EP0973620B2 - Device and method for cleaning or drying work pieces - Google Patents

Abstract

The apparatus for cleaning and drying of workpieces includes a treatment chamber (1) which has at least one controllable liquid outlet (4) and can sustain a reduced pressure. The chamber accommodates a spray unit (8a, 8b) for delivery of a cleaning liquid and/or a gaseous medium, and is provided with a workpiece carrier (12). The latter is translatable or rotatable and/or the spray unit is rotatable. Also claimed is a method for cleaning workpieces which includes loading of the workpieces into the chamber, production of a liquid bath which at least partially surrounds the workpieces, and production of a reduced pressure in the gas space above the bath. It further includes introduction of a cleaning liquid and/or a gaseous medium under pressure into the treatment chamber, and displacement of the workpiece carrier so that the workpieces alternately pass through the liquid bath and the gas space above it.

Description

The present invention relates to a method for cleaning and drying workpieces.

The removal of manufacturing residues such as oils, fats or chips on workpieces, the finest structures with holes, undercuts, gaps and other recesses, has been largely reserved cleaning processes using solvents. On the one hand, the solvents serve to dissolve grease and oil residues and, due to the low surface tension, allow the cleaning fluid to penetrate into the smallest capillary recesses and gaps. A disadvantage of such cleaning methods is the use of chemical solvents that require a costly aftertreatment or disposal of the cleaning liquid.

Previously known devices and methods for solvent-free cleaning of workpieces are only inadequate for cleaning workpieces with filigree recesses and surface structures.

An apparatus and a method for solvent-free cleaning of workpieces is known from DE 43 17 862 A1 known. Here, workpieces are placed in a wash tank, which is then hermetically sealed and in which a negative pressure is generated. Due to the negative pressure, liquid is sucked into the wash tank via a line connection, with air subsequently being blown into the resulting liquid bath.

The DE 92 17 047 U1 describes a device for cleaning workpieces, in which the workpieces are surrounded by a washing liquid bath, in which a gaseous medium is injected under pressure. In an air space above the Waschflüssigkeitsbades a negative pressure can be generated.

The DE 37 02 675 A1 describes a device for wet cleaning of workpieces, in which by means of a liquid jet, a turbulence flow is generated in a dip bath, in which the workpieces are arranged for cleaning.

From the EP 0 507 294 A1 a device for cleaning of workpieces is known, which has a treatment container and arranged in the treatment container workpiece carrier for receiving workpieces. A spray unit arranged in the treatment tank is rotatably arranged around the workpiece carrier and has outlet nozzles for discharging a cleaning liquid. In addition, a flood pipe is provided to flood the cleaning tank wholly or partly with a cleaning liquid. By means of the described device, a method for cleaning workpieces is feasible, in which the workpieces are cleaned in a dipping process by flooding the cleaning container or in a spray cleaning process by applying the workpieces with a cleaning jet from the spray cleaning unit.

The DE 44 46 587 A1 describes a cleaning device with a tank in which a batch can be cleaned by means of cleaning liquid, which is discharged via nozzles of a supply line. In the treatment tank, a negative pressure can be generated. He further has in the lower part of a drain pipe, which is connected either via a circulation pump to the supply line, or which leads via a pump in a reservoir, which in turn is connected via a pump to the supply line.

The known devices and methods have the disadvantage that they are not very effective for cleaning workpieces with the smallest surface structures and in particular for cleaning very small workpieces that are introduced as bulk material in the cleaning container.

The aim of the present invention is therefore to provide a method for cleaning workpieces, with the reliable cleaning of even the smallest workpieces and workpieces with filigree surface structures is possible, which operates reliably based on aqueous cleaning fluids without the addition of solvents and the In particular, the above-mentioned disadvantages do not arise.

This object is achieved by a method for cleaning workpieces, which has the features of patent claim 1.

