Friction and Wear Research, Volume 3, 2015 www.seipub.org/fwr doi: 10.14355/fwr.2015.03.001
Tribological Behaviour of Epoxy Filled by Rubber Particles Samy A. M. Faculty of Engineering, Minia University, P. N. 61111, El‐Minia, EGYPT Abstract The aim of the present work is to study the friction and wear of epoxy filled by recycled rubber as flooring materials. The Friction test was carried out at different values of normal load 4, 6 and 8 N. Wear test was carried out by scratch tester equipped with an indenter to produce a scratch on a flat surface with a single pass. Test specimens in a form of a layer of 60 × 60 mm2 adhered into a wooden block. The tested materials were epoxy filled by 5, 10, 15, 20 and 25 wt. % contents of recycled rubber of different particle size. Test results show that, rubber particles significantly increased friction coefficient. This behavior related to the deformation of rubber during scratching. The minimum value of friction coefficient observed for epoxy free of rubber was 1.5 at 4 N normal load, while the maximum value was 2.5 showed by epoxy containing 10 wt. % rubber of0.5 – 1.0 mm particle size. The wear of epoxy composites decreased with increasing rubber content up to 20 wt. % for particle size ranged from 0.212 to 0.355 mm. The wear resistance of epoxy specimens was developed by adding rubber particles. Keywords Recycled Rubber, Friction Coefficient, Wear, Epoxy, Scratch Test
Introduction Flooring tile made of recycled rubber was tested to reduce the risk of slip and fall in schools, boutiques, hospitals, offices, conference rooms, homes, trade fair stands and homes for the aged should be reduced. Ceramic surfaces usually promote slips and occasionally lead to indoor accidents. The frictional behaviour of rubber mats made of recycled rubber and filled by polyurethane of different hardness was tested, [1]. Used polymeric materials are often burned or end up in landfills. Those methods represent serious pollution of the environment. The safe option is to recycle the used polymers as filling materials in epoxy and polyester flooring tiles. The frictional behaviour of flooring tiles made of recycled rubber was discussed. Experiments were carried out by the sliding of the bare foot against the tested rubber tiles of different thickness, [2], where friction coefficient was tested. It was found that at dry sliding, friction coefficient slightly increases with increasing rubber tile thickness and decreases with increasing load. At water and detergent lubricated sliding, friction coefficient decreases with increasing flooring thickness. The effect of filling materials on the friction coefficient of recycled rubber floorings was investigated,[3]. At dry sliding, friction coefficient slightly increased with increasing the content of the filling materials. At water lubricated sliding, friction coefficient significantly decreased with increasing filling material content. Detergent decreased friction coefficient lower than water. The lowest friction values were observed for tiles filled by 70 wt. % polyurethane. As the load increased friction coefficient decreased. Presence of sand particles on the sliding surfaces caused significant friction increase. The effect of surface roughness was explained, [4]. Surface roughness had insignificant effect on the frictional behaviour. In the presence of water on the sliding surface, rough surface displayed higher friction values than the smooth one. Rough surfaces of rubber tiles filled by polyurethane showed higher friction coefficient than the smooth ones at dry sliding. Detergent lubricated surfaces displayed higher friction coefficient for smooth rubber. In the presence of sand particles, friction coefficient significantly increased for the both smooth and rough surfaces. Rough surfaces displayed higher friction values than smooth ones. Finally, drastic friction decrease for smooth surface was noticed in the presence of water contaminated by sand particles. Slipping and falling are common phenomena in both workplaces and daily activities. The risks associated with
15
www.seipub.org/fwr Friction and Wear Research, Volume 3, 2015
slipping and falling are related to the materials of footwear/floor, contamination condition, and geometric design of the sole. Shoe soles of various tread design are very common, [5 ‐ 12]. Slip resistance of flooring materials is one of the major environmental factors affecting walking and materials handling behavior. Floor slipperiness may be quantified using the static and dynamic friction coefficient. Certain values of friction coefficient were recommended as the slip‐resistant standard for unloaded, normal walking conditions, [13, 14]. Relatively higher static and dynamic friction coefficient values may be required for safe walking when handling loads. There were two types of slips involved in pallet truck pulling. The slip distances of both of these slips interacted significantly with the weights of the load and the floor surface conditions, [15]. Soft material like rubber tends to a higher effective contact area and more pronounced microscopic deformations when mechanically interacting with the surface asperities of a rigid material, greater friction coefficients can be expected for rubber than for plastic, [16]. In the present work, it is aimed to investigate the friction and wear of epoxy test specimens filled by recycled rubber particles. The proposed composites are tested as flooring materials. Experimental The test rig, used in the experiments, was top scratching tester equipped with an indenter to produce a scratch on a flat surface with a single pass. The details of the test rig are shown in Fig. 1. The indenter, used in experiments, was a square insert (12 × 12 mm) of TiC of tip radius of 0.1 mm and hardness of 2800 kp/mm2. The scratch force was measured by the deflection of load cell. The ratio of the scratch force to the normal force was considered as friction coefficient. Wear was considered as the wear scar width of the scratch that measured by optical microscope with an accuracy of ± 1.0 μm.
