NZ248623A

NZ248623A - Cleaning electronic equipment: use of pressure vessel containing solvent

Info

Publication number: NZ248623A
Application number: NZ24862393A
Authority: NZ
Inventors: Wayne Stephen Webley; Dennis Michael Robinson
Original assignee: Electrical Salvage Nz Ltd
Priority date: 1993-09-09
Filing date: 1993-09-09
Publication date: 1996-11-26
Also published as: WO1995007153A1; AU7667094A

Description

248 62 Patents Form No. 5 No. 248623 Date: 9th September 1993 Patents Act 1953 COMPLETE SPECIFICATION METHOD OF CLEANING EQUIPMENT We, Electrical Salvage (NZ) Limited, of 14 Motueka Street, Nelson, New Zealand, a New Zealand company, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 248623 The present invention relates to a method of cleaning equipment, especially complex equipment the interior of which has been badly contaminated or dirtied, At present, this type of equipment, if it can be cleaned at all, is cleaned by wholly or partially dismantling the equipment, cleaning the parts using known washing or spraying techniques, and reassembling the parts. This process generally is expensive and time-consuming and requires a great deal of skilled labour.

It is an object of this invention to provide a method of cleaning complex equipment whereby the equipment does not need to be dismantled or whereby the degree of dismantling of the equipment is greatly reduced.

The present invention is especially useful for cleaning electrical or electronics equipment which has been salvaged from sunken vessels and is deeply contaminated by sea-water. The invention will be described with especial reference to this application, but it will be appreciated that the method of the invention may be applied to the cleaning of a wide variety of different articles and to a wide range of different types of contamination.

The present invention provides a method of cleaning equipment comprising immersing the equipment to be cleaned in a liquid solvent and then subjecting said equipment to a plurality of cycles of pressure variations in a sealed pressure vessel and/or to a plurality of cycles of temperature variations, returning said pressure and/or temperature to ambient conditions and removing said equipment from said solvent.

A method of cleaning equipment including the steps of: (1) Providing a pressure vessel; 248 6 23 (2) Placing the equipment to be cleaned in the vessel and immersing the equipment in a liquid solvent; (3) Sealing the pressure vessel and applying to the contents of the pressure vessel a plurality of cycles of pressure variations, each said cycle comprising increasing and/or decreasing the pressure in said pressure vessel relative to atmospheric pressure, and then returning said pressure to atmospheric pressure; (4) Removing the equipment from the vessel.

It is believed that the pressure variations have the effect of drawing the solvent deeply into and through the equipment, so that a majority of contaminants are removed. The pressure variations effectively "pump" the solvent in and out of the equipment, removing contamination in the process.

The cycles of pressure variation may constitute an increase in pressure over atmospheric pressure followed by a drop back to atmospheric pressure or a decrease in pressure below atmospheric pressure followed by a rise back to atmospheric pressure. A further possibility is that the pressure variation can be between below atmospheric pressure and above atmospheric pressure. The size of the pressure variation and the number of cycles of pressure variation are selected by experiment to suit the article being cleaned and the nature and extent of the contamination.

A method of cleaning equipment including the steps of: (1) providing a vessel; (2) placing the equipment to be cleaned in the vessel and subjecting said equipment to a plurality of cycles of temperature variation, each cycle comprising first immersing the equipment to be cleaned in a liquid solvent at a --,V J ■. . -s* * *r"\ 3 \ 11 KT ^35 \ 24 8 6 predetermined above-ambient temperature, heating said vessel for a time sufficient to allow said equipment to reach said predetermined temperature, and immersing said equipment at said predetermined temperature in a liquid solvent at a lower temperature; (3) returning said equipment to ambient temperature and removing said equipment from the solvent.

The equipment being cleaned may be immersed in the lower-temperature solvent eg. by draining the hot solvent out of the vessel and replacing it with lower-temperature solvent, or by lifting the equipment out of the hot solvent and placing it in the lower-temperature solvent.

It is believed that the cooling of the equipment in the lower-temperature solvent draws solvent deeply into the equipment, and so gives very thorough cleaning.

Preferably, the temperature variation cycle is repeated a number of times eg. 15.

Both temperature and pressure variation cycles may be used alone or in combination i.e. the solvent in the pressure vessel may be varied in pressure and also raised and lowered in temperature.

The solvent may be at any temperature at which the solvent remains predominantly liquid throughout the pressure cycle, providing that the solvent temperature is not so high as to damage the article being cleaned. Obviously, the maximum desirable temperature must be selected after consideration of the materials of the various components of the article to be cleaned.

However, providing the solvent temperature is not so high as to cause 24 8 6 damage, the higher the solvent temperature, the more rapid and effective the cleaning process.

