Refrigeration Lubricant Based on Polyolester for Use With HFCs and Prospect of Its Application With R-22 (Part 1) Tribological Characteristics

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1 Purdue Univerity Purdue epub International Refrigeration and Air Conditioning Conference School of Mechanical Engineering 1996 Refrigeration Lubricant Baed on Polyoleter for Ue With HFC and Propect of It Application With R22 (Part 1) Tribological Characteritic M. Muraki Mitubihi Oil Co. K. Tagawa Mitubihi Oil Co. D. Dong Saneki Techno Co. Follow thi and additional work at: Muraki, M.; Tagawa, K.; and Dong, D., "Refrigeration Lubricant Baed on Polyoleter for Ue With HFC and Propect of It Application With R22 (Part 1) Tribological Characteritic" (1996). International Refrigeration and Air Conditioning Conference. Paper Thi document ha been made available through Purdue epub, a ervice of the Purdue Univerity Librarie. Pleae contact epub@purdue.edu for additional information. Complete proceeding may be acquired in print and on CDROM directly from the Ray W. Herrick Laboratorie at Herrick/Event/orderlit.html

2 REFRIGERATION LUBRICANT BASED ON POLYOLESTER FOR USE WITH HFCS AND PROSPECT OF ITS APPLICATION WITH R22 (PART 1) TRIBOLOGICAL CHARACTERISTICS Maayohi Muraki and Kazuo Tagawa Mitubihi Oil Co., Ltd., Lubricant Reearch Laboratory, Japan Darning Dong Saneki Techno Co., Ltd., Japan ABSTRACT Tribological behavior wa evaluated for polyoleter bae oil and the formulated oil in ome HFC and HCFC refrigerant environment. HFC a well a R22 howed the boundary lubricating effect depending upon the olubility of ga in the oil. Thu, higher ga preure of the refrigerant improved the wear reitance. A ynergitic effect on antiwear propertie wa found when uing an aryl phophate together with a ulfurphophoru type additive whoe perfonnance wa comparable to that with the fonnulated alkylbenzene in R22. The urface analyi howed that the improvement of antiwear performance wa becaue of promoting the formation of a reaction film containing both iron phophate from aryl phophate and the decompoition product of polyoleter on the liding urface. INTRODUCTION In accordance with the predetermined chedule of the international treaty baed upon Montreal protocol, the production of chlorofluorocarbon (CFC) wa totally banned by the end of year 1995 and that of the hydrochlorofluorocarbon (HCFC) ha been phaed out to meet future regulatory legilation requirement. Intead, hydroflourocarbon (HFC) having no ozone depleting potential have been regarded a alternative refrigerant. Since the replacement of CFC eem to have been uccefully completed in houehold refrigerator and automotive air conditioner, the current major concern i application of HFC to air conditioner and low temperature refrigeration equipment. In refrigeration compreor application, one of the key iue i the lubricant performance which are primarily micibility with HFC, thermal and chemical tability and tribological propertie. Polyoleter (POE) have been regarded a one of the mot prominent candidate of refrigeration lubricant for HFC. However, it ha been pointed out that POE ha the drawback of hydrolyi which reult in ludge formation and wear enhancement in compreor [1]. Thu, POE lubricant have to be optimized from a viewpoint of chemical tructure of bae oil and the additive fonnulation. The preent paper decribe the tribological performance of the developed refrigeration lubricant baed upon a pecified combination of POE and the additive package. OILS TESTED AND SOLUBILITY OF Oll.JREFRIGERANT MIXTURE The bae oil of lubricant teted are a pentaerythritol type eter POE(A32) and an alkylbenzene AB having a branched alkyl ubtituent. Some propertie ofbae oil and compoition of additivecontaining POE are lited in Table 1 and 2, repectively. All the formulated POE contain in common a mall amount of a phenol type antioxidant and an epoxide type tabilizer whoe performance i decribed in part 2 report. In addition, an aryl phophate (AP) and a ulfurphophoru (SP) type antiwear additive were eparately or together added to improve the wear reitance, in which POEC contained a much AP a POEA and a much SPa POEB. Firt, the vicoity of oil/re:frigerant mixture wa meaured with a falling piton type vicometer a hown in Fig. I. Figure 2 how the vicoity a well a the olubility of refrigerant ga in the oil under a contant ga preure and temperature. The oil/refrigerant mixture howed the lower vicoity than the oil in the air for each oil. Decline of vicoity ofpoe 'With re:fiigerant wa more ignificant for R~22 than for HFC, and the vicoity ofpoe/hfc wa 273

