1、Synthetic Oils for Worm Gear Lubrication by: U. Mann, Klber Lubrication I American I J - TE-CHNICAL PAPER COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesSynthetic Oils for Worm Gear Lubrication Dr. Ulrich Mann, Klber Lubrication The statements and opi
2、nions contained herein are those of the author and should not be construed as an official action or opinion of the American Gear Manufacturers Association. Abstract Worm gears and combined helical/worm gears are often used as a simple and effective solution for power transmission applications. The l
3、oad carrying capacity of such gearboxes was increased constantly over the last ten years. Latest calculation methods, new materials, modern manufacturing procedures and, especially, suitable lubricants are the most important parameters for high performance gear drives. The presented paper shows seve
4、ral synthetic gear oils and their influence on wear and efficiency of highly loaded worm gears. The friction coefficient of the base oil as well as the additives is considered. Taking their extended service life into account, very often synthetic gear oils are the most economic solution. The results
5、 are based on measurements carried out on the Klber worm gear test rig. This test rig allows to measure input speed, input torque, output torque, bulk and sump temperature of the tested worm gear. It is also possible to ascertain the lubrication regime in the contact of worm and wheel. A detailed de
6、scription of the test rig is given in the paper. Finally, the measured results are compared with other investigations (e.g., measurements of friction coefficients) and DIN 3996 (Calculation of load capacity of cylindrical worm gear pairs). Copyright O 1999 American Gear Manufacturers Association 150
7、0 King Street. Suite 201 Alexandria, Virginia, 22314 October, 1999 ISBN: 1-55589-755-X COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesSynthetic Oils for Worm Gear Lubrication 1 Introduction Ulrich Mann, Product Manager Klber Lubrication Mnchen KG, Mun
8、ich, Germany Worm gears and combined helical worm gears are often used as a simple and effective solution for power transmission applications. The load carrying capacity of such gear boxes has con- stantly increased over the last few years. Latest calculation methods, new materials, modern man- ufac
9、turing procedures and, last but not least, suit- * able lubricants are the most important parameters for high performance gear drives. Typically, the development of new gear oils starts with basic investigations modeling the tribological contact. Therefore, test rigs such as the four ball tester and
10、 the oscillation-friction and wear tester are helpful. The best way to optimize a gear oil is to test samples in a real gear box, especially in terms of contact pressure and temperature. Sev- eral material combinations should be tested. This is the only way to develop a gear oil ensuring: o o o A go
11、od gear oil allows an increase of the load carrying capacity of a gearbox. low friction and high efficiency low operating temperatures to improve oil service life low wear and delayed fatigue of materials We have designed our own worm gear test rig to improve the development of high performance gear
12、 oils. The presented paper reports results ob- - tained from this test rig. 2 Test Rig 2.1 Set Up Figure 1 shows the worm gear oil test rig. The back-to-back test rig is driven by an electric mo- tor and loaded by a generator. The worm gear is a standard catalog gearbox with no modifications, except
13、 for provisions for measurements of several temperatures. _. torque 81 speed sensor outpa Flg. 1: Test Rig (schematic). The worm gear is sump lubricated (0.6 liters) with worm under (Figure 2). The housing (gray cast iron) is fan cooled. The setup of the test rig makes it possible to measure speed a
14、nd torque of the worm (input side). Calibrated torque measurement shafts are used to determine the torque. These torque mea- surement shafts were bought ready to operate, an extra calibration is not required. Combined page - i - COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Info
15、rmation Handling Serviceswith the output torque of the wheel, the overall efficiency of lhe gearbox can be calculated. material no. of teeth gear ratio i center distance a sumptempendure / shaft temperature Fig. 2: Determination of Temperatures and Lubrica- tion Regime. - Worm Wheel 16 MnCr 5 GC - C
16、uSnl2Ni 1 39 39 63 mm (approx. 2.5 inches) The test rig provides the opportunity to determine the lubricating regime in the mesh (Figure 2). Knowing the lubrication regime makes it easier to check e.g. how an additive package influences the running in behavior of a gear. The worm shaft is electrical
17、ly insulated against the housing. Therefore, a thin insulating layer is inserted be- tween the outer bearing .ring and housing. A low alternating (AC) voltage is applied to the worm and wheel. A short-circuit indicates mixed friction or metal to metal contacts, the full applied voltage indicates a s
18、eparating lubricant film. This con- tinuous operating method permits determination of changes in lubrication regime during the test run. The wear of the wheel is determined using the following two methods: (1) (2) Weight loss of the wheel after completion of the test run. Abrasion of the wheel flank
