MELTING DEVICE AND METHOD FOR MELTING MELTABLE PLASTIC MATERIAL, METHOD FOR MIXING REACTIVE PLASTIC COMPONENT

Abstract

A melting device includes a container capable of melting a material supplied in a free-flowing state and storing the material in a liquid state. The container includes a first storage section for storing the material in the free-flowing state, a second storage section for storing the material in the liquid state, and a dividing section provided between the first storage section and the second storage section and configured to hold back the material, when the material is in a non-molten or free-flowing state and to allow passage of the material from the first storage section into the second storage section, when the material is in a molten or liquid state.

Claims

1. A melting device, comprising a container capable of melting a material supplied in a free-flowing state and storing the material in a liquid state, said container comprising; a first storage section for storing the material in the free-flowing state, a second storage section for storing the material in the liquid state, a dividing section provided between the first storage section and the second storage section and configured to hold back the material, when the material is in a non-molten or free-flowing state and to allow passage of the material from the first storage section into the second storage section, when the material is in a molten or liquid state; a first supply and dispensing section for measured supply of the material in the free-flowing state to the first storage section; and/or a second supply and dispensing section for measured discharge of the material from the second storage section.

2. The melting device of claim 1, wherein the first supply and dispensing section operates continuously, and the second supply and dispensing section operates discontinuously.

3. The melting device of claim 1, further comprising: a heating device arranged to heat at least one of the first storage section and the dividing section so as to melt the material in the free-flowing state; a fill-level measuring device configured to measure a fill level of the material stored in the liquid state in the second storage section; and a control device configured to control a supply of the material in the free-flowing state by means of the first supply and dispensing section and/or to control a melting of the material by means of the heating device, in response to the fill level measured by the fill-level measuring device.

4. The melting device of claim 3, wherein the control device controls operation of the first supply and dispensing section and/or the heating device so that a quantity of material in the second storage chamber corresponds to an immediate demand.

5. The melting device of claim 4, wherein the quantity of material in the second storage chamber is limited to a prescribed number of downstream plastics processing operations.

6. The melting device of claim 5, wherein the prescribed number is 2 to 10 of downstream plastics processing operations.

7. The melting device of claim 5, wherein the prescribed number is 5.

8. The melting device of claim 4, wherein the quantity of material in the second storage chamber is limited to an amount sufficient for processing within a prescribed time.

9. The melting device of claim 8, wherein the prescribed time is less than or equal to 30 minutes.

10. The melting device of claim 8, wherein the prescribed time is less than or equal to 15 minutes.

11. A mixing arrangement, comprising: a mixing chamber capable of mixing reactive plastic components into a reactive mixture; a first melting device comprising a container capable of melting one of the plastic components supplied in a free-flowing state and storing the one of the plastic components in a liquid state, said container comprising a first storage section for storing the one of the plastic components in the free-flowing state, a second storage section for storing the one of the plastic components in the liquid state, and a dividing section provided between the first storage section and the second storage section and configured to hold back the one of the plastic components, when the one of the plastic components is in a non-molten or free-flowing state and to allow passage of the one of the plastic components from the first storage section into the second storage section, when the one of the plastic components is in a molten or liquid state; a first supply and dispensing section for measured supply of the one of the plastic components in the free-flowing state to the first storage section; and a second supply and dispensing section for measured discharge of the one of the plastic components from the second storage section to the mixing chamber, wherein the first and second supply and dispensing sections are synchronised with one another so that only a prescribed quantity of the one of the plastic components is melted in the melting device, which quantity corresponds to an immediate demand for the one of the plastic components.

12. The mixing arrangement of claim 11, wherein the quantity of the one of the plastic components is limited to a prescribed number of downstream plastics processing operations, in particular 2 to 10, preferably 5, or limited to an amount sufficient for processing within a prescribed time, in particular less than or equal to 30 minutes, preferably less than or equal to 15 minutes.

