Mechanical Loss Reduction at Thrust Bearings of Scroll Compressors Using R407C

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1 Prde University Prde e-pbs International Compressor Engineering Conference School of Mechanical Engineering 1996 Mechanical Loss Redction at Thrst Bearings of Scroll Compressors Using R47C F. Nishiwaki H. Hasegawa M. lkoma R. Matszaki S. Mramats Follow this and additional works at: Nishiwaki, F.; Hasegawa, H.; lkoma, M.; Matszaki, R.; and Mramats, S., "Mechanical Loss Redction at Thrst Bearings of Scroll Compressors Using R47C" (1996). International Compressor Engineering Conference. Paper This docment has been made available throgh Prde e-pbs, a service of the Prde University Libraries. Please contact epbs@prde.ed for additional information. Complete proceedings may be acqired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at Herrick/Events/orderlit.html

2 Mechanical Loss Redction at Thrst Bearings of Scroll Compressors Using R47C Fmitosbi Nishiwaki 1, Hiroshi Hasegawa 1, Mitshiro Ikoma 1 Ryoichi Matszaki 2 and Shiger Mramats 2 1 Hman Environment Research Laboratory,,Ltd , Yagmo-Nakamachi, Morigchi, Osaka 57, Japan 2 Compressor Division,,Ltd , Noji-cho, Ksats', Shiga 525, Japan ABSTRACT This paper presents the experimental research into high mechanical efficiency at thrst bearings of low-side scroll compressors for air conditioners with the new refrigerant R47C and Polyolester (POE) lbricant. In order to examine the friction loss at the thrst bearing nder a test condition which is close to the actal rnning condition of compressors, the athors developed a friction test machine that cold make the orbiting friction test nder the pressrized refrigerant atmosphere. Sbseqently, an evalating method of the friction loss at the thrst bearing was established. In the present stdy, the effects of friction parameters on the friction loss and the coefficient of friction were clarified by evalating the friction characteristics of the orbiting thrst bearing in the mixing environment of POE lbricant and R47C refrigerant. In addition, above mentioned reslts of the orbiting friction tests were confirmed by the reslts of compressor performance tests. As a reslt, the redction of the friction loss at the thrst bearing of the scroll compressor was sccessflly accomplished. 1. INTRODUCTION Becase of the ozone layer depletion isse, alternative refrigerants HFCs have been examined as the refrigerants for air conditioners. It is known that HFCs refrigerants with no chlorine have poor lbricity de to the effect of extreme pressre agent by chlorine, compared with HCFC22 refrigerantl,z,3)_ Ths, in order to develop the high efficient and high reliable compressors for air conditioners with HFCs refrigerants, the improvement in mechanical efficiency and wear resistance are becoming more important. In the scroll compressors for air conditioners, the improvement in mechanical efficiency necessitates the redction of the friction loss at each scroll compressor element, sch as the thrst bearing, the main jornal bearing, the sb jornal bearing, and so on. It is reported in a research concerned with the simlation for compressor performance that the friction loss at the thrst bearing is most large among the friction losses at sliding elements 4, 5 )_ However, it is the real state that the friction loss at the thrst bearing of scroll compressors has not been well stdied4,5, 6 )_ In the present stdy, the friction characteristics of the orbiting thrst bearing in the nxmg environment of Polyolester (POE) lbricant and R47C refrigerant were described. In addition, the test reslts for the orbiting friction and the compressor performance were also discssed. 263

2. FRICTION TEST APPARATUS AND PROCEDURE A schematic diagram of test apparats and test conditions employed in this stdy is shown in Fig. 1 and Table 1, respectively.

