Mist lubrication process

An improved mist lubrication process whereby excellent lubrication and misting properties are obtained utilizing synthetic ester mist lubricants derived from specific polyol esters, trimellitate esters and dimer diesters and a mixture of polyisobutylene polymers having different molecular weights is provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an improved mist lubrication process whereby 
excellent lubrication and misting properties are obtained utilizing 
synthetic ester mist lubricants derived from specific polyol esters, 
trimellitate esters and dimer diesters and a mixture of polyisobutylene 
polymers having different molecular weights. 
2. Description of the Prior Art 
Automatic lubrication using mist oils is well known and, for certain 
applications, recognized as the most effective and economical means of 
providing a controlled amount of lubricant to the point of lubrication. 
Mist oil lubrication is particularly useful when the point or area to be 
lubricated is not readily or safely accessible. 
Oil mist systems are extensively utilized for lubrication of equipment used 
in steel processing operations and have been found to be a particularly 
effective means of lubrication for the roll bearings in hot strip mills 
resulting in more efficient lubricant utilization and prolonged bearing 
life. The extended bearing life is generally believed to be the result of 
(1) more uniform lubricant distribution, (2) lower bearing temperatures, 
and (3) elimination of contaminants--these latter two benefits being the 
direct result of the positive air flow associated with the application of 
the mist to the bearing. 
In addition to having acceptable lubrication properties, the lubricants 
used in these systems must also have acceptable mist characteristics. High 
molecular weight polymers, such as polybutenes, polyisobutylenes, 
polyacrylates, and ethylene-propylene copolymers, are added to the base 
oil to develop proper mist characteristics. A general discussion of the 
effect of polymeric additives on mist properties is presented by T. D. 
Newingham in Lubrication Engineering, 33 (3), 128-132 (1977). 
U.S. Pat. No. 3,510,425 discloses a mist lubrication process which uses 
mineral oil-based mist oils containing 0.05 to 3.5 weight percent of a 
polyester. Polyesters which are useful for the formulation of the mist 
oils have number average molecular weights from 80,000 to 150,000 and are 
derived from esters of acrylic or methacrylic acid and C.sub.12--12 alkyl 
monohydric alcohols. 
A process of lubrication utilizing mineral oil-based mist lubricants is 
disclosed in U.S. Pat. No. 3,855,135. Polymeric additives employed for the 
process of U.S. Pat. No. 3,855,135 have viscosity average molecular 
weights from 10,000 to 2,000,000 and are selected from polystyrene and 
polystyrene in admixture with a polyacrylate or polybutene. From 0.01 to 2 
weight percent of the polymeric additive is added to the mineral oil to 
obtain acceptable mist characteristics. 
A process of micro-fog lubrication utilizing mineral lubricating oils 
containing a minor proportion of a polymeric additive having a number 
average molecular weight of at least 10,000 is also disclosed in British 
patent specification 1,099,450. The polymeric additives are products which 
are normally used as VI improvers in motor oils and especially those 
having low shear stability. Copolymers of vinyl acetate, alkyl fumarate 
esters and N-vinyl pyrrolidone having number average molecular weights of 
at least 100,000 are indicated to be particularly useful additives for the 
process. 
U.S. Pat. No. 3,805,918 discloses a process whereby undesirable stray mist 
in mist oil lubrication is reduced to low levels by using mist oils 
containing from 0.001 to 2 weight percent of an oil-soluble polyolefin 
mist suppressant. Oil-soluble copolymers of ethylene and C.sub.3-12 
mono-olefins and having average molecular weights greater than 5,000 are 
particularly useful additives. In addition to the use of petroleum-derived 
base oils, hydrocarbon base oils such as alkyl, aryl, and alkaryl 
phosphate esters, alkyl benzenes, polyoxyalkylene esters or glycols, ortho 
silicates and siloxanes and also indicated to be useful for the 
formulation of mist oil compositions employed for the process. 
Butene polymers are also utilized to obtain other lubricant compositions. 
For example, in U.S. Pat. No. 3,098,042 lubricant fluids and greases 
derived from either mineral or synthetic oils and containing a polymer of 
butene-1 having a molecular weight in the range 10,000 to 20,000 are 
disclosed. Various synthetic esters derived from mono- and/or dibasic 
acids and mono- or polyfunctional alcohols are disclosed as being useful 
for the preparation of these lubricants. The polybutene-1 can be utilized 
in an amount from about 0.5 to 12 weight percent. Conventional grease 
thickeners, such as salts and soaps of fatty acids, may also be present in 
the composition. Synthetic lubricants with good shear stability and cold 
temperature fluidity containing 10% to 95% diester with 90% to 5% of a 
polymer of butene are described in U.S. Pat. No. 3,860,522. The diesters 
are obtained from branched-chain dicarboxylic acids having from 16 to 22 
carbon atoms and aliphatic alcohols having fewer than 6 carbon atoms. The 
butene polymers have molecular weights from about 1,200 to 4,500. Neither 
of the above compositions, however, is utilized for oil mist applications. 
It would be highly useful if a process were available whereby superior 
lubrication and misting properties are obtained. It would be particularly 
advantageous if the process utilized readily available synthetic ester 
basestocks. 
SUMMARY OF THE INVENTION 
We have now quite unexpectedly discovered an improved process which 
utilizes mist lubricant compositions comprised of certain relatively high 
viscosity synthetic esters and a mixture of isobutylene polymers having 
different molecular weights. Synthetic esters which are employed in the 
process are polyol esters, trimellitate esters, and polymeric fatty acid 
esters having 40.degree. C. viscosities in the range 15 to 300 
centistokes. Two different polyisobutylene polymers are necessarily 
employed--one having an average molecular weight from 4,000 to 10,000 and 
the other having an average molecular weight from 25,000 to 300,000. 
With the present improved mist lubricant process, it is possible to 
efficiently generate acceptable mists over a wide range of operating 
temperatures. This feature makes it possible to obtain significantly 
increased throughputs. Additionally, by the process of this invention a 
significant improvement (15-20%) in bearing life is obtained over bearings 
lubricated with petroleum-based mist oils. 
