1、I 98FM9 I I I Studies on Improvement of Surface Durability of I Case-Carburized Steel Gear - Effects of Surface Finish Processes upon Oil Film Formation I by: M. Hashimoto, Sumitomo Heavy Industries, Ltd., S. Hoyashita and J. Iwata, Saga University 1 I TECHNICAL PAPER COPYRIGHT American Gear Manufac
2、turers Association, Inc.Licensed by Information Handling ServicesStudies on Improvement of Surface Durability of Case-Carburized Steel Gear - Effects of Surface Finish Processes upon Oil Film Formation Munetoh Hashimoto, Sumitomo Heavy Industries, Ltd., Shigero Hoyashita, Saga University, Jun Iwata,
3、 Saga University The statements and opinions 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 It is very difficult to precisely finish agear tooth surface to the extent of a few sub-micron w
4、ith grinding. Even if possible, the grinding time of the tooth surface will be very long and a grinding bum may often occur. The authors have adopted a barreling process as a final finish process in order to improve the ground and/or shot peened surface. Though the barrelling process is economical f
5、rom the viewpoint of the manufacturing process, there was a very important question whether or not the process is applicable to gears with complex configurations. The authors have found that the barrelling process is very effective for the improvement of gear tooth surface roughness without changes
6、in tooth profiles and tooth traces, which may have small tooth tip relief and/or crowning. In the present research, the surface durability of the high quality gear manufactured by a proposed new method was also investigated using a gear testing machine, which can measure the condition of oil film fo
7、rmation between a pair of gears during running. As the results of durability test, it was confirmed that the configuration of tooth surface of the barrelled gear scarcely changed after running, but that of the shot peened gear remarkably changed. The condition of the oil film formation in a running
8、test conducted using barrelled gears was very good even during start-up. Also, the duration of oil film formation in the case of the barrelled gear was superior to the one in the case of the ground orshot peened ones, because of the difference of metallic contact condition. Key Words: Gear, Case-Car
9、burized Gear, Surface Durability, Shot Peening, Barrelling, Surface Roughness, EHL, Tribology Copyright O 1998 American Gear Manufacturers Association 1500 King Street, .Suite 201 Alexandria, Virginia, 22314 October. 1998 ISBN: 1-55589-727-4 COPYRIGHT American Gear Manufacturers Association, Inc.Lic
10、ensed by Information Handling ServicesStudies on Improvement of Surface Durability of Case-Carburized Steel Gear - Effects of Surface Finish Processes upon Oil Film Formation - Specifications Module m Pressure angle a Number of teeth z Dia. of pitch circle d mm Helix angle “ Face width B mm Munetoh
11、Hashimoto: Senior Engineer, Sumitomo Heavy Industries, Ltd., Japan Shigeru Hoyashita: Lecture, Saga University, Japan Jun Iwata: Graduate Student, Saga University Gear 11 Gear 2 3 3 20 20 26 25 78 78 O 16 15 38 e 1. Introduction : From basic experimental results 11-3 conducted using a two roller con
12、tact fatigue testing machine, it was expected that a high quality gear whose bending fatigue strength and surface durability are appreciably higher could be manufactured, if a compressive residual stress is induced on and below a tooth surface of a gear by the shot penning process after grinding and
13、 the surface is smoothed by the barrelling process. In the present study, the authors propose a new manufacturing method for improving the surface property of the gear tooth by employing shot peening and barrelling processes after grinding. Though gear homing, in which a gear is polished by a worm-s
14、haped grinding wheel made of urethane rubber 4, and gear rapping, in which a gear is polished using abrasive and a helical gear made of cast iron or plastic 56, are generally tried in order to improve the tooth surface of gear, their finishing processes are apt to be influenced by the contact pressu
15、re and the relative velocity between surfaces of a tool and a gear, and only the strongly contacted regions may be removed. On comparison with them, the shot peening and barrelling processes have a possibility that the whole of the tooth surface is uniformly finished. The surface configuration will
