GB2463860A

GB2463860A - Moulding System and Method

Info

Publication number: GB2463860A
Application number: GB0815681A
Authority: GB
Inventors: Paul Nicolas Anderson; Andrew Mark Holden
Original assignee: ASS OF ROTATIONAL MOULDING; BRITISH PLASTICS FEDERATION; ASS OF ROTAMOULDERS IRELAND LT
Current assignee: ASS OF ROTATIONAL MOULDING; BRITISH PLASTICS FEDERATION; ASS OF ROTAMOULDERS IRELAND LT
Priority date: 2008-08-28
Filing date: 2008-08-28
Publication date: 2010-03-31
Also published as: GB0815681D0

Abstract

A system and method are described which may be used for rotational moulding. The system includes a microwave chamber 2, a mount 1 and a tool 4, the tool 4 having an interior cavity defining a mould for receiving a moulding material. A least a part of the exterior surface of the tool comprises a microwave receptive material preferably a coating. The microwave chamber 2 includes a microwave source 3. The mount 1 is arranged to mount the tool within the chamber, and the system is arranged to rotate one or more of: the tool when mounted on the mount; the chamber; and/or the microwave source about two axes of rotation. The mould may be moved in two directions through microwave energy emitted by the microwave source 3 to heat it a material within it. A breather tube (6, Figure 5) may provide an air passage between the cavity and the exterior of the chamber and may carry data communication cabling (7) of a temperature monitoring system.

Description

I

Moulding System and Method

Field of the Invention

The present invention relates to a moulding method and system that is particularly applicable to rotational moulding.

Background to the Invention

The term "rotamoulding" is used to refer to rotational moulding techniques.

Traditionally rotamoulding techniques can be split into four stages.

Prior to rotamoulding, a hollow mould is prepared such that the interior surfaces of the hollow mould define the product to be produced.

Stage I involves the charging of a hollow moulding tool with a predetermined amount of material such as a polymer powder or liquid which is equal to the final desired part weight to be produced. The tool is then closed to seal the polymer or other material within the tool.

In stage 2, the moulding tool is placed within an oven and is continually rotated. The temperature of the moulding tool is raised from room temperature to around 200-250 °C to melt the contained material. When the temperature of the inside surface of the mould is high enough, the polymer powder or liquid will start to adhere to it. As the tool is further rotated more material will build up on the inside surface of the tool. Eventually all the polymer will have melted and adhered to the inside surface of the mould.

For most rotamoulding machines the stage 2 relies on hot gas or flame powering the oven to heat the outer surface of the tool within which the polymer is circulating. The mould is heated from around room temperature to * 30 temperatures in the range of 200 to 250°C using an oven whose ambient temperature is between 300 to 350°C to reduce the polymer heating time to a minimum. Due to the need to rotate the mould during heating, a support arm or spindle on which the tool is mounted for rotation is also contained within the oven and also absorbs heats up and cools down during each rotamoulding cycle.

Therefore, the process is very energy inefficient as it doesn't just heat the tool.

Additionally, opening the oven to place or remove the tool looses heat and requires the oven to work to maintain its operating temperature.

In stage 3, the hot moulding tool is removed from the oven and cooling cycle begins. During this stage the tool is still rotated and the cooling process is normally assisted by either forced air or fine water spray. The rate of cooling will affect the quality of the final moulding.

Once the tool has reached a suitable temperature to remove the moulding, the * part is demoulded from the cooled mould in stage 4.

Stages I to 4 can be repeated as often as necessary to produce additional moulded items.

The main benefits of the rotamoulding process are that it suits the manufacture of hollow parts made in one piece which are essentially stress free. The process suits a short production run and there is no material.

wastage if tool is designed properly and the polymer is weighed out correctly.

As discussed above, in conventional rotamoulding machines, the moulding tool is mounted on a spindle arm which moves into the oven space during the heating phase of the rotamoulding cycle. The arm is free to rotate the moulding tool in 2 axes whilst heat is applied to the mould tool using a hot air convection oven.

