Friction Material Formulation Research Articles

Tribological Behavior of Friction Materials Containing Aluminum Anodizing Waste Obtained by Different Industrial Drying Processes

With sustainability dominating the industry, recycling the generated waste from different processes is becoming increasingly important. This study focuses on recycling waste generated during aluminum anodizing waste (AAW) in friction material formulations for automotive braking applications. However, before utilization, the waste needs to be pre-treated, which mainly involves drying. Hence, four different industrial drying methods were studied to dry the AAW, and the corresponding characteristics were observed by evaluating its residual humidity and crushability index. The waste powders were further characterized using FT-IR and SEM/EDXS to understand their constituents. The initial analysis showed that the waste subjected to the drying process P2 and P1 with the lowest final humidity fetched the most desirable results, with P1 having the simpler drying procedure. The AAW powders were added in a commercial friction material formulation at 6 and 12 wt.% and subjected to friction, wear, and non-exhaust particulate matter analysis. The worn surfaces were analyzed using SEM/EDXS evaluation to understand the extension and composition of the deposited secondary contact plateaus. It was seen that the 12 wt.% addition of waste processed using the P1 technique provided the most satisfactory friction, wear, and emission characteristics, along with expansive secondary contact plateaus with a good contribution of the waste in its formation. This study showed a good relationship between the processing method and a formulation’s tribological and emission characteristics, thereby paving the way for using this drying method for other waste requiring pre-treatment.

Effect of internal and external damping in the reduction of non-exhaust particulate matter emissions in a low metallic friction material formulation

Friction-induced vibrations in an automotive braking system are of serious concern, leading to different repercussions. Numerous conventional and unconventional methods have been proposed to curb these vibrations, which are also observed to be directly related to generating non-exhaust particulate matter emissions. In this study, an in-house formulated friction material, tested in the form of pins, was subjected to internal damping by adding rubber content from 0 to 3 wt% and external damping by wrapping the different pins in rubber tape. The DMTA showed a decrease in storage modulus and an increase in loss factor with the increase in rubber content. The pin density decreased with the increase in the rubber content. Dry sliding friction, wear, emissions, and vibrations tests were conducted on a pin on disc tribometer with relevant attachments to measure emissions and vibrations. A large drop in vibrations was observed with the rubber content, irrespective of external damping. On the other hand, a significant reduction in wear, emissions, and vibrations was observed with the sample containing the highest rubber addition and with the damping tape. This study showed the feasibility of employing the combination of internal and external damping, emphasizing the optimum rubber content in friction material formulations.

A comprehensive study on the particulate matter characteristics of a friction material containing blast furnace slags

Recent studies have indicated the positive aspects of adding blast furnace (BF) slags on the friction and wear properties of different composite materials. However, the corresponding studies on the extremely important particulate matter (PM) emissions characteristics are seldom explored. This one-of-a-kind study examined the PM characteristics of two types of BF slags in detail. The slags were added in an in-house formulated friction material formulation with limited constituents to highlight the role of the added slags. Pin on disc tests were conducted at a mild wear testing condition with added attachments to the equipment to count and collect emitted particles at different particle size range. A significant reduction in pin wear and collected emitted particles were seen with the slag presence. The friction coefficient of the slag specimens was slightly lower than the reference sample. Through SEM and TEM analysis, it was seen that the slags actively contributed to and supported the formation of smooth, compacted, and extended secondary contact plateaus. From this study, the utilization of slags for specific applications is further evaluated, paving the path for subsequent inclusion/ replacement of conventional constituents in friction material compositions.

The influence of the addition of different kinds of slags on the friction and emission behavior of a commercially employed friction material formulation

Keeping sustainability and the circular economy in mind, numerous studies have been conducted on the feasibility of the utilization of industrial wastes in friction material formulations for braking applications. One such highly produced waste is slags from blast furnaces. The present work focuses on the friction, wear, and emissions behavior of a commercially employed friction material formulation observing the inclusion of three kinds of slags. Two types of slags were obtained from a blast furnace; the difference was the cooling method. The third type of slag was collected from a basic oxygen steel furnace. The prepared samples were tested in the form of pins on a pin on disc equipment at 1.51 m/s, 1 MPa, and ambient conditions to replicate a mild braking scenario. Irrespective of the type of slag, the addition of the wastes observed either a decrease or similar emissions when compared to the virgin formulation. The friction and wear were in the range comparable to that of the reference composition; the CoF for slag specimens ranged between 0.49 and 0.51 compared to 0.45 for the reference composition. On the other hand, by inspection of the worn surfaces of the pins, it was seen that the slag-containing specimens had compact and expansive secondary contact plateaus with the inclusion of slag particles in their composition. Through this preliminary analysis, the possibility of the utilization of different slags is highlighted, especially in an already implemented commercial formulation, paving the path for further testing and validation.