3 2. FRICTION TEST APPARATUS AND PROCEDURE A schematic diagram of test apparats and test conditions employed in this stdy is shown in Fig. 1 and Table 1, respectively. This friction test machine, which was eqipped with the test section of the orbiting thrst bearing in the vessel filled with a high-temperatre and high-pressre mixtres of refrigeration oil and refrigerant, was developed by the athors to evalate the friction loss at the thrst bearing nder the test condition which is close to the actal rnning condition of compressors. The orbiting thrst bearing consists of two specimens. The pper specimen makes a orbiting motion. The lower specimen is fixed and loaded against the pper specimen. Hereafter, the pper specimen and the lower specimen are expressed as the orbiting specimen and the fixed specimen, respectively. Specifications of specimens are shown in Table 2,, and the appearance of the orbiting and fixed specimens are shown in Fig. 2 and Fig. 3, respectively. R47C refrigerant, which is mixed refrigerants of HFCs, is sed. Refrigeration oil is POE lbricant, whose kinematic viscosity is 65.6 nnn 2 /s(@4 C) and 8.2 nnn 2 /s(@1oc), withot an extreme pressre agent. Test specimens were rinsed in acetone by the ltrasonic washer for 1 mintes and monted in the friction test machine after dried. Friction tests was condcted for abot 14 hrs and the driven torqe of the orbiting specimen was measred. The load was increased in steps by 245 N per 3 seconds from 98 N p to the vale of the load shown in Table 1. The friction loss of the orbiting thrst bearing was calclated from following eqation 5 ). Wt-bTt Znn/6 (1) where W t -b is the friction loss of the orbiting thrst bearing, T t is the driven torqe of the orbiting specimen and n is the orbiting speed. Replacing the load acting nifonnly on the sliding srface with the concentrated load acting at the center of the orbiting specimen, the coefficient of friction of the orbiting thrst bearing, J.L, can be obtained as follows 5 ). J.LTt/(F ro) (2) where F is the load acting normally on the orbiting specimen and ro is the orbiting radis. By measring the driven torqe of the orbiting specimen and sing these eqations, the friction loss and the coefficient of friction of the orbiting thrst bearing were calclated. Frthermore, elimination of T t from eqations (1) and (2) reslts in Wt-bJ.L F ro Zn:n/6 (3) From eqations (3), it is noticed that the friction loss of the orbiting thrst bearing is in proportion to the coefficient of friction, the load, the orbiting radis and speed. So, by sbstitting the coefficient of friction obtained by the friction test, the load, the orbiting radis and speed in actal compressors into eqations (3), the friction loss at the orbiting thrst bearing in compressors can be predicted. 3. EXPERIMENTAL RESULTS AND DISCUSSION A typical example of the test time dependence on the friction loss and the coefficient of friction is shown in Fig. 4. The fixed specimen is a thrst plate type (carbon tool steel). This type has been developed as a orbiting thrst bearing for HFCs refrigerants de to its excellent wear resistance. The friction loss and the coefficient of friction decreases rapidly for 8 hrs after the test was started to make, ths approaching to a constant vale. This time which the friction loss and the coefficient of friction 264

become constant is the initial rnning-in time for the sliding srface. In actal compressor, it is well known that the inpt power decreases as the rnning time passes after assembling of compressor.

