FR2553186A1 - Improvements to machines for heating articles or products by condensing a vapour on to them - Google Patents

Abstract

The invention relates to thermal processing machines. The machine is one in which the article or product to be heated to a high temperature is passed into a chamber 4 which is filled with the vapour of a primary liquid produced in a boiler and insulated from the atmosphere by a mass 6 of vapour of a secondary liquid having a lower boiling point than that of the primary liquid. The secondary liquid is introduced into the machine separately from the primary liquid through an atomiser 23 working under pressure. The primary vapour is condensed by a coil 5 in which a preheated liquid is flowing at a temperature higher than the boiling point of the secondary liquid. Particularly useful in the electronics industry.

Description

 The invention relates to improvements to machines for heating articles or products by vapor condensation thereon.

 French patent 2 243 045 discloses a machine for heating an article to a high temperature, for example with a view to subjecting it to welding or brazing operations, by condensation of vapor from a liquid with a high boiling point on the latter, which comprises an enclosure open to the atmosphere and suitable for containing a primary liquid having a boiling point which is at least equal to said high temperature; heating means close to the lower end of the enclosure and suitable for boiling the primary liquid to produce primary steam used to heat the article, primary condensing means at a first height above the bottom of the enclosure and capable of condensing the primary vapor into primary liquid at the first height; primary condensate collecting means associated with the primary condensing means and suitable for collecting the dense primary vapor which comes therefrom; a first conduit communicating the primary condensate collecting means and the lower part of the enclosure and suitable for transporting condensed primary steam from the primary condensate collecting means to the lower part of the enclosure; means for establishing a secondary vapor mass in the enclosure above the primary vapor, this mass forming a sort of plug for the primary vapor; condensing means at a second height above the first height and suitable for condensing the secondary vapor into secondary liquid at the second height, secondary condensate collecting means associated with the secondary condensing means and suitable for collecting the secondary condensed steam which comes from these and a second conduit ensuring communication between the secondary condensate collecting means and the primary condensate collecting means, and suitable for transporting the condensed secondary steam from the secondary condensing collecting means to the collecting medium primary condensate.

 In this type of machine, the article is heated by the condensation of primary vapor on the article which is accompanied by the transfer of the latent heat of vaporization of said vapor. This calorific contribution quickly and uniformly raises the temperature from 11 articles to that of steam.

 This machine is relatively satisfactory in operation. However, the ever increasing demands of industrialists make that there is a need for an improved machine.

 The invention proposes to provide such an improved machine. More particularly, the invention relates to a machine for heating an article or product to a high temperature by vapor condensation thereon, which comprises - a chamber for heating the article or product to be heated, this chamber being clean receiving a vapor of primary liquid having a boiling point which is at least equal to said elevated temperature, - at least one passage opening into said chamber for supplying and evacuating said article or product to be heated, - means movement of the article or product to be heated from the inlet to the outlet of the machine, - heating means suitable for bringing to boiling a primary liquid contained in a boiler and for producing primary steam intended to be sent to said chamber, - primary condensing means capable of condensing the primary vapor into primary liquid, primary condensate collecting means capable of collecting the condensed primary vapor and returning it oyer au boiler - means for establishing - in said passage a mass of vapor of a secondary liquid having a boiling point lower than that of the primary liquid, said mass completely filling a section of said passage, - own secondary condensation means to condense the secondary vapor into secondary liquid, - secondary collecting means suitable for collecting the condensate of secondary vapor and for recycling it to the means for establishing the mass of secondary vapor, characterized in that the secondary liquid is introduced into the machine separately from the primary liquid, the means for establishing the secondary vapor mass comprising at least one device for spraying under pressure the secondary liquid projecting fine droplets of said secondary liquid into the section of said passage disposed between the primary condensing means and the secondary condensing means, and in that the primary condensing means include take a coil or the like traversed by a preheated fluid whose temperature is higher than the boiling point of the secondary liquid.

