WO1999043456A2

WO1999043456A2 - Heater for gaseous substances and core production with such a heater

Info

Publication number: WO1999043456A2
Application number: PCT/GB1999/000401
Authority: WO
Inventors: Dean Anthony Jones
Original assignee: Dean Anthony Jones
Priority date: 1998-02-10
Filing date: 1999-02-09
Publication date: 1999-09-02
Also published as: GB2333986B; GB2333986A; GB9902924D0; GB9902923D0; GB9902922D0; TW394714B; WO1999043456A3; GB2333985A; AU2530499A; GB2333984A

Abstract

Apparatus for use in the production in a core box of a casting core from a shaped mixture of sand, resin and solvent, said apparatus comprising a chamber to house the shaped mixture, said chamber having inlet means for gaseous material, and further comprising supply means to supply said inlet means of the chamber with firstly - and from a first heater - a gaseous curing mixture at a first temperature and, thereafter - from a second heater - with a flow of gas (e.g. air) at a second and elevated temperature to scavenge and/or drive out solvent in gaseous form from the shaped mixture and/or from the chamber. Each of the first and second heaters comprises a plurality of gas conduits in series with one another and arranged as a plurality of loops in the form of coils to provide in use a generally spiral gas path, and a plurality of electric heater elements within at least some of said gas conduits to provide for progressive temperature increase in gaseous material flowing from one conduit with heat element therein to the next. The gaseous curing mixture is pre-warmed prior to its admixture with the TEA and, in addition, said TEA and air, as a gaseous mixture, is heated by said first heater prior to passage to the shaped mixture to be cured.

Description

HEATER FOR GASEOUS SUBSTANCES AND CORE PRODUCTION WITH SUCH A HEATER

DESCRIPTION

Technical Field

This invention relates to the heating of gaseous substances and to the production of sand cores for use in the casting of metals.

Background Art

Electrical heating of gaseous substances is known, e.g. from GB-A-0745914, O-88/08758 and GB-A-2047510. However the efficiency of such devices, particularly where a finely controlled temperature is required for a gaseous output at a high flow rate. Such efficiency is required for many purposes, particularly (but not exclusively) for the production of sand cores for use in metals casting. Such sand core production is by mixing the sand with resin and solvent, shaping the mixture to the form of the desired item and, in order to aid curing of the resin, exposing the shaped item (e.g. in a core box) to a gaseous mixture consisting of a mist-like spray of unheated triethylamine (TEA) entrapped in an air stream (optionally a pre-warmed air stream) . This and similar processes have been well known for several years and are disclosed in US-A-4644994 , GB-A-1269202, GB-A-1269203 , GB-A-1209964 , US-A-5005630 , US- 4878533, US-4362204, US-4359082, US-4257438 and US-A- 3429848. Nonetheless, each of such prior art processes has a number of shortcomings and/or disadvantages, including the time taken for the resin to fully cure — often of the order of 30 minutes after stripping the cores from the mold or core box — and the time taken for all the solvent to diffuse out of the core — often of the order of 24 hours in ambient temperatures — thus limiting the scratch hardness of the core surface .

It is therefore considered desirable to provide a process and apparatus which can overcome or at least minimise the above-mentioned and/or other disadvantages and/or shortcomings of the prior art .

Summary of the Invention

According to a first aspect of the present invention there is provided a heater for gaseous substances, comprising a plurality of gas conduits in series with one another and arranged as a plurality of loops in the form of coils to provide in use a generally spiral gas path, and a plurality of electric heater elements within at least some of said gas conduits to provide for progressive temperature increase in gaseous material flowing from one conduit with heat element therein to the next .

Preferably, the coils are of generally rectangular outline. Advantageously the coils are of similar dimensions and are in substantial alignment with one another.

According to a second aspect of the present invention there is provided apparatus for use in the production of a casting core from a shaped mixture of sand, resin and solvent, said apparatus comprising: a chamber to house the shaped mixture, said chamber having an inlet for gaseous material ; and a heater according to said first aspect of the invention, said heater having an outlet coupled to the chamber inlet and having an inlet connected to a generator of a gaseous mixture of TEA entrapped in air .

Advantageously, said generator is provided with a mixing zone for TEA and entrapping air, said air being pre-warmed upstream of said mixing zone.

