WO1999048624A1

WO1999048624A1 - Device and method for cleaning working parts

Info

Publication number: WO1999048624A1
Application number: PCT/FR1999/000639
Authority: WO
Inventors: Michel Perrut; Vincent Perrut
Original assignee: Separex (Societe Anonyme)
Priority date: 1998-03-20
Filing date: 1999-03-19
Publication date: 1999-09-30
Also published as: FR2776213B1; FR2776213A1; ES2190645T3; DE69905140D1; EP1064105B1; EP1064105A1; ATE231749T1; DE69905140T2

Abstract

The invention concerns a device and a method for cleaning working parts, using a cleaning fluid, comprising a chamber (1) wherein is arranged a basket (7) containing the parts (27) to be cleaned, said basket (27) outer wall being spaced from the chamber (1) inner wall so as to provide between them a passage (9) for the cleaning fluid, the device further comprising intake means (25) for the cleaning fluid and means for extracting (15) it. Said device is characterised in that the chamber (1) base forms a ring-shaped chute (13) located beneath said passage (9), connected to the means extracting (15) the cleaning fluid, and inside which are arranged means for heating (17, 18) said fluid, and the intake means (25) are located in the chamber (1) upper part.

Description

DEVICE AND METHOD FOR CLEANING WORKPIECES

The present invention relates to a device intended for cleaning and degreasing working parts, in particular metal parts, and a method of implementing the latter.

It is known that the manufacture, in particular of metal parts and of certain assemblies, such as for example electronic circuits, must always be followed by a cleaning in order to eliminate on the one hand the dust and other solid particles which adhere to them. here and on the other hand the greases with which they have been coated, for example during manufacture.

Hitherto, chlorine solvents such as trichloroethane, carbon tetrachloride, chloroform, trichlorethylene, dichloromethane, perchlorethylene, etc. have been used to carry out such a cleaning operation. '' chlorofluorocarbon type solvents, such as that designated under the reference R113 (flugene), which are reputed to be less aggressive than chlorinated solvents, in particular with respect to metalloplastic assemblies.

However, it turns out that several of these chlorinated solvents, such as for example trichloroethane as well as most chlorofluorocarbons, are prohibited by the convention relating to the protection of the ozone layer. As regards chlorinated solvents not prohibited by the said convention, their use has been drastically regulated due to certain studies tending to demonstrate their carcinogenic and toxic characteristics. We then turned to light hydrocarbons, the use of which can only be envisaged in the context of very specific and very controlled techniques, because of their high flammability character. It has also been proposed to use fluorocarbon substitutes known as HCFCs or HFCs which are, in certain cases, directly substituted products of CFCs previously used, but which have the disadvantage of being of a much higher cost for a result often very inferior.

It has finally been proposed in a patent US-A-4,012,194 to use carbon dioxide in the liquid or supercritical state to ensure dry cleaning of textile products. More recently, it has been proposed in the patent US-A-

5.355.901 ensuring the cleaning of work pieces by means of a device using a supercritical fluid, which consists of an enclosure provided with a drum containing the pieces to be cleaned which is driven by a movement of rotation around a vertical axis, the carbon dioxide arriving by the periphery of the base of the enclosure and emerging from the latter by an axial pipe. Such a device has the drawback of requiring the carbon dioxide to be put into a supercritical state, which is costly in terms of means of implementation and in terms of costs of use.

The object of the present invention is to propose a device for cleaning work pieces which is particularly robust and which, moreover, is of a relatively low cost price and a reduced maintenance cost. compared to those of the prior art allowing the use of different cleaning fluids, and in particular liquefied gases such as carbon dioxide, nitrous oxide, halogenated hydrocarbons, light hydrocarbons, optionally added with surfactants , conventional organic solvents such as alcohols, ketones, esters.

The present invention thus relates to a device for cleaning work pieces, by means of a cleaning fluid, of the type comprising an enclosure in which is placed a basket containing the parts to be cleaned, the external wall of this basket being separated of the internal wall of the enclosure so as to provide between them a passage for the cleaning fluid, the device further comprising means for admitting the cleaning fluid and means for extracting the fluid from the latter, characterized in that the base of the enclosure forms an annular trough situated under said passage, which is connected to the means for extracting the cleaning fluid, and within which are arranged means for heating this fluid, and the intake means are located at the top of the enclosure.

