LUBRICANT FOR IMPROVED SURFACE QUALITY OF CAST ALUMINUM AND METHOD

Field of the Invention

[0001] The invention relates to lubricant formulations for use in the casting of

aluminum or aluminum alloy ingots or bodies. In particular, the invention relates to

using lubricants containing water and surfactants to improve the surface quality of cast

ingots or bodies, resulting in enhanced product recovery. A method for producing

aluminum or aluminum alloy ingots with enhanced surface quality is also disclosed.

Background of the Invention

[0002] The casting of alloys may be done by any number of methods known to

those skilled in the art, such as direct chill casting (DC), electromagnetic casting

(EMC), horizontal direct chill casting (HDC), hot top casting, continuous casting,

semi-continuous casting, die casting, roll casting, and sand casting.

[0003] Each of these casting methods mentioned above has a set of its own

inherent problems, but with each technique, surface imperfections can be an issue. In

the aluminum alloy casting art, molten metal (or melt for brevity) surface oxidation

can produce various surface imperfections in cast ingots such as pits, vertical folds,

oxide patches and the like, which can develop into cracks during casting or in later

processing. A crack in an ingot or slab propagates during subsequent rolling, for

example, leading to expensive remedial rework or scrapping of the cracked material.

One mechanical means of removing surface imperfections from an aluminum alloy

ingot is scalping. Scalping involves the machining off a surface layer along the rolling

faces of an ingot after it has solidified. However, scalping results in lost metal.

[0004] Rectangular ingot yields for high magnesium alloys such as 7050 and

other 7xxx alloys as well as 5182 and 5083 alloys are especially prone to surface

defects and cracking caused by initiation at vertical folds on the surface of the ingot.

In the past, beryllium has been added, usually at part per million (ppm) levels to some

of these alloys to control melt surface defects, and to prevent magnesium loss due to

oxidation. In addition, materials, especially those containing fluorine, such as boron

trifluoride and ammonium fluoroborate, have been used to promote uniform oxide

distribution and therefore reduce surface defects and cracking. However, the use of

these additives can be very costly and beryllium itself may fall into disuse due to

allegations regarding health, disposal, and environmental issues that it creates.

Furthermore, the use of gases can create toxic and corrosive gaseous atmospheres. For

these reasons, suitable replacement strategies to control the nature of oxides during

casting are needed.

[0005] In the casting of aluminum alloys it is also known in the art to use a

mold lubricant. Satisfactory ingot surfaces can be obtained using a lubricant that is

effective in keeping aluminum from sticking to the mold at high temperatures used in

casting aluminum alloys. In early casting practices, greases were commonly employed

as mold lubricants. However, with the advent of modern casting methods, including

continuous or semi-continuous casting, free flowing oils have been used to provide

continuous lubrication and have replaced the use of greases as mold lubricants.

[0006] Continuous casting refers to the uninterrupted formation of a cast body

or ingot. For example, the body or ingot may be cast on or between belts, as in belt

casting; between blocks, as in block casting; or in a mold or die that is open at both

ends, as in direct chill (DC) casting. Casting may continue indefinitely if the cast body

is subsequently cut into desired lengths. Alternately, the pouring operation may be

started and stopped when an ingot of desired length is obtained. The latter situation is

referred to as semi-continuous casting.

[0007] Continuous lubrication is required for fully continuous casting and offers

a number of advantages for semi-continuous casting. These advantages include

substantial reduction of flame and smoke, substantial reduction of dragging and

tearing tendencies near the end of the cast, and allowing casting practices that produce

better quality and more uniform surfaces.

[0008] Despite the use of continuous lubrication during casting, a limitation of

current ingot casting practice exists in the non-uniform growth of oxide at the

meniscus of molten metal at the mold interface. Non-uniform oxide growth at the

meniscus of the molten metal and mold interface is particularly problematic for

alloying elements that rapidly oxidize in air or in air containing moisture. For

example, alloys containing lithium and magnesium may oxidize rapidly and in both

cases, the vapor pressure of the element is higher than that of aluminum. As a result,

magnesium and lithium may diffuse to the surface of the ingot and react with oxygen

or moisture in tihe ambient air.