A novel path towards limiting non-exhaust particulate matter emissions of a commercial friction material through the addition of metallurgical slag

Keeping recycling and the circular economy in mind, this study explores the reduction in emission of a highly optimized, commercially employed friction material formulation through the addition of metallurgical slags from a basic oxygen furnace in varying quantities from 6 to 38 wt%. The various compositions were paired with a pearlitic grey cast iron counterface and tested on a pin on disc tribometer. The friction coefficient and pin wear increased with the slag addition but were still within the permissible limit when compared to the original formulation. Specimens with higher slag content observed extremely compacted and extended secondary contact plateaus, which also recorded significant slag presence. The extended plateaus detached in the form of chunks from the mating surfaces, which settled on the equipment hardware and restricted the production of airborne particles. From an industrial symbiosis perspective, the addition of metallurgical slags proved to be a promising way of obtaining green friction materials with reduced emissions.

Effect of the Addition of Waste Generated during the Plasma Cutting of Aluminum Products on the Friction and Emission Properties of a Commercial Friction Material Formulation

With recycling and reuse in mind, this study explores the possibility of the utilization of waste generated during the plasma cutting operations to produce aluminum products in a commercial friction material formulation for car braking applications. The as-received waste, analyzed in the form of a powder, was subjected to various characterization techniques to obtain its composition and phase constituents. The friction, wear, and emission analyses were organized in two ways: the first part focused on the selection of the most suitable waste content in the friction material formulation—10, 15, and 20 wt.%—tested in the form of pins, using a pin-on-disc tribometer. The second part evaluated the most suitable content in the formulation in the form of coupons on a subscale dynamometer to comprehend its friction and emission characteristics in a more complex scenario. Through the pin-on-disc analysis, it was seen that the 10 wt.% of waste in the formulation provided permissible friction and wear behavior, and similar emission magnitude and secondary plateau characteristics were seen, as compared to the reference composition. Similar results were recorded on the subscale dynamometer at mild braking conditions. At ‘severe’ testing conditions, a different trend was observed. Through this analysis, the possibility of the addition of this kind of waste in friction material composition has been evaluated deeply, paving a path for further analysis and possible implementation.

Study on the effect of the addition of bulk and exfoliated graphitic carbon nitride on the dry sliding behavior of a commercial friction material formulation through pin on disc and subscale dynamometer analysis

A novel analysis was conducted on the friction and wear properties of a commercial friction material formulation with the addition of bulk (named: gCN) and exfoliated (named: TEX6) graphitic carbon nitride in varying quantities: 4.5, 9, 13.5, and 18 wt%. The analysis was two-fold. In the first part, the samples were tested in the form of pins on a pin on disc testing equipment. The typical trend was that the friction coefficient magnitude increased with the addition of gCN. On the other hand, the friction coefficient decreased with the TEX6 addition. The pin wear reduced with the addition of gCN until 9 wt%. Beyond this amount, an increase in pin wear was observed. The TEX6 samples generally noted a decrease in pin wear with the increase in its content. An improvement in the characteristics of the secondary plateaus was seen with the increase in both gCN and TEX6 content. Through this study, the 13.5 wt% addition of both gCN and TEX6 was considered to display permissible friction and wear magnitude, and desirable extension and compaction of secondary contact plateaus. In the second part of the study, the formulation with 13.5 wt% of gCN and TEX6 was tested on a subscale dynamometer to replicate a real-life braking scenario. The friction and wear magnitudes were similar to the pin on disc study and the extension of the secondary contact plateaus was better than the virgin formulation. This study provides a complete analysis of the feasibility of the inclusion of g-C3N4 variations in automotive braking applications.

