WO2011035376A1

WO2011035376A1 - A mould or mould core and a method of manufacturing a mould or mould core

Info

Publication number: WO2011035376A1
Application number: PCT/AU2010/001244
Authority: WO
Inventors: Neil Wilson; Allan Meyer
Original assignee: Romar Engineering Pty Ltd
Priority date: 2009-09-24
Filing date: 2010-09-22
Publication date: 2011-03-31

Abstract

A mould 3.020 has a heating layer 3.022 formed on at least a portion of its cavity surface. The heating element is a resistive layer 4.030, preferably formed using nanotechnology techniques. An insulating layer 5.036 isolates the resistive layer from the mould surface. Electrodes 4.032, 4.034 are provided for establishing electrical connexion with an electrical power source. This device enables more precise control of heating of the mould charge than the bulk heating of the mould.

Description

A Mould or Mould Core and a Method of Manufacturing a Mould or Mould Core Field of the invention

[001] This invention relates to a mould construction and a method of using a mould.

[002] The invention is particularly suited for moulding processes where heat must be added to the mould charge when it is inside the mould cavity. The invention will be described in the context of an injection moulding process. The invention can be adapted for use with thermosetting materials such as silicone and for use with thermal cross-linking of materials, such as plastics.

Background of the invention

[003] When injection moulding using material such as silicone in liquid silicone injection moulding, the mould charge can be in a liquid form, and is heated and cured in the mould. The current practice of heating a mould charge inside a mould is to heat the mould to a predetermined temperature before injecting the mould charge into the mould. This uses a substantially greater amount of heat than is required to heat the mould charge. In addition, the cycle time is increased due to the time required to heat or reheat the mould to the predetermined temperature. The rate of heating or cooling the mould charge can affect the quality of the product.

[004] Mould cavities can have non-planar surfaces.

Summary of the invention

[005] In this specification, the term "thermal element" refers to a coating, layer, or plural layer arrangement which is capable of acting as an active heat source or a heat sink or both. That is, the thermal element can generate heat or absorb heat.

[006] According to an embodiment of the invention, there is provided a mould or a mould core having a thermal element applied to a substrate, the substrate including at least a part of the surface of the mould or core or both.

[007] The thermal coating can include at least one heating element applied to a substrate, the substrate including at least part of the surface of the mould cavity or mould core or both.

[008] The heating element can be a thin film layer.

[009] The heating element can be electrically insulated from the substrate. [010] A thermal insulation layer can be provided between the heating element and- the substrate.

[011] A thermal conduction layer can be provided proximate to the heating layer.

[012] A fluid cooling system can be provided proximate the heating layer.

[013] The fluid cooling system can be thermally connected to the thermally conductive layer.

[014] The cooling fluid can be a liquid.

[015] The cooling fluid can be a gas.

[016] The cooling system can be turned on after the mould charge has been thermally set or cross-linked.

[017] The mould can include a pair of electrodes connected to the or each heating element.

[018] The heating element can have at least one portion which is thicker than another portion of the heating element.

[019] The mould can include two or more electrically separate heating elements.

[020] The mould can include a second electrical insulation layer formed on the top of the heating element.

[021] The thermal element can be a Peltier device.

[022] The Peltier device can be a multi-layer device.

[023] The invention also provides a method of forming an electrical heating element on at least a portion of the surface of a mould cavity, including the steps of: depositing a first insulation layer on the said at least a portion of the mould surface, and

depositing an electrically resistive layer on the first insulation layer.

[024] The method can include the step of forming a second insulation layer on the electrically resistive layer.

[025] A thermal insulation layer can be provided between the resistive layer and the substrate. [026] The method can include the step of forming a pair of electrodes on the or each electrically conducting layer.

[027] The method can include forming two or more separate electrically isolated heating elements.

[028] The method can include forming at least one region of greater thickness in at least one heating element.

[029] A source of heating energy can be connected to the heating element.

