Surface Failure of Alumina Balls Due to Repeated Stresses Applied in Rolling Contact at Temperatures to 2000°F. R. J. Parker, S. J. Grisaffe and E. V. Zaretsky, NASA TN D-2274* 1964, p. 15. The five-ball fatigue tester was used to study the behavior of hot-pressed and cold-pressed and sintered alumina balls under repeated stresses applied in rolling contact. The failures that developed were shallow eroded areas unlike fatigue spalls found in bearing steels. The room-temperature load capacity of hot-pressed alumina was about onefifteenth that of a typical bearing steel and seven times that of cold-pressed and sintered alumina. Preliminary tests at zooo°F with molybdenum disulfide-argon mist lubrication indicate that alumina is capable of operating satisfactorily under high-temperature, rolling-contact conditions. Rubbing Contact Materials for Face Type Mechanical Seals. J. W. Abar, Lubrication Eng., 20 (IO) (1964) 381-386; 7 figs., I table, 5 refs. Silicon carbide, 85% alumina, 60/ONi tungsten carbide and alumina coatings on 316 stainless steel have been investigated for their limitations as water-lubricated, seal-face materials. The materials were tested rubbing against carbon graphite at rubbing speeds of 2,320 ft. per min and face loads of 300 p.s.i. PV limitations were found to be clearly defined by thermal failures which resulted in exaggerated carbon wear and in some cases seal failure. Thermal stress factors (incorporating physical properties) were established as a material selection criteria based on correlation made with the same and limiting PV values at which thermal failures occurred.
Research and Development on Advanced Graphite Materials, Oxidation-resistant Coatings for Graphite. Anon. (Union Carbide Corp.) ; AD 606, 8gz D, price $ 4.00, from the Clearinghouse, U.S.Dept. Comm., Springfield, Va. 22151, or order from any Dept. Comm. Field Office. (Union Carbide Corp., Lawrenceburg, Tenn., for the Air Force, July 1964. 12s pp.) The preceding 33 volumes of this series on the various phases of research and development of advanced graphite materials are listed by title in the present report. Oxidation tests by electrical-resistance heating showed that Sic-Si coatings were unattacked at 1700°C during the standard 5-h exposures. Several specimens exhibited similar protection at 1750 and 1800%. Above r700°C, however, a few samples showed a tendency toward rapid coating oxidation bordering on combustion. These failures can be prevented to a large extent by preoxidizing them at lower temperatures before proceed-
327 ing to the higher test temperatures. In any event, this coating sequence should provide excellent oxidation protection up to 1723°C the melting point of SiOe. The study also describes the application of coatings of titanium diboride, hexaboron silicide, and the magnesium, calcium, and strontium zirconates by arc-plasma spraying. It discusses coatings of Tic-TiN and SiC-Si applied to graphite by vapor desposition using the source-target method. 5.2.
The Wear of Copper, Aluminum, Mild Steel. and Zinc, and Their Wear Particle Shape Factors. E. F. Finkin, ASLE Tvans., 7 (1964) 377-382; 6 figs., 3 tables, Q refs. Unlubricated, highly-loaded sliding experiments were conducted for systems of mild steel, copper, aluminum, and zinc. Load is critical in determining the wear mode. A Cocks wedge mechanism is the primary method of wear for copper, and for aluminum until a critical temperature is reached. The wear of steel is characterized by the formation of small un-joined fragments. The surfaces of wear particles were of two types; copper showed one type, and aluminum, mild steel, and zinc the other. Wear particle shape can be characterized by the ratios of dimensions (Z/w) and (Z/h). These factors are easily determined with good accuracy, and have distributions which are both far different in form and mean values for the various metals. The mean values of the shape factors are independent of particle size, and of each other. Surface roughness is not related to wear particle size for highly-loaded sliding.
Wear Properties of Various Cast Irons Having Different Graphite Shapes. M. Homma and H. Ichimura, TGhoku Univ., Sci. Rep. Res. Inst., Ser. A, Phys.. Chem., Met., 15 (3) (1963) 107-123. The wearing properties of various cast irons of flake, spheroidal, eutectic or other shaped graphite structures were investigated. As the opposite specimens, wormy flake graphite cast iron was also used. The wear phenomena were analyzed by the wear trend line drawn by the least square method, and it was shown that semi-nodular graphite irons were most wear-resistant and reliable, followed by wormy flake graphite irons and cupola irons, and that the wears of nodular graphite iron and black heart malleable Fe were remarkably large. Investigation
ance of Steels. R. V. Kugel J., 43 (I)
and G. N. Smirnov, Russ. Eng. (1963) 30-34. (Translation of wear,
8 (1965) 320-331
I.&n. Mashirzostv., ‘$3 (I) (1963) 43-47 by Production, Engineering Research Association of Gt. Britain.) For abstract see .4ppI. Mrch. i&v., 17 (9) (1964) 747. The Friction and Wear of Hardened Phosphor Bronze and Cast Iron Controlled
H. J. Raker, Intern. J. Mach. lfCS.,.T (3) (1963) 159-176.
The Friction and Transfer of Polytetrafluoroethylene. Ii. R. Makinson and 1). Tahor, I’roc. Roy.