Preferably, the apparatus comprises temperature control means responsive to the temperature of the gaseous mixture at the heater outlet or chamber inlet and for controlling the heat output of said heater to provide a constant predetermined temperature for the gaseous mixture at said heater outlet or chamber inlet.

According to a third aspect of the present invention there is provided apparatus for use in the production of a casting core from a shaped mixture of sand, resin and solvent, said apparatus comprising: a chamber to house the shaped mixture, said chamber having an inlet for gaseous material; and a heater of gaseous material having an outlet coupled to the chamber inlet and having an inlet connected to a generator of a gaseous mixture of TEA entrapped in air, said generator being provided with a mixing zone for TEA and entrapping air and with means, located upstream of said mixing zone, for pre-warming that air.

Preferably, said generator is provided with a bypass conduit bypassing the said mixing zone whereby air can pass directly to said heater for heating therein and for passage onward to said core production chamber.

According to a fourth aspect of this invention there is provided apparatus for use in the production of a casting core from a shaped mixture of sand, resin and solvent, said apparatus comprising: a chamber to house the shaped, mixture, said chamber having inlet means for gaseous material; and supply means to supply said inlet means of the chamber with firstly a gaseous curing mixture at a first temperature and, thereafter with a flow of gas (e.g. air) at a second elevated temperature to scavenge and/or drive out solvent in gaseous form from the shaped mixture and/or from the chamber.

Preferably, the said supply means comprises a first heater of gaseous material to supply the gaseous curing mixture, and a separate second heater of gaseous material to supply the scavenging gas flow.

Advantageously, the first and second heaters are connected to one another via valve means operable to switch the supply to said chamber inlet from a first state in which said supply is derived from the first heater alone to a second state in which said supply is derived from the first and second heaters in series. Thus, in said second state, the gaseous material entering the second heater is derived from the first heater and is therefore at a raised temperature .

Preferably, the apparatus includes control means to control the time duration for the supply of the gaseous curing mixture and/or the time duration for the supply of the scavenging gas flow and/or the instant of time during an operating cycle when the valve means is operated.

In a preferred embodiment the said control means includes first and second temperature controllers, the first temperature controller being responsive to the temperature of the gaseous mixture at an outlet of the first heater, and the second temperature controller being responsive to the temperature of the gas (e.g. air) at an outlet of the second heater, each said temperature controller being arranged to control the heat output of the respective heater and provide at the outlets of the heaters substantially constant predetermined first and second temperatures for respectively the gaseous curing mixture and the scavenging gas .

According to a fifth aspect of the present invention there is provided a process of core production wherein a shaped mixture of sand, resin and solvent to be cured is exposed to a gaseous mixture of TEA and air, characterised in that said TEA and air, as a gaseous mixture, is heated by a heater according to said first aspect of the invention prior to passage to the shaped mixture to be cured.

Preferably, the said air is pre-warmed prior to its admixture with the TEA.

According to a sixth aspect of the present invention there is provided a process of core production wherein a shaped mixture of sand, resin and solvent to be cured is exposed to a gaseous mixture of TEA and air, characterised in that the air is pre-warmed prior to its admixture with the TEA and in that said TEA and air, as a gaseous mixture, is heated prior to passage to the shaped mixture to be cured.

The gaseous mixture is preferably applied to the said shaped mixture contained within a core box that is preheated, e.g. by a flow of air heated by the heater that subsequently heats the gaseous mixture of TEA and air.

Advantageously, the said flow of air to preheat the core box is derived from a bypass conduit that bypasses a passage in which the TEA is admixed with air. Preferably, the air to preheat the core box is provided at a first temperature higher than a second temperature at which the gaseous mixture of TEA and air is provided.

In preferred embodiments of the invention, said first temperature is greater than 80 °C (preferably at a temperature of 90°C) , and said second temperature is less than 80°C.

Advantageously, said gaseous mixture of TEA and air is heated electrically prior to passage to the shaped mixture to be cured.

The said gaseous mixture is preferably heated to a predetermined temperature under the control of temperature control means.

According to a seventh aspect of this invention there is provided a process of core production wherein a shaped mixture of sand, resin and solvent to be cured is exposed to a gaseous curing mixture and, after such exposure, solvent is removed from out of the core, characterised in that solvent liberation from out of the core is assisted by a flow of gas (e.g. air) at an elevated temperature.