[030] The source of energy can be an electrical energy supply.

[031] At least one of the layers can be applied by the sol-gel process.

[032] The layers can be applied by spray pyrolysis.

[033] The mould can include cooling fluid ducts.

[034] The invention also provides a method of moulding using a hot mould charge, the method including the steps of:

maintaining the mould body a first temperature below the setting temperature of the mould charge;

heating the surface heaters to a second temperature above the flow temperature of the mould charge prior to injecting the mould charge;

and

turning the surface heaters off when the mould charge has been injected.

[035] The method can also include the step of cooling the mould body via cooling fluid in cooling ducts in the mould.

Brief description of the drawings

[036] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[037] Figure 1 is a schematic illustration of an exemplary moulded product.

[038] Figure 2 is a schematic illustration of a mould part for moulding the top portion of the product of Figure 1.

[039] Figure 3 is a schematic illustration of a mould part for moulding the lower portion of the product of Figure 1.

[040] Figure 4 is a schematic illustration of a heater element of Figure 3. [041] Figure 5 schematically illustrates a partly exploded heater element being a modified version of the heater element of Figure 4.

[042] Figure 6 illustrates schematically an alternative electrode

arrangement.

[043] Figure 7 illustrates schematically an further alternative electrode arrangement.

[044] Figure 8 is a hypothetical graph illustrating temperature plotted against depth and time within a mould.

[045] Figure 9 schematically illustrates a Peltier device according to an embodiment of the invention.

[046] Figure 10 schematically illustrates the device of Figure 9 operating in the reverse mode to that shown in Figure 9.

[047] Figure 11 schematically illustrates a further Peltier arrangement.

[048] Figure 12 schematically illustrates a multi-layer Peltier arrangement.

[049] Figure 13 schematically illustrates a combination of a heating layer with a ducted cooling system.

[050] The numbering convention used in the drawings is that the digits in front of the full stop indicate the drawing number, and the digits after the full stop are the element reference numbers. Where possible, the same element reference number is used in different drawings to indicate corresponding elements.

Detailed description of the embodiment or embodiments

[051] The invention will be described with reference to the embodiments illustrated in the drawings.

[052] To reduce the complexity of the drawings and better illustrate the inventive concepts, the conventional operating elements of the moulding system, which are familiar to the person skilled in the technology, such as, eg, the injection valves, are not shown in the schematic illustrations.

[053] Figure 1 represents a moulded product 1.002 produced by a mould made according to an embodiment of the invention. The product is made from silicone and has an upper portion in the form of a first cylinder 1.004 and a lower portion in the form of a second cylinder 1.006 coaxial with the first cylinder, but of larger radius. [054] Figure 2 schematically illustrates a first mould portion adapted to form the upper cylinder portion 1.004 of the product 1.002. The mould has a cylindrical cavity defined by cylindrical wall 2.016 and closed at the top 2.012. A rim 2.014 projects transversely to the wall 2.016.

[055] Figure 3 represents the mating mould portion 3.020 adapted to combine with the mould portion of Figure 2 when moulding the product 1.002. A second cylindrical cavity is formed by cylindrical wall 3.026 closed at the base and having a transversely projecting rim 3.024. The projecting rims 2.014 and 3.024 are brought together under closing force during the moulding process and define the join line between the two mould halves.

[056] A heating element 3.022 is formed on the base of the second cylinder.

[057] The mould halves can be made of the conventional materials, such as steel or aluminium.

[058] The mould halves can also include cooling fluid ducts (not shown).

[059] As shown in Figure 4, the heating element 4.022 can be formed as a thin film element including a conductive layer 4.030 formed on an electrically insulating layer 4.036. A pair of electrodes or buss bars 4.032, 4.034 can be mounted on opposite sections of the conductive layer 4.030. The layer 4.030 is referred to as a conductive layer, rather than a resistive layer as, in the preferred embodiment, it is of relatively low resistivity. However, the term resistive layer could also be used to describe layer 4.030 as it is a resistive heating element.

