US2220125A - Degreasing - Google Patents

Description

Nov. 5, 1940.

M. Y. SEATQN 2,220,125

DEGREASING Filed April 2, l9 40 gwvmbma Max 31 60 11 72 M 9. W-gm Patented Nov. 5, 1940 UNITED STATES pacnnssmc Max Y. Seaton, Greenwich, Conn assignor to Westvaco Chlorine Products Corporation, New

York, N. Y., a corporation of Delaware Application April 2, 1940, Serial No. 327,541

fi claims. (Cl. 202-56) This invention or discovery relates to degreesing; and it comprises, in a method 01 vaporphase degreasing by a body of organic solvent vapor established and maintained as a layer be- 5 tween a supply of boiling solvent and a,supernatant atmospheric layer, with metal parts or other objects to be degreased being brought into contact with said body of solvent vapor, and with solvent vapor taken from a high level in said layer being condensed and returned, the improvement wherein water is removed from the system by contacting the vapor in said body, or the condensate formed therefrom, with a drying agent adapted to take up the water, advantageously by absorption; and it comprises apparatus adapted for application in the practice of this process; all as more fully hereinafter set forth and as claimed.

a0 Vapor-phase degreasing systems are wellknown and widely employed for the removal of grease, dirt, etc., from various types of 'metal objects. In some instances, metal sheets and other large objects are subjected to a degreasing 25 treatment of this type, and in other instances, nuts, bolts and other small machine elements are so treated, usually in baskets or racks adapted to hold a large number of these small pieces.

Generally speaking, a vapor-phase degreaser' includes a reservoir for solvent, means for heating the solvent in the reservoir and evaporating it therefrom, and a chamber above the reservoir. The chamber holds a body of solvent vapors evolved from the solvent in the reservoir, and is generally provided with a cooling coil or other cooling means positioned at an appropriate height in the chamber, andadapted to prevent the vapors from rising too far, or passing into 40 the air and out of the system. The degreaser is also provided with suitable means for conducting the articles to be degreased to, through and from the vapor chamber. This may include a suitable trolley system with baskets or racks for small 45 parts to be treated.

Any volatile grease solvent yielding relatively heavy vaporsthat is, vapors oi comparatively high molecular weight-can be used. In practice, halogenated derivatives of the aliphatic hy- 50 drocarbons, such as trichlorethylene, are particularly favored as solvents. They are substantially free from the fire hazard which accompanies the use of volatile hydrocarbons. In operation of a degreasing system, solvent in 55 the reservoir'is boiled, usually by passing steam,

at suitable pressure through heating coils in the reservoir. Solvent vapors are evolved andfpass upwardly into the degreasing chamber where, being considerably heavier than the atmosphere, they tend to form a more or less uniformlayer or lake. At or near the desired upper surface of this vapor layer or lake, cooling coils are provided on the sides of the chamber, and these coils are maintained at such temperature that any solvent vapors reaching them are condensed. The condensed vapors of clean solvent are ordinarily collected in an annular trough or channel extending around the chamber belowthe cooling coils, and from this trough, the condensate is returned to the system. It ,is generally returned to aclean'solvent reservoir, separate from, but communicating with, the evaporating reservoir. In some methods of operation, the articles to be degreased are dipped into the solvent reservoir before being held in contact with the solvent vapors.

As stated, the solvent vapors tend to form a substantially uniform layer between the boiling solvent and the supernatant atmospheric layer, because of their high specific gravity. In operation there'is, of course, an intermediate layer between the solvent vapor and the normal atmosphere, in which a certain amount of solvent vapor is mixed with air due to disturbances 39 caused by introducing articles to be degreased into the vapor lake and removing them therefrom. This intermediate layer generally does not extend substantially above the cooling coils, however, because the solvent content of such a layer, when proper solvents are employed, is readily condensed. It is generally desirable to so regulate the steam supply to the evaporating section that a minimum amount of solvent is 40 condensed by the cooling coils. Condensation of excessive amounts oi solvent vapor involves a waste of both steamand cooling water. In order to maintain a body of solvent vapor of the desired depth, however, it is necessary tosupply a certain excess of heat units and to condense a certain amount of solvent on the coils.

when a vapor-phase degreasing'system is in operation, articles more or less coated with grease and other dirt are immersed in the solvent vapor in any suitable manner Due to the relatively low temperature of the "work or treated material, the solventvapor condenses on its surface; and the condensed solvent then drips'oflf, carrying with it the grease and other dirt and impurities. These tend to accumulate in the solvent evaporating section, being generally less volatile than the solvent.

