Dry Lubricant Films for Aluminum Forming

During metal forming, lubricants are necessary to prevent direct contact, adhesion, transfer, and scuffing of workpiece materials and tools. Boric acid films, which can be firmly adhered to clean aluminum surfaces by spraying their methanol solutions, provide extremely low friction coefficients (≈0.04). The adhesion strengths of the bonded films vary with the type of aluminum alloy (6061, 6111, and 5754). Sheet metal forming tests indicate that boric acid films and combined films of boric acid and mineral oil can enable larger strains than commercial liquid and solid lubricants, showing that their lubricities are excellent for aluminum forming. Scanning electron microscopy analyses indicate that the dry boric acid films effectively separate the workpiece and die materials and, thus, prevent direct contact and preserve the surface qualities. Because boric acid is nontoxic and easily removed by water, the authors can expect these films to be environmentally friendly, cost-effective, and very efficient lubricants for sheet aluminum cold forming.     

Boundary Lubrication of Steel Surfaces with Borate,Phosphorus, and Sulfur Containing Lubricants at Relatively Low and Elevated Temperatures

Prolonging the life of engineering components through lubricant formulation to achieve better wear resistance and higher oxidation stability is of paramount importance to many mechanical systems, such as automotive gears and bearings. This can be accomplished with formulated lubricants that limit the generation of wear debris causing severe abrasion and protect the contacting surfaces through the formation of wear-resistant tribofilms. In this study, a ball-on-disk tribometer was used to characterize the friction and wear properties of steel surfaces slid in the boundary lubrication regime. An experimental scheme was developed to allow the statistical screening of various lubricant formulations. Sliding experiments were performed in baths of different lubricants at relatively low and elevated temperatures, approximately 32 and 100°C, respectively, under conditions of constant load and sliding speed. Surface profilometry, optical microscopy, and scanning electron microscopy were used to characterize the dominant friction and wear mechanisms. The tribological properties were found to strongly depend on the temperature and the additives (e.g., borate, phosphorus, and sulfur) present in the blended lubricants. The superior high-temperature wear performance of the lubricant with the higher borate content is indicative of the formation of a durable tribofilm that reduces metal-to-metal adhesion, material transfer, and surface plowing by wear debris.     

A comparative study on the performance of boric acid with several conventional lubricants in metal forming processes

During metal forming, lubricants are necessary to prevent direct contact, adhesion, transfer, and scuffing of workpiece materials and tools. The lubricating action of boric acid is due to its layered crystalline structure, and is similar to the structure of MoS₂ and graphite. However, boric acid lubrication could offer distinct advantages in terms of its application prior to forming and removal after a forming operation since it can be dispensed using water and alcohol solutions, raising the possibility of being environmentally friendly. Its effectiveness under actual conditions of metal forming operations such as rolling, forging, and sheet metal drawing and stretching has been evaluated in this study with both ferrous and non-ferrous work materials. It was found that boric acid provided lowest friction in sheet drawing and stretching operations, which is attributed to its lattice layer structure that facilitates easy sliding between molecular layers. Under predominantly compressive conditions of forming, liquid or semi-solid lubricants have performed better as they could squeeze out along with forwarding workpiece surfaces. The findings presented in this paper increase the prospect for developing boric acid as an effective lubricant in the cold forming of materials under certain conditions.     

Effect of Gear Surface and Lubricant Interaction on Mild Wear

In this study, a twin-disc test machine was used to simulate a rolling/sliding gear contact for three surface finishes, each run with two types of lubricants, thus seeking to develop insight into the tooth flank/lubricant tribological system. The test disc surfaces were case-carburised before the surfaces were produced by: transverse grinding followed by a mechanical abrasive polishing process; transverse grinding only; and transverse grinding followed by preheating as a final finishing step (intended to enhance the build-up of an easily sheared surface boundary layer using a sulphur additive). The twin-disc contact was lubricated with an ester-based environmentally adapted lubricant or a polyalphaolefin-based commercial heavy truck gearbox lubricant. To obtain information about the composition of chemically reacted surface layers, the specimens used were analysed using glow discharge-optical emission spectroscopy. The results indicate that the interactions between different surface finishes and lubricants have different impacts on friction behaviour, wear and the reacted surface boundary layer formed by the lubricant. Running a smooth (polished) surface with the appropriate lubricant drastically reduces the friction. Surface analysis of the ground surfaces gives clear differences in lubricant characteristics. The commercial lubricant does not seem to react chemically with the surface to the same extent as the EAL does. Micropitting was found on all ground discs with both lubricants, though at different rates. The highest amount of wear but less surface damage (i.e. micropits) was found on the preheated surface run with the commercial lubricant.     

