IES20010683A2

IES20010683A2 - A mould

Info

Publication number: IES20010683A2
Application number: IE20010683A
Authority: IE
Inventors: Patrick Joseph Feerick; Patrick Joseph Fahy
Original assignee: Emeracly Holdings Ltd
Priority date: 2000-07-21
Filing date: 2001-07-20
Publication date: 2002-02-20
Also published as: IE20010684A1; GB2364953B; GB2364953A; GB0117769D0

Abstract

A mould for rotationally moulding a thermoplastic article comprises a mould half (1) having a main body member (2) which defines a hollow interior region (3) which in turn forms part of a mould cavity within which the article is formed. A plurality of heating element segments (7) for heating the main body member (2) are formed by heating element tapes (20) which are embedded in a high temperature resistant epoxy resin, and extend over an outer idle surface (5) of the main body member (2). An outer shell (8) secured to a flange (18) extending around the main body member (2) defines with the main body member (2) a passageway (10) for accommodating cooling air there through. Air inlet ports (11) and air outlet ports (12) are provided to and from the passageway (10). Compression springs (25) act between the outer shell (8) and the heating element segments (7) for retaining the heating element segments (7) in abutting engagement with the main body member (2). A corresponding mould half is secured to the mould half (1) around the flange (18). The advantage of the mould according to the invention is that the main body member of the mould (2) is heated directly by the heating element segments (7) thereby avoiding the need for placing the mould in a heating oven during rotation thereof for forming the thermoformed article. <Figure 4>

Description

The present invention relates to a mould, and in particular, though not limited to a mould for use in thermoforming of plastics material, for example, a rotational mould, a vacuum forming mould, an injection mould, a blow mould, and the like. The invention also relates to a method for forming a heating means for heating the mould.

In the moulding of thermoplastic composites, thermoplastic RTM, in monomer casting, and indeed, in most thermoplastic forming processes moulds are required.

In general, it is essential that the temperature of the mould can be controlled within relatively tight tolerances. It is also desirable that heating of the mould should be accomplished relatively rapidly, and similarly, subsequent cooling should also be accomplished relatively rapidly. In general, in moulds heretofore this has not always been possible. For example, in rotational moulding processes, in general, the mould is rotated within an oven for heating thereof. A hot air environment is created within the oven which in turn heats the mould. This, in general, is a relatively inefficient heating process, and furthermore, is relatively, slow. Cooling, in general, is carried out by removing the mould from the oven and rotating it in a room temperature environment. Similarly, this tends to be a relatively slow and inefficient cooling process. In general, it is believed that in rotational moulding where the mould is heated in an oven, energy input efficiency of a maximum of only 2% can be achieved. This is undesirable. i OPEN TO PUBUC INSPECTION UNDER SECTION 28 AND RULE 23 tgt 1 Ο β 8 5 There is therefore a need for a mould which overcomes these problems.

The present invention is directed towards providing such a mould, and the invention is also directed towards a method for forming a heating means for a mould.

According to the invention there is provided a mould for moulding an article, the mould having a component forming working surface and an idle surface, and comprising a heating means abutting at least a part of the idle surface for heating the mould adjacent the heating means, for in turn heating at least an adjacent part of the working surface.

In one embodiment of the invention a plurality of heating means is provided abutting respective parts of the idle surface for heating corresponding parts of the mould, Preferably, each heating means is provided in the form of a segment, and each heating means defines the corresponding part of the idle surface being abutted by the heating means. Advantageously, the heat output from each heating means is substantially matched to the thermal mass of the part of the mould corresponding to the heating means.

In one embodiment of the invention a connecting means is provided to each heating means for supplying power the heating means.

In another embodiment of the invention the respective connecting means to the heating means are independently and selectively addressable.

In another embodiment of the invention each heating means comprises an electrically powered heating means. Preferably, each heating means comprises am electrically powered flexible heating means. Advantageously, the heating element of each heating means is provided in the form of a flexible tape. Ideally, the tape or the heating element of each heating means comprises a woven tape. Preferably, the tape of each heating element comprises an elongated electrically resistive heating wire woven into the tape.

In one embodiment of the invention the heating element of each heating means is embedded in a resin material for retaining the shape of the heating element. Preferably, the resin is an epoxy resin. Advantageously, the resin is a high temperature resistant resin. Ideally, the resin is a high temperature curing resin, and preferably, the temperature resistance of the resin is higher than the operating temperature of the mould.