The solvent employed is generally anhydrous or commercially dry-when it is introduced into .the system, but under some climatic conditio s hydrocarbons, and is widely used in vapor-phase degreasers- However, cheaper solvents, suchas carbon tetrachloride, for example, can be employed to advantage in degreasing systems if water is excluded from the system or promptly removed therefrom before it has an opportunity to cause solvent deterioration and metal corrosion. The exclusion or prompt removal of water is also advantageous in improving the efl'ectiveness ofa degreasing system, and the uniformity of its operation with any solvent.

In my copending application, Serial No. 220,378, of, which the present application is a continuation-in-part, I have disclosed that the difficulties encountered because of the entrance of moisture into a vapor-phase degreasing system can be avoided by providing in the system means for contacting the solvent vapors, or the condensate formed therefrom, or both, with suitable inorganic adsorbents, such as calcined magnesia, activated alumina, vated magnesia and like materials. I have also disclosed in the said application that by properly-' selecting these adsorbents, any acids which are formed in the system can be eliminated, and that the odoriferous substances formed from the greases and other impurities collected in the system during operation can also be eliminated.

In many instances, it is highly desirable to eliminate two or more of these undesired materials (water, acids and odoriferous bodies) ordi- 'narily encountered in vapor-phase degreasing systems, and this is readily accomplished in accordance with my said prior application. However, there are many other instances in which it is only necessary or desirable to eliminate the moisture. In such circumstances, I have found that highly desirable and beneficial results are obtained by the application of hygroscopic agents which do not have substantial adsorbent properties. Useful substantially non-adsorbent inorganic materials for this purpose include calcium chloride, magnesiumperchlora-te, P205, specially baked calcium sulfate, caustic soda (either in the anhydrous or monohydrated form), lime, and numerous other known desiccating or dehydrating agents. For the sake of convenience, materials of this type are generically designated herein as non-adsorbent inorganic drying agents. It should be understood, however, that some of these materials may have some adsorbent properties; but that the dehydration resulting from the use of such compounds depends more on absorption or chemical combination of the water than on adsorption. In many instances, the water taken up by the drying agents now contemplated causes liquefaction or solution of these agents.

activated bauxite, silica gel, acti- 1 tic soda, lime, etc.; and such dehydrating agents serve to neutralize acids present in the system, while'removing moisture therefrom.

. Afterthe drying agent to be employed in-accordance. with this invention is selected, it may be applied in various ways, as with the adsorbent materials described in my aforesaid prior application. For example, a basket of perforated metal or vwire screen containing lime or other dehydrating agent is suspended inthe body or stratum of solvent vapor in the degreasers, and any vapor coming in contact with this dehydrating agent is substantially freed from moisture. I find that it is generally evenmore effective, however, to provide a container 'of the selected drying agent in the path of the liquid condensed solvent returning from the cooling coils to thedegreaser reservoir. As previouslystated, the usual vaporphase degreaser includes an annular channel or gutter which collects the condensed solvent dropping from the cooling coils. With such an arrangement, it is a simple matter. to introduce a percolating tower containing lime or caustic soda or calcium chloride or other selected dehydrating agent into the line which returns the clean condensed solvent from this collecting channel to the clean solvent well, or to any other desired part of the system. If desired, part of the condensed solvent may flow through this tower in contact with the dehydrating agent, while part of it is by-passed around the tower directly back to the reservoir.