16、hardly change after processing. This method will be optimum for gear finishing with complicated tooth profile and tooth trace. Though the gear finished by the manufacturing method proposed in this study has a mirror-like tooth surface, the tooth surface roughness still has waviness component. Theref
17、ore, it was questioned whether its surface durability is higher than that of the only ground gear, or not. The surface durability of spur gears was then examined using a gear fatigue testing machine in practice. 2. Manufacturing Method of High Quality Gear: 2.1 Specifications of Gear Table 1 shows d
18、imensions of gears which were tested. Figure 1 shows shapes and dimensions of gears. The helix angle, , of a pair of helical gears was 16“. Gear 3 3 20 25 78 -1 6 38 -1- COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesThe tooth profiles and tooth trace
19、s of these gears are modified (amount of tooth tip relief; = 20 p m, crowning amount; % 20 pm). The amount of crowning of the spur gear is larger than that of the conventional gear. This aim was due to examine the adaptability of the shot peening and barrelling processes for manufacturing the gear w
20、ith complicated surface and examine load carrying capacity of the gear under very much large maximum contact pressure. The gear material was a chromium-molybdenum steel (SCM822H in JIS). A gear prepared by hobbing was carburized at 930 “c, kept at 850 “c for the brief time, and quenched by soaking i
21、n hot oil bath at 120 “c. After that, it was tempered at 160 “c. The hardness of the surface was about 750 HV and the depth of effective hardness about 1.2 mm. The tooth surfaces of gears were finished with a gear grinding machine having a worm-shaped grinding Al und um (#6- #1 O) (a) Spur gear 1 O0
22、 30-60 c I V (b) Helical gear Fig. 1 Shapes and dimensions of gears Table 2 Method of grinding Kind of wheel :SN-120-J-V53R Outside diameter :300 mm Rotational speed :1400 rpm (Roughing) (Finishing) Feed Z0.6 mm/rev 0.3 mm/rev Depth :0.03 mrn 0.2 mrn Table 3 Shot peening process parameters .i wheel.
23、 The tooth root was also ground together with the tooth surface in order to improve the bending fatigu strength. The method of grinding is shown in Table 2. 2.2 Shot Peening and Barrelling Processes The shot peening process parameters are shown in Table 3. The shot material is a spherical rounded st
24、eel wire. The shot peening process was applied to both sides of the gear tooth surface. The inlet angle of shot peening near a pitch point of a tooth is about 50”. A residual stress was detected at a crystallographic plane (211) by an X-ray diffraction method with Cr-Ka rays. Figure 2 shows the dist
25、ribution of residual stresses near the surface at a tooth root and near a pitch point. All residual P rn Or 1 ri a U b -4Oi v) v) L CI cn m P) -600 - -800 Pitch point Tooth root With shot peening W / A -1 200 I I I I 1 I O 50 100 150 200 250 300 Depth p m Fig. 2 Distributions of residual stresses .e
26、ar - 1e.lt. i!fiiciiiitig !f (kor atd 11.5 Ihdiirance. Yokendo (i980), 1135. (in Japanese) 5 Senba, M.: Gear, Vo1.9, NikkanKogyo-ShinbunSya (1966). 3595. (in Japanese) 6 Nakae, M., Hidaka, K. and Ariura, Y.: Gear Fitithttg witti n Nvlon Lap (A Lapping 14achirie atid I.apped Stirface), JSME. 62,594,
27、C (1996) 735. (in Japanese) 7 IS0 1328- 1. cvlitidrical gears -IS0 .ystem ?facetiraci,-, Part I: Bfititiotis and allowable valires of devrarions relevatit IO corresporiding,flanksank. ofgear teeth (1995). 1- 16. SI Hamrock. B.J. and Dowson. D.: Ball Rearing Lubrication - The Elasroh.vdrodvIiamics of
28、 Elliptical Contacts, John Wiley & 9 Ariura, Y., Ueno. T. and Nakanishi T.: Aii hivestigatroti of Siirface Failure of Siirface-Hardetied Gears bjs Scnriiiinp Electroti Microscopy Obsenatioris, Wear, 87 (1 983). 305-3 16. lo Hoyashita, S., Koga, K., Ashida, H. and bo, H.: E1feect.s of Siirface Hoiigh
29、ness atid Spin h40110ti OII Siirface Dirrabiliv and ractioti oeflicietii, JSME, 62, 599, C (1996-7). 2825- 2832. (in Japanese) li Kanisawa, H. and Sato, H.: jfect of Internal Oxidarion Laver on Pitring Strength of Carhiiricitig Steel.$, Heat treatment, 37-5 (1997-10). 287-292. (in Japanese) SOW (1981). 299-310. -9 - COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Services
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