EP0639747B1 - Process and apparatus for drying a cleaned workpiece which has been treated with a cleaning fluid - Google Patents

Description

Machining workpieces in particular require cleaning after machining in order to remove chips, but also components of coolants and cutting fluids adhering to the workpieces. For this purpose, the workpieces are sprayed with a cleaning liquid in a cleaning chamber and / or washed by immersing them in the cleaning liquid and moving the workpieces, whereupon they are dried in the cleaning chamber or a drying chamber arranged after it.

In the past, cleaning was often carried out with organic solvents, such as. As perchlorethylene, for reasons of environmental protection, however, predominantly aqueous cleaning agents containing surfactants have recently been used. While the organic solvents can be removed relatively easily by evacuating a chamber that receives the workpieces and thus evaporating the solvents, drying the workpieces is much more difficult when using aqueous cleaning fluids - many workpieces have surface areas with a contour that retains the cleaning fluid, e.g. B. blind holes (holes closed on one side), but also threaded holes, in the threads of which cleaning fluid remains.

The drying of the workpieces in production plants with short cycle times, as z. B. for the automotive industry is typical in the production of engine blocks, cylinder heads, gear housings and the like, since then only short time intervals are available for drying. In this regard, the latest requirements of the automotive industry are that only a time interval of significantly less than 1 min is available for drying a cleaned workpiece.

Since in many cases, and especially in the automotive industry, identical parts, such as engine blocks or cylinder heads, have to be cleaned and dried individually and one after the other in a production plant, a cleaned and to-be-dried workpiece is currently being placed in a chamber or another suitable station (where it is e.g. a special drying chamber, but can also be a cleaning chamber), which is equipped with compressed air-fed blowing nozzles, each of which is directed towards such a surface area with a contour that retains the cleaning liquid (which of course means precise positioning of the workpiece in of the chamber and therefore requires considerable design effort). Practice has shown, however, that even well-aligned blow nozzles and high compressed air pressure are often not sufficient to completely dry out holes and the like; this is e.g. B. the fact that the compressed air retained in a blind hole remaining cleaning fluid can not completely drive out of the one-sided closed hole, especially if it is a threaded hole in which the compressed air pushes the remaining cleaning fluid together in the threads, but prevent this that the remaining cleaning liquid can be driven out of the bore by the compressed air. After switching off the compressed air jet, the remaining cleaning liquid then runs, especially in vertically oriented bores, together in the lower bore area, so that even an inherent heat of the workpiece originating from the previously performed cleaning process can no longer cause complete evaporation of the remaining cleaning liquid. Further disadvantages of drying with compressed air jets are the inevitable high noise level, which can only be reduced with extensive and expensive soundproofing measures, the high compressed air consumption and the occurrence of moisture vapor that escapes when the chamber is opened into the factory hall and not only there to high air humidity lead, but also to the fact that active cleaning constituents of the cleaning liquid and contaminants carried by it are carried off to the outside.

Workpieces with surface areas, which have contours that hold back the cleaning liquid, cannot be dried satisfactorily with the known vacuum drying processes, especially not in the now desired, only short time intervals - with a blind hole that vertically or diagonally upwards during the drying process is oriented, the area of the area to be dried on which the vacuum can act is relatively small in relation to the volume of the remaining cleaning liquid to be evaporated.

Representative of the known vacuum drying processes are e.g. B. the methods described in DE-PS 37 15 168 and EP-0 476 235-A1. In the vacuum drying process according to DE-PS 37 15 168, the drying chamber is continuously evacuated, with ambient air possibly being admitted into the drying chamber via a valve during the evacuation, but without this in the drying chamber to let the prevailing vacuum drop too much (see the related discussion of DE-PS 37 15 168 in EP-0 476 235-A1 by the same applicant, namely column 1, lines 27-50, in particular lines 43-47). In the vacuum drying method according to EP-0 476 235-A1, a workpiece is to be dried by a "vacuum shock" by suddenly and completely opening a connecting line between a vacuum container serving as a vacuum store and the drying chamber; but if z. B. has accumulated cleaning liquid on the bottom of a vertically oriented blind hole, this is not completely expelled even by such a "vacuum shock" because the open surface which allows steam to escape is too small in relation to the liquid volume, and the same applies to troughs, especially if if the inherent heat of the workpiece to be dried is not high enough.

