tailieunhanh - Hydrodynamic Lubrication 2009 Part 9

Tham khảo tài liệu 'hydrodynamic lubrication 2009 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 7 Squeeze Film Pressure arises in a fluid film between two mutually approaching surfaces. This is called the squeeze effect and the fluid film is called the squeeze film. O. Reynolds referred to the squeeze effect in his famous paper on lubrication 1886 and stated that it was an important mechanism together with the wedge effect for the generation of pressure in a lubricating film. Especially when a sufficiently large wedge effect is not expected for example in the case of the small-end bearing of a crank for a reciprocating engine or in the case of an animal joint he wrote that the squeeze film effect was the only mechanism for pressure generation. It is surprising that the lubrication mechanism of animal joints was discussed over 100 years ago. The fact that the rubber sole of a shoe or a rubber tire on a car is very slippery on a wet road surface can be understood as a similar phenomenon. In this case a thin water film hinders the contact of the rubber and the road surface. In the above examples two mutually approaching surfaces were considered however two mutually receding surfaces are also worth considering. In this case since negative pressure arises in the fluid film this phenomenon is called negative squeeze. The case of two approaching surfaces is called positive squeeze. Further it is also interesting to consider situations in which positive and negative squeeze occur alternately. In the small-end bearing of a crank and in an animal joint a positive and a negative load acts by turns and positive and negative squeeze occurs alternately. In this case fluid is sucked into the gap between the two surfaces during the negative squeeze negative pressure arises and the fluid is squeezed out during the positive squeeze positive pressure arises and supports a load. It is interesting that even when the positive and negative movement of the two surfaces is perfectly symmetrical a positive load capability arises in many cases on balance through various mechanisms as .