WO1992007452A1 - Reusing liquids in a liquid cleaning apparatus - Google Patents

Reusing liquids in a liquid cleaning apparatus Download PDF

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Publication number
WO1992007452A1
WO1992007452A1 PCT/CA1991/000352 CA9100352W WO9207452A1 WO 1992007452 A1 WO1992007452 A1 WO 1992007452A1 CA 9100352 W CA9100352 W CA 9100352W WO 9207452 A1 WO9207452 A1 WO 9207452A1
Authority
WO
WIPO (PCT)
Prior art keywords
tank
water
liquid
liquid cleaning
cleaning agent
Prior art date
Application number
PCT/CA1991/000352
Other languages
French (fr)
Inventor
John Gileta
Alan S. Roberts
Original Assignee
Electrovert Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Electrovert Ltd. filed Critical Electrovert Ltd.
Publication of WO1992007452A1 publication Critical patent/WO1992007452A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K3/00—Tools, devices, or special appurtenances for soldering, e.g. brazing, or unsoldering, not specially adapted for particular methods
    • B23K3/08—Auxiliary devices therefor
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G5/00—Cleaning or de-greasing metallic material by other methods; Apparatus for cleaning or de-greasing metallic material with organic solvents
    • C23G5/02—Cleaning or de-greasing metallic material by other methods; Apparatus for cleaning or de-greasing metallic material with organic solvents using organic solvents
    • C23G5/04—Apparatus
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/22—Secondary treatment of printed circuits
    • H05K3/26—Cleaning or polishing of the conductive pattern
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/07—Treatments involving liquids, e.g. plating, rinsing
    • H05K2203/0779—Treatments involving liquids, e.g. plating, rinsing characterised by the specific liquids involved
    • H05K2203/0783—Using solvent, e.g. for cleaning; Regulating solvent content of pastes or coatings for adjusting the viscosity
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/15—Position of the PCB during processing
    • H05K2203/1509—Horizontally held PCB

Definitions

  • the present invention relates to liquid cleaning devices for cleaning work pieces such as printed circuit boards and the like upon which electric components have been soldered. More specifically, the present invention relates to a liquid cleaning apparatus utilizing a liquid cleaning agent with a density less than water. The improvement relates to reusing the cleaning liquid agent and water in a closed loop configuration.
  • Printed circuit boards and the like that have been soldered have deposits from flux resins and the like on the soldered surfaces which must be removed. Liquid cleaning agents are generally used for removal of such deposits, however many of the cleaning agents used today are either flammable or explosive when sprayed in the air. Furthermore, liquid cleaning agents cannot be dumped or discharged into normal sewage or draining systems because of contamination and pollution problems.
  • One cleaning agent used for cleaning circuit boards is a terpene based solvent.
  • the solvent is used in an enclosed cleaning machine and in some instances inert gas is provided within the enclosure to prevent fire or explosion.
  • inert gas is provided within the enclosure to prevent fire or explosion.
  • One example of a method and apparatus for cleaning work pieces is disclosed in copending Application Serial No. 456,108, filed December 22, 1989.
  • work pieces are conveyed on a conveyor down into a tank of solvent or water.
  • the work pieces rise up out of the tank into an enclosed area with liquid seals on both sides and they are sprayed with high pressure water jets within this enclosed area. Gas and vapors are contained within this enclosed area and can not escape through the entrance or the exit of the apparatus.
  • solvent sprays are immersed within the tank containing the solvent.
  • liquid cleaning agent includes any detergent, liquid saponifier or solvent that has a density less than that of water and when placed in a tank or container separates into a top layer and a bottom layer.
  • the liquid cleaning agent generally forms the top layer and the water forms the bottom layer. It would be feasible to reverse this and provide a liquid cleaning agent that was denser than water. In this situation, water would remain in the top layer and the liquid cleaning agent on the bottom layer.
  • the recycled liquids are passed through filters, strainers or the like during recycling to remove particulate material and other deposits removed from work pieces.
  • the predetermined ratio is such that the input feed to the distillation maintains both liquids in the desired proportions.
  • a still further aim of the present invention is to provide a liquid cleaning device having a liquid cleaning agent tank for initial immersion of work pieces and a final water tank for washing the liquid cleaning agent off the work pieces before they exit from the cleaning device.
  • Both the liquid cleaning agent tank and the water tank cascade inwards to a central cascade tank where the liquid cleaning agent and the water separate into two layers, one above the other, due to their different densities.
  • Some liquid cleaning agent maybe recirculated back to the liquid cleaning agent tank from the cascade tank and some water from the cascade tank maybe circulated back to the water tank. Thus recirculation of both the cleaning agent and the water occurs.
