US2399205A - Cleaning process - Google Patents

Description

AW 3 1945: c. A. CAMPBELL 2,399,205

CLEANING PROCESS Filed July 27, 1940 Patented Apr. 30, 1946 CLEANING PROCESS Charles A. Campbell, Detroit, Mich., assignor of thirty-five per cent to Blanche E. Campbell, five per cent to Rita Blanche Fossee, five per cent to Jean Madalyn Ballew, and five per cent to Charles A. Campbell, Jr., all of Grosse Pointe,

Mich.

Application July 27, 1940, Serial No. 347,929

15 Claims.

' The present invention relates to cleaning processes and materials and p r i l y Such as are applicable to the cleaning of metal parts in the process of manufacture in order to prepare their surfaces for such operations as plating, rustproofing, or painting.

Serious problems are encountered in cleaning metal parts where the parts have been subject to drawing or bufiing operations which leave upon the surface of the parts drawing or bufiing compounds. These materials are not only exceedingly diflicult to remove but in some cases they must be entirely removed before the metal parts can be further processed. This is true, for example, in preparations for electro-plating or for rust-proofing of the type in which a phosphate coating is formed on the parts. Bufling compounds which are left upon the surface contain inert materials, including finely divided emery or other abrasive and also saponiflable and semisaponifiable stearates, greases, and sometimes mineral oils. Drawing compounds contain soaps, degras, pigments, and sometimes rosin oil, and in addition, there is usually found upon the surface of the parts mineral oil, dust, carbon smut, and other types of inert material which strongly ad- 'heres to the surface but must, nevertheless, be

removed.

In the past, attempts have been made to remove drawing and buffing compounds by the use of alkali compounds in water, trichlorethylene, ordinary hydrocarbon solvents or solvent emulsions. Alkali compounds, while widely used in spray and dip cleaning to remove certain types of light soil, are not effective in removing stubborn deposits such, for example, as buffing and drawing compounds. There is also a tendency for the alkali to react chemically with the metal, particularl where the part being cleaned is a buffed zinc die casting. Trichlorethylene and similar synthetic organic solvents are extensively used in the vapor stage by heating the solvent to a vapor state and passing the work through the vapor. Solvents are most effective when used in the vapor phase, and trichlorethylene has been so used to a considerable extent. However, the solvent vapors are often noxious, even poisonous, and while they dissolve the greases and oils, they will not entirely carry off the inert materials. Therefore, it is often necessary to hand wipe parts which have been subject to vapor solvent cleaning. Ordinary hydrocarbon solvents have been used to a very limited extent in dip tanks, either hot or cold. Solvents are effective in dissolving greases and oils but have no effect on saponifiable materials. Moreover, solvents do not have the ability to carry inert or non-soluble materials in suspension. Stable solvent emulsions are used to a limited extent for cleaning, either by spray or dip methods, but the solvent in emulsion form loses much of its effectiveness as a cleaning agent. If heated, it tends to foam and much of the solvent is lost by evaporation.

It is the general object of the present invention to provide highly effective inexpensive methods, materials, and apparatus for conducting cleaning operations of the type mentioned, by means of which cleaning operations may be carried on without the disadvantages of the prior practices,

Another object of the invention is to provide a single cleaning bath which, when used either as a spray or dip bath or both, will effectively remove fatty acids, soaps, greases and inert materials without reacting with the metal part being cleaned. 1

Another object of the present invention isto provide a novel form of cleaning bath comprising an unstable mixture of a cleaning solvent and a solvent-water emulsion, which bath may be used in either spray or dip methods of cleaning, and which may be re-used repeatedly for a relatively long period.

Another object of the present invention is to provide a novel cleaning solution for use in preparing cleaning baths of the type mentioned.

Other objects, which include the provision of apparatus designed to carry out the cleaning operation in the best possible manner, including the provision of means for limiting loss of cleaning solution by evaporation, will become apparent from the following specification, the accompanying drawing, and the appended claims.

In the drawing,

Figure 1 shows a horizontal section, taken on the line I| of Fig. 2, of a spray washing machine of a type adapted for use in accordance with one phase of the present invention.

Fig. 2 shows a vertical section of the same ma chine taken on the line 22 of Fig. 1.