The solvent preferably is water, but may be any of a wide range of suitable solvents for example petrochemical based electrical cleaning solvents such as 'Castrol Techniclean EMC (Trade Mark) or 'Gamlen Solvent 265 B' (Trade Mark). If a flammable solvent is used, then the solvent temperature selected must be below the flashpoint of that solvent.

The solvent is selected with reference to the type of contamination to be cleaned. For example, for removing sea-water contamination, water, with possibly some detergent added, is an effective solvent. However, if heavy oil or grease contamination has to be removed, then a petrochemical-based solvent would be preferable.

The solvent may contain detergents and/or surfactants or other cleaning products dissolved therein, as appropriate for the type of contamination to be removed. A typical suitable detergent is 'Calpol' (Trade Mark) which is an aqueous solution of predominantly anionic detergent materials with some non-ionic components.

The equipment may be washed down and/or pre-cleaned with a solvent to remove surface dirt and grease before placing the equipment in the pressure vessel.

By way of example only, preferred embodiments of the present invention are described in detail, with reference to the accompanying drawing, which shows a diagrammatic side view of a pressure vessel.

Referring to the drawing, in a first embodiment of the invention, f T $4Q 6 2 equipment to be cleaned (eg an electric motor which has been submerged in sea-water) is first flushed for ten hours in clean running water and cleaned externally with a grease solvent, in known manner.

The equipment is then placed in a pressure vessel 2 and covered with water at about 35 °C. The water contains a detergent ('Calpol') at a concentration of about 0.1% by volume.

The pressure vessel 2 comprises a generally cylindrical body 3 with a bolted-on lid 4. The body 3 is fitted with a drain 5 at the base. Inlet and outlet pipes 7, 8, are connected to the body 3 near the base. The inlet 7 is connected to a fluid reservoir via a heater and fluid pump of known type (not shown), and the outlet 8 may be connected to waste or in a closed cycle to the fluid reservoir.

A pressure gauge 9 is connected to the lid 4 and also to a pipe 10 connected to a source of vacuum or to a compressor (not shown).

Once the equipment is in the vessel 2 and covered with water, the vessel 2 is evacuated via the pipe 10, to a pressure of -20" Hg (inches of mercury) over a period of 10 minutes, and is then allowed to return to atmospheric pressure. This pressure cycle is repeated 35 times.

The water-and-detergent solution in the vessel is then drained off and replaced by clean water at about 35 °C, and the pressure cycle is repeated a further 35 times. The vessel is drained of water, refilled with clean water at about 35" C, and the pressure cycle is repeated about 35 times. The water is drained from the vessel and vacuum may be applied once more, to remove any residual water from the equipment. Alternatively, once the water is drained, the cleaned equipment is removed and allowed to drain. 6 248623 In an alternative method in accordance with the present invention, the equipment is cleaned by subjecting it to a cycle of temperature variation, either alone or in combination with the cycle of pressure variation.

In this method, the equipment to be cleaned is placed in a vessel (which may be the pressure vessel 2) and is immersed in a solvent heated to a predetermined optimum temperature. The nature of the solvent and its temperature are selected as described above. Alternatively, the equipment may be immersed in solvent at ambient temperature, and the solvent and the equipment heated together. Heat is applied to the vessel for as long as is necessary to raise the equipment to said predetermined temperature. If the solvent used is water, said predetermined temperature typically is about 95 °C.

The heated equipment is then immersed in solvent at a lower temperature than said predetermined temperature, (typically at least 50 ° C lower) either by draining the hot solvent from the vessel and replacing it with the lower-temperature solvent, or by lifting the equipment out of the hotter solvent and immersing it in the cooler solvent in a separate vessel. The cooling draws solvent deeply into the equipment, giving very thorough cleaning. Preferably, the temperature variation cycle is repeated eg. 15 times before the equipment is returned to ambient temperature.

The equipment is then thoroughly dried in an oven at a temperature selected to be as high as possible without damaging the equipment e.g. a temperature of 250 "C for 10 hours. The equipment is then re-finished if necessary.

The cleaning is now completed and the cleaned equipment is tested in *48623 known manner to ensure it is working normally.

If the equipment normally is finished with a protective finish, then the cleaned and dried equipment is re-finished before being put back into service, using the type of finish normally applied to that type of equipment:- e.g. a printed circuit board would be re-coated; an electric motor armature would be revarnished and baked.

The efficiency of the cleaning process is tested primarily by tests showing that the cleaned equipment is functioning satisfactorily. For example, if the equipment is electrical equipment, the equipment is electrically tested. In the example given above, the electrical insulation resistance between each winding and the frame of the alternator, as well as the resistance between windings, was measured at an applied voltage of 500 volts D.C., and was found to be in excess of 50 million ohms. The operation of the alternator was tested under maximum rated load, and was found to be well within specification with regard to output voltage and current.

