EP0421902B1 - Vacuum drying process for various articles, and apparatus for carrying out the process - Google Patents

Description

The present invention relates to the general technical field of methods and devices for drying various parts or bodies from any production line.

The drying processes are used in various industries and, in particular, in the pharmaceutical industry, in the chemical industry, in the ceramic and synthetic materials industry, in the electrical engineering and electronics industry, and again, for example, in the optical industry and in the mechanical industry in general. Thus, the parts or bodies from a production line which are liable to undergo a drying phase, either following the manufacturing process itself, or following a cleaning or rinsing phase, can for example be components and printed circuits, simple or complex machining parts, made of metal, plastic or glass, etc.

The present invention therefore relates to the industrial problem of the removal of water and, more generally, of residual liquid substances on the surface or on any parts or bodies resulting from a process or a production chain and relates, more specifically, parts that cannot withstand too high temperatures.

The present invention relates, more particularly but not exclusively, to parts or bodies from a production line including a cleaning step at the end of which the parts are covered with a film of liquid or water or else contain, because of their porosity or their complexity of shape or structure (blind holes), a certain liquid mass.

In the field of cleaning, fluorocarbon compounds (for example CFC 113 ) are currently used very frequently as a cleaning agent which must then be eliminated by using either continuous drying processes, either to airtight tank drying processes. In the two cases previously mentioned, the drying principle is identical, and consists in evaporating the solvent on the parts by passing the parts through a zone of saturated steam in order to reach the maximum temperature of 47 °. The solvent is then evaporated off by passing the parts through a drying zone at a temperature close to or identical to that of ambient temperature. If the tank is used, evaporation is obtained by lowering the internal temperature of the tank to room temperature.

Fluorocarbon compounds are also used for drying parts that have been previously cleaned in an alkaline cleaning cycle. In these processes, the parts are generally subjected to a first cleaning with a detergent, then to a rinsing with water and finally to a drying by a device using a fluorocarbon compound which, heavier than water and additive to it. ci, moves the water to a decanter. Part of the water is also eliminated by the phenomenon of azeotropic vapor formation.

The two methods described above have, of course, a certain number of advantages, insofar as they make it possible to carry out the removal of water or of the solvent at a relatively low temperature (47 ° C.), which is economically bearable, and allows drying of parts sensitive to high temperatures. In addition, the low temperature rise allows the parts to be used very quickly after drying. The major drawback of these methods is the need to have recourse to the use of fluorocarbon compounds responsible for the destruction of the ozone layer around the globe. The use of these compounds is, moreover, now strictly regulated and in the long term their use should certainly be prohibited.

It has already been proposed to use replacement solvents having a similar drying action by displacement or by azeotropic vapor. This is how the fluorocarbon compounds were replaced respectively by chloride of methylene or with additive trichloroethane. The two aforementioned solvents have however proved to be dangerous for the health of users and operators. Furthermore, they are not harmless for parts to be dried and, in particular, for parts made of plastic materials for example.

Another proposal consisted in using an alcohol-based solvent, which of course presents a certain number of risks, in particular of explosion, so that this solution is hardly practiced. Finally, it has been proposed to use drying in a hot air oven at a temperature at least equal to 100 ° C. The parts are generally previously rinsed with deionized water in order to remove any traces of mineral salts after evaporation. The use of a relatively high drying temperature, in any case greater than 100 ° C., has numerous drawbacks in terms of the organization of a production chain and, in particular, requires a relatively long temperature rise phase. and therefore incompatible with industrial production requirements. The relatively high temperature of the parts after drying makes it moreover impossible, if not at least extremely difficult, to use them immediately after drying. The latter proposal therefore also proved to be ill-suited to the industrial context.

There are also known drying methods using dry air at an average temperature of 50 to 60 ° C. to evaporate the water on parts. These methods suffer from drawbacks linked to the length of the drying operation and to its imperfection in the case of parts to be dried having a large porosity or numerous cavities or blind holes. These processes also require large quantities of dry air.