 The supply of the secondary liquid by a route distinct from that of the primary liquid makes it possible to avoid a mixture of the primary and secondary liquids which tends to lower the boiling point of the primary liquid. On the other hand, the use of a device for spraying under pressure the secondary liquid, such as a sprayer or a sprayer boom, makes it possible to obtain a "cloud" of fine droplets of secondary liquid distributed in the section of said passage which vaporizes almost instantaneously on contact with the primary hot vapor. This ensures the constant presence of a secondary liquid vapor plug, the role of which is to establish a thermal discontinuity allowing a temperature profile to be achieved for the articles or products to be heat, prevent the primary liquid vapor from escaping from the machine, and dissolve any harmful degradation products, such as polyfluoroisobwene, from the primary liquid which is generally made up of a perfluoroearbide compound. Advantageously, the spraying member is supplied with secondary liquid by a metering pump, which ensures the regularity of the injection rate.

 according to a preferred embodiment, the primary condensation coil is associated with a device for heating the fluid which circulates, this device being provided with means for controlling and regulating the temperature of said fluid.

 According to another improvement, the means for heating the primary fluid comprise, on the one hand, a water bath consisting of a coolant in which the heating elements are immersed and, on the other hand, heating elements immersed directly in the primary liquid, the latter being activated only when the machine is started or when a load of articles or products is introduced into the machine. To avoid any local overheating likely to decompose the primary liquid, the maximum power dissipated by the heating elements immersed in the heat transfer fluid, brought back to the exchange surface represented by the part of the boiler immersed in the water bath and separating the heat transfer fluid from the primary liquid, will be less than 2 W / cm 2. Similarly, the heating elements immersed directly in the primary liquid must have a specific power of less than 2 W / cm 2.

 According to yet another improvement, the machine which is usually closed by a glass door while it is working and is provided with a hood overhanging this door and sucking the vapors leaving the machine when the door is opened to introduce the articles. keys or products in or out of the machine, is provided. in addition, pivoting flaps mounted at the end of the passage opposite the heating chamber which are actuated by the means for moving the article or product so as to close said passage when the door is open and the means of movement are in the position of loading or unloading of articles or products, and to disengage said passage-when said displacement means are engaged in said passage. These flaps increase the safety of operating the machine, preventing the latter from becoming found in direct communication with a large flow of vapors which, leaving the machine, would not be recovered by the hood for any reason (air flow for example). In addition, these flaps reduce the loss of liquids.

 The machine of the invention is useful in particular for welding or soldering operations, in particular of electronic components, of polymerization of articles or products made of thermosetting materials, of curing of adhesives, etc. In general, it is possible to 'use for all applications in which a conventional machine would be used.

 Other original features will appear on reading the following description, made with reference to the appended drawing, which will make the present invention well understood.

In the drawing, Figure 1 is a schematic view of an improved machine according to the invention.

Figures 2a and 2b are schematic partial views of the machine of Figure 1.

 The illustrated machine comprises a vertical tank 1, for example of rectangular section. This tank comprises, from the bottom up, several zones a boiler 2 filled with a primary liquid 3 (usually a liquid perfluorocarbon); a heating chamber 4 of the article or product to be heated filled, in service, with vapors of the primary liquid; a thermostatic coil 5 5 for condensing the vapors of primary liquid; a zone 6 filled with a mass of vapors of a secondary liquid (usually a chlorofluorocarbon) having a boiling point lower than that of the primary liquid, this mass of vapors forming a plug for the vapors of primary liquid; a cooled coil 7 for condensing the secondary liquid vapors; an additional cooled coil 8 serving as vapor guard.

 The primary liquid contained in the boiler 2 is heated, on the one hand - by a water bath 9 filled with a heat transfer fluid which is itself heated by heating elements 11 immersed in said fluid, the heating power of the elements II and the heat exchange surface between the water bath and the boiler being such that the specific power is less than -2W / cm 2, and, on the other hand, directly by heating elements 12 immersed directly in the primary liquid and having also a specific power of less than 2 W / cm 2. The heating elements It operates continuously to keep the primary liquid just boiling while the heating elements 12 are only activated when the cold primary liquid is brought when boiling (starting) or when a load of articles or products to be treated and introduced into the machine, the heating elements 12 being slaved to the elevator of the machine, as described below. The internal volume of the water bath is connected to an expansion vessel 13 cooled by a coil 14 with water circulation. A tap 15 makes it possible to drain the water bath while a tube 16 makes it possible to fill it with heat-transfer fluid. The coil 5 is used to condense the vapor of primary liquid but must be without effect on the vapor of secondary liquid so as to ability to obtain thermally stable operation of the machine. To do this, it is maintained at a temperature above the boiling point of secondary liquid by a circulation of thermostatically controlled water coming from a water heater 17 equipped with a thermocouple 18.

