Elemental Composition Study of Commercial Brake Pads for a Passenger Vehicle: A Case Study

Transcription

1 Elemental Composition Study of Commercial Brake Pads for a Passenger Vehicle: A Case Study AFIQAH O, FAUZIANA L, RASID O, WONG SV Vehicle & Safety Biomechanics Research Centre Malaysian Institute of Road Safety Research Taman Kajang Sentral, Kajang, Selangor MALAYSIA afiqah@miros.gov.my Abstract: - As a part of composite materials, brake pads are made of different material combinations. Commonly, the brake pads constituents are in a form of frictional additives, filler, binder and reinforcing fiber. Each constituent plays an important roles in ensuring the brake pads are intact together and function properly. Consumers rely on the price and quality of the brake pads in order to purchase the parts. This paper study the price variation of aftermarket brake pads and the correlation with the microstructural characterization of the parts. The brake pads were categorized according to the price range and compared with Original Equipment Manufacturer (OEM) parts. The brake pads studied contained Fe as the dominant metals but their ratio varied considerably. The microstructure of the composites were studied using Field Emission Scanning Electron Microscope (FESEM) and optical microscope, while the elemental composition of selected areas were characterized using Energy-dispersive X-ray spectroscopy (EDX). Based on this study there is no correlation between the brake pads price and elemental composition used in the parts. Key-Words: - composite material, microstructure, market price, fiber 1 Introduction Brake pads is a part of friction material component and are generally a composite with different combination of materials. The complex composition of brake pads typically formulated with more than 10 constituents, and more than 3000 different materials are used in different brands [1]. The performance of friction material is strongly affected by selection of ingredients [2]. Usually, commercial pads contain number of different constituents [3] and its include binders, fibers, fillers, friction modifiers and lubricants [4].Each of the constituents have different function in order to enhance the properties of the friction materials, and the selection of constituents usually based on trial and error [5]. Brake pad materials is subjected to severe solicitation during braking and it is affected strongly by the microstructure of the material [6]. Fiber materials provides mechanical strength and long before its ban, asbestos fibers was popular as reinforce fiber in brake pads due to its superior properties. The used of metal fibers to substitute asbestos has been highlighted in several studies [7-9] and proved to improve the performance properties of the friction materials. Binders hold the ingredients together while fillers were added to reduce cost and improve manufacturing ability. Addition of friction modifiers is to ensure the stable frictional properties and to control wear rate. Solid lubricants are used to stabilize the coefficient of friction, especially at elevated temperature. In commercial brake pads market, complete compositional revelation of brake friction material is rare since the information is treated as proprietary and manufacturers not obliged in any way to disclose it to customers [10]. However, most of the countries have issued number of regulations and requirements for the brake pads to perform accordingly in order to assure the safety of brake parts. For example, aftermarket brake pads manufacturer in Europe market must pass the brake pads performance testing according to ECE R90 before releasing the products to the market. For the time being, aftermarket brake pads sold in Malaysia are not fully controlled by enforcements. Each manufacturer has their own standard choice or raw materials and process that suits their final product performance. Without standards or specifications in place there no price controls in the market place. Commercial aftermarket brake pads sold in Malaysia comes with variation of brands and price. Consumers have the option to choose whether to install the Original Equipment Manufacturer ISBN:

2 (OEM) part or changing their pads aftermarket brands that are available in the market. OEM pads are labelled with the name of vehicle s manufacturer while aftermarket pads can have variety of labels, depending on the manufacturer. A primary concern in this case is certain brake pads have little information on the packaging, hence provided limited knowledge to the consumer. The objective of this work is to study whether there is relationship between variations of market price with the elemental composition of the brake pads. 2 Methods The studied material is commercial front brake pads sold for a selected passenger vehicle applications. Since different vehicle contain different brake system, brake pads sell for same model car was used in this research. 2.1 Collecting price data of brake pads In the period between June to July 2013, price data of brake pads for specific passenger vehicle were collected in the area of Semenyih, Bangi and Kajang. Convenience sampling were used for data collection. The vehicle is a common brand used in Malaysia and the data were collected in workshop, automotive spare parts and service centre. Theoretically, there will be a price different between the original equipment manufacturer (OEM) with aftermarket parts since the composition materials are different. Based on survey result, three aftermarket brake pads and one OEM brake pads were selected and purchased for further microstructural and material composition study. Three aftermarket brake pads each represents price category of cheap, medium and high; and compared with OEM parts. The brake pads were marked as S1 for cheap, S2 for medium and S3 for high. 2.2 Microstructural study The new brake pads selected from convenience sampling were analyzed by optical microscope and FESEM equipped with EDX microanalysis. Samples were cut into dimension of 1cm 3, grounded and polished to ensure a clear image under SEM. Microanalysis was used to identify the morphology and the composition of the pad material and to analyze the surface distribution of the particulates. All of the observations are made at the centre of the contact surface. As the structure of material is apparent, it is possible to distinct between different main constituents (e.g; fibers, binder, fillers and friction modifiers). 2.3 Material Composition of brake pads EDX analysis was performed to find the composition of each brake pads selected. The percentage weight of each elements in the formulations were compared to the corresponding element of the OEM specimen. 3 Results and Discussion 3.1 Price data of the brake pads From the price study, each of the retailers offering the same or different brand of brake pads that fit the model of passenger vehicle studied. The price varied ranging from MYR 25 to MYR 160. As the information stated in the packaging is minimal, consumers relied on the retailers as their primary information source before proceeds with the purchasing. 86% of the retailers will ask for price interest before proceeding with the recommendation. Some consumers may prefer a higher priced, whose brand signals a greater quality than the cheaper option. Figure 1 shows the graph bar of price range commercial brake pads for the selected passenger vehicle model, ranging from the cheapest to highest price. The expensive brake pads costs 6.4 times than the cheapest brake pads and the average price of brake pads for this selected model is MYR Based from the price variation, the brake pads were further classified as cheap, medium and high price. Cheap price ranged from RM0 RM45, medium range from >RM45-RM70 while high costs from >RM70 to RM 160. The classification of the price can be seen in Figure 2. The blue point represents the price of aftermarket brake pads while the red point represents OEM brake pads. As aftermarket represents by variation of brands, the OEM is actually the same product (installed for specific vehicle model) with variation of price depending on the retailers. The results show that the market price does not represent the quality of the product purchased. ISBN:

3 Figure 1: Price Variation of Brake Pads for specific passenger vehicle High: >RM72 Medium: >RM45 to RM72 Cheap: RM 0-RM 45 Figure 2: Price classification of brake pads 3.2 Microstructural study of selected brake pads Optical microstructure Figure 3 shows the observation on some regions of pads surface using optical microscope. From the results, it can be seen the distribution of the particles in the friction materials are different for each samples. The dispersion of resin binder (dark region) were much more inclusive in S1 and OEM samples compare to sample S2 and S3. The microstructure were further identified using FESEM. ISBN:

4 (a) (b) (c) (d) Figure 3 Microstructure of samples pads with magnification of 10x using optical microscopes; (a) sample S1 (b) sample S2 (c) sample S3 (d) sample OEM presents as dark colour in the microstructure while SEM microstructure less dark colour represents the compound that still The SEM image for all of the samples are shown in dominated by carbon. Sample S1 shows visible Figure 4. The image shows good dispersion of presence of Carbon agglomeration compare to other fillers within the binder in all commercial brake samples. Meanwhile, the steel fibre are showed by pads. Even though metallic and non-metallic fibers the light colour and the length of the fiber varied and particles are differ in size for each samples from one to another (short and long fibers). The (small and large), it is uniformly dispersed steel fibre can be seen dominating sample S2. throughout the matrix. From the observation, carbon ISBN:

5 (a) (b) C (c) (d) Figure 4 SEM observations of samples pads with magnification of 50x using (a) sample S1 (b) sample S2 (c) sample S3 (d) sample OEM 3.3 Elemental composition of brake pads Table 1 shows the elemental composition based on EDX analysis. It can be seen that the carbon is present in more or less equal amount in all formulations. High percentage of oxides can be found in S3, which may weaken inter atomic bonding and reduce its strength. OEM contains the least amount of oxygen. The dominant metal in the brake pads studied are iron (Fe), Magnesium (Mg) and Aluminium (Al). Magnesium is added to improve the quality and out of the four samples, S2 did not contain any magnesium. The percentage of iron varies from (high) and 5.66 (low). S2 contains the highest amount of iron, followed by OEM, S3 and S1. Use of metallic ingredients affected performance properties in beneficial way. Copper was most effective in boosting thermal conductivity and the element exist only in OEM sample. Small amount of Mn, Ni and Zn were found in S1 where the later was not found in OEM samples. One of the disadvantages of steel fiber is that it may be attacked by rust, therefore reduce the functionality as reinforcing fibers. The incorporation of zinc over the friction surface in S1 and S3 helps to form a sacrificial anode for rusting to occur [11]. Sample S3 contains P which also did not found on other samples. Table 1 Composition of brake pads in weight % Element S1 S2 S3 OEM C O Na Mg Al Si P S Cl ISBN:

6 K Mn Ca Fe Cu Ba Ni Zn Conclusion There are no clear effects between the price and the material composition of the brake pads. As aftermarket pads usually designed to imitate the performance of OEM, the material ingredients might be similar (more or less) to the amount of OEM or might be different. An overview on the available data shows that the average of many elements found on the samples were rather close. Through the comparison of Fe element as the main dominant metal in the studied brake pads, it can be seen that the low brake pads contain the least weight element of Fe in the composition. However, the highest weight element of Fe were found in medium rather than high brake pads. Hence, there is no direct correlation between the percentages of fiber element with the foundation of market price. The huge price variation between brake pads may result in product clone, which at the end endanger the vehicle consumer due to the brake safety issue. The same brake pads can be sold as cheap as MYR 35 and as high as MYR 150 at different retailers. Further studied on the brake performance of selected brake pads should be enhanced in order to rule out any duplication problem. References: [1] X1.Filip, P., Kovarik, L, Wright, M.A., Automotive brake lining characterization, In: Proceedings of 15 th Annual SAE Brake Colloqium,1997,p [2] Saffar, A, Shojaei, A. Effect of rubber component on the performance of brake friction materials. Wear, Vol , 2012, pp [3] A. Keskin.Investigation of using natural zeolite in brake pad. Scientific Research and Essays Vol 6 (23), 20011,pp [4] Selamat, M.S.B, Friction materials for brake application, Journal of Industrial Technology, SIRIM, Vol. 14(2), 2005, pp [5] L.G. Hayer, A. Bach, G.T Neilsen, P. Morfen, Tribological properties of automotive disc brakes with solid lubricants, Wear 232 (1999) pp [6] Amira, S., Mohamed, K., Riadh E., Anne-Lise C. & Yannick D. Study of the interaction between microstructure, mechanical and triboperformance of a commercial brake lining material. Materials and Design 59 (2014) pp [7] Mukesh K, Jayashree B. Optimized selection of metallic fillers for best combination of performance properties of friction materials: A comprehensive study. Wear 303 (2013) pp [8] Mukesh K., Jayashree B. Studies on reduced scale tribometer to investigate the effects of metal additives on friction coefficient- Temperature sensitivity in brake materials. Wear 269 (2010) pp [9] I. Sallit, C. Richard, R. Adam, & F. Robbe- Valloire. Characterization Methodology of a Tribological Couple: Metal Matrix Composite/ Brake Pads. Materials Characterization Vol 40 (1998) pp [10] D Chan & G W Stachowiak. Review of automotive brake friction materials. Proceedings of Institution Mechanical Engineers Vol 218 (2004). Part D: J. Automobile Engineering [11] Hell, M., Jaworek, W., Huppatz, W. and Wieser,D. Friction lining,especially for brakes and clutches, and a method for producing friction lining. US Pat , 2002 (United States Patent and Trademark Office. [12] Darius G. S., Mohamad N.B., Mohmad S.S., Talib R. J & Mustafar S., Brake Pad & Disc Materials, University Publication Centre (UPENA), ISBN: