Contraintes environnementales et évolution des lubrifiants et des systèmes de lubrification - Réunion CT Laminage, 6 Janvier 2021 - SF2M
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Contraintes environnementales et évolution des lubrifiants et des systèmes de lubrification Réunion CT Laminage, 6 Janvier 2021 Pierre Montmitonnet
PLAN Lubrifiants de mise en forme : du vert mais pas que
Bases et lubrifiants liquides: huiles minérales
► Huiles Minérales * paraffines = alcanes , linéaires ou branchés * aromatiques = benzene et dérivés
= hydrocarbures
peu toxiques mais polluantes
* naphtènes = cycles non-benzéniques
mode d'action 1: formation de film ± épais par viscosité
mode d'action 2: transport des additifs (importance du pouvoir solvant)
► Huiles Synthétiques:
alcanes purs, avec branchements réguliers (PAO)
O O
|| ||
Esters, R-COH + HO-R' R-C-O-C-R' (poly)éthers R-COH + HOC-R' R-C-O-C-R'
Bases ou additifs, les triglycérides
oBiosourcés et biodégradables… leur atout et leur talon d'Achille O
► Graisses animales et huiles végétale: tri-esters de glycérol
H2C-OH H2C-O-C-CH2-…-CH2 (HC=CH)-CH2-…-CH3
Les huiles et gras de toutes origines O
diffèrent par la distribution des longueurs HC-OH H-C-O-C-CH2-…-CH2 (HC=CH)-CH2-…-CH3
de chaînes, et la saturation (indice d'iode) + 3 acide gras
O
H2C-OH H2C-O-C-CH2-…-CH2 (HC=CH)-CH2-…-CH3
► Exemples:
► Acide butyrique H3C-CH2-CH2-COOH (lait, beurre) Acides caproïque, caprylique: H3C-(CH2)6/8-COOH (câpres)
► Acide laurique H3C-(CH2)10-COOH (baies de laurier) Acide myristique : H3C-(CH2)12-COOH (myrrhe)
► Acide palmitique H3C-(CH2)14-COOH (huile de palme) Acide stéarique H3C-(CH2)16-COOH (graisses animales)
► Acide arachidique H3C-(CH2)18-COOH (huile d'arachide) Acide béhénique H3C-(CH2)20-COOH (tournesol)
► Insaturés
► Acide oléique cis - H3C-(CH2)7-HC=CH-(CH2)7-COOH (huile d'olive) – linoléique (9,12 di-ene)
► Acide ricinoléique H3C-(CH2)5-CHOH-CH2-HC=CH-(CH2)7-COOH etc.
► excellents lubrifiants, bio-sourcés, connus et utilisés depuis l'antiquité et sans égaux aujourd'hui :
très visqueux (efficacité filmogène) et polaires ( additifs limites basse température)
► les triglycérides saturés (gras animaux) sont très visqueux, solides à l'ambiante (fusion vers 40°C) ;
les insaturés (huiles végétales) sont liquides à l'ambiante (sauf l'huile de palme).
► dans les lubrifiants modernes (en mise en forme), ils ne sont plus utilisés seuls,
mais comme additifs (de quelques % à 50%) avec des huiles minérales H2C-OH H2C-CH2OH
► pour des tôles plus propres, les triesters de glycérol sont remplacés:
HC-OH HC-CH2OH
esters de trimethylol-propane (Quaker)
d'acide triméllitique (Esso)...
H2C-OH H2C-CH2OH
► on utilise aussi des esters-phosphates (forte polarité additifs et surfactants)
O
+ 3 alcools gras O-C-CH2-…-CH2 (HC=CH)-CH2-…-CH3
O
O=P-O.H "Biomimétiques" car ~similaires
O=P ---O-C-CH2-…-CH2 (HC=CH)-CH2-…-CH3
O aux phospholipides formant les
parois des cellules animales
O-C-CH2-…-CH2 (HC=CH)-CH2-…-CH3
Entre lubrifiants solides et liquides
oles verres (formage à chaud)
► verres minéraux standard : SiO2-Na2O-CaO…
► Ils fondent à haute température (T > 700°C) liquides de très haute viscosité (105 - 1010 Pa.s).
► La propriété importante est la courbe h(T) composition détaillée du verre (fondants…)
► Des additifs extrême-pression (EP) ou des lubrifiants solides peuvent être ajoutés
Film de verre
► Applications : formage à chaud des métaux conteneur
- forgeage des superalliages, filière
Billette
- extrusion des aciers,
- extrusion ébauches tubes Zr…
Gargousse de verre
oles savons secs
► Solides à température ambiante, ils fondent à
T > 100-150°C cristaux liquides de haute viscosité
T > 300-400°C « vrais » liquides (de basse viscosité)
ou décomposition
► Applications comme lubrifiants :
- formage à froid des métaux (forgeage, tréfilage…)
- plastifiants pour polymères / lubrifiants internes
Thermogramme DSC
du stéarate de sodium
structures cristallines déterminées par DRX
► Exemples:
Oléate de Calcium CH3-(CH2)7-HC=CH-(CH2)7-COO-Ca-OOC-(CH2)7-HC=CH-(CH2)7-CH3
Stéarate de sodium : NaOH + acide stéarique (ou triglycérides) CH3-(CH2)16-COO-Na + H2O
oLes graisses
► Graisses = suspension d'huile dans une matrice de fibres de savon (ou feuillets d'argile, dispersion
colloïdale de PTFE…),
► Dans le cas du savon, elle est obtenue par cristallisation lente du mélange savon-huile après
saponification en phase huile
Soap fibers
► Effet éponge: à l'entrée du contact,
le "squelette solide" est comprimé
Oil droplet
et laisse partir l'huile qui est la phase lubrifiante;
lorsque cette huile sort du contact, elle est recapturée
► Les graisses au savon résistent tant que le "squelette solide" n'est pas détruit par de hautes
températures (= transition vers un cristal liquide, 100-200°C) ou un cisaillement excessif
Additifs solides minéraux lamellaires (MoS2, h-BN, graphite…)
► Principe : solides à structure cristalline lamellaire:
fortes liaisons dans le plan, très faibles liaisons entre lamelles
bonne résistance à la pression de contact, faible résistance au glissement = frottement
► Usages : En général utilisés pour des conditions sévères (T > 500°C, ultra-vide)
huiles moteurs (anciennes): MoS2 + graphite
mécanismes fonctionnant en ultra-vide (espace): MoS2
mise en forme des métaux
* graphite pour forgeage / laminage à chaud, remplacé par des "white lubricants" pour cause de saleté
* MoS2 pour filage à chaud du Zr (avec poudre de verre et liant silicaté)
► Modes d'application :
• dispersions dans l'eau (graphite), dans l'huile (graphite, MoS2) [alimentation continue ou dépôt]
• films compactés [durabilité limitée]
• vernis au graphite / MoS2 [durabilité accrue]
oMoS 2 vs graphite
MoS2
coefficient de frottement µ
La qualité cristallographique
est importante.
graphite
Cycle n°
0 4000 8000 12000 16000
► MoS2 : très bon à température ambiante dans le vide, mais craint l'humidité
(pontage entre lamelles cisaillement plus aussi aisé) et les hautes températures (oxydation, sublimation).
Possibilité de frottement bas à ultra-bas (µoHuiles contenant des nanoparticules ► Fort intérêt actuellement pour les huiles moteurs - Fullerènes et nanotubes de C (plus très en vogue) - MoS2 / WS2, forme "oignons" en concurrence avec la forme usuelle lamellaire - Oxydes - Métaux - core/shell (enveloppe oxyde contenant des nano-h-BN par exemple) ► Mise en forme: plutôt proposées jusqu'ici en laminage à chaud (pour lequel les huiles ont des limites) - Sulfonates de calcium surbasé (détergent) : cœur CaCO3 + chaînes sulfonates greffées - TiO2 -… ► Mode d'action: dépôt d'un film métallique / oxyde formé de nanoparticules compactées + éventuellement nano-lamelle de MoS2, h-BN…
Additifs limites: 3 familles, 3 types de réactions
Organo-soufrés, -chlorés : relarguent Cl ou S
couches anti-adhésion (FeS / FeS2 , FeCl2 )
• Organo-phosphorés: DTPZn, TCP, …
( lubrifiant solide)
verres de phosphates
(spécifiques des alliages ferreux)
• DTPMo verres de phosphates + MoS2
• Borates + molécules azotées BN
(spécifiques des alliages ferreux)
Additifs polaires (« onctuosité ») :
acides, alcools, esters, amines gras
(tous métaux et alliages)oQuelques résultats sur les additifs polaires
► Influence positive de la longueur de chaîne (Van der Waals plus de cohésion entre molécules)
► Acide (-COOH) > alcool (-COH) > amine (-NH2)
Jahanmir, Wear, 1985 Bowden & Tabor, 1964
H3C-(CH2)14-COH
Acides gras linéaires saturés
H3C-(CH2)14-COOH
H3C-(CH2)n-2-COOH► Perte d'efficacité due à la désorption Comportement basse / haute pression
Jahanmir, Wear, 1985
de multicouches d'additifs polaires
Briscoe, Proc. Roy. Soc. A, 1973
Stéarate de calcium,
Nombre variable de
couches moléculairesoFilms réactionnels d'additifs phosphorés (DTPZn pour huiles moteur : Martin, 1978)
Anti-usure (DTPZn ou ZDDP)
MoDTC, limiteur de frottement ( MoS2)
► films "épais" ( qq 100 nm), aux propriétés mécaniques essentielles pour le frottement et l'usure
► Ces additifs (initialement introduits dans les années 1950 comme anti-oxydants…) ont besoin de hautes températures qui
entraînent leur décomposition : « extrême-pression » = en fait haute température
► S et P polluent les pots catalytiques gros efforts de substitution, sans succès majeur à ce jour► Structure du tribofilm
(Bec et al., 1992)
• structure en "plots" discontinus
• structure multicouche :
- S libéré (Fe,Zn)S au contact de l'acier
- polyphosphates (Fe,Zn) vitreux par dessus
• gradient de propriétés mécaniquesLubrifiants liquides: émulsions
► Généralement huile dans eau (O / W), bien que les émulsions inverses (W / O) existent
crème Polaire (hydrophile)
eau
Gouttes = surfactant = amphiphile
mouillant huile
les parois Non-polaire (hydrophobe)
► Exemples d'émulsifiant (surfactant): nonyl-phénols éthoxylés (non–ioniques):
► Savons: Na-OOC-(CH2)16-CH3 (anioniques)
► Sels d'ammonium R-NH4+X- (cationiques)oMécanisme de lubrification par une émulsion: inversion accélérée par mouillage
► Démixtion à l'entrée du contact
seule l'huile entre Lignes de courant
les facteurs nécessaires à la formation de film:
* mouillage de l'huile sur la surface,
* (in)stabilité de l'émulsion Vcyl réservoir L
d'où l'extrême importance de l'émulsifiant
Vtôle
Xinversion Xplastique
(p=0) (p=s0)Par-delà les paraffines chlorées? Deux exemples d'études sur une substitution difficile
► J. Hardell, B. Prakash, Tribological performance evaluation of cold pilgering lubricants,
proc. ICTMP 2010 (Nice, 13-15 Juin 2010), P. Montmitonnet & E. Felder, eds, Presses des Mines, Paris, 2010.
Fn
Inox Duplex
Acier à outils
(mandrin ou matrice)Fn
► Essai de frottement jusqu'au grippage
int ext soufré ? int ext
70°C mixed ? Ac. L.
soufre
P.Cl.
150°C
soufre
P.Cl.Fn
int ext soufré ? int ext
mixed ? Ac. L.
soufre
P.Cl.
P.Cl. soufre► Essai 4 billes (grippage) ► Ici les soufrés font aussi bien que les paraffines chlorées – le résultat dépend du test! ► A priori, les paraffines chlorées réagissent avec la surface de l'inox, le soufre uniquement avec les aciers à outils
► Synthèse
Paraffines chlorées
EP inconnus
EP soufré (lub LàPP)
Acide laurique – pas d'EP► N. Bay, T. Nakamura, S. Schmid, Green Lubricants for metal forming,
proc. ICTMP 2010 (Nice, 13-15 Juin 2010), P. Montmitonnet & E. Felder, eds, Presses des Mines, Paris, 2010
AISI 304 vs P/M HSS tool (70°C),
Bending Under Tension Test
F1 F2
pc
2 Rw
s 0 .w.t 2 s 0 .w.t 2
F2 F1 . exp( µ. )
4 R 4R
Using several values of or F1,
s0 may be eliminatedAISI 316 vs P/M HSS die, Strip Reduction Drawing Test En production, bonne performance de Rhenus CXF125 aussi, mais seulement avec des outils revêtus TiAlN
AISI 316 vs P/M HSS tool (70°C), Découpe fine – frottement au retrait de l'outil
► Pour la mise en forme des inox, aucune des solutions n'est tout à fait à la hauteur des paraffines chlorées ; cette conclusion n'a pas été remise en cause à ma connaissance par les résultats publiés depuis. ► Des solutions acceptables peuvent être trouvées en combinant formulation du lubrifiant et acier à outil / revêtement, et spécifiques à une famille de procédés (avec leurs conditions de contact) ► Parmi les plus crédibles, la famille des esters, dont les "fatty acid methyl ester" utilisés purs (cf. expérience CEMEF en laminage à froid des inox). ► La tendance de l'utilisation de nanoparticules de tous types peut être interrogée aussi
Conclusion ► Nous pourrions parler des lubrifiants "blancs" (sans graphite) en forgeage à chaud : cette substitution est faite ► Les revêtements sont aussi en question: * phosphatation-savonage en filage à froid * et bien sûr le Cr dur à partir de bains de CrVI
Merci de votre attention Pierre Montmitonnet
ADDITIVES
The additives equation
Biobased oil stocks serve up different chemical
qualities than mineral oil base stocks.
By Mary Beckman
Contributing Editor
KEY CONCEPTS
For the lubricant industry, going renewable
The polarity of plant-based oils improves their ability to reduce friction on surfaces. means researchers and engineers have to find
new sources for base stocks that make up oils and
The chemical structure of additives affects how they perform in polar and nonpolar base stocks. greases. But making something last for the life of
your vehicle or farm implement out of something
Heat-treating plant-based oils makes their molecules longer and improves their viscosity.
that is inherently biodegradable is a tricky problem.
32 • SEPTEMBER 2020 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORGPart of the issue is characterizing bio- additives, a commercially available poly- test, enough load will eventually weld the
logically derived base stocks. Lubrication sulfide or a biobased polyester. Then they top ball to the lower balls. Higher weld
engineers have been working with petro- subjected the oils to a four-ball friction and points mean better protection by the ad-
leum products for over a century, but plant- wear test and a twist compression test. In ditives.
based oils haven’t been given as much at- the four-ball test, one metal ball sits atop Both additives yielded higher weld
tention by modern science. three stationary balls bathed in the lubri- points in either base stock. Polysulfide
And then there are additives. Formu- cant. The test puts force on the top ball resulted in two to four times higher weld
lating oils and greases requires an under- and rotates it. The torque of the rotation point than the polyester additive in 150N
standing of the chemical qualities of every- provides the coefficient of friction, and oil. In soybean oil, polysulfide had better
thing that goes into the mix and how those the scar from the twisting ball provides performance than polyester. The results
chemicals interact. standard wear information. The twist confirmed previous expectations.
“It’s something people have to pay atten- compression test works similarly except a The additives’ overall improvement of
tion to,” says STLE-member Ted McClure, cylinder sitting atop a flat workpiece re- the base oils depended on the base oil’s
technical resources manager, for Sea-Land places the top ball and three lower balls. chemical structure. For example, polyest-
Chemical Company and SLC Testing Ser- Comparing test results between oils allows er improved performance of mineral oil
vices in Westlake, Ohio. “Even between the researchers to see which combinations more than soybean, and polysulfide per-
additives, because it’s usually not just one reduce friction and wear under extreme formed better in soybean oil than mineral
additive—it’s a coordinated group of addi- pressure conditions, when the oils form a oil. This might be because polysulfide is
tives in a base stock.” very small boundary layer of lubricant. more reactive with steel than polyester and
Within the last 15 years or so, more will be more able to improve the perfor-
chemists have been testing and charac- Formulating oils and greases mance of polar soybean oil than polyester.
terizing biobased oils, especially soybean requires an understanding of the Additive interactions with base oils and the
oil. One of the hardest problems to over- chemical qualities of everything surfaces lubricated should be considered
come is the ease with which biobased oils as formulators develop biobased oils.
that goes into the mix and how
oxidize, a process that leads to breakdown
and becoming thick and rancid. They’ve
those chemicals interact.
Additives adding up to more
also explored soybean oil’s structure, how First, the team compared the base oils Another USDA study focused on the oxida-
it gets along with additives and even how themselves. Torque rises and falls over tion problem and found some synergy.
to modify the oil itself. time in the test, and soybean oil had a low- STLE-member B.K. Sharma, now at the
er and later peak in torque compared to Illinois Sustainable Technology Center,
Polar express 150N, showing that the setup with soybean University of Illinois at Urbana-Champaign,
Because a biobased oil, such as soybean oil exhibited lower friction than the mineral and colleagues tested a variety of antiox-
oil, normally functions in a living world of oil. This suggested that soybean oil’s polar idants in soybean oil, alone and in com-
water, its chemical structure is different molecules can adsorb onto the surface to binations.2 They used two pressurized
from mineral oils, which reside inertly in reduce friction. Mineral oil’s lack of polarity differential scanning calorimeter (PDSC)
rock. Polar molecules are a little bit pos- gives it no such advantage. tests. One heats up the oil and additives
itively charged on one end and a little bit Five percent polyester added to 150N and takes the temperature of the mixture
negatively charged on the other, which oil reduced both the amount of peak torque when oxidation starts, which gives off a
gives them particular characteristics. Soy- and friction, but it had no effect when add- burst of additional heat due to oxidation’s
bean oil is polar while mineral oil is not. ed to soybean oil. The soybean oil result exothermic nature. The other test heats
Additives have various chemical struc- was not surprising—since it is already up the oil to a set temperature and keeps
tures as well, and they might interact with chock full of esters, adding more doesn’t it there until, again, a burst of exothermic
polar and nonpolar base oils differently. help. But the nonpolar 150N benefitted heat indicates oxidation has begun. The
To explore these interactions, STLE- greatly from the added esters. “onset of oxidation” temperature from the
member Girma Biresaw, a research chem- When the team added 5% polysulfide first test and the “oxidation induction time”
ist, for the U.S. Department of Agriculture to the base stocks, both 150N and soybean from the second can be compared across
(USDA) in Peoria, Ill., S. J. Asadauskas and oil became much better lubricants—it cut formulations. Higher is better.
McClure examined two base stocks and both torque and friction. But adding even They compared four different antioxi-
two additives to see how the mix of chem- more polysulfide didn’t improve matters. dant additives and three different antiwear
ical structures influences the performance The team concluded that once there was additives for how well they preserved the
of the modified oil under extreme pressure enough polysulfide to coat the surfaces, oil. The antioxidants can do their jobs in
conditions.1 more wouldn’t help. several ways, such as by scavenging free
The researchers mixed and matched Finally, the team looked at a measure- radicals, unstable molecules that bounce
nonpolar paraffinic oil 150N, the more po- ment called the weld point. In the four-ball around and damage other molecules, or
lar soybean oil, and two extreme pressure by sacrificing themselves to convert dan-
WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY SEPTEMBER 2020 • 33ADDITIVES
gerous hydrogen peroxide to water and ing gears, they heated up the oil in such a grease the gears, they evaluated several
oxygen, stopping it in its tracks. These way as to make longer molecular chains antiwear additives in TP-SO using a four-
different means to the same end might al- within the oil, a process called thermal po- ball friction and wear test.
low antioxidants to work more effectively lymerization.4 The treatment resulted in a They found that a boron ester antiwear
together than alone. base stock called thermally polymerized additive combined with a compound called
First the bad news. The researchers soybean oil (TP-SO) that would have qual- ZDDP created the smallest wear scar. The
found that, when combined with antioxi- ified as an SAE Viscosity Grade of 190. scar was so small compared to the base
dant butylated hydroxytoluene, two of the Of course, then it wasn’t going to flow stock TP-SO that the two additives might
antiwear additives were actually making well at low temperatures. The first chemi- be working synergistically.
