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.