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ID==00_020102Header==SKF Oil Injection MethodChapter==Introduction - Why not let oil do all the hard work?Section==How does it work?

 _Status==0 _Order==120Contents==<h1>How does it work?</h1>

<oiminlineimg img="00_020102_1.gif" text="Figure 1" /oiminlineimg><oiminlineimg img="00_020102_2.gif" text="Figure 2" /oiminlineimg><oiminlineimg img="00_020102_3.gif" text="Figure 3" /oiminlineimg><oiminlineimg img="00_020103_1.gif" text="Figure 4" /oiminlineimg><oiminlineimg img="00_020103_1.gif" text="Figure 5" /oiminlineimg><br>When oil under pressure is pumped in between the mating surfaces of an inner ring and shaft (figure 1), the friction between the surfaces is almost completely eliminated ( = 0,005 if the surfaces are well finished) and the inner ring can easily be pushed up on to its seating. When dismounting, the inner ring will slide from its tapered seating if oil is injected between the mating surfaces. How is this possible?<br /><br />The explanation is simple. When oil is injected with a pressure which is some 20% higher than the pressure in the contact, leakage is limited by the throttlingeffect produced by the higher edge pressure at the sides of the inner ring conta

ct.The parts of the shaft outside the contact reduce the deformation nearest tothe side faces of the inner ring and this stiffening increases the edge pressure. The pressure distribution in the contact, p, is shown in the (figure 2). It is therefore sufficient to supply a quantity of oil which corresponds to the limited leakage.<br><br>The method is also dependent on the <a href="{CALC}Viscosity">viscosity</a> of the oil. Generally, oil with a viscosity of 300mm²/s, at ambient temperature, is adequate to provide good separation and to help ensure that the surfaces will not be damaged however many times mounting is repeated. The higher theviscosity, the less the leakage. Consequently, highly viscous oil or grease should not be used, since lubricant drainage may be incomplete. This is particularly true of grease where a certain amount will always remain in the contact.

<br><br>If the contacting surfaces are well cleaned before mounting and a mineral oil is used, it may be expected that the coefficient of friction () in the contact after the oil has been drained will equal 0,13, for steel components. The oil injection joint has an annular oil distribution groove and usually a helical drainage groove (figure 3) to facilitate oil distribution on injection and drainage when injection has been stopped.

<h3>Different contacts</h3>

<br>The oil injection method is not only used for tapered contacts but can also be u

sed for dismounting cylindrical contacts. Cylindrical joints are normally assembled by heating the outer component and placing on the inner component. Once theouter component has cooled, then a strong fit can result. <br><br>

When the inner ring (figure 4) is dismounted, using the oil injection method, it must be withdrawn at a certain speed to help ensure that the oil pressure is maintained, even after the oil groove has been exposed. Otherwise there is a riskthat the inner ring will stick. When withdrawal is correctly carried out there is no problem, but it is also possible to use an O-ring (figure 5) as a safeguard

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. When oil is injected, as indicated in the figure, the pressure can be kept up until the inner ring comes free after having passed the oil groove.<br />

<h3>Information, tools and other aids</h3><br>The oil injection method is used for low contact pressures (20 to 30 MPa / 2900to 4350 psi) in bearing arrangements as well as for high contact pressures in couplings. The method has been successfully used for contact pressures up to 400 MPa (58000 psi).<p>SKF Maintenance Products offers a comprehensive range of equipment to allow themethod to be employed. The range includes pumps for low pressures and oil injectors for high pressures. There is a choice of manually operated as well as pneumatically driven pumps and oil injectors for oil pressures of up to 400 MPa (58000 psi). The pneumatic pumps and oil injectors are primarily intended for large pressure joints<p>The online catalogue <a href=http://www.mapro.skf.com/mp3000e.htm target=_blank>SKF Maintenance and Lubrication Products</a> contains detailed descriptions of the available equipment which caters for almost all needs. Instructions coveringthe design and calculation of pressure joints will be found in this program, aswell as information on the relevant equipment.