METHOD AND DEVICE FOR CLEANING METAL WORKPIECES

Abstract

In conventional methods for cleaning the surface of workpieces in automatic production by means of vapor or hot water, the temperature of workpieces can undergo such a change that the dimensions exceed tolerances as a result of the thermal expansion, and subsequent mounting or processing is only possible after a thermal treatment step. Cleaning is performed by scanning a jet of vapor or hot water over the surface of the workpiece and carrying out this process at reduced pressure, so that the residues of condensed vapor or water that are present on the surface evaporate at least partially, and thereby extract from the workpiece heat that has been supplied by the vapor or the hot water. Preferably, the cleaned surface is at the same time dried.

Claims

1-27. (canceled)

28. A method for cleaning a surface of a metal workpiece by means of at least one jet of vapor and/or hot water impinging on the surface at a point of impingement. wherein the point of impingement is moved relative to the surface in a scanning manner in a scanning direction and surface contaminants are transported in the scanning direction; and wherein the method is performed in a closed container in a reduced pressure atmosphere, so that residues of condensed vapor or water that are present on the surface behind the point of impingement in the scanning direction at least partially evaporate, thereby at least partially extracting from the workpiece the heat supplied by the jet.

29. The method according to claim 28, wherein the jet is a jet of steam.

30. The method according to claim 28, wherein the surface of the workpiece is dried behind the point of impingement in the same process step.

31. The method according to claim 28, wherein, after the end of the cleaning or cleaning and drying, a temperature of the workpiece differs by no more than 5 K from a temperature of the workpiece before the start of cleaning.

32. The method according to claim 28, wherein the scanning is effected by moving the workpiece and/or at least one nozzle.

33. The method according to claim 28, wherein the scanning takes place over a scan path, which results from superimposing a circular movement and a linear movement.

34. The method according to claim 28, wherein several nozzles are present.

35. The method according to claim 34, wherein the nozzles are arranged in one or more planes around the workpiece.

36. The method according to claim 33, wherein the workpiece is guided in a linear manner past an arrangement with at least one nozzle rotating around an axis parallel to and at a distance from its own axis.

37. The method according to claim 32, wherein the nozzles and/or the workpiece are moved in an oscillating manner.

38. The method according to claim 33, wherein the direction of the linear movement is vertical.

39. The method according to claim 38, wherein the jet forms an angle of between 90 and 135? with the direction of the linear movement.

40. The method according to claim 28, wherein water run-off or water splashes are collected in a sump at the bottom of the container and pumped off.

41. The method according to claim 31, wherein before the cleaning or the cleaning and drying, an aqueous solution of a cleaning agent is applied to the workpiece, preferably by spraying.

42. The method according to claim 41, wherein a surface temperature of the workpiece behind the point of impingement, viewed in scanning direction, is measured in a contactless manner, and the reduced pressure, and a mass flow of said vapor or hot water, are controlled accordingly.

43. The method according to claim 42, wherein after the end of the cleaning or cleaning and drying the temperature of the workpiece differs by no more than 2 K from the temperature before the cleaning.

44. A device for cleaning a surface of a workpiece comprising; a treatment chamber having an opening, which allows the passage of the workpiece to be cleaned and which can be pressure-sealed; a holder for the workpiece, with which the workpiece can be held and moved within the treatment chamber; at least one nozzle arrangement each having one or more nozzles, wherein the holder and the at least one nozzle arrangement can be moved relative to each other; a negative pressure generator of a negative pressure connected to an interior of the treatment chamber; an assembly for generating hot water or steam under increased pressure, the assembly being connected to the nozzles, and means for adjusting the temperature of the hot water or steam and/or means for adjusting a mass flow flowing through the nozzles.

45. The device according to claim 44, wherein the negative pressure generator comprises a vacuum pump and the assembly comprises a vapor generator.

46. The device according to claim 44, further comprising a filter unit through which the negative pressure generator vacuum pump sucks steam with contaminant residues out of the treatment chamber.

47. The device according to claim 46, wherein a further filter stage and/or a separator stage is attached to the filter unit from which recovered cleaning fluid is fed to the assembly for generating hot water or steam in a closed circuit.

48. The device according to claim 44, wherein the means for adjusting the mass flow adjusts the pressure of the water or vapor and/or the flow resistance of lines carrying the water and/or vapor.

49. The device according to claim 44, wherein the nozzle arrangement comprises at least one nozzle rotating around an axis parallel to and/or at a distance from its own axis.

