Disc Test Rig Research Articles

NEW METHODOLOGIES FOR ASSESSING CAVITATION LOAD AND RESISTANCE OF STRUCTURAL MATERIALS AND PROTECTIVE COATINGS IN NUCLEAR POWER INDUSTRY. PART I. MONOFRACTIONAL APPROACH

The paper presents a new method for assessing the cavitation load and durability of structural materials and protective coatings. To determine the cavitation load on a rotating disk or other test rig, a new method for extracting erosion loads based on tests of reference materials on a reference cavitation rig is proposed. Direct measurements of the cavitation load in a cavitation tunnel with a slot cavitator, performed using piezoelectric sensors, made it possible to obtain information on the spatial distribution of the impact load. As an analytical function for modeling cumulative erosion curves in the monofractional approach, the logarithmic formula of L. Sitnik is used, assuming that cavitation erosion is a stochastic process described using fatigue theory. Armco iron is chosen as a reference material, in view of the weak dependence of its erosion rate on cavitation qualitative features. Therefore the local load value could have been extracted from the eroded surface profile of the Armco iron sample. Using the example of TiN coating analysis on stainless steel and VT3-1 titanium alloy, the time dependencies and threshold characteristics of their resistance were determined depending on the parameter of the density of the supplied energy.

Influence of Free Water Droplets on Film Formation Under Point Contact Grease Lubrication

Abstract The influence of the grease-water two-phase emulsion on the bearing tracks on the film formation has been studied by carrying out optical interferometry experiments on a ball disk test rig to observe the dynamic film-forming behavior of lubricating grease under steady-state and micro-oscillation conditions. It is found that free water causes a brief rise in the grease film under steady-state conditions, specifically due to the grease-water phase connecting the oil reservoirs on both sides. The experiment determines that the state of the phase before entering the elastohydrodynamic lubrication (EHL) contact is water-in-oil. For the reciprocating motion and oscillation, the effects of the amount of free water and the length of the motion stroke are discussed in detail. It is found that for reciprocating movements with long stroke lengths, the effect of free water is summarized to enhance the fluidity of the fibrous mass of the grease thickener in the first few cycles of the movement. For shorter stroke lengths, the effect of free water is a scouring effect on the contact zone grease after 100 cycles. This paper provides new insights into the effects that cause water pollution to the point of contact lubrication during the transformation from reciprocating motion to fretting.

Experimental Investigation on Tribological Behaviour of Copper Diamond Composites

In the present study, a range of copper diamond composites were prepared using powder metallurgy. The impact of volume fraction of diamond on tribological behaviour and its effective dispersion with copper powder was studied. Composites containing dispersion of hard particles in a metal matrix are widely used for automotive and other structural applications. Sliding wear has a vital role in the performance of electrical sliding contacts used in electric and electronic devices. Thermal considerations are also equally important for the sustainability of electronic parts. Product life and its reliability of sliding contacts are directly proportional to wear phenomenon. Due to these reasons and to meet the demands of improving thermal properties of materials for electronic components, a new composite material composed of diamond and copper was developed. The ball mill was used for 4 hours at 300 rpm for grinding and blending copper, diamond into fine powder. Being a cost-effective technique, normal sintering and powder metallurgy method were adopted for composite preparation where spark plasma sintering and other techniques were found to be very costly. Diamond was added in different volume fraction (1% wt., 3% wt. and 5% wt.) as reinforcement to analyse the influence of diamond particle concentration, distribution and its particle size on thermal conductivity and wear behaviour. A transmission electron microscope was used to characterize the morphology of powder. XRD analysis was used to identify the crystalline phases present in the composites. A wear test was performed on pin on disk test rig. The wear test illustrated that higher diamond content improves the wear resistance of the composite.

Novel In-Situ Observation of the Grease Constituents in Elastohydrodynamic Contacts by Fluorescence Microscopy

Grease is important lubricant for ball bearings as it is used much more often than oil. However, mechanism of the lubrication is not completely clear, especially concerning the role of the thickener in the lubricating process. It was shown that contribution of the thickener to film thickness build-up varies with operating conditions. Also, its influence on the resistive torque of the bearing was proved. However, all studies were in-direct showing its effects. This paper presents new in-situ fluorescence method of the grease constituents’ observation, where both, thickener, and base oil can be observed independently. Two different fluorescence dyes are used to distinguish grease constituents with the use of different microscope setup. Moreover, the new method was tested on two different test rigs. First is typical ball on disc test rig widely used for study of elastohydrodynamic lubrication. Second is ball on ring test rig which more closely represents radial ball bearing conditions. It was shown that thickener engagement is very different for each geometrical configuration.

Occurrence of Grease Lubricated Impact-Sliding Composite Wear

In industrial chain drives, the sleeve slides on the pin and impact loading occurs due to the polygon effect, while the collision between the ball and cage usually produces an impact-sliding motion in the rolling element bearings. Aiming at addressing the occurrence of surface damage caused by the impact-sliding motion, a ball–disk test rig employing optical interference technology was designed and built to realize load variation. Two kinds of commercial grease types, Klüber Centoplex 3 and Centoplex 2EP, were used in the experiments when the glass disk slides at a constant speed while the steel ball collides into them. The sliding and impact motions were controlled by PLC programming. After the experiments, the mid-section grease film distributions were measured using DIIM software. The results show that surface damage can rapidly occur even in the first working cycle, and that the phenomenon is affected by the sliding speed, maximum load, and grease consistency. When the sliding speed is low, multiple contacts of asperity peaks occur in the interior contact region and develop into adhesive wear. When the sliding speed increases, surface wear starts to occur at the side-lobe position of the elastohydrodynamic lubrication (EHL) horseshoe shape and extends with time accompanied by obvious surface scratches. The wear mechanism investigated provides valuable visible information for the further exploration of impact-sliding composite wear. It is suggested that great attention should be paid to impact-sliding wear occurring with grease lubrication since such working conditions are very common in industrial applications.

Experimental Investigation of Effect of Fiber Length on Mechanical, Wear, and Morphological Behavior of Silane-Treated Pineapple Leaf Fiber Reinforced Polymer Composites

The development of the best properties in polyester composite from pineapple leaf fiber (PALF) as a reinforcing material is a subject of interest. The properties of PALF are reliant upon fiber length, wherein technical difficulties in production of long fibers and processing for better characteristics in polyester composites possess inherent challenges. The PALFs are subjected to silane treatment for altering fiber properties. This research attempts to analyze the impact of silane-treated PALF with varying fiber lengths (5, 10, 15, 20, and 25 mm) on the performance of natural fiber composites (NFC) properties. Open mold and hand lay-up techniques were employed to develop the polyester composites. The prepared PALF-based polyester composites were examined for different properties (impact, flexural, tensile strength, and wear rate). Coefficient of friction and wear studies are performed on the prepared composites subjected to different loads (10, 20, and 30 N) via a pin on disc test rig. Polymer composite fracture surfaces were analyzed to observe the interfacial bonding between fibers and matrix via scanning electron microscopy (SEM). SEM results showed that the application of silane treatment resulted in better surface topography (fiber length of 5–10 mm showed smooth surface resulted in crack proliferation possessing low fracture toughness of 15–32 MPa; whereas a 15–20 mm fiber length resulted in better fiber–matrix bonding, improving the fracture toughness from 42–55 MPa) as a result of change in chemical structure in PALF. The 20 mm length of PALF resulted in better properties (flexural, tensile, impact, and wear resistance) which are attributed to fiber–matrix interfacial bonding. These properties ensure the developed polymer composites can be applied to walls, building insulation, and artificial ceilings.

Towards a Standard Approach for the Twin Disc Testing of Top-Of Rail Friction Management Products

A wheel/rail friction coefficient that is too low can result in damage to the wheel and rail due to slips and slides, delays and safety concerns. A friction coefficient that is too high can result in excessive wear, noise and rolling contact fatigue. Changing contact and environmental conditions cause variations in wheel/rail friction, so friction management products, applied via wayside or on-board applicators, are used to either increase or decrease the friction coefficient so that an improved level is reached. They can be split into three classes; traction enhancers, lubricants and top-of-rail products (including water-based, oil/grease-based and hybrid products). This paper focuses on top-of-rail products and describes the different apparatus, contact conditions, product application methods and result interpretation that have been used to test these products and highlights the requirement for a more standardised test method. A proposed test method is outlined, which uses a twin disc test rig to collect “effective level of friction” and “retentivity” data to assess product effectiveness. More comparable and standardised data will ensure that maximum benefit is obtained from each set of results and help both product development and the approvals process.

Oil debris and viscosity monitoring using optical measurement based on Response Surface Methodology

This paper aims at the development of a method for monitoring oil debris as well as oil viscosity, using the optical measurement. An on-line optical oil debris sensor is designed firstly, then a multi-target tracking algorithm based on Gaussian Mixture Model is custom-developed to compute the properties (velocity, diameter) of wear debris in micro-flow channel through images captured by sensor. A mathematical relationship between debris velocity and debris diameter, debris density, oil flow, oil viscosity, oil temperature is statistically established using a three-level-five-factor box behnken design approach based on response surface methodology analysis. Then the analysis of variance is used to confirm the significance of the variables and their interactions. Finally, to validate the mathematical model, an experiment is carried out to compare its performance to that of results obtained using a pin disc test rig. The results demonstrate the measurement error of debris density and oil viscosity is 6.07% and 7.97%, respectively. The proposed approach has excellent suitability to monitor the oil condition.

Optimization of disc geometry and hardness distribution for better transferability of fatigue life prediction from disc to FZG tests

FZG tests have become a standard for the determination of fatigue lifetime and other key operational parameters in gear applications. This testing configuration is considered to be closer to the real-field application than other rigs such as twin disc testers, although FZG requires a significantly more complex sample preparation in addition to not allowing for the variation of key test parameters. Despite the fact that DIN 3990 recommends the use of disc tests if no other gear test results are available, it must be noted that the transferability of results from twin disc to FZG gear tests has not been properly assessed in the available literature.For the present study, gears made of case hardened 22MnCr5 with different carburisation depths were tested under lubricated conditions using a FZG test rig. The results, including S–N curves, were compared with twin-disc tests performed by the authors with modified disc geometries, in order to assess the transferability of the results between both configurations. Additionally, worn samples have been characterised in terms of residual stresses and microstructure for one case hardening depths in FZG tests at different tooth flank locations and compared with disc tests. It has been found that a good match between FZG and twin disc test rig results can be found for an appropriate twin disc sample geometry and hardness distribution, opening the way for transferability between both test configurations.

Design and Development of a Twin Disc Test Rig for the Study of Squeal Noise from the Wheel – Rail Interface

Design and Development of a Twin Disc Test Rig for the Study of Squeal Noise from the Wheel – Rail Interface

Iron Oxide and Water Paste Rheology and Its Effect on Low Adhesion in the Wheel/Rail Interface

The “wet-rail” phenomenon results in low adhesion between wheel and rail throughout the year, occurring transiently on a slightly wet, or drying railhead. It has been previously proposed that it is caused by a mixture of iron oxides and small amounts of water (from dew or precipitation) on the railhead that form a friction reducing paste. This paper outlines a novel combination of rheology, modelling and experimental work using a twin disc test rig to determine how the rheology of this iron oxide paste affects adhesion. The yield strength of different types of iron oxides, along with solid oxide fraction of the friction reducing paste, was assessed and used as an input into an “adhesion model” for assessing water and oxide suspensions. The rheological and modelling results were compared against very low adhesion recorded in twin disc experimental validation when simulating the wet-rail phenomenon.

Study on performance of thrust disk as auxiliary impeller

Thrust disk as auxiliary impeller has a vital effect on the big power pump unit with wet motor. It can balance the axial force of the unit, provide power for internal cooling circulation circuit of motor, and further reduce the axial length of the unit. Due to the motor chamber space is limited, and the transmission medium is liquid which needs to consider the effect of cavitation, the research of thrust disk of auxiliary impeller is different from the previous studies of rotating channel. In this paper, the hydraulic performance and cavitation characteristics of thrust disk as auxiliary impeller are investigated experimentally under different conditions. A thrust disk test rig was established to obtain data under different rotation speeds and flow points. Three types of volutes with different outlet angles were designed to match the thrust disk as auxiliary impeller in experiments. Results indicate that the law of speed proportion for the traditional centrifugal pump is not applicable to the head of thrust disk as auxiliary impeller. In addition, the flow coverage increases slightly with rotation speed. Furthermore, the higher the speed is, the larger the NPSHs is, and the narrower the range of NPSH is. Besides, the smaller the outlet angle is, the higher the head of the thrust disk as auxiliary impeller is, the worse anti-cavitation performance is. The research could provide reference and guidance for the design of thrust disk as auxiliary impeller.

Tribological behaviour of non-asbestos brake pad material

Asbestos is being banned worldwide due to its carcinogenic nature and potential health hazardousness from its dust and fumes. There is need to replace asbestos friction materials by environmentally friendly material with appropriate frictional and wear characterestics. The aim of this paper is to evaluate tribological behaviour of asbestos free brake pad material. A friction material viz: CL-3003 made up of high amount of fine brass fibres with synthetic nitrile butadiene rubber, were manufactured using hot press compression moulded to prepare a sample. In this paper the tribological behaviour of the material under consideration was studied using DUCOM (TR-20LE) make Pin on disc test rig. Coefficient of friction and wear rate were evaluated under a set of tribo-parameters using Taguchi’s analysis technique. L9 Orthogonal Array was chosen to study an effect of four parameters at three levels. Experimental result reveals S/N ratios, variance analysis and parameter ranking based on their contribution. Mathematical equations were developed for friction and wear rate within the acceptable range of parameters. Further detailed studies can be extended under simulative test conditions to evaluate optimum stopping distance.

Experimental and numerical studies of positive texture effect on friction reduction of sliding contact under mixed lubrication

Textured surfaces have been remarkable in improving the frictional performance of sliding contacts, particularly at instances such as boundary or mixed lubrication regimes. This article reports the results of an experimental and numerical study carried out by introducing surface textures in the form of protrusions to investigate its effects on friction performance under a mixed lubrication regime. The surface textures produced by the chemical etching process are tested on the pin on disc test rig by varying area density and height of the texture. In numerical simulation, the modified Reynolds equation (Patir–Cheng flow model) and asperity contact model (Greenwood–Tripp model) are solved for hydrodynamic and asperity pressures, respectively. The results indicate that the experimental measurements are qualitatively in good agreement with numerical predictions. Furthermore, the simulations are performed for different texture shapes by varying texture area density, height, and sliding velocity. The results depict that a maximum friction reduction of 87% with elliptical textures compared to the un-textured case.

Study the Effect of Oil Viscosity on Friction Coefficient at Point Contact Elasto-Hydrodynamic Lubrication Based on Experimental Analysis

This study presents an experimental work for elasto-hydrodynamic lubrication (EHL) in point contact case. In this study, experimental studies have been conducted to show how friction varies over a wide range of running conditions. The effect of the change in parameters such as lubricant’s viscosity, base oil type, and load on power loss is investigated. The oils have used (5W-20, 10W-30, 10W-40 and 20W-50) which have a different grade of viscosity. The test is conducted using a ball on disc test rig. Different loads have been used (30, 40, 50, and 60 N). The boundary conditions are: the oil’s temperature is (25 oC temperature room); the radius of ball is (0.018 m). The coefficient of friction of oils for each load has been calculated. At the same load and same initial conditions the results shows, the increase in friction coefficient with the increase of viscosity is almost linear with an average slope of 1.4 (Pa.s)-1. Also, the increase in load results in linear increase in friction coefficient by an average slope of 0.63 N-1

The effect of rolling speed on lateral adhesion at wheel/rail interface under dry and wet condition

A rolling contact two disk test rig is used to measure the lateral adhesion ratio under dry and wet conditions, and the results show that after the application of water the lateral adhesion ratio decreases. This effect is especially evident for low speed at large angle of attack, and the reduction rate is almost up to 50%. In contrast, the effect of water application on the lateral adhesion ratio at high speed is almost negligible. In this research, the effect of rolling speed on the lateral adhesion ratio under dry and wet conditions are also investigated. It is found that the lateral adhesion ratio decreases with rolling speed under dry conditions; while after the application of water, the measured results show an opposite trend. Furthermore, a model of wheel/rail contact mechanics is developed based on previous models and experimental measurements. Using this model, the simulated friction creep curves shift down with the increase of rolling speed. In comparison with previous mathematicla models, the correlations of this theoretical model with measured lateral adhesion ratios at various rolling speeds are much improved.