Fig. 3 is a side view on a reduced scale, taken on the line 33 of Fig. 2, parts being broken away to show a portion of the interior of the machine.

In accordance with the present invention, metal parts are cleaned by subjecting them to the action of an unstable mixture of a cleaning solvent emulsion and an unemulsified cleaning solvent, which unstable mixture is referred to throughout this specification as the bath, or cleaning bath. This bath is made up of a solvent emulsion containing any suitable cleaning solvent, water, and an emulsifying agent such as a soap. This portion of the bath, which is referred to throughout as the emulsion, is a stable solvent and water emulsion having the property of being able to clean by wetting action and dispersion. The cleaning bath, in addition to the cleaning emulsion, contains solvent in. an amount greater than can be emulsified with the cleaning emulsion, with the result that the additional solvent remains separate from the emulsion and tends to float on the surface ofthe bath in a layer. This unemulsified solvent is normally, but not necessarily, the same as the solvent in the emulsion.

The cleaning bath of the present invention may be used for cleaning either by the dip or the spray method.

In the dip method of cleaning, the parts to be cleaned are simply dipped into the material, which is preferably maintained during dip cleaning at a temperature in the order of 180 F. The parts to be cleaned, when dipped into the bath, first enter and then pass through the solvent layer at the top before entering the emulsion beneath the solvent layer. This exposes the material to be removed from the part to the action of the solvent first. When this material contains greasy and oily substances, as well as inert particles, the solvent penetrates the material to be removed. wets or coats the inert constituents thereof and acts generally to soften the grease and oily matter in the material. As the part moves into the cleaning emulsion, in which it is preferably held for a short period depending upon the amount of material which must be removed, the emulsion causes a further wetting, emulsifying and softening of the material and also tends to cause a dispersion of the material on the surface of the part and in the cleaning emulsion, thu loosening it and spreading it to a condition in which it will be readily removed in subsequent rinsing operations. Then, as the part is removed from the bath out through the solvent layer for a second time, the penetrating and softening action of the solvent is repeated and, in addition, the mechanical movement of the solvent over the work causes a partial or complete removal of the loosened, softened, and dispersed material originally upon the part to be cleaned. The penetrating and wetting properties of the solvent being uperior to those of the emulsion cause an initial penetration and coating by the solvent that facilitates subsequent penetration and dispersion by the emulsion.

The dip method may be carried out in the manner illustrated diagrammatically in Fig. 4. As there shown, an open tank I contains the cleaning bath. The bath is made up of two layers; namely, the emulsion layer 2 and the solvent layer 3 overlying the emulsion with an interface 4 between the two. The work 5, which may be supported in any desired manner, as by a hook 6, is lowered into the bath entirely through the solvent layer and into the body of the emulsion and then withdrawn;

If the dip method of cleaning is used alone, as soon as the part is removed from the cleaning bath, it should be subject to a rinsing operation, preferably in the form of a water spray which will mechanically remove and wash away any remaining vestige of foreign material and the cleaning bath. The free solvent in the bath greatly facilitates rinsing, apparently because the solvent has a greater attraction to the surface of the metal than does the emulsion, with the result that a thin film of solvent separates the emulsion from the metal surface and prevents adhering of the emulsion to the metal part. At the same time, the emulsion blankets and prevents drying out of the solvent between the washing operation and the rinsing operation and serves as a carrier for inert materials and solvent. As a result the metal part is very readily rinsed to a free, clean surface, upon which no trace of foreign material can be seen and which, additionally, is sufficiently clean chemically to take electroplating or rust-proofing treatments successfully.

The above described cleaning bath of the present invention may also be used to excellent advantage in spray cleaning, in which event it is mechanically mixed in any suitable manner and sprayed directly upon the work to be cleaned by any suitable spray nozzle.

A machine suitable for carrying out the spray cleaning process is illustrated in the drawing. As there shown the machine comprises a sheet metal casing of any desired construction having side walls l0 and II, top wall l2, and bottom wall IS. The lower portion of the casing has a projection at one side defined by an auxiliary side wall l4 spaced outwardly from the wall II at the upper part of the machine on the same side. The oil'set between the walls II and I4 is closed by a plurality of hinged lids l5, l6, and IT. The ends of the machine are partially closed by end walls i8 which are entirels closed at their lower portions but have at their upper central portions openings l9 through which the work to be cleaned is passed.