50. The device according to claim 44, wherein the nozzles of a nozzle arrangement are arranged on a nozzle carrier which is rotatable around an axis of rotation directed towards the workpiece and wherein each of the nozzles forms an angle of between 0 and 45?, preferably 0 to 15?, with the axis of rotation, wherein this angle can be the same or different for all the nozzles of this nozzle arrangement.

51. The device according to claim 50, wherein the nozzle carrier has a rotor blade structure.

52. The device according to claim 44, further comprising means for measuring a surface temperature of the workpiece.

53. The device according to claim 52, further comprising a closed-loop control system for the negative pressure and the mass flow flowing through the nozzles based on the measured surface temperature.

54. The device according to claim 44, wherein the holder can be moved into and out of the treatment chamber and comprises a pressure-resistant closure for the opening of the treatment chamber.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0052] The invention is explained in more detail below with reference to the attached drawings by way of example and without limiting the scope of protection.

[0053] FIG. 1 shows a schematic longitudinal section through a device according to the invention according to a first embodiment.

[0054] FIG. 2 shows a schematic side view of the workpiece with the scan path of the device according to FIG. 1 drawn in.

[0055] FIG. 3 shows a schematic cross-section through a device according to the invention according to a second embodiment.

[0056] FIG. 4 shows a schematic side view of the workpiece with scan paths of the device according to FIG. 3 drawn in;

[0057] FIG. 5 shows an alternative exemplary embodiment with recirculation of the cleaning fluid as a simplified flow diagram.

DETAILED DESCRIPTION WITH REFERENCE TO THE FIGURES

[0058] In FIG. 1 a device for performing the method according to the invention is illustrated in a schematic longitudinal section. The device comprises a container 1, which is open at the top and can be sealed in a vacuum-tight manner by a lid 2 with the participation of a gasket 3. The container 1 continues downwards via a connecting tube 13 into a sump container 10. In the container 1, a workpiece 4 to be cleaned is accommodated and is held by a holder. For reasons of clarity, this holder and the feed-through through the container edge needed for performing the optional linear and rotating movement of the workpiece 4 are not shown here, but can be readily added by the person skilled in the art. This holder with the workpiece 4 can perform a rotating movement around an axis 5, as described by the closed arrow 7, at the same time as a linear movement in the direction of the arrow 6, which lies in the axis 5 here. The axis of rotation 5 of the workpiece is oriented in a vertical direction here.

[0059] In the sump container 10, during operation of the device, a sump 11 can form as a result of the runoff of water that may be contaminated, which can be drained off or removed by suction via a sump valve 12.

[0060] In the container 1, a negative pressure can be generated if the pump 20 sucks air out of the interior of the container 1 via the vacuum line 21. The vacuum line 21 can be attached to the sump container 10 or directly to the container 1.

[0061] In the wall of the container 1, a nozzle 27 is installed, which is connected via a line 26 to a generator unit for vapor or hot water. This unit is controllable in terms of the pressure and temperature of the vapor or hot water. The mass flow of the respective medium can also be controlled thereby. The nozzle 27 forms an obtuse angle a of, in this case, e.g. about 110? with the vertical or with the axis 5 of the workpiece. The jet 28 of the medium (vapor or hot water) impinges at virtually the same angle on the surface of the workpiece 4 at a point of impingement.

[0062] In the wall of the container 1, furthermore, an infrared temperature sensor 31 is installed, in which the measurement point 36 on the surface of the workpiece 4 is imaged by an infrared lens on a detector, which emits a signal corresponding to the surface temperature via a measuring line 32. To measure the negative pressure, moreover, a vacuum sensor 30 is installed in the wall of the container 1, which emits a signal corresponding to the negative pressure in the container 1 via a measuring line 33.

[0063] A controller unit 35 receives signals via the measuring lines 32 and 33 and, via the control lines 40 and 41, controls the mass flow of the respective medium emitted by the generation unit 25 such that the temperature measured by the temperature sensor 31 via the measuring line 32 takes a preset target value.

[0064] For the cleaning and drying of a workpiece 4, the container 1 is first opened by removing the lid 2 and the workpiece 4 is brought into the operating position, where it is held in a rotatable and displaceable manner by the holder (not shown). It is initially located in the lower starting position shown with dotted lines. The container 1 is sealed in an airtight manner with the aid of the gasket 3 by putting on the lid 2. The generator unit 25 and the vacuum pump 20 are then switched on via the controller unit 35 and the linear and rotating movement of the workpiece 4 is started. First the end surface of the workpiece 4 is cleaned by the vapor or hot water jet 28 and then the side surface. After the temperature at the measurement point 36, moving across the surface, has been measured by the temperature sensor 31, mass flow and negative pressure are regulated by the controller unit 35 from the initially preset starting values such that the preset target temperature is obtained at the measurement point 36.