PHYSICOCHEMICAL ASPECTS OF THE WORK OF PASSENGER CAR BRAKE LININGS. PART II THE EFFECT OF LUBRICATING ADDITIVES

The paper presents the influence of various systems of lubricating additives which determine the performance of the friction materials of brake linings. The base hybrid friction material formulation was modified with various types of lubricating additives. These additives are divided into groups containing commonly used lubricating materials: carbons and sulphides, compounded in various proportions, influencing the formation and structure of the so-called third body layer (TBL) on the surface of the brake disc because of braking. Raman Spectroscopy (RS), time of flight Secondary Ion Mass Spectroscopy (ToF-SIMS) and high-resolution scanning electron microscopy with an X-ray analyser (SEM-EDS) equipped with a focus ion beam (FIB) were used for chemical and morphological analysis of the surface layer of brake disc after breaking tests. The results of the physicochemical analysis of TBL were correlated with the results of tribological tests (according to the SAE-J2522 procedure, commonly known as AK-Master) on a brake dynamometer adapted to the measurements of acoustic signals (NVH – noise, vibration, and harshness). The obtained results confirm the important role played by the so-called third body layer, formed on the surface of the brake disc for safety (COF), durability (wear of friction elements) and the acoustic spectrum accompanying braking.

Utilization of Metallurgical Slags in Cu-free Friction Material Formulations

The aim of our research was to indicate the suitability of metallurgical slags (two blast furnace slags and one steel furnace slag) as the components of Cu-free friction materials. The base mixture consisted of nine components including phenolic resin, graphite, tin sulphide, steel and aramid fibers, iron powder, a mixture of barite with calcite, and vermiculite. To this base mixture, the slags with a particle size below 0.1 mm were added individually in the amount of 20 wt.%. A base friction mixture with alumina in the amount of 20 wt.% represented the reference. Samples for the friction-wear tests were produced in the form of pins by hot press molding. The prepared pins were tested using a pin-on-disc tester in a drag mode at the pressure of 1 MPa and a constant sliding speed of 1.51 m/s for 90 min. The samples with slags exhibited slightly lower values of steady-state friction coefficient compared to the reference composite with alumina, and at the same time produced lower wear particle emissions. The particle concentration was reduced for the samples with slowly cooled blast furnace and steel furnace slag. The results obtained indicated steel furnace slag as a promising component of Cu-free friction composites.

Influence of ground granulated blast furnace slag on the tribological characteristics of automotive brake friction materials

PurposeThe main purpose of this study in the field of automotive brake friction material is to find an effective material to replace the environmentally hazardous copper in the brake pad formulation.Design/methodology/approachCu is used as functional filler in various forms in the friction material formulation. Because of its hazardous impact to the aquatic life, a suitable replacement of Cu is the main focus of this research. Three novel friction composite materials using ground granulated blast furnace slag (GGBFS) as a suitable alternative for Cu were developed by increasing its Wt.% from 5% to 15% in the step of 5%.FindingsThe physical, mechanical and chemical properties of the developed friction composites were tested as per the industrial standards. The tribological properties were analyzed as per SAE J661 standard using the chase test rig. Initial studies revealed that the friction composite having 5% GGBFS exhibited better physical, mechanical and chemical properties with excellent frictional performance having minimal fluctuations even at higher temperatures. Nonetheless, the results showed that the friction composite containing 15 Wt.% GGBFS revealed a better wear resistance property compared with the other two composites due to the tribo lubricating layer formation at the frictional interface. Scanning electron microscope analysis was performed to understand the wear mechanism and tribo layer formations through topography studies.Originality/valueThis paper explains the influence of GGBFS as a replacement of barytes in brake pads formulation to enhance the tribological performance.

Suppression of Brake Noise and Vibration Using Aramid and Zylon Fibers: Experimental and Numerical Study.

Aramid pulp/fiber is the most vital ingredient of brake friction material (FM) formulation. It is perpetually added to achieve quality brake pads/shoes and improve the overall friction and wear performance. Additionally, novel Zylon fibers have a superior property to aramid fibers. However, no studies give insights on their influence on brake noise and vibration (NV) performance. In the current work, a series of six different types of eco-friendly brake pads was developed. The first five contain aramid pulp, aramid short fibers, and Zylon fibers of different sizes (1, 3, and 6 mm) as the theme ingredients (3 wt %) by keeping the parent composition identical. Additionally, one more pad was developed that contains no aramid/Zylon fibers (i.e., reference pad). The pads were characterized for physical and mechanical properties. The damping and natural frequencies of pads were measured experimentally and numerically. All brake pads were evaluated for detailed NV performance by following the SAE J 2521 test schedule. In addition, numerical simulation was performed to validate the experimental brake squeal results. Results revealed that aramid/Zylon fiber-based pads improved the porosity, damping, and compressibility. Overall, brake noise and vibrations were improved for aramid/Zylon fiber-based pads by 1.2–1.5 dBA and 20–25%, respectively, compared to the reference pad. The complex eigenvalue analysis (CEA) proved that squeal was mainly influenced by the damping and density of the pad materials. Thus, aramid/Zylon fiber-based pads can effectively suppress the instability of the brake system and reduce the brake squeal propensity.

