MELTING UNIT FOR A MOULDING MACHINE AND A MOULDING MACHINE

Abstract

A melting unit for an injection unit of a moulding machine, includes a melting vessel, an induction coil surrounding the melting vessel at least in areas for the inductive melting of a conductive material to be arranged in the melting vessel. At least in that area where it is surrounded by the induction coil, the melting vessel has an irradiation area that is substantially permeable to an electromagnetic field, and has a delivery opening for the melted conductive material. The melting vessel consists of a non-metallic material at least in the radiation area and in that the melting vessel has an uninterrupted lateral surface.

Description

BACKGROUND OF THE INVENTION

The invention relates to a melting unit for an injection unit of a moulding machine, an injection unit with such a melting unit, and a moulding machine with such an injection unit.

Generic melting units, injection units and moulding machines are found in DE 10 2016 006 917 A1 and EP 3 075 465 A1.

In the state of the art the lateral surface of the melting vessel in the radiation area is interrupted in the form of a slit, in order to allow the electromagnetic field generated by the induction coil to penetrate into the radiation area. This is disadvantageous because it results in an inhomogeneous melting process for the conductive material (usually metal) to be melted and melted conductive material can leak from this slit during the injection. A cooling of at least the material of the melting vessel surrounding the radiation area is imperative.

The object of the invention is to provide a generic melting unit, a generic injection unit and a moulding machine in which at least one, preferably all, of the problems discussed above are avoided.

SUMMARY OF THE INVENTION

This object is achieved by a melting unit as described below, an injection unit with such a melting unit, and a moulding machine with such an injection unit. Advantageous embodiments of the invention are also described.

The radiation area is that area of the melting vessel which holds the induction coil and in which the electromagnetic field generated by the induction coil acts during operation. The injection area is that area of the melting vessel which includes the delivery opening and which is under the influence of the injection forces resulting from the injection pressure during operation.

The non-metallic material of the radiation area can be e.g. graphite, stone (without conductive components to any extent relevant for the formation of eddy currents), ceramic, ceramic alloy or glass.

The melting vessel is preferably formed as an elongate body, particularly preferably with a cylindrical or prismatic shape, which has a chamber that is accessible from the outside via a delivery opening.

A metal or a material made of a metal alloy is preferably used as the conductive material to be melted.

According to the invention, the melting vessel has an uninterrupted lateral surface over its entire length (optionally apart from openings, closed during operation, for windows, sensors or the like). Due to the closed design, the melted conductive material can be injected into the cavity at higher injection speeds, as it is impossible for melted conductive material to leak, or even spurt out, from anywhere other than the delivery opening.

Through the use of a non-metallic material for the melting vessel at least in the radiation area, the electromagnetic field of the induction coil can penetrate into the radiation area over the entire lateral surface and the conductive material to be melted can heat up homogeneously. Tests were able to demonstrate that less time was needed to achieve complete melting of the conductive material to be melted. The risk of the conductive material to be melted bursting out is also substantially reduced. A cooling of the radiation area is not necessary, as no relevant eddy currents form in the non-metallic material of the melting vessel.

The melting vessel preferably has substantially the shape of a tube with a continuous chamber, wherein one end of the tube forms the delivery opening for the melted conductive material. The other end of the tube can be used for the insertion of an injection plunger. The area of the tube extending away from the delivery opening forms the injection area. That area of the tube which is surrounded by the induction coil forms the radiation area, where the melting of the conductive material to be melted takes place. The injection plunger can be arranged outside the radiation area irrespective of the injection process. In this case, the chamber of the melting vessel, starting from the delivery opening, forms an injection area, a radiation area preferably directly adjoining the latter and a storage area for the injection plunger preferably directly adjoining that.

In one embodiment of the invention it is provided that the melting vessel consists of a metallic material in the injection area and consists of a non-metallic material in the radiation area. The metallic material has a higher mechanical resilience, which can be important in the area of the injection area. In other words, in this embodiment example the tube is composed of an axial portion made of metallic material (which has the delivery opening) and an axial portion made of non-metallic material (in which the induction coil is arranged over a part of the length and the injection plunger is arranged). It can be provided here that in that area where the metallic material butts against the non-metallic material it surrounds the latter in the form of a sleeve.

In an alternative embodiment of the invention it is provided that the melting vessel consists of a non-metallic material up to the delivery opening (preferably the melting vessel as a whole). Here there is no point of abutment between injection area and radiation area. A mechanical strengthening structure is preferably provided at least in the injection area.

A dispensing device can be provided, by which a mould-release agent can be applied to the inside of the melting vessel at least in the radiation area, wherein a chemical reaction between the melted conductive material and the non-metallic material of the radiation area can be prevented by the mould-release agent. A contact and resultant undesired chemical reactions of substances possibly contained in the conductive material to be melted with the inside of the melting vessel can hereby be avoided.

