Scuffing Conditions Research Articles

Nanoparticle lubricant additives applied in a CNC lathe ball screw component for improving the quality of machined workpieces: A case study

A lathe ball screw is a mechanical actuator that translates rotational motion to linear motion. These machine elements are lubricated to reduce friction and wear since they can affect dimensions of the machined workpiece, measured by Cp and Cpk process capability indicators, and the number of equipment shutdowns. In this work, different nanoparticles (NPs) were added to a commercial lubricant for machine tool slideways with the purpose of reducing coefficient of friction (COF) and wear. NPs of SiO2, CaCO3 and montmorillonite clay (MMT) were added to the lubricant in concentrations on 0.01 and 0.05 wt%. Four ball tests performed under scuffing conditions showed that the best concentration was 0.01 wt% for all NPs, with improvements in load-carrying capacity of 13–15%. Higher concentrations resulted in agglomeration and these large NP clusters were not able to infiltrate the contact area to reduce friction and wear. Block-on-ring tests showed that 0.01 wt% MMT reduced wear and COF by 83% and 81%, respectively. Finally, machining tests were performed in a CNC lathe with the 0.01 wt% MMT nanolubricant for the ball screw component. Improvement was measured by keeping track of the dispersion of the workpiece dimensions, the process capability indicators Cp and Cpk and the number of equipment shutdowns for adjustments. The addition of MMT NPs to the lubricant improved Cp and Cpk by 34% and 52%, indicating a lower variation on the work piece measurements. Furthermore, equipment shutdowns were reduced by up to 50%, improving the process efficiency and lowering manufacturing costs.

Lubrication Performance of Sunflower Oil Reinforced with Halloysite Clay Nanotubes (HNT) as Lubricant Additives

This study evaluates the tribological performance of nanolubricants of a vegetable oil (sunflower oil) reinforced with different concentrations of environmentally-friendly nanoparticles of halloysite clay nanotubes (HNTs). Tribological characterization was performed under different conditions to determine its effect on the nanolubricants’ performance and optimal HNT concentration. The tribological performances under low and high contact pressures were analyzed with a block-on-ring tribometer following the ASTM G-077-05 standard procedure. The extreme pressure (EP) properties of the nanolubricants were determined with a T-02 four-ball tribotester according to the ITeE-PIB Polish method for testing lubricants under scuffing conditions. In addition, the lubrication performance of the newly-developed vegetable oil-based nanolubricants was evaluated in an industrial-type application through a tapping torque test. The results indicated that at a low contact pressure 1.5 wt.% HNTs/sunflower oil provided the best tribological behavior by decreasing the coefficient of friction (COF) and wear volume loss by 29 and 70%, respectively. For high contact pressures, 0.05 wt.% HNTs lowered COF and wear by 55% and 56%, respectively. The load-carrying capacity increased by 141% with 0.10 wt.% HNTs compared to the sunflower oil. A high tapping torque efficiency was obtained with HNTs that can prolong tool life in the machining process. Therefore, this study suggests that HNTs/sunflower oil could be used as green lubricants for industrial applications.

Optimization and Nanoreinforcements of Lubricant Concentration for Steel Sheet Forming Process

In metal-mechanic industry, lubricants are applied to improve products’ quality and tools useful life, while reducing friction and wear, also removing the generated heat during the material processing. Tribological evaluations are performed varying the water content of two widely used lubricants in automotive metal-forming operations. Evaluations are first performed to determine the optimal lubricant dilutions, followed by reinforcement of 2D-nanostructures of hexagonal Boron Nitride (h-BN). Tribological characterization under extreme pressures (EP) are performed with a four-ball tribometer according to the Institute for Sustainable Technologies –National Research Institute (ITeE-PIB) Polish method under scuffing conditions. The optimized concentrations are determined for Ecodraw and Montgomery lubricants, representing a 28% and 3% improvement in pressure loss limit at 1:8 and 1:6 concentrations, respectively. Block-on-ring tribotest is used to determine the coefficient of friction (COF) of the optimized lubricant dilutions and h-BN nanolubricants, which represent ~10% improvement. These results could be attributed to diverse factors such as a layering mechanism of the 2D nanostructures, soft van der Waals forces between 2D h-BN layers, and the deposition of h-BN on the worn surface, decreasing the shearing stress and COF. Finally, thermal conductivity evaluations showed an enhancement by 30% and 15% with addition of h-BN, demonstrating the potential of 2D nanostructures for improving the efficiency on antiwear and thermal transport.