[060] Preferably the insulating layer 4.036 also has good thermal insulation characteristics.

[061] The electrodes can be connected to an external source of electrical power via conductive leads which can pass through the walls of the mould or which can be fed into the cavity via the rim.

[062] The electrical power source can be the mains power, such as 240 v,

50 Hz. Alternatively the power supply can be a DC power supply. The power supply can have a controllable output. The resistance of the conductor layer can be designed to provide the optimal heat energy input to the mould shot.

[063] A power regulation arrangement can be provided to ensure that the input heat energy is as required. Thus, the current and voltage can be monitored to determine the input power. Alternatively, the resistance of the conductive layer can be measured or calibrated at intervals and then only one of the voltage or current needs to be monitored, since the power can be calculated from any two of voltage, current and resistance.

[064] In a preferred embodiment, the conductive layer 4.030, the insulation layer 4.036 and the electrodes 4.032, 4.034 can be formed by nanotechnology processes to provide very thin layers.

[065] In an alternative embodiment, the electrodes 4.032, 4.034 can be formed on the insulator layer 4.036, and the conductive layer then formed on top of the electrodes.

[066] A second heating element may optionally be provided in the top 2.012 of the first mould cavity.

[067] Figure 5 illustrates a modified version of the heater element arrangement of Figure 4. The insulator layer 5.036 projects beyond the conductive layer 5.030. A second insulator layer 5.040 is applied over the top of the conductor layer and electrodes. The insulation layers 5.036, 5.040 project beyond the edges of the conductive layer.

[068] The insulative layer 5.040 can also be designed to provide abrasion resistance for the underlying layers.

[069] Preferably the insulation layer 5.040 has high electrical insulation characteristics and good thermal conduction characteristics.

[070] In a further embodiment, heating elements can be incorporated in the join line portions of the mould, such as in rim 3.024 or rim 2.014. This provides the operator with the option of controlling the setting or cross-linking of the join line material separately from the mould charge.

[071] The insulative layers, the conductive layer, and the electrodes can be formed using nanotechnology processes. Thus the sol-gel process can be used to form the components. Alternatively, spray pyrolysis can be used to form one or more of the layers. Other methods of forming the layers can include dip coating, spray coating, spluttering, chemical deposition, physical deposition, and other methods suitable for depositing conductive or insulative materials. Preferably the method is adapted for nano-deposition.

[072] Very thin layers can thus be made.

[073] The layers can have a thickness of between 1 micron & 1000 micron. [074] The composition of the resistive layer can be for example, a mixture of tin oxide and indium oxide, or an alloy of indium with 9% tin. The layers can be applied by RF Sputtering, vapour phase deposition, the sol-gel process, etc. The layer thickness can range from 0.2 m to over 100 μηη. The resistivity can range from less than 2 Ω/cm² to over 40 Ω/cm² Other compositions can be used. The book Integrating Electrical heating Elements in Appliance Design, Thor Hegbom, Marcel Dekker.lnc 1997, at Chapter 7 describes various compositions and methods of application of thin film heaters.

[075] The composition of the base insulator can be Teflon.

[076] During the moulding process, the mould material, eg, silicone, can be injected cold, eg, at ambient temperature. The heating element can then be switched on and deliver sufficient heat energy to raise the material to the cure temperature within a predetermined time. Alternatively, the heating element can be pre-heated.

[077] In conventional cold injection moulding, the mould body is pre-heated to a temperature above the cure temperature of the mould charge. Thus, as the mould charge is injected into the mould, the skin layer will be rapidly raised above the cure temperature, while the material more distant from the mould wall will be heated more slowly. Arrangements embodying the present invention can heat the mould charge more evenly than is achievable using conventional pre-heated moulds.