The above-described rotamoulding process does have several limitations: It is not suited to large production runs due to the long cycle times in comparison to other plastic processing technologies; It can be labor intensive due to the effort in charging and demoulding the moulding tool; It has long cycle times due to the reliance on heating the polymer and mould from room temperature to the moulding temperature, and then cooling the tool and component down again during each moulding cycle; It is not only the tool that absorbs heat during stage 2, but part of the spindle arm and mould support system are also heated in the oven; Oven efficiency can be as low as 3% for gas fired ovens, ovens are not always fully sealed and oven heat is lost through opening and closing the oven twice in every moulding cycle; and, The cost of rotamoulding is also heavily affected by energy costs of operating the oven.

Therefore there is a need for a more energy efficient heating route for rotamoulding process to improve its economic cost.

Statement of Invention

According to an aspect of the present invention, there is provided a moulding system comprising a microwave chamber, a mount and a tool, the tool having an interior cavity defining a mould and is arranged to receive a moulding material, at least a part of the exterior surface of the tool comprising a microwave receptive material, the microwave chamber including a microwave source, the mount being arranged to mount the tool within the chamber, wherein moulding system is arranged to rotate one or more of: the tool when mounted on the mount; the chamber; and/or the microwave source about two axes of rotation to move moulding material within the tool in Iwo directions through microwave energy emitted by the microwave source.

The microwave receptive material may comprise a coating.

The coating may have a thickness of between I and 30 mm.

The microwave receptive coating may include microwave susceptor particles selected from a group including silicon carbide, iron oxide and carbon black.

The moulding system may be arranged to rotate the tool in a first axis of rotation and rotate the microwave source in a second axis of rotation.

The moulding system may be arranged to independently control the speed of rotation in the first and second axes.

The moulding system may be arranged to rotate the tool in two axes of freedom within the microwave chamber The microwave source may be controllable to generate a variable output power ranging from 1 kilo watt to 500 kilo watts.

The moulding system may further comprise a breather tube providing an air passage to the interior cavity.

The breather tube may provide an air passage between the interior cavity and a location exterior of the microwave chamber.

The moulding system may further comprise temperature monitoring means for monitoring the temperature of the interior cavity of the mould.

The moulding system may further comprise control means for controlling the microwave source in dependence on the output of the temperature monitoring means.

The temperature monitoring means may include one or more thermocouples in the interior cavity or embedded within the tool wall.

The temperature monitoring means may include data communications cabling connecting the thermocouple(s) to a temperature monitoring system external to the microwave chamber.

The data communications cabling may comprise microwave shielded signal cables.

The data communications cabling is preferably routed inside the breather tube.

According to another aspect of the present invention, there is provided a microwave comprising a chamber, a microwave source arranged to generate microwave energy within the chamber, a mount for mounting a moulding tool within the chamber in the path of the microwave energy and a rotation system, wherein the rotation system is arranged to rotate one or more of the chamber, the microwave source and the mount means about two or more axes to move* the path of microwave energy with respect to the mount.

According to another aspect of the present invention, there is provided a method of moulding a product comprising: coating a hollow moulding tool with a microwave receptive material; charging the moulding tool with a moulding material; mounting the moulding tool within the path of a microwave source; and, rotating the moulding tool in at least two axes with respect to the path of the microwave source.

According to another aspect of the present invention, there is provided a moulding tool comprising a body having interior and exterior surfaces, the interior surfaces defining a cavity, wherein the interior surfaces and the cavity in combination comprise a mould, at least a portion of the exterior surfaces include a microwave receptive material, the material of the body being arranged to conduct heat from the microwave receptive material to the cavity upon exposure to a microwave source.

The tool may comprise two or more parts which, when joined together, * 30 substantially block the passage of microwave energy into the cavity.

The material of the body may includes metal.

This invention relates to the use of microwaves for the heating process for a rotational moulding, which can be applied to new or existing rotamoulding machinery. Using a microwave chamber which defines the heating chamber within which the tool for the moulding rotates on the end of a spindle arm, the tool can be heated directly using microwave energy to melt the polymer contained within the tool to form a rotamoulded part.

The polymer can be in either liquid or pellet or powder form, or a combination.

Brief Description of the Drawings

Embodiments of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a sectional view of a moulding system according to an aspect of the present invention; Figure 2 is a perspective view of aspects of the system of Figure 1; Figure 3 is a schematic diagram of a moulding system according to another aspect of the present invention; and, Figure 4 is a schematic diagram of another moulding system according to an aspect of the present invention.