[0065] If vapor is used for the cleaning, contaminants on the surface of the workpiece 4 are removed from the surface partly mechanically by the transferred momentum of the vapor jet and also by dispersion in the water resulting from condensation and are entrained by the water. A hot water jet acts in a similar fashion. Some of this water runs along and off the surface of the workpiece 4 and some of it is splashed and lands on the interior wall of the container 1, where it can also run off downwards. Finally, some of the water also remains on the surface, wetting it, and evaporates, extracting heat from the surface. The run-off water passes via the connection 13 into the sump container 10 and forms the sump 11, which can be drained off through the valve 12, e.g. while the container 1 is open for workpiece changeover, or can be pumped off, e.g. continuously.

[0066] FIG. 2 illustrates the progress of the cleaning according to the exemplary embodiment of the invention shown in FIG. 1. As a result of the linear movement of the workpiece 4, the vapor jet or hot water jet first impinges on the side surface of the workpiece 4 at the point of impingement 51 and then migrates along the hypothetical scan path 50 around the workpiece 4 in a helical manner until it has scanned the entire surface. The linear and rotating movements are coordinated such that the workpiece 4 is moved in a linear manner by one stroke h during one rotation. The point of impingement 51, 52 is not punctiform but, because of the oblique position of the nozzle 27, approximately elliptical with the larger axis directed in the vertical direction. As shown by the successively attained points of impingement 52, a certain overlap occurs in the points of impingement in adjacent branches of the scan path 50. This means that the cleaning process is repeated and the cleaning effect is improved. The extent of the overlap can be modified by adjusting the stroke h.

[0067] FIG. 3 shows a diagram of a second embodiment of the device according to the invention in cross-section, wherein only the modified parts are illustrated. In this embodiment, four nozzles 68 are arranged in a plane on the circumference of the container 1 at equal angular separations from each other. These act on the surface of the workpiece 4 simultaneously.

[0068] FIG. 4 illustrates the route of the four scan paths 60 generated by the nozzles 68 of the embodiment shown in FIG. 3 on the surface of the workpiece 4. In this case, the workpiece 4 is moved in a linear manner by the stroke h in 1 turn. Again, the points of impingement 61 of the adjacent scan paths 60 overlap and the extent of the overlap can be adapted by adjusting the stroke as required.

[0069] To demonstrate the cleaning and drying effect, a cylinder head for a car engine was treated according to the invention. A commercial adhesive film was placed on to a smooth, cleaned and dried surface where it adhered firmly over the whole area. In a comparative test with a cylinder head that had been cleaned in a conventional manner with compressed air, the adhesive film could not be attached even to the same smooth area.

[0070] In FIG. 5, parts with identical construction or function are referred to using the same reference signs as in FIGS. 1-4.

[0071] This exemplary embodiment differs primarily in the development of the recirculation circuit by means of which cleaning fluid is recovered from the treatment chamber 1. The vapor clouds generated by the negative pressure and the temperature are sucked out of the treatment chamber 1 by the vacuum pump 20 via a first filter unit 71 and then fed to a downstream second filter and separator stage 72, which comprises an oil separator 74. The outlet of the filter unit 71 opens into the oil separator 74. On the outlet side, the vacuum pump 20 is connected to a condensation unit 73, the return of which likewise opens into the oil separator 74. From a clean tank 75 in the second filter and separator stage 72, via a water pump 76 in a feed line 77, the vapor generator 25 is fed. As a result of the output pressure of the vapor generator 25 and the suction action of the vacuum pump 20, it is ensured that vapor is injected with high dynamic jet pressure. In addition, residual heat from the recovered cleaning fluid is utilized by the circuit according to FIG. 5, so that additional energy savings are achieved. Fresh water is only supplied as necessary based on the losses in the second filter and separator stage 72.

[0072] FIG. 5 also illustrates schematically a holder 78 for the workpiece 4 which can be moved automatically into and out of the treatment chamber on two axes H, V. The holder 78 simultaneously forms a pressure-resistant closure for the opening of the treatment chamber 1 in the operating position.

[0073] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.