For the process, a lubricant is generated in air maintained at a 
temperature of 100.degree. F. to 225.degree. F. and pressure of 10 to 100 
psig, pneumatically transported to a metal surface to be lubricated, 
coalesced into larger droplets, and deposited on the metal surface to 
provide a lubricating film thereon. The mist lubricant employed for the 
present improved process is comprised of (1) 45 to 95 parts by weight 
synthetic ester selected from the group consisting of (a) polyol esters 
derived from an aliphatic polyol having from 2 to 8 hydroxyl groups and 3 
to 12 carbon atoms and an aliphatic monocarboxylic acid or mixture of 
aliphatic monocarboxylic acids having from 5 to 20 carbon atoms; (b) 
trimellitate esters derived from trimellitic acid or trimellitic anhydride 
and an aliphatic alcohol having from 8 to 16 carbon atoms; and (c) 
polymeric fatty acid esters derived from a polymeric fatty acid containing 
75% or more C.sub.36 dimer acid and a C.sub.1-13 mono-functional alcohol; 
(2) 8 to 40 parts by weight, on a 100 percent polymer basis, 
polyisobutylene having an average molecular weight from 4,000 to 10,000; 
and (3) 0.1 to 1 part by weight, on a 100% polymer basis, isobutylene 
polymer having an average molecular weight from 25,000 to 300,000, is 
employed. The compositions typically have 40.degree. C. viscosities of 125 
to 750 centistokes and, more generally, 175 to 550 centistokes. Especially 
advantageous mist oil compositions contain 55 to 85 parts by weight 
synthetic ester, 12 to 30 parts by weight polyisobutylene having a weight 
average molecular weight of 4,500 to 8,500, and 0.25 to 0.85 part by 
weight polyisobutylene having an average molecular weight from 50,000 to 
200,000. Minor amounts of petroleum diluent(s) and effective amounts of 
conventional lubricant additives may also be present. 
DETAILED DESCRIPTION OF THE INVENTION 
Excellent lubrication and misting properties are obtained with the improved 
lubrication process of this invention whereby oil mist lubricants 
comprised of specific synthetic esters of relatively high viscosity, a 
first polyisobutylene polymer of relatively low molecular weight, and a 
second polyisobutylene polymer having a significantly higher average 
molecular weight than said first polyisobutylene, are utilized. The ester 
and polyisobutylene polymers are employed in specified ratios in order to 
achieve the desired balance of mist characteristics and lubricating 
properties. The present lubrication process finds particular advantage for 
the lubrication of roll bearings in hot strip mills. 
Mist lubrication processes are well known and numerous mist lubrication 
systems as well as operating conditions therefor are described in the 
literature. In general terms, mist lubrication processes involve 
generating an oil mist, also sometimes referred to as a micro-fog or 
aerosol, and pneumatically transporting said mist in air or other inert 
gas to the point(s) requiring lubrication. The mist is passed through a 
reclassifier, an orifice which causes the very small oil droplets to 
coalesce or condense into larger droplets, before being directed onto the 
object being lubricated. 
Mist generators are used to form the oil mists. Generally these generators 
consist of a reservoir for the lubricant which is connected to a venturi 
by means of an oil lift (siphon) tube. As compressed gas, usually air, is 
passed through the venturi the lubricant is drawn from the reservoir and, 
as it is intimately mixed with the air, formed into droplets. The 
air/droplet mixture is then contacted in the generator with a baffle which 
causes the larger droplets to condense and the condensate is returned to 
the oil reservoir. The smaller oil droplets, generally having diameters of 
3 microns or less, remain dispersed in the air and are pneumatically 
transported through manifold distribution lines to the point of 
lubrication. 
The amount and nature of the mist formed can be varied by changing the 
temperature of the air and the air pressure (velocity). Pressures between 
10 psig and 100 psig and, more preferably, from 20 psig to 80 psig are 
employed. Air temperature will generally range from 100.degree. F. to 
225.degree. F. It is especially advantageous if the air temperature is 
maintained between 125.degree. F. and 200.degree. F. 
The mist distribution system is designed to carry the oil/air dispersion to 
the point of lubrication with minimal condensation. Accordingly, the 
length of the lines should not be too long and care must be exercised in 
its design. For example, the number of bends in the line should be kept to 
a minimum and sharp bends should be avoided. Also, there should be no low 
points in the line where condensate can collect and create a blockage. 
Distribution lines are generally sloped, either toward the generator or 
toward the point of lubrication, to avoid collection of condensate. Drain 
legs are provided as necessary. Auxiliary lines generally come off of the 
top of the main distribution line. In general, the design requirements for 
the auxiliary lines are the same as for the main manifold or header. 
The oil/air dispersion is passed through a reclassifier (orifice) to 
convert (coalesce) the small oil droplets into larger droplets and 
increase the velocity of the oil/air dispersion--both of which insure 
maximum wetting of the surface to be lubricated. The size and type of the 
reclassifier will vary depending on the particular application involved 
and the oil/air dispersion characteristics. 
In these processes, the amount of lubricant which is processed, i.e., 
misted, is referred to as "throughput." Throughput is expressed as a unit 
of weight or volume per unit of time, e.g., grams/hour, and is further 
broken down into the following three components: (a) dropout, (b) 
reclassified oil, and (c) stray mist. Dropout is the amount of mist which 
is condensed in the lines and never reaches the reclassifier. Mist which 
is condensed in the distribution lines may be returned to the mist 
generator and remisted. Reclassified oil is the actual amount of lubricant 
which is applied to the surface being lubricated. Mist which is not 
applied to the surface being lubricated but rather escapes into the 
atmosphere is referred to as stray mist or stray fog. Since throughput is 
equal to (a)+(b)+(c), stray mist is obtained by determining the difference 
between the throughput and the sum of (a) and (b). Dropout, reclassified 
oil, and stray mist are often reported as a percent of throughput or can 
be represented as a ratio. 
From the foregoing, it is evident that even though high throughput can be 
achieved in a particular process, the distribution of mist components may 
render the process unuseable or uneconomical. For example, excessive 
amounts of line condensate (dropout) or excessive amounts of stray mist 
can result in inadequate delivery of lubricant at the point of 
lubrication. Stray mist is particularly troublesome since this is 
lubricant which is lost. This not only creates a hardship from an economic 
standpoint but it also presents a health and safety hazard. Thus, in 
developing an acceptable mist lubrication process and selecting a mist oil 
for such system, the distribution of mist components (a), (b) and (c) must 
be taken into consideration along with the throughput. 
Additionally, acceptable lubrication must be obtained with the process in 
order to have a completely acceptable oil mist system. This requires that 
the mist oil, in addition to having good mist properties, also exhibit 
good lubricity, oxidation stability, antiwear and extreme pressure 
properties, antirust/anticorrosion properties, and possibly other 
characteristics dependent upon the particular application involved. The 
lubricant must also be essentially free from undesirable waxes. Waxes can 
build up in the reclassifier heads and cause restriction or complete 
blockage thereof. In either event, insufficient lubricant will be 
delivered to the point of lubrication and, in the case of bearings, can 
substantially shorten the life of the bearing. 
The lubricant must also exhibit good wettability or spreadability on the 
surface(s) to which it is applied. One of the problems most frequently 
encountered with mist lubrication process for large bearings, such as 
those utilized on rolling mills, is lack of uniformity of lubricant 
distribution over all bearing and roll neck surfaces. This lack of 
adequate lubricant film results in excessive localized wear and premature 
bearing failure. "Dry neck" or areas of insufficient lubrication on the 
roll neck are frequently observed upon disassembly of mist oil lubricated 
roll bearings. Processes wherein all of the bearing and roll neck surfaces 
are uniformly coated with the mist lubricant significantly prolong bearing 
life and reduce operating costs. 
With the process of this invention, effective amounts of oil mist are 
readily produced while obtaining good oil mist distribution, i.e., low 
stray mist and low line condensate. Also, high throughputs are possible 
over a wide range of operating temperatures and pressures and undesirable 
wax deposits are minimized, and in most cases, completely eliminated. 
Additionally, and quite unexpectedly, improved wettability and 
spreadability of the mist oil lubricant is obtained so that, when used to 
lubricate rolling mill bearings, a uniform continuous film of lubricant is 
deposited on the bearing and roll neck. 
The foregoing improvements are obtained with the process of this invention 
which utilizes a mist lubricant composition containing a synthetic ester 
and a mixture of two polyisobutylene polymers having different average 
molecular weights. The synthetic esters employed are relatively high 
viscosity polyol esters, trimellitate esters, or polymeric fatty acid 
esters. These esters have 40.degree. C. viscosities in the range 25 to 300 
centistokes. Particularly advantageous mist oil compositions for the 
process are obtained when the viscosity (40.degree. C.) of the synthetic 
ester is between 50 and 250 centistokes. 
Polyol esters which can be used are derived from aliphatic polyols having 
from 3 to 12 carbon atoms and 2 to 8 hydroxyl groups. More generally, the 
polyol will contain 5 to 8 carbon atoms and 2 to 4 hydroxyl groups. 
Illustrative aliphatic polyols of the above types include neopentyl 
glycol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, 
2,2,4-trimethyl-1,5-pentanediol, trimethylolethane, trimethylolpropane, 
glycerol, pentaerythritol, dipentaerythritol, tripentaerythritol or the 
like. Technical pentaerythritol which contains mono, di-, tri- and higher 
pentaerythritols in varying proportions can also be used. Neopentyl 
glycol, trimethylolpropane and trimethylolethane are particularly useful. 
The polyols are reacted, partially or completely, with an aliphatic 
monocarboxylic acid or mixture of aliphatic monocarboxylic acids having 
from 5 to 20 carbon atoms. The C.sub.5-20 aliphatic monocarboxylic acids 
can be branched or straight-chain and may be saturated or can contain 
unsaturation. They can be obtained from natural fats or oils or 
synthetically produced via oxo, Koch or other known reactions. 
Illustrative aliphatic monocarboxylic acids include valeric acid, 
isovaleric acid, caprylic acid, capric acid, lauric acid, myristic acid, 
palmitic acid, isopalmitic acid, stearic acid, isostearic acid, ricinoleic 
acid, oleic acid, linoleic acid, and mixtures thereof. Mixed acids derived 
from coconut oil, lard oil, tall oil, safflower oil, corn oil, tallow, 
soybean oil, palm oil, castor oil, rapeseed oil, and the like may also be 
utilized. Polyol esters obtained from the esterification of 
trimethylolpropane with C.sub.12-18 aliphatic monocarboxylic acids or 
mixtures thereof, such as trimethylolpropane trioleate and 
trimethylolpropane triisostearate, are particularly useful for the 
preparation of the mist oil compositions used for the present process. The 
polyol esters typically have acid values less than 15 and hydroxyl values 
less than 100. More usually, acid and hydroxyl values of the polyol ester 
will be less than 8 and less than 25, respectively. 
Useful trimellitate esters are obtained from trimellitic acid or 
trimellitic anhydride and aliphatic mono-functional alcohols having from 8 
to 16 carbon atoms. Trimellitic acid and trimellitic anhydride are, of 
course, well known chemical products as are methods for their preparation. 
The aliphatic alcohols may be a straight-chain or branched primary, 
secondary, or tertiary alcohols. Illustrative alcohols include n-octyl 
alcohol, capryl alcohol, isooctanol, 2-ethylhexanol, decyl alcohol, 
isotridecyl and isodecyl alcohols, lauryl alcohol, myristyl alcohol, cetyl 
alcohol, and the like. Especially advantageous trimellitate esters are 
derived from C.sub.10-13 aliphatic alcohols or alcohol mixtures. Isodecyl 
trimellitate, isotridecyl trimellitate and mixtures thereof, i.e., 
isodecyl/isotridecyl trimellitate, are particularly useful esters of this 
type. Acid values of these esters are generally less than 15 and, more 
preferably, less than 5. Hydroxyl values are typically less than 10 and, 
more preferably, less than 3. 
The polymeric fatty acid esters are derived from polymeric fatty acids 
containing 75 percent or more C.sub.36 dimer acid and C.sub.1-13 
mono-functional alcohols. Polymeric fatty acids are known as are methods 
for their manufacture. They are obtained by the polymerization of 
olefinically unsaturated monocarboxylic acids containing from about 16 to 
20 carbon atoms, such as oleic acid, linoleic acid and the like. Processes 
for their production typically include: treatment of unsaturated fatty 
acid with acid catalysts such as HF, BF.sub.3, and the like; thermal 
polymerization of unsaturated fatty acids conducted in the presence or 
absence of treated or untreated clay catalysts; and treatment of 
unsaturated fatty acids with peroxides. By way of illustration of the 
preparation of polymeric fatty acids, reference may be had to U.S. Pat. 
Nos. 2,793,219 and 2,955,121. Polymeric fatty acids from the 
polymerization of unsaturated fatty acids are primarily comprised of dimer 
and trimer acids; however, there may also be present in the mixture some 
higher acids and unreacted monomer. 
C.sub.36 polymeric fatty acids are obtained by the polymerization of 
C.sub.18 unsaturated monocarboxylic acids, such as oleic acid and linoleic 
acid or mixtures thereof (e.g., tall oil fatty acids). These polymeric 
fatty acid products have as their principal components C.sub.36 dimer and 
C.sub.54 trimer acids. Excellent results are obtained with acids of this 
type which contain 75% by weight or more and C.sub.36 dimer acid, the 
remainder of the product consisting essentially of C.sub.54 trimer. High 
dimer content polymeric fatty acids containing substantially reduced 
amounts of higher polymer acids and unreacted unsaturated monocarboxylic 
acid can be obtained by molecular distillation or by the use of other 
highly efficient distillation procedures. The polymeric fatty acid may 
also be hydrogenated prior to use. Polymeric fatty acids of this type are 
commercially available products sold under the trademark Empol.RTM. Dimer 
Acids. 
Useful alcohols for the preparation of the polymeric fatty acid esters are 
aliphatic branched- or straight-chain, mono-functional alcohols having 
from 1 to 13 carbons. Representative mono-alcohols include methanol, ethyl 
alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, isoamyl 
alcohol, neopentyl alcohol, n-hexyl alcohol, n-octyl alcohol, 
2-ethylhexanol, decyl alcohol, isodecyl alcohol, isotridecyl alcohol, 
lauryl alcohol, and the like. Minor amounts of polyfunctional alcohols 
such as ethylene glycol, 1,2- or 1,3-propanediol, 1,3-, 1,4- or 
2,3-butanediol, 2,2,4-trimethyl-1,5-pentanediol, 1,6-hexanediol, neopentyl 
glycol, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, 
dipentaerythritol, tripentaerythritol, and the like may also be present 
with the monofunctional alcohol(s). Particularly advantageous polymeric 
fatty acid esters are obtained from polymeric fatty acids containing 85% 
or more C.sub.36 dimer acid and C.sub.8-10 aliphatic mono alcohols. 
Diisodecyl dimerate and di-2-ethylhexyl dimerate are especially 
advantageous. The polymeric fatty acid esters generally have acid values 
less than 100 and, more usually, less than 10. Hydroxyl values are 
generally less than 10 and, more preferably, less than 3. 
A mixture of isobutylene polymers of different average molecular weights 
are necessarily employed with the above-identified synthetic esters to 
obtain the mist oil compositions used for the present improved process. 
Typically, two polyisobutylenes are utilized--the first, referred to 
herein as the low molecular weight polyisobutylene, has an average 
molecular weight from 4,000 to 10,000, and the second, referred to herein 
as the high molecular weight polyisobutylene, has an average molecular 
weight from 25,000 to 300,000. Molecular weights referred to herein are 
weight average molecular weights (M.sub.w). Small amounts of other 
butylene polymers not falling within the above-identified molecular weight 
ranges may also be present. Particularly useful mist oil compositions of 
this invention are obtained when the low molecular weight polyisobutylene 
has an average molecular weight of 4,500 to 8,500 and the high molecular 
weight polyisobutylene has an average molecular weight of 50,000 to 
200,000. 
The isobutylene polymers essentially conform to the formula 
##STR1## 
where x is an integer representing the number of repeating units. Polymers 
of the above types are known and widely utilized throughout the industry. 
They are obtained by polymerizing isobutylene feeds which usually contain 
minor amounts of butene-1 and/or butene-2. When the term polyisobutylene 
or isobutylene polymer is used herein, it is intended to encompass the 
aforementioned types of polymers. 
The isobutylene polymers are obtained using known conventional 
polymerization techniques. The polymerization may be carried out in an 
inert hydrocarbon in which case a polymer solution containing from about 
30 to 80 percent polyisobutylene will be obtained. If desired, diluent may 
also be added to the polymer when the polymerization is complete. 
Isobutylene polymer solutions may be utilized in the formulation of the 
mist oils. This can facilitate handling and blending of the 
polyisobutylene with the synthetic ester. All parts and percentages 
recited herein for the polyisobutylenes are, however, calculated on a 100% 
polymer basis. Inert hydrocarbon present in the mist oil composition as a 
result of the use of an isobutylene polymer solution does not detract from 
the overall misting and lubrication characteristics of the products. 
Useful mist oil compositions for the process contain 45 to 95 parts by 
weight synthetic ester, 8 to 40 parts by weight, on a 100 percent polymer 
basis, low molecular weight polyisobutylene, and 0.1 to 1 part by weight, 
on a 100 percent polymer basis, high molecular weight polyisobutylene. 
More preferably, the mist oil compositions contain 55 to 85 parts 
synthetic ester, 12 to 30 parts by weight low molecular weight 
polyisobutylene and 0.25 to 0.85 part by weight high molecular weight 
polyisobutylene. 
Especially useful ISO 220, 320, and 460 mist oil lubricants, the grades 
most widely used in the industry for lubrication of bearings in hot strip 
mills, which provide excellent mist and lubrication properties in the 
present process are obtained by combining 63 to 78 parts 
di-2-ethylhexyldimerate (40.degree. C. viscosity 91 centistokes; viscosity 
index 155; pour point -50.degree. F.; acid value &lt;3; and hydroxyl value 
.ltoreq.2), 14 to 28 parts polyisobutylene having a number average 
molecular weight of about 7,500-7,600) and 0.33 to 0.66 part 
polyisobutylene having a number average molecular weight of about 
89,000-90,000). Compositions and typical characteristics of 220, 320, and 
460 ISO grade products, formulated with effective levels of additives are 
as follows: 
______________________________________ 
ISO ISO ISO 
220 320 460 
______________________________________ 
COMPOSITION (TS BY WEIGHT) 
Di-2-ethylhexyldimerate 
78 71 63 
Polyisobutylene (--M.sub.w 7,500-7,600) 
14 21 28 
Polyisobutylene (--M.sub.w 89,000-90,000) 
0.66 0.50 0.33 
TYPICAL CHARACTERISTICS 
Viscosity (ASTM-D-445) 
40.degree. C., cSt. 219 316 466 
100.degree. C., cSt. 26 33 44 
Viscosity Index (ASTM-D-2270) 
149 147 148 
Total Acid Number (ASTM-D-974) 
2.1 1.9 2.5 
(mg KOH/gm) 
Specific Gravity, 60/60.degree. F. 
0.902 0.904 0.900 
(ASTM-D-1298) 
Flash Point, .degree.F. (ASTM-D-92) 
430 420 415 
Pour Point, .degree.F. (ASTM-D-97) 
-40 -25 -20 
______________________________________ 
One or more additives is commonly included in the mist oil formulation 
employed for this process. Conventional additives are used and typically 
include antioxidants, antiwear/EP agents, rust and corrosion inhibitors, 
metal deactivators, foam inhibitors, demulsifiers, and the like. Many of 
these additives have overlapping functions, i.e., be multifunctional. For 
example, certain additives may impart both antiwear and extreme pressure 
properties or function both as a metal deactivator and a corrosion 
inhibitor. Cumulatively, these additives typically do not exceed 8 percent 
and, more usually 5 percent, of the mist oil formulation. 
Oxidation inhibitors which can be employed include the phenolic 
antioxidants derived from t-butylphenol, such as 
4,4'-methylenebis(2,6-di-t-butylphenol), 
2,6-di-t-butyl-N,N-dimethylamino-p-cresol, and 
thiodiethylenebis(3,5-di-t-butyl-4-hydroxy)hydrocinnamate, and the like; 
arylamines including N,N'-diphenyl phenylenediamine; diphenyl amines such 
as p-octyldiphenyl amine, p,p'-dioctyldiphenyl amine and the like, 
N-phenylnaphthylamines such as N-phenyl-1-naphthylamine, 
N-phenyl-2-naphthylamine, N-(p-dodecylphenyl)-2-naphthlamine and the like; 
dinaphthylamines such as di-1-naphthylamine, di-2-naphthylamine and the 
like; phenothiazines, such as N-alkyl phenothiazine; dithiocarbamate 
derivatives; etc. From 0.5 to about 1.5 part antioxidant is generally 
employed. 
Generally about 0.3 to 2 parts of an antiwear agent and 1 to 2 parts of an 
extreme pressure (EP) agent are included in the mist oil. Illustrative 
agents of these types include: sulfurized fatty acid and fatty acid 
esters, such as sulfurized isooctyl tallate; sulfurized terpenes; 
sulfurized olefins; organopolysulfides; organophosphorous derivatives 
including amine phosphates, alkyl acid phosphates, dialkyl phosphates, 
aminedithiophosphates, trialkyl or triaryl phosphorothionates, trialkyl 
and triaryl phosphines, dialkyl phosphites, e.g., triphenyl phosphate, 
trinaphthyl phosphate, tricresyl phosphate, diphenyl cresyl or dicresyl 
phenyl phosphate, naphthyl diphenyl phosphate, triphenyl 
phosphorothionate; dithiocarbamates, such as an antimony 
dialkyldithiocarbamates; xanthates; and the like. 
Metal deactivators (passivators) and rust/corrosion inhibitors include 
dibasic acids, such as azelaic acid; propyl gallate; quinolines; quinones 
and anthraquinones; benzotriazole derivatives, such as tolyltriazole; 
benzoquanamine; aminoindazole; metal alkyl sulfonates, such as barium 
dinonyl naphthalene sulfonate; ester and amide derivatives of alkenyl 
succinic anhydrides (or acids); and the like. From 0.02 to 0.2 parts 
additives of these types are generally used. 
Small amounts, most usually 0.005 to 0.05 part of an antifoam agent, can 
also be present including silicone oils, acrylates and other conventional 
products known to suppress foaming. Also, it may be advantageous to 
include a small amount, usually 0.001 to 0.05 part, of a demulsifying 
agent. Known demulsifiers can be employed for this purpose, such as metal 
alkyl sulfonates, alkylated phenols, alkoxylated alkylphenols, monohydric 
alcohols, alkylene glycols, and the like. 
It is also possible, and often advantageous, to utilize the so-called 
"multipurpose" or "universal" additive packages which are available from 
additive manufacturers for the formulation of the mist oils used for the 
present process. These are sold under various trademarks and tradenames, 
such as "Elco 345," "Hitec 323," "Lubrizol 5034," and the like. These 
additive packages typically impart good oxidation stability, antiwear and 
extreme pressure properties to the formulated fluid. When the additive 
package is utilized in low concentrations, however, it may be necessary to 
add additional corrosion inhibitor and defoamant. 
The following examples illustrate the various embodiments of the invention 
more fully. All parts and percentages are on a weight basis unless 
otherwise indicated. Molecular weights reported throughout were determined 
by gel permeation chromatography using a Waters Associates HPLC Model 204 
instrument fitted with a differential refractive index detector (Model 
R401). The detector was set at an attenuation of 16. Ultrastyragel.RTM. 
columns of 10.sup.4, 10.sup.3, 500 and 100.ANG. connected in series and 
maintained at 35.degree..+-.0.1.degree. C. were used. Tetrahydrofuran, at 
a flow rate of 1.0 milliliter per minute, was used as the eluting solvent. 
