Ether Amides In Aqueous Lubricants

Abstract

Metals, when rolled or otherwise compressed, are lubricated by an aqueous solution of an organic, polar, surface-acting composition having a negative heat of solution which is an ether amide which is soluble in the water at a lower temperature but insoluble in the water at the temperature to which the aqueous solution is heated during compression of the metal. This aqueous lubricant eliminates the fire hazard involved in the use of the present non-aqueous lubricants.

Parent Case Text

This application is a continuation-in-part of my application Ser. No. 791,259 filed Jan. 15, 1969 now abandoned.

Description

This invention relates to the use of an aqueous lubricant on metals, including aluminum and magnesium, etc. during size reduction, as in rolling, extrusion or other compression. The aqueous lubricant is to replace the oil-based lubricants presently employed, and because of the large amount of water present the aqueous lubricant is preferred because it eliminates the fire hazard which is present when highly heated metal and an oil are brought into contact with one another. By eliminating the fire hazard, size reduction operations can be carried out at faster speeds at which the metal is heated to a higher temperature at which the danger of fire would be increased if an oil lubricant were used.

The solute of the aqueous lubricant used in carrying out the invention is a material which has a negative heat of solution and is more soluble in water at a lower temperature at which it is supplied to the rolling or extrusion system, and is less soluble at a higher temperature to which it is heated during the rolling or extrusion so that it separates from solution as a solid or liquid and serves as a lubricant.

The lubricant is an organic, polar, surface-acting composition--an ether amide--which has a negative heat of solution and is soluble in water at a lower temperature and separates at the higher temperature to which it is heated during the operation. It is free from mineral oil.

The ether amides which are useful in carrying out this invention have the following representative formulas: ##SPC1##

In which R is an alkyl, cycloalkyl, aryl, aralkyl or alkaryl group of six to 24 carbon atoms; m is 0, 1 or 2; and n equals the number of recurring alkyl ether groups and may be any number from 2 to 100, inclusive. The amide group contributes water solubility equivalent to about three or four ether groups. In other words, if R+m/n+3 = about 0.5 to 2.5, or preferably 0.8 to 2.0, a good lubricant is obtained with a concentration of about 5 to 10 or 20 per cent of the amide in water. Compounds of the first formula are listed in Table I and compounds of the second formula are listed in Table II. These compounds are listed as representative of those which can be used satisfactorily. ##SPC2## ##SPC3##

The concentrations of the chemical compounds having negative solubility, as they are used in aqueous solutions may vary from a few tenths of one per cent up to 25 or 50 per cent or more, and is usually 1 to 20 per cent, depending upon the nature of the compound and the temperatures to which the aqueous solution is subjected in the treatment of different metals. In most instances, the amount dissolved in the aqueous phase will depend on the viscosity and lubricity obtained. Generally, a clear solution which is easily pumped is required so that the solution may be filtered to remove suspended particles. Such filtration is generally essential for the production of a metal product with a bright unmarred finish.

The temperatures of solution and separation of the lubricant will vary, depending upon the metal being treated and the method of treatment. Usually the lubricant should be soluble at about room temperature. The temperature of rolling will depend upon the metal, etc. In rolling, the aqueous lubricant may be sprayed on upper and lower rolls, or the lower roll may be immersed in a bath of the lubricant. In extrusion the lubricant is added in any desired manner.

The invention is further described in connection with the accompanying drawings which are largely schematic.

FIG. 1 is a vertical section through equipment for a rolling operation; and

FIG. 2 is a vertical section through equipment used in extrusion.

FIG. 1 is illustrative of the application of the invention to one method of rolling a metal; namely, the cold-rolling of aluminum. It will be noted that the thickness of the metal 1 is reduced to that shown at 2 as the metal is passed between the rolls 4 and 5.

The tank 7 contains a clear, aqueous solution of lubricant which is continuously or periodically drawn off through the pipe 10 and filtered and returned through the pipe 11, usually some going to the spray head 13 and the balance being returned through the pipe 14 to the tank. If the filtering operation is carried out only periodically at long intervals, some of the clear lubricant from the tank 7 can be pumped directly to the spray 13 through pipe 14 for spraying the upper roll 4 while the lower roll 5 is rotated while partially submerged in the lubricant contained in the tank. As the aluminum or other metal is reduced from the thickness 1 to the thickness 2, a great deal of heat is given off and the rolls 4 and 5 become heated. The temperature of the bath may be controlled manually or automatically within a few degrees below the precipitation temperature to prevent overheating which would precipitate the lubricant. Water or lubricant may be added as required to maintain the desired concentration.

In starting up the operation the liquid sprayed on to the roller 4 and the entire liquid within the tank is clear. As the rolls 4 and 5 heat up, these rolls become hot enough to cause separation of the lubricant from the water solution either as a separate liquid phase or in particular form. The drawing illustrates how, after the rolls 4 and 5 have been heated up, the liquid is converted to particulate form on the roll 4 due to its heat, and the heat of the roll 5 tends to cause separation of the solute adjacent the roll 5 as it is rotated in it. Thus the lubricant is supplied as a clear aqueous solution at a lower temperature and as heat is generated by the rolling operation and the rolls 4 and 5 become more and more heated the lubricant separates more rapidly after contact with the heated roll 4, and the lubricant surrounding the roll 5 separates and the separated phase adheres to the roll as it continues to rotate and carry the separated lubricant to the interface between the roll and the metal being treated. It is here that the lubricant which separates at a higher temperature performs its useful function. For example, in rolling aluminum, the separation may start at any temperature between 30.degree. and 95.degree. C.