Advantageously, the elevated temperature is above the maximum permissible temperature for the gaseous curing mixture .

In one preferred embodiment the gaseous curing mixture is a mixture of TEA and air.

Advantageously, the gaseous curing mixture is heated — after mixing — prior to passage to the shaped mixture to be cured. Said heating may be effected by electrical heating means, e.g. a heater according to said first aspect of the present invention.

Preferably, the said exposure to the gas flow at elevated temperature is for a period of time substantially longer than the exposure to the gaseous curing mixture . For example, exposure to the gaseous curing mixture may be for a period of between 1/10 to U as long as the period of exposure to the gas flow at elevated temperature.

The said elevated temperature may be in the range 150°C to 180°C; preferably it is set to a value between approximately 175°C to 180°C.

Advantageously, the temperature of the gaseous curing mixture is no greater than 80 °C; preferably it is set to a value between approximately 75°C and 80°C.

Brief Description of the Drawings

By way of example one embodiment of this invention will now be described with reference to the accompanying drawings of which:

Figure 1 is a schematic diagram of apparatus according to this invention for use in the production of casting cores; Figure 2 is a schematic diagram of a heater according to this invention and for use in the apparatus of Fig 1; and Figure 3 is a circuit diagram of temperature control means for the heater of Fig 2.

Detailed Description of Example (s) of the Invention The illustrated apparatus 10 is for use in the production, with the aid of TEA as catalyst, of cores 11 from a shaped mixture of sand, resin and solvent for use in the casting of metals . The cores 11 are formed -.in a chamber 12 having a gas inlet manifold 15. A two-way bypass valve 50 having an inlet 56 and first and second outlets 52,54 has one outlet 52 connected to the gas inlet manifold 15 to the chamber 12. The valve's inlet 56 is coupled to an outlet 16 at the downstream end of a first heater unit 20 of gaseous material, and the valve's second outlet 54 is connected to the inlet 58 of a second heater unit 60 that has an outlet 62 connected to the gas inlet manifold 15 to chamber 12. The two-way bypass valve 50 is a motorised L-type ball valve that is pneumatically or electrically operable from a control unit as described below.

The heater unit 20 has an input 18 for gaseous material, this input 18 being coupled by a conduit 19 to a generator

30 of a gaseous mixture of TEA entrapped in pre-warmed air.

Heater 60 is mounted on top of heater 20 by support struts 67. Heater 20 and heater 60 are each of similar construction and, as shown in Fig 2, each comprises a plurality of gas conduits 24 in series with one another to provide together a single gas flow path. The conduits 24 are arranged as a plurality of generally rectangular-shaped loops, composed of linear lengths interconnected by curved right-angular bends, such that they combine to form the single gas flow path as one of somewhat spiral-like form. This arrangement of conduits 24 provides a low overall physical volume for the heater whereby it can be compact in size, and also provides for a potentially turbulent airflow through the heater's conduits 24.

A plurality of separate electric heater elements 25 are provided at intervals within some of the gas conduits 24. These heater elements 25 provide for progressive temperature increase in the gaseous material flowing, in turbulent fashion, from one conduit 24 (with heat element 25 therein) to the next. In the illustrated example, the single gas flow path is composed of two or three generally rectangular loops 24 disposed in parallel vertical planes, the six upright legs of the loops each containing a separately controlled electrical heating element 25 of nominal 2k rated output (to provide an overall 12kW rating) .

Each of the heater units 20 and 60 is provided with associated control means. For heater 20 the control means includes a control and display unit 70 (Fig 1) that provides a visual temperature display, e.g. via radial thermometer guages 27a and 27b, of the temperature of the gaseous material at (or adjacent to) the heater inlet 18 and the heater outlet 16. The temperature display is provided in response to signals obtained (via a unit such as 26 of Fig 2) from at least one thermocouple 28 responsive to the temperature of the gaseous material at

(or adjacent to) the heater's outlet 16. In the illustrated embodiment of this invention three thermocouples 28 are provided. One of these thermocouples 28 is to control the heat output of heater 20 such that it provides a substantially constant predetermined set temperature (e.g. in the range between 70° and 80°) for the gaseous mixture at the heater's outlet 16. Of the two further thermocouples 28, one is to control the heat output of heater 20 to a higher set temperature (e.g. 90°C) during a preheating or warm-up stage of the process — when air at that higher temperature is supplied from heater 20 via the outlet 52 of valve 50 to the inlet manifold 15 of the molding chamber 12 — and the other of these two further thermocouples 28 is to effect automatic shut down of the heated flow of gas and the molding process if the temperature rises beyond a predetermined set upper limit (e.g. 110°C) . The three thermocouples 28 are coupled by electric cabling 72 to the control and display unit 70 that serves to control the power supplied to heater elements 25 of heater 20 via electric power cabling 74.

