GB1591370A - Cleaning methods and apparatus - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO CLEANING METHODS AND APPARATUS (71) I, LARS KRISTOFFER WENDELBO JENSEN, Risdalsvej 2A, 8260 Viby J, Denmark, of Danish nationality, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of gently cleaning large and substantially flat workpieces, such as serigraphic silk-screen frames, and to an apparatus for cleaning such workpieces.

It is well known to effect cleaning of workpieces by means of recirculated cleansing liquid or solvent which through nozzles is sprayed against the workpiece either directly or in connection with soft, rotating brushes. For removal of colourstuff residue on silk-screen frames, after use thereof, it has been customary either to wash the frame by manual brushing with cleansing liquid or to use cleaning machines having rotating brushes and liquid through nozzles.

The manual method is very laborious and involves serious environmental and economic problems due to evaporation of the cleansing liquid. Also in the said cleaning machine a considerable evaporation occurs, because the rotating brushes require much space and because it is difficult to avoid vapour exhaust from this space in connection with the sluicing in and out of the workpieces. Additionally, the rotating brushes are not fully effective in some inner corner portions of the silk-screen frames. The supply of the solvent though nozzles requires a relatively clean solvent for avoiding choking of the nozzles; it is unavoidable, however, that the circulating solvent is contaminated substantially by the colourstuff removed from the workpiece, and normally, therefore, the machines are provided with distillation equipment which contributes to a very high cost level of the known machines.

It is the purpose of the invention to provide a cleaning method of the type referred to, which is effective and advantageous in several respects, e.g. requiring no distillation of the solvent.

According to the invention there is provided a method of gently cleaning large and substantially flat workpieces, such as serigraphic silk-screen frames, wherein the workpiece is supported generally parallel with and close to a free surface of a body of cleaning liquid, and a plurality of paddles are rotated in the liquid and in a plane generally parallel to the free surface thereof to cause the liquid to be splashed against the workpiece over substantially the entire area thereof.

With this method there is no need to move the liquid through nozzles, so it may be used even with a very high degree of contamination. The paddles may work quite close to the workpiece, so no large free space will be required. The paddles splash the liquid against the workpiece in a broad and suitably strong flow for rapid and effective cleaning thereof.

Some types of workpieces such as the said silk-screen frames, however, are difficult to clean solely by the action of the liquid as an extremely strong spraying or splashing would be liable to damage the workpiece. Thus it is desirable to add some type of mechanical treatment corresponding to the known use of brushes. Such a treatment is in fact obtainable in an extremely simple and effective manner in connection with the method according to the invention as it is realized that because the cleaning liquid may be contaminated to practically an unlimited extent, it is - pos- sible to make it artificially "coarse" by adding an amount of macro particles which, when slung against the workpiece together with the solvent, show a considerable mechr anical cleaning effect. The type of these particals, which should of course be nonsoluble in the cleaning liquid; may be chosen to suit the particular cleaning purpose. Experiments have shown that small balls of expanded polystyrene are very efficient, as bv their being thrown turbulently against the workpiece they will both beat and rub the workpiece surface in a gentle but effective manner.

The invention also provides an apparatus for cleaning large and substantially flat workpieces, such as serigraphic silk-screen frames, comprising means defining a space adapted to contain a body of liquid having a free surface, means for supporting a workpiece in a cleaning position close and generally parallel to said free liquid surface, and a plurality of rotary paddles arranged to rotate generaly in a common plane substantially parallel to said free liquid surface and within said liquid, whereby, in use, rotation of said paddles causes liquid to be splashed against the workpiece.

This apparatus may be very simple in design, a.o. because it will normally need no distillation equipment. After use the contaminated cleaning liquid may normally be cleaned sufficiently by precipitation of the impurities e.g. by standing overnight.

In a preferred embodiment of the invention the body of cleansing liquid consists of a volume of liquid contained in a substantially flat vat and having a free upper surface. In an alternative embodiment there is a falling body or blanket of liquid with a free surface from which liquid is splashed by the rotary paddles.

In the following the invention is described in more detail with reference to the accom p,anying drawing, in which: Fig. 1 is a perspective view of an apparatus according to the invention, and Fig. 2 is a sectional view of a corresponding, though slightly modified apparatus shown filled with solvent.