The solute which separates on the roll 4 as the spray becomes heated and the solute which separates on the roll 5 as it becomes heated adhere to the rolls and are carried to the interface where they serve to lubricate the surface between the roll and the metal, thereby forming a smooth surface on the metal as well as cooling it while it is being compressed. The advantages of this method of producing a lubricant are not immediately apparent.

Heretofore, lubricants used in extruding or rolling metals when used with water, have been in a necessarily very stable finely divided or nearly colloidal emulsion form. The manufacture of a finely divided emulsion has been difficult and it has also been difficult to maintain the emulsion over different conditions of operating temperatures and speeds. In order to be a good lubricant, the lubricant must be brought out and made available to the metal surface. The better lubricants were made as emulsions which were deliberately made unstable so that the lubricant would separate out as a distinct phase. However, such unstable emulsions are difficult to handle and frequently are so heterogeneous that they do not give a uniform coating of lubricant at all times.

This invention overcomes the above difficulties by providing a homogeneous solution containing a controlled amount of lubricant which lubricant is freed at the point and at the time most needed for lubricity. Upon cooling, the lubricant re-enters solution and maintains a uniform concentration of the bath. As the lubricant is separated from the aqueous phase by the increase in temperature, some, or nearly all, of the water is evaporated, which further concentrates the lubricant. This evaporation of the water leaves behind a uniform film of lubricant on the rolls 4 and 5 which is transferred to the metal. Although evaporation also occurs in the usual emulsion system, the remaining lubricant film is spotty and, therefore, does not yield a smooth and continuous deposit on the roll or on the metal as does the lubricant of this invention.

In the practice of this invention the cold-rolling system, when it is first started, will not contain heat in the rolls 4 or 5, or in the metal 2. Therefore, the rolls should be heated up by some means, either electrically or by steam, in

The solutes which may be used in preparing the lubricant solutions may be compounds well known in the literature, or they may be new compounds which have properties desired in the aqueous lubricant. A mixture of compounds having different properties may be employed to give the desired solubility and lubricity at required temperatures.

The following are examples of the amide ethers which may be used in carrying out this invention. In the table, only two examples are shown to illustrate the effect of the ethylene oxide groups on the amide-type of derivative. The tallow amide is saturated and is somewhat less soluble than the unsaturated amide and separates at a lower temperature. The tests were made on heating a 1% aqueous solution of the amide ether:

Moles Ethylene Separation Point Amide Oxide .degree.C. __________________________________________________________________________ Red oil 5 90 Hydrogenated 5 85 tallow amide __________________________________________________________________________

In rolling a metal such as aluminum, for example, the ingot is usually passed through one set of rolls in one direction and then, after narrowing the bite of the rolls, it is passed between the same rolls in the opposite direction, and this is repeated to gradually reduce the thickness of the sheet-usually without much widening of the sheet. Eventually it is often transferred to other rolls for the final rolling operation or operations. As the thinning process proceeds the temperature of the sheet increases. In operations where an oil lubricant has been employed the speed of the operation has to be reduced to prevent the metal from becoming so hot as to ignite the oil. An advantage of the use of an aqueous lubricant is that the danger of ignition is eliminated and the speed of the operation can be increased because the water is a better coolant and the evaporation of water operates to keep the rolls and the treating bath cool. If the speed of the operation is too fast using the conventional non-aqueous lubricants, eventually the bath temperature becomes very high and there is an economic loss of volatile hydrocarbon and ester-type of lubricant medium. The rolls also become too hot, and the rolled sheet is neither as smooth nor bright as desired. The advantage of using the aqueous system is that the speed of the rolling operation can be increased four or five fold because the heat is easily carried off or controlled both by the evaporation of the water and by the high heat capacity of water. The amount of water evaporated may be considerable, but this is infinitesimally small in comparison to the losses that would be effective if an equal quantity of non-aqueous lubricant were evaporated.

In the practice of this invention, from 1 to 20 per cent or more of the compound, and preferably 5 to 10 per cent, having a negative heat of solution is dissolved in water to form a clear, homogeneous solution.

Claims

I claim:

1. The method of rolling or extruding metals which comprises rolling or extruding a metal while its surface is lubricated with mineral-oil-free aqueous solution of 1 to 20 per cent of an ether amide which is soluble in the water at the temperature and concentration at which it is supplied for use in the method and has the formula ##SPC4##

in which R is an alkyl, cycloalkyl, aryl, aralkyl or alkaryl group of six to 24 carbon atoms; m is 0, 1 or 2; and n equals the number of recurring alkyl ether groups and may be any number from 2 to 100, inclusive, and from which the lubricant is separated as the solution is heated by heat generated by the compression of the metal, and thereby separating lubricant from the solution and depositing it on the surface of the metal being tested.

2. The method of claim 1 in which the ether amide has the formula

3. The method of claim 1 in which the ether amide has the formula

4. The method of claim 1 in which the metal article is a metal sheet. 5. The method of claim 1 in which metal is lubricated as it is rolled, and the separation temperature of the aqueous lubricant is between substantially 30.degree. and 95.degree. C.