The control means for heater 60 includes a second control and display unit 75 (Fig 1) to provide a visual temperature display e.g. via one or more radial temperature guages, of the gas temperature at or adjacent to the outlet 62 of the heater 60. This temperature control may be obtained from a thermocouple sensing arrangement similar to that provided for heater 20 or, alternatively — and as shown in Fig 1 — from just a single high temperature thermocouple (not shown) provided in the outlet 62 of heater 60. In such a case, the signal from this thermocouple is transmitted to the second control and display unit 75 which, by controlling the power supplied via cabling 76 to the heater elements 25 of heater 60, provides air from outlet 62 at a controlled elevated set temperature in the range 170 °C to 180°C, preferably 175°C.

The gaseous material provided to the inlet 18 of heater 20 is derived from the gas generator 30 and is a gaseous mixture of triethylamine (TEA) entrapped in air, preferably pre-warmed air. The gas generator 30 comprises an inlet 32 for ambient air which, under the control of a solenoid valve 31 and a pressure regulator 37, is passed on to an air pre-warmer 39 incorporating one or more electrical heating elements 34. Warmed air then passes from pre-warmer 39 along a conduit 33 and across a dispenser nozzle 35 that produces a fine mist spray of TEA, e.g. with particles of micron size. The TEA is drawn from a reservoir 36 to which the liquid TEA is supplied via a TEA inlet valve 40 and a pump 38.

From the mixing chamber or zone provided by conduit 33, the air-entrapped TEA is then supplied, as a gaseous mixture, to the outlet 42 of the gas generator 30 which is connected to inlet 18 of the heater unit 20.

To facilitate pre-heating of the core box provided by chamber 12, a bypass conduit 44 is provided between the air inlet 32 and the mixture outlet 42. This bypass conduit 44 has flow control means, comprising a solenoid valve 45 and pressure monitoring control valve 46, to control the flow of secondary air (e.g. at a pressure of between approximately 30 to 40 psi) from bypass conduit 44 entering the outlet 42 — that otherwise leads from the TEA-air mixing chamber or conduit 33. It will be appreciated that valve 40 is closed to shut off the supply of TEA when the valve 45 is to be opened. Thus the secondary air from conduit 44 can be heated, on its own and without added TEA, by the heater 20. By thus providing direct preheating of chamber 12, start up problems can be avoided or at least minimised, and it is possible to reduce

(a) the time required for start up of the curing process and for actual core production,

(b) the number of imperfect or scrap cores produced, and

(c) the quantity of TEA required for curing of the cores 11, and also possibly to increase the outer skin strength of the cores produced whereby they can be removed sooner from the core box.

From the foregoing it will be appreciated that the cores 11 — which are formed as shaped mixture of sand, resin and solvent and which are to be cured in chamber 12 — can be exposed to a gaseous mixture of TEA and air, and that this gaseous mixture, with the TEA therein, can be heated to the pre-determined temperature desired prior to passage to the chamber's inlet 15. With apparatus of the illustrated embodiment it has been found that, by warming of the TEA-and-air mixture, the catalytic reaction provided by the TEA is dramatically accelerated and improved, the desired core mass strength can be achieved almost immediately and, upon ejection of the cores from the core box chamber 12, they demonstrate a substantially improved scratch hardness (i.e. resistance to scratching) and core strength. It is furthermore considered that the resultant cores 11 may require less time (so- called air purge time) for liberation and dissipation of retained solvents than that required in prior art arrangements. Such a reduction in the air purge time of the core mass aids meeting of environmental safeguards and also minimises the risk of such solvents being liberated during use of the cores for actual metal casting. Moreover it has been found that such improved results could be achieved using reduced quantities of the catalyst and resin, and hence savings in the cost of materials.