Tribological evaluation of electroless Ni–B coating on metal-working tool steel

The aim of this research is to evaluate the tribological characteristics of the electroless Ni–B film under extreme pressure conditions, with coating thickness of 3 μm, 6 μm, and 12 μm in the as-plated condition and with incorporation of heat treatment (HT) (200 °C by 90 min). An electroless method is employed for Ni–B coating deposition on D2 tool steel specimens. A synthetic fluid was used as a lubricant, with a water–oil ratio of 10:1. Tribological evaluations were performed on a block-on-ring configuration according to ITEePib Polish method for testing lubricants under conditions of scuffing. Results indicate that electroless technology improved the coefficient of friction (COF) of the tool steel, ranging from 15 to 30%, with 3 μm to 12 μm of coating, respectively. This enhancement was increased by applying a heat treatment to the coated components, showing improvements of 24–38% with 3 mm to 12 mm, respectively. It is also observed that wear of the evaluated coupons also showed improvements ranging from 35 to 60%. These results demonstrate the potential of an electroless technique on materials suitable for metal-forming tooling and components, while decreasing friction and wear of mechanical components.

Experimental evaluation of the tribological behaviour of CeO2 nanolubricants under extreme pressures

Lubrication of moving components is critical for lowering friction and reducing energy consumption. Nanoparticles have been recently studied as additives for improving the load-carrying capacity and overall tribological performance of lubricants employed for metal-mechanic applications. Cerium oxide is a lanthanide metal oxide (rare earth) with environmentally friendly characteristics that is widely used for consumer products, and most recently for enhancing the tribological performance of composite materials and lubricants. In this work, formulated polymeric lubricants employed for metal forming processes with dispersed cerium oxide (CeO2) nanoparticles were characterized under extreme pressure (EP) conditions. Nanoparticle concentrations of 0.01, 0.05, and 0.10 wt.% were dispersed by homogenization and ultrasonication in the selected lubricant. Tribological characterization under EP was performed with a T-02 four-ball tribometer according to the ITeE-PIB Polish method for testing lubricants under conditions of scuffing. This method applies and increasing load of 0-7200 N to the tribopair in a very short amount of time (18s) and is employed to find the maximum pressure a lubricant film can withstand. The scuffing load (Pt), and pressure loss limit or load carrying capacity (poz) were determined after each test. Wear scar diameters (WSDs) of worn ball materials were measured with an Alicona optical 3D measurement system. The anti-wear (AW) and friction-reducing characteristics of CeO2 nanolubricants were determined with a T-05 block-on-ring test. No seizure was found for all lubricants likely due to the presence of additives in the polymeric lubricant. Nanoparticles were found to delay scuffing initiation at concentrations up to 0.05 wt.%, and the load required for scuffing increased by 35 %. The load-carrying capacity was enhanced by up to 84% with only 0.01 wt.% CeO2. Higher concentrations (0.10 wt.%) had a detrimental effect, most likely due to nanoparticle agglomeration. The coefficient of friction (COF) was lowered from 0.035 for the polymeric lubricant to 0.006 with a concentration of 0.01 wt.% CeO2.The tribological results obtained by both tests demonstrate that CeO2 nanoparticles have friction-reducing and EP characteristics, making them suitable as lubricant additives in the metal-mechanic industry.