A New Tribological Approach for Lubricated Sliding Contact of Pitted Metallic Curvature Cup

Interest in the development and application of plant-based lubricants for medical use is increasing. This study investigates palm oil lubricants as environmentally friendly and renewable resources to optimize the motion in an ergonomic simulated metal hip prosthesis with modification to the acetabular cup surface. Although metal hip replacements are extensively used, minimizing metal-on-metal friction and wear using safe lubricants requires further investigation. The main physical properties of palm kernel oil and palm fatty acid distillate are considered. The viscosity, wear scar, and coefficient of friction are compared to hyaluronic acid. A modified pin-on-disc tribometer simulates friction and wear on a 28-mm-diameter acetabular cup and microscopy image analysis is used to examine the wear scar. The physical properties of palm oil derivatives reduce friction and wear. In brief, the most significant results of this study include the effect of lubricant and number of pits on wear and friction coefficient. The contribution of this research work is to maintain stability and increase the lifetime of ergonomic metal hip implants.     

Boron in Tribology: From Borates to Ionic Liquids

Boron compounds are widely used in a range of tribological applications such as friction modifiers, antioxidants, antiwear additives, and in many cases as environmentally friendly lubricants. The chemical nature and structure of boron compounds provide multifunctionality. They are used as (1) solid lubricants such as boric acid and hexagonal boron nitride, (2) liquid lubricants such as ionic liquids, (3) lubricant additives such as borate derivatives of various organic and inorganic compounds, and (4) coatings such as cubic boron nitride and different metal borides. Boron is also one of the most favorable elements for coatings and thin films in biotribological and biomedical applications. This review outlines the growing role of boron in lubrication over the past several decades, summarizes the main findings, and identifies future challenges related to boron chemistry.     

The Effect of Temperature on the Tribological Behavior of RBD Palm Stearin

The wide use of petroleum-based oils raises concerns with regard to pollution, and the rising of awareness of greenhouse gases has created a demand for the use of environmentally friendly and biodegradable lubricants for industrial applications. Vegetable oils are one of the bio-oils that have been promoted as a replacement for petroleum products, in part due to their environmentally friendly characteristics; they are nontoxic, biodegradable, and easy to dispose of. Many researchers have performed studies on sunflower oil, corn oil, and soy oil, but few have studied palm oil as a lubricant. Palm oil produced in a high-throughput manner could fulfill the demand for bio-based lubricants. In this study, the influence of temperature on friction and wear performance for refined, bleached, and deodorized (RBD) palm stearin and additive-free paraffinic mineral oil is presented. The experiments were conducted using a four-ball tribotester. Test temperatures of 55, 65, 75, and 85°C were used. The sliding speeds were set to 1,200 rpm. Experiments were run for 1 h under a 392.4 N load. The results of RBD palm stearin were compared with those of paraffinic mineral oil. The experimental results showed that the RBD palm stearin had better performance compared to paraffinic mineral oil in terms of reducing frictional constraints.     

Tribological Effects of Vegetable Oil as Alternative Lubricant: A Pin-on-Disk Tribometer and Wear Study

The investigation of lubricated friction and wear is an extended study. The aim of this study is to investigate the friction and wear characteristics of double fractionated palm oil (DFPO) as a biolubricant using a pin-on-disk tribotester under loads of 50 and 100 N with rotating speeds of 1, 2, 3, 4, and 5 ms^?1 in a 1-h operation time. In this study, hydraulic oil and engine oil (SAE 40) were used as reference base lubricants. The experiment was conducted using aluminum pins and an SKD 11(alloy tool steel) disc lubricated with test lubricants. To investigate the wear and friction behavior, images of the worn surface were taken by optical microscopy. From the experimental results, the coefficient of friction (COF) rose when the sliding speed and load were high. In addition, the wear rate for a load of 100 N for all lubricants was almost always higher compared to lubricant with a load of 50 N. The results of this experiment reveal that the palm oil lubricant can be used as a lubricating oil, which would help to reduce the global demand for petroleum-based lubricants substantially.     