[078] It is generally desirable to have a fairly uniform current distribution in the conductor layer. Figure 6 illustrates schematically an alternative electrode arrangement in which a central electrode 6.050 forms one side of the resistance connection, and a pair of peripheral electrodes 6.032, 6.034 can be connected to the other side of the power supply. A lead 6.042 can be connected to the central electrode to facilitate connection to the power supply. The lead can be insulated from the conductor layer by an insulator layer 6.046. This prevents current from the conductor layer flowing to the lead except via the electrodes 6.032, 6.034, 6.050. Thus the lead does not interfere with the current distribution in the conductor layer 6.030.

[079] In a further modification shown in Figure 7, a single annular peripheral electrode 7.044 and a central disc electrode 7.050 can be connected to respective sides of the power supply. A lead 7.042 from the central electrode can also be taken out across the conductor layer and the annular electrode, with an insulation layer 7.046 between the lead and the conductor layer and the annular electrode. A further insulating layer can be deployed on top of the lead. [080] In a still further arrangement, a plurality of alternative electrodes can be formed on or under the conductor layer, with alternative conductors connected to opposite sides of the power supply.

[081 ] However, in some instances it may be desirable to change the current density in different portions of the conductor layer, and this can also be achieved by shaping the electrodes to control the current distribution. The principle being that the closer the portions of the opposite electrodes are spaced, the greater the current in the intervening portion of the conductor layer. Hence, a uniform thickness conductor layer can be used in conjunction with profiled electrodes to control the current distribution within the conductor layer. For example, in the arrangement of Figure 4, the current density would be least across the diagonal intersecting the centre of the two electrodes, while the current density would be greatest in the portion of the conductor layer proximate the ends of the electrodes.

[082] While the conductor layer, the insulation layers and the electrodes are shown as circular, they can be designed in any shape required to fit the mould wall. The layers can conform to two dimensional or three dimensional surfaces.

[083] Figure 8 is a hypothetical graph illustrating temperature plotted against depth and time within a mould. The vertical axis is the temperature axis. The time axis is angled downwardly, or projecting out of the plane of the page (assuming the temperature axis to lie in the plane of the page), while the depth axis is angled upwards, or projecting behind the plane of the page.

[084] Temperatures of up to 250°C can be used to cure the silicone.

Silicone can cure at the rate of about 5 sec/mm thickness for a given input temperature. Temperatures of between 1 10°C to 250°C can be used.

[085] Temperature at the mould surface with an input power of Pi is illustrated by line 8.102, and the surface temperature with input power of P₂ is illustrated by line 8.104. P₂ is greater than P^ .

[086] At depth D, the temperature profile for an input power of Pi is illustrated by line 8.106, and line 8.108 illustrates the temperature profile at depth D with an input power of P₂.

[087] A plane defined by lines A & B is drawn through the cure temperature

TCU E- A cure locus can be drawn where the temperature profile line at a particular depth intersects the cure plane. Thus the line 8.1 10 represents the cure temperature locus with an input power of Pi . Similarly, the cure locus at P₂ is represented by line 8.1 12.

[088] With an input power of the material at the surface takes a time period to reach the cure temperature. With an input power of P^ the material at depth D takes t₂ to reach the cure temperature.

[089] With an input power of P₂, the material at the surface takes a time period t₃ to reach the cure temperature. With an input power of P₂, the material at depth D takes to reach the cure temperature.

[090] This graph illustrates the ability of the system according to the invention to control the cure process. It is also possible, in accordance with the invention to change the input power during a moulding operation to achieve a desired cure rate profile.

[091 ] In addition, different portions of the mould surface can be heated at different rates, this can be achieved by having separate conductor layers at different locations. This can be achieved by depositing separate conductor layers at different locations with a physical space between the separate layers. Alternatively, a single layer can be deposited and then dividing lines can be etched out of the conductor layer to form the separate conductor layers. Separate electrode pairs can be applied to the separate conductor layer locations so they can be heated at different rates.