  • the present invention provides in a liquid cleaning apparatus for cleaning work pieces, including a cleaning tank for containing a liquid cleaning agent having a different density to water and being separable therefrom, a water tank, an enclosure means containing the cleaning tank and the water tank, and means for conveying work pieces from an entrance to an exit of the enclosure, passing the work pieces through the cleaning tank and the water tank, the improvement of a closed loop system for cleaning the liquid cleaning agent and water comprising; cascade tank between the cleaning tank and the water tank, to receive liquid cleaning agent and water from the two tanks, metering means to meter a predetermined flow of liquid cleaning agent from the cascade tank, and a predetermined flow of water from the cascade tank, evaporator means to evaporate metered liquid cleaning agent and metered water together, condenser means to condense vapor from the evaporator means, decanter tank means for condensate from the condenser means adapted to separate water and liquid cleaning agent into layers determined by density in the decanter tank means, and pump means to pump liquid cleaning agent
  • a process of cleaning work pieces in a liquid cleaning apparatus whenever the work pieces are immersed in a first liquid followed by immersion in a second liquid, the first and second liquids being separable and having different densities, the improvement of recycling the first and second liquids comprising the steps of : metering a portion of the first liquid, metering a portion of the second liquid, combining the two portions, distilling the combined portions to a vapor gas phase, and condensing the vapor gas to liquid phase and separating the first liquid from the second liquid.
  • a process of cleaning work pieces in a liquid cleaning apparatus wherein the work pieces are immersed in a liquid cleaning agent within an enclosure, the liquid cleaning agent having a different density to water and being separable therefrom, and subsequently immersed in water prior to drying
  • the improvement of recycling the liquid cleaning agent and water comprising the steps of: cascading liquid cleaning agent from a cleaning tank into a cascade tank, and filtering and pumping a portion of the liquid cleaning agent in the cascade tank back into the liquid cleaning tank, cascading water from a water tank to an intermediate tank, and from the intermediate tank into the cascade tank, and filtering and pumping a portion of the water from the cascade tank back to the water tank, metering a further portion of the liquid cleaning agent from the cascade tank and a further portion of the water from the cascade tank to provide a combined predetermined ratio flow of liquid cleaning agent and water, distilling the combined predetermined ratio flow to a vapor gas phase, condensing the vapor gas to liquid cleaning
  • Figure 1 is a schematic view showing a liquid cleaning device according to one embodiment of the invention.
  • FIG 2 is a schematic view showing the recycling arrangement for liquid cleaning agent and water suitable for the cleaning device illustrated in Figure 1.
  • a liquid cleaning device is illustrated in Figure 1 wherein a conveyor 10 moves work pieces such as printed wiring boards, circuit boards and the like that have electrical components soldered thereon, through an enclosure 12 initially passing through a cleaning tank 14 which contains a liquid cleaning agent such as a detergent, liquid saponifier, solvent or the like.
  • the cleaning agent has a density generally less than water, but in some cases more than water, providing the density is not the same as water.
  • the cleaning agent is a terpene based liquid solvent. This solvent is flammable or explosive when sprayed in air and therefore sprays 16 are provided, immersed within the cleaning tank 14.
  • a pump 18 and filter 20 circulate solvent from the cleaning tank 14 through line 22, passing to the spray 16 which spray above and below the conveyor 10.
  • the cleaning tank 14 cascades into a cascade tank
  • the conveyor 10 conveys work pieces over the cascade tank 24 through water sprays 26 positioned above an intermediate tank 28.
  • a pump 30 and filter 32 collect water from the intermediate tank 28 and recirculate water through line 34 to the sprays 26. Most water from the sprays 26 drains back into the intermediate tank 28 which in turn overflows into the cascade tank 24.
  • a first liquid seal divider 36 is positioned above the cleaning tank 14.
  • the work pieces are conveyed on the conveyor 10 under the first liquid seal divider 36 to provide an enclosed area 38 in which the water sprays 26 operate. Thus any vapor from the sprays 26 is contained within the enclosure 38.
  • the conveyor 10 enters a water tank 40, passing under a second liquid seal divider 42 to complete the enclosed area 38.
  • the conveyor 10 then passes up through a dryer section 44 where steam jets 46 assist in blowing water droplets off the work pieces on the conveyor 10.
  • a dehumidifier 47 similar to that shown in copending application filed August 28, 1990, removes moisture and solvent vapor from the system for complete recycling. Substantially dry and clean gas only exits at stack 48.
  • the water tank 40 cascades or overflows into the intermediate tank 28 which in turn cascades or overflows into the cascade tank 24.