Statistical method for evaluating and ranking lubricants through micromechanical heterogeneity mapping of surfaces that experienced lubricated sliding

Abstract

The requirements for improved fuel economy and reduced vehicle emission have driven the lubricant industry to develop new lubricants for engines and other dynamic systems. The selection of appropriate lubricant formulation is a complicated process involving extensive and costly bench and field tests. Thus, there is a demand for developing quick, effective and less costly methods to evaluate and rank lubricants. The authors previously proposed a statistical technique for evaluating and ranking lubricants through examining spatial variations in local mechanical properties of a worn surface after lubricated sliding testing using a micromechanical probe. Examination of the mechanical heterogeneity of worn surface has been turned out a promising approach for prescreening lubricants before further bench and field tests. Research was conducted to further investigate the suitability of such a method to evaluate lubricant performance during lubricated wear tests for a number of engineering materials and in particular, to identify which mechanical property (e.g. hardness, Young's modulus, creep behaviour) was the most sensitive and reliable indicator of the surface mechanical heterogeneity. Efforts were also made to identify the optimum indentation load range for evaluating the mechanical heterogeneity. It was demonstrated that the statistical method based on the heterogeneity of worn surfaces was effective for evaluating and ranking lubricants. Microhardness was proven to be the most suitable parameter for evaluation of the mechanical heterogeneity of worn surfaces, especially for harder materials.     

Lubrication potential of boron compounds: An overview

Boron compounds are emerging as promising materials for a wide range of applications in automotive and industrial lubrication systems. Several studies conducted on boron compounds have revealed that they exhibit desirable properties for preparing stable and compatible lubricant components for a new generation of lubricating oil formulations. Boron‐containing lubricants have major tribological advantages, such as antiwear efficiency, good film strength, high‐temperature resistance, and self‐lubricating properties. The increasing number of patents concerning boron‐containing lubricants illustrates commercial interest in this area. Boron lubricants can be used in many forms, such as oxides, esters, and boric acid. Therefore, it can be expected that a new generation of lubricant formulations includes boron compounds. This paper presents an overview of various solid and liquid lubricants containing boron as an important ingredient, and is intended to aid the development of new lubricants.     

Lubricant test methods for sheet metal forming

Sheet metal forming of tribologically difficult materials such as stainless steel, Al-alloys and Ti-alloys or forming in tribologically difficult operations like ironing, punching or deep drawing of thick plate requires often use of environmentally hazardous lubricants such as chlorinated paraffin oils in order to avoid galling. The present paper describes a systematic research in the development of new, environmentally harmless lubricants focusing on the lubricant testing aspects. A system of laboratory tests has been developed to study the lubricant performance under the very varied conditions appearing in different sheet forming operations such as stretch forming, deep drawing, ironing and punching. The laboratory tests have been especially designed to model the conditions in industrial production. Application of the tests for evaluating new lubricants before introducing them in production has proven successful and has in a number of examples assisted the substitution of environmentally hazardous lubricants by more friendly ones in industrial production.     

Tribological Study Comparing PAG and POE Lubricants Used in Air-Conditioning Compressors under the Presence of CO2

Polyalkylene glycol (PAG) and polyolester (POE) synthetic lubricants are good candidates for air-conditioning systems that work with alternative refrigerants such as carbon dioxide (CO₂). Both synthetic lubricants are widely used in air-conditioning compressors and have been optimized for use with hydrofluorocarbon (HFC) refrigerants. However, it is still not clear which lubricant is more suitable for use in compressors operating with CO₂ as a refrigerant. This study compares the performance of PAG and POE lubricants of the same viscosity (ISO VG 68) used in air-conditioning compressors. The materials used were Al390-T6 disks and hardened steel SAE 52100 pins. The tests were performed using a high pressure tribometer (pin-on-disk configuration) in the presence of CO₂. The results showed that scuffing and wear resistance of Al390-T6 tested with PAG were superior compared to the samples tested with the POE lubricant. Chemical analysis using X-ray photoelectron spectroscopy showed that PAG tends to promote the formation of carbonate layers on the surface, leading to improvement in the tribological performance of the interface.     