The efficiency of the cleaning also is tested by analysing samples of the final rinsing water for chloride ion content, in the case of sea water contamination. Test results for the example given above showed that the chloride ion level in the final rinse water was 8 parts per million.

It will be appreciated that the type of contamination governs the contaminant to be tested for. To establish the correct cleaning sequence for a specific item of equipment contaminated in a specific way, the equipment is cleaned using a short flushing time, a suitable solvent, and a few short pressure or temperature cycles. The solvent drained from the vessel is tested for the 8 2<0 62j appropriate contaminant, and the cleaning time, solvent temperature, solvent additives, and number and intensity of pressure or temperature cycles are adjusted as necessary until the contaminant level drops to an acceptable level. 248623

Claims

WHAT WE CLAIM IS:

1. A method of cleaning equipment comprising immersing the equipment to be cleaned in a liquid solvent and then subjecting said equipment to a plurality of cycles of pressure variations in a sealed pressure vessel and/or to a plurality of cycles of temperature variations, returning said pressure and/or temperature to ambient conditions and removing said equipment from said solvent.

2. A method of cleaning equipment including the steps of: (1) Providing a pressure vessel; (2) Placing the equipment to be cleaned in the vessel and immersing the equipment in a liquid solvent; (3) Sealing the pressure vessel and applying to the contents of the pressure vessel a plurality of cycles of pressure variations, each said cycle comprising increasing and/or decreasing the pressure in said pressure vessel relative to atmospheric pressure, and then returning said pressure to atmospheric pressure; (4) Removing the equipment from the vessel.

3. The method as claimed in Claim 1 or Claim 2 wherein the or each pressure cycle comprises a pressure of at least 20 inches of mercury above or below atmospheric pressure. 248623

4. The method as claimed in Claim 2 or Claim 3 wherein after step (3) and before step (4), the solvent is drained from the pressure vessel and the pressure vessel is refilled with solvent and said pressure cycle is reapplied.

5. The method as claimed in any preceding claim wherein at least 35 pressure cycles are applied.

6. The method as claimed in Claim 4 wherein said solvent in step (2) is water to which a detergent and/or surfactant has been added and said solvent in said step between said steps (3) and (4) is water.

7. The method as claimed in Claim 6 wherein said solvent is at a temperature of 35°C.

8. A method of cleaning equipment including the steps of: (1) providing a vessel; (2) placing the equipment to be cleaned in the vessel and subjecting said equipment to a plurality of cycles of temperature variation, each cycle comprising first immersing the equipment to be cleaned in a liquid solvent at a predetermined above-ambient temperature, heating said vessel for a time sufficient to allow said equipment to reach said predetermined temperature, and immersing said equipment at said predetermined temperature in a liquid solvent at a lower temperature; (3) returning said equipment to ambient temperature and removing said ,,."c 11 », \ -j '?-■ > "•'*' "";1Of.l \;equipment from the solvent.;248;

9. The method as claimed in Claim 8 wherein said equipment is immersed in said lower-temperature solvent by draining from the vessel the solvent at said ip* predetermined temperature and replacing it with solvent at said lower temperature.

10. The method as claimed in Claim 8 wherein said equipment is immersed in said lower-temperature solvent by removing said equipment from said vessel, placing said equipment in a further vessel, and immersing said equipment in said lower-temperature solvent.

11. The method as claimed in any one of Claims 8-10 wherein said cycle of temperature variation is repeated at least 15 times.

12. The method as claimed in any one of Claims 8-11 wherein said predetermined temperature is 95 °C and said lower temperature is 45 °C.

13. The method as claimed in any one of Claims 2, 4, and 6-12 inclusive wherein before said step (2), the equipment to be cleaned is flushed with a stream of solvent.

14. The method as claimed in any one of Claims 2,4, and 6-13 inclusive wherein before step (2) the exterior surfaces of said equipment are cleaned with a solvent. 24 8 6 23

15. The method as claimed in any preceding claim wherein said solvent is water.

16. The method as claimed in any one of Claims 1-14 wherein said solvent is water to which a detergent and/or surfactant has been added.

17. The method as claimed in any preceding claim wherein said solvent is a petrochemical-based solvent.

18. A method of cleaning equipment as claimed in Claim 2 and substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

19. A method of cleaning equipment as claimed in Claim 8 and substantially as hereinbefore described. ELECTRICAL SALVAGE (NZ) LIMITED. By Their authorised agents, P.L. BERRY & ASSOCIATES. 13