기능성 유기 소재 특론 HARDNESS FRICTION, WEAR, ABRASION 201050413 박 길 영

4.4 HARDNESS HARDNESS – 단단한 정도. 일정한 하중으로 재료의 표면을 압입할 때 나타나는 국부적인 저항. 경도 측정 목적 : - 시료의 경도 값 측정 : 굳기 추정, 시료의 가공 상태나 내마모성 판단. 측정 방법 : - Indentation Hardness test(압입 경도 측정) - Scratch Hardness test(긋기 경도 측정) - Rebound Hardness test(반발 경도 측정)

Ball Hardness Figure 4.20 Hardness test indentors [R]Rockwell; [H]Ball; [B]Brinell; [V]Vickers; [K]Knoop-tukon; (R)Rockwell R indentor; (M)Rockwell M indentor; (E) 1cm scale; (E’)1 in scale - 유럽에서 사용 - 강구 사용<직경 5 mm (0.2 in)> - 하중 36.5 kgf (358 N) - 측정 값 (N/mm2 or MPa) - Engineering plastics : soft -> 100 N/mm2 stiff -> 150 N/mm2

International Rubber Hardness Figure 4.23 Hardness tester(IRHD) [ZWICK] Figure 4.21 Hardness test indentors [S]Shore [B]Barcol; [I] IRHD; (A)Shore A indentor; (D)Shore D indentor; (S)IRHD standard indentor; (M) IRHD micro indentor; (E) 1mm scale; (E’) 0.1 in scale - ASTM D1415 Standard : spherical indentor(ball) of diameter d = 2.5 mm (≈ 1 in) load FM, 5.6 N (≈ 1.25 lbf) micro-test : d ≈ 0.4 mm (≈ 0.015 in) FM, ≈ 0.15 N (≈ 0.035 lbf)

Barcol Hardness Figure 4.21 Hardness test indentors [S]Shore [B]Barcol; [I] IRHD; (A)Shore A indentor; (D)Shore D indentor; (S)IRHD standard indentor; (M) IRHD micro indentor; (E) 1mm scale; (E’) 0.1 in scale Figure 4.24 Hardness tester(Barcol impressor) [GARDNER] - 딱딱하게 강화된 열경화성 플라스틱의 경도 측정. - ASTM D2583 - 최소 시험편 두께 1.5mm - 50B-90B의 범위

Miscellaneous Methods Brinell test spherical indentor of diameter d = 10 mm (≈ 0.4 in) Acetal : 205 N/mm2 HB 비교적 큰 시편 Vickers test square pyramidal indentor of angle 136° Acetal : 185 N/mm2 HV 시편이 작을 때 사용. Knoop-Tukon test ASTM D1474 elongated pyramidal indentor 측정 감도 좋음, 박판에 사용.

Scratch test - Trace or scratch left by sharp pencils of standard hardnesses - H(Hard), B(Black) < 9H 8H 7H 6H 5H 4H 3H 2H H HB B 2B 3B 4B 5B 6B > - Harder materials scratch softer ones - Mohs Hardness Scale<1(talc)-10(diamond)> - Fingernail(2), Polymer(1~2)

4.5. FRICTION, WEAR, AND ABRASION Frictional, Tribology로 언급 bearings bushings gears cams pistonring thrust plates http://www.google.co.kr/images

Friction Figure 4.25 Coefficient of friction measurement [G]Inclined plate method; [T]Towed sled method; (S)Test specimen surface(sled); (S’)Mating surface(plate); (T)Sled; (A)Angle of plate inclination; (L)Load celll (D) Sled drive Coefficient of friction (μ) : ratio of the sliding force Fs to the normal force Fn : ratio of the shear stress S to the normal pressure Pn starting coefficient(μs), kinetic coefficient(μd) Velocity(V) 25 cm/s, Pressure(P) 0.2MPa - Additives : Fluorocarbon polymers, brass, graphite and carbon

Wear progressive damage at the interface of two sliding surfaces adhesive wear abrasive wear - at low velocities V, excessive pressures P - at low pressures P, high velocities V - expressed as the thickness reduction per unit time << “ wear factor”, K >> http://www.google.co.kr/images

Figure 4.26 Wear tests geometries [P]Pin-cylinder; [B]Bar-cylinder; [D]Pin-disk; [W]Thrust washer; [L]Load; (S)Test specimen; (S’)Mating surface fluorocarbon polymer (PTFE) - maximum static pressure : 약 17MPa (≈ 1000 psi) - maximum speed under low load : 50 cm/s (≈ 100 ft/min) - wear factor K : 2500 (inch/h, Psi*ft/min) acetal POM or polyamide PA - maximum static pressure : 약 35 MPa (≈ 5000 psi) - maximum speed under low load : 150 cm/s (≈ 300 ft/min) - wear factor K : 50 (inch/h, Psi*ft/min)

Abrasion abrading element metal file steel wool grinding wheel sand paper, sand jet, slurry http://www.google.co.kr/images

Figure 4.27 Taber abraser [T]Top view; [S]Side view; (W),(W’)Abrasive wheels; (A)Abrasion track; (T)Turntable; (H)Hub; (L)Load; (S)Test specimen; (E) 1cm scale; (E’) 1 in scale Taber rotary test(ASTM D1044) - 10 cm(4 in) test specimen(S), standard abrasive wheels(W) - milligrams(mg) of weight loss per 1000 cycles