Any desired means for conveying the work through the machine may be utilized, but, as shown in the drawing, it is preferred to utilize a chain type of conveyor which runs upon ,an I-beam track 20 extending entirely through the machine and the openings IS in the end walls I8 thereof. The chain conveyor, indicated generally at 22, is provided with a plurality of longitudinally spaced hooks 23 for supporting the work 24 to be cleaned.

The machine is divided into three compartments 25, 26, and 21. The compartment 25 is the washing compartment. Compartment 26, which is the first rinsing stage, is separated from compartment 25 by a wall 28. Compartment 26, in turn, is. separated from compartment 21, the second rinsing stage, by means of a wall 29 similar to the wall 28. The walls 28 and 29 have openings 30 and 3i therein, which openings are similar to the openings l9 in the end walls [8. The lower portions of the compartments 25, 25, and 21, which are separated from each other by the lower portions of the walls 28 and 29, form reservoirs for retaining the washing fluid and rinse water, respectively. That is, the lower portion of the compartment 25 forms a reservoir for the washing fluid while the lower portions of compartments 25 and 21 form separate reservoirs for rinse water.

Mounted in the compartment 25 adjacent the side walls H and 12 are a plurality of vertically extending spray pipes 32 connected by suitable piping to the discharge outlet 36 of a pump 38. The vertically extending spray pipes are provided throughout their length with a plurality of spaced nozzles of any desired form, such as milled slots in the pipe, adapted to spray the cleaning material upon the work carried by the chain conveyor 22. It will be noted that the last spray pipes are positioned very close to the wall 28, with the result that the wall 28 forms a baiile acting to prevent the cleaning fluid from entering the first rinsing compartment. r

The cleaning material which is discharged by the spray pipes 32 falls back into the reservoir in the bottom of the spray compartment 25 and means are provided for drawing the cleaning material from this reservoir and conducting it to the intake of pump 38. It will be noted, as shown in Fig. 2 of the drawing, that the cleaning bath in the reservoir comprises an underlying body of emulsion indicated '40 upon the top of which is a layer 42 of unemulsified solvent. These two immiscible liquids have a distinct interface the level of which is indicated by the line 48 in Fig. 2. It is necessary, in order to properly conduct the washing operation, to draw into pump 38 a mixture of these two immiscible fluids and this is accomplished in the machine illustrated in the drawing by connecting the pump intake 44 to a pipe 45, the open end of which extends vertically and lies just below the interface 43 of the two liquids. As a result of this arrangement, the pump suction draws in part upon the solvent layer 42 and in part from the underlying emulsion layer 40, thus drawing in a mechanical mixture of the two immiscible liquids. The action of the pump, as well as the turbulence created by the spray, renders this mechanical mixture an exceedingly intimate one, with the result that the free or unemulsified solvent is thoroughly dispersed through the spray.

Aside from the simplicity of this method of mixing the two layers, the method has the further advantage that the relative proportions of the two liquids may be readily varied in any given installation by varying the distance between the top of pipe 45 and the interface 43, or, in other words, by adjusting the level of the interface. This may be done readily, since the system is a closed one, by varying the quantity and proportions of the cleaning bath in the reservoir.

The ratio of the amounts of the two liquids,

- lent results have been secured in an installation in which the pump capacity was 500 gallons per minute, the intake pipe diameter was four inches, and the distance between the top of the pipe and the interface was from four to six inches. It is, of course, necessary to make additions to the bath from time to time to compensate for evaporation loss and the bath which adheres to the work which otherwise might vary the level of the interface.

The two rinsing stages 26 and 21 are identical and each comprises a plurality of vertical rinsing spray pipes 46 and 41, respectively, connected by suitable piping to the discharge side of individual pumps 48 and .49, respectively. The pump inlets 50 and 5| are connected directly to the rinse water reservoirs in the lower parts of compartments 26 and 21, so that the rinse water is re-cir- 'culated. Re-circulation of the rinse water is desirable not only because it results in a saving of water, but also a saving of heat since the water is sprayed at the preferred temperature of 120F. It will be noted that the last washing sprays 32 are positioned quite close to the first rinsing sprays46, being separated only by the wall or The cleaning bath in the reservoir of compartment 25, as well as the rinse water in the reservoir of compartments 28 and 21, is maintained at the desired temperature, preferably F.,-by any suitable means such as thermostatically controlled steam coils, not shown, in the bottoms of the reservoirs.