Finally, parts drying methods are known, in which the parts to be dried are subjected to a temperature rise in a hermetic enclosure and the liquid phase is eliminated by evaporation under vacuum (see, for example, document FR-A-625 501).

The object of the invention is to propose a method and a device for drying parts which do not have the drawbacks of the techniques of the prior art, and which make it possible not to have recourse to fluorocarbon compounds, while allowing drying at low temperature.

A secondary object of the invention is to provide a process and device allowing direct drying in air, without solvent, and this in a very short time.

An additional object of the invention consists in proposing a method and a device whose overall energy consumption is particularly economical, and whose fields of application are multiple.

• on soumet les pièces à sécher à une élévation de température dans une enceinte hermétique,
• on procède, par évaporation sous vide, à l'élimination de la phase liquide,
  ce procédé consistant à :
  • a) - introduire les pièces à sécher dans l'enceinte qui est ensuite fermée hermétiquement,
  • b) - élever la température interne de l'enceinte à une valeur comprise entre 50 et 90° C et, de préférence, entre 50 et 70° C,
  • c) - stabiliser la température interne de l'enceinte avec celle des pièces en ménageant une étape de temporisation d'une durée d'au moins 1 minute et, de préférence, variant entre 1 minute 30 secondes et 3 minutes,
  • d) - soumettre ensuite l'intérieur de l'enceinte hermétique à un vide partiel compris entre - 0,5 et - 1 bar pendant une durée comprise entre 30 secondes et 3 minutes, tout en assurant, à l'intérieur de l'enceinte, une recirculation forcée de l'air sur les pièces à sécher,
  • e) - resoumettre l'intérieur de l'enceinte à la pression atmosphérique ambiante,
  • f) - ouvrir l'enceinte et retirer les pièces.

The object of the invention is achieved by a process for drying parts or bodies from a production line, excluding food products, such as components and printed circuits, parts made of metal, plastic or glass, in which:

• the parts to be dried are subjected to a rise in temperature in an airtight enclosure,
• the liquid phase is eliminated by evaporation under vacuum,
  this process consisting in:
  • a) - introduce the parts to be dried in the enclosure which is then hermetically closed,
  • b) - raising the internal temperature of the enclosure to a value between 50 and 90 ° C and, preferably, between 50 and 70 ° C,
  • c) - stabilize the internal temperature of the enclosure with that of the parts by providing a time delay step of a duration of at least 1 minute and, preferably, varying between 1 minute 30 seconds and 3 minutes,
  • d) - then subject the interior of the hermetic enclosure to a partial vacuum of between - 0.5 and - 1 bar for a period of between 30 seconds and 3 minutes, while ensuring, inside the enclosure , forced air recirculation on the parts to be dried,
  • e) - resubmit the interior of the enclosure to ambient atmospheric pressure,
  • f) - open the enclosure and remove the parts.

• un système de régulation de la température de l'enceinte relié au moyen de chauffage,
• un organe moteur, de préférence un vérin hydraulique, de commande de l'ouverture et de la fermeture du couvercle,
• une vanne de remise en pression,
• et un moyen de ventilation disposé à la partie inférieure de l'enceinte sous un moyen de stockage ajouré pour les pièces à sécher, ledit ventilateur étant en relation avec un réseau de conduites d'air forcé assurant la recirculation de l'air à travers l'enceinte et créant un flux d'air traversant le moyen de stockage ajouré et les pièces en un sens unique.

• La fig. 1 montre une vue de face d'une enceinte de séchage conforme à l'invention.
• La fig. 2 montre une vue latérale d'une enceinte de séchage conforme à l'invention.
• La fig. 3 montre une vue supérieure montrant le dessus d'une enceinte conforme à l'invention.
• La fig. 4 illustre, de façon schématique, une installation automatique incluant des phases de nettoyage, de rinçage et enfin de séchage de pièces issues d'un procédé de fabrication.
• La fig. 5 montre, selon une coupe transversale, une variante de réalisation d'un dispositif conforme à l'invention.