However, to further reduce the air purge time of the cores and remove as quickly as possible the liberated solvents, the chamber 12 is subjected to a scavenging air flow derived, at elevated temperature, from the second heater 60. This scavenging air flow at elevated temperature is supplied after ending the supply of the initial gaseous curing mixture of TEA and air (at lower temperature) from heater unit 20. For example the supply of gaseous curing mixture of TEA and air may be for a predetermined initial period of, say, 3 seconds, whereas the supply of the scavenging air flow may be for a subsequent, longer, period of, say, 5 to 50 seconds. As already stated this scavenging air flow is at an elevated temperature substantially above that of the TEA/air curing mixture.

For example, whilst the TEA/air curing mixture may be supplied at a temperature less than 90°C, e.g. from say 70°C to 80°C (i.e. below the chemical breakdown temperature of the TEA component) , the elevated temperature may for example be in the range of 150 to 190°C (preferably 150°C to 175°C) .

It will be appreciated that the two supplies — of TEA/air mixture and of the air alone (at higher temperature) — may be derived from two separate and independent heaters and that these may be of a construction as that described above with reference to Fig 2 or of some other construction. However, in order to provide for such elevated temperatures in as efficient a manner as possible, the two heaters 20 and 60 are each of a construction as that of Fig 2 and are linked via the bypass valve 50. The latter is operated — after sufficient time has elapsed for the TEA/air mixture to flow into the manifold 15 — so that the heater unit 20 continues to operate but now transfers heated air (on its own and derived from the bypass conduit 44 of generator 30) via the outlet 54 of valve 50 to the inlet 62 of the heater 60. The two heaters 20,60 then operate in series, and heater 60 does not need to elevate the air temperature from a base at ambient temperature but only from a base at the already raised temperature provided by heater 20.

It is envisaged that, with such an arrangement utilising both heaters 20 and 60 to provide for hot air purging or scavenging of the chamber 12 , the temperature of that scavenging air can approach a desired elevated and preset level of the order of 190°C. This is achieved in a staged manner from an input of ambient cold air to inlet 32 of generator 30, an output of warmed air at, say, 80°C at the outlet 16 from heater 20 and into the inlet 58 of heater

60, and an output of air at the elevated set temperature

(in the range 150°C to 190°C) from the outlet of heater 60. It is considered that providing for-. a period of scavenging of the chamber 12 with air at such elevated temperature purges out quickly and efficiently the solvents liberated by the curing process. It is also considered that this, elevated temperature scavenging, together with the post- admixture heating of the TEA/air gaseous curing mixture, permits an improvement in core quality and/or production reliability, a reduction in the quantities of resins and catalysts required, a reduction in the machine's overall cycle times for core production turnaround, and a reduction in the level of fumes arising from the cores during and after their production and arising during metal casting from such cores . As indicated above the process is controlled by control means 70,75 (which may optionally be combined into a single unit) to provide for temperature sensing and indication on suitable temperature indicators (e.g. radial guages) and, in response to the sensed temperature signals, to control the electrical power supply to the heating elements (and hence heat output) of the heaters 20 and 60. The above- described construction of the first and second heaters 20 and 60 permits a finely controlled temperature (e.g. within ±5°C) for the gaseous output of each — i.e. of the TEA/air curing mixture output of heater 20, the pre-warming air output of heater 20 or the air-alone output from heater 60 — and that this can be achieved even with a substantial gas flow rate of the order of 20 to 40m/sec at a pressure of up to, say, 50 psi. Additionally or alternatively, the control means 70,75 can provide for the appropriate timing cycle for operation of the core production process and the timed operation of the bypass valve 50 and the valves 40 and 45. Thus the control means can allow for suitable setting of the initial time period (e.g. of, say. 3 or 4 seconds) for the supply via bypass valve 50 in a first position of the TEA/air gaseous mixture from heater 20, for switching over of the bypass valve 50, and for suitable setting of the subsequent initial time period (e._.g. of, say, up to 50 seconds) for the supply via bypass valve 50 (in a second position) of the scavenging air at elevated temperature from heater 60.

In a possible modification, the TEA-air curing mixture is left unheated after being mixed in the generator 30, and the mixture is passed to chamber 12 and the cores 11 in this unheated state for a set time before (by operation of valve 50) it is switched off and the scavenging flow is switched on.