In order to avoid contamination of the rinse water by the vapor from the washing spray and for the further purpose of preventing loss of cleaning material due to evaporation, there is provided a circulating and condensing system shown best in Fig. 3. As there shown, there is provided an air conduit 54 leading fromthe top of the machine casing at a point on the washing compartment side of partition 28, as shown in dotted lines in Fig. l. The conduit 54 leads to the intake of a fan 56, which discharges into a conduit 51 leading back into the top "or the casing at a point just inside of the entering end wall l8, also shown in dotted lines in Fig. 1. By withdrawing air and vapor from a point adjacent to but on the washing compartment side of the opening 30 in partition 28, a flow of air from the rinsing compartment'into the washing compartment is created, which is effective to prevent entry of the vapor from the washing spray to the rinsing compartments. By leading the vapor and air back through the discharge conduit 5'! into the opposite end of the washing compartment, any of the vapor which has condensed will be returned to the cleaning bath and a certain amount of the uncondensed vapor, if any, when coming in contact with the washing spray, will likewise be condensed. A portion of the balance may flow outwardly through the opening IS in the end wall i8, while the rest will flow towards the inlet pipe 54. By placing a condenser, shown more or less diagrammatically at 50 in the inlet pipe 54, it is possible to condense a greater portion of the vapors drawn into the pipe 54. As a result, loss of cleaning fluid is further reduced. The form of condenser shown is of the water cooled type utilizing a source of water which enters the condenser from a pipe 62 and is discharged through pipe 63. It is preferable to constantly overflow the rinse tanks in order to remove any dirt or foreign material that may collect as a scum on the surface, and, therefore, it is advantageous to run the condensing water from pipe 63 directly into the rinse water reservoirs. This may be done in any desired manner, such as that indicated by the dotted line pipes 64 and B5 in Fig. 3. Suitable means, such as the two overflow pipes 66 and 81, may be provided to take the overflow from the rinse tanks.

The particular arrangement and proportions of the washing machine are not critical as it is possible to utilize a longer machine or one which is arranged in general U-shape instead of being arranged in a straight line, and any desired number and arrangement of washing and rinsing sprays may be utilized.

One advantage of the spray cleaning method is that a much more dilute bath may be used, and in addition, the material may be sprayed at the relatively low temperature of 120 F. The action of the bath in spray cleaning is somewhat similar to that described in connection with the dip process, except that the various phases of the attack on the material to be removed from the parts occur more or less simultaneously; that is to say, the unemulsified solvent penetrates and softens the grease and oil constituents of the material and wets the inert constituents; while the emulsion wets, emulsifies and softens certain of the ingredients and disperses the material. The mechanical force of the spray assists the penetration, dispersion and removal of; the material.

In some cases, for example, where it is necessary to remove heavily caked buffing compounds from zinc die castings preparatory to electroplating, it is advisable to use both the dip and spray cleaning methods in succession. In this combination process, the parts to be cleaned are first dipped in the cleaning bath in the manner previously described and are then subject to a spray cleaning operation without any intermediate rinse. The spray cleaning operation should be conducted on the part before it has time to dry, although it is found that the cleaning emulsion from the dip bath tends to prevent or retard drying for a reasonable interval between the two washing operations, with the result that it is possible to have an intervening interval of several minutes.

When the cleaning bath of the present invention is used for removing ordinary bumng or drawing compounds, whether in the dip or spray process, the material removed from the parts to be cleaned gradually contaminates the cleaning bath and reduces its efficiency. The most serious contamination is caused by the soapy constituents which find their way into the cleaning bath, since they act as emulsifying agents and gradually increase the capacity of the bath to emulsify the excess solvent. Accordingly, as the baths are used continuously the excess solvent which initially floats upon the bath in a separate clear layer is gradually emulsified withthe cleaning emulsion beneath, and the free solvent layer reduces in amount until eventually it entirely disappears, all of the solvent having been emulsified with the cleaning emulsion. As soon as the bath becomes a complete stable emulsion its cleaning efliciency is greatly reduced.