Sk. (London), 281A (1964) 49-61; 14 figs., jr refs. Earlier work has shown that the friction of polytetrafluorocthylenc (I’TFE) increases with increasing velocity and dccrcases with rise of temperature as though a relaxation process were involved. A study by microscopy, interference microscopy and electron microscopy of the friction tracks formed when I’TFI’ slides on itself or on “clean” glass shows that there are basically two friction rtigimes. At high speeds or low temperatures the friction is high (p = 0.07~0.3) and there is fairly massive transfer and movement of polymer. The details depend on the sliding conditions but in general the transfer is in the form of lumps, ribbons or sheets, the thickness generally exceeding a few tenths of a micrometre. At low speeds and moderate temperatures a very different behaviour is observed : the friction is low (p < 0.07) and a thin film of PTFJi is laid down or drawn over the surfaces. This film may show strong adhesion to the surfaces if they are clean. It is very fibrous and has a thickness varying between about roe and 400 A; in addition it has a highly-oriented crystal structure. The low friction under these conditions is not due to poor adhesion but to easy shear of r&want units of the PTFE crystal. :is the speed of sliding is increased or the temperature diminished the viscous force to shear the film increases until a stage is reached where the shear force exceeds the strength of the boundaries between crystals or grains. The higher friction is then accompanied by the transfer of relatively large fragments of PTFK. These two rGgimes in the frictional bchaviour ma) thus be interpreted in terms of a relaxation time for intra-crystalline flow. The small change in friction at higher speeds suggests that the shear of larger units within the polymer is not appreciably rntc tlcpendcnt. (SCCalso I~‘Pcz~,, 8 ([email protected]
) 1, 70.) Operation of PTFE Bearings in Seawater. \V. 1). Craig, Jr., Lubvicut~on E*zg., 20 (1~)
IL figs., I table, 5 refs.
Igsau, 8 (1965) 320-331
Wear and friction characteristics of I’TFI.1 fabric-lined spherical bearings were determined for bearing pressures between 16,000 and 35,000 p.s.i. at oscillation speeds from I0 104 cyc/min and at angles from 5-90 degrees while immersed in sea water. Water immersion decreases the friction, but increases the rate of wear threefold compared with operation in air. h wear mechanism is postulated that involves lubrication by wear debris particles during a portion of the oscillation cycle. Design Data on TFE-fabric Bearings. H. A. Cress and J. R. Goldgraben, dlarh. [email protected]
, 36 (1964) 151-101. Fabric wol’en of TFfS fibers- a high-strength making form of tctrafluoroethylene-is inroads in many low-speed, high-load bearing applications. Typical uses include aircraftcontrol rotl-cm1 bearings, automotive balland-sock& joints, and large, heavily-loaded radio telescope hearings. Relatively little data were available in a form useful to the designer of this type of bearing. A summary is arranged for maximum effectiveness as a design tool ~.~based on the authors’ testing ant1 on the compiling of scattered data of man) investigators, evaluating them, and reducmg them to common design parameters. Wear Resistance V.N. Kestel’man,
Sov. Plastics (LA&J~L), (I L) (1964) 5X; r fig., 2 rcfs. It is sho\vn that Penton (a chlorinated thermoplastic polvether) has z.5- 3 times the wear rrsistance, -in rubbing on a hard alloy disc, of thermostabilised nylon-O. Plastics Bearing Materials. Ii. J. Fabian, M&r. Des~pz Eug., 59 (March)
(1904) 90~95 ; 5 tables. This paper gives a survey of the plastics used for journal and slecvc hearings, including complete data on PI’ limits, friction and compatibility with other coefficients, materials. Polyimide Plastics withstand High Temperatures. N. W. ‘Todd and I;. .I. U’olff, ?>!&I,. /ksig?t Eq., 59 (.\ugust) (1964) 86-91; 13 figs., 2 tables. Kcw data sho\v that polyimide plastics ha\re excellent mechanical, electrical and wear properties from 480 75o”F, combined with excellent chemical and radiation reSlStance.
Induction of Papillary Growths in the Heart. S Rodhard, Y. liinoshita and M. Mantes,
SC~PUCE, 143 (1964) 1341~1342; L figs., 15 refs. l’apillary growths appeared on the atria1 endocartiium of dogs at sites where adjacent