oxidation worse. cals they tested for their formulation were Having come up with a formulation for
Now the good news. The third antiwear proprietary pour-point depressants. They bio-GO, the team put it up against five com-
additive, antimony dialkyldithiocarbamate chose one that allowed the oil to pour at -15 mercial gear oils. Bio-GO had the second
(ADDC), reduced oxidation in the soybean C rather than its beginning point of -9 C. to highest viscosity index of the oils and
oil. All four antioxidants also worked as ad- Because the USDA requires biobased oils created the second-smallest scar in the
vertised. But when researchers matched to be at least 58% renewable to be certified, four-ball wear test. Although it performed
three of the antioxidants with ADDC, the the team tested the addition of synthetic admirably in those tests, it began to oxidize
results were synergistic. This meant that oils as well on the pour point. Based on the at the lowest temperature of the set. The
when they worked together, the effect was results, their final formulation would have commercial oils hit at least 269 C before
more than the sum of its parts. 30.5% by weight of the Group V synthetic oxidizing, whereas bio-GO became unsta-
The team explored one other aspect aromatic ester base oil. ble at 220 C.
of the additives—the base oil stock. When One of the biggest problems with veg- Overall, the researchers were encour-
they used the additives in soybean oil that etable oils is oxidation. To find a suitable aged that thermal polymerization could
contained larger amounts of oleic acid, the additive, they tested TP-SO with nine dif- produce a biobased gear oil that held its
additives provided more antioxidant ac- ferent antioxidants. They used a PDSC to own in bench tests.
tivity. The onset of oxidation temperature measure the “onset of oxidation tempera- Just like with the gear oil, exploring
surpassed 250 C, suggesting manipulating ture.” Based on the results, they chose two ways to balance the biodegradability and
the saturation content of base stocks would antioxidants to add to their base stock. renewability of bio-base stocks with the
be another way to increase the oxidation “Of course, an industrial lubricant need for a long stable life is a problem for
stability of biobased oils. needs to do one thing well, and that is which scientists, increasingly, are holding
lubricate,” the researchers wrote. “This is their own.
Heating up for gear oil an especially important factor in gear oil
Mary Beckman is a freelance science writer
Treating the base oil itself before adding applications.”
based in Richland, Wash. You can contact
modifiers is a method a group used in a To make sure their formulation would
her at mbeckman@nasw.org.
publication in 2013. Researchers led by
Kenneth Doll at USDA in Peoria developed
a soybean oil-based gear oil and compared
its performance to commercially available
gear oils.3 They performed a series of tests
to determine the final mix of their bio-base
stock, which they called bio-GO.
First, since regular soybean oil does not
have the viscosity for an application involv-
REFERENCES
1. Biresaw, G., Asadauskas, S.J. and McClure, T.G. (2012), “Polysulfide and biobased extreme pressure additive performance
in vegetable vs paraffinic base oils,” Industrial and Engineering Chemistry Research, 51 (1), pp. 262-273. Available at
https://pubs.acs.org/doi/10.1021/ie2015685.
2. Sharma, B.K., Perez, J.M. and Erhan, S.Z. (2007), “Soybean Oil-Based Lubricants: A Search for Synergistic Antioxidants,”
Energy Fuels, 21, 4, pp. 2408-2414. Available at https://pubs.acs.org/doi/10.1021/ef0605854.
3. Arca, M., Sharma, B.K., Perez, J.M. and Doll, K.M. (2013), “Gear oil formulation designed to meet bio-preferred criteria as
well as give high performance,” International Journal of Sustainable Engineering, 6 (4), pp. 326-331. Available at
http://dx.doi.org/10.1080/19397038.2012.725430.
4. Erhan, S.Z. and Bagby, M.O. (1998), “Vegetable oil-based offset printing inks,” 5713990, Feb. 3, 1998. Available at
https://patents.google.com/patent/US5713990A/en.
34 • SEPTEMBER 2020 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORGVous pouvez aussi lire
