WO1996022181A1

WO1996022181A1 - Mould heating method and heated mould

Info

Publication number: WO1996022181A1
Application number: PCT/GB1996/000286
Authority: WO
Inventors: Rowland Frank Evans
Original assignee: Rowland Frank Evans
Priority date: 1995-01-20
Filing date: 1996-01-19
Publication date: 1996-07-25
Also published as: GB9501108D0

Abstract

A mould heating arrangement wherein the mould is at a cooler temperature during filling with working material than during material curing (or vulcanising). Means to cool the mould before injection of a fresh material shot are disclosed, whereby to reduce the mould fill temperature below the material curing temperature. Also disclosed is a mould heating method which includes adding a fixed amount of heat to the mould each cycle and by adding a supplementary amount of heat to the mould for a selected portion of the cycle; and a moulding machine (1) which includes a mould having a mould cavity (16), heating means (20, 22) for the mould, and heating control means characterised by a primary heating means (20) and a secondary heating means (22), the primary heating means being further from the mould cavity than the secondary heating means.

Description

MOULD HEATING METHOD AND HEATED MOULD

FIELD OF THE INVENTION

This invention relates to a mould heating method and heated mould, and in particular to a heating method for a thermosetting-plastic injection mould.

BACKGROUND TO THE INVENTION

The constituents of thermosetting plastics are typically placed cold in a (hot) mould of suitable size and shape, and heated in the mould until the constituents chemically react; the mould is opened when the reaction is complete, and the (hot) moulded article ejected, whereupon the cycle is repeated. For convenience the description below refers to a polymer shot, injected for polymer heat curing, though the method and apparatus applies to other moulded parts e.g. those of vulcanised rubber.

As compared to extrusion moulding, which is continuous, processes for making articles of thermosetting resinous materials - including injection moulding, injection compression moulding, and compression moulding - are typically discontinuous, notwithstanding that one moulding cycle usually quickly follows another.

DISCLOSURE OF THE PRIOR ART

A method and apparatus for press moulding articles is known from GB2,235,645A. The materials to be moulded are placed in the mould either loose or as a pre-formed sheet. After removal from the press the mould is cooled, before ejection of the article; the method described is "transfer moulding", and is suited to long cycle times, with the article being thermo-formed. However the moulds are purpose built, and not suited to localised cooling of the cores and cavities, at the moulding station.

An injection moulding process is known which comprises placing (as by injecting) cool polymer constituent into the moulding cavity of a heated mould, holding the constituent under pressure until the polymer is heat-cured, opening the mould, and ejecting the cured polymer from the moulding cavity. This process is repeated as a cyclic process, with a fresh shot of polymer subsequently injected as part of another cycle. The mould cools during moulding, primarily by transfer of heat to the constituent.

A known method of heating the mould is by a hot liquid flowing continuously in mould conduits alongside the moulding cavity; known liquids are superheated water, steam, and hot oil. The additional heat supplied to the mould by the hot liquid is used {a} to make up heat lost from the mould to the environment; and {b} to make up heat lost to the polymer shot, necessary in order to bring the mould and thus the successive polymer shots up to reaction temperature and to hold the shot at that temperature until curing is complete. There is however a delay between the liquid being heated outside the mould, and the liquid being pumped into the mould, as well as a delay before the heat travels into the constituent.

Another known method of heating the mould is by electrically heated elements placed alongside the moulding cavity. There is a delay before the elements become heated, ready to transfer heat by conduction into the mould body.

For both of the above methods of heating the mould, the mould temperature is measured, and the respective hot liquid flow or electrical current set at a steady value selected with the intent that the mould will remain within a pre¬ selected operating temperature range throughout the cycle. This temperature range is chosen (a) to have a maximum which is not so high as to cause premature curing and delivery of faulty articles, and (b) to have a minimum which is not so low as to fail to initiate curing, or to delay curing whereby either to extend the cycle time or to deliver faulty articles.

The known methods of mould temperature control utilise continuous steady state input heat control, regardless of the changing cyclic moulding machine operations or of the material heat input needs.