Samples were dissolved in tetrahydrofuran (50 mg/ml THF) and a 50 
microliter aliquot injected for each determination. Ten polystyrene resins 
of known molecular weight (ranging from 240,000 to 601) were employed as 
the standards for the determinations. Mist properties were determined in 
accordance with the general procedure of ASTM D 3705-78. For the tests, 
the temperature of the oil was maintained at 120.degree. F. Air 
temperatures used for the determinations were 150.degree. F., 175.degree. 
F. or 200.degree. F.

EXAMPLE I 
An ester-based mist oil composition was prepared and used in a hot strip 
mill to lubricate bearings (19 inch I.D. double roller type) on the rolls 
of a rotary forger. The mist lubricant was obtained by blending 63.1 parts 
di-2-ethylhexyl dimerate (40.degree. C. viscosity 91 centistokes; 
viscosity index 155; pour point -50.degree. F.; acid value &lt;3, and 
hydroxyl value .ltoreq.2) with 27.5 parts isobutylene polymer of MHD w 
7573 and 0.33 part isobutylene polymer of MHD w 89,793. Blending was 
carried out at 90.degree. C. and the polyisobutylenes were dissolved in 
inert hydrocarbons before combining with the ester. The resulting blend 
was cooled to approximately 60.degree. C. and 3.5 parts of a commercial 
ashless multipurpose gear oil additive (Elco.RTM. 345) added with 
agitation. The mist lubricant (ISO grade 460) had the following 
properties: 
______________________________________ 
Viscosity (ASTM-D-445) 
40.degree. C., cSt. 466 
100.degree. C., cSt. 44 
Viscosity Index (ASTM-D-2270) 
148 
Total Acid Number (ASTM-D-974) 
2.5 
(mg KOH/gm) 
Specific Gravity, 60/60.degree. F. 
0.900 
(ASTM-D-1298) 
Flash Point, .degree.F. (ASTM-D-92) 
415 
Pour Point, .degree.F. (ASTM-D-97) 
-20 
______________________________________ 
Mist characteristics were determined at 175.degree. F. and 200.degree. F. 
and were as follows: 
______________________________________ 
175.degree. F. 
200.degree. F. 
______________________________________ 
Oil Output (grams/hour) 
32.8 39.6 
Percent Reclassified Oil 
76.9 77.5 
Percent Line Condensate 
12.1 11.4 
Percent Stray Mist 11.0 11.1 
______________________________________ 
It is apparent from the data that minimal dropout and very low stray mist 
was obtained while maintaining high throughputs. While comparable 
throughputs can be obtained with commercially available mineral oil-based 
mist lubricants, under the operating conditions necessary to generate such 
throughputs, significant wax deposits which restrict the delivery of the 
mist lubricant and, in some cases, cause complete blockage of the 
reclassifier head are obtained upon extended periods of operation. No wax 
buildup was obtained with the above-formulated synthetic ester mist 
lubricant and it was possible to continuously operate the system without 
changing the mist distribution or significantly adjusting the operating 
conditions. 
The ester-based lubricant was employed in a hot strip mill for the mist 
lubrication of roll bearings. The ester-based lubricant was misted in air 
(70-80 psig; 170-200.degree. F.) using a commercial mist generator having 
a sump of 2-3 gallons. The oil was heated to approximately 100.degree. F. 
in the sump. Mist was drawn from the generator by 21/2 inch lines and 
transported through the manifold to the reclassifiers. Conventional 
reclassifier heads containing 9 0.067" holes were employed. Excellent 
misting was observed and no restriction or clogging of the reclassifier 
heads was noted. Additionally, superior lubrication was obtained. Fifteen 
to twenty percent increase in tonnage per bearing was obtained with the 
above-formulated synthetic ester lubricant compared to the commercial 
mineral oil-based mist lubricant which was previously used in the mill. 
Additionally, during routine maintenance and servicing (which is regularly 
performed after processing 150,000 tons), "dry neck" (areas of 
insufficient lubrication) was virtually eliminated on the roll necks 
lubricated in accordance with the process of this invention using the 
ester-based mist oil composition. "Dry neck" was observed in almost every 
case on the outside portion of the roll neck where the bearing is seated 
with the petroleum-based mist lubricants. 
Over a period of ten weeks of plant operation, thirty bearings were 
lubricated with the above-formulated synthetic ester ISO 460 mist 
lubricant and an equal number of bearings were lubricated using a 
commercial ISO 460 petroleum-based mist lubricant. All of the bearings 
were in the same mill line so that both groups of bearings were evaluated 
under comparable operating conditions, i.e., had essentially the same work 
histories. Also, essentially the same amount of lubricant was applied to 
both sets of bearings. During the period, only one bearing lubricated with 
the ester-based mist oil "burned-up," i.e., the bearing became 
mechanically frozen. On the other hand, 12 of the bearings lubricated with 
the petroleum-based mist oil were "burned-up." Upon routine examination at 
the regular maintenance intervals, an additional eight bearings from the 
latter group were judged to be damaged and had to be scrapped. None of the 
bearings lubricated with the synthetic ester lubricants were observed to 
be damaged upon inspection during these regular maintenance checks. Cost 
savings realized using the ester-based mist oil, including bearing and 
roll usage and the cost of the oil, was calculated to be over $10,000 per 
week. 
EXAMPLE II 
To demonstrate the criticality of the lubricant composition for the process 
and the need to utilize a mixture of lower and higher molecular weight 
isobutylene polymers, three ISO 460 grade mist oil compositions were 
prepared following the procedure of Example I. The lubricant compositions 
prepared were as follows: 
______________________________________ 
IIA IIB IIC 
______________________________________ 
Di-2-ethylhexyl Dimerate 
63.1 62.5 63.1 
Polyisobutylene (--M.sub.w 7573) 
27.5 -- 28.4 
Polyisobutylene (--M.sub.w 89,793) 
0.33 11.2 -- 
Additive 3.5 3.5 3.5 
______________________________________ 
Mist properties were determined at 150.degree. F. for each of the above ISO 
460 formulations with the following results: 
______________________________________ 
IIA IIB IIC 
______________________________________ 
Oil Output (grams/hour) 
31.8 4.1 38.7 
Percent Reclassified Oil 
74.4 68.3 71.4 
Percent Line Condensate 
10.8 6.3 6.3 
Percent Stray Mist 
14.8 25.3 22.3 
______________________________________ 
It is apparent from the above data that formulations IIB and IIC have 
unacceptably high levels of stray mist. Stray mist is generally considered 
to be acceptable if it is 15% or less. In no event can stray mist above 
20% be tolerated. Additionally, the throughput obtained with product IIB 
was unacceptable. Only product IIA, wherein the ester was combined with 
both a high and low molecular weight polyisobutylene, gave both acceptable 
throughput and acceptable mist characteristics and were suitable for use 
in the lubrication of roll bearings. 