  • the liquid cleaning agent from cleaning tank 14 cascades into the cascade tank 24 from one side and water from the water tank 40 and the intermediate tank 28 cascades into the cascade tank 24 from the other side.
  • the liquid cleaning agent which is solvent in this particular case, separates from the water.
  • the solvent being lighter, forms a top layer and the water a bottom layer.
  • a liquid cleaning agent pump 50 collects liquid cleaning agent from the top layer of the cascade tank 24 through line 52, passes through filter 54 and pumps the liquid cleaning agent into the cleaning tank 14.
  • a water pump 56 collects water from the lower layer of the cascade tank 24 through line 58, passes it through a filter 60 and into the intermediate tank 28.
  • a pump 62 collects water from the intermediate tank 28 in line 64, passes it through filter 66 into the water tank 40.
  • the cascading effect may be intermittent by running the pumps at intervals with no cascading or pumping occurring when the pumps are turned off. Alternatively, the pumps maybe run continuously to provide a continuous cascading effect.
  • the filters provided in the system remove particulate matter and the like that circulate through the pumps. Whereas filters are defined as such throughout the specification, the term can include strainer and other devices that assist in removing particulate matter and the like.
  • the filters are generally placed before the pumps to avoid passing particulate material through the pumps.
  • Filter 66 maybe a carbon type filter to remove rosins and organic matter and thus improve the purity of water in the water tank 40. Carbon type filters may also be used elsewhere in the system where appropriate to remove rosins and other particulate material from the recirculating liquids.
  • a drain from the bottom of the cleaning tank 14 has a solenoid valve 68 therein and a line 70 connects to line 58 circulating water from the cascade tank 24 to the intermediate tank 28. Opening the solenoid valve 68 permits accumulated water in the cleaning tank 14 to be pumped through the filter 60 and recirculated to the water in the intermediate tank 28.
  • a line maybe provided to recirculate the accumulated water to the cascade tank 14.
  • liquid cleaning agent line 72 collects liquid cleaning agent from the top layer of the cascade tank and a water line 74 collects water from the lower layer of the cascade tank 24.
  • liquid cleaning agent line 72 passes through a metering pump 76 after a filter 78.
  • the water line 74 passes through a water metering pump 80 after a filter 82.
  • the metering pumps allow metered flows of the liquid cleaning agent and water to be pumped from the cascade tank 24.
  • the liquid cleaning agent and water are mixed after the metering pumps 76 and 80 in line 84 and pass to a still or evaporator 86.
  • the metered feed to the still 86 permits the desired ratio of liquid cleaning agent and water in the boiling sump of the still 86.
  • the desired ratio allows co-distillation of both the liquid cleaning agent and water in some cases this is at a temperature not normally exceeding the boiling point of water or the liquid cleaning agent. In the case of a terpene based solvent, the lower temperature provides safer distillation and avoids possible thermal decomposition.
  • a mixing arrangement is required to ensure that terpene and water remain mixed in the still.
  • a circulating pump 87 is shown in Figure 2 which takes the solvent and water in the still 86 and sprays the mixture through immersed jets or nozzles back into the still 86 to ensure the terpene and water do not separate.
  • Other mixing devices such as mechanical skimmers may also be provided to agitate the mixture and ensure separation does not occur.
  • Terpene and water evaporate in the still 86.
  • the feed of terpene and water are controlled at a preset ratio to ensure both liquids are always present in the sump and one or other does not get depleted through the distill action process.
  • Some flux residues and other deposits do not distill and remain in the boil sump and are drained away through drain 88 or are otherwise periodically removed.
  • a program of cleaning the still is required at predetermined intervals to ensure that the residues and deposits remaining therein are removed.
  • a condenser 90 and the condensed products, namely water and liquid cleaning agent are fed into a decanter tank 92.
  • the liquid cleaning agent or terpene rises to the top layer and the water settles to the bottom layer.
  • Condensed water and liquid cleaning agent from the dehumidifier 47 above the dryer section 44 drains through line 93 into the decanter tank 92.
  • the terpene is then pumped through line 94 back into the cleaning tank 14 as shown in Figure 1 and the water is pumped through water line 96 back to the water tank 40 shown in Figure 1.
  • a steam generator, 98 shown in Figure 1 takes a portion of the water from line 96 for the steam jets 46.
  • terpene When terpene is used as the liquid cleaning agent, there is sometimes a requirement for a nitrogen blanket in both the still 86 and the decanter 92 to avoid the possibility of combustion or explosion of the solvent in air. By keeping air away from the solvent, one avoids this potential hazard.
  • inert gas may be provided in the enclosure 12 above the four tanks. This would be necessary if the temperature is above 60 °C, which is the flashpoint of terpene.