In a drying process according to the older German patent application P 42 37 335.2 from Dürr GmbH, the cleaned workpiece is placed in a drying chamber which can be closed in a pressure-tight manner and held there stationary so that nozzles provided in the chamber are directed towards the workpiece surface areas with contours that retain cleaning liquid. The chamber is then closed in a pressure-tight manner and evacuated to evaporate cleaning liquid, whereupon a valve which connects the nozzles to the atmosphere surrounding the chamber is opened; When the pressure is equalized, the nozzles generate air jets which are aimed at contours that hold back cleaning liquid on the workpiece surface areas and are intended to remove and distribute cleaning liquid retained by the workpiece. The chamber is then evacuated again to evaporate the remaining cleaning liquid.

However, it has been shown that even with this improved drying process, workpieces, such as cylinder heads, cannot be dried satisfactorily and adequately within the short drying times recently required for the drying process.

The invention was based on the object of providing a drying method with which workpieces to be dried individually can be dried satisfactorily even after cleaning with an aqueous cleaning liquid in a shorter time than is possible with the drying methods described above.

Starting from a method for drying an individual workpiece cleaned after machining with an aqueous cleaning liquid, which has surface areas with contours retaining cleaning liquid, in at least one chamber, in which the workpiece is subjected to air jets for removing and distributing cleaning liquid, one of which Workpiece-receiving chamber is evacuated to evaporate residual cleaning liquid, this object can be achieved according to the invention in that the workpiece is subjected to the drying process with an initial temperature of at least about 45 ° C, rotated during the blowing with air jets and in the chamber during an evaporation period of at least 8 seconds and at most 30 seconds is exposed to a vacuum and that the air pressure in the chamber - based on atmospheric pressure - during the entire evaporation period at least essentially is continuously reduced to a minimum value of approximately 4 mbar to approximately 0.5 mbar.

By rotating the workpiece during the blow-off, cleaning fluid remaining on the workpiece can also be removed completely more completely from contours retaining surface areas with cleaning fluid than is the case in the known drying methods with the aid of compressed air-fed nozzles and aligned with these surface regions. In the method according to the invention, therefore, those problems can be avoided which occur in the known drying methods with nozzles aligned with the surface areas mentioned as a result of the workpiece not being positioned exactly. Furthermore, it is not necessary to blow off the workpiece with compressed air, since it has proven to be completely sufficient to generate the air jets used to blow off the workpiece with the aid of a blower. As a result, costly noise reduction measures can also be dispensed with, and the energy consumption is far lower than when working with compressed air.

Often the workpieces are cleaned with heated cleaning fluid, e.g. B. with heated to 70 ° C or 80 ° C cleaning liquid, which leads to the fact that the workpieces still have a significant inherent heat during the drying process following the cleaning; But even if the cleaning liquid is not heated separately, the workpieces have a temperature of at least approx. 45 ° C at the end of the cleaning process, because during the cleaning process the cleaning liquid pumped around by pumps is brought to temperatures due to the waste heat from these pumps lead to a final temperature of the cleaned workpieces of at least approx. 45 ° C. However, it is obvious that the cleaned workpieces can be dried more quickly and completely, the higher their temperature at the beginning of the drying process.

The method according to the invention is further based on the finding that it is completely sufficient for evaporation of cleaning liquid remaining on the workpiece after the workpiece has been blown off, during the evaporation period the pressure in the chamber receiving the workpiece - starting from approximately atmospheric pressure - at least in the significantly lower continuously, d. H. that it is not necessary to suddenly evacuate the chamber to a large extent, which means that the outlay on equipment can be drastically reduced, since it is sufficient to connect a simple vacuum pump to the chamber and gradually evacuate it and the pressure in the chamber to a value to reduce, which is not greater than about 4 mbar, but in no case has to be less than about 0.5 mbar in order to get by with an evaporation period of at most about 30 seconds. It has been shown that if these values are adhered to, a longer dwelling of the workpiece in the evacuated chamber is unnecessary and cannot further improve the drying result.

Finally, it should be pointed out that when working without compressed air, a strong formation of steam (cleaning liquid atomized by the compressed air jets) can be avoided, so that the drying method according to the invention also eliminates the disadvantage of known drying methods in which the workpiece is blown off with compressed air jets, namely that Swaths of nebulized cleaning liquid emerge into the hall surrounding the drying station and into these cleaning-effective components of the cleaning liquid, but also dirt components and components of cooling and cutting fluids used in the machining of workpieces.

In preferred embodiments of the drying method according to the invention, the pressure in the chamber in which the remaining cleaning liquid is evaporated is reduced only to a value of approximately 2 mbar or approximately 3 mbar, since if the other values listed above have been observed, it has been shown that after reaching a pressure of 2 mbar, no residual cleaning liquid remained on the workpiece to be dried.