The period of time required for the cleaning bath to reach this completely emulsified stage depends upon the amount of cleaning which is done, the initial size of the bath, the proportion of solvent initially present, and the amount of soapy or. emulsifying agents in the dirt or soil which is being removed from the parts to be cleaned. Under severe conditions, the bath may become completely emulsified in from four to eight hours. When this occurs, the bath should no longer be used.

It has been found that when the soil being removed contains these materials, which act as emulsifying agents, the efllciency and the useful life of the bath may, when used in the spray proccess, be very greatly increased by keeping the cleaning emulsion in an acid condition and controlling the acidity within certain well defined limits. Thus, in one case involving the rev oval of buffing compound from zinc die castings, when sufiicient acid or acid reacting salt was added to the cleaning emulsion to maintain a pH in the order of 2.0-3.5, the useful life of the bath was increased from four to thirty-two hours.

Maintenance of an acid condition of the cleaning emulsion produces a number of important results. First, it prevents emulsification of the excess solvent by the emulsifying elements of the material removed from the work; second, it prevents a permanent colloidal dispersion of the dispersable elements of the soil in the cleaning emulsion which would load the emulsion and decrease its dispersing or cleaning power; and, third, it reacts with the dispe'rsable substances to change them into a relatively hard, non-sticky form in 75 which they will not adhere to the work, and in which they will not enter into objectionable reactions with the work. This change in consistency is apparently effected without causing the particles to drop or release the inert materials carried by or embedded in them. In addition, it is found that the small particles of dispersable material, which have been reacted upon by the acid tend to float in the solvent layer and thus do not contaminate the cleaning emulsion. These particles are not afiected by the solvent and hence do no harm, even though present in relatively large amounts. On the other hand, when the bath has served its useful life, the solvent layer may be drawn off and reclaimed in any suitable form of settlin tank. The solvent is in relatively pure condition since, except for the relatively hard non-sticky particles which fioat in it and can be readily removed, by skimming or other mechanical separating methods, it contains only a relatively small quantity of completely dissolved oils or greases which were removed from the work.

In most cases the above described acid treatment cannot be used in the dip washing method because of the fact that the acid in the cleaning emulsion will etch the metal parts in production.

For some reason, not entirely understood, this etching may be eliminated in the spray washing method, even though an exceedingly chemically active metal, such as zinc, is being cleaned. Apparently, thi is due to a blanketing of the metal by a film of unemulsified solvent in which there is no acid. At least, itis noted that if under any given conditions etching occurs in'the acidified spray cleaning operation it can be eliminated without changing the pH either by increasing the amount of solvent in the bath or by dipping the work either in pure solvent or the regular dip bath immediately before the spray cleaning operation, or by both of these expedients. In addition, temperature plays an important part in the tendency of the acid to attack the metal, and it is noted that there is much less likelihood of acid attack at the temperature of F. which is preferred, than at higher temperatures.

While the acid control treatment cannot ordinarily be utilized in the dip cleaning method, it is possible to use the acid treatment for the purpose of reclaiming the solvent from the bath used in dip cleaning operations. In this case, after the bath has served its useful life, sufiicient acid is added to break the emulsion, thus releasing the excess solvent, and to react with the dispersed constituents of the dirt load to float them in a non-sticky form in the solvent layer from which they can be removed, as previousl described. The particular ingredients to be used in accordance with the cleaning methods outlined above may be widely varied, as may the proportions of the materials used. These variations depend in any particular case upon the nature of the cleaning operation to be carried on and other factors. As a general guide, a number of specific examples are hereafter given, along with an indication of the factors influencing the choice of constituents as well as the relative proportions of the various ingredients.

While as previously indicated, the cleaning emulsion is a cleaning solvent and water emulsion formed by any suitable soap or other emulsifying agent, it is preferred to use as the emulsifying agent an amine soap formed from oleic acid, since such soaps have excellent wetting and penetrating properties and, in addition, are soluble in oils which, for reasons to be pointed out hereafter, is anadvantage.