The apparatus comprises a flat, upper vat 2 supported by legs 4 and slightly below its top edge provided with a horizontal carrier grate structure 6 on which the article or articles to be cleaned can be placed, e.g.

a silk-screen frame and (in a carrier basket not shown) various printing tools such as wipers and scrapers. In the bottom of the vat is arranged a number of rotors 8 having horizontally projecting paddle blades 10 rotating with vertical shafts 12, which (see Fig. 2) are let down through raised dome shaped portions 14 of the bottom 16. At their lower ends the shafts 12 are provided with chain wheels 18 driven by a common chain 20 by a motor 22. The vat is covered by a lid 24 shown in dotted lines in Fig. 1, and preferably constructed such that a front portion thereof may be swung up sufficiently to allow the cleaning articles to be taken in and out; Holding means (not shown) may be arranged to temporarily hold the lid in an inclined, open position allowing the articles to be taken in and out, without giving rise to any consideable vapour outlip from the vat.

Underneath the vat 2 is arranged a tank 26 for solvent, which is feedable to the vat through a pipe 28 and a pump P. The vat has a bottom outlet 30 connected to the top of the tank via a valve 32 with valve handle 34 (Fig. 1) and a pipe 36. In the bottom of the tank 26 is mounted a sludge tray 38 which may be lifted off from the tank for being emptied, the tank being closed by a removable lid 40. Moreover, an overrun connection (not shown) may be established from the vat to the tank.

When the apparatus is to be used practically the entire volume of solvent in the tank 26 is pumped up into the vat in which the liquid level will be flush with or slightly above the level of the paddle blades 10. The workpiece to be cleaned is laid on the grate 6, and the motor 22 is started, whereby the paddle blades will splash solvent upwardly against the workpiece. Preferably the workpiece or -pieces should not entirely cover the grate 6, so that some solvent is even splashed up in the space between the lid and the top side of the workpiece to cause ia cleaning effect also on said top side by the violent turbulence of the solvent slung up by the paddle blades. In case of a silk-screen frame the side thereof having faced the printed surface by the printing operation will not normally need any high amount of cleaning, and when this side is oriented upwardy on the grate 6 the frame will normally be clensable in a satisfactory manner without being turned on the grate.

As mentioned, it is an important aspect of the invention that the cleaning liquid may be used in admixture with an amount of lightweight macro particles which are in Fig.

2 shown floating in the surface of the solvent and designated 46. It is preferred to make use of balls of expanded polystyrene, e.g. in an amount of some 3 kg per m3 solvent. The balls may have a diameter of e.g.

5-25 mm, and for the cleaning of silkscreen frames it has proved advantageous to use equal amounts of balls having diameters of 10 mm and 20 mm, respectively. The large balls seem to give the best cleaning effect, but the smaller balls are desirable for extending the improved cleaning to areas adjacent inner corners of the frame structure.

The balls show a gentle, yet so efficient cleaning action that the cleaning of a usual silk-screen frame can be done in few minutes, while the standard for the known, more expensive cleaning machines is 1S 20 minutes.

The liquid and balls slung up by the paddle blades will fall back again direct into the vat, so in operation there is no circulation through pipes, nozzles or filter. The vat itself may be shaped as a flat structure, as the distance from the paddle blades 10 up to the top side of the grate 6 need not be more than some 5-10 cm. This in its turn means that solvent evaporation may be kept at a minimum.

Several articles may be cleaned consecutively while the solvent is present in the vat 2, but from time to time, normally at the end of the working day, the solvent (and most of the balls) is caused to be moved back to the tank 26 by opening of the valve 32 and to remain there for some hours, normally overnight. Hereby at least a considerable part of the cleaned off material gets the opportunity to precipitate into the bottom tray 38, which may periodically be taken out and emptied. Seldom, of course, the solvent will hereby be completely cleaned, but as mentioned it is not at all important that it is particularly clean in normal operation.

The invention is not limited to the embodiment shown, as for instance the apparatus may be designed according to the tunnel princip]e, for treating articles moving through the tunnel. The solvent and the said particles or balls should not necessarily be slung upwardly from a horizontal bath, but e.g. outwardly from a falling "blanket" of liquid. The sludge tank 26 may be wheel supported and connected to the vat through flexible hoses so las to be easily drawn out for emptying of the bottom tray 38. Besides, the tank may be placed as desired, even above the vat when the pump and the downlet valve are suitably arranged.

WHAT I CLAIM IS:- 1. A method of gently cleaning large and substantially flat workpieces, such as serigraphic silk-screen frames, wherein the workpiece is supported generally parallel with and close to a free surface of a body of cleaning liquid, and a plurality of paddles are rotated in the liquid and in a plane generally parallel to, the free surface thereof to cause the liquid to be splashed against the workpiece over substantially the entire area thereof.

2. A method according to claim 1, characterized by the use of a cleaning liquid to which is added an amount of lightweight macro particles which are non-soluble in the liquid.