According to the invention the cleaning fluid can consist of a liquefied gas in the vicinity of its boiling point. This cleaning fluid may be chosen from carbon dioxide, nitrous oxide, light hydrocarbons, light halogenated hydrocarbons.

The cleaning fluid may be supplemented with surfactants. It may also be added with an organic solvent such as in particular an alcohol, a ester, a ketone, or an unsaturated hydrocarbon such as in particular α-pinene.

It was found that the natural convection movements created by such an arrangement made it possible to achieve a cleaning quality of the same level as that obtained with the chlorinated solvents previously used.

In one embodiment of the invention, the enclosure and the basket are cylindrical in shape and the basket is mounted for rotation about a central and vertical axis.

In another embodiment of the invention, stirring means are provided at the base of the enclosure under the basket. The latter may be means for driving the basket in rotation or stirring means such as a propeller.

The present invention also relates to a method of cleaning work pieces by means of a cleaning fluid, in an enclosure provided with a basket in which said pieces are arranged, and with means making it possible to ensure circulation by convection of the cleaning liquid in an annular passage created between the internal face of the enclosure and the external wall of the basket, characterized in that the enclosure is filled with the cleaning fluid so that the level of the latter is slightly below the upper area of the basket from which it is in communication with the annular passage, and that this level is maintained throughout the cleaning. We will describe below, by way of examples not limiting, various embodiments of the present invention, with reference to the accompanying drawings in which:

Figure 1 is a schematic vertical sectional view of a cleaning device according to the invention. FIG. 2 is a view in vertical section of an alternative embodiment of the cleaning device of FIG. 1.

Figure 3 is a partial vertical sectional view of another alternative embodiment of the device according to the invention.

Figure 4 is a schematic elevational view of an embodiment of the invention.

Figures 5a, 5b and 5c are schematic views in partial section of three means for distributing the cleaning fluid on the cross section of the basket containing the parts to be cleaned.

The cleaning device shown in the figure

I consists of an autoclave 1 formed by a cylindrical enclosure 3 which is closed at its upper part by a cover 5 and which contains a cylindrical basket 7 whose vertical axis coincides with the vertical axis yy 'of the autoclave 1. The external diameter of the basket 7 is less than the internal diameter of the enclosure 3, so as to provide between these two elements an annular passage 9 of spacing d.

The base of the enclosure 3 includes a central core

II cylindrical with a diameter close to that of the basket 7, so as to form between its external wall and the internal wall of the enclosure 3 an annular chute 13. The base of this chute 13 is joined to a pipe for discharging liquids 15. The chute 13 receives heating means 17 consisting of an electrical resistance. These heating means 17 may however be constituted by any other means capable of providing heat to the fluid, and in particular by a tubular exchanger 18 (FIG. 3) in which a heat transfer fluid circulates.

The basket 7, which is open at its upper part, consists of deformed sheet metal elements and is closed at its base by a metal cloth 19 or by a perforated metal disc. Its upper part is spaced from the cover 21 by a distance e _. a few centimeters, sufficient to allow the passage of the treatment fluid during the operation of the autoclave as explained below. The cover 5 is provided with means 21 making it possible to secure it in leaktight manner to the upper part of the enclosure 3. This cover 5 comprises, in its center, a pipe 25 for supplying fresh liquid carbon dioxide. Under these conditions, the implementation of the cleaning autoclave according to the invention is done as described below.