The object of the invention is achieved thanks to a device for implementing the method comprising a hermetic drying enclosure equipped, with a heating means, with a removable opening means, consisting of a cover arranged at the upper part of the enclosure, and a vacuum pump, the enclosure comprising:

• a system for regulating the temperature of the enclosure connected to the heating means,
• a motor member, preferably a hydraulic cylinder, for controlling the opening and closing of the cover,
• a pressure relief valve,
• and a ventilation means arranged at the lower part of the enclosure under an openwork storage means for the parts to be dried, said fan being in relation to a network of forced air ducts ensuring the recirculation of air through the enclosure and creating a flow of air passing through the perforated storage means and the parts in a single direction.

• Fig. 1 shows a front view of a drying enclosure according to the invention.
• Fig. 2 shows a side view of a drying enclosure according to the invention.
• Fig. 3 shows a top view showing the top of an enclosure according to the invention.
• Fig. 4 illustrates, schematically, an automatic installation including phases of cleaning, rinsing and finally drying of parts resulting from a manufacturing process.
• Fig. 5 shows, in a cross section, an alternative embodiment of a device according to the invention.

Figs. 1 to 3 illustrate a device according to the invention which makes it possible to implement the drying process according to the invention. The device comprises an airtight enclosure 1 in the form of a vacuum drying tank limited by an outer casing 2 made of stainless steel sheet for example. The hermetic enclosure 1 can, of course, be of varied shape and of variable volume depending on the nature of the product or the parts to be dried, and according to the average flow rate of the production chain. For information only, it is possible to use a cylindrical tank with a height of 500 mm and a diameter of 450 mm.

The hermetic enclosure 1 comprises an interior casing 3 , for example made of stainless steel. It is possible to improve the insulation of the airtight enclosure by introducing mineral fibers between the outer casing 2 and the inner casing 3 , as is well known to those skilled in the art.

In a manner also known, the hermetic enclosure 1 can be fitted with pressure safety valves (not shown in the figures) and reinforcement ribs or bars 4 fixed for example by welding to the external housing 2 .

The hermetic enclosure 1 is equipped with a removable opening means 5 preferably arranged at its upper part and which consists of a cover 6 , integral with an axis 7 around which it is mounted for rotation by means of a drive member 8 , in this case a hydraulic cylinder. The latter can be, for example, fixed by one end to the outer casing 2 and by the other end directly or indirectly to at least one spar 9 secured to the cover 6 . The seal between the cover 6 and the outer 2 and inner 3 housing is provided in a known manner by an elastic seal 11 .

The temperature rise of the hermetic enclosure 1 is ensured by heating elements 12 arranged inside the enclosure 2 and applied for example to the wall of the internal housing 3 . Preferably, they are placed in the middle part or at the top of the airtight enclosure 2 .

The heating elements 12 are provided to ensure a temperature below 100 ° C, of the order of 90 ° C and, of preferably between 50 to 70 ° C and provided with conventional temperature control means intended to maintain a constant set temperature within the range mentioned above. These elements are not part of the object of the invention and will therefore not be described in more detail.

The sealed enclosure 2 is equipped with a vacuum pump 13 , capable of providing a partial vacuum inside the enclosure of the order of - 0.5 to - 1 bar. As an indication, it is possible to use a vacuum pump by compressed air with several stages of vacuum.

The vacuum circuit inside the hermetic enclosure 1 is completed by the mounting of a pressure relief valve 14 inside the hermetic enclosure 1 . The valve 14 is advantageously arranged at the lower part of the enclosure 1 , so as to prevent, when the re-pressure is carried out by admission of ambient air therefore necessarily having a certain humidity, that drops of condenstation are reformed on the rooms.

The interior of the hermetic enclosure 1 is preferably provided, in its middle part, with support means 16 intended to support an openwork storage means 17 for the storage of the parts or components to be dried. Advantageously, the perforated storage means consists of a mesh basket 17 provided with gripping means 18 intended to facilitate the automatic insertion and removal of the basket 17 . Instead of the basket 17 , it is, of course, possible to have recourse to the provision of one or more mesh grids, superimposed or not.