Load cell
Balance Wight
Normal Load
Tool Holder Tool Holder Digital Screen
FIG. 1 SCRATCH TESTER
The specimens were prepared in a form of a layer of 60 × 60 mm2 and 5 mm thickness adhered to a wooden block, Fig. 2. The tested materials were epoxy filled by different contents of recycled rubber of (0.212 ‐ 0.355 mm), (0.355 ‐ 0.5 mm), (0.5 ‐ 1.0 mm), (1.0 ‐ 2.0 mm) and (2.0 ‐ 3.0mm) particle size. The friction test was carried out at different values of normal load.
Rubbe
Scratch Direction
Epoxy
Scratch Tool Wear Scar
FIG. 2 EPOXY TEST SPECIMENS FILLED BY RUBBER PARTICLES. FIG. 3.THE SCRATCH MECHANISM
16
Friction and Wear Research, Volume 3, 2015 www.seipub.org/fwr The recycled rubber was added to epoxy with different content 5, 10, 15, 20 and 25 wt. %. Experiments were carried out at 4, 6 and 8 N normal load. Scratch mechanism shown in Fig. 3. Results and Discussion Figure 4 shows the relation between friction coefficient and rubber content. It can be noticed that the friction coefficient decreased with increasing rubber content for 4 and 6 N normal load up to 15 wt. % rubber content. Then the value of friction coefficient increased to maximum value at 25 wt. % rubber content. This behaviour confirms the higher friction values displayed by rubber. The maximum friction coefficient was observed at 25wt. % rubber content for all normal loads. Friction coefficient of epoxy composite filled by rubber is shown in Fig. 5. Friction coefficient increased with increasing rubber content up to 10wt. % then decreased for 15 and 20wt. %. The reduction in friction is due to the weakness of bond between epoxy resin and rubber as well as the random distribution of rubber particles. Addition of rubber up to 25wt. % can increase friction coefficient to maximum values. This behavior may be related to increase bonding between epoxy resin and rubber particles and the deformation of rubber particles, Fig. 6. Maximum values of friction coefficient were observed at 25wt. % rubber content at applied load of 4 N.
Rubber Particle Size
Rubber Particle Size
0.212 – 0.355 mm
0.355 – 0.5 mm
FIG. 4 FRICTION COEFFICIENT OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (0.212 ‐ 0.355 MM) PARTICLE SIZE.
FIG. 5 FRICTION COEFFICIENT OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (0.355 ‐ 0.5 MM) PARTICLE SIZE Rubber Particles
Scratch Tool
Wear scar
17
www.seipub.org/fwr Friction and Wear Research, Volume 3, 2015
Sliding Direction
Scratch Tool Rubber Particles
Rubber Particles
Epoxy specimens FIG. 6 RUBBER PARTICLES DEFORMED AGAINST SCRATCH TOOL.
Friction coefficient of epoxy test specimens filled by rubber of (0.5 ‐ 1.0 mm) particle size is shown in Fig. 7. Friction coefficient increased with increasing rubber content up to 10 wt. %. Maximum values of friction coefficient were observed for epoxy containing 10 wt. % rubber at applied load of 4 N, while the minimum value of friction coefficient was observed for epoxy free of rubber. Figure 8 shows the relation between friction coefficient and rubber content, for epoxy test specimens filled by rubber of (1.0 ‐ 2.0 mm) particle size. It can be noticed that the friction coefficient increased with increasing rubber content. It was observed that increasing particle size caused remarkable friction decrease. This behavior may be related to the separation of rubber particles from specimens. The maximum value of friction coefficient was displayed by test specimens containing 25 wt. % rubber particles at 8 N normal loads. Figure 9 shows the relation between friction coefficient and rubber content, for epoxy test specimens filled by rubber of (2.0 ‐ 3.0 mm) particle size. It can be noticed that the friction coefficient increased with increasing rubber content up to 15 wt. %. Increasing rubber content to 20 wt. % and 25 wt. % decreased friction coefficient. This behavior may be related to the decreasing bond between rubber particles and epoxy resin.
Rubber Particle Size 0.5 – 1.0 mm
Rubber Particle Size 1.0 – 2.0 mm
FIG. 7 FRICTION COEFFICIENT OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (0.5 ‐ 1.0 MM) PARTICLE SIZE.
FIG. 8 FRICTION COEFFICIENT EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (1.0~2.0 MM) PARTICLE SIZE
Wear of epoxy test specimens versus rubber content is shown in Fig. 10. Wear increased with increasing applied load. Increasing rubber content shows significant decrease in wear values. This behavior may be related to the difficulty of scratch tool to cut rubber particles, Fig. 11. The lower value of wear scar width was observed for specimens containing 15 wt. % rubber particles. Figure 12 shows the relation between wear scar width and rubber
18
Friction and Wear Research, Volume 3, 2015 www.seipub.org/fwr content, for epoxy test specimens filled by rubber of (0.355 ‐ 0.5 mm) particle size. The minimum value of wear scar width was observed at 10 wt. % rubber content at 4 N normal loads. Rubber Particle Size 0.212 – 0.355 mm
Rubber Particle Size 2.0 – 3.0 mm
FIG. 9 FRICTION COEFFICIENT OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (2.0 ‐ 3.0 MM) PARTICLE SIZE. sliding
FIG. 10 WEAR OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (0.212 ‐ 0.355 MM) PARTICLE SIZE
Scratch Tool Rubber Particles
Rubber Particles
Epoxy specimens
FIG. 11RUBBER PARTICLES DIFFICULT TO CUT BY SCRATCH TOOL Rubber Particle Size 0.355 – 0. 5 mm
FIG. 12 WEAR OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (0.355 ‐ 0. 5 MM) PARTICLE SIZE.
19
www.seipub.org/fwr Friction and Wear Research, Volume 3, 2015
Epoxy test specimens filled by rubber of (0.5 ‐ 1.0 mm) particle size showed the same trend observed for epoxy filled by (0.355 ‐ 0.5 mm) particle size, Fig. 13. This behavior may be related to the nonhomogeneity between epoxy and rubber particles. Figure 14 shows that increasing rubber particle size to (1.0 ‐ 2.0 mm) caused insignificant effect on wear value. The minimum values of wear were observed at specimens containing 10 wt. % rubber at 4 N normal load. As for epoxy test specimens filled by rubber of (2.0 ‐ 3.0 mm) particle size, significant increase in wear scar width was noticed which was related to increase of the ability of rubber particles to separate from epoxy resin due to increasing particle size of rubber.
Rubber Particle Size 0.5 – 1.0 mm
Rubber Particle Size 1.0 – 2.0 mm
FIG. 13 WEAR OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (0.5 ‐ 1.0 MM) PARTICLE SIZE.
FIG. 14 WEAR OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (1.0 ‐ 2.0 MM) PARTICLE SIZE.
Rubber Particle Size 2.0 – 3.0 mm
FIG. 15 WEAR OF EPOXY TEST SPECIMENS FILLED BY RUBBER WITH (2.0 ‐ 3.0 MM) PARTICLE SIZE.
Conclusions 1. Rubber particles increased friction coefficient, due to the increased deformation of rubber. 2. Minimum values of friction coefficient for epoxy specimens free of rubber were 1.5 at 4 N normal loads. 3. Maximum value of friction coefficient was 2.5 showed by epoxy specimens containing 10 % rubber of (0.5 – 1.0 mm) particle size at 4 N normal load. 4. Wear of epoxy composite decreased with increasing rubber content up to 20 wt. % for(0.212 – 0.355 mm) particle size. 5. Wear resistance of epoxy specimens was developed by adding rubber particles.