  • the cleaning tank 14 is heated first and then cooled to maintain the temperature well below 60 °C.
  • the cascade tank 24 is not heated or cooled.
  • the intermediate tank 28 is heated, as is the water tank 40.
  • the cleaning tank 14 and the water tank 40 have a capacity of about 90 to 180 litres.
  • the intermediate tank 28 and the cascade tank 24 are smaller.
  • the flow of solvent and water cascading to the cascade tank 24 is in the range of about 5 to 20 litres per minute, the preferred range being 5 to 10 litres per minute.
  • the water tank 24 has the water heated to just below boiling point so that work pieces passing into the dryer section 44 are close to the boiling point of water. This high temperature promotes evaporation and drying of the work pieces.

Abstract

Recycling of liquids in a liquid cleaning device permits the savings of solvent liquids and avoids throwing out contaminating liquids that can contribute to pollution. A closed loop system is provided for cleaning liquid agent and water in liquid cleaning apparatus that includes a cleaning tank (14) for containing a liquid cleaning agent having a different density to water and being separable therefrom, a water tank (40), an enclosure (12) containing the cleaning tank (14) and the water tank (40) on a conveyor (10) for conveying work pieces through the apparatus. A cascade tank (24) is located between the cleaning tank (14) and the water tank (40) to receive liquid cleaning agent and water from the two tanks, a system for metering a predetermined flow of liquid cleaning agent from the cascade tank (24) and water from the cascade tank (24) to an evaporator (86) to evaporate and then condense in a condenser (90) the liquid cleaning agent and water. The two liquids are allowed to separate in a decanter tank (92) and recirculated to the cleaning tank (14) and the water tank (40).

Description

REUSING LIQUIDS IN A LIQUID CLEANING APPARATUS
The present invention relates to liquid cleaning devices for cleaning work pieces such as printed circuit boards and the like upon which electric components have been soldered. More specifically, the present invention relates to a liquid cleaning apparatus utilizing a liquid cleaning agent with a density less than water. The improvement relates to reusing the cleaning liquid agent and water in a closed loop configuration.
Printed circuit boards and the like that have been soldered have deposits from flux resins and the like on the soldered surfaces which must be removed. Liquid cleaning agents are generally used for removal of such deposits, however many of the cleaning agents used today are either flammable or explosive when sprayed in the air. Furthermore, liquid cleaning agents cannot be dumped or discharged into normal sewage or draining systems because of contamination and pollution problems.
One cleaning agent used for cleaning circuit boards is a terpene based solvent. The solvent is used in an enclosed cleaning machine and in some instances inert gas is provided within the enclosure to prevent fire or explosion. One example of a method and apparatus for cleaning work pieces is disclosed in copending Application Serial No. 456,108, filed December 22, 1989. In this cleaning apparatus, work pieces are conveyed on a conveyor down into a tank of solvent or water. The work pieces rise up out of the tank into an enclosed area with liquid seals on both sides and they are sprayed with high pressure water jets within this enclosed area. Gas and vapors are contained within this enclosed area and can not escape through the entrance or the exit of the apparatus. In one embodiment, solvent sprays are immersed within the tank containing the solvent.
In a second copending Application, U.S. Serial No. 574,342, filed August 28, 1990, a drying system for a liquid cleaning apparatus is disclosed. This apparatus provides a dryer for drying work pieces as they leave a final water washing tank. The vapor in the drying zone is passed through a dehumidifier so the vapor condenses and dry gas is circulated through the dryer.
In the past, contaminated liquid cleaning agents were generally discarded, in some cases they were treated prior to disposal. Rinse water which after cleaning work pieces was often contaminated, was discharged into drains, and was often diluted with further water to comply with discharge requirements. In other cases, the rinse water required other treatment prior to dumping, in order to comply with regulations.
In examining methods of treating contaminated rinse water, including recovery of the rinse water, it was found that distillation of water containing a low concentration of liquid cleaning agent did not provide an efficient method of separating the cleaning agent from the water, particularly in the case of terpene based solvents. There is a need to provide a closed loop system not only to avoid atmospheric pollution, but to reuse the liquid cleaning agent or solvent and also to reuse the water, with topping up where required but avoiding having to throw out water with a low concentration of a liquid cleaning agent mixed therein or dirty liquid cleaning agents.
The term, liquid cleaning agent, referred to in the text includes any detergent, liquid saponifier or solvent that has a density less than that of water and when placed in a tank or container separates into a top layer and a bottom layer. The liquid cleaning agent generally forms the top layer and the water forms the bottom layer. It would be feasible to reverse this and provide a liquid cleaning agent that was denser than water. In this situation, water would remain in the top layer and the liquid cleaning agent on the bottom layer.