In one embodiment of the invention the adjacent heating means substantially abut each other.

In another embodiment of the invention an outer shell is provided adjacent but spaced apart from the idle surface for defining with the idle surface a passageway for accommodating a heat exchange medium therethrough for transferring heat from the heating means and the mould for cooling thereof. Preferably, at least one input port is provided to the passageway at one end thereof and at least one output port is provided from the passageway at the other end thereof for accommodating the heat exchange medium through the passageway. Advantageously, the respective inlet and outlet ports are located in the outer shell. Advantageously, the passageway is adapted for accommodating a heat exchange medium provided by cooling air. 1. In another embodiment of the invention an urging means is provided for urging each heating means into abutting engagement with the idle surface. Preferably, the urging means accommodates relative movement between each heating means and the idle surface of the mould for facilitating heat expansion and contraction of the mould relative to the heating means. Advantageously, the urging means acts between the outer shell and each heating means for urging the respective heating means into engagement with the idle surface, and ideally, each urging means comprises a resilient urging means.

In one embodiment of the invention each urging means is provided by a compression spring.

In another embodiment of the invention at least one urging means are provided for urging each heating means into abutting engagement with the idle surface.

In a further embodiment of the invention a heat transfer facilitating medium is provided between each heating means and the adjacent idle surface. Preferably, the heat transfer facilitating medium is provided by a heat transfer facilitating paste.

In one embodiment of the invention the mould is provided in two halves which are separable for facilitating removal of a moulded article.

In another embodiment of the invention the mould is of sheet material defining the respective working and idle surfaces on the respective opposite sides thereof.

In one embodiment of the invention the mould is adapted for forming thermoplastics material.

In another embodiment of the invention the mould is a rotational mould.

In a further embodiment of the invention the mould is a blow mould.

In a still further embodiment of the invention the mould is an injection mould.

Further the invention provides a method for forming a heating means for a mould for moulding an article wherein the mould comprises a component forming working surface and an idle surface, the method comprising the steps of forming the heating means on at least a part of the idle surface with the heating means abutting the idle surface and defining the part of the idle surface adjacent the heating means so that the heating means heats the adjacent part of the idle surface for in turn heating the adjacent part of the working surface. ΙΕΟ 1 06 8 J In one embodiment of the invention a plurality of heating elements are formed on the idle surface in the form of segments.

Preferably, each heating means is located on the idle surface for accommodating 5 relative movement between each heating means and the idle surface for facilitating heat expansion and contraction of the mould relative to the heating means. Advantageously, the adjacent heating means substantially abut each other.

In one embodiment of the invention each heating means is formed from a flexible 10 heating element. Preferably, each heating element is provided in the form of a flexible tape. Advantageously, the heating element is provided by an elongated electrically resistive heating wire woven into the flexible tape. Ideally, the heating element of each heating means is embedded in a resin for retaining the shape of the heating element.

In one embodiment of the invention the resin is an epoxy resin. Preferably, the resin is a high temperature resistant resin. Advantageously, the resin is a high temperature curing resin. Ideally, the temperature resistance of the resin is higher than the operating temperature of the mould.

In one embodiment of the invention each heating means is formed by laying up the corresponding heating element on the idle surface. Preferably, the idle surface is coated with the resin prior to laying up of the heating elements on the idle surface of the mould. Advantageously, a further coat of resin is applied to the heating elements »Ε ο 1 06 8 3 after the heating elements have been laid up on the idle surface of the mould. Ideally, a release agent is coated onto the idle surface of the mould prior to applying the resin to the idle surface.

Ideally, the resin is cured while each heating means is still in position on the mould, and preferably, each cured heating means is removed from the mould and the idle surface of the mould is coated with a heat transfer facilitating medium prior to the heating elements being replaced on the idle surface. Preferably, the heat transfer facilitating medium is a heat conductive paste for facilitating heat transfer between the corresponding heating element and the mould.

In one embodiment of the invention each heating means is shaped to most efficiently heat the corresponding part of the mould.

In another embodiment of the invention the heat output from each heating means is substantially matched to the thermal mass of the part of the mould corresponding to the heating means.