[0009] Distribution of the surface oxide on the ingot head and at the meniscus

plays an important role in fold prevention or formation. Data from previous research

shows that humid air can produce an oxide/hydroxide film that protects magnesium-

containing alloys from runaway or uncontrolled magnesium oxidation at molten metal

temperatures. Since the weight gain of the magnesium-containing alloy is

significantly reduced in humid air as compared to dry air, the oxide layer is thinner and

the oxide distribution is believed to be more uniform. Another mechanism that plays a

part in the transformation of molten metal to solid metal is the heat transfer at the mold

wall between the molten metal and lubricant coated mold wall.

[0010] There remains a need for an effective alternative to beryllium and

fluorine containing materials to prevent surface imperfections, such as vertical folds,

pits, oxide patches and the like from forming during aluminum ingot casting, and to

control the nature and distribution of oxides, particularly when casting aluminum that

is alloyed with elements like magnesium and lithium. Such an invention would be

instrumental in preventing cracks, which can form during casting or can develop in

later processing. Finally, the invention preferably would have no adverse affect on

alloy properties.

[0011] The primary object of the present invention is to provide a lubricant

composition that allows for uniform distribution of surface oxide at the meniscus

formed between the molten aluminum and the mold during the continuous and semi-

continuous casting of aluminum alloy ingots.

[0012] Another object of the present invention is to provide a lubricant

composition that promotes a uniform and controlled rate of heat transfer at the

interface formed between the molten aluminum and the mold during the continuous or

semi-continuous casting of aluminum alloy ingots.

[0013] A still further object of this invention is to provide a casting lubricant

that promotes uniform oxide distribution without requiring the use of toxic and

corrosive gaseous atmospheres, and thus eliminating associated emissions and

equipment corrosion.

[0014] Still another object of this invention is to provide a method tfiat

promotes uniform oxide distribution on aluminum alloy ingots or castings that does

not require beryllium additions to the alloy and fluorine containing atmospheres.

[0015] A final object of the invention is to provide a casting lubricant

composition that allows for a stable meniscus during the continuous and semi-

continuous casting of aluminum alloy ingots.

[0016] These and other objects and advantages are met or exceeded by the

instant invention, and will become more fully understood and appreciated with

reference to the following description.

Summary of the Invention

[0017] In the present invention it is believed that when water and surfactant are

added to casting lubricants, the improved lubricant formulation can provide a method

for uniformly distributing the surface oxide at the meniscus. Uniform distribution of

the oxide at the meniscus reduces vertical fold formation that can lead to cracks in the

aluminum ingot. In addition, the mixture promotes uniform heat transfer around the

mold. Uniform heat transfer around the mold allows the solidifying aluminum alloy to

stay in contact with the mold longer and form a thicker and stronger ingot shell. Water

has an extremely high heat of vaporization when compared to other liquids that can

further pull heat away from the meniscus and be affecting this interaction. Uniform

heat transfer will also lead to reduced vertical fold formation and associated cracking.

[0018] Water and surfactant are added to existing lubricant bases to prepare the

lubricant formulations of this invention. The lubricant formulation is mixed in a high

speed mixing operation, such as blending or shearing, or any other mixing operation

known by those skilled in the art to provide dispersions, emulsions, and/or true

solutions. At this stage, the formulation is ready to use as a casting lubricant.

[0019] In the process of casting aluminum alloy ingots, the lubricant

formulation of this invention is supplied to the oil ring of a cooled continuous or semi-

continuous casting mold, which subsequently lubricates the inner wall of the

continuous casting mold. Molten aluminum alloy is cast into the mold. It is believed

that the lubricant allows for uniform distribution of the surface oxide at the meniscus

of the lubricated inner mold wall and the molten aluminum base alloy interface.

Brief Description of the Drawings

[0020] Figure 1 is a flowchart for preparation of the formulation of the lubricant

of the instant invention.