Detailed Description

Figure 1 is a sectional view of a moulding system according to an aspect of the present, invention.

The system includes a microwave chamber 2 and a spindle arm 1. The spindle arm is configured to receive the moulding tool 4. The spindle arm can rotate the tool 4 about 2 axes.

In this embodiment, the spindle arm I is part ofa carousel type rotamoulding machine.

A microwave generator head 3 mounted on the top of the chamber. The component tool 4 is free to rotate within the chamber 3 in one axis of rotation, while the spindle arm I is free to rotate in a second axis of rotation.

Figure 2 is a perspective view of aspects of the system of Figure 1.

Figure 2 shows how access is gained to the rotamoulding tooling 4 as part of the microwave chamber 2 is removed leaving the bottom base pate to the chamber 5 and the tool.

Figure 3 is a schematic diagram of a moulding system according to another aspect of the present invention.

Figure 3 Shows how the microwave oven 2 is applied to two or more tools 4 rotating on the spindle arm 1.

Figure 4 is a schematic diagram of another moulding system according to an aspect of the present invention.

Figure 4 Shows the use of a clam shell microwave chamber 2 arrangement surrounding the rotamoulding tooling 4.

Figure 5 is an exploded view of the moulding tool 2 and base plate 5 of Figure 1 (note that the tool is inverted compared to that of Figure 1).

Figure 5 illustrates aspects of a preferred embodiment in which a breather tube 6 passes through the base plate 5 into the interior of the tool 2. This forms an air pathway from the interior of the mould, through the centre of the mould support structure to the microwave oven wall and out through the base of the spindle arm. The air pathway enables transfer of air between the tool interior and the outside of the oven to avoid pressure build-ups within the tool during heating which are detrimental to the molding process.

Embodiments of the present invention seek to improve the energy efficiency of the rotamoulding process by using microwaves to directly heat the surface of the tool. Energy is only used to directly heat the tool which then indirectly heats the polymer within the tool. It is not required to heat the air surrounding the tool in the heating chamber or any part of the spindle arm required to rotate the tool within the heating chamber. Once the heating and consolidation phase is completed the microwave source is turned off and access to the tool is provided for the cooling phase. Therefore the process has a greater energy efficiency and reduces the heat losses incurred with the conventional process.

One embodiment of the present invention is a method for producing rotational moulding components using microwave energy to heat the rotamoulding tooling. In this approach, a microwave generator is attached to a microwave chamber capable of receiving and processing a mould in two axes of rotation.

In the case of a carousel machine the tool rotates in the microwave chamber in one axis of rotation and the microwave chamber is attached to the spindle arm of the rotamoulding machine to achieve a second axis of rotation.

The specific arrangements discussed to achieve rotation about two axes are not essential. It is simply necessary that the tool is rotated about the two axes with respect to the microwave generator to ensure even application of microwave energy. The tool may be rotated in the microwave chamber and generator or both.

In one alternative arrangement, the microwave generator and chamber may be arranged to be rotatable about the two axes with the tool mount being fixed.

A microwave receptive coating is applied to the outer surface of the tool which is then mounted on the spindle arm or other mount in the chamber.

Microwave energy is then applied to the tool whilst it is rotated through the two axes of rotation.

The microwave receptive coating is preferably applied to the outer surface of the tool with a coating thickness of between 1 to 30 mm. It may contain microwave susceptor particles such as silicon carbide, iron oxide or carbon black which generate heat on exposure to microwave energy.

The tool is heated by applying an external tool coating that can be applied to new or existing rotamould tooling, which is receptive to microwave energy and produces a controlled temperature rise to provided a heat source to the tool when a microwave field is applied, The microwave chamber is designed to allow access to the tool for loading and unloading the mould and allowing external cooling.

The microwave generator will typically be of the type which generates variable output power ranging from 1 kilo watt to 500 kilo watts.