BRIEF DESCRIPTION OF DRAWINGS

Embodiment examples of the invention are discussed with reference to the figures. There are shown in:

FIGS. 1a,b are sectional representations of a detail of a first embodiment of a moulding machine according to the invention and a front view thereof;

FIGS. 2a,b show a first and a second stage of a loading process using the melting unit of FIG. 1;

FIGS. 3a-c are, respectively, a side view of a melting vessel of a second embodiment of a melting unit according to the invention, a front view thereof, and a sectional view;

FIG. 4 shows the application of a mould-release agent to an inner wall of the melting vessel; and

FIG. 5 is a schematic view of a moulding machine according to the invention

DETAILED DESCRIPTION OF THE INVENTION

A moulding machine 1 according to the invention is represented schematically in FIG. 5. A movable moulding platen 14 (the drive for moving the movable moulding platen 14 is not represented) and a stationary moulding platen 13 are arranged on a frame 16. Rails for guiding the movable moulding platen 14 can be provided, but are not necessary in every design.

The stationary moulding platen 13 and the movable moulding platen 14 each carry one mould half 15. After the mould halves 15 have been closed by moving the movable moulding platen 14 onto the stationary moulding platen 13 until the mould halves 15 are in contact, the melted conductive material can be injected into a cavity formed in the mould halves 15 through an injection plunger 11, which can be moved translationally back and forth by an injection drive 12. After a possible holding-pressure phase the melted conductive material cools and forms the desired moulded part. The moulded part can be removed from the cavity by means of the delivery device 10.

In this embodiment example the delivery device 10 for the conductive material 4 to be melted is mounted on the stationary moulding platen 13, but could also be arranged elsewhere on the frame 16 or next to the frame 16 independently of it.

In the embodiment example shown the injection is effected through the stationary moulding platen 13. Other configurations are conceivable, such as e.g. an injection between the moulding platens 13, 14 (L-shaped assembly arrangement or 90-degree arrangement of the injection unit relative to the machine axis).

Details regarding embodiments of the melting unit, here formed by the melting vessel 2, the injection plunger 11, the injection drive 12, the induction coil 3 and the delivery device 10 for the conductive material 4 to be melted, can be derived from FIGS. 1 to 4. In the embodiment example of FIGS. 1 and 2 the melting vessel 2 is formed in two parts. The embodiment example of FIG. 3 shows a one-part formation of the melting vessel 2. Independently of the design measures otherwise shown, the melting vessel 2 naturally always has a delivery opening 6 for the melted conductive material.

FIG. 1a shows a detail representation along the section A-A of FIG. 1b in the area of the melting vessel 2.

The melting vessel 2 is formed substantially tubular (with an uninterrupted lateral surface) and has at the left-hand end in FIG. 1a a delivery opening 6, which communicates with the mould half 15 (not represented) arranged on the stationary moulding platen 13. An opening, into which the injection plunger 11 is inserted, is arranged at the right-hand end in FIG. 1a. The state after the delivery of the conductive material 4 to be melted (here formed as a moulding blank) but still before the conductive material 4 is melted is shown. The melting is effected in a manner known per se (optionally after generation of a vacuum in the melting vessel 2 by a suction device, not represented) by means of the induction coil 3, which is arranged along an axial portion of the radiation area 5. The induction coil 3 generates an electromagnetic field, which induces eddy currents in the conductive material 4 to be melted. The Joule heat formed thereby melts the conductive material 4 to be melted.

The melting vessel 2 has an injection area 7, extending from the delivery opening 6 in the direction of the radiation area 5, which in this embodiment example extends directly to the radiation area 5.

The melting vessel 2 is formed from a non-metallic material (e.g. graphite, stone, glass, ceramic or ceramic alloy) in the radiation area 5, in which the induction coil 3 is arranged. No, or at least no relevant, eddy currents are induced in this non-metallic material, which is why no cooling of the melting vessel 2 is necessary in the radiation area 5. The electromagnetic field can penetrate into the radiation area 5 over the entire circumference of the uninterrupted lateral surface and homogeneously heats the conductive material 4 to be melted.

In order to allow for high injection pressures, which can arise in the injection area 7 immediately in front of the mould halves 15, in this embodiment example the melting vessel 2 is formed from a metallic material in the injection area 7. A tempering device for tempering (cooling or heating) the injection area 7 could be provided in the injection area 7, but this is not imperative. It is advantageous that no tempering device is necessary in any case in the injection area 5. In that area where it butts against the non-metallic material, the metallic material surrounds the latter in the form of a sleeve (this is not strictly necessary, but it increases the mechanical stability of the melting vessel 2).