A further disadvantage of these known methods of heating the mould is that all of the mould is to be heated to the steady value of the penultimate paragraph i.e. a pre-set operating temperature; this operating temperature is selected to be within the pre-determined temperature range within which that mould should be maintained over the cycle i.e. not only when readied to receive the mould shot, but also during receiving and then warming the mould shot, and during subsequent curing of the material.

STATEMENT OF THE INVENTION

We now propose a mould heating arrangement characterised in that the mould is at a cooler temperature during filling with working material than during material curing (or vulcanising). As compared to the known arrangements of which we are aware, the mould temperature is deliberately kept lower than the prior art average mould temperature during cavity filling, and deliberately kept higher than the prior art average temperature during material curing. Thus there is a two-stage heating regime, with a lower mould temperature at mould closing than at mould opening. Thus the known tendency for the material to start curing whilst still being injected (blocking the cavity inlet, and/or producing faulty parts, differentially cured) is reduced, if not eliminated; whilst the material onca injected can be elevated to a high temperature (for rapid curing, to reduce the cycle time and increase machine output).

In a particular arrangement we propose to force cool the mould before injection of a fresh material shot, whereby to reduce the mould fill temperature below the material curing temperature (for both endothermic and exothermic materials).

We also propose a mould heating method which includes adding a fixed amount of heat to the mould each cycle characterised by adding a supplementary amount of heat to the mould for a selected portion of the cycle.

Thus we have recognised that for consistent product moulding the amount of heat instantaneously required by the mould changes during a moulding cycle. In a preferred embodiment the supplementary heat is added after the start of a cycle, usefully after the mould has been filled with polymer; usually the supplementary heat will be added near to the mould cavity. If the supplementary heat is added away from the mould cavity, requiring longer to conduct to the cavity, the supplementary heat will typically be added before filling has been completed.

On larger moulds different zones of the mould can be controlled at different selected temperatures, or within different selected temperature ranges. Usefully the mould will be cooler away from the (or each) cavity than it is nearer the cavity, whereby to provide a large heat sink which tends to "insulate" the cavity from ambient temperature changes. In a preferred embodiment the supplementary heat is added as a single "pulse". In an alternative embodiment (suited particularly for processes requiring long cycle times) the supplementary pulse can be provided in small segments; alternatively stated there are a large number of small heat pulses. The use of the supplementary pulse(s) is intended to maintaain at least the minimum required mould temperature over the cycle, without the maximum permitted mould temperature being breached.

Usefully the mould temperature will be measured close to the mould cavity, specifically within an "inner zone" close to the (injected) shot of material, and acts as a reference temperature for the moulding cavity; the average mould temperature at this measurement position is compared to a set temperature. Thus mould (cavity) temperature variations during the cycle can be kept within the acceptable range, specifically above the minimum permissible moulding temperature.

In a preferred embodiment the mould temperature of both the inner and an outer zone will be separately measured, the temperature of the inner zone being used as the (mould cavity) reference teperature, whilst that of the outer zone is used for a mould body temperature check, to confirm proper operation of the primary heating means.

Desirably a reference temperature trend (from temperature readings averaged over a full or a part of selected succeeding cycles, preferably successive cycles, or alternatively taken at a consistent point in each succeeding cycle) obtained by signals from an inner zone probe would be acted upon if it occurred over at least three successive cycles; with such a trend having been noted, action to correct the supplementary heat input by a change in the supplementary or secondary heating means (timing and/or rating) can often be effected prior to an upper or lower temperature limit (respectively defining the acceptable temperature range) being breached.

We also provide a moulding machine which includes a mould having a mould cavity, heating means for the mould, and heating control means characterised by a primary heating means and a secondary heating means, the primary heating means being further from the mould cavity than the secondary heating means. Thus there is an outer heating zone provided by the primary heating means and an inner heating zone provided by the secondary heating means. Preferably the heating control means is adapted to permit continuous energisation of the primary heating means and discontinuous energisation of the secondary heating means whereby the primary heating means can help maintain the mould cavity above a minimum operating temperature (notwithstanding environmental or other changes) whilst the secondary heating means can help heat the material shot to curing temperature whilst maintaining the mould cavity above the minimum operating temperature i.e. despite the intermittent (cyclic) introduction into the moulding cavity of a cold material "shot". Thus during normal cyclic processing in accordance with the invention the rate of heat input into the mould will vary during a cycle by the provision of the supplemental heating, and can furthermore be varied from cycle to cycle.