19、 while running. The measurement is based on a continu- ous measurement of the wheel tooth thick- ness. Thus, it can be assessed whether the wear is a result of running in or of the actu- al operating conditions. The permanent measurement of the wheel tooth thickness is based on the evaluation of the
20、 rela tive angle between worm shah and wheel. A change of this angle, caused by reduced tooth thickness, indicates wear. The wear rate (pm/h) is determined as the average slope of the measured reduction of tooth thickness. As mentioned, the measurement of different tem- peratures is part of the stan
21、dard test. These are (acc. to Figure 2): o o oil sump temperature oli o housing temperature Uhouslng o ambient temperature U- The bulk temperature U, is measured in the cen- ter of the worm, relatively close to the mesh. bulk temperature of worm shaft UM These parameters are recorded online and eval
22、u- ated on a PC system. A more detailed description of the test rig and its features is given in l. 2.2 Gear Set A new gear set is used for every tested oil. While assembling the gearbox the contact pattern is ad- justed to the outlet side of the mesh and is ap- proximately 50 % of the flank. 2.3 Te
23、st Conditions The test rig is used for the development and test- ing of worm gear oils. It is not our aim to test gear sets. Thus, we perform a standard running in procedure with the test oil at low speed and stepwise increase load to achieve comparable starting conditions for every test. Each test
24、starts with a 50 hour run in. At constant speed, the load is increased stepwise up to the maximum torque. page - 2 - COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesThe maximum torque corresponds to the rated load of the.gear set. polyglycol (EO : PO =
25、 1:I) PG460-1 The test run itself is conducted at constant load and speed. The standard parameters are: o input speed n, = 350 rpm, output torque T, = 300 Nm or o input speed n, = 1200 rpm, output torque T2 = 250 Nm After 300 hrs the standard test is finished. CLP (A/16,6/140) 12 220 The tests with
26、low speed and high torque were given preference due to the fact that especially at low film thickness the additives show their influence on wear. On the other side, load inde- pendent losses (friction losses at the seals, splashing oil etc.) are relatively low at this speed. The calculated efficienc
27、y of the gear box is mainly effected by the friction losses in the gear contact. polyalphaolef in PAO460-2 3 Test Oils CLP, food grade lubricant (A/8,3/90) 12 160 Table 2 shows some data of the tested lubricants. For the tests a variety of different synthetic oils were chosen and compared to a miner
28、al oil, which is often used for lubricating all types of gearboxes including worm gear drives. E460 requirements made on CLP oils. Each oil passes the FZG scuffing test with loadstage greater than 12. CLP, rapidly biodegradable (A/8,3/90) 12 ester 150 The M460 oil is based on a paraffinic mineral oi
29、l and meets the CLP requirements. It contains a sulphur phosphor additive package. This oil was selected as a reference oil, because it is widely used in common gear applications. The polyglycol PG460-1 was chosen as a typical modern high performance gear oil. The ratio of ethyleneoxyde to propylene
30、oxyde is 1 : 1. These types of base oils offer low friction coefficients 141. This means that low oil temperature and high efficiency can be expected, especially for gear- boxes with high sliding portion in the mesh. PG460-2 was designed as a so called food grade lubricant, .e. the formulation of th
31、e oil meets the guidelines of sec. 21 CFR 178.3570 of FDA. In other words, only listed raw materials are used for the formulation of this product. The base oil prop- erties are comparable to PG460-1. PAO460-1 is a polyalphaolefin. This oil contains a sulphur/phosphor additive package and was origina
32、lly developed for application in spur, heli- I Notes I Base Oll I Viscosity index I Oil I I I I I I M460 I paraffinic mineral 95 CLP (A/8,3/90) 12 I I I I I I I CLP, Yood grade lubricant I (A/16,6/90) 12 poly gly col (EO : PO = 1 : 1) I PG460-2 I I I I I I I I PAO460-1 I polyalphaolefin 150 CLP (A/1
33、6,6/140) 12 The viscosity of each oil is 465mm*/s t 40 OC (IS0 VG 460). All oils are fully formulated (R : WNm nllrdcabraslon: -.- pnl(h Fig. 4: Test Results for Polyglycol PG460-1. o 50lo0#0200250500 o 5oKK)w20D2M500 The test results for the PG460-1 show lower tem- peratures (Figure 4b). After 150
34、hrs the bulk tem- perature of the worm remains constant at 70 OC (158 OF). At the same time, the efficiency reaches 78 % (Figure 4d). Figure 4c gives an explanation of this high efficiency: After a period of approx. 50 hrs, where the gear runs with full load, the film thickness increases and the lub
35、rication conditions wad: M460 become better. This might be caused by adaption rwtC0ndt)onr: mar: inpnrpeedn: SSOrpm rvdghtkssuhmtg processes in the contact area, e.g. influenced by the additives. Taking the lubrication regime into ouwutueti: 900Nm ttwibrsdon. o.sipnvh MuilnghPI mhgum PI 4 a - 0 2002
36、50500 o 50xy)1502002K)300 -tno-M NNilngmIii1 Fig. 3: Test Resuits for Mineral Oil M460. Figure 3 shows an example of a test run per- formed with the M460 oil. Most measurements were evaluated after 250 hours of test run. The evaluation of temperatures (Figure 3b) shows a shaft temperature of approx.
