower part of the piston (40). The rod (41) has a smaller diameter than the piston (40) so as to define a shoulder (42) of the piston which forms an abutment surface.

In the piston (40) there is a chamber (43) communicating with a duct (44) which extends into the piston rod (41).

A one-way non-return valve (V) is arranged between the piston chamber (43) and the piston rod duct (44). The one-way non-return valve (V) allows the flow of material from the duct (44) of the piston rod to the chamber (43) of the piston and not vice versa.

A cap (45) is arranged at the upper end of the piston (40) to close the piston chamber (43). The cap (45) has ducts (46) which put the piston chamber (43) in communication with the chamber (31) of the metering tank body.

With reference to Fig. 3, the piston rod (41) extends below and passes through the injection plate (7) and the fixed table (5). The piston rod (41) has a lower end connected, by means of a flexible tube (47), to the static mixer (22). In this way the duct (23) of the static mixer (22) is in communication with the duct (44) of the piston rod.

Returning to Fig. 3A, a first sleeve (50) is mounted on the fixed table (5) and protrudes from the top of the fixed table, passing through the injection plate (7) and ending inside the chamber (31) of the dosing tank body. The piston rod (41) is slidably mounted within the first sleeve (50), to slide vertically. Then the first sleeve (50) acts as a guide for the piston rod (41).

With reference to Fig. 4A, the first sleeve (50) has an upper edge (50a) disposed in the chamber of the metering tank. The upper edge (50a) of the first sleeve acts as a stop for the piston (40). In fact, as shown in Fig. 3A, the shoulder (42) of the piston abuts against the upper edge (50a) of the first sleeve.

The first sleeve (50) is a micrometric adjustment ring nut screwed to the fixed table, so as to adjust the stroke of the piston (40) and therefore the quantity of material to be loaded into the chamber (31) of the dosing tank.

A second sleeve (51) is fixed to the injection plate (7) and protrudes from the top of the injection plate ending in the chamber (31) of the metering tank body. The second sleeve (51) is slidably mounted on the first sleeve (50). Then the first sleeve (50) acts as a guide for the second sleeve (51).

With reference to Fig. 3A, the second sleeve (51) has an upper edge (51a) disposed in the chamber of the metering tank. The upper edge (51a) of the second sleeve acts as an abutment surface to abut against the shoulder (42) of the piston, so as to push the piston (40) towards the other for the transfer of the material from the chamber (31 ) of the dosing tank to the injection nozzle (4).

The operation of the machine (100) according to the invention is described below.

With reference to Figs. 1, 2, 3 and 3A the machine (100) is fed with the fluid material through the inlet (21) of the power supply unit. The fluid material flows at low pressure into the channels (23) of the three static mixers (22), mixing with the colorant injected through the colorant inlets (24) of the static mixers.

The fluid material mixed with the dye flows through the flexible tube (47) and the conduit (44) of the piston rod. The non-return valve (V) is opened by the material pressure. In this way the material can flow into the piston chamber (43). Through the ducts (46) of the piston cap, the material flows from the piston chamber into the chamber (31) of the dosing tank, causing the piston (40) to retract to a limit switch position; that is, until the piston meets the upper edge (50a) of the first sleeve. This limit switch position is set by acting on the micrometric adjustment ring of the first sleeve (50).

Once the dosing tanks (S) have been filled, the servo motor drive (10) is activated. Then the motor (10), by means of the belt (13), the screw (14) and the nut screw (15), moves the mobile table (6). The mobile table (6), by means of the columns (8), moves the injection plate (7). The injection plate (7) moves the second sleeves (51) which cause the piston (40) to advance (see Figures 4 and 4A).

The pressure that is generated, in this way, inside the chamber (31) of the dosing tank full of material determines, at the same time, the closure of the non-return valve (V) and the high pressure injection of the material, through the channel (32) of the cross member and the injection nozzles (4). With reference to Figs. 5 and 6 the material is injected from the nozzles (4) into a cavity of a mold (200).