[0021] Figure 2 is a schematic characterization of a DC continuous casting

mold used in the method of this invention.

[0022] Figures 3a and 3b show the faces of aluminum alloy ingots cast with the

use of a standard lubricant and the lubricant formulation of the present invention.

[0023] Figure 4 is a graph showing the isothermal thermogravimetric analysis

of 5083 aluminum alloy in dry and wet air.

[0024] Figure 5 is a graph showing the isothermal thermogravimetric analysis

of 7050 aluminum alloy in dry and wet air.

[0025] Figure 6 is a flowchart for preparation of the formulation of a lubricant

with increased water content resulting from the use of a higher percentage of

surfactant.

[0026] Figure 7 is a flowchart for preparation of the formulation of a lubricant

with increased water content resulting from the use of a selected compound.

[0027] Figure 8 is a graph showing surfactants that increased the lubricant water

content to greater than about 0.5 %.

[0028] Figure 9 is a graph showing compounds or mixtures of compounds that

increased the lubricant water content to greater than about 0.5 %.

[0029] Figure 10 is a graph showing water solubility in formulations other than

glycerol trioleate.

[0030] Figure 11 is a graph showing nonionic surfactants used to increase the

lubricant water content.

[0031] Figure 12 is a flowchart for preparation of the formulation of a lubricant

composition having a lubricant base, water, surfactant, and a high viscosity organic

material.

[0032] Figure 13 is a graph showing the kinematic viscosity values for water

additions to glycerol trioleate.

[0033] Figure 14 is a graph showing the percent change in kinematic viscosity

values for different amounts of a single molecular weight poly alpha olefin (PAO 25)

in glycerol trioleate.

[0034] Figure 15 is a graph showing the percent change in kinematic viscosity

values for three different molecular weight poly alpha olefins at 50 vol% and with 0.1

wt% water in glycerol trioleate.

Detailed Description of Preferred Embodiments

[0035] All component percentages herein are by weight percent unless

otherwise indicated. Also, when referring to any numerical range of values, such

ranges are understood to include each and every number and/or fraction between the

stated range minimum and maximum. A range of about 0.05 % to about 0.5 % by

weight of water, for example, would expressly include all intermediate values of about

0.06, 0.07, and 0.08% water, all the way up to and including 0.4 and 0.49 % water.

The same applies to each other numerical property and/or elemental range set forth

herein.

[0036] The instant invention provides a casting lubricant formulation and

method for using this formulation that substantially reduce vertical fold formation that

can lead to cracks in an aluminum ingot. In particular, it is believed that practice of

the instant invention allows for uniform distribution of the surface oxide at the

meniscus of the molten aluminum alloy. In addition, practice of the instant invention

leads to uniform heat transfer around a casting mold.

[0037] Referring now to Figure 1, a flowchart for preparation of the lubricant of

this invention is presented. The invention improves on existing lubricants used in the

casting of aluminum and aluminum base alloy ingots and forms, and in the general

manufacture of aluminum products, using thermomechanical processes such as, but

not limited to, casting, extrusion, hot and cold rolling, and forging.

[0038] In a preferred embodiment, an existing aluminum alloy casting lubricant,

glycerol trioleate, is used as the lubricant base. This is evidenced by box number 1 in

the flow chart. Box number 2 in the flowchart evidences the amount of water and

surfactant that is mixed with the lubricant base. About 0.05% to about 0.5% by weight

of water could be added to the lubricant base, but about 0.1 % to about 0.4% by weight

of water is preferred. Similarly, less than about 0.25% by weight of surfactant could

be added to the lubricant base, but about 0.05% to about 0.2% of surfactant is

preferred. The types of lubricant that can be used include for example, but without

limitation, glycerol trioleate, ethyl oleate, methyl oleate, butyl ricinoleate, methyl

acetyl ricinoleate, butyl oleate, glycerol triacetyl ricinoleate, butyl acetyl ricinoleate,