temperature control and a regulation thermostat 19.- At the outlet of the coil 5, the water temperature is controlled by the thermocouple 29 before being rejected, a thermostat 21 controlling the stopping of the machine in the event of overheating and another thermostat 22 controlling the water flow by means of solenoid valves, as described below. The primary liquid condensate which forms on the coil, in service, flows directly onto the walls of the tank, which therefore serve as means for collecting the condensate, and falls back into the boilers.
The secondary liquid is sprayed under pressure in the form of fine droplets in the zone 6 by means of a ramp 23 pierced with a plurality of spraying orifices. The ramp 23 is supplied with secondary liquid by a metering pump 24 with flow and with adjustable operating frequency. In serviceability, the droplets which come out of the spraying orifices come into contact with the hot treated joints, causing the film of primary liquid which could have formed on them, and / or primary vapor, which produces their immediate vaporization.

 The coils 7 and 8 are traversed in series by a stream of cold water. At the location of these coils, the tank has a section of dimensions slightly larger than the rest of the tank so as to provide, below the coil 7, a gutter 25 used to collect the secondary liquid condensed on said coils and flowing. From the gutter, the secondary liquid is directed to a Florentine vase 26. In fact the secondary vapors, which are in contact with atmospheric air are charged with water which, combined with a certain thermal degradation resulting from their contact with the vapors of the primary liquid, gives rise to the formation of hydrochloric and hydrofluoric acids which must be separated. In the vessel 26, the supernatant acid water is eliminated by overflow in the conduit 27, while the purified secondary liquid is sent via the conduit 28, into the reservoir 29 of secondary liquid, from which the metering pump 24 is supplied. the Florentine vase 26 is cooled by a coil 30 with water circulation in order to accelerate the separation of the phases and comprises at its lower part a water inlet 31 used to backwash the secondary liquid.

A flow meter 32 makes it possible to control the flow rate of the washing water. Both the coil 30 and the inlet 31 are supplied with cold tap water from a device 33 enabling the water pressure to be achieved.

A safety device 34-mounted downstream of the device prevents the machine from starting up in the event of a shortage
The water leaving the coil 30 which has only slightly heated, passes successively in the serpentine 7, in the coil 8, then after the flow meter 35, is divided into two streams whose flows are controlled by the solenoid valves 36 and 37 which are themselves controlled by the above-mentioned thermostat 22. The first of these currents crosses the conduit 38 to reach the coil 14 of the expansion vessel described above, and from there is sent to the heater 17 via the conduit 39. The other of these currents borrows the conduit 40 before being rejected. As long as the thermostat 22 judges that the water is cold enough, most of the water passes through the conduit 38. As soon as the water temperature exceeds a predetermined threshold, the valves are actuated to direct the water having passed the flow meter 35 to the discharge. This system allows significant water savings. As the primary liquid is capable of partially dissolving certain products, for example welding fluxes, carried by the parts to be treated which therefore accumulate in the primary liquid contained in the boiler and as the solubility of these dissolved products decrease with temperature , these impurities must be removed before the primary liquid has completely cooled down after a period of work. To this end, an assembly is provided consisting of a pump 41, a pre-filter 42 and a filter 43, with interchangeable cartridges, connected to the boiler by the conduits 44 and 45.

This assembly is started, during the cooling of the primary liquid, by a thermostat 46 immersed in the primary liquid. A pressure switch 47 makes it possible to control the degree of clogging of the pre-filter and of the filter and to change their cartridges when it proves useful.