3. A method according to claim 1 or 2, wherein the macro particles comprise balls of expanded polystyrene.

4. An apparatus for cleaning large and substantially flat workpieces, such as serigraphic silk-screen frames, comprising means defining a space adapted to contain a body of liquid having a free surface, means for supporting a workpiece in a cleaning position close and generally parallel to said free liquid surface, and a plurality of rotary paddles arranged to rotate generally in a common plane substantially parallel to said free liquid surface and within said liquid, whereby, in use, rotation of said paddles causes liquid to be splashed against the workpiece.

5. An apparatus according to claim 4, characterized in that it comprises a substantially flat vat covered by a lid and adapted to receive a cleaning liquid up to a predetermined level, a number of motor driven paddles are located in the vat and have horizontal paddle blades located approximately at said predetermined level and mounted on vertical shafts so as to be rotatable to splash liquid upwardly, and said supporting means comprises an open carrier grate structure mounted horizontally at a level between the paddles and the lid.

6. An apparatus according to claim 5, characterized in that the vat is connected with a liquid tank through pump and valve means in such a manner that at least substantially the entire volume of cleaning liquid is transferably between the vat and the tank, the tank being provided with means such as a removable bottom tray for enabling removal of precipitations therefrom.

7. An apparatus according to any one of the claims 4 to 6, characterized in that cleaning liquid contained thereby has added thereto an amount of lightweight macro particles.

8. An apparatus according to claim 7, wherein the macro particles comprise balls of polystyrene.

9. A method of cleaning large and substantially flat workpieces, substantially as herein described with reference to the drawings.

10. An apparatus for cleaning workpieces substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. means that solvent evaporation may be kept at a minimum. Several articles may be cleaned consecutively while the solvent is present in the vat 2, but from time to time, normally at the end of the working day, the solvent (and most of the balls) is caused to be moved back to the tank 26 by opening of the valve 32 and to remain there for some hours, normally overnight. Hereby at least a considerable part of the cleaned off material gets the opportunity to precipitate into the bottom tray 38, which may periodically be taken out and emptied. Seldom, of course, the solvent will hereby be completely cleaned, but as mentioned it is not at all important that it is particularly clean in normal operation. The invention is not limited to the embodiment shown, as for instance the apparatus may be designed according to the tunnel princip]e, for treating articles moving through the tunnel. The solvent and the said particles or balls should not necessarily be slung upwardly from a horizontal bath, but e.g. outwardly from a falling "blanket" of liquid. The sludge tank 26 may be wheel supported and connected to the vat through flexible hoses so las to be easily drawn out for emptying of the bottom tray 38. Besides, the tank may be placed as desired, even above the vat when the pump and the downlet valve are suitably arranged. WHAT I CLAIM IS:-

1. A method of gently cleaning large and substantially flat workpieces, such as serigraphic silk-screen frames, wherein the workpiece is supported generally parallel with and close to a free surface of a body of cleaning liquid, and a plurality of paddles are rotated in the liquid and in a plane generally parallel to, the free surface thereof to cause the liquid to be splashed against the workpiece over substantially the entire area thereof.

2. A method according to claim 1, characterized by the use of a cleaning liquid to which is added an amount of lightweight macro particles which are non-soluble in the liquid.

3. A method according to claim 1 or 2, wherein the macro particles comprise balls of expanded polystyrene.

4. An apparatus for cleaning large and substantially flat workpieces, such as serigraphic silk-screen frames, comprising means defining a space adapted to contain a body of liquid having a free surface, means for supporting a workpiece in a cleaning position close and generally parallel to said free liquid surface, and a plurality of rotary paddles arranged to rotate generally in a common plane substantially parallel to said free liquid surface and within said liquid, whereby, in use, rotation of said paddles causes liquid to be splashed against the workpiece.

5. An apparatus according to claim 4, characterized in that it comprises a substantially flat vat covered by a lid and adapted to receive a cleaning liquid up to a predetermined level, a number of motor driven paddles are located in the vat and have horizontal paddle blades located approximately at said predetermined level and mounted on vertical shafts so as to be rotatable to splash liquid upwardly, and said supporting means comprises an open carrier grate structure mounted horizontally at a level between the paddles and the lid.

6. An apparatus according to claim 5, characterized in that the vat is connected with a liquid tank through pump and valve means in such a manner that at least substantially the entire volume of cleaning liquid is transferably between the vat and the tank, the tank being provided with means such as a removable bottom tray for enabling removal of precipitations therefrom.

7. An apparatus according to any one of the claims 4 to 6, characterized in that cleaning liquid contained thereby has added thereto an amount of lightweight macro particles.

8. An apparatus according to claim 7, wherein the macro particles comprise balls of polystyrene.

9. A method of cleaning large and substantially flat workpieces, substantially as herein described with reference to the drawings.

10. An apparatus for cleaning workpieces substantially as herein described with reference to the accompanying drawings.