Once the injection is complete, the closing pin (70) of the injection nozzles is advanced through the cylinders (71), blocking the injection point of the mold cavity (200). At this point, after the extraction of the solidified pieces from the mold, the process can start again with the filling of the dosing tanks (S).

Although the machine according to the invention is particularly suitable for thermoplastic and thermosetting materials (such as liquid silicone), it is understood that the present invention extends to a machine for injection molding of any type of fluid material, such as for example waxes for crayons or candles and also in the food sector (such as chocolate).

Equivalent variations and modifications can be made to the present embodiment of the invention, within the reach of a person skilled in the art, which however fall within the scope of the invention.

Claims (10)

CLAIMS 1) Injection molding machine (100) comprising: - a base (1), - two sides (2) fixed to the base, - a feeding unit (20) fixed to the sides, into which the fluid material to be printed is fed, - an upper crosspiece (3) fixed to the sides (2), - a plurality of injection nozzles (4) mounted on the upper crosspiece (3), to inject fluid material into a mold (200), - a plurality of dosing tanks (S) mounted on the upper crosspiece (3), in which each dosing tank (S) is connected to the feeding group (20) and to the respective injection nozzle (4) to feed fluid material towards the injection nozzle, - an injection plate (7) mounted sliding vertically between the two sides (2) and supporting a plurality of actuators (40, 41) which act within the respective dosing tanks (S) to push the fluid material towards the nozzles injection (4), - drive means (10, 13, 14, 15, 6, 8) to move said injection plate so as to allow the transfer of fluid material from the dosing tanks to the injection nozzles, in which said metering tanks (S), said injection plate (7) and said actuators (40, 41) are separate and independent from the mold (200). 2) Injection molding machine (100) according to claim 1, wherein each actuator (40, 41) comprises a piston (40) slidably mounted in a chamber (31) of the dosing tank and a stem (41) which protrudes from the dosing tank (S), said piston (40) having a chamber (43) communicating with the chamber (31) of the metering tank and with a duct (44) which extends into the stem and is connected to the supply unit (20), to allow the passage of fluid material from the feed unit (20) to the chamber (31) of the dosing tank. 3) Injection molding machine (100) according to claim 2, comprising a non-return valve (V) disposed within each piston (40) between the piston chamber (43) and the piston rod duct (44), to allow the passage of material only from the rod duct towards the piston chamber. 4) Injection molding machine (100) according to claim 2 or 3, comprising a flexible tube (47) which connects the duct (44) of the rod of each piston to said supply unit (20). 5) Injection molding machine (100) according to any one of claims 2 to 4, comprising: - fixed table (5) fixed to the sides (2) of the machine, - a plurality of first sleeves (50) mounted on the fixed table (5) and having an upper edge (50a) which extends into the dosing tank to act as a limit switch for the piston (40) which abuts against said upper edge (50a) of the first sleeve, wherein said piston rod (41) is slidably mounted within said first sleeve (50). 6) Injection molding machine (100) according to claim 5, wherein said first sleeve (50) is a micrometric ring nut which can be adjusted in position so as to adjust the stroke of said piston (40). 7) Injection molding machine (100) according to claim 5 or 6, wherein said fixed table (4) is arranged below said injection plate (7) and said first sleeve (50) crosses said injection plate (7). 8) Injection molding machine (100) according to any one of claims 5 to 7, comprising a plurality of second sleeves (51) supported by said injection plate (7) and slidably mounted on said first sleeves (50), each second sleeve (51) having an abutment surface (51a) able to abut against said piston (40) to push the piston and cause the transfer of the fluid material from the metering tanks to the injection nozzles. 9) Injection molding machine (100) according to any one of the preceding claims, wherein said feeding group (20) comprises a plurality of static mixers (22) for mixing the fluid material to be molded with dyes, each static mixer (22 ) being connected to the respective dosing tank (S). 10) Injection molding machine (100) according to any one of the preceding claims, wherein said drive means (10, 13, 14, 15, 6, 8) comprise a motor (10) which rotates a belt (13 ) which makes a screw (14) rotate in a scroll (15) integral with a mobile table (6) connected by means of columns (8) to said molding plate (7).