The influence of the addition of aluminum anodizing waste on the friction and emission behavior of different kinds of friction material formulations

The study focuses on the characterization and one-of-a-kind utilization of aluminum anodizing waste (AAW) in different friction material formulations. Through TGA and FT-IR analysis, the AAW was observed to have a dominant presence of hydroxide, sulfate hydrate, and a fraction of alumina. After heat treatment at 400 ℃ for 4.5 h, the AAW also constituted of AlOx, obtained from the conversion of hydroxides. The AAW was included in two kinds of friction material compositions – a basic composition (BC) with few constituents, and a commercial composition (CFM), wherein, the AAW was added at 12, 24, and 32 wt% of variation, and subjected to friction, wear, and emission analysis. The tests were conducted on a pin on disc testing equipment at 1.51 m/s, 1 MPa, and room temperature testing conditions. The analysis with BC revealed the mild abrasive nature of the AAW, along with acceptable friction, wear, and emission characteristics. With the CFM, the steady state CoF trends, permissible CoF, pin and disc wear, and desirable emission characteristics were observed with 12 wt% addition of AAW. Higher AAW content led to the degradation of wear and emission characteristics of the CFM specimens. Through this preliminary investigation, the possibility of the recycling/utilization of AAW was explored comprehensively, paving the path for further exploration and feasibility analysis of the inclusion of AAW in braking applications.

A novel study on the reduction of non-exhaust particulate matter emissions through system vibration control.

The need to reduce non-exhaust particulate matter emissions is of paramount importance as they pose repercussions on human lives and the environment. In this study, a novel way to limit emissions is proposed based on the minimization of the vibration of the mating bodies. Two model friction material formulations were tested in the form of pins and paired with a pearlitic grey cast iron disc counterface in a laboratory pin on disc apparatus. To reduce the vibrations, a damping tape was wrapped around the pins. With the damping of vibration, a significant drop in the emissions was recorded, and this was correlated with the friction layer establishment during sliding, which observed low disruption. It is believed that the use of this method for reducing emissions can accompany the optimization phase of the brake squeal noise of friction materials, thereby, providing new design perspectives.

Ecological Transition in the Field of Brake Pad Manufacturing: An Overview of the Potential Green Constituents

Nowadays, the drive for green products has undergone a rapid increase following the global ecoawareness and the severe regulations aimed at preventing the environment from further damage. The use of ecosafe constituents in materials for harsh applications, such as brake pad systems, can be a possible solution for reducing health hazards arising from particle release during braking. Based on this, the present study provides a bibliographic review of green alternative constituents for friction material formulation, focusing the attention on their influence on the tribological properties of the final composites. The traditional materials still used in commercial brake pads are shortly described, with the aim to provide an overview of the current situation. In the final part of the review, following the trend of circular economy, works dealing with the use of waste as an ingredient of friction materials are also reported. The whole literature screening points out that much work is still required to obtain completely green friction materials. Indeed, few works dealing with the phenolic resin replacement, proposing inorganic ecosafe materials such as geopolymers, are present. On the contrary, the use of natural fibers is widely investigated: palm kernel, flax, agave and aloe can be identified as promising constituents based on the literature results and the generated patents.

Study on the Effect of the Addition of Aluminum Anodizing Waste in Different Friction Material Formulations

Study on the Effect of the Addition of Aluminum Anodizing Waste in Different Friction Material Formulations

A hybrid multiple‐criteria decision‐making approach for selecting optimal automotive brake friction composite

In this research article, a hybrid multiple-criteria decision-making approach was implemented to select the optimal brake friction formulation according to several conflicting performance-defining criteria. Friction material formulations based on different abrasives (magnesium oxide, iron oxide, zinc oxide, aluminum oxide, titanium dioxide, zirconium dioxide, and silicon dioxide) were designed, fabricated, and tested for various tribological properties. The inclusions of aluminum oxide proved best from performance and fade coefficient of friction, friction stability, friction fluctuations, and friction variability point of view but confirmed worst in terms of wear and disc temperature rise. The lowest wear and lowest rise in disc temperature were exhibited by zinc oxide added composite. The highest recovery coefficient of friction was displayed by silicon dioxide added composite. Since no single composite alternative could merely satisfy all the desired attributes. To find the optimum composite option for automotive braking application, hybrid analytic hierarchy process (AHP)–criteria importance through intercriteria correlation (CRITIC)–technique for order of preference by similarity to ideal solution (TOPSIS) was used to make the final decision. The results show that the formulation with titanium dioxide as abrasive exhibits the optimal properties.