To ensure the mixing and circulation of the air contained inside the airtight enclosure 1 , provision is made to have, at the lower part of the enclosure, under the mesh basket 17 , a means of ventilation consisting, for example, in a fan 19 , of centrifugal type, provided with stirring blades 21 . Air circulation is advantageously improved by a forced air duct network 22 delimited by deflector panels 23 mounted parallel to the walls of the internal housing 3 and above the stirring blades 21 . The forced air lines 22 thus run along the walls of the internal housing 3 and stop at a distance from the cover 6 , so as to create a flow of one-way stirring air indicated by the reference 24 ( fig. 2 ) which ascends inside the conduits 22 and descends into the central part of the hermetic enclosure 1 , in which the receiving basket 17 is arranged, the descending flow therefore being brought and forced to pass through the basket 17 and the parts that it contains.

Fig. 5 shows an alternative embodiment of the device according to the invention which does not differ from the variant shown in FIGS. 1 to 3 , only through the arrangement of the forced air duct network 22 . In this variant, the pipes 22 ' are interposed directly between the fan 19 and the underside of the basket 17 , so that the basket 17 occupies the entire section of the air stream at the outlet of the fan 19 . The forced air lines 22 ′ are then in the form of connection pipes fixed to the outlet of the fan 19 . If necessary, it is also possible to incorporate, in the conduits 22 ′ through which the air flow passes, all or part of the heating elements 12 . In this second variant, the forced air flow therefore crosses the basket 17 and the parts in a single ascending direction, the air recirculation being effected laterally and descendingly in the enclosure 1 , according to arrow F.

In the two previous variants, it is particularly advantageous to use a centrifugal type fan, capable of ensuring a forced air flow as homogeneous as possible and an air speed at least equal to 5 m / s and preferably between 5 and 10 m / s. Such operating characteristics positively influence the quality and speed of drying.

The forced air lines 22 can be arranged so as to cover the entire internal housing 3 or, on the contrary, as shown in FIGS. 1 and 2 , be arranged punctually on two opposite faces of the airtight enclosure 1.

The method according to the invention consists in subjecting the parts to be dried to a rise in temperature in the airtight enclosure 1 . To this end, the cover 6 is opened by retraction of the hydraulic cylinder 8 and pivoting around the axis 7 . The basket 17 containing the parts or components to be dried is then introduced into the hermetic enclosure 1 and comes to rest against the support elements 16 , the cover 6 then being closed. Before the introduction of the parts, it is possible to preheat the sealed enclosure 1 and to raise it, preferably, to a constant temperature below 100 ° C and, advantageously, between 50 and 70 ° C approximately, by means of the heating element 12 controlled by a regulation system by means of which the displayed set temperature, included in the above-mentioned interval, is observed. The uniformity of the temperature can, moreover, be favored by the commissioning of the fan 19 . Prior to the introduction of the parts, it is also advantageous, to reduce the drying time inside the airtight enclosure 1 , to preheat the parts to be dried. This preheating operation, external to enclosure 1 , can be ensured in the case of a production line by a rinsing phase in a hot water bath at the temperature of use of the drying tank for one minute. for example. Without limitation, the preheating temperature can usefully be between 50 and 90 ° C.

Once the parts to be dried introduced into the enclosure, the temperature inside the enclosure 1 is raised to a temperature between 50 and 90 ° C and, preferably, between 50 and 70 ° C. This This step is all the more brief as the rooms and / or the enclosure 1 have been preheated beforehand. When the set temperature is reached, the heating elements 12 are stopped and the temperature is increased for the parts which, due to their thermal inertia, require a delay stage so that their temperature stabilizes at internal temperature of enclosure 1 . Depending on the type of parts and their thermal capacity, this time delay or thermal stabilization step has a duration of at least 1 minute and, preferably, varies between 1 minute 30 seconds and 3 minutes.

