Device and method for cleaning or drying workpieces

Drying and gas or vapor contact with solids – Process – With contacting of material treated with solid or liquid agent

Reexamination Certificate

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Details

C034S350000, C034S085000, C034S092000, C034S227000

Reexamination Certificate

active

06253462

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a device and a method for cleaning and drying workpieces.
BACKGROUND OF THE INVENTION
Removal of manufacturing residues, for example oil, grease or chips from workpieces which have fine structural features with bores, recesses, fissures and other openings, has until now essentially been performed using solvent-based cleaning methods. The solvents dissolve grease and oil residues, but also facilitate penetration of the cleaning fluid into very small capillary openings and fissures because of the small surface tension. Such cleaning methods, however, disadvantageously use chemical solvents which require a complex post-treatment or disposal of the cleaning fluid.
The known devices and methods for cleaning workpieces without using a solvent are inadequate for cleaning workpieces with filigree openings and surface structures.
A device and a method for cleaning workpieces which does not require a solvent, is known from DE 43 17 862 A1. Workpieces are here introduced in a wash tank which is then closed air-tight and a reduced pressure is generated in the tank. This reduced pressure causes liquid to be drawn into the wash tank through a pipe connection; subsequently air is blown into the liquid bath.
DE 92 17 047 U1 describes a device for cleaning workpieces wherein the workpieces are surrounded by a bath with a wash liquid into which a gaseous medium is blown under an excess pressure. A reduced pressure can be generated in an air space above the bath containing the wash liquid.
DE 37 02 675 A1 describes a device for wet cleaning workpieces wherein a turbulent flow is produced in a immersion bath using a liquid jet, wherein the workpieces to be cleaned are arranged in the immersion bath.
EP 0 507 294 A1 discloses a device for cleaning work pieces which includes a treatment vessel and a workpiece support arranged in the treatment vessel for receiving workpieces. A spray unit which is disposed in the treatment vessel and has discharge nozzles for discharging a cleaning fluid, is arranged so as to be rotatable above the work piece support. Also provided is a flooding pipe for entirely or partially flooding the cleaning vessel with a cleaning fluid. The device described above can be used to carry out a method for cleaning workpieces wherein the workpieces are cleaned using an immersion process by flooding the cleaning vessel or, alternatively, a spray process by applying to the work pieces a cleaning jet from a spray cleaning unit.
DE 44 46 587 A1 describes a cleaning device with a tank which can be used to clean a charge using a cleaning liquid supplied through nozzles of a supply line. A reduced pressure can be generated in the treatment vessel. A discharge pipe is located in the lower section of the treatment vessel, with the discharge pipe being either connected to the supply line via a circulation pump or via a pump to a storage tank, wherein the storage tank is in turn connected to the supply line via a pump.
The known devices and methods have the disadvantage of not being very effective for cleaning workpieces having small surface features and, in particular, for cleaning small workpieces which are introduced into the cleaning vessel in the form of loose parts.
It is therefore an object of the present invention to provide a device for cleaning workpieces which allows reliable cleaning of small workpieces and of workpieces having filigree surface structures. The device should also operate reliably when cleaning fluids that do not contain solvents are used, and should eliminate the disadvantages described above.
It is another object of the invention to provide a method for cleaning and drying workpieces which can be carried out using the device of the pr invention.
SUMMARY OF THE INVENTION
Accordingly, the device includes a treatment vessel in which a workpiece support for receiving the workpiece to be cleaned is arranged. A spray unit having discharge nozzles for discharging cleaning fluids and/or a gaseous medium is arranged inside the treatment vessel which has a controllable liquid flow and wherein a reduced pressure can be generated. The workpiece support and/or the spray unit are also arranged so as to be able to rotate in the treatment vessel.
With the device of the invention, even small workpieces can be reliably cleaned and grease and oil residues can be removed from small recesses and openings. For this purpose, a liquid bath is provided in the treatment vessel which at least partially surrounds the workpieces supported by the workpiece support. At the same time, when a reduced pressure is generated in the region above the liquid bath using a vacuum pump connected to a first suction port, a cleaning fluid and, as needed, also a gaseous medium are introduced through the spray unit into the liquid bath and into the region above the liquid bath. The impact of the cleaning fluid discharged from the spray unit and impinging on the workpieces causes a spontaneous evaporation in the region above the liquid bath, wherein the released energy causes the gas particles to impact the workpieces with a high velocity, thereby producing a thorough cleaning effect. The cleaning fluid and the gaseous medium, which may also be introduced, cause turbulence and cavitation effects in the liquid bath which result in an explosive release of contaminants that adhere to the workpieces and of contaminants that are present in the capillary inclusions of the workpieces. By rotating or periodically raising and lowering the workpiece support, the workpieces are permanently exposed to the different cleaning processes both in the liquid bath and above the liquid bath. In particular, the workpieces pass an active boundary region which exists between the liquid bath and the reduced pressure region located above the bath.
For maintaining an at least approximately constant liquid level in spite of the continuous introduction of cleaning fluid, a controllable liquid flow is provided which discharges per unit time a quantity of liquid which corresponds to the quantity of liquid introduced. The liquid discharge port preferably also includes a valve which is opened and closed periodically.
The device according to the invention has the additional advantage that it can be used not only to clean workpieces, but also to dry the cleaned workpieces.
For this purpose, after the cleaning fluid or the liquid bath is discharged, a gaseous medium is introduced into the treatment vessel under excess pressure through the discharge nozzles of the spray unit, wherein the gas jet impinging on the workpieces removes the residual liquid adhering to the workpieces which is then withdrawn. The residual liquid is preferably withdrawn using the vacuum pump or another suction device provided according to one of the embodiments of the invention, wherein the additional suction device is connected to a second suction port of the treatment vessel. In particular, the second suction device is provided for rapidly withdrawing the liquid vapors that remain in the treatment vessel immediately following the cleaning process. A reduced pressure produced by the vacuum pump in the treatment vessel accelerates the evaporation of the residual liquid that were removed from the workpieces by the gas jet. By rotating the spray unit in the treatment vessel, gas jets are applied to the workpieces from continuously changing directions so as to dry the workpieces as thoroughly as possible. The workpieces can also be continuously intermixed by simultaneously rotating the workpiece support, in particular when loose parts are cleaned and/or dried, so that during the drying process all workpieces are exposed to the gas jets.
Advantageously, the treatment vessel may include heating devices disposed on the outside of the vessel for heating the treatment vessel during the drying process.
According to another embodiment of the invention, heat radiators are arranged inside the treatment vessel, whereby heat radiation is directed towards the workpieces during the drying process. This feature and the reduced pres

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