The solvent constituent of the solvent emulsion is preferably largely made up of the same solvent which forms the unemulsified solvent layer on the cleaning bath. Excellent results havesbeen secured with a mineral spirit solvent falling between kerosene and naphtha in volatility, but kerosene, naphtha, or other solvents for oil or grease may be used. Chlorinated aliphatic hydrocarbon grease solvents, such as carbon tetrachloride, or chlorinated aromatic hydrocarbon grease solvents, such as orthodichlorobenzene, may be employed if desired. It should be noted, however, that the excess chlorinated hydrocarbon, being heavier than water, will form a layer beneath the emulsion. It is apparent also that any desired combinations of solvents may be used.

It is preferred to use, in addition to the solvent, a smaller quantity of pine oil, since pine oil (steam distilled) has good wetting and penetrating properties and is an effective floatation agent which will assist floatation of the particles of acid reacted dispersible material.

In orderto make available for sale and shi ment a mixture of all of the ingredients (excepting water and acidifiers) necessary to carry on the process, it is preferred to combine the soap and solvent constituents, including oil, if any is present, in a clear stable solution, so that no settlin or layering of the material will occur prior to use. It is partly for this reason that the use of an amine soap is preferred, since soaps of this type are soluble in hydrocarbon solvents and oils to a certain extent. In addition, if necessary, a. suitable coupling or blending agent such as ethylene glycol monobutyl ether or cyclohexanol may be used to bring the soap and oil and solvent constituents into a stable solution. The pine oil itself acts to a certain extent as a blending agent. It is obvious that various proportions and ingredients may be used, but as an example, one satisfactory formula is as follows:

The above mixture of ingredients forms a clear amber solution which is ermanently stable and which, therefore, is ready for addition to a suitable quantity of water for use at any time. It contains not only the solvent and emulsifying agent necessary to form the emulsion but also the excess solvent necessary in the cleaning bath. It may be combined with any desired amount of water up to one part of solution to fifty parts of water, and when 50 combined with water becomes an unstable mixture of the cleaning emulsion and excess solvent. A certain percentage of the pine oil and mineral spirit solvent in the above mixture goes into the emulsion, but a substantial percentage of both of these ingredients simply remains on top of the bath as a clear unemulsified layer. The amount of solvent in the solution does not appear to be critical except that it must be more than the amount which will be emulsified by the emulsifying agent present. For example,

- Gallons Triethanolamine 2 Oleic acid 4 Ethylene glycol monobutyl ether 2 Pine oil 15 Mineral spirits solvent 95 it is found that the quantity of solvent may be doubled or the solution may be mixed with an equal quantity of reclaimed solvent without materially affecting the results secured.

The amount of water which should be added to od, a much smaller quantity of water is used, satisfactory results having been secured with four p rts of water to one of the above solution. Substantially the same results, however, are secured with eight parts of water, one part of the above solutionand one part of reclaimed solvent. In the spray method, excellent results have been secured with thirty to forty parts of water to one art of either the above solution or a half and half mixture of that solution and reclaimed solvent. These proportions, however, do not appear to be very critical, except, as previously indicated, in the spray cleaning method it is generally necessary in any given case to adjust the proportions of water and solution in the cleaning spray by experiment in order to avoid etching of the metal when acid is used in the emulsion.

So far as the acid treatment is concerned, it may be carried on by any water soluble acid or acid reacting salt capable of producing a solution or a cleaning emulsion having the desired pH. Among the inorganic acids which may be used successfully are sulphuric acid, phosphoric acid, pyrophosphoric acid and phosphorous acid. Nitric, hydrochloric and acetic acids cannot be used because they are too volatile and cause obnoxious 0r poisonous fumes at F. Among the organic acids which, may be used successfully are oxalic acid, maleic acid, monochloro acetic acid, dichloro acetic acid, bromo acetic acid, and phthalic acid. Formic acid cannot be used because it is too volatile at 120, and trichloro acetic acid, which is otherwise satisfactory, is inconvenience to use because its hygroscopic character makes handling difiicult. In addition to the above acids, certain inorganic salts which ionize or hydrolyze to give an acid solution may also be used. For example, sodium bisulphate and potassium bisulphate, which ionize to give an acid solution, may be used satisfactorily to produce a cleanin emulsion having the desired pH. Aluminum sulphate, which both ionizes and then hydrolyzes to giv an acid reaction, can be used, although when used alone will produce a minimum pH of only 3.5, which is not sumciently low for most purposes. It is obvious, also, that mixtures of any of the above acids and/or salts may be used if desired.