Usefully the primary and secondary mould heating means will be provided by separate heating devices, or by hot fluid in separate heating conduits. Alternatively, and perhaps typically on smaller moulds, a variable heat source could be provided, e.g. the primary heating means being a continuous low level of heating, the secondary heating means being a discontinuous high level of heating for process related or time related periods. SHORT DESCRIPTION OF THE DRAWINGS

The invention will be further described by way of example with reference to the accompanying schematic drawings, in which:-

Fig.l is a side view of a moulding machine;

Fig.2 is a side sectional view of two mould halves, with a cured polymer article ready for ejection;

Fig.3 is a front view of one half of an open dual mould, showing a polymer feed channel;

Fig.4 is a schematic circuit arrangement for mould heating control;

Fig.5 is another schematic circuit arrangement for mould heating control;

Fig.6 is a further schematic circuit arrangement for mould heating control;

Fig.7 is also a schematic circuit arrangement for mould heating control;

Fig.8 is a schematic comparison of base and supplementary pulsed heating during a cycle; and,

Fig.9 is a schematic comparison of three alternative supplementary heating modes. DESCRIPTION OF EXEMPLARY EMBODIMENTS

The moulding machine 1 has a base 2, which in use is fixed to a floor (not shown) of a moulding shop. Typically there will be a number of similar moulding machines side by side.

Secured to base 2 is a fixed platen 3 and an actuator 4; actuator 4 in this embodiment is hydraulically operated but alternatively could be mechanically operated using a toggle mechanism in known fashion.

Connecting fixed platen 3 and actuator 4 are tie bars 5 upon which movable platen 6 is supported for sliding movement towards and away from fixed platen 3, under the control of actuator 4. Removably secured to platens 3,6 are respective core blocks 14 which when brought together form a moulding cavity into which cold polymer can be injected. The cold polymer is heated whilst in the cavity until cured, adopting the shape of the cavity, and when the platens have been separated the cured article is ejected whereby to permit another machine cycle for the production of another article.

It is important that the polymer be held within a specified temperature range during curing, to avoid faulty articles.

In an embodiment according to the invention, and as seen in Fig.2, each platen 3,6 has three parts 11,12,13, secured together by known means (not shown), conveniently bolts. Base plate 11 is of metal and has apertures (not shown) receiving tie bars 5.

Intermediate plate 12 has on its face remote from base 11 a recess 7 in which is located an induction coil 19 (in this embodiment of copper) forming part of primary heating means 20. Recess 7 is covered by front plate 13, which in its face remote from the intermediate plate 12 has recesses 8 in which are located respective induction coils 21 (in this embodiment of copper) forming part of secondary heating means 22. Recesses 8 when moulding machine 1 is in use are, as shown, covered by core block 14.

The plates are of ferrous metal. Plates 12,13 form one heating platen, comprising a coil plate and a cover plate; plates 13,14 form a second heating platen, again comprising a coil plate and a cover plate i.e. the core block acts as the cover plate. The coils are thus embedded in the ferrous metal; when alternating current is fed to the coils, eddy currents are induced in each plate, and these rapidly heat the respective plates.

As seen in the embodiment of Fig.2 the plates need not be of the same thickness for each mould half. Furthermore the recesses can be differently positioned in the plates of the two mould halves.

In this embodiment there are dual cores 16 in each mould half. Cores 16 are dimensioned so as to make cured articles 18; in an alternative embodiment an alternative core block is fitted to base 12.

Primary heating means 20 is axially and laterally spaced from both cores 16; as seen in Fig.3 the primary heating means 20 extends adjacent an outer periphery of the plate 12 and is of a dimension to surround both of the cores 16.

Axially spaced from both cores (but less distant than primary heating means 20) is a secondary heating means 22; a secondary heating means closely surrounds the outer perimeter of a core. Thus each secondary heating means 22 is of a dimension substantially equivalent to that of the outer dimension of respective core 16.

