فرسودگی حلقه های چرخشی در سازه های جرثقیل
Abstract
1-Introduction
2-Slewing ring description
3-Ball force and contact angle calculation [4, 5]
4-Finite element local model with non-linear contact
5-Fatigue analysis
6-Parametric analysis results
7-Conclusion
Acknowledgements
References
Abstract
In the case of Crane industry sector, with high requirements of security and performance, slewing rings are important parts of equipment and manufacturers need to guarantee their mechanical strength and durability. Since more than ten years, on demand of industrial groups, CETIM is working on slewing rings in the fields of tests, design and calculations. For the last couple of years, extensive work has been done to develop a calculation methodology giving access to forces in balls of rings. These forces, used as input of local non-linear finite element models including contact definition, allow stress state calculations in tracks of rings. Fatigue analysis is then conducted based on appropriate criteria taking into account the complex multiaxial stress state and the gradient of material properties due to the surface treatment of the tracks (induction hardened parts). Parametric calculations have been made in order to estimate the influence of some parameters such as contact angle of the balls, geometric conformity, mechanical clearance and depth of treated material. Results allow identifying most important parameters and show how these parameters influence the damage location on the slewing rings, with good correlation with physical observations on damaged components. A synthesis of this long term work is presented in this paper.
Introduction
From 1997 to 2015, CETIM worked together with industrial partners in order to develop robust methodologies dedicated to slewing rings design [1, 2, 3]. Before 2005, studies focused on slewing rings assemblies. Exhaustive tests and calculations have been performed resulting in a general method for designing slewing ring assembly. This work has led to software tool called CetimPEARL. To calculate the assembly, a force by sector is needed. Until 2005, a formula assuming perfect sinusoidal repartition has been used to calculate forces in balls. From 2005 to 2010, a methodology based on finite element method has been developed to calculate accurately the repartition of ball forces around slewing ring. This methodology uses nonlinear springs to simulate contact. It’s necessary to use this method when stiffness of support structure is not uniform. Section 3 of this paper presents this calculation method. Force and contact angle calculated from the previous global approach are then used as input to a local finite element model which considers nonlinear contact between ball and track. The stress state in tracks is calculated with this model, presented in section 4. Once calculated the stress field in the tracks, corresponding to a realistic loading sequence, a fatigue analysis may be carried out thanks to an appropriate fatigue criterion. In order to take into account the complex multiaxial stress state involved in such case (contact fatigue), the Dang Van criterion was used. Section 5 describes the model.