In a further embodiment of the invention a connecting means is provided to each heating means for powering the heating means. Preferably, the connecting means of the respective heating elements are independently addressable.

The advantages of the invention are many. By virtue of the fact that the heat output of the heating element segments can be matched to the requirement of the mould, IE Ο 1 Ο 6 8 3 and furthermore, by virtue of the fact that the heating element segments are attached to the idle surface of the main body member of the mould relatively rapid heating of the mould can be achieved. Additionally, when the heating element segments have been isolated from the power supply and the cooling air is passed through the passageway, the mould is rapidly cooled. Accordingly, the temperature of the mould can be changed significantly more rapidly than has been the case with moulds known heretofore, and furthermore, the heating efficiency of the mould is significantly higher. Indeed, it is believed that efficiencies of twenty times the efficiencies of moulds known heretofore can be achieved using the mould according to the invention, particularly when the mould is a rotational mould.

A particularly important advantage of the invention is that it provides direct heating of the mould by the heating element segments, thereby avoiding the need for heating the mould in a heating oven during rotational forming of the thermoplastic article in the mould when the mould is a rotational mould.

The invention will be more clearly understood from the following description of a preferred embodiment thereof which is given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of one half of a mould according to the invention, Fig. 2 is a partly exploded perspective view of the half of the mould of Fig. 1 Fig. 3 is a further exploded perspective view of the half of the mould of Fig. 1, Fig. 4 is a partly cut away perspective view of the half of the mould of Fig. 1, Fig. 5 is a transverse cross-sectional side eievational view of a detail of the half of the mould of Fig. 1, and Fig. 6 is a plan view of a detail of the half of the mould of Fig. 1.

Referring to the drawings there is illustrated one half of a rotational mould according to the invention for use in a rotational moulding process, for moulding a thermoplastics material. The half of the mould is indicated generally by the reference numeral 1. The other half of the mould may be the same or different, however, the construction and arrangement of such rotational moulds will be well known to those skilled in the art. The mould half 1 comprises a main body member 2 which defines a hollow interior region 3 having a component forming working surface 4 for forming a portion of the surface of the article or component to be formed, and an opposite idle surface 5. A heating means provided by a plurality of electrically powered heating element segments 7 are located on the idle surface 5 for heating the body member 2 as will be described below. An outer shell 8 is mounted on the body member 2, and is spaced apart from the idle surface 5 and the heating element segments 7 to form a passageway 10 for a heat exchange medium, namely, cool air to be circulated between the outer shell 8 and the body member 2 for cooling the heating element segments 7 and body member 2. Air inlet ports 11 and air outlet ports 12 are provided in the outer shell 8 for accommodating the heat exchange medium into and out of the passageway 10.

Turning now in more detail to the main body member 2 of the mould half 1, the body member 2 is of relatively heavy gauge sheet metal material and comprises a pair of side walls 15 joined by an end wall 16 and a top wall 17 extending between the respective side and end walls 15 and 16. A flange 18 extends around the main body member 2 from the side and end walls 15 and 16 for co-operating with a corresponding flange of a corresponding mould half for facilitating securing the mould half 1 to the corresponding mould half so that the hollow interior region 3 of the mould half 1 defines with an appropriately shaped hollow interior region of the other mould half, a mould cavity within which the article or component is to be formed.

The heating element segments 7 are formed from electrical heating elements provided in the form of flexible tape heating elements 20, see Fig. 6, which are embedded in epoxy resin in order to impart rigidity to the heating element segments 7 as will be described below. The heating elements 20 elements 20 in tape form are of the type sold under the Trade Mark AMPTEX by Amptex Company of Stafford, United Kingdom. An elongated electrical resistive wire heating element 21 is woven into the tape 20 to form the heating element. The tape 20 with the wire heating element 21 woven therein is relatively flexible and can be bent and shaped to define the portion of the idle surface 5 corresponding to the particular heating element segment 7. Each heating element segments 7 comprises a plurality of the heating element tapes 20 and the wire heating element 21 are appropriately connected within each segment 7 to provide a connecting means, namely, two connecting wires 23 from each heating element segment 7 for connecting to a power supply, typically, an AC mains power supply. The epoxy resin in which the heating element tapes 20 are embedded is a high temperature resistant epoxy resin, being temperature resistant to a temperature well above the normal operating temperature of the mould.