First of all, the parts 27 to be cleaned are placed inside the basket 7 and the latter is introduced inside the autoclave 1, then the cover 5 is closed using the sealing means 21 The cleaning fluid, for example carbon dioxide in the liquid state, at a temperature T ₀ lower than the ambient temperature, namely approximately 10 ° C., is introduced into the upper part of the autoclave 1 by driving 25. He then flows onto the parts 27 to be cleaned, rids them of the various pollutants which adhere to their surface and drives them into the chute 13. After a certain time, the autoclave 1 is partially filled with cleaning fluid at liquid state, at a temperature slightly higher than T ₀ . As shown in FIG. 1, it is arranged that the upper level N of the treatment fluid admitted into the enclosure is situated slightly below the upper opening of the basket 7. The heating device 17 disposed at the inside the chute 13 is activated and causes local vaporization of the cleaning fluid which is in contact with it. Under these conditions, the cleaning fluid which, at this point, is in a two-phase state, gives rise to a phenomenon of natural convection such that the cleaning fluid rises in the annular passage 9 comprised between the internal wall of the enclosure. 3 and the outer wall of the basket 7, as shown by the arrows F in FIG. 1. When this two-phase fluid arrives at the upper part of the autoclave, it meets the .fluid 9 arriving via line 25 which is located at the temperature T ₀ , so that it cools on contact with the latter causing at least partial recondensation of the gaseous fraction which then descends and comes into contact with the parts to be treated. A part of the cleaning fluid, equal to the quantity of fluid admitted by the pipe 25 is extracted by the withdrawal pipe 15.

The present device makes it possible to naturally create a movement of the cleaning liquid relative to the parts, a movement which gives it great efficiency.

Furthermore, the cleaning fluid which is heated and which is partially vaporized in contact with the heating means 17 has a lower solvent power than that of the fluid which circulates in the basket 7, so that the dissolved pollutants are not entrained by the movement. convection and are collected in the chute 13, from where they are drawn off through the pipe 15. Such a drive is favored by the extraction of a cleaning fluid flow identical to that admitted at the top of the autoclave . The same is true of dust which is more easily entrained by pollutants and the fluid leaving the autoclave than by the heated fluid which rises by convection through the annular passage 9. At the end of the operation, the arrival of cleaning in the autoclave is stopped and the racking continues, causing the pressure to drop. However, it is then important to continue heating the fluid using the heating means 17 in order on the one hand to avoid the rapid drop in temperature within the autoclave 1 and on the other hand to continue to add enthalpy to the current which leaves the autoclave in order to facilitate the subsequent separation of fluid-pollutants.

In addition, when the pressure drops below a certain given pressure P _m , gas, preferably air or nitrogen, is injected from a reservoir 40 maintained at this pressure; quickly the cleaning fluid is replaced by this gas which can then be easily discharged, after having interrupted its supply until the pressure prevailing in the autoclave 1 is equal to that of the atmosphere, without, however, causing a sharp lowering of the temperature within the autoclave 1, as would be the case if one decompressed directly to the atmospheric pressure the cleaning fluid. In the case where carbon dioxide is used as cleaning solvent, the said given value _^ e P _m is chosen between 106 and 25.105Pa. Example 1: As a first example, the implementation of a cleaning operation relating to one hundred and twenty machined parts made of stainless steel, with an average unit mass of the order of 200 g and which are polluted by cutting oil, metal particles and dust remaining from their machining operation. For this purpose, an autoclave 1 was used, the enclosure 3 of which is cylindrical in shape, the height of which is 80 cm and the base diameter is 28 cm, inside which is placed a basket 7, also cylindrical, of vertical axis yy 'whose diameter is 25 cm, so that the annular passage 9 formed between its external surface and the internal surface of the enclosure 3 is 1.5 cm. This basket 7 is open at its upper part, and the latter is located at a distance d, equal to 10 cm, from the cover 5. The bottom of the basket 7 is formed by a wire mesh 19. The base of the enclosure 3 forms an annular chute 13, the height of which is of the order of 7.5 cm and the width of 5 cm, which is located just below the annular passage 9. Inside this chute 13, an electrical resistance is arranged 17 whose power is approximately 3 kilowatts and which consists of a tube wound in spiral. The bottom of this same chute 13 comprises an extraction pipe 15 as shown in FIG. 1.

To implement the device according to the invention, the pieces 27 to be treated are placed in bulk in the basket 7, then, after closing the cover 5, 35 kg of carbon dioxide are introduced into the autoclave. in the liquid state, at a temperature of 10 ° C, at a flow rate of 250 kg / h. The autoclave was filled so that the level N of admitted liquid carbon dioxide was approximately 5 cm below the upper part of the basket 7. The intake of fresh carbon dioxide was then adjusted to a flow rate of 100 kg / h and its extraction via line 15 has an identical flow rate, so as to keep the level N of carbon dioxide substantially constant. The heating resistor 17 was then supplied for a period of 25 minutes during which the cleaning operation took place.