3 in the order ofr44a > R47C > R134a Thi order i the oppoite to that of oberved olubility of refrigerant in POE a hown in the figure. On the other hand, when compared between POE and AB for R22, the vicoity of POE decreaed more ignificantly than that of AB. Thee indicate that the vicoity of the oil in the preence of refrigerant i governed by the olubility of ga in the oil. TRIBOMETER AND TESTING CONDITIONS The experimental apparatu for friction and wear tet wa a blockonring type tribometer. The ring and the block are made of nickel chromium molybdenum teel (SAE462) and alloy tool teel (SABOl), repectively. They were machined and heat treated to a hardne HRC 5862 for the ring and HRC 2832 for the block. The ring wa 35mm in outer diameter and 8.7mm in width, and the block wa 6.35mm in width. The urface ofboth the tet pecimen were ground to the initial urface roughnee le than R.. of.2 JL m. After the tet chamber wa evacuated, refrigerant ga wa charged up to the required preure. Then, the tet wa tarted under a predetermined load and the initial bulk temperature. During the tet both the frictional force and bulk temperature were recorded on a peronal computer. After the tet, the pecific wear rate wa determined baed on the width of the wear car on the block and the wear lo of the ring. The experiment were carried out under the liding peed of.5m/, the initial bulk temperature of8 C and the load in the range from 75N(76.5kg) to 125N(127.5kg) for the tet duration of 6 minute. EFFECT OF REFRIGERANTS Figure 3 how the frictional characteritic of POE bae oil determined varying ga preure. Under the ga preure of1kpa(l.okg/cm2), the coefficient of friction abruptly increaed to reach the eizure before the end of the run. When elevating ga preure up to 2kPa(2.kg/cm~, the coefficient of friction became teady tate during the run. Meanwhile, the coefficient of friction under the highet ga preure continued to decreae until the end of run. It i apparent that the increae in ga preure prevented eizure and reduced the coefficient of friction. The pecific wear rate for POE bae oil varying the refrigerant i given in Fig.4. The combination of POE/R22 howed much lower wear rate than POEIHFC. On the other hand, the wear rate with R44A wa the highet of the data in HFC, R47C the intermediate and R134a the lowet. The order of anti wear performance with refrigerant agree well with that of olubility of refrigerant in POE a hown in Fig.2. It implie that antiwear performance of POE bae oil may be correlated with the olubility of refrigerant in the oil. EFFECT OF ADDITIVES Figure 5 compare the antiwear propertie of the formulated oil lited in table 2 in R134a environment. The wear rate increaed conitently with load for each oil. All the formulated POE howed the low wear rate compared with that for POE bae oil under the load from 75N(76.5kg) to 1N(l2kg), in which POEC containing both AP and SP wa uperior to both POEA and POEB. Under the highet load of the preent experimental condition, however, both POEA and POEB became almot ineffective while POEC remained it effect whoe wear rate wa alm()t equal to that for the formulated ABA in R22. That i, a ynergitic effect ofthe additive on wear reitance wa found when uing AP together with SP type additive. Wear behavior of the formulated POE wa compared varying refrigerant under the highet load condition a hown in Fig.6. A i evident in the figure, POEC how the highet wear reitance of the POE in each refrigerant On the other hand, when comparing between the data obtained varying refrigerant for each additivecontaining POE, it i common to the reult for all the POE that the wear rate in R134a i the highet, R47C the intermediate and R44A the lowet That i, the variation in wear rate with refrigerant for the additivecontaining POE i contrary to that obtained for POE bae oil in Fig.4. A hown earlier, the wear rate for POE bae oil wa coniderably influenced by the amount of diolved refrigerant in the oil. Thu, thi contradictory reult implie that a competitive adorption 274

