| 1. |
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| 2. |
- Isaksson, Ove
(författare)
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Numerical analysis of elastohydrodynamic contacts using power-law lubricant with special reference to water-based hydraulic fluids
- 1987
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Ingår i: ASLE transactions. - : Informa UK Limited. - 0569-8197. ; 30:4, s. 501-507
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Tidskriftsartikel (refereegranskat)abstract
- A numerical solution of the elastohydrodynamic lubrication problem for pure rolling with non-Newtonian lubricants is outlined. The non-Newtonian rheological model used is a modified power-law tau equals K multiplied by (times) gamma **n. At low shear rate gamma less than gamma //b, the lubricant is Newtonian, but when gamma greater than gamma //b the lubricant becomes non-Newtonian, tau equals K multiplied by (times) gamma **n. At high shear rate ( gamma yields infinity ) the lubricant becomes Newtonian again with the same viscosity as the base lubricant. By using this rheological model a modified Reynolds' equation is derived. The influence of the n-value and gamma //b on the film thickness has been investigated. Plots of the pressure distribution and film thickness within the contact for fluids with G-values in the range 169-986 is presented. These G-values are typical for water-based hydraulic fluids. For fluids with low n-values (n less than 0. 5) the pressure profile approaches the Hertzian pressure distribution and the minimum film thickness is that given by the base fluid viscosity.
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| 3. |
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| 4. |
- Isaksson, Ove
(författare)
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Rheology for water-based hydraulic fluids
- 1987
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 115:1-2, s. 3-17
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Tidskriftsartikel (refereegranskat)abstract
- High water-based hydraulic fluids with slightly higher viscosities than water, for instance 95-5 emulsions and micro-emulsions, do not show any significant deviation from a Newtonian fluid. Adding polymeric viscosity improvers for the purpose of increasing the viscosity will be successful as long as the shear rate is low. However, as the shear rate is increased, higher than about 10**3 s** minus **1, the viscosity will decrease and the advantage of the improver will vanish. The shear rate available was too low to break down the viscosity improvers. This is shown by the fact that the shear stress curve is reversible. Non-Newtonian fluids approach a more Newtonian behavior when the temperature is increased. The viscosity increase with pressure is much lower for water-based fluids than for a mineral oil. The pressure coefficient is about 10 times higher for mineral oils. The pressure coefficient increases if the water content of a water-based fluid is reduced.
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| 5. |
- Isaksson, Ove
(författare)
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Rheology of jet fuel contaminated hydraulic fluid
- 1988
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Konferensbidrag (refereegranskat)abstract
- The viscosity at different pressures, temperatures and shear rates has been investigated. Furthermore, traction measurements between a steel ball and steel plate have been carried out. The results are compared with theoretical predictions. A decrease in oil film thickness due to viscosity loss has been established for fluids containing jet fuel. The pressure-viscosity-coefficient, the viscosity increase with pressure, is not effected by adding jet fuel to the hydraulic fluid.
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| 6. |
- Isaksson, Ove
(författare)
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Water-based hydraulic fluids : rheology and elastohydrodynamic lubrication
- 1986
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Experiments have been carried out to measure traction, antiwear and rheological properties of water-based hydraulic fluids. Four types of fluids have been examined, emulsions, micro-emulsions, synthetic solutions and water-glycols. A numerical solution of the elastohydrodynamic lubrication problem for pure rolling with non-Newtonian lubricants is also outlined. The non-Newtonian rheological model used is a power-law, ... Non-Newtonian behaviour has been established for fluids with polymeric viscosity improvers. These non-Newtonian effects are less pronounced at high temperatures. The surface charge for emulsion droplets increases the viscosity considerably but on the other hand ionic contaminations decrease the viscosity. The viscosity increase with pressure is much lower for water-based fluids than for mineral oils. For fluids with low n-values (n < 0.5) the pressure profile in elastohydrodynamic contacts approaches the Hertzian pressure distribution and the minimum film thickness will be that given by the base fluid viscosity. The wear-rate is lowest for those fluids having the highest pressureviscosity coefficient along with a Newtonian behaviour. The water-glycols give low traction coefficients but will not prevent wear at high loads. There is a decrease in both wear rate and traction for emulsions having a less pronounced droplet stability. The same improvement is reached using micro-emulsions, with smaller droplets.
