Statik ve dinamik yük altında çalışan salınım hareketli kaymalı yataklar

Abstract

Bu çalışma üç ana bölümden oluşmaktadır. Birinci bölümde bir hidrodinamik kaymalı yatak dizayn edilirken dikkat edilmesi gerekli olan hususların neler olduğu ifa de edilmiş ve bir kaymalı yatağın basit ve hızlı bir şekilde dizayn edilebilmesi için bazı pratik diyagramlar tez içinde sunulmuştur. Aynı bölüm içersinde yer alan ve bilhassa dinamik yüklemeler neticesinde karşımıza çıkan Squeeze film etkisinin ne olduğuda kısa bir şekil­de özetlenmiştir.Salınım hareketli yatak, özellikle pistonlu makina- larm piston-biyel kolu yatağı olarak ve çeşitli makina- larda bazı çubuk mekanizmalarının yatağı olarak karşını­za çıkar. Dinamik yüklerin söz konusu olduğu bu yatak çeşidinde sürtünme ve film durumunun nasıl teşekkül etti ğinin saptanması amacıyla ayrıca bir deneyde yapılmıştırYapılmış olan deneylerde, salınım hareketli yatağa statik ve dinamik yükler uygulanmıştır. Yatağa uygulanan dinamik yük fonksiyonu olarak sinüsoiaal değişen yük a- lmmıştır. Deneyler yük ve mil frekansının bir olduğu hal için yapılmış ve sadece eksenel kanallı bir yatak kullanılmıştır. Yatağa uygulanan yük karakteristiği dört farklı şekildedir ve bu dört farklı yükleme durumu için yataktaki sürtünme kuvveti ve film durumu izlenmiştir.Deney sonuçlarının takdiminde bu dört yükleme duru­mu için dört farklı mil frekansı-sürtünme kuvveti eğri­leri çizilmiştir. Her bir şekile ait eğrilerden birinin değişik hızlardaki film durumunu belirleyen fotoğrafla- rıda sürtünme kuvveti eğrileriyle beraber verilmiştir.

This study consists of two basic parts. The first part includes the principles of designing a hydrodynamic sliding bearing, and some diagrams for the quick design of a bearing. It also summarizes the phenomenon occured in case of dynamic loads, called squeeze films.The second part, of this study contains an ex­perimental investigation of the state of friction and oil film of sliding bearings which is oscillated under static and dynamic loading.We can see some examples of above mentioned, bearings in machinery, such as the connecting rod small end bearings in the internal combustion engines and bearings of rod mechanisms in some machines. Up to now, the statically loaded condition was investigated in al­most every study on the subject and all of these were experimental except a few theoretical studies.One of the theoritical studies is made by Assoc. Professor Sait Yiicenur. In the theoritical part of this study, components of the pressure produced by the wedge effect and the squeeze film effect between the bearing and journal surfaces is assumed and calculated separately using the same boundary conditions. The to­tal pressure is:[l ] P = Pu+Pw The vertical and the horizontal components of the bearing load carried by the oil film, are given by the following equations: Fx = r. p(0).Cos0.d6 = Fk (e,e, , , t.) « e = o P(0) 6 = Fy = r. t)Sin9.d0 = Fy (e.e,On solving these equations for e and d€ = e = fi (e, ,t) dtd= e = f2 (e, ,t)dt a set of two simultaneous differantial equations is ob­tained .The oscillation motion given to the main bearing shaft is obtained by using a centric three-rod mechanism In experiments, bearing sleeves having only axial grooves are used.The bearing body is made of steel and its inner and outher surfaces are grinded.The static load is applied under of the bearing by means of a hydrostatic bearing which has two oil pocket. The lower of the hydrostatic bearing is loaded by means of a lever.The dynamic load is applied above of the bearing by means of another hydrostatic bearing which has also two oil pocket.The upper hydrostatic bearing is loaded by means of a rod-spring. There is a steel ball between the above hydrostatic bearing and rod-spring. So that , the eccentric settlement is prevented. The high pressurised oil is flowed between the stell bearing body and hydrostatic bearings. So that , the metallic contact is prevented and the freedom of rotation of sliding bearing is gaint.The short arm of the three rod mechanism is rotated a D.C. motor. At the same time, this spindle rotates another spindle by means of a chain mechanism. There is a rolling bearing which is bore eccentric, one of the end of spindle. This eccentric bore rolling bearing drives the rod-spring to apply a sinusoidal force on the bearing.The friction force on the bearing is measured with two strain-gages which is attached on the dinamometer ring.There are two capacitive pick-up on the bearing and they are settled perpendicular to each other so that, the distance of the journal center according to bearing center is measured.During the experiment, all bearings is oiled with- Mobil Vactra Oil Light.Static and dynamic load is applied on oscillating bearing and dynamic load function is sinusoidal. All experiments are made only for the state at which the rate of load and journal frequency is equal to one, and a bearing which has only axial grooves is used. The load characteristic is in four different types and fric­tion force is measured and at the same time oil film be­tween the bearing and journal is watched on oscilloscope screen. To Show the experiment result, different journal frequency-friction force diagrams for each of these four different load charecteristic, and friction force curves have been drawn. Also photographs those show the posi­tion of the film at different speeds for the state rep­resented by one of the curves in each diagram have been taken. Conclusion :X) Under static loading conditions, there can be no oil film formation, the friction in the bearing is a mixed type and it is sum of the viscous resistance and the boundary frictions. Under uni-directional alternating loading condi­tions, eventhough the coefficient of friction is lower, friction is of a mixed type and there is no oil forma­tion. In the bearing, squeeze films effect takes an im­portant role, in some cases it supports the load by it­self and prevents the shaft bearing contact. Under two directional sinusoidal loading condi­tions, the load is supported by the squeeze films effect and there is a viscous friction in the bearing. Fric­tion is determined by the viscosity of the oil, shaft velocity and bearing geometry. Under shock loads that may be en countered in many operating conditions, bearing-journal contact can be prevented by the squeeze films.