4 between refrigerant and additive occurred on the liding urface in the cae offormulated POE. SURFACE OBSERVATION AND SURFACE ANALYSIS Figure 7 how the urface obervation of ring by mean of an optical microcope. It i oberved that there are ome part imilar to the block material on the urface for POEA, meanwhile the urface for POEC i generally mooth. It i inferred that adheion occurred on the liding urface which reulted in tranfer of the mating material to the ring urface. The urface of ring were analyzed by X ray photoelectron pectrocopy (XPS). Figure 8 how the XPS pectra of the detected element, and table 3 ummarize their atomic concentration at the outermot urface. In Fl pectra hown in Fig.&( a), the binding energy (B.E.) at the peak i the ame for all the reult, which indicate the preence offef2. The atomic concentration off i in the order ofpoea > POEB >POEC. The peak at B.E. in P2p pectra, which i conunon to the reult for all the POE, i acribed to FeP4. The atomic concentration ofp for POECi approximately three time a high a thoe for both POEA and POEBa hown in table 3. Thi tendency i almot oppoite to the reult obtained with F element. Meanwhile, Ci pectrum for POECi appreciably different from thoe with the other POE. That i, the intenity in the range ofb.e. from 286 to 29eV, which i due to a chemical bond ofc and uch a carbonyl, carboxylic and ether group, i higher for POEC than for the other. Thi indicate that the concentration of the decompoition and reaction product of eter bae oil in the film i higher for POEC than for the other POE. The peak at B.E. of529.ev in Ol pectra i due to FeOx while the range from 53 to 533eV i acribed to oxygen having a chemical bond with carbon. POEC how much lower intenity of FeOx but higher intenity ofc than both POEA and POEB, which reaonably agree with the reult in Ci pectra. DISCUSSION From thee reult, it may be concluded that the refrigerant play an important role in boundary lubrication depending upon the olubility of ga in the oil when lubricated with POE bae oil in R22 and HFC. On the other hand, there mut be a competitive adorption accompanying a reaction film between refrigerant and antiwear additive on the liding urface when the formulated POE are ued, in which the effect of additive i predominant. SP type additive ha a role of promoting formation of iron phophate derived from aryl phophate and iron oap from eter bae oil on the urface. With repect to the mechanim of wear reduction baed on the interaction between the two additive, further tudy would be required. CONCLUSIONS Friction and wear performance of polyoleter with and without additive were tudied with a block on ring type tribometer in ome HFC and R22 refrigerant environment. The reult obtained are a follow. (1) HFC refrigerant play a boundary lubrication role on the bai of formation of metal fluoride depending upon the olubility of ga in the oil which effectively prevent adheion and reduce wear amount. (2) Addition of aryl phophate together with SP anti wear additive in POE i beneficial for anti wear performance which i almot comparable to that for the formulated alkylbenzene in R22. (3) When additivecontaining oil are ued, there mut be a competitive adorption between refrigerant and additive onto the liding urface. REFERENCE [1] Muraki M. : Proc. Int. Sym. on R22 & R52 Alter. Ref., Japan 1994,

5 Table 1 Propertie of bae oil Structure Vicoity, C Vicoity index LCST 1), oc with R134a with R47 with R44A with R22 POE(A32) AB pol yo leter <6 <6 1) Lower Critical Solubility Temperature Table 2 Compoition of formulated oil alky!benzene <6 POEA POEB POEC ABA Bae oil POE (A32) Additive AQl) Epoxide AP2l SP 3 ) 1) Antioxidant 2) Aryl phophate 3) Sulfurphophoru type additive AB thermocouple coil refligerant ga 1~~.15 vicoity in the air ~,.,,., 1.~... ;E) 5.z en oil Fig.l Falling piton type vicometer 3 R134a R47C R44A R22 R22 POE (A32) AB Fig.2 Vicoity and olubility of oillrefligerant mixture ( Temp.: 8 C, Ga Pre.: 6kPa( 6.kg/cm 2 ) ) 276

6 c ,.b t c <1) (..) 8.1 u 6kPa(6.kglcm 2) Tet time, min Fig.3 Frictional characteritic of POE (A32) (Ref.: R134a, Load: 75N(76.5kg)) z N 1 6 ~ 1 ;a <1) ~ 6 R134a R47C R44A R22 Fig.4 Anti wear propertie of POE (A32) ( Ga pre.: 6kPa(6.kg!cm 2), Load: 75N(76.5kg)) ~1 N E 6 75N looon 125N D POE(A32) K3l ABA I R22 ~ POEA R134a R47C m2!l POEB POEC R44A Fig.5 Wear rate for formulated oil v load (Ref.: R134a, Ga pre.: 6kPa(6.kg/cm 2)) Fig.6 Antiwear propertie in HFC ref1igerant (Ga pre.: 6kPa(6.kg/cm 2 ), Load: l25n(l27.5kg)) liding (a) POEA Fig. 7 Sliding rnface of ring after the tet (Ref.: R134a, Ga pre.: 6kPa(6.kg!cm 2), Load: 125N (127.5kg)) (b) POEC 277

7 Binding energy, e V Binding energy, ev (a) F1 (c) Cl Binding energy, ev Binding energy, ev (b) P2p (d) 1 Fig.8 XPS pectra for liding urface of ring with FOE (Ref.: R134a, Ga pre.: 6kPa(6.kglcm 2), Load: 125N (127.6kg)) POEA POEB POEC Table 3 Atomic concentration of detected element at outermot utface Fe Load: 125N(127.6kg) c F p (Ref.: R134a, Ga pre.: 6kPa(6.kg/cm 2 ),) 278