 Ia machine also includes the following control and safety devices - A thermostat 48 immersed in the primary liquid and ensuring llarr8t of heating by the heating elements 12 at the end of the rise in temperature of the primary liquid during the start-up phase of the machine.

- thermocouples 49 and 50 to measure the temperatures of the vapors of the primary and secondary liquids, respectively.

- a thermostat 51 immersed in the heat transfer fluid and controlling the start or stop of the heating elements II in order to control the heating power and prevent any untimely overheating.

- a level controller 52 controlling the level of the primary liquid in the boiler and stopping the machine in the event of insufficiency.

- A level controller 53 controlling the level of the secondary liquid in the tank 29 and triggering an alarm in the event of insufficiency.

 The machine further comprises an "elevator" used to introduce and then remove the articles or products to be treated in the machine and to support them during their treatment. This elevator consists of a mesh basket 54 connected to a suitable conventional motor-reducer training device (not shown) making it possible to independently regulate the speed of descent, the speed of ascent, the duration of the intermediate stage in the secondary steam. and the duration of the plateau in the primary steam, which makes it possible to obtain any desired heat treatment profile. the intermediate bearing avoids excessively brutal thermal shocks to the articles to be treated during the rise in temperature (lowering of the basket) and allows the articles to leave the zone protected by the vapors at a sufficiently low temperature to avoid any damage. controls the switching on and off of the heating elements 12 (once the start-up phase has ended).

The elements 12 are put into action at the start of the descent of the basket 54 and stopped at the start of its ascent, by means of a simple switch (not shown)
The machine finally comprises, at its upper part, a pair of flaps 55 articulated at 56 and each secured to a wing 57 arranged perpendicular to the corresponding flap. These flaps close the entry of the machine when the basket is in the raised position and are in the effecé position when the basket is lowered in the machine, the rotation of said flaps around the axes 56 being controlled directly by the action of the basket on the wings 57 , as illustrated more particularly in FIGS. 2a and 2b which show the two possible positions of the flaps. In this way, the risks of untimely steam escape are reduced to a minimum, concomitantly improving safety in use. Finally, a hood (not shown) equipped with sliding glazing and extraction, prevents the appearance of vapors around the workstation in the event that vapors have accidentally escaped from the machine.

 The machine of the invention finally allows the use of mixtures of two primary liquids with different boiling points when it is desired to treat articles or products at an intermediate temperature between said boiling points. As in such a case the mixture of primary liquids normally tends to deplete by constituting the most volatile primary, there is provided, according to the invention, a thermometric probe 70 immersed in the bath of primary liquid and connected to a device regulation 71 with adjustable temperature threshold. When the temperature of the primary liquid bath exceeds the temperature threshold chosen as a result of the depletion of the most volatile primary component, the regulation device 71 controls the actuation of a metering pump 72 injecting into the boiler, via line 73, an adjustable predetermined additional quantity of the most volatile primary liquid constituent, taken from a reservoir 74 containing a reserve of this most volatile constituent.

 As primary liquids, inert perfluorocarbon compounds are usually used. Useful primary liquids commercially available are in particular the products of the registered trademark FLUORINERT (sold by the company 3M) whose boiling points range, depending on the types, from 560C to 215 C, and of the registered trademark GALDEN (sold by the AUSIMONT SPA company of the MONTEDISON group) whose boiling points are included in the ranges 218-2280C (GALDEN LS) and 255-2720C (GALDEN H5).

 As secondary liquids, chlorofluorocarbon compounds are usually used. Useful secondary liquids commercially available are in particular the products sold under the registered trademark FLUGENE by the company CHLOE CHIMIE, such as Flugene 113 (trichlotrifluoroethane) whose boiling points are 470C, or under the registered trademark FREON sold by EI DU PONT DE NEMOURS AND COMPANY, whose boiling point is also close to 470C.

 It should be noted that the temperature of the secondary vapors in zone 6 is generally higher than the boiling point of the secondary liquid used because there is a certain mixture of the trapped and secondary rapeurs at the interface between the chamber 4 and zone 6.