The inventive method allows reliable cleaning even the smallest workpieces with removal of grease and oil residues from the smallest recesses and openings. For this purpose, a liquid bath is generated in the treatment tank, which at least partially surrounds the workpieces held by the workpiece carrier. Parallel to generating a negative pressure in the region above the liquid bath by means of a vacuum pump connected to a first suction opening, cleaning liquid and optionally a gaseous medium are introduced into the liquid bath and the area above the liquid bath via the spray unit. In the area above the liquid bath, when the cleaning liquid discharged from the spraying unit impinges on the workpieces Spontaneous evaporations, whereby gas particles bounce on the workpieces at high speed due to the released energy and achieve a considerable cleaning effect. In the liquid bath, turbulence and cavitation effects occur due to the cleaning liquid introduced under excess pressure and the optionally introduced gaseous medium, which cause explosive discharges of firmly adhering contaminants and of contamination in capillary inclusions of the workpieces. By rotating or periodically raising and lowering the workpiece carrier, the workpieces are permanently supplied to the different cleaning processes in the liquid bath and above the liquid bath and pass through the particularly cleaning-active interface region between the liquid bath and the overlying negative pressure region.

In order to maintain an at least approximately constant liquid level despite continuous introduction of cleaning liquid, the controllable liquid outlet is provided, over which per unit of time a quantity of liquid corresponding to the newly supplied quantity of liquid expires. For this purpose, the liquid outlet preferably has a valve which is periodically opened and closed.

The inventive method also has the advantage that it can be used in addition to the cleaning of workpieces for drying the cleaned workpieces.

For this purpose, after the cleaning liquid or the liquid bath has drained off, a gaseous medium is introduced under excess pressure via the outlet nozzles of the spray unit into the treatment tank, wherein the gas jet impinging on the workpieces removes liquid residues adhering to the workpieces which are sucked off. The suction is preferably carried out by the vacuum pump or via a further, provided according to an embodiment of the invention further suction device which is connected to a second suction opening of the treatment vessel. The further suction device serves, in particular, to quickly suck the liquid vapors located in the treatment tank immediately after the cleaning process. A negative pressure generated by the vacuum pump in the processing tank accelerates the vaporization of the liquid residues removed from the workpieces by the gas jets. By rotating the spray unit in the treatment tank, the workpieces are constantly exposed to gas jets from constantly changing sides in order to effect as complete a drying as possible. By simultaneous rotation of the workpiece carrier is carried out, especially in bulk, a constant mixing of the workpieces, so that in the course of the drying process all workpieces are exposed to the gas jets.

Advantageous embodiments of the invention are the subject of the dependent claims.

Advantageously, the treatment tank has externally mounted heaters for heating the treatment tank during the drying process.

Furthermore, it is provided to arrange heat radiators in the interior of the treatment container, which emit during the drying process directed to the workpieces heat radiation, which causes supported by the existing in the treatment tank vacuum evaporation of adhering to the workpieces liquid residues. Advantageously, the heat radiators are rotatably arranged around the workpiece carrier in the treatment tank.

According to the cleaning method according to the invention, a liquid bath is produced in a treatment container in which a workpiece carrier for receiving the workpieces is arranged, and a negative pressure is generated in the treatment container in an area above the liquid bath. The workpiece carrier or the workpieces are in this case partially surrounded by the liquid bath.

Cleaning liquid and / or a gaseous medium are then introduced under excess pressure into the treatment vessel via outlet nozzles of a spray unit, wherein the liquid jets or the jets of the gaseous medium are preferably directed onto the workpieces. During this process, the workpiece carrier is moved in the treatment container in such a way that the workpieces alternately pass above and below a liquid level of the liquid bath, so as to be exposed alternately to the different cleaning processes which take place above, below and in the boundary region between the liquid bath and the vacuum region to become. The movement of the workpiece carrier can be done for example by periodic lifting and lowering or by rotation.

Preferably, the liquid level is maintained at least approximately constant during the cleaning process to ensure that the workpieces pass alternately above and below the liquid level as the workpiece carrier moves. The formation of the liquid bath into the treatment tank can be carried out by initial flooding of the treatment tank to a predetermined level of liquid level, this level of liquid level is kept approximately constant when flowing further cleaning liquid via a controllable liquid flow. Another way to generate the liquid bath is to keep the liquid drain closed at the beginning of the cleaning process until a corresponding amount of cleaning liquid has been introduced into the treatment tank via the spray unit.

Liquid vapors, which form in the negative pressure region above the liquid bath, are sucked off, wherein the suction preferably takes place via a vacuum pump provided for generating the negative pressure. Advantageously, during the cleaning process, a rotation of the spray unit, wherein the outlet nozzles of the spray unit preferably move in opposite directions to a rotational movement of the workpiece carrier.