37、 11 5 OC (239 OF). The total efficiency of the gearbox is nearly 60 %. Figure 3c represents the determination of the lubrication regime. If the curve is on top of the diagram, mainly mixed friction in the contact zone appears. A curve at the bottom means better lubricating conditions and a more or l
38、ess separat- ing oil film. Using this method, it is not possible to measure the exact film thickness, e.g. minimum film thickness h,. In the case-of oil M460, the test shows mixed friction. This leads to continu- ous wear of the wheel (Figure 4a). The apparent - account, this excellent efficiency ca
39、n be interpret- ed as a result of the low friction coefficient of the base oil 5. The measured weight loss of the wheel is very low. This weight loss seems to be a result of running in wear. Figure 4a shows no reduction of teeth thickness during the entire test run. The measurements for PG460-2 show
40、 interesting results (Figure 5). While measured temperatures and efficiency are comparable to the results for PG460-1, a clear run in effect is recognizable. Also after finishing the running in procedure (stepwise increase of load) the wear of the wheel continues. It is not until after 150 hrs that
41、th8 wear of the wheel stops. This might be explained by the size and orientation of the contact pattern. When the contact pattern reaches its maximum page - 4 - COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Services$3 - NMb I running ti: 300Nrn tlMkabrsdlon:
42、 0.07pW Fig. 6: Test Results for Polyalphaolefin PA0460-1 The results for oil PAO460-1 (Figure 6) show a shaft temperature of approx. 100 “C. The rnea- sured efficiency becomes stable at approx. 67 %. The wear rate is relatively low (0.07 pm/h). After approx. 50 hrs, a separating oil film occurs. Th
43、is PAO460-2 (Figure 7) shows similar shaft temperatures and efficiencies as PAO46Q-1. Due to the lack of a separating oil film the wear rate is higher (0.41 pm/h). Apparently the additives in estd: PA-2 teat mtions: m inputspeedn -. Srpm weightlact.wheel:3.79g outputtorque+;. 500Nm fienlcabredon: 0.
44、41 pm Fig. 7: Test Results for Polyalphaolefin PAO460-2. the PAO460-2 oil do not form a protective layer that is sufficient to prevent wear on the wheel flanks. O 50 100 i50 200250300 O 50 IW i50 200 250 300 running bme m Flg. 8: Test Results for Synthetic Ester E460. The test results for the synthe
45、tic ester E460 are shown in Figure 8. Efficiencies are nearly 70 % and temperatures are around 100 OC. The wear rate is approx. 0.44 pm/h. As with PAO460-2, no separating lubricating oil film is formed under the selected test conditions. The following figures show two further tests which were conduc
46、ted with PG460-1 and PAO460-2 at page - 5 - COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Serviceshigher speed (n, = i200 rpm) and at a reduced torque (T, =. 250 Nm) *Shan -4-m -o- -MiMent riidWb I JO0 : 200 _. . “,i Do uo200250Ico “O SO OO Is0 200 250360 G
47、. . g3 . tsstdl: po460-1 mndltbns: WW. bipitspdn: 1200ipm rrulghtlorr,whi:224g outpR-f2: 250m ffankahsioa oR2rm Fig. 9: Test Results for Polyglycol PG460-1. As shown in Figure 9, the initial temperatures of the PG460-1 were higher. The shaft temperature is around 95“C, which is due to the increased
48、churning losses. The efficiency is again around 80 %. This proves that the running in under these test conditions takes longer and ends only after approx. 100 hrs. Only then is a separating lubri- cating oil film formed and the wear rate reduced to zero. The increased weight loss of the wheel may be
49、 caused by the unfavorable wear behavior during the running in. q71 - . i;$?/ ?. 20 . - i . . i“ . . .(a3 . - st i 5,s Flg. 1 O: Test Results for Polyalphaolefin PA0460-2. When comparing these results with those for PAO460-2 (Figure 1 O), the shaft temperatures are again around 100 “C. The oil sump temperature, however, is higher too.The fficiency is at a con- stant 75 %. A separating oil film is formed only after a comparatively long operating time (approx. 220 hrs.). Then the wear rates decreases drast- cally. The wear rate was 0
