Static friction of normal and reversed metal–polymer sliding pairs

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The static friction coefficient of tested polymer–steel friction pairs as a function of unit pressure p_ Normal sliding pairs

Sample material	Unit pressure p [MPa]
	0.5	1.0	2.0
PE-UHMW	0.10 ± 0.002	0.09 ± 0.001	0.08 ± 0.001
POM	0.09 ± 0.001	0.08 ± 0.001	0.07 ± 0.001
PTFE	0.05 ± 0.001	0.06 ± 0.001	0.05 ± 0.001

Percentage changes in static friction coefficient values for normal sliding pair in comparison with reversed pair

	Unit pressure p [MPa]
	0.5	1	2	Average
PE-UHMW (%)	−16.7	−18.2	−27.3	−20.7
POM (%)	−43.7	−42.8	−41.7	−42.7
PTFE (%)	−44.4	−25.0	−16.7	−28.7

The static friction coefficient of tested steel-polymer friction pairs as a function of unit pressure p_ Reversed sliding pairs

Counterbody material	Unit pressure p [MPa]
	0.5	1.0	2.0
PE-UHMW	0.12 ± 0.001	0.11 ± 0.001	0.11 ± 0.001
POM	0.16 ± 0.002	0.14 ± 0.002	0.12 ± 0.002
PTFE	0.09 ± 0.002	0.08 ± 0.001	0.06 ± 0.001

Mechanical parameters of polymers selected for tests [18]

	Density [g/cm3]	E-modulus [MPa]	Glass transition temperature [°C]	Melting point [°C]	Softening point [°C]
PE-UHMW	0.93	730	−100	135	80
POM	1.41	2400	−240 to 180	167	150
PTFE	2.6	750	−97	327	-