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Tapered gas seals
opment of basic processing technology for bearing quality silicon nitride balls' by H.M. Dalai e t el. It can be obtained, price £1.19 (microfiche)or £4.10 (reproduced paper-copy), quoting AD-A053 330, from TechAlert, TRC, Orpington, Kent, BR5 3RF, UK*
pared with a theoretical analysis of temperature rises due to sliding, rolling and compression in the contact zone. These can have a profound effect on lubricant rheology and, hence, on traction and EHD film thickness.
Temperature and EHD contacts
Further information is contained in a 56-page report 'The role of temperature in EHD' by J.W. Kennel e t el. It can be obtained price £1.19 (microfiche) or £4.10 (reproduced papercopy), by quoting AD-A054 320, from TechAlert, TRC, Orpington, Kent, BR5 3RF, UK*
Experiments have been conducted at the Battelle Columbus Laboratories in the US to secure data for an analysis of temperature effects and the behaviour of lubricants in EHD contact conditions. Two series of experiments were conducted using two independently driven steel discs which could be loaded together into lubricated contact. Four lubricants were tested. Speed, load and disc slippage were varied and special transducers allowed temperature and pressure measurements to be made in the contact zone. A report describing the work also briefly comments on causes and effects of temperature changes in EHD contact conditions. In the first series of experiments traction and slip were investigated. Disc slippage was varied by reducing the input frequency to the upper disc high-frequency induction motor drive relative to that of the lower disc drive. Traction was measured with a load cell constraining the upper disc support unit. Traction/slip curves were generated for lubricant inlet temperatures of 50°C and 65°C, speeds of 2960 and 6000 rev/min and loads to about 1400 N giving contact pressures up to 1.1 GPa. The second series made use of a novel thin-film temperature and pressure transducer system - a titanium temperature transducer (thermistor) coated onto the lower disc over a vapour-deposited manganin pressure transducer. The transducers were positioned so that contact temperature and pressure could be detected simultaneously. With a dual signal output to an oscilloscope it was thus possible not only to measure temperature and pressure but also to relate one to the other through the contact zone. The effects on temperature of varying slip, rolling speed (1400 and 1800 rev/min) and contact pressure (0.7 GPa and 1.1 GPa) were investigated. The results showed that very high temlberature rises can occur both with pure rolling and with combined rolling and sliding. Measured data were com-
Tapered gas seals
An analysis by NASA has shown that an annular gas path seal with a clearance decreasing in the flow direction has a stiffness much greater than that of a straight seal. Use of the tapered seal completely eliminates the negative stiffness that sometimes occurs with the straight type. Tapered seals show only a modest increase in leakage. Annular pressure seals are known to generate significant forces when the working fluid is a liquid. This is not surprising if one considers that an annular clearance seal is essentially a journal bearing, although usually with larger clearance than normal journal bearing practice. The larger clearance reduces the hydrodynamic forces generated, but the pressure difference across the seal introduces an additional means of producing seal forces. These vary directly with pressure across the seal and can reach appreciable magnitude in high-pressure seals. For liquids, it has already been demonstrated that seal stiffness can be considerably increased by making the inlet seal clearance larger than the outlet clearance. Since similar forces are generated when the sealed fluid is compressible, it was felt appropriate to analyse the radial stiffness of annular gas path seals. A significant result of the analysis was that the stiffness of straight seals can sometimes be negative. This is associated with low ratios of seal exit clearance to seal length. It results from the compressibility of the gas and so does not occur with liquids. Negative stiffness could cause rapid failure of floating-ring seals, and is not a desirable feature of rigidly-mounted seals. The stiffness of tapered seals, on the other hand, is always positive. The design can therefore be used to ensure stability of floating ring seals and
assist in providing rotor support with rigidly mounted seals. Owing to the greater average flow area, leakage of tapered seals is greater than for the straight type. Because of the greater stiffness, however, it may be possible to operate tapered seals with smaller clearances than straight seals, thus minimizing the leakage penalty. Further information is contained in a 23-page report 'Stiffness of straight and tapered annular gas path seals' by D.P. Fleming. It can be obtained price £1.19 (microfiche)or £1.50 (reproduced paper-copy), quoting N78-23385, from TechAlert, TRC, Orpington, Kent, BR5 3RF, UK*
Disc lubricated bearings Disc lubricated bearings have a number of advantages over other self-contained bearings using ring, chain, roller or wick lubricators. They include: the ability to provide a constant flow rate over a wide range of speeds; no heat generation by the lubricator; no lubricator wear; and reduced bearing length. A paper by Kaufman and Raimondi in the October 1978 issue of ASLE Transactions describes a new type of disc-lubricated bearing developed for use on forced draft, induced draft, and heavy duty process fans. The range of applications is not, however, limited to fans: they could be used in any form of rotating equipment requiring a self-contained bearing. The paper presents results of extensive tests on 125 mm and 254 mm diameter bearings for various clearances, speeds and loads. Both pure radial loading and combined radial and thrust loads were applied.A thermal analysis of the bearing system correlates welt with test results. "Performance of a centrifugal disklubricated bearing" by H.N. Kaufman and A.A. Raimondi is published in ASLE Transactions, Volume 21, by ASLE, 838 Busse Highway, Park Ridge, Illinois 60068, USA
CIRP Annals Over 100 papers were presented.during the open sessions of the 28th General Assembly of CIRP, held in Eindhoven. The majority of the papers are published in Volume 27/1 of CIRP Annals, Manufacturing Technology: some of the papers will be of interest to tribologists.