If desired, a non-adsorbent drying agent may be employed in a percolating tower through which the recondensed solvent passes, and in which it is dehydrated, and a suitable adsorbent may be simultaneously employed in contact with the solvent vapors to remove odoriferous substances, etc., therefrom.

In order that my invention may be more readily understood, it will now be described with reference to the accompanying drawing, in which the single figure is a somewhat diagrammatic illustration of a cross sectional view of a vapor phase degreasing apparatus adapted for operation in accordance with my invention.

In the drawing, the walls or shell 2 enclose a degreaser having a bottom portion which is divided into a vaporizing section or evaporator 4 and a clean solvent well 6. The vaporizing section 4 is provided with steam coils 8 which are supplied with steam from any suitable source (not shown) in quantity suflicient to vaporize the desired amount of solvent. The vaporized solvent rises into the chamber above the vaporizing section to a predetermined level, such as that indicated by the line 9, and any substantial quantity of vapor rising above this level is condensed by the cooling coils l2. These coils are advantageously individually controlled, so that effective cooling can be accomplished at any desired level. Condensate formed by the operation of the cooling coils collects in the annular channel M, from which it may be returned to any desired part of the system, such as the clean solvent well 6,

removal therefrom of water or acids, or odoriferous substances, or a plurality of these undesired constituents, depending on the contents of the said basket.

In another and generally more advantageous embodiment of my invention, the condensate collected in the channel or gutter l4 passes through a suitable conduit 22, which is advantageously controlled by valve 23, into a percolating tower 24 or other suitable vessel. This tower or container is advantageously provided with ,a removable cap or cover 26, and a removable basket of perforated metal or wire screen 28 fitted rather snugly in its interior. This basket is filled with a suitable drying agent such as lime or caustic soda or calcium chloride, advantageously in granular form, through which condensate delivered through the passage 22 must trickle or percolate on its way back to the system. This results in an effective drying'of the condensed solvent, which then flows through a pipe 30 back to the clean solvent reservoir 6. Part of the condensed solvent may be by-passed around the percolating tower, as by flowing directly from the collecting channel l4 back to the clean solvent reservoir 6 through the pipe 16, if desired. In this procedure, the valve 18 and the pipe I6 are adjusted to maintain the desired level in the channel I4. Alternatively, the valve I8 may be closed entirely.

If desired, I may, as previously stated, employ both the external percolating tower 24 and the internal suspended basket 20; and the two consary or desirable to. employ both of these expedients simultaneously, however.

Clean solvent collected in the reservoir 6 overflows into the evaporating section 4, from which it is again vaporized into the degreasing chamber. I have found that in all the embodiments of my invention water is readily eliminated from the system when employing suitable drying agents of the type mentioned hereinabove; and acids and odoriferous substances may also be eliminated or minimized if desired.

My invention has been described hereinabove with special reference to certain types of construction, methods of operation, and choices of dehydrating agents which are now considered desirable, but it is to be understood that these references are made by way of illustration only, and that the invention is not limited to them, but may be variously embodied and practiced within the scope of the appended claims.

What I claim is:

-1. In a process of vapor-phase degreasing, wherein a body of organic solvent vapor of high molecular weight is established and maintained between an underlying boiling body of the liquid solvent, and a supernatant atmospheric layer, with cooling and condensation of solvent vapor passing upwardly above a pre-determined level in said body of vapor, and return of condensed solvent to the system, the improvement comprising contacting solvent vaporized from said boiling body of solvent and before its return thereto with a drying agent to remove water therefrom.

2. The process of claim 1, wherein said drying agent is a substantially non-adsorbent inorganic material.

3. The process of claim 1, wherein the said drying agent is contacted with vaporized solvent in said body of solvent vapor.

4. The process of claim 1, wherein the said drying agent is contacted with solvent after said condensation thereof.

5. The process of claim 1, wherein said drying agent comprises material having an alkaline reaction which neutralizes acidity in the said L solvent.

MAX Y. SEATON.

Images