A plurality of resilient urging means, namely, compression springs 25 are located in the passageway 10 and act between the outer shell 8 and the respective heating element segments 7 for urging the heating element segments 7 into tight heat conducting engagement with the idle surface 5 and also for retaining the heating element segments 7 in position on the idle surface 5. In this embodiment of the invention one compression spring 25 is provided for retaining each heating element segment 7 in position. The urging action of the compression springs 25 while being sufficiently strong for retaining the heating element segments 7 abutting the idle surface 5 in heat conducting engagement therewith, is such as to permit relative movement between the heating element segments 7 and the main body member 2 for accommodating expansion and contraction of the main body member 2 during heating and cooling thereof. Additionally, the compression springs 25 act as spacers for spacing the heating element segments 7 from the outer shell 8 for forming the passageway 10 for accommodating cooling air therethrough for cooling both the heating element segments 7 and the main body member 2. Mounting brackets (not shown) secure the outer shell 8 to the flange 18 extending around the main body member 2, and the connecting wires 23 from the respective heating element segments 7 extend between the outer shell 8 and the flange 18 through recesses 26 in the outer shell 8.

Turning now to the method for forming the heating element segments 7, initially the heat output density required to raise the mass of the main body member 2 to the required thermoforming temperature in a desired time is calculated, and heating tape 20 which provides the appropriate heat output density is selected. The shapes and sizes of the respective heating element segments 7 are then determined. A consideration taken into account when determining the shape and size of the heating element segments is the requirement to provide for relative movement between the main body member 2 and the respective heating element segments 7 during expansion and contraction as the main body member 2.. Additionally, the heat output of each heating element segment 7 is substantially matched to the thermal mass of the part of the main body member 2 corresponding to the segment 7. When the sizes and shapes of the heating element segments 7 have been determined, the heating tapes 20 are cut to the appropriate lengths ready for laying up onto the main body member 2.

Initially a release agent is coated onto the idle surface 5 of the main body member 2 for preventing bonding of the epoxy resin to the idle surface 5. A coat of epoxy resin is then applied to the idle surface 5 over the release agent, and the lengths of heating tape 20 are embedded in the epoxy resin for forming the respective heating element segments 7. The wire heating elements 21 of the respective heating tapes IE Ο 1 ο 6 8 3 of each heating element segment 7 are appropriately joined, and two connecting wires 23 are provided extending from each heating element segment 7 for connecting the respective heating element segments 7 to an AC power supply. A further coat of epoxy resin is applied over the heating tapes 20 and fibreglass matting is then embedded in the second coat of epoxy resin. The main body member 2 is then transferred into a high temperature curing oven for curing the epoxy resin at the appropriate curing temperature.

After curing the main body member 2 is removed from the curing oven, and the heating element segments 7 are removed from the main body member 2. The release agent is removed from the idle surface 5 of the main body member 2, which is coated with a heat transfer facilitating medium, namely, a heat transfer paste for facilitating heat transfer between the respective heating element segments 7 and the main body member 2. The heating element segments 7 are placed in contact with the idle surface 5 of the main body member 2 and the outer shell 8 with the compression springs 25 abutting the corresponding heating element segments 7 is secured to the main body member 2 by means of the brackets (not shown) engaging the flange 18.

Although not illustrated, the connecting wires 21 are led to a central connecting circuit (not shown) housed in a control box (also not shown) carried on the outer shell 8. The connecting wires 23 may be connected together in the control circuit for in turn connecting to an AC mains power supply, or alternatively, the connecting wires 23 of the respective heating element segments 7 may be connected in the connecting circuit to be independently and selectively addressable, so that the power supply to each heating element segment 7 can be independently and selectively controlled.

An inlet manifold (not shown) to the air inlet ports 11 is provided for supplying cooling air to the passageway 10, and an outlet manifold (not shown) is provided from the air outlet ports 12 for accommodating the cooling air away from the mould half 1.

While only one mould half, namely, the mould half 1 of the mould has been illustrated, the other mould half will be substantially similar to the mould half 1, subject to the shape of the article to be thermoformed, and the other mould half will have a main body member which will be heated by corresponding heating element segments, and an outer shell will also be provided for forming with main body member of the other mould half a passageway for cooling air for cooling the other mould half simultaneously while the mould half 1 is being cooled.