EXAMPLE III 
To further demonstrate the criticality of the molecular weight of the 
polyisobutylene used for the formulation of the ester-based mist 
lubricants used in the process, the following comparative example is 
provided. For this example, a mist oil formulation based on 
di-2-ethylhexyl dimerate and isobutylene polymers within the prescribed 
molecular weight range was prepared and compared with formulations 
prepared using a polyisobutylene outside the specified molecular weight 
range. The average molecular weight of the combined polyisobutylenes, 
i.e., polymer blend, was the same in each formulation (MHD w 8550). Each 
of the oils was also formulated to the same viscosity, i.e., ISO grade 
460. The mist oil formulations were as follows: 
______________________________________ 
IIIA IIIB IIIC 
______________________________________ 
Di-2-ethylhexyl Dimerate 
63.1 60.0 34.5 
Polyisobutylene (--M.sub.w 7573) 
27.5 -- -- 
Polyisobutylene (--M.sub.w 89,793) 
0.33 -- 4.08 
Polyisobutylene (--M.sub.w 77,284) 
-- 2.35 -- 
Polyisobutylene (--M.sub.w 3199) 
-- 30.2 -- 
Polyisobutylene (--M.sub.w 1874) 
-- -- 49.64 
Additive 3.5 3.5 3.5 
______________________________________ 
Mist properties were determined at 175.degree. F. and the following results 
obtained: 
______________________________________ 
IIIA IIIB IIIC 
______________________________________ 
Oil Output (grams/hour) 
32.8 20.8 15.9 
Percent Reclassified Oil 
76.9 66.2 66.8 
Percent Line Condensate 
12.1 20.2 16.0 
Percent Stray Mist 
11.0 13.6 17.3 
______________________________________ 
It is evident from the above data that products IIIB and IIIC which were 
formulated with an isobutylene polymer outside the specified molecular 
weight range have significantly lower throughputs than product IIIA. 
Products IIIB and IIIC are totally unsatisfactory as mist oils for the 
lubrication of bearings as a result of the low throughput and the high 
percentage of oil which is not delivered for lubrication, i.e., condensed 
in the line or permanently lost as stray mist. Only product IIIA, 
formulated in accordance with the present invention, had a throughput and 
balance of mist properties making it acceptable for use in mist systems 
for the lubrication of bearings. 
EXAMPLE IV 
To demonstrate the versatility of the present invention and the ability to 
utilize lower viscosity synthetic mist oils, a lubricant composition was 
formulated in accordance with the following recipe: 
______________________________________ 
Parts 
______________________________________ 
Di-2-ethylhexyl Dimerate 
77.5 
Polyisobutylene (--M.sub.w 7573) 
14.5 
Polyisobutylene (--M.sub.w 89,793) 
0.66 
Elco .RTM. 345 Multipurpose Additive 
3.5 
______________________________________ 
The mist oil composition had the following properties: 
______________________________________ 
Viscosity (ASTM-D-445) 
40.degree. C., cSt. 219 
100.degree. C., cSt. 26 
Viscosity Index (ASTM-D-2270) 
149 
Total Acid Number (ASTM-D-974) 
2.1 
(mg KOH/gm) 
Specific Gravity, 60/60.degree. F. 
0.902 
(ASTM-D-1298) 
Flash Point, .degree.F. (ASTM-D-92) 
430 
Pour Point, .degree.F. (ASTM-D-97) 
-40 
Mist Characteristics at 175.degree. F.: 
Oil Output (grams/hour) 
52.4 
Percent Reclassified Oil 
75.7 
Percent Line Condensate 
13.1 
Percent Stray Mist 11.4 
Mist Characteristics at 200.degree. F.: 
Oil Output (grams/hour) 
63.6 
Percent Reclassified Oil 
74.4 
Percent Line Condensate 
11.4 
Percent Stray Mist 14.2 
______________________________________ 
The lubricant was an effective mist oil suitable for the lubrication of 
bearings. An effective mist oil having comparable properties is obtained 
when the formulation is prepared substituting 2 parts sulfurized isooctyl 
tallate, 1 part phenyl .alpha.-naphthylamine, 1 part tricresylphosphate, 
0.05 part benzotriazole, 0.05 part dodecenylsuccinate half ester of 
ethylene glycol, 0.005 part Dow DC-200 polydimethylsiloxane, and 0.01 part 
propylene glycol for the commercial additive package. 
EXAMPLE V 
An ISO 320 mist oil composition suitable for lubricating bearing was 
obtained by blending the following ingredients: 
______________________________________ 
Di-2-ethylhexyl Dimerate 
70.7 
Polyisobutylene (--M.sub.w 7573) 
20.7 
Polyisobutylene (--M.sub.w 89,793) 
0.50 
Commercial Universal Additive 
3.5 
Package (20.5% S; 1.1% P) 
______________________________________ 
Physical properties and mist characteristics of the resulting mist oil 
composition were as follows: 
______________________________________ 
Viscosity (ASTM-D-445) 
40.degree. C., cSt. 316 
100.degree. C., cSt. 33 
Viscosity Index (ASTM-D-2270) 
147 
Total Acid Number (ASTM-D-974) 
1.9 
(mg KOH/gm) 
Specific Gravity, 60/60.degree. F. 