The primary heating means 20 provides an outer zone of heating which is continuously energised during a cycle for background heating, whereby principally to compensate for ambient heat losses, whilst the supplementary or secondary heating means 22 provides an inner zone of heating, discontinuously energised, principally to supply heat to the process at a particular time or over selected periods during a moulding cycle.

In one embodiment the secondary heating means 22 is rated at 2.5KwH to cater for a polymer curing requirement of l.lKwH. In an advantageous embodiment the required heat from the secondary heating means 22 can be added in less than half the moulding cycle time; alternatively stated the secondary heating means 22 is energised for less than 50% of the time the primary heating means 20 is energised.

In the Fig.3 embodiment, both the primary and secondary heating means are low frequency induction coils, fed by respective primary wiring 24 and secondary wiring 26. Thus there are separate heating devices i.e. separate primary and secondary heating means 20,22. In an alternative embodiment, suited either for small moulding machines or for moulding machines located in a temperature controlled environment, only secondary heating means 22 is provided; the secondary heating means is run for part of a cycle at a low rating (25-40%) i.e. for mould body heating, and for the remainder of the cycle at 100% i.e. for mould cavity heating.

In one embodiment the primary and/or secondary heating means can be disconnected, to be removed and/or replaced when the core block 14 is changed, each core block having its own size and shape of primary 20 and (in particular) of secondary 22, heating means. In one embodiment there is a plug and socket connection between the secondary heating means 22 and secondary wiring 26; in an alternative embodiment there is a releasable connection in wiring 26. In a preferred embodiment the plates cannot be disconnected. In an alternative embodiment the heating means are electrical resistance-heated platens. However we prefer to use induction-heated platens to which a core block is removably clamped since we have found it possible to maintain a surface temperature across the platen which varies by less than 2°C; in a preferred embodiment there are multiple small induction coils embedded in the induction plates, interconnected one with another.

We have found that induction heated platens have the advantage of low thermal inertia, with rapid response time so that high powered heating coils can be used with only a small temperature over-shoot (if any) above the desired mean curing temperature; with high powered heating coils, the supplementary heat (secondary heating means 22) can quickly be added, allowing pulsed heating of the cores 16 and of the material to be cured. Induction heated platens also have the advantage that the mould steel (or other mould metal) around and forming the moulding core becomes the heating element for the material shot, with a high conversion efficiency (usually over 95%) of the electrical energy into available heat energy).

In an embodiment such as that of Fig.2, using induction- heated platens, there can be a single large induction coil for the primary heating means 20 for ambient heating control, and a plurality of separate induction coils, mounted closer to the moulding cavity than the primary heating means 20, for the secondary heating means 22, i.e. for rapid "start-up", and during cyclic operation for rapid mould temperature compensation for the injected cold material.

In an alternative embodiment one or both of the heating means is a fluid such as injected steam, or is an electrical heating element. Adjacent each core 16 is a temperature probe 28b, for a purpose to be described below. Remote from each core is a temperature probe 28a. Thus there is a temperature probe 28a,28b for the respective outer (ambient) and inner (material shot) heating zones. In alternative embodiments there is a temperature probe for only one of the cores, or for one of the mould halves.

Each core has a polymer feed channel 30, connected in this embodiment to a common feed line 32. In an alternative embodiment there is a feed channel in only one mould half i.e. one channel for one cavity.

AThe invention will be explained in more detail with reference to Fig.2, wherein both halves of the mould have primary and secondary heating means. The mould halves have been separated by known means, to allow cured articles 18 to be ejected, with the mould halves thereafter brought together for the injection of a fresh shot of material through respective channels 30, with the mould then ready to start a new cycle.

In use, in this embodiment primary heating means 20 is energised continuously. Such continuous mould heating can be set at a value to compensate for mould heat losses to the environment. The mould "background" temperature due to primary heating means 20 alone will not effect curing.

At start-up, prior to the first moulding cycle, secondary heating means 22 is energised continuously (as is primary heating means 20) so as rapidly to bring the mould up to the background temperature, within the predetermined mould operating temperature range for the specified process. Thus in the embodiment described this will occur before the first shot of polymer is injected. In a preferred embodiment, secondary heating means 22 is more highly rated than primary heating means 20, to reduce start-up delay. For a mould already pre-heated as in the preceding paragraph or following a moulding cycle, secondary heating means 22 is energised only intermittently; specifically secondary heating means 22 is energised only after the mould halves have been brought together and the fresh shot of polymer injected, whereby rapidly to replace mould heat which has been used to raise the polymer temperature.