The Size Effect of Boron Nitride Particles on the Tribological Performance of Biolubricants for Energy Conservation and Sustainability

The size of particulate additives in a bio-based lubricant influences their friction and wear performance during sliding contact. The present investigation evaluates the effect of boron nitride particle size on the tribological performance of canola oil-based lubricant mixtures. During sliding experiments, micron-, submicron-, and nanometer-sized boron nitride particle additives were considered. Friction and wear measurements were carried out on the prepared lubricant mixtures using a pin-on-disk tribometer at ambient conditions. A scanning electron microscope and optical profilometer were used for topographical studies to evaluate the influence of particle size on wear damage and surface roughness. The results revealed that the nanometer-sized particulate mixture outperformed micron- and submicron-sized particulate combinations in terms of friction and wear performance and provided a 90 % smoother surface finish. Furthermore, the tribological response of canola oil containing micron- or submicron-sized particles was found to be significantly enhanced by the addition of nano-sized particles, where the friction and wear were reduced by 40 and 70 %, respectively. It was inferred that the nano-sized particles were able to better coalesce in the asperity valleys due to their small size and spherical shape, which provided them with enhanced tribological properties in comparison with the micron- and submicron-sized particles that were larger and exhibited a plate-shaped in geometry. Newly developed non-dimensional surface roughness parameters were introduced to quantify the influence of particle size and the mechanisms involved in the tribological phenomena. The state of lubricants derived from bio-based feedstock were subsequently explored for their influence on energy conservation and sustainability, as well as their potential impact on the lubricant market place.     

Environmentally adapted lubricants,Part I. An overview

The requirement for environmentally adapted lubricants has begun to play an increasingly important role in many industrial applications, particularly in the last two decades. The present‐day requirements for biodegradable and eco‐friendly lubricants imply that lubricants have properties that can minimise, if not eliminate, negative environmental impact, such as contamination of soil and water, caused by lost lubrication, leakage and accidents. The dominant factors that have a direct impact on the environment and which characterise the lubricant and its chemical composition, are toxicity, bio‐accumulation and biodegradability. Biodegradability is perhaps the most important factor which determines the fate of lubricant in the environment. Various commercial, governmental, and regulatory initiatives exist that protect the interests of the consumer. Life cycle analysis can help in assessing the total environmental impact of lubricants. This paper reviews the essential requirements of environmentally adapted lubricants, i.e., chemical composition, eco‐toxicity, biodegradability, bio‐accumulation, and eco‐labelling schemes, and life cycle analysis.     

Influence of fatty acid additives on the tribological performance of sunflower oil

Vegetable oils are potential substitutes for petroleum‐based lubricants because they are environmentally friendly, renewable, less toxic and readily biodegradable. The addition of free fatty acids has been shown to increase the lubrication performance of vegetable oils at elevated temperatures. The purpose of this study was to evaluate the relationship between the length of the carbon chain in the fatty acid and its effectiveness as an additive for a range of elevated temperatures. Stearic, arachidic and behenic fatty acid additives were added to commercial sunflower oil. All fatty acid additives were shown to be effective in lowering the wear rate and coefficient of friction in ball‐on‐disc tribological tests. The overall carbon chain length was not observed to have a consistent influence on the effectiveness of the additive. All additives were less effective at temperatures above 100°C. Copyright © 2010 John Wiley & Sons, Ltd.     

Lubricated wear behavior of leaded α+β brass

In this research investigation, the lubricated wear behavior of leaded α+β brass sliding against stainless steel counterface was studied with the aid of a pin-on-disk apparatus. The main objective of this work was to study the effect of aqueous based environments on the interface and tribological characteristics of this tribosystem, as in several cases the formation of a thin corrosion product layer can act as a lubricating film, decreasing the coefficient of friction of the tribosystem. Thus distilled water and 3.5% NaCl solutions were used as possible lubricants and were then compared with a commercial SAE 80 W lubricant, which is extensively used in many light and heavy-duty, automotive, commercial or industrial applications. From the experimental results obtained, Stribeck curves for each lubricative environment were exacted and analyzed. In addition, by evaluating changes in the coefficient of friction of the tribosystem in accordance with the observed wear mechanisms, the characteristic lubrication regimes (elastodynamic, mixed and boundary) were identified in these curves.     