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| 7. |
- Lundberg, Jan
(författare)
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Lubrication of a rotating ball in normal approach
- 1989
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 130:1, s. 203-212
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study has been made of the degree of lubrication, which is defined as the number of interacting asperities, when a rotating spherical body approaches a plane during rotation. The normal velocity was varied between 0.1 and 0.5 m s-1 and the sliding velocity between 0 and 9.2 m s-1. The experiments show that the oil viscosity is the most important lubricant parameter. The degree of lubrication is not affected by either the normal velocity, the pressure viscosity coefficient or the shear strength proportionality constant. An increase in the sliding velocity gives a decrease in lubrication of between 25% and 65% depending on the surface roughness and type of lubricant. The surface roughness is also a most important factor impeding good lubrication. To avoid wear one has to increase the viscosity from 8 to 145 mm2 s-1 if the mean surface roughness Ra is increased from 0.01 to 0.14.
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| 8. |
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| 9. |
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| 10. |
- Brewe, D.E., et al.
(författare)
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Effect of vibration amplitude on vapor cavitation in journal bearings
- 1986
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Ingår i: Nordic Symposium on Tribology, Lulea, Sweden, 15-18 Jun. 1986. - Luleå : Högskolan i Luleå.
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Konferensbidrag (refereegranskat)abstract
- Computational movies were used to analyze the formation and collapse of vapor cavitation bubbles in a submerged journal bearing. The effect of vibration amplitude on vapor cavitation was studied for a journal undergoing circular whirl. The boundary conditions were implemented using Elrod's algorithm, which conserves mass flow through the cavitation bubble as well as through the oil-film region of the bearing. The vibration amplitudes for the different cases studied resulted in maximum eccentricity ratios ranging from 0.4 to 0.9. The minimum eccentricity ratio reached in each case was 0.1. For the least vibration amplitude studied in which the eccentricity ratio varied between 0.1 and 0.4, no vapor cavitation occurred. The largest vibration amplitude (i.e., eccentricity ratios of 0.1 to 0.9) resulted in vapor cavitation present 76 percent of one complete orbit.
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| 11. |
- Brewe, David E., et al.
(författare)
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The effect of vibration amplitude on vapour cavitation in journal bearings
- 1987
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 115:1-2, s. 63-73
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Tidskriftsartikel (refereegranskat)abstract
- Computational movies were used to analyse the formation and collapse of vapour cavitation bubbles in a submerged journal bearing. The effect of vibration amplitude on vapour cavitation was studied for a journal undergoing circular whirl. The boundary conditions were implemented using Elrod's algorithm which conserves mass flow through the cavitation bubble as well as the oil film region of the bearing. In the calculations, 0.1 ε εmax, where ε is the instantaneous eccentricity and 0.4 εmax 0.9 for the different cases studied. For the case 0.1 ε 0.4, no vapour cavitation occurred. For the case in which 0.1 ε < 0.9, vapour cavitation was present for 76% of the total time
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| 12. |
- Ekerfors, Lars O.