Basically, a workpiece to be dried can be blown off in one and the same chamber and exposed to a vacuum in order to evaporate the cleaning liquid that has not been removed by the blowing off. However, this is only recommended if the total time available for blowing off and evaporation (namely the cycle time minus non-productive times) is sufficiently long, taking into account the workpiece structure, the inherent heat of the cleaned workpiece at the start of the drying process and other parameters relevant to the drying process to achieve a satisfactory drying result. Preferred embodiments of the drying method according to the invention are characterized in that the evaporation period is only about 15 seconds, and in such a case, taking into account the cycle times required today, a workpiece to be dried can be blown off in a single station and exposed to a vacuum to evaporate the remaining cleaning liquid . In other cases, in which the cycle time does not allow such a procedure, the workpiece to be dried is blown off in two successive stations or subjected to a vacuum.

It is particularly advantageous if the drying process according to the invention is designed so that the workpiece arranged during the blowing with air jets in a chamber and the air for generating the air jets is at least partially guided in a circuit containing a blower and is at least partially dehumidified outside the chamber. Part of the drying air can e.g. B. derived from the hall roof, but particularly preferred embodiments are in which the entire drying air circulates in a closed circuit. Apart from a further reduction in the noise level, this embodiment has the further advantages that an appreciable excess pressure in the chamber during the blowing off of the workpiece and thus steam escape from the chamber is avoided and splash water can be drained off in a controlled manner. The at least partial dehumidification of the drying air behind the chamber can be accomplished by cooling and / or separating drops, for example by means of a baffle plate. If, as already mentioned, the workpiece is blown off in the chamber in which the remaining cleaning liquid is evaporated by evacuating the chamber, it is also recommended that the air used to blow off the workpiece be circulated through a bypass bridging the chamber during the evaporation period to guide and further dehumidify, so that for the process of dehumidifying the drying air there is also the period during which the remaining cleaning liquid is evaporated by evacuating the chamber.

Finally, to improve the drying result or to shorten the drying time, it may be advisable to heat the air to generate the air jets and / or the chamber to be evacuated.

On the basis of the above, it can be seen that the invention also relates to a device for carrying out the method according to the invention, which has a chamber for receiving the workpiece to be dried, in which blow nozzles for blowing off the workpiece are arranged, and according to the invention, such a device is characterized an air circuit containing the chamber, its nozzles, at least one blower and a dehumidifier, and a workpiece carrier rotatably mounted and rotatably drivable in the chamber.

Fig. 1

eine Prinzipskizze der ersten Ausführungsform der erfindungsgemäßen Einrichtung, und

Figuren 2A und 2B

Prinzipskizzen der aufeinanderfolgenden Stationen der zweiten Ausführungsform.

Further advantages of the invention result from the appended claims and / or from the following description and the attached drawing of two preferred embodiments of the device according to the invention; show in the drawing:

Fig. 1

a schematic diagram of the first embodiment of the device according to the invention, and

Figures 2A and 2B

Schematic diagrams of the successive stations of the second embodiment.

Fig. 1 shows a drying chamber 10, which has a cross-sectionally angular or conical bottom 12 and a hood 14, with the help of which the drying chamber can be loaded and unloaded from above and sealed airtight. In the side walls of the drying chamber, a shaft 16, indicated by dash-dotted lines, is rotatably supported, the one shaft end being passed pressure-tight through the right side wall of the drying chamber in accordance with FIG. The wave 16 is divided into two and holds a workpiece carrier 20 between its two parts, into which a cleaned and to be dried workpiece 22 can be inserted so that the shaft 16 together with workpiece carrier 20 and workpiece 22 can be rotated without the workpiece being displaced relative to the workpiece carrier becomes.

A nozzle plate 24 is fastened to the hood 14, which in turn carries a plurality of nozzles 26 which are directed towards a workpiece 22 held by the workpiece carrier 20 and communicate with an air chamber 28 which is formed by the actual hood 14 and the nozzle plate 24.

An air circuit formed by a ring pipe 30 and the drying chamber 10 contains, in succession, a first shut-off valve 32, a dehumidifier 34, a blower 36 and a second shut-off valve 38, the dehumidifier preferably being a cooler, but which also baffles for separating May contain moisture droplets. A bypass pipe 40 arranged between the dehumidifier 34 and the blower 36 on the one hand and the two shut-off valves 32 and 38 on the other hand contains a third shut-off valve 42. A drain line 44 branches off from the lower branch of the ring pipe 30 and is normally closed by a drain valve 46.