It is an aim of the present invention to provide a closed loop system for a liquid cleaning device that recycles liquid cleaning agents and water insuring that both the liquid cleaning agent and the water are cleaned and reused. The recycled liquids are passed through filters, strainers or the like during recycling to remove particulate material and other deposits removed from work pieces.
It is a further aim of the present invention to provide a system wherein two liquids which have different densities and are separable such as a liquid cleaning agent and water are mixed in a predetermined ratio prior to distillation. The predetermined ratio is such that the input feed to the distillation maintains both liquids in the desired proportions.
A still further aim of the present invention is to provide a liquid cleaning device having a liquid cleaning agent tank for initial immersion of work pieces and a final water tank for washing the liquid cleaning agent off the work pieces before they exit from the cleaning device. Both the liquid cleaning agent tank and the water tank cascade inwards to a central cascade tank where the liquid cleaning agent and the water separate into two layers, one above the other, due to their different densities. Some liquid cleaning agent maybe recirculated back to the liquid cleaning agent tank from the cascade tank and some water from the cascade tank maybe circulated back to the water tank. Thus recirculation of both the cleaning agent and the water occurs. The present invention provides in a liquid cleaning apparatus for cleaning work pieces, including a cleaning tank for containing a liquid cleaning agent having a different density to water and being separable therefrom, a water tank, an enclosure means containing the cleaning tank and the water tank, and means for conveying work pieces from an entrance to an exit of the enclosure, passing the work pieces through the cleaning tank and the water tank, the improvement of a closed loop system for cleaning the liquid cleaning agent and water comprising; cascade tank between the cleaning tank and the water tank, to receive liquid cleaning agent and water from the two tanks, metering means to meter a predetermined flow of liquid cleaning agent from the cascade tank, and a predetermined flow of water from the cascade tank, evaporator means to evaporate metered liquid cleaning agent and metered water together, condenser means to condense vapor from the evaporator means, decanter tank means for condensate from the condenser means adapted to separate water and liquid cleaning agent into layers determined by density in the decanter tank means, and pump means to pump liquid cleaning agent from the decanter tank means to the liquid cleaning tank and water from the decanter tank means to the water tank.
In another embodiment, there is provided in a process of cleaning work pieces in a liquid cleaning apparatus, whenever the work pieces are immersed in a first liquid followed by immersion in a second liquid, the first and second liquids being separable and having different densities, the improvement of recycling the first and second liquids comprising the steps of : metering a portion of the first liquid, metering a portion of the second liquid, combining the two portions, distilling the combined portions to a vapor gas phase, and condensing the vapor gas to liquid phase and separating the first liquid from the second liquid. In a further embodiment there is provided in a process of cleaning work pieces in a liquid cleaning apparatus, wherein the work pieces are immersed in a liquid cleaning agent within an enclosure, the liquid cleaning agent having a different density to water and being separable therefrom, and subsequently immersed in water prior to drying, the improvement of recycling the liquid cleaning agent and water, comprising the steps of: cascading liquid cleaning agent from a cleaning tank into a cascade tank, and filtering and pumping a portion of the liquid cleaning agent in the cascade tank back into the liquid cleaning tank, cascading water from a water tank to an intermediate tank, and from the intermediate tank into the cascade tank, and filtering and pumping a portion of the water from the cascade tank back to the water tank, metering a further portion of the liquid cleaning agent from the cascade tank and a further portion of the water from the cascade tank to provide a combined predetermined ratio flow of liquid cleaning agent and water, distilling the combined predetermined ratio flow to a vapor gas phase, condensing the vapor gas to liquid cleaning agent and water, and separating the liquid cleaning agent and water, returning the cleaning agent to the liquid cleaning tank and the water to the water tank.
In drawings which illustrate embodiments of the invention:
Figure 1 is a schematic view showing a liquid cleaning device according to one embodiment of the invention.
Figure 2 is a schematic view showing the recycling arrangement for liquid cleaning agent and water suitable for the cleaning device illustrated in Figure 1.
A liquid cleaning device is illustrated in Figure 1 wherein a conveyor 10 moves work pieces such as printed wiring boards, circuit boards and the like that have electrical components soldered thereon, through an enclosure 12 initially passing through a cleaning tank 14 which contains a liquid cleaning agent such as a detergent, liquid saponifier, solvent or the like. The cleaning agent has a density generally less than water, but in some cases more than water, providing the density is not the same as water. In the specific embodiment shown, the cleaning agent is a terpene based liquid solvent. This solvent is flammable or explosive when sprayed in air and therefore sprays 16 are provided, immersed within the cleaning tank 14. A pump 18 and filter 20 circulate solvent from the cleaning tank 14 through line 22, passing to the spray 16 which spray above and below the conveyor 10.
