In this lubrication regime, the load is sufficiently high enough for the surfaces to elastically deform during the hydrodynamic action.( mating gears or rolling bearings)Īs the oil enters the contact zone between a ball and raceway (by rolling action), the oil’s pressure rises sharply. Elasto-hydrodynamic lubrication is the condition that occurs when a lubricant is introduced between surfaces that are in rolling contact, such as ball and rolling element bearings. So, unlike hydrodynamic lubrication, this kind of lubrication does not require motion of one surface relative to another. Hydrostatic lubrication is obtained by introducing the lubricant, into the load-bearing area at a pressure high enough to separate the surfaces with a relatively thick film of lubricant. Relative motion of the surfaces is not required in this case. Hydrostatics Lubricant is forced into the bearing at a pressure high enough to separate the surfaces. However, when the load is applied, the journal moves to an increasingly eccentric position, thus forming a wedge-shaped oil film where load-supporting pressure is generated. Sufficiently supplied with oil and external load is zero, the journal will rotate concentrically within the bearing. In a plain journal bearing, the position of the journal is directly related to the external load. Hydrodynamic lubrication is also called full-film lubrication. The film pressure is created by the moving surface itself pulling the lubricant into a wedge-shaped zone at a velocity sufficiently high to create the pressure necessary to separate the surfaces against the load on the bearing. Hydrodynamic lubrication does not depend upon the introduction of the lubricant under pressure, though that may occur but it does require the existence of an adequate supply at all times. Hydrodynamic lubrication means that the load-carrying surfaces of the bearing are separated by a relatively thick film of lubricant, so as to prevent metal-to-metal contact, and that the stability thus obtained can be explained by the laws of fluid mechanics. The lubricant pressure is self-generated by the moving surfaces drawing the lubricant into the wedge formed by the bounding surfaces at a high enough velocity to generate the pressure to completely separate the surfaces and support the applied load. This is a stable regime of lubrication and metal-to-metal contact does not occur during the steady state operation of the bearing.
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Hydrodynamic or full film lubrication is the condition when the load carrying surfaces are separated by a relatively thick film of lubricant. Different forms of lubrication can be identified for self-pressure generating lubricated contacts: i) Hydrodynamic ii) Hydrostatics iii) Elasto-hydrodynamic iv) Partial or mixed v) Boundary. The crankshaft and connecting-rod bearings must operate at high temperatures and under varying load conditions. All these applications require lubrication to reduce friction, wear, and heating. Gear teeth mate with each other by a combination of rolling and sliding. A follower may either roll or slide on the cam. In an antifriction bearing, the main relative motion is rolling. In a sleeve bearing, a shaft, or journal, rotates or oscillates within a sleeve, or bushing, and the relative motion is sliding. CHAPTER (1) Hydrodynamic Bearings in Diesel Enginesġ.1- INTRODUCTION The object of lubrication is to reduce friction, wear, and heating of machine parts that move relative to each other.
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