Jan Lundberg

Influence of surface roughness on normal-sliding lubrication

Abstract Contact between machine components can involve normal, sliding and rolling motion, either singly or in combination. Combined normal and sliding motion, which occur for example in the meshing of gear teeth and in heavily-loaded rolling elements, can present problems for lubrication. The purpose of the present experimental study was to investigate how surface roughness affects the lubricant film characteristics under conditions of combined normal and sliding motion. The experimental arrar gement consisted of a rotating roller which impacted a stationary ball in the presence of a lubricant. Under the same conditions of normal surface approach, increasing the surface roughness significantly decreased the level of roller sliding that could occur without breakdown of the lubricating film. This behaviour was similar to a step function. Of the several surface roughness parameters investigated, only those which involved the maximum peak-to-valley height correlated well with experimental results. In general, surface roughness had a greater effect on oil film breakdown than did either viscosity or load.

Study of lubricated impact using optical interferometry

Abstract An experimental study of lubricated impacts between a steel ball and a flat glass surface has been performed. The experimental set-up consists of a O70 mm ball mounted on a pendulum which impacts onto a lubricated glass disc. The contact region is studied by means of optical interferometry using a monochromatic light source, a microscope and a high-speed video recording equipment. The lubricants are of PAO type and the viscosity ranges from 27 to 2600 mm 2 s −1 at the test temperature. The impact velocity is varied between 0.08 and 0.29 m s −1 . A dimple occurs at the centre of the contact where the lubricant is trapped. The influence of viscosity and impact velocity on the dimples depth and diameter is studied.

A new method for determining the mechanical stability of lubricating greases

Mechanical stability is of central importance when dealing with the long-term service-length of grease-lubricated roller bearings. Poor stability will lead to consistency degradation of the grease, because of mechanical forces between the rolling parts of the bearing. The result can be leakage of grease through seals, or at worst a total failure of the bearing. The present investigation was initiated because present-day methods for prediction of mechanical stability show weak correlation with real service-length. The aim of the project was to develop a useful alternative. In order to fulfil this, both field tests and laboratory tests were carried out. In the field tests, nine different commercial greases were examined in the wheel bearings of five ore wagons, used for transporting ore by rail road from the Kiruna Mine in northern Sweden to Narvik in northern Norway for shipping to foreign markets. The test ore wagons travelled a distance of about 300,000 km during a period of 3 years. Small samples of greases were taken, on eight different occasions, for consistency testing. After the end of the test period, the damages on the bearings were also studied. In the laboratory tests, new undestroyed greases of the same brand as in the field tests were examined using conventional methods, such as the SKF V2F, the Roll Stability Test and the Grease Worker. Comparisons between the field tests and these laboratory tests indicate poor correlation. In addition to these conventional methods, the relevance of the shear strength of the greases to the prediction of the mechanical stability was also tested. The shear stress tau L, depends on the applied pressure p, thus tau L, = tau 0 + gamma p where tau 0 is the shear stress at atmospheric pressure. Gamma is a property of the lubricant in the same way as viscosity or density. It was found that gamma correlates well with the mechanical stability in service. Increased gamma values lead to a decrease in the mechanical stability. One reasonable explanation is that high gamma values correspond to high shear stresses in the grease, and thus severe conditions for the thickener.

Remaining useful life estimation : Review

This paper reviews the recent modelling developments in estimating the remaining useful life (RUL) of industrial systems. The RUL estimation models are categorized into experimental, data driven, physics based and hybrid approaches. The paper reviews some typical approaches and discusses their advantages and disadvantages. According to the literature, the selection of the best model depends on the level of accuracy and availability of data. In cases of quick estimations which are less accurate, the data driven method is preferred, while the physics based approach is applied when the accuracy of estimation is important.