20
Friction and Wear Research, Volume 3, 2015 www.seipub.org/fwr REFERENCES
[1]
El‐Sherbiny Y. M., Mohamed M. K. and Ali W. Y., ʺPrevention of Slip Accidents by Using Rubber Floor Matʺ, Journal of the Egyptian Society of Tribology Vol. 9, No. 1, January 2012, pp. 24 – 38, (2012).
[2]
Elham B. R., Khashaba M. I. and Ali W. Y., ʺFriction Coefficient of Smooth and Rough Recycled Rubber Flooring Tilesʺ, Journal of the Egyptian Society of Tribology Vol. 9, No. 3, July 2012,pp. 53 – 65, (2012).
[3]
Elham B. R., Khashaba M. I. and Ali W. Y., ʺEffect of Filling Materials on the Friction Coefficient of Recycled Rubber Flooringʺ, Journal of the Egyptian Society of Tribology Vol. 9, No. 4, October 2012, pp. 55 – 66, (2012).
[4]
Elham B. R., Khashaba M. I. and Ali W. Y., ʺEffect of Surface Roughness on Friction Coefficient of Recycled Rubber Flooringsʺ, Journal of the Egyptian Society of Tribology Vol. 10, No. 1, January 2013, pp. 1 – 13, (2012).
[5]
Gabriel P., Thomas A. G., Busfield J.J.C., ʺInfluence of Interface Geometry on Rubber Frictionʺ, Wear 268, pp. 747 – 750, (2010).
[6]
Gert Heinrich, Manfred Kluppel., ʺRubber friction, tread deformation and tire traction ʺ, Wear 265, pp. 1052 – 1060, (2008).
[7]
Liwen Liu, Kai Way Li b, Yung‐Hui Lee, Ching Chung Chen, Chih‐Yong Chen ., ʺ Friction measurements on ‘‘anti‐slip” floors under shoe sole, contamination, and inclination conditions ʺ, Safety Science 48, pp. 1321 – 1326, (2010).
[8]
El‐Sherbiny Y. M., Samy A. M. and Ali W. Y., “Friction Coefficient of Rubber Sliding Against Dusty Indoor Flooring”, Journal of the Egyptian Society of Tribology, Vol. 7, No. 4, October 2010, pp. 11 – 25, (2010).
[9]
El‐Sherbiny Y. M., Mohamed M. K., Ali W. Y., “Friction Coefficient Displayed by Footwear Walking Against Rubber Floorings Fitted by Cylindrical Treads”, Journal of the Egyptian Society of Tribology, Vol. 8, No. 1, January 2011, pp. 1 – 12, (2011).
[10] Mohamed M. K., Samy A. M., Ali W. Y., “Friction Coefficient of Rubber Shoes Sliding Against Ceramic Flooring”, September 27 – 29, 2010, TribologieFachtagung, Göttengen, Germany, pp. 46.1 – 46.13, (2010). [11] Kai W. L., Horng H. W., Yu‐Chang L., “The effect of shoe sole tread groove depth on the friction coefficient with different tread groove widths, floors and contaminants”, Applied Ergonomics 37, pp. 743 – 748, (2006). [12] Li K. W., Yu R., Han X. L., “Physiological and psychophysical responses in handling maximum acceptable weights under different footwear–floor friction conditions”, Applied Ergonomics 38, pp. 259 – 265, (2007). [13] Miller J. M., “‘‘Slippery’’ work surface: toward a performance definition and quantitative coefficient of friction criteria”, J. Saf. Res. 14, pp. 145 ‐ 158, (1983). [14] Grönqvist R., ʺMechanisms of friction and assessment of slip resistance of new and used footwear soles on contaminated floorsʺ, Ergonomics 38, pp. 224 ‐ 241, (1995). [15] Lia K. W., Chang C. C., Chang W. R., “Slipping of the foot on the floor when pulling a pallet truck”, Applied Ergonomics 39, pp. 812 ‐ 819, (2008). [16] Derler S., Kausch F., Huber R., “Analysis of factors influencing the friction coefficients of shoe sole materials”, Safety Science 46, pp. 822 ‐ 832, (2008).
21