polyalphaolefins, polyisobutylenes, castor oil, peanut oil, corn oil, canola oil,

cottonseed oil, olive oil, rapeseed oil, safflower oil, sesame oil, sunflower oil, soybean

oil, linseed oil, coconut oil, palm kernel oil, neat's-foot oil, lard oil, tallow oil, and

combinations thereof. Any type of water can be used, but soft water is preferred. For

purposes of this invention, soft water is to be defined as water with a low content of

polyvalent cations. It will be appreciated by those of ordinary skill in the art that

polyvalent cations are ions that have more than one positive charge. Examples of

polyvalent cations are calcium (Ca ), magnesium (Mg ), iron (Fe and Fe ), and

aluminum (Al ⁺³ ). The surfactant can be cationic, anionic, nonionic, or combinations

thereof. The surfactant used in this invention was Kimberly Clark® Professional Pink

Lotion Soap. This soap is available from the Kimberly Clark Corporation. The

mixture is then subjected to high shear for about 5 minutes as represented by box

number 3 in the flowchart. High shear is defined as at least 100 revolutions per

minute (RPM). Shearing devices including, but not limited to, household blenders,

can be used to shear the mixture. The lubricant so formulated, as represented by box

number 4 in the flowchart, is applied to a casting mold in any manner that is familiar

to those skilled in the art of casting aluminum alloys.

[0039] It is believed that a major benefit of the lubricant of this invention is

realized in uniformly distributing surface oxides at the meniscus during DC casting of

aluminum. However, it is recognized by those skilled in the art that the lubricant of

this invention can be used in any theraiomechanical processing of aluminum and its

alloys. These processing steps include, but are not limited to casting, hot and cold

rolling, forging, and extrusion.

[0040] Referring now to Figure 2, a cross-section of a DC casting mold 10,

which can be used to cast aluminum alloy ingots according to the instant invention, is

schematically depicted. The DC casting mold 10 comprises molten metal 11 from a

furnace. The molten metal is held in a trough 12. A control pin 13 activates and

deactivates the flow of molten metal 11 into a distributor bag 14, which distributes the

molten metal into the cooled mold 15. The molten metal 11 in the cooled mold 15

may form an oxide skim 16. The inner wall 17 of the cooled mold 15 is cooled by a

liquid cooling jacket 18 that cools the mold 15 and floods the solidified ingot surface

19 with cooling liquid 20. The liquid is preferably water, but could be any liquid

suitable for cooling the ingot 22. The liquid flows from a liquid pump (not shown)

that is connected to the sides of the cooling jacket 18. The inner wall 17 is also

continuously lubricated with a formulation of the instant invention by using an oil ring

21 positioned at or near the meniscus of where the molten metal 11 in the mold 15

contacts the inner wall 17 of the cooled mold 15. An oil ring is preferred, but other

methods of continuously lubricating the mold inner wall could be used. In a preferred

embodiment, the lubricant formulation comprises about 0.1% to about 0.4% by weight

of water and 0.05% to about 0.2% by weight of surfactant with the remaining

percentage being glycerol trioleate base. Molten metal 11 in the mold 15 solidifies

into a solidified ingot 22. The solidified ingot 22 rests on a starting block 23. The

starting block 23 rests on a starting block holder 24. The starting block holder 24 is

attached to a platen 25. The platen can be lowered or raised by a cylinder ram 26. As

molten metal 11 in the mold 15 solidifies into a solidified ingot 22, the cylinder ram 26

is lowered, which causes the solidified ingot 22 to also be lowered according to the

directional arrows 27 superimposed onto the schematic cross section of the DC mold

10. As the cylinder ram 26 and solidified ingot 22 are lowered, the control pin 13 is

activated to allow more molten metal 11 in the trough 12 to flow into the cooled mold

15 via the distributor bag 14, and ingots of aluminum alloy are cast, the length of such

ingots being constrained only by the movement of the cylinder ram 26. During the

ingot casting operation, the solidified ingot 22 is in contact with the inner wall 17 and

is continuously lubricated with the lubricant of this invention via the oil ring 21 or any

other method used to continuously lubricate the mold inner wall, thusly providing a

process for minimizing undesirable surface defects, such as vertical folds that were

described earlier. During the practice of this invention, there is no requirement for the

undesirable practice of alloying the aluminum with beryllium, nor is there any reliance

on using toxic materials such as ammonium fluoroborate or boron trifluoride to

prevent oxidation during casting.