In another modification the outlets 52,62 are connected to two limbs of a three-way or Y-coupling that has its third limb connected directly (or via a single line) to the inlet manifold 15 of the mold curing chamber 12. This avoids the need for the outlets 52 and 62 to be independently connected to two separate ports to the inlet manifold 15 via the two separate lines 51,61 illustrated.

Other modifications and embodiments of the invention, which will be readily apparent to those skilled in this art, are to be deemed within the ambit and scope of the invention, and the particular embodiment (s) hereinbefore described may be varied in construction and detail, e.g. interchanging (where appropriate or desired) different features of each, without departing from the scope of the patent monopoly hereby sought .

Claims

1. A heater for gaseous substances comprising a plurality of gas conduits in series with one another and arranged as a plurality of loops in the form of coils to provide in use a generally spiral gas path, and a plurality of electric heater elements within at least some of said gas conduits to provide for progressive temperature increase in gaseous material flowing from one conduit with heat element therein to the next .

2. A heater according to Claim 1, wherein the coils are of generally rectangular outline.

3. A heater according to Claim 1 or Claim 2, wherein the coils are of similar dimensions and are in substantial alignment with one another.

4. Apparatus for use in the production of a casting core from a shaped mixture of sand, resin and solvent, said apparatus comprising: a chamber to house the shaped mixture, said chamber having an inlet for gaseous material; and a heater according to any one of Claims 1 to 3 having an outlet coupled to the chamber inlet and having an inlet connected to a generator of a gaseous mixture of TEA entrapped in air.

5. Apparatus according to Claim 4, wherein said generator is provided with a mixing zone for TEA and entrapping air, said air being pre-warmed upstream of said mixing zone.

6. Apparatus according to Claim 4 or Claim 5, comprising temperature control means responsive to the temperature of the gaseous mixture at the heater outlet or chamber inlet and for controlling the heat output of said heater to provide a constant predetermined temperature for the gaseous mixture at said heater outlet or chamber inlet.

7. Apparatus for use in the production of a casting core from a shaped mixture of sand, resin and solvent, said apparatus comprising: a chamber to house the shaped mixture, said chamber having an inlet for gaseous material; and a heater of gaseous material having an outlet coupled to the chamber inlet and having an inlet connected to a generator of a gaseous mixture of TEA entrapped in air, said generator being provided with a mixing zone for TEA and entrapping air and with means, located upstream of said mixing zone, for pre-warming that air.

8. Apparatus according to Claim 7, wherein said generator is provided with a bypass conduit bypassing the said mixing zone and for directing air to said heater for heating therein and passage onward to said core production chamber.

9. Apparatus according to Claim 7 or Claim 8, comprising temperature control means responsive to the temperature of the gaseous mixture at the heater outlet or chamber inlet and for controlling the heat output of said heater to provide a constant predetermined temperature for the gaseous mixture at said heater outlet or chamber inlet.

10. Apparatus according to any one of Claims 7 to 9 wherein said heater accords with any one of Claims 1 to 3.

11. Apparatus for use in the production of a casting core from a shaped mixture of sand, resin and solvent, said apparatus comprising: a chamber to house the shaped mixture, said chamber having inlet means for gaseous material; and supply means to supply said inlet means of the chamber with firstly a gaseous curing mixture at a first temperature and, thereafter with a flow of gas (e.g. air) at a second elevated temperature to scavenge and/or drive out solvent in gaseous form from the shaped mixture and/or from the chamber.

12. Apparatus according to Claim 11 wherein the said supply means comprises a first heater of gaseous material to supply the gaseous curing mixture, and a separate second heater of gaseous material to supply the scavenging gas flow.

13. Apparatus according to Claim 11 wherein the first and second heaters are connected to one another via valve means operable to switch the supply to said chamber inlet from a first state in which said supply is derived from the first heater alone to a second state in which said supply is derived from the first and second heaters in series (whereby the gaseous material entering the second heater is derived from the first heater and is therefore at a raised temperature) .

14. Apparatus according to any one of Claims 11 to 13 characterised by control means to control the time duration for the supply of the gaseous curing mixture and/or the time duration for the supply of the scavenging gas flow and/or the instant of time during an operating cycle when the valve means is operated.