[092] In a further alternative, the thickness of the conductor layer can be varied at different locations. This may be done, for example, by deposition a first conductor layer over the entire surface to be heated, and then selectively depositing further layer or layers at specified locations to increase the thickness of the layer at the specified locations. The resistivity of the layer varies inversely in relation to the thickness of the layer. The thicker layers will carry additional current compared with the adjacent non-thickened layer portions.

[093] The heating element can be applied to a planar surface, a convex surface, or a concave surface. The heating element can be applied to either a mould core or mould cavity, or both.

[094] Figure 9 schematically illustrates a Peltier device according to an embodiment of the invention. A Peltier device operates on the basis that a junction between a pair of certain dissimilar materials such as metals will heat up if a current passes through the junction in one direction, and will cool if the current is reversed. The device illustrated by way of example in Figure 9 has a first metal layer 9.062 and a second metal layer 9.066. Links such as 9.064 of the first metal contact the second metaf layer at junction 9.076, and links 9.078 of the second metal contact the first layer at junction 9.078 The links are separated by insulation 9.070 in the interstices between the links.

[095] Electrode 9.061 and 9.063 form part of the electrical supply path delivering current to the device. Arrows 9.072 and 9.074 indicate a current flow in a first direction. This current flow causes the junction 9.076 to cool, and junction 9.074 to heat.

[096] The layers 9.062 and 9.066 can cover a substantial portion of the surface of the substrate.

[097] Figure 10 illustrates the device of Figure 9 operating in the reverse mode to that shown in Figure 9. When the current flow is reversed, junction 10.076 becomes hot and junction 0.078 cools. Thus, it is possible to use a Peltier arrangement to deliver cering heat and then to cool the mould charge.

[098] Figure 11 illustrates a further Peltier arrangement. In this arrangement, the dissimilar metals 11.084, 11.086 are laid out in parallel lines with a common interface which forms the Peltier junction. A second Peltier junction is formed by the strips 11.090, 11.092. The strips 11.086, 11.092 are joined by an isthmus 11.096 of the same material. Electrodes 11.080, 11.082 deliver the electrical current to the strips 11.084, 11.090 respectively. Insulator strips 11.088 can be provided so that a number of such Peltier devices can be assembled in parallel.

[099] The temperature differential provided by a Peltier couple is of the order of 70°C in the unloaded state, and less when the device is transferring heat energy, thus, a stack of several Peltier devices need to be used to deliver a temperature of the order of 300°C under thermal load conditions. Figure 12 illustrates a multi-layer Peltier arrangement. Second metal layers 12.066, 12.069 are

sandwiched between first metal layers 12.062, 12.067, 12.071. Electrodes 12.063, 12.061 deliver current to the upper and lower layers 12.062, 12.071 respectively.

[0100] Figure 13 shown an alternative arrangement according to an embodiment of the invention. A resistive layer 13.030 has a pair of electrodes attached to opposed edges. An electrical insulation layer 13.054 is located between the resistive layer 13.030 and a thermally conductive layer 13.052. The thermally conductive layer may be a metal with good thermal conductivity, or it may be made from carbon nanotubes or other suitable material. A cooling fluid duct 13.056 can be provided in thermal conductive contact with the thermal conductive layer 13.052. [0101] In operation, the mould can be preheated before ht e mould charge is injected into- the mould, and the mould charge can be heated by the resistive layer 13.054. During the curing phase, no cooling fluid id pumped through the duct 13.056. When the charge has cured, cooling fluid can be pumped through the duct 13.056. The timing of the curing process will be determined by the amount of heat energy delivered through the resistive layer

[0102] An electrical power supply shown schematically as battery 12.202 in

Figure 12 , with power control means (switch 12.202) are connected to the electrodes. A controller or processor 12.200 can be programmed to control the heat energy input based on the depth of the cavity, and the cure or cross-link rate of the charge. Metering equipment, such as ammeter 12.206 and voltmeter 12.208 can provide control signals to the controller 12.200.