The cleaning method according to the invention further provides for carrying out the above-mentioned method steps several times in succession, wherein between the individual cleaning processes, the liquid bath is discharged almost abruptly via the liquid outlet. Due to the resulting suction effect, a further cleaning effect is achieved on the workpieces. The draining of the liquid bath is accelerated by generating an overpressure by means of compressed air injected via the spray unit.

For drying the workpieces following the cleaning process, it is provided to drain the cleaning liquid from the treatment tank and then to introduce a gaseous medium under pressure into the treatment tank via outlet nozzles of a spray unit. The liquid vapor which results when the gaseous jet impinges on the liquid adhering to the workpieces is sucked out of the treatment container. The suction is preferably carried out via a vacuum pump, wherein a generated by the vacuum pump in the treatment vessel vacuum accelerates evaporation of the liquid residues. The workpiece carrier and / or the spray unit are rotated during the drying process, on the one hand to achieve a continuous mixing of the workpieces with bulk material and, on the other hand, to expose the workpieces from all directions to the gaseous jet. In particular for drying sensitive workpieces, it is provided to keep the workpiece carrier stationary during the drying process and to rotate the spray unit around the workpiece carrier.

The drying process can be accelerated by heating the treatment tank by means of internally or externally mounted heaters.

According to a method for drying workpieces is provided to generate a negative pressure in a treatment vessel in which the workpieces are received by a workpiece carrier, and further to generate in the interior of the treatment vessel directed onto the workpieces heat radiation. The high-energy thermal radiation causes, supported by the negative pressure formed in the container interior, an evaporation of the adhering to the workpieces liquid. In order to expose the workpieces evenly to the heat radiation, there is a rotation of the workpiece carrier and / or a device to which the heat radiators are attached. The liquid vapors are sucked out of the container interior. The suction is preferably carried out by the vacuum pump required for generating the negative pressure. According to one embodiment of the drying method is provided, preferably via outlet nozzles of a spray unit to introduce a gaseous medium under pressure in the treatment vessel. This causes on the one hand, that liquid residues are blown away from the workpieces, wherein the liquid residues evaporate through the vacuum and the supplied heat and the resulting liquid vapors are sucked through the vacuum pump. On the other hand, by introducing the gaseous medium, a temporary weakening of the negative pressure, whereby the vacuum pump causes an increased suction effect in the container interior and whereby the liquid vapors are sucked out of the container interior faster.

Fig. 1

eine Vorrichtung mit einem zylinderförmigen Behandlungsbehälter im axialen Querschnitt;

Fig. 2

eine Vorrichtung im axialen Querschnitt in perspektivischer Ansicht;

Fig. 3

eine Vorrichtung mit stationären Wärmestrahlern im radialen Querschnitt;

Fig. 4

eine Vorrichtung mit rotierbaren Wärmestrahlern im radialen Querschnitt;

Fig. 5

eine Vorrichtung in perspektivischer Ansicht.

The device and the method according to the invention will be explained in more detail in the following text with reference to exemplary embodiments. Show it:

Fig. 1

a device with a cylindrical treatment container in axial cross-section;

Fig. 2

a device in axial cross section in a perspective view;

Fig. 3

a device with stationary radiant heat in the radial cross section;

Fig. 4

a device with rotatable heat radiators in the radial cross section;

Fig. 5

a device in perspective view.

In the figures, unless otherwise indicated, like reference numerals designate like parts with the same meaning.

The essential components of the device are described below with reference to Fig. 1 to 4 explains Fig. 3 a sectional view of the device along the in Fig. 1 drawn section line BB 'is. Fig. 2 also shows the device cut in the axial direction in perspective View, where sectional areas are shaded for clarity.

The device has a substantially cylindrical treatment container 1, which has a controllable liquid outlet 4 and a first suction opening 7 for connection of a vacuum pump for generating a negative pressure in the interior of the treatment container 1. Furthermore, a second suction opening 6 is provided for the connection of a further suction device, which essentially serves for rapid suction of liquid vapors following a cleaning process which can be carried out with the device. The further suction device preferably causes a much larger gas exchange than the vacuum pump, but is not suitable for generating a vacuum.