The temperature of the (typically metal) tool can be monitored using one or more thermocouples attached to the inner wall surface or embedded within the tool wall in such a way that the thermocouple signal cables are shielded against the microwave energy. In the preferred embodiment of Figure 5, the thermocouple cables 7 are passed through the breather tube 6. This arrangement is advantageous because exposure of the thermocouple wires to the microwaves results in interference with data signals received from the thermocouples. This can means inaccurate readings, lack of readings altogether or even damage to recording equipment. Additionally, if wires pass through the chamber walls of the microwave oven, the holes for the wires also lead to microwave leakage from the system. The breather tube 6 therefore has a dual function: allowing the tool to breath with external air and providing a route for a number of thermocouples to pass into the tool without being exposed to direct contact with microwave energy Preferably, the tool is formed from two or more parts that when joined together and clamped produce a safe shield against microwaves passing into the inside of the tooling Optionally, the tool is made metal such as steel and/or Aluminium.

Claims

Claims 1. A moulding system comprising a microwave chamber, a mount and a tool, the tool having an interior cavity defining a mould and is arranged to receive a moulding material, at least a part of the exterior surface of the tool comprising a microwave receptive material, the microwave chamber including a microwave source, the mount being arranged to mount the tool within the chamber, wherein moulding system is arranged to rotate one or more of: the tool when mounted on the mount; the chamber; and/or the microwave source about two axes of rotation to move moulding material within the tool in two directions through microwave energy emitted by the microwave source.
2. A moulding system according to claim 1, wherein the microwave receptive material comprises a coating.
3. A moulding system according to claim 2, wherein the coating has a thickness of between I and 30 mm.
4. A moulding system according to any preceding claim, wherein the microwave receptive coating includes microwave susceptor particles selected from.a group including silicon carbide, iron oxide and carbon black.
5. A moulding. system according to any preceding claim, wherein the moulding system is arranged to rotate the tool in a first axis of rotation and rotate the microwave source in a second axis of rotation.
6. A moulding system according to claim 5, wherein the moulding system is arranged to independently control the speed of rotation in the first and second axes.
7. A moulding system according to any of claims I to 4, wherein the moulding system is arranged to rotate the tool in two axes of freedom within the microwave chamber
8. A moulding system according to any preceding claim, wherein the microwave source is controllable to generates a variable output power ranging from 1 kilo watt to 500 kilo watts.
9. A moulding system according to any preceding claim, further comprising a breather tube providing an air passage to the interior cavity.
10.A moulding system according to claim 9, wherein the breather tube provides an air passage between the interior cavity and a location exterior of the microwave chamber.
11.A moulding system according to any preceding claim, further comprising temperature monitoring means for monitoring the temperature of the interior cavity of the mould.
12.A moulding system according to claim 11, further comprising control means for controlling the microwave source in dependence on the output of the temperature monitoring means.
13.A moulding system according to claim 11 or 12, wherein the temperature monitoring means includes one or more thermocouples in the interior cavity or embedded within the tool wall.
14.A moulding system according to claim 13, wherein the temperature monitoring means include data communications cabling connecting the thermocouple(s) to a temperature monitoring system external to the microwave chamber.
15.A moulding system according to claim 14, wherein the data communications cabling comprise microwave shielded signal cables.
16.A moulding system according to claim 14 or 15 when dependent on claim 9, wherein the data communications cabling is routed inside the breather tube.
17.A microwave comprising a chamber, a microwave source arranged to generate microwave energy within the chamber, a mount for mounting a moulding tool within the chamber in the path of the microwave energy and a rotation system, wherein the rotation system is arranged to rotate one or more of the chamber, the microwave source and the mount means about two or more axes to move the path of microwave energy with respect to the mount.
18.A method of moulding a product comprising: coating a hollow moulding tool with a microwave receptive material; charging the moulding tool with a moulding material; mounting the moulding tool within the path of a microwave source; and, rotating the mou(ding tool in at (east two axes with respect to the path of the microwave source.
19.A moulding tool comprising a body having interior and exterior surfaces, the interior surfaces defining a cavity, wherein the interior surfaces and the cavity in combination comprise a mould, at least a portion of the exterior surfaces include a microwave receptive material, the material of the body being arranged to conduct heat from the microwave receptive material to the cavity upon exposure to a microwave source.
20.A tool according to claim 19, wherein the tool comprises two or more parts which, when joined together, substantially block the passage of microwave energy into the cavity.21 A tool according to claim 19 or 20, wherein the material of the body includes metal.