In the embodiment example of FIG. 3 the melting vessel 2 is formed over its entire length from a non-metallic material such as graphite, stone, ceramic, ceramic alloy or glass. Here a mechanical strengthening structure 8 (for example a shrink sleeve) for the melting vessel 2 is arranged in the injection area 7. This serves to prevent damage to the melting vessel 2 by forces occurring during the injection in the injection area 7 (which can result from injection pressures of up to 1800 bar). Alternatively the melting vessel 2—at least in the injection area 7—could be formed sturdier than is necessary when a mechanical strengthening structure 8 is used. Alternatively or additionally, instead of a mechanical strengthening structure 8, a non-metallic material with a sufficiently high mechanical resilience could be used. Depending on the choice of the conductive material 4 to be melted (e.g. in the case of aluminium) forces that are so large as to require particular measures in order to protect the melting vessel 2, consisting as a whole from non-metallic material, do not, in any case, occur during injection.

FIGS. 2a (section along B-B) and 2b (section along C-C) show different stages of a process of loading the melting vessel 2 with the conductive material 4 to be melted. The statements regarding the loading process apply to both embodiments of the melting vessel 2 discussed.

The moulding blank (generally: the conductive material 4 to be melted) is held on a gripper 17 in a tube 18 and inserted into the delivery opening 6 via a robotic arm, not represented, of the delivery device 10 (FIG. 2a). The moulding blank is deposited by the gripper 17 in the radiation area 5 (FIG. 2b).

After the delivery device 10 has left the area between the mould halves 15, the mould halves 15 are closed. The air contained in the melting vessel 2 can be removed by suction as required. Additionally or alternatively, the melting vessel 2 could be flooded with a protective gas. In both cases the melted conductive material can be prevented from reacting with oxygen contained in the ambient air.

The following statements apply to both embodiments discussed:

Contrary to what is represented, a window could be arranged in the melting vessel 2 in order to measure the temperature of the conductive material 4 to be melted through this window. It can thereby be ensured that the conductive material 4 to be melted is in fact completely melted before injection. As an alternative or in addition to such a temperature measurement, the necessary process variables (e.g. field intensity and exposure time of the electromagnetic field) can be determined by series of tests or model calculations.

Contrary to what is represented, the conductive material 4 to be melted could be inserted into the melting vessel 2 in a form other than that of a moulding blank, e.g. in the form of a powder or granular material.

Contrary to what is represented, the delivery device 10 could also be formed as shown in EP 3 075 465 A1.

LIST OF REFERENCE NUMBERS

• 1 moulding machine
• 2 melting vessel
• 3 induction coil
• 4 conductive material to be melted
• 5 radiation area of the melting vessel
• 6 delivery opening of the melting vessel
• 7 injection area of the melting vessel
• 8 mechanical strengthening structure for the melting vessel
• 9 dispensing device for mould-release agent
• 10 delivery device for the conductive material to be melted
• 11 injection plunger
• 12 injection drive
• 13 stationary moulding platen
• 14 movable moulding platen
• 15 mould half
• 16 frame of the moulding machine
• 17 gripper of the delivery device
• 18 tube of the delivery device

Claims

1. A melting unit for an injection unit of a moulding machine, comprising a melting vessel, an induction coil surrounding the melting vessel, at least in areas for the inductive melting of a conductive material to be arranged in the melting vessel, wherein at least in that area where it is surrounded by the induction coil the melting vessel has an irradiation area that is substantially permeable to an electromagnetic field, and a delivery opening for the melted conductive material, wherein the melting vessel consists of a non-metallic material at least in the radiation area and in that the melting vessel has an uninterrupted lateral surface.

2. The melting unit according to claim 1, wherein the melting vessel consists of the non-metallic material up to the delivery opening, wherein it is preferably provided that a mechanical strengthening structure for the melting vessel is provided in an injection area adjacent to the delivery opening or extending up to the latter.

3. The melting unit according to claim 1, wherein the melting vessel has an injection area, extending from the delivery opening in the direction of the radiation area, which consists of a metallic material, wherein it is preferably provided that the injection area extends up to the radiation area.

4. The melting unit according to claim 3, wherein a tempering device for tempering the injection area is provided.

5. The melting unit according to claim 1, wherein the non-metallic material of the radiation area is graphite, stone, ceramic, ceramic alloy or glass.

6. The melting unit according to claim 1, wherein a dispensing device is provided, by which a mould-release agent can be applied to an inside of the melting vessel at least in the radiation area, wherein a chemical reaction between the melted conductive material and the non-metallic material of the radiation area can be prevented by the mould-release agent.

7. The melting unit according to claim 1, wherein a delivery device for the conductive material to be melted is provided.

8. The melting unit according to claim 6, wherein the dispensing device for the mould-release agent is arranged on the delivery device or formed by it.

9. An injection unit for a moulding machine with at least one melting unit according to claim 1.

10. The moulding machine with an injection unit according to claim 9.