The cleaning tank 14 cascades into a cascade tank
24 positioned so that the liquid continuously overflows into the cascade tank 24. The conveyor 10 conveys work pieces over the cascade tank 24 through water sprays 26 positioned above an intermediate tank 28. A pump 30 and filter 32 collect water from the intermediate tank 28 and recirculate water through line 34 to the sprays 26. Most water from the sprays 26 drains back into the intermediate tank 28 which in turn overflows into the cascade tank 24.
A first liquid seal divider 36 is positioned above the cleaning tank 14. The work pieces are conveyed on the conveyor 10 under the first liquid seal divider 36 to provide an enclosed area 38 in which the water sprays 26 operate. Thus any vapor from the sprays 26 is contained within the enclosure 38. After the work pieces are conveyed beyond the water sprays 26, the conveyor 10 enters a water tank 40, passing under a second liquid seal divider 42 to complete the enclosed area 38. The conveyor 10 then passes up through a dryer section 44 where steam jets 46 assist in blowing water droplets off the work pieces on the conveyor 10. A dehumidifier 47 similar to that shown in copending application filed August 28, 1990, removes moisture and solvent vapor from the system for complete recycling. Substantially dry and clean gas only exits at stack 48. The water tank 40 cascades or overflows into the intermediate tank 28 which in turn cascades or overflows into the cascade tank 24. Thus the liquid cleaning agent from cleaning tank 14 cascades into the cascade tank 24 from one side and water from the water tank 40 and the intermediate tank 28 cascades into the cascade tank 24 from the other side. In the cascade tank 24 the liquid cleaning agent, which is solvent in this particular case, separates from the water. The solvent being lighter, forms a top layer and the water a bottom layer. To insure that cascading occurs, a liquid cleaning agent pump 50 collects liquid cleaning agent from the top layer of the cascade tank 24 through line 52, passes through filter 54 and pumps the liquid cleaning agent into the cleaning tank 14. A water pump 56 collects water from the lower layer of the cascade tank 24 through line 58, passes it through a filter 60 and into the intermediate tank 28. Similarly, a pump 62 collects water from the intermediate tank 28 in line 64, passes it through filter 66 into the water tank 40. With the pumps operating, there is a cascading effect of the liquid cleaning agent into the cascade tank 24, and the water from the water tank 40 to the intermediate tank 28 to the cascade tank 24. The cascading effect may be intermittent by running the pumps at intervals with no cascading or pumping occurring when the pumps are turned off. Alternatively, the pumps maybe run continuously to provide a continuous cascading effect.
The filters provided in the system remove particulate matter and the like that circulate through the pumps. Whereas filters are defined as such throughout the specification, the term can include strainer and other devices that assist in removing particulate matter and the like. The filters are generally placed before the pumps to avoid passing particulate material through the pumps. Filter 66 maybe a carbon type filter to remove rosins and organic matter and thus improve the purity of water in the water tank 40. Carbon type filters may also be used elsewhere in the system where appropriate to remove rosins and other particulate material from the recirculating liquids. A drain from the bottom of the cleaning tank 14 has a solenoid valve 68 therein and a line 70 connects to line 58 circulating water from the cascade tank 24 to the intermediate tank 28. Opening the solenoid valve 68 permits accumulated water in the cleaning tank 14 to be pumped through the filter 60 and recirculated to the water in the intermediate tank 28. In another embodiment a line maybe provided to recirculate the accumulated water to the cascade tank 14.
Because of the differences in density between the liquid cleaning agent and water, layers are formed in cascade tank 24 and thus a liquid cleaning agent line 72 collects liquid cleaning agent from the top layer of the cascade tank and a water line 74 collects water from the lower layer of the cascade tank 24. As shown in Figure 2, liquid cleaning agent line 72 passes through a metering pump 76 after a filter 78. The water line 74 passes through a water metering pump 80 after a filter 82. The metering pumps allow metered flows of the liquid cleaning agent and water to be pumped from the cascade tank 24. The liquid cleaning agent and water are mixed after the metering pumps 76 and 80 in line 84 and pass to a still or evaporator 86. The metered feed to the still 86 permits the desired ratio of liquid cleaning agent and water in the boiling sump of the still 86. The desired ratio allows co-distillation of both the liquid cleaning agent and water in some cases this is at a temperature not normally exceeding the boiling point of water or the liquid cleaning agent. In the case of a terpene based solvent, the lower temperature provides safer distillation and avoids possible thermal decomposition. In some instances, a mixing arrangement is required to ensure that terpene and water remain mixed in the still. A circulating pump 87 is shown in Figure 2 which takes the solvent and water in the still 86 and sprays the mixture through immersed jets or nozzles back into the still 86 to ensure the terpene and water do not separate. Other mixing devices such as mechanical skimmers may also be provided to agitate the mixture and ensure separation does not occur.