(författare)
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Boundary lubrication in screw-nut transmissions
- 1985
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This report deals with the function of screw-nut transmissions (powerscrews). Two aspects of this function have been investigated. Owing to different running parameters, primarily sliding speed and average pressure between the sliding surfaces of the thread, the coefficient of friction and the efficiency will vary within wide limits. The running parameters can be summarized in a dimensionless number, the Sommerfeldt number S. The problem, which has reference to boundary lubrication, is solved by a theoretical model. The model is based on two types of interaction between the sliding surfaces, namely solid friction at asperity peaks and liquid friction in the voids between the asperities. An optimal interval of the Sommerfeldt number, where the coefficient of friction is at its minimum, has been established: 0.025 < S opt < 0.042. As a result of friction between the sliding surfaces, heat is developed, which is conducted through the material of the screw and nut. The developed heat can cause high temperatures on the sliding surfaces of the thread. The capability of performance is limited by the development of high temperatures in the thread, where the running temperature of the actual lubricant must not be exceeded. Physically, the phenomenon relates to heat conduction. A theoretical model is put forward. In the model the screw is replaced by a cylindrical rod and a hollow cylinder corresponds to the nut. The equation of heat conduction is stated and solved for the case ofsteady state in the actual regions. It is shown that an infinitely thin wall of the hollow cylinder is the most severe case with a maximum rise in temperature. The result is presented in the form of a diagram with dimensionless temperature, rod speed and length of cylinder. The report ends with recommendatons for how the results can be used for designing screw-nut transmissions. In this context three numerical examples are given.
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| 13. |
- Hamrock, Bernard J., et al.
(författare)
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Measurement of the Density of Base Fluids at Pressures to 2.2 GPa
- 1986
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Ingår i: ASLE annual meeting.
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Konferensbidrag (refereegranskat)abstract
- The influence of pressure on the density of six base fluids is experimentally studied for a range of pressures from 0.422 to 2.20 GPa. An important parameter used to describe the results is the change in relative volume with change in pressure dv sub r/dp. For pressures less than the solidification pressure (p ps) a small change in pressure results in a large change in dv sub r/ps. For pressures greater than the solidification pressure (p ps) there is no change in dv sub r/dp with changing pressure. The solidification pressures of the base fluids varies considerably, as do the slopes that the experimental data assumes for p ps. A new formula is developed that describes the effect of pressure on density in terms of four constants. These constants vary for the different base fluids tested
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| 14. |
- Hiratsuka, Kentichi, et al.
(författare)
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Wear of amorphous alloys rubbed against pure metals
- 1986
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Ingår i: Proceedings of the Twentyninth Japan Congress on Materials Research. - Kyoto : Society of Materials Science. ; , s. 105-110
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Konferensbidrag (refereegranskat)abstract
- In this paper the authors describe the results of their study on the wear of amorphous alloys rubbing against several pure metals. This study reveals the dependence of wear of amorphous alloys on the kind of the mating metals. Using X-ray micro analysis of the worn surfaces it is observed that the antiwear property of the amorphous alloy is enhanced with the formation of oxide film of the mating metal
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| 15. |
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| 16. |
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| 17. |
- Höglund, Erik, et al.
(författare)
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Experimental Investigation of the Shear Strength of Lubricants Subjected to High Pressure and Temperature
- 1986
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 108:4, s. 571-577
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Tidskriftsartikel (refereegranskat)abstract
- In order to evaluate the relationship between limiting shear strength and pressure for a lubricant an experimental apparatus has been built. Pressures up to 2. 2 GPa and temperatures up to 200 degree C are attainable simultaneously. Thus the limiting shear strength-pressure relationship has been surveyed in a wide range. Several types of natural and synthetic lubricants have been tested. The results show that all the mineral oils tested behave in quite a similar way. Synthetic lubricants do not show this behavior, but the relationship between limiting shear strength and pressure depends strongly upon the chemical base of the synthetic lubricants. The behavior of grease does not differ from that of liquid lubricants. The pressures at which the lubricants change from a liquid to a solid behavior have also been measured.