Nanoparticles of Zn and ZnO as extreme pressure (EP) additives for lubricants

The tribological behavior of moving components and tooling in the automotive industry is a critical issue for improving tool life and increasing efficiency. This work discusses the effects of Zn and ZnO nanoparticle additives homogeneously dispersed within a metal-forming synthetic fluid at various filler fractions: 0.01, 0.05 and 0.10wt.%. Nanolubricants were evaluated under scuffing conditions at extreme pressures (EP) conditions using a four-ball tribotester in order to obtain the load-carrying capacity (poz) behavior, and overall tribological characteristics. This method has shown, with great precision, the influence of the nanofillers on the EP behavior of conventional lubricants. Worn surfaces were characterized through Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) to determine the tribological mechanisms of nanoparticles. An Alicona 3D surface measuring system was used for measuring the surface roughness of the wear scars. Both nanoparticles exhibited better friction-reducing and anti-wear properties compared to the base synthetic fluid. For Zn-based nanolubricants, an enhancement of ~180% in poz was obtained with 0.10wt.%, showing the effect of the spherical nanostructures that were tribosintered onto the surface due to the EPs of the test. Furthermore, the highest enhancement in poz (up to 250%) was achieved with incorporation of 0.10wt.% of ZnO demonstrating the potential of nanolubricants for improving the efficiency of mechanical components.

Temperature dependence of the extreme-pressure behavior of CuO and TiO2 nanoparticle additives in metal-forming polymeric lubricants

PurposeThe purpose of this work is to investigate the effect of temperature on the extreme-pressure (EP) properties of CuO and TiO2 nanoparticle-filled polymeric lubricants for metal-forming processes.Design/methodology/approachThis paper studies the effect of nanoparticle additives of CuO and TiO2 on the load-carrying capacity of a metal-forming polymer lubricant used for deep-drawing at varying temperatures. EP measurements are performed with a four-ball tribotester according to the ITeE-PIB Polish method for testing lubricants under scuffing conditions. Tests are run at 25, 40, 60 and 75°C to further decrease the lubricant film thickness and determine the effect on the load-carrying capacity and the tribological mechanisms of nanoparticles. The tribological mechanisms of nanoparticles is studied using energy dispersive spectrometry (EDS).FindingsResults indicate that nanoparticle additives increase the load-carrying capacity of the polymeric lubricant at all concentrations up to 60°C attributed to a mending effect and a reduction in the area of contact of moving surfaces; at 75°C, the improvement is lowered due to nanoparticle re-agglomeration. The best results are found with TiO2 nanoparticles due to their smaller size compared to CuO.Practical implicationsNanoparticles of CuO and TiO2 are potential EP additives for metal-forming lubricants, providing protection to working components and extending tool life.Originality/valueThese results show the effectiveness and the tribological mechanisms of nanoparticle additives under EP conditions and increasing temperatures found in metal-forming processes.

Tribological performance of halloysite clay nanotubes as green lubricant additives

Nanoparticles have been recently explored as lubricant additives for improving tribological performance of metal-forming tools. Halloysite clay nanotubes (HNTs) are naturally-occurring, low-cost, and non-toxic nanoparticles, making them attractive as green lubricant additives. In this study, HNTs were dispersed at varying concentrations (0.01, 0.05, and 0.10wt%) within a polymeric lubricant for metal-forming applications. The ITeE-PIB Polish method for testing lubricants under scuffing conditions was conducted with a four-ball tribotester in order to obtain the scuffing load and load-carrying capacity (poz) under extreme pressures (EP), as this method has demonstrated to be sensitive to extreme-pressure additives; a block-on-ring test was used to obtain wear volume loss and coefficient of friction (COF). Surface roughness of worn materials was characterized with an optical 3D-surface measurement system. Results showed that 0.05wt% HNTs delayed scuffing initiation, and increased the scuffing load and load-carrying capacity by 50% and ~72%, respectively. Wear volume loss and COF were both lowered by ~70%, and surface roughness was reduced due to the formation of a tribofilm. The improved lubrication provided by environmentally-friendly HNT lubricant additives shown in this study may result in considerable cost savings through lower energy consumption and longer tool life.