The Influence of Lubrication on Head and Disk Wear

Magnetic disks are usually lubricated with fluorocarbon-type lubricants to reduce head and disk wear during the start/stop process of the disk rotation. In this paper, the influence of disk lubrication on the tribological characteristics of the head/disk interface is investigated by pin-on-disk wear tests and the head/disk friction tests.

The anti-wear performance of a lubricant is very high. For example, a lubricant coating of 8.4 × 10^?5 mg/cm² exhibits 1/20 of the ferrite pin wear rate of an unlubricated disk. For a lubricated disk, ferrite pin wear decreases at increased sliding velocities as high as 10 m/s, while pin wear increases rapidly with increased velocity for an unlubricated disk. The lubricant used here performs well in suppressing the wear increase caused by increased load. Regarding friction characteristics, however, an excessive amount of lubricant induces severe head/disk sticking, causing head crash. With respect to head/disk sticking, the upper-limit of the amount of lubricant is 8.4 × 10^?5 mg/cm².     

Tribological Features of Refined,Deodorized, and Bleached Palm Olein with Mineral Oil Blend

Vegetable oils have been investigated to replace petroleum-based lubricants due to their environmentally friendly characteristics, and these oils have become an important source of biolubricants. For the purpose of ensuring the ability of vegetable oils as a neat or partial biolubricants, image processing techniques were employed to explore the tribological characteristics of vegetable oil with a mineral oil blend. Refined, bleached, and deodorized palm olein blended with mineral oils was investigated using a four-ball tribotester and design of experiments with volumetric blend ratios of 20 to 80%. An optimized value E53.11/RB46.89 was obtained from the investigation, in compliance with ASTM D4172 standard. From the results, the E53.11/RB46.89 blend reduces the friction coefficient and wear scar diameter as well as the material lost in comparison with neat mineral oil. It is concluded that the E53.11/RB46.89 blend could be a potential partial biolubricant due to its negligible negative impact on wear and it provides satisfactory performance as a lubricant.     

Studies on Degradation Mechanisms of Tape Lubricants in a High Vacuum Environment

Degradation and tribological performance of several tape lubricants were studied during sliding in a high vacuum environment. Gaseous products generated from the head–tape interface and friction force were detected and monitored as function of sliding distance by using a quadrupole mass spectrometer and strain gauges. Chemical analyses of the commercial tape lubricants were done to better understand the degradation processes and degradation products in the sliding tests. Experimental results showed that the commercial metal evaporated (ME) tape lubricants include fatty acid and perfluoropolyether (PFPE) compounds. The degradation products from the commercial tape include small fluorine containing fragments from the PFPE lubricant and small hydrocarbon fragment from fatty acid. In addition, three other species, H₂, C₂H₅ and CO₂ were detected in the case of ME tapes and they were generated from the degradation of the diamond-like carbon (DLC) coating on the tape surface. The commercial metal-particle (MP) tape used fatty acid and fatty acid ester lubricants. Only hydrocarbon fragments were detected in the MP tapes' sliding tests, no H₂, C₂H₅ and CO₂ were found. The coefficient of friction of these two tapes increased with sliding and depletion of lubricant on the tape surface. The trend of the coefficient of friction was different for ME and MP tapes because of the differences in the lubricant and lubricant distribution on these two tape surfaces. Z-Dol and stearic acid were used to lubricate ME tapes, their test results were analyzed and compared with the commercial tapes' test results.     

Study of pentaerythritol tetraoleate ester as industrial gear oil

Attention has been paid to biodegradable lubricating oils in the field of lubricant application because of environmental pollution control measures. In Europe and in some part of Asia, the use of environmentally acceptable lubricant is supported by environmental labels. Synthetic and vegetable oil‐based esters offer the best choice in formulating environment‐friendly lubricants. Pentaerythritol tetraoleate ester has been synthesised using polyol such as pentaerythritol and oleic acid with indigenous ion exchange resin (Indion‐130) catalyst. The product was characterised for its physicochemical properties and was evaluated for lubrication performance. This was then compared with extreme pressure type of industrial gear oil VG‐68 (IS 8406:1993). The product was found to have good potential for use as a base stock for formulation as extreme pressure type of industrial gear oil VG‐68 (IS 8406:1993). Copyright © 2011 John Wiley & Sons, Ltd.