With the arrangement of the invention, selected known materials which are to be heat cured, or rubber based materials which are to be vulcanised, can for instance be injected into the moulding cavity (typically at a low ambient temperature of between 40°C and 90°C), to be heated in the mould to an elevated reaction temperature (typically of between 100°C and 250°C). The selected material is held under pressure during curing (or vulcanising) as by the injection unit or by full closure of the mould.

In one embodiment the secondary heating means 22 once energised remains energised for a set period during a cycle; in an alternative embodiment, secondary heating means 22 once energised is subsequently energised in spaced segments, the timing of the segments being selected to keep the mould within the operating temperature range. This latter alternative embodiment is particularly useful for mouldings requiring longer cycle times, to minimise the problem (noted even in a stable thermal environment) of continuous thermal losses; but able also to react to sudden increased environmental loss e.g. upon the opening of moulding shop delivery door.

A signal representing the mould temperature adjacent a core or cavity, as monitored by its respective temperature probe 28b, is fed without interruption (analogue) through line 38 to a temperature averaging unit 40 (Fig.4). In this embodiment temperature probe 28b is closer to the mould core or cavity than the secondary heating means 22, being less than half way from the core or cavity towards the secondary heating means 22.

Timer Tl sends a (timing) signal to temperature averaging unit 40 once each cycle of the mould; and the averaged temperature between two such signals is transmitted, once each cycle but during the following cycle, from temperature averaging unit 40 to temperature comparator 42. This (averaged temperature) signal is compared with a pre-set temperature signal from temperature set point unit 44, with an output difference signal (corresponding to the difference between the averaged measured temperature and the pre-set temperature) being produced.

Once each cycle the output difference signal from temperature comparator 42 is sent to calculator 46. If a zero, neutral or "no change" output difference signal is sent to calculator 46, timer T2 in turn is unchanged, so that secondary heating means 22 repeats the heat regime of the previous cycle. If a positive or negative output difference signal is sent to calculator 46, timer T2 by way of power actuator 50 is caused to effect a longer or shorter energisation of the secondary heating means 22 than for the preceding cycle. In a preferred embodiment, to prevent "hunting" or excessive operation of timer T2, temperature comparator 42 has an inbuilt threshold, preferably adjustable, so that a positive or negative temperature output difference signal (above or below pre-set limits) is only sent to calculator 46 for a large temperature change and thus only occasionally, as when there is a temperature spike caused by a sudden environmental change (e.g. moulding shop delivery door left open in cold weather).

The output difference signal from temperature comparator 42 is also sent to temperature error memory 48. Thus the difference signal is stored in the memory and if a trend occurs (of increasing or decreasing difference), over three successive cycles, or in an alternative embodiment over a greater number of cycles, then a trend signal is sent to calculator 46, appropriately to increase or decrease the period for which timer T2 effects energisation (by way of power actuator 50) of supplementary secondary heating means 22.

In an alternative embodiment temperature error memory can activate timer T2 directly, sending a positive or negative signal in accordance with the trend "direction" i.e. increase or decrease away from the required temperature, and the rate of change.

In a further alternative embodiment, and again to inhibit "hunting", the correction signal to timer T2 in response to a trend indication can be of constant size, effecting the required change (in response to one trend signal) in the supplementary heating means in a number of discrete, smaller steps.

The correction of timer T2 in response to a trend signal has the advantage that the minimum and maximum permitted mould temperatures, though frequently and perhaps even regularly approached, should only rarely be breached; and then only in exceptional circumstances (such as when moulding shop fire sprinklers are operated leading to a low temperature spike).

Timer Tl not only sends a cycle signal to temperature averaging unit 40, but also to temperature error memory 48 and timer T2. The signal to temperature averaging unit 48 indicates the start of a new cycle and is useful particularly with an embodiment where no signal is sent from temperature comparator 42. The signal to timer T2 also indicates the start of a new cycle, to which timer T2 reacts after a period necessary for completion of the polymer injection.