Extreme pressure properties of nanolubricants for metal-forming applications

Purpose – The purpose of this paper is to evaluate the extreme pressure properties of CuO and TiO2 nanoparticle additives with the incorporation of a surfactant within a synthetic fluid for metal-forming applications. Design/methodology/approach – The paper studies the effect of CuO and TiO2 nanoparticle additives at various concentrations (0.01, 0.05 and 0.10 wt. per cent) in a synthetic lubricant fluid under extreme pressure conditions. Oleic acid surfactant is added to the nanolubricant to improve dispersion and stability of nanoparticles. Extreme pressure tribological tests are performed on a four-ball T-02 tribotester according to the ITEePib Polish method for testing lubricants under conditions of scuffing. Findings – The results show that the addition CuO and TiO2 nanoparticles under the presence of OA resulted in an increase of the load-carrying capacity (poz) of the lubricant up to 137 and 60 per cent, respectively. The seizure load was also increased by 50 and 15 per cent, respectively. Practical implications – The results show that CuO and TiO2 nanoparticles can be successfully used as additives improving extreme pressure properties of lubricants. Originality/value – This demonstrates the potential of nanoparticle additives using surfactants for improving the extreme pressure properties of lubricants. These nanolubricants can be used for metal-forming applications like deep-drawing, achieving an increased tool life.

Thermal transport and tribological properties of nanogreases for metal-mechanic applications

This study investigates the effect of incorporating nanoparticles – TiO2, Al2O3, CuO, and multi-walled carbon nanotubes (MWNTs) – within greases Mobilgrease 28 and Uniflor 8623B on their thermal transport and tribological properties. Nanoparticle filler fractions, varying from 0.01 to 0.10wt%, were homogeneously dispersed within selected greases. Two tribological tests were performed on a four-ball tribotester; ASTM D5183, and the ITeEPib Polish method for testing lubricants under scuffing conditions. Anti-wear properties resulted in up to 20% wear scar diameter (WSD) reduction using a very low filler fraction of 0.01wt% TiO2. For the extreme pressure test, the increase on the load-carrying capacity was found to be ~19% with a filler fraction of 0.05wt% CuO. A guarded hot-plate method-based apparatus was used in order to characterize thermal conductivity of nanogreases, showing an enhancement of ~28% in thermal conductivity with the addition of 0.10wt% MWNTs. These results demonstrate the potential of nanoparticle additives for improving thermal properties of greases while decreasing friction and wear of mechanical components.

Antiwear and Extreme Pressure Properties of Nanofluids for Industrial Applications

This study investigates the effect of CuO, TiO2, Al2O3, and multiwalled nanotube (MWNT) nanoparticles at various treat rates on the tribological properties, namely, wear, coefficient of friction (COF), and pressure of seizure (poz), of metalworking fluids during lubricating processes in diverse industrial applications. Results are reported based on two methods: wear scar diameter (WSD) and COF by ASTM D5183 and poz by the Institute for Sustainable Technologies–National Research Institute (ITEePib) Polish method for testing lubricants under scuffing conditions. Results showed significant improvements with small filler concentrations of nanoparticles. CuO nanofluids showed a diminishment of 86% for WSD at 0.01 wt%, whereas TiO2 resulted in an increase in poz of up to ∼250% at 0.05 wt% compared to pure conventional fluid.

Qualitative discrimination between API GL performance levels of manual transmission fluids by comparing their EP properties determined in a new four-ball scuffing test

To prove that a candidate MTF meets the requirements of a given API performance level, one needs to perform extremely expensive and time-consuming tribological tests on entire lorry units.A new, quick and inexpensive four-ball test method, performed under scuffing conditions was used for testing EP properties of MTFs of GL-1 to GL-5(LS) performance levels. The test makes it possible to discriminate between API performance levels in a “qualitative” way—by the friction torque analysis. For interpretation of the results, scuffing models in different phases were developed on the basis of tribological tests and surface microanalyses.

Predictive Modeling of Scuffing Performance of Gear Oil with MoDTC Using Response Surface Methodology

This paper presents an experimental investigation of the influence of scuffing conditions on two-roller test rig. The prediction of Scuffing load capability model for the gear oils containing molybdenum dithiocarbomate (MoDTC) was developed based on the response surface methodology. A good agreement between the predicted and actual scuffing resistance was observed within ±5% significance level.

A method for testing lubricants under conditions of scuffing. Part II. The anti‐seizure action of lubricating oils

AbstractThis paper describes an investigation of lubricating oils under extreme‐pressure (EP) conditions in a specially modified four‐ball tester. A new test method developed at the Tribology Department of ITeE described in Part I of this paper was used. In this, during a test run, the applied load is increased continuously and the friction torque is measured. A sudden increase in the friction torque indicates the collapse of the lubricating film — where scuffing is initiated. The load at this moment is called the scuffing load. If the load is increased further, it is possible to observe scuffing propagation until seizure occurs, i.e., a defined, maximum friction torque is reached. Thus, scuffing is considered as a process leading to seizure.Using the method, tribological experiments were performed employing various lubricating oils consisting of viscosity‐index improvers and antiwear (AW) and extreme‐pressure (EP) additives added to a base oil. Mineral and synthetic base oils of different kinematic viscosities were used. The aim was to investigate the influence of such lubricants on scuffing initiation and propagation with the present methodology.In Part I it was shown that scuffing initiation depends strongly on the kinematic viscosity of the lubricant; the higher the viscosity, the greater the scuffing load. The presence of AW and EP additives in the lubricant increases the scuffing load significantly. It was also shown that the kinematic viscosity of the lubricant oils has no effect on scuffing propagation. However, scuffing propagation is significantly mitigated by AW and, to a greater extent, by EP additives. The results of surface analyses show the decisive nature of the chemical reactions of AW and EP additives with the steel ball surface under scuffing conditions, as well as the possible diffusion of sulphur and phosphorus. Chemical reactions and diffusion lead to the creation of an inorganic surface layer (probably iron sulphide), the good anti‐seizure properties of which limit scuffing propagation.

A method for testing lubricants under conditions of scuffing. Part I. Presentation of the method

AbstractA method for the tribological assessment of lubricants under conditions of scuffing is presented. The method uses a four‐ball tester, and allows one to assess the effect of lubricant on scuffing intensity through an analysis of changes in the friction torque and wear of the stationary balls, at continuously increasing load. The behaviour of a lubricant under scuffing conditions can be characterised using the so‐called limiting pressure of seizure poz, which depends on the load at which the balls seize and the average value of the wear area calculated from the wear‐scar diameters measured on the stationary balls.A comparison is made ‐ from the point of view of the resolution, time consumption, and cost ‐ of the new method with the existing, standard tests, using a four‐ball tester and a gear test rig (FZG). It is concluded that the proposed method, unlike standard FZG and certain four‐ball tests, enables one to differentiate between gear oils, in agreement with their API GL performance level. The very short run‐time of the new method enables one to perform more tests and obtain a low standard deviation. The new method is much cheaper than the standard four‐ball and FZG methods.

Tribological Properties of AW/EP Additives Under Different Thermal Conditions

The authors have investigated the action of compositions containing AW/EP additives under scuffing conditions and the influence of temperature on the wear of friction elements lubricated with selected compositions. It has been stated that postponing of scuffing initiation is not always sufficient to obtain very good strength of the surface layer and decreased wear. Furthermore, the results show the influence of temperature and load on the additive action. Extreme friction conditions result in greater wear intensity and change in the lubricating action of additives.