For example, for a primary liquid having a
P. eb. equal to 2150C (FluorinertFC ~ 70) and a secondary liquid having a P. eb. equal to 47: (Flugene R 113), there is produced a mixture containing approximately 5% of primary vapor and 95% of secondary vapor and having a boiling point of 80-900C.

 Thanks to the machine's adjustment possibilities, it is possible to set up an operating regime that guarantees the stability of the vapor phases.

 Apart from the features indicated, the machine of the invention is of conventional operation.

 It goes without saying that the embodiments described are only examples and Iron could modify them in particular by substitution of technical equivalents, without departing from the scope of the invention.

Claims (10)

REVElDICATIONS 1. A machine for heating an article or product at a high temperature by vapor condensation thereon, which comprises  A heating chamber (4) of the article or product to be heated, this chamber being adapted to receive a vapor of the primary liquid having a boiling point which is at least equal to said high temperature, - at least one passage opening into said chamber for supplying and evacuating said article or product to be heated, - displacement means (53) of the article or product to be heated from the inlet to the outlet of the machine, - heating means suitable for bring to the boil a primary liquid (3) contained in a boiler and to produce primary steam intended to be sent to said chamber, - primary condensing means (5) suitable for condensing the primary steam into primary liquid, - primary condensate collecting means suitable for collecting the condensed primary steam and returning it to the boiler, - means for establishing in said passage a mass (6) of vapor of a secondary liquid having a lower boiling point than that ui of the primary liquid, said mass completely filling a section of said passage, - secondary eondensation- (7,8) means suitable for condensing the secondary vapor into secondary liquid, - secondary collecting means (25) suitable for collecting the condensate secondary steam and recycling it to the means for establishing the secondary steam mass, characterized in that the secondary liquid is introduced into the machine separately from the primary liquid, the means for establishing the secondary steam mass comprising at least a member (-23) for pressure spraying of the secondary liquid projecting fine droplets of said secondary liquid into the section of said passage arranged between the primary condensing means and the secondary condensing means, and in that the primary condensing means (5) include a coil or the like through which a preheated fluid passes whose temperature is above the boiling point of the secondary liquid. 2. A machine according to claim 1, char. in that the primary condensing coil is associated with a device y for heating (17) the fluid which circulates, this device being mwii of means for controlling and regulating (18, 19) the temperature of said fluid. 3. A machine according to claim 1 or 2, caz in that the means for heating the primary fluid comprise on the one hand, a water bath consisting of a heat transfer fluid (1 O) in which are immersed heating elements ( 11) and, on the other hand, heating elements (12) immersed directly in the primary liquid, the latter being activated only when the machine is started or when a load of articles or products is introduced in the machine. 4. A machine according to claim 3, char. in that the specific power of the heating elements is - less than 2 W / cm 2. 5. A machine according to any one of claims 1 to 4, char. In that it is further provided with pivoting flaps (54) mounted at the end of the passage opposite to the heating chamber which are actuated by the means for moving the article or product so as to close said passage when the door is open and the movement means are in the position of loading or unloading the articles or products, and to release said passage when said means - movement have engaged in said passage. 6. A machine according to any one of claims 1 to 5, char. in that the machine further comprises means (41) for pumping the primary liquid contained in the boiler, means for filtering (42, 43) the pumped primary liquid and means for recycling (45) the filtered primary liquid to the boiler. 7. A machine according to claim 6, car.en that the pumping means (41) are started during the cooling of the primary liquid (3). 8. A machine according to any one of claims I to 7, char. in that the secondary liquid condensate is purified in a Florentine vase (26) before being returned to the spraying member (23).  9. A machine according to claim 3, char. in that the heating elements (12) immersed in the primary liquid are put into action when the elevator is lowered and stopped when it is raised. 10. A machine according to any one of claims 1 to 9, characterized in that it further comprises means for controlling (70,71) the boiling temperature of the primary liquid, cooperating with means ( 72, 73, 74) allowing the introduction into the boiler, when necessary, of a supplement of the most volatile constituent of the primary liquid, when the latter consists of a mixture of two constituents with dots different boiling points, in order to correct any excessive variation in the boiling point of the mixture.