Inside the treatment container 1, a workpiece carrier 12 for receiving workpieces is arranged, wherein the workpiece carrier 12 is rotatably mounted in the treatment container 1 about a longitudinal axis A-A '. The workpiece carrier 12 serves on the one hand for receiving individual large workpieces and on the other for receiving baskets 18 with bulk material, wherein the baskets are liquid and gas permeable. In the interior of the treatment container 1 there is furthermore a spray unit 8a, 8b for introducing cleaning liquid or a gaseous medium into the container interior. The spray unit consists in the embodiments shown in the figures of two parallel arranged substantially rectangular running pipe loops, one of which serves for the discharge of cleaning liquid and the other for the discharge of a gaseous medium. The two pipe loops 8a, 8b each have a plurality of outlet nozzles directed at the workpiece carrier. The spray unit formed from the two pipe loops 8a, 8b is likewise rotatably mounted around the container axis A-A '.

For loading the treatment container with workpieces, a closable supply opening 16 is provided on one side of the treatment container 1. The workpiece carrier 12 has a number of rollers, which facilitates retraction of the workpieces accommodating basket 18 in the treatment tank 1.

The inventive method for cleaning workpieces will be explained below with reference to the device shown in the figures. After introduction of the workpieces carrying basket 18 in the treatment tank 1, a flooding of the treatment tank 1 with a cleaning liquid except for a predetermined liquid level 100, 102, wherein the workpiece carrier 12 and the workpieces receiving basket 18 is partially surrounded by the liquid bath 50 takes place. In Fig. 1 For example, two different liquid levels are shown. A partial vacuuming of the space 52 located above the liquid bath takes place by means of the vacuum pump connected to the first suction opening. In addition, cleaning liquid is introduced via the outlet nozzles of one of the pipe loop of the spray unit 8a, 8b under pressure in the container interior, wherein the supply of the cleaning liquid from the outside via a central shaft 40, via which also the workpiece carrier 12 and the spray unit 8a, 8b are rotatably mounted ,

When the cleaning liquid is introduced under pressure into the treatment tank 1, essentially three different cleaning processes result. In the space 52 above the liquid bath, when the liquid jets strike the workpieces, explosive spontaneous evaporations of the treatment liquid occur, whereby the released energy causes the detachment of contaminants and firmly adhering coating and surface contaminants. The pressure of the cleaning liquid, which is preferably in the range of 2.0 to 15.0 bar, and formed in the space 52 vacuum, preferably between 0.2 to 0.6 bar can be coordinated so that it only when hitting the cleaning liquid on the workpieces comes to evaporations. To improve the cleaning effect, the cleaning liquid is heated to a temperature of about 60 to 85 ° C. In the liquid bath 50 turbulent underwater currents develop through the introduction of the cleaning fluid, which cause a cleaning effect on the workpieces. In addition, it is possible to introduce a gaseous medium under overpressure via the other of the two tube loops of the spray unit 8a, 8b, wherein the gaseous medium in the liquid bath 50 amounts to additional turbulence.

By rotation of the workpiece carrier 12 about the axis A-A ', the workpieces located in the basket 18 are alternately fed to the different cleaning processes in the space 52 above the liquid bath and in the liquid bath 50. Furthermore, by rotation of the workpiece carrier 12, the workpiece of the charge located in the basket 18 is permanently mixed in order to expose all the workpieces during the cleaning process to the cleaning processes acting on the batch from the outside. In the space 52 above the liquid bath the workpieces are acted upon by rotation of the workpiece carrier 12 from different directions with the exiting from the outlet nozzles liquid jets. In this case, the spray unit 8a, 8b can remain stationary, wherein a part of the pipe loops 8a, 8b is arranged above and a part below the liquid level 100, 102 in order to inject cleaning liquid into both the space 52 and the liquid bath 50. Advantageously, the spray unit 8a, 8b is rotated counter to the workpiece carrier 18 about the axis A-A 'during the cleaning process.

The rotation of the workpiece carrier 12 causes in the liquid bath 50 an additional turbulent flow which enhances the cleaning effect. In addition, by the rotation of the workpiece carrier 12 permanent gas fractions are introduced into the liquid bath 50, which achieve there as gas bubbles of various forms cleaning effects on the workpieces.