13. The mixing arrangement of claim 11, further comprising a second melting device comprising a container capable of melting another one of the plastic components supplied in a free-flowing state and storing the other one of the plastic components in a liquid state, said container comprising a first storage section for storing the other one of the plastic components in the free-flowing state, a second storage section for storing the other one of the plastic components in the liquid state, and a dividing section provided between the first storage section and the second storage section and configured to hold back the other one of the plastic components, when the other one of the plastic components is in a non-molten or free-flowing state and to allow passage of the other one of the plastic components from the first storage section into the second storage section, when the one of the plastic components is in a molten or liquid state.

14. The mixing arrangement of claim 13, wherein the one of the plastic components is caprolactam with a first additive, in particular an activator, and wherein the other one of the plastic components is caprolactam with a second additive, in particular a catalyst.

15. The mixing arrangement of claim 6, further comprising: a third supply and dispensing device for a measured supply of a first additive, in particular an activator, to the mixing chamber; and a fourth supply and dispensing device for a measured supply of a second additive, in particular a catalyst, to the mixing chamber, wherein a supply of the one of the plastic components and the first and second additives by means of the second, third and fourth supply and dispensing devices are synchronised with one another as a function of time and quantity, so that the one of the plastic components and the first and second additives are mixed together in the mixing chamber to form the reactive mixture.

16. A method for melting meltable plastic material, comprising: supplying a meltable material in a free-flowing state to a first storage section of a melting device; melting the material in the first storage section of the melting device; storing the molten material in a liquid state in a second storage section of the melting device; discharging the molten material in the liquid state; and separating the first storage section and the second storage section such that the material in its non-molten or free-flowing state remains in the first storage section and, in a molten or liquid state, is capable to flow from the first storage section into the second storage section.

17. A method for mixing reactive plastic components, comprising: supplying a measured quantity of the reactive plastic components in a free-flowing state to respective melting devices; melting the reactive plastic components in the respective melting devices; supplying a measured quantity of the molten plastic components to a mixing chamber; mixing the molten plastic components with one another into a reactive mixture in the mixing chamber; and coordinating the supply of the reactive plastic components to the respective melting devices and the supply of the molten plastic components to the mixing chamber such that only prescribed quantities of the reactive plastic components are melted in the respective melting devices in correspondence to an immediate demand for the plastic components.

18. The method of claim 17, wherein the quantities of the plastic components are limited to a prescribed number of downstream plastics processing operations, in particular 2 to 10; preferably 5, or limited to amounts sufficient for processing within a prescribed time, in particular less than or equal to 30 minutes, preferably less than or equal to 15 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is described in more detail below by means of preferred embodiments with reference to the attached drawings.

[0031] FIG. 1 shows a schematic depiction of a mixing arrangement according to a first embodiment of the invention.

[0032] FIG. 2 shows a detailed view of a melting device according to the first embodiment of the invention.

[0033] FIG. 3 shows a schematic depiction of a mixing arrangement according to the second embodiment of the invention.

[0034] FIG. 4 shows a schematic depiction of a mixing arrangement according to the third embodiment of the invention.

[0035] FIG. 5 shows a schematic depiction of a mixing arrangement according to a variation of the third embodiment of the invention.

[0036] FIG. 6 shows a schematic depiction of a conventional mixing arrangement according to the state of the art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0037] FIG. 1 shows a mixing arrangement 2 for mixing liquid reactive plastic components according to a first embodiment. This serves to prepare the plastic components so that they can subsequently be used in downstream treatment processes for plastic parts production.

[0038] This mixing arrangement 2 features a first storage container 4A in which a first mixture 6A consisting of a first plastic component, e.g. caprolactam, together with a first additive, e.g. an activator, is stored. They are each in a free-flowing (e.g. granular, flaked, powdered or similar) form so that the plastic components do not as yet react with the respective additive and can be stored for longer in this form.

[0039] The two mixtures 6A and 6B are supplied to a first melting device 10A or a second melting device 10B by means of a first vacuum conveyor 8A and a second vacuum conveyor 8B (or any other suitable conveyor device). These melting devices 10A and 10B are structurally identical and their structure and manner of functioning are described in further detail below.