0.904 
(ASTM-D-1298) 
Flash Point, .degree.F. (ASTM-D-92) 
420 
Pour Point, .degree.F. (ASTM-D-97) 
-25 
Mist Characteristics at 175.degree. F.: 
Oil Output (grams/hour) 
41.7 
Percent Reclassified Oil 
75.5 
Percent Line Condensate 
13.9 
Percent Stray Mist 10.5 
Mist Characteristics at 200.degree. F.: 
Oil Output (grams/hour) 
55.0 
Percent Reclassified Oil 
74.5 
Percent Line Condensate 
11.8 
Percent Stray Mist 13.8 
______________________________________ 
EXAMPLE VI 
To demonstrate the ability to use other synthetic esters, and ISO 460 mist 
lubricant was prepared using a blend of isotridecyl and isodecyl 
trimellitate. The mist oil composition was formulated in accordance with 
the usual procedure as follows: (40.degree. C. viscosity 250 centistokes; 
acid value 0.02; hydroxyl value 1.8; pour point -20.degree. F.) 
______________________________________ 
Parts 
______________________________________ 
Isotridecyl Trimellitate 
79.5 
Polyisobutylene (--M.sub.w 7573) 
14.0 
Polyisobutylene (--M.sub.w 89,793) 
0.17 
Additives 3.5 
______________________________________ 
Mist characteristics (175.degree. F.) were as follows: 
______________________________________ 
Oil Output (grams/hour) 
34.9 
Percent Reclassified Oil 
74.5 
Percent Line Condensate 
14.5 
Percent Stray Mist 11.0 
______________________________________ 
The product exhibited good lubrication properties and is an effective 
lubricant for roll bearings in hot strip mills. It can also be used in 
mist systems for the lubrication of pump, turbine and motor bearings. 
EXAMPLE VII 
A mist oil composition based on trimethylolpropane triisostearate 
(40.degree. C. viscosity 90 centistokes; acid value 5; hydroxyl value 10; 
pour point -15.degree. F.) and suitable as a bearing lubricant was 
formulated as follows: 
______________________________________ 
Parts 
______________________________________ 
Trimethylolpropane Triisostearate 
68.5 
Polyisobutylene (--M.sub.w 7573) 
23.1 
Polyisobutylene (--M.sub.w 89,793) 
0.28 
Elco .RTM. 345 3.5 
______________________________________ 
The above-prepared lubricant composition had a 40.degree. C. viscosity of 
459 centistokes and 175.degree. F. mist characteristics were as follows: 
______________________________________ 
Oil Output (grams/hour) 
31.7 
Percent Reclassified Oil 
73.9 
Percent Line Condensate 
15.5 
Percent Stray Mist 10.6 
______________________________________ 
Comparable mist and lubrication properties are obtained when the commercial 
additive is replaced with 4 parts antimony dialkyldithiocarbamate, 1 part 
tricresylphosphate, and 1 part barium dinonylnaphthalene sulfonate. 
EXAMPLE VIII 
An ISO 460 mist oil suitable for use in the process of this invention was 
prepared by blending 56.5 parts trimethylolpropane trioleate (40.degree. 
C. viscosity 228 centistokes; acid value 4; hydroxyl value 4; pour point 
-50.degree. F.) with 33.0 parts polyisobutylene (MHD w 7573) and 0.40 part 
polyisobutylene (M.sub.w 89,793). 3.5 Parts of a commercial "universal" 
additive package were also included in the formulation. The resulting 
blend had a 40.degree. C. viscosity of 454 centistokes and exhibited 
superior lubrication and misting characteristics. Mist characteristics 
(175.degree. F.) were as follows: 
______________________________________ 
Oil Output (grams/hour) 
29.2 
Percent Reclassified Oil 
71.8 
Percent Line Condensate 
16.4 
Percent Stray Mist 11.8 
______________________________________ 
The product is effective for the lubrication of roll bearings in hot strip 
mills. There was no evidence of wax buildup after extended periods of 
operation and visual inspection of the roll neck and bearing surfaces 
indicated good spreadability of the lubricant. 
EXAMPLE IX 
A series of ISO 460 mist oil compositions useful in the process were 
prepared using varying levels of the high and low molecular weight 
polyisobutylenes. Compositions were as follows: 
______________________________________ 
IXA IXB IXC 
______________________________________ 
Di-2-ethylhexyl Dimerate 
63.1 63.1 63.1 
Polyisobutylene (--M.sub.w 7573) 
25.8 27.1 28.0 
Polyisobutylene (--M.sub.w 89,793) 
0.99 0.50 0.17 
Additive 3.5 3.5 3.5 
______________________________________ 
Mist characteristics were determined at 175.degree. F. (except for IXA) and 
200.degree. F. with the following results: 
______________________________________ 
IXA IXB IXC 
______________________________________ 
Mist Characteristics at 175.degree. F. 
Oil Output (grams/hour) 
NOT 33.1 39.9 
Percent Reclassified Oil 
TESTED 77.9 76.7 
Percent Line Condensate 12.4 9.8 
Percent Stray Mist 9.7 13.5 
Mist Characteristics at 200.degree. F. 
Oil Output (grams/hour) 
35.9 44.5 39.6 
Percent Reclassified Oil 
76.0 77.1 74.5 
Percent Line Condensate 
14.1 10.6 11.6 
Percent Stray Mist 
9.9 12.3 13.9 
______________________________________ 
EXAMPLE X 
A mist lubricant for the process was prepared following the general 
procedure of Example I except that the high molecular weight 
polyisobutylene used had an average molecular weight of 77,284. To obtain 
the composition, 63.1 parts di-2-ethylhexyl dimerate was blended with 27.5 
parts polyisobutylene (M.sub.w 7573) and 0.39 part of the high molecular 
weight isobutylene polymer. A commercially available "universal" additive 
package was also included in the blend at a 3.5 parts level. The resulting 
mist lubricant had a viscosity (40.degree. C.) of 464 centistokes. Mist 
characteristics determined at 175.degree. F. were as follows: 
______________________________________ 
Oil Output (grams/hour) 
32.0 
Percent Reclassified Oil 
72.7 
Percent Line Condensate 
14.8 
Percent Stray Mist 12.4 
______________________________________ 
The product also had lubrication properties comparable to the product of 
Example I and is effective for the mist lubrication of hot roll mill and 
other bearings.