4 become constant is the initial rnning-in time for the sliding srface. In actal compressor, it is well known that the inpt power decreases as the rnning time passes after assembling of compressor. In this stdy, the measred asymptotic vale of the friction loss was defined as one of tested specimen. In the case of the thrst plate type (carbon tool steel), the friction loss was 45 W and the coefficient of friction was Effect of Srface Roghness At first, the effect of srface roghness of fixed specimens on the friction loss and the coefficient of friction was examined. Fig. 5 shows the test data for the friction loss and the coefficient of friction vs. the srface roghness Ra (before test) of the fixed specimens for the type of plain disk. Srface roghness Ra (before test) of orbiting specimens were J.Lm. As can be seen, the friction loss and the coefficient of friction decreases, as the srface roghness Ra of fixed specimens decreases. In the case of the srface roghness Ra of 1.39 rn, the sliding srface of the orbiting specimen was worn by 9-22 IJ. m and the color of POE lbricant became black. In other cases, wear was scarcely observed. 3.2 Effect of Oil Groove Next, the friction characteristics were evalated for the case with oil groove made on the sliding srface of fixed specimens in order to form oil film. The test data for a single groove and a doble groove type are also shown in Fig. 5. If the srface roghness of fixed specimens is the same, the friction loss and the coefficient of friction for fixed specimens with oil groove become smaller than those for the plain disk type. The friction loss and the coefficient of friction were scarcely affected by the difference of the configration between single groove and doble groove shown in Fig. 3. It was conclded that the friction loss decreased since oil film was formed easily by making the oil groove. 3.3 Effect of Frictional Conditions To clarify the effect of frictional conditions on the friction loss and the coefficient of friction, the friction characteristics for the fixed specimens of plain disk type were evalated by changing frictional conditions. ( 1) Effect of Load and Orbiting Speed The effect of the load and the orbiting speed on the friction loss and the coefficient of friction are shown in Fig.6 and Fig.7, respectively. The friction loss increases proportionally to an increase in the load and the orbiting speed, bt the coefficient of friction is almost constant. (2) Effect of Orbiting Radis Table 3 shows the effect of the orbiting radis on the friction loss and the coefficient of friction. In the present experiments, the effect of the orbiting radis on the friction loss was scarcely fonded. However, as seen in Table 3, the coefficient of friction increased by decreasing the orbiting radis. It is considered for this reason that the oil film-forming properties become poor as the orbiting radis decreases. (3) Effect of Oil Temperatre The effect of the oil temperatre on the friction loss and the coefficient of friction is shown in Fig.8. The friction loss and the coefficient of friction at 6 oc and 75 oc were almost the same, bt at 95 'C the friction loss and the coefficient of friction increased rapidly. In this case, the sliding srface of the orbiting specimen was worn by JL m and the color of POE lbricant became black. It is considered that the oil film-forming properties become poor as the oil viscosity decreases with an increase of the oil temperatre. 265

5 4. COMPRESSOR PERFORMANCE TEST Using the scroll compressor with 8 kw refrigerating capacity, the effect of the thrst bearing type on the compressor inpt power for R47C and R41A was examined in the ARI condition. The test reslts for the compressor performance and the orbiting friction are shown in Table 4. The tendencies ofboth test reslts were the same regardless of refrigerant types, and it was fond that the friction loss for the single groove type is most low among these 3 types. Frthermore, it was revealed that the difference in the friction loss of the compressor inpt power between the thrst plate type (carbon tool steel) and the single groove type is abot 1 % of the friction loss at the thrst bearing, considering the athor's simlation reslts with regard to the compressor performance. As a reslt, by making the oil groove, the mechanical loss at the thrst bearing cold be redced by abot 1 %. 5. CONCLUSIONS In order to redce the friction loss at the thrst bearing of the scroll compressors for alternative refrigerant, the effects of the friction parameters on the friction loss and the coefficient of friction were examined by condcting the orbiting friction tests nder the pressrized mixing environment of POE and R47C. The following conclsions were obtained. 1) The friction loss and the coefficient of friction decrease by redcing the srface roghness of the sliding srface and making the oil groove. 2) The friction loss increases and the coefficient of friction is constant, as the load and the orbiting speed increase. 3) The test reslts for the orbiting friction agree with one for the compressor performance tests. Frthermore, it was conclded that the friction loss at the thrst bearing of the scroll compressor cold be redced by optimizing the sliding material, the configration of the sliding srface and the frictional condition. REFERENCES 1. Mizhara,K.," Lbrication in Alternative HFC Refrigerants," Jornal of Japanese Society of Tribologists, \bl.38, No.5 (1993) Mizhara,K.,et al.," The Friction and Wear Behavior in Controlled Alternative Refrigerant Atmosphere," STLE Paper No.92-TC-3B-3 (1992) Hasegawa,H.,et al., "The Friction and Wear characteristics in Refrigerant Atmosphere," Proceedings of JAST Tribology Conference Tokyo (May 1991) Ishii,T.,et al.," A Stdy on High Mechanical Efficiency of a Involte Scroll Compressor," Trbomachinery (Trbomachi:nery Society of Japan), Vol.21, No.1 (1993) Ishii,T.,et al.," Dynamic Behavior of A Scroll Compressor (Dynamic Analysis)," Transaction of the Japan Society of Mechanical Engineers, Vol.53, No.491 (1987) lshii,t.,et al.," Mechanical Efficiency of Varios Large Capacity Scroll Compressors," Transaction of the Japan Society of Mechanical Engineers, Vol.53, No.495 (1987)