Finally, a vacuum pump 48 is provided, which is connected to the drying chamber 10 via an evacuation line 52 containing a shutoff valve 50.

A dirt trap 54 is arranged in the bottom 12 above the confluence of the ring pipe 30 in this bottom.

The workpiece carrier 20, as is known from such drying devices, is designed such that when the workpiece 22 is rotated, all areas of the workpiece surface to be blown off can be acted upon by the air jets generated by the nozzles 26.

To dry a workpiece 22 in the device shown in FIG. 1, the workpiece is first inserted into the workpiece carrier 20, whereupon the hood 14 is closed and the drying chamber 10 is thus made airtight. Then, with the valves 42, 46 and 50 closed and the motor 18 switched on, the rotating workpiece 22 is blown off from all sides with air jets generated by the nozzles 26, the drying air being circulated and at least partially dehumidified by the dehumidifier 34 becomes.

After the blow-off is completed, the valves 32 and 38 are closed, the valves 42 and 50 are opened and the vacuum pump 48 is switched on. Then, over a period of time, called the evaporation period, the air pressure in the drying chamber 10 is reduced more or less continuously and the cleaning liquid remaining on the workpiece 22 is thereby evaporated, while at the same time the previously used drying air continues to circulate via part of the ring pipe 30 and the bypass pipe 40 guided and dehumidified by the dehumidifier 34 as much as possible. At the same time, in order to save time, the workpiece carrier 20 is rotated into its loading and unloading position by means of the motor 18 and then stopped.

If the desired vacuum is reached in the drying chamber 10 at the end of the evaporation period, the vacuum pump is activated 48 switched off, the drying chamber 10 opened with the aid of the hood 14 and the dried workpiece 22 removed from the drying chamber 10. If necessary, the drying chamber 10 can be ventilated by a ventilation valve (not shown) before the hood 14 is swung open or raised, should ventilation of the previously evacuated drying chamber 10 not be possible via the evacuation line 52 and the switched off vacuum pump 48 when the valve 50 is open.

After loading the drying chamber 10 with a new workpiece to be dried, closing the valves 42 and 50 and opening the valves 32 and 38, the drying process begins again.

If cleaning liquid collects in the lower branch of the ring pipe 30 during the blowing off of a workpiece, this cleaning liquid can be drained off via the drain valve 46 during loading and unloading of the drying chamber 10.

The device shown in FIGS. 2A and 2B differs from that according to FIG. 1 only in that two chambers 10 'and 10''are provided, in the first one, namely in chamber 10', a workpiece 22 'to be dried is blown off is, whereupon the workpiece is brought into the second chamber 10 ″ and there exposed to a vacuum and completely dried. Those parts of the device according to FIGS. 2A and 2B which correspond to parts of the device according to FIG. 1 have been provided with the same reference numerals as in FIG. 1, but with the addition of a dash or two dashes. As a precaution, it should be noted that - based on the sequence of the drying process - the chamber 10 '' is arranged behind the chamber 10 '.

In the device part shown in FIG. 2A, a workpiece 22 ′ to be dried is thus rotated and blown off, whereupon it is brought into the chamber 10 ″ of the device part shown in FIG. 2B. Since, in preferred embodiments of the drying method according to the invention, the workpiece 22 'is not rotated as long as it is exposed to a vacuum, the chamber 10' 'is provided with a stationary workpiece carrier 20' '. Any cleaning liquid that may collect on the bottom 12 ″ of the chamber 10 ″ can be drained off via a drain line 44 ″ and a drain valve 46 ″.

Otherwise, the procedure in the device shown in FIGS. 2A and 2B corresponds to the procedure in the device in FIG. 1, but with the difference that the drying air cannot be further dehumidified while the workpiece to be dried is exposed to a vacuum , since the next workpiece to be dried is already blown off in the chamber 10 '.

At a cycle time predetermined by a production system, when using the device shown in FIGS. 2A and 2B, approximately twice the time is available both for blowing off the workpiece to be dried and for evaporating the remaining cleaning liquid, compared to the operation of the device shown in Fig. 1.

The rotation of the workpiece to be blown off, which is caused by the motor 18 or 18 ', can easily be controlled in such a way as is necessary for optimal emptying of all blind holes and other cavities in the workpiece.

A particular advantage of the device shown in FIG. 1 is the fact that the fan 36 does not have to be switched off and started up again.