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| 18. |
- Höglund, Erik
(författare)
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Influence of polyalkylmethacrylate and sulphurized ester on oil film thickness in an elastohydrodynamic point contact
- 1987
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 115:1-2, s. 223-234
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this investigation is to determine how additives in a base oil affect the central oil film thickness in an elastohydrodynamic rolling point contact. The experiments have been carried out using a sapphire disc and a steel ball and the film thickness has been measured by means of optical interferometry. A detailed description of the apparatus is given.Two different additives have been used, polyalkylmethacrylate (PMA) and sulphurized ester (SE). Each of them have been mixed in a superrefined naphthenic base oil at five different concentrations.The results show that the central oil film thickness increases with increasing concentration of additive. This is because the additives increase the oil viscosity. If this effect is compensated for, 0.1 wt.% PMA or 0.63-2.5 wt.% SE give the best relative oil film build-up. There is consequently no reason to use more additive in the base oil unless one wants to have a thicker oil film because of the viscosity-increasing effect
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| 19. |
- Höglund, Erik
(författare)
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Relationship between lubricant shear strength and chemical composition of the base oil
- 1989
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 130:1, s. 213-224
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Tidskriftsartikel (refereegranskat)abstract
- A new method for the experimental evaluation of the shear strength of lubricants at high pressures and temperatures is presented. The main parts of the experimental apparatus are a lubricated sintered-carbide surface and an impacting steel ball. A picture-processing system is used to examine the ball trajectory after impact and to calculate the limiting shear strengthpressure coefficient of the lubricant. Using this apparatus the influence of the chemical composition of the base oil on the limiting shear strengthpressure coefficient has been investigated. It was found that the chemical structure of the oil is of major importance in determining the shear strength. Additives have no significant effect on the shear strength.
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| 20. |
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| 21. |
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| 22. |
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Jacobson, Bo, et al.
(författare)
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Correlation of rheological characteristics of lubricants with transmission efficiency measurements
- 1985
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The power efficiency of a helicopter transmission has been analyzed for 11 lubricants by looking at the Newtonian and non-Newtonian properties of the lubricants. A non-Newtonian property of the lubricants was the limiting shear strength proportionality constant. The tests were performed on a high-pressure, short-time shear strength analyzer. The Newtonian and non-Newtonian properties of the lubricants were used in obtaining a power efficiency formula.
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| 27. |
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| 28. |
- Jacobson, Bo
(författare)
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High pressure-short time shear strength analyzer for lubricants
- 1985
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 107:2, s. 220-223
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Tidskriftsartikel (refereegranskat)abstract
- High pressure rheology of lubricants under transient pressure and shear stress loads is studied experimentally. The total compression time is about 140 mu s and the maximum pressure during the impact time is 5. 5 GPa. The results from this high speed test apparatus agree well with static tests of the shear strength increase with pressure up to 2. 2 GPa
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| 29. |
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| 30. |
- Jacobson, Bo
(författare)
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Rolling contact and EHD
- 1985
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 4:1, s. 1-22
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Tidskriftsartikel (refereegranskat)
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- Johannesson, Hans L., et al.
(författare)
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Calculation of the pressure distribution in an arbitrary elastomeric seal contact
- 1989
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 130:1, s. 3-15
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Tidskriftsartikel (refereegranskat)abstract
- When using the inverse hydrodynamic theory to calculate leakage flow and frictional force in an elastomeric seal contact, the pressure distribution is a necessary input. Up till now, assumed or measured pressure distributions usually have been used. One of the authors has earlier presented a semiempirical method for calculating the pressure distribution in an O-ring seal contact. The new calculation method, presented in this paper, is a generalization and an improvement of this earlier work. The method presented is mainly analytical and is based on calculations of the boundary strains in the contact zone and a model of the material behavior, which is based on the pressure dependence of the material compressibility. A computer program has been developed and two test examples are treated. A comparison with experiments is made.
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| 35. |
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| 36. |
- Kassfeldt, Elisabet
(författare)
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Analysis and design of hydraulic cylinder seals
- 1987
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydraulic cylinder seal performance is studied experimentally and theoretically. The seal performance is discussed in terms of friction force and oil leakage, which are due to the oil film build-up in the seal contact. The theoretical analysis is based both on calculated and measured contact pressure distributions. The compressibility of seal materials is determined experimentally, and it is shown that the compressibility is a pressure dependent material property. A method for calculation of the contact pressure distribution for a seal with an arbitrary cross-section is proposed, based on geometrical considerations and the experimentally determined compressibility. The pressure calculations are verified experimentally. Theoretically calculated oil film thicknesses in a seal contact are compared with measured film thicknesses. The increase of film thickness with increasing sliding velocity shows a good agreement between theory and experiment. The oil film is thicker in the experiments due to the surface roughness of the seal. A complete theoretical analysis of the seal performance is developed to be used as a design tool.