Role of Velocity Discontinuity Imparted by Copper and Nickel Coatings of Different Thickness

In mating pairs system, the pairs will have relative motion among themselves resulting in damage of contacting surfaces. During such relative motions friction and wear occurs. Extensive research has been carried out for identifying friction and wear effects. One of the important factors is found to be discontinuity in velocity at the interacting surfaces. This discontinuity in velocity was found to have a major role in affecting coefficient of friction and wear.In the present investigation to impart velocity discontinuity copper and nickel coatings of different thickness, were coated on mild steel pin. The copper coating was incorporated by thermal spray technique and nickel coating was carried by electroplating technique. Experiments have been conducted using pin on disc test rig with speed 500 rpm, load 30 newton and sliding time 30 seconds. The shear force was monitored in personal computer and coefficient of friction was estimated. Scanning electron micrograph (SEM) and Energy dispersive analysis X-ray (EDAX) was carried out. The coefficient of friction was found to be dependent on type of coating materials. Coefficient of friction was in the range of 0.51 to 0.52 for copper coating and 0.43 to 0.46 for nickel coating. The observed features in scanning electron micrograph attribute dependency of friction coefficient on coating thickness. The energy dispersive analysis X-ray study reveals no oxidation of copper, nickel and iron.

Wheel squeal noise control under water-based friction modifiers based on instantaneous rolling contact mechanics

Friction modifiers have been shown to be effective in reducing wheel squeal noise but not reliable in eliminating the phenomenon. To investigate this, wheel squeal noise under water-based friction modifiers is predicted using a mathematical model taking into account assumed instantaneous traction-creep behaviour. The instantaneous lateral creep curves are determined from quasistatic measurements under water-based friction modified conditions and used to obtain analytical predictions of wheel squeal noise levels that are verified numerically and experimentally based on a two disk testrig. Similar levels of squeal are obtained in both dry and water-based friction modified conditions at higher speeds despite the measured lateral creep curve not showing ‘falling friction’. For low speed, the water-based friction modification is shown to be successful in eliminating squeal except for very high angles of attack where noise levels are still greatly reduced. Subsequently, the efficient modelling is used to identify what modifications to the creep curve provide the best squeal noise reduction and elimination capabilities.

Analysis of wear behavior and surface properties of detonation gun-sprayed composite coating of Cr3C2–NiCr–CeO2on boron steel

The present paper reports the analysis of wear behavior and surface properties of detonation gun-sprayed composite coating of chromium carbide–nichrome–cerium oxide (Cr3C2–NiCr–CeO2) on boron steel. Experiments were performed to have complete understanding of wear rate and volume loss for the worn out surfaces. X-ray diffraction and scanning electron microscopy analysis were used for phase detection and microstructural characterization. Addition of rare earth metal improves the stickiness and avoids corrosion in the coating. Pin on disc test rig was used for the experimental purpose, and wear rate was calculated at three loads (30 N, 60 N and 90 N) in both dry and lubricating conditions. These tests were done for different cycles (to completely understand the wear behavior). From the results, it could be concluded that in lubrication state when the applied load is less, Cr3C2–NiCr+10% CeO2coated sample shows the better result as compared to Cr3C2–NiCr+5% CeO2and uncoated samples.

Simulation and understanding the wet-rail phenomenon using twin disc testing

Abstract Low adhesion due to the wet-rail phenomenon is a year round problem for the rail industry. It is thought to occur due to wear debris and iron oxides combined with small amounts of water, often from dew or light rain. It occurs without visible contamination and the transient, low moisture conditions mean that it has previously been difficult to study and has not been simulated in a laboratory, which limits understanding and inhibits the development of mitigation methods. This work simulates the wet-rail phenomenon on a twin disc test rig for the first time and concludes that iron oxide and water alone can form a paste and produce low traction values that are comparable to oil or leaf contamination.