TRIBOLOGY international February 1979
45
pared with a theoretical analysis of temperature rises due to sliding, rolling and compression in the contact zone. These can have a profound effect on lubricant rheology and, hence, on traction and EHD film thickness.
Temperature and EHD contacts
Further information is contained in a 56-page report 'The role of temperature in EHD' by J.W. Kennel e t el. It can be obtained price £1.19 (microfiche) or £4.10 (reproduced papercopy), by quoting AD-A054 320, from TechAlert, TRC, Orpington, Kent, BR5 3RF, UK*
Experiments have been conducted at the Battelle Columbus Laboratories in the US to secure data for an analysis of temperature effects and the behaviour of lubricants in EHD contact conditions. Two series of experiments were conducted using two independently driven steel discs which could be loaded together into lubricated contact. Four lubricants were tested. Speed, load and disc slippage were varied and special transducers allowed temperature and pressure measurements to be made in the contact zone. A report describing the work also briefly comments on causes and effects of temperature changes in EHD contact conditions. In the first series of experiments traction and slip were investigated. Disc slippage was varied by reducing the input frequency to the upper disc high-frequency induction motor drive relative to that of the lower disc drive. Traction was measured with a load cell constraining the upper disc support unit. Traction/slip curves were generated for lubricant inlet temperatures of 50°C and 65°C, speeds of 2960 and 6000 rev/min and loads to about 1400 N giving contact pressures up to 1.1 GPa. The second series made use of a novel thin-film temperature and pressure transducer system - a titanium temperature transducer (thermistor) coated onto the lower disc over a vapour-deposited manganin pressure transducer. The transducers were positioned so that contact temperature and pressure could be detected simultaneously. With a dual signal output to an oscilloscope it was thus possible not only to measure temperature and pressure but also to relate one to the other through the contact zone. The effects on temperature of varying slip, rolling speed (1400 and 1800 rev/min) and contact pressure (0.7 GPa and 1.1 GPa) were investigated. The results showed that very high temlberature rises can occur both with pure rolling and with combined rolling and sliding. Measured data were com-
Tapered gas seals
An analysis by NASA has shown that an annular gas path seal with a clearance decreasing in the flow direction has a stiffness much greater than that of a straight seal. Use of the tapered seal completely eliminates the negative stiffness that sometimes occurs with the straight type. Tapered seals show only a modest increase in leakage. Annular pressure seals are known to generate significant forces when the working fluid is a liquid. This is not surprising if one considers that an annular clearance seal is essentially a journal bearing, although usually with larger clearance than normal journal bearing practice. The larger clearance reduces the hydrodynamic forces generated, but the pressure difference across the seal introduces an additional means of producing seal forces. These vary directly with pressure across the seal and can reach appreciable magnitude in high-pressure seals. For liquids, it has already been demonstrated that seal stiffness can be considerably increased by making the inlet seal clearance larger than the outlet clearance. Since similar forces are generated when the sealed fluid is compressible, it was felt appropriate to analyse the radial stiffness of annular gas path seals. A significant result of the analysis was that the stiffness of straight seals can sometimes be negative. This is associated with low ratios of seal exit clearance to seal length. It results from the compressibility of the gas and so does not occur with liquids. Negative stiffness could cause rapid failure of floating-ring seals, and is not a desirable feature of rigidly-mounted seals. The stiffness of tapered seals, on the other hand, is always positive. The design can therefore be used to ensure stability of floating ring seals and
assist in providing rotor support with rigidly mounted seals. Owing to the greater average flow area, leakage of tapered seals is greater than for the straight type. Because of the greater stiffness, however, it may be possible to operate tapered seals with smaller clearances than straight seals, thus minimizing the leakage penalty. Further information is contained in a 23-page report 'Stiffness of straight and tapered annular gas path seals' by D.P. Fleming. It can be obtained price £1.19 (microfiche)or £1.50 (reproduced paper-copy), quoting N78-23385, from TechAlert, TRC, Orpington, Kent, BR5 3RF, UK*
Disc lubricated bearings Disc lubricated bearings have a number of advantages over other self-contained bearings using ring, chain, roller or wick lubricators. They include: the ability to provide a constant flow rate over a wide range of speeds; no heat generation by the lubricator; no lubricator wear; and reduced bearing length. A paper by Kaufman and Raimondi in the October 1978 issue of ASLE Transactions describes a new type of disc-lubricated bearing developed for use on forced draft, induced draft, and heavy duty process fans. The range of applications is not, however, limited to fans: they could be used in any form of rotating equipment requiring a self-contained bearing. The paper presents results of extensive tests on 125 mm and 254 mm diameter bearings for various clearances, speeds and loads. Both pure radial loading and combined radial and thrust loads were applied.A thermal analysis of the bearing system correlates welt with test results. "Performance of a centrifugal disklubricated bearing" by H.N. Kaufman and A.A. Raimondi is published in ASLE Transactions, Volume 21, by ASLE, 838 Busse Highway, Park Ridge, Illinois 60068, USA
CIRP Annals Over 100 papers were presented.during the open sessions of the 28th General Assembly of CIRP, held in Eindhoven. The majority of the papers are published in Volume 27/1 of CIRP Annals, Manufacturing Technology: some of the papers will be of interest to tribologists.
TRIBOLOGY international February 1979
45