The interior of the sealed enclosure is then subjected to a partial vacuum of between - 0.5 and - 1 bar by switching on the vacuum pump 13 , while ensuring forced recirculation of the air on the parts to be dry using fan 19 and lines 22 . The retained vacuum level is maintained for a period of at least 30 seconds, which is sufficient to remove a film of water on smooth parts. In the case of complex parts comprising, for example, blind holes which have made it possible to accumulate water by retention, the vacuum level can be maintained for a period of up to three minutes (non-dandruff water). By way of nonlimiting example, a vacuum of - 0.9 bars can be reached in about two minutes, the complete drying time being between two minutes thirty and three minutes for example. These values correspond to maintaining the vacuum level of - 0.9 bars for at least thirty seconds and, preferably, between thirty and sixty seconds.

During the drying operation, the air charged with water vapor inside the enclosure is continuously heated by the heating element or elements 12 , and the circulation of air inside the the enclosure is ensured by the rotation of the blades 21 . An optimal heat exchange is thus obtained, reducing the total drying time.

The vacuum pump 13 is then stopped and by opening the re-pressure valve 14 , the interior of the hermetic enclosure 1 gradually returns to ambient atmospheric pressure. The duration of the re-atmospheric pressure phase is regulated by the degree of opening of the re-pressurization valve 14 , the duration of the re-atmospheric pressure varying from 5 seconds to 15 seconds, and being preferably equal to about ten seconds. The return to ambient atmospheric pressure can be effected by admitting ambient air having a certain humidity or by admitting dry air and hot if necessary. As an indication, the hot air may have an average temperature of the order of 40 ° C. After this atmospheric pressure resetting phase, the cover 6 is again opened and the basket 17 is removed from the airtight enclosure 1 .

In the event that drying is incomplete, in particular in the case of parts with low thermal inertia, it may prove necessary to repeat one or more complete drying cycles before removing the parts by carrying out a new stage of heating the parts. and the enclosure, followed by a time-out step, then by vacuuming while respecting the parametric values indicated.

Fig. 4 illustrates an alternative embodiment in which the drying process is fully automated and is included, as an operational phase, in an industrial chain.

The device comprises a slide 31 on which is slidably mounted a movable carriage 32 driven by a motor member, and the movement of which is entirely automated by a control system. The mobile carriage 32 is provided with robotized gripping arms responsible for handling the basket 17 . The parts subsequently intended to be dried and coming from a production line are deposited in the basket 17 and arrive at an entry station 33 located under the slide 31 . The robotic arms of the carriage 32 then take hold of the basket 17 and transport it by sliding along the slide 31 in station A which can be, for example, a unit responsible for cleaning the parts and requiring for example a rise in temperature of the 'around 60 °. The cleaning operation being carried out, the basket is transferred by the robotic arms to station B which can, for example, be a cold and water rinsing station, the basket 17 then being transferred to station C where the parts of the basket 17 are subjected to rinsing with demineralized water at a temperature of for example between 50 and 90 ° C. The rinsing operation at station C corresponds to the preheating phase of the drying process according to the invention. The basket 17 is then transferred to the drying module corresponding to station D and introduced into the airtight enclosure 1 . The drying operation is carried out in accordance with the steps described above and the drying basket is then transferred to the outlet station 34 .

The process thus described has the advantage of drying parts or bodies from a production line without using fluorocarbon compounds, and without requiring a high drying temperature, since the internal temperature of the hermetic enclosure remains , in all cases, less than 100 ° C. The method and the device according to the invention also make possible rapid drying of all the parts, insofar as the parts to be dried are preheated. This feature makes it possible to introduce the method and the drying device according to the invention into an industrial production line without unnecessarily lengthening the manufacturing time.

Furthermore, the vacuum levels required are sufficient to allow a drying operation limited in time and the technical means of implementation are of relatively simple design and maintenance.

Finally, it should be noted that the drying method described, as well as the implementation device are suitable for multiple and varied uses, and that the parts or bodies liable to undergo the drying operation are not limited and can be chosen from fragile parts that cannot withstand high temperatures.