[0041] To test the lubricant formulation, a lubricant was formulated according

to the teachings of this invention as described in the following example.

EXAMPLE

[0042] 7200 grams of glycerol trioleate, 8 grams of water, and 4 grams of

Kimberly Clark® Professional Pink Lotion Soap were combined and sheared, via use

of a household blender, at high speed (1000 RPM) for five minutes. The lubricant

formulation was used in the casting of Aluminum Alloy 5083 and 7050. Casting

position 1, which was used as the control, utilized only glycerol trioleate as the

lubricant. As can be seen in figure 3 a, the resultant aluminum alloy ingot was covered

with vertical folds. Casting position 2 alternated between using glycerol trioleate and

the lubricant formulation of the present invention. As represented in figure 3b, the

resultant aluminum alloy ingot had only a few light vertical folds when the lubricant

formulation of the present invention was used.

[0043] The distribution of the surface oxide on the ingot head and at the

meniscus plays an important role in fold prevention or formation. Figures 4 and 5

represent the isothermal thermogravimetric analysis of 5083 and 7050 alloys in dry air

100 and wet air 200, respectively. For purposes of this invention, dry air is air with a

dew point of 59° F or less and wet air with a dew point between 60° F and 100° F.

Data from previous research shows that wet air 200 can produce an oxide/hydroxide

film that protects the high magnesium alloy from runaway or uncontrolled magnesium

oxidation at molten metal temperatures. Since the weight gain of the magnesium-

containing alloys is significantly reduced as compared to dry air 100, the surface oxide

is thinner and is believed to be more uniformly distributed. This change in oxide

distribution would play a significant role in vertical fold suppression. Introducing the

oxygen, in this case in the form of water mixed with oil and surfactant, provides the

method for changing the metal oxide distribution at the meniscus. The critical

technical part is to form a homogeneous distribution of water in the oil so water would

be limited, but available uniformly over the surface of the casting mold and at the

meniscus immediately before solidification. The water may be uniformly dispersed in

the oil as a dispersion, emulsion, a true solution, or a combination thereof. For

purposes of this application, the term dispersion is defined as the distribution of a

substance, as fine particles or droplets, evenly throughout a medium, the term

emulsion is defined as distributing a substance throughout a medium via use of an

emulsifier, such as a surfactant, to help link the substance and the medium together,

and the term true solution is defined as a homogeneous mixture formed by mixing a

solid, liquid, or gaseous substance with a liquid or sometimes a gas or solid.

Uniformly distributing the water in this manner reduces vertical folds and the

possibility of associated cracking by also controlling the heat transfer between the

molten metal and the lubricant interface on the inner wall of the mold, thereby

allowing the solidified shell to stay in contact with the mold longer and form a thicker

and stronger shell.

[0044] A key for lubricant formulations is to have no undissolved or

precipitated solid phases that can plug the small orifices delivering the lubricant to the

surface of the mold. With this limitation, all lubricants formulated within this

invention are effectively single phase mixtures of components, representing

thermodynamically stable solutions or blends, or stable dispersions or emulsions that

are defined, for the purposes of this invention, as not forming separate phases after 30

months of storage.