The pH of the cleaning emulsion can be varied as desired to fit the requirements of the particular cleaning operation under consideration. It is found, for example, that in removing buffing compounds from zinc die castings that a pH of 3.5 is suflicient to prevent emulsification of the bath, but that a greater acidity, namely, a pH between 2.0 to 3.3 is necessary to cause an acid reaction on the dispersible material in order to throw it out of the cleaning emulsion and render it nonsticky in character. In cleaning zine die castings, any greater acidity (or lower pH) than a pH of 2.0 was found to result in etching and the production of an invisible film or surface condition on the metal that interfered with plating operations. The minimum and maximum pH for the solution when cleaning different metals and with various proportions of the cleaningbath may be readily determined by trial in accordance with the foregoing principles.

The use of acid or acid reacting materials to increase the useful life of the bath forms no part of the.present invention, since that phase of the herein described process is disclosed and claimed in an application of Boleslaus J. Szatyn, Serial No. 347,911, filed herewith. In the usual cleaning operation no acid need be employed.

In the appended claims, the term emulsion is used to refer to a stat e emulsion or colloidal suspension of waterv and some other immiscible liquid in the presence of an emulsifying agent such as a soap or the like. The term solvent is used to refer to cleaning solvent liquids adapted to dissolve greases and oils and other similar materials. The term coupling or blending agent refers to such compounds as ethylene glycol monobutyl ether, cyclohexanol, pine oil and other higher alcohols which have the property of blending soaps and oils to produce a stable solution.

While several embodiments and examples of the present invention are given, it will be understood that change may be made in the apparatus, methods, various ingredients and proportions without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

l. The method of cleaning articles which comprises providing a bath containing an unstable mixture of a grease solvent and water emulsion and unemulsified-grease solvent in which the unemulsified solvent forms a layer on top of the emulsion, dipping the articles to be cleaned entirely through the solvent layer into the emulsion, and withdrawing the parts from the bath.

2. The method of spray cleaning metal parts with a mechanical mixture of two immiscible liquids which comprises drawing the mixture from a tank through an outlet opening located in proximity to the interface between the two liquids, spraying the mixture so drawn upon the metal parts and collecting the sprayed mixture in the tank.

3. The method of spray cleaning metal parts with a mechanical mixture of two immiscible liquids which comprises drawing the mixture from a tank through an outlet opening located in proximity to the interface between the two liquids, spraying the mixture so drawn upon the metal parts, collecting the sprayed mixture in the tank, and maintaining the interface at a desired level for the purpose of controlling the relative amounts of the two liquids drawn into the inlet.

4. The process of cleaning metal parts for the purpose of removing bufling or drawing compounds and the like in preparation for surface treatment, comprising the steps of immersing the parts into a, cleaning bath having a grease solvent layer and an underlying body of grease solvent emulsion until the parts are located entirely within theunderlying body of emulsion, removing the parts from said bath and while they are still wet with the bath subjecting said parts to a spray of a mechanically combined unstable mixture of a grease solvent emulsion and an unemulsified grease solvent.

5. The method of cleaning articles which comprises spraying the articles with a mechanically combined unstable mixture of a grease solvent and water emulsion and an unemulsified grease solvent which is of less density than water, collecting the sprayed mixture, remixing and recirculating said mixture through the cleaning spray.

6. The method of cleaning metal parts which comprises spraying the parts with a mechanically combined unstable mixture of a grease solvent and water emulsion and an unemulsified grease solvent which is of less density than water, collecting the sprayed mixture, remixing and recirculating said mixture through the cleaning spray, said grease solvent containing pine oil and a htidrocarbon grease solvent that is lighter than we r.

7. The method of cleaning metal part which comprises spraying the parts with a mechanically combined unstable mixture of a grease solvent and water emulsion and an unemulsified grease solvent which is of less density than water, 001- lectlng the sprayed mixture, remixing and recirculating said mixture through the cleaning spray, said grease solvent containing pine oil and a hydrocarbon grease solvent that is lighter than water, said mixture containing an amine soap made from oleic acid, said soap being present in an amount insufllcient to emulsify all of the solvent.

