US2431657A - Process of controlling lubricating emulsions - Google Patents

Description

Patented Nov. 25, 1947 PROCESS OF CONTROLLING LUBRICATING EMULSION S Judson A. De Cew, Mount Vernon, N. Y.

No Drawing. Application September 16, 1942, Serial No. 458,570

1 Claim.

In machine shop practice it is customary to use large quantities of compounds called cutting oils, which consist largely of mineral oil, blended with water soluble materials acting as emulsifying agents. These compounds are mixed with water by merely pourin them into a large excess of water and stirring the mixture at which time either emulsions or solutions are formed. These diluted oils, containing from two parts to twenty parts of oil to one hundred parts of water, are poured over the cutting tool, in order to keep it cool and at the same time, offer some lubricating effect in helping the metallic shaving slip past the surface of the tool, and to prevent later oxidation of the metallic surface of the object being treated.

The present state of the art is that a great many different compounds are used and all that is known about them by the operator is that some work better than others under different conditions and each product is used in whatever concentration is required.

I have discovered the principle under which these emulsions or solutions function and the means by which this function can be used to the greatest advantage.

It is elementary knowledge that an oily surface cannot be wetted and that a Wet surface cannot be oiled. How then can a metallic surface which has been made wet by pouring over it an aqueous lubricant in which the water is in great excess, be made oily by means of an oil emulsion. This is only possible when the emulsion used has the capacity to deposit an oily film over the metallic surface and this capacity depends upon the diffusion pressure exerted by the oil in colloidal solution.

This diffusion pressure varies with the concentration of the oil particles (which must be below a certain size in the emulsified state), and particularly with the ratio of oil to the emulsifying agent. For example, if a cutting compound dissolved readily in cold water to a clear solution, then there will be no oil particles in emulsion to expose a large surface area thereof to collect a negative charge. Thus, the oil will not be drawn to the anode or positively charged metallic surface by electrical attraction. In contrast, if the compound on dilution, is broken up into relatively large oil particles, such as of the size of suspen- 2 sions, the area surface exposed by each particle will be so small that these particles will not migrate to an anodic surface by electrical attraction.

This invention comprises producing an oil emulsion in which the oil particles are substantially of the dimensions of a hydrosol, namely, between .1 and .001 i and in which the negative electrical potential is greater than the positive charge of the emulsifying agent. This unbalanced potential then causes the negatively charged oil particles to migrate to the positively charged metallic surface to which it is exposed, and they will be deposited upon that surface by adsorption forming an oily film. This means that the least amount of emulsifying agent must be used and in order to produce the required emulsion under this condition, special means of emulsification may be used.

In order to disperse the oil into a particle size of a hydrosol it is necessary to partly dilute the compound, using a small amount of emulsifying agent, with the dilution taking place under conditions which will produce the least amount of decomposition and the means of doing this are, as follows:

The compound should be given a mechanical treatment step by being forced under pressure through an atomizing device into hot Water containing a protective colloid or a weakly alkaline solution or both. The protective colloid may be of vegetable origin such as a solution of starch or soy bean protein or of animal origin such as casein or glue. The latter may be used if antiseptics are used along with them to prevent decomposition.

Although any protective colloid may be used the amount must be just suflicient to stabilize the emulsion to a point where the hydrosol will not break down or agglomerate into a suspension of relatively coarse particles, and sufficient to encourage the formation of a hydrosol instead of a solution upon final dilution.

When an alkali is used in the first stage of dilution, I prefer to use a 1 6 normal solution of borax which will have a pH of 9.2 and if any other alkali is used, it should be adjusted to produce a solution having a pH of between 8 and 10. The borax solution may also be used between these limits.

When diluting the cutting compound in a hot alkaline solution of such a pH, the oil disperses into finer particles than if diluted in water alone and the hydrosol will retain its particle size over a longer period.

Procedure.The oil to be emulsified should be subjected to a physical treatment step of being placed in a heating tank and brought to a temperature of approximately 180 F. The oil, such as engine oil, is subjected to a chemical treatment step comprising being mixed together with a suitable emulsifying agent such as 15% of a sulphonated oil, a soap or oleic acid. A suitable emulsifying agent is one that is soluble in the oil to be emulsified and in the aqueous solution that is to be a part of the emulsion.

From this tank there is a discharge pipe which carries it to the mechanical treatment step comprising an atomizing apparatus. where it is pressure blended (at not substantially less than 1 00 pounds pressure per square inch), with hot water at approximately 180 F. In this hot water there is the protective colloid or alkaline solution which dilutes the compound into a practically undecomposed solution. That is, this hot water has been brought to a normal alkalinity by the addition of borax and containing 1% soy bean protein. The mixture will have a concentration of from 15% to of oil.

Thereupon, the mixture is immediately discharged intocold water where the dispersion of the oil takes place. In the final stage of dilution, the oil will be in the proportion of from 2 to 5 parts of oil to 100 of water.

