Elsevier

Wear

Volume 317, Issues 1–2, 15 September 2014, Pages 1-7
Wear

Tribological behavior of polyamide 66/rice bran ceramics and polyamide 66/glass bead composites

https://doi.org/10.1016/j.wear.2014.04.019Get rights and content

Highlights

  • Rice bran ceramics (RBC) particles or glass beads (GBs) were filled with polyamide.

  • Both composites showed lower friction than pure resin at low sliding velocities.

  • Both composites showed lower wear than pure resin at low sliding velocities.

  • RBC particles and GBs prevented the formation and growth of roll-shaped particles.

  • RBC particles possessed were less aggressive to a counterpart material than GBs.

Abstract

Hard particulate fillers are used to improve the mechanical and tribological properties of thermoplastic resins. This study investigated the fundamental tribological behavior of polyamide 66 (PA66) resin composites containing rice bran ceramics (RBC) particles or glass beads (GBs) at a wide range of normal loads and sliding velocities under dry condition, and the utility of hard particulate fillers as a low-friction and high-wear-resistant filler is discussed. PA66/RBC and PA66/GB composites showed low friction and low wear compared with pure PA66, particularly at a low sliding velocity. Based on observations of the worn surfaces, RBC particles and GBs prevented the formation and growth of roll-shaped particles on the wear track at low sliding velocities, resulting in low wear. In addition, regarding the wear of the counterpart material, RBC particles are less aggressive than GBs.

Introduction

In recent years, development in the engineering of plastics has allowed thermoplastic resins to be used in parts of machine elements instead of metals. For use as triboelements, thermoplastic resins have often been combined with various fillers [1], [2], [3], [4], [5], [6], [7]. Solid lubricants, such as polytetrafluoroethylene, graphite, and molybdenum disulfide, bring low friction and either low wear due to the formation of lubricative transfer films [8], [9], or relatively high wear because of their removal [7], [10], [11], [12]. Fibrous fillers, such as carbon and glass fibers (GFs), can improve the mechanical properties and wear resistance of the matrix as a result of load support effects and high wear resistance of the fillers. Particulate fillers can also be useful for improving mechanical and tribological properties [13].

Rice bran ceramics (RBC), which is a hard porous carbon material, is made from rice bran [14]. RBC is manufactured by carbonizing a mixture of defatted rice bran and phenol resin in nitrogen gas at 900 °C. This ceramics material is composed of soft amorphous carbon corresponding to the defatted rice bran and hard glassy carbon corresponding to the phenol resin. RBC is a high-performance, multifunctional material offering high hardness (HV=4.4 GPa), high strength (σc=173 MPa), low density (ρ=1.26 Mg/m3), a porous structure, and low Young׳s modulus (E=11 GPa). Furthermore, RBC shows low friction and low wear under dry condition [15]. As a result, RBC particles are expected to find use as hybrid fillers that provide low friction and high wear resistance characteristics. In previous studies, thermoplastic resin/RBC composites were developed, and their friction and wear properties were experimentally ascertained [16], [17]. According to the study [16], five thermoplastic resins, namely, polyamide 66 (PA66), polyamide 11, polyoxymethylene, polybutylene terephthalate, and polypropylene, were used as matrix resins. Thermoplastic resin/RBC composites displayed lower friction and higher wear resistance compared with their pure resins. A PA66/RBC composite also showed superior tribological properties than a PA66/GF composite. The GF filler substantially improved the composite strength, although it did not improve the friction coefficient and wear. In another study [17], the effects of RBC particles on wear resistance of copper composites containing the particles were investigated. RBC particles improve the fracture toughness of the composite and reduce the friction coefficients, resulting in a mild wear mode. This indicates that RBC particles have great potential in industry as an anti-wear filler.

The tribological behaviors of glass-filled thermoplastic composites were reported [18]. Four forms of glass were used: GFs, hollow glass beads (GBs), solid GBs, and glass flakes. According to the results, the GF-filled composite and solid GB-filled composite showed the lowest wear, whereas the hollow GB-filled composite showed the highest wear.

Thus, it has been demonstrated that use of RBC particles or GBs as a filler improves the tribological properties, particularly the wear resistance, of thermoplastic resins. However, a comparison of RBC particles with GB fillers as low-friction and high-wear-resistant fillers has not been reported.

The present study investigated the fundamental tribological behavior of PA66 resin composites filled with either RBC particles or GBs at a wide range of normal loads and sliding velocities under dry condition. In addition, the utility of hard particulate fillers as low-friction and high-wear-resistant fillers is discussed.

Section snippets

Material preparation

The mean diameters of the RBC particles (Sanwa Yushi Co., Ltd., Japan) and GBs (Potters-Ballotini Co., Ltd., Japan) were 4.9 µm and 5.0 µm, respectively. The shape of the GBs was spherical, whereas that of the RBC particles was anisotropic, as shown in Fig. 1. The surfaces of the GBs were not treated with any coupling agent. The mechanical properties of both fillers are listed in Table 1. Each filler was compounded with pure PA66 by kneading at the same volume fraction of filler, i.e., 26 vol%.

Friction and wear properties of PA66/RBC and PA66/GB composites

Fig. 3 illustrates the typical variations in the friction coefficients plotted against the number of repeated passages. When the sliding velocity was 0.01 m/s and normal load was 1.96 N, the friction coefficients for pure PA66 increased gradually with more friction cycles and reached 0.50. Conversely, the PA66/RBC composite showed stable and low friction coefficient values. The friction coefficients for the PA66/GB composite showed middle values between those of the other materials. When the

Conclusions

  • (1)

    The values of friction coefficients for the PA66/RBC and PA66/GB composites were lower than those for pure PA66 at a sliding velocity of 0.01 m/s.

  • (2)

    High specific wear rates (>1×10−8 mm2/N) were observed for pure PA66 at low sliding velocities, which were unfavorable for use in a dry sliding bearing. In contrast, the wear rates of the PA66/RBC and PA66/GB composites were low (≤1×10−8 mm2/N), particularly at low sliding velocities.

  • (3)

    The use of RBC particles and GBs as hard particular fillers prevented

Acknowledgments

This work was supported by Japan Society for the Promotion of Science Grant-in-Aid for Scientific Research (No. 24360058). The authors would like to thank Tatsuhiro Urabe and Ryota Ifuku for their help in conducting the experiments.

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