Timer Tl itself reacts to a trigger signal from line 52, which can be fed thereto independently of moulding machine operation, and from cycle time set point 54. The trigger signal is used to re-initiate the timer Tl every cycle in order that this will be synchronised with the machine cycling, valuable if the machine cycle time is not constant; the trigger signal can be selected in accordance with a moulding machine function e.g. mould closing, completed polymer injection etc. The cycle time set point 54 is an input to identify the duration of each process cycle.

It will be understood therefore that timer T2 will turn on the power actuator 50 a specified time interval after the trigger signal is received via timer Tl (the specified interval being set to permit the mould to be closed and the injection completed for a given trigger signal), and that the power actuator 50 for the secondary heating means 22 will remain on for the time set in timer T2 and then will be turned off until the next trigger signal arrives from Tl .

In the embodiment of Fig. 5 the trigger signal from line 52 is transmitted directly to the temperature averaging unit

40, to the temperature error memory unit 48 and to timer unit T2. Thus, in this embodiment timer Tl is not required, and the cyclical temperature control of the mould is dependent directly upon the cycling of the machine. However, in the event that the machine stops cycling, provision is made for these units alternatively to receive a cycle timing signal from a pre-set timer Til, having a fixed cycle time; the signal from line 52 disables pre-set timer Til i.e. the signal from line 52 takes precedence, at least for that cycle. In the embodiment of Fig.6, calculator 46 is controlled by percentage heating set point unit 60. Unit 60 determines the proportion of the total cycle for which timer T2 permits supplementary heating by way of power actuator 50. Calculator 46 is controlled directly by timer Tl, which in turn is controlled either by cycle time set point 54 or by a trigger signal from line 52. In alternative embodiments (dotted lines) timer T2 is controlled by the trigger signal from line 52, or by an output signal from timer Tl.

In a further alternative embodiment timer T2 is controlled by cycle time calculator 62 which receives a processor or machine cycling signal from line 64.

In the embodiment of Fig.7 the power actuator 50 is energised by a signal from "and gate" 66, which in turn has received a signal from heating window enable unit 68; preferably the heating window enable unit 68 is controlled by the trigger signal from line 52, but alternatively (dotted lines) by a processor cycling signal from line 54.

In an alternative embodiment the "and gate" 66 receives a signal from standard temperature controller 69 which receives signals from temperature sensor input line 38.

Thus, as shown in Fig.8, a known temperature controller output 70 delivers repeated short bursts or pulses of heating, on a regular and continual basis, at less than full power. A heating controller of Fig.7 delivers bursts or pulses of heating (72), each of greater (e.g. 100%) power, but only for the period during which the heating window is enabled i.e. over only a part of a cycle e.g. after shot injection and during the chemical reaction (curing).

For each of the described embodiments, the time the secondary heating means 22 is operative will depend both on the quantity of polymer or other material to be moulded, and on its thermo-chemical nature; the externally supplied secondary heating will be less if the chemical reaction is exothermic, and some part-cycle cooling (rather than supplementary heating) may be needed.

Our results of tests of the reaction time for a standardised pulse of low or mains frequency induction (LFI/MFI) heating, electric (resistance) heating, and hot flowing oil heating is shown in Fig.9. The blocks below the horizontal line represent the quantity and timing of heat input, whilst the curves above the line represent the distribution of heat provided to the mould. With LFI heating the heat provided to the mould is almost instantaneous and is over 95% efficient. The oil conduit flow has the slowest reaction (to the need for increased core or cavity heating). Also the heating efficiency (proportion of available supplied supplementary heat used to warm the core or cavity is lowest for oil heating.

Advantages of the invention over prior art arrangements are that mould heat-up or start-up time can be reduced e.g. from 3 hours to under 2 hours; a lower "fill" temperature should improve finished part quality; an elevated cure (or vulcanising) temperature should reduce cycle time, with increased output yet without loss of quality; reduced temperature variations (even those due to ambient temperature variations) at specified points in the cycle should improve finished part quality; variations in the ambient temperature or in the primary heating means 20 can be compensated by the pulsed heating from secondary heating means 22; the invention can be utilised for single, dual or preferably multi-zone heating, with a temperature sensor in each zone so that the zone temperatures can be individually controlled i.e. a reference temperature for each zone fed to the or a controller system.