We then proceeded to stop the cleaning device and recover the parts. To do this, while continuing to heat the fluid contained in the autoclave, the supply of carbon dioxide was stopped and the pressure was allowed to drop to a value of 10 Pa, then then admitted into the autoclave 1 nitrogen from an external tank 40 (Figure 4) at the operating pressure P _m = 10 Pa of the autoclave. Under these conditions, the cleaning fluid consisting of carbon dioxide was gradually replaced by nitrogen, so that after a time of the order of five minutes, it could be considered that the dioxide of carbon was completely eliminated, and it was then possible to stop the nitrogen supply to the autoclave and allow it to empty to atmospheric pressure. After cutting the electrical supply to the resistor 17, the cover 5 was removed and the basket 7 was removed to recover the treated parts there.

The weighing of these pieces showed an average weight loss of 2.65 g, and a subsequent extraction with dichloromethane of the fats likely to remain in contact with it revealed an average weight loss of 0.05 g.

By way of comparison, the pollutants linked to identical parts, not treated by the process according to the invention, were extracted using dichloromethane in a tank agitated by ultrasound according to a well-established technique, and noted an average weight loss of 2.7g per piece, which corresponds to the total quantity extracted previously.

In an alternative embodiment shown in FIGS. 5a to 5c, the pipe 25 for supplying fresh liquid carbon dioxide is provided with means intended to promote good distribution of this fluid over the entire upper section of the basket 7. These means are constituted for example by an injector 16a, a distributor 16b formed by a perforated disc or a sintered metal of the sprinkler type, or by a concentric bundle of perforated tubes 16c, for example 6 tubes arranged in a star.

In one embodiment of the invention shown in FIG. 2, the relative movement of the cleaning fluid is improved with respect to the parts 27 to clean by rotating the cleaning tank 7 around its vertical axis yy '. To do this, the base of the basket 7 is provided with a hub 30 which is extended downwards by an axial shaft 32 which is set in rotational movement by means of a motor 34.

Furthermore, in this embodiment, the basket 7 is provided, at its upper part, with a perforated zone 31 from the base of which the cleaning fluid which rises by convection through the annular passage 9 can penetrate in the basket 7. This is why during the admission of the cleaning fluid, we will make sure to bring the level N thereof, slightly below the base of the zone 31 and we will then maintain it there. during treatment. Example 2:

The treatment operation was repeated, in the same autoclave, using machined parts, of the same type as the previous ones, but by rotating the basket 7 around its vertical axis yy 'at a speed of 30 revolutions / minute, all the other operating parameters being kept constant.

As before, the parts were weighed, and the latter showed an average weight loss of 2.7 g, and subsequent extraction with dichloromethane of the fats liable to remain in contact with the treated parts did not make it possible to note no variation in the average mass of these, which demonstrates that all the fats were indeed extracted by the process, which establishes the great efficiency of the latter. One could also, as shown in FIG. 3, replace the means for rotating the basket 7 by stirring means consisting of a propeller 36, movable in rotation around a vertical holding shaft 23, and which is driven by magnetic stirring means 12 contained in the central core 11.

Of course, the means of rotation of the basket 7 could also be combined with the agitation provided by the propeller 36.

Tests carried out with stirring means consisting of a propeller 36 of 15 cm in diameter, have made it possible to demonstrate that, the extraction of grease obtained by the device, carried out on identical parts, was also 2.7 g.

The device according to the invention makes it possible to use a wide variety of cleaning fluids, such as nitrous oxide, light hydrocarbons, pure halogenated light hydrocarbons or in mixtures optionally supplemented with surfactants, conventional organic solvents such as 'an alcohol, an ester or a ketone.

Example 3:

By way of example, the device according to the invention has thus been used using, as cleaning fluid, nitrous oxide. The implementation of the treatment process was carried out as described in the first example, and a completely satisfactory degreasing of parts was obtained since the weighing of these showed an average weight loss of 2.66g.