[0045] By increasing the solubility of water in the lubricant, the tendency to

have undissolved or precipitated water phase is reduced. It is generally believed that

the water content of casting lubricants should be limited because of the concern for

explosions. This concern is alleviated if the water can not be trapped under the

aluminum. For this reason, the lubricant is added above the meniscus so the lubricant

drips into the meniscus and is not trapped under the molten aluminum. In order to

increase the amount of soluble water in the lubricant, surfactants other than Kimberly

Clark ^® Professional Pink Lotion Soap have been used. As shown in Figure 8, there

were five surfactants that were able to increase the water content of the lubricant to

greater than about 0.5 wt%. Figure 6 shows a flowchart for the preparation of this

lubricant. As evidenced by box number 2, the percentage of water in the lubricant is

between about 0.1 % and about 3.5 % by weight. The percentage of surfactant is less

than about 20% by weight and preferably between about 0.05% to about 10% by

weight.

[0046] In addition, compounds such as phosphates, borates, fluorides, and

silicates have been added to increase the performance of the lubricant. Other

compounds could be used, but these compounds, or mixtures containing them, were

selected based on their ability to form single phase mixtures or stable dispersions or

emulsions in the lubricant and their ability to react with the aluminum, or to generate a

deposit on it, thus providing a surface layer at the meniscus. The surface layer acts as

a barrier to control friction and minimize sticking of the aluminum to the mold and in

this way, provides a second means of improving aluminum-die contact conditions.

Since many forms of compounds are polar, inorganic salts and related compounds,

such as salts of alkali and alkaline earth metals, their solubility in glycerol trioleate is

limited. However, as shown in Figure 9, 0.8 % of water saturated with 6 % boric acid

was solubilized in glycerol trioleate with the aid of surfactants such as hexylene

glycol, which enhances the stability of the mixture of water and the dissolved boric

acid in the glycerol trioleate. This provides the combined benefits of the water and the

inorganic friction-controlling material. Alternatively, these elements in

organometallic species, such as trioctyl phosphate, can be dissolved directly in

glycerol trioleate, and with the aid of hexylene glycol, can be present along with

higher levels (0.8 %) of dissolved water as well. Figure 7 shows a flowchart for the

preparation of a lubricant with increased water content when mixed with a compound

as described above. As evidenced by box number 2, the percentage of water in the

lubricant is between about 0.1 % and about 0.8 % by weight. The percentage of

surfactant is less than about 20% by weight and preferably between about 0.05% to

about 10% by weight.

[0047] Figure 10 shows water solubility in additional formulations. In

Formulation A, which incorporates 2 % boric acid with glycerol trioleate, 4.0 %

hexylene glycol, and 4.0 % methanol, 0.8% water can be stabilized. However, in the

presence of an additional 10 % hexylene glycol, the water content in the formulation is

increased to 2.0 %. In addition, castor oil can also hold a larger amount of water,

around 1.0 %, than glycerol trioleate, which may be increased through the use of

surfactants herein.

[0048] Figure 11 shows that when certain selected nonionic surfactants were

used, instead of the surfactants in Figure 8, even higher levels of water were soluble in

glycerol trioleate. The highest level of soluble water obtained was 3.5 wt% using 5 %

Tergitol 15-S-7, a product that is well suited to stabilizing water in oil formulations

due to its ability to balance suitably both its affinity for water and its affinity for lipids,

such as oils, waxes, fats, and other related and derived compounds. The percentage of

surfactants in figures 8 and 11 is less than about 20% by weight and preferably

between about 0.05 % to about 10 % by weight.

[0049] It should be recognized that the dissolved water content of the lubricant

base can vary with composition, manufacturing procedures, and handling and storage

practices. The instant invention provides a means to increase the water content above

the normal limit at a given temperature and to generate a known final water content

based on analyzing the base oil initially for water content or treating it to achieve its

known water content limit prior to treating with surfactant or other compounds and

additional water.

[0050] It should also be recognized that the metal oxide distribution at the

meniscus can be changed by introduction of oxygen, in whole or in part, via the

surfactants, especially the oxygen-rich non-ionic surfactants, such as hexylene glycol

and the Tergitol 15-S products.