[0103] In the current process of moulding plastics, the mould charge is injected hot, and the heat is drawn off via the mass of the mould body, cooling ducts can be provided in the mould body so cooling fluid can be circulated to cool thee mould body. However, in order to ensure that the plastics mould charge flows correctly during the injection phase, it is current practice to heat the mould to above 120°C. Thus a significant amount of time is required to cool the mould body sufficiently for the plastics to set before opening the mould. Thus the invention provides a method of moulding plastics in which the mould body does not need to be pre-heated. The mould body is maintained at a low temperature, and the surface heaters are turned on slightly before the mould charge is injected so the surface is at a sufficient temperature to prevent setting of the mould charge while the mould charge is being injected. When the mould charge has been injected, the surface heaters are turned off and the cooling process commences with the heat of the mould charge being drawn out through the body of the mould. Again, cooling ducts can be provided in the body to assist in cooling. Also, if a Peltier arrangement is used, this can be run to cool the thermal element. In this arrangement, the sprue through which the plastics charge is delivered to the mould can also be heated to ensure a smooth flow of the plastics material.

[0104] In this specification, reference to a document, disclosure, or other publication or use is not an admission that the document, disclosure, publication or use forms part of the common general knowledge of the skilled worker in the field of this invention at the priority date of this specification, unless otherwise stated. [0105] In this specification, terms indicating orientation or direction, such as

"up"; "down", "vertical", "horizontal", "left", "right" "upright", "transverse" etc. are not intended to be absolute terms unless the context requires or indicates otherwise. These terms will normally refer to orientations shown in the drawings.

[0106] Where ever it is used, the word "comprising" is to be understood in its

"open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

[0107] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

[0108] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims

1. A mould or mould core having at least one thermal element applied to at least part of a substrate, the substrate being the surface of the mould cavity or mould core.

2. A mould or mould core as claimed in claim 1 , wherein the thermal element is a thin film layer heating element.

3. A mould or mould core as claimed in claim 1 or claim 2, wherein the thermal element is electrically insulated from the substrate.

4. A mould or mould core as claimed in any one of the preceding claims, including a pair of electrodes connected to the or each thermal element.

5. A mould or mould core as claimed in any one of the preceding claims, wherein the thermal element has at least one portion which is thicker than another portion of the thermal control element.

6. A mould or mould core as claimed in any one of the preceding claims, wherein the thermal element includes two or more electrically separate heating elements.

7. A mould as claimed in any one of the preceding claims, including a second electrical insulation layer formed on the top of the thermal element.

8. A mould as claimed in any one of the preceding claims, including a thermal insulation layer formed between the substrate and the thermal element.

9. A method of forming an electrical heating element on at least a portion of the surface of a mould cavity or mould core, including the steps of:

depositing a first insulation layer on the said at least a portion of the mould surface, and

depositing an electrically resistive layer on the first insulation layer.

10. A method of forming an electrical heating element on at least a portion of a substrate as claimed in claim 9, including the step of forming a second insulation layer on the electrically resistive layer.

11. A method as claimed in claim 9 or claim 0, including the step of forming a pair of electrodes on the or each electrically conducting layer.

12. A method as claimed in any one of claims 9 to 11 , including forming two or more separate electrically isolated heating elements.

13. A method as claimed in any one of claims 9 to 12, including forming at least one region of greater thickness in at least one heating element.

14. A method of thermally controlling a mould cavity charge including the steps of heating or cooling a thermal control layer on the surface of the mould or mould core, for a period determined by the thickness of the cavity.

15. A method of moulding using a hot mould charge, the method including the steps of:

and

turning the surface heaters off when the mould charge has been injected.

16. A method as claimed in claim 15 including the step of cooling the mould body via cooling fluid in cooling ducts in the mould.

17. A mould or mould core including a thermal layer substantially as herein described with reference to the accompanying drawings.

18. A method of moulding a product substantially as herein described with reference to the accompanying drawings.