Example 4:

In another exemplary implementation of the invention, the cleaning device was applied to the degreasing of electronic printed circuits, partially covered with solder flux residues. These circuits were treated in a device according to the invention implemented as well as in the first example, and a satisfactory degreasing was obtained since the amount of fat extracted from the circuits was 3.6 g, while for a degreasing of reference to dichloromethane the quantity of fat extracted from these same parts was 3.7 g. It is noted however, in this embodiment that, if the degreasing has proved satisfactory, there were visible traces of whitish dust on the surface of the circuits.

Example 5:

This is why in a variant of this embodiment, pure carbon dioxide has been used as cleaning fluid, added with 5% by mass of an unsaturated hydrocarbon, namely α-pinene. . Degreasing has been found to be of the same quality as that obtained in the previous example, while also improving cleaning, since on the treated printed circuits there is no longer any trace of pollution.

The device according to the invention thus makes it possible to use different liquefied gases, and in particular carbon dioxide, to replace the solvents currently prohibited or in the process of being prohibited, with an efficiency equal to that provided by the latter, and this by means of a simple and reliable device to be implemented.

Such simplicity is essentially due to the natural convection caused on the periphery of the walls of the enclosure of the autoclave which avoids the use of a circulation pump as is necessary in state cleaning systems. prior art.

Furthermore, the combination of this convection system with forced convection means, obtained for example by the use of a circulation turbine, makes it possible to further improve the efficiency of this device.

Of course, and although the device and the method according to the invention have been described in the context of cleaning metal parts, it could also be used for cleaning textile parts.

Claims

1.- Device for cleaning work pieces, by means of a cleaning fluid, of the type comprising an enclosure (1) in which is placed a basket (7) containing the pieces (27) to be cleaned, the external wall of this basket (7) being spaced from the inner wall of the enclosure (1) so as to provide a passage between them

(9) for the cleaning fluid, the device further comprising intake means (25) for the cleaning fluid and extraction means (15) thereof, characterized in that the base of the enclosure (1) forms an annular chute (13) located under said passage (9), which is connected to the extraction means (15) of the cleaning fluid, and 1 inside which are arranged heating means (17, 18) of this fluid, and the means of admission

(25) are located at the top of the enclosure (1).

2.- Device according to claim 1 characterized in that the cleaning fluid consists of a liquefied gas in the vicinity of its boiling point.

3.- Device according to one of claims 1 or 2 characterized in that the cleaning fluid is a liquefied gas chosen from carbon dioxide, nitrous oxide, light hydrocarbons, light halogenated hydrocarbons.

4.- Device according to one of the preceding claims characterized in that the cleaning fluid is supplemented with surfactants.

5.- Device according to one of claims 2 to 4 characterized in that the cleaning fluid is added with an organic solvent such as in particular an alcohol, an ester, a ketone, or an unsaturated hydrocarbon such as in particular α-pinene.

6.- Device according to any one of the preceding claims, characterized in that the enclosure (3) and the basket (7) are of cylindrical shape with a vertical axis (yy ').

7.- Device according to claim 6 characterized in that the basket (7) is rotatably mounted about the vertical axis (yy ¹ ).

8.- Device according to any one of the preceding claims, characterized in that stirring means are provided, at the base of the enclosure (3) under the basket (7).

9.- Device according to any one of the preceding claims, characterized in that the intake (25) of cleaning fluid comprises means for distributing the cleaning fluid over the section of the basket.

10.- Device according to any one of the preceding claims, characterized in that the basket (7) is provided, at its upper part, with a perforated zone (31) from the base of which it is in communication with the annular passage (9).

11.- Method of cleaning work pieces by means of a cleaning fluid, in an enclosure (3) provided with a basket (7) whose bottom is open, in which said pieces are arranged, and means allowing to ensure the circulation by convection of the cleaning liquid in an annular passage (9) created between the internal face of the enclosure (3) and the external wall of the basket (7) characterized in that the enclosure (3) is filled with the cleaning fluid so that the level (N) of this the latter is slightly below the upper zone of the basket (7) from which the latter is in communication with the annular passage (9), and that this level (N) is maintained throughout the cleaning.