[0051] In addition to uniform distribution of the surface oxide on the ingot head

and at the meniscus and uniform heat transfer around a casting mold, controlling the

stability of the meniscus during casting also plays an important role in fold prevention

and formation. An unstable meniscus is often observed during casting by the change

of the meniscus shape running along and around the mold face. It is believed that

increasing the viscosity of the casting lubricant will provide less fluidity and thus

greater stability of the molten metal meniscus. A casting lubricant composition that

allows for a stable meniscus during the continuous and semi-continuous casting of

aluminum alloy ingots is needed. For the purposes of this invention, a stable meniscus

can be defined as maintaining a near constant contact angle between the casting mold

and the molten aluminum alloy. There is increased resistance to meniscus deformation

in order to maintain a constant distance between the molten aluminum and the cold

mold surface. It is believed that having a meniscus with increased stability will

substantially reduce the possibility of the molten metal from adhering to and being

dragged down the side of the mold. Reducing this possibility, in turn, will increase the

surface quality of the resultant aluminum alloy ingot or billet.

[0052] It is believed that when water, surfactant, and organic materials having

high viscosity are added to casting lubricants, the improved lubricant formulation can

provide a method for uniformly distributing the surface oxide at the meniscus in

addition to creating a more stable meniscus. The organic material would also

preferably have a low vapor pressure. A low vapor pressure organic material would be

one that has a boiling point above 100° C. Having a stable meniscus with a uniform

distribution of oxide reduces vertical fold formation that can lead to cracks in the

aluminum ingot or billet. The lubricant formulation is mixed in a high speed mixing

operation, such as blending or shearing, or any other mixing operation known by those

skilled in the art to provide stable dispersions, stable emulsions, and/or true solutions.

At this stage, the formulation is ready to use as a casting lubricant.

[0053] In the process of casting aluminum alloy ingots, the lubricant

formulation is supplied to the oil ring of a cooled continuous or semi-continuous

casting mold, which subsequently lubricates the inner wall of the continuous casting

mold. Molten aluminum alloy is cast into the mold. It is believed that the lubricant

allows for uniform distribution of the surface oxide at the meniscus in addition to

increasing its stability.

[0054] Referring to Figure 12, a flowchart for preparation of the lubricant is

presented. The invention improves on existing lubricants used in the casting of

aluminum and aluminum base alloy ingots and forms, and in the general manufacture

of aluminum products, using thermomechanical processes such as, but not limited to,

casting, extrusion, hot and cold rolling, and forging.

[0055] In the preferred embodiment, an existing aluminum alloy casting

lubricant, glycerol trioleate, is used as the lubricant base. This is evidenced by box

number 1 in the flow chart. Box number 2 in the flowchart evidences the amount of

water, surfactant, and high viscosity organic material that are mixed with the lubricant

base.

[0056] About 0.05% to about 0.5% by weight of water could be added to the

lubricant base, but about 0.1 % to about 0.4% by weight of water is preferred.

Similarly, less than about 0.25% by weight of surfactant could be added to the

lubricant base, but about 0.05% to about 0.2% of surfactant is preferred. Finally,

between about 5% to about 90% by weight of high viscosity organic material could be

added to the lubricant base, but between about 10% to about 80% by weight of high

viscosity organic material is preferred. The types of lubricant that can be used include

for example, but without limitation, glycerol trioleate, ethyl oleate, methyl oleate, butyl

ricinoleate, methyl acetyl ricinoleate, butyl oleate, glycerol triacetyl ricinoleate, butyl

acetyl ricinoleate, polyalphaolefins, polyisobutylenes, castor oil, peanut oil, corn oil,

canola oil, cottonseed oil, olive oil, rapeseed oil, safflower oil, sesame oil, sunflower

oil, soybean oil, linseed oil, coconut oil, palm kernel oil, neat's-foot oil, lard oil, tallow

oil, and combinations thereof. Any type of water can be used, but soft water is

preferred. For the purposes of this invention, soft water is to be defined as water with

a low content of polyvalent cations. It will be appreciated by those of ordinary skill in

the art that polyvalent cations are ions that have more than one positive charge.