[0040] The mixture 6A liquefied by means of the first melting device 10A and the second mixture 6B liquefied by means of the second melting device 10B are supplied to a mixing head 14 via corresponding supply lines 12A and 12B. A filter 16A, 16B and a dispensing unit 18A, 18B or pump is provided in each of the supply lines 12A and 12B. Surplus material is directed or circulated from the mixing head 14 back into the respective melting device 10A or 10B via corresponding return lines 20A and 20B.

[0041] The respective mixture 6A and 6B is injected into a mixing chamber 24 via corresponding inlet nozzles 22A or 22B provided in the mixing head 14 and mixed together and the resulting reactive mixture 26 is conveyed into a mould cavity (not shown) via an outlet nozzle 34, by means of a piston 28 which is actuated by a hydraulic block 30 and controlled by a corresponding mixing head control unit 32.

[0042] FIG. 2 shows an enlarged depiction of the first melting device 10A. Since both melting devices 10A, 10b are structurally and functionally identical a common description of the melting device 10 follows.

[0043] The melting device 10 is essentially formed of a (e.g. one-piece) container 36 which is divided by a dividing grid 38 into a vertically upper first chamber 40 and a vertically lower second chamber 42. The base component mixture 6 is supplied to the first (upper) chamber 40 by the vacuum conveyor 8. The dividing grid 38 is configured so that, as long as it is in granular form, the supplied mixture 6 cannot fail or get through the dividing grid 38 into the second chamber 42. In other words, the mesh size of the dividing grid is smaller or finer than the particle size of the free-flowing starting mixture 6 supplied to the first chamber 4 and stored in the storage container 4.

[0044] The dividing grid 38 can be heated by a heating device 39 so that mixture 6 lying on the dividing grid 38 in the first chamber 40 can be melted or liquefied by means of the dividing grid 38. In a liquid form the molten mixture 6 can flow or drip through the dividing grid 38 into the second (lower) chamber 42 and subsequently get into the supply line 12.

[0045] The manner of functioning of the melting device is described below.

[0046] The container 36, or the two chambers 40, 42 are designed so that only the immediately required quantities of free-flowing base material or liquefied material 6 need to be kept available. Thus the first chamber 40 can accommodate preferably 10 to 20 kg of the granular mixture 6 and the second chamber 42 can accommodate molten material, which is just sufficient for a prescribed small number of plastics processing operations, e.g. maximum 5 shots, or for plastics processing operations within a prescribed time period, e.g. maximum 15 minutes.

[0047] In this way the necessary plastic components can be prepared on demand or according to a formula. In this way only small quantities of liquid base components are produced in each case which can be directly processed. Thus small quantities are melted, but this generally happens continuously.

[0048] The dispensing and supply device (vacuum conveyor 8) which supplies the free-flowing base mixture 6 to the first chamber 40 of the melting device 10, and the dispensing and supply device (dispensing unit 18) which removes the molten material 6 from the second chamber 42 of the melting device 10 are correspondingly synchronised with one another in relation to control or regulation technology, i.e. the vacuum conveyor 8A. 8B is controlled (via an integrated or central control device) so that it only supplies as much free-flowing plastic material 6 to the first chamber 40 as corresponds to the quantity of liquid plastic material that is extracted from the second chamber 42. The second chamber 42 only functions as a kind of short-term buffer in order to be able to even out potential fluctuations caused by the discontinuous demand in the downstream treatment processes. The melting process on the other hand can occur continuously.

[0049] FIG. 3 shows a functional diagram of a mixing arrangement 2 according to a second embodiment, which only differs from the first embodiment in relation to the structure of the mixing head 14 and the supply of the molten material to the mixing head 14. Instead of the molten material being supplied and dispensed via pumps 18A and 18B, this is carried out via dispensing cylinders 18A and 18B which are arranged directly in front of or on the mixing head 14, are connected to the supply lines 12A or 12B and by which the quantities to be injected into the mixing chamber 24 may be precisely dispensed. The return fines 20A and 20B can thus be done without in this variant. The mixing head 24 has a correspondingly altered structure, but is functionally similar in relation to the first embodiment as described above.