Wear and scuffing characteristics of composite polymer and nickel/ceramic composite coated piston skirts against aluminum and cast iron cylinder bores

The purpose of this research was to evaluate the tribological behavior and compatibility between coated piston skirts and aluminum or cast iron bore counterfaces. Aluminum piston skirts with either composite polymer coatings (CPCs) or nickel/ceramic composite coatings (NCCs) were evaluated. Among the NCC coated piston skirts, Ni–P–BN showed consistent low wear on either cast iron or the aluminum bores. The tin plated piston skirt generated low wear depths on cast iron or 390 Al bore surfaces, but higher wear depths on 413 Al or 356 Al bore. All the CPCs generated much less wear on cast iron or aluminum cylinder bores compared with the Ni–P–SiC or Ni–P–Si3N4 skirt coatings. Even the wear tests using 413 Al and 356 Al bores showed very low wear depths. Among the CPCs, two coatings with different percentages of molybdenum disulfide and graphite particles dispersed in the resin generated the lowest wear on 390 Al bore. Using a CPC over a hard-anodized surface, the bore wear depth was further reduced and became much more consistent compared with using a CPC alone. The response of the coatings to a simulation of the oil starvation associated with scuffing conditions revealed that the CPCs had intrinsic resistance to scuffing. However, the durability was not very good. The Ni–P–BN coating had intrinsic resistance to scuffing and good durability when sliding against 390 Al bore in the unlubricated conditions. The hard anodized surfaces with the CPCs showed much improved coating durability with good scuffing resistance.

Correlation of Scuffing Experiments With EHL Analysis of Rough Surfaces

Scuffing experiments were conducted on a twin disk machine using straight mineral oil. The purpose of these experiments was to validate some existing scuffing theories based on the breakdown of lubrication film in concentrated partial ehl (elastohydrodynamic lubrication) contacts. The verify these scuffing theories, a model for solving the complete inlet half ehl solution to the line contact between two rough longitudinally ground surfaces was developed. This ehl contact model was based on a newly developed concept, “average gap.” The effect of surface roughness on lubrication was taken into account by simulating the contacts between many different pairs of rough surfaces. In order to solve for the ehl contact solutions of the two disks under scuffing conditions, the actual run-in surface profiles of the mating disks, digitized just prior to failure, were used. Finally the correlations were made between the scuffing theory and the experimental data.

The influence of surface roughness texture on the temperature and scuffing in sliding contact

The influence of the surface roughness value and surface roughness texture on temperature and scuffing was experimentally investigated using a machine in which a flat unmoving specimen interacted with a rotating roller. The frictional force and temperature under scuffing conditions were measured. To measure the temperature, a special system based on an IR technique was designed. The IR temperature measurements enabled an estimate of the temperature at micro-contacts between interacting asperities. Based on experimental data, the effect of surface roughness value and texture on scuffing load, surface temperature and power emitted in the contact was shown. Using an asperity deformation model, the forces in asperity contact were calculated. On the assumption that the heat source moves through the semi-infinite body, the temperature in micro-contact was also estimated. Two types of scuffing were observed: first, global scuffing which occurred mainly for transverse roughness; second, local scuffing which occurred mainly for longitudinal roughness. The global scuffing was an unstable process and was caused by exceeding the critical power emitted in the contact. The local scuffing was caused by high temperature increments which appeared between interacting asperities and which caused local melting of the steel surfaces. The IR measurements and the calculations of local temperatures in the micro-contacts between interacted asperities confirmed these hypotheses.

On Scuffing Conditions under Rolling/Sliding Contact : 3rd Report, In the Case of 0.45% Carbon Steel Quenched

Using a two-disc machine scuffing conditions were investigated with a 0.45% carbon steel quenched which had high surface hardness and low ability to form oxide film compared with an annealed or a refined carbon steel reported in the previous papers. The following results were obtained. (1) It was confirmed that there were three critical surface temperatures with respect to incipient scuffing. In order to prevent scuffing at each critical temperature the film parameter must be kept above a certain value according to the operating condition represented by the product of the load and the sliding speed. (2) When the film parameter became below unity, the formation of oxide film effective in decreasing the coefficient of friction and enhancing the scuffing resistance was promoted unless scuffing took place. (3) The rotational ratio of a high speed disc to the mating low speed disc, integral or hunting, also affected EHL film formation and scuffing resistance.