Examples of polyvalent cations are calcium (Ca ⁺² ), magnesium (Mg ⁺² ), iron (Fe ⁺² and

Fe ⁺³ ), and aluminum (Al ⁺³ ). The surfactant can be cationic, anionic, nonionic, or

combinations thereof. The surfactant used in this invention was Kimberly Clark®

Professional Pink Lotion Soap. This soap is available from the Kimberly Clark

Corporation. A high viscosity organic material is defined as an organic material with a

viscosity value of at least 10 centistokes at 100° C. The range of viscosity values for

this preferred embodiment is between about 10 centistokes to about 8000 centistokes

with a preferred range of about 15 centistokes to about 4000 centistokes at 100° C.

The types of high viscosity organic materials that could be used include, for example,

but without limitation, poly alpha olefins, polybutylene, castor oil, high molecular

weight esters (Oleon radialube 7396, Radialube 7597, and Clariant L-4, all at 40° C),

polyacrylates, Ketjenlube, polyglycerol esters, polyalkylene glycols, polypropylene

glycols, polyvinyl alcohols, oligomerized vegetable oils, and stannous octoate.

[0057] The mixture is then subjected to high shear for about 5 minutes as

represented by box number 3 in the flowchart. High shear is defined as at least 100

revolutions per minute (RPM). Shearing devices including, but not limited to,

household blenders, can be used to shear the mixture. The lubricant so formulated, as

represented by box number 4 in the flowchart, is applied to a casting mold in any

manner that is familiar to those skilled in the art of casting aluminum alloys.

[0058] To examine the effect that the high viscosity organic material had on the

lubricant base, several tests were performed. Water was mixed with glycerol trioleate

at 0.1 and 0.2 wt% under high shear. Depending on the permeability of the lubricant

base to water, surfactant could be used. However, for the purposes of these tests, a

surfactant was not used. After mixing, the kinematic viscosities were measured at 40°

and 100° Celsius to obtain a viscosity index. For the purposes of this invention,

kinematic viscosity is defined as a measure of the internal resistance to flow of a liquid

under gravity. The kinematic viscosities were about 42 centistokes at 40° C and about

8 centistokes at 100° C for 0 wt %, 0.1 wt %, and 0.2 wt% water. As shown in figure

13, the values for the kinematic viscosities did not change from that obtained for

glycerol trioleate alone. Further tests were made using various amounts of single

molecular weight poly alpha olefin having 25 centistokes viscosity at 100° Celsius

(PAO 25). PAO 25 was the sole additive to the lubricant base, which was glycerol

trioleate. As shown in figure 14, at the 50 vol% formulation using PAO 25, the

viscosity increased from values obtained for glycerol trioleate by 55% and 32% for

measurements made at 40° and 100° Celsius. While the poly alpha olefin 25 provided

increased viscosities, higher molecular weight poly alpha olefin materials were

evaluated to obtain even greater increases in viscosity values. As shown in figure 15,

using poly alpha olefin having 40 centistokes at 100 ° C (PAO 40) and poly alpha

olefin having 100 centistokes at 100° Celsius (PAO 100), both at 50 vol%, the

viscosity values increased by 1.5 and 3.5 times that obtained from glycerol trioleate

alone. The addition of 0.1 wt% water did not affect the viscosity values for the new

formulations shown in figure 15. The use of high viscosity organic materials with a

lubricant base, such as glycerol trioleate, provides a substantial increase in the

viscosity of the lubricant. It is believed that the use of this higher viscosity lubricant

during casting of aluminum alloy ingots or billets will provide less fluidity and thus

greater stability of the meniscus at the interface between the molten aluminum and the

casting mold. Less fluidity and greater stability of the meniscus would improve ingot

and billet surface quality, thus enhancing product recovery.

[0059] It will be readily appreciated by those skilled in the art that modifications

may be made to the invention without departing from the concepts disclosed in the

forgoing description. Such modifications are to be considered as included within the

following claims unless the claims, by their language, expressly state otherwise.

Accordingly, the particular embodiments described in detail herein are illustrative only

and are not limiting to the scope of the invention which is to be given the full breadth

of the appended claims and any and all equivalents thereof.