The oil particles in this final mixture will have substantially the subdivision of a hydrosol, the particles being microscopically visible and exhibiting. the Brownian movement. These particles will be all negatively charged and will exert diffusion pressure in proportion to their exposed surface. These oil particles will migrate towards and seize upon any positively charged surface such as a freshly exposed metallic surface and form a film of oil thereon. This makes it possible todeposit oil upon a wet surface, which under.

other conditions is not possible; That is what might be called oil-plating. Such an oily film will form by adsorption upon the metallic surface when the concentration of oil is only 2 parts to 100 of water.

The principles of this invention are, as follows:

1stthe efiiciency of emulsion lubrication results from the formation of an oil film upon awet metallic surface by adsorption: 2donly oil particles of a finer state of division than suspensions or having a diameter less than .1, assume a negative electrical charge sufficient to exert diffusion pressure which causes the formation of the oil film over the positively charged wet surface, and 3d-the hydrosols are produced by a combination of mechanical, physical and chemical treatment steps, each function of which is essential. The mechanical means are the high pressures required for instantaneous mixing and emulsifying action. The physical means are the special temperatures used. The chemical means are the emulsifying agents.

Another principle of my invention is that the particle size of the dispersed oil and the diffusion pressure exerted thereby are more important than the character of the oils used, since the diffusion pressure is proportional to the number of particles exhibiting Brownian movement.

In the operation of my emulsifying system the proportions of protective colloid material and the- I instance as copper.

alkalinity of the solution must be adjusted to the stability of the compounds being used. Although it is desirable to use only those compounds that are unstable by ordinary methods of dilution, it is still possible to improve the character of an over-stabilized compound which on dilution does not liberate enough oil particles of the proper dimension.

In diluting such a compound it is necessary to make it less stable, and this is accomplished by using in the first stage of dilution, a very weak solution of boric acid. A T 6 normal solution of boric "acid has a pH of 52 and therefore an aqueous solution of boric acid having "a pH of between 5.2 and '7, can be used to render the compound sufficiently unstable to liberate the oil particles at the proper dimensions so that they will have the proper electrical potentials.

As this invention is devised to cover the dilution of various types of compounds, it is not possible to specify the exact conditions for each compound for these must be adjusted to produce the type of dispersion required which can only be determined and controlled after microscopic examination of the dispersion.

The purpose of heating the oil and then diluting it in a hot aqueous solution at temperatures as high as F. is to obtain an instantaneous solution but in order to prevent coalescence of the oil particles at that temperature, it must be instantaneously cooled by dilution in cold water. Lesser temperature produces coarser particle sizes. The purpose of using a protective colloid or weak alkali is to reduce the surface tension on the oil particles and prevent them becoming united into larger particles. The amount of emulsifying agent used has an effect On the other conditions, in that the less agent used, the more critical becomes the temperature and the pressure, the latter of which might even require raising.

Once the dispersion is obtained by mechanical or physical means, the dispersed oil can exert a definite diffusion pressure because of the amount of surface area and yet be stable because of the reduced surface tension. In other words, itis stabilized at the point of instability where it is the most ffective. In this connection, the final dilution is also important for the more dilute is the final dispersion, the more stable are the oil particles since they are not so close together.

Since it is a function of the operation of this invention, that the oil particles be so treated that they exhibit the Brownian movement and carry a negative charge of electricity, it is important that the metal to be lubricated and cooled, to which the oil particles are to be attracted, are charged positively in order to act as an anode. The metal of the cutting tool itself is usually positively charged, but the metal being operated onmay be normally negatively charged, such for In such a case, when it is important that the oil particles be attracted to the-metal being cut as well as to the cutting tool, my proposalis to supply the negative metal with enough electricity to render its charge into a positive one so that it too will attract negatively charged oil particles to itself as an anode.

I claim:

A method of making lubricating emulsions which comprises forming an aqueous compound of an emulsifiable lubricant and an emulsifying agent that is soluble in the lubricant and in the water, atomi'zing such compound into hot water to form a solution therewith while controlling the proportion of emulsifying agent used in the 5 compound to be substantially the minimum for yielding such a solution by such atomization, discharging such solution into cold water wherein due to dilution and change of temperature, particles of the lubricant pass from solution phase to emulsion phase wherein they are in suspension and a majority of which are small enough to exhibit the Brownian movement, stabilizing the emulsion for minimizing coalescence of the 1ubri cating particles, and adjusting the pH of the emulsion until the negative charges of the lubricating particles overbalance the positive charges of the emulsifying agent in the solution on the basis of lowering the pH to reduce deposited potential.

JUDSON A. DE CEW.

REFERENCES CITED The following references are of record in the file of this patent:

OTHER REFERENCES Emulsions and Foams by Berkman & Egloff, page 174, Reinhold Publishing Corp. (Copy in Division 64.)

Theory of Emulsions by Clayton, page 193, P. Blakistons Son 8: Co. (Copy in Division 64.)

.Colloid Chemistry, Alexander (4th ed), Van Nostrand Co. Inc. (1937), p. 104 and p. 109.