High-speed video photographs of lubrication breakdown in squeeze-sliding contact

Abstract Using photographs from a high-speed video camera it was confirmed that the main part of breakdown of a lubricating film will appear at the end of the contact time for a contact simultaneously subjected to squeeze and sliding motion. This corresponds with earlier findings using totally different equipment for electric detection of the asperity contact. The present investigation used glass and steel as the lubricated surfaces, instead of steel and steel as was the case in the earlier investigation. In combination with far less stiff equipment, the new materials gave longer contact time and larger elastic deformations of the contact bodies. It was also verified that increased surface roughness, increased sliding velocity and decreased viscosity increase the risk of oil film breakdown.

Robust‐optimum multi‐attribute age‐based replacement policy

Purpose – A common model in the age‐based replacement policy is based on the cost attribute and assumes that the model parameters are known. In practice, the model parameters are estimated from limited historical data, which brings uncertainty into the model. Moreover, minimizing the cost is not the only goal of the maintenance activity. From the decision makers point of view, the multi‐attributes and the uncertainty of the age‐based replacement policy are two important aspects to take into consideration in the decision‐making process. The purpose of this paper is to propose an approach for a robust‐optimum multi‐attribute age‐based replacement policy.Design/methodology/approach – The proposed approach is based on a combination of the multi‐attribute age‐based replacement policy and robust design problem philosophy. A case study is provided for illustrating the application of the proposed method.Findings – It is found that the proposed approach can determine the interval time for preventive replacement t...

Grease lubrication of roller bearings in railway waggons. Part 1: field tests and systematic evaluation to determine the optimal greases

Describes a comprehensive field test to determine the best grease for spherical roller bearings in railway waggon wheels and increase the knowledge of grease lubrication. Nine different fully‐formulated commercial greases were examined in the wheel bearings of five ore waggons, used for transporting ore commercially by railroad from the Kiruna Mine in northern Sweden to Narvik in northern Norway for shipping to foreign markets. After the end of the test period, the wear and electrical damage, as well as the rust on the bearings, were also studied. In order to find out the optimum grease for this application, draws up a specification of requirements and uses a systematic approach to development of an evaluation method that could be applied to greases in actual service.

Lubrication of machine elements during combined squeeze and sliding motion

The motion when two parts in a machine come into contact can be a normal, sliding or rolling approach, or a combination of the three. The case of combined normal and sliding motion can be very unfa ...

Economic model for maintenance decision: a case study for mill liners

Purpose – Wear life of mill liners is an important parameter concerning maintenance decision for mill liners. Variations in process parameters such as different ore properties due to the use of multiple ore types influence the wear life of mill liners whereas random order of processing, processing time and monetary value of different ore types leads to variation in mill profitability. The purpose of the present paper is to develop an economic decision model considering the variations in process parameters and maintenance parameters for making more cost‐effective maintenance decisions.Design/methodology/approach – Correlation studies, experimental results and experience of industry experts are used for wear life modeling whereas simulation is used for maximizing mill profit to develop economic decision model. The weighting approach and simulation have been considered to emphasize the contribution of parameters such as ore value and processing time of a specific ore type to a final result.Findings – A model...

A simplified solution to the combined squeeze-sliding lubrication problem

Abstract The unfavourable elastohydrodynamic lubrication situation in combined squeeze and sliding motion has been analysed both theoretically and experimentally. In experiments a rotating roller impacted and rebounded on a lubricated surface. It was found that oil film breakdown always occurs at the end of the impact time, when the contact force is low. It has also been found that there exists an upper limit for the sliding velocity. Below this limiting velocity no oil film breakdown occurs. This paper is an initial attempt to explain theoretically why oil film breakdown takes place towards the end of the impact, and why an increasing sliding velocity reduces the capability of the oil film to separate the lubricated surfaces. If the oil films elastic and damping behaviour are taken into consideration it can be shown that a considerable phase shift between maximum contact force and oil film breakdown will arise. It has been found that the squeeze action dominates the pressure formation in the contact and thus the hydrodynamic effect of sliding motion is moderate. Furthermore, several effects, such as non-newtonian behaviour, surface roughness, temperature rise, starvation and deformations, which are not included in the theoretical model, may decrease the oil film thickness if the sliding velocity increases.