The heating element segments 7 as discussed above are so sized and shaped as to most efficiently heat the adjacent parts of the main body member 2. The temperatures required for the various parts of the working surfaces 4 are initially determined, as is the thermal mass of the main body member 2 adjacent the respective parts of the working surface 4. The heat input required to the corresponding parts of the idle surface 5 are then computed and after that the most efficient sizes and shapes of the respective heating element segments 7 is determined for providing the appropriate heat inputs to the respective parts of the idle surface 5 and in turn the working surface 4.

In this embodiment of the invention since the mould according to the invention is particularly suitable for rotational moulding of thermoforming plastics materials, and since the typical thermoforming temperature range of such thermoplastics materials is in the range of 120°C to 210°C, the epoxy resin chosen is chosen to be temperature resistant to a temperature of at least 220°C. This, in practice, requires that the epoxy resin should have a curing temperature of approximately 220°C. io In use, with the mould half 1 connected to its corresponding mould half and the assembled mould mounted on a rotating arm of a rotational moulding apparatus, and the heating element segments 7 connected to an AC power supply and a cooling air supply connected to the inlet manifold (not shown) and the outlet manifold connected to an exhaust supply, the mould is ready for use. The appropriate amount of thermoplastics material, typically, in powder form is placed in the mould cavity formed by the hollow interior region 3 of the mould half 1 and the corresponding hollow interior region of the other mould half (not shown). The mould halves are secured together, and the rotating arm commences rotating the mould about two axes perpendicular to each other. Electrical power is supplied to the heating element segments 7 for heating thereof and the mould is simultaneously rotated about the two axes. This will be well known to those skilled in the art. After a predetermined time when the article has been thermoformed, power is isolated from the heating element segments 7 and cooling air is supplied to the inlet manifold (not ΙΕΟ 1 06 8 3 shown) and delivered through the passageway 10 for cooling the main body member 2 and the heating element segments 7. It will of course be appreciated that the other mould half which in general will have corresponding heating element segments 7 and will likewise be provided with a supply of cooling air through a corresponding passageway, and accordingly, the respective heating element segments of the respective mould halves will be heated simultaneously or the simultaneous heating thereof will be appropriately controlled if the respective heating element segments are independently addressable, and the respective mould halves will similarly be cooled simultaneously. io After cooling of the mould the respective mould halves are separated and the moulded article is removed.

While the mould according to the invention has been described for use in rotational moulding of a thermoplastics article, the mould according to the invention may be any type of mould, for example, a blow mould, a vacuum forming mould or an injection mould. Additionally, while the mould has been described for moulding thermoplastics materials, it will be readily apparent to those skilled in the art that the mould may be used for moulding any other type of thermoforming material.

Needless to say, while the mould half has been described with reference to Figs. 1 to 6 as being a mould having a rectangular shaped hollow interior region, it will be readily apparent to those skilled in the art that the mould may define a hollow interior region and in turn a cavity of any desired shape. The mould illustrated in Figs. 1 to 6 IE ο 1 Ο 6 8 3 has been illustrated solely for the purpose of ease of understanding of the invention.

Claims

1. A mould for moulding an article, the mould having a component forming working surface and an idle surface, and comprising a heating means abutting at least a part of the idle surface for heating the mould adjacent the heating means, for 5 in turn heating at least an adjacent part of the working surface.

2. A mould as claimed in Claim 1 in which a plurality of heating means is provided abutting respective parts of the idle surface for heating corresponding respective parts of the mould, and each heating means is provided in the form of a 10 segment, and each heating means defines the corresponding part of the idle surface being abutted by the heating means, the heat output from each heating means being substantially matched to the thermal mass of the part of the mould corresponding to the heating means. 15

3. A mould for moulding an article, the mould being substantially as described herein with reference to and as illustrated in the accompanying drawings.

4. A method for forming a heat means for a mould for moulding an article wherein the mould comprises a component forming working surface and an idle 20 surface, the method comprising the steps of forming the heating means on at least a part of the idle surface with the heating means abutting the idle surface and defining the part of the idle surface adjacent the heating means so that the heating means heats the adjacent part of the idle surface for in turn heating the adjacent part of the working surface.

5. A method for forming a heating means on a mould, the method being substantially as described herein with reference to and as illustrated in the accompanying drawings.