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| 37. |
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| 38. |
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| 39. |
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| 40. |
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| 41. |
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| 42. |
- Lundberg, Jan
(författare)
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Rheological properties of lubricating fluids
- 1987
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Obliteration (gobbing) caused by water based lubricating fluids is studied experimentally by analyzing the flow through a small channel. Flow measurements, energy dispersive X-ray microscopy and photos show, that the rate of gobbing depends on which type of fluid that is being used. The explanation of the obliteration is chemical reactions between the fluids and surrounding material or dust in the fluids. In order to get a better understanding of the rheology of emulsions, the migration of visible spheres, with varying density, flowing downstreams through a vertical, rectangular channel, is studied. The results from the experiments show, that the equilibrium position of a sphere is a function of the density difference between the sphere and surrounding fluid. A density difference of 0.5 per mille is enough to give stable positions. A theory is presented, which gives good agreement with the experimental results. Experiments have also been carried out in order to measure the effective viscosity of emulsions, flowing through a small horizontal channel. The viscosity is lower than the value obtained in a rotational viscosimeter. A theoretical explanation is proposed. An interesting example of two-phase flow is studied by means of a new prototype of a nozzle which lubricates a water jet with air. With this experimental nozzle, the dynamic pressure of the water jet increases 37 per cent. The explanation of this improvement is that some of the air forms a layer between the tube wall and the water, thus reducing friction between wall and water, giving a higher velocity of the water jet. With the results from the experimental nozzle in mind, five different full scale water cannon nozzles are designed, each with a certain method of air injection. The casting length, water flow and power consumption are measured and compared to a conventional nozzle. The performance is strongly dependent on the rate of water flow. For water flows of order 7 dm3/s, an increase in casting length of 12 per cent was achieved compared to a conventional nozzle. To achieve the same casting length, a conventional nozzle needs 39 per cent more power. Unfortunately the water flow with the new nozzle decreased with up to 48 per cent. For water flows of order 3 dm3/s, an increase in casting length of 93 per cent was achieved. To achieve the same casting length, a conventional nozzle needs 90 per cent more power. The water flow with the new nozzle decreased with 36 per cent. The final paper is an investigation of the lubrication between a plate and a rotating ball in normal approach. The normal velocity was varied between 0.1 and 0.5 m/s and the sliding velocity between 0 and 9.2 m/s. The experiments show, that the viscosity is the most important lubricant parameter. The normal velocity, the pressure viscosity coefficient, and the shear strength proportionality constant do not affect the degree of lubrication. An increase of the sliding velocity gave a decrease of the degree of lubrication between 25 and 65 per cent depending on surface roughness and type of lubricant. The surface roughness is also of great importance in getting good lubrication. To avoid wear, one has to increase the viscosity from 8 to 145 mm2/S if the mean surface roughness, Ra, is increased from 0.01 to 0.14.
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| 43. |
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| 44. |
- Nilsson, Bruno
(författare)
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Lubrication failures in wire drawing
- 1986
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Ingår i: Wire Industry. - 0043-6011. ; 53:627, s. 275-278
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Tidskriftsartikel (refereegranskat)abstract
- This article is the third and final part of a series. The Lubritronic detector permits introduction of condition maintenance and limitation of manpower simultaneously with saving of dies and reducing the amount of waste wire. By adding data acquisition and signal processing it should be possible to control the drawing speed close to the ultimate limit, resulting in an increase in production
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| 45. |
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| 46. |
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| 47. |
- Prakash, Braham, et al.
(författare)
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Failure analysis of plain bearings
- 1987
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Ingår i: National Seminar on Bearings. - New Delhi : National Productivity Council. ; , s. V-5/1-V-5/26
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 48. |
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