6 Rotary Shaft Orbiting Motion Orbiting Specimen Ff:: Sliding Srface Fixed Specimen Fig.l Schematic Diagram of Test Apparats Table 2 Specifications of Specimens Specimens Types Materials Table 1 Test Conditions Atmosphere Mixing Environment of POE and R47C Amont of Refrigeration 12 (wt%) Amont of Oil 4 (crn3) Oil Temperatre 6, 75, 9 (C) Oroiting Radis 2.5, 3.4 (mm) Load 147, 294, 441 (N) Orbiting Plain Disk Etectic Graphite Cast Iron Thrst Plate Carbon Tool Steel Fixed Plain Disk Gray Cast Iron Single Groove Gray Cast Iron Doble Groove Gray Cast Iron Orbiting Speed 6, 9, 12 (:pm) Single Oil G.-oo e Type Dobl Oil Groove TyPe ( Oil Q-oovco Width 2.2mm) ( 11 Groo'-c Width 2.wm ) Fig. 2 Shape and Dimensions of Orbiting Specimen Fig. 3 Shape and Dimensions of Fixed Specimens 267

7 8 '-' 9c-----, :, Load: 2.94 kn a ; +- j Orbiting Speed: 9 rpm o ' : : Orbiting Radis: 3.4 mm "" 7Q Oq;: + : ; "" KXh : : ' : ' : '"'Ocx:tl! :! ' : so : ---- : ; r. 9 : o:ocooa : :, o?- oo'bopc;ooo-o : j ' : ;Oooo 4 : j + - ' o ,_--'4'---._6.-..a.._1 o ' 3 Test Time (hr) Fig.4 Test Time Dependence of Friction Loss and Coefficient of Friction ::t :::::.sz t) ;:::: '- ::::: E 7.15 ::t Oil Temperatre: 6 6 'C Load: 2.94 kn Orbiting Radis: 3.4 mm "".1 so J: tl.5 ;: 'G 3 ie Orbiting Speed (rpm) Fig.7 Effect of Orbiting Speed -.sz '- ::::: a).s ;: i 55,.. : : so :.. ; 6"'""1"""""" 45.;.. 4 '"]'"'"""" I : 35 o Plain Disk 3 6 Single Groove Doble Groove 25--L Srface Roghness Ra of Fixed Specimens ( JJ. m).6 ::t.5.4.;:::::.:::,_ '-.3 s Fig.5 Effect of Srface Roghness of Fixed Specimens (Test Condition Load:2.94 kn, Orbiting Speed: 9 rpm, Orbiting Radis:3.4 mm) 6 Orbiting Speed: 9 rpm.15 ::t,, Orbiting Radis: 3.4 mm so.2 Oil Temperatre: 6 "C '-'.1 "' ;:::: Load (kn) Fig.6 Effect of Load '- c 'i:) E 12 Load: 2.94 kn,, Orbiting Speed: 9 rpm 1.15 ::t Orbiting Radis: 3.4 mm '-'.9.1 tl ;: 8 :::::.9 6 'E -.5,_ 4 2. so Oil Temperatre (C) Fig.8 Effect of Oil Temperatre Table 3 Effect of Orbiting Radis Coefficient of Friction Loss (W) Radis(mrnL Friction fl Orbiting Table 4 Reslts of Compressor Performance Test and Orbiting Friction Test. Compressor Perfonnance Test Types of Inpt Power (W) Thrst Bearing R47C R41A Orbiting Friction Test '- E Friction Loss Coefficient of (W) Friction,. Thrst Plate (Carbon Tool Steel) Plain Disk Single Groove

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Prde University Prde e-pbs International Compressor Engineering Conference School of Mechanical Engineering 198 Estimation, of the Starting Torqe, of Refrigerant Rotary Compressors S. Nagatomo S. Kato