Terpene and water evaporate in the still 86. The feed of terpene and water are controlled at a preset ratio to ensure both liquids are always present in the sump and one or other does not get depleted through the distill action process. Some flux residues and other deposits do not distill and remain in the boil sump and are drained away through drain 88 or are otherwise periodically removed. A program of cleaning the still is required at predetermined intervals to ensure that the residues and deposits remaining therein are removed.
Steam and cleaning agent vapor pass through a condenser 90 and the condensed products, namely water and liquid cleaning agent are fed into a decanter tank 92. In the decanter tank 92, the liquid cleaning agent or terpene rises to the top layer and the water settles to the bottom layer. Condensed water and liquid cleaning agent from the dehumidifier 47 above the dryer section 44 drains through line 93 into the decanter tank 92. The terpene is then pumped through line 94 back into the cleaning tank 14 as shown in Figure 1 and the water is pumped through water line 96 back to the water tank 40 shown in Figure 1. In one embodiment, a steam generator, 98 shown in Figure 1 takes a portion of the water from line 96 for the steam jets 46.
When terpene is used as the liquid cleaning agent, there is sometimes a requirement for a nitrogen blanket in both the still 86 and the decanter 92 to avoid the possibility of combustion or explosion of the solvent in air. By keeping air away from the solvent, one avoids this potential hazard. Furthermore, inert gas may be provided in the enclosure 12 above the four tanks. This would be necessary if the temperature is above 60 °C, which is the flashpoint of terpene. In the case of terpene, the cleaning tank 14 is heated first and then cooled to maintain the temperature well below 60 °C. The cascade tank 24 is not heated or cooled. The intermediate tank 28 is heated, as is the water tank 40.
In one embodiment, the cleaning tank 14 and the water tank 40 have a capacity of about 90 to 180 litres. The intermediate tank 28 and the cascade tank 24 are smaller. The flow of solvent and water cascading to the cascade tank 24 is in the range of about 5 to 20 litres per minute, the preferred range being 5 to 10 litres per minute. The water tank 24 has the water heated to just below boiling point so that work pieces passing into the dryer section 44 are close to the boiling point of water. This high temperature promotes evaporation and drying of the work pieces.
Whereas metering has been disclosed to ensure the ratios of the two liquids are passed to the still, other methods may be employed which are reproducible and reliable. For example two pumps of different capacities may be employed. The required accuracy of the predetermined ratio metered, depends on the liquids and other factors.
Various changes may be made to the embodiments described herein, without departing from the scope of the invention which is limited only by the following claims.

Claims

The embodiments of the present invention in which an exclusive property or privilege is claimed are defined as follows:
1. In a liquid cleaning apparatus for cleaning work pieces, including a cleaning tank (14) for containing a liquid cleaning agent having a different density to water and being separable therefrom, a water tank (40), an enclosure means (12) containing the cleaning tank (14) and the water tank (40), and means for conveying (10) work pieces from an entrance to an exit of the enclosure (12), passing the work pieces through the cleaning tank (14) and the water tank (40), the improvement of a closed loop system for cleaning the liquid cleaning agent and water comprising; cascade tank (24) between the liquid cleaning tank (14) and the water tank (40), to receive liquid cleaning agent and water from the two tanks, metering means to meter a predetermined flow of liquid cleaning agent from the cascade tank (24), and a predetermined flow of water from the cascade tank (24), evaporator means (86) to evaporate metered liquid cleaning agent and metered water together, condenser means (90) to condense vapor from the evaporator means, decanter tank means (92) for condensate from the condenser means (90), adapted to separate water and liquid cleaning agent into layers determined by density in the decanter tank means (92) , and pump means to pump liquid cleaning agent from the decanter tank means (92) to the liquid cleaning tank (14) and water from the decanter tank means (92) to the water tank (40).
2. The liquid cleaning apparatus according to claim 1, wherein recirculating means ensure the liquid cleaning agent is recirculated from the cascade tank (24) to the cleaning tank and water is circulated from the cascade tank (24) to the water tank (40).
3. The liquid cleaning apparatus according to claim 2, wherein filter means are provided for the recirculating means and the metering means.
4. The liquid cleaning apparatus according to claim 1, including an intermediate tank (28) between the water tank (14) and the cascade tank (24) and wherein the water from the water tank (40) cascades into the intermediate tank (28) which in turn cascades into the cascade tank (24).
