TRIBOLOGICAL CHARACTERISTICS OF GRADED PENCIL CORES ON PAPER

Despite the long, rich history and widespread use of pencils and paper , the literature of tribology is remarkably devoid of published resear ch on the subject. The present investigation was conducted to investig ate the effects of writing core (i.e. ''lead'') grade on the wear resp onse and static and kinetic friction coefficients associated with writ ing on three types of paper: standard 20 lb copier paper, heavier mani la cover stock, and Tyvek(TM), a spunbonded olefin paper product commo nly used for mailing envelopes and surgical clothing. Three mechanical pencil core grades (2B, HB, and 2H) were used. These materials varied in Knoop microindentation hardness by a factor of approximately two. Static friction coefficients were determined from simple, inclined-pla ne tests of the various core-paper combinations, and kinetic friction coefficients were determined by pin-on-disk tests. Against all but the Tyvek(TM), static friction coefficients were not dependent on core gr ade or paper type. Kinetic friction coefficients were not clearly corr elated with paper type or core grade; however, significant differences in the core wear and paper in-filling characteristics were observed. Scanning electron microscopy and quantitative image analysis were used to study the manner and extent to which the core wear particles were embedded and agglomerated within the tangled fibers of the papers. A c lear correlation was observed between the degree of transfer of wear p articles to the paper and the hardness of the core in two of the three paper types.