Experimental study on the temperature evolution in the railway brake disc

Increasing operating speed of modern passenger railway vehicles leads to higher thermal load on the braking system. Organic composite brake pads are poor thermal conductors, hence frictional heat is absorbed mainly by the disc. In this study three brake pad types were tested on the dynamometer. Metallic fibres, steel and copper, were introduced to the formulation of two materials. The third was a non-metallic material – a reference case. Dynamometer test comprised emergency brake applications to determine the frictional characteristics of the materials and constant-power drag braking to analyse the effect of metal fibres on temperature evolution, measured by six thermocouples embedded in the brake disc. Mean friction coefficient is analysed and discussed. It is concluded that conductive fibre in the friction material formulation may influence its tribological characteristics. Despite high thermal conductivity, metal fibres in the concentration tested in this study, did not reduce temperature of the brake disc.

Experimental study on the effect of formulation modification on the properties of organic composite railway brake shoe

Friction materials used to manufacture railway brake shoes are assessed with consideration of a wide variety of their functional, frictional and mechanical properties. To meet the versatile requirements posed by brake system manufacturers and railway operators, formulation of contemporary organic composite friction materials are fairly complex containing in some cases even more than a dozen different ingredients. To conduct the design process of new materials effectively, it is necessary to understand the influence of individual raw materials on properties of the composite. In this study two organic composite friction materials were compared extensively allowing for investigation of influence of two ingredients, namely quartz and petroleum coke, on the properties of the composite. Discussion of results includes analysis of instantaneous and mean dynamic coefficient of friction in relation to initial velocity, contact force and temperature. Both full- and reduced-scale dynamometer test results are discussed. In addition, the mechanical properties of the materials are presented and compared. All tested characteristics were influenced by the formulation modification. The effect was pronounced enough to allow drawing conclusions on qualitative relation between formulation and properties of the composite friction material.

A pin-on-disc tribometer study of disc brake contact pairs with respect to wear and airborne particle emissions

In the EU, PM10 from the wear of disc brakes can contribute up to 50% of the total non-exhaust emissions from road transport. The wear originates from the contact surfaces of the friction material and the disc. One possible way to decrease PM10 emissions is to change the materials of the contact pair in terms of composition and coatings. The wear and particle emissions of three novel friction material formulations, one novel disc formulation, one disc WC/CoCr coating realized with the HVOF technique, and one disc surface treatment realized by a nitriding process, were investigated. Pin-on-disc tests were run to rank the novel materials in terms of specific wear rate and particle number and mass rate. The results show that it is possible to achieve a reduction in particle emissions of up to 50% by changing the materials of the contact pair.

Correlation of field and experimental test data of wear in heavy commercial vehicle brake liners

The correlation between the wear behavior of a heavy commercial vehicle (HCV) brake liner tested under controlled laboratory conditions and that in actual field conditions is investigated. A brake liner study for friction and wear is performed on an inertia brake dynamometer (IBD) at different temperatures (200 °C, 250 °C, and 300 °C) using 6000 brake actuations in a laboratory. The total wear loss of the brake liner at three different temperatures for 6000 brake actuations in IBD is found to be 1.12 mm. The actual field test is conducted on four different HCVs, namely, a city bus (CB), a high speed bus (HSB), a highway truck (HWT), and a tipper lorry (TL). These HCVs run at different terrain/traffic conditions and load conditions. When comparing the predicted life of the brake liner through the IBD test with the actual life of the brake liner in different HCVs, a vast difference is observed. Due to the large variation of liner life observed between the actual and predicted tests, an extensive field test is conducted. In the field test, the liner with identical formulation is fitted in the four types of HCVs. The predicted life of the liner using IBD is then correlated with the field test observation and a correlation factor is determined. Based on this correlation factor, the predicted life of the liner and the achieved life on the HCV are found to be fairly close. This study will be useful to design the friction material formulation and to predict the actual life of the brake liner for various HCVs.