5. The liquid cleaning apparatus according to claim
4, wherein recirculating means ensure the liquid cleaning agent is recirculated from the cascade tank (24) to the cleaning tank (14) , and wherein water f om the cascade tank (24) is recirculated to the intermediate tank (28), and water from the intermediate tank (28) recirculated to the water tank (40).
6. The liquid cleaning apparatus according to claim
5, wherein filters strainers or the like are provided for each of the recirculating means.
7. The liquid cleaning apparatus according to claim 1 including a dryer section (44) in the enclosure means (12), the dryer section (44) having dehumidification means (47) associated therewith to condense moisture and liquid cleaning vapor in the dryer section (44), and drain means to return water and liquid cleaning agent from the dehumidification means (47) to the decanter tank means (92).
8. The liquid cleaning apparatus according to claim 1, wherein the liquid cleaning agent is a terpene based solvent and solvent temperature in the decanter tank means (92) is restricted to below 60 °C.
9. The liquid cleaning apparatus according to claim
I, wherein the liquid cleaning agent is a terpene based solvent and wherein an inert gas cover is provided in the enclosure (12) and above the decanter tank means (92) .
10. In a process of cleaning work pieces in a liquid cleaning apparatus, wherein the work pieces are immersed in a first liquid followed by immersion in a second liquid, the first and second liquids being separable and having different densities, the improvement of recycling the first and second liquids comprising the steps of metering a portion of the first liquid, metering a portion of the second liquid, combining the two portions, distilling the combined portions to a vapor gas phase, and condensing the vapor gas to liquid phase and separating the first liquid from the second liquid.
II. The process according to claim 10 wherein the work pieces are immersed in a first liquid tank followed by a second liquid tank, and wherein separated first liquid and second liquid after condensing is recycled to the first liquid tank and the second liquid tank.
12. The process according to claim 11 wherein first liquid from the first liquid tank and second liquid from the second liquid tank are cascaded into a cascade tank, and the first liquid and the second liquid are metered from the cascade tank.
13. In a process of cleaning work pieces in a liquid cleaning apparatus, wherein the work pieces are immersed in a liquid cleaning agent within an enclosure, the liquid cleaning agent having a different density to water and being separable therefrom, and subsequently immersed in water prior to drying, the improvement of recycling the liquid cleaning agent and water comprising the steps of: cascading liquid cleaning agent from a liquid cleaning tank into a cascade tank and filtering and pumping a portion of the liquid cleaning agent in the cascade tank back to the liquid cleaning tank, cascading water from water tank into an intermediate tank, and from the intermediate tank into the cascade tank, and filtering and pumping a portion of the water from the cascade tank back into the water tank, metering a further portion of the liquid cleaning agent from the cascade tank and a further portion of the water from the cascade tank, distilling the further portion of the liquid cleaning agent and the further portion of the water when mixed together to a vapor gas phase, condensing the vapor gas to liquid cleaning agent and water, and separating the liquid cleaning agent and water and returning the cleaning agent to the liquid cleaning tank and the water to the water tank.
14. The process of cleaning work pieces according to claim 13 including pumping and filtering water from the cascade tank back into the intermediate tank and pumping and filtering water from the intermediate tank back into the water tank.
15. The process of cleaning work pieces according to claim 13 wherein the separating takes place in a decanter tank the liquid cleaning agent forming a top layer and the water forming a bottom layer.
16. The process of cleaning work pieces according to claim 13 wherein the liquid cleaning agent is a terpene based solvent.
17. The process of cleaning work pieces according to claim 16 including the addition of inert gas in the distilling step and in the separating step.
18. The process of cleaning work pieces according to claim 13 wherein a portion of the water returning to the water tank after separation is passed through a steam generator to form steam applied to the work pieces from a steam jet prior to drying.
19. The process of cleaning work pieces according to claim 15 wherein separation takes place in a decanter tank maintained at a temperature below 60 °C.
PCT/CA1991/000352 1990-10-10 1991-10-07 Reusing liquids in a liquid cleaning apparatus WO1992007452A1 (en)

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US595,469 1990-10-10

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FR2736655A1 (en) * 1995-07-13 1997-01-17 Francais Prod Ind Cfpi Removing paint from aluminium, zinc and magnesium substrates

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Publication number Priority date Publication date Assignee Title
EP0608700A1 (en) * 1993-01-27 1994-08-03 DR. O.K. WACK GmbH Process for the recovery of a fluid dissolved in a rinsing bath
FR2736655A1 (en) * 1995-07-13 1997-01-17 Francais Prod Ind Cfpi Removing paint from aluminium, zinc and magnesium substrates

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