In this transition region between the liquid and gaseous state of aggregation, spontaneous evaporations and condensations occur permanently, with the cleaning liquid having a maximum reduced surface tension in the transition state to the gas phase allows penetration of the cleaning liquid itself in capillary column and recesses of the workpieces. The evaporation of the cleaning liquid in this boundary region is enhanced by the cleaning jets occurring on the liquid surface, which cause a permanent fluidization of the liquid surface.

The liquid vapors accumulating in the gas space 52 are permanently sucked off via the first suction opening 7 by the vacuum pump during the cleaning process. In order to keep the desired liquid level at least approximately constant despite the permanent supply of cleaning liquid via the spray unit 8a, 8b, one portion of the liquid bath 50 corresponding to the inflowing amount of cleaning liquid is discharged via the liquid outlet 4 per unit time. For this purpose, the liquid outlet 4 has a valve which is not shown in more detail in the figures and which is opened and closed at regular intervals to discharge the liquid. The permanent flow of cleaning liquid from the liquid bath 50, which is replaced by the cleaning liquid supplied via the spraying unit 8a, 8b, has the advantage that during the cleaning process, dirt accumulating in the liquid bath 50 is permanently removed.

The described cleaning process is preferably carried out several times in succession, wherein between the individual processes, the liquid bath 50 is very quickly at least partially drained via the liquid outlet 4, this creates a strong suction on the workpieces, entraining adhering to the workpieces debris. The discharge of the liquid bath 50 is advantageously accelerated by generating an overpressure by means of compressed air introduced via the spray unit.

The device is also suitable for drying wet workpieces following the cleaning process. After the end of the cleaning process, the cleaning liquid is drained via the liquid outlet 4 and the liquid outlet 4 is closed. Subsequently, a gaseous medium, in particular air, is injected under excess pressure into the treatment tank 1. The adhering to the workpieces liquid residues are torn away by the gas jet and evaporate, wherein the forming liquid vapor is preferably sucked by the vacuum pump via the first suction opening 7. A negative pressure generated by the vacuum pump in the treatment tank 1 also accelerates the evaporation of the liquid residues discharged from the workpieces. By rotation of the workpiece carrier 18, the workpieces are permanently mixed and applied from different sides with the gas jets for drying. Preferably, the workpiece carrier 18 and the tube loop 8b rotate in opposite directions about the axis A-A 'of the treatment container.

The drying effect is enhanced by heating the container interior, wherein the heating is generated by externally mounted, not shown here heaters or arranged in the container interior heat radiator 10 a, 10 b. The heat radiators are preferably directed to the workpiece carrier 12 and the workpieces and, as in the Fig. 1 and 3 shown as stationary heat radiator 10 a stationarily arranged on a container inner wall or, as in Fig. 4 represented as rotatable heat radiator 10b arranged on a parallel to the pipe loops 8a, 8b of the spray unit arranged pipe loop 8c, which is rotatably mounted together with the spray unit 8a, 8b about the axis AA 'of the treatment vessel. The heat radiators 10a, 10b are, as in particular from Fig. 1 emerges formed as elongated elements which extend in the axial direction in the treatment tank 1.

For particularly sensitive workpieces, it is possible to leave the workpiece carrier 12 stationary and only to rotate the spray unit 8a, 8b or the spray unit 8a, 8b together with the pipe loop 8c for the heat radiators 10b around the workpiece.

Before carrying out the actual drying process, it is provided to suck off the liquid vapors still present in the cleaning tank 1 from the cleaning process via the second suction opening 6. This serves to accelerate the drying process, since the suction device connected to the second suction opening 6 allows a larger gas exchange than the vacuum pump.

The temperature of the introduced via the spray unit 8a, 8b gaseous medium is dependent on the temperature sensitivity of the workpieces to be dried between 50 and 200 ° C, correspondingly varies the pressure of the introduced gaseous medium between 0.5 bar and 10 bar, wherein in the container interior, a vacuum is formed between 0.2 bar and 0.6 bar.

The device also allows a further drying process in which a Drying of the workpieces by the heat radiation emitted by the heat radiators 10a, 10b takes place in conjunction with a vacuum generated in the container interior by the vacuum pump. This method is particularly suitable for drying mechanically less resilient components, such as electronic components, which would be destroyed by using the above-described drying method by the high pressure of the gas jets.