Claims (15)

1. Process for drying parts or articles leaving a production line, such as components and printed circuits, parts in metal, plastic material
   or glass, but with the exception of food products, in which process:

   - the parts to be dried undergo a rise in temperature inside the sealed enclosure,

   - the liquid phase is eliminated by evaporation in vacuo,
   said process consisting in:

   a) introducing the parts to be dried into the enclosure which is then hermetically sealed,

   b) raising the temperature inside the enclosure to a value ranging between 50 and 90°C and preferably between 50 and 70°C,

   c) stabilizing the temperature inside the enclosure with that of the parts by including a retarding step of at least 1 minute and preferably varying between 1 minute 30 secs and 3 minutes,

   d) then subjecting the inside of the sealed enclosure to a partial vacuum comprised between - 0.5 and - 1 bar for a period varying between 30 seconds and 3 minutes, while ensuring inside the enclosure, a forced recirculation of air over the parts to be dried,

   e) re-subjecting the inside of the enclosure to the ambient atmospheric pressure,

   f) opening the enclosure and bringing out the parts.
2. Process according to claim 1, characterized in that it consists; before step a), in preheating the parts and/or the enclosure to a temperature preferably equal to the drying temperature.
3. Process according to claim 2, characterized in that it consists in preheating the parts outside the enclosure in a bath of hot water for one minute.
4. Process according to claim 1 or 2, characterized in that it consists, in step b), in preheating the parts inside the sealed enclosure, by forced recirculation of the air confined in the enclosure, for a period varying from 1 to 2 minutes.
5. Process according to claim 4, characterized in that it consists in effecting the forced recirculation of the air by means of at least one fan of centrifugal type ensuring an air speed of at least 5 m/s, and preferably between 5 and 10 m/s.
6. Process according to claim 1, characterized in that it consists in permanently heating the air filled with steam inside the sealed enclosure.
7. Process according to claim 1, characterized in that it consists in creating a vacuum of - 0.9 bar inside the sealed enclosure, which vacuum is reached in about two minutes, and in keeping said vacuum level for at least thirty seconds, and preferably, between thirty and sixty seconds.
8. Process according to claim 1, characterized in that it consists in reaching the ambient atmospheric pressure after drying in 5 to 15 seconds and preferably, in about 10 seconds.
9. Process according to claim 1 or 8, characterized in that it consists in returning the pressure inside the sealed enclosure to the ambient atmospheric pressure after drying by admitting in dry hot air.
10. Process according to one of the preceding claims, characterized in that it consists, after step e), in repeating one or more complete drying cycles according to steps b) to e).
11. Device for carrying out the process according to one of claims 1 to 10, comprising a sealed drying enclosure (1), equipped with heating means (12), removable opening means (5), constituted of a lid (6) placed at the upper part of the enclosure (1), and a vacuum pump (13), the enclosure (1) comprising:

    - a system for controlling the temperature of the enclosure, connected to the heating means (12),

    - a driving member (8), preferably a hydraulic jack, for controlling the opening and closing of the lid (6),

    - a re-pressurizing valve (14), and

    - fan means (19) placed at the lower part of the enclosure under a perforated storage means (17) for the parts to be dried, said fan means being connected with a network of forced air pipes (22) ensuring recirculation of the air through the enclosure (1) and creating an air flow which goes through the perforated storage means (17) and the parts in one direction only.
12. Device according to claim 11, characterized in that the network of forced air pipes (22) is directly interposed between the fan means (19) and the perforated storage means (17), in order to create an air flow ascending therethrough.
13. Device according to claim 11, characterized in that the network of forced air pipes (22) is placed along the walls of the internal housing (3) of the enclosure (1), the pipes stopping at a distance from the lid (6), so as to create an air flow ascending through the pipes (22) and descending into the central part of the enclosure so as to flow through the storage means (17).
14. Device according to one of claims 11 to 13, characterized in that the fan means is a centrifugal-type fan with blades.
15. Device according to one of claims 11 to 13, characterized in that the perforated storage means is a meshed receiving basket (17).

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