[0050] FIG. 4 shows a functional diagram of a mixing arrangement 2 for mixing liquid, reactive plastic components according to a third embodiment. It is immediately obvious from FIG. 4 that in contrast to the first and second embodiments, one, two or a number of additives are not added at the beginning, i.e. before the melting process, but are instead first supplied directly to the mixing head 14 or the mixing chamber 24. With this in mind, only one storage container or repository 4 for the (pure or unmixed or additive-free) plastic components 7, e.g. caprolactam, is provided. The plastic components 7 can be stored there in a solid or free-flowing form (granular, flaked, powdered or similar form), or also in liquid form.

[0051] By means of a conveyor unit 8 (vacuum conveyor, pump or similar), the plastic components 7 are supplied to the melting device 10 or, more exactly stated, a first chamber 40. The melting device 10 has a funnel-shaped container 36 which in turn is divided by a dividing grid 38 into the vertical upper first chamber 40 and a vertical lower second chamber 42. The dividing grid 38 is configured so that the mixture supplied, as long as it is in a granular or very viscous liquid state, does not fail or get through the dividing grid 38 down into the second chamber 42. In other words, the mesh size of the dividing grid 38 is smaller or finer than the particle size of the free-flowing plastic components 7 stored in the storage container 4 and supplied to the first chamber 40, or the grid 38 holds the viscous material 7 back.

[0052] In contrast to the first and second embodiments, alternatively or in addition to the dividing grid 38, the first chamber 40 can be heated. Specifically, as shown in FIG. 4, the wails of the first chamber 40 can be provided with a heating strip 37, which can heat the walls of the first chamber 40 so that the plastic components 7 stored briefly in the first chamber 40 are melted and liquefy. In a molten or liquefied state, the plastic components 7 flow or drip through the dividing grid 38 into the second chamber 42 located below. An outlet opening in the floor of the second chamber 42 is connected with a dispensing unit 18 via a supply line 12 by means of which the liquefied plastic components 7 are supplied to a mixing head 14 or mixing chamber 24. A return line 20 feeds any surplus quantity of plastic components 7 back into the melting device 10, more exactly stated into the second chamber 42, or makes possible a circulation.

[0053] The dispensing unit 18 has a dispensing cylinder 44 and a dispensing piston 46 which is operable by a motor. The dispensing cylinder 44 can be designed to be capable of being heated and for this purpose is provided with a heating device 50, for example, built into the cylinder walls. In this way it can be ensured that the liquefied plastic components 7 do not coot down or change their viscosity. The liquefied plastic components 7 are supplied from the second chamber 42 of the melting device 10 into the dispensing cylinder 44 via a first section of the supply line 12 and by means of the dispensing piston 46 are supplied to the mixing chamber 24 under pressure via the second section of the supply line 12.

[0054] One, two three or a number of additives 52A, 52B, 52C are supplied to the mixing head 14, more exactly stated the mixing chamber 24, from the relevant containers 54A, 54B, 54C in which they are stored via respective conveyor units 56A, 56B, 56C so that they mix with the supplied liquefied plastic components 7 in the mixing chamber 24 to form a reactive mixture 28 which can be output by the mixing head 14 for further processing.

[0055] In relation to the additives, at least one activator and one catalyst may be involved, which initiate the chemical reaction of the caprolactam in the mixing head 14.

[0056] The precise dispensing of the additive may be carried out by the respective conveyor units 56A, 56B, 56C and/or by a control valve arrangement 58 provided in the mixing head 14.

[0057] FIG. 5 depicts a variation on the third embodiment which differs in that the supply of the plastic components 7 by means of the dispensing unit 18 occurs so that a circulation or return line 20 can be done without.

[0058] The invention has been described by means of preferred embodiments, but is not however limited to these.

[0059] Thus in a further developed form of the third embodiment, for example, the activator or the catalyst may already be mixed with the plastic components 7 in the storage container 4 and the other of the two additives first fed directly into the mixing chamber 24.