15. Apparatus according to Claim 14 wherein said control means includes first and second temperature controllers, the first temperature controller being responsive to the temperature of the gaseous mixture at an outlet of the first heater, and the second temperature controller being responsive to the temperature of the gas (e.g. air) at an outlet of the second heater, each said temperature controller being arranged to control the heat output of the respective heater and provide at the outlets of the heaters substantially constant predetermined first and second temperatures respectively for the gaseous curing mixture and the scavenging gas .

16. Apparatus according to any one of Claims 11 to 15 wherein each said heater is in accordance with any one of Claims 1 to 3.

17. A process of core production wherein a shaped mixture of sand, resin and solvent to be cured is exposed to a gaseous mixture of TEA and air, characterised in that said TEA and air, as a gaseous mixture, is heated by a heater according to any one of Claims 1 to 3 prior to passage to the shaped mixture to be cured.

18. A process of core production according to Claim 17, wherein the air is pre-warmed prior to its admixture with the TEA.

19. A process of core production wherein a shaped mixture of sand, resin and solvent to be cured is exposed to a gaseous mixture of TEA and air, characterised in that the air is pre-warmed prior to its admixture with the TEA and in that said TEA and air, as a gaseous mixture, is heated prior to passage to the shaped mixture to be cured.

20. A process of core production according to any one of Claims Claim 17 to 19, wherein said shaped mixture is contained within a core box, said process being characterised in that the core box is pre-heated.

21. A process of core production according to Claim 20, characterised in that the core box is pre-heated by a flow of air heated by the heater that subsequently heats the gaseous mixture of TEA and air.

22. A process of core production according to Claim 21, characterised in that said flow of air to preheat the core box is derived from a bypass conduit that bypasses a passage in which the TEA is admixed with air.

23. A process according to any one of Claims 20 to 22, wherein the air to preheat the core box is provided at a first temperature higher than a second temperature at which the gaseous mixture of TEA and air is provided.

24. A process according to Claim 23, wherein said first temperature is greater than 80┬░C (preferably at a temperature of 90┬░C) , and said second temperature is less than 80 ┬░C.

25. A process of core production according to Claim 19 or to any one of Claims 20 to 24 when dependent therefrom, wherein said gaseous mixture of TEA and air is heated electrically prior to passage to the shaped mixture to be cured.

26. A process of core production according to any one of Claims 17 to 25, characterised in that said gaseous mixture of TEA and air is heated to a predetermined temperature under the control of temperature control means .

27. A process of core production wherein a shaped mixture of sand, resin and solvent to be cured is exposed to a gaseous curing mixture and, after such exposure, solvent is removed from out of the core, characterised in that solvent liberation from out of the core is assisted by a flow of gas (e.g. air) at an elevated temperature.

28. A process according to Claim 27 wherein the elevated temperature is above the maximum permissible temperature for the gaseous curing mixture .

29. A process according to Claim 27 or Claim 28 herein the gaseous curing mixture is a mixture of TEA and air.

30. A process according to any one of Claims 27 to 28, wherein the gaseous curing mixture is heated ΓÇö after mixing ΓÇö prior to passage to the shaped mixture to be cured.

31. A process according to Claim 30, wherein said heating is be effected by electrical heating means.

32. A process according to Claim 30 or Claim 31, wherein said heating is effected by a heater according to any one of Claims 1 to 3.

33. A process according to any one of Claims 27 to 32 wherein the exposure to the gas flow at elevated temperature is for a period of time substantially longer than the exposure to the gaseous curing mixture .

34. A process according to Claim 33 wherein exposure to the gaseous curing mixture is for a period of between 1/10 to Vi as long as the period of exposure to the gas flow at elevated temperature.

35. A process according to any one of Claims 27 to 34, wherein the said elevated temperature is in the range 150 ┬░C to 180┬░C.

36. A process according to any one of Claims 27 to 35, wherein the said elevated temperature is set to a value between approximately 175┬░C to 180┬░C.

37. A process according to any on╬▓ of Claims 27 to 36, wherein the temperature of the gaseous curing mixture is no greater than 80┬░C.

38. A process according to any one of Claims 27 to 37, wherein the temperature of the gaseous curing mixture is set to a value between approximately 75┬░C and 80┬░C.