8. The method of cleaning metal parts which comprises spraying the parts with a mechanically combined unstable mixture of a grease solvent and water emulsion and an unemulsified grease solvent which is of less density than water, collecting the sprayed mixture, remixing and recirculating said mixture through the cleaning spray, said grease solvent containing a major proportion of a hydrocarbon grease solvent that is lighter than water, a minor proportion of pine oil and a small quantity of triethanolamine, said mixture employing as an emulsifying agent an amine soap made from oleic acid, said soap being present in an amount insumcient to emulsify all of the solvent.-

9. The method of cleaning metal parts which comprises spraying the parts with a mechanically combined unstable mixture of a grease solvent and water emulsion and an unemulsiiied grease solvent which is of less density than water, collecting the sprayed mixture, remixing and recirculating said mixture through the cleaning spray, said grease solvent containing a major proportion of hydrocarbon grease solvent that is lighter than water, a minor proportion of pine oil and a small quantity of ethylene glycol monobutyl ether.

10. The method of cleaning articles which comprises spraying the articles with a mechanically combined unstable mixture of a grease solvent and water emulsion and an unemulsified grease solvent, collecting the sprayed mixture, remixing and recirculating said mixture through the cleaning spray.

11. The method of cleaning metal parts which comprises providing a bath containing an unstable mixture of a grease solvent and water emulsion and unemulsified grease solvent in which the unemulsified solvent forms a layer on top of the emulsion, dipping the parts to be cleaned entirely through the solvent layer into the emulsion, and withdrawing the parts from the bath, said grease solvent containing pine oil and a hydrocarbon grease solvent that is lighter than water, and the water constituent of the emulsion being in amount at least four times the volume of all other ingredients of the mixture.

12. The methodofcleaning metal parts which comprises providing a bath containing an unstablemixture of a grease solvent and water emulsion and unemulsifled grease solvent in which the unemulsified solvent forms a layer on top of the emulsion, dipping the parts to be cleaned entirely through the solventlayer into the emulsion, and withdrawing the parts from the bath, said grease solvent containing pine oil and a hydrocarbon grease solvent that is lighter than water, said mixture containing an amine soap made from oleic acid, said soap being present in an amount insufficient to emulsify all of the solvent, and the water constituent of said emulsion being in amount at least four times the volume of all other ingredients of the mixture.

13. The method of cleaning metal parts which comprises providing a bath containing an unstable mixture of a grease solvent and water emulsion and unemulsified grease solvent in which the unemulsified solvent forms a layer on top of the emulsion, dipping the parts to be cleaned entirely through the solvent layer into the emulsion, and withdrawing the parts from the bath, said grease solvent containing a major proportion of a hydrocarbon grease solvent that is lighter than water, a minor proportion of pine oil and a small quantity of triethanolamine, said mixture employing as an emulsifying agent an amine soap made from oleic acid, said soap being present in an amount insufiicient to emulsify all of the solvent, and the water constituent of said emulsion being in amount at least four times the volume of all other ingredients of the mixture.

14. The method of cleaning metal parts which comprises providing a bath containing an unstable mixture of a grease solvent and water emulsion and unemulsified grease solvent in which the unemulsified solvent forms a layer on top of the emulsion, dipping the parts to be cleaned entirely through the solvent layer into the emulsion, and withdrawing the parts from the bath, said grease solvent containing a major proportion of hydrocarbon grease solvent that is lighter than water, a minor proportion of pine oil and a small quantity of ethylene glycol monobutyl ether, and the water constituent of said emulsion being in amount at least four times the volume of all other ingredients of the mixture. 15. The method of cleaning an article which consists in maintaining a cleaning bath consisting of an emulsion of grease solvent in water and an overlying layer of unemulsified grease solvent which is lighter than water, drawing material from the bath at a point located below the unemulsified grease solvent layer and in proximity to the interface between the two liquids, spraying the material so drawn on the article, collecting the sprayed material in the bath, and maintaining an unstable mixture of said unemulsified grease solvent and said emulsion in the material so sprayed on the article.

CHARLES A. CAMPBELL.

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