After the chamber 10 or 10 ″ has been evacuated, it can also be vented via the valves 32 and 46 or the valve 46 ″ before the hood 14 or 14 ″ is opened.

With the inventive method or the inventive device, as shown in Fig. 1, z. B. at a cycle time of only 25 seconds dry a cylinder head of a 4-cylinder 4-valve engine satisfactorily in only 15 or 16 seconds, the workpiece being blown off during approximately half the drying time and exposed to a vacuum during approximately the other half of the drying time was, if the workpiece was previously cleaned with a 55 ° C hot cleaning liquid and subjected to the drying process with a resulting workpiece initial temperature of about 50 ° C. The workpiece temperature after drying was then approximately 34-37 ° C.

When using the device shown in FIGS. 2A and 2B, even better drying results are obtained with the same cycle time, because a period of approximately 15 seconds is then also available for the evaporation of the remaining cleaning liquid in a vacuum.

Claims (16)

1. Process for drying a single workpiece which has been cleaned with an aqueous cleaning fluid after machining and has surface areas with contours retaining cleaning fluid, in at least one chamber, wherein the workpiece is acted upon with jets of air to remove and distribute cleaning fluid, and the chamber is then evacuated to evaporate residual cleaning fluid, characterized in that the workpiece (22; 22') is subjected at an initial temperature of at least approximately 45° C to the drying process, is turned while it is being blown with jets of air and is exposed to a vacuum in the chamber (10'; 10") for an evaporation period of at least 8 seconds and at the most 30 seconds, and in that the air pressure in the chamber (10'; 10") - starting from atmospheric pressure - is lowered during the entire evaporation period at least essentially continuously to a minimum value of from approximately 4 mbar to approximately 0.5 mbar.
2. Process as defined in claim 1, characterized in that the air pressure in the chamber is lowered during the evaporation period to a minimum value of approximately 3 mbar.
3. Process as defined in claim 1, characterized in that the air pressure in the chamber is lowered during the evaporation period to a minimum value of approximately 2 mbar.
4. Process as defined in any one or several of claims 1 to 3, characterized in that the evaporation period lasts approximately 15 seconds.
5. Process as defined in any one or several of claims 1 to 4, characterized in that the workpiece (22; 22') is arranged in a chamber (10; 10') while it is being blown with jets of air, and in that the air for generating the jets of air is at least partially circulated in a circuit (10, 30, 34, 36; 10', 34', 36', 30') comprising a fan (36; 36') and is at least partially dehumidified outside the chamber.
6. Process as defined in claim 5, characterized in that the air is dehumidified by cooling-down.
7. Process as defined in claim 5 or 6, characterized in that the air is dehumidified by means of a droplet separator (34; 34').
8. Process as defined in any one or several of claims 1 to 7, characterized in that the workpiece (22) is blown with the jets of air in the chamber (10) to be evacuated.
9. Process as defined in claims 5 and 8, characterized in that during the evaporation period the air is circulated in a circuit via a by-pass (40) bridging the chamber (10) and is dehumidified while circulating.
10. Process as defined in any one or several of claims 1 to 9, characterized in that the air for generating the jets of air is heated.
11. Process as defined in any one or several of claims 1 to 10, characterized in that the chamber (10; 10") to be evacuated is heated.
12. Apparatus for carrying out the process as defined in any one or several of the preceding claims comprising a chamber (10; 10') for receiving the workpiece (22; 22') in which blow nozzles (26; 26') are arranged for blowing the workpiece, characterized by an air circuit (10, 34, 36, 30; 10', 34', 36', 30') comprising the chamber (10; 10'), the nozzles (26; 26') thereof, at least one fan (36; 36') and an air dehumidifier (34; 34'), and by a rotationally driveable workpiece carrier (20; 20') rotatably mounted in the chamber.
13. Apparatus as defined in claim 12, characterized in that the air dehumidifier (34; 34') comprises a droplet separator.
14. Apparatus as defined in claim 12 or 13, characterized in that the air dehumidifier (34; 34') comprises an air cooler.
15. Apparatus as defined in any one or several of claims 12 to 14, characterized by air circuit valves (32, 38) separating the chamber (10) from the air circuit, and by a vacuum pump (48) connectable via a valve (50) to the chamber (10).
16. Apparatus as defined in claim 15, characterized by a by-pass line (40) which is arranged between the air circuit valves (32, 38), on the one hand, and fan (36) and air dehumidifier (34), on the other hand, and contains a shut-off valve (42).

Images