| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 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. |
- 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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| 6. |
- 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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