Claims

1. A mould heating arrangement characterised in that the mould is at a cooler temperature during filling with working material than during material treatment, said treatment being one of curing and vulcanising.

2. A mould heating arrangement according to claim 1 characterised by means to cool the mould before injection of a fresh working material shot, whereby to reduce the mould fill temperature below the material curing temperature.

3. A mould heating method according to claim 1 for a cyclic processor (1) which includes adding a fixed amount of heat to the mould each cycle characterised by adding a supplementary amount of heat to the mould for a selected portion of the cycle.

4. A mould heating method according to claim 3 characterised by one of adding the supplementary heat after the start of a cycle, usefully after the mould has been filled with a material to be treated such as a polymer, at or near to the mould cavity (16) or by adding the supplementary heat remote from the mould cavity and before mould filling has been completed, in both cases so that the supplementary heat can reach the cavity before moulding has been completed.

5. A mould heating method according to claim 3 or claim 4 characterised in that different zones of the mould are heated to different selected temperatures, or to within different selected temperature ranges, in that the mould is cooler away from the (or each) cavity (16) than it is nearer the cavity whereby to provide a large heat sink which tends to "insulate" the cavity from ambient temperature changes, and in that the supplementary heat is added as one of a single continuous "pulse" or as a series of separate small pulse segments.

6. A mould heating method according to claim 3 or claim 4 characterised in that the mould temperature is measured at a measurement position close to the mould cavity, specifically within an "inner zone" close to the (injected) shot of material, the mould temperature measurement acting as a reference temperature for the mould cavity, and in that the average mould temperature at this measurement position is compared to a set temperature whereby mould (cavity) temperature variations during the cycle can be kept within an acceptable range, and specifically can be kept above the minimum permissible moulding temperature.

7. A mould heating method according to claim 5 characterised in that the mould temperature of both the inner and an outer zone are separately measured, the temperature of the inner zone being used as the (mould cavity) reference temperature, whilst the temperature of the outer zone is used for a mould body temperature check whereby to permit confirmation of proper operation of the primary heating means (20).

8. A mould heating method according to claim 6 or claim 7 characterised in that a mould temperature signal is obtained by one of averaging temperature signals from an inner zone probe (28b) over a full or part cycle and alternatively by a signal taken at a consistent point in each respective cycle, in that said mould temperature signals are examined to detect a reference temperature trend obtained from the values of said signals from at least three succeeding cycles, preferably from at least three successive cycles, and in that with such a trend having been noted, action to correct the supplementary heat input by a change in at least one of the timing or rating of the secondary heating means (22) is effected prior to one of an upper or a lower temperature limit being breached, said upper and lower limits defining an acceptable temperature range.

9. A moulding machine (1) adapted to use a mould heating arrangement according to claim 1 and which includes a mould having a mould cavity (16), heating means (20,22) for the mould, and heating control means characterised by a primary heating means (20) and a secondary heating means (22), the primary heating means being further from the mould cavity than the secondary heating means.

10. A moulding machine according to claim 9 characterised by an outer heating zone provided by the primary heating means (20) and an inner heating zone provided by the secondary heating means (22), and by the heating control means being adapted to permit continuous energisation of the primary heating means and discontinuous energisation of the secondary heating means whereby the primary heating means can help maintain the mould cavity above a minimum operating temperature whilst the secondary heating means can help heat the working material shot to treatment temperature whilst maintaining the mould cavity above the minimum operating temperature whereby to permit compensation for mould cooling from the intermittent (cyclic) introduction into the moulding cavity (16) of a cooler working material "shot".

11. Operating means for a cyclic processor (1) which includes a mould adapted to be heated by a mould heating arrangement according to claim 1 characterised in that during normal cyclic processing the rate of heat input into the mould is varied during a cycle by the provision of supplementary heating, and in that the supplementary heating can be varied from cycle to cycle.

12. An operating system according to claim 11 characterised in that separate primary and secondary mould heating means are provided by one of separate heating devices (20,22) and separate heating conduits containing fluid pre-heated prior to entering the conduits.