The adhering to the workpieces liquid residues evaporate by the heat radiation, the boiling point is greatly reduced by the vacuum. In the case of stationary heat radiators, a rotation of the workpiece carrier 18 takes place in order to expose the workpieces from all sides to the heat radiation. Furthermore, the in FIG. 4 The device shown the ability to rotate the heat radiator 10b through the pipe loop 8c to the workpiece carrier 18 and to leave the workpiece carrier 18 stationary or rotate the workpiece carrier 18 and the pipe loop 8c in opposite directions to permanently suspend the workpieces from different directions of heat radiation.

The forming in the container interior liquid vapor is sucked through the first suction port 7 and the vacuum pump. Preferably, a gaseous medium, in particular air, is briefly blown into the container interior at defined time intervals via one of the pipe loops of the spray unit 8a, 8b in order to temporarily increase the pressure in the container interior and thus reduce the vacuum. To restore the vacuum, the introduced air is sucked off via the vacuum pump, whereby the liquid vapors are removed more quickly from the treatment tank 1 through this short-term increased gas exchange. The introduced air further causes liquid residues to be blown away from the workpieces so as to effect a faster evaporation of the adhered liquid residues.

LIST OF REFERENCE NUMBERS

1

treatment tank

4

liquid drain

6

first suction opening

7

second suction opening

8a, 8b

Pipe grinding with outlet nozzles

8c

Rotary device for heat radiators

10a, 10b

Radiant heaters

12

Workpiece carrier

16

feed

18

Workpiece basket

22

Rolls of the workpiece carrier

50

liquid bath

52

headspace

100, 102

Liquid water levels

A-A '

Axle of the treatment tank

B-B '

intersection

Claims (9)

1. A method for cleaning workpieces, in which the workpieces are introduced into a treatment container (1) in which a workpiece carrier (12) for accommodating the workpieces are disposed, and in which cleaning fluid subjected to excess pressure is introduced into the treatment container via outlet nozzles (8a, 8b) of a spray unit (8a, 8b) directed onto the workpieces,
   with the following method steps:

   - producing of a fluid bath (50) in the treatment container (1), which at least partially surrounds the workpieces;

   - generating of a low pressure in a gas chamber (52) situated above the liquid bath (50);

   characterised by the following method step during the introduction of cleaning fluid via the outlet nozzles (8a, 8b) in the gas space (52) and simultaneously into the liquid bath:

   - moving the workpiece carrier (12) in the treatment container (1) in such a manner that the workpieces alternately pass through the liquid bath (50) and the gas space (52) present above the liquid bath (50).
2. A method according to Claim 1,
   characterised in that a water level (100-102) of the liquid bath (50) is kept at least approximately constant.
3. A method according to Claim 1 or 2,
   characterised in that the workpiece carrier (12) is rotated around an axis A-A' of the treatment container for the alternating introduction of the workpieces into the liquid bath (50) and into the gas chamber (52).
4. A method according to one of Claims 1 to 3,
   characterised in that liquid vapours are sucked out of the gas chamber (52).
5. A method according to one of Claims 1 to 4,
   characterised in that the spray unit (8a, 8b) rotates in the treatment chamber (1), preferably in the opposite direction to the workpiece carrier.
6. A method according to one of Claims 1 to 5,
   characterised in that liquid is at least partially drawn off from the liquid bath (50) at regular time intervals.
7. A method according to one of Claims 1 to 6, which comprises the following method steps for drying the workpieces:

   - removal of the cleaning fluid from the treatment container;

   - introduction of a gaseous medium under excess pressure via outlet nozzles of the spray unit (8a, 8b) into the treatment container (1);

   - drawing off of liquid vapours from the interior of the treatment container (1);

   - rotation of the spray unit (8a, 8b) and/or of the workpiece carrier (12) in the treatment container (1).
8. A method according to Claim 7,
   characterised in that a low pressure is produced in the treatment container (1).
9. A method according to Claim 11,
   characterised in that the interior of the treatment container (1) is heated by means of heat radiators (10a, 10b), which are mounted externally on the treatment container (1) or which are disposed in the interior of the treatment container (10 and are directed onto the workpiece carrier (12).

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